JP2001106568A - CRYSTAL-GRAIN-ORIENTED CERAMICS, MANUFACTURING PROCESS OF THE SAME AND PRODUCTION PROCESS OF PLATELIKE Ba6Ti17O40 POWDER FOR MANUFACTURING THE SAME - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a crystal-grain-oriented ceramic product which has properties equivalent to those of a BT(barium titanate BaTiO3) single crystal polarized in the direction of <111> and is manufactured by a low-cost manufacturing process, to provide a manufacturing process of the grain-oriented ceramic product and also to provide a production process of a platelike Ba6Ti17O40 powder for manufacturing the grain-oriented ceramic product. SOLUTION: This crystal-grain-oriented ceramic product consists of a polycrystal of a perovskite compound containing at least Ba and Ti, wherein each of the constituent crystal grains of the polycrystal has an oriented pseudocubic 111} plane. This manufacturing process of the grain-oriented ceramic product comprises: mixing a platelike Ba6Ti17O40 powder with a perovskite forming raw material capable of reacting with the platelike Ba6Ti17O40 powder to form a perovskite compound, to obtain a mixture; forming the mixture into a green body so as to orient the platelike Ba6Ti17O40 powder; and heating the green body. The production (synthesis) process of the platelike Ba6Ti17O40 powder comprises a step of heating a raw material capable of forming an oxide containing Ba and Ti in a ratio of Ba to Ti of 6:17, together with a substance which is a liquid or capable of being converted into a liquid when heated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention is, grain oriented ceramics, relates to a manufacturing method and a manufacturing method of the grain oriented ceramics for producing plate-like Ba ₆ Ti ₁₇ O ₄₀ powder of the crystal oriented ceramic, and more particularly, bimorph piezoelectric elements, vibration Crystal oriented ceramics suitable as a piezoelectric material used for a pickup, a piezoelectric microphone, a piezoelectric ignition element, an acceleration sensor, a knocking sensor, a piezoelectric actuator, a sonar, an ultrasonic sensor, a piezoelectric buzzer, a piezoelectric speaker, a transmitter, a filter, and the like, and a method of manufacturing the same. And a method for producing plate-shaped Ba ₆ Ti ₁₇ O ₄₀ powder for producing crystallographically oriented ceramics.

[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 obtained by applying a direct current to a ferroelectric ceramic and subjecting it to a so-called polarization process in which the direction of the domain of the ferroelectric is aligned in a fixed direction. In order to align spontaneous polarization in a certain direction by polarization processing,
Since a perovskite-type crystal structure in which spontaneous polarization can be three-dimensionally is advantageous, most of practically used piezoelectric ceramics are perovskite-type ferroelectric ceramics.

The perovskite ferroelectric ceramics include, for example, Pb (Zr.Ti) O ₃ (hereinafter referred to as “PZT”), and PZT3 obtained by adding a lead-based composite perovskite to PZT as a third component. Ingredient system,
BaTiO ₃ (hereinafter referred to as “BT”), Bi
_0.5 Na _0.5 TiO ₃ (hereinafter referred to as “BNT”) and the like are known.

It is known that the piezoelectric properties of perovskite-type compounds differ depending on the direction of the crystal axis.
For example, Proceedings of the 16th Ferroelectric Application Conference P25-26
(Wada et al.) State that a BT single crystal polarized in the <001> direction, which is a spontaneous polarization direction, shows nearly 1% strain at room temperature, but at the same time has large hysteresis.
It has been reported that a BT single crystal polarized in the> direction can obtain high characteristics such as a small hysteresis in the electric field-strain behavior and a large piezoelectric constant under a low electric field.

Japanese Patent Publication No. 63-24950 discloses an anatase type titanium dioxide acicular particle powder which is elongated in the a-axis direction or a hydrous titanium dioxide acicular particle powder which becomes the anatase acicular particle powder by heating. By using a mixture of barium oxide or a barium compound that becomes barium oxide by heating, a molded body in which the directions of elongation of the acicular particles are oriented in substantially the same direction is produced, and by sintering the molded body, a B whose axes are oriented in substantially the same direction
It discloses that a T sintered body can be obtained. Further, it is disclosed that when the obtained sintered body is polarized in the orientation direction, the electromechanical coupling coefficient in the orientation direction becomes significantly larger than that of a non-oriented BT sintered body.

[0007]

The lead-based piezoelectric ceramics represented by PZT have higher piezoelectric properties than other piezoelectric ceramics, and most of the piezoelectric ceramics currently in practical use are used. is occupying. 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.

Further, BT ceramics have relatively high piezoelectric properties among lead-free piezoelectric materials, and are used for sonar and the like. Further, among solid solutions of BT and other lead-free perovskite compounds (eg, BNT), those exhibiting relatively high piezoelectric properties are known. However, these lead-free piezoelectric ceramics
Compared with PZT, piezoelectric characteristics are lower and higher characteristics are desired.

On the other hand, a BT single crystal polarized in the <111> direction exhibits a low hysteresis and a high piezoelectric constant that cannot be obtained with a non-oriented BT polycrystal. However, single crystals are expensive. In addition, the production of a single crystal of a solid solution tends to cause a composition shift, and is not suitable as a practical material. Furthermore, single crystals are inferior in fracture toughness, so it is difficult to use them under high stress, and there is a problem that the range of application is limited.

[0010] On the other hand, if the crystal grains constituting the sintered body can be oriented in a certain direction, the anisotropy of the piezoelectric characteristics can be utilized to the utmost, so that the characteristics of the piezoelectric ceramic can be improved. Can be expected. However, Japanese Patent Publication No. 63-
The sintered body obtained by the method disclosed in Japanese Patent No. 24950 has a {100} plane uniaxially oriented in pseudo cubic display. A sintered body having such an orientation has a large hysteresis in the electric field-strain behavior because the domain is easily moved, and is unsuitable for an actuator for performing accurate positioning. In addition, there is a problem that energy loss increases due to hysteresis, and self-heating easily occurs.

An object of the present invention is to provide a crystallographically-oriented ceramic having the same characteristics as a BT single crystal polarized in the <111> direction by an inexpensive production process, a method for producing the same, and such a crystallographic orientation. An object of the present invention is to provide a method for producing plate-like Ba ₆ Ti ₁₇ O ₄₀ powder used for producing ceramics.

[0012]

Means for Solving the Problems In order to solve the above problems, the crystal oriented ceramics according to the present invention comprises at least B
a polycube of a perovskite-type compound containing a and Ti, and the pseudocubic {11} of each crystal grain constituting the polycrystal
The gist is that the 1｝ plane is oriented.

In the crystal oriented ceramics according to the present invention having the above structure, the pseudo cubic {111} plane of each crystal constituting the polycrystal of the perovskite type compound is oriented, and is polarized in the <111> direction. Then, similarly to the BT single crystal polarized in the <111> direction, domain inversion is suppressed when an electric field is applied in the positive direction. Therefore, compared to a non-oriented perovskite-type polycrystal, the hysteresis is small under a low electric field, and the piezoelectric constant is large.

Further, according to the method for producing a crystallographically-oriented ceramic according to the present invention, there is provided a plate-like powder whose developed surface has lattice matching with a pseudocubic {111} plane of a perovskite-type compound;
A mixing step of mixing a perovskite-forming raw material that reacts with the plate-like powder to become a perovskite-type compound; a molding step of forming the mixture obtained in the mixing step so that the plate-like powder is oriented; And a sintering step of heating the compact obtained in the step.

In the method for producing a crystallographically-oriented ceramic according to the present invention having the above structure, a plate-like powder having a lattice matching between a developed surface and a pseudo-cubic {111} plane of perovskite is used as a starting material. Therefore, when the plate-like powder reacts with the perovskite-forming raw material, the perovskite compound is synthesized while maintaining the preferred orientation direction.
Therefore, a mixture of a plate-like powder and a perovskite-forming raw material is formed so that the developed surface of the plate-like powder is oriented, and heated at a predetermined temperature, to synthesize a perovskite crystal with a pseudo-cubic {111} plane developed and The sintering proceeds, and a crystallographically-oriented ceramic having a pseudo-cubic {111} plane can be easily obtained.

Further, the method for producing a plate-like Ba ₆ Ti ₁₇ O ₄₀ powder for producing a crystallographically oriented ceramic according to the present invention comprises:
The gist of the invention is to heat a raw material capable of producing an oxide in which Ba: Ti = 6: 17 together with a liquid or a substance which becomes liquid by heating.

Ba₆Ti₁₇O₄₀Is the {001} plane
Surface energy is lower than other surfaces.
are doing. Therefore, the oxidation of Ba: Ti = 6: 17
Of raw materials that can produce substances in liquid phase where atoms can be easily diffused
Then, the {001} plane with low surface energy is wide
Plate-shaped Ba with so-called "self-form" developed ₆
Ti₁₇O₄₀A powder can be obtained. Moreover, this
Plate-shaped Ba₆Ti₁₇O ₄₀$ 00 which is the development side of powder
The 1｝ plane is a pseudocubic {111} of a perovskite compound.
Since it has lattice matching with the surface, it is used as a starting material.
In this case, a crystallographic ceramic with a pseudo-cubic {111} plane
Can be easily manufactured.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail. The crystallographically-oriented ceramic according to the present invention is made of a polycrystalline perovskite-type compound containing at least Ba and Ti. The “perovskite compound containing at least Ba and Ti” specifically refers to BT and any binary or more binary perovskite compound having BT as an end component.
Can be represented by the following equation.

[0019]

Embedded image xBaTiO ₃ + (1-x) ABO ₃

In the formula 1, ABO ₃ may be any as long as it forms a perovskite compound by forming a solid solution with BT. The ABO _{3, specifically, BNT, Bi 0.5 K 0.5 TiO} 3, KN
_{bO 3, NaNbO 3, PbTiO 3} , PbZrO 3,
Pb (Mg _1/3 Nb _2/3 ) O ₃ is a preferred example. ABO ₃ may be a combination of two or more compounds selected from these compounds.

In the formula 1, the value of x representing the mole fraction of BT may be within the range of 0 <x ≦ 1. However, when a plate-like Ba ₆ Ti ₁₇ O ₄₀ powder described later is used as a template, the value of x is 0.025 ≦ x ≦ 1.
Is desirably within the range. This is because x <0.02
In the case of No. 5, plate-shaped B used as a template
This is because the amount of a ₆ Ti ₁₇ O ₄₀ powder decreases, and the degree of orientation of the obtained polycrystalline ceramic decreases.

Further, the grain oriented ceramics according to the present invention is characterized in that the pseudo cubic {111} plane of each crystal grain constituting the polycrystal is oriented in one direction. here,
“Pseudo cubic {HKL}” generally means that a perovskite-type compound has a structure distorted from a cubic crystal such as tetragonal, orthorhombic, or trigonal. Means to display the Miller index. The degree of orientation of each crystal grain is specifically expressed by a crystal orientation degree Q (HKL) by a Lotgering method represented by the following equation (1).

[0023]

(Equation 1)

However, in the equation (1), ΔI (hkl)
And Σ′I (HKL) are the sum of the X-ray diffraction intensities from all crystal planes (hkl) measured for the crystallographically-oriented ceramic and the crystallographically equivalent specific crystal plane (HKL), respectively. It is the sum of X-ray diffraction intensities. On the other hand, ΣI ₀ (hkl) and Σ′I ₀ (HKL) have the same composition as the crystallographically-oriented ceramic, respectively, and have X from all the crystal planes (hkl) measured for the non-oriented polycrystalline ceramic. The sum of the X-ray diffraction intensities and the sum of the X-ray diffraction intensities from a crystallographically equivalent specific crystal plane (HKL).

Therefore, the equation (1) indicates that when each crystal grain is non-oriented, the degree of crystal orientation Q (HKL) is 0%, and the {HKL} planes of all the crystal grains are oriented in one direction. If there is, it becomes 100%.

In the case of the crystallographically oriented ceramics according to the present invention, at least the pseudo cubic {111}
It is necessary that the crystal orientation degree Q (111) of the plane is not 0. In order to obtain a crystallographically-oriented ceramic having low hysteresis and high piezoelectric constant, the larger the degree of crystal orientation Q (111) of the pseudo-cubic {111} plane, the better.

Further, the density of polycrystalline ceramics generally affects mechanical properties such as strength and fracture toughness, and electrical properties such as dielectric constant and piezoelectric constant. These points are the same for the crystal oriented ceramics according to the present invention. As the relative density of the sintered body increases, better mechanical properties and piezoelectric properties can be obtained. Specifically, the relative density of the crystallographically-oriented ceramic is desirably 95% or more.

Next, the operation of the grain oriented ceramics according to the present invention will be described. The orientation dependence of the electric field-strain behavior of the BT single crystal is discussed in detail in the above-mentioned "16th Ferroelectric Application Conference Proceedings P25-26". According to this, when the BT single crystal is polarized in the <001> direction, rearrangement of the domain structure easily occurs due to the electric field applied in the positive direction, thereby causing large hysteresis in the electric field-strain behavior. For <111
When the polarization treatment is performed in the> direction, the movement of the domain wall is suppressed, whereby the electric strain is proportional to the applied electric field and shows no hysteresis under a low electric field.

Such a unique property obtained by subjecting a BT single crystal to a polarization treatment in the <111> direction is achieved by performing a polarization treatment in a direction in which a plurality of equivalent spontaneous polarization vectors are present, so that the BT single crystal can be engineered in the BT single crystal. It is believed that a unique domain structure called an ard-domain structure was introduced.

In the crystallographically-oriented ceramic according to the present invention, low hysteresis and high piezoelectric constant can be obtained by orienting the pseudo-cubic {111} plane of each crystal grain constituting the polycrystal in one direction. BT single crystal <11
It is considered that a domain structure almost the same as that in the case where the polarization treatment was performed in the 1> direction can be introduced into the polycrystalline ceramic, thereby suppressing the movement of the domain wall.

Next, the plate-like powder for producing a crystallographically-oriented ceramic according to the present invention will be described. In general, the perovskite-type compound has extremely small anisotropy of the crystal lattice, so that it is extremely difficult to produce a polycrystal in which a specific crystal plane is oriented in a specific direction by a normal sintering process.

According to the present invention, in order to solve this problem, a plate-like powder satisfying specific conditions is oriented in a molded body, and the plate-like powder is used as a template (reactive crystal template) to prepare a perovskite-type compound. It is characterized in that the synthesis and sintering are performed, whereby the pseudo cubic {111} plane of each crystal grain constituting the polycrystal is oriented in one direction.

In order to enable the production of the grain oriented ceramics according to the present invention, the plate-like powder must satisfy the following conditions. First, the plate-like powder must have a shape that can be easily oriented in one direction during molding. For that purpose, the average aspect ratio of the plate-like powder is desirably 3 or more. If the average aspect ratio is less than 3, it is difficult to orient the plate-like powder in one direction during molding, which is not preferable. The average aspect ratio of the plate-like powder is more preferably 5 or more.

Second, it is necessary that the developed surface (the surface occupying the largest area) of the plate-like powder has lattice matching with the pseudo-cubic {111} plane of the perovskite-type compound. Even in the case of a plate-like powder having a predetermined aspect ratio, if the developed surface does not have lattice matching with the pseudocubic {111} plane of the perovskite-type compound, the {111} plane is regarded as the oriented plane. It is not preferable because it does not function as a template for producing crystallographically-oriented ceramics.

Here, the lattice matching means the lattice size of the developed surface of the plate-like powder and the pseudocubic ｛11 of the perovskite type compound.
It refers to the value obtained by dividing the difference in the lattice size of the 1｝ plane by the lattice size of the developed plane of the plate-like powder. A smaller value of the lattice matching indicates that the plate-like powder functions as a good template. The value of lattice matching is preferably 20% or less, and more preferably 10% or less.

Strictly speaking, the lattice matching means strictly the lattice matching between the plate-like powder and the crystallographically-oriented ceramic to be produced, and the perovskite compound containing at least Ba and Ti has a composition There is a property that the lattice constant does not change so much even if is changed. Therefore,
When selecting the material of the plate-like powder, BT
The determination may be made from the viewpoint of whether or not there is lattice matching with the 1｝ plane.

Third, the plate-like powder must react with a perovskite-forming raw material described later and become a part of a perovskite-type compound having a composition represented by the above-mentioned formula (1). Therefore, the plate-like powder itself does not necessarily need to be a perovskite compound. The plate-like powder is selected from a compound or a solid solution containing at least one of the cation elements contained in the perovskite compound represented by the formula (1).

Fourth, in order to produce the grain oriented ceramics according to the present invention at low cost, a plate-like powder satisfying the above-mentioned conditions must also be able to be produced at low cost. For this purpose, the plate-like powder has a surface energy of a crystal plane having lattice matching with the pseudo-cubic {111} plane of the perovskite compound (hereinafter referred to as a “specific crystal plane”) that is a surface of another crystal plane. It is desirable to be made of a material having a crystal structure smaller than the energy. A material having such a crystal structure can easily synthesize a so-called "self-shaped" developed plate-like powder by synthesizing in a liquid phase in which atoms can be easily diffused, in which a specific crystal plane occupies a large area. That's why.

If the material satisfies the above conditions,
Each of them functions as a template for producing the crystallographically-oriented ceramic according to the present invention. Such materials satisfying various compounds, but a solid solution. Among _{these, Ba 6 Ti 1 7 O 40} ( hereinafter referred to as "B6T17".), The surface energy of the {001} plane Since it is small and has a very good lattice matching between the {001} plane of B6T17 and the pseudo-cubic {111} plane of the perovskite-type compound, if this is a plate-like powder, it functions as an extremely excellent template. I do.

A plate-like B6T1 suitable as a template
The 7 powder is a raw material capable of generating an oxide of Ba: Ti = 6: 17 (hereinafter referred to as “oxide generating raw material”).
Can be easily produced by heating together with a liquid or a substance which becomes liquid by heating.

The most effective method for synthesizing plate-like B6T17 is a method of heating an oxide-forming raw material together with a flux (flux method). The oxide generation raw material used for the synthesis is not particularly limited as long as it can generate an oxide in which Ba: Ti = 6: 17. Specifically, an oxide powder containing Ba and / or Ti, or a salt such as a carbonate or a nitrate may be mentioned as a preferred example.

As the flux, specifically,
NaCl, KCl, a mixture of NaCl and KCl, BaC
l ₂ , KF and the like are mentioned as preferable examples. However, when BaCO ₃ is used as one of the oxide generation raw materials, it is not preferable to use KCl as a flux because BaCl ₂ is generated and Ba in the raw material is consumed. Therefore, in this case, a flux other than KCl may be used. From the viewpoint of reactivity, the flux is NaCl
NaCl single phase is more desirable than a mixture of KCl and KCl.
BaCl ₂ is most preferable for producing high-purity B6T17 as a flux into which alkali impurities are not mixed.

[0043] For example, using a BT powder and a TiO ₂ powder as the oxide yielding feedstock, when using NaCl as a flux, a BT powder and TiO ₂ powder in a molar ratio of 6: 1
1 and mix with flux
What is necessary is just to heat at the temperature of 1300 degreeC. Thereby, the {001} plane having a low surface energy is preferentially developed, and a plate-like B6T17 powder having a large aspect ratio can be easily synthesized. NaCl which is a flux
Can be removed by washing with warm water. When BaCl ₂ is used as the flux, BT powder and T
The iO ₂ powder may be mixed at a molar ratio of 6:11, a flux may be added thereto, and the mixture may be heated at a temperature of 1000 ° C to 1400 ° C. When KF is used as the flux, the same conditions as those for BaCl ₂ may be used.

A plate-like B suitable as a template
Another effective method for synthesizing 6T17 powder is a method in which a non-plate-like B6T17 powder synthesized by a solid-phase reaction method is heated together with an alkaline aqueous solution in an autoclave (hydrothermal synthesis method). Even with such processing, {001}
A plate-like B6T17 powder with a developed surface can be easily synthesized.

Next, a method for producing a crystallographically-oriented ceramic according to the present invention will be described. The method for producing a crystallographically-oriented ceramic according to the present invention includes a mixing step, a forming step, and a sintering step.

The mixing step is a step of mixing the above-mentioned plate-like powder with the perovskite-forming raw material. The perovskite-forming raw material may be any as long as it reacts with the plate-like powder in the sintering step described below to become a perovskite-type compound.

Therefore, the composition of the perovskite-forming raw material is determined according to the composition of the plate-like powder to be used and the composition of the perovskite-type compound to be produced. Further, as the perovskite generation raw material, oxide powder, composite oxide powder (including perovskite compound powder), salts such as carbonate, nitrate, oxalate and acetate, sol solution, aqueous solution and the like can be used.

The mixing ratio between the plate-like powder and the perovskite-forming raw material can be arbitrarily determined according to the required characteristics of the crystallographically-oriented ceramic to be produced. However,
If the mixing ratio of the plate-like powder is too small, the degree of orientation of the obtained sintered body is undesirably reduced. In addition, the mixing of the plate-like powder and the perovskite-forming raw material may be performed in a dry manner, or may be performed in a wet manner by adding an appropriate solvent such as water or alcohol. At this time, a binder and / or a plasticizer may be added as needed.

The molding step is a step of molding the mixture obtained in the mixing step so that the plate-like powder is oriented. The molding method is not particularly limited as long as the developed surface of the plate-like powder can be oriented in one direction. Specifically, the doctor blade method, extrusion,
Pressing, rolling, and the like are preferred examples.

Further, in order to increase the thickness of the molded body in which the plate-like powder obtained by these methods is oriented (hereinafter, referred to as “oriented molded body”) or to increase the degree of orientation, the oriented molded body is formed. On the other hand, processing such as lamination pressure bonding, pressing, and rolling (hereinafter, referred to as “orientation processing”) may be performed. In this case, any one type of orientation treatment may be performed on the oriented molded body, or two or more types of orientation treatment may be performed. Further, one type of alignment treatment may be repeatedly performed on the oriented molded body a plurality of times, or two or more types of alignment treatment may be repeated a plurality of times.

The sintering step is a step of synthesizing a perovskite compound and sintering the generated perovskite compound by heating the oriented formed body obtained in the forming step. The optimum sintering temperature may be selected according to the composition of the crystallographically-oriented ceramic to be produced. For example, when the composition of the crystallographically-oriented ceramic is a BT single phase, it is desirable to perform sintering at a temperature of 1200 ° C. or higher.

The sintering may be performed in the air,
In order to obtain a high-density sintered body, it is desirable to perform sintering in an oxygen atmosphere. This is because, generally, when sintering progresses and isolated pores are formed inside the sintered body, sintering is hindered by the atmospheric gas remaining inside the pores, but when sintering in an oxygen atmosphere, This is because oxygen remaining in the pores is easily discharged to the outside through the grain boundaries and does not hinder sintering.

In the case of an oriented molded article containing a binder, a heat treatment mainly for degreasing may be performed before the sintering step. In this case, the heat treatment may be performed at least at a temperature sufficient to thermally decompose the binder.

When a heat treatment mainly for degreasing is performed, the degree of orientation of the plate-like powder in the oriented green body may decrease. In addition, when the perovskite compound is synthesized from the plate-like powder and the perovskite-forming raw material, the oriented molded body may swell. Such a decrease in the degree of orientation,
Or to suppress the decrease in density due to swelling of the oriented molded body, after performing a heat treatment mainly for degreasing,
It is desirable to further perform a hydrostatic pressure (CIP) treatment on the oriented molded body.

The optimum temperature of the heat treatment performed before the CIP treatment differs depending on the composition of the crystallographically-oriented ceramic.
In general, it is desirable that the temperature be higher than the temperature at which the synthesis reaction of the perovskite compound starts and lower than the temperature at which the densification greatly proceeds. For example, when the composition of the crystallographically-oriented ceramic is BT single phase, the temperature of the heat treatment is 800
C. to 1100.degree. C. is desirable.

Next, the operation of the method for producing a crystallographically-oriented ceramic according to the present invention will be described. In the production method according to the present invention, since the plate-like powder is used as a starting material, if the plate-like powder is molded using a molding method in which a force acts on the plate-like powder in one direction, the force acts in the direction in which the force acts. An oriented molded body in which the developed surface of the plate-like powder is oriented can be easily obtained. Further, when the obtained oriented molded article is further subjected to an orientation treatment, the degree of orientation of the plate-like powder in the oriented molded article can be further improved.

Further, since a plate-like powder whose developed surface has lattice matching with the pseudo-cubic {111} plane of perovskite is used, an oriented molded body containing the plate-like powder and a perovskite-forming raw material is suitably used. When heated at an appropriate temperature, the plate-like powder functions as a template, and synthesis and sintering of the perovskite compound proceeds while maintaining the preferred orientation direction of the plate-like powder. Therefore, it is possible to easily obtain a crystallographically-oriented ceramic having a high sintered body density and a high degree of orientation of the pseudo-cubic {111} plane.

[0058]

EXAMPLES Example 1 A plate-like B6T17 powder for producing a crystallographically-oriented ceramic was produced by a flux method.
That is, the BT powder and the TiO ₂ powder are mixed at a molar ratio of 6:11.
And mixed with a ball mill. Then, after mixing the same weight of NaCl as this mixture, put it in a platinum crucible, and at a temperature of 1000 ° C. to 1300 ° C. for 1 hour each.
Heated for hours. After cooling to room temperature, the lump was repeatedly washed with hot water to remove chlorides to obtain a synthetic powder.

Each of the synthetic powders was a plate-like powder having an aspect ratio of 3 or more. Particularly, the aspect ratio of the powder synthesized at 1100 ° C. or more was 5 or more. FIG. 1 shows an SEM photograph of the powder synthesized at 1150 ° C. FIGS. 1A and 1B are SEM photographs of three visual fields randomly selected for the same sample. FIG. 1 shows that a plate-like powder having a large aspect ratio was obtained.
Further, when X-ray diffraction was performed on the synthetic powder, each powder was almost single-phase B6T17.

(Example 2) NaCl was used as a flux.
A plate-like B6T17 powder was synthesized under the same conditions as in Example 1 except that a mixed flux of 1: 1 and KCl was used. Each of the obtained synthetic powders was a plate-like powder having an aspect ratio of 3 or more. When X-ray diffraction was performed on the synthetic powder, the synthetic powder showed B6T17
In addition, some by-products were contained.

Example 3 BaCl ₂ was used as a flux.
Plate-like B6 under the same conditions as in Example 1 except that
T17 powder was synthesized. Each of the obtained synthetic powders was a plate-like powder having an aspect ratio of 3 or more. Further, when X-ray diffraction was performed on the synthetic powder, each powder was almost single-phase B6T17.

Example 4 A plate-like B6T17 powder for producing a crystallographically-oriented ceramic was produced by a hydrothermal synthesis method.
That is, BaCO ₃ and TiO ₂ were mixed at a molar ratio of 6:17 and mixed with a ball mill. This is 1300 ° C
For 4 hours to obtain equiaxed B6T17 powder. This was placed in a decarbonated KOH aqueous solution, sealed in a Teflon-coated pressure vessel, and heated to 180 ° C. to obtain a plate-like B6T17 powder. The aspect ratio of the obtained plate-like powder was 5 or more.

(Example 5) The plate-like B obtained in Example 1
Crystal oriented ceramics were produced using 6T17 powder. That is, a plate-like B6T17 powder and a BaCO ₃ powder were mixed at a molar ratio of 1:11, and this was put into a ball mill together with ethanol and acetone, and wet-mixed with a ball mill. After a lapse of a predetermined time, a binder (polybutyl alcohol) and a plasticizer (dibutyl phthalate) were added and further wet-mixed with a ball mill. Using the obtained slurry, a tape was formed by a doctor blade device.

After laminating the dried tapes and pressing them at 80 ° C., they were rolled by a roll press machine to obtain oriented molded articles having a thickness of about 1 mm. After heat-treating the oriented molded body at 800 ° C. for 2 hours, it was subjected to a 300 MPa CIP treatment, and further heated in air at 1300 ° C. for 4 hours to obtain a crystal oriented ceramic.

When X-ray diffraction was performed on a plane parallel to the tape surface of the crystallographically-oriented ceramic, a diffraction pattern as shown in FIG. 2A was obtained. It is a single-phase BT, and it can be seen that the diffraction peak of the (111) plane is relatively higher than the diffraction pattern of the non-oriented BT ceramic shown in FIG. Lotger calculated from this pattern
The {111} orientation degree of ing was 0.39. The relative density of the obtained crystallographically-oriented ceramic is 86%.
Met.

(Example 6) The plate-like B6 obtained in Example 1
Same as Example 5 except that a mixture of T17 powder, BaCO ₃ powder, and commercially available BT powder (average particle size: 0.1 μm) at a molar ratio of 1:11:17 was used as a starting material. Under these conditions, a crystallographically-oriented ceramic was produced. However, the heat treatment performed before the CIP treatment is 1000
C. for 2 hours.

When X-ray diffraction was performed on a plane parallel to the tape surface of the crystallographically-oriented ceramic, a diffraction pattern as shown in FIG. 2B was obtained. It is a single-phase BT, and it can be seen that the diffraction peak of the (111) plane is relatively higher than the diffraction pattern of the non-oriented BT ceramic shown in FIG. Lot calculated from this pattern
The {111} orientation degree of Gering was 0.63. Further, the relative density of the obtained crystal oriented ceramics was 93%.

(Example 7) Plate B6 obtained in Example 1
T17 powder, BaCO ₃ powder and solid phase synthesized BNT
Powder (average particle size: 0.3 μm) in a molar ratio of 1:11:17
An oriented molded body having a thickness of about 1 mm was produced under the same conditions as in Example 5 except that the starting material was used as a starting material. After heat-treating this oriented molded body at 800 ° C. for 2 hours, it was subjected to a 300 MPa CIP treatment, and further heated in an oxygen atmosphere at 1200 ° C. for 10 hours to obtain a crystal oriented ceramic.

When X-ray diffraction was performed on a plane parallel to the tape surface of the crystallographically-oriented ceramic, the diffraction peak of the (111) plane was relatively higher than that of a non-oriented ceramic having the same composition of perovskite. Was high. The Lotgering {111} orientation degree calculated from this pattern was 0.57. Further, the relative density of the obtained crystal oriented ceramics was 98%.

(Example 8) The plate-like B6 obtained in Example 3
The same conditions as in Example 5 except that the starting material was a mixture of T17 powder, BaCO ₃ powder, and commercially available BT powder (average particle size: 0.1 μm) at a molar ratio of 1:11:34. Below, an oriented molded body having a thickness of about 1 mm was produced. After heat treating the oriented molded body at 900 ° C. for 2 hours,
CIP treatment of MPa is performed, and further performed in an oxygen atmosphere at 135.
Heating was performed at 0 ° C. for 10 hours to obtain a crystallographically-oriented ceramic.

When X-ray diffraction was performed on a plane parallel to the tape surface of the crystallographically-oriented ceramic, it was a single-phase BT.
The diffraction peak on the surface was relatively high. The Lotgering {111} orientation degree calculated from this pattern was 0.70. The relative density of the obtained crystallographically-oriented ceramic was 99%.

A disk-shaped sample was prepared from the plate-shaped sintered body so that the orientation plane was plane, and a silver electrode was provided on the plane, and polarization treatment was performed. Then, 5 × 10 ⁵ V / m in the positive direction
Was applied to measure the strain. The results are shown in FIG. The obtained crystallographically-oriented ceramic has d ₃₃ = 212.
pm / V, and no hysteresis was observed as shown in FIG.

(Comparative Example 1) A disc-shaped sample was prepared in the same manner from non-oriented BT ceramics, and a silver electrode was provided on a plane, and polarization treatment was performed. Next, an electric field of 5 × 10 ⁵ V / m was applied in the positive direction, and the strain was measured. The results are shown in FIG.
Non-oriented BT ceramics have d ₃₃ = 186 pm / V
And hysteresis was observed as shown in FIG.

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

For example, in the above-described embodiment, the normal pressure sintering method is used as the sintering method. However, after the normal pressure sintering, HIP processing may be performed to further densify the sintered body. Further, sintering may be performed by using a hot press method instead of the normal pressure sintering method. In particular, when the hot press method is used, the crystallographically oriented ceramics are further densified, and the {111}
The degree of orientation can be further improved.

In the above embodiment, tapes of the same composition produced by the doctor blade method are laminated to produce an oriented molded article. Tapes of different compositions are laminated to form an oriented molded article. May be sintered. In terms of production technology, the production of oriented molded products by extrusion molding is
More desirable due to low cost.

Further, in the above embodiment, an example was described in which the present invention was applied to a single solution of BT or a solid solution of BT and BNT. However, the present invention was similarly applied to a solid solution of BT and another perovskite compound. Can be applied, whereby the same effect as in the above embodiment can be obtained.

[0078]

The crystal oriented ceramics according to the present invention is
It is composed of a polycrystal of a perovskite-type compound containing at least Ba and Ti, and the pseudo-cubic {111} plane of each crystal grain constituting the polycrystal is oriented, so that domain inversion is suppressed. There is. This also has the effect of reducing the hysteresis under a low electric field and increasing the piezoelectric constant.

Further, according to the method for producing a crystallographically oriented ceramic according to the present invention, there is provided a plate-like powder whose developed surface has lattice matching with the pseudocubic {111} plane of the perovskite-type compound;
A mixing step of mixing a perovskite-forming raw material that reacts with the plate-like powder to become a perovskite-type compound; a molding step of forming the mixture obtained in the mixing step so that the plate-like powder is oriented; And a sintering step of heating the molded body obtained in the step, so that the plate-like powder oriented in the molded body functions as a template of the perovskite compound, and the pseudo-cubic {111} plane is oriented. There is an effect that crystal-oriented ceramics can be easily obtained.

Further, the method for producing a plate-like Ba ₆ Ti ₁₇ O ₄₀ powder for producing a crystallographically oriented ceramic according to the present invention is as follows.
Since a raw material capable of producing an oxide having Ba: Ti = 6: 17 is heated together with a liquid or a substance which becomes liquid by heating, {001} having lattice matching with the pseudocubic {111} plane of the perovskite compound. There is an effect that a plate-like powder having a developed surface can be easily obtained.

As described above, according to the present invention, a piezoelectric material having excellent piezoelectric characteristics under a low electric field can be obtained by an inexpensive manufacturing process. For example, a piezoelectric material such as a bimorph piezoelectric element, a vibration pickup, a piezoelectric microphone, When applied to various conversion elements such as piezoelectric actuators, the invention contributes to downsizing and high output of the conversion element, and is an invention that has an extremely large industrial effect.

[Brief description of the drawings]

FIG. 1 is a drawing substitute photograph (three visual fields for the same powder) of a plate-like B6T17 powder synthesized at 1150 ° C.

FIGS. 2 (a) and 2 (b) show X of the crystallographically-oriented ceramic obtained in Example 5 and Example 6, respectively.
FIG. 2C shows the X-ray diffraction pattern of the non-oriented BT.
It is a line diffraction pattern.

FIG. 3A is a view showing an electric field-strain behavior of the crystallographically-oriented ceramic obtained in Example 8, and FIG.
(B) is a diagram showing the electric field-strain behavior of the non-oriented BT obtained in Comparative Example 1.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshio Kimura 2-1-20 Shimoda-cho, Kohoku-ku, Yokohama-shi, Kanagawa F-term (reference) 4G031 AA06 AA11 BA10 CA01 CA02 CA04 GA07 4G077 AA07 AB02 BB04 BB10 BC42 CC02 EC04 FE11 GA03 GA06 HA11

Claims (3)

[Claims] 1. A crystal comprising a polycrystal of a perovskite-type compound containing at least Ba and Ti, wherein the pseudo-cubic {111} plane of each crystal grain constituting the polycrystal is oriented. Oriented ceramics. 2. A plate-like powder having a lattice matching with a pseudocubic {111} plane of a perovskite compound,
A mixing step of mixing a perovskite-forming raw material that reacts with the plate-like powder to become a perovskite-type compound; a molding step of forming the mixture obtained in the mixing step so that the plate-like powder is oriented; And a sintering step of heating the compact obtained in the step. 3. A plate-shaped Ba ₆ Ti ₁₇ for producing crystallographically-oriented ceramics, wherein a raw material capable of producing an oxide of Ba: Ti = 6: 17 is heated together with a liquid or a substance which becomes liquid by heating. Method for producing O ₄₀ powder.