JPH05155696A - Production of single crystal of barium titanate - Google Patents

Abstract

PURPOSE:To produce a large-size, single crystal of barium titanate having good characteristics by an industrially advantageous method. CONSTITUTION:A polycrystalline barium titanate is joined with a single crystal of barium titanate as a seed crystal and then heated so that the single crystal is grown from the polycrystal by solid phase reaction. In this process, a barium titanate powder produced by titania dispersion method is used as the source powder to produce the polycrystal.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a single crystal of barium titanate.

[0002]

2. Description of the Related Art A single crystal of barium titanate is a non-linear optical crystal used for optical communication and information processing, and is used as a phase conjugate wave generating medium applicable to high-resolution image processing, real-time holograms, laser resonators, etc. It is a material that can be expected to be used for. By the way, in a tetragonal barium titanate effective as a single crystal of barium titanate, since it cannot be obtained by directly crystallizing directly from a solution as shown in the phase diagram, conventional KF, BaCl ₂ as a flux was used as a flux. In reality, the single seed crystal of barium titanate is grown by the top seeded solution growth method (TSSG method) using a TiO ₂ -rich melt.

[0003]

By the way, in the above-mentioned conventional method for producing a single crystal of barium titanate, when the flux method is adopted, the single crystal of barium titanate is only a small single crystal called a butterfly type. There is a problem that you can not. In addition, when the above-mentioned TSSG method is adopted, a high temperature of 1,450 ° C or higher is required,
Further, since the platinum crucible is used, the manufacturing cost is high and the inclusion of impurities during the growth of the single crystal is inevitable.
Further, the manufacturing method involves problems such as a large loss of raw materials, a large single crystal cannot be obtained, and it takes time to grow a single crystal. Therefore, it is an object of the present invention to address these issues.

[0004]

SUMMARY OF THE INVENTION The present invention is a titanium crystal in which a barium titanate single crystal is bonded to a polycrystal of barium titanate as a seed crystal and heated, and a single crystal is grown from the polycrystal by a solid-phase reaction. A method for producing a single crystal of barium acid salt, characterized in that barium titanate powder produced by a titania dispersion method is adopted as a polycrystal powder for forming the polycrystal.

The polycrystal powder used in the present invention is produced by the titania dispersion method, and is used as a polycrystal by performing usual calcination, molding and firing. The titania dispersion method described above is a slurry prepared by dispersing fine titanium oxide or titanium oxide hydrate in the submicron state in water or an organic solvent in which barium is dissolved, and the slurry is prepared by the means shown below. It is a method of obtaining a powder by reaction, precipitation, drying, calcination and pulverization. That is, while stirring the above slurry at high speed, ammonium carbonate or oxalic acid as a precipitant is added to and mixed with the slurry, and the temperature is 60 to 90 ° C. and the pH is 6
The reaction is carried out under reaction conditions of ~ 10 and the barium compound is precipitated. After completion of the reaction, the precipitate is separated, washed with water or alcohol, dried, dried, calcined and pulverized to obtain a powder having a composition of BaTiO ₃ . Calcination temperature is 1,000-1,200 ℃
The reaction does not proceed sufficiently at 1,000 ° C or lower, and the particles of the powder become coarse at 1,200 ° C or higher.

In the case of joining a barium titanate polycrystal and a single crystal, the joining surfaces are polished with a diamond grindstone or the like to preferably have a smoothness Rmax of 0.2 μm or less, and the following method (1) is used. The polished surfaces of both crystals are bonded as they are without any treatment. (2) A salt aqueous solution of an organic acid or an inorganic acid containing a metal element constituting the crystal is interposed between both polished surfaces to bring them into contact with each other. (3) A bonding method is employed in which a solution that dissolves the crystal in part is interposed between both polishing surfaces and baked and bonded as described above.

[0007]

In the production method of the present invention, a solid-phase reaction is generated at the interface where the fine crystal particles constituting the polycrystal of barium titanate and the single crystal as the seed crystal are bonded to each other, and A large single crystal is grown by gradually coalescing polycrystalline fine crystal particles into a large single crystal. As a result, a method for producing a barium titanate single crystal having good characteristics is obtained. Further, if the production method of the present invention is adopted, a large single crystal of barium titanate having good characteristics can be obtained, and a single crystal can be produced using an ordinary electric furnace without using a platinum crucible. Since it is possible to produce a large number of single crystals, the manufacturing cost is reduced, and a homogeneous single crystal can be obtained without the inclusion of impurities during the growth of the single crystal. . Further, in the manufacturing method, the loss of raw materials is small, and it does not take much time to grow a single crystal.

By the way, in the manufacturing method of the present invention,
As a polycrystal powder for forming the polycrystal, barium titanate powder produced by a titania dispersion method is adopted. By the titania dispersion method, a powder having a good sinterability with a controlled size and shape can be obtained. When a polycrystal formed by using the obtained polycrystal powder is used, almost 100% single crystal can be formed, and the firing density of the single crystal is about 99% of the theoretical density. On the other hand, when the polycrystal powder produced by the oxalate method or powder mixing method is adopted, almost 100% single crystal can be obtained, but the size and shape are controlled to have good sinterability. It is difficult to obtain the obtained polycrystal powder and there is a problem in reproducibility, and the firing density of the obtained single crystal is about 96%.

[0009]

【Example】

(Example) Titania dispersion method by multi-imaging of the crystal powder prepared _{TiO 2: 54.0g, BaCl 2 ·} 2H 2 O: Weigh 165.1 g, both of these compounds are dissolved in water 12l. However, TiO ₂ is only dispersed. Next, oxalic acid was weighed 1.5 times equivalent to BaCl ₂ .2H ₂ O (about 128 g) and dissolved in 1.8 l of water, and this aqueous solution was mixed with TiO ₂ and BaCl ₂ mentioned above.
-Add dropwise to the solution of both compounds of 2H ₂ O while stirring.
In this case, the solution is adjusted to pH 8 with aqueous ammonia, the temperature is kept at 75 ° C. to react, and the reaction product is precipitated. The obtained precipitate is separated, washed with water, dried, calcined in the air for 3 hours and then pulverized to obtain a polycrystal powder. Preparation of polycrystal Powder for polycrystal is molded to obtain a molded product, which is fired in an oxygen atmosphere at 1280 ° C for 6 hours to obtain a polycrystal.
Cut into 5 mm x 5 mm x 5 mm square to make a polycrystalline sample.

Single crystal growth A single crystal of barium titanate (5 mm × 5 mm × 0.3 mm) prepared by the flux method was adopted as a seed single crystal, and the joining surface between the polycrystal sample and the seed crystal was a diamond grindstone. The surface is polished by a tin plate so as to have a smoothness Rmax = 0.05 μm, and dilute nitric acid is applied to the joint surface. The obtained joined body is heat-treated at 1,370 ° C. for 10 hours in an oxygen atmosphere in an electric furnace to make a polycrystalline single crystal. The obtained single crystals are all transparent and almost 100%
It was single-crystallized, and the firing density was 99%. The results are shown in Table 1 together with the other characteristics and manufacturing characteristics of the single crystal.

(Comparative Example 1) TiCl ₄ and BaCl ₂ were weighed so as to have a composition of BaTiO ₃ and dissolved in water to prepare a mixed aqueous solution, which was brought into contact with an aqueous solution of oxalic acid as a precipitant to form a precipitate. The precipitate was separated, dried, calcined at 1,000 ° C. for 3 hours, crushed, molded, and fired at 1,280 ° C. This fired body was cut into the same size as that of the example to obtain a polycrystalline sample, and the same seed crystal as in the example was used, and heat treatment was performed under the same conditions to grow a single crystal. All the obtained crystals were transparent and almost 100% were single crystals. However, the firing density of the single crystal was 96%. The results are shown in Table 1 together with the other characteristics and manufacturing characteristics of the single crystal.

(Comparative Example 2) A single crystal of barium titanate was produced by pulling up a melt by the TSSG method using BaO and TiO ₂ as raw materials. 35 mol% of BaO and TiO ₂ and 65 m
280 g was weighed so as to have an ol% composition, filled in a platinum crucible, set in a pulling device, and heated to about 1,470 ° C. to melt to obtain a uniform melt. Then melt this melt at 1,400 ℃
BaTi, which is a seed attached to a platinum holder after cooling to
O ₃ single crystal is brought into contact with the solution and rotating at 60 rpm, 0.5 ℃ / h
The temperature was lowered at r, and the seed crystal was pulled up at a speed of 0.1 mm / hr. The single crystal was completely pulled up at a melting temperature of 1,332 ° C. for about 140 hours, and then cooled at 50 ° C./hr. The obtained single crystal weighed about 25 g and had a diameter of 35 mm and a length of 10 mm. However, the firing density of the single crystal was 99% or more. The results are shown in Table 1 together with the other characteristics and manufacturing characteristics of the single crystal.

[0013]

[Table 1]

(Discussion) In order to produce a single crystal of barium titanate, a single crystal of barium titanate is bonded to a polycrystal of barium titanate as a seed crystal and heated to form a single crystal by solid-phase reaction. Solid state reaction method to grow
It is excellent in terms of production cost and the like, and it is advantageous to adopt the solid-phase reaction method as an industrial means. Regarding the characteristics of the single crystal, the solid-phase reaction method is slightly inferior to the other methods in terms of the firing density of the single crystal, but even in the solid-phase reaction method, titania dispersion as a polycrystal powder is carried out as in the present invention. When the barium titanate polycrystal powder produced by the method is adopted, a single crystal comparable to the firing density of the single crystal can be obtained.

Claims (1)

[Claims] 1. A method for producing a single crystal of barium titanate, which comprises bonding a single crystal of barium titanate as a seed crystal to a polycrystal of barium titanate and heating the same to grow a single crystal by solid-phase reaction. And a barium titanate powder produced by a titania dispersion method is employed as the polycrystal powder for forming the polycrystal.