JP5488199B2 - Method for producing composite oxide powder - Google Patents

Description

  The present invention relates to a method for producing a complex oxide, and more particularly to a method for producing a complex oxide that can be suitably used as a ceramic raw material for a ceramic electronic component.

Conventionally, as a method for producing (synthesizing) composite oxides such as BaTiO ₃ , BaZrO _{3, and} SrTiO ₃ used as ceramic raw materials, a solid-phase reaction in which the composite oxides are synthesized by firing (calcining) the raw materials at a high temperature. The law is widely known. However, in this method, since it is manufactured through a heat treatment (firing) step at a high temperature, there is a problem that the particle size is large and the particle tends to be non-uniform.

  Therefore, as a method for solving such problems, a method of synthesizing a complex oxide by a chemical reaction in a solution has been proposed as follows.

(1) One of them relates to a method for producing a ceramic raw material powder such as BaTiO ₃ or SrTiO ₃ (see Patent Document 1).
In the case of the method of Patent Document 1, nitrates and chlorides are used as starting materials, and alkali is added to an aqueous solution in which these are dissolved in water. First, B site elements such as Ti and Zr are precipitated as hydroxides. After that, by adding an organic acid such as oxalic acid, citric acid, tartaric acid, etc., the A site element such as Ba, Sr, Ca, etc. is precipitated as an organic acid salt, and the powder obtained by calcination, washing with water and drying is calcined. The ceramic raw material powder is obtained by pulverization.

  (2) As another method for synthesizing a composite oxide by a chemical reaction in a solution, a method similar to the method of Patent Document 1 has been proposed (see Patent Document 2). In the case of the method of Patent Document 2, B site element hydroxides such as Ti and Zr are precipitated in a first tank, and A site element organic acids such as Ba, Sr and Ca are precipitated in a second tank. After precipitating the salt, the slurry in the first tank and the slurry in the second tank are mixed, filtered, washed with water, and dried, and the powder obtained by calcination and pulverization is used to obtain a ceramic raw material powder. Yes.

(3) Still another method of synthesizing a composite oxide by a chemical reaction in a solution relates to a method of synthesizing BaTiO ₃ powder by a so-called oxalic acid method. Ti ions and Ba ions are converted into barium titanyl oxalate. Then, BaTiO ₃ is obtained through the steps of washing, filtration and calcination (see Non-Patent Document 1).

Japanese Patent Publication No.2-10089 Japanese Patent Publication No.2-10091

Material integration vol. 21 No. 7 (2008) pp86-91 “Nanopowder of barium titanate by oxalic acid method”

  However, in the case of the method of Patent Document 1, since the A site element is precipitated after the B site element is first precipitated, the components of the A site and the B site are separately precipitated. The dispersibility of each element in the whole is not necessarily good, and there is a problem that the uniformity tends to be insufficient.

  Also, in the case of the method of Patent Document 2, as in the case of Patent Document 1, each component of the A site and B site is separately precipitated and then mixed together. There is a problem that the dispersibility and homogeneity of the elements are almost the same as those of the solid phase method and are not always satisfactory.

On the other hand, in the method of the cited document 3, since each component of the A site and the B site is precipitated as one compound (barium titanyl oxalate), there is an advantage that the dispersibility of Ba and Ti is uniform at the atomic level. .
However, a precipitate powder can be obtained only with the composition of the compound, and there is a problem that the degree of freedom in composition is low.
Furthermore, since the precipitated powder is an aggregate of about several tens of μm, there is a problem that this aggregate skeleton remains after calcination, and coarse particles tend to remain in the composite oxide (for example, BaTiO ₃ ) that is the final product.

  The present invention solves the above-described problems, and efficiently produces a complex oxide having a high degree of freedom in composition, having a target composition, and being fine and excellent in uniform dispersibility of each element. An object of the present invention is to provide a method for producing a composite oxide that can be used.

In order to solve the above problems, the method for producing a composite oxide of the present invention comprises:
(a) at least one selected from the group consisting of Ba chloride, Sr chloride, Ca chloride and La chloride, and at least one of Ti chloride and Zr chloride A step of preparing an aqueous solution containing substance B and tartaric acid,
(b) By adjusting the pH of the aqueous solution to the alkali side, at least one of Ba, Sr, Ca and La derived from the substance A, and at least one of Ti and Zr derived from the substance B Precipitating a composite oxide precursor comprising:
(c) The composite oxide precursor is heat-treated to synthesize a composite oxide containing at least one selected from the group consisting of Ba, Sr, Ca and La and at least one of Ti and Zr as main components. And the step of performing.

  In the method for producing a composite oxide of the present invention, the amount of tartaric acid added is 0.3 to 2.0 times the sum of the molar amounts of metal ions contained in the aqueous solution in the step (a). A range is desirable.

  In the method for producing a composite oxide of the present invention, the method for adjusting the pH of the aqueous solution to the alkali side is at least one selected from the group consisting of ammonium hydroxide, sodium hydroxide, potassium hydroxide, and lithium hydroxide. It is desirable to use a method of adding seeds to the aqueous solution.

  The method for producing a composite oxide of the present invention comprises a substance A that is at least one selected from the group consisting of Ba chloride, Sr chloride, Ca chloride, and La chloride, Ti chloride, and By adjusting the pH of an aqueous solution containing at least one of the Zr chlorides and the tartaric acid to the alkali side, at least one of Ba, Sr, Ca and La derived from the substance A, and the substance B And precipitating a composite oxide precursor containing at least one of Ti and Zr derived from the material, heat treating the composite oxide precursor, and at least one selected from the group consisting of Ba, Sr, Ca and La Since a composite oxide containing at least one of Ti and Zr as a main component is synthesized, the degree of freedom in composition is high, the target composition is fine, and each element is uniform. To dispersibility The becomes a composite oxide can be efficiently produced.

That is, in the present invention, the complex oxide precursor is precipitated by adjusting the pH of the aqueous solution in which the substances A and B are dissolved to the alkali side. Excellent precipitated powder can be obtained.
Therefore, a composite oxide having a target composition can be synthesized by heat-treating (calcining) the obtained composite oxide precursor at a relatively low temperature of 700 to 800 ° C., for example.

  In addition, the composite oxide powder (calcined powder) obtained by performing the above heat treatment is a loose agglomerate composed of fine primary particles of about 100 nm. Thus, it becomes possible to obtain a composite oxide having a uniform particle size.

  In addition, according to the present invention, a precipitated powder (composite oxide precursor) according to the charged composition can be obtained, and the composite oxide having the target composition can be efficiently obtained by heat-treating (calcining) it. Can do. Therefore, it can be said that the present invention is extremely significant in that it is excellent in uniform dispersibility of elements and at the same time has a high degree of freedom in composition.

  In the method for producing a composite oxide of the present invention, the amount of tartaric acid added is 0.3 to 2.0 times the sum of the molar amounts of metal ions contained in the aqueous solution containing substance A, substance B and tartaric acid. (In other words, most of the metal ions in the aqueous solution can be recovered as a precipitate by adjusting the molar ratio to 0.3 to 2.0 times). (Precursor) can be obtained, and the dispersibility of the metal ions in the precipitate is increased, so that the present invention can be made more effective.

In the method for producing the composite oxide of the present invention, as a method for adjusting the pH of the aqueous solution to the alkali side, at least one selected from the group consisting of ammonium hydroxide, sodium hydroxide, potassium hydroxide, and lithium hydroxide is used. By adopting the method of adding to the aqueous solution, it becomes possible to reliably precipitate the precipitated powder (complex oxide precursor) according to the charged composition.
In the present invention, as described above, the method is not limited to the method of adding alkali. For example, urea powder that does not correspond to alkali in the powder state is added to the aqueous solution and hydrolyzed as in the following formula. It is also possible to configure so that the pH of the aqueous solution is adjusted to the alkali side by generating alkali (NH ₃ ).
(NH ₂ ) ₂ CO + H ₂ O → 2NH ₃ + CO ₂

It is a figure which shows the SEM image of the precipitated powder (complex oxide precursor) obtained in Example 1, (a) is 5000 times and (b) is 30000 times. It is a figure which shows the result of the WDX element mapping analysis of the precipitated powder obtained in Example 1. FIG. It is a figure which shows the X-ray-diffraction pattern of the complex oxide powder obtained by calcining the precipitated powder in Example 1. Is a diagram showing an SEM image of the composite oxide powder precipitated powder obtained by calcination (BaTiO ₃ powder) in Example 1, is (a) 5000 times, (b) those of 30000 times. In the comparative example 1, it is a figure which shows the result of the WDX element mapping analysis of the precipitated powder obtained using barium carbonate as a barium raw material. In the comparative example 1, it is a figure which shows the result of the WDX element mapping analysis of the precipitation powder obtained using barium hydroxide as a barium raw material. It is a figure which shows the TG curve of the precipitated powder containing Ba and Ti produced using various barium salts of barium chloride, barium carbonate, and barium hydroxide. Is a diagram showing an SEM image of the composite oxide powder precipitated powder obtained by calcination in Example 3 (BaTiO ₃ powder) is (a) 5000 times, (b) those of 30000 times. It is a figure which shows the result of the WDX elemental mapping analysis of the precipitated powder obtained in Example 4. It is a diagram showing an X-ray diffraction pattern of the composite oxide powder obtained by calcining the precipitate powder in Example 4 (BaZrO ₃ powder). It is a figure which shows the SEM image of the complex oxide powder obtained by calcining the precipitated powder in Example 4, (a) is 5000 times, (b) is 30000 times. It is a figure which shows the result of the WDX elemental mapping analysis of the precipitated powder obtained in Example 6. Is a diagram showing an SEM image of the precipitate powder composite oxide powder obtained by calcination (La ₂ Zr ₂ O ₇ powder) in Example 6, (a) is 3000 times, (b) is 30000 times Is.

  Examples of the present invention will be described below to describe the features of the present invention in more detail.

(1) Water was added to a 16% aqueous solution of titanium tetrachloride to prepare an aqueous solution having a Ti concentration of 0.5 mol / L (liter). And barium chloride dihydrate was added to this aqueous solution so that Ba density | concentration might be 0.5 mol / L, and transparent aqueous solution was obtained.
Next, tartaric acid is added to the aqueous solution so as to be 0.5 times the sum of the moles of Ba and Ti in the aqueous solution, and an aqueous solution in which Ba chloride, Ti chloride, and tartaric acid are dissolved. Was prepared.

(2) Then, aqueous ammonia (ammonium hydroxide 28% aqueous solution) was added dropwise to this aqueous solution to adjust the pH to about 10 to obtain a precipitated powder as a composite oxide precursor.
The operations (1) and (2) were both performed at room temperature with stirring.

(3) Next, the obtained precipitated powder is filtered, washed and dried, and then calcined under predetermined conditions (temperature and time) to obtain a calcined powder (composite oxide powder) (this example) Then, BaTiO ₃ powder) was obtained.

(Evaluation)
The precipitated powder obtained in the step (2) was observed with a scanning electron microscope. SEM images of the precipitated powder are shown in FIGS. 1 (a) and 1 (b). 1 (a) and 1 (b), it can be seen that the primary particles have a particle size of about several tens of nanometers, and the aggregate in which the primary particles have gathered has a particle size of about several μm.

Moreover, a molded body is prepared using the precipitated powder obtained in the step (2), and the surface is subjected to element mapping analysis by WDX (wavelength dispersive X-ray analyzer), and the dispersed state of Ba and Ti. Evaluated. The result is shown in FIG.
FIG. 2 shows that no concentration segregation is observed in any of Ba and Ti, and a uniform dispersion state is obtained.

  X-rays of the precipitated powder obtained in the step (2) and the calcined powder (composite oxide powder) obtained by heat treatment (calcined) at 500 to 700 ° C. in the step (3). The diffraction pattern is shown in FIG. The heat treatment (calcination) was performed by keeping for 1 h at the maximum temperature (temperature on the vertical axis in FIG. 3).

FIG. 3 shows that the precipitated powder (composite oxide precursor) that has not been calcined is amorphous. It can also be seen that the single phase is not sufficiently formed even at the heat treatment (calcination) temperatures of 500 ° C. and 600 ° C.
On the other hand, when the heat treatment (calcination) temperature is 700 ° C., it can be seen that a single phase of BaTiO ₃ is obtained.

  4 (a) and 4 (b) show SEM images of calcined powder (composite oxide powder) heat-treated (calcined) at 900 ° C. for 3 hours. 4 (a) and 4 (b), it is understood that the calcined powder (composite oxide powder) is a powder in which primary particles of about 100 nm are gradually aggregated. The size of the aggregate is about several μm as in the case of the precipitated powder shown in FIGS. 1 (a) and 1 (b).

<Comparative example>
Precipitated powder was obtained in the same manner as in Example 1 except that barium carbonate and barium hydroxide octahydrate were used instead of barium chloride dihydrate in Example 1.

  Then, element mapping analysis was performed by WDX for each of the precipitated powder obtained using barium carbonate and the precipitated powder obtained using barium hydroxide octahydrate. The results are shown in FIG. 5 and FIG. As shown in FIG. 5 and FIG. 6, element segregation was observed in any of the precipitated powders.

  FIG. 7 shows TG curves of the precipitated powder obtained using various barium salts of barium chloride, barium carbonate, and barium hydroxide.

According to FIG. 7, when barium chloride is used, the weight reduction is completed at 700 ° C., whereas when barium carbonate and barium hydroxide are used, the weight reduction continues to 900 ° C. Recognize. As a result of pre-calcining the precipitated powder using barium carbonate and barium hydroxide as barium raw materials at various temperatures, it was confirmed that the single phase of BaTiO ₃ was obtained at a temperature of 900 ° C. or higher. It was done.

From Example 1, it was confirmed that according to the production method of the present invention, no concentration segregation was observed in any of Ba and Ti, and a uniformly dispersed precipitated powder was obtained.
It was also confirmed that a single target phase was obtained even when heat treatment (calcination) at a relatively low temperature.

  Furthermore, as the precipitated powder, a precipitated powder in which fine primary particles are gently aggregated is obtained. As a result, the complex oxide powder (calcined powder) is also loosely aggregated (calcined powder). It was obtained and it was confirmed that crushing after calcination was easy. Moreover, the aggregated particle diameter was several μm, and it was confirmed that it was relatively small.

A precipitated powder as a composite oxide precursor was obtained in the same manner as in Example 1 except that the Ba / Ti ratio was changed in the range of 0.95 to 1.05.
Then, the obtained precipitated powder was calcined at 900 ° C. for 3 hours to obtain a calcined powder (composite oxide powder). The calcined powder was subjected to composition analysis by XRF (fluorescence X-ray analysis). Table 1 shows the relationship between the charged composition and the composition determined by XRF analysis.

  From Table 1, it can be seen that calcined powder (composite oxide powder) having almost the same composition as the charged composition was obtained.

  From Example 2, according to the method of the present invention, it is possible to produce a complex oxide powder having a target composition even when the target composition deviates greatly from the stoichiometric ratio, and the degree of freedom in composition is increased. It was confirmed to be large.

In Example 1 described above, ammonia water was added to precipitate the powder that was a precursor of the composite oxide. In Example 3, sodium hydroxide aqueous solution (50% aqueous solution) was used instead of ammonia water. ) Was used to prepare a precipitated powder, and the precipitated powder was calcined under predetermined conditions to prepare a composite oxide powder (BaTiO ₃ powder).
In Example 3, precipitated powder and composite oxide powder were produced in the same manner and under the same conditions as in Example 1 except that an aqueous sodium hydroxide solution was used instead of aqueous ammonia.

  The precipitated powder prepared in Example 3 was evaluated for the dispersion state of Ba and Ti by the same method as in Example 1. As a result, no concentration segregation was observed in any of Ba and Ti, and the dispersion state was uniform. It was confirmed that

Moreover, when the phase of the calcined powder (composite oxide powder) obtained by calcining the precipitated powder at 900 ° C. for 3 hours was identified by X-ray diffraction, it became a BaTiO ₃ single phase. It was confirmed.

  Further, SEM images of the calcined powder (composite oxide powder) are as shown in FIGS. 8A and 8B, and in the same manner as in Example 1 using ammonia water, fine primary particles are present. It was confirmed that a gentle aggregate was formed.

  From Example 3, it was confirmed that the same effect was obtained even when sodium hydroxide was used instead of the ammonia water.

(1) Barium chloride dihydrate and zirconium oxychloride octahydrate were prepared at a molar ratio of 1: 1, and water was added to dissolve both to obtain a transparent aqueous solution. Both the Ba concentration and the Zr concentration in the aqueous solution were 0.5 mol / L.
In the present invention, it is desirable to use oxychloride (ZrOCl ₂ .8H ₂ O) as zirconium chloride from the standpoint of stability.
Then, tartaric acid was added to this aqueous solution with stirring at room temperature. The amount of tartaric acid added was 0.7 times the sum of the moles of Ba and Zr in the aqueous solution.

  (2) Then, ammonia water (28% aqueous solution) was added dropwise to the aqueous solution to which tartaric acid was added while stirring at room temperature to adjust the pH to about 9.5 to obtain a precipitated powder.

(3) Next, the obtained precipitated powder is filtered, washed, dried, and then calcined under predetermined conditions to obtain a calcined powder (composite oxide powder) (in this example, BaZrO ₃ powder). It was.

(Evaluation)
For the precipitated powder, the dispersion state of Ba and Zr was evaluated in the same manner as in Example 1. As a result, as shown in FIG. 9, it was confirmed that there was no concentration segregation in Ba and Zr, and a uniform dispersion state was obtained.

  Further, the X-ray of the precipitated powder obtained in the step (2) and the calcined powder (composite oxide powder) obtained by heat treatment (calcination) at 500 to 700 ° C. in the step (3). The diffraction pattern is shown in FIG. The heat treatment (calcination) was performed by keeping for 1 h at the maximum temperature.

FIG. 10 shows that the precipitated powder is amorphous. It can also be seen that a BaZrO ₃ single phase was obtained at a heat treatment (calcination) temperature of 700 ° C.

  11A and 11B show SEM images of calcined powder (composite oxide powder) obtained by heat treatment (calcination) at 800 ° C. for 3 hours. 11 (a) and 11 (b), it is understood that the calcined powder (composite oxide powder) is a powder in which fine primary particles are gently aggregated.

From Example 4, it was confirmed that the same effect as in Example 1 was obtained when BaZrO ₃ was produced as a composite oxide powder.

(1) Water was added to a 16% aqueous solution of titanium tetrachloride to prepare an aqueous solution having a Ti concentration of 1.0 mol / L. Thereafter, strontium chloride hexahydrate was added so that the Sr concentration was 1.0 mol / L to obtain a transparent aqueous solution.
Then, tartaric acid was added to this aqueous solution with stirring at room temperature. The amount of tartaric acid added was 0.5 times the sum of the moles of Sr and Ti in the aqueous solution.

  (2) Then, a sodium hydroxide aqueous solution (50% aqueous solution) was added dropwise to the aqueous solution to which tartaric acid was added while stirring at room temperature, thereby adjusting the pH to about 13 to obtain a precipitated powder.

(3) Next, the obtained precipitated powder is filtered, washed, dried, and then calcined under predetermined conditions to obtain a calcined powder (composite oxide powder) (SrTiO ₃ powder in this example). Obtained.

(Evaluation)
For the precipitated powder, the dispersion state of Sr and Ti was evaluated in the same manner as in Example 1. As a result, it was confirmed that there was no concentration segregation in Sr and Ti, and a uniform dispersion state was obtained.

In addition, regarding the calcined powder (composite oxide powder) obtained by calcining the precipitated powder at 800 ° C. for 3 hours, the phase was identified by X-ray diffraction, and it was found to be a single SrTiO ₃ phase. Was confirmed.

From Example 5, it was confirmed that the same effect as in Example 1 was obtained when SrTiO ₃ was produced as a composite oxide powder.

(1) Lanthanum chloride heptahydrate and zirconium oxychloride octahydrate were prepared at a molar ratio of 1: 1, and water was added to dissolve both to obtain a transparent aqueous solution. Both the La concentration and the Zr concentration in the aqueous solution were 0.5 mol / L.
Then, tartaric acid was added while stirring the aqueous solution at room temperature. The amount of tartaric acid added was 0.5 times the sum of the moles of La and Zr in the aqueous solution.

  (2) Aqueous ammonia (28% aqueous solution) was added dropwise to the aqueous solution to which tartaric acid was added while stirring at room temperature to adjust the pH to about 10 to obtain a precipitated powder.

(3) Next, the obtained precipitated powder is filtered, washed and dried, and then calcined under predetermined conditions to obtain a calcined powder (composite oxide powder) (in this example, La ₂ Zr ₂ O ₇ powder).

(Evaluation)
For the precipitated powder, the dispersion state of La and Zr was evaluated in the same manner as in Example 1. As a result, as shown in FIG. 12, it was confirmed that there was no concentration segregation in La and Zr and a uniform dispersion state was obtained.

Moreover, about the calcined powder (composite oxide powder) obtained by calcining the precipitated powder at 800 ° C. for 3 hours, the phase was identified by X-ray diffraction. As a result, the La ₂ Zr ₂ O ₇ single phase It was confirmed that

  FIGS. 13A and 13B show SEM images of calcined powder (composite oxide powder) obtained by heat treatment (calcination) at 1300 ° C. for 3 hours. 13 (a) and 13 (b), it can be seen that the calcined powder (composite oxide powder) is a powder in which minute primary particles are gently aggregated. Moreover, it turns out that the magnitude | size of the aggregate is also about several micrometers.

From Example 6, it was confirmed that the same effect as in Example 1 was obtained when La ₂ Zr ₂ O ₇ was produced as the composite oxide powder.

(1) As raw materials a) Barium chloride dihydrate,
b) strontium chloride hexahydrate,
c) calcium chloride dihydrate,
d) lanthanum chloride heptahydrate,
e) 16% aqueous solution of titanium tetrachloride,
f) Zirconium oxychloride octahydrate was prepared, each raw material was prepared so as to have the composition shown in the composition column of Table 2, and water was added to prepare an aqueous solution. Each aqueous solution was adjusted so that the total number of moles of metal ions was 1 mol / L.

  And tartaric acid was added, stirring this aqueous solution at normal temperature. The amount of tartaric acid added was as shown in Table 2. In addition, the value of the tartaric acid amount in Table 2 is a value indicating how many times the sum of the number of moles of metal ions in the aqueous solution corresponds.

  (2) Then, ammonia water (28% aqueous solution) was added dropwise to the aqueous solution to which tartaric acid was added while stirring at room temperature to adjust the pH to about 10 to obtain a precipitated powder.

  (3) Next, the obtained precipitated powder is filtered, washed, dried, and then calcined under predetermined conditions to obtain calcined powder (each composite oxide having the composition shown in the column of composition in Table 2). Powder).

(Evaluation)
About each precipitation powder wash | cleaned and dried, the dispersion state of each element was evaluated by the method similar to the case of Example 1. FIG. As a result, it was confirmed that there was no concentration segregation in each element and a uniform dispersion state was obtained.

  Moreover, the phase of each calcined powder (composite oxide powder) obtained by calcining each of the washed and dried precipitated powders at 800 ° C. for 3 hours was identified by X-ray diffraction. It was confirmed that the phase was a single phase.

  Furthermore, as a result of performing SEM observation on each calcined powder (composite oxide powder), it was confirmed that the calcined powder was a loose aggregate composed of fine primary particles.

  From Example 7, it was confirmed that the same effects as in Example 1 were obtained when various composite oxide powders as shown in Table 2 were produced.

(1) Barium chloride dihydrate and zirconium oxychloride octahydrate were prepared at a molar ratio of 1: 1, and water was added to dissolve both to obtain a transparent aqueous solution. Both the Ba concentration and the Zr concentration in the aqueous solution were 0.5 mol / L.
Tartaric acid was added to the aqueous solution while stirring at room temperature. In this example, as shown in Table 3, the amount of tartaric acid added was changed in the range of 0.2 to 3.0 times the sum of the number of moles of Ba and Zr in the aqueous solution. In addition, the value of the tartaric acid amount in Table 3 is a value indicating how many times the sum of the number of moles of metal ions in the aqueous solution corresponds.

  (2) Then, by adding dropwise ammonia water (28% aqueous solution) to each aqueous solution to which tartaric acid was added at different ratios while stirring at room temperature, the pH was adjusted to about 9.5, and the precipitated powder was Obtained.

(3) Next, the obtained precipitated powder is filtered, washed and dried, and then calcined at 1000 ° C. for 3 hours to obtain a calcined powder (composite oxide powder) (BaZrO _{3 in} this example). Powder).

(Evaluation)
Table 3 shows the results of phase identification of the obtained calcined powder (composite oxide powder) by X-ray diffraction.
In addition, the sample marked with ○ (no) in the column of “Result (existence / absence of heterogeneous phase)” in Table 3 is a sample confirmed to be a single phase of BaZrO ₃ , and the sample marked with × (yes) Is a sample in which a heterogeneous phase was observed.

From Table 3, it can be seen that the amount of tartaric acid added is desirably 0.3 to 2.0 times the sum of the number of moles of metal ions in the aqueous solution.
That is, when the amount of tartaric acid added is less than 0.3 times, Ba ions are more eluted into the filtrate, and a large amount of ZrO ₂ is produced as a different phase. On the other hand, when the amount of tartaric acid added is more than 2.0 times, the elution of Zr ions into the filtrate increases, and a large amount of BaCO ₃ is produced as a different phase.
This tendency is not limited to the case of the BaZrO ₃ system, and it has been confirmed that there is a similar tendency in any composition system.

  In addition, this invention is not limited to the said Example, The conditions (temperature, etc.) at the time of heat-processing (calcination) the preparation method and component density | concentration of raw material aqueous solution containing tartaric acid, and precipitation powder (complex oxide precursor). Various applications and modifications can be made within the scope of the invention.

Claims (3)

(a) at least one selected from the group consisting of Ba chloride, Sr chloride, Ca chloride and La chloride, and at least one of Ti chloride and Zr chloride A step of preparing an aqueous solution containing substance B and tartaric acid,
(b) By adjusting the pH of the aqueous solution to the alkali side, at least one of Ba, Sr, Ca and La derived from the substance A, and at least one of Ti and Zr derived from the substance B Precipitating a composite oxide precursor comprising:
(c) The composite oxide precursor is heat-treated to synthesize a composite oxide containing at least one selected from the group consisting of Ba, Sr, Ca and La and at least one of Ti and Zr as main components. And a process for producing a composite oxide.   2. The composite according to claim 1, wherein the amount of tartaric acid added is in the range of 0.3 to 2.0 times the sum of the molar amounts of metal ions contained in the aqueous solution in the step (a). Production method of oxide.   The method of adjusting the pH of the aqueous solution to the alkali side is a method of adding at least one selected from the group consisting of ammonium hydroxide, sodium hydroxide, potassium hydroxide, and lithium hydroxide to the aqueous solution. The method for producing a composite oxide according to claim 1 or 2.