JP3526886B2 - Method for producing composite oxide - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a metal alkoxide complex for obtaining a complex oxide used for a laminated ceramic capacitor and the like, and a method for producing a complex oxide such as a perovskite oxide from the metal alkoxide complex. And a sintered body, a plate-shaped body and a film of the obtained perovskite oxide.

[0002]

2. Description of the Related Art A solid-phase reaction method or a wet method is generally used to produce various composite oxides such as perovskite oxides which are widely used in multilayer ceramic capacitors and the like.

When the solid-phase reaction method is used, it is difficult to effectively remove impurities derived from the raw materials or in the process, so that there are many impurities, and composition nonuniformity is likely to occur due to poor mixing when the raw materials are mixed. In addition, there is a problem that high temperature firing of 1000 ° C. or higher is required.

As the wet method, there are a so-called coprecipitation method using a metal salt, a hydrolysis method using a metal alkoxide, and the like. In the coprecipitation method, impurities derived from raw materials are likely to remain, and compounds having different precipitation conditions are treated under the same conditions. However, since the composition is likely to be non-uniform, the heat treatment requires a high temperature, and a step of breaking the agglomerated particles is required.

Further, in the hydrolysis method, a metal alkoxide mixed alcohol solution is obtained and a hydrolysis reaction is carried out, and the obtained oxide or hydroxide precipitate is dried, pulverized and calcined to obtain the target compound. . Also in this method, when obtaining the metal alkoxide mixed alcohol solution, for example, when the metal alkoxide complex as a raw material is unstable and gels in an alcohol solution, or when performing large-scale processing in industrial production,
Since it is difficult to maintain the homogeneity of the composition in the reaction tank, a composite compound may not be obtained. Also, the point that a high temperature is required for the heat treatment is similar to the above method. Further, there are problems that impurities derived from raw materials and processes are likely to remain, and the price becomes expensive.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a complex oxide having high purity and maintaining precise compositional uniformity, particularly a metal alkoxide for obtaining a tetragonal perovskite type oxide at a low heat treatment temperature. It is to provide a method for producing a complex, a method for producing a complex oxide from the obtained metal alkoxide complex, and a sintered body, a plate-shaped body and a film of the obtained tetragonal perovskite type oxide.

[0007]

Such an object is achieved by the following constitutions (1) to (8). (1) In a mixed solvent containing a saturated alcohol having 1 to 5 carbon atoms and benzene, a first metal of Ba and a second metal of Ti are used.
A method for producing a composite oxide, comprising producing an alkoxide complex having a metal, isolating the metal alkoxide complex to obtain a metal alkoxide complex, heat-treating the metal alkoxide complex, and sintering. (2) The method for producing a composite oxide according to (1), which is a sintered body of tetragonal perovskite oxide. (3) A method for producing a composite oxide, which is a sintered body of the tetragonal perovskite oxide according to the above (2), having an average crystal grain size of 0.01 to 100 μm. (4) The method for producing a composite oxide according to (1) above, wherein a plate-shaped body of tetragonal perovskite oxide is obtained. (5) The method for producing a composite oxide according to (1) above, wherein a tetragonal perovskite oxide film is obtained. (6) The method for producing a composite oxide according to any one of (1) to (5), wherein the metal is present in the mixed solvent in a total amount of 0.01 to 5 mol / L in terms of metal. (7) The mixing ratio of benzene and alcohol of the mixed solvent is such that (benzene) / (alcohol) is 1 to molar ratio.
10. The method for producing a composite oxide according to any one of (1) to (6), which is 10. (8) The method for producing a composite oxide according to any one of (1) to (7) above, wherein a single crystal metal alkoxide complex is obtained.

[0008]

FUNCTION AND EFFECT The present invention provides an alkoxide complex having two or more kinds of metals constituting the target composite oxide,
Obtained in a mixed solvent containing alcohol and benzene or a benzene derivative. Then, the metal alkoxide complex is deposited as a single crystal and isolated.

Since the complex forms a single crystal, the composition of the obtained composite oxide is precisely controlled, the purity is high, and the composition is highly uniform. In addition, by using the means of recrystallization, it is possible to achieve a higher purity.

When a similar reaction is carried out in an alcohol solvent in which benzene or a benzene derivative is not present, in most cases, the reaction product eventually gels and becomes insoluble.

In particular, when a perovskite type oxide is obtained, the single crystal obtained by the method of the present invention is used in an oxidizing atmosphere.
Tetragonal crystals can be obtained even if heat treatment is performed at a temperature lower than the conventional temperature of about 0 to 600 ° C. Tetragonal perovskite oxide is a ferroelectric substance. Therefore, there is no need for heat treatment to turn a cubic paraelectric into a tetragonal crystal, and the temperature for sintering etc. can be made lower than before, and the wide range of choices such as conditions and materials used. With.

Furthermore, when obtaining the above-mentioned single crystal, by selecting the deposition conditions such as the deposition temperature and the concentration, single crystals of various shapes such as plate-like, needle-like or film-like can be obtained. By performing heat treatment while maintaining these shapes, ferroelectric perovskite compounds having various shapes such as a plate shape and a film shape can be obtained without going through a molding step.

[0013]

Specific Structure The specific structure of the present invention will be described in detail below.

In the production method of the present invention, of two or more kinds of metals constituting the target composite oxide, for example, one metal or its alkoxide and the other metal or its alkoxide are used as alcohol, benzene or benzene. An alkoxide complex is obtained by reacting in a mixed solvent containing a derivative. From the solution containing the metal alkoxide complex obtained by the reaction, the metal alkoxide complex is deposited as a single crystal. At this time, the shape of the obtained single crystal can be plate-like, needle-like, or film-like depending on the purpose.

By subjecting this single crystal to further heat treatment, a composite oxide can be obtained, and in particular, tetragonal perovskite oxides having various shapes other than fine powder can be obtained.

(1) Complexation reaction Ba and Ti are used as the raw material metal components used in the production of the metal alkoxide complex. These raw material metal components may be used in predetermined amounts so that the final product has a desired composition. By using these metals, for example, perovskite oxide, spinel oxide, etc. can be obtained.

In particular, in order to obtain a perovskite oxide, Ba and Ti are used as raw material metal components used for producing the metal alkoxide complex. Ferroelectric perovskite oxides can be obtained by using these raw material metal components in predetermined amounts so that the final product has a desired composition.

The reaction of such raw material metal components is as follows.
There are the following modes.

(A) A metal alkoxide complex of the raw material metal component alone is obtained, and two or more kinds of the metal alkoxide complexes are reacted. (b) Reacting at least one metal with at least one alcohol and at least one metal alkoxide complex. (c) Two or more kinds of metals and alcohol are used. (d) In (b) and (c) above, a metal salt is used instead of the metal.

These methods can be used.

As the alcoholate ligand of the alkoxide complex as the raw material, the same one as the alkoxy group of the solvent alcohol is preferably used. Metals that can be used as the alkoxide complex include Ba and Ti.
Specific examples of the alkoxide complex used include methoxide, ethoxide, propoxide, butoxide, pentyl oxide, ethoxyethoxide and methoxyethoxide of these metals. For example, Ti (OC3 H7-i
) 4.

The number of alcoholato ligands in the starting alkoxide complex is usually 1-6. In the same alkoxide complex, the alcoholate ligands coordinated to the metal are usually the same, but they may be different depending on the case.

It is also preferable to use the metal as it is, but examples of such materials include Ba, Ca, Sr and N.
a, K, Li, etc. can be mentioned. Further, examples of the metal salt include halides such as chlorides and bromides of the metals and Pb exemplified above, and organic acid salts and oxides such as acetates and oxalates of the above metals.

The raw materials used in the complexation reaction to obtain the tetragonal perovskite oxide, the reaction conditions, the isolation of the obtained complex, the method for producing the oxide, and the sintering will be described in detail below.

First, among the above-mentioned metals, the first raw material metal component of Ba and the second raw material metal component of Ti are expressed by the following formula: (first raw material metal component) / (second raw material metal component) It is preferable to use it in an atomic ratio of about 0.3 to 3.3.

If the first raw material metal component is too much, gelation occurs,
It will cause precipitation. Further, if the amount of the first raw material metal component is too small, the yield of the composite alkoxide complex will decrease.

The solvent used is a mixed solvent containing alcohol and benzene or a benzene derivative.

Alcohols preferably used include
There are saturated alcohols having 1 to 5 carbon atoms such as methyl alcohol, ethyl alcohol, propyl alcohol and butyl alcohol.

[0029]

Each of these alcohols and benzene may be used alone as a mixed solvent, two or more of each may be used as a mixed solvent, or one of them may be used alone and the other of two or more may be used as a mixed solvent. .

The mixing ratio of benzene and alcohol component is
(Benzene) / (alcohol) in a molar ratio of 1 to 10,
More preferably, it is set to 2-6. If the alcohol component is too large, crystals will not easily precipitate, while if it is too small, the metal raw material components will be difficult to dissolve.

The total amount of raw material metal components in such a mixed solvent is 0.01 to 5 mol / L in terms of metal, preferably 0.2 to
It is preferable to add it so that the concentration becomes 2 mol / L. A single crystal can be efficiently obtained in this concentration range. If the concentration of the raw material metal component is higher than this range, precipitation tends to occur without forming crystals, and if it is too low, crystals are less likely to precipitate.

Using such a raw material, a reaction treatment is carried out in an inert gas atmosphere at a temperature of 10 to 80 ° C., more preferably 15 to 60 ° C., preferably 30 minutes to 100 hours.
If the reaction temperature is too high, the solvent will boil or react rapidly, and the reaction will not proceed stably. If the reaction temperature is too low, the reaction rate is too slow, and the reaction takes a long time, which is not preferable.

If the reaction time is too short, the reaction and dissolution will be insufficient, and if it is too long, the effect will not change.

When a metal is used as a raw material, it is preferable to wash it with methyl alcohol, benzene or the like in advance, and it is preferable to further purify the solvent to be used by an appropriate means such as dehydration or distillation. By carrying out the above reaction after such pretreatment, a product with higher purity can be obtained.

As described above, the content ratios of the first and second raw material metal components, the concentration of the metal components in the solvent, the composition and ratio of the mixed solvent used, and the atmosphere, temperature, time, etc. used for the reaction are controlled. By doing so, it is possible to obtain a composite compound in which the composition and the stoichiometric ratio are precisely controlled and the purity is high and the composition is uniform.

By such a reaction, a metal alkoxide complex complex [presumed to be BaTi (OR) ₆ .xC ₆ H ₆ or the like: OR is an alcoholato ligand (alkoxy group)] is produced.

(2) Isolation of Complex The reaction solution thus obtained is allowed to stand at 0 to 35 ° C, the temperature is set to about 30 to 60 ° C to evaporate the solvent, and the temperature is set to 0 to 0 ° C. Crystals can be precipitated by lowering the temperature to about -20 ° C. After this it is isolated.

At this time, for example, by controlling the conditions at the time of precipitation, the concentration of the produced metal alkoxide complex in the mixed solvent, and changing the precipitation temperature, for example, plate-like, needle-like or Film-like crystals with various morphologies and thicknesses can be obtained.

The plate-like crystals have, for example, a metal component concentration in the mixed solvent of about 0.4 to 1 mol / L in terms of metal, and 1
Hold at a temperature of about 5 to 30 ° C. Under such conditions,
Plate-like crystals having an average length of one side of the main surface of 1 to 20 mm are obtained.

Further, the needle-like crystals are deposited while the concentration of the metal component in the mixed solvent is about 0.4 to 1 mol / L in terms of metal in total and the mixed solvent is concentrated at a temperature of about 30 to 50 ° C. while concentrating the mixed solvent. Under such conditions, crystals having an average major axis length of about 1 to 10 mm and an aspect ratio of about 5 to 20 obtained by dividing the average major axis length by the average minor axis length can be obtained.

The film-like crystal has, for example, a metal component concentration in the mixed solvent of about 0.4 to 1 mol / L in terms of metal, and a container for containing the reaction solution at the time of crystallization is a flat substrate. It can be obtained by gradually precipitating and growing crystals under the temperature condition of about 5 to 15 ° C. At this time, by controlling the shape of the flat substrate and the amount of the reaction solution, it is possible to obtain a film crystal having an arbitrary shape and thickness.

The precipitated crystals may be recrystallized one or more times in order to improve the crystal purity. The above solvent is used for recrystallization.

Crystals of the metal alkoxide complex thus obtained are, for example, BaTi (OR) ₆ .xC ₆ H ₆
[OR is an alcoholate ligand (alkoxy group)], which is a single crystal of a complex metal complex. It can be confirmed that the obtained crystal has such a single crystal form by morphological observation with a polarization microscope or the like, or by a method such as X-ray diffraction, fluorescent X-ray analysis, optical microscope, or elemental analysis.

(3) Perovskite Oxide The single crystal is preferably heated to 200 to 1000 ° C., more preferably 300 to 1000 ° C. in an oxidizing atmosphere excluding carbon dioxide gas.
Heat treatment is preferably performed at 850 ° C. for about 30 minutes to 12 hours. As a result, a dealkoxy reaction occurs, and at the same time, crystallization and densification that form a perovskite structure occur. And
A tetragonal ferroelectric perovskite oxide is obtained.

If the heat treatment temperature is too low, the transition to the oxide tends to be insufficient, while if it is too high, the oxide is abruptly formed and the shape is disturbed or the oxide is cracked. . If the heat treatment time is too short, the reaction will be insufficient,
Too long becomes impractical.

It can be confirmed by X-ray diffraction (XRD) or transmission electron microscope (TEM) that the perovskite oxide obtained by such heat treatment is tetragonal.

The oxidizing atmosphere during the heat treatment is, for example, an atmosphere containing water vapor, in addition to the atmosphere excluding carbon dioxide gas.
A high oxygen concentration atmosphere or an atmosphere containing ozone may be used. It is preferable to remove carbon dioxide gas in these atmospheres.

When obtaining a plate-shaped, needle-shaped or film-shaped perovskite oxide, a complex single crystal having a corresponding shape is obtained,
A tetragonal perovskite oxide can be formed while leaving the plate-like, needle-like, or film-like shape. In these cases, the crystals of the colorless and transparent complex usually turn white as the dealkoxy reaction proceeds. When this is heat-treated, a tetragonal perovskite oxide is obtained.

In the case of the plate-shaped, a plate-shaped tetragonal perovskite oxide having an arbitrary size in which one side of the main surface has an average length of about 0.01 to 20 mm is obtained. In the case of needles, the average major axis length is about 0.01 to 10 mm and the aspect ratio is 5 to 5.
A needle-shaped tetragonal perovskite oxide having an arbitrary size of about 20 can be obtained. In the case of a film, a tetragonal perovskite oxide in the form of a film having an arbitrary thickness of about 0.01 to 2 mm can be obtained.

When a fine powdery perovskite oxide is obtained for sintering which will be described later, the obtained single crystal is crushed in air without carbon dioxide gas or in an inert gas,
The heat treatment may be performed under the above conditions. The average particle size of the obtained fine particles is usually about 0.002 to 0.1 μm.

The obtained perovskite oxide is sintered in the case of powder or plate. That is, it is preferably molded in an oriented state, sintered in an oxidizing atmosphere, preferably at a temperature of 600 to 1400 ° C., preferably for 30 minutes to 6 hours, and used as a dielectric sintered body. If the sintering temperature is too low or the sintering time is too short, it becomes difficult to sinter, while if it is too high or too long, the grains become too large and the strength of the sintered body becomes insufficient. At this time, grains having an average crystal grain size of about 0.01 to 100 μm are usually obtained.

Further, a fine powder of metal alkoxide complex,
A preferable composite oxide sintered body can also be obtained by obtaining a plate-shaped or needle-shaped single crystal, molding it, and sintering it. The sintering conditions in this case may be the same as the above sintering conditions.

The fine powdery tetragonal perovskite oxide thus obtained is used as a low temperature sintering dielectric paste or the like, and the plate-like tetragonal perovskite oxide is surface-oriented and sintered It is possible to obtain a uniaxially aligned sintered body and use it for an optical shutter, an optical storage element, or the like. In addition, the acicular tetragonal perovskite oxide is oriented in the acicular direction and sintered to obtain a uniaxially aligned sintered body, which can be used as electrostriction, a piezoelectric element, or the like. Further, the film-shaped tetragonal perovskite oxide can be used for a memory element, an optical shutter, or the like.

[0055]

EXAMPLES The present invention will be described in more detail below by showing specific examples of the present invention.

Example 1 Using metal Ba and titanium tetraisopropoxide [Ti (OC ₃ H ₇ -i) ₄ ] as raw material metal components, Ba was used.
An amount such that the atomic ratio of / Ti was 1 was put into a mixed solvent of isopropyl alcohol (IPA) and benzene, mixed by stirring, and kept at 45 ° C for reaction and dissolution.
All treatments were performed under Ar atmosphere. The mixing ratio of IPA and benzene is benzene / IPA, and the molar ratio is 4
And In addition, the concentration of the metal raw material components added to the mixed solvent used was 1.0 mol / L in total in terms of metal. The metal Ba used had been washed in advance with benzene and methyl alcohol. Furthermore, the IPA and benzene used were dehydrated and distilled and purified.

After being kept under such conditions, after 16 hours, the red transparent liquid was kept at 18 ° C. for 1 day, and it was confirmed that crystals were precipitated. The solvent of the solution containing the obtained crystals was removed, and the crystals were washed with benzene. The obtained crystal was subjected to a structural analysis by a four-axis X-ray diffractometer and a Ba / Ti ratio analysis by a fluorescent X-ray analyzer. The BaTi alkoxide complex had a chemical formula of BaTi (OC ₃ H ₇ -i) ₆
· It xC is ₆ H ₆ and estimated single crystal was confirmed.

Next, the obtained crystals were heat-treated at 600 ° C. for 3 hours in the air excluding carbon dioxide gas. The resulting white fine powder had an average particle size of 0.03 μm. Further, as a result of analysis by XRD and TEM, it was confirmed to be a tetragonal crystal. In addition, as a result of TEM observation, it was confirmed to be a single crystal.

Comparative Example 1 When benzene was removed as the solvent to be used and IPA was added in an equimolar amount to the removed benzene, the reaction was carried out in the same manner as in Example 1 and no crystals grew. This solution gelled and insolubilized when left for one week, and a single crystal was not obtained.

Example 2 The solution containing the crystal obtained in Example 1 was allowed to stand for one week to grow a crystal, and one side of the main surface had an average length of 8 mm and a thickness of 1 mm.
mm plate-like crystals were obtained.

This crystal was heat-treated at 800 ° C. for 3 hours in the air excluding carbon dioxide, and the average length of one side of the main surface was about 6.
Plate-like BaTiO ₃ crystals with a thickness of 0.75 mm were obtained. When this crystal was analyzed by X-ray diffraction, it was a tetragonal crystal.

Example 3 The BaTiO ₃ tetragonal plate crystal obtained in Example 2 was shaped in an oriented state and sintered in air at 1000 ° C. for 1 hour to obtain a sintered body having a dielectric constant of 1800. It was The average grain size was 0.2 μm.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI C30B 29/22 C04B 35/00 A (56) Reference JP-A-3-285827 (JP, A) JP-A-3-115106 ( JP, A) JP 5-319927 (JP, A) JP 5-306165 (JP, A) JP 5-306122 (JP, A) JP 5-39535 (JP, A) JP HEI 5-51755 (JP, A) JP 63-307118 (JP, A) JP 59-213665 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C07C 31 / 00 C07C 29/00 C04B 35/00 C01G 1/00 C01G 23/00

Claims (8)

(57) [Claims] 1. An alkoxide complex having a first metal of Ba and a second metal of Ti is formed in a mixed solvent containing a saturated alcohol having 1 to 5 carbon atoms and benzene, and this metal alkoxide complex is A method for producing a composite oxide, which comprises isolating and obtaining a metal alkoxide complex, heat-treating this metal alkoxide complex, and sintering. 2. The method for producing a composite oxide according to claim 1, which is a sintered body of tetragonal perovskite oxide. 3. The method for producing a composite oxide, which is a sintered body of tetragonal perovskite oxide according to claim 2, having an average crystal grain size of 0.01 to 100 μm. 4. The method for producing a composite oxide according to claim 1, wherein a plate-shaped body of tetragonal perovskite oxide is obtained. 5. The method for producing a composite oxide according to claim 1, wherein a tetragonal perovskite oxide film is obtained. 6. The method for producing a composite oxide according to claim 1, wherein the metal is present in the mixed solvent in a total amount of 0.01 to 5 mol / L in terms of metal. 7. The method for producing a composite oxide according to claim 1, wherein the mixing ratio of benzene and alcohol in the mixed solvent is (benzene) / (alcohol) in a molar ratio of 1 to 10. . 8. The method for producing a composite oxide according to claim 1, wherein a single crystal metal alkoxide complex is obtained.