JPH0524089B2 - - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing ABO ₃ perovskite oxides. More specifically, the present invention provides:
The present invention relates to a method for producing an oxide powder with excellent powder properties by controlling the amount of specific impurities in a specific process in a known production method for this oxide.

Perovskite oxides, either by themselves or in the form of a solid solution of two or more of these oxides, are widely used as ferroelectric and piezoelectric materials in capacitors and the like. Most of these materials are commercialized as sintered bodies obtained by baking and solidifying their powders. In this case, the quality is significantly influenced by the degree of sintering, and therefore, a powder with excellent powder characteristics is desired as a raw material for producing a good sintered body.

Prior Art The following method is known as a method for producing perovskite oxides.

(1) A method in which oxide powders of each component element are mixed and the mixture is heated to a high temperature to cause a solid phase reaction.

(2) A method in which oxalic acid is dropped into an aqueous solution containing ions of each component element to coprecipitate each component element as an oxalate salt, and the coprecipitated oxalate salt is thermally decomposed.

(3) A method in which a mixture of alkoxides of each component element is hydrolyzed, coprecipitated, and the coprecipitated hydrolyzate is thermally decomposed.

However, these methods have some problems and are not necessarily satisfactory. For example, the solid phase reaction (1) not only has problems with the manufacturing process in that it requires high temperatures and long periods of time, but also has problems with the product powder. That is,
This is because the powder obtained by this method is difficult to sinter, and therefore requires the use of high temperatures or the use of a sintering accelerator for sintering. In the coprecipitation method (2), it is difficult to coprecipitate each component in the desired ratio because the oxalates of each component have different solubility in water, which is the coprecipitation medium. The disadvantage is that it is difficult to obtain a composition with the same composition. Further, although the coprecipitation method (3) has the advantage of producing a product with high purity and high uniformity, it has the disadvantage that it is not easy to manufacture because each component is used as an alkoxide.

Possible solutions and their problems One of the present inventors has conducted intensive studies to eliminate the drawbacks of these conventional methods, and has proposed an improvement to the oxalate method described in (2) above. . That is, oxalic acid is soluble in ethanol, and Zr ions, Ti
Utilizes the property that oxalates of ions and oxalates of ions selected from the group of Pb, Ba, Sr, or Ca (hereinafter collectively referred to as A ions) are completely insoluble in ethanol. Then, A ions and Ti ions are reacted with oxalic acid in ethanol, and these ions are coprecipitated as oxalate (Japanese Patent Application Laid-open No. 59-39722), and A ions and Zr ions or ( By co-precipitating Zr + Ti) ions as oxalates (Japanese Patent Application Laid-Open No. 131505/1982), a precipitate (precursor of perovskite oxide) with a desired composition and high purity and uniform particle size can be obtained. When this is thermally decomposed, active ATiO ₃ , AZrO ₃ , or A(Zr·Ti)O ₃ fine powder, which is extremely easy to sinter, is obtained. In the technology disclosed therein,
A ion is used as an aqueous solution of the nitrate or an ethanol-containing aqueous solution. On the other hand, it is said that titanium ions and zirconium ions are preferably used as an aqueous solution or an ethanol-containing solution of titanium oxynitrate or zirconium oxynitrate. When chloride is used as a source of these ions, chloride ions tend to remain in the coprecipitate, and even if the coprecipitate is fired at a high temperature, chlorine ions remain and the fired product (i.e., the target oxide) is sintered. This is because when Pb is used as the A ion, insoluble lead chloride is generated in the mixed aqueous solution.
The method for producing titanium oxynitrate is to hydrolyze titanium tetrachloride with aqueous ammonia to precipitate it as a hydroxide, and then pour the titanium hydroxide obtained through this process into nitric acid and dissolve it to produce titanium oxynitrate. A method for obtaining the solution is disclosed, and it is also disclosed that a zirconium oxynitrate solution can also be obtained by a similar method using zirconium oxychloride as a raw material.

A titanium ion or zirconium ion from these compounds and A ion are reacted with oxalic acid in the presence of ethanol to obtain an oxalate coprecipitate,
This is filtered, dried, and crushed to a temperature at which thermal decomposition is completely completed and no weight change is observed (700
The desired perovskite-type oxide can be obtained by firing at -1000°C, but according to the disclosure, the fired product is ground and mixed again.
This powder is molded and sintered at 1000-1400°C.

That is, in this prior improved technique, the finely powdered perovskite-type oxide obtained by sintering the coprecipitate cannot be directly used for molding because the particles are fused to each other. A re-grinding and mixing step was necessary.

This re-grinding and mixing step, which is necessary in the prior improved invention, not only increases the process cost and reduces the reliability of the final product due to the contamination of impurities, but also always poses a problem due to the characteristics of perovskite oxide powder. . In other words, the development of technology for manufacturing highly flexible piezoelectric films by combining these perovskite-type oxide powders with polyvinylidene fluoride resin, polyoxymethylene resin, nitrile butadiene rubber, etc. is progressing. In some cases, an easily dispersible fine powder with a uniform particle size distribution and no crystal distortion is required, but fine powder obtained by re-grinding and mixing causes crystal distortion, making it difficult to obtain the expected performance. This is because it is known that it will not be possible.

SUMMARY OF THE INVENTION The present inventors have made extensive studies on the phenomenon of mutual fusion of fine particles of baked goods, and in this prior improved technology, a small amount of chlorine ions remaining in a mixed aqueous solution of starting material ions cause fine particles to fuse together during the firing stage. The present invention was achieved by discovering the fact that the fusion phenomenon is induced, and by further discovering that the fusion can be suppressed by lowering the chlorine ion concentration to a predetermined value or less.

Therefore, the method for producing a perovskite oxide according to the present invention is directed to an ABO ₃ type perovskite oxide (where A represents at least one element selected from the group consisting of Ba, Sr, Ca and Pb, and B teeth
At least one element selected from the group consisting of Ti and Zr) is contacted with oxalic acid in the presence of ethanol to form a precursor of the oxide. In the method of producing the oxide by generating a precipitate and thermally decomposing the precursor precipitate, the chlorine ion is
It is characterized in that it contains no more than 0.05 atoms per atom of the element.

One embodiment of obtaining the aqueous solution or ethanol-containing aqueous solution in this production method is that
Preparing Ti ions by hydrolyzing titanium alkoxide to generate titanium hydroxide and dissolving this titanium hydroxide in nitric acid, and supplying ions other than Ti ions from salts other than chlorides of each element. It consists of

In addition, one of the other embodiments of obtaining the aqueous solution or ethanol-containing aqueous solution in this production method is to generate titanium hydroxide by hydrolyzing titanium chloride with Ti ions as element B and converting the titanium hydroxide to nitric acid. The method consists of supplying ions other than Ti ions from salts other than chlorides of each element, and washing the titanium hydroxide to remove chloride ions.

In any of these embodiments, a preferred specific example of the salt other than chloride is nitrate.

Effects By controlling the chloride ion content of the constituent element ion aqueous solution or ethanol-containing aqueous solution to a specific level or less when forming the oxalate coprecipitate according to the present invention, a perovskite type with excellent powder properties can be produced. A precursor compound giving an oxide is obtained.

In other words, the oxide obtained by filtering, drying, crushing, and then sintering the precursor compound precipitated as an oxalate does not have a state in which the powder particles are fused together, but when ultrasonic dispersion is performed in water. It has the property of being easily dissociated into individual particles by means such as methods, and has a perfect crystal structure.

For evaluation of the present invention, please refer to what will be described later.

Detailed description of the invention Production of perovskite oxide precursor precipitate The perovskite oxide targeted by the present invention is
ABO type ₃ , in which the A element is Ba, Sr, Ca
and at least one selected from the group consisting of Pb
The element B is at least one element selected from the group consisting of Ti and Zr.

Element B The titanium raw material used in the present invention is usually prepared by dissolving titanium hydroxide in nitric acid. Specifically, titanium tetrachloride is converted into titanium hydroxide with aqueous ammonia, and this is washed with water to remove chlorine ions so that the Cl/Ti (atomic ratio) in the reaction solution is 0.05 or less, preferably 0.02 or less. You just need to set the washing conditions so that If it is desired to obtain titanium hydroxide with even less chlorine ions, an alkoxide such as tetraisopropyl titanium may be hydrolyzed. Titanium hydroxide obtained by either method is subjected to the oxalate precipitation reaction as titanium oxynitrate dissolved in nitric acid.

Zirconium oxynitrate can also be synthesized using zirconium oxychloride as a raw material in the same manner as titanium, but zirconium oxynitrate is more stable over time than titanium oxynitrate, so it can be used for the reaction simply by dissolving a commercially available product in water. I'm struggling.
Even when manufacturing perovskite compounds such as AZrO ₃ where the B element is Zr, the Cl/Zr (atomic ratio) in the aqueous solution or ethanol-containing aqueous solution is
The object of the present invention can be achieved by setting it to 0.05 or less, preferably 0.02 or less.

Element A Perovskite-type oxides that can be synthesized by the method of the present invention include PbTiO ₃ , PbZrO ₃ , Pb(Ti・Zr)
O ₃ ． BaTiO ₃ , SrTiO ₃ , CaTiO ₃ . _BaZrO3 ,
Examples include SrZrO ₃ and CaZrO ₃ .

The water-soluble compounds of element A necessary for synthesizing these compounds can be suitably combined and subjected to the sulfate precipitate formation reaction, but salts other than chlorides,
In particular, nitrates are most suitable. In either case, in an aqueous solution containing various ions or an aqueous solution containing ethanol, Cl/Ti, Cl/Zr, or
It is necessary to select the purity of the raw materials so that Cl/(Ti+Zr) is 0.05 or less, preferably 0.02 or less.

Co-precipitation The perovskite-type oxide precursor is obtained as a coprecipitate by reacting an aqueous solution or an ethanol-containing aqueous solution of a compound of each element that provides element A ions and B element ions with sulfuric acid in the presence of ethanol. It goes without saying that the greatest feature of the invention lies in controlling the chlorine content of the aqueous solution or ethanol-containing aqueous solution).

Specifically, after adding ethanol to the aqueous solution to an extent that no clouding occurs, an ethanol solution of oxalic acid is preferably added dropwise with vigorous stirring.
Alternatively, a method may be used in which the aqueous solution or the ethanol-containing aqueous solution is dropped into an ethanol solution of oxalic acid. Depending on the type of metal ion, adding ethanol to the aqueous solution may cause instability such as clouding, so it may be preferable to use an ethanol-free aqueous solution as the ion solution of each element.

In addition, high concentration of nitric acid is generated in the mother liquor due to the formation of oxalate coprecipitate, and this may react with, for example, titanyl lead oxalate, resulting in a large amount of Ti remaining in the mother liquor according to the following equation. It is known for the research by Kazuhisa et al. (Telecommunications Research Institute, Research and Practical Application Report Special Issue No. 28 (1975), etc.).

PbTiO(C ₂ O ₄ ) ₂ +2HNO ₃ → PbC ₂ O ₄ + TiO(NO ₃ ) ₂ +H ₂ C ₂ O _4However , according to the method of the present invention, for example, when PbTiO ₃ is the target, coprecipitation is performed. Pb( _C2
Since only a negligible amount of O ₄ ) dissolves in an aqueous solution, by quantifying the amount of titanium ions dissolved in the solution, conditions can be easily set to form precipitates of Pb and Ti in a stoichiometric ratio. . Furthermore, by increasing the metal ion concentration in the aqueous solution, the amount lost to the liquid can be reduced.

It is preferable to use a large amount of ethanol, about 200 moles per mole of oxalic acid. The amount of oxalic acid needs to be at least an amount that completely converts each elemental metal ion to oxalate, but
It is preferable to add about 25% more than the theoretical amount. The temperature of the oxalate salt formation reaction can be from 0°C to around room temperature.

A white precipitate forms upon addition of oxalic acid. Through this process, a white cake is obtained. In order to remove nitrate ions, unreacted oxalic acid, chloride ions, etc. contained in the cake, it is preferable to redisperse the cake in ethanol and remove the remaining mother liquor by replacing it with ethanol.

The obtained white cake is dried and then crushed to obtain a perovskite-type oxide precursor powder. Crushing at this stage is important in ensuring the flow of an appropriate amount of oxygen during the subsequent sintering. Note that the dry cake can be easily pulverized by a weak grinding force, and there is no need to completely disperse the particles at this stage, so there is no risk of contamination with impurities from the pulverizing means.

Production of perovskite type oxide fine powder The precursor powder is heated to an appropriate temperature, for example, 500-
Bake at 1000℃. It is desirable that the calcination temperature be low, but since the temperature at which thermal decomposition is completely completed varies depending on the compound, it is necessary to carry out the calcination at a temperature at which no weight change is observed.

Evaluation of the present invention (1) When the in-air firing pattern of the precursor powder obtained from the solution exceeding the chloride ion concentration specified in the present invention was traced by differential thermogravimetric analysis,
In the case of PbTiO ₃ , weight loss is observed even above the temperature at which thermal decomposition ends, and the amount of weight loss at 700°C is proportional to the amount of residual Cl.

On the other hand, at a chlorine concentration within the range of the present invention, there is virtually no weight change in the region above about 500°C, which is considered to be the crystal transition point.

That is, according to the method of the present invention, there is no need to take an unnecessarily high calcination temperature to remove residual chlorine, and the temperature exceeds the crystal transition point of the target perovskite-type oxide (and their solid solution) and the precursor At any temperature above the decomposition temperature of body substances〓
By firing, a fine powder with excellent crystallinity can be obtained.

(2) When we observed fine oxide powder (for example, PbTiO ₃ ) obtained by calcining the precursor powder at 700 to 800°C with a controlled chlorine concentration as specified in the present invention using a scanning electron microscope, we found that the fine particles were fused. No signs of contamination were observed. Furthermore, an appropriate amount of fine powder was poured into water, and a suspension was obtained using an ultrasonic cleaner for several tens of seconds. After dispersing this on a sample stage using a dropper, electron microscopic observation revealed that individual fine particles were It was recognized that they exist separately.

On the other hand, PbTiO ₃ whose chlorine concentration is above the specified value
In the case of powder, it was observed that particles were fused everywhere at the stage of firing at 700℃.
At 1000℃, a fusion phenomenon was observed throughout the visual field.
This fusion between particles cannot be resolved even by ultrasonic dispersion, and most of the particles do not become suspended, but immediately settle when the ultrasonic wave is stopped, and even those that are slightly suspended become huge particles. It was observed as a particle fused body.

That is, according to the method of the present invention, there is no fusion between the calcined particles, and a fine powder with excellent dispersibility can be obtained.

(3) Precursor powders (for example, for PbTiO ₃ ) whose chlorine concentration is controlled below the chlorine concentration specified in the present invention can only obtain a diffraction peak of almost amorphous Pb (C ₂ O ₄ ); In addition to the sharp diffraction peak of Pb (C ₂ O ₄ ) obtained from the precursor powder based on the chlorine concentration,
2θ=8.6°, 17.2°, 19.5°, 22.7°, 26.0°, 29.7°
Unidentified sharp peaks were observed at these positions.

From these facts, according to the method of the present invention,
It is characterized by the fact that it significantly promotes the amorphization and refinement of the oxalate itself, and as a result, it
It is presumed that a highly crystalline perovskite-type oxide can be easily obtained by calcination.

(4) The particle size of the crystallized fine powder (for example, PbTiO ₃ ) obtained by the method of the present invention is
0.2μm, 0.15μm when fired at 700℃, which is too small to be achieved by conventional grinding methods. According to the present invention, a product having an even narrower particle size distribution can be obtained.

Since the perovskite oxides (and solid solutions thereof) obtained by the method of the present invention have the above-mentioned properties, they can be used for the following applications.

(a) Barium titanate (BaTiO ₃ ) can be used for multilayer ceramic capacitors. Multilayer ceramic capacitors using ultrafine particles of BaTiO ₃ synthesized from metal alkoxides have been put into practical use, but the method of the present invention allows easily dispersible ultrafine particles with high crystallinity to be produced in a simpler process than the alkoxide method. Therefore, we can expect low-cost, high-performance products.

(b) Piezoelectric materials such as PbTiO ₃ and Pb(Zr・Ti)O ₃ can be used, for example, in ultrasonic diagnostic equipment, flaw detectors,
It can be used in applications such as pressure sensors, buzzers, microphones, speakers, stereo pickups, and piezoelectric actuators, and when combined with rubber or polymers, it can also be used in applications such as blood pressure monitors and wide-surface speakers. can. In the case of composites with rubber or polymers, baking after composite is impossible, so the highly crystalline and easily dispersible ultrafine particles of the present invention can be made into thin films,
It can be said to be an appropriate material that can meet demands such as increased ceramic content.

Experimental Examples Example 1 200 ml of commercially available tetraisopropyl titanium was added dropwise to 2800 ml of distilled water to obtain hydroxide. After this was filtered, washing was repeated three times with 400 ml of pure water to obtain titanium hydroxide. This is ice-cooled commercially available special grade concentrated nitric acid 80
ml, and after standing for day and night, it was filtered to obtain a titanium oxynitrate solution. The Ti concentration was determined gravimetrically as TiO ₂ and a result of 0.1066 g-Ti/ml was obtained. Add 19.7ml of titanium oxynitrate solution to special grade lead nitrate.
In addition to the mixed solution of 13.2222g and 184ml of pure water, Ti/
A solution of Pb (atomic ratio) = 1.11 was obtained and cooled to 1°C. Oxalic acid in an amount equivalent to 2.4 mol per 1 mol of lead titanate assumed in this mixed solution was dissolved in ethanol and cooled to 1°C. The amount of ethanol used was 269 mol per 1 mol of oxalic acid. While the cooled solution was being vigorously stirred, the oxalic acid ethanol solution was added dropwise at a rate of 1.1 ml/min to obtain a white precipitate. The white cake obtained by suctioning and filtering this white precipitate was stirred and dispersed in 480 ml of ethanol, and the filtering procedure was repeated three times. Bake at 700℃ for 2 hours,
BET surface area 5.6m ² /g, Pb/Ti (atomic ratio) = 1.00,
The crystal form determined by X-rays was tetragonal PbTiO ₃ , and a lead titanate powder was obtained with a crystallite diameter of 416 Å determined from the 202 plane diffraction peak and a particle diameter of 0.13 μm determined from the BET surface area.

When this lead titanate powder was observed using a scanning electron microscope, aggregates of particles of 0.1 to 0.2 μm were observed. Furthermore, this lead titanate was dissolved in water for approximately
Suspend by applying vibration in an ultrasonic cleaner for 30 seconds, place a portion of the suspension on an electron microscope sample stage with a dropper, dry, and observe the particle state after normal processing. did. It was observed that particles with a diameter of 0.1 to 0.2 μm were well dispersed.

Example 2 40 ml of titanium tetrachloride was dissolved in a mixture of 520 ml of pure water and 40 ml of concentrated hydrochloric acid, and 296 ml of commercially available ammonia water was added dropwise thereto to form a hydroxide precipitate.
Through this process, titanium hydroxide is obtained, which is 1000
It was washed by dispersing it in 1 ml of pure water and filtered.
The entire amount of titanium hydroxide obtained by repeating this washing operation three times was added dropwise to 200 ml of ice-cooled nitric acid with gentle stirring to obtain a titanium oxynitrate solution. The Ti concentration in this titanium oxynitrate solution was determined as TiO ₂ by gravimetric analysis, and a result of 0.0251 g-Ti/ml was obtained. Furthermore, the chlorine concentration in this titanium oxynitrate solution was determined by silver nitrate titration, and a result of Cl/Ti (atomic ratio) of 0.02 was obtained.

Collect 31.4 ml of this titanium oxynitrate solution, then dissolve 5.4919 g of commercially available special grade lead nitrate, which is an equimolar amount to Ti, in 53.3 ml of distilled water to make a lead nitrate aqueous solution, and add this to the titanium oxynitrate solution. It was mixed with titanium nitrate solution, and the mixed solution was cooled to 2.4°C.

Next, the lead titanate 1 assumed in this mixed solution
Oxalic acid was dissolved in ethanol in an amount corresponding to 4.0 moles per mole. The amount of ethanol used was 169 mol per 1 mol of oxalic acid.
This oxalic acid ethanol solution was cooled to 2.4° C. and then added dropwise to the cooled mixture at a rate of 0.8 ml/min while stirring vigorously to obtain a white precipitate.
The white cake obtained by suctioning this white precipitate is
The mixture was stirred and mixed with 200 ml of ethanol and filtered by suction. After repeating this operation three times, the resulting white cake was dried at 110°C, crushed, and left in the air.
Baked at 700℃ for 2 hours, BET surface area 2.7m ² /g,
Crystallite diameter 460 Å (101 planes) determined by X-ray diffraction,
A lead titanate powder with a particle size of 0.28 μm determined from the BET surface area was obtained.

When this lead titanate powder was observed using a scanning electron microscope, no fusion of particles was observed. It was observed that the particles were easily separated by ultrasonic dispersion in water.

Comparative Example 1 Titanium hydroxide obtained in the same manner as in Example 2 was dissolved in nitric acid without washing to obtain a titanium oxynitrate aqueous solution. The Ti concentration of this titanium oxynitrate was 0.0229 g-Ti/ml, and the Cl/Ti (atomic ratio) was 1.05.

Take 20.2 ml of titanium oxynitrate solution and then
A lead nitrate solution was prepared by dissolving 3.2098 g of commercially available special grade lead nitrate, which is an equimolar amount to Ti, in 139 ml of distilled water.
This was mixed with the titanium oxynitrate solution, and the mixed solution was cooled to 4.3°C.

Next, 2.4 mol of oxalic acid was dissolved in ethanol per 1 mol of lead titanate, and the oxalic acid/ethanol ratio was set to 1/467 mol/mol.
This was cooled to 4.3°C. This oxalic acid ethanol solution was added dropwise to the above-mentioned cooled mixture at a rate of 1.0 ml/min while stirring vigorously to obtain a white precipitate.
This white precipitate was washed by the method of Example 2, dried at 110°C, crushed in an agate mortar, and then calcined in air at 700°C for 2 hours to obtain a BET surface area of 1.15 m ² /g, Pb/Ti (atomic ratio) = 0.81, the crystal shape determined from X-rays is tetragonal
A lead titanate powder was obtained which is PbTiO ₃ and has a crystallite diameter of 338 Å determined from its 101-plane diffraction peak and a particle diameter of 0.65 μm determined from its BET surface area.

When this lead titanate powder was observed using a scanning electron microscope, it was found that particles with a particle size of around 5 μm were fused together. It was observed that even ultrasonic dispersion did not completely eliminate this fusion.

Claims (1)

[Claims] 1 ABO ₃ type perovskite oxide (however,
A represents at least one element selected from the group consisting of Ba, Sr, Ca and Pb, and B represents Ti and
At least one element selected from the group consisting of Zr) is brought into contact with an aqueous solution containing ions of an element or an aqueous solution containing ethanol with oxalic acid in the presence of ethanol to precipitate a precursor of the oxide. The method for producing the oxide by thermally decomposing the precursor precipitate is characterized in that the aqueous solution or ethanol-containing aqueous solution does not contain 0.05 or more chlorine ions per atom of B element. A method for producing perovskite-type oxides. 2. Ti ions as element B were prepared by hydrolyzing titanium alkoxide to generate titanium hydroxide and dissolving this titanium hydroxide in nitric acid, and ions other than Ti ions were prepared by adding ions other than chlorides of each element. 2. The method according to claim 1, wherein the aqueous solution or ethanol-containing aqueous solution containing no more than 0.05 atoms of chlorine ions per atom of B element is obtained by supplying from a salt. 3. The method according to claim 2, wherein the salt other than chloride is a nitrate. 4. Prepare Ti ions as element B by hydrolyzing titanium chloride to generate titanium hydroxide and dissolving this titanium hydroxide in nitric acid,
By supplying ions other than Ti ions from salts other than chlorides of each element and washing the titanium hydroxide to remove chlorine ions, 0.05 or more chlorine ions are contained per atom of B element. The method according to claim 1, wherein the aqueous solution or ethanol-containing aqueous solution is obtained. 5. The method according to claim 4, wherein the salt other than chloride is a nitrate.