JPS63215598A - Production of barium borate single crystal having low temperature phase - Google Patents

Abstract

PURPOSE:To readily obtain a barium borate single crystal consisting of pure low temperature phase structure, by blending BaCl2 and NaBO2 with NaCl which is a flux at a specific molar ratio and heating and melting the blend to carry out reaction and depositing the resultant BaB2O4 as a crystal in the flux. CONSTITUTION:1-13.5mol. sodium chloride as a flux is blended with a raw material consisting of 1mol. barium chloride and 2mol. sodium metaborate. Then the blend is heated and melted to carry out reaction and barium borate which is reaction product is deposited as a crystal in the flux. Thus a single crystal of beta-BaB2O4, consisting of prism- or needle-like transparent crystal, containing no high temperature phase and wholly consisting of pure low temperature phase structure is obtained. The single crystal has large nonlinear optical effect and is strong to injure by laser and useful as nonlinear optical material.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to the growth of barium borate (β-BaB20,) Jl crystal, which has recently been discovered as a promising nonlinear optical crystal and has a low-temperature phase structure.

[Prior Art] A nonlinear optical material that has a large nonlinear optical effect and is resistant to laser damage is long-awaited as one of the optical materials that will support a variety of light wave techniques in the future.

Under such circumstances, it was predicted through crystal detailed research that β-BaB204 crystal would have a large nonlinear optical constant, and its effect was actually proven [C, Chu
Angtian et al.: 5cientia
5inica (Seties B), Vol, 28.
No. 3.235 (1,985) There has been a sudden interest in growing high-quality single crystals of β-BaB20m of practical size.6 BaBzO1 crystals can be grown at temperatures around 925℃ and above Here we have the crystal structure R3cmpga, and below that we have the crystal structure R3cmpga.
It is a crystal with so-called structural phase transition property, which adopts 3-C. As shown in Figure 1, in the phase diagram, BaO and B2O melt at a molar ratio of 1:1 to form a compound B.
Even if one tries to directly grow a single crystal from this composition melt using a pulling method (CZ method), etc., the phase transition will not occur properly. Because of the completeness, even if the crystal temperature falls below the transition point, the high temperature phase structure is quenched and brought directly to the low temperature phase temperature, and at room temperature, the structure is a mixture of high temperature phase (α phase) and low temperature phase (β) phase. becomes.

The nonlinear optical effect is due to the low-temperature phase structure β-B lacking inversion symmetry.
Found only in aB20a. Therefore, the desired crystal is β
It is a single crystal consisting of only a single phase, and some kind of ingenuity is required to grow it.

As an example of growing a β-BaB20j single crystal, the only known method is one that utilizes a part of the eutectic reaction between BaB201 and NazB20a shown in the phase diagram of FIG.

[H, Qingzhen at al, :Acta
Pbys, 5inica Vol, 30°No, 4.
pp. 559 (1981), see here. The key point of this method is to grow crystals in the β phase region below the transition temperature, within the range of raw material compositions Ma and Mb (Fig. 2), and at the same time as the transition temperature Tc. β-BaB201 is directly pulled up using the top seeding CZ method between crystal temperatures Te.

The specific operating procedure will be explained by taking as an example a raw material having a composition Ma. First, raw materials are placed in a crucible, completely melted, and reacted, and then the temperature is slowly lowered.

A seed crystal is immersed in the melt at a temperature Tc at which crystals begin to precipitate from the melt, and pulled up while continuing to lower the temperature. As the crystal grows, the remaining melt composition changes from Ma to Mb, and the crystal is separated from the melt just before the eutectic point, and then cooled to room temperature.

[Problems to be solved by the invention] The above-mentioned known method has a maximum of 100
Only a temperature range of less than 30 degrees Fahrenheit can be used, and only a small amount of the raw material charged into the crucible precipitates as crystals. Therefore, a large crucible and a large amount of raw material are required, and the relationship between the cooling rate of the melt and the rate of pulling the crystals is limited. There are also technical difficulties such as this, and a lifting device is also required.

This invention proposes another new method for easily growing β-BaB20jJ@ crystals. Starting from a combination of raw materials different from known examples, single crystals of practical size can be obtained using simpler equipment and growing techniques. It has the advantage of being

[Two steps to solve the problem] In this invention, barium chloride (BaC12) and sodium metaborate (NaBO2) are used as starting materials, along with which sodium chloride (NaC1) is added as a flux and heated. , is melted and the chemical reaction shown in the following formula is carried out.

BaCl2+2NaBO2+nNaCl→BaB20a
+ (n+2)NaCl At this time, the temperature of the melt is slowly lowered to precipitate barium borate, which is a reactive acid, as a single crystal in the flux.

[Operation] In the above reaction which forms the main point of this invention, NaC1
does not directly participate in the reaction, but only serves as a flux, suppressing the reaction rate, and reducing the amount of β produced by the reaction.
- Dilute the concentration of BaB204 to prevent frequent nuclear generation,
It works to promote enlargement of crystal size. At the same time, NaCl holds the precipitated crystals and the crystals adhere to the platinum crucible wall.

Prevents cracking due to the difference in thermal expansion with platinum,
In addition, volumetric contraction during solidification separates the crucible from the inside, making it extremely easy to take out.

[Example code] Next, this invention will be explained in detail.

The starting materials NaBO2, BaCl2 and the flux NaCl were vacuum dried to a concentration of 23.0 wt%, respectively.
Weighed 34.5wt% and 42.5wt%.

Approximately 50 gr in total was placed in a 50 cc platinum crucible with a lid, kept at 900 °C for 5 hours to completely melt, and then heated to 700 °C.
10"C/hr up to ℃, 20" below that up to 400℃
C/hr, and then furnace-cooled to room temperature. After that, the solidified material in the crucible is taken out, the NaCl is dissolved away with running water, and the β-BaBg○4 single crystal of about 100 ml is precipitated therein.

[Effects of the Invention] As explained above, this invention is a method for producing barium borate using barium chloride and sodium metaborate as raw materials, by mixing 1 to 13.5 moles of sodium chloride with the raw materials as a flux and melting the mixture. By allowing barium borate, which is a reaction product, to form a single crystal in a flux, columnar or acicular transparent crystals with a clean crystal habit and a size of up to limφXl0mm can be grown, and as a result of measurement with an XIt & diffractometer, The crystal does not contain any high-temperature phase and consists entirely of a pure low-temperature phase structure.
It was proven to be a 20A single crystal.

[Brief explanation of the drawing]

Figure 1 is the phase diagram of BaO-8203 system, Figure 2 is BaB2
Phase diagram of the O4-Na2B20 system. In the figure, C is a group of congruends with a molar ratio of 1:1. . C: Molar precipitation 1:10 points

Claims (1)

[Claims] In the production reaction of barium borate using barium chloride and sodium metaborate as raw materials, 1 to 13.5 moles of sodium chloride are mixed as a flux to 1 mole of barium chloride and 2 moles of sodium metaborate as raw materials. A method for growing a low-temperature phase barium borate single crystal, which is characterized by heating and melting to cause a reaction, and precipitating the reaction product barium borate as crystals in a flux.