JPS62176915A - Preparation of fine particle of bi2ti2o7 - Google Patents

Abstract

PURPOSE:To obtain the titled fine particles having uniform particle size distribution, little variation of composition, and high purity in high yield without requiring heat-treatment, by allowing a hydrolyzed product of a Ti compd. etc., with a water-soluble Bi compd. to react by the wet process under a specified pH and specified temp. CONSTITUTION:A hydrolyzed product of a Ti compd. or a water-soluble Ti compd. (e.g. TiCl4) is mixed with a water-soluble Bi compd. (e.g. BiCl3) in 0.2-0.7 molar ratio of Bi/Ti, and the mixture is dissolved in water. Alkali such as KOH is added to the aq. soln. to prepare aq. soln. of strong alkali having >=12.0pH, which is subjected to wet reaction at >=220 deg.C in an autoclave, etc. The reaction product is washed with water, filtered and dried.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing Bi 2Ti 207 fine particles used as a ferroelectric material for electronic components such as capacitors.

[Summary of the invention]

In the present invention, when synthesizing Bi 2Ti 207 fine particles, which are ferroelectric materials, this synthesis is carried out in a strongly alkaline aqueous solution with a pH of 12.0 or more by adjusting the molar ratio of Bi and Ti (hereinafter referred to as B
abbreviated as i/Ti) 0.2 to 0.7, reaction temperature 22
The precipitate obtained by the synthesis reaction is washed with water, filtered, and dried at a temperature of 0°C or higher, so that the particle size is small and the particle size distribution is uniform, making it possible to wet-synthesize i 2Ti 207 fine particles. It is.

[Conventional technology]

In recent years, in the semiconductor field, advanced microfabrication techniques have made it possible to realize smaller integrated circuits (ICs) and large-scale integrated circuits (LSI). In addition, GaAs-based materials, which have a high signal processing speed, are being actively used.

Along with this, the capacitors used in these devices are required to be of higher quality, smaller, and lighter than conventional products.

In addition, due to the miniaturization and weight reduction of electrical equipment, such as the development of the so-called 8-video video, which is a significantly smaller version of the conventional video, the electronic components used, especially capacitors, are becoming smaller and lighter and of high quality. desired.

By the way, in the case of electronic components that are desired to be smaller and lighter, ensuring their performance is a major issue.For example, in chip capacitors, which are one of the main components, it is necessary to increase the capacity and to withstand high frequency characteristics. Research is underway to improve this. The electrical characteristics of ceramic multilayer capacitors, which are generally widely used as chip capacitors, depend on the dielectric constant of the dielectric material used, the thickness of the dielectric layer, the lamination, the number of stages, etc. Further improvements such as sinterability are desired.

In order to meet these demands, research on ferroelectric materials is being conducted from various angles at various research institutions, and B' 2Ti 207 is one of the dielectric materials with many excellent properties. is attracting attention.

Conventionally, as a method for producing fine particles of bismuth titanate, bismuth oxide (Biz03) and titanium oxide (T
iOz) in a ball mill, 1.200~
A known method is to carry out a solid phase reaction at a high temperature of 1,300°C, then pulverize using a ball mill etc. and sieve.0 [Problems to be solved by the invention] However, such methods The bismuth titanate fine particles obtained by the manufacturing method are formed at high temperatures for a long time and then ground for an even longer time, so they are contaminated with impurities such as metal oxides, have a poor particle size distribution, and are difficult to avoid including coarse particles. The present invention was proposed in view of the above-mentioned circumstances, and has the disadvantage that Bi 2Ti 20 has a small particle size, a uniform particle size distribution, and no contamination with impurities.
7 fine particles can be synthesized by wet reaction BizTi 207
The present invention aims to provide a method for producing fine particles.

[Means to solve the problem]

The present inventors have discovered that 12Ti is fine and has a good particle size distribution.
2 (h) As a result of long-term intensive research to develop a synthesis method that can wet-synthesize microparticles, we have found that a hydrolysis product of a titanium compound or a water-soluble titanium salt and a water-soluble bismuth compound are wet-synthesized in an aqueous solution. During the reaction, the p of this aqueous solution
Bi by setting H and reaction temperature within predetermined ranges.
It was found that zTi 207 fine particles were obtained in a single phase, and the particle size was fine and uniform.

The present invention was completed based on such knowledge, and the present invention is based on the fact that a hydrolysis product of a titanium compound or a water-soluble titanium salt and a water-soluble bismuth compound are mixed at a molar ratio of 0.2 to 10% Ti. Blend so that the pH is 0.7 and the pH is 12.0.
The method is characterized in that the reaction is carried out in the above strong alkaline aqueous solution at a reaction temperature of 220° C. or higher.

That is, in order to produce BizTi 207 fine particles in the present invention, a hydrolysis product of a titanium compound or,
A water-soluble titanium salt and a water-soluble bismuth compound are subjected to a wet reaction in an alkaline aqueous solution at high temperature using an autoclave or the like to produce a fine particle precipitate, and the obtained fine particle precipitate is washed with water or hot water.

By removing alkali metal ions such as Na and Li, f
It is sufficient to carry out over-drying. In this case, the obtained fine particle precipitate is already in a crystalline state and a special heat treatment step for crystallization is not necessary. Here, the pH and temperature of the aqueous solution during the above wet reaction. is important, and by setting the reaction temperature in the range of p) (12,0 to 13.8 and 220°C or higher, Bi2Ti207 fine particles can be obtained as a single phase.0 According to the experiments of the present inventors, the above wet method In the reaction, Bi
The molar ratio of Bi and Ti (Bi/Ti) was 1:2, the pH of the aqueous solution was changed, and the reaction temperature was 25°C in an autoclave.
A wet reaction was carried out at 0° C. for a reaction time of 3.5 hours, followed by washing with water, filtration, and drying. The relative production amount of 13i2Ti207 fine particles was measured, and the results shown in FIG. 1 were obtained. Note that the relative production amount of BizTizOy fine particles here is a value determined from the peak area of the diffraction X-ray peak (800) obtained by performing X-ray diffraction using a copper target and a nickel filter (the same applies hereinafter). 0From this figure 1,
Bi 2Ti if the pH is in the range of 12.0 to 13.8
It was confirmed that 207 fine particles were synthesized as a single phase in a high yield.0 Note that an alkaline solution with a pH of 13.8 corresponds to a KOH solution of approximately 1.54 d-/j.

Further, in the above wet reaction, the reaction temperature may be set to 220° C. or higher. For example, pH 13.5, Bi/Ti
= 1/2, a wet reaction was carried out in an autoclave for 3.5 hours while changing the reaction temperature, and the relative production amount of Bi2Ti207 fine particles obtained by washing with water, filtration, and drying was measured, and the results shown in Figure 2 were obtained. Obtained. From this figure 2, Bi
It was confirmed that the amount of 2T i 207 fine particles produced increased as the reaction temperature became higher, and that the reaction temperature should be set to 220° C. or higher. The upper limit of the reaction temperature is considered to be about 400°C if an autoclave or the like is used, but for practical purposes it is 250°C.
On the other hand, the molar ratio of Bi and Ti contained in the starting materials Bi
/Ti is preferably within the range of Bi /Ti =0.2 to 0.7. If the Bi /Ti ratio is outside the above range, the amount of Bi.2Ti 207 produced is extremely reduced. For example, the pH of the aqueous solution is set to 13.5, the mixing molar ratio of Bi and Ti as starting materials is changed, a wet reaction is carried out at 250°C for 3.5 hours in an autoclave, and l3i2Ti20y fine particles are obtained by washing with water, filtration, and drying. When the relative production amount of was measured, the results shown in FIG. 3 were obtained. According to the analysis by the present inventors, it was found that when 13i/Ti is 0.8 or more, B14(Ti04)3 exists and B'2Ti207 fine particles are not generated.
If i/Ti is within the range of 0.2 to 0.7, then Bi
It was confirmed that 2Ti207m microparticles could be synthesized in a single phase and at a high yield, and that the production amount reached its maximum especially when Bi/Ti = 0.5.

Furthermore, in the above wet reaction, Bi/Ti =1/
2. After adjusting the pH of the aqueous solution to 13.5 and performing a wet reaction at 250°C in an autoclave while changing the reaction time,
When we measured the relative production amount of BizTizO7 fine particles that had been washed, filtered, and dried, we obtained the results shown in Figure 4.From this Figure 4, we can see that the relative production amount of fine particles increases with time. It was found that when the reaction time was about 60 minutes or more, the relative production amount was 85% or more.

[For production]

A hydrolysis product of a titanium compound or a water-soluble titanium salt and a water-soluble bismuth compound are prepared in an alkaline aqueous solution with a pH of 12.0 or higher, with a mole of Bi and Ti of 2 to 0.7, and a reaction temperature of 220°C or higher. By carrying out a wet reaction, Bi 2Ti 207 fine particles having a small and uniform particle size and containing no impurities are synthesized without heat treatment.

〔Example〕

The present invention will be explained below using more specific examples. It goes without saying that the present invention is not limited to the following examples.

Example 1 50g of titanium chloride (TiCJ4) was placed in a beaker,
Pure water was added dropwise to this over 2 to 3 minutes to prepare a titanium chloride aqueous solution. Potassium hydroxide (KOH) is added to this aqueous solution.
was added to adjust the pH to 7.0. Next, 41.56 g of bismuth chloride (BiCj3) was added to this solution, and then potassium hydroxide (KOH) was added to adjust the pH to 7.0, followed by further addition of pure water and the solution was closed at 500 m/m.

Next, collect 5Qm of this aqueous solution, add potassium hydroxide (KOH) to it, add pure water, and make an IQQ solution with a pH of 13.5.
An aqueous solution of m/m was prepared. Then, this aqueous solution was heated to 250°C while stirring in a closed container (autoclave) for 3.
The reaction was allowed to proceed for 5 hours. The white precipitate produced after the reaction was repeatedly subjected to decantation to remove impurities such as alkali ions, followed by washing with water, filtration, and drying at 100° C. overnight.

FIG. 5 shows the results of analyzing the fine particles obtained by the above-mentioned operation by X-ray diffraction method. The diffraction pattern shown in Fig. 5 is A
STM (The American 5oci)
ety forTesting Materials)
The lattice constant of this Bi2Ti207 fine particle was calculated from the X-ray diffraction data, and the Bi2T
It was confirmed that the i207 fine particles were cubic crystals with ao = 20.7201 〇Example 2 509 (7) Chloride f Tough (TiCx4) Dropped into 500 m of ice water over 3 to 5 minutes. A titanium chloride aqueous solution was prepared. Add concentrated ammonia water (NH40) to this aqueous solution.
H) was added to form a white suspension, and aqueous ammonia (NH40H) was added to this suspension to adjust the pH to 7.0.

Next, add bismuth chloride (Bi CJ 3) to this solution.
1.56 g was added, followed by potassium hydroxide (KOH), and then pure water was added to adjust to p) (13.0 lQQQm/solution.

Next, 100 m/100 m of this solution was collected and reacted in a closed container (autoclave) at 250° C. for 3.5 hours while stirring. After the reaction, the white precipitate produced was repeatedly subjected to decantation to remove impurities such as alkali ions, washed with water, filtered, and then dried at 100° C. for one day.

When the fine particles obtained by the above operation were analyzed by X-ray diffraction, the diffraction pattern was exactly the same as that of the bismuth titanate fine particles shown in FIG. 5, and therefore, the fine particles were cubic Bi 2Ti 207. I understand.

Example 3 50g of titanium chloride 7 (Tick4) was soaked in ice water.
/ to prepare an aqueous titanium chloride solution. Potassium hydroxide (KOH) was added to this aqueous solution to adjust the pH to 7.0, and then pure water was added and the solution was closed at 500 m/s.

Next, this solution was sampled at 5Qm/bismuth chloride (BiC).
υ was added at 4.21 g, then 4.0 g of potassium hydroxide (KOH) was added, and pure water was added and the solution was closed at 100 m/0. The reaction was carried out at ℃ for 8 hours.

After the reaction, impurities such as alkali ions are removed by repeating decantation of the raw white precipitate.
After further washing with water and filtration, it was dried at 100°C for a day and a night.

When the fine particles obtained by the above operation were analyzed by X-ray diffraction, the diffraction pattern was exactly the same as that of bismuth titanate shown in FIG. 5, and therefore, the fine particles were cubic BizTi20? It turned out to be.

Example 4 Titanium chloride (Ti
CJ4) was added dropwise to prepare an aqueous titanium chloride solution.

A sodium hydroxide (NaOH) solution was added to this aqueous solution to adjust the pH to 7.9, and then water was added to adjust the pH to 500 m/s.

Next, bismuth nitrate (Bj(NO3)3.5H
20) Add 63.9 g, followed by potassium hydroxide (KO
Add potassium hydroxide (KO) to pH 7, Q.
Add H) and pure water p) (13,0 solution 100ffi/
Next, 100 m/ml of this solution was collected, and the 0 was placed in a sealed container (
The reaction was carried out for 3.5 hours at 250'C in an autoclave). After the reaction, the white precipitate produced was repeatedly subjected to decantation to remove impurities such as alkali ions, washed with water and filtered, and then dried at 80°C for one day.

When the fine particles obtained by the above procedure were analyzed by X-ray diffraction, the diffraction pattern was exactly the same as that of bismuth titanate shown in FIG. Therefore, this fine particle was found to be cubic Bi2Ti207.

〔Effect of the invention〕

As is clear from the above explanation, in the present invention, a hydrolysis product of a titanium compound or a water-soluble titanium salt and a water-soluble bismuth compound are blended in a predetermined ratio, and the pH is 12.
Since the wet reaction is carried out in an alkaline aqueous solution with a concentration of 0 or more and a reaction temperature of 220°C or more, the particle size is minute and the particle size distribution is uniform. zTi 207 fine particles can be synthesized without heat treatment. be able to. The obtained Bi2Ti5+Q7 fine particles are suitable for various electronic materials such as electrostrictive materials, piezoelectric materials, and transparent ceramic materials. Also, unlike the conventional method of mechanically making fine particles using a ball mill etc., Because it is wet-synthesized, there is no metal oxide as an impurity, and Bi is produced with little compositional fluctuation.
2Ti 20? Fine particles are obtained.

[Brief explanation of drawings]

Figure 1 is a characteristic diagram showing the pH dependence of the relative production amount of BizTizO7 fine particles, Figure 2 is a characteristic diagram showing the temperature dependence of the relative production amount of BizTi 207 fine particles, and Figure 3 is a B
i zTi 20 Relative production amount of fine particles Bi/Ti (
Figure 4 is a characteristic diagram showing the dependence on Bi2Ti (molar ratio).
Figure 5 is a characteristic diagram showing the wet reaction time dependence of the relative production amount of 207 fine particles.
It is a diffraction X-ray spectrum of i zTi 207 fine particles.

Claims (1)

[Claims] A hydrolysis product of a titanium compound or a water-soluble titanium salt and a water-soluble bismuth compound are mixed in such a manner that the molar ratio of Bi to Ti is 0.
2 to 0.7, and reacting in a strong alkaline aqueous solution with a pH of 12.0 or higher at a reaction temperature of 220°C or higher.