JP2005228865A - Manufacturing method of piezoelectric ceramic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a piezoelectric ceramic with which a degree of polarization can stably be increased and saturated in the piezoelectric ceramic whose crystal structure changes to cubic, tetragonal and orthorhombic as a temperature is lowered. <P>SOLUTION: The manufacturing method of the piezoelectric ceramic has a first step for performing a first polarization processing on the piezoelectric ceramic which has a crystal structure of cubic at high temperature, and whose phase reversibly changes to tetragonal and orthorhombic in a temperature region where the ceramic becomes tetragonal; and a second step for performing a second polarization processing on the piezoelectric ceramic in the same direction as the first polarization processing in a temperature region where the ceramic becomes orthorhombic. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing piezoelectric ceramics, and more specifically, it is possible to stably increase and saturate the degree of polarization of piezoelectric ceramics that undergo a phase transition to cubic, tetragonal, or orthorhombic as temperature decreases. The present invention relates to a method for manufacturing a piezoelectric ceramic.

  Piezoelectric materials are materials that have a piezoelectric effect, and their forms are classified into single crystals, ceramics, thin films, polymers, and composites (composites). Among these piezoelectric materials, in particular, piezoelectric ceramics are widely applied in the fields of electronics and mechatronics because they have high performance, a large degree of freedom in shape, and material design is relatively easy.

  Piezoelectric ceramics are obtained by applying so-called polarization treatment (polling) in which a ferroelectric electric field is applied with a direct current electric field that is higher than the coercive electric field and the direction of domain (domain) of the ferroelectric is aligned. In piezoelectric ceramics, an isotropic perovskite-type crystal structure in which the direction of spontaneous polarization can be taken three-dimensionally is advantageous in order to align spontaneous polarization in a certain direction by polarization treatment. For this reason, most of the piezoelectric ceramics in practical use are isotropic perovskite ferroelectric ceramics.

As the isotropic perovskite type ferroelectric ceramic, for example, Pb (Zr · Ti) O ₃ (hereinafter referred to as “PZT”), PZT3 in which lead-based composite perovskite is added as a third component to PZT. Component systems such as BaTiO ₃ , Bi _0.5 Na _0.5 TiO ₃ , (K, Na) NbO ₃ are known. Among these, lead-based piezoelectric ceramics represented by PZT have higher piezoelectric properties than piezoelectric ceramics that do not contain any lead (hereinafter referred to as “lead-free piezoelectric ceramics”). It accounts for the majority of piezoelectric ceramics in practical use. Therefore, piezoelectric ceramics (hereinafter referred to as “low lead”) or lead-free piezoelectric ceramics having a piezoelectric characteristic equivalent to that of PZT and having a low lead content are required.

  In most cases, PZT compounds have a so-called “morphotropic phase boundary (MPB)” in which the crystal system changes from tetragonal to rhombohedral (trigonal) by changing the ratio of Zr and Ti. In general, a PZT piezoelectric ceramic that has been put to practical use has a composition in the vicinity of MPB or a rhombohedral crystal side with slightly rich Zr. This is because (1) the composition near the MPB or rhombohedral side has extremely small anisotropy of the crystal lattice, and high piezoelectric characteristics can be obtained, and (2) the temperature dependence on the ratio of Zr and Ti. Therefore, by optimizing the composition, the tetragonal or rhombohedral crystal structure can be maintained without phase transition up to the Curie temperature, and stable temperature characteristics can be obtained.

By the way, isotropic perovskite type compounds generally have a cubic crystal structure at a high temperature and thus do not have spontaneous polarization. However, when the temperature decreases, the isotropic perovskite type compound passes through a phase transition point (Curie point) and becomes tetragonal. It becomes a crystal structure and causes spontaneous polarization. In addition, certain isotropic perovskite compounds (for example, BaTiO ₃ , (K, Na) NbO ₃ , or solid solutions in which some of these cationic elements are substituted with other cationic elements) It is also known that a phase transition from tetragonal to orthorhombic as the temperature decreases. In this case, the direction of spontaneous polarization varies depending on the crystal structure, and is, for example, the pseudo cubic [100] axis direction for tetragonal crystals and the pseudo cubic [110] axis direction for orthorhombic crystals.

  In addition, each crystal grain constituting the piezoelectric ceramic has a lowest energy in the crystal grain when the phase transition from the cubic crystal (paraelectric phase) to the tetragonal crystal (ferroelectric phase) through the Curie point, Divided into many domains with different spontaneous polarization. Therefore, the piezoelectric ceramic immediately after sintering does not exhibit piezoelectricity because the spontaneous polarization of each of these domains and the piezoelectric effect caused thereby cancel each other. On the other hand, when a DC electric field higher than the coercive electric field is applied to such a piezoelectric ceramic, the domain wall that is the boundary between the domain and the domain moves, and the domain area having a polarization direction close to the electric field direction The proportion of increases. Moreover, such a domain structure is maintained even if the electric field is reduced to zero. For this reason, the piezoelectric ceramic after the polarization treatment exhibits piezoelectricity.

  Such polarization treatment of piezoelectric ceramics has conventionally formed electrodes on the upper and lower surfaces of a sintered body processed into a disk shape, and a DC electric field of about 1 to 5 kV / mm in silicon oil at around 100 ° C. for several minutes to In general, it is performed by applying several tens of minutes. However, the piezoelectric ceramic is usually in a state in which each crystal grain is randomly oriented. Therefore, unlike a single crystal, it is very difficult to obtain a completely single domain structure by polarization treatment.

  Piezoelectric ceramics have a plurality of domain components depending on the crystal structure. For example, in the case of tetragonal crystal, there are a 180 ° domain in which the direction of spontaneous polarization is different by 180 ° and a 90 ° domain that is different by 90 °. When such a polycrystal is subjected to polarization treatment, the direction of spontaneous polarization of each of the 180 ° domain and the 90 ° domain is aligned with the electric field direction by domain rotation.

  Among these, the 180 ° domain inversion simply replaces the direction of displacement, so that the spontaneous polarization easily aligns with a low electric field, and no significant distortion is caused at that time. On the other hand, since the 90 ° domain rotation must change the direction in which the crystal should be displaced by 90 °, it involves mechanical deformation and rotation when spontaneous polarization is aligned. As a result, a high electric field is required to cause 90 ° domain rotation.

  Therefore, even with a composition having essentially high piezoelectric characteristics, there is a limit to the reachable piezoelectric characteristics with the conventional polarization treatment method. In addition, since the 90 ° domain in which the spontaneous polarization is rotated in the electric field direction by the polarization treatment is mechanically and thermally unstable, the 90 ° domain returns to the original 90 ° domain during use, resulting in poor stability and durability. was there.

  Furthermore, among piezoelectric ceramics, PZT piezoelectric ceramics are so-called “soft materials” whose crystal lattices are easily deformed (low coercive electric field), so that high piezoelectric properties can be obtained by polarization treatment, but piezoelectric properties are There was a problem that it was easy to vary.

  In order to solve this problem, various polarization methods have been conventionally proposed. For example, Patent Document 1 discloses that after saturation polarization of PZT having a composition belonging to the vicinity of a phase boundary or rhombohedral (trigonal) side, an electric field higher than the coercive electric field is applied at a temperature from 0 ° C. to −50 ° C. In addition, a method of performing reverse polarization with a polarization degree smaller than the polarization degree during saturation polarization is described. This document describes that a desired degree of polarization can be obtained easily and accurately by such a method.

  Patent Document 2 describes a polarization method in which a PZT piezoelectric ceramic is first polarized by applying a voltage at room temperature and then polarized by applying a voltage at a high temperature. This document describes that this method increases the electromechanical coupling coefficient Kp immediately after polarization of the PZT piezoelectric ceramic, thereby improving the durability of the displacement characteristics.

  In Patent Document 3, first, a PZT piezoelectric ceramic is heated to a temperature that is 1/2 the Curie point to a temperature that is lower than or equal to the Curie point, and at this temperature, the piezoelectric ceramic is saturated and polarized, and then this is 0 ° C. or lower. In addition, a method is described in which the piezoelectric ceramic is rapidly cooled to a temperature of 2 ° C., and the piezoelectric ceramic is heated again to a temperature half the Curie point to a temperature below the Curie point, and the piezoelectric ceramic is saturatedly polarized at this temperature. According to this document, rapid cooling generates an internal charge in the direction opposite to the spontaneous polarization inside the piezoelectric ceramic, and the spontaneous polarization is pinned by the internal charge during the second polarization process, thus improving durability during driving. The point to do is described.

  Patent Document 4 describes a method in which a PZT piezoelectric ceramic is subjected to a polarization treatment, and then the PZT piezoelectric ceramic subjected to the polarization treatment is subjected to an aging treatment (for example, thermal aging at 200 ° C. to 250 ° C.). . This document describes that the 90 ° domain rotation component is removed by the aging process and only the 180 ° domain inversion component is used, so that the deterioration of the characteristics of the piezoelectric body is suppressed and stabilized.

Further, Patent Document 5, with respect to PZT based piezoelectric ceramic, all polarization degree of interest is extremely half at a temperature T _A as occupied only by 180 ° domain inversion component, then aged at that temperature T _A The method of doing is described. According to this document, the ratio of the 180 ° domain inversion component to the degree of polarization is governed only by temperature, so that the target degree of polarization can be reached with high accuracy and the 90 ° domain rotation component is eliminated by aging. Further, it is described that the thermal and temporal stability of piezoelectric characteristics is improved.

Japanese Patent No. 2783022 Japanese Patent No. 3070799 Japanese Patent No. 3075033 Japanese Patent Laid-Open No. 07-172914 JP 2000-183422 A

  When various polarization methods described in Patent Documents 1 to 5 are applied to PZT-based piezoelectric ceramics, variations in piezoelectric properties are reduced, or the 90 ° domain rotation component is removed, thereby stabilizing the piezoelectric properties. It is said that the durability and durability are improved. However, the above-described method basically uses only a stable 180 ° domain inversion component obtained by saturation polarization of the PZT-based piezoelectric ceramic, so that the reachable degree of polarization is limited. In addition, when PZT piezoelectric ceramics are discarded, there is a possibility that lead in the ceramics may be eluted by acid rain and the like, and because it contains lead oxide (PbO) with a high vapor pressure, there is a burden on the environment. There is a problem of being big. Therefore, there is a demand for piezoelectric ceramics that have low lead or non-lead and have piezoelectric characteristics equivalent to PZT.

On the other hand, in lead-free piezoelectric ceramics, for example, (K, Na) NbO ₃ or a solid solution in which a part of the cation element contained therein is replaced with another element (hereinafter referred to as KNN-based). Those having relatively high piezoelectric properties, such as piezoelectric ceramics, are known. However, the KNN piezoelectric ceramic is generally a so-called “hard material” in which the crystal lattice is hardly deformed (high coercive electric field). Therefore, in order to obtain a high degree of polarization by polarization treatment, it is necessary to apply a high electric field at a high temperature at which the crystal lattice is easily deformed. Even under such conditions, the conventional polarization method cannot provide piezoelectric characteristics equivalent to those of the PZT piezoelectric ceramics.

  Furthermore, some lead-free piezoelectric ceramics have a cubic crystal structure at high temperatures, and reversibly phase change to tetragonal and orthorhombic when the temperature is lowered. Some types of KNN piezoelectric ceramics have two crystal states, orthorhombic and tetragonal, within the temperature range in which the piezoelectric ceramic is used. Even if the methods described in Patent Documents 1 to 5 described above are applied to such lead-free piezoelectric ceramics, high piezoelectric characteristics that are not conventionally obtained cannot be obtained. In addition, there has never been an example in which a polarization method that positively uses such characteristics has been proposed for piezoelectric ceramics having two crystal states of orthorhombic and tetragonal depending on temperature.

  The problem to be solved by the present invention is that the degree of polarization can be stably increased and saturated in a piezoelectric ceramic whose crystal structure changes to cubic, tetragonal or orthorhombic as the temperature is lowered. The object is to provide a method of manufacturing a piezoelectric ceramic.

  In order to solve the above problems, a method for manufacturing a piezoelectric ceramic according to the present invention comprises a piezoelectric ceramic having a cubic crystal structure at a high temperature and reversibly phase-converting into a tetragonal crystal and an orthorhombic crystal when the temperature is lowered. A first step of performing a first polarization treatment in a temperature region that becomes a tetragonal crystal, and a second polarization in the temperature region that becomes an orthorhombic crystal and in the same direction as the first polarization treatment. And a second step for performing the processing.

  In a piezoelectric ceramic whose crystal structure changes to cubic, tetragonal and orthorhombic as the temperature is lowered, the first polarization treatment is performed in the tetragonal region, and then the second polarization treatment is performed in the orthorhombic region. By performing the above, the degree of polarization can be stably increased and saturated. This is because (1) the direction of spontaneous polarization is aligned with the electric field direction by polarization treatment in the tetragonal region, and (2) the domain structure is regenerated by cooling such piezoelectric ceramics to the orthorhombic region. And a new 180 ° domain inversion component in the orthorhombic region is generated, and (3) the direction of spontaneous polarization of the newly generated 180 ° domain inversion component is in the orthorhombic region. This is considered to be due to the alignment in the electric field direction by the polarization treatment.

Hereinafter, an embodiment of the present invention will be described in detail. First, a piezoelectric ceramic to which the present invention is applied will be described. The piezoelectric ceramic to which the present invention is applied may be any material as long as it has a cubic crystal structure at a high temperature and reversibly transforms into a tetragonal crystal and an orthorhombic crystal when the temperature is lowered. There is no particular limitation. Specifically, (K, Na) NbO ₃ , BaTiO _{3 and the} like, and those in which some of these cationic elements are substituted with other cationic elements are listed as suitable examples.

  Among these, a compound represented by the following formula (1) (hereinafter referred to as “KNN compound”) exhibits relatively high piezoelectric characteristics, and furthermore, by applying the method according to the present invention, piezoelectric characteristics can be obtained. Is particularly preferable. Further, the phase transition temperature from tetragonal to orthorhombic is in the temperature range of −50 ° C. to 200 ° C., but particularly those having high properties at room temperature are in the temperature range of 0 ° C. to 100 ° C. Since it exists in the temperature range of 30 degreeC-100 degreeC, there exists an advantage that a two-step polarization process can be performed comparatively easily. Furthermore, among the KNN compounds represented by the formula (1), those having high characteristics at room temperature have a tetragonal crystal structure in the temperature range of 100 ° C to 150 ° C.

_{{Li x (K 1-y} Na y) 1-x} {Nb 1-z-w Ta z Sb w} O 3 ··· (1)
(However, 0 ≦ x ≦ 0.2, 0 ≦ y ≦ 1, 0 ≦ z ≦ 0.4, 0 ≦ w ≦ 0.2,
x + z + w> 0)

The KNN compound represented by the formula (1) is composed of potassium sodium niobate (K _1-y Na _y NbO ₃ : KNN), which is a kind of isotropic perovskite compound, and has an A site element (K, Na). Is replaced with a predetermined amount of Li and / or a part of the B site element (Nb) is replaced with a predetermined amount of Ta and / or Sb. In the formula (1), “x + z + w> 0” indicates that at least one of Li, Ta, and Sb may be included as a substitution element.

  In the formula (1), “y” represents the ratio of K and Na contained in the KNN compound. The KNN compound only needs to contain at least one of K or Na as the A site element. That is, the ratio y between K and Na is not particularly limited, and can take any value between 0 and 1. In order to obtain high piezoelectric characteristics and the like, the value of y is preferably 0.05 or more and less than 0.75, more preferably 0.20 or more and 0.70 or less, and further preferably 0.35 or more and 0.00. 65 or less, more preferably 0.40 or more and 0.60 or less, and still more preferably 0.42 or more and 0.60 or less.

“X” represents a substitution amount of Li for substituting K and / or Na which are A site elements. Replacing a part of K and / or Na with Li provides the effect of improving the piezoelectric characteristics, increasing the Curie temperature, and / or promoting densification. Specifically, the value of x is preferably 0 or more and 0.2 or less. If the value of x exceeds 0.2, the piezoelectric properties (piezoelectric d ₃₁ constant, electromechanical coupling coefficient k _p , piezoelectric g ₃₁ constant, etc.) are not preferable. The value of x is preferably 0 or more and 0.15 or less, and more preferably 0 or more and 0.10 or less.

  “Z” represents the amount of Ta substituted for Nb which is a B-site element. If a part of Nb is replaced with Ta, an effect of improving the piezoelectric characteristics and the like can be obtained. Specifically, the value of z is preferably 0 or more and 0.4 or less. If the value of z exceeds 0.4, the Curie temperature is lowered, and it becomes difficult to use as a piezoelectric material for home appliances and automobiles. The value of z is preferably 0 or more and 0.35 or less, and more preferably 0 or more and 0.30 or less.

  Further, “w” represents the substitution amount of Sb that substitutes Nb, which is a B site element. If a part of Nb is replaced with Sb, an effect of improving the piezoelectric characteristics and the like can be obtained. Specifically, the value of w is preferably 0 or more and 0.2 or less. If the value of w exceeds 0.2, the piezoelectric characteristics and / or the Curie temperature are lowered, which is not preferable. The value of w is preferably 0 or more and 0.15 or less, and more preferably 0 or more and 0.10 or less.

  Note that the piezoelectric ceramic composed of the KNN compound represented by the formula (1) is preferably composed only of this, but it can maintain an isotropic perovskite type crystal structure, and various properties such as sintering characteristics and piezoelectric characteristics can be maintained. Other elements or other phases may be included as long as they do not adversely affect the properties.

As such “other elements”, specifically, other monovalent cation elements (eg, Ag ⁺ , Cs ^+, etc.) that replace the A site element of the KNN compound, the first KNN system Other pentavalent cation elements (for example, V ⁵⁺ , Re ⁵⁺ etc.) that replace the B site element of the compound are listed as an example. Another example is substitution by a combination of other divalent cation elements (for example, Ca ²⁺ , Sr ^2+, etc.) that substitute the A site element of the KNN compound and vacancies.

Further, the “other element” that replaces the A site element and the B site element may be a combination in which the sum of these valences becomes hexavalent. Specific examples include a combination of Ba ²⁺ and Ti ^4+, a combination of Sr ²⁺ and Ti ^4+, a combination of Ca ²⁺ and Ti ⁴⁺ , and the like. Moreover, only “hexavalent metal elements (for example, W ⁶⁺ , Mo ⁶⁺ etc.)” may be included as “other elements” for replacing the B site element. In this case, defects are formed at the A site so that the valence of the entire cation element is hexavalent.

Furthermore, as the “other phase”, specifically, additives, sintering aids, by-products, impurities, etc. (for example, Bi ₂ O ₃ , CuO, MnO, etc. resulting from the production method and starting materials used) ₂ , NiO, etc.). The smaller the content of other elements or other phases that may adversely affect the piezoelectric characteristics or the like, the better.

  In the piezoelectric ceramic to which the present invention is applied, each crystal grain may be non-oriented, or a specific crystal plane may be oriented in one direction. However, the piezoelectric ceramic to which the present invention is applied is particularly effective when a specific crystal plane is oriented in one direction. Here, “the specific crystal plane is oriented” means that the crystal grains are arranged so that the specific crystal planes of the compound constituting the piezoelectric ceramic are parallel to each other (hereinafter referred to as this The crystal grains are arranged so that a specific crystal plane is parallel to one axis penetrating the sintered body (hereinafter referred to as such). Is called “axial orientation”).

  The type of crystal plane being oriented is not particularly limited, and is selected according to the direction of spontaneous polarization of the compound constituting the piezoelectric ceramic, the use of the crystal oriented ceramic, the required characteristics, and the like.

  For example, when the piezoelectric ceramic is made of an isotropic perovskite type compound, the oriented crystal plane is selected according to the purpose, such as pseudo cubic {100} plane, pseudo cubic {110} plane, pseudo cubic {111} plane, etc. Is done. In addition, “pseudocubic {HKL}” is generally an isotropic perovskite type compound having a structure slightly distorted from cubic such as tetragonal, orthorhombic, and trigonal, but the distortion is slight. This means that it is regarded as a cubic crystal and displayed as a Miller index.

  Further, when a specific crystal plane is plane-oriented, the degree of plane orientation can be represented by an average degree of orientation F (HKL) by the Lotgering method expressed by the following equation (1). .

In Equation 1, ΣI (hkl) is the sum of X-ray diffraction intensities of all crystal planes (hkl) measured for the crystal oriented ceramics, and ΣI ₀ (hkl) is the same as that for the crystal oriented ceramics. It is the sum total of X-ray diffraction intensities of all crystal planes (hkl) measured for non-oriented ceramics having a composition. Σ′I (HKL) is the sum of X-ray diffraction intensities of crystallographically equivalent specific crystal planes (HKL) measured for crystal-oriented ceramics, and Σ′I ₀ (HKL) is the crystal It is the sum total of X-ray diffraction intensities of specific crystal planes (HKL) crystallographically equivalent measured for non-oriented ceramics having the same composition as oriented ceramics.

  Therefore, when the crystal grains constituting the polycrystal are non-oriented, the average degree of orientation F (HKL) is 0%. Further, when the (HKL) planes of all the crystal grains constituting the polycrystal are oriented parallel to the measurement plane, the average degree of orientation F (HKL) is 100%.

  In general, the higher the proportion of oriented crystal grains, the higher the piezoelectric properties. For example, in the case where a specific crystal plane is plane-oriented, in order to obtain high piezoelectric characteristics, the average orientation degree F (HKL) by the Lotgering method expressed by the formula 1 is 30% or more. Preferably, it is 50% or more. In this case, the specific crystal plane to be oriented is preferably a plane perpendicular to the polarization axis. For example, when the piezoelectric ceramic is made of a KNN compound represented by the formula (1), the specific crystal plane to be oriented is preferably a pseudo-cubic {100} plane.

  When a specific crystal plane is axially oriented, the degree of orientation cannot be defined by the same degree of orientation (formula 1) as the plane orientation. However, the average orientation degree (hereinafter referred to as “axial orientation degree”) by the Rotgering method for (HKL) diffraction when X-ray diffraction is performed on a plane perpendicular to the orientation axis is used to determine the axial orientation. The degree can be expressed. In addition, the degree of axial orientation of the molded body in which the specific crystal plane is almost completely axially oriented is the same as the degree of axial orientation measured for the molded body in which the specific crystal plane is almost completely plane-oriented. .

  Piezoelectric ceramics in which a specific crystal plane is oriented in one direction are: (1) An anisotropic shaped powder having lattice matching with a specific crystal plane of the target piezoelectric ceramic whose development plane (surface with the largest area); The anisotropic powder is reacted with or without reacting with the second powder to be the target piezoelectric ceramic, and (2) is molded so that the anisotropic powder is oriented in one direction. 3) It is obtained by firing the obtained molded body at a predetermined temperature.

  When a raw material containing an anisotropically shaped powder that satisfies a predetermined condition is molded using a doctor blade method, an extrusion molding method, or the like, the anisotropically shaped powder is oriented in one direction by a shearing force acting during molding. When such a compact is fired, the development surface of the anisotropically shaped powder is inherited as a specific crystal surface of the target piezoelectric ceramic. Therefore, a crystallographically-oriented ceramic in which a specific crystal plane is oriented in one direction is obtained.

For example, a crystallographically-oriented ceramic composed of a KNN-based compound represented by the formula (1) is an anisotropic shaped powder, and a (K, Na) NbO ₃ (KNN) plate-like powder having a pseudo cubic {100} plane as a development plane On the other hand, a mixture of a second powder composed of an oxide, hydroxide, salt or the like containing Li, Sb and / or Ta so as to have a stoichiometric ratio is used as a starting material. Can be produced by molding and baking.

  Further, the KNN plate-like powder can be produced by the following method. That is, first, a plate-like powder composed of a bismuth layered perovskite type compound represented by the following formula (2) and having a development plane of {001} is synthesized using a flux method. The plate-like powder of the bismuth layered perovskite type compound having the {001} plane as the development plane has a good lattice matching with the KNN pseudocubic {100} plane, so that the pseudocubic { It functions as a template for synthesizing KNN plate-like powder having a 100} plane as a development plane.

(Bi ₂ O ₂ ) ²⁺ (Bi _0.5 AM _m-1 Nb _m O _{3m + 1} ) ^2- (2)
(Where m is an integer of 2 or more, AM is at least one alkali metal element selected from Li, K and Na)

Next, a compound containing K and / or Na is added to the plate-like powder so that (K, Na) NbO ₃ plate-like powder and Bi ₂ O ₃ are produced from this plate-like powder, and reacted in the flux. . After completion of the reaction, the flux is removed, and the excess component Bi ₂ O ₃ is dissolved in an acid or the like or volatilized to make the pseudo-cubic {100} plane a development plane, and (K, Na) A plate-like powder composed of NbO ₃ is obtained.

  Next, a method for manufacturing the piezoelectric ceramic according to the first embodiment of the present invention will be described. The method for manufacturing a piezoelectric ceramic according to the present embodiment includes a first step and a second step.

  First, the first step will be described. In the first step, a piezoelectric ceramic that has a cubic crystal structure at a high temperature and reversibly undergoes phase transition to tetragonal or orthorhombic when the temperature is lowered is subjected to a first polarization treatment in a temperature region that becomes tetragonal. It is a process of performing.

  The polarization method in the first step is not particularly limited, and various methods can be used. In the polarization treatment, generally, electrodes are formed by a method such as coating Au electrodes on the upper and lower surfaces of a sintered body processed into a disk shape by sputtering, and a predetermined direct current is applied in an insulating silicon oil heated to a predetermined temperature. This is done by applying the field for a predetermined time. In the first step, the polarization treatment may be performed using such a method, or another method may be used as long as the piezoelectric ceramic can be sufficiently polarized.

Polarization temperatures T ₁ in the first step may be a temperature of at least piezoelectric ceramics takes a tetragonal crystal structure. The specific polarization temperature T ₁ is selected as an optimum temperature according to the composition of the piezoelectric ceramic, the polarization method, the required characteristics, and the like. In general, the higher the polarization temperature T ₁ is increased, but decreases the workability, the crystal lattice is easily deformed, polarization treatment is facilitated.

For example, when the piezoelectric ceramic is made of a KNN compound represented by the formula (1), the orthorhombic to tetragonal transition point varies depending on the composition and changes from −50 ° C. to 200 ° C. In this case, the polarization temperatures T ₁ in the first step, at least, may be a temperature higher than the phase transition point. In general, the higher the temperature, the easier the lattice deformation becomes, so the temperature is higher than the orthorhombic → tetragonal transition temperature and higher than the Curie temperature (tetragonal → cubic phase transition temperature). It is preferable to perform polarization treatment at temperature. On the other hand, when the polarization temperature T ₁ is too high, because the workability is lowered undesirably. In particular, when the polarization treatment is performed in insulating silicon oil, the polarization temperature T ₁ in the first step is preferably 180 ° C. or lower, more preferably 150 ° C. or lower, and further preferably 130 ° C. or lower.

  The magnitude of the DC electric field applied during polarization is selected in accordance with the composition, required characteristics, polarization temperature, etc. of the piezoelectric ceramic. In general, the higher the DC electric field at the time of polarization, the higher the degree of polarization can be obtained. However, if the DC electric field becomes too large, there is a risk that the piezoelectric ceramic will be cracked by strain generated at the time of polarization. In order to obtain high piezoelectric characteristics, it is preferable that the direct current electric field has such a magnitude that the piezoelectric ceramic is saturatedly polarized in the tetragonal region and does not crack.

  The polarization process in the first step may be a process in which a DC electric field having a specific magnitude is applied only once at a specific temperature, or the same or different magnitude at the same or different temperature. You may perform the process which applies a DC electric field in multiple times. In order to obtain high piezoelectric characteristics, it is preferable to perform a plurality of polarization processes at the same or different temperatures until the piezoelectric ceramics are saturated and polarized.

  In addition, when performing polarization processing a plurality of times, the magnitude of the DC electric field at the time of each polarization processing may be the same or different. In particular, if polarization is first applied with a low DC electric field, and then the polarization is applied by sequentially increasing the magnitude of the DC electric field, saturation polarization can be facilitated without causing cracks in the piezoelectric ceramic. . This method is particularly effective when conditions necessary for saturation polarization are unknown.

  The time for applying the DC electric field is not particularly limited, and an optimum time is selected according to the composition, shape, required characteristics, etc. of the piezoelectric ceramic. The time for applying the DC electric field may be a time for completing the domain rotation under the conditions of the given polarization temperature and DC electric field. Usually, it is about several minutes to several tens of minutes, typically about 10 minutes.

The direction in which the direct current electric field is applied during the first polarization treatment is not particularly limited, and an optimum direction is selected according to the composition, shape, required characteristics, and the like of the piezoelectric ceramic. However, when the piezoelectric ceramic is made of crystal-oriented ceramics, the direct current electric field has an optimum direction depending on the orientation mode, the type of specific crystal plane being oriented, etc., so that the maximum piezoelectric characteristics can be obtained. Select. Basically, it is preferable to polarize in the same direction as the crystal orientation in which large elongation can be expected.
For example, when the piezoelectric ceramic is made of a KNN-based compound represented by the formula (1) and is a crystal-oriented ceramic in which the pseudo-cubic {100} plane is plane-oriented, when the piezoelectric longitudinal effect is mainly used, the direct current electric field is It is preferable to apply in a direction perpendicular to the plane on which the pseudo cubic {100} plane is oriented. On the other hand, when the piezoelectric lateral effect is mainly used, the DC electric field is preferably applied in a direction perpendicular to or parallel to the plane in which the pseudo cubic {100} plane is oriented depending on the application.
Here, the “vertical direction” does not mean only when the specific crystal plane is completely perpendicular to the orientation plane in which the crystal plane is oriented, but between the polarization direction and the direction perpendicular to the orientation plane. It means that there may be some gap between them. That is, as long as 180 degreeC domain inversion can be pulled out, there may be a gap between them. In order to efficiently bring out 180 ° C. domain inversion, the angle of deviation between the two is preferably 45 ° or less, and more preferably 30 ° or less. This also applies to the “parallel direction”.

  Next, the second step will be described. In the second step, the second polarization treatment is performed on the piezoelectric ceramic that has been subjected to the first polarization treatment in the tetragonal region in the temperature region that is further orthorhombic and in the same direction as the first polarization treatment. It is a process to be performed.

  The polarization method in the second step is not particularly limited. As in the first step, the polarization treatment may use a method in which a DC electric field is applied in insulating silicon oil heated to a predetermined temperature, or any other method as long as the piezoelectric ceramic can be sufficiently polarized. The method may be used.

Polarization temperature T ₂ in the second step may be a temperature of at least piezoelectric ceramics take orthorhombic crystal structure. Specific polarization temperature T _2, the composition of the piezoelectric ceramic, depending on the polarization method or the like, to select an optimum temperature.

For example, if composed of KNN-based compound piezoelectric ceramic is represented by (1), the polarization temperature T ₂ may be a temperature lower than at least orthorhombic → tetragonal transition temperature. The orthorhombic to tetragonal transition point of the compound represented by the formula (1) is in the temperature range of −50 ° C. to 200 ° C., but those having particularly high characteristics at room temperature are in the temperature range of 0 ° C. to 100 ° C. Furthermore, it exists in the temperature range of about 30 degreeC-100 degreeC. On the other hand, the polarization temperature T ₂ in the second step may be lower than room temperature (25 ° C.), but if the polarization temperature T ₂ is too low, lattice deformation is difficult to occur, which is not preferable. Also, when performing the polarization treatment in insulating silicone oil in, when the polarization temperature T ₂ becomes too low, moisture in the atmosphere is mixed into the insulating silicone oil, there is a possibility that insulation can not be maintained. Therefore, in such a case, the polarization temperature T ₂ in the second step is preferably at least 10 ° C..

  The magnitude of the DC electric field applied during polarization is selected in accordance with the composition, required characteristics, polarization temperature, etc. of the piezoelectric ceramic. In general, the higher the DC electric field at the time of polarization, the higher the degree of polarization can be obtained. However, if the DC electric field becomes too large, the piezoelectric ceramic may be cracked due to strain at the time of polarization. In order to obtain high piezoelectric characteristics, it is preferable that the direct current electric field has such a magnitude that the piezoelectric ceramic is saturatedly polarized in the orthorhombic region and does not crack.

  The polarization process in the second step may be a process in which a DC electric field having a specific magnitude is applied only once at a specific temperature, or the same or different magnitude at the same or different temperature. You may perform the process which applies a DC electric field in multiple times. In order to obtain high piezoelectric characteristics, it is preferable to perform a plurality of polarization processes at the same or different temperatures until the piezoelectric ceramics are saturated and polarized.

  In addition, when performing polarization processing a plurality of times, the magnitude of the DC electric field at the time of each polarization processing may be the same or different. In particular, if polarization is first applied with a low DC electric field, and then the polarization is applied by sequentially increasing the magnitude of the DC electric field, saturation polarization can be facilitated without causing cracks in the piezoelectric ceramic. . This method is particularly effective when conditions necessary for saturation polarization are unknown.

  The time for applying the DC electric field is not particularly limited, and an optimum time is selected according to the composition, shape, required characteristics, etc. of the piezoelectric ceramic. The time for applying the DC electric field may be a time for completing the domain rotation under the conditions of the given polarization temperature and DC electric field. Usually, it is about several minutes to several tens of minutes, typically about 10 minutes.

The direction in which the DC electric field is applied in the second polarization process is the same as the direction in which the DC electric field is applied in the first polarization process. After performing the first polarization treatment in the tetragonal region, and then performing the second polarization treatment in the same direction as the first polarization treatment in the orthorhombic region, a piezoelectric ceramic having high piezoelectric characteristics is obtained.
Here, “the same direction” does not mean only the case where the direction of the first polarization process and the direction of the second polarization process are completely the same, but the direction of the first polarization process and the second direction. This means that there may be a slight deviation from the direction of the polarization treatment. That is, as long as 180 ° domain inversion can be derived, there may be a deviation between the two directions. In order to efficiently bring out 180 ° C. domain inversion, the angle of deviation between the two is preferably 45 ° or less, and more preferably 30 ° or less.

  Note that the first step and the second step may be performed once each, or the first step and the second step may be alternately repeated. In this case, the first step needs to be the first step, but the last step may be either the first step or the second step. As described above, when the first step and the second step are alternately repeated, the 180 ° domain inversion component can be effectively used, and thus high piezoelectric characteristics can be obtained.

Moreover, when shifting from the first step to the second step, the piezoelectric ceramics may be cooled rapidly or may be gradually processed. In general, after the polarization treatment in the tetragonal region, the smaller the cooling rate when cooling to the orthorhombic region, the more the strain is released, so the 90 ° domain rotation component disappears and only the 180 ° domain inversion component remains. It tends to be easier. However, in the present invention, since the polarization treatment is further performed after the phase transition of the piezoelectric ceramic, a favorable polarization state can be obtained in either case of rapid cooling or slow cooling.
Further, when shifting from the first step to the second step, the transition may be made in a state where an electric field is continuously applied to the piezoelectric ceramic. In this case, the polarization process in the second step can be performed continuously. During the transition from the first step to the second step, the crystal structure of the piezoelectric ceramic undergoes a phase transition from tetragonal to orthorhombic, and the domain structure of each crystal grain is reconstructed in an electric field applied state. Since the polarization process is performed, a good polarization state can be obtained similarly.

Further, after the first step and / or after the second step, the piezoelectric ceramic may be aged. When aging is performed, a thermally or mechanically unstable component is removed, so that there is an advantage that deterioration of piezoelectric characteristics during use is suppressed. The aging conditions are not particularly limited, and optimal conditions may be selected according to the composition, shape, required characteristics, etc. of the piezoelectric ceramic.
Further, when the piezoelectric ceramic is used for a microphone, a speaker, a sonar, a knock sensor, etc., electrodes are usually formed on both sides of the piezoelectric ceramic. On the other hand, when piezoelectric ceramics are used for laminated actuators, certain types of piezoelectric transformers, bimorphs, etc., sheet-like piezoelectric ceramics and electrodes are alternately laminated. Furthermore, when piezoelectric ceramics are used in certain knock sensors, traveling wave type ultrasonic motors, etc., a plurality of electrodes are formed on the front surface and the back surface is formed to polarize adjacent regions in opposite directions. A common electrode is formed. In any case, the 180 ° domain inversion can be effectively extracted by performing the first step and the second step described above on the region sandwiched between the opposing electrodes.

  Next, the operation of the piezoelectric ceramic manufacturing method according to the present embodiment will be described. According to the manufacturing method according to the present embodiment, the degree of polarization can be stably increased and saturated, and a piezoelectric ceramic having higher piezoelectric characteristics than the conventional method can be obtained. Although the details of the reason are not clear, it is thought to be due to the following reasons.

  In general, the degree of polarization of a piezoelectric ceramic is the sum of the degrees of spontaneous polarization possessed by individual crystal grains constituting the ceramic (polycrystal). The spontaneous polarization axis of each crystal grain varies depending on the crystal structure, and is a pseudo cubic [100] axis direction in tetragonal crystal and a pseudo cubic [110] axis direction in orthorhombic crystal. The number of equivalent spontaneous polarization axis directions varies depending on the crystal structure, and is 6 for tetragonal crystals and 12 for orthorhombic crystals. Within each crystal grain, a plurality of domain components having different angles between the spontaneous polarization axes are formed, and the degree of polarization and the direction of the polarization axis of each crystal grain are determined as the sum, and the sum total is innumerable. The degree of polarization and the polarization axis of ceramics made of crystal grains are determined.

  In the piezoelectric ceramic immediately after sintering, the spontaneous polarization axis in each crystal grain or in each crystal grain is in a random direction, so the degree of polarization of the entire ceramic is zero. Such a piezoelectric ceramic can be polarized only by applying a high electric field in a desired direction and aligning the direction of the spontaneous polarization axis.

  Further, the type of domain component formed in the crystal grain varies depending on the crystal structure. For example, in the case of tetragonal crystal, there are a 180 ° domain and a 90 ° domain. For example, in the case of orthorhombic crystals, there are a 120 ° domain and a 60 ° domain in addition to the 180 ° domain and the 90 ° domain.

  When a high electric field is applied to piezoelectric ceramics in which various domain components are mixed, each domain component rotates and the proportion of domains having a polarization direction close to the electric field direction increases. In this case, 180 ° domain inversion does not involve large distortion, but non-180 ° domain rotation (90 ° domain rotation, 120 ° domain rotation, 60 ° domain rotation, etc.) is known to involve large distortion. . Therefore, in order to stably increase the degree of polarization and suppress variations, it is desirable to make maximum use of 180 ° domain inversion, and as a result, a piezoelectric ceramic having a large piezoelectric d constant can be obtained.

FIG. 1 shows changes in the direction of spontaneous polarization when the conventional method and the method according to the present embodiment are used. Piezoelectric ceramics have a cross-section that is represented by a horizontally long rectangle, and the direction of spontaneous polarization inside the piezoelectric ceramic is schematically depicted by several arrows in the vertical and horizontal directions. These arrows do not indicate the crystal particles constituting the piezoelectric ceramic and the crystal orientation thereof.
FIGS. 1A and 1A conceptually show the direction of spontaneous polarization of a non-oriented piezoelectric ceramic having a tetragonal crystal structure, and the state before the polarization treatment. Arbitrary spontaneous polarization axis directions inherent in non-oriented piezoelectric ceramics are schematically represented by four arrows in the vertical direction and the horizontal direction. Although not drawn in the figure, the tetragonal spontaneous polarization axis is in the pseudo-cubic [100] direction.
As described above, in the tetragonal crystal, there are a 180 ° domain and a 90 ° domain, and therefore, in FIGS. 1A and 1A, each is represented by a vertical arrow and a horizontal arrow. It is expressed. Since the direction of spontaneous polarization by each domain is in an arbitrary direction, the degree of polarization of the entire piezoelectric ceramic is zero.

  When an electric field E is applied to such a piezoelectric ceramic in the vertical direction, as shown in FIGS. 1 (a) and (2), the domain indicated by the downward arrow is inverted by 180 ° domain inversion in the electric field direction. Then, a 90 ° domain rotation in which the domain indicated by the left and right arrows rotates in the electric field direction occurs. As a result, the direction of spontaneous polarization of each domain is aligned with the direction of the electric field, and the entire ceramic exhibits piezoelectric characteristics.

  However, the 180 ° domain inversion is not accompanied by a large strain, whereas the 90 ° domain rotation is accompanied by a large strain, so that the 90 ° domain rotation component returns to the original 90 ° domain during use, and the piezoelectric properties Cause deterioration. Therefore, when used for applications requiring durability, aging is performed after polarization treatment to remove unstable distortion components. As a result, the degree of polarization of the piezoelectric ceramic can be obtained with only a stable 180 ° domain rotation component, as shown in FIGS.

  In contrast, the non-oriented piezoelectric ceramic having a tetragonal (T) and orthorhombic (O) crystal structure at high and low temperatures, respectively, has a first polarization in the tetragonal region (for example, 100 ° C.). When processing is performed, 180 ° domain inversion and 90 ° domain rotation occur as described above. As a result, as shown in FIGS. 1 (b) and (1), the ceramics as a whole did not have spontaneous polarization, but as shown in FIGS. 1 (b) and (2), the spontaneous polarization axes were aligned in the electric field direction. It is done.

  Next, when this piezoelectric ceramic is cooled to room temperature, it passes through the phase transition point and the crystal structure undergoes phase transition to orthorhombic (O). At this time, the spontaneous polarization axis changes from a tetragonal (T) pseudo cubic [100] axis to an orthorhombic (O) pseudo cubic [110] axis. Further, it is considered that the domain structure is reconstructed due to a decrease in symmetry from tetragonal (T) to orthorhombic (O).

  It is not clear how the domain structure changes due to the phase transition, but since the spontaneous polarization formed by the 180 ° domain rotation is not distorted, most of it reflects directly in the vertical direction of the piezoelectric ceramics. It is thought that it is done. On the other hand, since the spontaneous polarization axis formed by the 90 ° domain rotation is accompanied by distortion, it is considered that stress is relaxed along with the phase transition and is divided into several spontaneous polarization axis components capable of domain rotation. When the tetragonal crystal (T) is changed to the orthorhombic crystal (O), the number of equivalent spontaneous polarization axes is increased, so that a new spontaneous polarization axis capable of domain rotation is also added. This point is considered to be the same when the 90 ° domain rotation component is restored to the original state by performing aging and / or slow cooling after the first step.

  As described above, it is considered that the domain component newly generated by the phase transition may be rotated by 180 ° domain by polarization processing in the orthorhombic region, or may be rotated by 90 ° domain. In FIGS. 1B and 1C, the small arrow on the right side schematically represents the spontaneous polarization axis component newly formed by the phase transition. Further, the newly generated spontaneous polarization axis component is in a state in which it is directed in an arbitrary direction in order to stabilize so that its own energy is minimized.

  Next, when such a piezoelectric ceramic is polarized in an orthorhombic region (for example, room temperature), 180 ° domain inversion and 90 ° domain rotation occur as shown in FIGS. And the direction of the spontaneous polarization axis is aligned with the electric field direction. However, since it is considered that a component capable of 180 ° domain rotation in the orthorhombic (O) region is newly generated by the phase transition, as shown in FIGS. Even if aging is performed, not all of the newly generated domain components are restored, and the newly generated 180 ° domain rotatable components remain aligned in the polarization direction. Therefore, the degree of polarization can be stably increased and saturated as compared with the conventional method, and high piezoelectric characteristics can be obtained.

  This point is considered to be almost the same in the case of crystal-oriented ceramics. That is, in the case of piezoelectric ceramics having a tetragonal crystal (T) and orthorhombic crystal (O) crystal structure at a high temperature and a low temperature, respectively, and having a specific crystal plane (for example, pseudo-cubic {100} plane) oriented in a plane. Immediately after sintering, the degree of polarization is zero as a whole, but since the plane perpendicular to the polarization axis is oriented, the proportion of 180 ° domain is considered to be higher than that of non-oriented ceramics. . FIG.1 (c) (1) represents such a state typically.

  When an electric field E is applied to such a crystal-oriented ceramic in a direction perpendicular to the orientation plane, domain rotation (mainly 180 ° domain inversion) occurs, as shown in FIGS. The direction of the spontaneous polarization axis is aligned with the electric field direction. Next, when this is cooled to the orthorhombic (O) region, as shown in FIGS. 1 (c) and (3), the domain structure is reconstructed by the phase transition, and some of the spontaneous polarization axes are It is thought that it is divided into spontaneous polarization axis components that can rotate the domain.

  Further, when such a crystal oriented ceramic is polarized in the orthorhombic region, the direction of the newly generated spontaneous polarization axis is aligned with the electric field direction as shown in FIGS. . Moreover, since the pseudo-cubic {100} plane is oriented, it is considered that the proportion of components newly generated by phase transition and capable of 180 ° domain inversion is higher than that of non-oriented ceramics. As a result, as shown in FIGS. 1C and 5, even when aging is performed after polarization, most of the newly generated components remain aligned in the electric field direction. Therefore, the degree of polarization can be stably increased and saturated as compared with the conventional method, and high piezoelectric characteristics can be obtained.

  As described above, the method according to the present embodiment can effectively extract the 180 ° domain rotation component by utilizing the crystal phase transition from tetragonal to orthorhombic, and thus has a characteristic with the spontaneous polarization axis aligned. It is thought that good piezoelectric ceramics can be obtained. In addition, when the piezoelectric ceramic subjected to such treatment is further subjected to the treatment in the first step and the treatment in the second step, the 180 ° domain rotation component that could not be extracted in the first step and the second step. It is considered that a stable and reliable spontaneous polarization state based on 180 ° domain rotation is obtained. Furthermore, when the present invention is applied to a piezoelectric ceramic in which a specific crystal plane is oriented, a domain structure close to a single crystal is obtained, and exhibits higher piezoelectric characteristics than non-oriented ceramics having the same composition.

  Next, a method for manufacturing a piezoelectric ceramic according to the second embodiment of the present invention will be described. The method for manufacturing a piezoelectric ceramic according to the present embodiment includes a first step and a second step.

  The first step in the present embodiment is the same as the first embodiment in that the first polarization process is performed in the temperature region where tetragonal crystals are formed, but the first region and the second region are adjacent to the piezoelectric ceramic. The first and second regions are different from each other in that the first polarization process is performed in opposite directions. The second step in the present embodiment is the same as the first embodiment in that the second polarization treatment is performed in the orthorhombic temperature region, but the first region and the second region are Each is different in that the second polarization process is performed in the same direction as the first polarization process. The other points regarding the “piezoelectric ceramics”, “first polarization process”, and “second polarization process” are the same as those in the first embodiment, and thus the description thereof is omitted.

  In the present embodiment, the shape, size, arrangement method, and the like of the first region and the second region are not particularly limited, and can be arbitrarily selected according to the use, required characteristics, and the like of the piezoelectric ceramic.

  For example, when using piezoelectric ceramics as a driving source of a traveling wave type ultrasonic motor, a certain kind of knock sensor, etc., first, plate-shaped piezoelectric ceramics such as a rectangular shape, an arc shape, or a ring shape are manufactured. Next, a common electrode is formed on one plate surface of the piezoelectric ceramic, and the isolated first electrode and second electrode are adjacent to the other plate surface at positions corresponding to the first region and the second region, respectively. To form. In this case, one first electrode and one second electrode may be formed on the piezoelectric ceramic, or two or more first electrodes and two or more second electrodes may be alternately formed. May be. In addition, the distance between the first electrode and the second electrode is appropriately adjusted so that the piezoelectric ceramic has a required function.

  When the piezoelectric ceramic is a crystal-oriented ceramic, when the piezoelectric ceramic is used as a driving source for a traveling wave type ultrasonic motor, the piezoelectric ceramic is a crystal in which a predetermined crystal plane is oriented parallel to the plate surface. Oriented ceramics are preferred, and crystal oriented ceramics in which a plane perpendicular to the polarization axis is oriented parallel to the plate surface are particularly preferred.

  When the first polarization treatment is performed on the piezoelectric ceramic in which the first region and the second region are formed in a tetragonal temperature region, direct current electric fields in opposite directions are applied to the first electrode and the second electrode. Is applied, the first region and the second region are polarized in opposite directions.

Next, when the second polarization process is performed on the piezoelectric ceramic in the orthorhombic temperature region, the second region is in the same direction as the first polarization process with respect to the first region and the second region, respectively. When the polarization process is performed, the degree of polarization in the first region and the second region can be increased stably in the opposite directions and saturated. The piezoelectric ceramics thus obtained are formed in opposite directions and adjacent to each other with a high degree of polarization. For example, this is applied to a traveling wave type ultrasonic motor, a certain knock sensor or the like. If applied, a higher output can be obtained compared to the conventional method.
Note that the polarization of adjacent regions may be performed simultaneously or individually. When the adjacent regions are simultaneously polarized, specifically, one of the first electrode and the second electrode described above may be connected to +, the other is connected to −, and the common electrode may be polarized at a single potential at a time. When the adjacent regions are individually polarized, specifically, polarization may be first performed between the first electrode and the common electrode, and then polarized in the opposite direction between the second electrode and the common electrode.

  Next, a method for manufacturing a piezoelectric ceramic according to the third embodiment of the present invention will be described. The method for manufacturing a piezoelectric ceramic according to the present embodiment includes a process A and a process B.

  Step A is a step of performing a first polarization process and a second polarization process in the first direction on the piezoelectric ceramic. In this case, the “first direction” can be arbitrarily selected according to the use, required characteristics, and the like of the piezoelectric ceramic. For example, when the piezoelectric ceramic is used as a Rosen type piezoelectric transformer, it is preferable that the piezoelectric ceramic is formed in a plate shape and the longitudinal direction thereof is the “first direction”. Specifically, an output electrode P is formed on one end surface in the longitudinal direction of a long plate-shaped piezoelectric ceramic, and the input electrodes are opposed to each other on the upper and lower plates on the end surface side facing the electrode. Q and R may be formed, and the first polarization process and the second polarization process may be performed in the longitudinal direction. That is, an electric field may be applied between the electrode P and the electrodes Q and R to perform the first polarization process and the second polarization process. Here, the first polarization process and the second polarization process are the same as the first polarization process and the second polarization process described in the piezoelectric ceramic manufacturing method according to the second embodiment of the present invention. Yes, the first polarization process is performed in the temperature region where tetragonal crystals are formed, and the second polarization process is performed in the temperature region where orthorhombic crystals are formed.

  Step B is a step of performing a first polarization process and a second polarization process in a second direction different from the first direction on a part of the piezoelectric ceramic subjected to the process A. In this case, the size, position, and the like of the second direction and the area where the process B is performed can be arbitrarily selected according to the use of the piezoelectric ceramic, the required characteristics, and the like. For example, when the piezoelectric ceramic is used as a Rosen-type piezoelectric transformer, the “second direction” is preferably a direction perpendicular to the first direction, and the region where the process B is performed is on one side of the plate-shaped piezoelectric ceramic. About half the area is preferred.

  When the piezoelectric ceramic is a crystal-oriented ceramic, when the piezoelectric ceramic is used as a Rosen-type piezoelectric transformer, the plane perpendicular to the polarization axis may be oriented in any direction. However, in order to obtain high conversion efficiency, the piezoelectric ceramic is preferably a crystal-oriented ceramic in which a plane perpendicular to the polarization axis is oriented parallel to the plate surface.

  The other points regarding the “piezoelectric ceramics”, “first polarization process”, and “second polarization process” are the same as those in the first embodiment, and thus the description thereof is omitted.

  When the first polarization process and the second polarization process are performed in the first direction on the piezoelectric ceramic, the degree of polarization in the first direction can be stably increased and saturated. Next, when the first polarization process and the second polarization process are performed in a second direction on a part of such piezoelectric ceramics, the degree of polarization in a second direction different from the first direction is stabilized. Can be increased and saturated. The piezoelectric ceramics obtained in this way are formed in different directions and regions with a high degree of polarization. Therefore, if this is applied to, for example, a Rosen-type piezoelectric transformer, the conversion is higher than in the conventional method. Efficiency is obtained.

  Next, a method for manufacturing a piezoelectric ceramic according to the fourth embodiment of the present invention will be described. The method for manufacturing a piezoelectric ceramic according to the present embodiment includes a process C, a process D, and a process E.

  Step C is a step of producing a laminate of a plurality of piezoelectric ceramics and a plurality of electrodes. The manufacturing method of a laminated body is not specifically limited, A various method can be used. The laminated body is usually produced by forming an electrode layer on one or both sides of a piezoelectric ceramic molded body formed into a sheet shape by a technique such as printing, and laminating, pressing and sintering. The number of piezoelectric ceramics laminated is set to an optimum number according to the use of the laminated body. For example, a bimorph is composed of a laminate of two piezoelectric ceramic layers and three electrode layers formed on the middle and the upper and lower surfaces of the laminate. Further, for example, the low-impedance portion of the laminated actuator, the laminated piezoelectric transformer, etc. includes k (k ≧ 2) piezoelectric ceramic layers, and the total (k + 1) formed in the middle of each piezoelectric ceramic layer and on the upper and lower surfaces of the laminated body. ) It consists of a laminate of individual electrode layers.

  Step D is a step in which after such a laminate is manufactured, the first polarization treatment and the second polarization treatment are performed on the m-th piezoelectric ceramic sandwiched between the electrodes. In this case, the polarization direction of the mth piezoelectric ceramic is not particularly limited, and an optimum direction is selected according to the use of the laminate.

  In step E, at the same time as step D or separately from step D, the nth (n ≠ m) piezoelectric ceramic sandwiched between the electrodes is subjected to the first polarization in the same or different direction as the mth piezoelectric ceramic. This is a step of performing the treatment and the second polarization treatment.

  The polarization direction of the nth piezoelectric ceramic varies depending on the use of the laminate. For example, in the case of bimorph, there are a type that polarizes two piezoelectric ceramic layers in the same direction and a type that polarizes in the opposite direction. For example, in the case of a laminated actuator, adjacent piezoelectric ceramic layers are polarized in opposite directions. Furthermore, in the case of a laminated piezoelectric transformer, the low impedance portion is composed of a laminate of a plurality of piezoelectric ceramic layers and electrode layers, and adjacent piezoelectric ceramic layers are polarized in the same direction (plate thickness direction). . On the other hand, the high impedance portion of the multilayer piezoelectric transformer is composed of a single piezoelectric ceramic layer having electrodes formed on the upper and lower surfaces thereof, and is polarized in the plate thickness direction of the high impedance portion.

  In addition, the polarization processing of the nth piezoelectric ceramic layer may be performed simultaneously with the polarization processing of the mth piezoelectric ceramic or may be performed individually. For example, when the adjacent piezoelectric ceramic layers are polarized in the same direction and at the same time, the potential of each electrode may be decreased stepwise and polarized at a time. Also, for example, when adjacent piezoelectric ceramic layers are polarized in opposite directions and simultaneously, each electrode may be alternately connected to + and-and polarized at once. On the other hand, when the adjacent piezoelectric ceramic layers are individually polarized, the electrodes formed on both surfaces of the mth piezoelectric ceramic layer are connected to + and −, respectively, and after the mth piezoelectric ceramic layer is polarized, n The electrodes formed on both surfaces of the th piezoelectric ceramic layer may be connected to + and-, respectively, and the n th piezoelectric ceramic layer may be polarized.

  The other points regarding the “piezoelectric ceramics”, “first polarization process”, and “second polarization process” are the same as those in the first embodiment, and thus the description thereof is omitted.

  In a laminate of a plurality of piezoelectric ceramics and a plurality of electrodes, when the first polarization treatment and the second polarization treatment are performed on the mth region sandwiched between the electrodes, the polarization degree of the mth region is stabilized. Can be increased and saturated. Next, the first polarization process and the second polarization process are performed on the nth region sandwiched between the electrodes simultaneously with or separately from the mth region and in the same or different direction as the mth region. Then, the polarization degree of the nth region can be stably increased / saturated. In the laminate obtained in this way, the adjacent piezoelectric ceramic layers are polarized in the same direction or in different directions, and each piezoelectric ceramic layer has a high degree of polarization. When applied to a piezoelectric transformer, the performance is improved as compared with the conventional method.

(1) Synthesis of NaNbO ₃ (NN) plate powder.
Bi ₂ O ₃ powder, Na ₂ CO ₃ powder and Nb ₂ O ₅ powder so as to have a Bi _2.5 Na _3.5 Nb ₅ O ₁₈ (hereinafter referred to as “BINN5”) composition in stoichiometric ratio. Were weighed and wet mixed. Next, 50 wt% NaCl was added as a flux to the raw material, and dry mixed for 1 hour.

  Next, the obtained mixture was put in a platinum crucible and heated under the conditions of 850 ° C. × 1 h to completely dissolve the flux, and further heated under the conditions of 1100 ° C. × 2 h to synthesize BINN5. It was. The temperature rising rate was 200 ° C./h, and the temperature lowering was furnace cooling. After cooling, the flux was removed from the reaction product with a hot water bath to obtain BINN5 powder. The obtained BINN5 powder was a plate-like powder having a {001} plane as a development plane.

Next, this BINN5 plate powder was mixed with an amount of Na ₂ CO ₃ powder necessary for NN synthesis, and heat-treated at 950 ° C. for 8 hours in a platinum crucible using NaCl as a flux.

Since the obtained reaction product contains Bi ₂ O ₃ in addition to the NN powder, after removing the flux from the reaction product, it is put into HNO ₃ (1N) and Bi produced as an extra component. ₂ O ₃ was dissolved. Further, this solution was filtered to separate the NN powder and washed with ion exchange water at 80 ° C. The obtained NN powder was a plate-like powder having a pseudo cubic {100} plane as a development plane, a particle size of 10 to 20 μm, and an aspect ratio of about 10 to 20.

(2) Preparation of crystal oriented ceramics having {Li _0.02 (K _0.5 Na _0.5 ) _0.98 } {Nb _0.94 Sb _0.06 } O ₃ composition.
NN plate-like powder produced in (1), and non-plate-like NN powder, KN (KNbO ₃ ) powder, KT (KTaO ₃ ) powder, LS (LiSbO ₃ ) powder and NS (NaSbO ₃ ) powder Weighed so as to obtain the composition as follows, and performed wet mixing for 20 hours.

A binder (Sekisui Chemical Co., Ltd., ESREC (registered trademark) BH-3) and a plasticizer (butyl phthalate) and 1 mol of {Li _0.02 (K _0.5 To each of Na _0.5 ) _0.98 } {Nb _0.94 Sb _0.06 } O ₃ , 10.35 g and 10.35 g were added, respectively, and further mixed for 2 hours.

The blending amount of the NN plate-like powder was such that 5 at% of the A-site element of the KNN compound (ABO ₃ ) synthesized from the starting material was supplied from the NN plate-like powder. Further, the non-plate-like NN powder, KN powder, KT powder, LS powder and NS powder include predetermined amounts of K ₂ CO ₃ powder, Na ₂ CO ₃ powder, Nb ₂ O ₅ powder, Ta ₂ O ₅ powder and / or Alternatively, a mixture containing Sb ₂ O ₅ powder was prepared by a solid phase method in which the reaction product was heated at 750 ° C. for 5 hours and the reaction product was ball milled.

  Next, the mixed slurry was formed into a tape having a thickness of 100 μm using a doctor blade device. Furthermore, by laminating, pressing and rolling this tape, a plate-like molded body having a thickness of 1.5 mm was obtained. Next, the obtained plate-like molded body was degreased in the air under the conditions of heating temperature: 600 ° C., heating time: 2 hours, heating rate: 50 ° C./h, cooling rate: furnace cooling. Further, after the degreased plate-like molded body was subjected to CIP treatment at a pressure of 300 MPa, in oxygen, the firing temperature was 1100 ° C., the heating time was 1 hour, and the temperature rising / falling rate was 200 ° C./hr. Atmospheric pressure sintering was performed.

(3) Evaluation of sintered body characteristics and piezoelectric characteristics of crystal oriented ceramics having {Li _0.02 (K _0.5 Na _0.5 ) _0.98 } {Nb _0.94 Sb _0.06 } O ₃ composition .
About the obtained sintered compact, the average orientation degree F (100) of the {100} plane by the Lotgering method about a sintered compact density and a surface parallel to a tape surface was measured. The average degree of orientation F (100) was calculated using the formula (1). The relative density of the crystallographically-oriented ceramic obtained in this example was 95% or more. Further, the pseudo cubic {100} plane was oriented parallel to the tape surface, and the average orientation degree of the pseudo cubic {100} plane by the Lotgering method reached 82%.

Next, after polarization treatment was performed on the crystal-oriented ceramics, the piezoelectric strain constant (d ₃₁ ), the electromechanical coupling coefficient (k _p ), and the piezoelectric voltage sensor g coefficient (g ₃₁ ), which are piezoelectric characteristics, were measured. In addition, the temperature dependence of the piezoelectric d ₃₁ constant and the Curie temperature in the temperature range of −50 ° C. to 350 ° C. were evaluated as necessary.

  First, a disk-shaped sample having a thickness of 0.7 mm and a diameter of 11 mm whose upper and lower surfaces are parallel to the tape surface is prepared from the obtained sintered body by grinding, polishing, and processing, and Au electrodes are formed on the upper and lower surfaces. Was coated by sputtering. Next, after setting the disk-like sample in insulating silicon oil at 100 ° C. and holding it for about 3 minutes to make the temperature of the sample constant, an electric field of 1 kV / mm is applied in the vertical direction of the disk-like sample for 10 minutes. The first polarization treatment ”was performed (Sample No. 1).

  Immediately after the application of the voltage was stopped, it was transferred into insulating silicon oil at room temperature (about 25 ° C.) and rapidly cooled. The insulating silicon oil adhering to the sample was washed with an acetone solvent, and its piezoelectric characteristics were measured at room temperature by the resonance antiresonance method.

Hereinafter, in the same manner, 2 kV / mm (sample No. 2), 3 kV / mm (sample No. 3), 4 kV / mm (sample No. 4) in an insulating silicon oil at 100 ° C. for the same sample. And an electric field of 5 kV / mm (sample No. 5) were sequentially applied, and the respective piezoelectric characteristics were measured at room temperature. Further, the sample (sample No. 5 in the case of this example) with the highest piezoelectric d ₃₁ constant was left at room temperature and aged for about 20 hours, and then the piezoelectric characteristics were measured again at room temperature (sample) No. 6).

In addition, with respect to the sample (sample No. 6) obtained with the highest piezoelectric d ₃₁ constant and aged at room temperature, a voltage of 4 kV / mm was further applied for 10 minutes in the vertical direction of the disk-shaped sample in insulating silicon oil at room temperature. After performing the “second polarization treatment” to be applied, the piezoelectric characteristics were evaluated at room temperature (Sample No. 7). Further, this sample was allowed to stand at room temperature and aged for about 20 hours, and then its piezoelectric characteristics were evaluated again at room temperature (sample No. 8). Table 1 shows the polarization conditions and piezoelectric characteristics of each sample.

In the case of the present example, the highest piezoelectric d ₃₁ constant was obtained when the first polarization treatment was performed with the electric field strength set to 5 kV / mm (sample No. 5). In contrast, the piezoelectric characteristics did not deteriorate even when aging was performed at room temperature (Sample No. 6). Further, the sample No. 6 was subjected to the second polarization treatment with an electric field strength of 4 kV / mm, the piezoelectric characteristics were further improved (Sample No. 7). In addition, the piezoelectric characteristics did not deteriorate even when aging was performed at room temperature (Sample No. 8). Piezoelectric properties after the second polarization treatment (Sample No.5), as compared to the piezoelectric characteristics after the first polarization treatment (Sample No.7), _{d 31} at room temperature is 1.10 times, kp is 1. _{14-fold, g 31} was improved to 1.32 times.

{Li _0.02 (K _0.5 Na _0.5 ) _0.98 } {Nb _{0 .0} } According to the same procedure as in Example 1 except that the firing temperature of the degreased plate-like molded body was 1125 ° C. A crystallographically-oriented ceramic having a ₉₄ Sb _0.06 } O ₃ composition was produced.

  With respect to the obtained crystallographically-oriented ceramics, the sintered body density and the average degree of orientation were evaluated under the same conditions as in Example 1. The relative density of the crystallographically-oriented ceramic obtained in this example was 95% or more. Further, the pseudo cubic {100} plane was oriented parallel to the tape surface, and the average orientation degree of the pseudo cubic {100} plane by the Lotgering method reached 82%.

  Next, according to the same procedure as in Example 1, the first polarization treatment and aging at room temperature, and the second polarization treatment and aging at room temperature were performed. Table 2 shows the polarization conditions and piezoelectric characteristics of each sample.

In the case of the present example, the highest piezoelectric d ₃₁ constant was obtained when the first polarization treatment was performed with the electric field strength set to 5 kV / mm (sample No. 5). On the other hand, even when aging was performed at room temperature, the piezoelectric characteristics were not deteriorated except that d ₃₁ was slightly reduced (Sample No. 6). Further, the sample No. 6 was subjected to the second polarization treatment with an electric field strength of 4 kV / mm, the piezoelectric characteristics were further improved (Sample No. 7). On the other hand, even when aging was performed at room temperature, the piezoelectric characteristics hardly deteriorated except that d ₃₁ slightly decreased (Sample No. 8). The piezoelectric properties after the second polarization treatment (Sample No. 7) are 1.05 times d ₃₁ at room temperature and kp is 1.5 times that of the piezoelectric properties after the first polarization treatment (Sample No. 5). _{13-fold, g 31} was improved to 1.25 times.

In FIG. The temperature dependence of the piezoelectric d ₃₁ constant measured for 8 is shown. The maximum value of d ₃₁ at −50 to 350 ° C. reached 146.7 pm / V at 94 ° C., and the Curie temperature was 318 ° C. From FIG. 2, it is considered that the phase transition temperature from orthorhombic to tetragonal is about 94 ° C., and the phase transition temperature from tetragonal to cubic is about 318 ° C. When the crystal phase of this disc-like sample was examined using an X-ray diffractometer, it was confirmed that it was orthorhombic at room temperature, tetragonal at 100 ° C., and cubic at 350 ° C.

{Li _0.02 (K _0.5 Na _0.5 ) _0.98 } {Nb _0.88 Ta _0.10 Sb _0.02 } O ₃ {Li _0.02 (K _0.5 Na _0.5 ) _0.98 } {Nb _0.88 Ta _{0 .0} , following the same procedure as in Example 1, except that the firing temperature of the shaped compact was 1125 ° C. Crystal oriented ceramics having a composition of ₁₀ Sb _0.02 } O ₃ were produced.

  With respect to the obtained crystallographically-oriented ceramics, the sintered body density and the average degree of orientation were evaluated under the same conditions as in Example 1. The relative density of the crystallographically-oriented ceramic obtained in this example was 95% or more. Further, the pseudo cubic {100} plane was oriented parallel to the tape surface, and the average degree of orientation of the pseudo cubic {100} plane by the Lotgering method reached 81%.

  Next, according to the same procedure as in Example 1, the first polarization treatment and aging at room temperature, and the second polarization treatment and aging at room temperature were performed. Table 3 shows the polarization conditions and piezoelectric characteristics of each sample.

In the case of the present example, the highest piezoelectric d ₃₁ constant was obtained when the first polarization treatment was performed with the electric field strength set to 5 kV / mm (sample No. 5). In contrast, even when aging was performed at room temperature, the piezoelectric characteristics hardly deteriorated (Sample No. 6). Further, the sample No. 6 was subjected to the second polarization treatment with an electric field strength of 4 kV / mm, the piezoelectric characteristics were further improved (Sample No. 7). In addition, the piezoelectric characteristics did not deteriorate even when aging was performed at room temperature (Sample No. 8). Piezoelectric properties after the second polarization treatment (Sample No.7), as compared to the piezoelectric characteristics after the first polarization treatment (Sample No.5), _{d 31} at room temperature is 1.35 times, kp is 1. 37 _{times, g 31} was improved to 1.49 times.

{Li _0.02 (K _0.5 Na _0.5 ) _0.98 } {Nb _0.88 Ta _0.10 Sb _0.02 } O ₃ The shaped compact was hot-pressed in oxygen at a firing temperature of 1125 ° C., a heating time of 1 hour, a pressing force of 35 kg / cm ² (3.43 MPa), and a temperature rising / falling rate of 200 ° C./h. Otherwise, following the same procedure as in Example 1, {Li _0.02 (K _0.5 Na _0.5 ) _0.98 } {Nb _0.88 Ta _0.10 Sb _0.02 } O ₃ composition Crystal-oriented ceramics were produced.

  With respect to the obtained crystallographically-oriented ceramics, the sintered body density and the average degree of orientation were evaluated under the same conditions as in Example 1. The relative density of the crystallographically-oriented ceramic obtained in this example was 95% or more. Further, the pseudo cubic {100} plane was oriented parallel to the tape surface, and the average degree of orientation of the pseudo cubic {100} plane by the Lotgering method reached 87%.

  Next, according to the same procedure as in Example 1, the first polarization treatment and aging at room temperature, and the second polarization treatment and aging at room temperature were performed. Table 4 shows the polarization conditions and piezoelectric characteristics of each sample.

In the case of the present example, the highest piezoelectric d ₃₁ constant was obtained when the first polarization treatment was performed with the electric field strength set to 5 kV / mm (sample No. 5). On the other hand, even when aging was performed at room temperature, the piezoelectric characteristics hardly deteriorated (sample No. 6) except that d ₃₁ slightly decreased. Further, the sample No. 6 was subjected to the second polarization treatment with an electric field strength of 4 kV / mm, the piezoelectric characteristics were further improved (Sample No. 7). On the other hand, even when aging was performed at room temperature, the piezoelectric characteristics were not deteriorated except that d ₃₁ was slightly decreased (Sample No. 8). The piezoelectric characteristics after the second polarization treatment (Sample No. 7) are 1.10 times d ₃₁ at room temperature and kp is 1.times. Compared to the piezoelectric characteristics after the first polarization treatment (Sample No. 5). _{16-fold, g 31} was improved to 1.25 times.

In FIG. The temperature dependence of the piezoelectric d ₃₁ constant measured for 8 is shown. The maximum value of d ₃₁ at −50 to 350 ° C. reached 117.6 pm / V at 92 ° C., and the Curie temperature was 331 ° C. From FIG. 3, it is considered that the phase transition temperature from orthorhombic to tetragonal is about 92 ° C., and the phase transition temperature from tetragonal to cubic is about 331 ° C. When the crystal phase of this disc-like sample was examined using an X-ray diffractometer, it was confirmed that it was orthorhombic at room temperature, tetragonal at 100 ° C., and cubic at 350 ° C.

2 at% of the A-site element is supplied from the NN plate-like powder, and {Li _0.02 (K _0.5 Na _0.5 ) _0.98 } {Nb _0.81 Ta _0.14 Sb _0.05 } According to the same procedure as in Example 1, except that the starting materials are blended so as to have an O ₃ composition, and the firing temperature of the plate-shaped molded body after degreasing is 1150 ° C., {Li _0.02 (K _0.5 Crystal oriented ceramics having a composition of Na _0.5 ) _0.98 } {Nb _0.81 Ta _0.14 Sb _0.05 } O ₃ were prepared.

  With respect to the obtained crystallographically-oriented ceramics, the sintered body density and the average degree of orientation were evaluated under the same conditions as in Example 1. The relative density of the crystallographically-oriented ceramic obtained in this example was 95% or more. Further, the pseudo cubic {100} plane was oriented parallel to the tape surface, and the average degree of orientation of the pseudo cubic {100} plane by the Lotgering method reached 75%.

  Next, according to the same procedure as in Example 1, except that the electric field strength at the time of the first polarization treatment is 3 kV / mm at the maximum and the electric field strength at the time of the second polarization treatment is 2 kV / mm, Polarization treatment and aging at room temperature, and second polarization treatment and aging at room temperature were performed. Table 5 shows the polarization conditions and piezoelectric characteristics of each sample.

In the case of this example, the highest piezoelectric d ₃₁ constant was obtained when the first polarization treatment was performed with the electric field strength set to 2 kV / mm (sample No. 2). On the other hand, even when aging was performed at room temperature, the piezoelectric characteristics hardly deteriorated (sample No. 4) except that d ₃₁ slightly decreased. Further, the sample No. 4 was subjected to a second polarization treatment with an electric field strength of 2 kV / mm, the piezoelectric characteristics were further improved (Sample No. 5). On the other hand, even when aging was performed at room temperature, the piezoelectric characteristics hardly deteriorated (sample No. 6) except that d ₃₁ slightly decreased. The piezoelectric characteristics after the second polarization treatment (sample No. 5) are 1.09 times as high as the d ₃₁ at room temperature and the kp is 1.times. Compared to the piezoelectric characteristics after the first polarization treatment (sample No. 2). 25 _{times, g 31} was improved to 1.51 times.

{Li _0.02 (K _0.5 Na _0.5 ) _0.98 } {Nb _0.81 Ta _0.14 Sb _0.05 } O ₃ {Li _0.02 (K _0.5 Na _0.5 ) _0.98 } {Nb _0.81 Ta _{0 .0} , following the same procedure as in Example 1, except that the firing temperature of the shaped compact was 1150 ° C. Crystal-oriented ceramics having a composition of ₁₄ Sb _0.05 } O ₃ were prepared.

  With respect to the obtained crystallographically-oriented ceramics, the sintered body density and the average degree of orientation were evaluated under the same conditions as in Example 1. The relative density of the crystallographically-oriented ceramic obtained in this example was 95% or more. Further, the pseudo cubic {100} plane was oriented parallel to the tape surface, and the average degree of orientation of the pseudo cubic {100} plane by the Lotgering method reached 72%.

  Next, according to the same procedure as in Example 1, the first polarization treatment and aging at room temperature, and the second polarization treatment and aging at room temperature were performed. Table 6 shows the polarization conditions and piezoelectric characteristics of each sample.

In the case of the present example, the highest piezoelectric d ₃₁ constant was obtained when the first polarization treatment was performed with the electric field strength set to 5 kV / mm (sample No. 5). On the other hand, even when aging was performed at room temperature, the piezoelectric characteristics hardly deteriorated (sample No. 6) except that d ₃₁ slightly decreased. Further, the sample No. 6 was subjected to the second polarization treatment with an electric field strength of 4 kV / mm, the piezoelectric characteristics were further improved (Sample No. 7). On the other hand, even when aging was performed at room temperature, the piezoelectric characteristics hardly deteriorated except that d ₃₁ slightly decreased (Sample No. 8). Piezoelectric properties after the second polarization treatment (Sample No.7), as compared to the piezoelectric characteristics after the first polarization treatment (Sample No.5), _{d 31} at room temperature is 1.13 times, kp is 1. 21 _{times, g 31} was improved to 1.34 times.

In FIG. The temperature dependence of the piezoelectric d ₃₁ constant measured for 8 is shown. The maximum value of d ₃₁ at −50 to 350 ° C. reached 123.2 pm / V at 61 ° C., and the Curie temperature was 285 ° C. From FIG. 4, it is considered that the phase transition temperature from orthorhombic to tetragonal is about 61 ° C., and the phase transition temperature from tetragonal to cubic is about 285 ° C. When the crystal phase of this disc-like sample was examined using an X-ray diffractometer, it was confirmed that it was orthorhombic at room temperature, tetragonal at 100 ° C., and cubic at 350 ° C.

{Li _0.02 (K _0.5 Na _0.5 ) _0.98 } {Nb _0.81 Ta _0.14 Sb _0.05 } O ₃ {Li _0.02 (K _0.5 Na _0.5 ) _0.98 } {Nb according to the same procedure as in Example 1 except that the firing temperature of the shaped compact was 1150 ° C. and the heating time was 5 hours. Crystal-oriented ceramics having a _0.81 Ta _0.14 Sb _0.05 } O ₃ composition were produced.

  With respect to the obtained crystallographically-oriented ceramics, the sintered body density and the average degree of orientation were evaluated under the same conditions as in Example 1. The relative density of the crystallographically-oriented ceramic obtained in this example was 95% or more. Further, the pseudo cubic {100} plane was oriented parallel to the tape surface, and the average degree of orientation of the pseudo cubic {100} plane by the Lotgering method reached 85%.

  Next, according to the same procedure as in Example 1, except that the electric field strength at the time of the first polarization treatment is 3 kV / mm at the maximum and the electric field strength at the time of the second polarization treatment is 3 kV / mm, Polarization treatment, aging at room temperature, and second polarization treatment were performed. Table 7 shows the polarization conditions and piezoelectric characteristics of each sample.

In the case of this example, the highest piezoelectric d ₃₁ constant was obtained (sample No. 1) when the first polarization treatment with an electric field strength of 1 kV / mm was performed. On the other hand, even when aging was performed at room temperature, the piezoelectric characteristics hardly deteriorated (sample No. 4) except that d ₃₁ slightly decreased. Further, the sample No. 4 was subjected to the second polarization treatment with an electric field strength of 3 kV / mm, the piezoelectric characteristics were further improved (Sample No. 5). Piezoelectric properties after the second polarization treatment (Sample No.5), as compared to the piezoelectric characteristics after the first polarization treatment (Sample No.1), _{d 31} at room temperature is 1.14 times, kp is 1. 29 _{times, g 31} was improved to 1.52 times.

In FIG. The temperature dependence of the piezoelectric d ₃₁ constant measured for 5 is shown. The maximum value of d ₃₁ at −50 to 350 ° C. reached 146.4 pm / V at 40 ° C., and the Curie temperature was 241 ° C. From FIG. 5, it is considered that the phase transition temperature from orthorhombic to tetragonal is about 40 ° C., and the phase transition temperature from tetragonal to cubic is about 241 ° C. When the crystal phase of this disc-like sample was examined using an X-ray diffractometer, it was confirmed that it was orthorhombic at room temperature, tetragonal at 100 ° C., and cubic at 350 ° C.

{Li _0.02 (K _0.5 Na _0.5 ) _0.98 } {Nb _0.81 Ta _0.14 Sb _0.05 } O ₃ The shaped compact was hot-pressed in oxygen at a firing temperature of 1150 ° C., a heating time of 1 hour, a pressing force of 35 kg / cm ² (3.43 MPa), and a temperature rising / falling rate of 200 ° C./h. Otherwise, following the same procedure as Example 1, {Li _0.02 (K _0.5 Na _0.5 ) _0.98 } {Nb _0.81 Ta _0.14 Sb _0.05 } O ₃ composition Crystal-oriented ceramics were produced.

  With respect to the obtained crystallographically-oriented ceramics, the sintered body density and the average degree of orientation were evaluated under the same conditions as in Example 1. The relative density of the crystallographically-oriented ceramic obtained in this example was 95% or more. Further, the pseudo cubic {100} plane was oriented parallel to the tape surface, and the average degree of orientation of the pseudo cubic {100} plane by the Lotgering method reached 85%.

  Next, according to the same procedure as in Example 1, the first polarization treatment and aging at room temperature, and the second polarization treatment and aging at room temperature were performed. Table 8 shows the polarization conditions and piezoelectric characteristics of each sample.

In the case of the present example, the highest piezoelectric d ₃₁ constant was obtained when the first polarization treatment was performed with the electric field strength set to 5 kV / mm (sample No. 5). On the other hand, even when aging was performed at room temperature, the piezoelectric characteristics were not deteriorated except that d ₃₁ was slightly reduced (Sample No. 6). Further, the sample No. 6 was subjected to the second polarization treatment with an electric field strength of 4 kV / mm, the piezoelectric characteristics were further improved (Sample No. 7). In contrast, the piezoelectric characteristics hardly deteriorated even when aging was performed at room temperature (Sample No. 8). The piezoelectric characteristics after the second polarization treatment (Sample No. 7) are 1.06 times d ₃₁ at room temperature and kp is 1.5 compared to the piezoelectric characteristics after the first polarization treatment (Sample No. 5). 19 _{times, g 31} was improved to 1.44 times.

In FIG. The temperature dependence of the piezoelectric d ₃₁ constant measured for 8 is shown. The maximum value of d ₃₁ at −50 to 350 ° C. reached 204.8 pm / V at 71 ° C., and the Curie temperature was 261 ° C. From FIG. 6, it is considered that the phase transition temperature from orthorhombic to tetragonal is about 71 ° C., and the phase transition temperature from tetragonal to cubic is about 261 ° C. When the crystal phase of this disc-like sample was examined using an X-ray diffractometer, it was confirmed that it was orthorhombic at room temperature, tetragonal at 100 ° C., and cubic at 350 ° C.

{Li _0.02 (K _0.5 Na _0.5 ) _0.98 } {Nb _0.81 Ta _0.14 Sb _0.05 } O ₃ The shaped compact was hot-pressed in oxygen under conditions of a firing temperature of 1150 ° C., a heating time of 1 hour, a pressing force of 50 kg / cm ² (4.90 MPa), and a temperature rising / falling rate of 200 ° C./h. Otherwise, following the same procedure as Example 1, {Li _0.02 (K _0.5 Na _0.5 ) _0.98 } {Nb _0.81 Ta _0.14 Sb _0.05 } O ₃ composition Crystal-oriented ceramics were produced.

  With respect to the obtained crystallographically-oriented ceramics, the sintered body density and the average degree of orientation were evaluated under the same conditions as in Example 1. The relative density of the crystallographically-oriented ceramic obtained in this example was 95% or more. Further, the pseudo cubic {100} plane was oriented parallel to the tape surface, and the average orientation degree of the pseudo cubic {100} plane by the Lotgering method reached 96%.

  Next, according to the same procedure as in Example 1, except that the electric field strength at the time of the first polarization treatment is 3 kV / mm at the maximum and the electric field strength at the time of the second polarization treatment is 3 kV / mm, Polarization treatment and aging at room temperature, and second polarization treatment and aging at room temperature were performed. Table 9 shows the polarization conditions and piezoelectric characteristics of each sample.

In the case of this example, the highest piezoelectric d ₃₁ constant was obtained (sample No. 1) when the first polarization treatment with an electric field strength of 1 kV / mm was performed. On the other hand, when aging was performed at room temperature, the piezoelectric characteristics slightly decreased (Sample No. 4). Further, the sample No. 4 was subjected to the second polarization treatment with an electric field strength of 3 kV / mm, the piezoelectric characteristics were further improved (Sample No. 5). In contrast, even when aging was performed at room temperature, the piezoelectric characteristics hardly deteriorated (Sample No. 6). The piezoelectric characteristics after the second polarization treatment (sample No. 5) are 1.11 times d ₃₁ at room temperature and kp is 1.1 compared to the piezoelectric characteristics after the first polarization treatment (sample No. 1). 18 _{times, g 31} was improved to 1.30 times.

In FIG. 6 shows the temperature dependence of the piezoelectric d ₃₁ constant measured for 6; The maximum value of d ₃₁ at −50 to 350 ° C. reached 177.1 pm / V at 59 ° C., and the Curie temperature was 257 ° C. From FIG. 7, it is considered that the phase transition temperature from orthorhombic to tetragonal is about 59 ° C., and the phase transition temperature from tetragonal to cubic is about 257 ° C. When the crystal phase of this disc-like sample was examined using an X-ray diffractometer, it was confirmed that it was orthorhombic at room temperature, tetragonal at 100 ° C., and cubic at 350 ° C.

According to the same procedure as in Example 8, {Li _0.02 (K _0.5 Na _0.5 ) _0.98 } {Nb _0.81 Ta _0.14 Sb _0.05 } O ₃ oriented crystal ceramics Was made. With respect to the obtained crystallographically-oriented ceramics, the sintered body density and the average degree of orientation were evaluated under the same conditions as in Example 1. The relative density of the crystallographically-oriented ceramic obtained in this example was 95% or more. Further, the pseudo cubic {100} plane was oriented parallel to the tape surface, and the average orientation degree of the pseudo cubic {100} plane by the Lotgering method reached 82%.

  Next, except that the temperature during the first polarization treatment is 62 ° C., the electric field strength during the first polarization treatment is 4 kV / mm at the maximum, and the electric field strength during the second polarization treatment is 3 kV / mm. According to the same procedure as in Example 1, the first polarization treatment and aging at room temperature, and the second polarization treatment and aging at room temperature were performed. Table 10 shows the polarization conditions and piezoelectric characteristics of each sample.

In the case of this example, the highest piezoelectric d ₃₁ constant was obtained (sample No. 1) when the first polarization treatment with an electric field strength of 1 kV / mm was performed. On the other hand, even when aging was performed at room temperature, the piezoelectric characteristics were not deteriorated except that d ₃₁ was slightly reduced (Sample No. 5). Further, the sample No. 5 was subjected to the second polarization treatment with an electric field strength of 3 kV / mm, the piezoelectric characteristics were further improved (Sample No. 6). On the other hand, even when aging was performed at room temperature, the piezoelectric characteristics hardly deteriorated (sample No. 7) except that d ₃₁ slightly decreased. The piezoelectric characteristics after the second polarization treatment (Sample No. 4) are 1.02 times d ₃₁ at room temperature and the kp is 1.2 times that of the piezoelectric characteristics after the first polarization treatment (Sample No. 1). _{14-fold, g 31} was improved to 1.32 times. Almost no effect of room temperature polarization on d ₃₁ was seen, but a sufficient effect on kp and g ₃₁ was observed.

In FIG. 7 shows the temperature dependence of the piezoelectric d ₃₁ constant measured for 7. The maximum value of d ₃₁ at −50 to 350 ° C. reached 167.6 pm / V at 61 ° C., and the Curie temperature was 246 ° C. From FIG. 8, it is considered that the phase transition temperature from orthorhombic to tetragonal is about 61 ° C., and the phase transition temperature from tetragonal to cubic is about 246 ° C. When the crystal phase of this disk-shaped sample was examined using an X-ray diffractometer, it was confirmed that it was orthorhombic at room temperature, tetragonal at 65 ° C., and cubic at 350 ° C.

According to the same procedure as in Example 8, {Li _0.02 (K _0.5 Na _0.5 ) _0.98 } {Nb _0.81 Ta _0.14 Sb _0.05 } O ₃ oriented crystal ceramics Was made. With respect to the obtained crystallographically-oriented ceramics, the sintered body density and the average degree of orientation were evaluated under the same conditions as in Example 1. The relative density of the crystallographically-oriented ceramic obtained in this example was 95% or more. Further, the pseudo cubic {100} plane was oriented parallel to the tape surface, and the average degree of orientation of the pseudo cubic {100} plane by the Lotgering method reached 87%.

  Next, the temperature at the time of the first polarization treatment is 165 ° C., the electric field strength at the time of the first polarization treatment is 4 kV / mm at the maximum, and the electric field strength at the time of the second polarization treatment is 3 kV / mm. According to the same procedure as in Example 1, the first polarization treatment and aging at room temperature, and the second polarization treatment and aging at room temperature were performed. Table 11 shows the polarization conditions and piezoelectric characteristics of each sample.

In the case of this example, the highest piezoelectric d ₃₁ constant was obtained (sample No. 1) when the first polarization treatment with an electric field strength of 1 kV / mm was performed. On the other hand, when aging was performed at room temperature, the piezoelectric characteristics slightly decreased (Sample No. 5). Further, the sample No. 5 was subjected to the second polarization treatment with an electric field strength of 3 kV / mm, the piezoelectric characteristics were further improved (Sample No. 6). In contrast, even when aging was performed at room temperature, the piezoelectric characteristics hardly deteriorated (Sample No. 7). The piezoelectric characteristics after the second polarization treatment (Sample No. 6) are 1.11 times d ₃₁ at room temperature and kp is 1.1 compared to the piezoelectric characteristics after the first polarization treatment (Sample No. 1). 24 _{times, g 31} was improved to 1.43 times.

{Li _0.02 (K _0.5 Na _0.5 ) _0.98 } {Nb _0.81 Ta _{0 .0} , following the same procedure as in Example 8, except that NN plate powder was not used as a starting material _. A non-oriented sintered body having a ₁₄ Sb _0.05 } O ₃ composition was produced.

  About the obtained non-oriented sintered compact, the sintered compact density and average orientation degree were evaluated on the same conditions as Example 1. FIG. The relative density of the non-oriented sintered body obtained in this example was 95% or more. The pseudo cubic {100} plane was oriented parallel to the tape surface, and the average degree of orientation of the pseudo cubic {100} plane by the Lotgering method was 0%.

  Next, according to the same procedure as in Example 1, except that the electric field strength at the time of the first polarization treatment is 4 kV / mm at the maximum and the electric field strength at the time of the second polarization treatment is 3 kV / mm, Polarization treatment and aging at room temperature, and second polarization treatment and aging at room temperature were performed. Table 12 shows the polarization conditions and piezoelectric characteristics of each sample.

In the case of this example, the highest piezoelectric d ₃₁ constant was obtained when the first polarization treatment with an electric field strength of 4 kV / mm was performed (Sample No. 4). On the other hand, even when aging was performed at room temperature, the piezoelectric characteristics hardly deteriorated (sample No. 5) except that d ₃₁ slightly decreased. Further, the sample No. 5 was subjected to the second polarization treatment with an electric field strength of 3 kV / mm, the piezoelectric characteristics were further improved (Sample No. 6). On the other hand, even when aging was performed at room temperature, the piezoelectric characteristics hardly deteriorated (sample No. 7) except that d ₃₁ slightly decreased. The piezoelectric properties after the second polarization treatment (Sample No. 6) are 1.11 times d ₃₁ at room temperature and kp is 1.1 compared to the piezoelectric properties after the first polarization treatment (Sample No. 4). 22 _{times, g 31} was improved to 1.34 times.

{Li _0.02 (K _0.5 Na _0.5 ) _0.98 } {Nb _0.81 Ta _{0 .0} , following the same procedure as in Example 7, except that NN plate powder was not used as a starting material _. A non-oriented sintered body having a ₁₄ Sb _0.05 } O ₃ composition was produced.

  About the obtained non-oriented sintered compact, the sintered compact density and average orientation degree were evaluated on the same conditions as Example 1. FIG. The relative density of the non-oriented sintered body obtained in this example was 95% or more. Further, the pseudo cubic {100} plane was oriented parallel to the tape surface, and the average degree of orientation of the pseudo cubic {100} plane by the Lotgering method was 1%.

  Next, according to the same procedure as in Example 1, except that the electric field strength at the time of the first polarization treatment is 4 kV / mm at the maximum and the electric field strength at the time of the second polarization treatment is 3 kV / mm, Polarization treatment and aging at room temperature, and second polarization treatment and aging at room temperature were performed. Table 13 shows the polarization conditions and piezoelectric characteristics of each sample.

In the case of this example, the highest piezoelectric d ₃₁ constant was obtained when the first polarization treatment with an electric field strength of 4 kV / mm was performed (Sample No. 4). On the other hand, even when aging was performed at room temperature, the piezoelectric characteristics hardly deteriorated (sample No. 5) except that d ₃₁ slightly decreased. Further, the sample No. 5 was subjected to the second polarization treatment with an electric field strength of 3 kV / mm, the piezoelectric characteristics were further improved (Sample No. 6). In contrast, even when aging was performed at room temperature, the piezoelectric characteristics hardly deteriorated (Sample No. 7). The piezoelectric properties after the second polarization treatment (sample No. 6) are 1.04 times d ₃₁ at room temperature and kp is 1.4 compared to the piezoelectric properties after the first polarization treatment (sample No. 4). 23 _{times, g 31} was improved to 1.49 times.

{Li _0.04 (K _0.46 Na _0.54 ) _0.96 } {Nb _0.84 Ta _0.10 Sb _0.06 } O _{3 The} starting material is blended so as to have a composition, and molding after degreasing The body was hot-pressed in oxygen at a firing temperature of 1150 ° C., a heating time of 1 hour, a pressing force of 35 kg / mm ² (3.43 MPa), and a temperature rising / falling rate of 200 ° C./h. According to the same procedure as in Example 1, {Li _0.02 (K _0.46 Na _0.54 ) _0.98 } {Nb _0.84 Ta _0.10 Sb _0.06 } O ₃ crystal orientation Ceramics were produced.

  With respect to the obtained crystallographically-oriented ceramics, the sintered body density and the average degree of orientation were evaluated under the same conditions as in Example 1. The relative density of the crystallographically-oriented ceramic obtained in this example was 95% or more. Further, the pseudo cubic {100} plane was oriented parallel to the tape surface, and the average orientation degree of the pseudo cubic {100} plane by the Lotgering method reached 92%.

  Next, according to the same procedure as in Example 1, except that the electric field strength at the time of the first polarization treatment is 4 kV / mm at the maximum and the electric field strength at the time of the second polarization treatment is 3 kV / mm, Polarization treatment and aging at room temperature, and second polarization treatment and aging at room temperature were performed. Table 14 shows the polarization conditions and piezoelectric characteristics of each sample.

In the case of this example, the highest piezoelectric d ₃₁ constant was obtained when the first polarization treatment with an electric field strength of 4 kV / mm was performed (Sample No. 4). In addition, the piezoelectric characteristics did not deteriorate even when aging was performed at room temperature (Sample No. 5). Further, the sample No. 5 was subjected to the second polarization treatment with an electric field strength of 3 kV / mm, the piezoelectric characteristics were further improved (Sample No. 6). In contrast, even when aging was performed at room temperature, the piezoelectric characteristics hardly deteriorated (Sample No. 7). Piezoelectric properties after the second polarization treatment (Sample No.6), as compared to the piezoelectric characteristics after the first polarization treatment (sample No.4), _{d 31} at room temperature is 1.10 times, kp is 1. 16 _{times, g 31} was improved to 1.37 times.

In FIG. 7 shows the temperature dependence of the piezoelectric d ₃₁ constant measured for 7. The maximum value of d ₃₁ at −50 to 350 ° C. reached 180.1 pm / V at 36 ° C., and the Curie temperature was 257 ° C. From FIG. 8, it is considered that the phase transition temperature from orthorhombic to tetragonal is about 36 ° C., and the phase transition temperature from tetragonal to cubic is about 257 ° C. When the crystal phase of this disc-like sample was examined using an X-ray diffractometer, it was confirmed that it was orthorhombic at room temperature, tetragonal at 100 ° C., and cubic at 350 ° C.

(Comparative Example 1)
The starting material is blended so as to have a composition of (K _0.5 Na _0.5 ) NbO ₃ , and the degreased molded body is calcined in oxygen at a firing temperature of 1125 ° C., a heating time of 5 hours, and a pressure of 35 kg. / K ² (3.43 MPa), temperature increase / decrease rate: (K _0.5 Na _0.5 ) NbO ₃ composition according to the same procedure as in Example 1 except that hot pressing was performed at 200 ° C./h. A crystallographically-oriented ceramic having the following characteristics was prepared.

  With respect to the obtained crystallographically-oriented ceramics, the sintered body density and the average degree of orientation were evaluated under the same conditions as in Example 1. The relative density of the crystallographically-oriented ceramic obtained in this example was 95% or more. Further, the pseudo cubic {100} plane was oriented parallel to the tape surface, and the average degree of orientation of the pseudo cubic {100} plane by the Lotgering method reached 98%.

Next, following the same procedure as in Example 1, the first-stage polarization treatment and aging at room temperature, and the second-stage polarization treatment and aging at room temperature were performed. In addition, since the orthorhombic to tetragonal transition point of (K _0.5 Na _0.5 ) NbO ₃ is about 200 ° C., the polarization treatment at 100 ° C. and at room temperature both takes place in the orthorhombic region. It becomes processing. Table 15 shows the polarization conditions and piezoelectric characteristics of each sample.

In the case of Comparative Example 1, the highest piezoelectric d ₃₁ constant was obtained when the first-stage polarization treatment with an electric field strength of 5 kV / mm was performed (Sample No. 5). In contrast, even when aging was performed at room temperature, the piezoelectric characteristics hardly deteriorated (Sample No. 6). However, the sample No. On the other hand, even when the second-stage polarization treatment with an electric field strength of 4 kV / mm was performed, no improvement in piezoelectric characteristics was observed (Sample No. 7). In addition, the piezoelectric characteristics did not deteriorate even when aging was performed at room temperature (Sample No. 8). 2-stage piezoelectric properties after polarization treatment (Sample No.7), compared to the first stage piezoelectric properties after polarization treatment (Sample No.5), _{d 31} is 1.00 times at room temperature, kp is 0.95 times, g ₃₁ was 0.92 times and d ₃₁ was not changed, but kp and g ₃₁ were rather lowered.

(Comparative Example 2)
According to the same procedure as in Example 1, except that the starting material was blended so as to have a (K _0.5 Na _0.5 ) NbO ₃ composition, and the firing temperature of the plate-shaped molded body after degreasing was 1075 ° C. Crystal-oriented ceramics having a (K _0.5 Na _0.5 ) NbO ₃ composition were prepared.

  With respect to the obtained crystallographically-oriented ceramics, the sintered body density and the average degree of orientation were evaluated under the same conditions as in Example 1. The relative density of the crystallographically-oriented ceramic obtained in this example was 95% or more. Further, the pseudo cubic {100} plane was oriented parallel to the tape surface, and the average orientation degree of the pseudo cubic {100} plane by the Lotgering method reached 96%.

  Next, following the same procedure as in Example 1, the first-stage polarization treatment and aging at room temperature, and the second-stage polarization treatment and aging at room temperature were performed. Table 16 shows the polarization conditions and piezoelectric characteristics of each sample.

In the case of Comparative Example 2, the highest piezoelectric d ₃₁ constant was obtained when the first-stage polarization treatment with an electric field strength of 5 kV / mm was performed (Sample No. 5). In contrast, even when aging was performed at room temperature, the piezoelectric characteristics hardly deteriorated (Sample No. 6). However, the sample No. On the other hand, even when the second-stage polarization treatment with an electric field strength of 4 kV / mm was performed, no improvement in piezoelectric characteristics was observed (Sample No. 7). In contrast, the piezoelectric characteristics hardly deteriorated even when aging was performed at room temperature (Sample No. 8). 2-stage piezoelectric properties after polarization treatment (Sample No.7), compared to the first stage piezoelectric properties after polarization treatment (Sample No.5), _{d 31} is 1.02 times at room temperature, kp is _{1.00-fold, g 31} is 0.99 _times, little change was observed in the _d 31, kp and _{g 31.}

(Comparative Example 3)
According to the same procedure as in Example 8, {Li _0.02 (K _0.5 Na _0.5 ) _0.98 } {Nb _0.81 Ta _0.14 Sb _0.05 } O ₃ oriented crystal ceramics Was made. With respect to the obtained crystallographically-oriented ceramics, the sintered body density and the average degree of orientation were evaluated under the same conditions as in Example 1. The relative density of the crystallographically-oriented ceramic obtained in this example was 95% or more. Further, the pseudo cubic {100} plane was oriented parallel to the tape surface, and the average orientation degree of the pseudo cubic {100} plane by the Lotgering method reached 80%.

  Next, the electric field intensity at the time of the first polarization treatment was set to 4 kV / mm at the maximum, and the second polarization treatment was not performed, and the first polarization treatment and the room temperature were performed according to the same procedure as in Example 1. Aging was performed. Table 17 shows the polarization conditions and piezoelectric characteristics of each sample.

In the case of Comparative Example 3, the highest piezoelectric d ₃₁ constant was obtained when the first polarization treatment with an electric field strength of 4 kV / mm was performed (Sample No. 4). On the other hand, even when aging was performed at room temperature, the piezoelectric characteristics hardly deteriorated (sample No. 5) except that d ₃₁ slightly decreased. However, since the room temperature polarization was not performed, the same high piezoelectric characteristics as in Example 8 were not obtained.

In FIG. The temperature dependence of the piezoelectric d ₃₁ constant measured for 5 is shown. The maximum value of d ₃₁ at −50 to 350 ° C. reached 156.7 pm / V at 63 ° C., and the Curie temperature was 245 ° C. From FIG. 10, it is considered that the phase transition temperature from orthorhombic to tetragonal is about 63 ° C., and the phase transition temperature from tetragonal to cubic is about 245 ° C. When the crystal phase of this disk-shaped sample was examined using an X-ray diffractometer, it was confirmed that it was orthorhombic at room temperature, tetragonal at 65 ° C., and cubic at 350 ° C.

  Table 18 shows manufacturing conditions and piezoelectric characteristics of the sintered bodies obtained in Examples 1 to 14 and Comparative Examples 1 to 3.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention. For example, in the above-described examples, the example in which the present invention is mainly applied to the KNN-based compound has been described. However, the scope of the present invention is not limited to this, and the cubic to tetragonal crystals are reduced as the temperature decreases. The present invention can be similarly applied to other piezoelectric ceramics that undergo phase transition to orthorhombic crystal.

  The present invention includes an acceleration sensor, a pyroelectric sensor, an ultrasonic sensor, an electric field sensor, a temperature sensor, a gas sensor, a knocking sensor, a yaw rate sensor, an air bag sensor, a piezoelectric gyro sensor, and other various sensors, an energy conversion element such as a piezoelectric transformer, and a piezoelectric sensor. Low loss actuators such as actuators, ultrasonic motors, and resonators or low loss resonators, capacitors, bimorph piezoelectric elements, vibration pickups, piezoelectric microphones, piezoelectric ignition elements, sonar, piezoelectric buzzers, piezoelectric speakers, oscillators, filters, etc. It can be used as a method for producing a material. Further, it can also be used as a method for producing a dielectric material used for capacitors, multilayer capacitors and the like.

FIG. 1A is a schematic diagram showing a state of spontaneous polarization when a conventional method is used, and FIGS. 1B and 1C are diagrams of the spontaneous polarization when the method of the present application is used. It is a schematic diagram which shows a state. It is a diagram showing temperature dependence of the piezoelectric d ₃₁ constant of the piezoelectric ceramic obtained in Example 2. It is a diagram showing temperature dependence of the piezoelectric d ₃₁ constant of the piezoelectric ceramic obtained in Example 4. It is a diagram showing temperature dependence of the piezoelectric d ₃₁ constant of the piezoelectric ceramic obtained in Example 6. It is a diagram showing temperature dependence of the piezoelectric d ₃₁ constant of the piezoelectric ceramic obtained in Example 7. It is a diagram showing temperature dependence of the piezoelectric d ₃₁ constant of the piezoelectric ceramic obtained in Example 8. It is a diagram showing temperature dependence of the piezoelectric d ₃₁ constant of the piezoelectric ceramic obtained in Example 9. is there. It is a diagram showing temperature dependence of the piezoelectric d ₃₁ constant of the piezoelectric ceramic obtained in Example 10. It is a diagram showing temperature dependence of the piezoelectric d ₃₁ constant of the piezoelectric ceramic obtained in Example 14. It is a diagram showing temperature dependence of the piezoelectric d ₃₁ constant of the piezoelectric ceramic obtained in Comparative Example 3.

Claims (16)

A first step of subjecting a piezoelectric ceramic having a cubic crystal structure at a high temperature and reversibly phase-transforming to tetragonal or orthorhombic when the temperature is lowered to a first polarization treatment in a temperature region where it becomes tetragonal. When,
A method of manufacturing a piezoelectric ceramic, comprising: a second step of performing a second polarization process in the temperature region where the piezoelectric ceramic is orthorhombic and in the same direction as the first polarization process.   The said 1st process and / or the said 2nd process respectively perform the polarization process 1 time or 2 times or more in the same or different temperature until the said piezoelectric ceramics carry out saturation polarization. Manufacturing method of piezoelectric ceramics.   The method for manufacturing a piezoelectric ceramic according to claim 1 or 2, wherein the first step and the second step are alternately repeated. The piezoelectric ceramic is
General _{formula: {Li x (K 1-} y Na y) 1-x} {Nb 1-z-w Ta z Sb w} O 3
(However, 0 ≦ x ≦ 0.2, 0 ≦ y ≦ 1, 0 ≦ z ≦ 0.4, 0 ≦ w ≦ 0.2)
The method for producing a piezoelectric ceramic according to claim 1, comprising a polycrystal of an isotropic perovskite type compound represented by the formula: The polarization treatment temperature T _{1 in} the first step is in a temperature range of [orthogonal crystal → tetragonal phase transition temperature] <T ₁ ,
5. The method of manufacturing a piezoelectric ceramic according to claim 4, wherein the polarization treatment temperature T _{2 in} the second step is in a temperature range of T ₂ <[orthogonal crystal → tetragonal phase transition temperature]. The method for manufacturing a piezoelectric ceramic according to claim 5, wherein the polarization treatment temperature T _{2 in} the second step is in a temperature range of 10 ° C. ≦ T ₂ <[orthogonal crystal → tetragonal phase transition temperature]. The polarization treatment temperature T _{1 in} the first step is in a temperature range of [orthogonal crystal → tetragonal phase transition temperature] <T ₁ ≦ 180 ° C.,
5. The method of manufacturing a piezoelectric ceramic according to claim 4, wherein the polarization treatment temperature T _{2 in} the second step is in a temperature range of T ₂ <[orthogonal crystal → tetragonal phase transition temperature]. The method for manufacturing a piezoelectric ceramic according to claim 7, wherein the polarization treatment temperature T _{2 in} the second step is in a temperature range of 10 ° C. ≦ T ₂ <[orthogonal crystal → tetragonal phase transition temperature]. The piezoelectric ceramic is made of a crystal whose cubic cubic {100} plane is oriented,
The first step and the second step, respectively, perform the first polarization process and the second polarization process in the same direction as a crystal orientation in which a large elongation can be expected. The manufacturing method of the piezoelectric ceramic in any one. The piezoelectric ceramic is made of a crystal whose cubic cubic {100} plane is oriented,
In the first step, the first polarization treatment is performed in a direction perpendicular to a plane in which a pseudo cubic {100} plane is oriented,
The method for manufacturing a piezoelectric ceramic according to claim 1, wherein the second step performs the second polarization process in the same direction as the first polarization process. The piezoelectric ceramic is made of a crystal whose cubic cubic {100} plane is oriented,
In the first step, the first polarization treatment is performed in a direction parallel to the plane in which the pseudo-cubic {100} plane is oriented,
The method for manufacturing a piezoelectric ceramic according to claim 1, wherein the second step performs the second polarization process in the same direction as the first polarization process.   The method for producing a piezoelectric ceramic according to any one of claims 9 to 11, wherein the piezoelectric ceramic has a degree of orientation of a pseudo-cubic {100} plane by a Lotgering method of 30% or more. In the first step, a first region and a second region are formed adjacent to the piezoelectric ceramic, and the first region is subjected to the first polarization process in opposite directions. Yes,
13. The method according to claim 1, wherein the second step performs the second polarization process in the same direction as the first polarization process in the first region and the second region, respectively. The manufacturing method of the piezoelectric ceramic of description. Performing the first polarization process and the second polarization process in a first direction on the piezoelectric ceramic; and
And a step B of performing the first polarization process and the second polarization process in a second direction different from the first direction with respect to a part of the piezoelectric ceramic subjected to the process A. The method for manufacturing a piezoelectric ceramic according to claim 1.   The method of manufacturing a piezoelectric ceramic according to claim 14, wherein the second direction is a direction perpendicular to the first direction. Step C for producing a laminate of a plurality of the piezoelectric ceramics and a plurality of electrodes,
Performing the first polarization process and the second polarization process on the m-th piezoelectric ceramic sandwiched between the electrodes; and
Simultaneously with the step D or separately from the step D, the nth (n ≠ m) piezoelectric ceramic sandwiched between the electrodes is the same as or different from the mth piezoelectric ceramic. The manufacturing method of the piezoelectric ceramics in any one of Claim 1-12 provided with the process E which performs the polarization process of this, and the said 2nd polarization process.

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