JP4135701B2 - Ceramic powder and its precursor - Google Patents

Description

The present invention is based on ceramic plate-like particles having a layered perovskite 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 ceramic powder and its precursor.

It has been conventionally known to produce oriented ceramics using ceramic powder made of plate-like particles having a high average aspect ratio (see Embodiment 1).
Here, the oriented ceramic is a polycrystalline ceramic, which is a ceramic in which crystals of crystal grains constituting the same 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.
Examples of the various electrical and magnetic properties include dielectricity, pyroelectricity, piezoelectricity, ferroelectricity, magnetism, ionic conductivity, electronic conductivity, and thermoelectricity.

For this reason, when various sensors and devices using various electrical and magnetic properties are made of the above-mentioned oriented ceramics, these sensors and devices having excellent performance can be obtained.
The various sensors and devices include sensors such as acceleration sensors, pyroelectric sensors, ultrasonic sensors, magnetic sensors, electrolytic sensors, temperature sensors, gas sensors, energy conversion elements such as thermoelectric conversion and piezoelectric transformers, piezoelectric actuators, Examples thereof include a low-loss actuator such as an ultrasonic motor and a resonator, a low-loss resonator, a capacitor, and an ion conductor.

In addition, as a method for using ceramic powder composed of plate-like particles having a high average aspect ratio, for example, a composite material may be provided by providing various functional material layers having excellent electrical and magnetic properties on the surface thereof.
In such a composite material, since the ceramic powder has a high surface area and shape anisotropy, it is excellent in various electrical and magnetic properties and exhibits anisotropy in its functional properties. Therefore, an excellent chemical sensor, dispersed particles for electrorheological fluid, an electricity storage device, an energy conversion device, and the like can be produced using the composite material.

  In addition, the ceramic powder composed of plate-like particles having a high average aspect ratio is used as a host material when synthesizing ceramics that are difficult to obtain oriented ceramics by ordinary synthesis methods, as shown in Examples 1 and 3 described later. You can also.

In particular, the above-mentioned ceramic powder having a composition containing bismuth such as bismuth titanate (Bi ₄ Ti ₃ O ₁₂ ) is used as a raw material for oriented piezoelectric ceramics, a raw material for oriented thermoelectric ceramics, and an electrorheological fluid It has excellent properties that can be used for dispersed particles.

  And as a manufacturing method of the ceramic powder which consists of such a plate-like particle | grain, the method of synthesize | combining using the flux of chloride and sulfate which consists of bismuth and titanium is known (refer nonpatent literature 1).

However, impurity anions such as chloride ions and sulfate ions remain in the ceramic powder obtained by the synthesis using the flux. It is difficult to clean and remove these impurity anions from the ceramic powder.
In addition, it is known that as the amount of impurity anions that easily move by an electric field such as Cl ⁻¹ , NO ₃ ⁻¹ , and SO ₄ ⁻² excluding oxygen increases, the insulating property of the dielectric / ferroelectric material decreases. ing.

Therefore, the insulating ceramic produced using the above ceramic powder has low insulation, and thus the capacitor, piezoelectric ceramic, etc. produced using this ceramic have low performance under a high electric field.
It is also known that the ceramic powder is dispersed in oil and used as an electrorheological fluid. However, since the insulating property of the electrorheological fluid is low, the electric clutch produced using the electrorheological fluid has a large electric loss.
Further, when a capacitor or the like is produced using the ceramic powder, the loss is increased.

  Furthermore, the ceramic powder may be fired and used as a sintered body. However, since these impurity anions remain after sintering, the insulating property of the sintered body was also low (see Non-Patent Document 2). For this reason, the dielectric ceramics and the like prepared from this sintered body have low performance.

By the way, the following method is shown by the following nonpatent literature 3 as a manufacturing method of ceramics.
Ceramic material according to the manufacturing method described above, Bi ₂ O ₃ becomes from powder and TiO ₂ powder, which is the molar ratio _{Bi 2 O 3: TiO 2 =} 45: formed by a proportion of 55. In this molar ratio, Bi ₂ O ₃ is 23 mol% in excess of the necessary amount for forming Bi ₄ Ti ₃ O ₁₂ produced by this production method.

First, the ceramic raw material is formed into pellets, and then the pellets are calcined and calcined at 750 ° C. for 48 hours and then at 850 ° C. for 48 hours.
Thereafter, the calcined body is pulverized to obtain a pulverized ceramic.
Subsequently, after re-molding the pulverized ceramic, main firing was performed at 1100 ° C. for 48 hours to obtain a ceramic.

However, the degree of orientation of this ceramic is low and it is hardly different from ordinary ceramics.
Even if plate-like crystal particles having a large average aspect ratio of Bi ₄ Ti ₃ O ₁₂ are produced during the calcination, the plate-like crystal particles are destroyed when the calcined body is pulverized. It is because it ends up.

On the other hand, in the calcined body, crystal grains of Bi ₄ Ti ₃ O ₁₂ are firmly bonded with an excess of Bi ₂ O ₃ . For this reason, it is necessary to pulverize for a long time. Therefore, the process becomes expensive.
Further, as the calcined body becomes denser, it becomes extremely difficult to evaporate and remove excess Bi ₂ O ₃ . Therefore, even in the main firing, a part of the excess Bi ₂ O ₃ remains, and the purity of the obtained ceramic may be lowered and the characteristics may be impaired.

When the ceramic raw material has a composition that does not generate excessive Bi ₂ O ₃ , Bi ₄ Ti ₃ O ₁₂ is synthesized by a solid-phase reaction, and the average aspect ratio of crystal grains is reduced. Therefore, it is not possible to obtain oriented ceramics from this unless it is combined with a hot forge or the like. Furthermore, the degree of orientation of the oriented ceramics obtained in this way was low, and it did not have exceptional performance compared with non-oriented ceramics (see comparative samples C2 and C3 described later).

Inoue, et al. , Ceramic Bull. , Pp. 704-708, 1983 Inoue, et al. , Ceramic Association, Vol. 92, pp 416-419, 1984 The Ceramic Society of Japan, 1996 Proceedings, P378 (1996)

  In view of such problems, the present invention is intended to provide a ceramic powder and a precursor thereof capable of producing oriented ceramics with a high degree of orientation and having high insulating properties.

The ceramic powder of the present invention is a ceramic powder for producing oriented ceramics used for various sensors or devices,
The ceramic powder is composed of ceramic plate-like particles having a layered perovskite 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 ceramics having a layered perovskite crystal structure containing the bismuth of the plate-like powder are Bi ₄ Ti ₃ O ₁₂ (bismuth titanate), Bi ₂ VO _5.5 , Bi ₂ WO ₆ , Bi ₃ TiNbO ₉ , Bi _3. TiTaO 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 , PbBi 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, and BaBi ₅ Ti ₄ or consisting of a compound selected from FeO _18, these A ceramic powder comprising a combination of two or more compounds .

Examples of ceramics having a layered perovskite crystal structure containing bismuth according to the present invention include Bi ₄ Ti ₃ O ₁₂ (bismuth titanate), Bi ₂ VO _5.5 , Bi ₂ WO ₆ , Bi ₃ TiNbO ₉ , Bi ₃ TiTaO _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 , PbBi 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, can be mentioned BaBi ₅ Ti ₄ FeO ₁₈ or the like. Further, a mixed layered bis-ass layered perovskite in which two or more of these compounds are combined may be used (for example, J. Am. Ceram. Soc. 78, 11: 3142-44, 1995).

  The plate-like particles have an average aspect ratio of 3 or more. For this reason, by subjecting the ceramic powder to orientation molding such as doctor blade molding, extrusion, rolling, uniaxial pressing, centrifugal molding, wet pressing, and anisotropic pressing, the long axis direction of the plate-like particles It is possible to obtain a molded article with a high degree of orientation.

  In addition, 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 produced using the electrorheological fluid, a large yield stress is generated when an electric field is applied. Excellent performance can be demonstrated.

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

The content of impurity anions in the ceramic powder is 1000 ppm or less.
When the content of impurity anions in the ceramic powder exceeds 1000 ppm, the insulating properties of the oriented ceramics and the electrorheological fluid produced using the ceramic powder may be lowered.
For this reason, for example, when a capacitor is formed using this electrorheological fluid, the loss increases, and thus the performance may be greatly reduced.

Further, the degree of such a decrease in insulation and the height of loss varies depending on the type of remaining impurity anions and the type of device produced. However, in general, when impurity anions exceeding 1000 ppm are present, performance degradation that cannot be ignored occurs.
Note that the impurity anion refers to ions such as Cl ⁻¹ , NO ₃ ⁻¹ , and SO ₄ ⁻² excluding oxygen that are easily moved by an electric field.

  The average aspect ratio can be obtained from the dimensional ratio by photographing the plate-like particles with a scanning electron microscope and measuring the dimensions in the major axis direction and the minor axis direction. The amount of 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.
For this reason, the ceramic powder according to the present invention has a large shape anisotropy.

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

And as above-mentioned, the above-mentioned oriented ceramics are excellent in various electrical and magnetic properties having crystal orientation, and these sensors have excellent performance by making various sensors and devices using this. Can get the device.
For example, an excellent piezoelectric ceramic can be produced from the ceramic powder made of Bi ₄ Ti ₃ O _{12 according} to the present invention.

In addition, the ceramic powder according to the present invention has a small amount of impurity anions that cause a decrease in insulation.
For this reason, the ceramic powder of this invention is excellent in insulation, and the dielectric material, piezoelectric material, etc. which were created from this show the outstanding performance. Therefore, an excellent capacitor, piezoelectric actuator, etc. can be created.

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

Next, in the above method for producing a ceramic powder, an oxide of an element other than Bi constituting the ceramic having a layered perovskite crystal structure containing bismuth to be obtained, or a compound that becomes an oxide by thermal decomposition and Bi _2. O ₃ and
And preparing a ceramic raw material in which Bi ₂ O ₃ is 5 mol% or more in excess of an amount necessary to form a ceramic having a layered perovskite crystal structure containing bismuth,
Next, the first step of forming ceramics having a layered perovskite crystal structure containing bismuth by heating them to the melting point of Bi ₂ O ₃ or more is performed.
The obtained ceramics having a layered perovskite crystal structure containing bismuth is pulverized and treated with an acid to perform a second step of forming a powder composed of the ceramic plate-like particles.

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 ₂ O ₅ , Examples thereof include oxides such as Fe ₂ O ₃ , V ₂ O ₅ , and WO ₃ .

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

When the excess amount of Bi ₂ O ₃ in the ceramic raw material is less than 5 mol%, there is a possibility that a ceramic powder having a high average aspect ratio cannot be obtained.
Moreover, although there is no upper limit in particular of excess amount, even if an excess amount exceeds 100 mol%, since an effect will be saturated, it will become 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 ceramic powder with low purity can be obtained.

Moreover, it is preferable to perform the heating in said 1st process by hold | maintaining at a temperature of 824-1100 degreeC for at least 30 minutes in the atmosphere containing oxygen.
The atmosphere may be air, but an oxygen atmosphere is more preferable.
Thereby, the production | generation of a plate-shaped crystal can be accelerated | stimulated more. This is because, as will be described later, in the center of the Bi ₂ O ₂ layer in the layered perovskite crystal structure containing bismuth, there is an oxygen-aligned plane parallel to the c-plane, and the first step is performed in an oxygen atmosphere. This is because the interfacial energy with the gas phase can be further reduced.

  Moreover, the rate of temperature decrease from the above temperature after the end of the first step is preferably 50 ° C. or more, more preferably 100 ° C. or more per hour. When the temperature lowering rate is slow, a large number of single crystals may be formed, 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 milling. Thereby, acid can be spread to every corner in the acid treatment, and excess Bi ₂ O ₃ can be completely removed. Moreover, the ceramic powder which consists of plate-shaped particle | grains with a uniform magnitude | size can be created.

In the wet ball milling, balls having a diameter of 3 mm or more are preferably used. 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.
The wet ball milling is preferably performed at a rotational speed of about 30 to 200 times per minute.

Next, any inorganic acid can be used for the acid treatment in the second step. Of these, hydrochloric acid and nitric acid are particularly preferred. Furthermore, it is more preferable to use nitric acid, which is a water-soluble reactant with Bi ₂ O ₃ and can be easily removed.
The amount of acid in the acid treatment is preferably larger than the chemical equivalent that reacts with excess Bi ₂ O ₃ , preferably 20 mol% or more. The acid concentration is preferably in the range of 0.01 to 10 N. However, if the treatment time of nitric acid is too long, Bi is also extracted from the layered perovskite crystal structure containing Bi, so the treatment time must not be too long. Usually, excessive Bi can be removed by treatment within 1 hour.

Next, as post-treatment after the completion of the second step, it is preferable that the impurity anions in the acid adhering to the surface of the obtained ceramic powder or the compound of the impurity anions and bismuth be quickly washed away.
For this purpose, it is desirable to wash the powder after removing the acid with a weak alkaline aqueous solution such as aqueous ammonia. Moreover, it is preferable to wash with ion exchange water several times after the washing, preferably with distilled water.

Next, the operation of the ceramic powder manufacturing method will be described below.
In the above production method, the amount of Bi ₂ O ₃ in the ceramic raw material is excessive, and the ceramic raw material is maintained 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, Bi ₂ O ₃ in the liquid phase is generated, and the amount of Bi ₂ O ₃ is excessive, so that a layered perovskite crystal structure containing bismuth in the presence of the liquid phase Bi ₂ O ₃ is formed. The synthesis and grain growth of the ceramics it has proceeded.

For this reason, atom diffusion is facilitated as compared with the solid phase reaction, and a plate-like crystal having a surface with a low surface energy in the crystal structure and a spreading surface perpendicular to the major axis direction can be easily generated.
Moreover, since the production | generation of the plate-shaped crystal | crystallization in said 1st process is complete | finished in a short time, a manufacturing process can be shortened and manufacturing cost can be made cheap.

By the way, in general, in a layered perovskite crystal structure containing bismuth, a Bi ₂ O ₂ layer exists between connected perovskite unit cells. For this reason, the interface energy between the liquid phase Bi ₂ O ₃ is lowered. Therefore, when the layered perovskite crystal structure containing bismuth is covered with the liquid phase Bi ₂ O ₃ , the plate-like particles having the c-plane interface have a high energy gain.
That is, the c-plane is a surface having a low surface energy in the crystal structure.

Therefore, in the first step, a plate-like crystal having a c-plane in the layered perovskite crystal structure containing bismuth and having a spreading plane perpendicular to the major axis direction can be easily generated.
As described above, the ceramic (precursor) bonded with Bi ₂ O _{3 in} which the plate crystals are excessively present can be obtained by the first step.

In the second step, the ceramic (precursor) obtained in the first step is pulverized and acid-treated.
Since the excess Bi ₂ O ₃ is dissolved and removed by the acid treatment, Bi ₂ O ₃ can be removed without destroying the shape of the plate crystal obtained in the first step.

The plate-like particles constituting the ceramic powder obtained through the first step and the second step are perpendicular to the major axis in the c-plane of the layered perovskite crystal structure containing bismuth produced in the first step. It is a plate-like crystal with a broad surface.
Therefore, according to the present invention, a ceramic powder made of a plate-like powder having a high average aspect ratio can be obtained.

Further, in the above manufacturing method, the above-described oxide or a compound that becomes an oxide by thermal decomposition and Bi ₂ O ₃ are used as the ceramic raw material, and no impurity anion is contained in the ceramic raw material. Therefore, in this production method, the impurity anion may be mixed only in the acid treatment in the second step.
Therefore, a ceramic powder having a low content of impurity anions can be obtained as compared with conventional synthesis methods using chlorides and sulfates as raw materials.

  As mentioned above, according to the said manufacturing method, said outstanding ceramic powder can be obtained.

Embodiment 1
A ceramic powder according to an embodiment of the present invention, a method for producing the same, and an oriented ceramic produced using the ceramic powder will be described.
The ceramic powder of this example is a ceramic powder made of plate-like particles of Bi ₄ Ti ₃ O ₁₂ which is a ceramic having a layered perovskite 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.
A ceramic having a layered perovskite crystal structure containing bismuth to be obtained, that is, an element other than Bi constituting Bi ₄ Ti ₃ O _12, that is, Ti oxides of TiO ₂ and Bi ₂ O ₃ , In addition, a ceramic raw material in which Bi ₂ O ₃ is 10 mol% in excess of the amount necessary to form the ceramic is prepared.

Next, by heating them to a temperature equal to or higher than the melting point of Bi ₂ O ₃ , that is, 900 ° C., a first step of forming ceramics made of Bi ₄ Ti ₃ O ₁₂ is performed, and the obtained ceramics (precursor) is obtained. The 2nd process of forming the powder which consists of said ceramic plate-shaped particle | grains by grind | pulverizing and acid-treating is performed.

Next, the manufacturing method of 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 are contained in a molar ratio Bi ₂ O ₃ : TiO ₂ = 2.2: 3. That is, in this ceramic raw material, Bi is excessive by 10 mol%.
The ceramic raw material was mixed with water by a ball mill, and this was heated in the air or in oxygen at 900 ° C. for 4 hours, and the first step was performed to obtain a ceramic (precursor) as a reaction product.

The ceramics (precursor) was mixed in 1N nitric acid with a wet ball mill using zirconia balls for 1 hour, and the second step was performed to obtain a slurry-like substance.
Thereafter, the slurry was subjected to suction filtration, and the obtained substance was sufficiently washed with ammonia water and ion exchange water.
Thereafter, the washed product was dried to obtain a ceramic powder.
The ceramic powder obtained by performing the first step in the atmosphere is designated as sample 1, and the ceramic powder obtained by carrying out in oxygen is designated as sample 2.

When the ceramic powder concerning Sample 1 and Sample 2 was examined by X-ray diffraction, it was confirmed that these were Bi ₄ Ti ₃ O ₁₂ .
Further, when impurity anions (nitrate ions and chloride ions) remaining in Sample 1 and Sample 2 were examined using a reductive distillation / indophenol blue absorbance method and potentiometric titration method, these impurity anions were not detected. That is, it was found that the impurity anions contained in Sample 1 and Sample 2 were less than 500 ppm.

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

Next, a method for producing oriented ceramics made of Bi _0.5 Na _0.5 TiO ₃ using the ceramic powder according to Sample 1 as a host material and the oriented ceramics obtained thereby will be described.
The sample 1 which is a host material is mixed with Na ₂ CO ₃ , TiO ₂ and Bi ₂ O ₃ which are guest materials. This mixture is subjected to doctor blade molding to obtain a molded body. The obtained molded body is rolled to obtain a rolled body.

Next, hydrostatic pressure is applied to the rolled body. Thereafter, this was sintered at 1150 ° C. for 10 hours in oxygen to obtain a sintered body.
The perovskite phase composed of Bi _0.5 Na _0.5 TiO ₃ in the obtained sintered body had a (100) plane uniaxially preferentially expressed in pseudo cubic crystal, and the degree of orientation by the Lottgering method was 30%.
That is, oriented ceramics could be produced from Sample 1.

Next, the comparative sample C1 will be described.
This is an example in which ceramic raw materials similar to those of Sample 1 and Sample 2 were used, but ceramic powder having a small average aspect ratio was generated because the firing conditions in the first step were different.
First, the ceramic raw material used when manufacturing the sample 1 and the sample 2 is prepared. The ceramic raw material was heated in the atmosphere at a temperature of 800 ° C. for 4 hours to obtain a ceramic.

The obtained ceramics were mixed in 1N nitric acid in a wet ball mill using zirconia balls for 1 hour using the same process as Sample 1 and Sample 2 described above, and the second step was performed. Obtained.
Thereafter, the slurry was subjected to suction filtration, and the obtained substance was sufficiently washed with ammonia water and ion exchange water. Thereafter, the washed product was dried to obtain a ceramic powder according to comparative sample C1.

The comparative sample C1 was Bi ₄ Ti ₃ O ₁₂ according to X-ray diffraction, but the shape of the powder was close to a spherical shape and most had an average aspect ratio of 1.5 or less.
Further, in the same manner as the sample 1, the above-described 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 was 7%, and it was difficult to say that it was an excellent oriented ceramic. Moreover, 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 in} an amount necessary and sufficient to form Bi ₄ Ti ₃ O ₁₂ is used.
First, a ceramic raw material containing Bi ₂ O ₃ powder and TiO ₂ powder in a molar ratio Bi ₂ O ₃ : TiO ₂ = 2: 3 is prepared.

The ceramic raw material was mixed with water by a ball mill, and this was heated in the atmosphere or oxygen at 900 ° C. for 4 hours to obtain a ceramic as a reaction product.
Next, the obtained ceramic was mixed in 1N nitric acid with a wet ball mill using zirconia balls for 1 hour 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 exchange water, and the obtained washed product was dried to obtain a ceramic powder.
The ceramic powder obtained by heating in the atmosphere is referred to as a comparative sample C2, and the ceramic powder obtained by performing in oxygen is referred to as a comparative sample C3.

When the ceramic powder according to the comparative samples C2 and C3 was examined by X-ray diffraction, it was confirmed that these were Bi ₄ Ti ₃ O ₁₂ .
Further, the shapes of the comparative samples C2 and C3 were both close to a spherical shape, and most of the powders had an average aspect ratio of 1.5 or less.
Further, a Bi _0.5 Na _0.5 TiO ₃ sintered body was prepared by using the comparative sample C2 as a host material in the same manner as the sample 1, and the degree of orientation was 8%, which is not an excellent oriented ceramic. won. Moreover, various characteristics were not different from non-oriented ceramics.

  From the above, it has been found that an excellent oriented ceramic with a high degree of orientation can be produced from the ceramic powder according to this example. Moreover, it turned out that the ceramic powder with a large average aspect-ratio and few content of impurity anions can be obtained from the manufacturing method concerning this example.

Embodiment 2
This example is a method for producing a ceramic powder using hydrochloric acid for the acid treatment in the second step.
The ceramic raw material used in the manufacturing method of this example is the same ceramic raw material as that in the case of preparing the sample 1 of the first embodiment. And the same 1st process as the case where the sample 1 of Embodiment 1 was created was given with respect to the said ceramic raw material, and ceramics (precursor) was obtained as a reaction product.
Next, the 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, the obtained substance was sufficiently washed with ammonia water and ion exchange water, and the washed product was dried to obtain a ceramic powder.
The ceramic powder obtained by performing the first step in the atmosphere is designated as sample 3, and the ceramic powder obtained by carrying out in oxygen is designated as sample 4.

When the ceramic powder concerning Sample 3 and Sample 4 was examined by X-ray diffraction, it was confirmed that these were Bi ₄ Ti ₃ O ₁₂ .
Further, when impurity anions (chlorine ions) remaining in Sample 3 and Sample 4 were examined in the same manner as in Example 1, 900 ppm of residual chlorine was detected. When examined in the same manner as in Example 1, the average aspect ratio of Sample 3 was about 3.9, and 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
In this example, a ceramic powder manufacturing method using a ceramic raw material containing Bi ₂ O ₃ in excess will be described, the performance of the obtained ceramic powder, and oriented ceramics prepared from this ceramic powder.

The ceramic raw material used in this example consists of Bi ₂ O ₃ powder and TiO ₂ powder, and these are contained in a molar ratio of Bi ₂ O ₃ : TiO ₂ = 1: 1. That is, in this ceramic raw material, Bi is in excess of 50 mol%.
The ceramic raw material was mixed with water by a ball mill, heated in oxygen at 900 ° C. for 4 hours, and the first step was performed to obtain a ceramic (precursor) as a reaction product.

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

When the ceramic powder according to Sample 5 was examined by X-ray diffraction, it was confirmed that these were Bi ₄ Ti ₃ O ₁₂ .
Further, when impurity anions (nitrate ions and chlorine ions) remaining in the sample 5 were examined by the same method as in Embodiment 1, these impurity anions were not detected. That is, it was found that the impurity anion contained in the sample 5 was less than 500 ppm. Further, when the average aspect ratio of Sample 5 was determined in the same manner as in Example 1, the average aspect ratio was about 20.

Next, using the sample 5 as a host material and NiO, TiO ₂ , PbO, Bi ₂ O ₃ as guest materials, a sintered body made of Bi _0.5 Na _0.5 TiO ₃ was prepared in the same manner as in Example 1. .
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 an oriented ceramic superior to the sample 5 can be produced.

Further, the sample 5 to the host _{material, NiO, TiO 2, PbO,} Bi 2 O 3 with a guest material, further NiO, PbO, consisting _{Bi 0.5 Pb 0.5 Ni 0.25 Ti 0.75} O 3 TiO ₂ as conversion material sintered body It was created.
The conversion material is a substance for reacting with the sample 5 as the host material, that is, Bi ₄ Ti ₃ O ₁₂ to generate Bi _0.5 Pb _0.5 Ni _0.25 Ti _0.75 O ₃ .

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 prepared in the same manner as in Embodiment 1.
When the degree of orientation of this sintered body was measured in the same manner as in Example 1, the degree of orientation was 78%. That is, it was found that an oriented ceramic superior to the sample 5 can be produced.

Embodiment 4
This example explains how the performance of a dielectric made of ceramic powder varies 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 production method as in Embodiment 3.
A dielectric is produced using this ceramic powder.

First, the ceramic powder was hot pressed (pressure: 20 MPa) at a temperature of 1050 ° C. for 1 hour to obtain a hot pressed body (dielectric). Next, the hot press body was polished, and then a gold electrode was provided thereon, and an electric field of 40 kV / cm was applied in 100 ° C. silicon oil.
When the leakage current at this time was measured, it was less than 1 mA / cm ³ .

By the way, as shown below, a ceramic powder having a high content of impurity anions was prepared to obtain a dielectric.
That is, the same weight of powder mixed at a ratio of Bi ₂ O ₃ : TiO ₃ = 2: 3 (molar ratio, corresponding to stoichiometric ratio) and powder mixed at NaCl: KCl = 1: 1 (molar ratio). Weigh and mix.
The powder thus obtained was heated in a platinum crucible at a temperature of 1050 ° C. for 1 hour.
The lump obtained by the heating was washed in warm water and subjected to suction filtration to obtain a powder.

When the above powder was examined, the composition was Bi ₄ Ti ₃ O ₁₂ , which was 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 contained 0.24% by weight (2400 ppm) of chlorine ions.
Finally, the powder was hot pressed by the same method as described above to obtain a hot pressed body (dielectric). Next, the hot press body was polished, and then a gold electrode was provided thereon, and an electric field of 15 kV / cm was applied in 100 ° C. silicon oil.

When the leakage current at this time was measured, a current exceeding 2 mmA / cm ³ was observed. That is, it was found that the leakage current in this hot press body was higher than that of the above-described impurity anion content, and a higher leakage current flowed at a lower voltage.

  From the above, it was found that the smaller the content of impurity anions, the smaller the leakage current, and thus the better the insulation.

  As described above, according to the present invention, an oriented ceramic with a high degree of orientation can be produced, and a ceramic powder and a precursor thereof having high insulation can be provided.

Claims (4)

A precursor for obtaining a ceramic powder having an impurity anion content of 1000 ppm or less,
A plate-like ceramic powder having a layered perovskite type crystal structure containing bismuth, Ri Do from the Bi ₂ O _3,
The amount of Bi ₂ O ₃ in the precursor is 5 mol% or more,
The ceramics having a layered perovskite crystal structure containing the bismuth of the plate-like powder are Bi ₄ Ti ₃ O ₁₂ (bismuth titanate), Bi ₂ VO _5.5 , Bi ₂ WO ₆ , Bi ₃ TiNbO ₉ , Bi _3. TiTaO 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 , PbBi 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, and BaBi ₅ Ti ₄ or consisting of a compound selected from FeO _18, these A combination of two or more of the compounds
A precursor of a ceramic powder, wherein the plate-like powder is bonded by the Bi ₂ O ₃ . 2. The composition according to claim 1, comprising an oxide of an element other than Bi constituting the ceramic having a layered perovskite crystal structure containing bismuth or a compound that becomes an oxide by thermal decomposition and Bi ₂ O ₃ , and contains the bismuth. Preparing a ceramic raw material in which Bi ₂ O ₃ is in excess of 5 moles more than the amount necessary for forming a ceramic having a layered perovskite crystal structure , and then heating them to the melting point of Bi ₂ O ₃ precursor of ceramic powder characterized in that it is obtained by. A ceramic powder obtained by pulverizing and acid-treating the precursor according to claim 1 or 2 to form a powder comprising the ceramic plate-like particles. A ceramic powder for producing oriented ceramics for use in various sensors or devices,
The ceramic powder is composed of ceramic plate-like particles having a layered perovskite 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 ceramics having a layered perovskite crystal structure containing the bismuth of the plate-like powder are Bi ₄ Ti ₃ O ₁₂ (bismuth titanate), Bi ₂ VO _5.5 , Bi ₂ WO ₆ , Bi ₃ TiNbO ₉ , Bi _3. TiTaO 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 , PbBi 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, and BaBi ₅ Ti ₄ or consisting of a compound selected from FeO _18, these A ceramic powder comprising a combination of two or more compounds .