JP2007204336A - Lead free piezoelectric ceramic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lead free piezoelectric ceramic having an excellent denseness, hardly causing an insulation breakdown and comprising an alkali-niobium based compound. <P>SOLUTION: The lead free piezoelectric ceramic is composed of a polycrystalline substance 1 containing an alkali-niobium based compound represented by a composition formula ABO<SB>3</SB>(A is Li+Na+K, B is Nb, Nb+Ta, Nb+Sb, Nb+Ta or Nb+Ta+Sb and O is oxygen) as a main phase. The polycrystalline substance 1 has a core particle 2 and a shell particle 3 having a different composition from each other within a range of the composition formula ABO<SB>3</SB>as the crystal grains constituting the substance. In the polycrystalline substance 1, core particles 2 and shell particles 3 form a composite particle 4 having a pseudo-core shell structure in which a plurality of shell particles 3 are arranged so as to surround the core particle 2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a lead-free piezoelectric ceramic made of a polycrystal having an alkali niobium compound represented by the composition formula ABO ₃ as a main phase. For example, lead suitable for a laminated piezoelectric ceramic for medium-high voltage (electric field strength) It relates to free piezoelectric ceramics.

  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.

Examples of the isotropic perovskite type ferroelectric ceramic include Pb (Zr · Ti) O ₃ (hereinafter referred to as “PZT”) and PZT3 in which lead-based composite perovskite is added to PZT as a third component. Component systems and the like are known.
Lead-based piezoelectric ceramics typified by PZT have high piezoelectric properties 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.

As a piezoelectric ceramic not containing lead, there is a polycrystalline body made of an ABO ₃ -based compound. Specifically, an alkali niobium compound in which A is an alkali metal and B is Nb or Nb and a pentavalent metal, or a barium titanate compound or titanium in which A is at least Ba or Sr and B is at least Ti. Examples include strontium acid compounds.
However, these lead-free piezoelectric ceramics have a problem of low piezoelectric characteristics as compared with PZT. Therefore, in order to obtain a large displacement, it was necessary to apply a high electric field. In that case, higher insulation characteristics are required. As a result, there is a problem that partial discharge occurs and dielectric breakdown is likely to occur particularly when used under a high voltage.

  In such a background, in the polycrystalline ceramics composed of a barium titanate compound or a strontium titanate compound, the so-called so-called so-called so-called so-called so-called so-called so-called polycrystal ceramics, the grain boundaries of the crystal grains and the interior of the grains are different. Polycrystalline ceramics composed of core-shell structured particles have been developed (see Patent Documents 1 to 9). In such polycrystalline ceramics, the composition of the core portion and the shell portion is different in each crystal grain constituting the polycrystalline ceramic, and therefore, high insulation characteristics are imparted to the shell portion. Thus, the insulation resistance when used in a high electric field can be improved.

However, it is difficult to obtain a core-shell structure as described above, for example, in the alkali niobium compounds such as (K, Na) NbO ₃ compounds. Alkali niobium compounds are difficult to be fired and difficult to be densified, and voids and open pores are easily generated during firing. For this reason, there has been a problem that polycrystalline ceramics made of an alkali niobium-based compound cause partial discharge under a high electric field and easily cause dielectric breakdown.

Japanese Patent No. 3418091 JP 2002-362970 A JP 2002-362971 A Japanese Patent Laid-Open No. 10-330160 Japanese Patent Laid-Open No. 10-308321 Japanese Patent No. 3487539 Japanese Patent No. 3125386 Japanese Patent No. 3289500 JP 2004-345927 A

  The present invention has been made in view of such conventional problems, and is intended to provide a lead-free piezoelectric ceramic made of an alkali niobium compound that has excellent denseness and is difficult to cause dielectric breakdown. .

The present invention relates to a polycrystal having an alkali niobium compound represented by the composition formula ABO ₃ (A is Li + Na + K, B is Nb, Nb + Ta, Nb + Sb, Nb + Ta, or Nb + Ta + Sb, O is oxygen) as a main phase. A lead-free piezoelectric ceramic comprising:
The polycrystalline body has core particles and shell particles having different compositions within the range of the composition formula ABO ₃ as crystal grains constituting the polycrystalline body,
In the polycrystal, the core particle and the shell particle form a composite particle having a pseudo core-shell structure in which a plurality of the shell particles are arranged so as to surround the core particle. It exists in piezoelectric ceramics (Claim 1).

In the lead-free piezoelectric ceramic of the present invention, the composite particles having the pseudo core-shell structure are formed. That is, in the lead-free piezoelectric ceramic, the polycrystal is composed of the core particles and the shell particles having different compositions, and the core particles and the shell particles form the composite particles having the pseudo core-shell structure. is doing.
Therefore, the lead-free piezoelectric ceramic is excellent in denseness and can reduce voids and open pores.

  That is, generally, in the case of alkali niobium compounds, the natural growth form of crystal grains is cubic, so that crystal grains having different crystal orientations prevent crystal growth from each other, are difficult to be densified, and easily form voids and open pores. Tend. On the other hand, in the lead-free piezoelectric ceramic of the present invention, a plurality of the shell particles arranged so as to surround the core particles can fill the space between the core particles. Therefore, the lead-free piezoelectric ceramic is excellent in denseness and can suppress generation of voids and open pores. Therefore, for example, even under a high electric field, it is possible to suppress the occurrence of partial discharge that occurs starting from a void or the like, and to make it difficult for dielectric breakdown to occur.

Next, the pseudo core shell structure will be described.
The pseudo core-shell structure in the lead-free piezoelectric ceramic of the present invention is different from the conventional core-shell structure of barium titanate compounds and strontium titanate compounds. That is, in the conventional core-shell structure, one crystal grain has a core part and a shell part inside, and an element different from the core part is intentionally diffused in the shell part. Therefore, the conventional core-shell structure is a structure composed of particles in which different component distributions exist between the inside (core portion) and the outer peripheral portion (shell portion) of one crystal grain. On the other hand, in the said pseudo core shell structure, the core part and shell part in the conventional core shell structure consist of different crystal grains. That is, the pseudo core-shell structure is composed of different particles such as the core particles and the shell particles arranged around the core particles.
In the conventional core-shell structure, the shell portion has a component composition in which a small amount of additional elements are added to the core portion, whereas in the pseudo-core-shell structure in the present invention, the core particle and the shell particle are the same. Despite having the basic composition (ABO ₃ ), the conventional core-shell structure is different from the above-described pseudo-core-shell structure in that the specific element component amount is different between the core particle and the shell particle.

  As described above, according to the present invention, it is possible to provide a lead-free piezoelectric ceramic made of an alkali niobium compound that has excellent denseness and hardly causes dielectric breakdown.

Next, a preferred embodiment of the lead-free piezoelectric ceramic of the present invention will be described.
The core particle is composed of an alkali niobium compound represented by the composition formula ABO ₃ having a higher content of the component elements Na, Ta, and Sb than the average composition of the entire lead-free piezoelectric ceramic, and the shell particles are Preferably, the lead-free piezoelectric ceramic is made of an alkali niobium compound represented by the composition formula ABO ₃ having a higher content of the component elements K and Nb than the average composition of the entire lead-free piezoelectric ceramic.
In this case, the density can be further improved, and the generation of voids and open pores can be further suppressed. As a result, the occurrence of dielectric breakdown can be further suppressed.

Further, when the composition of the core particle and the composition of the shell particle are compared, it is preferable that there is a composition difference of 10 to 50% with respect to the composition of the same element.
When the compositional difference is less than 10%, the number of the shell particles is small, and it may be difficult to obtain a sufficiently dense sintered body by suppressing growth during the sintering process. On the other hand, if it exceeds 50%, in addition to the originally required piezoelectric characteristics, the amount of K in the shell particles, for example, becomes excessive, resulting in an increase in electrical conductivity and a decrease in insulation characteristics. The composition difference is more preferably 3 to 30%, and further preferably 3 to 25%.

The composition difference between the core particles and the shell particles can be measured, for example, as follows.
That is, for example, composition analysis can be performed by using an X-ray microanalyzer (EPMA), performing EPMA analysis (element mapping analysis) at an acceleration voltage of 15 kV, and then performing ZAF correction to obtain the composition. it can. After performing element mapping analysis and identifying core particles and shell particles from the element distribution, the elemental analysis results of each particle are obtained. In order to obtain a more precise analysis value, EPMA point analysis is performed on each particle, and after ZAF correction, an accurate composition of each particle is obtained.

The composite particles preferably have an average particle size of 0.15 to 30 μm.
If the average particle diameter of the composite particles is less than 0.15 μm, high piezoelectric characteristics may not be realized. On the other hand, if it exceeds 30 μm, high piezoelectric properties can be expected, but the strength as a sintered body may be reduced. As a result, for example, when the above lead-free piezoelectric ceramics are used as various piezoelectric elements, the life of the element due to fatigue failure due to repeated operation may be significantly shortened.
The average particle size of the composite particles can be measured by a so-called intercept method using, for example, a mirror image of the lead-free piezoelectric ceramic and then using a scanning electron microscope (SEM) photograph of the polished surface.

The alkali niobium-based compound has the general formula: {Li _x (K _{1 -y} Na _y ) _{1 -x}} {Nb _{1 -zw} Ta _z Sb _w } O ₃ (where 0 ≦ x ≦ 0.2, An isotropic perovskite type compound represented by 0 <y <1, 0 ≦ z ≦ 0.4, 0 ≦ w ≦ 0.2, x + z + w> 0) is preferable.
In this case, the piezoelectric characteristics and dielectric characteristics of the lead-free piezoelectric ceramic can be further improved. Further, the temperature dependence of the dielectric constant and the piezoelectric displacement, that is, the variation in characteristics such as the dielectric constant and the piezoelectric displacement due to the temperature change can be reduced.

In the above general formula, “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, “y” represents the ratio of K and Na contained in the isotropic perovskite compound. In a general isotropic perovskite type compound, it is sufficient that at least one of K and Na is contained as an A site element. In the present invention, in order to realize the above pseudo core shell structure, K and Na are used. It is essential that both exist simultaneously. Therefore, the range of y in the above general formula is 0 <y <1 as described above. Moreover, since y> 0, that is, Na is an essential component, the lead-free piezoelectric ceramic can exhibit an excellent piezoelectric g ₃₁ constant.
In the above general formula, the range of 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 total number of electrical solutions Kp of the crystal oriented ceramics can be further improved. Even more preferably, 0.20 ≦ y <0.70, even more preferably 0.35 ≦ y ≦ 0.65, and even more preferably 0.35 ≦ y <0.65. 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 above general formula is preferably 0 <x ≦ 0.2.
In this case, since Li is an essential component in the compound represented by the above general formula, the polycrystalline body can be fired more easily at the time of production, and the piezoelectric characteristics are further improved. The Curie temperature (Tc) can be further increased. 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, enabling firing with fewer 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 above general formula can be set to x = 0.
In this case, the above general formula is represented by (K _{1 -y} Na _y ) (Nb _{1 -zw} Ta _z Sb _w ) O ₃ . In this case, when producing the lead-free piezoelectric ceramic, since the raw material does not include the lightest Li-containing compound such as LiCO ₃ , the raw materials are mixed, When producing the lead-free piezoelectric ceramic made of a crystal, variation in characteristics due to segregation of the raw material powder can be reduced. The dispersion of the raw material powder tends to be particularly large, for example, in the case of producing a polycrystalline body having a crystal orientation ceramic structure, which will be described later, and in this case, the above-described effect of reducing the variation in characteristics is more prominent. It can be demonstrated. Further, when x = 0, a higher relative dielectric constant and a relatively large piezoelectric g constant can be realized.
In the above general formula, 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 above general formula, when the value of z exceeds 0.4, the Curie temperature is lowered, and there is a possibility that the use as a piezoelectric material for home appliances and automobiles becomes difficult.
The range of z in the above general formula is preferably 0 <z ≦ 0.4.
In this case, Ta is an essential component in the compound represented by the above general formula. Therefore, in this case, the sintering temperature is lowered, and Ta serves as a sintering aid, so that the pores in the polycrystalline body can be reduced.

The value of z in the above general formula can be set to z = 0.
In this case, the general formula is represented by {Li _x (K _1−y Na _y ) _1−x } (Nb _1−w Sb _w ) O ₃ . In this case, the compound represented by the above general formula does not contain Ta. Therefore, in this case, the lead-free piezoelectric ceramic can exhibit excellent piezoelectric characteristics without using an expensive Ta component during its production.
In the above general formula, 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.
The value of w in the above general formula is preferably 0 <w ≦ 0.2.
In this case, Sb is an essential component in the compound represented by the above general formula. Therefore, in this case, the sintering temperature of the polycrystalline body can be lowered, the sinterability can be improved, and the stability of the dielectric loss tan δ can be improved.

The value of w in the above general formula can be set to w = 0.
In this case, the above general formula 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 does not contain Sb, and the lead-free piezoelectric ceramic made of the polycrystalline body can exhibit a relatively high Curie temperature.
In the above general formula, the value of w is more preferably 0 ≦ w ≦ 0.15, and further preferably 0 ≦ w ≦ 0.10.

  The polycrystal is preferably composed only of the isotropic perovskite type compound represented by the above general formula, but the isotropic perovskite type crystal structure can be maintained, and sintering characteristics, piezoelectric characteristics, etc. Other elements or other phases may be included as long as these properties are not adversely affected.

The polycrystal preferably has a crystal-oriented ceramic structure in which specific crystal planes of the crystal grains constituting the polycrystal are oriented.
In this case, the piezoelectric characteristics and dielectric characteristics of the lead-free piezoelectric ceramic can be further improved.
In general, in crystal-oriented ceramics, it is difficult to achieve 100% crystal orientation. Therefore, when an electric field is applied, the strain directions of crystal grains having different crystal orientations differ, and voids are present. As a result of stress concentration on this, mechanical destruction such as cracks is likely to occur starting from this stress. On the other hand, in the present invention, since it has the pseudo core shell structure, even if it has a crystal orientation ceramic structure as described above, the displacement of the shell particles can alleviate strain. As a result, even if it has a crystallographically-oriented ceramic structure, the occurrence of mechanical breakdown such as cracks can be suppressed. Moreover, since generation | occurrence | production of a crack can be suppressed in this way, the electric current which flows through a crack surface is suppressed and generation | occurrence | production of an electrical breakdown is also suppressed. In addition, a phenomenon in which charges due to the positive piezoelectric effect accompanying the occurrence of cracks appear on the crack surface is suppressed. Therefore, partial discharge accompanying the generation of cracks can be suppressed, and as a result, dielectric breakdown can be suppressed.

  “Specific crystal planes are oriented” means, for example, that the crystal grains are arranged so that the specific crystal planes of the crystal-oriented ceramic made of the compound represented by the general formula are parallel to each other. (Hereinafter, such a state is referred to as “plane orientation”), or each crystal grain is arranged so that a specific crystal plane A is parallel to one axis penetrating the polycrystal. (Hereinafter, such a state is referred to as “axial orientation”).

The polycrystal preferably contains one or more elements selected from a transition metal element having an atomic number of 21 to 29, an alkaline earth metal, Al, Bi, and Si (Claim 6).
In this case, in addition to the improvement of the insulation characteristics by the pseudo core shell structure, the insulation characteristics can be further improved by the effect of each element described above. That is, in this case, due to the synergistic effect of the pseudo core shell structure and each of the above-described elements, it is possible to show more excellent insulating characteristics and ensure high reliability.

The above transition metal elements of atomic numbers 21 to 29, alkaline earth metals, Al, Bi, and Si may be contained in the form of elements, but are contained in the form of compounds containing these elements. May be.
Specific examples of the transition metal element compounds having atomic numbers 21 to 29 include, for example, Sc ₂ O ₃ , Cu ₂ O, NiO, Fe ₂ O ₃ , Mn ₂ O ₃ , V ₂ O ₅ , TiO ₂ , CoO, Cr ₂ O ₃ , LaMnO ₃ , LaFeO ₃ or the like can be used.
Further, as the alkaline earth compound, for example, MgO, CaO, SrO, BaO, BaTiO ₃ , MgAl ₂ O ₄ , MgFe ₂ O ₄ , MgWO ₄ , SrTa ₂ O _{6 and the} like can be used.
As the Al compound, for example, Al ₂ O ₃ , FeAlO ₃ , AlSb, CaTiO ₃ , CaZrO _{3 and the} like can be used.
As the Bi compound, for example, Bi ₂ O ₃ , Bi ₄ Ti ₃ O ₁₂ , Bi ₂ WO ₆ , Bi ₂ Sb ₃ , BiFeO ₃ , Bi _2.5 Na _3.5 Nb ₅ O ₁₈ can be used.
As the Si compound may be, for example, _{SiO 2, FeSi, Ni 2 Si} , FeSi 2, NbSi 2, TaSi 2, TiSi 2, WSi 2 , and the like.

In the lead-free piezoelectric ceramic, Cu ₂ O, CuO, K ₄ CuNb ₈ O ₂₃ , K _5.4 Cu _1.3 Ta ₁₀ O ₂₉ , CuNb ₂ O ₆ , CuTa ₂ O are used with respect to 1 mol of the alkali niobium compound. It is preferable that 0.0005 to 0.03 mol of at least one selected from ₆ , KNbO ₃ and K ₃ Li ₂ Nb ₅ O ₁₅ is added.
In this case, generation of open pores can be further suppressed.
When the addition amount is less than 0.0005 mol, there is a possibility that the above-described effect that the generation of open pores can be further suppressed cannot be obtained sufficiently. On the other hand, if it exceeds 0.03 mol, the insulation characteristics are improved, but an Nb-rich heterogeneous phase with low piezoelectric characteristics appears in the structure, and the piezoelectric characteristics of the lead-free piezoelectric ceramics may be greatly reduced.

Next, a method for producing the lead-free piezoelectric ceramic will be described.
The lead-free piezoelectric ceramic can be produced, for example, by performing the following raw material mixing step, forming step, and firing step.
That is, in the raw material mixing step, raw materials for producing the alkali niobium compound represented by the composition formula ABO ₃ are mixed to prepare a raw material mixture. Next, in the molding step, the raw material mixture is molded to produce a molded body. Next, in the firing step, the molded body is fired to produce a lead-free piezoelectric ceramic made of the polycrystalline body. Further, in the firing step, a heating process in which heating of the molded body is started to increase the temperature, and the molded body is held at a temperature T1 ° C. (provided that 600 ≦ T1 ≦ 1500) for 0.1 minute or longer. A first holding step and a step that is continuous with the first holding step and holds the molded body at a temperature T2 ° C. (T2 ≧ 300) lower than the temperature T1 ° C. for 10 minutes or more. A holding process and / or a process that is continuous with the first holding process and cools the molded body from a temperature T1 ° C. at a temperature drop rate of 60 ° C./h or less is performed.

  The temperature raising process before the first holding process (temperature T1-200 ° C. or higher, T1 or lower), the first holding process (temperature T1), the temperature lowering process after the first holding process (temperature T1 or lower, T1 to 500 ° C.), In the temperature range of the second holding process (temperature T2), a liquid phase is generated from the raw material mixture, and the liquid particles are considered to form the shell particles around the core particles. Therefore, the size of the shell particles can be controlled by appropriately adjusting the temperature of the first holding process and the holding time held at the temperature. As a result, the piezoelectric characteristics and dielectric characteristics of the lead-free piezoelectric ceramic can be controlled.

Further, when the holding temperature T1 ° C. in the first holding process is out of the range of 600 ≦ T1 ≦ 1500, the pseudo core-shell structure cannot be formed, and the denseness of the lead-free piezoelectric ceramic may be reduced. There is. The holding temperature T1 (° C.) is preferably 1000 ≦ T1 ≦ 1300.
Further, even when the holding time at the holding temperature T1 ° C. is less than 0.1 minutes, the pseudo core-shell structure cannot be formed, and the denseness may be lowered. Preferably, the holding time at the temperature T1 ° C. is 30 minutes or longer, more preferably 60 minutes or longer. Moreover, in order to suppress that an open porosity becomes large, the upper limit of the retention time in temperature T1 degreeC is good for 2000 minutes or less. More preferably, it is 600 minutes or less, More preferably, 300 minutes or less is good.

Further, in the second holding process, when T2 <300, there is a possibility that sintering of the molded body does not proceed sufficiently. In addition, the pseudo-core shell structure cannot be sufficiently formed, and the voids of the polycrystalline body may not be sufficiently reduced. More preferably, the temperature T2 is preferably T2 ≧ 600.
On the other hand, when the holding time at T2 is less than 10 minutes, the pseudo-core shell structure cannot be sufficiently formed, and the voids of the polycrystalline body may not be sufficiently reduced. Moreover, since there exists a possibility that productivity may fall, the upper limit of the holding time in temperature T2 is good for 2000 minutes or less.

Further, it is preferable that the holding temperature T1 (° C.) in the first holding process and the holding temperature T2 (° C.) in the second holding process satisfy a relationship of 5 ≦ (T1−T2) ≦ 300. .
In the case of (T1-T2) <5, the pseudo core shell structure cannot be sufficiently formed, and voids in the polycrystalline body may not be sufficiently reduced. On the other hand, in the case of (T1-T2)> 300, there is a possibility that firing of the molded body does not proceed sufficiently. In either case, there is a possibility that the lead-free piezoelectric ceramic made of the resulting polycrystalline material will be insufficiently densified.

  Further, in the cooling process, when the temperature lowering rate exceeds 60 ° C./h, the pseudo core-shell structure cannot be sufficiently formed, and the voids in the polycrystal may not be sufficiently reduced. There is. More preferably, the temperature lowering rate in the cooling process is 40 ° C./h or less. More preferably, it is 20 ° C./h or less, even more preferably 10 ° C./h or less, and still more preferably 5 ° C./h or less. Moreover, since there exists a possibility that productivity may fall, 1 degreeC / h or more is good for a temperature fall rate.

  In the cooling process, cooling can be performed to room temperature, but the above cooling process can be performed only in a temperature range in which sintering is promoted in order to shorten the entire process time. In this case, the cooling process is preferably performed up to a temperature T1-500 ° C. More preferably, it is good to carry out to T1-300 degreeC, More preferably, to T1-100 degreeC.

Example 1
In this example, a lead-free piezoelectric ceramic made of a polycrystal having a crystal orientation ceramic structure is manufactured.
The lead-free piezoelectric ceramic of this example has the general formula {Li _x (K _{1 -y} Na _y ) _{1 -x}} {Nb _{1 -zw} Ta _z Sb _w } O ₃ , x = 0.065, y = 0.55 , Z = 0.09, w = 0.08, isotropic perovskite type compound, that is, {Li _0.065 (K _0.45 Na _0.55 ) _0.935 } {Nb _0.83 Ta _0.09 Sb _0.08 O _62.4 } O ₃ It is made of a polycrystal having a crystal orientation ceramic structure in which a specific crystal plane of a crystal grain is oriented, with the alkali niobium compound as a main phase. The polycrystalline body 1 has core particles 2 and shell particles 3 having different compositions as crystal grains constituting the polycrystalline body 1 (see FIG. 2). In the polycrystalline body 1, the core particle 2 and the shell particle 3 form a composite particle 4 having a pseudo core-shell structure in which a plurality of shell particles 3 are arranged so as to surround the core particle 2.

Hereinafter, the manufacturing method of the lead-free piezoelectric ceramic of this example will be described.
(1) Production of anisotropically shaped powder First, a specific crystal having an orientation plane in which a specific crystal plane (hereinafter referred to as “crystal plane a”) is oriented, and the orientation plane constitutes a target polycrystal. A first anisotropic shaped powder composed of first oriented particles having lattice matching with a plane (hereinafter referred to as “crystal plane A”) is prepared. Specifically, in this example, an anisotropically shaped powder B made of Bi _2.5 Na _3.5 Nb ₅ O ₁₈ is produced, and a plate-like first anisotropic made of NaNbO ₃ is produced using this anisotropic shaped powder B. A shaped powder (anisotropic shaped powder A) is prepared.

That is, first, Bi ₂ O ₃ powder, Na ₂ CO ₃ powder and Nb ₂ O ₅ powder with a stoichiometric ratio such that Bi _2.5 Na _3.5 Nb ₅ O ₁₈ (hereinafter referred to as “BINN5” as appropriate) is obtained. 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 Na ₂ CO 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. In the platinum crucible, heat treatment was performed at 950 ° C. for 8 hours.
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. This is designated as powder sample A1.
The obtained NN powder was a plate-like powder having a pseudo cubic {100} plane as an orientation plane, an average particle diameter of 15 μm, and an aspect ratio of about 10 to 20.

(2) Preparation of fine particle powder Next, the fine particle powder which produces a polycrystal by sintering with the said anisotropically shaped powder (NN powder) as follows is produced.
In this example, as described later, the composition of the target ceramic represented by the general formula ABO ₃ {Li _0.065 (K _0.45 Na _0.55 ) _0.935 } {5 at% of the A site element in Nb _0.83 Ta _0.09 Sb _0.08 } O ₃ NN powder is blended so that is supplied from the element of NN powder (anisotropically shaped powder).
Therefore, in the production of the fine particle powder, first, the composition of the target ceramic {Li _0.065 (K _0.45 Na _0.55 ) _0.935 } {Nb _0.83 Ta _0.09 Sb _0.08 } O ₃ is subtracted from the blended amount of the NN powder. Na ₂ CO ₃ powder with a purity of 99.99% or more, K ₂ CO ₃ powder, Li ₂ CO ₃ powder, Nb ₂ O ₅ powder, Ta ₂ O ₅ powder, and Sb ₂ O ₅ powder so as to have a composition Weighed and wet mixed with ZrO ₂ balls for 24 hours using an organic solvent such as acetone or alcohol as a medium.

Thereafter, calcined at a temperature of 750 ° C. for 5 hours, and further wet pulverized with a ZrO ₂ ball for 24 hours using an organic solvent as a medium to obtain a calcined powder (fine particle powder) having an average particle size of about 0.5 μm. It was. This is designated as Powder Sample B1.

(3) Fabrication of molded body Next, the stoichiometric amounts of the powder sample A1 and the powder sample B1 to be the target composition {Li _0.065 (K _0.45 Na _0.55 ) _0.935 } {Nb _0.83 Ta _0.09 Sb _0.08 } O ₃ The mixture was weighed in a stoichiometric ratio and wet mixed with a ZrO ₂ ball for 24 hours using an organic solvent as a medium to obtain a slurry of a raw material mixture.
Thereafter, polyvinyl butyral resin (PVB) as a binder and dibutyl phthalate as a plasticizer are added to the slurry with a desired composition ({Li _0.065 (K _0.45 Na _0.55 ) _0.935 } {Nb _0.83 Ta _0.09 Sb _0.08 } O _3. ) About 10.35 g of each was added to 1 mol, and further mixed for 2 hours.

  Next, using a doctor blade device, a slurry of a raw material mixture in which a binder and a plasticizer were mixed was formed into a tape having a thickness of about 100 μm. Furthermore, the tape-shaped molded body was laminated, pressure-bonded and rolled 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: 750 ° C., heating time: 5 hours, heating rate: 50 ° C./hr, cooling rate: furnace cooling. Furthermore, the CIP process was performed to the plate-shaped molded object after degreasing | defatting by pressure: 300MPa. The molded body thus obtained is designated as a molded sample D1.

(4) Firing Next, the molded body (molded sample D1) obtained as described above is fired to produce a lead-free piezoelectric ceramic made of a polycrystalline body. In firing the molded sample D1, a heating process, a first holding process, and a cooling process were performed.
That is, first, the molded sample D1 is placed in a heating furnace, heated up to a temperature of 900 ° C. at a heating rate of 200 ° C./h, heated up to a temperature of 1020 ° C. at a heating rate of 45 ° C./h, and further heated to a temperature of 1115 ° C. The temperature was raised at a heating rate of 10 ° C./h. Next, a holding process was performed, and the temperature was held at 1115 ° C. for 5 hours. Next, it was cooled to a temperature of 1010 ° C. at a temperature decrease rate of 5 ° C./h. Then, it cooled to room temperature with the temperature-fall rate of 200 degrees C / h, and produced the polycrystal body which consists of crystal orientation ceramics.
In this way, a lead-free piezoelectric ceramic made of a polycrystalline body having a crystal orientation ceramic structure having {Li _0.065 (K _0.45 Na _0.55 ) _0.935 } {Nb _0.83 Ta _0.09 Sb _0.08 } O ₃ as a main phase was obtained. This is designated as Sample E1.

  Note that degreasing and firing may be performed in a single continuous step. In that case, the compact is put in a heating furnace, heated to a degreasing temperature of 600 ° C. at a heating rate of 50 ° C./h, held at a temperature of 600 ° C. for 1 to 5 hours (degreasing process), and then a temperature of 900 The temperature is increased to 200 ° C. at a temperature increase rate of 200 ° C./h, the temperature is increased to a temperature of 1020 ° C. at a temperature increase rate of 45 ° C./h, and further the temperature is increased to 1115 ° C. at a temperature increase rate of 10 ° C./h. Next, a holding process is performed and the temperature is held at 1115 ° C. for 5 hours. Next, it is cooled to a temperature of 1010 ° C. at a temperature drop rate of 5 ° C./h, and then cooled to a room temperature at a temperature drop rate of 200 ° C./h to obtain a lead-free piezoelectric ceramic made of a polycrystal similar to the sample E1. it can.

Next, in this example, the crystal structure of the obtained sample E1 (lead-free piezoelectric ceramic) was examined by a scanning electron microscope (SEM). The result is shown in FIG. For convenience of explanation, FIG. 2 shows a structure of main crystal grains in a portion surrounded by a dotted line in FIG.
As is known from FIGS. 1 and 2, the lead-free piezoelectric ceramic of this example had a core particle 2 and a shell particle 3 as crystal grains constituting the polycrystalline body 1. In the polycrystalline body 1, the core particle 2 and the shell particle 3 formed a composite particle 4 having a pseudo core-shell structure in which a plurality of shell particles 3 are arranged so as to surround the core particle 2.

Moreover, in this example, the composition analysis of the lead-free piezoelectric ceramic of the sample E1 was performed with an X-ray microanalyzer (EPMA: Electron Probe Micro-Analysis).
EPMA analysis was performed using JXA-8200 manufactured by JEOL. The analysis was performed at an acceleration voltage of 15 kV, and then ZAF correction was performed. Table 1 shows the results of the composition analysis of each constituent element in the core particles and the shell particles obtained by the EPMA analysis.
Moreover, the difference between each elemental composition in the core particle and each elemental composition in the shell particle was calculated from the result of the EPMA analysis. The results are shown in Table 2. In Table 2, the compositional difference between the constituent elements of the core particle and the shell particle is shown by the difference with respect to the elemental composition of the core particle.

As is known from Tables 1 and 2, it can be seen that the core particles contain a lot of Na, Ta, and Sb, and the shell particles contain a lot of K and Nb. The difference in composition reaches 3 to 25%. The average composition of the core particles and the shell particles was approximately {Li _0.065 (K _0.45 Na _0.55 ) _0.935 } {Nb _0.83 Ta _0.09 Sb _0.08 O _62.4 } O ₃ . Although not clearly shown in the present specification, as a result of XRD measurement, the sample E1 has a perovskite structure, and consistency with the composition was recognized.

(Example 2)
This example is made of a polycrystal having a crystal orientation ceramic structure represented by the above general formula: {Li _x (K _{1 -y} Na _y ) _{1 -x}} {Nb _{1 -zw} Ta _z Sb _w } O ₃ It is an example which manufactures lead free piezoelectric ceramics.
Specifically, the general formula _{{Li x (K 1-y} Na y) 1-x} {Nb 1-zw Ta z Sb w} In _{O 3 x = 0.065, y =} 0.60, z = 0 .10, isotropic perovskite type compound having a composition of w = 0.065, that is, isotropic perovskite represented by {Li _0.065 (K _0.40 Na _0.60 ) _0.935 } (Nb _0.835 Ta _0.10 Sb _0.065 ) O ₃ A lead-free piezoelectric ceramic made of a polycrystalline body having a crystal orientation ceramic structure in which a specific crystal plane of crystal grains is oriented with a type compound as a main phase is produced.

Specifically, first, an anisotropic shaped powder (NN powder) was produced. As this anisotropically shaped powder, the same powder sample A1 of Example 1 was prepared.
Moreover, the fine particle powder was produced.
In producing the fine particle powder of this example, the composition of the target ceramic {Li _0.065 (K _0.40 Na _0.60 ) _0.935 } (Nb _0.835 Ta _0.10 Sb _0.065 ) O ₃ is obtained by subtracting the NN powder composition. Weigh Na ₂ CO ₃ powder, K ₂ CO ₃ powder, Li ₂ CO ₃ powder, Nb ₂ O ₅ powder, Ta ₂ O ₅ powder, and Sb ₂ O ₅ powder with a purity of 99.99% or more so that Then, it was produced in the same manner as the powder sample B1 of Example 1. This is designated as Powder Sample B2. The powder sample B2 is a calcined powder (fine particle powder) having an average particle diameter of about 0.5 μm.

Next, in the same manner as in Example 1, the powder sample A1 and the powder sample B2 are chemically _treated to have the target composition {Li _0.065 (K _0.40 Na _0.60 ) _0.935 } (Nb _0.835 Ta _0.10 Sb _0.065 ) O _3. A slurry was prepared by weighing at a stoichiometric ratio, and molded and degreased to produce a molded body. Production, molding, and degreasing of the slurry were performed in the same manner as in Example 1. The molded body thus obtained is designated as a molded sample D2.

Next, the obtained molded sample D2 is put in a heating furnace, heated to a temperature of 900 ° C. at a heating rate of 200 ° C./h, heated to a temperature of 1020 ° C. at a heating rate of 45 ° C./h, and further heated to a temperature. The temperature was raised to 1115 ° C. at a temperature raising rate of 10 ° C./h. Next, a holding process was performed, and the temperature was held at 1115 ° C. for 5 hours. Next, it was cooled to a temperature of 1010 ° C. at a temperature decrease rate of 5 ° C./h. Then, it cooled to room temperature with the temperature-fall rate of 200 degrees C / h, and produced the polycrystal body which consists of crystal orientation ceramics. In this way, a lead-free piezoelectric ceramic composed of a polycrystalline body having a crystal orientation ceramic structure having {Li _0.065 (K _0.40 Na _0.60 ) _0.935 } (Nb _0.835 Ta _0.10 Sb _0.065 ) O ₃ as a main phase was obtained. This is designated as Sample E2.

  For the sample E2, the crystal structure was examined by a scanning electron microscope (SEM) in the same manner as the sample E1 of Example 1. As a result, sample E2 also had core particles and shell particles as crystal grains constituting the polycrystal as in sample E1. In the polycrystal, the core particle and the shell particle form a composite particle having a pseudo core-shell structure in which a plurality of shell particles are arranged so as to surround the core particle. In addition, the sample E2 was subjected to EPMA analysis in the same manner as in Example 1. As in the sample E1, the core particles contained a large amount of Na, Ta, and Sb, and the shell particles contained K and Nb. Many were included, and the difference in composition reached 3 to 25%.

Further, in this example, for comparison with the sample E2, it is made of a crystal oriented ceramic having {Li _0.065 (K _0.40 Na _0.60 ) _0.935 } (Nb _0.835 Ta _0.10 Sb _0.065 ) O ₃ as a main phase. A lead-free piezoelectric ceramic (sample C2) made of a polycrystalline body having no structure was produced.
In producing the sample C2, first, an anisotropic shaped powder (powder sample A1) and a fine particle powder (powder sample B2) were produced in the same manner as the sample E2, and these were prepared with the desired composition ({Li _0.065 (K _0.40 Na _0.60 ) _0.935 } (Nb _0.835 Ta _0.10 Sb _0.065 ) O ₃ ) was mixed with a binder and a plasticizer to prepare a raw material mixture. Further, in the same manner as in the sample E2, a slurry of the raw material mixture was molded, and the molded body was obtained by laminating, pressing and rolling, and then subjected to degreasing and CIP treatment. In this way, a molded sample D2 similar to the sample E2 was obtained.

Next, the molded sample D2 is fired to produce a lead-free piezoelectric ceramic made of a polycrystal of crystal-oriented ceramic.
The molded sample D2 was fired under the following conditions.
First, the molded sample D2 was placed in a heating furnace and heated to a temperature of 1115 ° C. at a temperature rising rate of 200 ° C./h (temperature rising process). Subsequently, this temperature was maintained at 1115 ° C. for 5 hours. Then, it cooled to room temperature with the temperature-fall rate of 200 degrees C / h, and produced the polycrystal body which consists of crystal orientation ceramics.

In this way, a polycrystalline body made of crystallographic ceramics having {Li _0.065 (K _0.40 Na _0.60 ) _0.935 } (Nb _0.835 Ta _0.10 Sb _0.065 ) O ₃ as a main phase was obtained. This is designated as Sample C2.
Similarly to Example 1, the crystal structure of Sample C2 was examined with a scanning electron microscope (SEM). As a result, Sample C2 was similar to Sample E1 of Example 1 and Sample E2 of this example. The pseudo core shell structure was not confirmed.

(Example 3)
This example is a lead obtained by adding an additive to a compound represented by the above general formula: {Li _x (K _{1 -y} Na _y ) _{1 -x}} {Nb _{1 -zw} Ta _z Sb _w } O ₃ It is an example which produces free piezoelectric ceramics. Specifically, an isotropic perovskite type compound having the same composition as the sample E2 in Example 2, that is, {Li _0.065 (K _0.45 Na _0.55 ) _0.935 } (Nb _0.83 Ta _0.09 Sb _0.08 ) O ₃ etc. A lead-free piezoelectric ceramic made of a polycrystal having an isotropic perovskite compound as a main phase and CuO added as an additive is prepared.

Specifically, first, an anisotropic shaped powder (NN powder) was produced. As this anisotropically shaped powder, the same powder sample A1 of Example 2 was prepared.
Moreover, the fine particle powder was produced.
In producing the fine particle powder of this example, the composition of the target ceramic {Li _0.065 (K _0.40 Na _0.60 ) _0.935 } (Nb _0.835 Ta _0.10 Sb _0.065 ) O ₃ is obtained by subtracting the NN powder composition. Weigh Na ₂ CO ₃ powder, K ₂ CO ₃ powder, Li ₂ CO ₃ powder, Nb ₂ O ₅ powder, Ta ₂ O ₅ powder, and Sb ₂ O ₅ powder with a purity of 99.99% or more so that Further, the additive CuO is added so that the amount of CuO added is 0.001 mol with respect to 1 mol of the target ceramic composition {Li _0.065 (K _0.45 Na _0.55 ) _0.935 } (Nb _0.83 Ta _0.09 Sb _0.08 ) O _3. The sample was prepared in the same manner as the powder sample B2 of Example 2 except that the points were mixed. This is designated as Powder Sample B3. The powder sample B3 is a calcined powder (fine particle powder) having an average particle diameter of about 0.5 μm.

Next, in the same manner as in Example 2, the powder sample A1 and the powder sample B3 were removed from the target composition {Li _0.065 (K _0.45 Na _0.55 ) _0.935 } (Nb _0.83 Ta _0.09 Sb _0.08 ) O except for the added CuO. _The slurry was weighed at a stoichiometric ratio of ₃ to form a slurry, and molded and degreased to produce a molded body. Production, molding, and degreasing of the slurry were performed in the same manner as in Example 1. The molded body thus obtained is designated as a molded sample D3.

Next, the obtained molded sample D2 is put in a heating furnace, heated to a temperature of 900 ° C. at a heating rate of 200 ° C./h, heated to a temperature of 1020 ° C. at a heating rate of 45 ° C./h, and further heated to a temperature. The temperature was raised to 1115 ° C. at a temperature raising rate of 10 ° C./h. Next, a holding process was performed, and the temperature was held at 1115 ° C. for 5 hours. Next, it was cooled to a temperature of 1010 ° C. at a temperature decrease rate of 5 ° C./h. Then, it cooled to room temperature with the temperature-fall rate of 200 degrees C / h, and produced the polycrystal body which consists of crystal orientation ceramics.
In this way, from the polycrystalline body having a crystal orientation ceramic structure in which {Li _0.065 (K _0.45 Na _0.55 ) _0.935 } (Nb _0.83 Ta _0.09 Sb _0.08 ) O ₃ is added as the main phase and the additive (CuO) is added. A lead-free piezoelectric ceramic (sample E3) was obtained.

In this example, lead-free piezoelectric ceramics (sample E4) were prepared in the same manner as the sample E3 except that the amount of CuO added was changed.
That is, the sample E4 has a composition of the target ceramic {Li _0.065 (K _0.40 Na _0.60 ) _0.935 } (Nb _0.835 Ta _0.10 Sb _0.065 ) O ₃ so that the composition of the NN powder is subtracted. purity 99.99% or more Na ₂ CO ₃ powder, K ₂ CO ₃ powder, Li ₂ CO ₃ powder, Nb ₂ O ₅ powder, Ta ₂ O ₅ powder, and Sb ₂ O ₅ powder were weighed and further the CuO Prepared by adding the additive CuO and mixing so that the amount added is 0.002 mol per 1 mol of the target ceramic composition {Li _0.065 (K _0.45 Na _0.55 ) _0.935 } (Nb _0.83 Ta _0.09 Sb _0.08 ) O ₃ It was produced in the same manner as the sample E3 except that the fine particle powder was used.

In this example, lead-free piezoelectric ceramics (sample E5) were prepared in the same manner as the sample E3 except that K ₄ CuNb ₈ O ₂₃ was used as an additive instead of CuO.
That is, the sample E5 has a composition in which the composition of the target ceramic {Li _0.065 (K _0.40 Na _0.60 ) _0.935 } (Nb _0.835 Ta _0.10 Sb _0.065 ) O ₃ is subtracted from the blended amount of the NN powder. A Na ₂ CO ₃ powder, a K ₂ CO ₃ powder, a Li ₂ CO ₃ powder, a Nb ₂ O ₅ powder, a Ta ₂ O ₅ powder, and a Sb ₂ O ₅ powder with a purity of 99.99% or more are weighed, and further K ₄ CuNb ₈ O ₂₃ are formed so that 0.001mol for purposes ceramic composition _{{Li 0.065 (K 0.45 Na 0.55} ) 0.935} (Nb 0.83 Ta 0.09 Sb 0.08) O 3 1mol of the additive K ₄ CuNb ₈ O ₂₃ The sample was prepared in the same manner as the sample E3 except that a fine particle powder prepared by mixing and using was used.

In this example, a lead-free piezoelectric ceramic (sample E6) in which the additive K ₄ CuNb ₈ O ₂₃ was added in an amount of 0.002 mol was prepared.
That is, the sample E6 has a composition in which the composition of the target ceramics {Li _0.065 (K _0.40 Na _0.60 ) _0.935 } (Nb _0.835 Ta _0.10 Sb _0.065 ) O ₃ is subtracted from the blended amount of the NN powder. A Na ₂ CO ₃ powder, a K ₂ CO ₃ powder, a Li ₂ CO ₃ powder, a Nb ₂ O ₅ powder, a Ta ₂ O ₅ powder, and a Sb ₂ O ₅ powder with a purity of 99.99% or more are weighed, and further K ₄ CuNb ₈ O ₂₃ are formed so that 0.002mol for purposes ceramic composition _{{Li 0.065 (K 0.45 Na 0.55} ) 0.935} (Nb 0.83 Ta 0.09 Sb 0.08) O 3 1mol of the additive K ₄ CuNb ₈ O ₂₃ The sample was prepared in the same manner as the sample E3 except that a fine particle powder prepared by mixing and using was used.

The fine particle powder of K ₄ CuNb ₈ O ₂₃ was produced as follows.
First, K ₂ CO ₃ powder, CuO powder and Nb ₂ O ₅ powder with a purity of 99.99% or more are weighed so that the composition of the target ceramic is K ₄ CuNb ₈ O _23, and an organic solvent such as acetone or alcohol is weighed. Was mixed with a ZrO ₂ ball for 24 hours.
Thereafter, calcination is performed in an air atmosphere at a temperature of 750 ° C. for 5 hours, and wet pulverization is performed with a ZrO ₂ ball for 24 hours using an organic solvent as a medium, whereby K ₄ CuNb ₈ O ₂₃ having an average particle diameter of about 0.5 μm. A fine particle powder was obtained. As a result of XRD measurement, the synthesized fine particle powder was identified as K ₄ CuNb ₈ O ₂₃ .

In this example, four types of lead-free piezoelectric ceramics (sample C3 to sample C6) were prepared for comparison with samples E3 to E6.
Samples C3 to C6 were prepared in the same manner as Samples E3 to E6, respectively, except that the firing conditions were changed.
That is, Sample C3 was produced by producing a molded body in the same manner as Sample E3, and firing this molded body under the same firing conditions as Sample C2 in Example 2. Similarly, Sample C4 to Sample C6 were prepared by producing molded bodies in the same manner as Sample E4 to Sample E6, respectively, and firing each molded body under the same firing conditions as Sample C2 in Example 2. It is.

  Next, the crystal structures of Sample E3 to Sample E6 and Sample C3 to Sample C6 were examined with a scanning electron microscope (SEM) as in Example 1. As a result, in sample E3 to sample E6, a pseudo core-shell structure in which shell particles were arranged around the core particle was observed as in sample E1, but in sample C3 to sample C6, the pseudo core-shell structure was It was not confirmed.

(Experimental example)
In this example, the bulk density and open porosity of various lead-free piezoelectric ceramics (sample E2 to sample E6 and sample C2 to sample C6) manufactured in Examples 2 and 3 were examined.

"The bulk density"
First, the dry weight (dry weight) of each sample was measured. Further, each sample was immersed in water, vacuum degassed, and water was permeated into the open pores of each sample, and then the weight of each sample (water content) was measured. Next, the volume of open pores present in each sample was calculated from the difference between the moisture content and the dry weight. Moreover, the volume of the part except an open pore was measured about each sample by the Archimedes method. Next, the bulk density of each sample was calculated by dividing the dry weight of each sample by the total volume of each sample (the sum of the volume of the open pores and the volume of the portion excluding the open pores). The results are shown in Table 3.

"Open porosity"
The open porosity is
First, the volume of open pores present in each sample is calculated from the difference between the dry weight of each sample and the weight when water is permeated into the open pores. Next, using the Archimedes method, the volume of each sample excluding the calculated volume of the open pores is measured.
The open porosity can be calculated by dividing the volume of the open pores by the total volume of each sample (the sum of the volume of the open pores and the volume of the polycrystalline material excluding the open pores) and multiplying by 100. The results are shown in Table 3.

As is known from Table 3, Samples E2 to E6 had a higher bulk density than Samples C2 to C6. Sample E2 to Sample E6 and Sample C2 to Sample C5 are compared with each other in the same composition, that is, Sample E2 and Sample C2, Sample E3 and Sample C3, Sample E4 and Sample C4, Sample E5 and Sample C5, When Sample E6 and Sample C6 were compared, in any case, Samples E2 to E6 had a smaller open porosity.
Therefore, it can be seen that Samples E2 to E6 have few voids and open pores and are excellent in denseness. Therefore, the samples E2 to E6 are less likely to cause dielectric breakdown, and can sufficiently exhibit various dielectric characteristics and piezoelectric characteristics that can be inherently exhibited by the alkali niobium compounds having the respective compositions.

The microscope picture which shows the crystal structure of the lead-free piezoelectric ceramic (sample E1) concerning Example 1. FIG. Explanatory drawing which shows the structure of the crystal structure of the lead-free piezoelectric ceramic (sample E1) concerning Example 1. FIG.

Explanation of symbols

1 Polycrystalline 2 Core particle 3 Shell particle 4 Composite particle

Claims (7)

Lead-free made of a polycrystalline material having a main phase of an alkali niobium compound represented by the composition formula ABO ₃ (A is Li + Na + K, B is Nb, Nb + Ta, Nb + Sb, Nb + Ta, or Nb + Ta + Sb, O is oxygen) Piezoelectric ceramics,
The polycrystalline body has core particles and shell particles having different compositions within the range of the composition formula ABO ₃ as crystal grains constituting the polycrystalline body,
In the polycrystal, the core particle and the shell particle form a composite particle having a pseudo core-shell structure in which a plurality of the shell particles are arranged so as to surround the core particle. Piezoelectric ceramics. According to claim 1, said core particles, than the average composition of the entire lead-free piezoelectric ceramics consist component elements Na, alkali niobate-based compound Ta, and the content of Sb is represented by many above composition formula ABO ₃ The shell particles are composed of an alkali niobium compound represented by the composition formula ABO ₃ having a higher content of component elements K and Nb than the average composition of the entire lead-free piezoelectric ceramic. Piezoelectric ceramics.   3. The lead-free piezoelectric ceramic according to claim 1, wherein the composite particles have an average particle size of 0.15 to 30 [mu] m. 4. The alkali niobium-based compound according to claim 1, wherein the alkali niobium compound has a general formula: {Li _x (K _1−y Na _y ) _1−x} {Nb _1−zw Ta _z Sb _w } O ₃ ( However, it is an isotropic perovskite type compound represented by 0 ≦ x ≦ 0.2, 0 <y <1, 0 ≦ z ≦ 0.4, 0 ≦ w ≦ 0.2, x + z + w> 0). Lead-free piezoelectric ceramics.   5. The lead-free structure according to claim 1, wherein the polycrystal has a crystal-oriented ceramic structure in which specific crystal planes of the crystal grains constituting the polycrystal are oriented. 6. Piezoelectric ceramics.   6. The polycrystalline body according to claim 1, wherein the polycrystal includes one or more elements selected from a transition metal element having an atomic number of 21 to 29, an alkaline earth metal, Al, Bi, and Si. Lead-free piezoelectric ceramics 7. The lead-free piezoelectric ceramic according to claim 1, wherein Cu ₂ O, CuO, K ₄ CuNb ₈ O ₂₃ , K _5.4 Cu _1.3 Ta ₁₀ O is used with respect to 1 mol of the alkali niobium compound. ₂₉ , CuNb ₂ O ₆ , CuTa ₂ O ₆ , KNbO ₃ , and K ₃ Li ₂ Nb ₅ O ₁₅ are added at least 0.0005 to 0.03 mol of lead-free piezoelectric Ceramics.