JPS62230623A - Production of perovskite-type compound containing tungsten - Google Patents

Abstract

PURPOSE:To obtain fine powder of an easily sinterable tungsten-containing lead-type perovskite compound expressed by formula PbAxW1-xO3, by preliminarily precipitating a part of lead or component A and whole tungsten in the form of tungstate and precipitating the remaining components. CONSTITUTION:A tungsten-containing lead-type perovskite-type compound expressed by formula PbAxW1-xO3 (x is 1/2 or 2/3; A is Fe, Ni, etc.) is produced by the following method. An aqueous solution of a tungstate of an amount necessary for forming the objective composition is mixed with an aqueous solution of lead or the component A of an amount equivalent to the tungsten in the tungstate. A tungstic acid salt of lead or the component A is precipitated by this process. The precipitate is suspended in water or an alcohol and the obtained slurry is mixed with an aqueous solution or alcoholic solution of lead and/or component A of amounts necessary for attaining objective composition. A homogeneous precipitate of the whole components can be produced from the above liquid mixture. The precipitate is filtered, dried and calcined at 400-1,000 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a perovskite compound having a fine submicron particle size. In particular, the present invention relates to a method for producing a tungsten-containing lead-based perovskite compound that has a particle size suitable for multilayer capacitors and has easy sinterability.

Generally, lead-based perovskite-type compounds are widely used as piezoelectric materials, but in recent years (because they have a higher dielectric constant than conventionally used dielectric materials such as barium monotitanate, the capacitance per unit volume has increased). (2) Since the sintering temperature is low, it is possible to use silver, which is cheaper than palladium, which is conventionally used as the internal electrode, and (3) There are also many types of materials. Because of the large number of dielectric materials, it is possible to develop many new materials for dielectrics by varying the composition, so it is being actively researched and developed as a dielectric material.

The tungsten-containing lead-based perovskite compound described in the present invention (hereinafter referred to as the compound of the present invention) is a type of lead-based perovskite compound with ant and AJ components of F.
e, co, Ni, MO, Zn.

General formula PbAx, which is one or more elements selected from Cd, Mn, and In, and contains tungsten
It is a group of compounds having a perovskite structure represented by Wl-X O3 (x-1/2 or 2/3).

(Pam ratio, law f3) (Prior art) Dry methods and wet methods are known as conventional methods for producing lead-based perovskite compounds.

The dry method is a method in which powders of oxides as constituent components are mixed according to their composition ratios, and this is calcined.

However, with this method, it is difficult to obtain raw material powder with a uniform composition;
There are also many pyrochlore phases. Furthermore, since it is necessary to increase the calcination temperature in order to increase the production rate of the peObskite phase, this causes the particles to become coarser, which has the disadvantage of making it difficult to easily sinter.

In the wet method, a mixed solution containing all of the constituent components is prepared, and a precipitate forming liquid such as an alkali is added to this to cause co-precipitation.
A common method is dry calcining.

However, although this method makes it easy to obtain powder with excellent uniformity,
Because of its uniformity, it has the disadvantage that it coagulates during precipitate formation, drying, and calcination to form secondary particles, resulting in coarse particles and difficulty in sintering.

In addition, in this method, since the concentration of the precipitate-forming liquid is constant, if the precipitate-forming ability of each component differs, for example,
Some components produce 100% precipitate, while others produce 10% precipitate.
There is a drawback that 0% precipitate may not be formed and it is difficult to obtain the desired composition.

Since the grain size of 1 g of ceramics made using these conventional BeObskite type compounds is 10μ or more, especially when used in multilayer capacitors, the thickness of the layer is about 11, making it possible to make the ceramics smaller and have a larger capacity. This is where the limit is reached.

In addition, in the case of the compound of the present invention, the tungsten component contained does not precipitate in an alkali but in an acid, so tungsten and other components are allowed to coexist in the same liquid to eliminate the precipitation of other components in the fine particles. It is virtually impossible to obtain.

(Objective of the Invention) The object of the present invention is to overcome the drawbacks of conventional methods for producing the compound of the present invention and to provide a compound with fine particles and easy sinterability.

(Structure of the Invention) In order to achieve the above-mentioned object, the present inventors discovered that lead or A, which was impossible to co-precipitate with tungsten, as a result of 12m research.
Part of the ingredients and the total amount of tungsten are tungsten
! When the salt is precipitated and the remaining components are precipitated with a precipitate-forming solution such as an alkali, it is a double operation, so the concentration of the precipitate-forming solution can be adjusted to conditions suitable for precipitate formation at each stage, and the remaining components are precipitated. It has been found that the composition of the components can be made as desired, and because it is a double precipitate while being uniformly dispersed, there is no formation of secondary particles due to coagulation.

The compound of the present invention obtained by calcining the precipitate thus obtained is submicron fine particles, which makes it easy to sinter, so this powder is molded and calcined. The grain size of the ceramics obtained using this method can be significantly smaller than that of ceramics obtained from compounds obtained using the dry method, so it was found to be ideal for not only piezoelectric materials and disk-shaped capacitors, but also multilayer capacitors. . Based on these findings, the present invention was completed.

(Summary of the Invention) The gist of the present invention is that, in a method for producing raw material powder of the compound of the present invention, (1) an aqueous solution containing the entire amount of W necessary for the target composition is reacted with an aqueous solution of Pb in an amount equivalent to this tungsten; Then, a precipitate of tungsten H lead is generated, and an aqueous solution in which this precipitate is dispersed is uniformly mixed with an aqueous solution of an amount of Pb component insufficient for the target composition and an aqueous solution of component A in an amount necessary for the target composition,
Either add a precipitate-forming solution to this to make a uniform precipitate of all components, or (2) react an aqueous solution of W in an amount necessary for the desired composition with an aqueous solution of component A in an equivalent amount to tungsten as component A. After generating the acid salt, the precipitate is either directly mixed with an aqueous medium, or a slurry suspended in a filtered alcohol medium is mixed with an aqueous Pb acid component solution or an alcohol solution in an amount insufficient for the desired composition. Generate a coprecipitate of Pb and A components using a precipitation forming solution, or
Or, for the Pb component, mix the lead precipitate and the same amount of lead compound into the tungstate slurry of component A, or homogeneize the entire component obtained by either method (1) or (2) above. The precipitate is filtered, dried (hereinafter sometimes referred to as a precursor), and calcined at 400 to 1000°C.

In the above precipitation process, an aqueous solution of Pb or A component equivalent to tungsten is required in the step of precipitating the tungstate salt of Pb or A component. The amount may be more than equivalent to tungsten and less than the amount required for the target composition. If an equivalent amount or more is used, in the step of obtaining a precipitate of Pbl and/or A component that is insufficient to the target composition, the insufficient amount will be, for example, the following pile.

■After forming a precipitate of tungstate of pb or component A, when forming the next precipitate using the same solution, obtain the precipitate of tungstate from the required amount of the component in objective 7. FFI was truly grateful for the extra power it added at the time.

■Instead of forming the next precipitate in the same solution, tungsten i'll! After filtering the salt precipitate, when forming the next precipitate, reduce the equivalent amount to tungsten from the required amount of the component in the target composition.

In addition, as a practical dielectric material, a solid solution of the composition of the present invention and another Pb-based beta-Obskite type compound is often used. In this case, the other pb-based perovskite type compound is mixed with the precipitate of the compound of the present invention before calcination and made into a solid solution by calcining, or during the process of obtaining the precipitate of the compound of the present invention, There is a method in which a precipitate is generated, a precipitate containing the entire composition of the practical material is obtained, and the precipitate is calcined to form a solid solution. Since the present invention can be a useful means for any of these methods,
The invention may be used for the above purposes.

In addition, when producing the compound in the present invention, the sinterability and electrical properties of ceramics obtained using the compound are measured by tII.
In order to achieve Iw, a slight R component such as Mn08iO, Bi
2'223 may also be added by adding a compound such as O. In this case, it is also possible to add it uniformly by allowing it to coexist in the aqueous solution during any of the manufacturing steps.

In addition, it may be added by a dry method or a wet method after the compound according to the present invention is prepared.

In the present invention, (B) a precursor containing two or more different A components is obtained at the same time, for example, (PbZn+zzW+zzOa) o, s・(PbC
otzzW+/zO3) o, s precursors are obtained and these are calcined (fired), or Tb) for example (PbZn
Precursors of perovskite compounds with different A components, such as +ziW+zzOi) and PbCo+zJ+zzO+, are obtained separately in advance, mixed and calcined (fired), or (C) PbA (material), type perovskite compounds A composite perovskite compound can be obtained by mixing the precursor with other perovskite compounds, such as PbBWO, BaTi0=, etc., and calcining (baking) the mixture. Such composite perovskite-type compounds usually provide dielectrics with better properties and performance than perovskite-type compounds in which the A component is alone.

Furthermore, in the present invention, in order to control the sinterability and electrical properties of ceramics made from perovskite compounds,
For example, a small amount of a compound such as MnO□, SiO□, Bi, 01, etc. may be added to the reaction system at any stage during the production process of the perovskite compound. Further, after producing the perovskite compound, the above components may be added by a dry method or a wet method.

Condensation of the precipitate is suppressed during the drying and calcination steps, resulting in good results.

Further, in the tungsten salt of component A, if it is soluble in the neutral region, such as iron tungstate, cleaning may be performed with weakly acidic water (+) H5 such as nitric acid.

The obtained precipitate is dried and calcined at 400-1000°C. If the calcination temperature is less than 400°C, the perovskite production reaction and degassing will be insufficient, and the bulk density of the obtained raw material powder will be low. If the temperature exceeds 1000°C, the powder particles become coarse and the sinterability deteriorates. Therefore, the calcination temperature is 400-1
000°C is suitable. This allows uniform,
A compound with high bulk density and easy sinterability can be obtained.

(Effect of the invention) According to the present invention, the following excellent effects are achieved.

(1) Since double precipitates are generated without co-precipitating all of the constituent components, these precipitates are in a mutually dispersed state, which prevents the formation of secondary particles during drying and calcination as in conventional coprecipitation. few. Therefore, a material with high bulk density and easy sinterability can be obtained.

(2) Since double precipitation is generated, it is suitable for each component3)
Since a uniform, fine-grained, easily sinterable compound without the non-uniformity of the composition as in the conventional dry method is obtained, by sintering this, ceramics with fine grain size can be obtained. This is ideal for stacked capacitors.

Example 1 Ammonium tungstate solution (vI4 was prepared by dispersing 0.08 io1 of H2WO4 (Wako Hyakuyaku) in 80+el of water and adding 200 at of 4.2% NH3 water (Wako Hyakuyaku) during boiling. This will be referred to as an AT solution hereinafter. ), add 240+g of lead nitrate (Wako supplement, special grade) aqueous solution under stirring.
(0,24io1 asPb) L, PbWO4
to precipitate. Next, ammonium bicarbonate (Wako Hyakuyaku) aqueous solution 260ml (0.38i).

1) is added dropwise to precipitate the remaining Pb2+f.

Into this reaction slurry, under stirring, Iff was added an aqueous solution of ferric nitrate (Wako Hyakuyaku, special grade) (hereinafter referred to as Fe(NO3)3 aqueous solution) >550 ml (0,16 sol as Fe) and 4.
Drop 2% NH3 water 2401+ at the same time and add 1 liter at 7-8
"e (OH) 3 is precipitated. After the precipitation is completed, 3
Stir for 0 minutes, filter and wash the cake with water. This cake was dried at 100℃ overnight and then calcined at 700℃ for 2 hours.
A compound of Pb(Fe2/3W1/3)03 was obtained. This X-ray diffraction diagram is shown in FIG. (Cu pole/monochromator
RAD-II, manufactured by Tsukuriku Denki) This X-ray diffraction diagram showed a perovskite structure slightly containing a pyrochlore structure.

Example 2 In Example 1, ATFB liquid was added to 600ml (0°1
2sol asW) and 400at (
0,12sol asZn) and NH as a precipitant.
3 Instead of water, use 9.8% sodium hydroxide (Wako Hyakuyaku,
Pb(z
Barrel the compound of n112W1/2)03.

Example 3 In Example 1, the AT solution was added to 600 ml (0°1
210+ asW) nickel nitrate aqueous solution (Wako Hyakuyaku, special grade) 40011 instead of Fe(NO3)3 aqueous solution
(0,12sol asN i ) is used to precipitate R agent!
- Pb"" 1/2 by using 9.8% sodium hydroxide aqueous solution 1201 instead of NH3 water
Compound W1/□)03 is obtained.

Example 4 Sodium tungstate solution 150g+l (0°1
0 sol asW), under stirring, add 100 ml of cobalt nitrate (Wako supplement, special grade) aqueous solution <0.20 Ilol a
sCO) dropwise followed by addition of dilute nitric acid to pH 4 to precipitate C0WO4. The reaction slurry is filtered and the cake on the Futsche is washed with 1) H4 dilute nitric acid to remove salts and excess CO2+.

After washing, the cake is dispersed in ethanol, PbO powder (Naoshima Kasei>0.20101) is added to this slurry, stirred, and filtered. Baked and P b (CO1/2
W1/2) Compound 03 is obtained.

Example 5 In Example 4, 150 ml of manganese nitrate aqueous solution (0.20 molasMn
) by using Pb (Mn, , , W1/2
) Compound 03 is obtained.

Example 6 In Example 4, 100 g of cadmium chloride aqueous solution + I (0,20
d) by using Pb(Cd1/2W1/2
” 3 compounds are obtained.

Comparative example 1 PbO (Naoshima Kasei> 0.31ot, Fe 203
(Dowa Chemical) 0.1sol, WO3 (New Nippon Metal) Q
, imol were mixed in a ball mill, filtered, dried overnight at 100°C, and dried at 700°C for 2 hours.
Pb (Fe2/3 Wl/3) 0 after calcination for an hour
Compound 3 is obtained. The XS;+ diffractogram (FIG. 2) showed a mixture containing a significant amount of pyrochlore structure compared to perovskite structure.

Comparative example 2 PbO0. 3tol, WO 30. 03*ol
, Fe2o30.0825I101. Nb2o5(
Mitsui Kinkuta Mining Co., Ltd.) 0.0525 mol was mixed 24 hours a day in acetone using a ball mill. After filtration and drying, 800℃
After calcination for 2 hours, wet grinding was performed in a ball mill to obtain Pb.
(Fe2/3 W1/3) O, 3 (Fel/2N
bl/2) 0.703 is obtained. This X-ray diffraction diagram (Figure 3)
indicates a mixture of perovskite structure and pyrochlore structure, and the average grain size was determined by electron microscopy to be 1. , 3 μm.

Example 7 To 300 ml of AT solution (0.08*ol asW), add lead nitrate (Wako auxiliary medicine. special grade) water I11 80 while stirring.
Drop 0 ml (Q. 8sol asPb) and
bWO4 is precipitated. Then ammonium bicarbonate (
Wako wear medicine. Special grade) aqueous solution 120011 (1.72*o
1) was added dropwise to precipitate the remaining Pb2''. To this reaction slurry, 1100+ el of water was added to the Fe-Nb8 combined solution (0.14101 niobium pentoxide hydrate) and heated and stirred. 12■olj was added to dissolve Nb, followed by 0.44nOI of ferric nitrate (Wako Hyakuyaku).
) and 4.

2000 ml of 2% Nl-13 water was added dropwise at j51 o'clock, and the iron-niobium co-precipitated hydroxide was precipitated while maintaining the discharge at 8 to 8.5. This reaction solution was poured with filtered water, dried at 100°C overnight, and calcined at 700°C for 2 hours.

The calcined product was wet-pulverized twice in a ball mill to produce Pb(Fe1/
2Nb1/2) 0.1 (F02/3W1/3) 0.30
Compound 3 is obtained.

This X-ray diffraction diagram (Figure 4) shows a perovskite structure, and the average particle diameter is 0 as determined by electron microscopy.

It was 2 μm.

Example 8 First, the Fe-Nb mixed solution used in Example 4 (however, ferric nitrate was 0.28*ol) and 4.2% NH3 water 1
At the same time, 700 ml of lead nitrate aqueous solution was added.
0 ml (0.56 sol as Pb) and ammonium bicarbonate aqueous solution 940 layer 1 (1.34 sol) were simultaneously added dropwise, and the reaction solution was filtered, washed with water, and dried overnight at 100°C to obtain Pb:Fe:Nb-2:1: A dried mixed precipitate of 1 is obtained.

Next, in the same manner as in Example 1, Pb:l”e:W-3:2
:1 mixed precipitate dried product is obtained.

Both were wet mixed with acetone in a ball mill for 24 hours, filtered, dried overnight at 100°C, and calcined at 700°C for 2 hours to form p b (Fe 1/2 Nb 1/2 >
.

7 (Fe2/3 W1/3)0.303 is obtained.

Example 9 After adding 0.25 wt% of Mn02 to the compounds obtained in Example 7 and Comparative Example 2 using a ball mill, 8 wt. did. The obtained granules were press-molded at a pressure of 1 TON/cd to form a green molded body, and then the green molded body was subjected to thermal decomposition of polyvinyl alcohol at 400°C for 3 hours in an electric furnace, and then the sintered density was saturated. The temperature was raised to a temperature at which the temperature started to decrease, and the mixture was fired for 2 hours to obtain a sintered body.

The weight and dimensions of this sintered body were measured to determine the sintered density at a predetermined temperature. In addition, the grain diameter of the surface was measured using an optical microscope and a scanning electron microscope photograph.

Furthermore, the sintered body was polished to a thickness of 1 mm and coated on both sides with an ion coater.
The relative dielectric constant at one Curie point and one Curie point was measured by measuring the temperature change in capacitance up to ℃. Furthermore, the dielectric constant, dielectric loss tangent, and resistivity at room temperature were measured.

The above results are shown in Table 1. From Table 1, it can be seen that the method of the present invention has superior sinterability and finer grains compared to the comparative example, and exhibits the same electrical properties.

Note that the electrical properties include capacitance, specific Mfa rate, and ll!
The l positive electric current was measured using a Yokogawa Hewlett-Packard ILF impedance analyzer (4192A).
12, and the resistivity was determined from the current value 1 minute after application of MDCIV using a Pifan meter manufactured by Yokogawa Hewlett-Packard (4140B>f).

[Brief explanation of drawings]

FIG. 1 is a x151 diffraction pattern of the raw material powder obtained in Example 1, FIG. 2 is in Comparative Example 1, FIG. 3 is in Comparative Example 2, and FIG. 4 is in Example 7.

Claims (1)

[Claims] A lead-based perovskite compound containing tungsten represented by the general formula PbA_xW_1_-_xO_3 (
However, x=1/2 or x=2/3, A=Fe, Co
, Ni, Mn, Mg, Zn, Cd, In.
(or two or more types), by mixing an aqueous solution of tungstate in the amount required for the desired composition and an aqueous solution of lead or component A in an amount equivalent to this tungsten,
After precipitating lead or tungstate of component A,
A slurry obtained by suspending this precipitate in water or an alcoholic medium is mixed with an aqueous or alcoholic solution of lead and/or component A in an amount insufficient for the target composition, and a lead compound and/or component A is mixed. or, after forming a precipitate of component A, a lead compound of the same quality and amount as this lead compound is mixed into a slurry of tungstate of component A; The precipitate was filtered and dried, 400 to 1000
A method for producing a tungsten-containing lead-based perovskite compound, comprising a step of calcining at ℃.