JP2825060B2 - Beta-barium borate single crystal processing surface modification method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF relates modification method of the present invention is beta-barium borate (β-BaB ₂ O ₄₎ single-crystal work surface, β-BaB ₂ O ₄ which is particularly applicable to wavelength conversion element
The present invention relates to a method for modifying a processed surface of a seed crystal for growing a single crystal by a pulling method.

[0002]

_2. Description of the Related Art In order to grow a β-BaB ₂ O ₄ single crystal from a BaB ₂ O ₄ composition melt using a seed crystal by a pulling method, it is necessary to prevent a heat shock when the melt is brought into contact with the melt. It was necessary to use a rod-shaped seed crystal which did not generate cracks and increased the heat radiation on the surface to satisfy the heat flow conditions for crystallizing the β phase as a low-temperature phase at the growth interface. Conventionally, as a seed crystal that satisfies these conditions, a platinum rod is used instead of the seed crystal, and an as-grown crystal with a diameter of about 3 mm and a length of about 30 mm grown at the tip thereof has been used.

[0003]

It is very difficult to grow a crystal in a shape required for a rod-shaped seed crystal by using a platinum rod in place of the seed crystal, for example, to control the diameter in the longitudinal direction. Therefore, the yield when β-BaB ₂ O ₄ single crystal was grown using this seed crystal was as low as about 10%. In order to grow a β-BaB ₂ O ₄ single crystal with good yield, it is essential to grow a seed crystal. Therefore, growth using a processed seed crystal has been desired. However, at present, the processed seed crystal cannot satisfy the thermal conditions for growing the β phase, which is a low-temperature phase, directly from the BaB ₂ O ₄ composition melt. In order to grow a β-BaB ₂ O ₄ single crystal with the processed seed crystal, it is necessary to remove the strain remaining on the surface of the processed rod-shaped seed crystal and to modify the surface to a mirror-like state. there were.

[0004] It is an object of the present invention to provide a method for modifying a processed surface of a β-BaB ₂ O ₄ single crystal capable of easily removing a processing strain of a seed crystal and obtaining a mirror surface.

[0005]

SUMMARY OF THE INVENTION A β-BaB ₂ O ₄ single crystal processed into a rod-like seed crystal is converted into a BaB ₂ O ₄ having a composition in which the β-BaB ₂ O ₄ single crystal is slightly melted. By dipping in a mixed melt of a single crystal and a flux component (for example, Na ₂ O powder), distortion is removed in the process of melting the processed surface layer of the single crystal, and the surface can be made a smooth mirror surface state.

[0006]

When the surface of the seed crystal is polished with a # 3000 abrasive, irregularities of several tens of μm are formed on the surface.
In addition, distortion generated during cutting and polishing is accumulated, and cracks and the like are likely to occur. BaB having a composition in which β-BaB ₂ O ₄ crystal is slightly melted
_When dipping in a mixed melt of ₂ O ₄ and a flux (eg, Na ₂ O), the atoms on the surface are melted and the strain is removed. Where a mixture of compositions where the crystals are slightly melted
When dipping in a solution, BaB ₂ O ₄ and flux
Of the melt composition at which the β phase
Β-BaB ₂ O ₄ single crystal in equilibrium
Dipping at a temperature 0-5 ° C higher than the existing temperature
Say that In addition, since the atomic arrangement is rearranged so that the surface energy is minimized, the unevenness of the surface is reduced, and the surface becomes smooth and mirror-finished. By strictly controlling the temperature of the melt, the amount by which the surface layer of the crystal melts can also be strictly controlled, so that there is no excessive melting.

[0007]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an equilibrium diagram of BaB ₂ O ₄ —Na ₂ O,
FIG. 2 is an enlarged view of a portion A in FIG. Below β-Ba
An example in which a flux melt of Na ₂ O is used as a dipping melt in which a processed surface of a B ₂ O ₄ seed crystal slightly melts will be described.

[0008] The concentration of Na ₂ O than the equilibrium phase diagram of Figure 1 is 2
The theoretical β phase of BaB ₂ O ₄ crystallizes between 925 and 755 ° C. when the content is ₂ to 32 mol%. However, since the actual melt has a supercooling property of about 10 to 20 ° C., Na ₂ O
There is a possibility that a certain When dipping the seed crystal in the melt 30～32Mol% concentration BaB ₂ O ₄ · Na ₂ O will crystallize out. When the temperature of the melt becomes high, the flux component evaporates and the composition shifts. Therefore, it is desirable that the actual composition of the dipping melt is adjusted so that Na ₂ O is 25 to 30 mol% and the melting point temperature is about 890 to 800 ° C.
In the embodiment, 25 mol of Na ₂ O powder is added to BaB ₂ O ₄ powder.
1% was mixed to obtain a raw material for the dipping melt. This Ba
From the melt having the composition of Ba ₂ O ₄ -Na ₂ O, β-BaB ₂ O ₄
It can be seen that the temperature at which the single crystals coexist in the equilibrium state is 880 ° C.

The raw material is filled in a platinum crucible having a diameter of 40 mm using a vertical resistance heating furnace, and 883 ° C. higher than 880 ° C. by 3 ° C.
Melted. If the melting temperature is too high, the amount of melt from the seed crystal into the melt increases, so it is desirable to melt at + 5 ° C. or less from the melting point (the optimal melt temperature is determined by the size of the seed crystal and the amount of melt). ). Length 30 on this melt
After holding a seed crystal of β-BaB ₂ O ₄ having a shape having a thickness of 3 mm and a surface thereof polished with an abrasive No. 3000 of alumina for 1 hour, it was dipped in a melt. When the β-BaB ₂ O ₄ single crystal is dipped in the melt at 883 ° C., the crystal surface is melted and the composition of the melt changes from the dipping point 1 as shown by the arrow 2 in FIG. The liquid reaches an equilibrium state. After dipping for about 5 minutes, the seed crystal was slowly pulled out of the melt, rotated to shake off the flux components, and cooled to room temperature at 50 ° C./hr. The processing strain on the surface of the seed crystal taken out was removed, and an optically transparent mirror surface was obtained.

[0010] BaB is prepared by using a seed crystal whose surface is modified.
_{When an} attempt was made to pull up and grow a single crystal from a ₂ O ₄ composition melt, a single crystal of β-BaB ₂ O ₄ could be grown at a yield of almost 100%, and when a seed crystal was used with a conventional platinum rod, In comparison, the production yield of β-BaB ₂ O ₄ single crystal was significantly improved.

Similarly, Na ₂ B ₂ O ₄ , BaCl ₂ , Na
Even when a flux such as Cl is used, the surface can be modified by adjusting the melt composition at which the β phase is crystallized, setting the temperature slightly higher than the melting point, and dipping the processed seed crystal. .

[0012]

As described above, according to the present invention, β-Ba
By dipping the rod-shaped seed crystal into a melt having a composition in which the B ₂ O ₄ single crystal is slightly melted, the processing strain of the seed crystal can be easily removed and the surface can be mirror-finished. it can. For this reason, the yield of growing β-BaB ₂ O ₄ single crystal can be significantly improved.

[Brief description of the drawings]

FIG. 1 is an equilibrium diagram of BaB ₂ O ₄ —Na ₂ O.

FIG. 2 is an enlarged view of a portion A in FIG.

[Explanation of symbols]

 1 Dipping point 2 Arrow

Claims (2)

(57) [Claims] 1. A seed crystal processed into a rod shape for growing a β-BaB ₂ O ₄ single crystal as a nonlinear optical material by a pulling method,
β-BaB is contained in a flux solution having a melt composition in which a β phase composed of aB ₂ O ₄ and Na ₂ O flux is crystallized as primary crystals.
A modified beta-barium borate single crystal processing surface characterized in that dipping is performed at a temperature 0 to 5 ° C. higher than the temperature at which the ₂ O ₄ single crystal coexists in an equilibrium state to remove a processing distortion and obtain a mirror surface. Method. 2. The method according to claim 1, wherein the concentration of the Na ₂ O flux is 25 to 3
2. The method for modifying a processed surface of beta-barium borate single crystal according to claim 1, wherein the amount is 0 mol%.