JPS6335499A - Method for making single domain lithium tantalate single crystal - Google Patents

Abstract

PURPOSE:When a polydomain lithium tantalate crystal is embedded in a powder and converted into single domain, the characteristics of the powder are specified to enable the conversion of the crystal into single domain without formation of cracks. CONSTITUTION:Crystalline LiTaO3 2 is placed in the crucible 1 and the space is filled with a powder 3. The crystal 2 is heated up near the Curie point, an electric field is applied to the electrodes 4, then the crystal is gradually cooled down to convert into single domain. The powder 3 is desired to be unreactive with the crystal 2 and undiffusible, and have resistivity of 10<3>-10<6>OMEGA.cm. Such a powder is composed of lithium niobate, lithium tantalate or conductive SIALON. Thus, the crystal 2 is optimally and efficiently converted into single domain.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for dividing lithium tantalate (hereinafter referred to as LiTaO3) single crystal into a single domain.

[Conventional technology]

Among the methods for converting the LiTa0+ multi-domain crystal obtained by the conventional pulling method into a single domain, there are the following two methods for joining the crystal and the electrode. That is, (1) a noble metal electric bridge plate is placed opposite to the cut surface of the crystal with a ceramic interposed therebetween. (2)
Bond an electrode to the crystal surface.

In method (1), it is necessary to cut the crystal in its orientation after pulling it and before dividing it into segments, and cracks are likely to occur during cutting due to the presence of thermal strain or polarization strain within the crystal. In addition, if the pulling axis and single segmentation direction are different,
Since there are many parts that are lost due to the above-mentioned cutting, the yield is reduced. On the other hand, in method (2), a noble metal paste such as Pt or Ag is used as an electrode, but the single zone temperature 1
) Since the electric field is applied at a high temperature of 50° C., the electrode agent diffuses into the crystal, causing cranking and other undesirable phenomena. As a means to solve the above-mentioned problems, the LiTa0. Embedded in crystal powder, PT electrode plates are inserted into this powder in the direction of forming a single region, heated to a high temperature above the Curie temperature, and then slowly cooled by applying a DC voltage to the opposing Pt electrode plates. A method has been disclosed (see Japanese Patent Laid-Open No. 140400/1983).

[Problem that the invention seeks to solve]

According to the above-mentioned improved method, (1) it is possible to form a single domain with the as-grown shape, and (2) there are no problems such as diffusion of electrode material (and high yield can be expected). However, not only is there no disclosure regarding the characteristics of the powder in which the crystal is to be embedded, but there is also a description that seems to include all materials from electrical insulators to good electrical conductors, making it difficult to actually work. The problem is that it is difficult to apply.

In order to solve the above-mentioned problems, the present invention has discovered the characteristics necessary for the powder material in which the crystals are to be embedded as a result of two various experiments, and has developed an optimal single domainization method for l,1TaO+ single crystals. The purpose is to provide.

[Means for solving problems]

In order to solve the above-mentioned conventional problems, the present invention has nine aspects.

A. embedding the entire lithium tantalate multi-domain crystal in powder or only the portion to be made into a single domain; inserting an electrode plate into the powder at a portion of the multi-domain crystal that faces the electric field application direction; In a method for converting the multi-domain crystal into a single domain by applying an electric field between the electrode plates near the Curie temperature and then gradually cooling the body.

B. The powder is composed of a material that does not react with the crystal and is non-diffusive near the Curie temperature.

The electrical resistivity of the C0 powder near the Curie temperature is 10' to 10'Ω·Cl11.

This technical method was adopted. Furthermore, LiTag
The Curie temperature of , which varies depending on the composition and growth conditions, is around 600°C.

In the present invention, if the electrical resistivity of the powder surrounding or embedding all or a part of the crystal to be made into a single domain is less than 10 3 Ω·cm near the Curie temperature, that is, a material with relatively high electrical conductivity is used, the powder Current flows only in the

This is inconvenient because current no longer flows through the crystal to be made into a single domain. On the other hand, if the electrical resistivity exceeds 10'Ω・cm, the voltage drop in the powder part will be too large, so the prescribed voltage will not be applied to the crystal, and the biasing force for forming a single domain will decrease, which is preferable. do not have.

As the above-mentioned powder constituent materials, the following can be used, as well as mixtures or composites of two or more of these, or even mixtures or composites of these or the above mixtures or composites and other binding materials. good. However, in the case of a complex system.

Naturally, combinations in which the respective powder constituent materials and crystalline materials cause chemical reactions with each other must be avoided.

As the powder constituent material, for example, lithium niobate, lithium tantalate, conductive sialon, zirconia, titania, etc., whose electrical resistivity at high temperatures is appropriately adjusted, can be used.

[Effect]

Due to its configuration, the L i Ta 03 multi-domain crystal can be used for a given amount of energy without causing any reaction or diffusion between the electrodes or the powder surrounding all or part of the crystal. By applying an electric field, jl-segmentation is performed.

(Example) Fig. 1 is an explanatory diagram of a single segmentation processing state showing an embodiment of the present invention, and Fig. 2 is a diagram showing the relationship between temperature, voltage, and time. is shown by a solid line, and the voltage is shown by a broken line.First, the diameter of 60m grown by biaxial pulling
After taking out a LiTag single crystal with a length of 100 mm from the growth furnace (not shown), it is directly charged into an alumina crucible 1 as shown in FIG.
around [,1Tao:
Fill with + powder 3. Note that within this powder 3, electrode plates 4 made of Pt are disposed, for example, facing each other in the z-axis direction.

Then, the crucible 1 with the crystal 2 charged therein is charged into a soaking electric furnace (not shown), and while heated and maintained at 750°C, a DC voltage of, for example, 200 μ is applied between the electrode plates 4 and 4. 2 and then slowly cooled at a rate of 80°C/hour. That is, in FIG. 2, the temperature is increased at a rate of 80"C/hour, and when the temperature of the crystal 2 reaches 60"C, a DC voltage of IOV is applied as shown by the broken line, and the primary crystal is From time t0 when the temperature of 2 reached 750"C, the applied voltage was gradually increased at a rate of 200 V/hour, and from time t1 to 20"
Hold at 0■. Time 1. The temperature of the crystal body 2 is lowered from time t2, 300 minutes after.

Time 1. At a time of 12 to 15 hours after LiTa0. When 45 single crystals were single-domained as above 0 to end the single-crystal single-domain process, all 45 crystals were completely single-domained, and no crank occurred. There were 2 pieces.

In this embodiment, a case has been described in which the pulling axis and the single segmentation direction are the same, but even if the two directions are different, the effect is the same. Further, the powder to be filled around the entire crystal body or the portion to be divided into a single region is not limited to the 1,1 Taos crystal powder, and it goes without saying that other powder materials such as those mentioned above can be used. Furthermore, there are 9 methods for growing single crystals.
Naturally, it can also be used for crystals produced by other means, such as the zone melt method. Further, as the constituent material of the electrode plate, in addition to noble metals such as PT, ceramics such as conductive sialon can be used.

〔Effect of the invention〕

Since the present invention has the structure and operation as described above,
It is possible to form a single domain of l, i T a O3 single crystal without cracking, without diffusion or evaporation of the electrode agent, in the same state after the growth of the crystal, and without the annealing process. It can be carried out. Furthermore, by specifying the electrical resistivity of the powder material in the single-zoning process, there is an effect that optimal and efficient processing can be performed.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a single segmentation processing state showing an embodiment of the present invention, and FIG. 2 is a diagram showing the relationship between temperature, voltage, and time. 2: Crystal, 3: Powder, 4: Electrode plate.

Claims (2)

[Claims] (1) Embed the entire lithium tantalate multi-domain crystal in powder or only the portion that is to be made into a single domain, and insert an electrode plate into the powder at a portion of the multi-domain crystal that faces the direction in which an electric field is applied. , a method for converting the multi-domain crystal into a single domain by applying an electric field between the electrode plates near the Curie temperature and then slowly cooling the powder, in which the powder does not react with the crystal near the Curie temperature. A method for forming a lithium tantalate single crystal into a single domain, characterized in that the material is non-diffusive and has an electrical resistivity of 10^3 to 10^6 Ω·cm near the Curie temperature. (2) A method for forming a lithium tantalate single crystal into a single domain according to claim 1, wherein the material constituting the electrode plate is ceramic.