JPH03218996A - Production of lithium niobate single crystal - Google Patents

Abstract

PURPOSE:To prevent the cracking of a large-sized lithium niobate single crystal obtd. by a pulling method at the time of treatment for forming a single domain and annealing by putting the single crystal on a tray covered with crushed pieces of such single crystals and subjecting the single crystal to treatment for forming a single domain and annealing. CONSTITUTION:A large-sized lithium niobate single crystal obtd. by a pulling method is put on a tray, preferably a platinum tray covered with crushed pieces (3-5mm size) of defective lithium niobate single crystals and residue after slicing by >=1cm thickness and the single crystal is subjected to treatment for forming a single domain and annealing by heating in an electric furnace to obtain a large-sized lithium niobate single crystal used for an acoustic surface wave filter.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an improved method for producing lithium niobate single crystals for use in surface acoustic wave filters.

[Prior Art] A large single crystal of lithium niobate is used for a bullet surface wave filter. Lithium niobate crystals are usually made from lithium dibutate obtained by mixing lithium carbonate and niobium pentoxide in a congruent composition ratio and firing at a high temperature.

This raw material is melted in a platinum lupus in a high-frequency induction heating furnace and pulled up to form large crystals (referred to as pools). After cooling it for a while, it is kept at a temperature of 1000°C or higher for several tens of hours in a separate resistance heating furnace, annealed, and then subjected to a single-zone treatment. In the single-segmentation process, the pool is heated to a temperature above the Curie temperature in a resistance heating furnace using a ceramic plate made of sintered lithium niobate as an electrode and a lead wire is applied, followed by cooling. It passes through the Curie temperature and becomes polarized.

However, as mentioned above, when the pool is annealed and then subjected to a single domain treatment, at the interface with the lithium niobate ceramic plate on which the pool is placed during annealing,
The single-segmentation process has the problem that cracks are likely to occur at each cleavage plane of the pool, which is extremely disadvantageous in terms of both quality and productivity.

[Problems to be Solved by the Invention] The purpose of the present invention is to solve the above-mentioned problems and to provide a lithium niobate monolith that can prevent the occurrence of cracks during pool annealing and single segmentation processing. An object of the present invention is to provide a method for producing crystals.

[Means to solve the problem]

In order to achieve the above object, the present invention installs a lithium niobate single crystal (pool) obtained by a pulling method on a plate covered with crushed lithium niobate single crystals, and divides the pool into a single domain. It is characterized by the fact that it undergoes chemical treatment and annealing.

[For use] The pulverized niobium lithium single crystal that can be used in the method of the present invention may be manufactured by any method as long as it is a single crystal, but it is preferably one that is qualitatively equivalent to the pool. . Therefore, it is preferable to use a material obtained by the pulling method, and even a defective product or a product left after cutting is acceptable. As for the pulverization method, the single crystal is cut into a wafer shape with a thickness of 0.5 to 1 mm using a slicer, etc., and then washed with water and an organic solvent, etc.
5 mm or less, preferably 3 to 3 mm using a mortar, ball mill, etc.
It is preferable that the particles be made into 51 square granules.

The sizes of the crushed products do not necessarily have to be the same;
~5 mm is desirable, and any shape is acceptable, but pellets are preferred.

The plate is preferably made of a material that can withstand high temperatures and oxidation, and platinum is particularly suitable. When placing the pulverized products on the plate, it is important to pack them as close as possible without any gaps.

The thickness of the pulverized product spread is desirably 1cII1 or less, and the width thereof may be larger than the bottom of the pool to be installed on top of the pulverized product. When installing a pool on top of the pulverized product on the plate, it is sufficient to stand the pool vertically, and for annealing, the pool may be treated as it is in a furnace. Further, by attaching lead wires to the upper part of the pool and the lower part of the dish and passing an electric current through the pool, it is possible to heat the pool in an electric furnace and perform a single-zone treatment.

[Example-1] A two-year-old lithium butate single crystal obtained by the pulling method was cut into wafers with a thickness of 0.5mm to 1III+ using an internal blade slicer, and the surface dirt was washed with water and ethanol. Thereafter, it was made into a pellet of 1 to 5 mm square in an alumina mortar. Next, use a platinum plate to measure 10cm x 10cm.
A dish of 1 cm was prepared, and the pellets were spread in the dish to a thickness of 1 cm. This plate was placed on a fireproof brick, and the lead wire was wired between the plate and the firebrick. 8 on top of the beret
A boule of 0 mmφX15C)ma+ was stood vertically, a ceramic plate was placed on top of the pool, and a platinum plate with lead wires was placed on top of the ceramic plate. In this way, it was placed in an electric furnace and held at 1190° C. for 1 hour while flowing an electric current, and then cooled and passed through the Curie temperature to perform a single-sector treatment. As a result, no cracks were observed at all.

[Example 2] A sample consisting of a platinum plate, pellets, and pool that was completely the same as in Example 1 except that no lead wire was wired was annealed at about 1200° C. for 2 days in a resistance heating furnace.

As a result, no cracks were observed at all.

[Effects of the Invention] By carrying out the method of the present invention, the pool obtained by the pulling method can be subjected to annealing and single-area processing without causing cracks.

Claims (1)

[Claims] A lithium niobate single crystal obtained by the pulling method is placed on a plate covered with pulverized lithium niobate single crystals, and the lithium niobate single crystal is subjected to single-sector treatment and annealing. A method for producing lithium niobate single crystal.