JP2905321B2 - Lithium borate single crystal and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium borate single crystal and a method for producing the same, and more particularly to a lithium borate single crystal of improved quality which is useful as a surface acoustic wave material and a method for producing the same.

[0002]

2. Description of the Related Art Lithium borate single crystal represented by Li _x B _y O ₁₂ has conventionally been produced by mixing a lithium compound and boric acid, calcining the mixture to form a lithium borate glass, and then melting the mixture. In this method, a lithium borate single crystal is grown from the melt by the Bridgman method.

However, in this method, since boric acid (B ₂ O ₃ ) used here contains a large amount of water as structural water, when lithium borate glass made from this is melted, this water Melts into the melt, and this is incorporated into the growing single crystal, causing bubbles in the crystal.It is reported that bubbles are likely to form when water enters the raw material at 2,000 ppm or more. (See the Institute of Electronics and Communication Engineers, Technical Report Vol. 84, No. 58, pp. 57-64).

[0004]

Therefore, in the production of lithium borate single crystals by the Bridgman method, a method of extremely slowing the growth rate (Journal Crystal Gloss Vol. 99, pp. 811-814) is used. ), And a method of optimizing the crystal rotation speed (see IEICE, Technical Research Report, Vol. 87 (80), pp. 15-22).
If the growth rate is reduced, productivity becomes very poor, so that it is not industrial. If the number of rotations of the crystal is reduced, bubbles are collected at the center of the crystal, and it is impossible to completely remove the bubbles.

[0005]

The present invention SUMMARY OF] is a method of manufacturing such a disadvantage the resolved lithium borate single crystal, which was mixed with lithium compounds and boric acid, pre
Boric acid with a moisture content of 0.2% or less
Titanium glass as raw material with a water content of 1% or less
A single crystal is grown from a melt melted in the atmosphere .

That is, the present inventors have conducted various studies on a method for producing a high-quality lithium borate single crystal having few air bubbles. As a result, the method for producing a lithium borate single crystal is caused by structural water in boric acid as a raw material. From this, it is known that a lithium borate single crystal with few bubbles can be obtained by using a material having a reduced structure water, but even in such a case, the growth atmosphere of the single crystal contains a large amount of moisture. And that the water in the atmosphere dissolves in the melt, so that bubbles in the single crystal do not decrease. Therefore, when the water in the growth atmosphere of the single crystal is reduced to 1% or less, the water in the atmosphere becomes Since it does not dissolve in the melt, a single crystal with few bubbles can be reliably obtained, and it has been confirmed that a high-quality single crystal can be manufactured. The present invention has been completed Te. This is described in more detail below.

[0007]

According to the present invention, the Bridgman method is used to reduce the quality of air bubbles.
Method for producing excellent lithium borate single crystal
This is especially true when the water content is less than 0.2%.
Lithium oxalate glass is used as raw material and has a water content of 1
% Of a single crystal from a melt melted in an atmosphere of not more than 0.1% .

In the case of lithium tetraborate used as a surface acoustic wave material, an infrared absorption spectrum of a transparent glass produced by melting and quenching the polycrystal is taken, and the transmission at 3,600 cm ^{-1 having} absorption by OH groups is taken. When the moisture contained in the glass is calculated from the transmittance I, the thickness of the sample is A (cm), and the transmittance Iθ when there is no OH absorption at 3,600 cm ⁻¹ , the water content is 100 × A ⁻¹ × Since it is expressed by log (Iθ / I), it is 500 ppm from this calculation formula. When a single crystal is grown from that glass,
The amount of water contained in the single crystal is 50 ppm by the same measuring method. From this, the water contained in the melt has a concentration difference of about 10 times or more between water dissolved in the melt and water dissolved in the crystal during crystallization. At the solid-liquid interface, those which do not form a solid solution in the crystal due to water in the melt are crystallized while protruding from the vicinity of the interface. However, if for some reason, for example, a subtle growth rate, a change in the melt concentration, etc., the melt is incorporated into the crystal,
Water that could not be dissolved in the crystal remained in the crystal as bubbles during crystallization, which caused deterioration of the crystal.

The production of the lithium borate single crystal according to the present invention is carried out by a known method. Therefore, this is done by mixing a lithium compound, for example, 1 mol of lithium carbonate and 1 mol of boric acid, and calcining at about 500 ° C. to produce a lithium borate glass, which is heated to 920 ° C. or more to be melted and melted. A single crystal may be grown from the liquid by the Bridgman method . The boric acid used here usually contains water as structural water, but the water content of lithium borate glass
In order to make the amount 0.2% or less, it is preferable to make the water content 0.2% or less . Even in the atmosphere in which a single crystal is grown, water may be contained in several percent or more. If water is taken into the melt from the atmosphere, even if the water content in the raw material is controlled to be small, It is clear that water in the atmosphere causes bubbles. Accordingly, the present invention provides a method of growing a high quality single crystal having a low water content by controlling the water content in the raw material and the water content in the growth atmosphere in the method for producing a lithium borate single crystal. Things.

Thus, according to this method, lithium borate having a water content of 0.2% or less due to structural water contained in boric acid.
Even if a single crystal is grown by the Bridgman method from a melt of molten glass , the atmosphere at this time usually contains a few percent of water. The melt is incorporated into the melt and changes in the growth rate during the growth of the single crystal, and changes in the melt temperature change the melt into crystals .
It was found that when incorporated , water that could not form a solid solution in the crystals remained in the crystals as bubbles during crystallization, thereby deteriorating the quality of the crystals.

According to the present invention, in order to solve such disadvantages, the amount of water in the atmosphere in the furnace during the growth of a single crystal by the Bridgman method is set to 1% or less. Since the amount of water is small, the water in the atmosphere is not taken into the melt during the growth of the single crystal.Therefore, this water does not remain in the single crystal as bubbles during crystallization. The advantage is that a good quality lithium borate single crystal without bubbles can be obtained.

Although the amount of water in the growth atmosphere of the lithium borate single crystal is set to 1% or less in the above description, it is preferably set to 0.2% or less, and the lithium borate single crystal obtained by the present invention is preferably used. It has been confirmed that when the amount of water contained in this exceeds 200 ppm, bubbles will be generated.
It is preferable that the content be 200 ppm or less.

[0013]

Next, examples of the present invention and comparative examples will be described. Example 1 Lithium carbonate having a purity of 4N and boric acid in a molar ratio of 1.00: 1.0
It was weighed and mixed so that it became 0, calcined at about 500 ° C, melted by heating it to 920 ° C or more, and quenched to produce lithium borate glass. Was measured by infrared absorption and found to be 1,200 ppm.

Then, 200 g of this was placed in a platinum cylindrical crucible having a diameter of 50 mm, melted in an atmosphere containing 0.07% of water, and then heated in a Bridgman furnace having a temperature gradient of 20 ° C./cm at a growth point of 0.5 mm / cm 2. When the crystal was lowered at the speed at the time, a lithium borate single crystal having few bubbles was obtained. The water content in the crystal was measured by infrared absorption and found to be 120 ppm.

Comparative Example 1 The lithium borate glass produced in the example was subjected to zone purification in a dry atmosphere, and the water content of the glass was measured by infrared absorption to be 0.08%. Then, 200 g of this was placed in a platinum cylindrical crucible having a diameter of 50 mm, melted in an atmosphere containing 2% of water, and then heated to 0.5 mm / hour in a Bridgman furnace having a temperature gradient of 20 ° C./cm at the growth point. When the lithium borate single crystal was made to fall at a constant rate, the obtained single crystal had many bubbles, and the water content measured by infrared absorption was 250 ppm.

Comparative Example 2 Lithium carbonate having a purity of 4N and boric acid in a molar ratio of 1.00: 1.0
After weighing and mixing so as to be 0 and calcining at about 500 ° C., the amount of water contained therein was measured by infrared absorption and found to be 0.25%. Then, 200 g of this diameter
Put into a 50 mm platinum cylindrical crucible, melt in an atmosphere containing 2% water, and slowly lower at a rate of 0.5 mm / hour in a Bridgman furnace where the temperature gradient at the growth point is 20 ° C./cm. When a lithium borate single crystal was prepared, the obtained single crystal had many bubbles, and the water content measured by infrared absorption was 400 ppm.

[0017]

The present invention relates to a method for producing a single crystal of lithium borate, which is obtained by melting a lithium borate glass having a water content of 2,000 ppm (0.2%) or less by the Bridgman method. When growing a lithium single crystal, the water content in the growth atmosphere of this lithium borate single crystal is reduced to 1% or less, but according to this, the water in the atmosphere is added to the melt. Since the dissolution is reduced, it is possible to obtain a single crystal with less bubbles having a water content of 200 ppm or less and thus to obtain a lithium crystal borate single crystal of good quality.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshihiko Nagao 2-3-1-1, Isobe, Annaka-shi, Gunma Prefecture Shin-Etsu Chemical Co., Ltd. Precision Functional Materials Laboratory (56) References JP-A-63-69796 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) C30B 28/00-35/00

Claims (3)

(57) [Claims] 1. A lithium borate glass having a water content of 0.2% or less, obtained by mixing a lithium compound and boric acid and calcining the material in advance , is used as an atmosphere having a water content of 1% or less.
A method for producing a lithium borate single crystal, comprising growing a single crystal from a melt melted in an atmosphere . 2. The lithium borate single crystal has a water content of 20%.
2. The method for producing a lithium borate single crystal according to claim 1, wherein the concentration is 0 ppm or less. 3. The lithium borate single crystal produced by the method according to claim 1, wherein the water content is 200 ppm or less.