JPH03228821A - Production of multiple oxide powder - Google Patents

Abstract

PURPOSE:To obtain homogeneous multiple oxide powder contg. no pyrochlore phase by adding alkali to a mixed aq. soln. contg. water soluble compds. of at least two of specified metallic elements, adding a Pb compd. to the resulting slurry and hydrothermally treating this slurry. CONSTITUTION:Alkali is added to a mixed aq. soln. contg. water soluble compds. or hydroxides of at least two of metallic elements B1-Bn (B is a di- to hexavalent element) so as to adjust the pH to 10-12 and the resulting slurry is hydrothermally treated at 150-250 deg.C under satd. vapor pressure to 200kg/cm<2> pressure. A Pb compd. is then added to the treated slurry and this slurry is hydrothermally treated at 150-250 deg.C under satd. vapor pressure to 200 kg/cm<2> pressure to obtain a multiple oxide having multiple perovskite structure represented by the formula (where A is Pb and n >=2).

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing ultrafine composite oxide powder having a composite perovskite structure.

(Prior art) Conventionally, the method for manufacturing composite oxide powder having a composite perovskite structure involves (a) mixing raw material powders such as oxides and carbonates of each element constituting the composite oxide in a predetermined composition ratio; (b) A dry method in which the mixture is calcined and then crushed.
Special Publication No. Sho 62-14488, Special Publication No. Sho 61-5311
As described in Publication No. 5, a precipitate of the A site or the B site is generated, a component compound of the B site or the A site is added thereto, and the obtained precipitate product is dried and then calcined at a high temperature. method, (c) a method of calcining a mixture of A site component and B site component in the presence of a melting agent as described in Japanese Patent Publication No. 63-100001;
D) A coprecipitation method in which a mixed solution containing all of the constituent components in a predetermined composition ratio is prepared, a precipitant such as an alkali is added to this to form a coprecipitate, and the coprecipitate is calcined. It has been known.

(Problems to be Solved by the Invention) However, in the traditional dry method (a), uniform mixing and dispersion is impossible because the particle size of the starting material oxide or carbonate powder is coarse. In the calcination process, only a composite oxide powder containing a mixture of pyrochlore and perovskite phases can be obtained, and furthermore, since it is pulverized by mechanical crushing after calcination, it is difficult to obtain ultrafine powder of about 0.1 μm. It was impossible. In addition, in the wet methods (a) and (d), like the dry method, both involve calcination and mechanical pulverization, so it is impossible to obtain ultrafine powder of about 0.1 μm. In the co-precipitation method (d), the pH at which the precipitates of each element forming the composite oxide are generated is different, resulting in a time lag in the formation of the precipitates of each element, making it impossible to mix uniformly at the molecular level. In addition, method (c) uses chlorides such as sodium chloride and potassium chloride as fluxes, so these fluxes are removed after calcination. During firing, chlorine ions are not completely removed and remain, and these chlorine ions react with Pb, a component of the composite oxide, during firing, resulting in PbC, which is volatile at high temperatures.
There was a problem in that 12 was produced and PB was lost through evaporation, which tended to cause a deviation in composition.

In addition, in any of the above methods, pyrochlore type compounds are likely to be produced, and if baking is performed at a high temperature to prevent this, components such as PbO will evaporate, resulting in compositional fluctuations.

Therefore, the present invention makes it possible to produce a composite oxide powder having a uniform composition and a particle size of about 0.1 μm without requiring calcination, mechanical pulverization, or high-temperature calcination. This is a technical issue.

(Means for Solving the Problem) The present invention provides, as a means for solving the problem, general formula: A(B, B2-=-Bn)03 (wherein A is Pb
5B,,B2,...Bn each have a valence of 2
-6, where n is an integer of 2 or more. ), in which a mixed aqueous solution of at least two selected from the group consisting of water-soluble compounds and hydroxides of metal elements constituting the B site of the general formula; , after adding an alkali to form a slurry and hydrothermally treating the generated slurry, adding a predetermined amount of a PB compound constituting the A site,
The present invention provides a method for producing a composite oxide powder, which further comprises hydrothermal treatment.

The water-soluble compounds include nitrates and other inorganic acid salts of B-site constituent elements, alkoxides, and organic acid salts such as acetates and oxalates, but when made into an aqueous solution, CI
Compounds such as hydrochlorides and sulfates that produce ions and anions such as S04 ions are excluded. These water-soluble compounds or hydroxides may be used in combination of two or more types depending on the composition of the intended ceramics, and
These compounds do not necessarily need to be of the same type as raw materials.

In addition, the alkoxide has the general formula ・(RO)nM(RO
is an alkoxy group, M is a metal such as barium, titanium, zirconium, lead, magnesium, or a rare earth element, and n is a positive integer. ) includes all compounds represented by
It is desirable to have an alkoxy group having 15 or less carbon atoms, preferably 8 or less carbon atoms.

The PB compounds constituting the A site include nitrates and other inorganic acid salts, alkoxides, and organic acid salts such as acetates and oxalates, but when made into an aqueous solution, anions such as C1 ions and S04 ions Compounds such as hydrochlorides and sulfates that produce

Alkali includes aqueous solutions of alkali metal hydroxides and aqueous ammonia. When generating slurry,
Preferably, the pH is between 10 and 14.

The hydrothermal treatment is preferably carried out at a temperature of 150 to 250° C. and a vapor pressure of saturated vapor pressure to 200 kg/cm 2 .

(Function) In the present invention, when an alkali is added to a solution of a water-soluble compound and/or hydroxide of an element constituting the B site and a hydrothermal reaction is performed, an amorphous compound of the B site is generated, and this is combined with the amorphous compound of the A site. After adding the thermally decomposable water-soluble compound of the site constituent element, a hydrothermal reaction is performed to produce an ultrafine composite oxide powder having a composite perovskite structure.

Examples of the present invention will be described below.

(Example 1) 50.2 mol of Nb(OH), Mg(CH3COO)2.
1 mol of 4H7OO was dispersed and dissolved in 200 ml of pure water, stirred vigorously with a homomixer, and then an aqueous NaOH solution was added to adjust the pH to 12. This aqueous solution was placed in an autoclave and kept at 250°C and saturated vapor pressure for 5 hours.
After hydrothermal treatment and cooling, the generated oxide slurry contains P.
b(NO3) 20.3 mol added, in autoclave, 1
Hydrothermal treatment was performed for 5 hours at 50° C. and saturated vapor pressure.

After cooling, the product was washed with pure water to completely remove sodium ions, then washed with acetone, and then dried to obtain a composite perovskite oxide powder.

X-ray diffraction analysis of the obtained powder revealed that Pb(M
Only the diffraction peak of g+/3Nb, z3)03 confirmed that it was a composite perovskite type oxide. Also,
When this composite perovskite type oxide powder was measured by TEM, it was confirmed that the powder had a particle size of 0.1 to 0.12 μm and an extremely narrow particle size distribution.

Next, 6% by weight of vinyl acetate binder was added to the composite perovskite type oxide powder, and after granulation,
m, and was molded into a disc shape with a thickness of 1 mm, and fired at 1200°C for 2 hours to obtain a disc porcelain.

Coat silver paste on both sides of this porcelain and heat it at 800°C for 3
An Ag electrode was formed by baking under conditions of 0 minutes, and its dielectric loss (tan δ), relative dielectric constant (εr), and Curie point (Tc) were measured. The results are shown below. Note that each measured value is an average value for 10 samples.

tan δ: 0.1% εr: 13000 (IKHz, room temperature) Tc
: -15°C (Example 2) Mg(CH3COO)2.4H200, 1 mol, Nb(
OH) 50.2 mol, T I (OC3H?) 40.0
0,526 mol was dispersed and dissolved in 200 ml of pure water, and hydrothermal treatment was performed in the same manner as in Example 1 under the same conditions. After cooling,
20.30526 mol of Pb(NO3) was added to the resulting slurry, and hydrothermal treatment was performed in an autoclave at 250° C. and saturated vapor pressure for 5 hours. After cooling, the mixture was washed with water, washed with acetone, and dried in the same manner as in Example 1 to obtain a composite perovskite oxide powder.

When the obtained powder was analyzed by X-ray diffraction, P1)
(Mg +/3N b 2/!l) o, s9g, 5T
Only diffraction of 10.01117503 was detected, confirming that it was a composite perovskite type oxide. Moreover, the particle size of this composite perovskite type oxide powder is 01~
It was in the range of 0.13 μm.

Example 1 using the composite perovskite oxide powder
A porcelain disc was obtained in the same manner as above, and its electrical properties were measured. The results are shown below.

tan δ: 0.2% εr: 12000 (IKHz, room temperature) Tc
: 12.0°C (Effect of the invention) As is clear from the above explanation, according to the present invention, an oxide of the B site is generated by a hydrothermal reaction, and a water-soluble compound of the constituent elements of the A site is added to the oxide of the B site. After addition, by further carrying out a hydrothermal reaction, a composite oxide powder with ultrafine particles of about 0.1 μm in size can be produced.

Furthermore, a composite oxide powder having a homogeneous composite perovskite structure containing no pyrochlore phase can be obtained without requiring calcining or mechanical pulverization during the manufacturing process. In addition, since there is no change in composition during cleaning due to evaporation of lead components or differences in solubility during the manufacturing process, excellent effects such as the ability to manufacture composite perovskite-type oxide powder with a desired composition are achieved.

Claims (3)

[Claims] (1) General formula: A(B_1B_2...B_n)O_
3 (However, A is Pb, B_1, B_2,...B
_n each represents an element having a valence of 2 to 6, and n is an integer of 2 or more. ), in which a mixed aqueous solution of at least two selected from the group consisting of water-soluble compounds and hydroxides of metal elements constituting the B site of the general formula; , after adding an alkali to form a slurry and hydrothermally treating the resulting slurry, the P constituting the A site is
A method for producing a composite oxide powder, which comprises adding a predetermined amount of compound b and further hydrothermal treatment. (2) The pH of the aqueous solution of the thermally decomposable compound is 10 to 12.
2. The method for producing a composite oxide powder according to claim 1, wherein the alkali is added so that (3) The method for producing a composite oxide powder according to claim 1 or 2, wherein the hydrothermal treatment is performed at a temperature of 150 to 250°C and a vapor pressure of saturated vapor pressure to 200 kg/cm^2.