JPS6335497A - Method for making single domain ferroelectric single crystal - Google Patents

Abstract

PURPOSE:When a specific electric field is applied to a single crystal, another electric field lower than the specific value is applied beforehand to effect smooth progress of single domain whereby the cracks in the single crystal is drasticly reduced. CONSTITUTION:A ferroelectric single crystal 4 (LiNbO3) is tightly enclosed through a crystal powder 3 of a specific resistance in a vessel 2 provided with a couple of electrodes 1 top and bottom, heated up near the Curie point and a specific electric field is applied to convert into single domain. At this time, before the temperature of the single crystal 4 reaches near the Curie point, another electric field corresponding to 3-15% of the specific one is applied. After the temperature reaches the Curie point, the electric field applied to the single crystal is gradually increased. Thus, the ferroelectric single crystal is made into single domain with inhibition of cracks.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is directed to the production of a single ferroelectric single crystal such as lithium niobate (hereinafter referred to as LiNb0°) or lithium tantalate (hereinafter referred to as LiTag). It concerns the regionalization method.

(Prior Art) Conventionally, for example, L i N b 03 single crystal is pulled into two, for example, two-axis, and divided into regions as shown in FIG. That is, a LiNbO5 single crystal 4 is sealed in a container 2 with electrodes 1 provided on the upper and lower sides via a crystal powder 3 having a predetermined electrical resistivity, heated to a predetermined temperature, and heated to a predetermined temperature by a power source 6 via a lead wire 5. Apply a voltage of Li in this case
The heating curve and voltage application curve of the NbO3 single crystal are shown in FIG. 3 by solid lines and broken lines, respectively. Generally, the temperature rise of a single crystal is around 100"C/hour. The holding temperature from time t0 to time t2 is 1150 to 1200.degree. C., which is slightly higher than the Curie temperature Tc. The temperature drop is around 100"C/hour. Then, the time t when the temperature starts to be maintained at a constant temperature
1. 30 minutes after 0. A voltage IV/cm was applied at time t2, and the temperature was further lowered from t2 after 30 minutes at +t
After 15 hours from 1, the voltage application is canceled. By the above operations, the single domain formation of the LiNb0z single crystal is completed.

[Problem that the invention seeks to solve]

Li N b O: 1 single-domained by the above method
A single crystal may have a single crystal crank when the above-mentioned segmentation is completed. These defects not only increase production costs.

It must be reduced as much as possible because it significantly deteriorates the quality characteristics of the single crystal. In order to solve the above problems, there is a method as shown in Fig. 4 (Japanese Unexamined Patent Publication No. 58-11
(See Publication No. 5096). FIG. 4 is a diagram corresponding to FIG. 3, and shows a method in which a predetermined voltage is applied to the single crystal in a gradual manner so as to give a slope over one hour. That is, this is done for the purpose of preventing the occurrence of cranking due to steep voltage application as shown in FIG. 3 above. However, even with this method, there is still a problem in that it is not possible to completely prevent the occurrence of cracks in the single crystal.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for forming a ferroelectric single crystal into a single domain, which eliminates the problems existing in the conventional methods and completely prevents the occurrence of cracks.

[Means for solving problems]

One aspect of the present invention is to solve the above-mentioned conventional problems.

A step of providing electrodes for applying an electric field at or near both ends of an A0 ferroelectric single crystal, heating the single crystal to a temperature near the Curie temperature, and applying a predetermined electric field to the single crystal at this temperature. In a method for single domainization of ferroelectric single crystals including.

B. Applying an electric field of 3 to 15% of the predetermined electric field before the single crystal reaches a temperature near the Curie temperature.

C0 After the single crystal reaches a temperature near the Curie temperature, the electric field applied to the single crystal is gradually increased to the predetermined electric field.

This technical method was adopted.

In the present invention, an electric field of 3 to 15% of the predetermined electric field is applied in advance; however, if a predetermined electric field is applied to the single crystal from the beginning, the amount of distortion generated by the electric field application peculiar to ferroelectric materials is large. This is inconvenient as it causes cracks. Thus, the ferroelectric single crystal loses its ferroelectricity above the Curie temperature, and by applying an electric field, it becomes possible to invert the electrodes or form a single domain. However, even if the temperature of the single crystal reaches the Curie temperature, the above-mentioned single domainization is not started all at once within the single crystal, and requires some time. In other words, in a region in a single crystal where it is easy to form a single domain, the process progresses relatively quickly even before the Curie temperature is reached, whereas in a region where it is difficult to form a single domain, the process progresses relatively quickly even before the Curie temperature is reached. This is presumed to be because the above-mentioned regionalization progresses relatively slowly even after reaching the target area. Furthermore, it can be estimated that part of the region that is easily formed into a single domain is in a state where electrode inversion or single domain formation is possible even before the temperature of the single crystal reaches the Curie temperature. Therefore, an electric field with a value slightly lower than the predetermined electric field, preferably 3 to 15% of the predetermined electric field strength.
By applying an electric field with a strength of 50%, the region that can be easily formed into a single area can be made into a single area. If the electric field strength is less than 3% of the predetermined electric field strength, the effect of starting the single domain formation before the Curie temperature of the single crystal is reached is insufficient. On the other hand, applying an electric field with a strength exceeding 15% is inconvenient because it applies a high electric field locally due to the non-uniformity of the surface and inside of the single crystal, which causes cranking. be.

[Effect] By applying the above-mentioned electric field, it is possible to advance single domainization from the single domain-easy region even before the temperature of the single crystal reaches the Curie temperature. It is also possible to prevent the occurrence of distortion on the surface and avoid the occurrence of cracks. It also has the effect of avoiding the disadvantage of inducing an undesired localized high electric field inside the heterogeneous and unstable single crystal before the single-domaining treatment.

[Example 1] FIG. 1 is a diagram showing a heating curve and a voltage application curve of LiNb0° single crystal in an example of the present invention.
Similarly to FIG. 4, the former is shown by a solid line, and the latter by a broken line. Diameter 90n+++ by 2-axis pulling
A LiNbo single crystal 4 grown to a length of 100 mm was sealed in a container 2 as shown in FIG. 2, and charged into an electric furnace (not shown).

Heating at a rate of 80"C/hour. When the temperature of the single crystal is 40"C/hour.
When the temperature reaches °C, the power supply 6 shown in FIG.
Apply a voltage of 1. Next, the temperature of the single crystal is 11
From time t0 when the holding temperature of 50°C was reached, the applied voltage was gradually increased at a rate of 20 cm/hour, and from time tl to 1
It is maintained at a predetermined voltage of 5 to 20V. Then, from time t2, 150 minutes after the start of holding this voltage, the temperature of the single crystal is lowered, and at time t3, 12 to 15 hours after 9 time L1, the voltage application is released, and the Ends the single area processing. When 80 single segmentation processes were performed as described above, only two cranks occurred.

[Example 2] Similar to Example 1, a 1Ta diameter 601 length 100 mm
Electrodes 1 as shown in FIG. 2 were arranged in the biaxial directions of the 03 single crystal, and heating and voltage application were performed according to the curve shown in FIG. That is, first, a LiTaO3 single crystal is
Heating is carried out at a rate of 0°C/hour, and a voltage of 1O■ is applied from the time the temperature reaches 40°C. Next, the temperature of the single crystal is 75
200 V/ from time t0 when the holding temperature of 0°C is reached.
The applied voltage was gradually increased according to the waiting time ratio, and at 9 time 1. From 20
It is held at a predetermined voltage of 0■. Then, from time t2, 300 minutes after the start of holding at this voltage, the temperature of the single crystal is lowered, and at time t3, 12 to 15 hours after time t1, the voltage application is released, and the single crystal domain of the LiTaO5 single crystal is lowered. Terminate the conversion process. 55 single area division processes were performed as described above.

Only one crack occurred.

In this example, l, 1Nbo: + single crystal and L
The example of i T a O3 single crystal has been described.

The same effect applies to other ferroelectric single crystals other than those mentioned above. Furthermore, the present invention is not limited to those in which the pulling axis and the direction of single segmentation are the same, and it goes without saying that the above can be applied in the same manner as in the case where the pulling axis and the direction of single segmentation are different. Furthermore, the temperature of the single crystal to which a voltage or electric field with a value lower than a predetermined voltage or electric field is applied should be determined by taking into account the type of single crystal, the orientation of one plane, the shape and two dimensions, etc. 85-1
It is preferable to select within a range of 50%.

〔Effect of the invention〕

Since the present invention has the structure and operation as described above, 1
In the process of single-domaining a ferroelectric single crystal, by applying an electric field lower than a predetermined electric field in advance, single-domaining can proceed smoothly. This has the effect of significantly reducing the occurrence of cracks.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the relationship between temperature, voltage, and time in an embodiment of the present invention, Fig. 2 is an explanatory diagram of the state of single domain treatment of a ferroelectric single crystal, and Figs. 3 and 4. FIG. 2 is a diagram showing the relationship between temperature, voltage, and time in each conventional method.

Claims (2)

[Claims] (1) Providing electrodes for applying an electric field at or near both ends of a ferroelectric single crystal, heating the single crystal to a temperature near the Curie temperature, and applying a predetermined electric field to the single crystal at this temperature. 3 to 1 of the predetermined electric field before the single crystal reaches a temperature near the Curie temperature.
A single component of a ferroelectric single crystal, characterized in that an electric field of 5% is applied and, after the single crystal reaches a temperature near the Curie temperature, the electric field applied to the single crystal is gradually increased to the predetermined electric field. regionalization method. (2) The ferroelectric material is lithium niobate (LiNbO_3
) or lithium tantalate (LiTaO_3), the method for producing a single domain of a ferroelectric single crystal according to claim 1.