JP2502608B2 - Method for producing single-domain lithium tantalate single crystal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing a single-domainized lithium tantalate single crystal, in particular, an electrode plate is arranged opposite to a side surface of the single crystal.
The present invention relates to an improvement in a method for dividing a lithium tantalate single crystal into a single domain by energization.

(Prior Art) Conventionally, as a method for domain-dividing a lithium tantalate single crystal pulled in the X-axis direction by the Czochralski method, a side surface of the pulled single crystal, that is, a surface in the Z-axis direction, for example, has a strip shape. A method is known in which positive and negative electrodes are placed opposite to each other so as to sandwich a single crystal, and a voltage is applied between both electrodes while heating to a temperature not lower than the Curie temperature, generally 610 ° C. or higher, thereby forming a single domain. .

In this method, however, platinum is usually used as the electrode plate, but there is a risk that the single crystal may be contaminated by platinum because of the inclusion of the platinum electrode in the single crystal. In this case, it is difficult to apply an electric field uniformly to the entire single crystal, and the resulting single crystal has the disadvantage of having crystal defects. A method has been proposed in which the powder of the above is filled and electricity is applied (Japanese Patent Publication No. 59-51156).
According to this, it is possible to prevent contamination of the single crystal with platinum and to apply a uniform electric field to the entire single crystal, and thus to obtain a single-domain crystal with few crystal defects. However, this has the economical disadvantage that it becomes extremely expensive because the material filled between the single crystal and the platinum electrode plate is the same kind of powder as the single crystal, and this powder also has a compositional variation. However, since this powder is a single crystal, the adhesion to the platinum electrode plate is poor, so the voltage applied to the platinum electrode plate is not uniformly conducted to the single crystal, and single domainization is not always performed well, There is a problem in that the obtained single crystal has variations in forming a single domain.

(Structure of the Invention) The present invention relates to a method for producing a single-domain domain lithium tantalate single crystal in which such disadvantages are solved, and it relates to a lithium tantalate single crystal pulled up and grown by the Czochralski method. Positive and negative electrodes are installed opposite to each other on the side surface, and a conductive material formed of carbon in a fibrous, felt, non-woven or cross shape is filled between the single crystal body and the electrode body, and a voltage is applied between both electrodes. It is characterized in that it is applied to form a single domain.

That is, as a result of various studies on the method of solving the disadvantage in the conventionally known single domainization method of lithium tantalate single crystal, the present inventors have found that the filler to be filled between the single crystal and the platinum electrode plate is When a conductive material made of carbon is molded into a fiber shape, felt shape, non-woven shape or cloth shape, this is a chemically stable material that does not react with lithium tantalate and has a flexible shape. It was found that the material is in good contact with the single crystal and the platinum electrode, so that the voltage application to the single crystal is uniform, and thus the obtained single crystal has a uniform domain with no variation. If the filler is formed carbon and it is easily available and inexpensive, it is significantly economically advantageous as compared with the known method using the powder of tantalic acid single crystal as the filler. In addition, since this molded filler has flexibility, it has good adhesiveness and also adheres well to uneven single crystals, so that a good single-domain lithium tantalate single crystal can be obtained. After confirming that it was given, the present invention was completed by conducting research on the type, shape, and structure of the filler used here.

The lithium tantalate single crystal used in the method of the present invention may be obtained by pulling and growing from a lithium tantalate melt by the Czochralski method.

The single domainization of the lithium tantalate single crystal is performed by arranging positive and negative electrode plates facing each other on the side faces of the single crystal and applying a voltage to the electrode plate. It may be made of gold or copper plated with gold, and its shape may be arcuate in cross section so as to adhere to the single crystal.

The method of the present invention is to fill the conductive material formed between the lithium tantalate single crystal and the electrode plate, the conductive material may be carbon, the shape of which is the shape of the electrode plate. Although it may be combined, it is preferable to form this into a fibrous, felt-like, non-woven fabric-like or cloth-like form, which makes it highly flexible, so single crystal, electrode plate The advantage is that the adhesiveness with is higher.

Next, the method of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a vertical sectional view showing a single domainization of a lithium tantalate single crystal according to the method of the present invention, and FIG. 2 is a transverse sectional view thereof. In this method, a lithium tantalate single crystal 1 Is placed on a support base 2 made of alumina or the like, and platinum electrodes 3, 3'having an arc-shaped cross section are attached to both sides of this single crystal, which are held by a band 5, Between the single crystal 1 and the platinum electrodes 3 and 3 ', a felt-like or cross-like carbon filler layer 4 is provided. Single domainization (poling) of lithium tantalate single crystal is carried out by charging them into a heating furnace and heating at a predetermined temperature, for example, Curie temperature of 610 ° C or higher, and then 5 to 25 V / cm between the electrodes. This is done by applying a voltage of 1. According to this, since the single crystal and the electrodes are connected through the flexible and formed conductive filler layer, the single crystal has irregularities. Also, since the filler layer adheres to the single crystal and the voltage applied to the electrode is uniformly applied to the single crystal, the single crystal is evenly divided into single domains and crystal defects do not occur. Since the material layer can be repeatedly used several tens of times, it is advantageous in that it has a large economic effect.

 Next, examples of the present invention will be described.

Example 1, Comparative Example A lithium tantalate single crystal body having a diameter of 82 mm and a length of 135 mm, which was grown by pulling up the X axis by the Czochralski method, was cut at both ends and subjected to polishing, and the Z axis direction on both side surfaces thereof. Platinum electrode plate with an arc cross section (arc length 50 mm, height 150 m
m, thickness 0.5mm), and made of carbon between this single crystal and the platinum electrode, thickness 7mm and standard weight 810
After filling a g / m ² felt-like compact and closely contacting the single crystal and the platinum electrode via this filler layer, this was charged into an electric furnace and the inside of the furnace was replaced with nitrogen gas. After that, a voltage of 110 V was applied to this electrode body while heating at 640 ° C. to perform single domainization of the single crystal body, and to obtain domainization uniformity of the obtained single domainized lithium tantalate single crystal. When a crystal strain polarization tester was used, it was confirmed that there was no non-uniform portion, which is a problem in terms of characteristics.

However, for comparison, it was decided to use 25 g of lithium tantalate single crystal powder as the filler in the above, but in this case, since it is a powder, it is necessary to make good adhesion between the single crystal body and the electrode plate. Since this is difficult, use this as a methylcellulose-based binder (Metcel manufactured by Shin-Etsu Chemical Co., Ltd.).
(SM50 product name) made into a paste, and this is about the thickness
It was adhered to the electrode plate at 3 cm, and the same treatment as above was carried out to make a single domain of the lithium tantalate single crystal. It was confirmed that there was a non-uniform
This was about 10% of the cross-sectional area of the single crystal.

The work of bringing the electrode plate into close contact with the paste-like product took about 25 minutes, but the felt-like molded product was attached in 5 minutes in the examples.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing a method for single domainization of a lithium tantalate single crystal according to the method of the present invention, and FIG. 2 is a transverse sectional view thereof. 1, ... Lithium tantalate single crystal, 2, ... Support base,
3, 3 '... Platinum electrode, 4, Filler layer, 5, Band.

Claims (1)

(57) [Claims] 1. A positive electrode and a negative electrode are installed opposite to each other on the side surfaces of a lithium tantalate single crystal grown by pulling and growing by the Czochralski method, and a fibrous, felt-like, or non-woven fabric made of carbon is formed between the single crystal and the electrode body. Alternatively, a method for producing a single-domain domain lithium tantalate single crystal, which comprises filling a cross-shaped conductive material and applying a voltage between both electrodes to achieve a single domain domain.