JPS5814398B2 - Method for producing lithium tantalate single crystal - Google Patents

Description

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

Conventionally, since LiTaOs single crystals are used as applied optical crystals, they have been required to be optically transparent without absorbing light due to lattice defects or impurities.

Normally, this LiTa03 single crystal is manufactured by Czokolawski (
This was done using a pulling method called the CZ) method.

For this pulling, the melting point of LITa03 single crystal is 165
Unless a crucible made of a material with a melting point much higher than 0°C is used, the composition of the crucible will partially melt and contain LiTaO as impurities.
s There is a risk that it will dissolve into the single crystal and cause coloration.

For this purpose, a crucible made of iridium, which has a melting point of 2454° C., has conventionally been used, but this iridium has the disadvantage that it is expensive and the cost of repairs after several pullings is high.

On the other hand, when LiTa03 single crystal is pulled and grown from a high-purity raw material, cracks occur in the crystal at a rate of about once for every few times the crystal is pulled, and as it has to be pulled again, the yield decreases. This caused an increase in costs.

However, when this LiTa03 single crystal is used in surface wave application devices or piezoelectric application devices, which have recently begun to attract attention, it is not necessarily transparent, and it may contain some impurities, and even if it is in a colored state, its characteristics may not be large enough. known to be unaffected.

The manufacturing method of the present invention has been devised in view of the above-mentioned problems, and provides a LiTa03 single crystal that is particularly useful for use as a surface wave application device or a piezoelectric application device.

It is generally believed that single crystals are more stable if they contain a certain amount of lattice defects.

Therefore, in the manufacturing method of the present invention, a low concentration of tungsten W in the form of tungsten trioxide W03 is added to a LiTaOs solution to grow a crystal, and tantalum Ta in the crystal is grown.
When W is placed at the position where W should be placed, since W is hexavalent compared to Ta, which is pentavalent, lithium Li lattice defects are formed as shown in the following equation for charge compensation.

However, ψ indicates a Li lattice defect.

In this way, by adding a small amount of W to the LtTa03 solution, Li
When a TaOa single crystal is grown, Li lattice defects are produced in the crystal.

Due to the occurrence of Li lattice defects, the number of cracks that occur during crystal pulling is reduced.

The figure shows the experimental results, with the horizontal axis plotting the W content (molch) relative to LiTa03, and the vertical axis plotting the number of cracks per 10 pullings.

In the same figure, when the W content is zero, that is, when raised as usual, the average number of cracks that occur is 0.1.
At ~0.2 molar ratio, the crack occurs once, and even at 2.0 molar ratio, the crack occurs 2.5 times, making it possible to suppress the number of cracks that occur compared to the conventional three times.

Specific examples will be described below.

A LiTaOa sintered body was placed in an alloy crucible made of platinum and rhodium with a diameter of 120 mmφ and a height of 120 tr, and the LiTaO3 was melted in a high-frequency heating furnace. After melting, a chip crystal of LtTaOs was rotated at low speed to form a crucible with a diameter of 6011 mm and a height of 100 mm.
When pulling and growing a LiTa03 single crystal of The product that contained it was able to suppress the occurrence of cracks to 1 out of 10.

That is, by containing 0.1 mole of W, the crack occurrence rate can be reduced to 1/3.

Although the LsTaO3 single crystal pulled by this production method was colored reddish brown due to the rhodium and W in the crucible, it did not have any effect when used in surface wave application devices.

In the above explanation, we have talked about upward growth using the Czokolawski (CZ) method, but the EF of the same upward growth
The present invention is also useful in manufacturing methods such as the G method, the pull-down method, and the Cyprus method.

As is clear from the above description, in the present invention, since tungsten is grown in a lithium tantalate solution, the incidence of cracks can be lowered compared to products grown without impurities such as tungsten.

Therefore, since the yield is improved, manufacturing costs can be reduced.

In addition, platinum-rhodium crucibles can be used for devices that do not require optical transparency, such as surface wave application devices and piezoelectric application devices, so there is no need to use expensive iridium crucibles, resulting in further cost reductions. The advantages of the production method of the present invention are significant.

[Brief explanation of drawings]

The figure is a curve diagram showing the relationship between the tungsten content in lithium tantalate and the number of cracks.

Claims (1)

[Claims] 1. A method for producing a lithium tantalate single crystal, which is characterized in that the lithium tantalate single crystal is grown, stored, and grown by containing a compound containing tungsten in the lithium tantalate solution. . 2. The method for producing a lithium tantalate single crystal according to claim 1, characterized in that the content of the tungsten is 0.01 to 2 mol. 3. The method for producing a lithium tantalate single crystal according to claim 1 or 2, wherein the growth of the lithium tantalate single crystal is carried out in an alloy crucible made of platinum rhodium.