JPH1192144A - Platy ceramic particles - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain platy ceramic particles having a perovskite structure and/or an RP type perovskite structure and capable of easily producing crystal oriented ceramics. SOLUTION: The platy ceramic particles are made of calcium titanate having a Ruddlesden-Popper type laminar perovskite structure and/or its solid soln. Each of the particles has an extended part in a direction parallel to perovskite structure layers (c-axis) and the aspect ratio (β/α) of the max. length β of the extended part to the thickness α of each of the platy particles is >=10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a Rudolsden-Popper type (R
The present invention relates to plate-like ceramic particles containing particles of calcium titanate having a layered perovskite structure and / or a solid solution thereof.

[0002]

2. Description of the Related Art Particles having shape anisotropy such as plate-like particles can be oriented by orientation molding such as tape molding and extrusion molding. By using the particles as at least a part of the raw material, an oriented molded article in which the particles are oriented can be produced. By reacting and sintering the oriented compact, the particles can be used as a template for the crystal orientation. Thereby, the crystal orientation of the bulk ceramics can be realized.

[0003] Rudolsden-Popper type (Ruddle
sden-Popper type (hereinafter abbreviated as RP type) Calcium titanate having a layered perovskite structure and / or a solid solution thereof has a crystal structure capable of producing plate-like particles.

[0004] If plate-like ceramic particles made of calcium titanate and / or a solid solution thereof can be produced, the use of these particles will make it possible to obtain R containing Ca and Ti.
Crystal orientation of bulk ceramics having a P-type layered perovskite structure or a perovskite structure can be achieved. The function of the bulk ceramic can be expected to be improved by this crystal orientation.

[0005]

However, heretofore, only the following non-oriented bulk ceramics or nearly spherical particles could be produced from the above calcium titanate and / or its solid solution.

Conventionally, calcium titanate and / or its solid solution has been used as an oxygen sensor (Japanese Patent Laid-Open No.
No. 155945, etc.) and dielectric materials (JP-A-6-187)
No. 825, etc.) and non-oriented bulk sintered bodies for the purpose of use, and powders (MME for crystal structure analysis).
lecombe, et. al. , Acta Crys
t. , B47, 305-314 (1994); So
lid State Chem. 101, 77-86
(1992)).

[0007] In these conventional techniques, bulk sintered bodies and powders are produced by using a usual solid phase method. For this reason, oriented bulk ceramics and particles having shape anisotropy could not be obtained.

[0008] Here, the ordinary solid phase method is a synthesis method in which mixed raw material powders (eg, oxides, carbonates, etc.) or their compacts are heated and reacted, that is, a synthesis method mainly comprising a solid phase reaction. It is.

The above solid phase reaction (ie, the reaction of the raw material powder proceeds by diffusion between solids without passing through a liquid phase or the like)
In the case of, the diffusion and reaction of the raw material particles from the contact point are mainly involved, the product is unlikely to have a shape derived from its crystal structure, and particles having a nearly spherical and isotropic shape are synthesized. .

[0010] Therefore, it is extremely difficult to obtain the crystal orientation of bulk ceramics by using the conventional particles made of calcium titanate or the like, which are extremely difficult to be oriented by orientation molding.

The present invention has been made in view of the above problems, and provides a plate-like ceramic particle from which crystal-oriented ceramics having a perovskite structure and / or an RP-type perovskite structure can be easily produced.

[0012]

A first aspect of the present invention is directed to Rudolsden.
Popper type (Ruddlesden-Popper type)
Plate-like ceramic particles made of calcium titanate having a layered perovskite structure and / or a solid solution thereof, wherein the particles are plate-like particles having a portion extending in a direction parallel to the perovskite structure layer (c-axis), and An aspect ratio (β / α) between the thickness (α) of the plate-like particles and the maximum length (β) of the spread portion is 10 or more.

Next, the RP type layered perovskite structure will be described. The crystal lattice of the above structure is represented by the general formula AX
(ABX ₃ ) _n . Where A and B are cations composed of one or more elements, X
Is an oxygen ion. As shown in FIG. 1B, the crystal lattice is a layer having a perovskite structure (ABX ₃ ).
_n and a layer (AX) having a rock salt structure alternately overlap in the c-axis direction. The perovskite structure is a structure in which A forms a simple cubic lattice, and B exists at the body center position and X exists at the face center position, as shown in FIG.

Further, the aspect ratio of the plate-like ceramic particles of the present invention is 10 or more. By molding a powder composed of such particles by an orientation molding method described below, an oriented molded article in which the plate-like particles are oriented can be obtained.
When the aspect ratio is 20 or more, a higher degree of particle orientation can be realized, which is more preferable.

Further, the plate-like ceramic particles according to the present invention comprise one or both of calcium titanate and a solid solution thereof. Examples of the compound composed of calcium titanate having the RP layered perovskite structure and / or a solid solution thereof include Ca ₃ Ti ₂ O ₇ and Ca ₄ T
i ₃ O ₁₀ , (Ca, Sr) ₃ Ti ₂ O ₇ , (Ca, S
r) ₄ Ti ₃ O ₁₀ , Ca ₃ (Ti, Sn) ₂ O ₇ , Ca
₄ (Ti, Sn) ₃ O ₁₀ , Ca ₄ (Ti, Sn) ₃ O ₁₀
And the like.

The operation of the present invention will be described below. The RP-type layered perovskite structure is a tetragonal crystal or a slightly distorted tetragonal crystal, and the latter will be discussed below as a pseudo-tetragonal crystal. The RP type layered perovskite structure is shown in FIG.
As shown in FIG. 1A, the perovskite structure layer and the rock salt structure layer overlap each other in the c-axis direction as shown in FIG. 1B. The plate-like ceramic particles according to the present invention are plate-like particles having a portion spread by a perovskite structure layer on a c-plane separated by two a-axes, as shown in FIG. 1 (c).

In general, a compound having a perovskite structure reflects piezoelectricity, dielectricity, microwave dielectricity, ferroelectricity, antiferroelectricity, magnetism, thermoelectricity, reflecting its crystal symmetry and crystal structure. It exhibits properties such as conductivity, electron conductivity, and ion conductivity. These properties are often anisotropic with respect to the crystal orientation.

Therefore, in a general polycrystalline bulk ceramic which is made of a compound having a perovskite structure but has no crystal orientation, the above-mentioned properties are different from those of a single crystal because the orientation of the crystal constituting the ceramic is random. It is significantly smaller than the state. If the crystallographically-oriented bulk ceramics have the same crystal orientation, the above-mentioned characteristics are closer to the state of a single crystal, the above-mentioned characteristics are enhanced, and an excellent device utilizing these characteristics can be manufactured.

In producing such a crystallographically-oriented bulk ceramic having a perovskite structure, the production method described below is used, and by using the plate-like ceramic particles according to the present invention as at least a part of the raw material, the crystallographic orientation is obtained. The obtained bulk ceramics can be obtained.

Here, a method for producing a perovskite-type crystal-oriented bulk ceramic using the plate-like ceramic particles of the present invention will be described. The plate-like ceramic particles according to the present invention have plate-like anisotropy in shape and an aspect ratio of 10 or more. Therefore, by subjecting the plate-shaped ceramic particles to orientation molding, the orientation of each particle can be easily made uniform. Examples of the orientation molding include extrusion molding, centrifugal molding, doctor blade, anisotropic pressing, and rolling.

Therefore, when producing the bulk ceramics having the perovskite structure, the plate-like ceramic particles according to the present invention are used at least as a part of the raw material (the remaining part of the raw material is finally formed of the ceramic having the perovskite structure). The heating and the reaction are performed in a state where the orientation of the plate-like ceramic particles is aligned by orientation molding.

Then, in the above-mentioned heating and reaction, the ceramic having the perovskite structure is formed using the orientation surface of the plate-like ceramic particles according to the present invention as a template. Thereby, the crystal orientation of the ceramic having the perovskite structure can be easily obtained.

As the crystallographically-oriented bulk ceramic obtained by the above method, a single-phase ceramic having a perovskite structure, and a composite ceramic comprising a portion having a perovskite structure and a portion having an RP layered perovskite structure can also be obtained. Of course, R
A single-phase crystal-oriented bulk ceramics having a P-type layered perovskite structure can also be obtained.

As described above, when the plate-like ceramic particles of the present invention are used, the perovskite structure and / or the RP
Crystal oriented bulk ceramics having a type layered perovskite structure can be easily produced.

Next, a method for producing the plate-shaped ceramic particles according to the present invention will be described. In order to obtain plate-like particles comprising the calcium titanate and / or a solid solution thereof of the present invention, it is preferable to use a melt method. As will be described in detail below, the melt method is a method in which a raw material powder is heated in a melt to produce a desired product. As described later, the heating is preferably performed at a temperature of 1300 ° C. or higher.

As the raw material powder, substances such as oxides, carbonates, nitrates, hydroxides and fluorides containing calcium titanate and / or a metal element constituting a solid solution thereof can be used. Further, in order to facilitate melting of the melt, the shape is preferably granular or powdery. For example, in order to produce a powder composed of particles of calcium titanate (Ca ₃ Ti ₂ O ₇ ), as shown in an embodiment described later, CaCO ₃
Alternatively, powders of Ca (OH) ₂ and TiO ₂ can be used.

Next, a method for heating the raw material powder in the melt will be described. This heating can be constituted by the following steps, for example. First, a compound (hereinafter, referred to as a flux) constituting a melt by melting is mixed with a raw material powder. The resulting mixture is heated to form a melt. Further, heating is continued thereafter, and the raw material powder is reacted in the melt to precipitate and grow plate-like ceramic particles. Finally, the flux is separated from the powder composed of the precipitated plate-like ceramic particles.

Next, the above flux will be described. If a solid phase reaction occurs between the raw material powders before the melt is formed, ceramic particles having a low aspect ratio will be generated. Therefore, it is preferable to use a substance having a low melting point as the flux. In addition, the melting point of the above flux is particularly 10
The temperature is preferably not higher than 00 ° C. This is because there are substances in the calcium titanate and / or solid solution thereof that initiate a solid-phase reaction at a temperature of about 1000 ° C.

It is preferable that the flux has a high solubility of the raw material powder in the melt. This facilitates the reaction, precipitation, and grain growth of the raw material powder through the liquid phase, and facilitates the synthesis of plate-like ceramic particles.

Preferably, the flux is a substance which does not react with the raw material powder and is easily separated from the raw material powder and the powder comprising the plate-like ceramic particles obtained therefrom. This makes it possible to obtain a target compound containing no component of the flux.

It is particularly preferable that the flux is a water-soluble substance. As a result, water can be used to separate the flux from the precipitated plate-like ceramic particles, so that the separation operation can be easily performed.
As a flux that satisfies the above conditions, for example,
Examples thereof include halides, carbonates, sulfates, and low melting point oxides. In addition, as the above flux, halides and sulfates are particularly difficult to react with the raw material powder.
Even more preferred.

The smaller the weight ratio of (raw material powder) / (flux), the better. Thereby, the raw material powder can be completely dissolved in the melt. Further, the weight ratio of (raw material powder) / (flux) is more preferably 2 or less. Thereby, the raw material powder can be sufficiently dissolved in the melt, and the reaction can be made more uniform.

Next, the heating of the raw material powder in the melt will be described. The heating includes three steps: a temperature raising step, a maximum temperature holding step, and a temperature lowering step. It is preferable that the temperature raising step is performed at a temperature raising rate of 1,000 ° C./hour or less. Thereby, the flux and the raw material powder can be uniformly dissolved. Further, the temperature may be maintained at a temperature equal to or higher than the melting point of the flux for 30 minutes or more during the temperature raising step. Also,
The maximum temperature holding step is a holding temperature of 1300 to 1600 ° C.
It is preferable to perform the process for 30 minutes or more. Thereby, the plate-like particles according to the present invention can be reliably synthesized.

When the holding temperature is lower than 1300 ° C., plate-like particles are not synthesized, and particles having an isotropic perovskite structure are synthesized (see Comparative Sample C1 described later). On the other hand, when the holding temperature is higher than 1600 ° C., a reaction occurs between the flux and the raw material powder and a heating vessel for heating them, and a furnace contamination and a composition fluctuation due to volatilization of the flux or the raw material powder occur. There is fear. If the duration is shorter than 30 minutes, the raw material powder may not react sufficiently, and the raw material powder may partially remain, resulting in the formation of powder having a non-uniform composition.

Further, in the cooling step, the cooling rate is 500 ° C.
/ Hr or less. Thereby, precipitation and grain growth of the plate-like ceramic particles can be sufficiently performed, and a powder composed of particles having a large particle size and a uniform size can be obtained. If the cooling rate is higher than 500 ° C./hour, the particle size of the plate-like ceramic particles may be too small. Further, the reaction of the raw material powder may be insufficient.

It is particularly preferable that the temperature drop rate is 300 ° C./hour or less. Thereby, the particle size of the plate-like ceramic particles can be increased. Further, the pattern of the temperature change in the temperature lowering step may be stepwise or wavy. Thereby, the reaction and the grain growth of the raw material powder can be promoted.

The atmosphere for the heating is preferably an oxidizing atmosphere such as air or oxygen. After each of the heating steps described above is completed, the plate-like ceramic precipitates in the melt (flux), and both are mixed.

Next, a method for separating plate-like ceramic particles in a mixed state with the melt will be described. When the flux is a water-soluble substance, the flux can be removed by washing with ion-exchanged water or pure water. Actually, the above-mentioned washing can be carried out by putting both in a mixed state into ion-exchanged water or pure water, stirring the mixture, and filtering or centrifuging the mixture. Note that these steps are preferably repeated until the flux becomes sufficiently low.

On the other hand, when the flux is easily dissolved in an acid or alkali solution, an acid or alkali solution can be used instead of the ion-exchanged water or pure water. However, in this case, it is necessary to subsequently wash the acid or alkali solution with ion-exchanged water or pure water.

The powder obtained by the above operation has a mica-like luster and is mainly composed of plate-like ceramic particles having an RP-type perovskite structure according to the present invention. However, some impurities such as fine particles having a perovskite structure or carbonate used as a raw material powder may be mixed. In this case, in order to take out only the plate-like ceramic particles according to the present invention, the obtained powder may be subjected to a treatment such as water separation or empty separation.

The RP-type layered perovskite structure has a structure in which a perovskite structure layer and a rock salt structure layer as shown in FIG. 1A overlap in the c-axis direction as shown in FIG. 1B. ing. The rock salt structure layer does not contain B, and thus does not contain the BX bond which is a strong bond forming the skeleton of the perovskite structure layer. Therefore, the rock salt structure layer has a crystal formed by a weaker bond than the perovskite structure layer including the BX bond.

In this production method, the raw material powder is heated in a melt or a solution. For this reason, the diffusion and precipitation of the raw material powder are performed through the liquid phase. Therefore, crystal growth occurs preferentially in the direction of strong bonding, and the crystal grows in a shape reflecting the strength of bonding in the crystal.

Therefore, in the above-described manufacturing method, the crystal grows preferentially in the a-axis direction, and as shown in FIG. 1C, is composed of plate-like particles in which the c-plane, which is the perovskite structure layer, is expanded. A powder can be obtained. Thereby, the c-axis oriented crystallographically-oriented ceramics can be easily obtained by subjecting the plate-like ceramic particles to orientation molding.

Next, the reason why the heat treatment is preferably performed at 1300 ° C. or higher will be described. In the heating step, the formation of the particles composed of calcium titanate having an RP-type layered perovskite structure and / or a solid solution thereof from the raw material is performed by using Ca having a perovskite structure which is a low-temperature stable phase.
It is thought to proceed via the formation of TiO _3.

This CaTiO ₃ has a phase transition point from orthorhombic to cubic at around 1260 ° C., becomes orthorhombic below 1260 ° C. and cubic above 1260 ° C. The lower limit of the heat treatment temperature, 1300 ° C., is due to this phase transition point, and more precisely, the above phase transition temperature is the lower limit of this heat treatment temperature.

The reason why particles of calcium titanate having a RP-type layered perovskite structure and / or a solid solution thereof are formed at a temperature equal to or higher than the above phase transition temperature will be described below. CaTiO ₃ having an orthorhombic perovskite structure has a considerably distorted structure as compared with a cubic system, and calcium titanate having an RP-type layered perovskite structure (or having a structure close thereto) which is tetragonal And / or to change the crystal structure of the solid solution to CaTiO ₃ having a cubic perovskite structure.
It is considered that a larger rearrangement of atoms is required as compared to the change from.

Therefore, at a temperature higher than the phase transition temperature at which CaTiO ₃ has a cubic perovskite structure, particles made of calcium titanate having a RP-type layered perovskite structure and / or a solid solution thereof can be formed more easily.

The shape of the plate-like particles constituting the plate-like ceramic particles thus obtained can be determined to some extent by visually observing the powder composed of the plate-like particles with the naked eye. Whether it has a gloss). However, to be precise, it can be confirmed by observing the morphology of the particles with a device such as an optical microscope, an electron microscope or a laser microscope.

The obtained plate-like ceramic particles are oriented and shaped, and the spread portion of the plate-like particles corresponds to the c-plane according to the X-ray diffraction pattern and local X-ray diffraction pattern of the obtained molded body. Can be confirmed.
The same can be confirmed by observing the obtained plate-like ceramic particles using a transmission electron microscope (TEM).

Embodiment Example This embodiment compares the plate-like ceramic particles (samples 1 and 2) according to the present invention, the method for producing these particles, and the performance of the compacts and sintered bodies produced using these particles. This will be described together with the samples (comparative samples C1 to C4).

The powder according to the present example is a powder containing plate-like particles made of calcium titanate having an RP-type layered perovskite structure, and the particles have a portion that spreads in a direction parallel to the perovskite structure layer (c-axis). Having an aspect ratio (β / α) of 10 between the thickness (α) of the plate-like particle and the maximum length (β) of the spread portion.
That is all.

Next, a method of manufacturing the plate-like ceramic particles according to the first and second samples according to the present embodiment will be described. First, powders of the raw material powders CaCO ₃ and TiO ₂ were weighed so as to have a ratio of 3: 2, and ethanol was added thereto for uniform mixing, followed by ball mill mixing for 24 hours. Thereafter, ethanol was removed, and after sufficiently drying, a flux in which KCl and NaCl were mixed in an equimolar ratio was added in the same amount as a raw material and mixed with a mortar to obtain a mixed powder.

Next, as shown in FIG.
0 was heated using heating vessel 2. As shown in FIG.
The heating vessel 2 includes a platinum crucible 21 and a lid 22 to cover the platinum crucible 21, and an alumina crucible 23 to store the platinum crucible 21 and a lid 24 to cover the platinum crucible 21. To prevent this, an alumina powder 25 is provided. Then, the mixed powder 20 was put into the platinum crucible 21, and then the heating vessel 2 was placed in a heating furnace.

Next, the heating container 2 is heated. The above-mentioned heating is performed in the air, and the heating rate and the cooling rate in the heating step and the cooling step are 200 ° C./hour, respectively.
The temperature was set to 0 ° C. × 8 hours (sample 2).

In order to encourage the flux to completely turn into a melt, the temperature was maintained at 800 ° C., which is the temperature at which the flux melts, for 2 hours during the heating. After the completion of the heating, the contents of the platinum crucible 21 were taken out, and the contents were washed about 20 times using ion-exchanged water, filtered, and dried to obtain a synthetic powder.

The obtained synthetic powder was a powder containing plate-like particles as shown in FIG. Particularly, as shown in FIG. 3 (b), the synthetic powder of Sample 2 synthesized at 1400 ° C. was a powder composed of only plate-like particles. Note that FIG.
Was photographed using a scanning electron microscope.

In these powders, the maximum length (β) of the spread portion of the plate-like particles determined from the particle size distribution measurement was as follows:
The average was 15 μm for the synthetic powder at 1300 ° C. and the average for the synthetic powder at 1400 ° C. according to Sample 2. Further, the thickness (α) of the plate-like particles determined from SEM (scanning electron microscope) observation was about 1 μm. As described above, the aspect ratio (β / α) of the plate-like particles in the synthetic powder according to Sample 1 was 15, and Sample 2 was 25.

From the X-ray diffraction pattern of the synthetic powder shown in FIG. 4, it was confirmed that each of the synthetic powders was a powder containing Ca ₃ Ti ₂ O ₇ particles having an RP layered perovskite structure.

Further, from the X-ray diffraction pattern of the molded body including the above-mentioned sample 2 described below, the plate-like particles constituting the sample 2 correspond to Ca ₃ Ti ₂ O ₇ , and the spread portion thereof is an RP-type layer-form. It was found that the plane was parallel to the perovskite structure layer (c-plane) of the perovskite structure.

As described above, the synthetic powder obtained by the synthesis method shown in this example corresponds to Ca ₃ Ti ₂ O ₇ having an RP-type layered perovskite structure, and in a direction parallel to the perovskite structure layer (c-plane). It was found that the plate-like ceramic particles of the present invention having a widened portion and having an aspect ratio (β / α) of 10 or more were included.

Next, Comparative Sample C1 was synthesized in the same manner as Samples 1 and 2. However, the synthesis temperature was lowered to 1200 ° C. for synthesis. As shown in FIG. 5, the obtained synthetic powder (comparative sample C1) was a powder composed of fine particles having an isotropic shape, and did not contain plate-like particles. Also, X in FIG.
According to the line diffraction pattern, the synthetic powder was a CaTiO ₃ single phase and did not contain a Ca ₃ Ti ₂ O ₇ phase. Thus, it was found that when the temperature at the time of synthesis was 1200 ° C. or lower, the target plate-like particles could not be obtained. FIG. 5 was photographed with a scanning electron microscope.

Next, a comparative sample C2 synthesized by the solid phase method was used.
4 will be described. Here, the comparative samples C2 to C4
The same raw material powder as in Samples 1 and 2 was weighed and added with ethanol to perform uniform mixing, followed by ball mill mixing for 24 hours. Then, after removing ethanol and drying sufficiently, put this powder in a MgO firing vessel,
1000 ° C (Comparative sample C2), 1200 ° C (Comparative sample C
3) Heat treatment was performed at 1400 ° C. (comparative sample C4).

As shown in FIGS. 6A and 6B, 100
In comparative samples C2 and C3 synthesized at 0 ° C and 1200 ° C,
No plate-like particles are present in the synthetic powder and the desired Ca ₃
The Ti ₂ O ₇ phase was not synthesized, and only the CaTiO ₃ phase was synthesized. As described above, even in the solid-phase method, Ca ₃ Ti ₂ O ₇ was not synthesized at 1200 ° C. or lower as in the case of the flux method.

On the other hand, as shown in FIG. 6C, the powder synthesized at 1400 ° C. as the comparative sample C4 was Ca ₃ Ti ₂ O
It was found that the particles consisted of _seven phases and were composed of plate-like particles. However, the individual plate-like particles agglomerated with each other to form massive secondary particles, and it was difficult to disintegrate them. That is, dispersed plate-like particles could not be obtained. Thus, it was not possible to obtain plate-like particles in a dispersed form by the solid phase method. FIG. 6 was photographed using a scanning electron microscope.

Next, using Sample 2 as host particles,
{100} of CaTiO ₃ having a perovskite structure
A crystal-oriented ceramic having a plane (display when indexed as cubic) was produced. Host powder and TiO
₂ Powder and Ca: Ti = 1: 1 were weighed, ethanol and hexane were added as solvents, mixed with a ball mill for 24 hours, further added a binder and a plasticizer, and mixed for 1 hour. Thus, a slurry was prepared.

This slurry was tape-formed by a doctor blade forming apparatus to obtain a tape-shaped product having a thickness of 0.1 mm. Further, 20 obtained tape molded bodies were laminated and pressed, and the laminated body was rolled by a twin-roll rolling mill until the thickness became half, thereby obtaining a molded body (x) having a thickness of about 1 mm. After degreasing the molded body at 600 ° C. to remove organic components,
Heat treatment was performed at 1600 ° C. for 10 hours in the air to obtain a sintered body (y).

When the X-ray diffraction pattern of the spread surface of the molded product (x) was measured, it was found that C
It was found that the diffraction peak corresponding to the (00l) plane of a ₃ Ti ₂ O ₇ was extremely high. That is, the spread surface of the host particles (Ca ₃ Ti ₂ O ₇ particles) is Ca ₃ Ti ₂
It was found that the spreading plane of the host particles in the molded body (x) corresponded to the c-plane of O ₇ and was oriented parallel to the spreading plane of the molded body. The degree of plane orientation of the host particles in the molded article (x) was determined by the following equation (Lottgering method), and it was found that the degree of orientation was 86%.

P = {I (008) + I (0010)} /
｛I (105) + I (008) + I (0010) + I
(200)｝ degree of orientation = (P−P ₀ ) / (1 / P ₀ ) (I (hkl) is the intensity of the diffraction peak corresponding to the (hkl) plane (tetragonal expression), and P ₀ is the same component and P of oriented molded body)

Next, when the X-ray diffraction pattern of the spread surface of the sintered body (y) was measured, as shown in FIG. 8, the sintered body (y) was an orthorhombic CaTiO ₃ single phase. I understood that. It is also found that the diffraction line corresponding to the (0k0) plane of the orthorhombic system (ie, the (h00) plane in cubic system) is significantly higher than that of a non-oriented sintered body (z) described later. Was.

When the degree of orientation of the {100} plane (cubic crystal display) of the sintered body (y) was determined by the following equation (Lottgering method), it was found that the degree of orientation was 93%. The density of the sintered body is 9 relative to the theoretical density.
8%.

P = {I (020) + I (040)} /
｛I (020) + I (040) + I (121) + I (1
23)｝ Degree of orientation = (P−P ₀ ) / (1−P ₀ ) (I (hkl) is the intensity of the diffraction peak corresponding to the (hkl) plane (expressed as orthorhombic), and P ₀ is the non-oriented P of the body

As described above, the plate-shaped ceramic particles according to the present example can obtain a compact (x) having a high c-plane orientation by orientation molding, and sinter the compact (x). As a result, it was found that a sintered body (y) having a high degree of {100} plane orientation, that is, a perovskite-type crystal oriented ceramic was obtained.

For comparison, CaTiO ₃ was sintered by a usual powder method. CaCO ₃ powder and T
The iO ₂ powder was mixed at a molar ratio of 1: 1 and mixed with 120
Calcination was performed at 0 ° C. for 2 hours to obtain a calcined powder. Next, the calcined powder was pulverized by a wet method (ball mill) and dried, and the obtained pulverized powder was molded by a uniaxial press and a cold isostatic press to obtain a molded body. This molded body is heated at 1400 ° C.
Heat treatment was performed for a time to obtain a sintered body (z). When the X-ray diffraction pattern of the surface of the obtained sintered body (z) was measured, as shown in FIG. 8, the sintered body (z) was orthorhombic CaTiO 2.
It became ₃ single phases.

However, the (0k0) plane (ie,
The (h00) plane orientation was not obtained in cubic crystal display, and the degree of orientation of the {100} plane (cubic crystal display) was calculated by the above equation. The degree of orientation was 0%. The sintered body density was 98% in relative density. Thus, it was found that the perovskite-type crystallographically-oriented ceramics could not be obtained by the ordinary powder method without using the plate-like ceramic particles according to the present example.

The operation and effect according to this embodiment will be described below. The plate-like ceramic particles according to the present example have a plate-like shape anisotropy and an aspect ratio of 10 or more.
Therefore, by subjecting the plate-shaped ceramic particles to orientation molding, the orientation of each particle can be easily aligned.

By performing reaction sintering using the orientation of the plate-like ceramic particles according to the present example, FIG.
As described above, it is possible to obtain an excellent crystallographically-oriented bulk ceramics having a perovskite structure.

As described above, the use of the plate-shaped ceramic particles of the present invention provides excellent piezoelectricity, dielectric properties, microwave dielectric properties, antiferroelectric properties, magnetism, thermoelectricity, electronic conductivity, ionic conductivity, and the like. Various crystal-oriented bulk ceramics having a perovskite structure can be obtained. Therefore, a high-performance device can be obtained by fabricating devices such as various sensors, filters, and oscillators utilizing the above-described characteristics with the above-mentioned crystal-oriented bulk ceramics.

[0078]

As described above, according to the present invention, it is possible to provide plate-like ceramic particles from which crystal-oriented bulk ceramics having a perovskite structure can be easily produced.

[Brief description of the drawings]

FIG. 1A is an explanatory view of a perovskite structure, FIG. 1B is an explanatory view of an RP-type perovskite structure, and FIG. 1C is a perspective view of plate-like ceramic particles according to an embodiment.

FIG. 2 is an explanatory diagram of a heating vessel used for synthesizing plate-like ceramic particles according to the embodiment.

FIG. 3 is a drawing substitute photograph (390 ×) of (a) Sample 1 synthesized at 1300 ° C. × 8 hours according to the embodiment;
(B) Drawing substitute photograph (390 times) of Sample 2 synthesized at 1400 ° C. × 8 hours.

FIG. 4 is a diagram showing X-ray diffraction patterns of powders of Samples 1 and 2 and Comparative Sample C1 according to the embodiment.

FIG. 5 is a drawing substitute photograph (1500 times) of a comparative sample C1 synthesized at 1200 ° C. for 8 hours according to the embodiment.

FIG. 6 is a drawing substitute photograph (3) of (a) Comparative sample C2 synthesized by a solid-phase reaction at 1000 ° C. according to the embodiment.
900x), (b) Drawing substitute photograph (390x) of comparative sample C3 synthesized by solid-phase reaction at 1200 ° C, (c)
Drawing substitute photograph (390 times) of comparative sample C4 synthesized by a solid-phase reaction at 1400 ° C.

FIG. 7 is a diagram showing an X-ray diffraction pattern of a compact (x) according to the embodiment.

FIG. 8 is a diagram showing X-ray diffraction patterns of a sintered body (y) and a sintered body (z) according to the embodiment.

[Explanation of symbols]

 1. . . 9. plate-shaped ceramic particles, . . Spreading part,

Claims (1)

[Claims] 1. Rudolsden-popper type (Ruddl)
esden-Popper type) Plate-like ceramic particles comprising calcium titanate having a layered perovskite structure and / or a solid solution thereof, wherein the particles have a portion extending in a direction parallel to the perovskite structure layer (c-axis). And the thickness of the plate-like particles (α)
A plate-like ceramic particle having an aspect ratio (β / α) of 10 or more to the maximum length (β) of the spread portion.