JPH0825829B2 - β-BaB 2 below O 2 below 4 Method for producing single crystal - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a β-BaB ₂ O ₄ (beta barium borate) single crystal that is a non-linear optical crystal, and more specifically, a high-quality β A method for producing a BaB ₂ O ₄ single crystal.

[Prior Art] BaB ₂ O ₄ exists as an intermediate compound of BaO—B ₂ O ₃ binary system, and the low temperature β-phase thereof is β-BaB ₂ O ₄ . further,
Β- in the BaO-B ₂ O ₃ binary system (self-flux system)
Since the temperature range in which BaB ₂ O ₄ is stably precipitated is extremely narrow,
It is known that it is difficult to grow a large single crystal from a BaO-B ₂ O ₃ binary system (EM Levin et al.
J.Res.Nath.Bur.Std. (US) 42 (1949) 131).

Therefore, various fluxes suitable for growing β-BaB ₂ O ₄ single crystal by adding to BaO-B ₂ O ₃ have been studied, and it has been recently reported that Na ₂ O is one of the most preferable fluxes. (Cheng et al. (1988): JCG 89p553−55
9. Feigelson et al. (1989): JCG 97, p.
352-365, Tang et al. (1980): ICCG 9). In the previous reports, a large and transparent one was obtained by growing a β-BaB ₂ O ₄ single crystal in the range of 16 to 30 mol% of Na ₂ O in the BaB ₂ O ₄ —Na ₂ O system. .

[Problems to be Solved by the Invention]

However, β-BaB ₂ O ₄ using Na ₂ O as a flux
Some single crystals have a part or part where the optical quality is not always sufficient, and if the part selected from the obtained single crystals has good optical quality and is practical, the yield rate is very low (about 20%).
%)). This optical quality defect appears as a decrease in the light transmittance of the single crystal and the occurrence of light damage.

Cause of the defect of the optical quality, Na ₂ O is incorporated as an impurity in single crystal, it is to form the light scattering bodies and that the smaller size is present as inclusions 10~100μm order. This inclusion is visible to the naked eye. Further, the light scatterer gives a cloudy feeling to the crystal, and in a remarkable case, it can be confirmed by observing the passage of passage by the Tyndall phenomenon when the laser light is passed.

An object of the present invention is to provide relatively large β-BaB ₂ O _{4 in which} the above-mentioned inclusions and light scatterers are absent or low.
It is to provide a method for producing a single crystal.

[Means for solving the problem]

The present invention substantially 50-60 mole% of BaO, from a melt consisting of 33 to 47 mol% of BaO ₃ and 3-7 mol% of Na ₂ O,
β-BaB ₂ O ₄ substantially flat contact interface between the substantially vertically held, and β-BaB ₂ O ₄ single crystal and the melt pulling axis of the single crystal relative to the specific surface of the single crystal Β-Ba
Β-Ba characterized by pulling up and growing B ₂ O ₄ single crystal
The present invention relates to a method for producing a B ₂ O ₄ single crystal.

The manufacturing method of the present invention is basically based on the conventionally known TSSG.
This can be done by applying the method (Top Seeded Solution Growth). That is, substantially BaO, B ₂ O ₃ and Na ₂
A melt is prepared from O, for example, by mixing barium carbonate, sodium borate and boric acid, and heating to a temperature above the liquidus line determined from the phase diagram to homogenize.

In _{BaO-B 2 O 3 -Na 2} O -based melts of the present invention, the BaO 50
60 mol%, B ₂ O ₃ and 33 to 47 mol%, a Na ₂ O 3 to 7 mol%
The reason for setting the range is that outside this range, the viscosity of the melt is high, and it is inappropriate for the growth of β-BaB ₂ O ₄ single crystal,
This is because other crystal phases are precipitated, or a large single crystal has a low quality due to the large content of Na ₂ O. Furthermore, the content of Na ₂ O in the melt is 3 to 7 mol%.
If the Na ₂ O content is less than 3 mol%, the viscosity of the melt increases and polycrystallization tends to occur.
This is because if the content exceeds mol%, the amount of light scatterers and inclusions in the obtained β-BaB ₂ O ₄ single crystal increases, which is not preferable. That is, by setting the content within the above range, a light-scattering body and a single crystal with less inclusion can be obtained for the first time.

Next, the temperature of the melt is lowered to a temperature just above the liquidus line, and seed crystals are seeded. After the seeding, the melt is gradually cooled at, for example, 0.3 to 1 ° C./day, and the crystal is grown while pulling the crystal at a rate of, for example, 0.3 to 2 mm / day.

The liquidus of the melt used in the present invention is in the range of 910 to 970 ° C.

In the present invention, the β-BaB ₂ O ₄ single crystal is seeded and pulled so that its pulling axis is substantially perpendicular to the singular plane of this single crystal. The β-BaB ₂ O ₄ single crystal has a plurality of singular planes, and for example, an a plane which is a plane perpendicular to the a axis can be mentioned. The pulling axis of the single crystal can be set perpendicular to the singular plane by a conventional method. Inclusion can be reduced by keeping the pull axis perpendicular to the singular plane.

Further, in the present invention, the single crystal is pulled up while keeping the contact interface between the β-BaB ₂ O ₄ single crystal and the melt having the above composition substantially flat. By growing a single crystal while keeping the contact interface flat, a β-BaB ₂ O ₄ single crystal with less inclusion can be obtained.

The contact interface is the rotation speed (ω) of the single crystal to be grown.
Is the ratio of the Na ₂ O content and the diameter of the single crystal to the diameter of the crucible (d).
It can be kept flat by appropriately adjusting in consideration of the above. For example, when Na ₂ O is 5 mol%, the contact interface can be kept flat by setting ω in the range of about 13 to 6 with d in the range of about 0.05 to 0.5. As a general tendency, when the Na ₂ O content and d are constant, the contact interface becomes concave on the crystal side when ω increases, and conversely when the ω decreases, the contact interface becomes convex on the crystal side. Further, when the Na ₂ O content and ω are constant, the contact interface becomes concave on the crystal side when d becomes large, and conversely when the d becomes small, the contact interface becomes convex on the crystal side. This is shown in FIG.
The contact interface can be kept flat by setting d and ω on the solid line in FIG.

Β-BaB ₂ O ₄ obtained by the method of the present invention can be used as a non-linear optical material in the visible and ultraviolet regions.

〔Example〕

 Hereinafter, the present invention will be further described based on examples.

Example 1 A crystal pulling apparatus (2060 manufactured by Ascal Co., Ltd.) by a high frequency heating method was used for growing crystals. The inside of the furnace of this equipment is a cylindrical refractory made of alumina installed in a high-frequency coil, and a platinum crucible with a height of 80 mm and an inner diameter of 77 mm is set inside it. Are using. A seed holder made of platinum was attached to the tip of this alumina tube to set a seed crystal whose crystal orientation was determined.

Barium carbonate (Furuuchi Chemical Co., Ltd., 99.99% BaCO ₃ ), sodium borate (High Purity Chemical Co., 99.999% NaBO ₂ ) and boric acid (High Purity Chemical Co., Ltd., 99.99% B ₂ O ₃ ), BaO 55 mol%, B ₂ O ₃ was mixed at a mixing ratio of 40 mol% and Na 05 mol% and mixed using an agate bee.

The crucible containing this mixture was set in the above apparatus, the temperature of the furnace was raised, and the mixture was melted and homogenized by maintaining it at a temperature above the liquidus line (1150 ° C) for about 10 hours, which is determined by the phase diagram. . After that, the temperature was lowered to a temperature (950 ° C.) immediately above the liquidus line, and seeding was performed at this point. The seed crystal used had a diameter of 4 mm and a thickness of 7 mm. Then, the temperature was further lowered, and while slowly cooling, the crystal was pulled up while rotating. The crystal is pulled in the a-axis direction perpendicular to the singular plane (a-plane), and the pulling speed is
1 mm / day, crystal rotation speed 3.5 rpm, melt cooling rate 0.3
~ 1 ° C / day. The contact interface between the crystal and the melt was flat. 14 days after the start of crystal growth, diameter 35mm, thickness 7mm
Of β-BaB ₂ O ₄ single crystal was obtained.

The obtained single crystal had few inclusions and had no light scattering when a laser beam was passed through. As a result of selecting a portion with good optical quality from this single crystal, the yield rate was about 40%.

The obtained crystal was cut in a fixed orientation, and the non-linear optical constant, the conversion efficiency damage threshold value, and the light transmittance were measured, and all were satisfactory values in terms of application.

Example 2 The composition of the melt was 55 mol% BaO, 39 mol% B ₂ O ₃ and Na ₂ O.
The same operation as in Example 1 was performed except that the amount was 6 mol%. As a result, as in Example 1, the diameter was 35 mm and the thickness was
7-mm β-BaB ₂ O with little inclusion and no light scattering
₄ single crystals were obtained.

Example 3 The composition of the melt was 56 mol% BaO, 40 mol% Ba ₂ O ₅ and Na ₂ O.
The same operation as in Example 1 was performed except that the amount was 4 mol%. As a result, as in Example 1, the diameter was 35 mm and the thickness was
Β-BaB with 6.5mm inclusion and no light scattering
_{A 2} O ₄ single crystal was obtained.

Comparative Example 1 - Composition of (self flux system) melt BaO 61 mol%, except that as a B ₂ O ₃ 39 mol% was subjected to the same procedure as in Example 1. However, when seeding was carried out, the crystal rapidly spread radially and did not grow as a single crystal, and only a polycrystal solidified product was obtained.

Comparative Example 2 The composition of the melt was BaO 37 mol%, B ₂ O ₃ 46 mol%, Na ₂ O
It was carried out except that the seed crystal was set perpendicularly to the c-axis, the pulling rate was 2 mm / day, the crystal rotation speed was 8 rpm, the melt cooling rate was 0.3 / hour, and the growing days were 7 days. In the same manner as in Example 1, a β-BaB ₂ O ₄ single crystal having a diameter of 45 mm and a thickness of 10 mm was obtained. As a result, the interface of the melt contacting the crystal during crystal growth was concave, and the growth surface of the obtained single crystal was convex. This single crystal had a lot of inclusions throughout, and there were white turbid parts.

Comparative Example 3 The composition of the melt was the same as in Comparative Example 2, and the pulling rate was 1.
2mm / day, set the seed crystal perpendicular to the c-axis, and set the crystal rotation speed.
Diameter is 40 mm and thickness is 6 mm in the same manner as in Example 1 except that the temperature is 13.8 rpm, the cooling rate is 0.043 ° C./hour, and the number of growing days is 13 days.
Of β-BaB ₂ O ₄ single crystal was obtained. The interface of the melt contacting the crystal during crystal growth was convex, and the growth surface of the obtained single crystal was convex. The surface of this single crystal was rough, and there was inclusion throughout.

As a result of selecting portions having good optical quality from the single crystals of Comparative Examples 2 and 3, the yield rate was 20% or less.

〔The invention's effect〕

According to the present invention, it is possible to produce a β-BaB ₂ O ₄ single crystal having few inclusions and containing almost no light scatterers, and by using this single crystal, an optical product is produced with a high yield rate. be able to.

[Brief description of drawings]

FIG. 1 shows the relationship between the crystal rotation number (ω), the crystal diameter / crucible diameter (d), and the shape of the crystal-melt contact interface when a melt having a Na ₂ O content of 5% was used.

Claims (1)

[Claims] 1. A β-BaB ₂ O ₄ single crystal from a melt consisting essentially of 50-60 mol% BaO, 33-47 mol% B ₂ O ₃ and 3-7 mol% Na ₂ O. While keeping the pulling axis of the single crystal substantially perpendicular to the singular plane of the single crystal and maintaining the contact interface between the β-BaB ₂ O ₄ single crystal and the melt substantially flat, β-BaB ₂ O ₄ beta-BaB ₂ method for producing O ₄ single crystal, characterized in that a single crystal is grown Te pulling.