JP3509491B2 - Shape anisotropic ceramic powder and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to Rudolsden-Popper (Ru
The present invention relates to a shape anisotropic ceramic powder having a ddlesden-Popper) type layered perovskite structure and a method for producing the same.

[0002]

BACKGROUND OF THE INVENTION Rudolsden-Popper
A ceramic powder having a layered perovskite structure of a den-Popper type (hereinafter, abbreviated as RP type) is conventionally prepared by heating and reacting mixed raw material powders (for example, oxides, carbonates, etc.), that is, a solid-phase reaction. It was manufactured by the powder synthesis method mainly.

By orienting a specific crystal axis of the polycrystalline ceramic, it is possible to produce a polycrystalline ceramic having characteristics close to those of a single crystal. As a result, it is possible to obtain a crystallographically-oriented ceramic excellent in piezoelectricity, dielectricity, ferroelectricity, antiferroelectricity, magnetism, thermoelectricity, electronic conductivity, ionic conductivity, etc. depending on a specific crystal axis. . The above-mentioned crystallographically-oriented ceramics have various orientations such as uniaxial pressurization by using, as at least a part of the raw material, a powder made of ceramics particles having shape anisotropy such as plate shape and scale shape and having a large aspect ratio. It can be manufactured by molding by a molding method and heat-treating it under appropriate conditions.

The above-mentioned crystallographically-oriented ceramics are sensors such as acceleration sensors, pyroelectric sensors, ultrasonic sensors, magnetic sensors, electric field sensors, temperature sensors and gas sensors, thermoelectric conversion, energy conversion elements such as piezoelectric transformers, piezoelectric actuators, It is an excellent material that can be used for a wide range of functional ceramic materials such as sonic motors, low-loss actuators such as resonators, low-loss resonators, capacitors, etc.

[0005]

However, when the reaction of the raw material powder proceeds due to the solid-phase reaction, that is, the diffusion between solids without passing through the liquid phase, the raw material powder and the ceramic powder obtained therefrom are A powder composed of ceramic particles having an isotropic shape close to a spherical shape is synthesized regardless of the crystal structure.

Therefore, although the ceramic particles having the RP-type layered perovskite structure synthesized by the above-mentioned manufacturing method have a slightly plate-like shape, their aspect ratio is as small as about 1 to 3. It is difficult to produce crystallographically-oriented ceramics from such ceramic powder.

In view of the above problems, the present invention aims to provide a shape anisotropic ceramic powder and a method for producing the same, which can easily produce a crystallographically oriented ceramic.

[0008]

The invention of claim 1 is a Rudolsden-
In a powder comprising ceramic particles having a Ruddlesden-Popper type layered perovskite structure, the ceramic particles are plate-like particles having a spreading portion in a direction parallel to the perovskite structure layer (C plane), and the above-mentioned plate-like particles For the particle thickness (α),
Aspect ratio (β /
α) is 5 or more in the shape anisotropic ceramic powder.

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 ) Represented by n. Here, A and B are cations each composed of a single element or a plurality of elements, and X is an oxygen ion or a halogen ion.

The crystal lattice has a layer (ABX ₃ ) having a perovskite structure, as shown in FIG. 1 (b).
n and a layer (AX) having a rock salt structure have a structure in which they are alternately stacked in the c-axis direction. The perovskite structure is a structure in which A forms a simple cubic lattice, B is located at the body center position, and X is located at the face center position, as shown in FIG.

The plate-like particles constituting the shape anisotropic ceramic powder of the present invention have an aspect ratio of 5 or more. A crystal-oriented ceramic can be easily obtained by molding such powder by an orientation molding method described later.
When the aspect ratio is 10 or more, it is possible to easily obtain a crystallographically-oriented ceramic having a higher degree of orientation.

Examples of the compound having the RP type layered perovskite structure include Sr ₂ TiO ₄ and S
r ₃ Ti ₂ O ₇ , Sr ₄ Ti ₃ O ₁₀ , Ca ₄ Ti
₃ O ₁₀ , Ca ₃ Ti ₂ O ₇ , Sr ₂ RuO ₄ , Sr ₂ S
nO ₄ , Sr ₂ MoO ₄ , Sr ₂ MnO ₄ , (La, S
r) CrO ₄ , (La, Sr) MnO ₄ , (La, S
r) ₂ MnO ₇ or other oxide, or K ₂ NiF ₄ , K
₂ CoF ₄ , K ₂ CuF ₄ , K ₂ MgF ₄ , K ₃ Zn ₂
Halides such as F ₇ can be mentioned.

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. The RP-type layered perovskite structure is shown in Fig. 1.
As shown in FIG. 1B, the perovskite structure layer and the rock salt structure layer as shown in FIG. 1A have a structure overlapping in the c-axis direction. And, as shown in FIG. 1 (c), the shape anisotropic ceramic powder according to the present invention has two a
It is a plate-like particle having a widened portion due to the perovskite structure layer on the C plane which is set by the axis.

By the way, a ceramic having a perovskite structure reflects its crystal symmetry and crystal structure,
It exhibits characteristics such as piezoelectricity, dielectricity, ferroelectricity, antiferroelectricity, magnetism, thermoelectricity, electronic conductivity, and ionic conductivity. Each of these characteristics often has anisotropy with respect to the crystal orientation. Therefore, in a normal polycrystalline ceramic in which the crystals are not oriented, the orientations of the crystals that make up the ceramic are random, and thus the above-mentioned characteristics are significantly smaller than in the single crystal state. However, in the case of a crystallographically-oriented ceramic in which the crystal orientations are uniform, the above-mentioned characteristics are closer to the single crystal state.

Such a crystallographically-oriented ceramic can be used as an excellent functional ceramic having piezoelectricity, dielectricity, ferroelectricity, antiferroelectricity, magnetism, thermoelectricity, electronic conductivity, ionic conductivity and the like. Therefore, high-performance devices can be obtained by producing devices such as various sensors utilizing the above-mentioned characteristics from the above-mentioned crystal-oriented ceramics.

The shape-anisotropic ceramic powder according to the present invention has a plate-like particle shape and an aspect ratio of 5 or more. Therefore, using the above-described excellent crystallographically-oriented ceramics, the above-mentioned anisotropically-shaped ceramic powder is used for orientation molding,
It can be easily obtained by heat treatment.

As a raw material for the above-mentioned crystallographically-oriented ceramics,
When only the shape-anisotropic ceramic powder A according to the present invention is used, the crystallographically-oriented ceramic having the RP-type layered perovskite structure is converted into the compound C having the perovskite structure related to A by reacting with the above A and A. When the raw material B is used, a crystallographically-oriented ceramic composed of C having a perovskite structure is used. When the raw material B which does not react with A is used, the composite crystallographically-oriented ceramic in which A and at least part of B are oriented. Can be obtained respectively.

As described above, according to the present invention, it is possible to provide a shape-anisotropic ceramic powder capable of easily producing a crystallographically-oriented ceramic.

Examples of the above-mentioned orientation molding include extrusion molding, centrifugal molding, doctor blade, anisotropic pressure, rolling and the like.

Next, the invention of claim 2 is Rudolsden-
Plate-shaped particles having a popper (Ruddlesden-Popper) type layered perovskite structure and having a spreading portion in a direction parallel to the perovskite structure layer (C plane), and having a thickness (α) of the plate-shaped particles, Aspect ratio (β /
In producing a shape anisotropic ceramic powder composed of plate-like particles having α) of 5 or more, the ceramic raw material for producing the shape anisotropic ceramic powder is heated in a melt or a solution. And a method for producing a shape anisotropic ceramic powder.

As the ceramic raw material, substances such as oxides, carbonates, nitrates, hydroxides, and fluorides containing metal elements or the like which compose the shape anisotropic ceramic powder to be obtained can be used. it can. Further, in order to facilitate melting and dissolution in the melt or solution, the shape thereof is preferably granular or powdery. Further, for heating in the solution, a solution containing metal ions may be used as the ceramic raw material.

Further, the above-mentioned manufacturing method includes (1) formation of a melt or solution, (2) melting and dissolution of a ceramic raw material in the melt or solution, and (3) different shape in the melt or solution. It mainly consists of four steps: precipitation and grain growth of isotropic ceramic powder, and (4) separation of the precipitated anisotropically-shaped ceramic powder and the compound (hereinafter referred to as flux) or solution forming a melt.

Next, a manufacturing method for heating the above ceramic raw material in a melt will be described. This manufacturing method includes, for example, the following steps. First, the flux that constitutes the melt by melting is mixed with the ceramic raw material. The resulting mixture is heated to form a melt. Further, after that, heating is appropriately continued to react the ceramic raw material in the melt to precipitate anisotropically-shaped ceramic powder and grow grains. Finally, the above-mentioned flux and the obtained anisotropically-shaped ceramic powder are separated.

Next, the above flux will be described. If the solid-phase reaction occurs before the melt is formed, a ceramic powder having a low aspect ratio will be produced. Therefore, the flux is preferably a substance having a low melting point. The melting point of the flux is preferably 1000 ° C. or lower. This is because some of the ceramics having the RP type layered perovskite structure start the solid phase reaction at a temperature of about 1000 ° C.

Further, it is preferable that the flux has a high solubility of the ceramic raw material in the melt. This facilitates reaction, precipitation, and grain growth of the ceramic raw material through the liquid phase, and facilitates synthesis of shape anisotropic ceramic powder.

The above-mentioned flux is preferably a substance that does not react with the ceramic raw material and is easily separated from the ceramic raw material and the shape anisotropic ceramic powder obtained therefrom. As a result, only the target shape anisotropic ceramic powder can be manufactured. Also,
It is possible to manufacture a highly anisotropic shape anisotropic ceramic powder.

In particular, the flux is preferably a water-soluble substance. This makes it possible to easily separate the flux and the precipitated shape anisotropic ceramic powder by using water. As the flux satisfying the above conditions, for example, halide, carbonate,
Examples thereof include sulfates and low melting point oxides. Also,
As the above-mentioned flux, halides and sulfates are particularly preferable because they hardly react with the ceramic raw material.

Further, the smaller the value of the weight ratio represented by the ceramic raw material / flux, the more preferable. By this,
The ceramic raw material can be completely dissolved in the melt. Further, it is more preferable that the weight ratio of ceramic raw material / flux is 2 or less. As a result, the ceramic raw material can be sufficiently dissolved in the melt, and the reaction can be made more uniform.

Next, the heating of the ceramic raw material in the melt will be described. The heating includes three steps of a temperature raising step, a maximum temperature holding step, and a temperature lowering step. The temperature raising rate in the temperature raising step is preferably 1000 ° C./hour or less. As a result, the flux and the ceramic raw material can be uniformly dissolved. Further, the temperature may be maintained for 30 minutes or more at a temperature equal to or higher than the melting point of the flux during the temperature raising step.

In the above-mentioned maximum temperature holding step, the holding temperature is 80
It is preferable to carry out the treatment at 0 to 1600 ° C. for a duration of 30 minutes or more. As a result, the ceramic raw material can be sufficiently dissolved in the melt. If the holding temperature is lower than 800 ° C., the ceramic raw material may not be melted uniformly. On the other hand, if the holding temperature is higher than 1600 ° C, a reaction occurs between the flux and the ceramic raw material and the heating container for heating them, which may cause contamination in the furnace and compositional change due to volatilization of the flux or the ceramic raw material. There is a risk of If the above duration is shorter than 30 minutes, the ceramic raw material may be non-uniformly dissolved.

In the temperature decreasing step, the temperature decreasing rate is 500 ° C.
/ Hour or less is preferable. As a result, the shape anisotropic ceramic powder can be sufficiently deposited and grown, and a powder having a large particle size and uniform size can be obtained. If the cooling rate is higher than 500 ° C./hour, the particle size of the anisotropically-shaped ceramic powder may be too small. Moreover, the reaction of the ceramic raw material may be insufficient.

It is particularly preferable that the temperature lowering rate is 300 ° C./hour or less. As a result, the particle size of the shape anisotropic ceramic powder can be increased. Also,
The pattern of temperature change in the temperature lowering step may be stepwise or wavy. As a result, the reaction and grain growth of the ceramic raw material can be promoted.

The atmosphere for heating is preferably an oxidizing atmosphere such as air or oxygen when the shape anisotropic ceramic powder to be obtained is an oxide. Further, when the shape anisotropic ceramic powder to be obtained is a halide, the atmosphere during the heating is preferably an inert atmosphere such as an argon atmosphere. After the above heating steps are completed, the shape anisotropic ceramics are precipitated in the melt (flux), and the two are in a mixed state.

Next, a method for separating the anisotropically-shaped ceramic powder mixed with the melt will be described. When the flux is a water-soluble substance, it can be removed by washing with ion-exchanged water or pure water. In practice, the both in a mixed state can be put in ion-exchanged water or pure water and stirred, and this can be filtered or centrifuged to perform the above washing. It is preferable to repeat these steps several times until the flux is sufficiently reduced.

On the other hand, when the flux is easily dissolved in an acid or alkaline solution, an acid or alkaline solution can be used instead of the ion-exchanged water or pure water. However, in this case, after that, it is necessary to 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 the shape-anisotropic ceramic powder of the RP type perovskite structure according to the present invention. However, fine particles having a perovskite structure or some impurities such as carbonate used as a ceramic raw material may be mixed. In this case, in order to take out only the shape anisotropic ceramic powder according to the present invention, the obtained powder may be subjected to a treatment such as water separation or air separation.

Also in the case of synthesizing in a solution, crystal growth by mass transfer through a liquid phase is similarly performed, and a plate-like grown crystal is obtained as in the case of synthesizing in a melt. Further, as the above solution, a neutral, acidic, basic aqueous solution or the like can be used. Among them, NaOH aqueous solution, KOH
It is desirable to use a basic aqueous solution such as an aqueous solution.

The operation of the present invention will be described. 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. The rock salt structure layer does not contain B, and therefore does not contain BX bonds which are strong bonds forming the skeleton of the perovskite structure layer.
Therefore, the rock salt structure layer has a crystal formed by a weak bond as compared with the perovskite structure layer containing a BX bond.

In the manufacturing method of the present invention, the ceramic raw material is heated in the melt or the solution. For this reason,
Diffusion and precipitation of the ceramic raw material takes place via the liquid phase. Therefore, crystal growth preferentially occurs in the strong bond direction, and the crystal grows in a shape that reflects the bond strength in the crystal.

Therefore, in the manufacturing method of the present invention, a
Crystals preferentially grow in the axial direction, and as shown in FIG. 1 (c), it is possible to obtain a powder composed of plate-like particles in which the C-plane, which is a perovskite structure layer, becomes a widened portion. Thus, by crystallizing the shape-anisotropic ceramic powder by orientation molding, it is possible to easily obtain a crystallographically-oriented ceramic with c-axis orientation.

As described above, according to the present invention, it is possible to provide a method for producing a shape-anisotropic ceramic powder, which enables easy production of crystal-oriented ceramics.

The shape of the plate-like particles constituting the shape-anisotropic ceramic powder thus obtained can be judged to some extent by observing the powder with the naked eye (mica-like gloss). Or not). However, to be exact, it can be confirmed by observing the powder morphology with a device such as an optical microscope, an electron microscope, or a laser microscope.

Further, the obtained shape anisotropic ceramic powder is subjected to orientation molding, and the obtained crystallographically oriented ceramic is subjected to an X-ray diffraction pattern, a local X-ray diffraction pattern, etc.
It can be confirmed that the expanded portion of the plate-like particles corresponds to the C plane. The same confirmation can be made by observing the shape anisotropic ceramic powder obtained above with a transmission electron microscope (TEM).

Next, according to the third aspect of the invention, it is preferable that at least a part of the ceramic raw material is carbonate, and the heating is performed in a reduced pressure atmosphere. In particular, the alkaline earth elements, the form of the carbonate is very stable, other than this example oxides, hydroxides, etc., CO ₂
Gradually transforms to carbonate in the presence (in air). Therefore, when these oxides or hydroxides of alkaline earth elements are used as the ceramic raw material, accurate weighing is difficult, and there is a possibility that compositional deviation may occur in the finally obtained compound. On the other hand, if the above carbonate is used as a ceramic raw material, accurate weighing can be easily performed and the effect of reducing the composition deviation can be obtained.

When the above-mentioned carbonate is used as at least a part of the ceramic raw material, forced evacuation is carried out at a temperature of 500 to 1000 ° C. in the temperature raising step to keep the atmosphere under reduced pressure, and thereafter, It is preferable to replace the depressurized atmosphere with air or oxygen to provide an oxidizing atmosphere. By raising the temperature under the reduced pressure, CO ₂ generated by the decomposition of the carbonate can be positively discharged, so that it is possible to prevent the carbonate as the ceramic raw material from remaining after the heat treatment.

Of course, if the composition of the raw material is analyzed beforehand, the above oxides, hydroxides, etc. can be used as the raw material. Since these raw materials are more unstable than carbonates, the reaction may be carried out at a low temperature, and it may be possible to synthesize the compound at a lower temperature. Further, in this case, it is not necessary to raise the temperature under reduced pressure as described above.

[0047]

DETAILED DESCRIPTION OF THE INVENTION

First Exemplary Embodiment A shape anisotropic ceramic powder according to an exemplary embodiment of the present invention will be described with reference to FIGS. 1 to 4. Figure 1 (a),
As shown in (b), the ceramic particles 1 constituting the anisotropically-shaped ceramic powder of this example are plate-like particles having an RP-type layered perovskite structure and having a spread portion 10 formed by the perovskite structure layer.

Then, as shown in FIG. 1C, the aspect ratio (β / α) of the maximum length (β) of the spread portion is about 10 with respect to the thickness (α) of the plate-like particles. .
Further, the shape anisotropic ceramics 1 of this example has the chemical formula Sr ₃
Ti ₂ O ₇ is a substance shown in FIG.
In the crystal structure of (b), cation A corresponds to Sr ion and cation B corresponds to Ti ion.

A method of manufacturing the anisotropically-shaped ceramic powder according to this example will be described. In the manufacturing method of this example, heating is performed in the atmosphere and KC is used as a flux.
1 and NaCl were used in a molar ratio of 1: 1. Moreover, Sr
A mixed powder in which CO ₃ and TiO ₂ were mixed in a molar ratio of 3: 2 was used.

First, the above-mentioned mixed powder was weighed, ethanol was added thereto, and ball mill mixing was carried out for 24 hours to uniformly mix them. After that, ethanol was removed and thoroughly dried to obtain a ceramic raw material. Next, the above flux was added to the above ceramic raw material in a weight ratio of 1: 1 and these were mixed for 30 minutes using a mortar.

Next, the mixture 20 of the ceramic raw material and the flux was heated using the heating container 2 shown in FIG. As shown in FIG. 2, the heating container 2 is a platinum crucible 2
1 and a lid 22 to cover it, and the platinum crucible 21
Alumina crucible 23 for storing and a lid 24 for covering the same
Alumina powder 25 is provided inside the alumina crucible 23. Then, the mixture 20 of the ceramic raw material and the flux is put into the platinum crucible 21, and then the heating container 2 is placed in a heating furnace.

Next, the heating container 2 is heated. The heating is performed in air, and the temperature raising rate and temperature lowering rate in the temperature raising step and the temperature lowering step are respectively 200 ° C./hour, and the maximum temperature holding step is 1200 ° C. × 8 hours. After the heating was completed, the content of the platinum crucible 21 was taken out, and the content was washed with ion-exchanged water 10 times or more, filtered, and then dried to obtain a powder.

An SEM photograph of the obtained powder is shown in FIG. 3 (a). As shown in the figure, the obtained powder is composed of plate-like particles having a size of several tens of μm and fine particles of several μm. The two types of particles were separated by water sluice separation. The SEM photograph of the plate-like particles thus obtained is shown in FIG. 3 (b).

Next, the X-ray diffraction pattern of the obtained powder is shown in FIG. The powder obtained was identified based on the figure. The plate-like particles were Sr ₃ Ti ₂ O ₇ having an RP-type layered perovskite structure, and the fine particles were SrT.
It was found to be iO ₃ . As shown in the figure, it was found that SrCO ₃ used as the ceramic raw material also remained in the obtained powder.

From the X-ray diffraction pattern, it was also confirmed that the spread portion of the plate-like particles corresponded to the perovskite structure layer, that is, the C plane. Further, from the SEM photograph, the plate-like particles have a thickness (α) of 2 to 3 μm, as shown in FIG.
The maximum length (β) of the expanded portion in (c) is 20 to 3
0 μm, so the aspect ratio (β / α) is 10
It turned out to be about. From the above, it was found that the shape anisotropic ceramic powder according to the present invention can be obtained by the manufacturing method of this example.

Embodiment 2 As shown in FIG. 5, this embodiment is a shape anisotropic ceramic powder made of Sr ₃ Ti ₂ O ₇ . The shape anisotropic ceramic powder of this example is manufactured by using the same ceramic raw material and flux as those of the first embodiment and using the same manufacturing method. However, regarding the heating of the melt and the ceramic powder, the temperature was raised in a reduced pressure atmosphere up to a temperature of 600 ° C. in the temperature raising step, and then the reduced pressure atmosphere was replaced with an oxygen atmosphere.

That is, in the temperature rising process, the temperature inside the heating furnace in which the heating container was introduced was evacuated to 10 ^-2 torr until the temperature reached 600 ° C. Then, after holding at this temperature for 2 hours, the evacuation was stopped, the inside of the heating furnace was replaced with oxygen, and the temperature was raised. The subsequent heating was always performed in an oxygen atmosphere.

The powder obtained by the manufacturing method of this example is the same as that of the first embodiment. That is, fine particles of SrTiO 3
A powder was obtained in which ₃ and plate-like particles of Sr ₃ Ti ₂ O ₇ were mixed. The plate-like particles have a thickness (α) of 2 to 3
μm, maximum length (β) of the widened part in Figure 1 (c)
Is 20 to 30 μm, and thus the aspect ratio (β /
α) is about 10. In addition, the particle size distribution of the powder obtained by the manufacturing method of this example and the particle size distribution of the powder obtained in Embodiment 1 were measured by a particle size distribution measuring device (HORIBA LA).
-910) and shown in FIG.

In the figure, the solid line in (a) is the powder of the first embodiment, and the broken line in (b) is the powder of the second embodiment. The curve showing the particle size distribution has two peaks, one peak of SrTiO ₃ and the other peak of Sr ₃ Ti ₂ O ₇ , that is, the shape anisotropic ceramic powder according to the present invention. According to the figure, in (b), the peak height corresponding to SrTiO ₃ is remarkably lower than in (a), and the proportion of the shape anisotropic particles is increased by increasing the temperature under reduced pressure. I understood.

Embodiment 3 As shown in FIG. 6, this embodiment is a shape anisotropic ceramic powder made of Sr ₃ Ti ₂ O ₇ . The shape anisotropic ceramic powder of this example is manufactured by using the same ceramic raw material and flux as those of the first embodiment and using the same manufacturing method. However, regarding the heating of the melt and the ceramic powder, the temperature in the heating step is 1000 ° C
During that period, the temperature was raised in a reduced pressure atmosphere, and then the reduced pressure atmosphere was replaced with an oxygen atmosphere. That is, heating was performed under the same conditions as in the second embodiment. However, the temperature of exhaust gas in the heating furnace is 100
It went to 0 degreeC.

SE of powder obtained by the manufacturing method of this example
The M photograph is shown in FIG. The SEM photograph was taken under the same conditions as in the first embodiment. From the above SEM photograph,
It was found that in the production method of this example, a powder composed of substantially pure plate-like particles was obtained. Also, the plate-like particles are
It was found that the thickness (α) was 1 μm and the maximum length (β) of the expanded portion in FIG. 1C was 5 μm, and thus the aspect ratio (β / α) was 5.

In the manufacturing method of this example, the heating furnace was evacuated to a high temperature of 1000.degree. Therefore,
It was found that the decomposition of SrCO ₃ of the carbonate used as the ceramics raw material could be greatly promoted, and therefore, as shown in FIG. 6, a powder composed of plate-like particles of substantially single phase was obtained. In addition, with the decomposition of the carbonate, the amount of nuclei necessary for the growth of the plate-shaped crystal grains increased. Therefore, the size of the plate-like particles was smaller than that in the first and second embodiments.

Embodiment 4 This example is a shape anisotropic ceramic powder made of Sr ₃ Ti ₂ O ₇ . The shape anisotropic ceramic powder of this example was manufactured by the same manufacturing method as in the second embodiment. However, a mixture of Na ₂ SO ₄ and Li ₂ SO ₄ in a molar ratio of 1: 1 was used as the flux.

The powder obtained by the manufacturing method of this example is the same as that of the second embodiment. That is, fine particles of SrTiO 3
A powder was obtained in which ₃ and plate-like particles of Sr ₃ Ti ₂ O ₇ were mixed. The plate-like particles have a thickness (α) of 2 to 3
μm, maximum length (β) of the widened part in Figure 1 (c)
Is 20 to 30 μm, and thus the aspect ratio (β /
α) is about 10.

Embodiment 5 As shown in FIG. 7, this embodiment is a shape anisotropic ceramic powder made of Sr ₃ Ti ₂ O ₇ . The shape anisotropic ceramic powder of this example was manufactured by the same manufacturing method as that of the first embodiment. However, the temperature reduction rate was 50 ° C./hour for the synthesis.

The powder obtained by the manufacturing method of this example is the same as that of the first embodiment. That is, fine particles of SrTiO 3
A powder was obtained in which ₃ and plate-like particles of Sr ₃ Ti ₂ O ₇ were mixed. The particle size and aspect ratio were also the same as in the first embodiment.

The particle size distribution of the powder obtained by the manufacturing method of this example was measured by a particle size distribution measuring device (HORIBALA-910).
As shown in the diagram (b) in FIG. 7, the powder of this example has a smaller particle size side than the powder of the embodiment 1 shown in the diagram (a) of the figure. That is, the peak corresponding to the SrTiO ₃ particles was lowered. Thus, by decreasing the temperature lowering rate, the proportion of Sr ₃ Ti ₂ O ₇ particles can be increased.

Embodiment 6 As shown in FIG. 7, this embodiment is a shape anisotropic ceramic powder made of Sr ₃ Ti ₂ O ₇ . The shape anisotropic ceramic powder of this example was manufactured by the same manufacturing method as that of the first embodiment. However, the temperature pattern of the temperature lowering process is wavy (triangular waveform), that is, after the maximum temperature is maintained at 1200 ° C,
After going back and forth between 800 ° C. and 1200 ° C. four times, the temperature was lowered to room temperature for synthesis. The rate of temperature increase / decrease when changing the temperature in a wavy pattern was 200 ° C./hour.

The powder obtained by the manufacturing method of this example is the same as that of the first embodiment. That is, fine particles of SrTiO 3
A powder was obtained in which ₃ and plate-like particles of Sr ₃ Ti ₂ O ₇ were mixed. The particle size and aspect ratio were also the same as in the first embodiment.

The particle size distribution of the powder obtained by the manufacturing method of this example was measured by a particle size distribution measuring device (HORIBALA-910).
As shown in the diagram (c) in FIG. 7, the powder of this example has a smaller particle size side than the powder of the embodiment 1 shown in the diagram (a) of the figure. That is, the peak height corresponding to SrTiO ₃ particles was lowered. As described above, it was found that the ratio of Sr ₃ Ti ₂ O ₇ can be increased by forming the temperature pattern of the temperature lowering step in the wavy pattern, as in the fifth embodiment.

Embodiment 7 This example is a shape anisotropic ceramic powder made of Sr ₃ Ti ₂ O ₇ . The shape anisotropic ceramic powder of this example was manufactured by the same manufacturing method as that of the first embodiment. However, Sr (OH) ₂ .8H ₂ O was used as the Sr raw material. Composition analysis of this Sr raw material by inductively coupled plasma emission spectrometry revealed that Sr was contained in an amount of 31.9% by weight. Based on this result, the raw materials were mixed so that the molar ratio of Sr: Ti was 1.45: 1, and synthesis was performed.

The powder obtained by the manufacturing method of this example is the same as that of the first embodiment. That is, fine particles of SrTiO 3
A powder was obtained in which ₃ and plate-like particles of Sr ₃ Ti ₂ O ₇ were mixed. The plate-like particles have a thickness (α) of 2 to 3 μm,
The maximum length (β) of the spread portion is about 10 μm, and thus the aspect ratio (β / α) is about 5.

The Sr ₃ Ti ₂ O ₇ particles synthesized in this example were particles having a relatively small aspect because they were synthesized with a composition that was Sr deficient due to the stoichiometric ratio of Sr ₃ Ti ₂ O ₇ . However, since the unstable hydroxide was used as a raw material, the ratio of SrTiO ₃ particles contained in the synthetic powder was reduced as compared with that of the embodiment example 1.

Embodiment 8 As shown in FIGS. 8 and 9, this example is a shape anisotropic ceramic powder made of Sr ₃ Ti ₂ O ₇ . The shape-anisotropic ceramic powder of this example has the same Sr
It was manufactured by a manufacturing method using hydroxide as a raw material. However, the synthesis was performed by mixing the raw materials so that the molar ratio of Sr: Ti was 2: 1.

As shown in FIG. 8, the powder obtained by the manufacturing method of this example was a powder in which plate-like particles Sr ₃ Ti ₂ O ₇ and minute amounts of fine particles SrTiO ₃ were mixed. The plate-like particles have a thickness (α) of about 2 μm and a maximum length (β) of the spread portion of about 15 μm, and thus an aspect ratio (β / α) of about 8.

A powder composed of plate-like particles in which the aspect ratio of the plate-like particles is increased and which is close to a single phase is heat-treated under reduced pressure by using a composition with an excess of Sr as compared with Example 7. Could be obtained without. The particle size distribution of the powder obtained by the manufacturing method of this example was measured by a particle size distribution measuring device (HORI
BALA-910) and measured as shown in FIG.
The two peaks seen in the particle size distribution were not observed, and the distribution consisted of only one peak consisting of plate-like particles.

Embodiment 9 This example is a shape anisotropic ceramic powder made of Sr ₂ MnO ₄ . The shape anisotropic ceramic powder of this example is
It was manufactured by the same manufacturing method as in the second embodiment. However,
A mixture of SrCO ₃ and MnO ₂ in a molar ratio of 2: 1 was used as a ceramic raw material.

The powder obtained by the manufacturing method of this example was mainly composed of plate-like particles of Sr ₂ MnO ₄ and mixed with fine particles of SrMnO ₃ and SrCO ₃ . In addition, the plate-like particles have a thickness (α) of 2 to 3 μm, and a maximum length (β) of the spread portion shown in FIG.
20 μm, so the aspect ratio (β / α) is 7
It became a degree.

Reference Example In this example, as a reference, a ceramic powder manufactured by a conventional manufacturing method will be described. First, Sr
_A ceramic powder made of ₃ Ti ₂ O ₇ will be described. The above powder is used as a ceramic raw material in Embodiment 1
The same as was used. However, the ceramic powder is manufactured in air or by utilizing a solid phase reaction.

First, SrC which is a ceramic raw material
Prepare a mixed powder in which O ₃ and TiO ₂ are mixed in a molar ratio of 3: 2. Ethanol was added to this mixed powder and ball mill mixing was carried out for 24 hours to uniformly mix them.
After that, it was thoroughly dried to remove ethanol. Then, the mixed powder was placed in a firing container made of MgO and heated in air at 1200 ° C. for 2 hours.

An SEM photograph of the powder obtained above is shown in FIG. The SEM photograph was taken under the same conditions as in the first embodiment. The X-ray diffraction pattern of the above powder is shown in FIG. The X-ray diffraction pattern is the first embodiment.
Was obtained under the same conditions as. As shown in the figure, the powder is a powder consisting entirely of Sr ₃ Ti ₂ O ₇ , and the shape of the particles forming the powder is somewhat plate-like. However, its particle size was as small as 1 μm or less, and the aspect ratio was as small as about 3.

From the above-mentioned reference examples, it was found that the conventional anisotropically-prepared solid-phase reaction method cannot produce the shape anisotropic ceramic powder of the present invention.

[0083]

As described above, according to the present invention, it is possible to provide a shape-anisotropic ceramic powder and a method for producing the same, by which crystal-oriented ceramics can be easily produced.

[Brief description of drawings]

1A is an explanatory view of a perovskite type structure, FIG. 1B is an explanatory view of an RP type perovskite type structure, and FIG. 1C is a perspective view of ceramic particles constituting a shape anisotropic ceramic powder.

FIG. 2 is an explanatory view of a heating container used for manufacturing shape anisotropic ceramic powder according to the first embodiment.

FIG. 3 is a drawing-substitute photograph (magnification: 390 times) of the shape anisotropic ceramic powder made of Sr ₃ Ti ₂ O _{7 according} to the first embodiment.

FIG. 4 is a diagram showing an X-ray diffraction pattern of a shape anisotropic ceramic powder made of Sr ₃ Ti ₂ O _{7 according} to the first embodiment.

FIG. 5 shows Sr ₃ Ti ₂ O according to the first and second embodiments.
FIG. 5 is a diagram showing the particle size distribution of the shape anisotropic ceramic powder of ₇ .

FIG. 6 is a drawing-substitute photograph (magnification: 1500 times) of the shape anisotropic ceramic powder made of Sr ₃ Ti ₂ O _{7 according} to the _third embodiment.

FIG. 7 shows Sr ₃ Ti ₂ O according to the fifth and sixth embodiments.
FIG. 5 is a diagram showing the particle size distribution of the shape anisotropic ceramic powder of ₇ .

FIG. 8 is a drawing-substitute photograph (magnification: 390 times) of the shape anisotropic ceramic powder made of Sr ₃ Ti ₂ O _{7 according} to the seventh embodiment.

FIG. 9 is a diagram showing a particle size distribution of shape anisotropic ceramic powder made of Sr ₃ Ti ₂ O _{7 according} to the _seventh embodiment.

FIG. 10 is a diagram showing an X-ray diffraction pattern of a ceramic powder made of Sr ₃ Ti ₂ O _{7 according} to a reference example.

FIG. 11 is a drawing-substitute photograph (magnification: 7300 times) of a ceramic powder made of Sr ₃ Ti ₂ O _{7 according} to a reference example.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-2-174003 (JP, A) JP-A-10-53465 (JP, A) JP-A-63-279514 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) C04B 35/00-35/22 C04B 35/42-35/51 C30B 1/00-35/00 C01G 23/00 CA (STN) JISST file (JOIS)

Claims (3)

(57) [Claims] 1. Rudolsden-Popper
In a powder composed of ceramic particles having a sden-Popper) type layered perovskite structure, the ceramic particles are plate-like particles having a spreading portion in a direction parallel to the perovskite structure layer (C plane), and A shape-anisotropic ceramic powder characterized in that the aspect ratio (β / α) of the maximum length (β) of the spread portion is 5 or more with respect to the thickness (α). 2. Rudolsden-Popper
sden-Popper) type layered perovskite structure and a plate-like particle having a spreading portion in a direction parallel to the perovskite structure layer (C plane), and having the above-mentioned spreading with respect to the thickness (α) of the plate-shaped particle. In producing a shape anisotropic ceramic powder composed of plate-like particles having an aspect ratio (β / α) of a maximum length (β) of 5 or more, a ceramic for producing the shape anisotropic ceramic powder A method for producing a shape anisotropic ceramic powder, which comprises heating a raw material in a melt or a solution. 3. The method for producing a shape anisotropic ceramic powder according to claim 2, wherein at least a part of the ceramic raw material is carbonate, and the heating is performed in a reduced pressure atmosphere.