JPH0524993A - Production of potassium salt single crystal - Google Patents

Abstract

PURPOSE:To prevent the potassium salt single crystal from being colored blue by growing the crystal under a specific temp. condition at the time of growing the crystal from a raw material melt by using a seed crystal. CONSTITUTION:The raw material 8 having a compsn. consisting of >54mol% K2O and <46mol% Nb2O5+-Ta2O5 is put into a platinum crucible 1 in a vertical type tubular furnace 5 having a heater 4. The seed single crystal 7 expressed by general formula KTaxNb1-xO3 (O<=x<=1) is immersed into the surface of this molten raw material 8 and is gradually pulled up, by which the single crystal of the same compsn. as the compsn. of the seed single crystal 7 is grown at the front end thereof and is pulled up. The temp. is increased up to the temp. at which the raw material 8 melts completely and the temp. is then lowered down to about the predicted equil. temp. and is regulated to the temp. at which the seed single crystal 7 does not grow or melt in the raw material melt 8. This temp. is designated as the equil. temp. The seed single crystal 7 is pulled up under the condition of the equiv. temp.-raw material melt temp. >1.5 deg.C in the supercooled state of the temp. of the raw material melt 8, by which the coloring of the grown and pulled-up single crystal to blue is prevented.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention is of the general formula KTa _X Nb.
_{The present} invention relates to a method for producing a potassium salt single crystal represented by _1-X O ₃ (0 ≦ x ≦ 1).

[0002]

KTa _X Nb _1-X O ₃ (0 ≦ x ≦ 1, hereinafter abbreviated as KTN) single crystal has a stoichiometric composition, that is, K
₂ O: (Nb ₂ O ₅ + Ta ₂ O ₅ ) = 50: 50 (molar ratio) does not cause congruent melting (congruent melting) in the melt, so that in the production of a single crystal, a high temperature containing excess K ₂ O is used. A seed crystal is attached to the melt, and the seed crystal grows by the precipitation of the crystal.

The KTN single crystal produced in this way is often colored blue. KT used for optical applications
It is fatal for the N single crystal to have such a coloring defect that reduces light absorption and electric resistance.

Conventionally, in order to solve this problem, KNb
In the crystal manufacturing process of O ₃ single crystal (when x = 0 in KTN single crystal), it is possible to eliminate coloring by soaking the raw material at a high temperature of 1150 ° C. to 1300 ° C. in Japan. J. Appl. Phys. 11 (1972) page 163. In the experiment by this method, 125
By performing the heat treatment (soaking) at 0 ° C. for 100 hours or more, the occurrence of blue coloring could be prevented with good reproducibility. However, the process before the crystal growth takes too much time, and the maximum operating temperature of the electric furnace for crystal production is set to the melting point (10
50 ° C.) to 200 ° C. or higher, which has drawbacks such as an increase in the price of the electric furnace and a shortened life of the heater wire.

In this method, the raw material composition is K ₂ O:
(Nb ₂ O ₅ + Ta ₂ O ₅ ) = 52.5: 47.5 (molar ratio) is effective at a relatively low flux concentration, but K ₂ O: (Nb ₂ O ₅ + Ta ₂ O ₅ ) = 54:46
At a relatively high flux concentration above the (molar ratio), the effect of eliminating coloring defects could not be obtained.

As another method, SnO ₂ or
Doping with ZrO ₂ etc. to eliminate coloring is described in J. C.
rystal Growth 99 (1990) 634, p. This method has a problem that the reproducibility is poor and the doping agent is likely to be nonuniformly distributed in the crystal, which adversely affects the optical properties such as the refractive index distribution of the crystal.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawback of blue coloring that occurs in the crystal during the crystallization process, which the prior art has.

[0008]

The present invention has been made to solve the above-mentioned problems, and has the general formula KTa _X Nb _{1- X.}
A potassium salt single crystal represented by O ₃ (0 ≦ x ≦ 1) is
In the method for producing a crystal by growing a seed crystal from a raw material melt, the raw material melt temperature is in a supercooled state lower than the equilibrium temperature, and its supercooling temperature, that is, the equilibrium temperature-
Provided is a method for producing a potassium salt single crystal, which is characterized by gradually growing crystals at a melt temperature of a raw material melt temperature of 1.5 ° C. or higher.

In the present invention, after the selected raw material is completely melted, the temperature of the melt is set to an appropriate temperature expected to be the equilibrium temperature and the seed crystals are immersed in the melt and kept for 30 hours or more. However, the equilibrium temperature can be determined by searching for the lowest temperature at which seed crystals do not grow. If this temperature is known once, the equilibrium temperature can be measured from the second time on the basis of this temperature, and therefore the equilibrium temperature measurement time can be greatly shortened.

As another method, in the step of preparing and synthesizing a melt before seed crystals are attached, the melt temperature is lowered from the completely molten state of the raw materials to precipitate crystals by spontaneous nucleation, and the melt temperature is further increased. Is raised to measure the temperature at which the precipitated crystals melt, and the temperature can be taken as the equilibrium temperature.

According to the present invention, after the seed crystal is immersed in the melt for crystal growth, the supercooling temperature is not kept within the range of 1.5 ° C. for 1.5 hours or more, or the supercooling temperature is 1. By adding seed crystals to a melt at 5 ° C. or higher and gradually growing the seed crystals, it is possible to stably produce crystals without coloring defects.

Although the principle of the method of eliminating the coloring defect of the present invention is not always clear, the experiments by the inventors revealed that the blue coloring of the KTN single crystal was particularly large in the vicinity of the seed crystal, that is, in the portion where the first precipitation growth occurred. It turned out to occur. Furthermore, even when the raw material melt is gradually cooled and solidified in the crucible without using seed crystals, blue coloring is often observed in the first deposited portion, and K ₂ O: (Nb ₂
It was found that even if the composition of O ₅ + Ta ₂ O ₅ ) was changed, a large amount of blue coloration occurred in the portion that was initially precipitated as the KTN phase. It was also found that the crucible residue that was slowly cooled and solidified after taking out the crystals in which blue coloring was generated in the vicinity of the seed crystals was not blue colored.

The raw material composition is K ₂ O: (Nb ₂ O ₅ +
In the case of Ta ₂ O ₅ ) = 52.5: 47.5 (molar ratio),
As a result of conducting a growing experiment in which the seed crystal was immersed in the melt and the temperature for growing the crystal was changed in the range of 0.5 ° C. to 4 ° C. from the equilibrium temperature, the coloring amount of the crystal was as shown in FIG. As is apparent from FIG. 1, the coloring defect has a supercooling temperature of substantially 1.
It occurs in the range of 5 ° C. or less, and it is understood that when the temperature is gradually lowered from the equilibrium temperature and crystal growth is performed, a coloring defect occurs at the initial stage of crystal growth within 1.5 ° C. below the equilibrium temperature.

From these facts, the equilibrium temperature of 1.
The effect of eliminating coloring defects is to pass the temperature range within 5 ° C as fast as possible, or to grow the crystal from a temperature lower than the equilibrium temperature by 1.5 ° C or more, that is, a supercooling temperature of 1.5 ° C or more. It is believed that this occurs and the present invention is based on these facts. Therefore, it is desirable that the time for passing within 1.5 ° C. is as short as possible. If this time is within 1.5 hours, coloring does not occur, but if it exceeds this time, the amount of coloring sharply increases.

[0015]

【Example】

(Example 1) KTN in which x = 0 in a KTN single crystal
TSO method of bO ₃ single crystal (Top Seeded Solution Grow
th method). The manufacturing apparatus used is shown in FIG. A raw material having a composition of K ₂ O: Nb ₂ O ₅ = 52.5: 47.5 (molar ratio) was put into the platinum crucible 1. This crucible is placed on an alumina ceramics table 2, and an alumina protective tube 3 and a vertical tubular furnace 5 to which a resistance heater 4 is attached are arranged outside the crucible and the temperature of the raw material melt is controlled by the resistance heater 4. Controlled.

After the seed crystal 7 attached to the tip of the seed holder 6 was immersed in the melt 8, the temperature was lowered while rotating the seed crystal to deposit and grow the crystal at the tip of the seed crystal.

The temperature control situation at that time is shown below. After the raw material is completely melted and heated to 1080 ° C and held for 2 hours, the melt temperature is lowered to near the expected equilibrium temperature and the seed crystal is brought into contact with the melt so that the seed crystal does not grow nor melt. The temperature of the melt was adjusted and the temperature was set as the equilibrium temperature.
Then, this seed crystal was once separated from the melt, and it was confirmed that the seed crystal did not grow at all. Then, the melt temperature was lowered from the equilibrium temperature by 2.5 ° C., and the seed crystal was brought into contact with the melt again to grow the crystal. As a result, a colorless and transparent single crystal of 50 mm square could be obtained.

(Example 2) After determining the equilibrium temperature in the same manner as in Example 1, the seed crystal was not cut from the melt, and the melt temperature was lowered at 2.5 ° C at 2 ° C / h as it was, to give the crystal. Raised. As a result, a colorless and transparent single crystal of 50 mm square could be obtained.

(Example 3) The same as Example 1 when x = 0 and a raw material composition of K ₂ O: Nb ₂ O ₅ = 56: 44 (molar ratio) was used. 50mm by method
A colorless and transparent single crystal with horns could be obtained.

[0020]

INDUSTRIAL APPLICABILITY The present invention has the effect of reproducibly preventing the occurrence of blue coloring defects during the growth of KTN crystals, and can improve the crystal yield. In addition, since it is possible to prevent the occurrence of blue coloring with good reproducibility without the need for heat treatment (soaking) at high temperatures as in the past, it is possible to lower the maximum operating temperature of the electric furnace, which reduces the price of the electric furnace itself. Not only can this be done, but the life of the heater wire can be extended and the time for the entire crystallization process can be shortened.

In the conventional method, the raw material composition is K ₂
O: (Nb ₂ O ₅ + Ta ₂ O ₃ ) = 52.5: 47.5
It is effective at a relatively low flux concentration of about (molar ratio), but K ₂ O: (Nb ₂ O ₅ + Ta ₂ O ₃ ) = 54:
While there was no effect at a relatively high flux concentration of 46 (molar ratio) or more, the present invention also enables growth from a high flux concentration with a large slope of the liquidus line in the phase diagram, which results in stable temperature during growth. The allowable range of properties is increased, and the crystal yield is improved along with the improvement of crystal quality. Furthermore, the effect that the optical properties such as the refractive index distribution of the crystal due to the inhomogeneous distribution in the crystal of the doping agent are not adversely affected is recognized.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between supercooling temperature and coloring amount.

FIG. 2 is a cross-sectional view illustrating a typical crystal growing device.

[Explanation of symbols]

1 platinum crucible 2 Alumina ceramics stand 3 Alumina protection tube 4 resistance heater 5 Vertical tubular furnace 6 seed holder 7 seed crystals 8 Raw material melt

Claims (7)

[Claims] 1. A general formula KTa _X Nb _1-X O ₃ (0 ≦ x ≦
In the method for producing a potassium salt single crystal represented by 1) by growing a crystal from a raw material melt using a seed crystal,
The raw material melt temperature is lower than the equilibrium temperature in a supercooled state, and the crystal is gradually grown from the supercooled temperature, that is, the equilibrium temperature-the raw material melt temperature is 1.5 ° C. or higher. Method for producing potassium salt single crystal. 2. A method for growing a seed crystal in a raw material melt having an equilibrium temperature or higher and growing the seed crystal without separating from the raw material melt, wherein the supercooling temperature is 0 ° C. or higher and lower than 1.5 ° C. The method for producing a potassium salt single crystal according to claim 1, wherein the time for which the seed crystal is attached to the melt in the range is 1.5 hours or less. 3. A seed crystal is attached to a raw material melt having an equilibrium temperature or higher, and thereafter the seed crystal is once separated from the raw material melt, and then the seed crystal is reapplied to the raw material melt having a supercooling temperature of 1.5 ° C. or higher. The method for producing a potassium salt single crystal according to claim 1, wherein the crystal is gradually grown around the seed crystal. 4. The method for producing a potassium salt single crystal according to claim 1, wherein the equilibrium temperature is the lowest temperature at which the seed crystal does not grow even if the seed crystal is added to the raw material melt and kept as it is for 30 hours or more. . 5. The equilibrium temperature is such that the temperature of the raw material is lowered from a completely molten state before seed crystals are attached to precipitate crystals.
The method for producing a potassium salt single crystal according to claim 1, wherein the temperature is raised again to dissolve the precipitated crystal. 6. The method for producing a potassium salt single crystal according to claim 1, wherein the raw material is not heated to a high temperature of 200 ° C. or higher of the melting point. 7. The method for producing a potassium salt single crystal according to claim 1, wherein the composition ratio of the raw materials is such that K ₂ O is 54 mol% or more and Nb ₂ O ₅ + Ta ₂ O ₅ is 46 mol% or less.