JP2976967B1 - Langasite single crystal growth method - Google Patents

Abstract

Abstract: [Problem] Langasite La ₃ G by CZ method (pulling method)
In the growth of a ₅ SiO ₁₄ single crystal, it suppresses the occurrence of macroscopic defects such as crystal cracks and inclusions, and reduces the brown coloring seen in normal growth, making it suitable not only for piezoelectric but also for optics. Provided are a growing method for obtaining a langasite single crystal, a method for modifying the single crystal, and an apparatus for growing the single crystal. SOLUTION: Lanthanum oxalate La ₂ (C ₂ O ₄ ) ₃ is 90
Lanthanum oxide La ₂ O obtained by firing at a temperature of 0 ° C. or less
Langasite La ₃ Ga ₅ SiO ₁₄ by CZ method using ₃ as raw material
A method for growing a single crystal, a method for modifying a single crystal of langasite by heat-treating the single crystal in a nitrogen atmosphere, and an opening for monitoring a growth state in a refractory for heat retention at the upper part of a crucible of a langasite single crystal growing apparatus by a CZ method. No langasite single crystal growing equipment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for growing a langasite La ₃ Ga ₅ SiO ₁₄ single crystal used for optical and piezoelectric purposes.

[0002]

2. Description of the Related Art Langasite single crystals were initially grown for optical use, but phase diagrams and growth tests of compounds of this system have been developed mainly in Russia [GGKhodzhabagyan, Russia
n J. Inorg. Chem., 32 (2), 1987, pp. 246-248]. In recent years, it has also been used for piezoelectric devices such as filters using surface acoustic waves, and reports related to crystal growth have been made (see Fukuda et al., Journal of Japanese Society for Crystal Growth 22 (5) 1995, p358). Was.

[0003] The crystal is grown exclusively by the CZ method (Czochralski meto).
d: pulling method), and iridium or an alloy of platinum and rhodium is used as the crucible. This crystal can be a large crystal if the crystal growth conditions are appropriate, but the crystal quality is sensitive to various crystal growth conditions [Shimamura et al., Proceedings of the 40th Symposium on Artificial Crystals 2A144 (1995) p10
3].

On the other hand, Japanese Patent Application Laid-Open No. 62-154681 discloses a PLZT electrostrictive porcelain for an actuator, which is different from langasite which is an optical porcelain material of the present invention. Their compositions are also quite different. Further, Japanese Patent Application Laid-Open No. 63-282188 discloses a single crystal production apparatus, which is based on a mere general CZ method (pulling method), and which is a CZ method specified in the present invention. No specific reference is made to a specific growth apparatus for a langasite single crystal according to the present invention.

Further, Japanese Patent Application Laid-Open No. 03-202087 discloses a method for producing an oxide single crystal, which is a production method based on a mere general CZ method (pulling method).
The specific growth method of the langasite single crystal by the CZ method specified in the present invention is not specifically described.
Also, in Japanese Patent Publication No. 07-055878, a method of controlling the diameter of a semiconductor single crystal is disclosed, but this method is based on a mere general CZ method (pulling method), and is specified by the present invention. The specific growth method of the langasite single crystal by the CZ method is not specifically described.

[0006]

A first problem to be solved in the present invention is how to select a raw material used for growing a crystal. Of course, the purity should be as high as possible, but even with relatively high purity raw materials such as 4n (99.99%), cracks, inclusions, twins and other macroscopic effects can sometimes occur. Therefore, a method for producing a raw material suitable for producing the crystal has been a problem.

A second problem to be solved is that the quality of the grown crystal is sensitive to the crystal growing conditions, and it is necessary to set precise conditions, and in particular, it is necessary to optimize the temperature gradient of the growing furnace. A third problem to be solved is to alleviate coloring of the grown crystal. This is a major problem particularly in optical applications. Also, in the case of a piezoelectric application, if this is based on a crystal defect, there is a possibility of being affected in some way, so it is desirable that there is no coloring.

The present invention has been made in view of the above, and has as its object the object of the present invention, which does not have the above-mentioned problems, is a high-quality langasite unit that exhibits excellent performance even in applications for optical and piezoelectric use. A method for producing raw materials to obtain crystals,
An object of the present invention is to provide a crystal growing method, a heat treatment modifying method for the crystal, and a crystal growing apparatus.

[0009]

The above objects and objects are solved and achieved by the present invention described below. That is, the present invention relates to a method of growing a langasite La ₃ Ga ₅ SiO ₁₄ single crystal, wherein 90 g of lanthanum oxalate La ₂ (C ₂ O ₄ ) ₃ is used.
Lanthanum oxide La ₂ O obtained by firing at a temperature of 0 ° C. or less
_{In the} method for growing a langasite single crystal characterized by using ₃ as a raw material, or the method for growing a langasite single crystal by a CZ method (pulling method), a method for growing a langasite single crystal in a range from 15 mm above a raw material melt surface in a crucible. 2 ° C temperature gradient
A method for growing a langasite single crystal, characterized in that the temperature gradient is set to ± 1 ° C./mm and the temperature gradient up to 50 mm above the temperature is set to 8 ° C./mm or less, or the growth status is monitored on a refractory for keeping heat at the upper part of the crucible. In the method of growing a langasite single crystal characterized by not providing an opening for, or in the method of growing a langasite single crystal not having the growth state monitoring opening, regardless of observation from a monitoring window when performing a seeding operation, A method for growing a langasite single crystal, characterized in that seeding is performed only based on information on a signal change from a weight sensor, or a method in which a divalent cation impurity contained as an impurity in a crystal growing material is suppressed to 10 ppm or less. A method for growing a single crystal of langasite, or a method of using nitrogen as a crystal growth atmosphere gas. It discloses a method for growing a gausite single crystal.

In the present invention, a method for producing lanthanum oxide La ₂ O ₃ having good solubility and reactivity with respect to the raw material is first determined. Next, a method for optimizing the vertical temperature gradient in the furnace, which has a great effect on suppressing the occurrence of cracks, inclusions, twins, and other macroscopic defects in the single crystal during crystal growth, is determined. The problem of crystal coloring can be solved by improving the purity of the raw material and selecting the growth atmosphere. Further, there is provided a langasite single crystal growing apparatus suitably used in the method.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be specifically described below. First, the lanthanum oxide La ₂ O of the present invention is used.
_The raw material preparation method using ₃ as a raw material is based on the test facts described below. Usually, the langasite La ₃ Ga ₅ SiO ₁₄ single crystal is composed of lanthanum oxide La ₂ O ₃ , gallium oxide Ga ₂ O ₃ ,
It is grown using each powder of silicon dioxide SiO ₂ as a raw material.
As a result of the trial test, it was found that lanthanum oxide La ₂ O ₃ was most closely related to the quality of the grown crystal, particularly the occurrence of macroscopic defects such as cracks. That is,
By using lanthanum oxide having good solubility and reactivity, a crystal with few defects can be obtained. The preparation of such lanthanum oxide is according to the following method.

First, a lanthanum compound is dissolved in an acid such as hydrochloric acid or nitric acid, and oxalic acid is added to the lanthanum compound to form lanthanum oxalate La ₂ (C ₂
O ₄ ) ₃ is precipitated. This may be filtered, dried and calcined at a temperature of 900 ° C. or less to obtain lanthanum oxide La ₂ O ₃ .
What is important here is that the firing temperature is set to 900 ° C. or lower, and firing at a temperature of 1000 ° C. or higher, which is usually performed, is not effective.

Next, the temperature gradient in the method of growing a langasite single crystal by the CZ method (pulling method) of the present invention was tested while variously changing the heat retaining conditions of the crystal growing furnace. And a temperature gradient of 2 ° C. ± 1 ° C./mm in a range from 15 mm to
By setting the temperature gradient up to 8 ° C./mm or less, it was found that the generation of macroscopic defects was suppressed most, and a good quality langasite single crystal was grown.

Further, in the present invention, a crystal growing furnace system not using a monitoring window has been found as the simplest method for realizing the temperature gradient. Conventionally, the monitoring window is important for grasping the state of crystal growth, and is considered to be particularly essential for seeding. However, according to the method using the weight sensor of the present invention, visual observation is not performed at all. It was confirmed that seeding was possible.

This method is based on the following procedure. FIG. 1 is a schematic cross-sectional view showing an example of the structure of a conventional growing device with a monitoring window. First, the raw material is melted while monitoring using such a device. Data. Thereafter, while monitoring the temperature of the thermocouple 10 using a crystal growing apparatus without a monitoring window according to the present invention as shown in FIG. Is gradually lowered. The weight sensor signal when the seed reaches the raw material surface is as shown in FIG. 3 to FIG.

In each figure, the horizontal axis represents the passage of time, and T ₀ represents the time of seed contact. FIG. 3 shows the case where the raw material is not melted, FIG. 5 shows the case where the melt temperature is considerably lower than the ideal temperature, and FIG. 6 shows the case where the melt temperature is too high. Good seeding is when the weight increases and does not change or decreases slightly.

In this manner, seeding can be performed by adjusting the temperature based on the weight signal without the monitoring window. According to this method, a langasite single crystal growing apparatus having a device for detecting the weight of a grown crystal without providing an opening for monitoring a growing state in the refractory for heat retention of the present invention is effective.

Next, a crystal growing method for suppressing divalent cation impurities contained as impurities in the crystal growing material of the present invention to 10 ppm or less and a crystal growing method using nitrogen as a crystal growing atmosphere gas will be described. It is clear from the test results that both the impurity such as the raw material and the crystal growth atmosphere are related to the coloring of the crystal, and the amount of the divalent cation impurity in the raw material is reduced by 10 p.
pm or less, and the crystal growth atmosphere must be pure nitrogen. Therefore, the single crystal growing method of the present invention in which the divalent cation impurity contained as an impurity in the crystal growing material is suppressed to 10 ppm or less and nitrogen is used as the crystal growing atmosphere gas has better results when both are satisfied. Bring.

The method for modifying a langasite single crystal according to the present invention, in which the grown langasite single crystal is further heat-treated in a nitrogen atmosphere, relates to the removal of the color of the crystal grown in an atmosphere containing oxygen. The crystals colored yellow or reddish brown are heat treated in a nitrogen atmosphere. As a result, absorption loss in optical applications can be reduced.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to the drawings based on embodiments, but the present invention is not limited to these embodiments.

Example 1 After commercially available lanthanum oxide La ₂ O ₃ having a purity of 99.99% was dissolved in nitric acid, oxalic acid was added thereto to add lanthanum oxalate La ₂ (C ₂ O ₄ ) _3.
The precipitate was dried by filtration and calcined in a rotary kiln at 850 ° C. or lower for 3 hours in air to obtain lanthanum oxide La ₂ O ₃ . Using this lanthanum oxide and commercially available powders of 99.99% pure gallium oxide Ga ₂ O ₃ and silicon dioxide SiO ₂ as raw materials, langasite La ₃ G with a stoichiometric composition.
a ₅ SiO ₁₄ was cultivated.

The crystal growing apparatus is a high frequency induction heating and pulling apparatus shown in FIG. 2, the crucible is made of iridium having a diameter of 50 mm and a depth of 50 mm, the total amount of raw materials is 600 g, the growing atmosphere is nitrogen containing 0.5% of oxygen, and the pulling rate is 1 mm / hr.
A light brown crystal having a diameter of about 25 mm and a length of 50 mm in a pulling direction Z was obtained. No macroscopic defects were found.

Comparative Example 1 Lanthanum oxalate La ₂ (C ₂ O ₄ ) ₃ was fired at a temperature of 1050 ° C.
Lanthanum La ₃ Ga ₅ SiO ₁₄ was grown in the same manner as in Example 1 except that lanthanum oxide La ₂ O ₃ of the same quality as that of a general commercial product obtained by firing for 3 hours was used. As a result, an opaque crystal containing many fine cracks was grown.

Example 2 A langasite La ₃ Ga ₅ SiO ₁₄ crystal was grown under the same conditions as in Example 1 using a crystal growing apparatus without a monitoring window having the configuration shown in FIG. 15m above the raw material melt surface in the crucible
The temperature gradient up to 50 m is 2 ° C./mm (see part A in FIG. 7), and the temperature gradient up to 50 mm above is approximately 5 ° C./mm.
Met. No cracks, inclusions, or twins were found in the obtained crystals. The seeding operation was performed by a signal from the weight sensor, and the temperature of the crucible thermocouple was raised by about 25 ° C. to obtain the state shown in FIG.

[Comparative Example 2] In Example 2, only the structure of the furnace was changed to a refractory with a monitoring window (see Fig. 1), and the others were grown in the same manner. The temperature gradient from the surface of the raw material melt in the crucible to 15 mm above is 1
It was 7.8 ° C./mm (refer to the portion B in FIG. 7). The obtained crystal had a large crack, and a part of the grown crystal was broken and dropped into the raw material melt.

Example 3 A langasite La ₃ Ga ₅ SiO ₁₄ crystal was grown in the same manner as in Example 1 except that the atmosphere for growing the crystal was pure nitrogen, and a pale yellow-green crystal was obtained.

Example 4 In Example 1, the raw material gallium oxide Ga ₂ O ₃ was purified to a purity of 5%.
When the crystal was grown by replacing n (99.999%) high-purity raw material with a growth atmosphere of pure nitrogen, the obtained crystal was colorless and transparent, and no macroscopic defect was observed. When the impurities in the raw material were analyzed, the difference between Example 1 and Example 4 was the content of divalent cation impurities such as Zn, Ca, and Cu. In Example 1, the content was 12 ppm. In the case of Example 4, the difference was 4 ppm, and this difference is presumed to be related to coloring.

Example 5 When the light brown crystal obtained in Example 1 was heat-treated at 1000 ° C. for 8 hours in nitrogen, the color faded to pale yellow.

[0029]

According to the present invention, a langasite single crystal which has few macroscopic defects such as crystal cracks and inclusions, has little brown coloring, and is preferably used not only for piezoelectrics but also for optics can be reproduced. A method for growing a langasite single crystal that can be manufactured well is provided, and a high-quality langasite single crystal exhibiting excellent performance can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a hot zone (with a window) of a conventional CZ growing apparatus.

FIG. 2 is a schematic sectional view showing a hot zone (without window, with weight sensor) of the CZ growing apparatus according to the present invention.

FIG. 3 is a graph showing a change in weight signal during seeding (when raw materials are not dissolved).

FIG. 4 is a graph showing a change in weight signal during seeding (at an appropriate temperature).

FIG. 5 is a graph showing a change in a weight signal during seeding (at a low temperature).

FIG. 6 is a graph showing a change in weight signal during seeding (at a high temperature).

FIG. 7 is a graph showing the temperature gradient above the surface of the raw material melt (however, A represents a good case, and B represents an unsuitable case).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulated refractory (alumina) 2 Heating high frequency coil 4 Raw material melt 5 Crucible 6 Seed 7 Shaft 8 Growth crystal 9 Windowless refractory 10 Thermocouple 11 Window refractory 12 Weight sensor

Claims (7)

(57) [Claims] 1. A method for growing a langasite La ₃ Ga ₅ SiO ₁₄ single crystal, comprising the steps of: lanthanum oxalate La ₂ (C ₂ O ₄ )
_{3. A} method for growing a langasite single crystal, characterized by using lanthanum oxide La ₂ O ₃ obtained by firing ₃ at a temperature of 900 ° C. or less as a raw material. 2. The method of growing a langasite single crystal according to claim 1, wherein said lanthanum oxide is used as a raw material, and said langasite single crystal is grown by a CZ method (pulling method). 3. The method of growing a langasite single crystal by the CZ method according to claim 1, wherein the method comprises:
3. The langasite single crystal according to claim 2, wherein the temperature gradient in the range up to m is 2 ° C. ± 1 ° C./mm, and the temperature gradient up to 50 mm above is set to 8 ° C./mm or less. Training method. 4. The langasite single crystal according to claim 2, wherein the method for growing a langasite single crystal by the CZ method does not provide an opening for monitoring a growth state in the refractory for keeping heat at the upper part of the crucible. Training method. 5. A method for growing a langasite single crystal in which an opening for monitoring a growth state is not provided in the refractory for heat insulation, wherein a signal change from a weight sensor is performed regardless of observation from a monitoring window when performing a seeding operation. 5. The method of growing a langasite single crystal according to claim 4, wherein seeding is performed using only information. 6. The method of growing a langasite single crystal according to the CZ method, wherein a divalent cation impurity contained as an impurity in a crystal growth raw material is suppressed to 10 ppm or less. The method for growing a langasite single crystal according to any one of the above. 7. The method of growing a langasite single crystal according to claim 2, wherein said method of growing a langasite single crystal by the CZ method uses nitrogen as a crystal growth atmosphere gas.