JPH10158087A - Ceramic powder and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain ceramic powder excellent in insulating property and capable of forming oriented ceramic having a high degree of orientation by using platy particles of ceramics having a Bi-contg. laminar perovskite type crystal structure, specifying the average aspect ratio of the platy particles and ensuring a specified impurity anion content. SOLUTION: This ceramic powder consists of platy particles of ceramics having a Bi-contg. laminar perovskite type crystal structure, e.g. Bi4 Ti3 O12 and has <=1,000ppm impurity anion content. The average aspect ratio of the platy particles is >=3, preferably 3-200. This ceramic powder is produced as follows; starting material consisting of oxides of the constituent elements of the ceramics except Bi or compds. convertible into the oxides by thermal decomposition and a larger amt. of Bi2 O3 than the amt. required to form the ceramics by >=5mol% is prepd. and heated to the m.p. of Bi2 O3 or above and the resultant ceramics is crushed and treated with an acid such as nitric acid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a ceramic having a layered perovskite-type crystal structure containing bismuth such as bismuth titanate (Bi ₄ Ti ₃ O ₁₂ ), which can be used as a raw material for producing oriented ceramics. The present invention relates to a ceramic powder composed of plate-like particles and a method for producing the same.

[0002]

2. Description of the Related Art It has been conventionally known to produce oriented ceramics using ceramic powder composed of plate-like particles having a high average aspect ratio (see Embodiment 1). Here, the oriented ceramics are polycrystalline ceramics in which crystals of crystal grains constituting the ceramics are uniaxially oriented. Such ceramics are polycrystalline but have characteristics close to single crystals, and are particularly excellent in various electrical and magnetic properties having crystal orientation. The various electrical and magnetic properties include dielectric, pyroelectric, piezoelectric, ferroelectric, magnetic, ionic, electronic, and thermoelectric properties.

[0003] For this reason, when various sensors and devices utilizing various electric and magnetic properties are made of the above-mentioned oriented ceramics, these sensors and devices having excellent performance can be obtained. The above various sensors and devices include acceleration sensors, pyroelectric sensors, ultrasonic sensors, magnetic sensors, electrolytic sensors, temperature sensors, gas sensors and other sensors, thermoelectric conversion, energy conversion elements such as piezoelectric transformers, piezoelectric actuators, Examples include low-loss actuators such as ultrasonic motors and resonators, low-loss resonators, capacitors, and ion conductors.

As a method of using ceramic powder composed of plate-like particles having a high average aspect ratio, for example, a composite material is provided by providing a functional material layer having various electrical and magnetic properties on the surface thereof. Can be Such a composite material is excellent in various electric and magnetic properties and anisotropy appears in its functional property because the ceramic powder has high surface area and shape anisotropy. Therefore, an excellent chemical sensor, dispersed particles for an electrorheological fluid, a power storage device, an energy conversion device, and the like can be manufactured from the above composite material.

Further, as described in Embodiments 1 and 3 below, a ceramic powder composed of plate-like particles having a high average aspect ratio is used as a host material for synthesizing ceramics, which is difficult to obtain oriented ceramics by a normal synthesis method. It can also be used as

It is to be noted that especially the above ceramic powder, whose composition is bismuth titanate (Bi ₄ Ti ₃ O ₁₂ )
Such materials containing bismuth have excellent properties that can be used as raw materials for oriented piezoelectric ceramics, raw materials for oriented thermoelectric ceramics, dispersed particles for electrorheological fluid, and the like.

As a method for producing such a ceramic powder composed of plate-like particles, there is known a method of synthesizing using a flux of chloride or sulfate composed of bismuth or titanium (for example, Inoue, et a
l. , Ceramic Bull. Pp. 704-7
08, 1983).

[0008]

However, impurity anions such as chloride ions and sulfate ions remain in the ceramic powder obtained by the synthesis using the above flux. It is difficult to wash and remove these impurity anions from the ceramic powder. And
The larger the amount of impurity anions that are easily moved by an electric field such as Cl ^-1 , NO ₃ ^-1 , and SO ₄ ^-2 excluding oxygen, the larger the dielectric material
It is known that the insulating properties of ferroelectric materials are reduced.

Therefore, the insulating properties of the oriented ceramics made by using the above-mentioned ceramic powder are low, so that the capacitors, piezoelectric ceramics and the like made by using the same have poor performance under a high electric field. It is also known that the above ceramic powder is dispersed in oil and used as an electrorheological fluid. However, due to the low insulation properties of this electrorheological fluid, the electric clutch made using it had a large electric loss. Also, when a capacitor or the like is made using the ceramic powder, the loss is high.

Further, the above-mentioned ceramic powder may be fired and used as a sintered body. However, since these impurity anions remain even after sintering, the insulating properties of the sintered body were low (Inoue, et al.,
Journal of the Ceramic Society of Japan, Vol. 92, pp 416-419, 19
1984). Therefore, the performance of dielectric ceramics and the like made from this sintered body was low.

By the way, as a method of manufacturing ceramics, the Ceramic Society of Japan ^, 96
8 (1996) shows the following method. The ceramic raw material according to the above manufacturing method is composed of Bi ₂ O ₃ powder and TiO ₂ powder, and these have a molar ratio of Bi ₂ O ₃ :
It is contained at a ratio of TiO ₂ = 45: 55. In addition,
This molar ratio is determined by the Bi ₄ Ti
There is a 23 mol% excess of Bi ₂ O ₃ over that required to form ₃ O ₁₂ .

First, the above ceramic raw material is formed into pellets, and then the pellets are calcined at 750 ° C. for 48 hours and then at 850 ° C. for 48 hours to form a calcined body. Thereafter, the calcined body is pulverized to form pulverized ceramics. Next, after the above-mentioned crushed ceramics are re-formed, 1100
Main firing at 48 ° C. for 48 hours to obtain ceramics.

However, this ceramic has a low degree of orientation, and is almost the same as ordinary ceramics. This is because even if plate-like crystal particles having a large average aspect ratio of Bi ₄ Ti ₃ O ₁₂ are generated during the above-mentioned calcination, these plate-like crystal particles are destroyed when the calcined body is pulverized. This is because

On the other hand, the calcined body is one in which Bi ₄ Ti ₃ O ₁₂ crystal grains are firmly bound by excess Bi ₂ O ₃ . Therefore, pulverization needs to be performed for a long time. Therefore, the process becomes expensive. Further, as the calcined body becomes denser, it becomes extremely difficult to remove excess Bi ₂ O ₃ by evaporation. For this reason, even in the main firing, a part of the excess Bi ₂ O ₃ remains, which lowers the purity of the obtained ceramic and may impair the characteristics.

It should be noted that excessive Bi ₂ O
If the composition is such that ₃ does not occur, Bi ₄ Ti
₃ O ₁₂ is synthesized by a solid-phase reaction, and the average aspect ratio of the crystal grains is reduced. Therefore, it is not possible to obtain oriented ceramics from this unless combined with hot forging or the like. Furthermore, the degree of orientation of the oriented ceramics thus obtained was low, and did not have particularly excellent performance as compared with non-oriented ceramics (see Comparative Samples C2 and C3 described later).

The present invention has been made in view of the above problems, and an object of the present invention is to provide a ceramic powder having a high degree of orientation and a high insulating property, and a method for producing the same.

[0017]

A first aspect of the present invention is a ceramic powder comprising plate-like ceramic particles having a layered perovskite-type crystal structure containing bismuth, wherein the plate-like particles have an average aspect ratio of 3 or more. And the content of impurity anions in the ceramic powder is 100
A ceramic powder characterized by being at most 0 ppm.

Bismuth-containing ceramics having a layered perovskite-type crystal structure according to the present invention include Bi ₄ Ti ₃ O ₁₂ (bismuth titanate) and Bi ₂ V
O _5.5 , Bi ₂ WO ₆ , Bi ₃ TiNbO ₉ , Bi ₃ T
iTaO ₉ , SrBi ₂ Nb ₂ O ₉ , SrBi ₂ Ta ₂
O ₉ , BaBi ₂ Nb ₂ O ₉ , BaBi ₂ Ta ₂ O ₉ ,
BaBi ₃ Ti ₂ NbO ₁₂ , PbBi ₂ Nb ₂ O ₉ , P
bBi ₂ Ta ₂ O ₉ , PrBi ₃ Ti ₃ O ₁₂ , HoBi
₃ Ti ₃ O ₁₂ , LaBi ₃ Ti ₃ O ₁₂ , CaBi ₄ Ti
₄ O ₁₅ , BaBi ₄ Ti ₄ O ₁₅ , SrBi ₄ Ti
₄ O ₁₅ , LaBi ₄ Ti ₃ FeO ₁₅ , PrBi ₄ Ti ₃
FeO ₁₅ , Ba ₂ Bi ₄ Ti ₅ O ₁₈ , Sr ₂ Bi ₄ Ti
₅ O ₁₈ , Pb ₂ Bi ₄ Ti ₅ O ₁₈ , Bi ₅ Ti ₃ FeO
₁₅ , Bi ₆ Ti ₃ Fe ₂ O ₁₈ , Bi ₉ Ti ₃ Fe
₅ O ₂₇ , CaBi ₅ Ti ₄ FeO ₁₈ , SrBi ₅ Ti ₄
FeO ₁₈ , PbBi ₅ Ti ₄ FeO ₁₈ , BaBi ₅ Ti
₄ FeO _{18 and the} like. Also, a mixed layered bisas layered perovskite in which two or more of these compounds are combined may be used (eg, J. Am. Cera).
m. Soc. Vol. 78, No. 3, pp. 3142-44, 1995
Year).

The above plate-like particles have an average aspect ratio of 3 or more. Therefore, doctor blade molding, extrusion, rolling, uniaxial pressing, centrifugal molding,
By performing orientation molding such as wet pressurization and anisotropic pressurization, it is possible to obtain a compact having a high degree of orientation in which the long axis directions of the plate-like particles are uniform.

For example, when the ceramic powder is suspended in an electrically insulating liquid to form an electrorheological fluid, and a device such as an electric clutch is made using the electrorheological fluid, a large yield stress is generated when an electric field is applied. Excellent performance of generating

When the average aspect ratio is less than 3, there is a possibility that only ceramics having the same performance as non-oriented ceramics can be produced. In addition, when the average aspect ratio is 10 or more, the obtained effect is more remarkable, so that it is preferable. Although there is no particular upper limit on the average aspect ratio, particles exceeding 200 are difficult to handle during mixing. Therefore, it is preferably set to 200 or less.

The content of impurity anions in the ceramic powder is 1000 ppm or less. The content of impurity anions in the ceramic powder is 1000
When the content exceeds ppm, there is a possibility that the insulating properties of the oriented ceramics and the electrorheological fluid prepared by using the above ceramic powder may be reduced. Therefore, for example, when a capacitor is formed using this electrorheological fluid, the loss is high, and the performance may be significantly reduced.

Further, the degree of such a decrease in the insulating property and the height of the loss differs depending on the type of the remaining impurity anion and the type of the prepared device. However, in general, when impurity anions exceeding 1000 ppm are present, performance degradation that cannot be ignored is generated. Note that the above-mentioned impurity anion, easily moved by the electric field, Cl ^-1 excluding oxygen, NO ₃ ^-1, shows an ion such as SO ₄ ^-2.

Further, the average aspect ratio can be determined by taking an image of the plate-like particle with a scanning electron microscope, measuring the dimensions in the major axis direction and the minor axis direction, and determining these dimensions. Further, the amount of the impurity anions can be determined by chemical analysis.

The operation of the present invention will be described below. The ceramic powder according to the present invention is composed of plate-like particles having an average aspect ratio of 3 or more, and is composed of plate-like particles having an impurity anion content of 1000 ppm or less. Therefore, the ceramic powder according to the present invention has large shape anisotropy.

Therefore, by subjecting the ceramic powder of the present invention to orientation molding such as the above-mentioned doctor blade molding, oriented ceramics having a high degree of orientation can be produced. In addition, the oriented ceramics have a pseudo-tetragonal c-axis in a layered perovskite-type crystal structure containing bismuth constituting the ceramic powder,
Alternatively, the pseudo-cubic a-axis in a crystal having a perovskite crystal structure prepared using the above-described crystal having a layered perovskite crystal structure as a host material is in a state of being uniaxially oriented.

As described above, the oriented ceramics are excellent in various electrical and magnetic properties having crystal orientation, and have excellent performance by producing various sensors and devices using the same. These sensors and devices can be obtained. For example, from the ceramic powder of Bi ₄ Ti ₃ O _{12 according} to the present invention,
Excellent piezoelectric ceramics can be made.

Further, the ceramic powder according to the present invention has a small amount of impurity anions which cause a decrease in insulation. For this reason, the ceramic powder of the present invention has excellent insulation properties, and dielectrics, piezoelectrics, and the like produced therefrom exhibit excellent performance. Therefore, excellent capacitors, piezoelectric actuators, and the like can be manufactured.

As described above, according to the present invention, it is possible to provide an oriented ceramic having a high degree of orientation and to provide a ceramic powder having a high insulating property.

Next, the invention of claim 2 relates to an oxide of an element other than Bi or a compound which becomes an oxide by thermal decomposition, which constitutes Bismuth-containing ceramics having a layered perovskite-type crystal structure and containing Bi. becomes more and ₂ O _3, and preparing a ceramic raw material is in excess Bi ₂ O ₃ than the amount necessary to form a ceramic having a layered perovskite type crystal structure containing the bismuth 5 mol% or more, then By heating these to a temperature equal to or higher than the melting point of Bi ₂ O ₃ , the first step of forming a ceramic having a layered perovskite-type crystal structure containing bismuth is performed, and the resulting ceramic has a layered perovskite-type crystal structure containing bismuth. By crushing and acid-treating the ceramics, the powder consisting of the above-mentioned ceramic plate-like particles is obtained. In method of manufacturing a ceramic powder which is characterized in that the second step of forming.

Specific examples of oxides of elements other than Bi include SrO, BaO, PbO, CaO, Pr ₂ O ₃ ,
Ho ₂ O ₃ , La ₂ O ₃ , TiO ₂ , Nb ₂ O ₅ , Ta
Oxides such as ₂ O ₅ , Fe ₂ O ₃ , V ₂ O ₅ and WO ₃ can be mentioned.

In addition, for an element which is not stable in an atmosphere containing carbon dioxide, such as an alkaline earth metal, a compound which becomes an oxide by thermal decomposition may be used instead of the above oxide. Examples of the compounds include carbonates, hydroxides, and organometallic compounds. Examples of the hydroxide include titanium hydroxide and iron hydroxide. Examples of the organometallic compound include metal alkoxides (titanium isoprooxide, sodium ethoxide and the like), lead acetate, lanthanum acetate, and the like. Among them, it is preferable to use compounds such as carbonates, hydroxides, and organometallic compounds that become oxides by thermal decomposition and do not become a source of impurity anions. However, for those in which oxides can be used, it is more preferable to use oxides. When carbonate is used as a part of the above ceramic raw material,
The heating in the first step is more preferably performed under reduced pressure in order to promote the decomposition of carbonate.

In the above ceramic raw material, Bi ₂ O
_If the excess amount of ₃ is less than 5 mol%, ceramic powder having a high average aspect ratio may not be obtained. Although there is no particular upper limit for the excess amount, the effect is saturated even if the excess amount exceeds 100 mol%, so that it is meaningless to increase the amount. In addition, it is difficult to completely remove Bi ₂ O ₃ in the second step, and there is a possibility that only low-purity ceramic powder is obtained.

It is preferable that the heating in the first step is performed by maintaining the temperature in the atmosphere containing oxygen at 824 to 1100 ° C. for at least 30 minutes. Also,
The atmosphere may be air, but an oxygen atmosphere is more preferable. Thereby, generation of plate crystals can be further promoted. This, as will be described later, the surface of arrangement of oxygen in the center of the Bi ₂ O ₂ layer in the layered perovskite type crystal structure containing bismuth is present in parallel to the c-plane, to perform the first step in an oxygen atmosphere Thereby, the interfacial energy with the gas phase can be further reduced.

After the completion of the first step, the temperature is reduced at a rate of 50 ° C./hr or more, more preferably 10 ° C./hr.
A rate of 0 ° C. or higher is preferred. If the cooling rate is low, a large number of single crystals may be generated, and a large number of plate-like powders may not be obtained.

Next, the pulverization in the second step is preferably performed by wet ball mill pulverization. This allows the acid to spread throughout the acid treatment, resulting in excess B
i ₂ O ₃ can be completely removed. Further, a ceramic powder composed of plate-like particles having a uniform size can be produced.

In the wet ball mill pulverization, it is preferable to use balls having a diameter of 3 mm or more. When the size of the ball is less than 3 mm in diameter, the formed plate-like particles may be further pulverized, and the average aspect ratio may be reduced. In the wet ball mill pulverization, it is preferable to perform the rotation at a rotation speed of about 30 to 200 times per minute.

Next, any inorganic acid can be used for the acid treatment in the second step. Among them, hydrochloric acid and nitric acid are particularly preferred. Further, it is more preferable to use nitric acid in which a reaction product with Bi ₂ O ₃ is water-soluble and easy to remove. The amount of the acid in the acid treatment is preferably an amount larger than the chemical equivalent reacting with excess Bi ₂ O _3, and more preferably an excess of 20 mol% or more. The concentration of the acid is preferably in the range of 0.01 to 10 normal. However, if the treatment time of nitric acid is too long, Bi is extracted from the layered perovskite-type crystal structure containing Bi, so that the treatment time must not be too long. Usually, treatment within one hour can sufficiently remove excess Bi.

Next, as a post-treatment after the completion of the second step, the impurity anion or the compound of the impurity anion and bismuth in the acid attached to the surface of the obtained ceramic powder is promptly washed and removed. preferable. For this purpose, it is desirable to wash the powder from which the acid has been removed with a weak alkaline aqueous solution such as aqueous ammonia. After the above-mentioned washing, it is preferable to wash with several times of ion-exchanged water, preferably distilled water.

Next, the operation of the present invention will be described below.
In the production method according to the present invention, the amount of Bi ₂ O ₃ in the ceramic raw material is excessive, and the ceramic raw material is kept at a temperature equal to or higher than the melting point of Bi ₂ O _{3 in} the first step. Thereby, in the first step, the liquid phase Bi ₂ O ₃
Is generated and the amount of Bi ₂ O ₃ is excessive, so that the synthesis and grain growth of a ceramic having a layered perovskite-type crystal structure containing bismuth in the presence of liquid phase Bi ₂ O ₃ proceeds.

Therefore, the diffusion of atoms becomes easier as compared with the solid-phase reaction, and a plate-like crystal having a surface having a low surface energy in the crystal structure as a divergent surface perpendicular to the major axis direction can be easily produced. In addition, since the generation of the plate-like crystal in the first step is completed in a short time, the manufacturing process is shortened, and the manufacturing cost can be reduced.

In general, in a layered perovskite-type crystal structure containing bismuth, a Bi ₂ O ₂ layer exists between connected perovskite unit cells. Therefore, the interfacial energy with the liquid phase Bi ₂ O ₃ is reduced. Therefore, when the layered perovskite-type crystal structure containing bismuth is covered with the liquid phase Bi ₂ O ₃ , plate-like particles having the c-plane as an interface have a large energy gain. That is, the c-plane is a plane having a low surface energy in the crystal structure.

Therefore, in the first step, it is possible to easily produce a plate-like crystal in which the c-plane in the bismuth-containing layered perovskite-type crystal structure has a divergent plane perpendicular to the major axis direction. As described above, by the first step,
Ceramics bonded by Bi ₂ O _{3 in} which the plate crystals are present in excess can be obtained.

In the second step according to the present invention, the ceramic obtained in the first step is pulverized and acid-treated. Due to the acid treatment, the excess Bi
_{Since 2} O ₃ is dissolved and removed, Bi ₂ O ₃ can be removed without destroying the shape of the plate-like crystal obtained in the first step.

The term “plate-like particles constituting the ceramic powder obtained through the first and second steps” refers to the c-plane of the bismuth-containing layered perovskite-type crystal structure generated in the first step. It is a plate-like crystal having a spreading surface perpendicular to the direction. Therefore, according to the present invention, a ceramic powder composed of a plate-like powder having a high average aspect ratio can be obtained.

Further, in the above-mentioned manufacturing method, Bi ₂ O ₃ and the above-mentioned oxide or a compound which becomes an oxide by thermal decomposition are used as the ceramic raw material, and the ceramic raw material contains impurity anions. Absent.
Therefore, in this production method, the only possibility that impurity anions may be mixed is the acid treatment in the second step. Therefore, it is possible to obtain a ceramic powder having a small content of impurity anions as compared with the conventional synthesis method using chlorides and sulfates as raw materials.

As described above, according to the manufacturing method of the present invention, an excellent ceramic powder as described in claim 1 can be obtained.

[0048]

BEST MODE FOR CARRYING OUT THE INVENTION

First Embodiment A ceramic powder according to an embodiment of the present invention, a method for producing the same, and an oriented ceramic produced using the same will be described. The ceramic powder of this example is a ceramic powder composed of plate-like particles of Bi ₄ Ti ₃ O ₁₂ which is a ceramic having a layered perovskite-type crystal structure containing bismuth. The average aspect ratio of the plate-like particles is 3 or more, and the content of impurity anions in the ceramic powder is 1000 ppm or less.

The method for producing the ceramic powder will be described. Ceramics having a layered perovskite crystal structure containing bismuth to be obtained, that is, B
i ₄ Ti ₃ O ₁₂ element other than Bi constituting the, i.e. more becomes TiO ₂ and Bi ₂ O ₃ is an oxide of Ti, and Bi ₂ O than that necessary to form the ceramic
Prepare a ceramic raw material in which ₃ is in excess of 10 mol%.

Next, these are heated to a temperature not lower than the melting point of Bi ₂ O ₃ , that is, 900 ° C., to thereby obtain Bi ₄ Ti.
_A first step of forming ceramics made of ₃ O ₁₂ is performed, and a second step of forming a powder of the above-mentioned plate-like particles of the ceramics is performed by crushing and acid-treating the obtained ceramics.

Next, the method for producing the ceramic powder will be described in detail. The ceramic raw material used in the production method of this example is composed of Bi ₂ O ₃ powder and TiO ₂ powder, and these have a molar ratio of Bi ₂ O ₃ : TiO ₂ = 2.2: 3.
In a proportion of That is, in this ceramic raw material, Bi is in excess of 10 mol%. The above ceramic raw material was mixed with water in a ball mill, and the mixture was heated at 900 ° C. for 4 hours in the air or oxygen, and the first step was performed to obtain a ceramic as a reaction product.

The above ceramics were mixed in 1 N nitric acid in a wet ball mill using zirconia balls for 1 hour, and the second step was carried out to obtain a slurry-like substance. Thereafter, the slurry was suction-filtered, and the obtained substance was sufficiently washed with ammonia water and ion-exchanged water. afterwards,
The washed material was dried to obtain a ceramic powder. Then, the ceramic powder obtained by performing the first step in the atmosphere is referred to as Sample 1, and the ceramic powder obtained by performing the first step in oxygen is referred to as Sample 2.

When the ceramic powders of Samples 1 and 2 were examined by X-ray diffraction, they were found to be Bi ₄ Ti ₃
O ₁₂ was confirmed. In addition, sample 1 and sample 2
The impurity anions (nitrate ion and chloride ion) remaining in the mixture were examined by reductive distillation / indophenol blue absorbance method and potentiometric titration method, and these impurity anions were not detected. That is, it was found that the content of the impurity anion contained in Samples 1 and 2 was less than 500 ppm.

Next, the sample 1 was observed with a scanning electron microscope, and the average aspect ratio was determined to be about 4.6 by measuring the dimensions in the major axis direction and the minor axis direction. Also,
Sample 2 was about 6.3.

Next, a method for producing an oriented ceramic made of Bi _0.5 Na _0.5 TiO ₃ using the ceramic powder according to the sample 1 as a host material and an oriented ceramic obtained by the method will be described. In the sample 1 as the host material, Na ₂ CO ₃ , T as the guest material was added.
iO ₂ and Bi ₂ O ₃ are mixed. This mixture is formed into a molded body by doctor blade molding. The obtained compact is rolled and formed into a roll.

Next, the rolled body is subjected to hydrostatic pressure. Then, this was sintered at 1150 ° C. for 10 hours in oxygen to obtain a sintered body. Bi _0.5 Na _0.5 TiO in the obtained sintered body
_The perovskite phase consisting of ₃ is pseudo-cubic (10
The 0) plane was uniaxial preferentially oriented, and the degree of orientation by Lotgering was 30%. That is, oriented ceramics could be manufactured from Sample 1.

Next, the comparative sample C1 will be described. This is an example in which the same ceramic raw material as in Samples 1 and 2 above was used, but ceramic powder having a small average aspect ratio was generated due to the different firing conditions in the first step. First, a ceramic raw material used when manufacturing the above-mentioned samples 1 and 2 is prepared. The ceramic material was heated at 800 ° C. for 4 hours in the atmosphere to obtain a ceramic.

The obtained ceramics were mixed for 1 hour in a 1N nitric acid by a wet ball mill using zirconia balls in the same process as Samples 1 and 2, and the second step was carried out. Substance was obtained. Thereafter, the slurry was suction-filtered, and the obtained substance was sufficiently washed with ammonia water and ion-exchanged water. afterwards,
The washed material was dried to obtain a ceramic powder according to Comparative Sample C1.

According to X-ray diffraction, the comparative sample C1 was Bi
₄ Ti ₃ O ₁₂ , but the shape of the powder was almost spherical,
Most had an average aspect ratio of 1.5 or less. Also,
Similarly to the sample 1, the comparative sample C1 was used as a host material to prepare a sintered body made of Bi _0.5 Na _0.5 TiO ₃ . However, the degree of orientation of this sintered body is 7%,
It was hard to say that it was an excellent oriented ceramic. In addition, various characteristics were not different from non-oriented ceramics.

Next, comparative samples C2 and C3 will be described. These are examples in which a ceramic raw material composed of Bi ₂ O ₃ and TiO ₂ is used in a necessary and sufficient amount to form Bi ₄ Ti ₃ O ₁₂ . First, Bi ₂ O ₃ powder and T
A ceramic raw material containing iO ₂ powder in a molar ratio of Bi ₂ O ₃ : TiO ₂ = 2: 3 is prepared.

The above ceramic raw material was mixed with water in a ball mill, and the mixture was placed in air or oxygen at 900 ° C. for 4 hours.
After heating for a period of time, ceramics were obtained as a reaction product. Next, the obtained ceramic was mixed in 1 N nitric acid for 1 hour in a wet ball mill using zirconia balls to obtain a slurry-like substance. Thereafter, the slurry was subjected to suction filtration, the obtained substance was sufficiently washed with ammonia water and ion-exchanged water, and the obtained washed material was dried to obtain a ceramic powder. The ceramic powder obtained by heating in air is referred to as Comparative Sample C2, and the ceramic powder obtained by heating in oxygen is referred to as Comparative Sample C3.

The ceramic powders of the comparative samples C2 and C3 were examined by X-ray diffraction.
₄ Ti ₃ O ₁₂ was confirmed. The shapes of the comparative samples C2 and C3 were almost spherical, and most powders had an average aspect ratio of 1.5 or less. Further, similarly the comparative sample C2 as Sample 1, the same as host material, was created a Bi _0.5 Na _0.5 TiO ₃ sintered body, the orientation degree is 8% hard to say that excellent oriented ceramic won. In addition, various characteristics were not different from non-oriented ceramics.

From the above, it has been found that excellent oriented ceramics having a high degree of orientation can be produced from the ceramic powder according to this example. Further, it was found from the manufacturing method according to this example that a ceramic powder having a large average aspect ratio and a small content of impurity anions could be obtained.

Embodiment 2 This embodiment is a method for producing a ceramic powder using hydrochloric acid in the acid treatment in the second step. The ceramic raw material used in the manufacturing method of this example is the sample 1 of the first embodiment.
Are the same ceramic raw materials as in the case of preparing Then, the above-mentioned ceramic raw material was subjected to the same first step as in the case where the sample 1 of Embodiment 1 was prepared, and a ceramic was obtained as a reaction product. Next, the above ceramics were mixed in 1N hydrochloric acid in a wet ball mill using zirconia balls for 1 hour, and the second step was performed to obtain a slurry-like substance.

Next, the slurry was subjected to suction filtration, and the obtained substance was sufficiently washed with ammonia water and ion-exchanged water. The washed material was dried to obtain a ceramic powder. Then, the ceramic powder obtained by performing the first step in the air is referred to as Sample 3, and the ceramic powder obtained by performing the first step in oxygen is referred to as Sample 4.

When the ceramic powders of Samples 3 and 4 were examined by X-ray diffraction, they were found to be Bi ₄ Ti ₃
O ₁₂ was confirmed. In addition, sample 3 and sample 4
When impurity anions (chlorine ions) remaining in the sample were examined in the same manner as in Example 1, 900 ppm of residual chlorine was detected. Further, when examined in the same manner as in Example 1, the average aspect ratio of Sample 3 was about 3.9, and that of Sample 4 was about 6.0. That is, it was found that the ceramic powder according to the present invention was obtained even when hydrochloric acid was used for the acid treatment in the second step.

Embodiment 3 This embodiment relates to a method for producing a ceramic powder using a ceramic raw material containing Bi ₂ O ₃ in excess, the performance of the obtained ceramic powder, and an oriented ceramic produced from this ceramic powder. It is for explanation.

The ceramic raw material used in this example is Bi
_It consists of ₂ O ₃ powder and TiO ₂ powder, which are contained in a molar ratio of Bi ₂ O ₃ : TiO ₂ = 1: 1. That is, in this ceramic material, Bi is 5
0 molar% excess. The above ceramic raw material was mixed with water in a ball mill, and the mixture was heated in oxygen at 900 ° C. for 4 hours to perform the first step, thereby obtaining a ceramic as a reaction product.

The above ceramics were mixed in 1 N nitric acid for 1 hour in a wet ball mill using zirconia balls, and the second step was performed to obtain a slurry-like substance. Thereafter, the slurry was suction-filtered, and the obtained substance was sufficiently washed with ammonia water and ion-exchanged water. afterwards,
The washed material was dried to obtain a ceramic powder for Sample 5.

The ceramic powder according to the sample 5 was X
Examination by line diffraction confirmed that these were Bi ₄ Ti ₃ O ₁₂ . Further, the impurity anions (nitrate ion and chloride ion) remaining in the sample 5 were used for the first embodiment.
Inspection by the same method as in Example 1 did not detect these impurity anions. That is, it was found that the content of the impurity anion contained in Sample 5 was less than 500 ppm.
When the average aspect ratio of Sample 5 was determined in the same manner as in Embodiment 1, the average aspect ratio was about 20.

Next, the sample 5 was used as a host material, NiO, TiO ₂ , PbO, and Bi ₂ O ₃ were used as guest materials, and Bi _0.5 Na _0.5 Ti
A sintered body made of O ₃ was prepared. When the degree of orientation of this sintered body was measured in the same manner as in Example 1, the degree of orientation was 56%. That is, it was found that oriented ceramics superior to Sample 5 could be manufactured.

The sample 5 was used as a host material, NiO,
TiO ₂ , PbO and Bi ₂ O ₃ were used as guest materials, and Ni
Bi _0.5 Pb using O, PbO, and TiO ₂ as conversion materials
_A sintered body made of _0.5 Ni _0.25 Ti _0.75 O ₃ was prepared.
Here, the conversion material is the sample _{0.5 as the} host material, that is, Bi _0.5 Pb _0.5 by reacting with Bi ₄ Ti ₃ O _12.
Ni _0.25 Ti _0.75 O ₃ is a substance for producing.

The host material, guest material, and conversion material are mixed. From this mixture, a sintered body made of Bi _0.5 Pb _0.5 Ni _0.25 Ti _0.75 O ₃ was produced in the same manner as in Embodiment 1. When the degree of orientation of the sintered body was measured in the same manner as in Example 1, the degree of orientation was 78%. That is, it was found that oriented ceramics superior to Sample 5 could be manufactured.

Embodiment 4 This embodiment describes how the performance of a dielectric material made of ceramic powder differs depending on the content of impurity anions contained in the ceramic powder. A ceramic powder having an impurity anion content of less than 500 ppm is prepared by the same manufacturing method as that of the third embodiment. A dielectric is made using this ceramic powder.

First, a temperature 105 was applied to the ceramic powder.
Hot pressing (pressure: 20 MPa) was performed at 0 ° C. for 1 hour to obtain a hot pressed body (dielectric). Next, the hot pressed body was polished, and then a gold electrode was provided thereon.
An electric field of 40 kV / cm was applied in silicone oil at 0 ° C. When the leakage current at this time was measured, it was 1 mA /
cm ³ .

As described below, a ceramic powder having a high impurity anion content was prepared to obtain a dielectric. That is, a powder mixed at a ratio of Bi ₂ O ₃ : TiO ₃ = 2: 3 (corresponding to a molar ratio and a stoichiometric ratio) and N 2
The powder mixed with aCl: KCl = 1: 1 (molar ratio) was weighed and mixed with the same weight. The powder thus obtained was heated in a platinum crucible at a temperature of 1050 ° C. for 1 hour. The lump obtained by the above heating was washed in warm water and subjected to suction filtration to obtain a powder.

When the powder was examined, its composition was Bi
₄ Ti ₃ O ₁₂ , washed 20 times with warm water, and further washed with aqueous ammonia. After washing, the powder was dried and the components were analyzed. As a result, it was found that the powder contained 0.24% by weight (2400 ppm) of chloride ions. Finally, the powder was hot-pressed in the same manner as described above to obtain a hot-pressed body (dielectric). Next, the hot pressed body was polished, and then a gold electrode was provided thereon, and an electric field of 15 kV / cm was applied in silicon oil at 100 ° C.

The leakage current at this time was measured.
Currents in excess of mmA / cm ³ were observed. That is, it was found that a higher leak current flows at a lower voltage with respect to the leak current in the hot-pressed body as compared with the leak current having a lower content of the impurity anions described above.

From the above, it was found that the smaller the content of the impurity anion, the smaller the leak current, and thus the more excellent the insulating property.

[0080]

As described above, according to the present invention, it is possible to provide a ceramic powder having a high degree of orientation and having high insulation properties, and a method of manufacturing the same.

Claims (2)

[Claims] 1. A ceramic powder comprising plate-like particles of a ceramic having a layered perovskite-type crystal structure containing bismuth, wherein the plate-like particles have an average aspect ratio of 3 or more, and an impurity anion of the ceramic powder is contained. A ceramic powder having a content of 1000 ppm or less. 2. Bismuth-containing ceramics having a layered perovskite-type crystal structure containing bismuth comprising Bi ₂ O ₃ and an oxide of an element other than Bi or a compound which becomes an oxide by thermal decomposition, and Bi ₂ O ₃ than the amount necessary to form a ceramic having a layered perovskite type crystal structure containing the bismuth 5
A first step of preparing a ceramic having a layered perovskite-type crystal structure containing bismuth by preparing a ceramic raw material in excess of mol% or more and then heating the raw material to a melting point of Bi ₂ O ₃ or higher is performed. Producing a ceramic powder having a lamellar perovskite-type crystal structure containing bismuth and subjecting it to an acid treatment to form a powder comprising plate-like particles of the ceramic. Method.