JPH0474319B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) This invention relates to a method for producing a single crystal, particularly a Bi ₁₂ SiO ₂₀ single crystal or Bi ₁₂ GeO ₂₀ using a pulling method.
This invention relates to a method for producing a single crystal. (Prior art) Bi ₁₂ SiO ₂₀ single crystal or Bi ₁₂ GeO ₂₀ single crystal, etc., have been known as single crystals that have both the Faraday effect and the Pockels effect. After heating and melting, a seed crystal attached to the tip of a pulling shaft is immersed in the molten raw material, and the material is gradually pulled up while rotating the pulling shaft, which is the so-called pulling method. In growing single crystals using the above technology, in order to dissipate the latent heat generated at the solid-liquid interface,
It is necessary to form a relatively steep temperature gradient directly above the melt, i.e. around 10 mm above the melt surface, but if this temperature gradient is too large, the growth of foreign crystal phases is inevitable, and cracks occur at the top of the pulled single crystal. Due to problems such as
It was common to set the temperature to 40°C/cm. (Problem to be solved by the invention) By the way, when producing single crystals such as Bi ₁₂ SiO ₂₀ and Bi ₁₂ GeO ₂₀ , simply applying the conventional technology will result in the growth of several to several crystals, especially in the shoulder region of the grown single crystal. ten μ
There were problems such as easy generation of bubbles and separation of the single crystal and the melt during the growth process. It is an object of the present invention to solve the above-mentioned conventional problems and to provide a new method capable of obtaining high-quality single crystals free of internal defects and cracks. (Means for solving the problem) This invention applies a pulling method to produce Bi ₁₂ SiO ₂₀ or
In producing a single crystal of Bi ₁₂ GeO ₂₀ , the temperature gradient from the melt surface in the crucible charged with the raw material for the single crystal to 10 mm above the pulling direction of the single crystal is set at 50 to 75°C/cm. to be adjusted to, followed by
This method of producing a single crystal is characterized by adjusting the temperature gradient up to 150 mm to 10° C./cm or less. First, 10 mm above the melt surface in the crucible.
The reason for regulating the temperature gradient between 50 and 75℃/cm is that if the temperature gradient from the melt surface to 10mm is less than 50℃/cm, the heat generated at the solid-liquid interface will not dissipate. 75
This is because if the temperature exceeds .degree. C./cm, a crystal phase different from the desired crystal tends to grow due to volatilization of Bi ₂ O ₃ . Further, the temperature gradient in the subsequent 150 mm is set to 10° C./cm or less because cracks are likely to occur if the temperature gradient in this region exceeds 10° C./cm. (Operation) In this invention, according to the above conditions, Bi ₁₂ SiO ₂₀
Alternatively, since a single crystal of Bi ₁₂ GeO ₂₀ is grown, the obtained single crystal does not have any bubbles or cracks, and the desired goal can be advantageously achieved. In order to realize the temperature gradient according to the present invention in the single crystal growth process, for example, _{in FIG} . It is preferable that the distance 1 between the crucible 3 and the after-heater 8 made of platinum, which controls the temperature gradient, be set to 20 to 50 mm, more preferably 25 to 40 mm, using a spacer 9 such as ceramic. (Example) Example 1 The crucible of the growth furnace shown in Figure 1 above (outer diameter 150
After charging 14 kg of Bi ₁₂ SiO ₂₀ sintered body into a sintered body (mm, height 150 mm), the above sintered body was melted by high-frequency induction heating, and the melt was maintained at 900°C as shown in Table 1. Under the conditions, the diameter is 60mm and the straight body length is 100mm.
A single crystal of Bi ₁₂ SiO ₂₀ was grown and the quality of the obtained single crystal was investigated. The results are also shown in Table 1. In addition, a <100> oriented seed crystal was attached to the tip of the pulling shaft.

[Table] In the growth of Bi ₁₂ SiO ₂₀ single crystal according to this invention,
There was no problem of the crystal separating from the melt during growth, and a high-quality single crystal without defects such as cracks or bubbles could be obtained. Also, cutting this single crystal,
After polishing, it was placed between orthogonal nicols and observed, and no internal distortion was observed. On the other hand, in the case of growing single crystals in comparative examples, it was confirmed that the crystal and melt separated during the growth, that cracks were generated, and that bubbles were present, making it impossible to obtain high-quality single crystals. . Example 2 Bi ₁₂ GeO ₂₀ was placed in a crucible of a growth furnace similar to Example 1.
After charging 14 kg of the sintered body, the sintered body was melted by high-frequency induction heating, and while maintaining the melt at 930°C, it was heated to a diameter of 60 mm and a straight body part under the conditions shown in Table 2.
A Bi ₁₂ GeO ₂₀ single crystal of 100 mm was grown and the quality of the obtained single crystal was investigated. The results are also shown in Table 2.

[Table] In growing the Bi ₁₂ GeO ₂₀ single crystal according to the present invention, the crystal does not separate from the melt during the growth process, and a single crystal of good quality without defects such as cracks or bubbles can be obtained. Ta. After cutting and polishing, this single crystal was placed between crossed Nicols and observed, but no internal strain was observed. On the other hand, in the comparative example, although the crystal and the melt did not separate during single crystal growth, it was confirmed that cracks occurred and bubbles were present, making it impossible to obtain a high quality single crystal. . (Effect of the invention) Thus, according to this invention, Bi ₁₂ SiO ₂₀ or
It advantageously avoids the separation of the crystal and melt during the growth process of Bi ₁₂ GeO ₂₀ single crystal, as well as defects such as bubbles, cracks, and thermal distortion, resulting in higher quality single crystals, improved yields in crystal manufacturing, and production. It is possible to significantly increase sexual performance.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the cross-sectional structure of a growth furnace. 1... Melt, 2... Single crystal, 3... Platinum crucible, 4... Refractory, 5... Refractory, 6... Pulling shaft, 7... High frequency coil, 8... Platinum after heater , 9...Spacer.

Claims (1)

[Claims] 1 Bi ₁₂ SiO ₂₀ or Bi ₁₂ GeO ₂₀ by applying the pulling method
When producing a single crystal, the temperature gradient from the melt surface in the crucible charged with the raw material for the single crystal to 10 mm above the pulling direction of the single crystal should be adjusted to 50 to 75°C/cm. , followed by a temperature gradient of 10 to 150 mm.
A method for producing a single crystal characterized by adjusting the temperature to ℃/cm or less.