JPH0651571B2 - Method for producing perovskite type compound containing tungsten - Google Patents

Description

The present invention relates to a method for producing a perovskite type compound having a fine submicron particle size. In particular, the present invention relates to a method for producing a tungsten-containing lead-based perovskite-type compound having a particle size suitable for a multilayer capacitor and having easy sinterability.

Generally, lead-based perovskite-type compounds have been widely used as piezoelectric materials, but in recent years (1) they have a higher dielectric constant than the commonly used dielectric materials such as barium titanate, and therefore have an electrostatic capacity per unit volume. It has a high capacity and is most suitable for downsizing of multilayer capacitors. (2) Since the sintering temperature is low, it is possible to use silver that is cheaper than palladium that has been conventionally used as an internal electrode. (3) Further types of materials Since it is possible to develop many new materials for dielectrics depending on the compositional variations, it is being actively researched and developed as a dielectric material.

The tungsten-containing lead-based perovskite-type compound (hereinafter referred to as the compound of the present invention) described in the present invention is one of the lead-based perovskite-type compounds, and the A component is F
The general formula PbA _x W _1-x O ₃ (where x = 1 / is one or more elements selected from e, Co, Ni, Mg, Zn, Cd, Mn, and In, and contains tungsten. 2 or 2/3), which is a group of compounds having a perovskite structure.

(Prior Art) As a conventional method for producing a lead-based perovskite-type compound, a dry method and a wet method are known.

The dry method is a method in which powders of oxides of the constituents are mixed according to their constituent proportions and calcined. However, with this method, it is difficult to obtain a raw material powder having a uniform composition, and there are many pyrochlore phases. Further, since it is necessary to raise the calcination temperature in order to increase the production rate of the perovskite phase, this causes the particles to be coarsened, which makes it difficult to easily sinter.

As a wet method, a method is generally used in which a mixed solution containing all the constituent components is prepared, and a precipitation forming liquid such as an alkali is added to the mixed solution to coprecipitate the mixture, followed by dry calcination. However, this method tends to produce a powder with excellent uniformity, but because of the uniformity, it precipitates during the formation of precipitates, during drying, and during calcination to form secondary particles, and the particles become coarse, making it easy to There is a drawback that it becomes difficult to become sinterable.

Further, in this method, since the concentration of the precipitate-forming liquid is constant, when the components have different precipitation-forming abilities, for example, one component produces 100% precipitation, while the other components produce 100% precipitation. It may not be formed, and there is a drawback that it is difficult to obtain a desired composition.

Since the grain size of ceramics obtained by using these perovskite type compounds according to the prior art is 10 μm or more, especially when practically used for a multilayer capacitor,
Since the layer thickness is restricted, it becomes a limit to miniaturization and large capacity.

Further, in the case of the compound of the present invention, since the tungsten component contained does not precipitate in alkali but precipitates with acid, tungsten and other components are allowed to coexist in the same liquid, and precipitates of other components of fine particles are formed. It is virtually impossible to get.

Furthermore, even when only the tungsten component is precipitated with an acid, it is necessary to precipitate the tungsten component as water-insoluble yellow tungstic acid (H ₂ WO ₄ ). When white tungstic acid (H ₂ WO ₄ · H ₂ O) is mixed with tungstic acid, since white tungstic acid is water-soluble,
When wet-mixing with the precipitation of other components, the tungsten component is dissolved and lost in water, so that a precipitate having a target component composition cannot be obtained, and as a result, a target component composition is obtained. A perovskite type compound cannot be obtained.

(Object of the Invention) The object of the present invention is to solve the drawbacks of the conventional methods in the production method of the compound of the present invention, to obtain a desired composition ratio of fine particles, easy sinterability and high production rate of perovskite phase. It is to provide a method for producing a compound.

(Structure of Invention) As a result of earnest research to achieve the above-mentioned object, the present inventors have
A part of the lead or A component, which could not be coprecipitated with tungsten, and the total amount of tungsten were precipitated as a tungstate insoluble in water or a weak acid, and the remaining components were precipitated with a precipitation forming solution such as an alkali. When it is carried out, since it is a double operation, the concentration of the precipitation-forming liquid can be set to a condition suitable for the precipitation formation at each stage, the composition of the precipitation component can be made to be a desired one, and a uniform dispersion can be obtained. However, since it was a double precipitate, it was determined that there was no formation of secondary particles due to coagulation.

The compound of the present invention obtained by calcination of the thus obtained precipitate is submicron fine particles, and since it is easy to sinter, the powder is molded and fired. The grain size of the obtained ceramics can be made extremely finer than that of the ceramics obtained from the compound of the dry method, so it was found that it is suitable for not only piezoelectric materials and disk capacitors but also multilayer capacitors. . The present invention has been completed based on these findings.

(Summary of the Invention) The summary of the present invention is that, in a method for producing a raw material powder of a compound of the present invention, (1) an aqueous solution containing all W necessary for a target composition is reacted with this tungsten and an equivalent Pb aqueous solution. A precipitate of lead tungstate is formed, and the aqueous solution in which the precipitate is dispersed and the amount of Pb component insufficient for the target composition and the amount of component A required for the target composition are uniformly mixed,
To this, a precipitation-forming liquid is added to form a uniform precipitate of all components, or (2) an aqueous solution of W necessary for the target composition is reacted with this tungsten and an equivalent amount of an aqueous solution of A component to obtain the tungsten of A component. After the acid salt is generated, the precipitate is suspended in an aqueous medium as it is or after being filtered and suspended in an alcoholic medium, a slurry obtained by mixing an aqueous solution of an Pb component or an alcohol solution in an amount insufficient for the target composition. Either the co-precipitate of the Pb and A components is formed by the precipitation forming liquid, or the lead compound of the same amount and the same amount as the Pb component is mixed with the slurry of the tungstate salt of the A component. A uniform precipitate of all components obtained by either method of (1) or (2) is filtered and dried (hereinafter referred to as
This is sometimes referred to as a precursor), 400 to 1000 ° C
It is characterized in that it is calcined in.

In the step of precipitating the tungstate of Pb or A component in the above precipitation step, an aqueous solution of Pb or A component in an amount equivalent to that of tungsten is required. To complete the reaction, the aqueous solution of Pb or A component is The amount may be equal to or more than the amount of tungsten and less than or equal to the amount required for the target composition. When used in an equivalent amount or more, in the step of obtaining a precipitate of Pb and / or A component in an amount insufficient for the target composition,
Regarding the amount of shortage, for example, specifically, the following amount will be obtained.

After forming a tungstate precipitate of Pb or A component, when the next precipitate is formed in the same solution as it is, the excess amount of tungstate precipitate added when the precipitation of tungstate is obtained from the necessary amount of the component in the target composition. The amount minus the amount.

When the next precipitate is formed after filtering the tungstate precipitate without forming the next precipitate in the same solution, the equivalent amount to tungsten is reduced from the required amount of the component in the target composition.

As a practical material for the dielectric, a solid solution of the composition of the present invention and another Pb-based perovskite compound is often used. In this case, the other Pb-based perovskite compound is mixed with the precipitate of the compound of the present invention before calcination to form a solid solution by calcining, or during precipitation of the compound of the present invention. There is a method of producing a precipitate, obtaining a precipitate containing the entire composition of a practical material, and calcining this to form a solid solution. The present invention can be a useful means in any of these methods,
The present invention may be used for the above purposes.

In producing the compound of the present invention, in order to control the sinterability and electrical characteristics of the ceramics obtained by using the compound, a minor component such as MnO ₂ , SiO ₂ , Bi ₂ O is used.
A compound such as ₃ may be added. In this case, it is also possible to add uniformly by coexisting with the aqueous solution in any of the manufacturing steps.

In addition, the compound according to the present invention may be added dry or wet after the preparation.

In the present invention, (a) precursors containing two or more different A components are simultaneously obtained, and for example, (PbZn _1/2 W _1/2 O ₃ ) _0.5 · (PbCo _1/2 W _1/2 O ₃ ) _0.5 precursor is obtained and these are calcined (baked), or (b) For example, (Pb
Zn _1/2 W _1/2 O ₃₎ and (as PbCo _1/2 W _1/2 O _3, obtained in advance separately precursor of perovskite compound component A different, mixing these, calcined (Calcination) or (c) a precursor of a PbAWO ₃ type perovskite compound is mixed with a precursor of another perovskite type compound, for example, PbBWO ₃ or BaTiO ₃ and calcined (calcination). Thus, a composite perovskite type compound can be obtained, and such a composite perovskite type compound usually provides a dielectric having excellent properties and performance as compared with a perovskite type compound having a single component A.

Further, in the present invention, in order to control the sinterability and electrical characteristics of the ceramics from the perovskite type compound,
A minute amount of a compound such as MnO ₂ , SiO ₂ or Bi ₂ O ₃ may be added to the reaction system at any stage during the production process of the perovskite type compound. Further, the above components may be added by a dry method or a wet method after the perovskite type compound is produced.

In the drying and calcination steps, precipitation is prevented from condensing and good results are obtained.

When the tungsten salt of the component A is soluble in a neutral region such as iron tungstate, the washing may be performed with a weakly acidic substance (pH about 5) such as nitric acid.

The obtained precipitate is dried and calcined at 400 to 1000 ° C. If the calcination temperature is lower than 400 ° C, the perovskite formation reaction and degassing are insufficient, and the bulk density of the obtained raw material powder becomes low. If it exceeds 1000 ° C., the powder particles become coarse and the sinterability deteriorates. Therefore, the calcination temperature is 400 ~
A temperature of 1000 ° C. is suitable. As a result, a compound having a uniform, high bulk density and easy sinterability can be obtained.

(Effects of the Invention) The present invention has the following excellent effects.

(1) Since the double precipitates are formed without coprecipitating all the constituents, these precipitates are in an interdispersed state, and secondary particles are not formed during drying and calcination as in conventional coprecipitation. Few. Therefore, a highly bulky and easily sinterable product is obtained.

(2) Since double precipitation is performed, the type and concentration of the precipitating agent suitable for each component can be selected, so that a powder of the target compound can be easily obtained.

(3) Since it is possible to obtain a uniform, fine particle and easily sinterable compound without nonuniformity of composition components as in the conventional dry method,
By sintering this, fine grain-sized ceramics can be obtained. This is the best choice for multilayer capacitors.

Example 1 0.08 mol of ammonium tungstate solution (H ₂ WO ₄ ) (Wako Pure Chemical Industries) was dispersed in 80 ml of water, and 200 ml of 4.2% NH ₃ water (Wako Pure Chemical Industries) was added during boiling. thing. Hereinafter referred to as an AT solution. ), 240 ml (0.24 mol asP) aqueous solution of lead nitrate (Wako Pure Chemical, special grade) with stirring
b) is added dropwise to precipitate PbWO ₄ . Then 260 ml (0.38 mol) of ammonium bicarbonate (Wako Pure Chemical) aqueous solution
Is added dropwise to precipitate the remaining Pb ²⁺ .

Ferric nitrate (Wako Pure Chemical,
Special grade) aqueous solution (hereinafter referred to as Fe (NO ₃ ) ₃ aqueous solution) 5
50 ml (0.16 mol as Fe) and 4.2% NH ₃ water 240 m
l is added dropwise at the same time to precipitate Fe (OH) ₃ at pH 7-8. After the completion of precipitation, the mixture is stirred for 30 minutes, filtered, and the cake is washed with water. Dry the cake at 100 ° C overnight,
It was calcined at 00 ° C. for 2 hours to obtain a Pb (Fe _2/3 W _1/3 ) O ₃ compound. This X-ray diffraction diagram is shown in FIG. (RAD-II manufactured by Rigaku Denki with Cu pole and monochromator) The 2θ value of the pyrochlore structure is 29.2 degrees ((2,2,2)) plane and 33.7 degrees ((4,0,0)
However, according to this X-ray diffraction diagram, the intensity of the peak at 2θ is extremely weak, so that the compound according to this example showed a perovskite structure containing a slight amount of a pyrochlore structure.

Example 2 In Example 1, 600 ml of AT solution (0.12 mol
asW) and Fe (NO ₃ ) ₃ instead of the aqueous solution, zinc nitrate aqueous solution (Wako Pure Chemical, special grade) 400 ml (0.12 mol asZn)
The compound of Pb (Zn _1/2 W _1/2 ) O ₃ is obtained by using 120 ml of a 9.8% sodium hydroxide (Wako Pure Chemical Industries, special grade) aqueous solution as a precipitant instead of NH ₃ water.

Example 3 In Example 1, 600 ml of AT solution (0.12 mol
ASW) and to Fe (NO _{3) 3} aqueous solution of nickel nitrate (Wako Pure Chemical instead of the aqueous solution, special grade) 400ml (0.12mol asNi) using, in place of aqueous NH ₃ as the precipitant, 9.8% sodium hydroxide solution 120ml By using Pb (Ni _1/2 W
A compound of _1/2 ) O ₃ is obtained.

Example 4 150 ml of sodium tungstate solution (0.10 mol
AsW), 100 ml (0.20 mol asCo) of cobalt nitrate (Wako Pure Chemical Industries, special grade) aqueous solution was added dropwise with stirring, and then diluted nitric acid was added to adjust the pH to ₄ to precipitate CoWo ₄ . The reaction slurry is filtered and the cake on the Nutsche is washed with dilute nitric acid, pH 4, to remove salts and excess Co ²⁺ .

After washing, the cake is dispersed in ethanol, 0.20 mol of PbO powder (Naoshima Kasei) is added to this slurry, and the mixture is stirred and then filtered. The cake is dried at 100 ° C. overnight and calcined at 700 ° C. for 2 hours to obtain a Pb (Co _1/2 W _1/2 ) O ₃ compound.

Example 5 A compound of Pb (Mn _1/2 W _1/2 ) O ₃ is obtained by using 150 ml of a manganese nitrate aqueous solution (0.20 mol as Mn) instead of the cobalt nitrate aqueous solution.

Example 6 In Example 4, a compound of Pb (Cd _1/2 W _1/2 ) O ₃ is obtained by using 100 ml (0.20 mol as Cd) of a cadmium chloride aqueous solution instead of the cobalt nitrate aqueous solution.

Comparative Example 1 PbO (Naoshima Kasei) 0.3 mol, Fe ₂ O ₃ (Dowa Kagaku)
1 mol, WO ₃ (Nippon Metals) 0.1 mol with a ball mill 24
After wet-mixing with acetone for hours, it is filtered, dried at 100 ° C. overnight, and calcined at 700 ° C. for 2 hours to obtain a compound of Pb (Fe2 / 3W1 / 3) O ₃ . This X-ray diffraction diagram (FIG. 2) showed a mixture containing a considerable amount of pyrochlore structure as compared with the perovskite structure.

Comparative Example 2 PbOO.3mol, WO ₃ 0.03mol, acetone _{Fe 2 O 3 0.0825mol, Nb 2} O 5 and (Mitsui Kinzoku) 0.0525Mol a ball mill, and wet-mixed for 24 hours. After filtration and drying, it is calcined at 800 ℃ for 2 hours, then wet-milled with a ball mill to obtain Pb (Fe2 / 3W1 / 3) 0.3 (Fe1
/2Nb1/2)0.70 ₃ is obtained. This X-ray diffraction diagram (FIG. 3) shows a mixture of a perovskite structure and a pyrochlore structure, and the average particle size was 1.3 μm by an electron microscope.

Example 7 To 300 ml (0.08 mol as W) of AT solution, 800 ml (0.8 mol as Pb) of lead nitrate (Wako Pure Chemical, special grade) aqueous solution was added dropwise under stirring to precipitate PbWO ₄ . Then, 1200 ml (1.72 mol) of an aqueous solution of ammonium bicarbonate (Wako Pure Chemical, special grade) is added dropwise to precipitate the remaining Pb ²⁺ . In this reaction slurry, an Fe-Nb mixed solution (0.14 mol of niobium pentoxide hydrate) was added.
1100 ml of water was added to 1 l, and the mixture was heated and stirred, and oxalic acid 1.
12 mol was added to dissolve Nb, and then 0.44 mol of ferric nitrate (Wako Pure Chemical Industries) was added and mixed)
Then, 2000 ml of 4.2% NH ₃ water was added dropwise at the same time to adjust the pH to 8
Precipitate the iron-niobium coprecipitated hydroxide while keeping it at 8.5. The reaction solution was filtered, washed with water, dried at 100 ° C. overnight, and calcined at 700 ° C. for 2 hours. Pb (Fe _1/2 Nb _1/2 ) _0.7 (Fe _2/3 W _1/3 ) _0.3 O ₃
To obtain the compound of

This X-ray diffraction diagram (FIG. 4) showed a perovskite structure, and the average particle size was 0.2 μm by electron microscopy.

Example 8 First, the Fe—Nb mixed solution used in Example 4 (however, ferric nitrate is 0.28 mol) and 4.2% NH ₃ water 1700 ml
Was added dropwise at the same time, and 560 ml of a lead nitrate aqueous solution (0.5
6mol as Pb) and ammonium bicarbonate aqueous solution 940ml
(1.34 mol) was added dropwise at the same time, and the reaction solution was filtered, washed with water, and dried at 100 ° C. overnight to obtain Pb: Fe: N.
A mixed precipitate dried product with b = 2: 1: 1 is obtained.

Next, in the same manner as in Example 1, Pb: Fe: W = 3: 2:
A mixed precipitation dryness of 1 is obtained.

Both of them were wet mixed with acetone in a ball mill for 24 hours, filtered, dried at 100 ° C. overnight, calcined at 700 ° C. for 2 hours, and Pb (Fe _1/2 Nb _1/2 ) _0.7 (Fe _2/3 W _{1 / 3} ) _0.3 O ₃ compound is obtained.

Example 9 0.25 wt% of MnO ₂ was added to and mixed with the compounds obtained in Example 7 and Comparative Example 2 using a ball mill, and 5 wt% polyvinyl alcohol 8 wt% solution was added to each compound to give granules. . The obtained granules were pressure-molded at a pressure of 1 TON / cm ² to give a green compact, and then the green compact was pyrolyzed with polyvinyl alcohol in an electric furnace at 400 ° C. for 3 hours. The temperature was raised to a temperature at which saturation started, and firing was performed 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. Also, the optical microscope and The grain size of the surface was measured with a scanning electron micrograph.

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

The above results are shown in Table 1. It can be seen from Table 1 that the method of the present invention has excellent sinterability as compared with the comparative example, has fine grains, and exhibits the same electrical characteristics.
The electrical characteristics, capacitance, relative permittivity, and dielectric loss tangent were measured at 1 KHz using a Yokogawa Hewlett-Packard LF impedance analyzer (4192A), and the resistivity was Yokogawa Hewlett-Packard. It was determined from the current value one minute after the application of DC1V using a Picoammeter (4140B).

[Brief description of drawings]

FIG. 1 is an X-ray diffraction diagram of the raw material powders obtained in Example 1, FIG. 2 in Comparative Example 1, FIG. 3 in Comparative Example 2, and FIG. 4 in Example 7.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masafumi Aoki 5-1, Ebishima-cho, Sakai City, Osaka Prefecture Sakai Chemical Industry Co., Ltd. (72) Tadao Nakatsuji 5-chome, Ebishima-cho, Sakai City, Osaka Prefecture Sakai Chemical Co., Ltd. Industrial Co., Ltd. (72) Inventor Kazuhisa Hidaka 5-1, Ebishima-cho, Sakai City, Osaka Prefecture Sakai Chemical Industry Co., Ltd. (72) Inventor Kayoko Segawa, 5-chome, Enoshima-cho, Sakai City, Osaka Sakai Chemical Industry Co., Ltd. (72) Inventor Yoshiyuki Kira 5-1, Ebishima-cho, Sakai City, Osaka Prefecture Sakai Chemical Industry Co., Ltd. (72) Inventor Shinichi Shirasaki 3-610-201 Takezono Sakuramura, Shinji-gun, Ibaraki (56) References 61-53115 (JP, A)

Claims (2)

[Claims] 1. A general formula PbA _x W _1-x O ₃ (wherein X is 1/2 or 2/3, A is Fe, C
1 or 2 or more elements selected from o, Ni, Mn, Mg, Zn, Cd and In are shown. ) In producing a lead-based perovskite-type compound containing tungsten represented by the formula: In a slurry prepared by suspending the precipitate in water or alcohol, and then mixing an aqueous solution or an alcohol solution of lead and the component A, which is insufficient for the required composition, with the lead compound and the component A. And a precipitate forming step for forming a precipitate, and the precipitate is filtered and dried to 400 to 1000.
A method for producing a lead-based perovskite-type compound, which comprises a firing step of firing at a temperature of ° C. 2. A general formula PbA _x W _1-x O ₃ (wherein X represents 1/2 or 2/3, A represents Fe, C
1 or 2 or more elements selected from o, Ni, Mn, Mg, Zn, Cd and In are shown. ) In producing a lead-based perovskite-type compound containing tungsten represented by the following formula, a required amount of an aqueous solution of tungstate having a required composition is mixed with the tungsten and an equivalent amount or more of the A component to obtain the tungsten of the A component. After precipitating the acid salt, in a slurry prepared by suspending the precipitate in water or an alcohol medium, an insufficient amount of lead and / or an aqueous solution or alcohol solution of the component A from the required composition is mixed, A lead compound and / or a component A precipitate is formed, or, for a lead component, after the formation of the component A precipitate, the same amount and amount of the lead compound is mixed with the slurry of the tungstate salt of the component A. And a calcination step in which the above-mentioned precipitate is filtered, dried, and calcined at a temperature of 400 to 1000 ° C. A method for producing an ito-type compound.