JP2002321974A - Method of manufacturing crystal-oriented ceramic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing crystal-oriented ceramics where crystal-oriented ceramics consisting of an isotropic perovskite-type compound and having a high degree of orientation can be manufactured and where the composition of A-site elements contained in the crystal-oriented ceramics can be easily controlled. SOLUTION: A plate-like powder which consists of a bismuth-layered titanate compound and whose developed faces have a lattice matching with the pseudo- cubic 100} face of the isotropic perovskite-type compound is mixed with a perovskite-forming raw material which reacts with the above plate-like powder to produce the isotropic perovskite-type compound and surplus components including a bismuth oxide (a mixing process). Next, the mixture is so molded that the plate-like powder is oriented (a molding process). Furthermore, the plate-like powder included in the resultant mold is made to react with the perovskite-forming raw material and on/after the reaction, the surplus components produced by the reaction are thermally/chemically removed (a reacting and removing process).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a crystallographically oriented ceramic, and more particularly, to a bimorph piezoelectric element, a vibration pickup, a piezoelectric microphone, a piezoelectric ignition element, an acceleration sensor, a knocking sensor, a piezoelectric actuator, a sonar, and an ultrasonic wave. The present invention relates to a method for producing a crystal oriented ceramic suitable as a piezoelectric material used for a sensor, a piezoelectric buzzer, a piezoelectric speaker, a transmitter, a filter, and the like.

[0002]

2. Description of the Related Art Piezoelectric materials are materials having a piezoelectric effect, and are classified into single crystals, ceramics, thin films, polymers, and composites. Among these piezoelectric materials, in particular, piezoelectric ceramics have high performance,
Because the degree of freedom of shape is large and material design is relatively easy,
It is widely applied in the fields of electronics and mechatronics.

[0003] Piezoelectric ceramics are ferroelectric ceramics.
A DC voltage is applied to the ferroelectric
So-called polarization treatment
You. To align spontaneous polarization in a certain direction by polarization processing
Isotropic perovska whose spontaneous polarization can take three-dimensionally
Because of its advantageous crystal structure,
Most piezoelectric ceramics are made of isotropic perovskite
G type ferroelectric ceramics. Here, "isotropic paper
The “lobskite-type ferroelectric substance” has the general formula: ABO
₃(A and B are metal elements), so-called Regular
Slight distortion from cubic type in Perovskite type compounds
A substance that causes spontaneous polarization by

As an isotropic perovskite type ferroelectric ceramic, for example, Pb (Zr.Ti) O ₃ (hereinafter referred to as “PZT”), and a lead-based composite perovskite as a third component with respect to PZT are used. PZT3 added
Component system, BaTiO ₃ , Bi _{0 . 5} Na _0.5 TiO ₃
(Hereinafter referred to as “BNT”).

[0005] Among these, lead-based piezoelectric ceramics represented by PZT have higher piezoelectric properties than other piezoelectric ceramics, and account for most of the piezoelectric ceramics currently in practical use. ing. However, since it contains lead oxide (PbO) having a high vapor pressure, there is a problem that the load on the environment is large. Therefore, a piezoelectric ceramic having low lead or lead-free and having the same piezoelectric characteristics as PZT is required.

On the other hand, BaTiO ₃ ceramics have relatively high piezoelectric properties among lead-free piezoelectric materials, and are used for sonar and the like. In addition, BaTiO
₃ and other lead-free perovskite compounds (eg, BNT
Among others, those exhibiting relatively high piezoelectric properties are known. However, these lead-free piezoelectric ceramics have a problem that their piezoelectric characteristics are lower than that of PZT.

Therefore, various proposals have conventionally been made to solve this problem. For example, JP-A-10-
139552 discloses a host material A (for example, Bi ₄ Ti ₃ O ₁₂ , Sr ₃ Ti ₂ O ₇ , Ca ₃₎ comprising a layered perovskite compound and having shape anisotropy.
Ti ₂ O ₇ ) and a guest material B having an isotropic perovskite structure or a raw material Q capable of producing the guest material B
And a guest material C for converting the host material A into an isotropic perovskite-type compound, molding these so that the host material A is oriented, and then heating and sintering. Proposed by the present applicant.

Japanese Patent Publication No. 63-24948 discloses a plate-like titanium dioxide having a developed C-plane, a compound containing barium (eg, barium oxide, barium carbonate, etc.), an organic binder, a plasticizer. A method for producing barium titanate porcelain, which comprises kneading a solvent and a solvent, forming the mixture under uniaxial pressure, and firing the obtained formed body.

[0009]

It is known that the piezoelectric properties of isotropic perovskite compounds generally differ depending on the direction of the crystal axis. Therefore, if the crystal axis having high piezoelectric characteristics can be oriented in a certain direction, the anisotropy of the piezoelectric characteristics can be utilized to the utmost, and higher characteristics of the piezoelectric ceramic can be expected. In fact, it is known that some single crystals made of a lead-free ferroelectric material exhibit excellent piezoelectric characteristics.

However, the single crystal has a problem that the production cost is high. In addition, a single crystal of a solid solution having a complicated composition is likely to cause a composition shift during manufacturing,
It is unsuitable as a practical material. Furthermore, single crystals have poor fracture toughness, so that it is difficult to use them under high stress, and there is a problem that the range of application is limited.

On the other hand, an anisotropically shaped powder (host material A) comprising a layered perovskite compound is disclosed in
As disclosed in Japanese Patent Application No. 0-139552, it functions as a reactive template for producing an isotropic perovskite compound. Therefore, if the host material A is oriented in the molded body and is reacted with the guest material C, even if the isotropic perovskite compound has a small crystal lattice anisotropy, the specific crystal plane is high. Crystal oriented ceramics oriented with the degree of orientation can be easily and inexpensively manufactured.

However, this method uses the host material A
And a guest material C to form an isotropic perovskite compound (general formula: ABO ₃ ). In the composition of the obtained crystallographically-oriented ceramic, the A-site element ( For example, Bi, S
r, Ca, etc.) always remain. Therefore, in this method, the most desirable composition cannot be realized, and the properties as the piezoelectric material may be impaired by the inevitable A-site element.

Japanese Patent Publication No. Sho 63-24948 discloses that titanium dioxide having a plate-like shape with developed C-plane is oriented in a molded body, and this is reacted with a compound containing barium. It is described that the obtained barium titanate porcelain can be obtained. However, it is difficult to produce a titanium dioxide single crystal powder having a plate-like shape and having lattice matching with an isotropic perovskite compound. Therefore, this method cannot produce isotropic perovskite ceramics with a high degree of orientation.

The problem to be solved by the present invention is that it is possible to produce a highly oriented crystal oriented ceramic comprising an isotropic perovskite compound, and to control the composition of the A-site element contained in the crystal oriented ceramic. An object of the present invention is to provide a method for easily producing a crystallographically-oriented ceramic.

[0015]

According to the present invention, there is provided a method for producing a crystallographically-oriented ceramic according to the present invention, which comprises a bismuth layered titanate compound and whose developed surface is a pseudo-isotropic perovskite compound. A mixing step of mixing a plate-like powder having lattice matching with a cubic {100} plane, and a perovskite-forming raw material that reacts with the plate-like powder to generate an excess component containing the isotropic perovskite compound and bismuth oxide And a molding step of molding the mixture obtained in the mixing step so that the plate-like powder is oriented, and a reaction between the plate-like powder and the perovskite-forming raw material contained in the molded article obtained in the molding step. And a reaction / removal step of removing the surplus components generated by the reaction.

The shaped body in which the plate-like powder has been oriented is heated to a predetermined temperature to react the plate-like powder with the perovskite-forming raw material, and the plate-like powder of the isotropic perovskite-type compound inheriting the orientation of the plate-like powder is obtained. Excess components including crystals and bismuth oxide are generated to form an intermediate sintered body. When this excess component is removed from the intermediate sintered body at the same time as or after the reaction, a crystallographically-oriented ceramic comprising an isotropic perovskite-type compound and having a pseudo-cubic {100} plane is obtained. Further, by optimizing the composition of the perovskite-forming raw material, a crystallographically-oriented ceramic composed of an isotropic perovskite-type compound having a high degree of orientation and substantially not remaining Bi as an A-site element can be obtained.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail. First, the plate-like powder used in the method for producing a crystallographically-oriented ceramic according to the present invention will be described. The plate-like powder is used as a reactive template for orienting an isotropic perovskite compound having a small crystal lattice anisotropy in a specific direction. In the present invention, a plate-like powder satisfying the following conditions is used.

First, a bismuth layered titanate compound is used for the plate-like powder. The bismuth layered titanate compound is used as the plate-like powder because (1) the anisotropy of the crystal lattice is large, the preparation of the plate-like powder is relatively easy, and (2) the perovskite generation raw material described later Bi can be easily removed out of the system by the reaction, and the composition of the A-site element contained in the isotropic perovskite compound can be easily controlled.

Second, as the plate-like powder, a powder whose developed surface (the surface occupying the largest area) has lattice matching with the pseudo-cubic {100} plane of the isotropic perovskite-type compound is used. Even in the case of a plate-like powder made of a bismuth layered titanate compound, if the developed surface does not have lattice matching with the pseudocubic {100} plane of the isotropic perovskite compound, the pseudocubic {100} This is not preferable because it does not function as a reactive template for producing a crystallographically oriented ceramic having a plane as an oriented plane.

Here, the “isotropic perovskite compound” generally refers to a compound represented by the general formula: ABO ₃ , and the crystallographically-oriented ceramic obtained by the production method according to the present invention includes: , T as a B site element
It is composed of an isotropic perovskite compound containing i. The reason why Ti is included as a B-site element is that the above-described bismuth layered titanate compound is used as the plate-like powder.

The crystal oriented ceramics that can be produced by the method according to the present invention are not limited to isotropic perovskite compounds containing only Ti as a B-site element. B site element (for example, C
r, Zr, Mn, Fe, Mo, Nb, Zn, Ta, W,
Ni) can be manufactured. The content of Ti in the isotropic perovskite-type compound, the types of other B-site elements and their contents are determined by the composition of the plate-like powder and the composition of the perovskite-forming raw material.

On the other hand, according to the manufacturing method of the present invention, A
It is also possible to produce a crystallographically-oriented ceramic comprising an isotropic perovskite compound containing Bi derived from a plate-like powder as a site element, but it does not substantially contain Bi as an A-site element (Bi ₂ O ₃ (Equivalent to 1 wt% or less in terms of conversion) Crystal-oriented ceramics made of an isotropic perovskite compound can also be produced. This is different from the conventional method.

As the A site element contained in the isotropic perovskite compound, specifically, in addition to Bi, B
a, Sr, Ca, La, and the like are mentioned as preferable examples, but are not limited thereto. The type and content of the A-site element in the isotropic perovskite compound are determined by the composition of the plate-like powder and the composition of the perovskite-forming raw material.

The quality of the lattice matching is determined by the difference between the lattice size of the developed surface of the plate-like powder and the lattice size of the pseudo-cubic {100} plane of the isotropic perovskite compound. The value divided by the lattice size (hereinafter this value is referred to as the “grid matching ratio”
That. ). A smaller value of the lattice matching ratio indicates that the plate-like powder functions as a good reactive template. In order to produce a highly oriented crystallographically oriented ceramic, the lattice matching ratio of the plate-like powder must be 2
It is preferably at most 0%, more preferably at most 10%.

The term “quasi-cubic {HKL}” means that an isotropic perovskite compound is generally tetragonal, orthorhombic,
It has a structure distorted from a cubic crystal such as a trigonal crystal, but since the distortion is slight, it means that the crystal is regarded as a cubic crystal and the Miller index is indicated.

Third, as the plate-like powder, a powder having a shape that can be easily oriented in a certain direction during molding is used. For that purpose, the average aspect ratio of the plate-like powder (= the average value of the diameter / thickness of the plate-like powder) is preferably 3 or more. If the average aspect ratio is less than 3,
It becomes difficult to orient the plate-like powder in one direction during molding. The average aspect ratio of the plate-like powder is more preferably 5 or more.

Generally, as the average aspect ratio of the plate-like powder increases, the orientation of the plate-like powder tends to be facilitated. However, when the average aspect ratio is excessively large, the plate-like powder is pulverized in a mixing step described later, and a molded article in which the plate-like powder is oriented may not be obtained. Therefore, the average aspect ratio of the plate-like powder is preferably 100 or less.

Further, the average value (average particle size) of the developed surface diameter of the plate-like powder is preferably 0.05 μm or more. If the average particle size of the plate-like powder is less than 0.05 μm, it becomes difficult to orient the plate-like powder in a certain direction due to shear stress acting during molding. In addition, since the gain of interface energy is reduced, epitaxial growth on template particles is less likely to occur when used as a reactive template in producing crystallographically oriented ceramics.

On the other hand, the average particle size of the plate-like powder is preferably 20 μm or less. When the average particle size of the plate-like powder exceeds 20 μm, the sinterability is reduced, and a crystal oriented ceramic having a high sintered body density cannot be obtained. The average particle size of the plate-like powder is more preferably 0.1 μm or more and 10 μm or less.

As the bismuth layered titanate compound suitable as the material of the plate-like powder, specifically, Bi ₄ Ti ₃ O
₁₂ (bismuth titanate), BaBi ₄ Ti ₄ O ₁₅ ,
A suitable example is a bismuth layered perovskite compound such as SrBi ₄ Ti ₄ O ₁₅ .

Each of these compounds has a $ 00
Since the surface energy of the {1} plane is smaller than the surface energy of the other crystal planes, a plate-like powder having a {001} plane as a developed plane and a predetermined shape can be easily produced. The {001} plane of these compounds has extremely good lattice matching with the pseudo-cubic {100} plane of the isotropic perovskite compound. Therefore, a plate-like powder made of these compounds is suitable as a reactive template for producing a crystallographically-oriented ceramic having an isotropic perovskite-type compound and having a {100} plane as an oriented plane.

The plate-like powder composed of the bismuth layered titanate compound is a raw material capable of producing the bismuth layered titanate compound (hereinafter, this is referred to as a “plate-shaped powder generating raw material”).
Can be easily produced by heating together with a liquid or a substance which becomes liquid by heating. When the raw material for forming a plate-like powder is heated in a liquid phase in which atoms can be easily diffused, a plate-like powder in which {001} planes having small surface energy are preferentially developed can be easily synthesized. In this case, the average aspect ratio and average particle size of the plate-like powder can be controlled by appropriately selecting the synthesis conditions.

As a method of producing the plate-like powder, specifically, a flux (for example, NaCl, KCl, NaCl
And KCl, BaCl ₂ , KF and the like. ) And a method of heating a plate-like powder forming raw material (flux method), a method of heating a non-plate-like bismuth layered titanate compound powder synthesized by a solid-phase reaction method together with an alkaline aqueous solution in an autoclave (hydrothermal synthesis method), and the like. Is a preferred example.

Next, a method for producing a crystallographically-oriented ceramic according to the present invention will be described. The production method according to the present invention includes a mixing step, a molding step, and a reaction / removal step.

First, the mixing step will be described. The mixing step is a step of mixing the above-mentioned plate-like powder and a perovskite-forming raw material. In this case, the plate-like powder may be composed of any one of the above-described bismuth layered titanate compounds, or may be a mixture of two or more compounds.

The “perovskite forming raw material” is
It reacts with the above-mentioned plate-like powder to generate an isotropic perovskite compound and a surplus component containing bismuth oxide. The composition and mixing ratio of the perovskite-forming raw material are determined according to the composition of the isotropic perovskite compound to be synthesized and the composition of the plate-like powder used as the reactive template. The form of the perovskite generating raw material is not particularly limited, and oxide powder, composite oxide powder, salts such as carbonate, nitrate, oxalate, acetate, alkoxide, and the like can be used.

For example, bismuth titanate (Bi ₄ Ti ₃
Barium titanate (Ba) using a plate-like powder of O ₁₂ );
In the case of producing a crystallographically-oriented ceramic made of TiO ₃ ), barium carbonate (B) is used as a perovskite-forming raw material.
It is preferable to use a Ba-containing compound such as aCO ₃ ), barium oxide (BaO), or barium hydroxide (Ba (OH) ₂ ). In this case, a Ba-containing compound corresponding to 3 moles of barium atoms may be added to 1 mole of bismuth titanate.

Formula 1 shows a reaction formula between bismuth titanate and barium carbonate. When bismuth titanate and barium carbonate are used as a plate-like powder and a perovskite-forming raw material, respectively, and these are reacted at a molar ratio of 1: 3,
As shown in the chemical formula 1, barium titanate which is an isotropic perovskite compound and bismuth oxide (Bi ₂ O ₃ ) which is an excess component can be produced. The reason why the formula 1 proceeds to the right is that the isotropic perovskite compound is more thermodynamically stable than the bismuth layered titanate compound.

[0039]

Embedded image Bi ₄ Ti ₃ O ₁₂ + 3BaCO ₃ → 3BaTiO ₃ + 2Bi ₂ O ₃ + 3CO ₂ ↑

The formula 1 represents an ideal reaction formula between bismuth titanate and barium carbonate, and there is a possibility that a more complicated reaction actually occurs. Ideally, the surplus component is desirably only bismuth oxide as shown in the formula (1).
i ₂ O ₃ and BaCO ₃ or Ba-Bi-O-based compound produced in the reaction with BaTiO _3, etc., also may contain other oxide components there. However, the surplus component may include an oxide component other than bismuth oxide as long as it does not hinder the removal of the surplus component in the heat treatment step described below.

The same applies to the case of synthesizing an isotropic perovskite compound other than barium titanate. When the isotropic perovskite compound is produced, all or a part of Bi contained in the bismuth layered titanate compound is removed. The composition and mixing ratio of the perovskite-forming raw material may be determined so that the plate-like powder is discharged as bismuth oxide outside the plate-like powder and a predetermined amount of the A-site element is introduced into the plate-like powder.

In the mixing step, the compound having the same composition as the isotropic perovskite compound obtained by these reactions is further added to the plate-like powder and the perovskite-forming raw material blended at a predetermined ratio. Non-plate-like fine powder (hereinafter referred to as “compound fine powder”) and / or a sintering aid may be added. When a compound fine powder or a sintering aid is further added to the plate-like powder and the perovskite forming raw material, there is an advantage that the sintered body can be easily densified.

In addition, when compounding the compound fine powder, if the compounding ratio of the compound fine powder is excessively large, the compounding ratio of the plate-like powder in the whole raw material is inevitably reduced, and the pseudo-cubic 得 100 ｝ The degree of orientation of the surface may be reduced. Therefore, it is preferable to select an optimum compounding ratio of the compound fine powder according to the required density of the sintered body and the degree of orientation of the pseudo-cubic {100} plane.

Further, the mixing of the plate-like powder and the perovskite-forming raw material, and the compound fine powder and the sintering aid compounded as required may be carried out by a dry method.
It may be carried out in a wet manner by adding an appropriate dispersion medium such as water or alcohol. Further, at this time, a binder and / or a plasticizer may be added as necessary.

Next, the molding step will be described. The molding step is a step of molding the mixture obtained in the mixing step so that the plate-like powder is oriented. Here, “plate-like powder is oriented” means that the developed surfaces of each plate-like powder are arranged parallel to each other (hereinafter, such a state is referred to as “plane-orientation”), or each plate-like powder is oriented. Means that the developed surface is arranged parallel to one axis penetrating the molded article (hereinafter, such a state is referred to as “axial orientation”).

The molding method is not particularly limited as long as it is a method capable of orienting the plate-like powder. As a molding method for plane-orientating the plate-like powder,
Specifically, a doctor blade method, a press molding method, a rolling method and the like are mentioned as preferable examples. Further, as a molding method for axially orienting the plate-like powder, specifically, an extrusion molding method, a centrifugal molding method and the like are mentioned as preferable examples.

Further, in order to increase the thickness of the molded product in which the plate-like powder is plane-oriented (hereinafter, referred to as “plane-oriented molded product”) and to increase the degree of orientation, the planar-oriented product is further treated. Processing such as lamination pressure bonding, pressing, and rolling (hereinafter, this is referred to as “plane orientation processing”) may be performed. in this case,
Any one of the plane orientation treatments may be performed on the plane-oriented molded body, or two or more kinds of plane orientation treatments may be performed. Further, one type of plane orientation treatment may be repeated a plurality of times on the plane-oriented molded body, or two or more types of orientation treatments may be repeated plural times.

Next, the reaction / removal step will be described.
The reaction / removal step is a reaction between the plate-like powder and the perovskite-forming raw material contained in the molded body obtained in the molding step, and
This is a step of removing excess components generated by the reaction.
When the molded body containing the plate-like powder and the perovskite-forming raw material is heated to a predetermined temperature, an isotropic perovskite-type compound and a surplus component are generated by these reactions, and at the same time, the generated isotropic perovskite-type compound Sintering proceeds.

The heating temperature is set so that the reaction and / or sintering proceeds efficiently and the generation of by-products other than the isotropic perovskite compound and bismuth oxide is suppressed.
The optimum temperature may be selected according to the plate-like powder to be used, the perovskite forming raw material, the composition of the crystallographically-oriented ceramic to be produced, and the like.

For example, in the case of manufacturing a crystallographically oriented ceramic comprising a single phase of barium titanate using bismuth titanate and barium carbonate, the heating temperature is 400 ° C. or higher.
300 ° C. or less is preferable, and 800 ° C. is more preferable.
Not less than 1250 ° C. In this case, the reaction may be performed in the atmosphere, in oxygen, under reduced pressure, or under vacuum. Further, as the heating time, an optimal time may be selected according to the heating temperature so that a predetermined reaction state and a sintered body density can be obtained.

The removal of the surplus components includes a method of removing thermally and a method of removing chemically. As a method of thermally removing, a method of heating a sintered body (hereinafter, referred to as an “intermediate sintered body”) in which an isotropic perovskite compound and an excess component are generated to a predetermined temperature to volatilize the excess component. It is.
Specifically, a method of heating the intermediate sintered body under reduced pressure or vacuum at a temperature at which excess components volatilize, and a method of heating the intermediate sintered body in air or oxygen at a temperature at which excess components volatilize. A suitable example is a method of heating for a time.

The heating temperature at the time of thermally removing the surplus component is set so that the volatilization of the surplus component proceeds efficiently and the generation of by-products is suppressed, so that the isotropic perovskite compound and the surplus component are removed. The optimum temperature may be selected according to the composition of the above. For example, when the isotropic perovskite compound is a barium titanate single phase and the surplus component is a bismuth oxide single phase, the heating temperature is preferably from 800 ° C. to 1300 ° C., more preferably from 1000 ° C. to 12 ° C.
50 ° C. or less.

The method of chemically removing the surplus components is a method of immersing the intermediate sintered body in a treatment liquid having a property of eroding only the surplus components and extracting the surplus components. As the treatment liquid to be used, an optimal treatment liquid may be selected according to the composition of the isotropic perovskite compound and the excess components. For example, when the isotropic perovskite compound is a barium titanate single phase and the excess component is a bismuth oxide single phase,
It is preferable to use an acid such as nitric acid or hydrochloric acid as the treatment liquid. In particular, nitric acid is suitable as a processing solution for chemically extracting excess components. In this case, if the heat treatment and the acid treatment are alternately repeated, the surplus components can be more effectively removed.

The reaction between the plate-like powder and the perovskite-forming raw material and the removal of excess components may be performed simultaneously, sequentially or individually. For example, under reduced pressure or vacuum, the compact is directly heated to a temperature at which both the reaction between the plate-like powder and the perovskite-forming raw material and the volatilization of the surplus components proceed efficiently, and the surplus components are removed simultaneously with the reaction. Is also good.

Further, for example, the compact is heated at a temperature at which the reaction between the plate-like powder and the perovskite-forming raw material proceeds efficiently in the atmosphere or oxygen to produce an intermediate sintered body (reaction step). Subsequently, the intermediate sintered body may be heated under a reduced pressure or a vacuum at a temperature at which excess component volatilization proceeds efficiently to remove the excess component (removal step). Alternatively, after producing the intermediate sintered body (reaction step), the intermediate sintered body is continuously
The excess component may be heated at a temperature at which the excess component volatilizes efficiently for a long time to remove the excess component (removal step).

Further, for example, after forming an intermediate sintered body and cooling the intermediate sintered body to room temperature (reaction step), the intermediate sintered body is immersed in a treatment solution to chemically remove excess components ( (Removal step). Alternatively, an intermediate sintered body is generated,
After cooling to room temperature (reaction step), the intermediate sintered body may be heated again to a predetermined temperature under a predetermined atmosphere to thermally remove excess components (removal step).

In the case of a molded body containing a binder, a heat treatment mainly for degreasing may be performed before the reaction / removal step. In this case, the degreasing temperature may be at least a temperature sufficient to thermally decompose the binder.

Further, when the oriented compact is degreased, the degree of orientation of the plate-like powder in the oriented compact may be reduced, or the oriented compact may be swollen. In such a case, it is preferable to further perform hydrostatic pressure (CIP) treatment on the oriented molded body after performing degreasing and before performing reaction and removal. If the degreased molded body is further subjected to hydrostatic pressure treatment, there is an advantage that a decrease in the degree of orientation due to degreasing or a decrease in the density of the sintered body due to swelling of the oriented molded body can be suppressed.

Further, after removing excess components from the intermediate sintered body, CIP treatment may be performed and the resultant may be refired. In order to increase the density, a method of further performing hot pressing on the sintered body after the heat treatment is also effective. Further, a method of adding compound fine powder, a method of CIP treatment, a method of hot pressing or the like may be used in combination. As for hot press, 20M only by pressure from top and bottom without using die
A method of applying a relatively small load of Pa or less is effective for increasing the density of the sintered body without lowering the degree of orientation.

When the crystallographically-oriented ceramic obtained by the manufacturing method according to the present invention is used, for example, as a piezoelectric composite, the crystallographically-oriented ceramic does not necessarily have to have a high density. Therefore, in such a case, compound fine powder is added to the raw material, or CIP
Mixing, molding, reaction / removal may be performed without performing treatment or the like, and the product obtained through these steps may be used as it is.

Next, the operation of the manufacturing method according to the present invention will be described. When the plate-like powder and the perovskite-forming raw material are mixed and molded using a molding method in which a force acts on the plate-like powder from one direction, the plate-like powder is formed by the shear stress acting on the plate-like powder. Orients throughout the body. When such a molded body is heated at a predetermined temperature, the plate-like powder and the perovskite-forming raw material react with each other to generate an isotropic perovskite-type compound and an excess component.

At this time, since there is lattice matching between the developed surface of the plate-like powder and the pseudo-cubic {100} plane of the isotropic perovskite-type compound, the developed surface of the plate-like powder is Cubic {100} plane of a perovskite compound. Therefore, the pseudo cubic 1
Plate crystals of an isotropic perovskite-type compound are formed in a state where the 00 ° plane is oriented in one direction.

The surplus component produced by the reaction has bismuth oxide as a main component, which has a low melting point and is easily extracted chemically. Therefore, at the same time as or after the reaction between the plate-like powder and the perovskite-forming raw material, excess components can be easily removed thermally or chemically from the intermediate sintered body.

The conventional method of producing only an isotropic perovskite compound using a plate-like powder composed of a layered perovskite-type compound as a reactive template is based on all the A-site elements contained in the plate-like powder and other raw materials. Only crystal-oriented ceramics made of an isotropic perovskite compound containing a B-site element can be manufactured.

On the other hand, the material of the plate-like powder must have a large crystal lattice anisotropy and have lattice matching with an isotropic perovskite compound. Depending on the composition of the isotropic perovskite-type compound described above, there may be no material that satisfies such conditions, or the search for such a material may be extremely difficult. Therefore, in the conventional method, there is a limit in controlling the composition of the obtained crystallographically-oriented ceramic, particularly in controlling the composition of the A-site element.

On the other hand, in the production method according to the present invention, since the bismuth layered titanate compound is used as the plate-like powder, the development surface is as good as the pseudocubic {100} plane of the isotropic perovskite compound. A plate-like powder having lattice matching can be easily obtained. Moreover, by reacting with a perovskite producing raw material having a predetermined composition,
Bi contained in the plate-like powder can be easily removed out of the system as a surplus component. Therefore, according to the manufacturing method according to the present embodiment, even a crystal-oriented ceramic made of an isotropic perovskite-type compound in which Bi does not remain as an A-site element can be easily manufactured.

[0067]

EXAMPLES (Example 1) First, Bi ₂ O ₃ and TiO ₂ were mixed at a molar ratio of 2: 3. Then, a NaCl + KCl mixed flux having the same weight as the mixture (mixing molar ratio of NaCl and KCl = 1: 1) was added to the mixture.
1) was added and further mixed. The resulting mixture was placed in a platinum crucible and heated at 1100 ° C. for 1 hour to obtain Bi ₄ Ti ₃
A plate-like single crystal powder (particle size: about 5 μm × thickness: about 0.5 μm) made of O ₁₂ was synthesized. After cooling the platinum crucible to room temperature, the lump in the platinum crucible was repeatedly water-bathed to remove chlorides, and Bi ₄ Ti ₃ O ₁₂ plate-like powder was obtained.

Next, the obtained Bi ₄ Ti ₃ O ₁₂ plate-like powder and BaCO ₃ were blended at a molar ratio of 1: 3, wet-mixed for a predetermined time, and then an organic binder and a plasticizer were added. And further mixed. Next, the obtained slurry was taken out and tape-formed using a doctor blade method. Further, the obtained tape was laminated and pressure-bonded, and further subjected to roll forming to produce a plane-oriented molded body having a thickness of about 1 mm. When X-ray diffraction was performed on the obtained plane-oriented molded product, B
It was confirmed that the pseudo-square {001} plane of the i ₄ Ti ₃ O ₁₂ plate-like powder was oriented parallel to the original tape surface.

Next, this plane-oriented molded body was placed in a vacuum heating furnace and heat-treated. The heat treatment is performed at 400 ° C. in the atmosphere.
After heating for 1 hour, the pressure in the furnace is continuously 133 Pa
The temperature was raised to 1200 ° C. while evacuation was performed as described below, and heating was performed at 1200 ° C. for 2 hours.

In the obtained crystal oriented ceramics,
X-ray diffraction was performed on a plane parallel to the original tape surface, and the identification of the crystal phase and the degree of orientation of the pseudo-cubic {100} plane were examined. FIG.
(A) shows an X-ray diffraction pattern. From FIG. 1 (a),
The crystallographically-oriented ceramic obtained in this example is composed of a single phase of BaTiO ₃ which is an isotropic perovskite compound, and has a remarkably high diffraction intensity between the (100) plane and the (200) plane in pseudo cubic representation. You can see that there is. Also,
When the components of this crystallographically-oriented ceramic were measured by ICP analysis, the Bi content was 0.2% by weight in terms of oxide.

(Example 2) Heat treatment was performed at 1000 ° C in air.
After heating for 1 hour, the pressure in the furnace is continuously 133 Pa
Except for elevating the temperature to 1200 ° C. while evacuating and heating at 1200 ° C. for 2 hours as described below, a crystal-oriented ceramic was prepared according to the same procedure as in Example 1, and the crystal phase was identified. And the degree of orientation of the pseudo-cubic {100} plane was evaluated. FIG. 1B shows an X-ray diffraction pattern. From FIG. 1 (b), even under the heat treatment conditions of this example, a crystallographically oriented ceramic consisting of BaTiO ₃ single phase and having extremely high diffraction intensity of (100) plane and (200) plane in pseudo cubic representation was obtained. It is understood that it is possible.

Example 3 The crystallographically-oriented ceramic obtained in Example 1 was further subjected to hot pressing to densify it. The hot pressing conditions are as follows: temperature: 135
0 ° C., heating time: 4 hours, pressure: 10 MPa. The relative density of the sintered compact after hot pressing was 99%.

Next, this sintered body was processed into a disk shape having a thickness of 0.5 mm and a diameter of 11 mm, and electrodes were provided on the upper and lower surfaces and polarized. Next, the electromechanical coupling coefficient Kp
Was measured, Kp = 0.38, which was about 20% higher than that of a non-oriented BaTiO ₃ sintered body having the same composition.

Comparative Example 1 A commercially available BaTiO ₃ powder was press-molded and hot-pressed under the conditions of a hot press temperature of 1350 ° C., a heating time of 4 hours and a pressure of 20 MPa to obtain a relative density of 99.5%. Was obtained. When the electromechanical coupling coefficient Kp of this non-oriented sintered body was measured under the same conditions as in Example 3, Kp =
0.32.

(Comparative Example 2) According to the same procedure as in Example 1, a plane-oriented molded product was produced. Next, after heating the obtained plane-oriented molded body at 400 ° C. for 1 hour in the air,
Heating was performed at 1300 ° C. for 4 hours in the atmospheric pressure. The obtained sintered body was subjected to X-ray diffraction under the same conditions as in Example 1. FIG. 1C shows an X-ray diffraction pattern.

In the obtained sintered body, as shown in FIG. 1 (c), in addition to BaTiO ₃ , by-products were generated.
A single-phase sintered body of TiO ₃ could not be obtained. By-products contained in the sintered body is considered to Bi-Ba-O-based composite oxide or the composite oxide and Bi ₂ O _3. Further, the obtained sintered body had low electric resistance and could not be polarized.

Although the embodiments of the present invention have been described in detail, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention. .

For example, in the above embodiment, an example in which the production method according to the present invention is applied to BaTiO ₃ has been mainly described. However, an isotropic perovskite compound containing an A site element other than Ba, and / or , Ti and B other than Ti
The present invention can be similarly applied to an isotropic perovskite compound containing both site elements.

Further, in the above-described embodiment, the hot pressing is performed after the heat treatment to densify the crystallographically oriented ceramics, but the HIP treatment may be performed after the heat treatment to densify the ceramic.

[0080]

The method for producing a crystallographically-oriented ceramic according to the present invention is characterized in that the plate-like powder oriented in the compact and the perovskite-forming raw material react with each other to produce an isotropic perovskite-type compound. Is inherited as the pseudo-cubic {100} plane of the isotropic perovskite-type compound, so that there is an effect that a crystallographically-oriented ceramic in which the pseudo-cubic {100} plane is oriented with a high degree of orientation can be obtained.

Further, since bismuth contained in the plate-like powder can be removed as an excess component when reacting with the perovskite-forming raw material, even if the isotropic perovskite-type compound in which Bi does not remain as an A-site element, In addition, there is an effect that a crystallographically-oriented ceramic having a high degree of orientation can be obtained.

[Brief description of the drawings]

1 (a) and 1 (b) are X-ray diffraction patterns of the crystallographically-oriented ceramics obtained in Example 1 and Example 2, respectively. FIG. 1 (c) is a comparative example. 2 is an X-ray diffraction pattern of the sintered body obtained in 2.

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Claims (3)

[Claims] 1. A bismuth layered titanate compound,
And a plate-like powder whose development surface has lattice matching with the pseudocubic {100} plane of the isotropic perovskite-type compound, and containing the isotropic perovskite-type compound and bismuth oxide by reacting with the plate-like powder. A mixing step of mixing a perovskite-forming raw material that generates an excess component; a molding step of molding the mixture obtained in the mixing step so that the plate-like powder is oriented; and a molding obtained in the molding step. A method for producing a crystallographically-oriented ceramic, comprising: a reaction between the contained plate-like powder and the perovskite-forming raw material contained therein; and a reaction / removal step of removing the surplus component generated by the reaction. 2. The reaction / removal step comprises heating the compact and reacting the plate-like powder with the perovskite-forming raw material, and simultaneously thermally removing the excess component generated by the reaction. The method for producing a crystallographically-oriented ceramic according to claim 1. 3. The reacting / removing step includes heating the molded body, reacting the plate-like powder with the perovskite forming raw material to form an intermediate sintered body, The method for producing a crystallographically-oriented ceramic according to claim 1, further comprising a removing step of thermally or chemically removing excess components.