JPH10203867A - Sintered barium titanate and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a sintered barium titanate having a dense texture at a relatively low sintering temperature by sintering a specific barium titanate raw material powder under specific conditions. SOLUTION: A powdery raw material of barium titanate having a Ba/Ti molar ratio of 1.01-1.08 is produced by dissolving a barium alkoxide and a titanium alkoxide in an organic solvent to obtain a mixed alkoxide solution having a concentration of 0.1-3mol/kg and adding water to the solution in an amount corresponding to 2-50 times the theoretical equivalent necessary for the hydrolysis reaction or mixing an aqueous solution of barium hydroxide having a barium concentration of 0.1-3mol/kg with an organic solvent solution of a titanium alkoxide having a concentration of 0.1-3mol/kg and drying the precipitate produced by the hydrolysis at 40-100 deg.C. The objective sintered barium titanate having a bulk density of >=5.71g/cm<3> is produced by calcining the above raw material powder at 300-900 deg.C, forming the calcination product, heating the formed article to 950-1100 deg.C at a heating rate of 0.1-50 deg.C/min and sintering at the temperature for 1-20hr.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a dielectric material, a piezoelectric material,
The present invention relates to a barium titanate sintered body used as a semiconductor and other various electronic materials and a method for producing the same, and also to a raw material powder for a barium titanate sintered body.

[0002]

2. Description of the Related Art A sintered body of barium titanate (BaTiO ₃ ) is used as a dielectric material such as a multilayer ceramic capacitor, a piezoelectric material, a semiconductor, and various other electronic materials.

Conventionally, as a method for producing such a raw material powder for a barium titanate sintered body, a solid phase reaction method in which a mixture of titanium oxide and barium carbonate is heated to a high temperature of 1300 ° C. or more to cause a solid phase reaction, ₄ , BaTiO (C ₂ O ₄ ) ₂ .4 by the reaction between BaCl ₂ and an aqueous solution of oxalic acid
An oxalate method of obtaining a precipitate of H ₂ O and thermally decomposing it,
Hydrothermal treatment of a mixture of barium hydroxide and titanium hydroxide, and a hydrothermal synthesis method of calcining the obtained reaction product, hydrolyzing a mixed alkoxide solution of barium alkoxide and titanium alkoxide, and obtaining the hydrolyzate Alkoxide method, calcining the reaction product obtained by hydrolysis of titanium alkoxide in barium hydroxide aqueous solution, hydroxide-alkoxide method, other coprecipitation method, sol-gel method, spray pyrolysis method, etc. There is.

Among these, when a barium titanate sintered body is produced by an oxalate method, a hydrothermal synthesis method or an alkoxide method, etc., the sintering temperature is lower than that produced by a solid phase reaction method. Although it can be reduced slightly, the sintering temperature is 1200 ° C. or more in any of the methods.

On the other hand, the study of the method of lowering the sintering temperature of barium titanate has been mainly on the method of synthesizing the raw material powder at a Ba / Ti molar ratio of 1.0 and the sinterability by the method. The following literature focuses on the Ba / Ti molar ratio.

1) Journal of the Ceramic Society of Japan, Vol. 98, pp. 794-800 (1990). The Ba / Ti molar ratio is 0.98-1.0 by spray pyrolysis.
A method of synthesizing BaTiO ₃ powder having a Ba / Ti molar ratio of 1.03 has been studied, and it is reported that densification proceeds at the lowest temperature when the Ba / Ti molar ratio is 1.03.

However, in this document, the sintering temperature is 1100 ° C. or more in any case,
It has been reported that when sintered at a temperature lower than 00 ° C., the relative density of the obtained barium titanate sintered body is less than 70%.

2) J. Am. Ceram. Soc., No. 56
Vol., Pp. 605-606 (1973) U.S. Pat. No. 3,330,697 discloses that a Ba source and a Ti source are added to a mixed solution of an α-oxy acid such as citric acid and a polyhydric alcohol such as ethylene glycol. A method (Pechini method) for producing BaTiO ₃ powder by uniformly dissolving at the molecular level, evaporating excess solvent by heating to form a resin, and thermally decomposing the resin is disclosed. And, in this document, the Ba / Ti molar ratio is 0.94 to
BaTiO ₃ raw material powder of 1.04 is synthesized, and its initial sintering process is studied from the isothermal shrinkage rate.

3) Japanese Patent Application Laid-Open No. Sho 62-297214 By reacting barium hydroxide with titania or titanium alkoxide in a protic solvent, B
A method for obtaining a high-density barium titanate fine powder having an a / Ti molar ratio of 0.99 to 1.02 is taught. However, in the examples of this publication, sintering of the powder is not performed.

4) Powder and powder metallurgy, Vol. 36, No. 7
27-730 (1989), J. Am. Ceram. S.
oc., Vol. 68, C, p. 292 (1985), Tokuho 0
JP-A-2-8996 and JP-A-58-20781 These documents and publications include lithium fluoride (LiF).
Is added to the barium titanate raw material powder, a barium titanate sintered body can be obtained even if the raw material powder is sintered at a low temperature.
It is taught that the sinterability is improved by controlling the Ti mole ratio to the Ba excess side. However, there is no description about sinterability in a barium titanate system to which a flux such as LiF is not added.

In the case of preparing barium titanate raw material fine particles by the method shown in the above (1) to (3) and sintering them at a low temperature to produce a barium titanate sintered body, It is difficult to say that the purpose has been sufficiently achieved.

[0012]

Incidentally, multilayer ceramic capacitors, which are widely used in recent years, are manufactured by simultaneously sintering a plurality of internal electrodes and dielectric layers. Therefore, the melting point of the metal used for the internal electrode must be higher than the sintering temperature. Therefore, if a barium titanate sintered body can be manufactured by low-temperature sintering, the choice of metals that can be used as electrodes can be increased, and inexpensive metal materials can be used as electrodes. If a technique capable of producing a barium titanate sintered body by such low-temperature sintering is developed, not only the energy saving effect but also the production cost of a capacitor containing a raw material such as a metal for an internal electrode can be reduced.

However, in the above-described conventional methods for producing a barium titanate sintered body, any of the above methods is used.
Unless sintered at a temperature of about 0 ° C., a high-density barium titanate sintered body cannot be obtained. Therefore, there is a demand for a method capable of producing a barium titanate sintered body having high density and uniformity even when the barium titanate raw material powder is sintered at a low sintering temperature.

An object of the present invention is to provide a method for producing a barium titanate sintered body that meets such a demand.

[0015]

Means for Solving the Problems The present inventors diligently studied a method for greatly reducing the sintering temperature of barium titanate raw material powder. As a result, if the barium titanate raw material powder is prepared so that the Ba / Ti molar ratio is slightly higher than the Ba side, the sinterability is remarkably improved, and the sinterability is greatly improved as compared with the conventional technology. It was found that the sintering temperature could be lowered.

Further, the barium titanate sintered body obtained in this manner has a dielectric property that is higher than that of a conventional barium titanate sintered body obtained by sintering at a high temperature of about 1250-1300 ° C. It was found that there was no change in physical properties such as these, and the present invention was completed.

Such barium titanate (BaTiO)
₃ ) To prepare the raw material powder, for example, barium hydroxide (Ba (OH) ₂ ), barium alkoxide (Ba)
(OR ₁ ) ₂ ) and titanium alkoxide (Ti (O
It can be produced by various methods such as a reaction with R ₂ ) ₄ ). R ₁ and R ₂ are alkyl groups which may be the same or different.

In the present invention, the barium titanate sintered body B
The Ba / Ti molar ratio in the barium titanate raw material powder is set to 1.01 so that the a / Ti molar ratio becomes 1.01 to 1.18.
Adjust so as to be 1.18.

However, since the Ba source remains unreacted and the like, the Ba / Ti molar ratio of the obtained powder is from 1.01 to 1.0.
If it does not become 1.18, it is necessary to increase the number of Ba sources and adjust it to a desired molar ratio.

The relationship between the molar ratio of Ba / Ti and the sintering temperature of the obtained powder is as follows. That is,
Barium titanate (BaTiO ₃ ) is usually represented by a stoichiometric composition having a molar ratio of Ba / Ti of 1.00 as is clear from its chemical formula. However, as the Ba / Ti molar ratio becomes larger than 1.00, the sintering temperature is greatly reduced, and the Ba / Ti molar ratio becomes 1.01 to 1.18, preferably 1.02 to 1.10, More preferably, 1.03 to 1.08.
In this case, the sinterability is dramatically improved,
In any case, the sintered body has a bulk density of 5 by sintering at 300 ° C lower from 950 ° C to 1100 ° C, or lower by sintering at 950 ° C to 1050 ° C, or by lower sintering at about 950 to 1020 ° C. It has been found that a dense barium titanate sintered body having a density of 0.71 g / cm ³ or more (relative density of 95% or more) can be obtained. The dielectric properties of the barium titanate sintered body obtained at this time are the same as those of the conventional sintered body.

The barium source used in the synthesis of the barium titanate raw material powder generally contains strontium as an impurity in an amount of about 1,000 to 10,000 ppm when not purified as a high-purity product. is there. For example, Ba (OH) ₂ .8H ₂ O has Sr of 0.3% by weight (3000 ppm) or less as a JIS special grade reagent standard (JIS K8577). In such a case, the limited range of the Ba / Ti molar ratio is 1.01 as (Ba + Sr) / Ti molar ratio in consideration of the impurity Sr.
It may be in the range of up to 1.18.

The relative density referred to here is JCPD.
S (Joint Committee on Powder Diffraction Standard
s) Theoretical density calculated from the lattice constant of BaTiO ₃ having a stoichiometric composition described in 5-0626 of the card;
Calculated as a percentage (%) with respect to 12 g / cm ³ , if the bulk density of the sintered body is not less than 5.71 g / cm ³ , the relative density is 9
It becomes 5% or more.

In the present invention, by setting the molar ratio of Ba / Ti in the barium titanate raw material powder in the range of 1.01 to 1.18 as described above, even if the sintering temperature is greatly reduced,
This results in densification of the obtained barium titanate sintered body. However, the barium titanate raw material powder B
When the molar ratio of a / Ti is less than 1.01, 950 ° C. to 11
At a sintering temperature of 00 ° C., the densification hardly proceeds. On the other hand, when the molar ratio of Ba / Ti exceeds 1.18, 950
° C. at a sintering temperature of C. to 1100 ° C., a dense sintered body of a relative density of 95% or more (sintered bulk density 5.71 g / cm ³ or more) can not be obtained.

In addition, Ba in the barium titanate raw material powder
/ Ti molar ratio varies, and if there is partial non-uniformity such as less than 1.01, the sinterability varies, and the relative density is 95% (the sintered body bulk density is 5.71 g).
/ Cm ³ ).

Therefore, the barium titanate raw material powder is
The Ba / Ti molar ratio is in the range of 1.01 to 1.18, preferably in the range of 1.02 to 1.10, and more preferably in the range of 1.03 to 1.03.
It is desirable to make uniform within the range of 1.08.

[0026]

Next, a specific method for carrying out the present invention will be described. The method for producing the barium titanate raw material powder used in the present invention is not limited to a specific method. For example, barium titanate raw material powder may be produced by reacting barium alkoxide and titanium alkoxide, or may be produced by reacting barium hydroxide and titanium alkoxide.

Hereinafter, this manufacturing method will be specifically described. (1) Production method of barium titanate raw material powder by reaction of barium alkoxide and titanium alkoxide By subjecting a mixed alkoxide of barium alkoxide and titanium alkoxide to hydrolysis reaction, barium titanate (BaTiO ₃ ) raw material powder can be obtained.

Barium alkoxide can be obtained by a direct reaction between barium metal and alcohol. Titanium alkoxide can be obtained by blowing ammonia gas into titanium tetrachloride dissolved in alcohol. These manufacturing methods are known.

Barium alkoxide [Ba (OR ₁ )
₂ , R ₁ = alkyl group] and titanium alkoxide [Ti
The type of (OR ₂ ) ₄ , R ₂ = alkyl group] is not particularly limited, and any type can be used. However, considering practicality, R ₁ and R _{2 each} have 1 to 6 carbon atoms. A linear or branched alkyl group having the same is preferred. Representative alkyl groups include, but are not limited to, methyl, ethyl, normal propyl, isopropyl, normal butyl, isobutyl, normal pentyl, normal hexyl, and the like. Also,
The alkyl groups for R ₁ and R ₂ may be the same or different.

As the barium alkoxide and the titanium alkoxide, not only specially purified high-purity products but also
General industrial grade products can also be used. The organic solvent for dissolving the mixed alkoxide of the barium alkoxide and the titanium alkoxide is not particularly limited as long as the mixed alkoxide is soluble, and alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, and normal butyl alcohol, hexane, heptane, Organic solvents such as aliphatic hydrocarbons such as octane and aromatic hydrocarbons such as benzene, toluene and xylene can be used, and these can be used alone or in combination of two or more. However, when using water-insoluble solvents such as benzene, toluene, and xylene, consider uniform hydrolysis by improving the compatibility with water during hydrolysis and miniaturization of the precipitation particle size by improving the hydrolysis rate. Then, methyl alcohol,
It is desirable to add a water-soluble solvent such as ethyl alcohol, isopropyl alcohol, and normal butyl alcohol. Uniform and fine particles prevent abnormal grain growth during sintering and have a high activity, which contributes to improvement of sinterability. As a method of adding the water-soluble solvent, when added to a mixed alkoxide solution of barium alkoxide and titanium alkoxide, or when added to water used for hydrolysis, or when added simultaneously with hydrolysis And so on. The amount of the water-soluble solvent depends on the concentration of the mixed alkoxide solution of barium alkoxide and titanium alkoxide, but is about 0.2 to 5 times the volume of water used for hydrolysis. Is appropriate. The concentration of the mixed alkoxide solution of barium alkoxide and titanium alkoxide to be used is 0.1 to 3 mol / kg, and preferably 0.5 to 2 mol / kg in consideration of practicality and economy.

By hydrolyzing such a mixed alkoxide solution, a desired barium titanate raw material powder can be obtained. In such a hydrolysis reaction, water may be added to a mixed alkoxide solution of barium alkoxide and titanium alkoxide with stirring, or the above-mentioned mixed alkoxide solution may be added to water. The amount of water to be added is 2 times the stoichiometric equivalent (stoichiometric amount) required for the hydrolysis reaction.
It is about 50 times, preferably about 5 times to 30 times.

For recovering the barium titanate raw material powder as a precipitate formed by the hydrolysis reaction, an existing solid-liquid separation method such as filtration and centrifugation can be appropriately selected. It is also possible to use the slurry of the hydrolyzate as it is without performing solid-liquid separation and to mold it. For drying the precipitate, general methods such as ventilation drying, vacuum drying and freeze drying can be employed. It is also possible to use spray drying or the like which can simultaneously perform solid-liquid separation and drying. The drying temperature is preferably as low as possible in order to prevent agglomeration of the obtained powder particles, and is preferably in the range of 40 to 100 ° C. in consideration of practicality. (2) Production method of barium titanate raw material powder by hydrolysis reaction of barium hydroxide and titanium alkoxide Barium titanate (BaTiO ₃ ) is obtained by mixing and hydrolyzing barium hydroxide and titanium alkoxide.
The production of the raw material powder may be performed as follows.

First, the barium hydroxide aqueous solution may be any method as long as the barium hydroxide aqueous solution can be obtained. In _{general, Ba (OH) 2 · 8H} 2 O barium hydroxide hydrate etc. or barium hydroxide anhydride, or a method of the barium oxide may be dissolved in water, and a barium alkoxide to hydrolyze water Method for obtaining barium oxide aqueous solution, Ba
A method of adding an alkali such as caustic soda to a water-soluble barium salt such as Cl ₂ or Ba (NO ₃ ) ₂ to remove impurities and then dissolving the obtained Ba (OH) ₂ .nH ₂ O in water, etc. There is.

The concentration of the aqueous barium hydroxide solution used is
There is no particular problem as long as the solubility is lower than the solubility. The amount of barium hydroxide dissolved per 100 g of water was 1.67 g at 0 ° C., 25
4.29 g at 80 ° C. and 101.4 g at 80 ° C., which have low solubility near room temperature.
It is practical and economical to use a barium concentration of about 0.1 to 3 mol / kg while heating at a temperature of ° C.

As the aqueous barium hydroxide solution, not only a high-purity product specially purified but also a general industrial grade product can be used. As the titanium alkoxide, those similar to the titanium alkoxide as described above can be used.

As the titanium alkoxide, not only a high-purity product specially purified as described above but also a general industrial grade product can be used. The organic solvent for dissolving the titanium alkoxide is not particularly limited as long as the titanium alkoxide is soluble, and alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, and normal butyl alcohol, and aliphatic hydrocarbons such as hexane, heptane, and octane. And organic solvents such as aromatic hydrocarbons such as benzene, toluene and xylene. These can be used alone or as a mixture of two or more. However, when a water-insoluble solvent such as benzene, toluene, or xylene is used, uniform hydrolysis by improving the compatibility with the aqueous barium hydroxide solution during hydrolysis, and precipitation particle size by improving the hydrolysis rate are improved. Considering miniaturization, it is desirable to add a water-soluble solvent such as methyl alcohol, ethyl alcohol, isopropyl alcohol, and normal butyl alcohol. Uniform and fine particles prevent abnormal grain growth during sintering and have high activity,
It contributes to improvement of sinterability. As a method of adding the water-soluble solvent, in any case, such as when added to the titanium alkoxide solution, or when added to the aqueous barium hydroxide solution, or when added simultaneously with the hydrolysis Good. The amount of the water-soluble solvent depends on the concentrations of the titanium alkoxide solution and the aqueous barium hydroxide solution, but is preferably about 0.2 to 5 times the volume of water in the aqueous barium hydroxide solution. Appropriate.

When a titanium alkoxide such as titanium isopropoxide and titanium normal butoxide which is liquid at room temperature is used as the titanium alkoxide, the reaction between the titanium alkoxide and barium hydroxide can be carried out without using an organic solvent. In consideration of the operability, it is preferable to use the compound by dissolving it in the above-mentioned organic solvent. When an organic solvent is used, the concentration of the titanium alkoxide solution is 0.1.
It is preferably 1 to 3 mol / kg, and preferably 0.5 to 2 mol / kg in consideration of practicality and economy.

The treatment after mixing and hydrolyzing the aqueous barium hydroxide solution and the titanium alkoxide is the same as the above-described mixed alkoxide of barium alkoxide and titanium alkoxide. (3) Sintering method of barium titanate raw material powder (i) Barium titanate raw material powder obtained by the above method or the like may be calcined and then molded and sintered to produce a barium titanate sintered body. preferable. The calcination temperature is not particularly limited. However, in order to remove remaining organic components and to reduce shrinkage during sintering, the calcination temperature is from 300 ° C to 900 ° C.
It is preferred that If the calcined powder is partially agglomerated, the barium titanate sintered body obtained by sintering may not be sufficiently densified, so that the calcined powder is preferably appropriately crushed and pulverized. . There is no particular limitation on the method of forming the calcined powder, and press forming, isostatic pressing, tape forming such as a doctor blade method, extrusion forming,
Conventional techniques such as injection molding and cast molding can be applied, and these molding methods may be combined.

(Ii) When the barium titanate raw material powder (molded body) calcined and formed as described above is sintered, a barium titanate sintered body is obtained. Depending on the molar ratio of Ba / Ti of the barium titanate raw material powder, it is selected between 950 and 1100 ° C. at normal pressure. That is, when sintering at a temperature higher than the optimum sintering temperature, the bulk density of the obtained sintered body may decrease. The heating rate and the sintering time also need to be appropriately selected depending on the shape of the molded body and the like. However, in general, in consideration of practicality and economy, the heating rate is usually 0.1 to 50. C./min, preferably 0.5 to 20.degree. C./min, and the sintering time is 1 to 20 hours, preferably about 2 to 8 hours. It is also possible to maintain the temperature for a certain period of time or change the rate of temperature rise during the temperature rise. The smaller the particle size of the obtained raw material powder, the higher the activity of the powder and the faster the rate of temperature rise, the more rapid densification occurs.
It is thought to cause cracking and deformation. Therefore, the smaller the particle size of the raw material powder, the slower the rate of temperature rise is preferable. These conditions are determined by the Ba / Ti molar ratio of the barium titanate raw material powder or the amount and particle size of the raw material powder to be sintered. The particle size of the raw material powder is preferably 0.15 μm or less, more preferably 0.1 μm or less.
It is preferably 10 μm or less, particularly preferably 0.075 μm or less.

The bulk density of the obtained barium titanate sintered body varies depending on the Ba / Ti ratio of the raw material powder, the sintering temperature, the sintering time, the sintering atmosphere, the shape of the compact, and the like.
In the present invention, the following conditions are particularly preferable for the relationship between the Ba / Ti ratio and the sintering temperature.

When the Ba / Ti ratio is 1.10 to 1.18, the sintering temperature is 1050 to 1100 ° C., particularly 107
0 to 1100 ° C., and when the Ba / Ti ratio is 1.08 to 1.10.
To 1100 ° C., particularly 1030 to 1100 ° C., and when the Ba / Ti ratio is 1.03 to 1.08, the sintering temperature is 950 to 1100 ° C., particularly 950 to 1100 ° C.
050 ° C. and a Ba / Ti ratio of 1.0
When it is 1 to 1.03, the sintering temperature is 1000 to 1
It is preferably 100 ° C, particularly preferably 1030 to 1100 ° C.

The barium titanate sintered body according to the present invention may contain a trace amount of another metal element in addition to titanium and barium.

[0043]

Embodiments of the present invention will be described below. The method for synthesizing the raw material powder is not limited to only the production method of the present invention exemplified below, and the conventional wet synthesis method, that is, oxalate method, hydrothermal synthesis method, coprecipitation method, sol-gel Method, spray pyrolysis method or the like can be applied.

[0044]

Example 1 1 g of deionized water degassed with 117 g of CO ₂
High purity Ba of 5.78g (0.05 mol) (OH) ₂ · 8
H ₂ O was added, and the mixture was heated to 80 ° C. and dissolved. High purity Ba
(OH) ₂ · 8H ₂ O was used which was purified Sr content in 100ppm or less. This solution is placed in N ₂ gas for 60
℃ the cooled, with stirring of 1 mol / kg concentration titanium tetra n- butoxide _{^{[Ti (O n Bu) 4}} ] in toluene solution 47.6g of [16.2 g as titanium tetra-n- butoxide (0.0476 mol) Ba / Ti molar ratio of 1.05] was added, and stirring was continued under reflux for 1 hour. Further heating was continued, and toluene and n-butyl alcohol were distilled off, and the mixture was stirred in an aqueous slurry at 100 ° C. for 2 hours. The resulting precipitate was evaporated to dryness under reduced pressure to give 8
After drying at 0 ° C., the mixture was sized with a 100-mesh sieve to obtain a barium titanate raw material powder. X-ray diffraction analysis of the obtained powder confirmed that the powder was BaTiO ₃ . This powder was calcined at 800 ° C. for 1 hour to obtain a calcined powder. The Ba / Ti molar ratio of the calcined powder was determined by a glass bead method using fluorescent X-rays. Its analysis value was 1.05. The Sr content in the calcined powder was 1
It was less than 00 ppm.

After the calcined powder was subjected to isostatic pressing at a pressure of ² ton / cm ² , the obtained compacts were separately heated at a temperature rising rate of 10 ° C./min for 2 hours at normal pressure for 2 hours. Sintering was performed to obtain barium titanate sintered bodies having different sintering temperatures. The bulk density of the obtained sintered body was 5.4 g / cm ³
The above sample was measured by the Archimedes method, and 5.4 g /
Samples smaller than cm ³ were calculated from the shape and weight. (The measurement method is described in “Ceramics”, Vol. 19, pp. 520-529 (1984), and Examples 2, 3, and 4
(Example 5, Table 1, Table 2, Table 3, Table 4, and Table 5 are the same.) The results are shown in Table 1 (No. 7). Table 1 also shows the results obtained by changing the Ba / Ti ratio and the sintering conditions according to this example.

[0046]

Example 2 1 g of 58 g of deionized water de-CO ₂ was added
5.78 g (0.05 mol) of high purity Ba (OH) _2.
8H ₂ O was added, and the mixture was heated to 80 ° C. and dissolved. High purity Ba
(OH) ₂ · 8H ₂ O was used which was purified Sr content in 100ppm or less. This solution is heated at 60 ° C. in N ₂ gas.
Was cooled to, 13.5 g as a solution in isopropyl alcohol 47.6 g [titanium tetraisopropoxide Ti (O ⁱ Pr) ₄ with stirring for 1 mol / kg concentrations of titanium tetraisopropoxide [Ti (O ⁱ Pr) _4]
(0.0476 mol) and the molar ratio of Ba / Ti is 1.
05] and stirring was continued under reflux for 2 hours. The heating was continued to evaporate the solvent, and the obtained precipitate was evaporated to dryness under reduced pressure, dried at 60 ° C., crushed in a mortar, sized with a 100-mesh sieve, and barium titanate raw material powder I got X-ray diffraction analysis of the obtained powder confirmed that the powder was BaTiO ₃ . This powder was calcined at 800 ° C. for 1 hour to obtain a calcined powder. FIG. 1 shows a transmission electron micrograph of the obtained calcined powder. According to this, it was a fine particle powder having an average particle diameter of about 0.05 μm. Calculate the Ba / Ti molar ratio of the calcined powder by fluorescent X
It was determined by the glass bead method using a line. The analysis value is
1.05. The Sr content in the calcined powder was 1
It was less than 00 ppm.

After the calcined powder was subjected to isostatic pressing at a pressure of ² ton / cm ² , the obtained compacts were separately heated at a heating rate of 1 ° C./min for 4 hours at normal pressure for 4 hours. Sintering was performed to obtain barium titanate sintered bodies having different sintering temperatures. The bulk density of the obtained sintered body was measured by the Archimedes method for a sample having a volume density of 5.4 g / cm ³ or more.
Samples less than m ³ were calculated from shape and weight.

The results are shown in Table 2 (No. 19). In addition,
Table 2 also shows the results of changing the Ba / Ti ratio and the sintering conditions according to this example.

[0049]

Example 3 1 g of 58 g of deionized water with CO ₂ removed
5.78 g (0.05 mol) of high purity Ba (OH) _2.
8H ₂ O was added, and the mixture was heated to 80 ° C. and dissolved. High purity Ba
(OH) ₂ · 8H ₂ O was used which was purified Sr content in 100ppm or less. To this solution was added methyl alcohol 58 g, and cooled to N ₂ 60 ° C. gas, stirring of 1 mol / kg concentration titanium tetra n- butoxide _{^{[Ti (O n Bu) 4}} ] in toluene solution 48.1 g [Titanium 1 as tetra n-butoxide Ti (O ⁿ Bu) ₄
6.4 g (0.0481 mol), with a Ba / Ti molar ratio of 1.04], and the mixture was stirred under reflux for 2 hours. Further heating was continued, the solvent was distilled off, and the obtained precipitate was evaporated to dryness under reduced pressure, dried at 60 ° C., and crushed in a mortar.
The particles were sized with a 100-mesh sieve to obtain barium titanate raw material powder. X-ray diffraction analysis of the obtained powder confirmed that the powder was BaTiO ₃ .
This powder was calcined at 800 ° C. for 1 hour to obtain a calcined powder. The Ba / Ti molar ratio of the calcined powder was determined by a glass bead method using fluorescent X-rays. The analytical value is 1.04
Met. The Sr content in the calcined powder was 100 ppm
It was below. Such a calcined powder is ² ton / cm ²
After being subjected to isostatic pressing under the above pressure, the obtained compacts are separately sintered under normal pressure at the temperature raising rate of 1 ° C./min for 4 hours each at the temperature shown in the table, and barium titanate sintering having different sintering temperatures is performed. I got a body. The bulk density of the obtained sintered body was 5.4 g / cm ³
The above sample was measured by the Archimedes method, and 5.4 g /
Samples smaller than cm ³ were calculated from the shape and weight.

The results are shown in Table 3 (No. 29). In addition,
Table 3 also shows the results obtained by changing the Ba / Ti ratio and the sintering conditions according to this example.

[0051]

Embodiment 4 Sr is doped with impurities (Sr / Ba = 1.8 mol%)
Barium diisopropoxide of 1 mol / kg concentration containing ratio) of _{^{[Ba (O i Pr) 2}} ] in toluene, isopropyl alcohol mixture solution ^{50g [Ba (O i Pr)} 2 as 12.8 g (0.05 mol )], A 1 mol / kg concentration of titanium tetraisopropoxide [Ti (O ⁱ P
₄ ) g of a toluene solution of [r) ₄ ] [13.6 g of titanium tetraisopropoxide (Ti (O ⁱ Pr) ₄ ]
(0.048 mol) corresponding to a Ba / Ti molar ratio of 1.04], and the mixture was heated to 60 ° C. with stirring. 117 g of deionized water from which CO ₂ had been removed was added thereto, and stirring was continued for 1 hour under reflux. Further heating was continued, and toluene and isopropyl alcohol were distilled off.
For 2 hours. The obtained precipitate was evaporated to dryness under reduced pressure, dried at 80 ° C., and sized with a 100-mesh sieve to obtain a barium titanate raw material powder. X-ray diffraction analysis of the obtained powder showed that the powder was BaTiO ₃
Was confirmed.

This powder was calcined at 800 ° C. for 1 hour to obtain a calcined powder. The Ba / Ti molar ratio and the (Ba + Sr) / Ti molar ratio of the calcined powder were determined by a glass bead method using fluorescent X-rays. As a result, the analytical value of the Ba / Ti molar ratio was 1.04. The analytical value of the (Ba + Sr) / Ti molar ratio was 1.06. 2% of this calcined powder
After being subjected to isostatic pressing at a pressure of on / cm ² , the obtained compacts were separately sintered under normal pressure at a temperature rising rate of 10 ° C./min for 2 hours each at the temperature shown in the table. A barium oxide sintered body was obtained. The bulk density of the obtained sintered body,
The sample of 5.4 g / cm ³ or more was measured by the Archimedes method, and the sample of less than 5.4 g / cm ³ was calculated from the shape and weight.

The results are shown in Table 4 [No. 36]. In addition,
Table 4 shows (Ba + Sr) / Ti according to this example.
The results of changing the ratio and the sintering conditions are also shown.

[0054]

Embodiment 5 Sr is doped with impurities (Sr / Ba = 1.8 mol%)
Barium diisopropoxide of 1 mol / kg concentration containing ratio) of _{^{[Ba (O i Pr) 2}} ] in toluene, isopropyl alcohol mixture solution ^{50g [Ba (O i Pr)} 2 as 12.8 g (0.05 mol )], A 1 mol / kg concentration of titanium tetraisopropoxide [Ti (O ⁱ P
₄ ) g of a toluene solution of [r) ₄ ] [13.6 g of titanium tetraisopropoxide (Ti (O ⁱ Pr) ₄ ]
(0.048 mol) and a Ba / Ti molar ratio equivalent to 1.04], and the mixture was heated to 60 ° C. with stirring. 32 g of ion-exchanged water from which CO ₂ was removed was added thereto, and stirring was continued for 2 hours under reflux. Further heating was continued to distill off the solvent, the obtained precipitate was evaporated to dryness under reduced pressure, dried at 60 ° C., crushed in a mortar, sized with a 100-mesh sieve, and barium titanate raw material powder I got X-ray diffraction analysis of the obtained powder confirmed that the powder was BaTiO ₃ .

This powder was calcined at 800 ° C. for 1 hour to obtain a calcined powder. The Ba / Ti molar ratio and the (Ba + Sr) / Ti molar ratio of the calcined powder were determined by a glass bead method using fluorescent X-rays. As a result, the analytical value of the Ba / Ti molar ratio was 1.04. The analytical value of the (Ba + Sr) / Ti molar ratio was 1.06. 2% of this calcined powder
After isostatic pressing at a pressure of on / cm ² , each of the obtained compacts was separately sintered under normal pressure at a temperature rising rate of 1 ° C./min for 4 hours each at the temperature shown in the table. A barium oxide sintered body was obtained. The bulk density of the obtained sintered body is set to 5.
The sample of 4 g / cm ³ or more was measured by the Archimedes method, and the sample of less than 5.4 g / cm ³ was calculated from the shape and weight.

The results are shown in Table 5 [No. 42]. In addition,
Table 5 shows (Ba + Sr) / Ti according to this example.
The results of changing the ratio and the sintering conditions are also shown.

[0057]

[Table 1]

[0058]

[Table 2]

[0059]

[Table 3]

[0060]

[Table 4]

[0061]

[Table 5]

[0062]

As is apparent from the above description, according to the present invention, 950-11 ° C., which is 200-300 ° C. lower than that of the prior art.
A dense barium titanate sintered body having a bulk density of 5.71 g / cm ³ or more (relative density of 95% or more) can be obtained at a sintering temperature of 00 ° C. As a result, an excellent effect that the manufacturing cost of a product represented by a multilayer ceramic capacitor or the like can be significantly reduced can be obtained.

[Brief description of the drawings]

FIG. 1 shows an electron micrograph of the barium titanate raw material powder obtained in Example 2.

Claims (14)

[Claims] 1. A barium titanate (BaTiO ₃ ) sintered body obtained by sintering at a temperature of 950 to 1100 ° C. and having a sintered body bulk density of 5.71 g / cm ³ or more. 2. A barium titanate (BaTiO ₃ ) sintered body obtained by sintering at a temperature of 950 to 1050 ° C. and having a bulk density of 5.71 g / cm ³ or more. 3. A barium titanate (BaTiO ₃ ) sintered body obtained by sintering at a temperature of 950 to 1020 ° C. and having a sintered body bulk density of 5.71 g / cm ³ or more. 4. The barium titanate (BaTiO ₃ ) sintered body according to claim 1, wherein the Ba / Ti molar ratio is 1.01 to 1.18. 5. The barium titanate (BaTiO ₃ ) sintered body according to claim 1, wherein a Ba / Ti molar ratio is 1.02 to 1.10. 6. The barium titanate (BaTiO ₃ ) sintered body according to claim 1, wherein the Ba / Ti molar ratio is 1.03 to 1.08. 7. A barium titanate raw material powder having a Ba / Ti molar ratio of 1.01 to 1.18 is heated at 950 to 1100 ° C.
A method for producing barium titanate (BaTiO ₃ ) having a bulk density of 5.71 g / cm ³ or more. 8. Ba / Ti of barium titanate raw material powder
Method for producing a barium titanate (BaTiO ₃₎ sintered body according to claim 7 molar ratio is 1.02 to 1.10. 9. Ba / Ti of barium titanate raw material powder
Method for producing a barium titanate (BaTiO ₃₎ sintered body according to claim 7 molar ratio is 1.03 to 1.08. 10. A Ba / Ti molar ratio of 1.01 to 1.18.
And a raw material powder for a barium titanate (BaTiO ₃ ) sintered body sintered at a temperature of 950 to 1100 ° C. 11. A Ba / Ti molar ratio of 1.02 to 1.10.
The barium titanate (BaTi) according to claim 10, which is
O ₃ ) Raw material powder for sintered body. 12. A Ba / Ti molar ratio of 1.03 to 1.08.
The barium titanate (BaTi) according to claim 10, which is
O ₃ ) Raw material powder for sintered body. 13. The raw material powder for a barium titanate sintered body according to claim 10, wherein the raw material powder is prepared by a hydrolysis reaction of a mixed alkoxide of a barium alkoxide and a titanium alkoxide. 14. The raw material powder for a barium titanate sintered body according to claim 10, which is prepared by mixing and hydrolyzing an aqueous barium hydroxide solution and a titanium alkoxide.