JP2012062229A - Method for producing complex oxide powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for efficiently and economically producing a perovskite complex oxide, which is minute and has a large surface area and high crystallinity, appropriately available for a dielectric layer or the like of a layered ceramic capacitor which has a number of dielectric layers and is made into a thin layer.SOLUTION: The perovskite complex oxide is generated by adding a hydroxide of an alkaline earth element to titanium oxide slurry and reacting it therewith, which is obtained by dispersing a titanium oxide powder, for which an integration width of a diffraction peak on a (101) plane to be measured by X-ray diffraction is less than or equal to 2.0°, in water. A titanium oxide powder having a specific surface area of 100 to 450 m/g is used. As a hydroxide of an alkaline earth element, a hydroxide containing no hydrate water is used. Furthermore, as a hydroxide of an alkaline earth element, barium hydroxide is used, thereby obtaining BaTiOpowder in the perovskite compound oxide.

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.

  As a method for producing a complex oxide powder capable of economically producing a complex oxide such as barium titanate having fine particles and excellent crystallinity, the following method has been proposed.

For example, as a method for producing a composite oxide powder having a perovskite structure represented by the general formula ABO ₃ , a hydroxide of an element constituting an A site component containing crystal water and a specific surface area of 250 m ² / g or more A mixing treatment step of mixing the titanium oxide powder having, and the mixing treatment step includes a solution generation step of generating a solution in which the A-site component is dissolved by only water of crystallization water by performing heat treatment; A method for producing a composite oxide powder is proposed, which includes a reaction step in which a titanium powder and a solution react to produce a reaction product, and the solution generation step and the reaction step proceed continuously. (See Patent Document 1).
Patent Document 1 discloses that the obtained composite oxide is calcined.

  And, according to the method of the invention of Patent Document 1, a composite oxide having few heterogeneous phases, desired ultrafine particles and excellent crystallinity is obtained, and this is calcined to obtain a cubic composite It is said that a tetragonal complex oxide excellent in crystallinity can be produced by transferring a crystal system from an oxide.

By the way, it is known that when the particle diameter of ceramic particles constituting a ceramic sintered body layer (for example, BaTiO ₃ ceramic layer) used as a dielectric layer of a multilayer ceramic capacitor becomes fine, the dielectric constant decreases. However, this decrease in dielectric constant is caused by a decrease in the crystallinity of the ceramic sintered body (ratio of the c axis to the a axis of the crystal axis (c / a axis ratio)).

  In order to solve this problem of lowering the dielectric constant, the stage of the raw material powder before sintering (for example, calcined powder of barium titanate material) before becoming a ceramic sintered body layer as a dielectric layer It is necessary that the powder has a fine particle size and has high crystallinity.

From this viewpoint, in Patent Document 1, the synthesized fine barium titanate powder is calcined at 900 to 1000 ° C., whereby the c / a axial ratio is 1.0075 to 1.0088 and the specific surface area is 7.31 to 1.31. A fine barium titanate powder of 3.88 m ² / g is obtained.

  However, when the element thickness of the multilayer ceramic capacitor (thickness of the dielectric layer interposed between the internal electrodes) is less than 1 μm, the actual situation is that the barium titanate powder obtained by the method of Patent Document 1 is not sufficient. is there.

  Further, as another method for producing a composite oxide, in an atmosphere in which no carbon dioxide exists, the titanium oxide particles and the water-soluble barium compound are equimolar to the number of moles of the titanium oxide particles, and the water-soluble barium compound. And a method for producing barium titanate powder having a reaction step of reacting at a temperature of 100 ° C. or lower in an aqueous solution having a pH of 11.5 or higher and 13.0 or lower (claim 2 of Patent Document 2). ).

  According to the method of the invention of Patent Document 2, it is said that barium titanate powder having a narrow particle size distribution can be produced at low cost while preventing the introduction of chlorine impurities.

However, in the method of the invention of Patent Document 2, barium titanate powder having a particle size of 0.085 to 0.115 μm is synthesized from titanium oxide having a specific surface area of 40 m ² / g. It is unlikely that the crystallinity is sufficiently high, and it is presumed that the crystallinity is low because no calcination was performed (paragraph 0025).

In addition, in the method of Patent Document 2, it is necessary to synthesize in an atmosphere in which CO ₂ does not exist, and there is a problem that the manufacturing process is restricted.

Further, neither of Patent Documents 1 and 2 clarifies the range of the powder characteristics necessary for the TiO ₂ material, and either of the methods of Patent Documents 1 and 2 can provide a multilayer ceramic capacitor with high characteristics. In reality, it is difficult to obtain a raw material powder having a small particle size and high crystallinity as required.

Japanese Patent No. 4200197 Japanese Patent No. 4057475

  The present invention solves the above-described problems, and has a large number of dielectric layers, and can be suitably used for applications such as a constituent material of a dielectric layer of a thin multilayer ceramic capacitor. An object of the present invention is to provide a method for producing a perovskite complex oxide that can efficiently and economically produce a perovskite complex oxide having a large surface area and high crystallinity.

In order to solve the above problems, a method for producing a perovskite complex oxide of the present invention includes:
A method for producing a perovskite complex oxide represented by the general formula ABO ₃ ,
A slurry preparation step of preparing a titanium oxide slurry in which a titanium oxide powder having an integral width of a diffraction peak of (101) plane measured by X-ray diffraction of 2.0 ° or less is dispersed in water;
A reaction step of generating a perovskite complex oxide by adding an alkaline earth element hydroxide to the titanium oxide slurry and reacting the slurry.

In the method for producing a perovskite complex oxide according to the present invention, the titanium oxide powder preferably has a specific surface area of 100 to 450 m ² / g.

  Moreover, it is preferable to use a hydroxide not containing hydration water as the hydroxide of the alkaline earth element.

Moreover, it is preferable that the hydroxide of the alkaline earth element is barium hydroxide and the perovskite complex oxide is BaTiO ₃ .

  Further, the A site is Ba, and a part thereof is substituted with Sr and / or Ca.

  Moreover, it is preferable to further include a step of heat-treating the perovskite complex oxide generated in the reaction step.

In the method for producing a perovskite complex oxide represented by the general formula ABO ₃ of the present invention, a titanium oxide powder having an integral width of a diffraction peak of (101) plane measured by X-ray diffraction of 2.0 ° or less is used. A slurry preparation step of preparing a titanium oxide slurry dispersed in water, and a reaction step of generating a perovskite-type composite oxide by adding an alkaline earth element hydroxide to the titanium oxide slurry and reacting the slurry. Therefore, it is possible to obtain a perovskite complex oxide having a specific surface area larger than that of a perovskite complex oxide obtained by a conventional solid-liquid reaction.

  That is, when a titanium oxide powder having an integrated width of a diffraction peak of (101) plane measured by X-ray diffraction of 2.0 ° or less is used, and a titanium oxide having an integrated width exceeding 2.0 ° is used. In comparison, it is possible to manufacture a perovskite complex oxide having a larger specific surface area without requiring a particularly complicated manufacturing process.

In the method for producing a perovskite-type composite oxide of the present invention, by having a specific surface area titanium oxide powder 100~450m ² / g, a specific surface area of more than 50 m ² / g a perovskite-type composite oxide efficiency It becomes possible to manufacture well.

  In addition, by using a hydroxide that does not contain hydration water as the hydroxide of the alkaline earth element, it can be added directly to the slurry in which the titanium oxide powder is dispersed as a solid, and the manufacturing process Can be simplified. Further, by using a hydroxide of an alkaline earth element that does not contain hydration water, the temperature rises due to the heat of dissolution when added to the slurry, so that the synthesis reaction is accelerated.

Further, when the alkaline earth element hydroxide is barium hydroxide, it is possible to efficiently produce BaTiO ₃ powder that is a perovskite complex oxide. In addition, by directly adding barium hydroxide containing no hydration water to the titanium oxide slurry, the temperature of the slurry rapidly rises to near 100 ° C. due to the heat of dissolution, thereby promoting the synthesis reaction and improving the perovskite type. The BaTiO ₃ powder that is a composite oxide can be produced more efficiently.

In addition, according to the present invention, it is also possible to produce a perovskite type complex oxide having a composition in which a part of Ba constituting the A site is substituted with Sr and / or Ca. By adjusting, a perovskite complex oxide having desired characteristics can be produced efficiently.
It should be noted that Sr and / or Ca component raw materials to be substituted for Ba can be contained in the titanium oxide slurry, and immediately before the alkaline earth element hydroxide immediately before the reaction step. Alternatively, it can be added to the titanium oxide slurry at the same time.

  In the present invention, a perovskite complex oxide having high crystallinity can be obtained by heat-treating the perovskite complex oxide produced in the reaction step to increase the c / a axial ratio.

  For example, by performing heat treatment at a temperature of 800 to 1000 ° C., a tetragonal perovskite complex oxide having a large c / a axial ratio (greater than 1) can be obtained. In the present invention, since the titanium oxide powder having an integral width of 2.0 ° or less is used, the grain growth in the heat treatment step is larger than that in the case of using titanium oxide having an integral width exceeding 2.0 °. It is possible to obtain a perovskite complex oxide having a high specific surface area and a high c / a axial ratio and high crystallinity.

Integral width of diffraction peak of (101) plane measured by X-ray diffraction of TiO ₂ used as Ti raw material in one example (Example 1) of the present invention, and barium titanate powder obtained by reaction It is a figure which shows the relationship of a specific surface area. It is a figure which shows the relationship between the specific surface area of the barium titanate powder after calcination obtained in Example 1 of this invention, and the c / a axial ratio of a crystal | crystallization.

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

No. having a specific surface area as shown in Table 1. 1-No. Nine anatase-type titanium oxide (TiO ₂ ) powders were prepared.

Then, the integral width of the (101) plane of each TiO ₂ powder was determined by X-ray diffraction (CuKα as a radiation source). The integral width was determined by measuring the peak of the (101) plane for each TiO ₂ powder using an X-ray diffractometer and dividing the peak area (integrated intensity) by the peak intensity. In Table 1, No. marked with *. 8 and 9 are comparative TiO ₂ that do not meet the requirements of the present invention.

Then, in Table 1, No. 1-No. Nine TiO ₂ powders and pure water were mixed to prepare nine types of titanium oxide slurries with a titanium oxide (TiO ₂ ) content of 23 wt%.
However, in the present invention, the titanium oxide concentration in the titanium oxide slurry is usually 10% by weight or more.

Then, each titanium oxide slurry produced was heated to 70 ° C., and then barium hydroxide was added so as to achieve a predetermined Ba / Ti ratio while stirring the titanium oxide slurry. In this example, barium hydroxide (Ba (OH) ₂ ) containing no hydration water was added as barium hydroxide in a solid state. By adding in a solid state, the temperature of the slurry rises to near 100 ° C. with the heat of dissolution, and the reaction can be started quickly.

In addition, the temperature of the titanium oxide slurry when adding barium hydroxide should just be 40 degreeC or more normally.
Also, barium hydroxide can be added as an aqueous solution. In that case, a necessary reaction can be performed by heating and raising the temperature.
However, as described above, since heat of dissolution can be effectively used for raising the temperature of the TiO ₂ slurry, it is desirable to add barium hydroxide that does not contain hydration water in a solid state.

After adding barium hydroxide as described above, barium titanate (BaTiO ₃ ) slurry was obtained by reacting titanium oxide and barium hydroxide while stirring for 1 hour at a temperature of 80 ° C. or higher. Then, the obtained slurry was dried to obtain barium titanate (BaTiO ₃ ) powder.
Table 1 and FIG. 1 show the relationship between the value of the integral width obtained as described above for TiO ₂ used as the Ti raw material and the specific surface area of the obtained barium titanate powder.

It can be seen from Table 1 and FIG. 1 that barium titanate powder having a large specific surface area can be obtained by using TiO ₂ having an integral width of 2.0 ° or less.

For example, no. No. 2 titanium oxide (integral width 1.58 °) and No. 2 Comparing the case where 8 titanium oxide (integral width 2.20 °) was used, both had a specific surface area of the raw material TiO ₂ of approximately 400 m ² / g, but the synthesized BaTiO ₃ powder The specific surface area is no. In the case of using titanium oxide No. ² (integral width 1.58 °), it was 58 m ² / g. When No. 8 titanium oxide (integral width 2.20 °) was used, No. 8 having an integral width of 2.0 ° or less was 33 m ² / g. It can be seen that barium titanate powder having a large specific surface area can be obtained when 2 titanium oxide is used.

Note that when TiO ₂ having an integrated width of the diffraction peak of the (101) plane measured by X-ray diffraction exceeding 2.0 ° is used, the barium titanate powder having a large specific surface area cannot be obtained. TiO ₂ having a low crystallinity of more than 2.0 ° is easily dissolved in alkali, and TiO ₂ dissolution-reprecipitation reaction is likely to occur. Therefore, grain growth or bonding between neighboring particles occurs, and hydroxylation occurs. The barium titanate powder obtained by the reaction with barium is also large in size and has a reduced specific surface area.

Furthermore, these powders were calcined using a heat treatment furnace at different temperature conditions in the range of 800 to 1000 ° C.
The relationship between the specific surface area of the calcined barium titanate powder and the c / a axial ratio of the crystals is shown in Table 2 and FIG.

  From Table 2 and FIG. 2, the barium titanate powder having a larger specific surface area after synthesis by solid-liquid reaction and before calcination has a higher c / a axial ratio and higher crystallinity after calcination. It can be seen that

  From the above examples, it was confirmed that according to the method of the present invention, a perovskite complex oxide having fine particles, a large specific surface area, and high crystallinity was obtained.

As described above, when TiO ₂ having an integral width of 2.0 ° or less is used, the barium titanate powder having a large specific surface area is obtained for the following reason. That is, TiO ₂ with high crystallinity having an integrated width of the diffraction peak of (101) plane measured by X-ray diffraction of 2.0 ° or less is hardly dissolved in alkali, and dissolution-reprecipitation reaction of TiO ₂ also occurs Since it is difficult to cause grain growth and bonding between neighboring particles, the barium titanate powder obtained by reaction with barium hydroxide has small particles and an increased specific surface area. As a result, it is possible to obtain barium titanate powder having fine crystallinity and high c / a axial ratio and high crystallinity even after calcination.

No. 1 in Table 1 was adjusted so that the final composition was (Ba _0.95 Ca _0.05 ) TiO ₃ . 5 titanium oxide (TiO ₂ ) powder, calcium carbonate (CaCO ₃ ) powder, and barium hydroxide (Ba (OH) ₂ ) powder were prepared.

Then, titanium oxide powder (No. 5 titanium oxide powder in Table 1), calcium carbonate (CaCO ₃ ) powder, and pure water were mixed, and the total content of TiO ₂ and CaCO ₃ was 23% by weight. A slurry was made.

The titanium oxide slurry containing the Ca component was heated to 70 ° C., and then barium hydroxide was added with stirring to obtain a predetermined Ba / Ti ratio.
Again, as barium hydroxide, barium hydroxide (Ba (OH) ₂ ) containing no hydration water was added in a solid state.
Then, it was obtained by performing the reaction was stirred for 1h at 80 ° C. or higher temperatures while retaining (Ba, Ca) a TiO ₃ slurry.
Thereafter, the obtained slurry was dried to obtain barium titanate powder ((Ba, Ca) TiO ₃ powder) in which a part of Ba was substituted with Ca.

According to the method of Example 2, it was confirmed that a perovskite type complex oxide powder having a large specific surface area and represented by the general formula (Ba _0.95 Ca _0.05 ) TiO ₃ was obtained.
The specific surface area of the perovskite complex oxide powder ((Ba _0.95 Ca _0.05 ) TiO ₃ powder) obtained by the above reaction was about 60 m ² / g.

In addition, this (Ba _0.95 Ca _0.05 ) TiO ₃ powder was calcined using a heat treatment furnace at different temperature conditions in the range of 800 to 1000 ° C.
As a result, when calcined under conditions such that the specific surface area is around 14 m ² / g (for example, conditions of 820 ° C. and 2 h), a highly crystalline perovskite having a c / a axial ratio of about 1.007 Type composite oxide powder ((Ba _0.95 Ca _0.05 ) TiO ₃ powder) was confirmed to be obtained.

In Example 2, calcium carbonate (CaCO ₃ ) powder was used as the Ca source. However, the Ca source is not limited to CaCO ₃ powder, and examples thereof include various kinds of calcium acetate, calcium nitrate, calcium hydroxide, and the like. It is also possible to use a salt.

No. 1 in Table 1 was adjusted so that the final composition was (Ba _0.95 Sr _0.05 ) TiO ₃ . 5 titanium oxide (TiO ₂ ) powder, strontium nitrate (Sr (NO ₃ ) ₂ ) powder, and Ba (OH) ₂ powder were prepared.

Then, titanium oxide powder (Titanium oxide powder No. 5 in Table 1), strontium nitrate (Sr (NO ₃ ) ₂ ) powder and pure water are mixed, and the total of TiO ₂ and Sr (NO ₃ ) ₂ A slurry having an amount content of 23% by weight was prepared.

The titanium oxide slurry containing the Sr component was heated to 70 ° C., and then barium hydroxide was added with stirring to obtain a predetermined Ba / Ti ratio.
Again, as barium hydroxide, barium hydroxide (Ba (OH) ₂ ) containing no hydration water was added in a solid state.
Then, after addition of barium hydroxide, was obtained by performing the reaction was stirred for 1h at 80 ° C. or higher temperatures while retaining (Ba, Sr) TiO ₃ slurry.
Then, the obtained slurry was dried to obtain barium titanate powder ((Ba, Sr) TiO ₃ powder) in which a part of Ba was substituted with Sr.

According to the method of Example 3, it was confirmed that a perovskite complex oxide powder having a large specific surface area and represented by the general formula (Ba _0.95 Sr _0.05 ) TiO ₃ was obtained. The specific surface area of the perovskite complex oxide powder ((Ba _0.95 Sr _0.05 ) TiO ₃ powder) obtained by the above reaction was about 60 m ² / g.

In addition, this (Ba _0.95 Sr _0.05 ) TiO ₃ powder was calcined using a heat treatment furnace at different temperatures in the range of 800 to 1000 ° C.
As a result, when calcined under conditions such that the specific surface area is around 14 m ² / g (for example, conditions of 830 ° C. and 2 h), a highly crystalline perovskite with a c / a axial ratio of about 1.007 Type composite oxide powder ((Ba _0.95 Sr _0.05 ) TiO ₃ powder) was confirmed to be obtained.

In Example 3, strontium nitrate (Sr (NO ₃ ) ₂ ) powder was used as the Sr source, but the Sr source is not limited to (Sr (NO ₃ ) ₂ ) powder. It is also possible to use strontium, strontium carbonate, or the like.

  The present invention is not limited to the above-described embodiments, and the solid content concentration of the titanium oxide slurry in which the titanium oxide powder is dispersed in water. When the alkaline earth element hydroxide is added to the titanium oxide slurry and reacted. Conditions such as reaction temperature and reaction time, range of specific surface area of titanium oxide powder as raw material, type of alkaline earth element, substitution ratio when part of A site is substituted with Sr and / or Ca, reaction process Various applications and modifications can be made within the scope of the invention with respect to the conditions for heat-treating the perovskite complex oxide produced in (1).

Claims (6)

A method for producing a perovskite complex oxide represented by the general formula ABO ₃ ,
A slurry preparation step of preparing a titanium oxide slurry in which a titanium oxide powder having an integral width of a diffraction peak of (101) plane measured by X-ray diffraction of 2.0 ° or less is dispersed in water;
And a reaction step of generating a perovskite-type composite oxide by adding an alkaline earth element hydroxide to the titanium oxide slurry and reacting it. A method for producing a perovskite-type composite oxide. The method for producing a perovskite complex oxide according to claim 1, wherein the titanium oxide powder has a specific surface area of 100 to 450 m ² / g.   The method for producing a perovskite complex oxide according to claim 1 or 2, wherein a hydroxide containing no hydration water is used as the hydroxide of the alkaline earth element. 4. The perovskite complex oxide according to claim 1, wherein the alkaline earth element hydroxide is barium hydroxide and the perovskite complex oxide is BaTiO _3. Method.   The method for producing a perovskite complex oxide according to claim 3, wherein the A site is Ba and a part thereof is substituted with Sr and / or Ca.   The method for producing a perovskite complex oxide according to any one of claims 1 to 5, further comprising a step of heat-treating the perovskite complex oxide generated in the reaction step.

Images