JP4474882B2 - CRYSTAL-ORIENTED CERAMIC AND ITS MANUFACTURING METHOD, AND ANISOTROPIC POWDER AND ITS MANUFACTURING METHOD - Google Patents

Description

  The present invention relates to a crystallographically-oriented ceramic and a method for producing the same, an anisotropically shaped powder and a method for producing the same, and more specifically, a crystal-oriented ceramic having a specific crystal plane oriented in one direction and a method for producing the same. Anisotropically shaped powder used as a template (seed crystal) for producing crystal-oriented ceramics, a method for producing the same, and dielectric elements, microwave dielectric elements, thermoelectric elements, pyroelectric elements using such crystal-oriented ceramics , Magnetoresistive element, magnetic element, piezoelectric element, superconductive element, resistive element, electron conductive element, ion conductive element, PTC element, and NTC element.

The perovskite type compound represented by the general formula: ABO ₃ has piezoelectricity, dielectricity, ferroelectricity, antiferroelectricity, magnetism, thermoelectricity, electronic conductivity, ionic conductivity, etc. (hereinafter referred to as “depending on the composition”). These are known to exhibit excellent characteristics such as “piezoelectric characteristics etc.” and are mainly used in the state of polycrystals. Polycrystalline ceramics composed of such perovskite compounds have conventionally synthesized powders composed of perovskite compounds by a solid-phase reaction method or flux method using a simple compound containing a relatively small number of cation elements as a starting material. The synthesized powder is then generally produced by a method of molding and sintering.

  On the other hand, it is known that the piezoelectric characteristics and the like possessed by the perovskite compound generally differ depending on the direction of the crystal axis. Therefore, if the crystal axis with high piezoelectric characteristics can be oriented in a certain direction, the anisotropy with piezoelectric characteristics can be utilized to the maximum, and a polycrystalline ceramic having high characteristics close to a single crystal can be obtained. There is a possibility that.

  However, since the perovskite type compound has extremely small anisotropy of the crystal lattice, the solid phase reaction method or the flux method has a powder having an isotropic shape close to a sphere or a cube (specifically, an aspect ratio of 1). .5 or less), and a powder having a large aspect ratio cannot be obtained. Moreover, when such a powder is shaped and sintered using a conventional manufacturing method, the obtained sintered body has the crystal grains randomly oriented. Therefore, even if the composition has essentially high piezoelectric characteristics, the piezoelectric characteristics and the like of the resulting sintered body are insufficient.

In order to solve this problem, various proposals have heretofore been made. For example, Patent Document 1 discloses a plate-like powder made of bismuth titanate (Bi ₄ Ti ₃ O ₁₂ ), which is a kind of bismuth layered perovskite compound, Bi ₂ O ₃ , Na ₂ CO ₃ , and TiO ₂ . Mixing at a predetermined ratio, shaping the mixture so that the plate-like powder is oriented, and sintering the mixture, sodium bismuth titanate (Bi _0.5 Na _0.5 TiO) which is a kind of perovskite type compound ₃ ) and a crystallographically-oriented ceramic with a degree of orientation of the pseudo-cubic {100} plane of 34% obtained by the Lotgering method is described.

Patent Document 2 and Non-Patent Document 1 describe a method for producing anisotropically shaped powder used for producing such crystal-oriented ceramics. That is, in Patent Document 2, a plate-like powder made of bismuth titanate (Bi ₄ Ti ₃ O ₁₂ ), Na ₂ CO ₃ , K ₂ CO ₃ , and TiO ₂ are mixed at a predetermined ratio, It is described that an anisotropically shaped powder composed of Bi _0.5 (Na, K) _0.5 TiO ₃ which is a kind of perovskite type compound can be obtained by heating in a flux.

Further, Non-Patent Document 1 discloses that an edge is obtained by heating Sr ₃ Ti ₂ O ₇ plate-like powder, which is a kind of Ruddlesden-Popper type layered perovskite compound, and TiO ₂ in KCl molten salt. It describes that a SrTiO ₃ plate-like powder having a length of 10 to 40 μm, a thickness of 1 to 4 μm, and a {100} plane as a development plane can be obtained.

JP-A-10-139552 JP 2000-203935 A M. E. Ebrahimi, et al., "Synthesis of Platelet SrTiO3 by Epitaxial Growth on Sr3Ti2O7 Core Paticles", Proceedings of the 13th IEEE International Symposium on Applications of Ferroelectrics, pp.239-242, 2002.

  Since layered compounds such as bismuth layered perovskite type compounds and Rudolsden-Popper type layered perovskite type compounds have large crystal lattice anisotropy, powders having shape anisotropy can be synthesized relatively easily. Further, among these layered compounds, the development plane of the anisotropically shaped powder made of a certain compound has good lattice matching with the pseudocubic {100} plane of the perovskite type compound.

  Therefore, as disclosed in Patent Document 1, when a mixture of an anisotropically shaped powder composed of a layered compound and a predetermined raw material is molded so that the anisotropically shaped powder is oriented, and sintered, the pseudocubic { A crystallographically-oriented ceramic made of a perovskite type compound having a 100} plane oriented in one direction is obtained. Further, as disclosed in Patent Document 2 and Non-Patent Document 1, when an anisotropically shaped powder made of such a layered compound is reacted with a predetermined raw material, the anisotropically shaped powder made of the layered compound becomes a lattice mold. An anisotropic shaped powder that functions as a (template) and is made of a perovskite type compound having a predetermined composition and whose development surface is a pseudocubic {100} surface can be synthesized.

  However, in the method for producing crystal oriented ceramics disclosed in Patent Document 1 or the method for producing anisotropic shaped powders disclosed in Patent Document 2 and Non-Patent Document 1, The cation element derived from the template always remains. Therefore, the most desirable composition may not be realized, and various characteristics such as piezoelectric characteristics may be damaged by the A site element and / or the B site element inevitably included.

  Furthermore, in the case of the method disclosed in Patent Document 1, it is necessary to use a relatively large amount of template in order to obtain a crystal-oriented ceramic having a high degree of orientation. However, the use of a large amount of template contributes to increasing the cost of crystallographically-oriented ceramics.

  The problem to be solved by the present invention is a perovskite-type compound polycrystal having a predetermined composition, and the pseudo-cubic {100} plane of each crystal grain constituting the polycrystal is oriented with a high degree of orientation. An object of the present invention is to provide a crystallographically-oriented ceramic whose composition control is relatively easy and a method for producing the same. Another problem to be solved by the present invention is an anisotropic shaped powder comprising a perovskite type compound having a predetermined composition, having a pseudo-cubic {100} plane as a development plane, and the composition control of which is relatively easy. And a manufacturing method thereof.

  Furthermore, another problem to be solved by the present invention is to provide a method for producing a crystallographically-oriented ceramic that can obtain a high degree of orientation even when a relatively small amount of template is used. Other problems to be solved by the present invention include dielectric elements, microwave dielectric elements, thermoelectric elements, pyroelectric elements, magnetoresistive elements, magnetic elements, piezoelectric elements, superconductivity using such crystallographically oriented ceramics. The object is to provide an element, a resistance element, an electron conduction element, an ion conduction element, a PTC element, and an NTC element.

In order to solve the above problems, the crystal-oriented ceramic according to the present invention is:
General _{formula: (Sr x A '1-} x) (Ti y B' 1-y) O 3
(However, 0 <x ≦ 1, 0 <y ≦ 1, A ′ is one or more divalent metal elements, and B ′ is one or more tetravalent metal elements.)
And the pseudo-cubic {100} plane of each crystal grain constituting the polycrystal is oriented.

Moreover, the method for producing a crystallographically oriented ceramic according to the present invention is
General _{formula: (Sr x A '1-} x) (Ti y B' 1-y) O 3
(However, 0 <x ≦ 1, 0 <y ≦ 1, A ′ is one or more divalent metal elements, and B ′ is one or more tetravalent metal elements.)
And the development plane is a pseudo-cubic {100} plane, and the aspect ratio of the maximum length (W _a ) of the development plane to the thickness (t _a ) ( A mixing step of mixing an anisotropically shaped powder having _a W _a / t _a ) of 2 or more and a matrix compound powder that becomes a first perovskite compound without or reacting with the anisotropically shaped powder; A molding step for molding the mixture obtained in the mixing step so that the development surface of the anisotropically shaped powder is oriented; and a sintering step for sintering the molded body obtained in the molding step. Is the gist.

The anisotropically shaped powder according to the present invention comprises a layered compound having a layered crystal structure, and its development surface has lattice matching with the pseudocubic {100} plane of the second perovskite compound, and A first anisotropic shaped powder is synthesized, wherein an aspect ratio (W _b / t _b ) of the maximum length (W _b ) of the developed surface with respect to the thickness (t _b ) is 2 or more, and the first anisotropic shaped powder And an ion exchange reaction raw material that generates the second perovskite compound and the surplus component by an ion exchange reaction with the first anisotropically shaped powder, and performs an ion exchange reaction in a solution or a melt, Obtained by thermally or chemically removing excess components,
General _{formula: (Sr x A '1-} x) (Ti y B' 1-y) O 3
(However, 0 <x ≦ 1, 0 <y ≦ 1, A ′ is one or more divalent metal elements, and B ′ is one or more tetravalent metal elements.)
And the development plane is a pseudo-cubic {100} plane, and the aspect ratio of the maximum length (W _a ) of the development plane to the thickness (t _a ) ( The gist is that W _a / t _a ) is 2 or more.

Furthermore, the method for producing an anisotropic shaped powder according to the present invention comprises a layered compound having a layered crystal structure, and its development plane has lattice matching with the pseudocubic {100} plane of the second perovskite compound, and a synthesizing step of synthesizing the first anisotropically shaped powder aspect ratio (W b _{/ t b)} is 2 or more the thickness of the maximum length of the developed plane for _{(t b) (W b)} , wherein Ion exchange of a first anisotropically shaped powder and an ion exchange reaction raw material that produces the second perovskite type compound and an excess component by an ion exchange reaction of the first anisotropically shaped powder in a solution or melt The gist of the invention is that it comprises an ion exchange step for carrying out the reaction and a removal step for removing the excess component thermally or chemically.

  When the first anisotropic shaped powder (AB) satisfying a predetermined condition is reacted with an ion exchange reaction raw material (C) that causes an interlayer ion substitution reaction in a solution or a melt, an object is obtained by an ion exchange reaction. A mixture of the second perovskite compound (AC) and the surplus component (B) is obtained. At this time, the development plane of the first anisotropically shaped powder is inherited as the pseudocubic {100} plane of the second perovskite type compound. Subsequently, when an excess component is removed from this mixture, an anisotropically shaped powder composed of a second perovskite compound having a predetermined composition and having a pseudo-cubic {100} plane as a development plane is obtained.

  Next, a mixture of the anisotropically shaped powder composed of the second perovskite compound and the matrix compound powder satisfying a predetermined condition is formed so that the anisotropically shaped powder is oriented, and sintered, Anisotropic crystal composed of the first perovskite compound is generated and grows in a state where the orientation orientation of the shaped powder is inherited. As a result, a crystallographically-oriented ceramic is obtained in which crystal grains having a pseudo cubic {100} plane as a development plane are oriented in a specific direction.

  In the anisotropic shaped powder obtained by such a method, the surplus component (B) is discharged during the ion exchange reaction, so that composition control is facilitated as compared with the conventional method. In addition, since anisotropically shaped powder having the same or similar crystal structure as the crystal oriented ceramic to be produced is used as a template, the crystal oriented ceramic having a high degree of orientation even if the amount of the template is relatively small. Is obtained.

  Hereinafter, an embodiment of the present invention will be described in detail. The crystallographically-oriented ceramic according to the present invention is composed of a polycrystal of the first perovskite compound represented by the general formula shown in the following formula (1), and the pseudo-cubic { 100} planes are oriented.

(Sr _x A ′ _1-x ) (Ti _y B ′ _1-y ) O ₃ (1)
(However, 0 <x ≦ 1, 0 <y ≦ 1, A ′ is one or more divalent metal elements, and B ′ is one or more tetravalent metal elements.)

  In the present invention, the first perovskite compound comprises at least Sr as the A site element. In this case, the A-site element may be composed of only Sr, or may contain an A-site element (element A ′) other than Sr. The type of the element A ′ is not particularly limited and may be at least a divalent metal element. Specific examples of the element A ′ include Pb, Ba, Ca, Mg, Zn, Co, and Fe.

  Further, the first perovskite compound is composed of at least Ti as a B site element. In this case, the B site element may be composed only of Ti, or may contain a B site element (element B ′) other than Ti. The type of the element B ′ is not particularly limited and may be at least a tetravalent metal element. Specific examples of the element B ′ include Zr, Hf, Sn, Ge, Si, and the like.

Specific examples of the first perovskite compound represented by the formula (1) include SrTiO ₃ , (Sr, Pb) TiO ₃ , (Sr, Pb) (Ti, Zr) O ₃ , (Sr, Pb). ) (Ti, Sn) O ₃ , (Sr, Pb) (Ti, Zr, Sn) O _{3, and the} like are preferable examples.

  The crystal-oriented ceramic according to the present invention is preferably composed only of the first perovskite type compound represented by the general formula shown in the formula (1). However, the crystal structure of the perovskite type can be maintained and sintered. Other elements or other phases may be included as long as they do not adversely affect various characteristics such as characteristics and piezoelectric characteristics.

Specific examples of such “other elements” include Pb, Ba, Ca, Mg, Zr, Sn, Ge, and Si. The “other phase” specifically includes additives, sintering aids, by-products, impurities, etc. (for example, Bi ₂ O ₃ , CuO, etc.) resulting from the production method described later and starting raw materials used. , MnO ₂ , NiO, etc.). The smaller the content of other elements or other phases that may adversely affect the piezoelectric characteristics or the like, the better.

  “Pseudocubic {100} plane is oriented” means that the crystal grains are arranged so that the pseudocubic {100} planes of the first perovskite type compound represented by the formula (1) are parallel to each other. (Hereinafter, such a state is referred to as “plane orientation”), or each crystal grain is arranged so that the pseudo-cubic {100} plane is parallel to one axis penetrating the molded body. It means both being arranged (hereinafter, such a state is referred to as “axial orientation”).

  In addition, “pseudocubic {HKL}” is generally a perovskite type compound having a structure slightly distorted from cubic such as tetragonal, orthorhombic, and trigonal, but the strain is slight. This means that it is regarded as a cubic crystal and displayed by Miller index.

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

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

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

  In general, the higher the ratio of oriented crystal grains, the higher the characteristics. Specifically, in the case where a specific crystal plane is plane-oriented, in order to obtain high characteristics, the average degree of orientation F (HKL) by the Lotgering method represented by the formula 1 is 20%. The above is preferable, and more preferably 50% or more. Further, by using the manufacturing method described later, even a crystallographically oriented ceramic having an average degree of orientation F (HKL) exceeding 90% can be produced.

  Since the crystallographically oriented ceramic according to the present invention is oriented in the pseudo cubic {100} plane, the properties in the orientation direction are higher than those of non-oriented ceramics having the same composition. In particular, when the compound of the first perovskite represented by the formula (1) has piezoelectric characteristics, the pseudocubic {100} plane is a plane perpendicular to the polarization axis, so that the pseudocubic {100} By orienting the plane, the piezoelectric characteristics in the orientation direction can be greatly improved.

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

  Since the crystallographically oriented ceramic according to the present invention is oriented in the pseudo cubic {100} plane, the piezoelectric characteristics and the like in the orientation direction are higher than those of the non-oriented ceramic. For this reason, the dielectric element, the microwave dielectric element, the thermoelectric element, the pyroelectric element, the magnetoresistive element, the magnetic element, the piezoelectric element, the superconducting element, the resistive element, the electron conducting element, the ion conducting element, the PTC element, and the NTC. If applied to an element or the like, various elements having high performance can be obtained.

  Next, the anisotropic shaped powder used for the production of the crystal oriented ceramics according to the present invention will be described. Ceramics with a complex composition such as perovskite type compounds are usually mixed with a simple compound containing the constituent elements so as to achieve a stoichiometric ratio, and after this mixture is formed and calcined, it is crushed and then crushed. Manufactured by a method of reshaping and sintering powder. However, with such a method, it is extremely difficult to obtain an oriented sintered body in which specific crystal planes of crystal grains are oriented in a specific direction.

  In order to solve this problem, the present invention performs the production of a perovskite-type compound and the sintering thereof by orienting an anisotropically shaped powder satisfying a predetermined condition in a molded body, and using this anisotropically shaped powder as a template. In this way, a specific crystal plane of each crystal grain constituting the polycrystal is oriented in one direction. In the present invention, an anisotropically shaped powder that satisfies the following conditions is used.

  First, as the anisotropically shaped powder, one made of a second perovskite compound having a composition represented by the general formula shown in the following formula (2) is used.

(Sr _x A ′ _1-x ) (Ti _y B ′ _1-y ) O ₃ (2)
(However, 0 <x ≦ 1, 0 <y ≦ 1, A ′ is one or more divalent metal elements, and B ′ is one or more tetravalent metal elements.)

  In this case, the second perovskite type compound constituting the anisotropically shaped powder may have the same composition as the first perovskite type compound constituting the crystal oriented ceramic to be produced, or a different composition. It may be that which has. The other points of the second perovskite compound are the same as those of the first perovskite compound, and thus the description thereof is omitted.

  Secondly, as the anisotropically shaped powder, a powder whose development surface (the surface having the widest area) consists of a pseudocubic {100} surface of the second perovskite compound is used. Naturally, the pseudo cubic {100} plane of the second perovskite compound has good lattice matching with the pseudo cubic {100} plane of the first perovskite compound. Therefore, the first perovskite-type compound can be obtained by orienting anisotropically shaped powder having a pseudo-cubic {100} plane as a developed surface in the molded body and sintering the oriented powder while maintaining the orientation orientation of the anisotropically shaped powder. An anisotropic shape crystal composed of

Thirdly, as the anisotropically shaped powder, an anisotropically shaped powder having a shape that can be easily oriented in a certain direction during molding is used. For that purpose, the aspect ratio (= W _a / t _a .W _a : the maximum length of the development surface of the anisotropic shaped powder. T _a : the thickness of the anisotropic shaped powder) is 2 or more. It is preferable that An aspect ratio of less than 2 is not preferable because it becomes difficult to orient the anisotropically shaped powder in one direction during molding. In order to obtain a highly oriented crystallographically oriented ceramic, the aspect ratio of the anisotropically shaped powder is preferably 5 or more, and more preferably 10 or more.

  In general, as the average aspect ratio of the anisotropically shaped powder increases, the orientation of the anisotropically shaped powder tends to be facilitated during molding. However, if the aspect ratio is excessive, the anisotropically shaped powder may be crushed in the mixing step described later, and a molded body in which the anisotropically shaped powder is oriented may not be obtained. Therefore, the average aspect ratio of the anisotropically shaped powder is preferably 100 or less.

Further, the maximum length W _a of the development surface of the anisotropically shaped powder is preferably 0.05 μm or more. If the maximum length W _a is less than 0.05 .mu.m, the anisotropically shaped powder by the shearing stress acting to orient in a certain direction it becomes difficult at the time of molding. In addition, since the gain of the interface energy is reduced, epitaxial growth on the template particles is less likely to occur when used as a template when producing crystal-oriented ceramics.

On the other hand, the maximum length W _a of the development surface of the anisotropically shaped powder is preferably 100 μm or less. If the maximum length W _a exceeds 100 [mu] m, the sintering property is lowered, not higher crystal oriented ceramics of sintered density can be obtained. Maximum length _{W a} is more preferably not 0.1μm or 50μm or less, and more preferably 0.5μm or 20μm or less. In particular, when W _a of the anisotropically-shaped powder is 0.5μm or more, and easier to orientation molding during tape casting, crystal-oriented ceramic having a high degree of orientation is obtained.

When a mixture of anisotropically shaped powders having different aspect ratios (W _a / t _a ) and / or maximum lengths (W _a ) is used as a template, the aspect ratio (W _a / t _a ) and / or the maximum length The average value of (W _a ) may be in the above range. 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, a plate shape, a column shape, a scale shape, and the like are preferable examples.

Specific examples of the anisotropically shaped powder used for producing the crystallographically oriented ceramics according to the present invention include SrTiO ₃ powder, Sr (Ti, Zr) O ₃ powder having a pseudo-cubic {100} plane as a development plane. (Sr, Pb) TiO ₃ powder, (Sr, Pb) (Ti, Zr) O ₃ powder, and the like are preferable examples. In order to obtain a crystallographically-oriented ceramic having a high degree of orientation, it is preferable to use an anisotropically shaped powder having the same composition as the crystal-oriented ceramic to be prepared. Moreover, when the crystal-oriented ceramic to be prepared is made of a solid solution containing two or more components, the anisotropic shaped powder may be made of any one or more end components.

  Furthermore, an anisotropically shaped powder that satisfies such conditions can be produced by various methods, and a powder obtained by a method according to the present invention (Topochemical Microcrystal Conversion: TMC conversion method) described later is particularly suitable. . The anisotropically shaped powder obtained by the method according to the present invention can produce a plate-like powder having the same composition as the intended ceramic composition, compared to the anisotropically shaped powder obtained by using other methods, and a small amount of template. Thus, there is an advantage that a crystallographically-oriented ceramic can be produced and the sinterability is improved due to a small number of templates (high density can be achieved at low temperature in a short time).

  Next, the method for producing the anisotropic shaped powder according to the present invention will be described. The method for producing an anisotropically shaped powder according to the present invention includes a synthesis step, an ion exchange step, and a removal step.

  First, the synthesis process will be described. The “synthesis step” is a step of synthesizing the first anisotropic shaped powder used as a reactive template for synthesizing the anisotropic shaped powder composed of the second perovskite type compound. In order for the first anisotropic shaped powder to function as a reactive template for synthesizing the anisotropic shaped powder according to the present invention, it is necessary to satisfy the following conditions.

  First, as the first anisotropic shaped powder, a powder composed of a layered compound having a layered crystal structure is used. Since the layered compound has a large crystal lattice anisotropy, it is relatively easy to synthesize a powder having a crystal plane with the smallest surface energy as a development plane and having shape anisotropy.

  Secondly, as the first anisotropic shaped powder, a powder whose development plane has lattice matching with the pseudo cubic {100} plane of the second perovskite type compound shown in the formula (2) is used. Even if the first anisotropically shaped powder having a predetermined shape does not have lattice matching with the pseudocubic {100} plane of the second perovskite type compound, It may not function as a reactive template for synthesizing the anisotropically shaped powder according to the invention.

  The quality of lattice matching is determined by the absolute value of the difference between the lattice size of the development plane of the first anisotropic shaped powder and the lattice size of the pseudocubic {100} plane of the second perovskite compound. This value can be expressed by a value divided by the lattice size of the powder development surface (hereinafter referred to as “lattice matching rate”). This lattice matching rate may be slightly different depending on the direction in which the lattice is taken. In general, the smaller the average lattice matching ratio (average value of the lattice matching ratio calculated for each direction), the more the first anisotropic shaped powder functions as a good reactive template. In order to obtain an anisotropically shaped powder that satisfies a predetermined condition, the lattice matching rate is preferably 20% or less, and more preferably 10% or less.

  Third, in order to easily synthesize the anisotropically shaped powder made of the second perovskite compound that can be easily oriented in one direction during molding, the first anisotropically shaped powder used for the synthesis is also It is desirable to have a shape that can be easily oriented in one direction during molding. This is because when the anisotropically shaped powder composed of the second perovskite compound is synthesized using the first anisotropically shaped powder as a reactive template, the average particle size of the anisotropically shaped powder obtained can be obtained by optimizing the reaction conditions. Although the diameter and / or aspect ratio can be increased or decreased, usually, only the crystal structure changes, and the powder shape hardly changes.

That is, it is preferable that the first anisotropic shaped powder has an aspect ratio (W _b / t _b ) of the maximum length (W _b ) of the development plane with respect to the thickness (t _b ) of 2 or more. The aspect ratio of the first anisotropic shaped powder is more preferably 5 or more, and further preferably 10 or more. Moreover, in order to suppress crushing in a post process, the aspect ratio of the first anisotropic shaped powder is preferably 100 or less.

Further, in order to obtain an anisotropically shaped powder having high sinterability, the maximum length W _b of the development surface of the first anisotropically shaped powder is preferably 100 μm or less. In order to obtain an anisotropically shaped powder that can be easily oriented, the maximum length W _b of the development surface of the first anisotropically shaped powder is preferably 0.05 μm or more. Maximum length _{W a} is more preferably not 0.1μm or 50μm or less, and more preferably 0.5μm or 20μm or less.

When a mixture of first anisotropic shaped powders having different aspect ratios (W _b / t _b ) and / or maximum lengths (W _a ) is used as the reactive template, the aspect ratio (W _b / t _b ) and / or or average value of the maximum length (W _a) may be in the range described above. 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, a plate shape, a column shape, a scale shape, and the like are preferable examples.

There are various types of layered compounds that satisfy such conditions. Among them, bismuth layered perovskite compounds represented by the general formula shown in the following formula (3) are preferable. Since the surface energy of the {001} plane (plane parallel to the (Bi ₂ O ₂ ) ²⁺ layer) is smaller than the surface energy of other crystal planes, the bismuth layered perovskite compound has the {001} plane as a development plane. Anisotropic shaped powder can be synthesized relatively easily.

  In addition, the {001} plane of the bismuth layered perovskite compound has extremely good lattice matching with the pseudocubic {100} plane of the second perovskite compound. Furthermore, by optimizing the composition of the ion exchange reaction raw material to be described later, Bi can be discharged as an excess component during the ion exchange reaction, so that the second perovskite type that does not substantially contain Bi as the A site element. Compounds can be synthesized. Moreover, the discharged Bi-containing compound can be removed relatively easily. Therefore, the bismuth layered perovskite type compound is particularly suitable as a material constituting the first anisotropic shaped powder.

(Bi ₂ O ₂ ) ²⁺ (A _m-1 B _m O _{3m + 1} ) ^2- (3)
(However, A is at least one element selected from Na ⁺ , K ⁺ , Sr ²⁺ , Pb ²⁺ , Ba ²⁺ and Bi ³⁺ , or a combination of these elements.
B is at least one element selected from Fe ³⁺ , Ti ⁴⁺ , Nb ⁵⁺ , Ta ⁵⁺ , and W ⁶⁺ , or a combination of these elements.
Elements A and B satisfy the relationship of α (m−1) + βm = 6 m, where α is the average valence of element A and β is the average valence of element B.
m is an integer from 1 to 8.
In addition, the case where A is composed only of Na ⁺ and / or K ⁺ and Bi ³⁺ and B is composed only of Nb ⁵⁺ is excluded. )

The bismuth layered perovskite compound represented by the formula (3) can also be represented as Bi ₂ A _m-1 B _m O _{3m + 3} . Specific examples of such bismuth layered perovskite compounds include Bi ₄ Ti ₃ O ₁₂ , SrBi ₄ Ti ₄ O ₁₅ , Sr ₂ Bi ₄ Ti ₅ O ₁₈ , SrBi ₂ Nb ₂ O _{9 and the} like. As mentioned. Among these, those containing at least Sr ²⁺ are preferable as the A site ion.

Such a first anisotropic shaped powder can be easily produced by heating raw materials such as oxides, carbonates and nitrates containing component elements together with a liquid or a substance that becomes liquid by heating. Specifically, an appropriate flux (for example, NaCl, KCl, a mixture of NaCl and KCl, BaCl ₂ , KF, etc.) is added to a predetermined raw material and heated at a predetermined temperature (flux method), to be produced. A preferred example is a method (hydrothermal synthesis method) of heating an amorphous powder having the same composition as the first anisotropic shaped powder together with an alkaline aqueous solution in an autoclave. In this case, the aspect ratio and average particle diameter of the first anisotropic shaped powder can be controlled by appropriately selecting the synthesis conditions.

  Next, the ion exchange process will be described. The “ion exchange step” is a step in which the first anisotropic shaped powder obtained in the synthesis step and the ion exchange reaction raw material are subjected to ion exchange in a solution or melt.

  Here, the “raw material for ion exchange reaction” refers to a material that generates a second perovskite compound and an excess component by an ion exchange reaction with the first anisotropic shaped powder. The form of the raw material for the ion exchange reaction is not particularly limited, and oxide powder, composite oxide powder, carbonate, nitrate, oxalate salt, alkoxide and the like can be used. The composition of the ion exchange reaction raw material is determined by the composition of the second perovskite compound to be produced and the composition of the first anisotropic shaped powder.

The “surplus component” refers to a substance other than the target second perovskite compound that can be easily removed thermally or chemically. For that purpose, it is desirable that the surplus component has a higher melting point or vapor pressure than that of the second perovskite compound, or a higher solubility in acid, alkali, or the like. Specific examples of the surplus component include Bi-containing compounds (for example, Bi ₂ O ₃ ).

  Further, “to perform ion exchange in a solution or melt” means that the first anisotropic shaped powder and ion exchange reaction raw material are heated in an appropriate flux (flux method), or the first anisotropic shape. Heating the powder and ion exchange reaction raw material together with a suitable aqueous solution in an autoclave (hydrothermal synthesis method).

For example, by using a first anisotropic shaped powder composed of Bi ₄ Ti ₃ O ₁₂ which is a kind of bismuth layered perovskite compound represented by the formula (3), SrTiO ₃ which is a kind of second perovskite compound is used. In the case of synthesizing the anisotropically shaped powder, a compound (oxide, hydroxide, carbonate, nitrate, etc.) containing Sr is used as a raw material for the ion exchange reaction. In this case, an Sr-containing compound corresponding to 3 mol of Sr atoms may be added as a raw material for ion exchange reaction to 1 mol of Bi ₄ Ti ₃ O ₁₂ .

An appropriate flux (for example, NaCl, KCl, a mixture of NaCl and KCl, BaCl ₂ , KF, etc.) is 1 wt% to 500 wt% with respect to the first anisotropic shaped powder having such a composition and the raw material for the ion exchange reaction. In addition, when heated to the eutectic point / melting point, an ion exchange reaction occurs between the first anisotropic shaped powder and the ion exchange reaction raw material in the melt, and an anisotropic shaped powder made of SrTiO ₃ and Bi _2. A surplus component mainly composed of O ₃ is generated.

Also, for example, an anisotropic shaped powder made of SrTiO ₃ is synthesized using a first anisotropic shaped powder made of SrBi ₄ Ti ₄ O ₁₅ which is a kind of bismuth layered perovskite type compound represented by the formula (3). In this case, an Sr-containing compound corresponding to 4 mol of Sr atoms may be added to 1 mol of SrBi ₄ Ti ₄ O ₁₅ as a raw material for ion exchange reaction. When an appropriate flux is added to the first anisotropic shaped powder and ion exchange reaction raw material having such a composition and heated to an appropriate temperature, the anisotropic shaped powder made of SrTiO ₃ and Bi ₂ O ₃ are mainly used. A surplus component as a component is generated.

Further, for example, when a first anisotropic shaped powder composed of a bismuth layered perovskite type compound such as Bi ₄ Ti ₃ O ₁₂ or SrBi ₄ Ti ₄ O ₁₅ is heated together with a strong acid in an autoclave, Bi in the first anisotropic shaped powder is obtained. Is replaced with H, and a surplus component containing Bi ₂ O ₃ as a main component is generated. Subsequently, when the hydrogen-substituted first anisotropically shaped powder and the Sr-containing compound are heated in an autoclave, H in the first anisotropically shaped powder is replaced with Sr, and an anisotropically shaped powder made of SrTiO ₃ is obtained. It is done. The same applies to other compositions.

  Next, the removal process will be described. The “removal step” is a step of thermally or chemically removing excess components discharged from the first anisotropic shaped powder after removing the flux from the mixture obtained in the ion exchange step with a hot water bath or the like as necessary. It is. Here, “removing the surplus component thermally” means heating the mixture of the anisotropically shaped powder made of the second perovskite compound and the surplus component to remove the surplus component as a melt or gas. Say. This method is effective when the difference in melting point or vapor pressure between the second perovskite compound and the surplus component is large.

For example, when the surplus component is a bismuth oxide (Bi ₂ O ₃ ) single phase, the mixture obtained in the ion exchange step is preferably heated at 800 ° C. or higher and 1300 ° C. or lower in the air or in a reduced pressure atmosphere. More preferably, heating temperature is 1000 degreeC or more and 1200 degrees C or less. As the heating time, an optimum temperature is selected according to the heating atmosphere, the heating temperature, and the like.

  Further, “chemically removing excess components” means that the mixture obtained in the ion exchange step is placed in a treatment solution having a property of eroding only the excess components, and the excess components are dissolved. This method is effective when the difference in solubility between the second perovskite compound and the surplus component in the treatment liquid is large.

For example, when the surplus component is a bismuth oxide (Bi ₂ O ₃ ) single phase, it is preferable to use an acid solution such as nitric acid or hydrochloric acid as the treatment liquid. In particular, nitric acid is suitable as a treatment liquid for chemically extracting surplus components mainly composed of bismuth oxide.

  Next, the effect | action of the manufacturing method of the anisotropic shaped powder which concerns on this invention is demonstrated. Since the second perovskite compound has a small crystal lattice anisotropy, it is difficult to directly synthesize an anisotropically shaped powder. It is also difficult to directly synthesize anisotropically shaped powder having a pseudo cubic {100} plane as a development plane.

  On the other hand, since a layered compound has a large crystal lattice anisotropy, it is easy to directly synthesize a powder having shape anisotropy. In addition, the development plane of the first anisotropically shaped powder made of a certain compound among the layered compounds has good lattice matching with the {100} plane of the second perovskite compound. Furthermore, the second perovskite type compound is generally thermodynamically more stable than the layered compound.

  Therefore, the first anisotropic shaped powder and the ion exchange reaction raw material, which are composed of a layered compound and whose development plane has lattice matching with the specific crystal plane of the second perovskite compound, are mixed with an appropriate solution or melt. When reacted in the liquid, the first anisotropically shaped powder functions as a reactive template, and easily synthesizes the anisotropically shaped powder composed of the second perovskite compound inheriting the orientation orientation of the first anisotropically shaped powder. be able to.

  Moreover, when the composition of the first anisotropic shaped powder (AB) and the raw material for ion exchange reaction (C) is optimized, an ion exchange reaction occurs between them, and the desired second perovskite compound (AC) and A mixture with the surplus component (B) is obtained. Therefore, it is possible to synthesize an anisotropically shaped powder composed of the second perovskite compound (AC) that does not substantially contain the surplus component (B).

In particular, when the first anisotropic shaped powder is composed of a bismuth layered perovskite type compound represented by the formula (3), Bi is discharged from the first anisotropic shaped powder during the ion exchange reaction, and Bi ₂ O ₃ is the main component. To generate surplus components. Moreover, the surplus component mainly composed of Bi ₂ O ₃ is extremely easy to remove thermally or chemically. Therefore, by removing excess components from the obtained reaction product, an anisotropic shaped powder substantially free of Bi, composed of the second perovskite type compound, and having a pseudo cubic {100} development surface is obtained. It is done.

  Next, the manufacturing method of the crystal orientation ceramics based on this invention is demonstrated. The method for producing a crystallographically-oriented ceramic according to the present invention includes a mixing step, a forming step, and a sintering step.

  First, the mixing process will be described. The “mixing step” refers to a step of mixing the anisotropically shaped powder and the matrix compound powder. Further, the “anisotropically shaped powder” refers to a powder composed of the second perovskite compound represented by the formula (2) as described above, and whose development surface is a pseudocubic {100} surface.

In order to facilitate the orientation of the anisotropically shaped powder at the time of molding, the anisotropically shaped powder has at least an aspect ratio (W _a ) of the maximum length (W _a ) of the development plane with respect to its thickness (t _a ). / T _a ) is preferably 2 or more, and at least the maximum length (W _a ) is preferably 100 μm or less as described above. In the mixing step, one kind of anisotropically shaped powder that satisfies such conditions may be used, or two or more kinds may be used in combination. Further, the anisotropically shaped powder may have the same composition as the crystal oriented ceramic to be produced, or the same composition as any one or more of the end components constituting the crystal oriented ceramic to be produced. You may have.

  The “matrix compound powder” refers to a substance that reacts with the anisotropically shaped powder or does not react with the first perovskite compound represented by the formula (1). The composition of the matrix compound powder is determined according to the composition of the second perovskite compound composing the anisotropically shaped powder and the composition of the first perovskite compound to be produced. Further, the form of the matrix compound powder is not particularly limited, and oxide powder, composite oxide powder, hydroxide powder, carbonate, nitrate, oxalate salt, alkoxide, etc. are used. Can do.

For example, in the case of producing grain oriented ceramics composed of SrTiO _3, as anisotropically shaped powder, when using the plate-like powder of SrTiO ₃ as a matrix compound powder may be used fine powder of SrTiO _3. Alternatively, a mixture of fine powders composed of a compound containing at least one element of Sr and Ti, which is blended at a stoichiometric ratio so that SrTiO ₃ is produced by a solid-phase reaction between them is used. May be.

Also, for example, when producing a crystallographically-oriented ceramic made of (Sr, Pb) TiO _3, when a plate-like powder made of SrTiO ₃ is used as the anisotropically shaped powder, a fine powder made of PbTiO ₃ is used as the matrix compound powder. May be used. Alternatively, it is a mixture of fine powders composed of a compound containing at least one element of Sr, Ti, and Pb, and (Sr, Pb) TiO ₃ is generated by a solid phase reaction between these and an anisotropically shaped powder. In addition, those blended in a stoichiometric ratio may be used. The same applies to the production of crystallographically oriented ceramics having other compositions.

  When the composition of the second perovskite compound constituting the anisotropically shaped powder is different from the composition of the first perovskite compound constituting the crystallographically-oriented ceramic, the matrix compound powder contains a fine perovskite compound. Powder may be included. In the mixing step, a sintering aid (for example, CuO) may be further added to the anisotropically shaped powder and the matrix compound powder blended at a predetermined ratio. When a fine powder composed of the first perovskite compound or a sintering aid is added to the starting material, there is an advantage that densification of the sintered body is further facilitated.

  Further, when the anisotropically shaped powder and the matrix compound powder are mixed, if the blending ratio of the anisotropically shaped powder becomes too small, the degree of orientation of the pseudo cubic {100} plane may be lowered. Therefore, the mixing ratio of the anisotropically shaped powder is preferably selected in accordance with the required sintered body density and orientation degree.

  In order to obtain a crystallographically-oriented ceramic with a degree of orientation of the pseudo-cubic {100} plane of 20% or more, the blending ratio of the anisotropically shaped powder is such that the B-site ions of the first perovskite type compound contained in the crystal-oriented ceramics. The ratio is preferably such that 0.1 at% or more is supplied from the anisotropically shaped powder. The blending ratio of the anisotropically shaped powder is preferably 2 at% or more of B site ions, and more preferably 5 at% or more of B site ions.

  Furthermore, the anisotropic shaped powder and the matrix compound powder, and the sintering aid to be blended as necessary may be mixed by a dry method, or wet by adding an appropriate dispersion medium such as water or acol. You can go there. Further, at this time, a binder and / or a plasticizer may be added as necessary.

  Next, the molding process will be described. The forming step is a step of forming the mixture obtained in the mixing step so that the development surface of the anisotropically shaped powder is oriented. In this case, the anisotropically shaped powder may be molded so as to be plane-oriented, or may be molded so as to be axially oriented.

  The molding method is not particularly limited as long as it is a method capable of orienting anisotropically shaped powder. Specific examples of the molding method for orienting the anisotropically shaped powder include a doctor blade method, a press molding method, and a rolling method. Specific examples of the molding method for axially orienting the anisotropically shaped powder include an extrusion molding method and a centrifugal molding method.

  Further, in order to increase the thickness of a molded body in which anisotropically shaped powder is surface-oriented (hereinafter referred to as “surface-oriented molded body”) or to increase the degree of orientation, it is further laminated and pressure-bonded to the surface-oriented molded body. , Pressing, rolling or the like (hereinafter referred to as “plane orientation processing”) may be performed. In this case, any one type of surface alignment treatment may be performed on the surface alignment molded body, or two or more types of surface alignment processing may be performed. Further, one type of surface alignment treatment may be repeated a plurality of times on the surface alignment molded body, or two or more types of alignment treatment may be repeated a plurality of times.

  Next, the sintering process will be described. The sintering step is a step of heating and sintering the molded body obtained in the molding step. When the molded body containing the anisotropically shaped powder and the matrix compound powder is heated to a predetermined temperature, the anisotropically shaped powder functions as a template, and an anisotropically shaped crystal made of the first perovskite compound is generated and grown. At the same time, sintering of the generated first perovskite compound proceeds.

  The heating temperature is such that the anisotropically shaped powder, matrix compound powder, and the like are produced so that the growth and / or sintering of the anisotropically shaped crystal proceeds efficiently and the compound having the desired composition is generated. What is necessary is just to select the optimal temperature according to the composition etc. of the crystal orientation ceramics to perform.

The optimum heating temperature varies depending on the composition of the first perovskite compound. For example, when producing the grain oriented ceramics composed of SrTiO ₃ using an anisotropically-shaped powder and the matrix compound powder consisting of SrTiO ₃ consisting SrTiO _3, the heating temperature is preferably 900 ° C. or higher 1300 ° C. or less. Further, the heating may be performed in any atmosphere such as air, oxygen, reduced pressure, or vacuum. Furthermore, the heating time may be selected in accordance with the heating temperature so as to obtain a predetermined sintered body density.

  The heating method may be any of normal pressure sintering methods or pressure sintering methods such as hot pressing, hot forging, HIP, etc., and the most suitable method depending on the composition and application of the crystallographically oriented ceramics. Can be selected.

  In the case of a molded body containing a binder, heat treatment mainly for degreasing may be performed before the sintering step. In this case, the degreasing temperature may be at least sufficient to thermally decompose the binder. However, degreasing is preferably performed at 500 ° C. or lower when the raw material contains an easily volatile material (for example, Na compound).

  Further, when the oriented molded body is degreased, the degree of orientation of the anisotropically shaped powder in the oriented molded body may decrease, or volume expansion may occur in the oriented molded body. In such a case, it is preferable to perform a hydrostatic pressure (CIP) treatment on the oriented molded body after the degreasing and before the heat treatment. If the hydrostatic pressure treatment is further performed on the degreased compact, there is an advantage that a decrease in the degree of orientation accompanying degreasing or a decrease in the density of the sintered compact due to the volume expansion of the oriented compact. In order to further increase the density and orientation of the sintered body, a method of further hot pressing the sintered body after the heat treatment is also effective.

  Next, the operation of the method for producing a crystal-oriented ceramic according to the present invention will be described. When anisotropically shaped powder and matrix compound powder are mixed and molded using a molding method in which force acts on the anisotropically shaped powder from one direction, the anisotropically shaped powder is anisotropically affected by the shear stress acting on the anisotropically shaped powder. The shaped powder is oriented in the compact. When such a molded body is heated at a predetermined temperature, the anisotropically shaped powder and the matrix compound powder react or do not react to produce the first perovskite compound.

  At this time, since there is lattice matching between the development surface of the anisotropically shaped powder and the pseudocubic {100} surface of the first perovskite compound, the development surface of the anisotropically shaped powder is generated in the first Inherited as a pseudo-cubic {100} face of a perovskite type compound. Therefore, in the sintered body, an anisotropic shaped crystal composed of the first perovskite compound is generated in a state where the pseudo cubic {100} plane is oriented in one direction.

  A conventional method for producing a perovskite type compound using an anisotropically shaped powder composed of a layered compound as a reactive template is a perovskite containing all the A site elements and B site elements contained in the anisotropic shaped powder and other raw materials. Only crystallographically-oriented ceramics or anisotropically shaped powders made of mold compounds can be produced.

  On the other hand, the material of the anisotropically shaped powder used as the reactive template needs to have a large crystal lattice anisotropy and lattice matching with the perovskite type compound. Depending on the composition of the perovskite-type compound, there may be no material satisfying such conditions, or the search may be extremely difficult. Therefore, in the conventional method, there is a limit to the composition control of the obtained crystallographically-oriented ceramic, particularly the composition control of the A-site element.

  In contrast, first, an anisotropically shaped powder is synthesized from a first anisotropically shaped powder made of a layered compound, and the first anisotropically shaped powder is used as a reactive template and is reacted with this ion. By optimizing the composition of the exchange reaction raw material, it is possible to synthesize an anisotropic shaped powder composed of the second perovskite type compound not containing an unnecessary A-site element and having a pseudo-cubic {100} plane as a development plane. . Subsequently, the anisotropically shaped powder thus obtained is oriented in a molded body and heated at a predetermined temperature, and is composed of a first perovskite type compound that does not contain an unnecessary A-site element and is pseudocubic {100 } Crystal-oriented ceramics with oriented surfaces are obtained.

  Since the manufacturing method according to the present invention can use a normal ceramic process as it is, even in the first perovskite type compound having a small crystal lattice anisotropy, the pseudocubic {100} plane is oriented with a high degree of orientation. Crystal oriented ceramics can be manufactured easily and inexpensively. Moreover, since the crystallographically-oriented ceramic obtained in this way is a polycrystal, it is excellent in strength, fracture toughness, etc., compared to a single crystal.

  In addition, since the anisotropically shaped powder has the same or similar crystal structure as the crystal oriented ceramic to be produced, the anisotropically shaped powder having a different crystalline structure was used as the reactive template. Compared to the case, a crystallographically-oriented ceramic having a high degree of orientation can be easily obtained. That is, even when the proportion of the anisotropically shaped powder is relatively small, a crystallographically-oriented ceramic having a high degree of orientation can be obtained.

SrCO ₃ powder (average particle size: 0.5 μm), Bi ₂ O ₃ powder (average particle size) so as to have a composition of SrBi ₄ Ti ₄ O ₁₅ (hereinafter referred to as “SBIT”) in a stoichiometric ratio. : 0.5 μm) and TiO ₂ powder (average particle diameter: 0.5 μm) were weighed and wet mixed. Next, 50 wt% of KCl was added as a flux to the raw material, and these were dry mixed. Next, the obtained mixture was put into a platinum crucible and heated under conditions of 1100 ° C. × 4 h to synthesize SBIT. After cooling, the flux was removed from the reaction product with a hot water bath to obtain SBIT powder. The obtained SBIT powder was a plate-like powder having a {001} plane as a development plane, an aspect ratio (W _b / t _b ) of about 10, and a development plane maximum length (W _b ) of about 7 μm. .

Next, to this SBIT plate-like powder, SrTiO ₃ and an amount of SrCO ₃ necessary to produce Bi ₂ O ₃ which is an excess component are added and mixed. 50 wt% of KCl was added. The mixture was then placed in a platinum crucible and heated at 950 ° C. × 8 h. This caused topochemical crystal conversion (hereinafter referred to as “TMC (Topochemical Mycrocrystal Conversion) conversion”), and a mixture of SrTiO ₃ and Bi ₂ O ₃ was produced in the platinum crucible.

Next, after removing the flux from the reaction product obtained by TMC conversion, this was immersed in 2.5N HNO ₃ for 1 h to dissolve Bi ₂ O ₃ produced as an excess component. Further, this solution was filtered to separate SrTiO ₃ powder and washed with ion exchange water at 80 ° C. The obtained SrTiO ₃ powder was a plate-like powder having a pseudo-cubic {100} plane as a development plane, an aspect ratio (Wa / ta) of about 10, and a maximum length (Wa) of the development plane of about 5 μm. . The following chemical formula 1 shows a synthesis reaction formula of the SrTiO ₃ plate powder.

FIG. 1 (a) and FIG. 1 (b) show SEM photographs of the synthesized SBIT plate powder and SrTiO ₃ plate powder, respectively. 1 that a plate-like powder having a large aspect ratio is obtained by the method according to the present invention. FIGS. 2A and 2B show X-ray diffraction patterns of the synthesized SBIT plate-like powder and SrTiO ₃ plate-like powder, respectively. FIG. 2 shows that SrTiO ₃ single-phase powder having a perovskite crystal structure is obtained from the SBIT plate-like powder. The crystal planes of the development planes of the SBIT plate-like powder and the SrTiO ₃ plate-like powder were confirmed to be a {001} plane and a pseudocubic {100} plane, respectively, by a casting method.

Bi ₂ O ₃ powder (average particle size: 0.5 μm) and TiO ₂ powder (average particle size) so as to have a Bi ₄ Ti ₃ O ₁₂ (hereinafter referred to as “BIT”) composition in stoichiometric ratio. : 0.5 μm), and these were wet mixed. Next, 50 wt% of a NaCl 50 wt% -KCl 50 wt% mixture was added as a flux to the raw material, and these were dry mixed. Next, the obtained mixture was put into a platinum crucible and heated under conditions of 1100 ° C. × 2 h to synthesize BIT. After cooling, the flux was removed from the reaction product with a hot water bath to obtain BIT powder. The obtained BIT powder was a plate-like powder having a {001} plane as a development plane, an aspect ratio (W _b / t _b ) of about 10, and a development plane maximum length (W _b ) of about 10 μm. .

Next, to this BIT plate-like powder, an amount of SrCO ₃ powder (average particle size: 0.5 μm) necessary to produce SrTiO ₃ and Bi ₂ O ₃ as an excess component is added and mixed, Further, 50 wt% of KCl was added as a flux to this raw material. The mixture was then placed in a platinum crucible and heated at 950 ° C. × 8 h. As a result, TMC conversion occurred, and a mixture of SrTiO ₃ and Bi ₂ O ₃ was formed in the platinum crucible.

Next, after removing the flux from the reaction product obtained by TMC conversion, this was immersed in 2.5N HNO ₃ for 1 h to dissolve Bi ₂ O ₃ produced as an excess component. Further, this solution was filtered to separate SrTiO ₃ powder and washed with ion exchange water at 80 ° C. The obtained SrTiO ₃ powder was a plate-like powder having a pseudo-cubic {100} plane as a development plane, an aspect ratio (Wa / ta) of about 10, and a maximum length (Wa) of the development plane of about 7 μm. . The following chemical formula 2 shows a synthesis reaction formula of the SrTiO ₃ plate powder.

3 (a) and 3 (b) show SEM photographs of the synthesized BIT plate-like powder and SrTiO ₃ plate-like powder, respectively. FIG. 3 shows that a plate-like powder having a large aspect ratio is obtained by the method according to the present invention. FIGS. 4A and 4B show X-ray diffraction patterns of the synthesized BIT plate powder and SrTiO ₃ plate powder, respectively. FIG. 4 shows that SrTiO ₃ single-phase powder having a perovskite crystal structure is obtained from the BIT plate-like powder. The crystal planes of the development planes of the BIT plate-like powder and the SrTiO ₃ plate-like powder were confirmed to be a {001} plane and a pseudocubic {100} plane by a casting method, respectively.

(Comparative Example 1)
SrTiO ₃ powder was synthesized using the flux method. That is, SrCO ₃ powder (average particle size: 0.5 μm) and TiO ₂ powder (average particle size: 0.5 μm) were weighed and wet-mixed so that the stoichiometric ratio was SrTiO ₃ composition. Next, 50 wt% of KCl was added as a flux to the raw material, and these were dry mixed. Next, the obtained mixture was put in a platinum crucible and heated under conditions of 1100 ° C. × 4 h. After cooling, the flux was removed from the reaction product with a hot water bath to obtain SrTiO ₃ powder. The following chemical formula ₃ shows a synthesis reaction formula of SrTiO ₃ powder.

FIG. 5 shows an SEM photograph of the synthesized SrTiO ₃ powder. FIG. 5 shows that the obtained SrTiO ₃ powder is an isotropic powder having an average particle diameter of about 0.5 μm and an aspect ratio of about 1.

According to the procedure shown in FIG. 6, a crystallographically-oriented ceramic made of SrTiO ₃ was produced. First, the SrTiO ₃ plate-like powder (template powder) of Example 1 obtained by TMC conversion and the isotropic SrTiO ₃ powder of Comparative Example 1 obtained by the flux method were wet mixed in a ball mill for 5 hours. As a dispersion medium, a mixed solvent of toluene (58 wt%) + ethanol (42 wt%) was used. Moreover, the compounding quantity of template powder was made into the quantity by which 10 at% of B site ion is supplied from template powder.

  A binder (manufactured by Sekisui Chemical Co., Ltd., ESREC (registered trademark) BH-3) and a plasticizer (butyl phthalate) were added to the slurry in an amount of 6 wt% and the total amount of the total powder contained in the starting material, respectively. After adding 6 wt%, the mixture was further mixed for 2 hours.

  Next, the mixed slurry was formed into a tape having a thickness of 90 μm using a doctor blade device. By laminating, thermocompression bonding and rolling of this tape, a plate-like molded body having a thickness of 1.5 mm was obtained. Next, the obtained plate-like molded body was degreased under the conditions of 600 ° C. × 2 hours in the air. Further, the degreased plate-shaped body was subjected to CIP treatment at a pressure of 3000 kg / cm 2 (294 MPa), and then subjected to atmospheric pressure sintering in oxygen at 1450 ° C. × 10 h.

  About the obtained sintered compact, the X-ray diffraction was performed about the surface parallel to a tape surface. FIG. 7 shows the X-ray diffraction pattern. From FIG. 7, it can be seen that the pseudo-cubic {100} plane is oriented parallel to the tape surface and with a high degree of orientation. In this example, the average orientation degree F (100) of the pseudo-cubic {100} plane by the Lotgering method was 99.33%.

(Comparative Example 2)
The same as Example 3 except that only the isotropic SrTiO ₃ powder obtained in Comparative Example 1 was used as a starting material, and the sintering conditions were 1350 ° C., 1400 ° C. or 1450 ° C. × 1 h. A sintered body made of SrTiO ₃ was produced according to the procedure. FIG. 8 shows an X-ray diffraction pattern measured on a plane parallel to the tape surface of the obtained sintered body. FIG. 8 shows that the obtained sintered body is non-oriented. In the case of the sintered body obtained in Comparative Example 2, the average orientation degree F (100) of the pseudocubic {100} plane by the Lotgering method was all 0%.

A crystallographically-oriented ceramic made of SrTiO ₃ was prepared according to the same procedure as in Example 3 except that the sintering condition was 1450 ° C. × 1 h.

A crystal-oriented ceramic made of SrTiO ₃ is prepared according to the same procedure as in Example 3 except that the blending amount of the SrTiO ₃ plate powder is equivalent to 5 at% of the B site ion and the sintering condition is 1450 ° C. × 1 h. did.

A crystal-oriented ceramic made of SrTiO ₃ is prepared according to the same procedure as in Example 3 except that the amount of SrTiO ₃ plate powder is equivalent to 1 at% of the B site ion and the sintering condition is 1450 ° C. × 1 h. did.

A crystallographically-oriented ceramic made of SrTiO ₃ was produced according to the same procedure as in Example 3 except that the sintering condition was 1350 ° C. × 1 h.

A crystal-oriented ceramic made of SrTiO ₃ was prepared according to the same procedure as in Example 3 except that the blending amount of the SrTiO ₃ plate powder was equivalent to 5 at% of the B site ion and the sintering conditions were 1400 ° C. × 1 h. did.

  9 to 13 show X-ray diffraction patterns measured on the surfaces parallel to the tape surface of the sintered bodies obtained in Examples 4 to 8, respectively. 9 to 13, it can be seen that all of the sintered bodies obtained in Examples 4 to 8 have the pseudo-cubic {100} plane oriented parallel to the tape surface and with a high degree of orientation. . FIG. 11 also shows that a crystallographically-oriented ceramic having a high orientation degree of 72.88% is obtained even though the template amount is only 1 at% of the B site ions.

A crystallographically-oriented ceramic made of SrTiO ₃ was prepared according to the same procedure as in Example 3 except that the blending amount of the SrTiO ₃ plate powder was 10 at% of B site ions and the sintering condition was 1400 ° C. × 1 h. The average orientation degree F (100) of the pseudo cubic {100} plane of the obtained crystal oriented ceramics was 92.64%.

A crystallographically-oriented ceramic made of SrTiO ₃ was prepared according to the same procedure as in Example 3 except that the blending amount of the SrTiO ₃ plate powder was 1 at% or 5 at% of the B site ion. The average orientation degree F (100) of the pseudo-cubic {100} plane of the obtained crystal oriented ceramics was 82.39% and 90.15%, respectively.

(Comparative Example 3)
As a comparative example, a crystallographically oriented ceramic was produced according to Japanese Patent Laid-Open No. 10-139552. Crystal oriented ceramics were produced using Sr ₃ Ti ₂ O ₇ plate-like powder, which is a kind of layered compound, as a reactive template. First, Sr ₃ Ti ₂ O ₇ plate powder was synthesized using a flux method. The obtained Sr ₃ Ti ₂ O ₇ plate-like powder had a {001} plane as a development plane, an aspect ratio of about 10, and a maximum length of the development plane of about 10 μm.

Next, a predetermined amount of the synthesized Sr ₃ Ti ₂ O ₇ plate powder, the isotropic SrTiO ₃ powder obtained in Comparative Example 1, and the TiO ₂ powder (average particle size: 0.5 μm) were weighed. Except for the above, a crystal-oriented ceramic was prepared according to the same procedure as in Example 3. _The amount of the Sr 3 _Ti 2 _{O 7} platelike powder is, 10at% of B site ions, 30 at% or 67 at% is the amount supplied from the plate-like powder.

  The following formula 4 shows that a ceramic production route (Example 3) by a crystal growth method (TMC-TGG method) using a plate-like powder obtained by TMC conversion as a template, a ceramic production route by a normal method (comparative example) 2) and a ceramic production route (Comparative Example 3) by a crystal growth method (RTGG method) using a reactive template. Table 1 shows the relationship between the sintering conditions and the degree of orientation of the sintered bodies obtained in Examples 3 to 10 and Comparative Examples 2 and 3.

  Furthermore, in FIG. 14A and FIG. 14B, the relationship between the amount of each crystal-oriented ceramic template obtained in Examples 3 to 10 and Comparative Example 3 and the degree of orientation of the pseudocubic {100} plane is shown. Show. In the case of the RTGG method, when the template amount was 10 at%, the degree of orientation of the pseudocubic {100} plane was about 20%. In the case of the RTGG method, the degree of orientation of the pseudocubic {100} plane when the template amounts were 30 at% and 67 at% was 46% and 62%, respectively.

  In contrast, when the TMC-TGG method was used, a high degree of orientation was obtained with a very small amount of template. That is, when the sintering temperature was 1450 ° C., the degree of orientation exceeded 70% when the template amount was 1 at%. When the template amount was 5 at%, the degree of orientation exceeded 80%. When the template amount was 10 at%, the degree of orientation exceeded 95%. Furthermore, when the template amount was 10 at%, the orientation degree of the pseudo-cubic {100} plane exceeded 90% regardless of the sintering temperature.

As a 0.95PbTiO ₃ -0.05SrTiO ₃ composition, except that it weighed a SrTiO ₃ platelike powder obtained in Example 1 (Template powder), and isotropic PbTiO ₃ powder synthesized by solid phase method Prepared a crystallographically oriented ceramic according to the same procedure as in Example 3.

(Comparative Example 4)
As a 0.95PbTiO ₃ -0.05SrTiO ₃ composition, and isotropic SrTiO ₃ platelike powder obtained in Comparative Example 1, except that weighed and isotropic PbTiO ₃ powder synthesized by solid phase method A sintered body was prepared according to the same procedure as in Example 3.

FIG. 15A and FIG. 15B show X-ray diffraction patterns measured on a plane parallel to the tape surface of the sintered bodies obtained in Example 11 and Comparative Example 4, respectively. In the case of Comparative Example 4 in which the SrTiO ₃ plate powder was not used, the degree of orientation of the pseudocubic {100} plane was 0%. On the other hand, in the case of Example 11 using the SrTiO ₃ plate-like powder, the degree of orientation of the pseudocubic {100} plane was 72.6%.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention. For example, in the above embodiment, the atmospheric pressure sintering method is used when producing the crystallographically-oriented ceramic, but other sintering methods (for example, hot pressing method, HIP treatment, etc.) may be used.

  In the above embodiment, the crystal oriented ceramics mainly composed of a single phase of the perovskite compound and the manufacturing method thereof have been mainly described. However, an appropriate subcomponent and / or subphase is added to the first perovskite type compound. Then, thermoelectric characteristics and ion conduction characteristics can be imparted. Therefore, if the manufacturing method according to the present invention is applied, even a crystallographically-oriented ceramic suitable as a thermoelectric material or an ion conductive material can be manufactured.

  The crystal oriented ceramics according to the present invention includes various sensors such as an acceleration sensor, pyroelectric sensor, ultrasonic sensor, electric field sensor, temperature sensor, gas sensor, knocking sensor, yaw rate sensor, airbag sensor, piezoelectric gyro sensor, and piezoelectric transformer. Low-loss actuator or low-loss resonator such as energy conversion element, piezoelectric actuator, ultrasonic motor, resonator, capacitor, bimorph piezoelectric element, vibration pickup, piezoelectric microphone, piezoelectric ignition element, sonar, piezoelectric buzzer, piezoelectric speaker, oscillator, filter Or a dielectric material, a thermoelectric conversion material, an ion conductive material, or the like used for a capacitor and a multilayer capacitor.

  The anisotropically shaped powder according to the present invention is particularly suitable as a template for producing the crystallographically-oriented ceramic according to the present invention, but the use of the anisotropically shaped powder according to the present invention is not limited to this. Alternatively, it can be used as a powder for a piezoelectric rubber composite material.

1 (a) and 1 (b) are SEM photographs of the SrBi ₄ Ti ₄ O ₁₅ plate powder and the SrTiO ₃ plate powder synthesized in Example 1, respectively. FIGS. 2A and 2B are X-ray diffraction patterns of the SrBi ₄ Ti ₄ O ₁₅ plate powder and the SrTiO ₃ plate powder synthesized in Example 1, respectively. 3 (a) and 3 (b) are SEM photographs of the Bi ₄ Ti ₃ O ₁₂ plate powder and the SrTiO ₃ plate powder synthesized in Example 2, respectively. 4 (a) and 4 (b) are X-ray diffraction patterns of the Bi ₄ Ti ₃ O ₁₂ plate powder and the SrTiO ₃ plate powder synthesized in Example 2, respectively. 4 is a SEM photograph of isotropic SrTiO ₃ powder synthesized in Comparative Example 1. It is process drawing which shows the manufacturing method of the crystal orientation ceramics which concern on this invention. 3 is an X-ray diffraction pattern of the crystallographically-oriented ceramic obtained in Example 3. 3 is an X-ray diffraction pattern of non-oriented ceramic obtained in Comparative Example 2. FIG. 4 is an X-ray diffraction pattern of the crystallographically-oriented ceramic obtained in Example 4. 6 is an X-ray diffraction pattern of the crystallographically-oriented ceramic obtained in Example 5. 7 is an X-ray diffraction pattern of the crystallographically-oriented ceramic obtained in Example 6. 7 is an X-ray diffraction pattern of the crystallographically-oriented ceramic obtained in Example 7. 7 is an X-ray diffraction pattern of the crystallographically-oriented ceramic obtained in Example 8. It is a figure which shows the relationship between the template amount of the crystal orientation ceramics obtained in Examples 3-10 and the comparative example 3, and the orientation degree of a pseudo cubic {100} plane. FIGS. 15A and 15B are X-ray diffraction patterns of the crystallographically-oriented ceramic obtained in Example 11 and the non-oriented ceramic obtained in Comparative Example 4, respectively.

Claims (23)

General _{formula: (Sr x A '1-} x) (Ti y B' 1-y) O 3
(However, 0 <x ≦ 1, 0 <y ≦ 1, A ′ is one or more divalent metal elements, and B ′ is one or more tetravalent metal elements.)
Comprising a polycrystal of the first perovskite compound represented by:
The pseudo-cubic {100} plane of each crystal grain constituting the polycrystal is oriented,
A crystallographically-oriented ceramic wherein the degree of orientation of the pseudocubic {100} plane by the Lotgering method of the first perovskite type compound is 70% or more. The crystallographically-oriented ceramic according to claim 1, wherein the first perovskite compound is SrTiO ₃ . General _{formula: (Sr x A '1-} x) (Ti y B' 1-y) O 3
(However, 0 <x ≦ 1, 0 <y ≦ 1, A ′ is one or more divalent metal elements, and B ′ is one or more tetravalent metal elements.)
And the development plane is a pseudo-cubic {100} plane, and the aspect ratio of the maximum length (W _a ) of the development plane to the thickness (t _a ) ( An anisotropic shaped powder having a ratio of W _a / t _a ) of 2 or more and a matrix compound powder that forms the first perovskite compound according to claim 1 without or reacting with the anisotropic shaped powder A mixing step to
A molding step of molding the mixture obtained in the mixing step so that the development surface of the anisotropically shaped powder is oriented;
A method for producing a crystallographically-oriented ceramic, comprising: a sintering step of sintering the compact obtained in the forming step. 4. The crystal according to claim 3, wherein the first perovskite compound in the crystal-oriented ceramic is mixed, molded, and sintered so that a pseudo cubic {100} plane orientation degree by the Lotgering method is 70 % or more. A method for producing oriented ceramics.   In the mixing step, the anisotropic shaped powder and the anisotropic shaped powder so that 0.1 at% or more of B site ions of the first perovskite type compound contained in the crystal-oriented ceramic are supplied from the anisotropic shaped powder, The method for producing a crystallographically-oriented ceramic according to claim 3 or 4, wherein the matrix compound is mixed. General formula: (Bi ₂ O ₂ ) ²⁺ (A _m-1 B _m O _{3m + 1} ) ²⁻
(However, A is at least one element selected from Na ⁺ , K ⁺ , Sr ²⁺ , Pb ²⁺ , Ba ²⁺ , and Bi ³⁺ , or a combination of these elements.
B is at least one element selected from Fe ³⁺ , Ti ⁴⁺ , Nb ⁵⁺ , Ta ⁵⁺ , and W ⁶⁺ , or a combination of these elements.
Elements A and B satisfy the relationship of α (m−1) + βm = 6 m, where α is the average valence of element A and β is the average valence of element B.
m is an integer from 1 to 8.
In addition, the case where A is composed only of Na ⁺ and / or K ⁺ and Bi ³⁺ and B is composed only of Nb ⁵⁺ is excluded. )
And has a lattice matching with the pseudo-cubic {100} plane of the second perovskite compound represented by the following general formula, and its thickness ( maximum length of the developed plane for t _b) aspect ratio _{(W b) (W b /} t b) is synthesized first anisotropically shaped powder is 2 or more, the first anisotropically shaped powder, the The second perovskite type compound and the ion exchange reaction raw material that generates an excess component by an ion exchange reaction with the first anisotropically shaped powder are subjected to an ion exchange reaction in a solution or melt, and the excess component is removed. Obtained by thermal or chemical removal,
General _{formula: (Sr x A '1-} x) (Ti y B' 1-y) O 3
(However, 0 <x ≦ 1, 0 <y ≦ 1, A ′ is one or more divalent metal elements, and B ′ is one or more tetravalent metal elements.)
Consisting of a single phase of the second perovskite compound represented by
Its developed plane consists pseudo-cubic {100} plane, and an aspect ratio _{(W a} / _t a) anisotropically is 2 or more the maximum length of the developed plane for its thickness _{(t a) (W a)} Shape powder. The anisotropically shaped powder according to claim 6, wherein the second perovskite type compound is SrTiO ₃ . The anisotropic shaped powder according to claim 6 or 7, wherein the maximum length (W _a ) of the development surface is 100 µm or less. General formula: (Bi ₂ O ₂ ) ²⁺ (A _m-1 B _m O _{3m + 1} ) ²⁻
(However, A is at least one element selected from Na ⁺ , K ⁺ , Sr ²⁺ , Pb ²⁺ , Ba ²⁺ , and Bi ³⁺ , or a combination of these elements.
B is at least one element selected from Fe ³⁺ , Ti ⁴⁺ , Nb ⁵⁺ , Ta ⁵⁺ , and W ⁶⁺ , or a combination of these elements.
Elements A and B satisfy the relationship of α (m−1) + βm = 6 m, where α is the average valence of element A and β is the average valence of element B.
m is an integer from 1 to 8.
In addition, the case where A is composed only of Na ⁺ and / or K ⁺ and Bi ³⁺ and B is composed only of Nb ⁵⁺ is excluded. )
The bismuth layered perovskite type compound represented by the formula ( 1) has a growth plane having lattice matching with the pseudo cubic {100} plane of the second perovskite type compound according to claim 6 and its thickness (t _b A synthesis step of synthesizing a first anisotropically shaped powder having an aspect ratio (W _b / t _b ) of the maximum length (W _b ) of the development surface with respect to
The first anisotropically shaped powder and an ion exchange reaction raw material that produces the second perovskite type compound and surplus component by an ion exchange reaction between the first anisotropically shaped powder and ions in solution or melt An ion exchange process for performing an exchange reaction;
A method for producing an anisotropically shaped powder, comprising a removal step of removing the surplus component thermally or chemically. The method for producing an anisotropic shaped powder according to claim 9, wherein the layered compound is Bi ₄ Ti ₃ O ₁₂ or SrBi ₄ Ti ₄ O ₁₅ .   A dielectric element using the crystal-oriented ceramic according to claim 1.   A microwave dielectric element using the crystallographically-oriented ceramic according to claim 1.   A thermoelectric element using the crystal-oriented ceramic according to claim 1.   A pyroelectric element using the crystallographically-oriented ceramic according to claim 1.   A magnetoresistive element using the crystal-oriented ceramic according to claim 1.   A magnetic element using the crystal-oriented ceramic according to claim 1.   A piezoelectric element using the crystal-oriented ceramic according to claim 1.   A superconducting element using the crystal-oriented ceramic according to claim 1.   A resistance element using the crystal-oriented ceramic according to claim 1.   An electron conducting device using the crystallographically-oriented ceramic according to claim 1.   An ion conductive element using the crystallographically-oriented ceramic according to claim 1.   A PTC element using the crystallographically-oriented ceramic according to claim 1.   An NTC element using the crystal-oriented ceramic according to claim 1.

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