JPS6234718B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention uses lithium tantalate (hereinafter referred to as LiTaO ₃
) relates to a single domain method for single crystals. It is known to single-sectorize LiTaO ₃ single crystals. (Special Publication No. 47-8450, JP-A-54-15196, etc.). For example, in order to make an X-axis pulled LiTaO ₃ single crystal into a single domain, as shown in Fig. 1, the pulled single crystal 3 is placed in an electric furnace 2 that can be heated with a heater 1, and an electrode 4 is placed on the Z plane. The switch 7 is turned on so that a voltage 6 can be applied from the lead wire 5.
The heating curve (solid line) and voltage application characteristics (broken line) of the LiTaO ₃ single crystal at this time are shown in FIG. In most cases, the temperature rise of single crystals is 200°C/hour, from t ₀
The holding temperature up to h ₂ is 650 °C, and the temperature drop is 200 °C/hour. Time to start holding at constant temperature t ₀ to 20
After a minute, a voltage is applied at _t1 , and after another 20 minutes, the temperature is lowered from _t2 , and one hour after _t1 , the voltage is turned off at _t3 . The above operations complete the single domain formation of the LiTaO ₃ single crystal. Now, the single polarization obtained in this way
In LiTaO ₃ single crystal, cracks in the single crystal are observed at the end of polarization. The size of this crack varies, and the largest one has a length in the X-axis direction.
They range in size from about 1mm wide on the outer surface of 10cm to those that can be easily seen with the naked eye. Also, the direction of the crack is not limited to the X-axis direction. The crack incidence during many experiments was approximately 5%. Cracks occurring in single crystals are not a desirable phenomenon not only in terms of production costs but also in terms of quality characteristics of single crystals and must be reduced as much as possible. In order to reduce cracks after polarization, the inventors conducted experimental research on various factors in the polarization method, and discovered that voltage application conditions for single crystals were also a cause of cracks, and completed this invention. did. That is, the present invention includes the steps of providing electrodes for applying an electric field to both ends of the Z axis of a LiTaO ₃ single crystal, heating this single crystal to a predetermined temperature, and applying a predetermined electric field to the single crystal at this predetermined temperature. In the method for single _- domaining a single crystal, the method is characterized in that the application of the predetermined electric field is performed slowly. According to numerous experiments, when applying a voltage, as shown by the broken line in Figure 3 (the solid line is the temperature of the single crystal),
Cracks can be prevented by applying the voltage gradually so as to give a slope with respect to time, and if the voltage is applied steeply as shown by the broken line in FIG. 2, many cracks occur. Table 1 shows the relationship between the gradualness of voltage application and the crack occurrence rate.

[Table] As shown in this table, if the voltage application is gentle, the crack occurrence rate is small; if the voltage application condition exceeds 15V/min, cracks occur frequently, and if the voltage application condition is 10V/min or less, there are very few cracks. The present invention will be explained below with reference to Examples. Example 1 As shown in FIG. 1, electrodes 4 were provided at both ends of the Z axis of a LiTaO ₃ single crystal with a diameter of 2 inches, and the crystal was inserted into an electric furnace 2 and heated to 650°C. After that, switch 7 is turned on and voltage 6 is gradually increased at a rate of 10V/minute, and the voltage continues to increase until it reaches 60V. After processing for 20 minutes at 650°C and 60V, the temperature is lowered at 200°C/hour. When n=800 pieces were subjected to single polarization processing in this way, 4 pieces were cracked. Example 2 As in Example 1, electrodes 4 were provided at both ends of the Z axis of a 2-inch LiTaO ₂ single crystal, and the material was inserted into an electric furnace 2.
Heat to 700℃. After that, switch 7 is turned on and voltage 6 is increased at a rate of 15V/minute, and continues to increase until it reaches 60V. After processing for 20 minutes at 700°C and 60V, the temperature is lowered at 200°C/hour. When n=600 single polarization processes were performed in this way, three cracks were found. As explained above, the present invention is characterized in that the electric field applied to the monopolar crystal is applied slowly in the single polarization method of LiTaO ₃ single crystal. Cracks are significantly reduced.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of an apparatus for single polarization treatment of LiTaO ₃ single crystal, Figure 2 is a diagram showing the heating curve and voltage application characteristics of a conventional LiTaO ₃ single crystal, and Figure 3 is a diagram showing the LiTaO according to the present invention. FIG _{. 3} is a diagram illustrating voltage application characteristics of a single crystal.

Claims (1)

[Claims] 1. Providing electrodes for applying an electric field at both ends of a lithium tantalate (LiTaO ₃ ) single crystal, heating the single crystal to a predetermined temperature, and applying a predetermined electric field to the single crystal at this predetermined temperature. In the method for single-segmenting a single crystal, the voltage is increased at a rate of 15 V or less per minute for applying the predetermined electric field. Regionalization method.