JP2008013395A - Method for manufacturing crystal-oriented ceramic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a crystal-oriented ceramic capable of manufacturing a crystal-oriented ceramic having a high degree of preferred orientation. <P>SOLUTION: The method for manufacturing a crystal-oriented ceramic comprises a preparatory process, a mixing process, a forming process, and a firing process. In the preparatory process, an anisotropically shaped powder 1 and a fine powder 2 having an average particle diameter of 1/3 or less than that of the anisotropically shaped powder are prepared. In the mixing process, a raw mix slurry 3 is prepared by mixing the anisotropically shaped powder 1, the fine powder 2, a forming aid, and a solvent. In the forming process, a formed body is made by spreading the raw mix slurry 3 on a carrier film 4 with a specified shear velocity. In the firing process, a crystal-oriented ceramic is obtained by heating the formed body to sinter the anisotropically shaped powder 1 and the fine powder 2. The viscosity of the raw mix slurry 3 at the shear velocity in the forming process is 1-8 Pa s and the raw mix slurry 3 is spread on the carrier film 4 at a thickness(μm)/width(mm) ratio of 0.01-1 in the forming process. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a crystallographically-oriented ceramic comprising a polycrystal having a perovskite type compound as a main phase and having a specific crystal plane of crystal grains constituting the polycrystal.

  Polycrystalline materials made of ceramics are used in various sensors such as temperature, heat, gas, and ions, electronic circuit components such as capacitors, resistors, and integrated circuit substrates, or optical or magnetic recording elements. It's being used. In particular, polycrystals made of ceramics with piezoelectric effect (hereinafter referred to as piezoelectric ceramics) are widely used in the fields of electronics and mechatronics because of their high performance, high degree of freedom in shape, and relatively easy material design. ing.

  Piezoelectric ceramics have been subjected to so-called polarization treatment in which an electric field is applied to ferroelectric ceramics to align the direction of the domain of the ferroelectric material in a certain direction. 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.

Isotropic perovskite type ferroelectric ceramics include, for example, Pb (Zr · Ti) O ₃ (hereinafter referred to as “PZT”), PZT3 component in which lead-based composite perovskite is added as a third component to PZT. System, BaTiO ₃ , Bi _0.5 Na _0.5 TiO ₃ (hereinafter referred to as “BNT”) and the like are known.

  Among these, lead-based piezoelectric ceramics represented by PZT have higher piezoelectric properties than other piezoelectric ceramics, and occupy most of the piezoelectric ceramics currently in practical use. However, since lead oxide (PbO) having a high vapor pressure is included, there is a problem that the load on the environment is large. Therefore, there is a demand for piezoelectric ceramics that have low or no lead and have piezoelectric properties equivalent to PZT.

On the other hand, BaTiO ₃ ceramics has a relatively high piezoelectric property among piezoelectric materials not containing lead, and is used for sonar. Some solid solutions of BaTiO ₃ and other lead-free perovskite compounds (for example, BNT) exhibit relatively high piezoelectric characteristics. However, these lead-free piezoelectric ceramics have a problem that the piezoelectric characteristics are low as compared with PZT.

In order to solve such problems, various piezoelectric ceramics have been proposed.
For example, there are isotropic perovskite-type potassium sodium niobate niobates that exhibit relatively high piezoelectric properties among non-lead-based materials and piezoelectric ceramics made of a solid solution thereof (see Patent Documents 1 to 6).
However, these lead-free piezoelectric ceramics have a problem that they cannot yet exhibit sufficient piezoelectric characteristics as compared with PZT-based piezoelectric ceramics.

In such a background, a piezoelectric element having a piezoelectric ceramic including ceramic crystal grains having shape anisotropy and having spontaneous polarization preferentially oriented in one plane is disclosed (see Patent Document 7).
In general, it is known that the piezoelectric characteristics and the like of an isotropic perovskite compound differ depending on the direction of the crystal axis. Therefore, if high crystal axes such as piezoelectric characteristics can be oriented in a certain direction, the anisotropy of piezoelectric characteristics can be utilized to the maximum, and high performance of piezoelectric ceramics can be expected. As disclosed in Patent Document 7, a plate-like powder having a predetermined composition is used as a reactive template, the plate-like powder and raw material powder are molded, and the molded body is sintered to obtain a specific crystal. According to the method of orienting the plane, high-performance crystal-oriented ceramics oriented to a specific crystal plane can be produced.

However, in order to obtain a crystal-oriented ceramic with a specific crystal plane oriented as described above, it is necessary to sufficiently align the crystal directions of the plate-like powder when molding the plate-like powder and raw material powder having different particle sizes. There is. Specifically, for example, when molding is performed by a tape molding method such as a doctor blade method, the plate-like powder is tilted in a certain direction by the shearing force of the blade, and the orientation is promoted. However, there is a problem that the orientation degree of the finally obtained crystal oriented ceramics cannot be sufficiently improved only by orientation by shearing force. For this reason, conventional crystal oriented ceramics have a problem that they cannot exhibit piezoelectric properties such as piezoelectric d ₃₁ constant and dielectric properties such as dielectric loss, which are excellent as expected for crystal oriented ceramics.

JP 2000-313664 A Japanese Patent Laid-Open No. 2003-300776 JP 2003-306379 A JP 2003-327472 A JP 2003-342069 A JP 2003-342071 A JP 2004-7406 A

  This invention is made | formed in view of this conventional problem, Comprising: The manufacturing method of the crystal orientation ceramics which can manufacture crystal orientation ceramics with a high degree of orientation is provided.

The present invention is a method for producing a crystallographically-oriented ceramic comprising a polycrystal having a perovskite type compound as a main phase, wherein a specific crystal plane A of crystal grains constituting the polycrystal is oriented,
An anisotropically shaped powder comprising anisotropically oriented particles comprising a perovskite type compound, wherein the crystal face having lattice matching with the specific crystal face A is oriented to form an oriented face, and the anisotropically shaped powder A preparatory step of preparing a fine powder having an average particle size of 1/3 or less of the above and producing the perovskite type compound that becomes the main phase of the polycrystal by sintering together with the anisotropically shaped powder; ,
A mixing step of mixing the anisotropically shaped powder, the fine powder, a molding aid, and a solvent to prepare a raw material mixture slurry;
A molding step of coating the raw material mixture slurry on a carrier film at a predetermined shear rate so that the oriented surfaces of the anisotropically shaped powder are oriented in substantially the same direction, and drying to produce a molded body;
A heating step of obtaining the crystal-oriented ceramic by heating the molded body and sintering the anisotropically shaped powder and the fine powder;
The viscosity of the raw material mixture slurry at the shear rate in the forming step is 1 to 8 Pa · s. In the forming step, the raw material mixture slurry is formed on the carrier film in thickness (μm) / width (mm). The present invention resides in a method for producing a crystallographically-oriented ceramic, wherein the coating is performed so that the ratio is 0.01 or more and 1 or less.

In the manufacturing method of the present invention, the crystal-oriented ceramic is manufactured by performing the preparation step, the mixing step, the forming step, and the firing step.
The most notable point in the present invention is that the viscosity of the raw material mixture slurry at the shear rate in the forming step is 1 to 8 Pa · s. In the forming step, the raw material mixture slurry is placed on the carrier film. The coating is such that the ratio of thickness (μm) / width (mm) is 0.01 or more and 1 or less. Thus, by controlling the viscosity of the raw material mixture slurry and the thickness / width ratio during coating, the degree of orientation of the anisotropically shaped powder in the molded body can be further improved. As a result, the above-mentioned crystallographically-oriented ceramic with a high degree of orientation can be produced.

As described above, the reason why the degree of orientation can be improved by controlling the viscosity of the raw material mixture slurry and the thickness / width ratio at the time of coating is not clear, but is considered as follows.
That is, the molded body formed on the carrier film shrinks when dried. This shrinkage occurs mainly in the thickness direction of the molded body but also in the width direction. The shrinkage behavior in the width direction differs between the vicinity of the surface of the molded body formed on the carrier film and the film side. Since the film side is bonded and restrained to the carrier film, shrinkage is more likely to proceed near the surface than the carrier film side. As described above, when the viscosity of the raw material mixture slurry and the thickness / width ratio at the time of coating are controlled, an appropriate shear force is applied to the molded body due to the difference in the degree of shrinkage between the surface vicinity of the molded body and the film side. It is thought to work. It can be estimated that this shear force contributes to the improvement of the degree of orientation.

Hereinafter, embodiments of the present invention will be described.
The crystallographically-oriented ceramic of the present invention comprises a polycrystal having a perovskite type compound as a main phase.
The polycrystal has a general formula (1) ABO ₃ (A site element is composed mainly of K, Na, K and Na, Li and K, Li and Na, or Li, K and Na, and B site element is Nb, Nb and Ta, Nb and Sb, or Nb and Ta and Sb as main components) is preferably used as the main phase (claim 2).
In this case, crystal oriented ceramics excellent in piezoelectric characteristics and dielectric characteristics can be obtained.
Moreover, in the said General formula (1), the below-mentioned additional element can also be contained in the A site and / or B site as a subcomponent other than the above-mentioned main component elements.
Here, “isotropic” means that when the perovskite structure ABO ₃ is expressed by a pseudo cubic basic lattice, the relative ratio of axial lengths a, b, c is 0.8 to 1.2, and the axial angle α , Β, γ are in the range of 80-100 °

Further, the polycrystal general formula _{(2): {Li x (} K 1-y Na y) 1-x} (Nb 1-zw Ta z Sb w) O 3 ( where, 0 ≦ x ≦ 0. 2, 0 ≦ y ≦ 1, 0 ≦ z ≦ 0.4, 0 ≦ w ≦ 0.2, x + z + w> 0) is preferably used as an isotropic perovskite compound. ).
The isotropic perovskite type compound represented by the general formula (2) can exhibit excellent piezoelectric properties among non-leaded piezoelectric ceramics. Therefore, in this case, the piezoelectric characteristics and dielectric characteristics of the crystal-oriented ceramic can be further improved.
In the general formula (2), “x + z + w> 0” indicates that at least one of Li, Ta, and Sb may be included as a substitution element.

In the above general formula (2), “y” represents the ratio of K and Na contained in the isotropic perovskite compound. In the compound represented by the general formula (2), it is sufficient that at least one of K or Na is contained as the A site element.
The range of y in the general formula (2) is more preferably 0 <y ≦ 1.
In this case, Na is an essential component in the compound represented by the general formula (2). Therefore, in this case, the piezoelectric g ₃₁ constant of the crystal-oriented ceramic can be further improved.
The range of y in the general formula (2) can be 0 ≦ y <1.
In this case, K is an essential component in the compound represented by the general formula (2). Therefore, in this case, the piezoelectric characteristics such as the piezoelectric d ₃₁ constant of the crystal-oriented ceramic can be further improved. Further, in this case, since the sintering at a lower temperature becomes possible as the K addition amount increases, the above-mentioned crystallographically-oriented ceramic can be produced with energy saving and low cost.
In the general formula (2), y is more preferably 0.05 ≦ y ≦ 0.75, and further preferably 0.20 ≦ y ≦ 0.70. In these cases, the piezoelectric d ₃₁ constant and the electromechanical coupling coefficient Kp of the crystal-oriented ceramic can be further improved. Even more preferably, 0.20 ≦ y <0.70 is satisfied, 0.35 ≦ y ≦ 0.65 is further preferable, and 0.35 ≦ y <0.65 is more preferable. Most preferably, 0.42 ≦ y ≦ 0.60.

“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.
The range of x in the general formula (2) is more preferably 0 <x ≦ 0.2.
In this case, since Li is an essential component in the compound represented by the general formula (2), the crystallographically-oriented ceramic can be more easily fired at the time of production, and has piezoelectric characteristics. This further improves the Curie temperature (Tc). This is because by making Li an essential component within the range of x described above, the firing temperature is lowered, and Li serves as a firing aid and enables firing with less voids.
If the value of x exceeds 0.2, the piezoelectric characteristics (piezoelectric d ₃₁ constant, electromechanical coupling coefficient kp, piezoelectric g ₃₁ constant, etc.) may be reduced.

Further, the value of x in the general formula (2) can be set to x = 0.
In this case, the general formula (2) is represented by _{(K 1-y Na y)} (Nb 1-zw Ta z Sb w) O 3. In this case, when producing the above-mentioned crystal oriented ceramic, since the raw material does not include the lightest compound containing Li, such as LiCO ₃ , the raw materials are mixed and the above crystal oriented ceramics are mixed. The variation in characteristics due to segregation of the raw material powder can be reduced. In this case, a high relative dielectric constant and a relatively large piezoelectric g constant can be realized. In the general formula (2), the value of x is more preferably 0 ≦ x ≦ 0.15, and further preferably 0 ≦ x ≦ 0.10.

“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. In the general formula (2), if the value of z exceeds 0.4, the Curie temperature is lowered, and there is a possibility that it may be difficult to use it as a piezoelectric material for home appliances and automobiles.
The range of z in the general formula (2) is preferably 0 <z ≦ 0.4.
In this case, Ta is an essential component in the compound represented by the general formula (2). Therefore, in this case, the sintering temperature is lowered, and Ta serves as a sintering aid, so that the number of pores in the crystal-oriented ceramic can be reduced.

In addition, the value of z in the general formula (2) can be set to z = 0.
In this case, the general formula (2) is represented by {Li _x (K _1−y Na _y ) _1−x } (Nb _1−w Sbw) O ₃ . In this case, the compound represented by the general formula (2) does not contain Ta. Therefore, in this case, the compound represented by the general formula (2) can exhibit excellent piezoelectric characteristics without using an expensive Ta component at the time of production.
In the general formula (2), the value of z is more preferably 0 ≦ z ≦ 0.35, and further preferably 0 ≦ z ≦ 0.30.

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. If the value of w exceeds 0.2, the piezoelectric characteristics and / or the Curie temperature are lowered, which is not preferable.
Moreover, it is preferable that the value of w in the said General formula (2) is 0 <w <= 0.2.
In this case, Sb is an essential component in the compound represented by the general formula (2). Therefore, in this case, the sintering temperature can be lowered, the sinterability can be improved, and the stability of the dielectric loss tan δ can be improved.

In addition, the value of w in the general formula (2) can be set to w = 0. In this case, the general formula (2) is represented by {Li _x (K _1−y Na _y ) _1−x } (Nb _1−z Ta _z ) O ₃ . In this case, the compound represented by the general formula (2) does not contain Sb and can exhibit a relatively high Curie temperature. In the general formula (2), the value of w is more preferably 0 ≦ w ≦ 0.15, and further preferably 0 ≦ w ≦ 0.10.

  The crystal-oriented ceramic is preferably composed only of the isotropic perovskite type compound represented by the general formula (2). However, the isotropic perovskite type crystal structure can be maintained, and sintering characteristics can be maintained. Other elements or other phases may be included as long as they do not adversely affect various characteristics such as piezoelectric characteristics.

The polycrystal is selected from, for example, a metal element belonging to Group 2 to 15 in the periodic table, a semimetal element, a transition metal element, a noble metal element, and an alkaline earth metal element with respect to 1 mol of the perovskite compound. One or more additional elements can be contained in an amount of 0.0001 to 0.15 mol.
In this case, piezoelectric characteristics such as the piezoelectric d ₃₁ constant, the electromechanical coupling coefficient Kp, and the piezoelectric g ₃₁ constant of the crystallographically-oriented ceramic, the dielectric constant, the dielectric loss, and the like can be improved. In the crystal oriented ceramics, the additive element may be substituted for the perovskite compound, but may be added externally and exist in the grain or grain boundary of the perovskite compound. . The additive element may be contained as a single additive element, but may be contained as an oxide or a compound containing the additive element.
When the content of the additive element is less than 0.0001 mol, there is a possibility that the effect of improving the piezoelectric characteristics and the like by the additive element cannot be sufficiently obtained. On the other hand, if it exceeds 0.15 mol, the piezoelectric properties and dielectric properties of the crystal-oriented ceramics may be lowered.

  Specific examples of the additive element include Mg, Ca, Sr, Ba, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Mo, Hf, W, There are Re, Pd, Ag, Ru, Rh, Pt, Au, Ir, Os, B, Al, Ga, In, Si, Ge, Sn, and Bi.

The additive element is preferably substituted and added at a rate of 0.01 to 15 at% with respect to any one or more of the A site element and / or the B site element in the perovskite type compound.
In this case, the piezoelectric properties such as the piezoelectric d ₃₁ constant, the electromechanical coupling coefficient Kp, and the piezoelectric g ₃₁ constant of the crystal oriented ceramics and the dielectric properties such as the relative dielectric constant can be further improved.
When the additive element is less than 0.01 at%, there is a risk that the effect of improving the piezoelectric characteristics and dielectric characteristics of the crystal-oriented ceramics cannot be sufficiently obtained. On the other hand, if it exceeds 15 at%, the piezoelectric properties and dielectric properties of the crystal-oriented ceramic may be deteriorated. More preferably, it is 0.01 to 5 at%, more preferably 0.01 to 2 at%, and still more preferably 0.05 to 2 at%.
Here, “at%” represents the number of substituted atoms with respect to the number of atoms of the A-site element and B-site element in the perovskite type compound at a fraction of 100.

In the crystal-oriented ceramic, a specific crystal plane A of crystal grains constituting the polycrystal of the crystal-oriented ceramic is oriented.
“Specific crystal plane A is oriented” means that the crystal grains are arranged so that the specific crystal planes A of the perovskite compound are parallel to each other (hereinafter, this state is referred to as “plane Orientation ”), or that each crystal grain is arranged so that a specific crystal plane A is parallel to one axis passing through the polycrystal (hereinafter, this state is referred to as“ It means both “axial orientation”.

  The type of the crystal plane A that is oriented can be selected according to, for example, the direction of spontaneous polarization of the perovskite type compound, the use of the crystal-oriented ceramic, the required characteristics, and the like. That is, the crystal plane A can be selected according to the purpose, such as a pseudo-cubic {100} plane, a pseudo-cubic {110} plane, or a pseudo-cubic {111} plane.

“Pseudo-cubic {HKL}” is generally an isotropic perovskite type compound having a structure slightly distorted from cubic such as tetragonal, orthorhombic, trigonal, etc., but the distortion is slight. This means that it is regarded as a cubic crystal and displayed by Miller index.
Further, when the specific crystal plane A is plane-oriented, the degree of plane orientation can be expressed by the average degree of orientation F (HKL) by the Lotgering method expressed by the following equation (1). it can.

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) has the same composition as the crystal oriented ceramics. It is the sum total of the X-ray diffraction intensities of all crystal planes (hkl) measured with respect to the non-oriented piezoelectric ceramic. 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) that are crystallographically equivalent measured for non-oriented piezoelectric 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 the above-mentioned crystallographically-oriented ceramic, higher properties are obtained as the proportion of oriented crystal grains increases. For example, when a specific crystal plane is oriented in a plane, in order to obtain high piezoelectric characteristics and the like, the average degree of orientation F (HKL) by the Lotgering method represented by the formula 1 is 80% or more. Is preferred. More preferably, the degree of orientation is 90% or more.
The specific crystal plane to be oriented is preferably a plane perpendicular to the polarization axis. Further, when the crystal system of the perovskite compound is tetragonal, the specific crystal plane A to be oriented is preferably a pseudo-cubic {100} plane. In this case, the piezoelectric characteristics and the like of the crystal-oriented ceramic can be further improved.

Next, each process (preparation process, mixing process, molding process, and firing process) in the production method of the present invention will be described.
The preparation step is a step of preparing the anisotropically shaped powder and the fine powder.
The anisotropically shaped powder is composed of oriented particles made of a perovskite type compound. In addition, the oriented particles have an anisotropic shape, and the crystal plane having lattice matching with the specific crystal plane A of the crystal grains constituting the polycrystal to be produced is oriented to form an oriented plane. ing.

The lattice matching can be expressed by a lattice matching rate.
In describing the lattice matching, for example, the case where the oriented particles are metal oxides will be described. That is, in the two-dimensional crystal lattice of the oriented surface in the oriented particles, for example, a lattice point made of oxygen atoms or a lattice point made of metal atoms, and a two-dimensional crystal lattice of the specific crystal plane A oriented in the polycrystal In the case where a lattice point composed of oxygen atoms or a lattice point composed of metal atoms has a similar relationship, lattice matching exists between them.
The lattice matching ratio is the absolute value of the difference between the orientation plane of the oriented particles and the lattice dimension at the similar position of the specific crystal plane A oriented in the polycrystal, and the lattice size of the orientation plane of the oriented grains. The value obtained by dividing by is expressed as a percentage.

The lattice dimension is a distance between lattice points in a two-dimensional crystal lattice of one crystal plane, and can be measured by analyzing a crystal structure by X-ray diffraction, electron beam diffraction, or the like. In general, as the lattice matching ratio decreases, the oriented particles have higher lattice matching with the crystal plane A and can function as a good template.
In order to obtain a crystallographically-oriented ceramic with a higher degree of orientation, the lattice matching rate of the oriented particles is preferably 20% or less, more preferably 10% or less, and even more preferably 5% or less.

  The “anisotropic shape” means that the dimension in the longitudinal direction is larger than the dimension in the width direction or the thickness direction. Specifically, shapes such as a plate shape, a column shape, a scale shape, and a needle shape are preferable examples. Moreover, the kind of crystal plane which comprises the said orientation surface can be selected according to the objective from various crystal planes.

  As the oriented particles, it is preferable to use particles having a shape that can be easily oriented in a certain direction during the molding step. For this reason, the oriented particles preferably have an average aspect ratio of 3 or more. When the average aspect ratio is less than 3, it becomes difficult to orient the anisotropically shaped powder in one direction in the molding step described later. In order to obtain the above-mentioned crystal-oriented ceramic with a higher degree of orientation, the aspect ratio of the oriented particles is more preferably 5 or more. The average aspect ratio is an average value of the maximum dimension / minimum dimension of the oriented particles.

  In addition, as the average aspect ratio of the oriented particles increases, it becomes easier to orient the oriented particles in the molding step. However, if the average aspect ratio is excessive, the oriented particles may be destroyed in the mixing step. As a result, in the molding step, a molded body in which the oriented particles are oriented may not be obtained. Therefore, the average aspect ratio of the oriented particles is preferably 100 or less. More preferably, it is 50 or less, and more preferably 30 or less.

The oriented particles are made of a perovskite type compound.
Specifically, the oriented particles include those having the same composition as the target isotropic perovskite compound, such as the compound represented by the general formula (1) or the general formula (2). Can be used.
Further, the oriented particles do not necessarily have the same composition as the target isotropic perovskite compound, such as the compound represented by the general formula (1) or the general formula (2). What is necessary is just to produce | generate as a main component the isotropic perovskite type compound represented by the said general formula (1) or the said general formula (2) by sintering with the fine powder mentioned later. Therefore, the oriented particles can be selected from compounds containing any one or more of the cationic elements contained in the isotropic perovskite compound to be produced, solid solutions, and the like.

Therefore, as the anisotropically shaped powder and the fine powder, the general formula (3) ABO ₃ (A site element is mainly composed of one or more elements selected from K, Na, Li, and B site element is An anisotropically shaped powder and a fine powder made of an isotropic perovskite compound represented by (a main component of one or more elements selected from Nb, Ta, and Sb) can be used.
In this case, an isotropic perovskite-type potassium sodium niobate crystal-oriented ceramic that exhibits relatively high piezoelectric properties among non-lead-based materials can be produced.

Examples of oriented particles satisfying the above conditions include NaNbO ₃ (hereinafter referred to as “NN”) and KNbO ₃ (hereinafter referred to as “KN”), which are a kind of isotropic perovskite compounds. , (K _1-y Na _y ) NbO ₃ (0 <y <1), or a predetermined amount of Li, Ta and / or Sb substituted and dissolved therein, the following general formula (4) What consists of a compound represented by these can be used.
_{{Li x (K 1-y} Na y) 1-x} (Nb 1-zw Ta z Sb w) O 3 ··· (4)
(However, x, y, z and w are 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, 0 ≦ w ≦ 1, respectively)

  The compound represented by the general formula (4) naturally has good lattice matching with the isotropic perovskite compound represented by the general formula (2). Therefore, the anisotropically-shaped powder (hereinafter referred to as “particularly anisotropic powder”) comprising the oriented particles represented by the general formula (4) and having the crystal plane A in the polycrystalline body and the plane having lattice matching with the crystal plane A. The “anisotropically shaped powder A”) functions as a reactive template for producing the above crystal-oriented ceramic. Further, since the anisotropically shaped powder A is composed of a cation element substantially contained in the isotropic perovskite type compound represented by the general formula (2), it is a crystal oriented ceramic with very few impurity elements. Can be manufactured. Among these, plate-like particles made of the compound represented by the above general formula (4) having a pseudo cubic {100} plane as the orientation plane are suitable as the orientation particles.

  Further, as the anisotropically shaped powder, for example, a powder made of a layered perovskite compound and having a crystal face with a small surface energy and lattice matching with the crystal face A in the polycrystal can be used. . Since the layered perovskite type compound has a large crystal lattice anisotropy, the layered perovskite type compound is composed of a layered perovskite type compound and has an anisotropically shaped powder (hereinafter referred to as “anisotropically shaped powder B”). Can be synthesized relatively easily.

As a first example of a layered perovskite compound suitable as a material for the anisotropically shaped powder B, for example, there is a bismuth layered perovskite compound represented by the following general formula (5).
(Bi ₂ O ₂ ) ²⁺ (Bi _0.5 Me _m-1.5 Nb _m O _{3m + 1} ) ^2- (5)
(Where m is an integer of 2 or more, Me is one or more selected from Li, K and Na)

In the compound represented by the general formula (5), the surface energy of the {001} plane is smaller than the surface energy of other crystal planes. Therefore, by using the compound represented by the general formula (5), it is possible to easily synthesize the anisotropically shaped powder B having the {001} plane as an orientation plane. Here, the {001} plane is a plane parallel to the (Bi ₂ O ₂ ) ²⁺ layer of the bismuth layered perovskite compound represented by the general formula (5). In addition, the {001} plane of the compound represented by the general formula (5) is very good lattice with the pseudo cubic {100} plane of the isotropic perovskite compound represented by the general formula (2). There is consistency.
Therefore, the anisotropically-shaped powder B comprising the compound represented by the general formula (5) and having the {001} plane as the orientation plane produces a crystallographically-oriented ceramic having the pseudo cubic {100} plane as the orientation plane. It is suitable as a reactive template for the above, that is, the anisotropically shaped powder. Moreover, when using the compound represented by the said General formula (5), it can adjust so that Bi may be substantially not included as an A site element by optimizing the composition of the fine powder mentioned later. Even when such an anisotropically shaped powder B is used, it is possible to produce a crystallographically-oriented ceramic having an isotropic perovskite compound represented by the general formula (2) as a main phase.

A second example of a layered perovskite type compound suitable as the material for the anisotropically shaped powder B is, for example, Sr ₂ Nb ₂ O ₇ . The surface energy of the {010} plane of Sr ₂ Nb ₂ O ₇ is smaller than the surface energy of other crystal planes, and the pseudo cubic {110 of the isotropic perovskite compound represented by the general formula (2). } There is very good lattice matching with the surface. Therefore, anisotropically shaped powder made of Sr ₂ Nb ₂ O ₇ and having an orientation plane of {010} is suitable as a reactive template for producing a crystal-oriented ceramic having an orientation of {110} plane. is there.

As a third example of a layered perovskite compound suitable as a material for the anisotropically shaped powder B, for example, Na _1.5 Bi _2.5 Nb ₃ O ₁₂ , Na _2.5 Bi _2.5 Nb ₄ O ₁₅ , Bi ₃ TiNbO ₉ , Bi ₃ TiTaO ₉ , K _0.5 Bi _2.5 Nb ₂ O ₉ , CaBi ₂ Nb ₂ O ₉ , SrBi ₂ Nb ₂ O ₉ , BaBi ₂ Nb ₂ O ₉ , BaBi ₃ Ti ₂ NbO ₁₂ , CaBi ₂ Ta ₂ O ₉ , SrBi ₂ Ta ₂ O ₉ , BaBi ₂ Ta ₂ O ₉ , Na _0.5 Bi _2.5 Ta ₂ O ₉ , Bi ₇ Ti ₄ NbO ₂₁ , Bi ₅ Nb ₃ O _{15 and the} like. The {001} plane of these compounds has good lattice matching with the pseudocubic {100} plane of the isotropic perovskite compound represented by the general formula (2). Therefore, anisotropically shaped powders comprising these compounds and having an orientation plane of {001} are suitable as a reactive template for producing crystal oriented ceramics having an orientation plane of pseudo cubic {100} plane. .

As a fourth example of the layered perovskite type compound suitable as the material for the anisotropically shaped powder B, for example, there are Ca ₂ Nb ₂ O ₇ , Sr ₂ Ta ₂ O _{7 and the} like. The {010} plane of these compounds has good lattice matching with the pseudo cubic {110} plane of the isotropic perovskite compound represented by the general formula (2). Therefore, anisotropically shaped powders made of these compounds and having {010} planes as orientation planes are suitable as reactive templates for producing crystal-oriented ceramics with pseudocubic {110} planes as orientation planes. .

Next, a method for producing the anisotropically shaped powder will be described.
Anisotropically shaped powder composed of a layered perovskite type compound having a predetermined composition, average particle size and / or aspect ratio (that is, the anisotropically shaped powder B) includes oxides, carbonates, nitrates and the like containing the component elements. Is a raw material (hereinafter referred to as “anisotropically shaped powder producing raw material”), and this anisotropic shaped powder producing raw material can be easily manufactured by heating it together with a liquid or a substance that becomes liquid by heating.

  When the anisotropically shaped powder-forming raw material is heated in a liquid phase in which atoms are easily diffused, a surface with a small surface energy (for example, the {001} surface in the case of the compound represented by the general formula (5)) is preferential. It is possible to easily synthesize the anisotropically shaped powder B that has been developed. In this case, the average aspect ratio and the average particle diameter of the anisotropically shaped powder B can be controlled by appropriately selecting the synthesis conditions.

As a method for producing the anisotropic shaped powder B, for example, an appropriate flux (for example, NaCl, KCl, a mixture of NaCl and KCl, BaCl ₂ , KF, etc.) is added to the raw material for producing the anisotropic shaped powder at a predetermined temperature. Preferable examples include a heating method (flux method) and a method of heating an amorphous powder having the same composition as the anisotropically shaped powder B to be produced in an autoclave together with an alkaline aqueous solution (hydrothermal synthesis method). .

  On the other hand, since the compound represented by the general formula (4) has a very small anisotropy of the crystal lattice, the compound is represented by the general formula (4) and has a specific crystal plane as an orientation plane. It is difficult to directly synthesize the anisotropically shaped powder (that is, the anisotropically shaped powder A). However, the anisotropically shaped powder A is manufactured by heating the above-mentioned anisotropically shaped powder B as a reactive template and a later-described reaction raw material B that satisfies a predetermined condition in a flux. Can do.

  In addition, when synthesizing the anisotropically shaped powder A using the anisotropically shaped powder B as the reactive template, if the reaction conditions are optimized, only the crystal structure changes, and the powder shape hardly changes. .

In order to easily synthesize the anisotropically shaped powder A that can be easily oriented in one direction during molding, the anisotropically shaped powder B used for the synthesis also has a shape that can be easily oriented in one direction during molding. It is preferable to have.
That is, even when the anisotropic shaped powder A is synthesized using the anisotropic shaped powder B as a reactive template, the average aspect ratio of the anisotropic shaped powder A is preferably at least 3 or more, more preferably 5 or more. More preferably, it is 10 or more. Moreover, in order to suppress the grinding | pulverization in a post process, it is preferable that an average aspect-ratio is 100 or less.

  The “reaction raw material B” refers to a material that reacts with the anisotropically shaped powder B to produce an anisotropically shaped powder A composed of at least the compound represented by the general formula (4). In this case, the reaction raw material B may generate only the compound represented by the general formula (4) by the reaction with the anisotropically shaped powder B. In the general formula (4), It may generate both the compound represented and the surplus component. Here, the “surplus component” refers to a substance other than the target compound represented by the general formula (4). Moreover, when an excess component produces | generates with the anisotropic shaped powder B and the reaction raw material B, it is preferable that an excess component consists of what is easy to remove thermally or chemically.

  As the form of the reaction raw material B, for example, oxide powder, composite oxide powder, carbonate, nitrate, oxalate salt, alkoxide, and the like can be used. The composition of the reaction raw material B can be determined by the composition of the compound represented by the general formula (4) to be produced and the composition of the anisotropically shaped powder B.

For example, an anisotropic shaped powder B made of Bi _2.5 Na _0.5 Nb ₂ O ₉ (hereinafter referred to as “BINN2”), which is one of the bismuth layered perovskite type compounds represented by the general formula (5), is used. Then, when synthesizing anisotropic shaped powder A composed of NaNbO ₃ (NN) which is one of the compounds represented by the general formula (4), the reaction raw material B includes a compound containing Na (oxide, water). Oxides, carbonates, nitrates, etc.) can be used.

An appropriate flux (for example, NaCl, KCl, a mixture of NaCl and KCl, BaCl ₂ , KF, etc.) is 1% by weight to 500% by weight with respect to the anisotropic shaped powder B and the reaction raw material B having such a composition. In addition, when heated to the eutectic point / melting point, an excess component mainly composed of NN and Bi ₂ O ₃ is generated. Bi ₂ O ₃ has a low melting point and is weak against acid, and therefore, after removing the flux from the obtained reaction product by washing with hot water or the like, it is heated at a high temperature or acid cleaning is performed. } The anisotropically shaped powder A made of NN with the plane as the orientation plane can be obtained.

Further, for example, using the anisotropically shaped powder B made of BINN2, (K _0.5 Na _0.5 ) NbO ₃ (hereinafter referred to as “KNN”) which is a kind of the compound represented by the general formula (4). In the case of synthesizing the anisotropically shaped powder A composed of), as the reaction raw material B, a compound containing Na (oxide, hydroxide, carbonate, nitrate, etc.) and a compound containing K (oxide, hydroxide) Compound, carbonate, nitrate, etc.) or a compound containing both Na and K may be used.

When an appropriate flux of 1 to 500% by weight is added to the anisotropic shaped powder B and the reaction raw material B having such a composition and heated to the eutectic point / melting point, KNN and Bi ₂ O ₃ are combined. Since an excess component as a main component is generated, if the flux and Bi ₂ O ₃ are removed from the obtained reaction product, an anisotropic shaped powder A composed of KNN having a {100} plane as an orientation plane can be obtained. .

  The same applies to the case where only the compound represented by the general formula (4) is produced by the reaction between the anisotropically shaped powder B and the reaction raw material B, and the anisotropically shaped powder B having a prescribed composition and the prescribed material. What is necessary is just to heat the reaction raw material B which has a composition in a suitable flux. Thereby, the compound represented with the said General formula (4) which has the target composition in a flux can be produced | generated. Further, if the flux is removed from the obtained reactant, an anisotropically shaped powder A having the above general formula (4) and having a specific crystal plane as an orientation plane can be obtained.

  Since the compound represented by the general formula (4) has a small crystal lattice anisotropy, it is difficult to directly synthesize the anisotropically shaped powder A. It is also difficult to directly synthesize the anisotropically shaped powder A having an arbitrary crystal plane as an orientation plane.

  On the other hand, the layered perovskite type compound has a large crystal lattice anisotropy, so that it is easy to directly synthesize anisotropically shaped powder. In addition, the orientation plane of the anisotropically shaped powder made of the layered perovskite compound often has lattice matching with a specific crystal plane of the compound represented by the general formula (4). Furthermore, the compound represented by the general formula (4) is thermodynamically stable as compared with the layered perovskite compound.

  Therefore, an anisotropically shaped powder B made of a layered perovskite compound and having an orientation plane having lattice matching with a specific crystal plane of the compound represented by the general formula (4) and the reaction raw material B are appropriately used. When the reaction is performed in a simple flux, the anisotropically shaped powder B can function as a reactive template. As a result, the anisotropically shaped powder A composed of the compound represented by the general formula (4) that inherits the orientation direction of the anisotropically shaped powder B can be easily synthesized.

  Further, when the composition of the anisotropically shaped powder B and the reaction raw material B is optimized, the A site element contained in the anisotropically shaped powder B (hereinafter referred to as “surplus A site element”) is surplus. An anisotropically shaped powder A made of a compound represented by the above general formula (4) that is discharged as a component and does not contain surplus A-site elements is produced.

In particular, when the anisotropically shaped powder B is composed of a bismuth layered perovskite compound represented by the general formula (5), Bi is discharged as a surplus A site element, and a surplus component mainly composed of Bi ₂ O ₃ is present. Generate. Therefore, if this surplus component is removed thermally or chemically, it is substantially anisotropic and is composed of a compound represented by the above general formula (4) and having a specific crystal plane as an orientation plane. Shape powder A can be obtained.

The oriented surface of the oriented particles is preferably a pseudo cubic {100} plane.
In this case, it is possible to obtain a crystallographically-oriented ceramic in which the temperature dependence of the displacement generated under a large electric field is improved in a tetragonal region where the orientation axis and the polarization axis coincide.

Next, the fine powder has a particle size of 1/3 or less of the anisotropically shaped powder.
When the particle size of the fine powder exceeds 1/3 of the particle size of the anisotropically shaped powder, in the molding step, the oriented surface of the anisotropically shaped powder is oriented in substantially the same direction, It may be difficult to form the raw material mixture slurry. More preferably, it is 1/4 or less, and further preferably 1/5 or less.
The particle size of the fine powder and the anisotropic shaped powder can be compared by comparing the average particle size of the fine powder and the average particle size of the anisotropic shaped powder. The particle diameter of the anisotropically shaped powder and the particle diameter of the fine powder are both the longest diameter.

The composition of the fine powder can be determined according to the composition of the anisotropically shaped powder and the composition of the isotropic perovskite compound such as the compound represented by the general formula (1) or (2) to be produced. . Specifically, for example, an anisotropic shaped powder and a fine powder having the same composition as the final perovskite compound represented by the general formula (1) or (2) can be used. Further, for example, the composition of the anisotropically shaped powder (cation composition) stoichiometrically from the composition (cation composition) of the final perovskite compound represented by the general formula (1) or (2). The composition of the anisotropically shaped powder and the fine powder can be determined so that the composition obtained by subtracting (the cation composition) becomes the composition of the fine powder (cation composition).
As the fine powder, for example, oxide powder, composite oxide powder, hydroxide powder, carbonate, nitrate, salt of main acid salt, alkoxide or the like can be used.

Examples of the fine powder include a compound represented by the general formula (1) or the general formula (2) that reacts with the anisotropic shaped powder by sintering together with the anisotropic shaped powder. In addition, those that produce the desired isotropic perovskite type compound can be used.
The fine powder may generate only the target isotropic perovskite compound by reaction with the anisotropically shaped powder, or both the target isotropic perovskite compound and the surplus component. It may be generated. When a surplus component is generated by the reaction of the anisotropically shaped powder and the fine powder, it is preferable that the surplus component is easily removed thermally or chemically.

Preferably, the anisotropically shaped powder and the fine powder have different compositions, and in the firing step, the anisotropically shaped powder and the fine powder cause a chemical reaction, thereby causing a main phase of the polycrystalline body. It is preferable to produce the perovskite type compound that becomes (Claim 5).
In this case, it is possible to easily synthesize the anisotropically shaped powder as a raw material for producing the crystal oriented ceramic.

Next, in the mixing step, the fine powder, the anisotropically shaped powder, the molding aid, and the solvent are mixed to prepare a raw material mixture slurry.
In the mixing step, the anisotropically shaped powder blended at a predetermined ratio and the fine powder are further composed of a compound having the same composition as the isotropic perovskite compound obtained by reaction of these substances. A regular fine powder (hereinafter referred to as “compound fine powder”) can be added. Further, for example, a sintering aid such as CuO can be added. When the compound fine powder and the sintering aid are added, there is an advantage that densification of the sintered body is further facilitated.

  In addition, when compounding the compound fine powder, if the compounding ratio of the compound fine powder is excessive, the compounding ratio of the anisotropically shaped powder occupying the whole raw material is inevitably reduced, and the degree of orientation of a specific crystal plane is reduced. May decrease. Therefore, it is preferable to select an optimum blending ratio of the compound fine powder according to a required sintered body density and orientation degree.

  When producing the perovskite type compound represented by the general formula (1), the blending ratio of the anisotropically shaped powder depends on one or more component elements in the anisotropically shaped powder. The ratio of the A site occupied in 1) is preferably 0.01 to 70 at%, and more preferably 0.1 to 50 at%. More preferably, 1 to 10 at% is good. Here, “at%” indicates the percentage of the number of atoms in 100 minutes.

  In the mixing step, the anisotropically shaped powder, the fine powder, the molding aid, and the compound fine powder and sintering aid added as necessary are added to the solvent and mixed in a wet manner. A raw material mixture slurry can be produced. Moreover, a dispersing agent, a plasticizer, etc. can also be added to the said raw material mixture.

Next, a production example of the raw material mixture slurry will be described.
That is, first, an anisotropically shaped powder and fine powder pulverized and sized to a predetermined particle size and shape are mixed with at least one selected from water, alcohol solvents, ester solvents, ketone solvents, aromatic solvents, and the like. Add solvent. Furthermore, one or more suitable dispersants selected from polycarboxylic acid dispersants, polyamide dispersants, acrylic polymer dispersants, nonionic activator dispersants, silicon dispersants and the like are powdered and solidified. For example, 0.5 to 2% by weight is added to the total amount. Next, a molding aid selected from polyvinyl butyral resin, cellulose resin, vinyl acetate resin, polyvinyl alcohol resin and the like is added, for example, 5 to 20% by weight with respect to the total amount of powder solids. Furthermore, plasticizers such as phthalic acid, acetic acid, glycol, adipic acid, and sepacic acid are added as necessary. By mixing these, the raw material mixture slurry can be prepared.

The above mixture slurry is mixed and pulverized using a rotary mill, an impeller mixer or the like to obtain a good dispersed slurry. The viscosity of the slurry is 1 to 8 Pa · s in terms of shear rate during coating in the molding process. If the viscosity is less than 1 Pa · s, it may be difficult to control the thickness of the molded body during molding. Moreover, when the viscosity is larger than 8 Pa · s, there is a possibility that a sufficient degree of orientation cannot be obtained. More preferably, the shear rate during coating is preferably 1 to 6, and more preferably 1 to 4.5.
The viscosity of the mixture slurry can be controlled, for example, by adjusting the solvent addition amount, the dispersant addition amount, the molding aid addition amount, the plasticizer addition amount, and the like.

It is preferable to use at least polyvinyl butyral having a polymerization degree of 200 to 1500 as the molding aid, and at least alcohol as the solvent.
In this case, a raw material mixture slurry having an excellent dispersion state can be obtained, and a molded body having a uniform orientation, a high density and a high strength can be obtained in the molding step. When the degree of orientation of polyvinyl butyral is less than 200, the strength of the molded body may be reduced. On the other hand, when it exceeds 1500, it becomes easy to carbonize when the molded body is degreased, and as a result, the sintered density may be lowered. Moreover, it is more preferable to use a mixed solvent of ethanol and 1-butanol and / or 2-butanol as the alcohol as the solvent.
Moreover, it is preferable to use a polymer dispersant having a polyoxyalkylene group as the dispersant. In this case, the dispersion state of the raw material mixture slurry can be further improved.

  Next, in the molding step, the raw material mixture slurry is applied on a carrier film at a predetermined shear rate so that the oriented surfaces of the anisotropically shaped powder are oriented in substantially the same direction, dried and molded. Create a body. Any molding method may be used as long as the anisotropically shaped powder can be oriented. Specific examples of a molding method for orienting the anisotropically shaped powder include sheet molding methods such as a doctor blade method and a die coater method.

In the molding step, the raw material mixture slurry is coated on the carrier film so that the thickness (μm) / width (mm) ratio is 0.01 or more and 1 or less.
If the thickness / width is less than 0.01, the molding apparatus may become very large. Therefore, it is not practical. On the other hand, if the thickness / width exceeds 1, the degree of orientation may decrease. More preferably, the thickness (μm) / width (mm) ratio is 0.1 to 0.9, and more preferably 0.5 to 0.8.

Further, in order to increase the thickness of the molded body in which the anisotropically shaped powder is surface-oriented (hereinafter referred to as “surface-oriented molded body”) or to increase the degree of orientation, the laminated powder is further laminated on the surface-oriented molded body. Processing such as pressure bonding, pressing, and rolling (hereinafter referred to as “plane orientation processing”) can be performed.
In this case, any one type of surface alignment treatment can be performed on the above-mentioned surface alignment molded body, but two or more types of surface alignment processing can also be performed. In addition, one type of plane alignment treatment can be repeatedly performed on the above-described plane alignment molded body, and two or more types of alignment treatment can be repeatedly performed a plurality of times.

Next, the firing process will be described.
The firing step is a step of heating the molded body to sinter the anisotropically shaped powder and the fine powder. In the firing step, the compact is heated by heating the compact, and the crystal-oriented ceramic composed of a polycrystalline body having a perovskite compound as a main phase can be produced. At this time, the perovskite type compound such as the compound represented by the general formula (1) or (2) can be produced by reacting the anisotropically shaped powder and the fine powder. Moreover, in the said baking process, an excess component is also produced | generated simultaneously depending on the composition of the said anisotropically shaped powder and / or fine powder.

  The heating temperature in the firing step is such that the reaction and / or sintering proceeds efficiently and a reaction product having the desired composition is produced, the anisotropic shaped powder to be used, the reaction raw material, and the crystal to be produced. The optimum temperature can be selected according to the composition of the oriented ceramics.

  For example, in the case of producing a crystallographically-oriented ceramic made of the compound represented by the general formula (2) using the anisotropically shaped powder A having the anisotropically shaped powder KNN composition, the heating in the firing step is The temperature can be 900 ° C. or higher and 1300 ° C. or lower. Further optimum heating temperature in this temperature range can be determined according to the composition of the compound represented by the above general formula (2) which is the target substance. Furthermore, as the heating time, an optimal time can be selected according to the heating temperature so that a desired sintered body density can be obtained.

  Moreover, when a surplus component produces | generates by reaction of the said anisotropically shaped powder and the said fine powder, a surplus component can be made to remain as a subphase in a sintered compact. Further, excess components can be removed from the sintered body. In the case of removing the surplus components, as described above, there are, for example, a method of removing thermally, a method of removing chemically, and the like.

  As a method for thermally removing, for example, a sintered body (hereinafter referred to as “intermediate sintered body”) in which a compound represented by the general formula (2) and an excess component are generated is heated at a predetermined temperature. However, there is a method of volatilizing excess components. Specifically, a method in which the intermediate sintered body is heated for a long time at a temperature at which excess components volatilize is given under reduced pressure or in oxygen.

  The heating temperature at the time of removing the surplus component thermally is such that the volatilization of the surplus component proceeds efficiently and the generation of by-products is suppressed, and the compound represented by the general formula (2) and / or Alternatively, an optimum temperature can be selected according to the composition of the surplus component. For example, when the surplus component is a bismuth oxide single phase, the heating temperature is preferably 800 ° C. or higher and 1300 ° C. or lower, more preferably 1000 ° C. or higher and 1200 ° C. or lower.

  Moreover, as a method of chemically removing the surplus component, for example, there is a method of immersing the intermediate sintered body in a processing solution having a property of eroding only the surplus component and extracting the surplus component. At this time, as the treatment liquid to be used, an optimal one can be selected according to the composition of the compound represented by the general formula (2) and / or the surplus component. For example, when the surplus component is a bismuth oxide single phase, an acid such as nitric acid or hydrochloric acid can be used as the treatment liquid. In particular, nitric acid is suitable as a treatment liquid for chemically extracting surplus components mainly composed of bismuth oxide.

  The reaction between the anisotropically shaped powder and the fine powder and the removal of surplus components may be performed simultaneously, sequentially, or individually. For example, the compact is directly heated to a temperature at which both the reaction between the anisotropically shaped powder and the fine powder and the volatilization of the surplus component proceed efficiently under reduced pressure or under vacuum, and the surplus component is removed simultaneously with the reaction. be able to. The additive element is substituted with the compound represented by the general formula (2), which is the target substance, in the reaction between the anisotropically shaped powder and the fine powder, or within the crystal grains as described above. / And disposed in the grain boundary.

  Further, for example, in the atmosphere or in oxygen, the intermediate sintered body is generated by heating the molded body at a temperature at which the reaction between the anisotropically shaped powder and the fine powder efficiently proceeds, and then the intermediate sintering is continued. The body can be heated under reduced pressure or under vacuum at a temperature at which the volatilization of the surplus components efficiently proceeds to remove the surplus components. In addition, after the intermediate sintered body is generated, the intermediate sintered body is subsequently heated in the atmosphere or oxygen for a long time at a temperature at which the volatilization of the surplus components efficiently proceeds to remove the surplus components. You can also.

  In addition, for example, after the intermediate sintered body is generated and the intermediate sintered body is cooled to room temperature, the intermediate sintered body is immersed in a treatment liquid to remove excess components chemically. Alternatively, after the intermediate sintered body is generated and cooled to room temperature, the intermediate sintered body is again heated to a predetermined temperature in a predetermined atmosphere to remove excess components thermally.

  The molded body obtained in the molding step can be subjected to a heat treatment mainly for degreasing prior to the firing step. In this case, the degreasing temperature can be set to a temperature that is at least sufficient to thermally decompose the molding aid (binder). However, in the case where a material that easily volatilizes (for example, Na compound) is contained in the raw material mixture, the degreasing is preferably performed at 500 ° C. or less.

  Moreover, when the molded body is degreased, the degree of orientation of the anisotropically shaped powder in the molded body may decrease, or volume expansion may occur in the molded body. In such a case, it is preferable to perform a hydrostatic pressure (CIP) treatment on the molded body after degreasing and before the firing step. In this case, it is possible to suppress a decrease in the degree of orientation accompanying degreasing or a decrease in the density of the sintered body due to the volume expansion of the molded body.

  Further, in the case where surplus components are generated by the reaction between the anisotropically shaped powder and the reaction raw material, when removing the surplus components, the intermediate sintered body from which the surplus components have been removed is further subjected to a hydrostatic pressure treatment. This can be refired. Moreover, in order to further raise a sintered compact density and orientation degree, a hot press can be further performed with respect to the sintered compact after the said baking process. Furthermore, a method of adding the above compound fine powder, a method such as CIP treatment, and hot pressing may be used in combination.

  In the production method of the present invention, as described above, the anisotropic powder B made of a layered perovskite compound that is easy to synthesize is used as a reactive template, and the compound made of the compound represented by the general formula (4) is used. The anisotropically shaped powder A can be synthesized, and then the anisotropically shaped powder A can be used as a reactive template to produce the crystal oriented ceramic. In this case, even if it is a compound represented by the said General formula (2) with small crystal lattice anisotropy, the said crystal orientation ceramics in which arbitrary crystal planes orientated can be manufactured easily and cheaply. .

  And if the composition of the said anisotropically shaped powder B and the reaction raw material B is optimized, even if it is the anisotropically shaped powder A which does not contain a surplus A site element, it is compoundable. Therefore, the composition control of the A-site element becomes easy, and a crystallographically-oriented ceramic having the main phase of the compound represented by the general formula (2) having a composition that cannot be obtained by the conventional method can be produced.

  As the anisotropically shaped powder, an anisotropically shaped powder B made of a layered perovskite compound can be used. In this case, in the firing step, the compound represented by the general formula (2) can be synthesized simultaneously with the sintering. Further, by optimizing the composition of the anisotropically shaped powder B to be oriented in the molded body and the reaction raw material to be reacted therewith, the target compound represented by the general formula (2) is synthesized, and the The surplus A site element can be discharged from the square powder B as a surplus component.

  In addition, when the anisotropically shaped powder B that generates a surplus component that can be easily removed thermally or chemically is used as the anisotropically shaped powder, it does not substantially contain the surplus A site element, and the above general formula A crystallographically-oriented ceramic comprising the compound represented by (2) and having a specific crystal plane oriented can be obtained.

(Example 1)
Next, examples of the present invention will be described.
This example is an example of manufacturing a crystallographically-oriented ceramic made of a polycrystal having a perovskite type compound as a main phase and having a specific crystal plane A of crystal grains constituting the polycrystal. In particular, in this example, the general formula _{(2): {Li x (} K 1-y Na y) 1-x} (Nb 1-zw Ta z Sb w) O 3 ( where, 0 ≦ x ≦ 0.2 , 0 ≦ y ≦ 1, 0 ≦ z ≦ 0.4, 0 ≦ w ≦ 0.2, x + z + w> 0), a crystallographically-oriented ceramic comprising a polycrystal having an isotropic perovskite compound as a main phase Manufacturing.

In the manufacturing method of this example, a preparation process, a mixing process, a molding process, and a heat treatment process are performed.
In the preparatory step, an anisotropic shaped powder composed of anisotropically oriented particles made of a perovskite type compound, wherein the crystal face having lattice matching with the specific crystal face A is oriented to form an oriented face; A fine powder that has an average particle size of 1/3 or less of the anisotropically shaped powder and that produces the perovskite compound by sintering together with the anisotropically shaped powder is prepared.
In the mixing step, the anisotropically shaped powder, the fine powder, the molding aid, and the solvent are mixed to produce a raw material mixture slurry.

In the molding step, as shown in FIG. 1, the raw material mixture slurry 3 is applied onto the carrier film 4 at a predetermined shear rate so that the oriented surfaces of the anisotropically shaped powder 1 are oriented in substantially the same direction, and dried. Thus, the molded body 5 is produced as shown in FIG. Moreover, the viscosity of the raw material mixture slurry 3 at the shear rate in the molding step is 1 to 8 Pa · s. In the molding step, the raw material mixture slurry is formed on the carrier film 4 with a thickness d (μm) / width w. (Mm) It coats so that ratio may be 0.01 or more and 1 or less.
In the firing step, the shaped body is heated to sinter the anisotropically shaped powder and the fine powder, thereby obtaining the crystallographically-oriented ceramic.

Hereafter, the manufacturing method of the crystal orientation ceramics of this example is demonstrated in detail.
In this example, an isotropic perovskite compound having a composition of x = 0.08, y = 0.5, z = 0.1, w = 0.06 in the general formula (2), that is, {Li _A crystal-oriented ceramic composed of a polycrystal having an isotropic perovskite type compound represented by _0.08 (K _0.5 Na _0.5 ) _0.92 } (Nb _0.84 Ta _0.1 Sb _0.06 ) O ₃ as a main phase is prepared. In this example, a crystal-oriented ceramic in which a pseudo cubic {100} plane is oriented as the specific crystal plane A is produced.

(1) Production of anisotropically-shaped powder First, as the anisotropically-shaped powder, a specific crystal plane A (having an orientation plane in which a specific crystal plane is oriented, and the oriented plane constitutes a target polycrystalline body ( A powder composed of oriented particles having {100} plane) and lattice matching is prepared as follows. Specifically, in this example, the anisotropically shaped powder B made of Bi _2.5 Na _3.5 Nb ₅ O ₁₈ is prepared, and the anisotropically shaped powder B is used to form a plate-like anisotropic shape made of NaNbO _3. A powder (anisotropically shaped powder A) is prepared.

That is, first, Bi ₂ O ₃ powder with a stoichiometric ratio of Bi _2.5 Na _3.5 Nb ₅ O ₁₈ (hereinafter referred to as “BINN5” as appropriate) and a commercially available Bi ₂ O ₃ powder having a purity of 99% or more, NaHCO ₃ powder and Nb ₂ O ₅ powder 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 is 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. did. The temperature rising rate was 200 ° C./hr, and the temperature lowering was furnace cooling. After cooling, the flux was removed from the reaction product by washing with hot water to obtain BINN5 powder (anisotropically shaped powder B). The obtained BINN5 powder was a plate-like powder having the {001} plane as the orientation plane.

Next, an amount of NaHCO ₃ powder (reaction raw material) necessary for the synthesis of NaNbO ₃ (hereinafter referred to as “NN”) is added to and mixed with the plate-like powder composed of BINN5, and NaCl is used as a flux. Then, heat treatment was performed at 950 ° C. for 8 hours in a platinum crucible.
Since the obtained reaction product contains Bi ₂ O ₃ in addition to the NaNbO ₃ powder, after removing the flux from the reaction product, it is put in an aqueous HNO ₃ solution and Bi ₂ produced as an excess component. O ₃ was dissolved. Further, this solution was filtered to separate the NN powder and washed with ion exchange water at 80 ° C. Thus, NN powder (anisotropically shaped powder A) was obtained as an anisotropically shaped powder.
The obtained NaNbO ₃ powder was a plate-like powder having a pseudo cubic {100} plane as an orientation plane, an average particle size of 15 μm, and an aspect ratio of about 10 to 20.

(2) Production of fine powder Next, the perovskite has an average particle size of 1/3 or less of the average particle of the anisotropically shaped powder and is sintered together with the anisotropically shaped powder as follows. Prepare a fine powder to form a mold compound.
In this example, the target ceramic composition represented by the general formula ABO ₃ {Li _0.08 (K _0.5 Na _0.5 ) _0.92 } (Nb _0.84 Ta _0.1 Sb _0.06 ) O ₃ contains 5 at% of the A site element of NN powder (different The fine powder and the anisotropic shaped powder (NN powder) are blended in the mixing step described later so as to be supplied from the element of the square shaped powder). Therefore, in the production of the fine powder, first, the target ceramic composition {Li _0.08 (K _0.5 Na _0.5 ) _0.92 } (Nb _0.84 Ta _0.1 Sb _0.06 ) O ₃ and a composition obtained by subtracting the blended amount of the NN powder. The NaHCO ₃ powder, KHCO ₃ powder, Li ₂ CO ₃ powder, Nb ₂ O ₅ powder, Ta ₂ O ₅ powder, and NaSbO ₃ powder with a purity of 99% or more that are industrially available are weighed, and organic Wet mixing was carried out with ZrO ₂ balls as a solvent for 20 hours.

Thereafter, calcination was performed at a temperature of 750 ° C. for 5 hours, and wet pulverization was performed with a ZrO ₂ ball for 20 hours using an organic solvent as a medium to obtain a calcined powder (fine powder) having an average particle diameter of about 0.5 μm. .
(3) Mixing Step Next, the anisotropically shaped powder and the fine particle powder produced as described above are mixed with the desired composition {Li _0.08 (K _0.5 Na _0.5 ) _0.92 } (Nb _0.84 Ta _0.1 Sb _0.06 ) O _3. And at a blending ratio such that 5 at% of the amount of Na (A site element) in the target composition is supplied from Na of the anisotropically shaped powder. Next, 1% by weight of a polyoxyalkylene polymer dispersant is added to the weight of the powder sample, 60% by weight of ethanol + 1-butanol as a solvent is added to the weight of the powder sample, and wetted with a ZrO ₂ ball for 20 hours. Mixing was performed. Thereafter, polyvinyl butyral resin (PVB) having a polymerization degree of 650 as a molding aid (binder) is added by 10% by weight with respect to the weight of the powder sample, and further dibutyl phthalate as a plasticizer is added to the weight of the powder sample. 5 wt% was added and mixed for 1 hour with an impeller mixer. This obtained the raw material mixture slurry.

  About the obtained raw material mixture slurry, the viscosity was measured using a rotation-control viscometer (HAAKE Rheometer Rheo Stress RS110). The viscosity was measured in an ethanol atmosphere, and the viscosity at the shear rate (25 (1 / sec)) at the time of applying the raw material mixture slurry described later was measured. The results are shown in Table 1 below.

(4) Molding Step Next, as shown in FIG. 1, the raw material mixture slurry 3 containing the anisotropic shaped powder 1 and the fine powder 2 is applied onto the carrier film 4 using a doctor blade device 9.
The doctor blade device 9 includes a blade 91 for applying a shearing force to the raw material mixture slurry 3 to adjust the thickness during molding, and a feed roller 92 for feeding the carrier film at a constant speed. The raw material mixture slurry 3 is supplied to this doctor blade device 9, and the raw material mixture slurry 3 is applied at a speed of 0.3 m / min on a silicone-coated carrier film 4 having a peeling force of 0.1 N / 50 mm, followed by drying. I let you. Thereby, as shown in FIG. 2, a sheet-like molded body 5 was formed on the carrier film 4. At this time, as shown in FIG. 1, by adjusting the gap between the blade 91 of the doctor blade device and the carrier film 4, the thickness of the slurry during coating is adjusted to 200 μm, and the slurry supply dam of the doctor blade device 9 is adjusted. By adjusting the width of the slurry, the width of the slurry during coating was adjusted to 260 mm. Here, the shear rate at the time of slurry coating is 16.7 × (coating speed of raw material mixture slurry (that is, moving speed of carrier film; 0.3 m / min) / (gap between blade and carrier film)) The shear rate under the above conditions is 25 (1 / sec) In this way, a molded body 5 having a thickness d: 200 μm and a width w: 260 mm was formed on the carrier film 4 (see FIG. 2). ).

  Subsequently, this tape-shaped molded body was laminated and pressure-bonded to obtain a plate-shaped molded body having a thickness of 1.5 mm. Subsequently, the obtained plate-shaped molded body was degreased. Degreasing was performed in the atmosphere under the conditions of heating temperature: 600 ° C., heating time: 5 hours, heating rate: 50 ° C./hr, cooling rate: furnace cooling.

(5) Firing step Next, the molded body obtained as described above is fired to produce crystal-oriented ceramics made of a polycrystalline body (firing step). In this firing process, three processes were performed: a temperature raising process, a holding process, and a cooling process.
That is, first, the degreased compact was placed in a heating furnace, and the temperature in the heating furnace was increased to 1100 ° C. at a temperature increase rate of 200 ° C./h (temperature increase process). Next, this temperature of 1100 ° C. was held for 1 hour (holding process). Next, it was cooled to a temperature of 1000 ° C. at a temperature lowering rate of 5 ° C./h, and further cooled from 1000 ° C. to room temperature at a temperature lowering rate of 200 ° C./h to take out a polycrystal.
In this way, a crystallographically oriented ceramic made of a polycrystal having {Li _0.08 (K _0.5 Na _0.5 ) _0.92 } (Nb _0.84 Ta _0.1 Sb _0.06 ) O ₃ as a main phase was obtained. This is designated as Sample E1.
Preparation conditions of sample E1, that is, shear rate (1 / s) at the time of molding, viscosity of raw material mixture slurry (Pa · s), thickness at coating (μm), width at coating (mm), thickness ( μm) and width (mm) ratio (thickness / width) are shown in Table 1 described later.

(Other examples and comparative examples)
Further, in this example, the viscosity of the raw material mixture slurry and the thickness / width ratio at the time of coating are changed from those in the case of the sample E1, and the others are the same as in the sample E1, and further seven kinds of crystal-oriented ceramics (sample E2, Sample E3 and Sample C1 to Sample C5) were prepared.
That is, Sample E2 was prepared in the same manner as Sample E1 except that a raw material mixture slurry having a viscosity of 4.2 Pa · s was prepared in the mixing step, and that this was used. Specifically, the raw material mixture slurry having a viscosity of 4.2 Pa · s was prepared by changing the solvent amount of the raw material mixture slurry (viscosity 1.5 Pa · s) in the sample E1 from 60 wt% to 45 wt%.

Sample E3 was prepared in the same manner as Sample E1 except that a raw material mixture slurry having a viscosity of 6.7 Pa · s was prepared in the mixing step, and that this was used. Specifically, the raw material mixture slurry having a viscosity of 6.7 Pa · s was prepared by changing the solvent amount of the raw material mixture slurry (viscosity 1.5 Pa · s) in the sample E1 from 60 wt% to 40 wt%.

Sample C1 was prepared in the same manner as Sample E1 except that a raw material mixture slurry having a viscosity of 8.9 Pa · s was prepared in the mixing step and that this was used. Specifically, the raw material mixture slurry having a viscosity of 8.9 Pa · s was prepared by changing the solvent amount of the raw material mixture slurry (viscosity 1.5 Pa · s) in the sample E1 from 60% by weight to 37% by weight.
Sample C2 was prepared in the same manner as Sample E1 except that the raw material mixed slurry was coated on a carrier film with a width of 150 mm. The width at the time of coating was adjusted by changing the width of the slurry supply dam of the doctor blade device.
Sample C3 was prepared in the same manner as Sample E1 except that a raw material mixture slurry having a viscosity of 4.2 Pa · s was prepared in the mixing step, and this raw material mixed slurry was coated on a carrier film with a width of 150 mm. . A raw material mixture slurry having a viscosity of 4.2 Pa · s was produced in the same manner as the sample E2. Moreover, the width | variety at the time of coating was adjusted by changing the width | variety of the slurry supply dam of a doctor blade apparatus similarly to the said sample C2.

Sample C4 was prepared in the same manner as Sample E1 except that a raw material mixture slurry having a viscosity of 6.7 Pa · s was prepared in the mixing step, and this raw material mixed slurry was coated on a carrier film with a width of 150 mm. . A raw material mixture slurry having a viscosity of 6.7 Pa · s was produced in the same manner as the sample E3. Moreover, the width | variety at the time of coating was adjusted by changing the width | variety of the slurry supply dam of a doctor blade apparatus similarly to the said sample C2.
Sample C5 was prepared in the same manner as Sample E1 except that a raw material mixture slurry having a viscosity of 8.9 Pa · s was prepared in the mixing step, and this raw material mixed slurry was coated on a carrier film with a width of 150 mm. . A raw material mixture slurry having a viscosity of 8.9 Pa · s was produced in the same manner as the sample C1. Moreover, the width | variety at the time of coating was adjusted by changing the width | variety of the slurry supply dam of a doctor blade apparatus similarly to the said sample C2.
For the sample E2, the sample E3, and the samples C1 to C5, the shear rate (1 / s) at the time of molding, the viscosity of the raw material mixture slurry (Pa · s), the thickness at the time of coating (μm), and the time of coating The width (mm), thickness (μm), and width (mm) ratio (thickness / width) are shown in Table 1 described later.

Next, the average orientation degree F of the {100} plane was measured as follows for the eight types of crystal oriented ceramics (samples E1 to E3 and samples C1 to C5) obtained as described above.
That is, using an X-ray diffractometer (RINT-TTR manufactured by Rigaku Corporation), the average orientation degree F (100) of {100} planes by the Lotgering method on the surface of each sample under the conditions of Cu-Kα, 50 kV / 300 mA. ) Was measured. The degree of orientation F was calculated using the formula 1 above. The results are shown in Table 1.

As known from Table 1, the crystallographic ceramics of Samples E1 to E3 prepared with a viscosity of the raw material mixture slurry of 1 to 8 Pa · s and a thickness / width during coating of 0.01 to 1 are 80%. A high degree of orientation was exhibited.
On the other hand, Sample C1 to Sample C5 outside the above range were insufficient with an orientation degree of less than 75%.
Sample C1 in which the viscosity of the raw material mixture slurry is out of the range of 1 to 8 Pa · s and Sample C2 to Sample C4 in which the thickness / width is out of the range of 0.01 to 1 are both insufficient in the degree of orientation. there were. Samples E1 to E3 in which both the viscosity of the raw material mixture slurry and the thickness / width during coating satisfy the above specific range showed a high degree of orientation of 83% or more. Moreover, the degree of orientation of the sample C5 in which both the viscosity of the raw material mixture and the thickness / width at the time of coating were out of the specific range was significantly reduced.

  Therefore, it can be seen that the viscosity of the raw material mixture and the thickness / width during coating have a great influence on the degree of orientation of the final crystallographic ceramics. Furthermore, it can be seen that a crystal-oriented ceramic with a high degree of orientation of 80% or more can be obtained by controlling these within the above specific range.

Explanatory drawing which shows a mode that a raw material mixture slurry is applied on a carrier film with a doctor blade apparatus concerning an Example. Explanatory drawing which shows the state which formed the molded object on the carrier film concerning an Example.

Explanation of symbols

1 Anisotropic powder 2 Fine powder 3 Raw material mixture slurry 4 Carrier film 5 Molded body

Claims (6)

A method for producing a crystallographically-oriented ceramic comprising a polycrystal having a perovskite type compound as a main phase, wherein a specific crystal plane A of crystal grains constituting the polycrystal is oriented,
An anisotropically shaped powder comprising anisotropically oriented particles comprising a perovskite type compound, wherein the crystal face having lattice matching with the specific crystal face A is oriented to form an oriented face, and the anisotropically shaped powder A preparatory step of preparing a fine powder having an average particle size of 1/3 or less of the above and producing the perovskite type compound that becomes the main phase of the polycrystal by sintering together with the anisotropically shaped powder; ,
A mixing step of mixing the anisotropically shaped powder, the fine powder, a molding aid, and a solvent to prepare a raw material mixture slurry;
A molding step of coating the raw material mixture slurry on a carrier film at a predetermined shear rate so that the oriented surfaces of the anisotropically shaped powder are oriented in substantially the same direction, and drying to produce a molded body;
A heating step of obtaining the crystal-oriented ceramic by heating the molded body and sintering the anisotropically shaped powder and the fine powder;
The viscosity of the raw material mixture slurry at the shear rate in the forming step is 1 to 8 Pa · s. In the forming step, the raw material mixture slurry is formed on the carrier film in thickness (μm) / width (mm). A method for producing a crystallographically-oriented ceramic, wherein the coating is performed so that the ratio is 0.01 or more and 1 or less. 2. The polycrystalline body according to claim 1, wherein the polycrystal has a general formula (1) ABO ₃ (the A site element is mainly composed of K, Na, K and Na, Li and K, Li and Na, or Li and K and Na. The B-site element is mainly composed of an isotropic perovskite compound represented by Nb, Nb and Ta, Nb and Sb, or Nb, Ta and Sb as main components. Manufacturing method. 3. The polycrystal according to claim 1, wherein the polycrystal has a general formula (2): {Li _x (K _1−y Na _y ) _1−x } (Nb _1−zw Ta _z Sb _w ) O ₃ (where 0 ≦ x ≦ 0.2, 0 ≦ y ≦ 1, 0 ≦ z ≦ 0.4, 0 ≦ w ≦ 0.2, x + z + w> 0) as the main phase A method for producing a crystallographically-oriented ceramic. 4. The anisotropically shaped powder and the fine powder according to claim 1, wherein the anisotropic powder and the fine powder are represented by the general formula (3) ABO ₃ (the A site element is one or more elements selected from K, Na, and Li). A crystal-oriented ceramic characterized by comprising an isotropic perovskite compound represented by: a main component and a B-site element comprising one or more elements selected from Nb, Ta and Sb as main components) Method.   5. The anisotropically shaped powder and the fine powder have different compositions according to claim 1, and in the firing step, the anisotropically shaped powder and the fine powder cause a chemical reaction. To produce the perovskite type compound that becomes the main phase of the polycrystal.   6. The method for producing a crystallographically-oriented ceramic according to claim 1, wherein polyvinyl butyral having a polymerization degree of 200 to 1500 is used as the molding aid and at least an alcohol is used as the solvent.

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