JPS5969490A - Manufacture of lithium tantalate single crystal - Google Patents

Abstract

PURPOSE:To obtain a single crystal free from coloration and cracks by carrying out a growth of the single crystal by the pulling up method from a melt of LiTaO3 in an irridium crucible in an inert gas atmosphere contg. a specified a amount of oxygen. CONSTITUTION:Powdered LiTaO3 is put into an irridium crucible to melt by by high-frequency heating. The fused substance is allowed to stand near the melting point and a seed crystal is brought into contact with the melted liquid under rotation to grow a single crystal by pulling up gradually. In this case, the growth of the single crystal is carried out in an inert gas atmosphere (e.g. nitrogen, argon or the like) contg. 0.5-2.5vol% of oxygen. By this method, the completeness and the quality of the crystal can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing lithium tantalate (LiTa03) single crystals.

LiNb0. , LiTaO3, Gd, Ga50.
Oxide single crystals such as these are obtained by placing these powders or lumps in a metal crucible, melting them by high-frequency heating, keeping the melt near the melting point, and bringing the seed crystal into contact with the melt without rotating it. It is manufactured by a method (so-called Czochralski method) in which a single crystal is grown under the seed crystal without being pulled up gradually.

LiTa0. Since the melting point of is about 1650° C., the crucible material must have a melting point above this temperature, and platinum, platinum-rhodium alloy, and iridium are used.

However, the melting point of platinum is 1769°C, which is close to the melting point of LfTaO.
Ta0. To grow a single crystal, a crucible made of platinum-rhodium alloy (melting point: 1900°C) or iridium (melting point: 2400°C) is generally used.

However, platinum-rhodium alloy crucibles are normally used in an atmospheric atmosphere, but according to this crucible, rhodium from the crucible melts into LiTaQ and the melt, and the rhodium also mixes into the grown crystal, causing coloration. Become. colored
It goes without saying that L I Ta Os single crystals are unsuitable for use in optical devices, but rhodium tends to be mixed into them uncontrollably, and there are also problems in use in pressure 1"1 elements and pyroelectric devices. On the other hand, Iridium Rusoposhi].

If used in the air, it will oxidize and wear out, so it must be used in an inert gas atmosphere.
When a LiT1108 single crystal is grown, a black colored crystal is obtained due to oxygen defects. This colored LIT
AOB crystals can be easily decolorized by heating to 1200-1300° C. in the atmosphere, but shallow cracks are likely to occur on the surface of the crystals. These cracks grow internally during the next process of poling and slicing, which causes a reduction in yield.

The present invention has no defects such as coloring or cracks, and optical elements,
LiTa is also suitable for measuring piezoelectric elements, pyroelectric elements, etc.
The present invention provides a crystal growth method for producing an O5 single crystal. In order to achieve this objective, the present invention has been developed to produce L by a pulling method from a 0° LiTa melt in an iridium crucible.
The iTaO3 single crystal is produced in that it is grown in an inert gas atmosphere containing 0.5 to 2.5% by volume of oxygen.

Obtained when the oxygen concentration in the atmosphere is less than 0.5% by volume
LiTaO5 is colored and requires separate heat treatment in the air to decolorize it. If this concentration exceeds 2.5% by volume, the iridium of the crucible material will be easily oxidized (#), which will not only cause damage to the crucible but also cause iridium to be mixed into the L I T a03 crystal, making it impossible to use the crystal as an optical element. There is a risk of Therefore, the oxygen concentration in the atmosphere is 0.5
-2.5% by volume. The inert gas may be appropriately selected from nitrogen, argon, etc.

LiTa0. grown by the method of the present invention. Since the J-silicon crystal does not have coloration due to oxygen defects, there is no need for a separate heat treatment. Furthermore, the method of the present invention does not generate oxygen defects during growth, thereby increasing the integrity of the crystal, and has the advantage of further improving the quality of the product 5q.

Example A LiTnO raw material was charged into an iridium crucible with a diameter of 100 mm, a height of 100 mm, and a thickness of 2 mm, and a LiTa (J) single crystal was grown using a high-frequency heating pulling device. The coil is housed in a chamber, making it possible to adjust the atmosphere.The crucible is placed in a fireproof container with an inner diameter of 150 m and a depth of 15 Q, and the space between the crucible and the container is filled with alumina bubbles. A heat insulating cylinder of the same size as the container is placed on top of the container to alleviate the temperature gradient at the top of the crucible.
O, ld- Attach the X-axis rod of the crystal and place the KN inside the chamber.
A mixed gas of 98% by volume and 9% by volume of O22 was introduced.

It was carried out at /hr in the crucible, and the diameter was 50m in about 16 hours.
A LiTaO3 single crystal having a straight body portion with a length of 100 mm was obtained.

After the crystals were separated from the 1iyl+ liquid, the heating power was gradually reduced to slowly cool the inside of the furnace. The crystals taken out after cooling to room temperature had an almost colorless light beige color and did not require decolorization. After poling the crystal, slicing was performed to obtain wafers, and as a result, no cracks were observed, and wafers were obtained in good yield.

Patent applicant: Sumitomo Metal Mining Co., Ltd. Applicant: Patent Attorney Kai Tsu Yasuzo Same: Patent attorney Hirayama - Sachi

Claims (1)

[Claims] LiTa0. A lithium tantalate single crystal is grown in which the LiTaO3 single crystal is grown from a melt by a pulling method in an inert gas atmosphere containing 0.5 to 2.5% by volume of oxygen. Production method.