JPH07100640B2 - Single crystal manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a single crystal, and more particularly to a method for producing a single crystal with less transition of refractory metal compound and sub-microcrystals by a floating zone method.

(Prior Art and Its Problems) High melting point metal compounds such as transition metal carbides, carbonitrides, diborides and hexaborides having a calcium hexaboride type crystal structure all have high hardness. And is used for various purposes. For example, carbides and carbonitrides of transition metals are considered to be promising as electronic materials, especially field emitters, in addition to being used as cermets for various cutting tools, wear-resistant parts and the like. Further, the transition metal diboride is being developed for applications such as cutting tools and high temperature structural members. Among the rare earth element hexaborides, lanthanum hexaboride has a low work function and a low vapor pressure at high temperatures, and is therefore used as a high-intensity thermionic electron source.

Flux method, floating zone method and the like are known as methods for growing single crystals of these refractory metal compounds. In particular, the floating zone method is suitable as a method for growing a large-sized single crystal of high quality, and various proposals have been made.

For example, Ceramics Vol. 11, No. 12, p. 1083 (1976) describes a method of growing a single crystal of a hexaboride such as LaB ₆ or a diboride such as ZrB ₂ by a floating zone method by high frequency induction heating. There is. Also, J. Less-Com
m. Metal, vol. 82, p. 63 (1981), a method for growing a single crystal of a transition metal carbide such as TiC by a high frequency induction heating floating zone method is disclosed. It has been reported that in these methods, the oscillation frequency of the high-frequency coil is 200 KHz, and the obtained crystal ingot has a large number of sub-fine crystals of about 1 to 2 mm ³ . For the above-mentioned various uses, it is desired to reduce the amount of sub-fine crystals in the crystal rod obtained by the floating zone method as much as possible.

(Technical Means for Solving Problems) The present invention provides a method for producing a single crystal of a refractory metal compound which satisfies the above-mentioned needs.

The present invention, when producing a single crystal of a refractory metal compound selected from carbides and carbonitrides of a transition metal having a NaCl type crystal structure by a floating zone method by high frequency induction heating, an oscillation frequency of a high frequency coil of 250 KHz ~ 1MHz
And the ratio of the length to the diameter in the fusion zone of the sintered rod made of a high melting point metal compound is 0.4 to 1.2.

Examples of the refractory metal compound used in the present invention include transition metal carbides and carbonitrides having a NaCl type crystal structure.

Specific examples of the transition metal carbide having a NaCl type crystal structure include TiC, ZrC, HfC, VC, NbC and TaC, and specific examples of the carbonitride include TiC _x N _y , ZrC _x N _y , HfC _x N _y , VC
_{and xN y} , NbC _x N _y and TaC _x N _y . In the above,
x <1, y <1, and x + y ≦ 1.

These refractory metal compounds are subjected to a treatment by a floating zone method after being sintered into a rod shape by a conventional method.

In the present invention, the oscillation frequency of the high frequency coil is 250 KHz, ~
It is 1 MHz, preferably 300 to 700 KHz. Oscillation frequency is 250
If it is less than KHz, the polycrystal skin that is inevitably formed on the surface of the grown crystal rod becomes thick and the amount of sub-microcrystals in the central single crystal region increases. When the oscillation frequency exceeds 1MHz,
It is difficult to grow a uniform single crystal because only the surface of the supply sintered rod is melted and the central portion is not melted.

The ratio of the length to the diameter in the fusion zone of the sintered rod made of a high melting point metal compound is 0.4 to 1.2, preferably 0.5 to 1.0. If this ratio is smaller than 0.4, the central portion of the feed sintered rod will not be sufficiently melted, and the solid-liquid interface will be too convex toward the melted portion side, and a uniform single crystal cannot be manufactured. If the above ratio exceeds 1.2, the length of the fusion zone becomes too long, the interface shape becomes concave toward the fusion zone, and a large number of particles are generated, making it difficult to obtain a single crystal.

An example of the floating zone method according to the present invention will be described with reference to FIG. 1 showing an outline of an apparatus used.

A rod-shaped sintered body with a holder 2 attached to a rotating shaft 1.
3A and 3B are supported. High frequency coil 4 to 250KHz ~ 1M
A high frequency within the range of Hz is generated, and the rod-shaped sintered body 3A is melted by induction heating to form a melting zone 5 having a ratio of length to diameter within the range of 0.4 to 1.2. While controlling the melting of the rod-shaped connecting body 3A at the upper end of the melting zone 5 and the precipitation of the rod-shaped single crystal 6 at the lower end of the melting zone 5, the rod-shaped sintered body 3A held by the holder 2 is gradually moved downward. By doing so, the rod-shaped single crystal 6 is grown. The moving speed of the holder 2 is preferably 3 to 30 mm / hr.

(Effects of the Invention) According to the present invention, both the transition density and the fine crystal density can be reduced to 1/5 to 1/10 as compared with a single crystal obtained by a known floating zone method. .

(Example) An example is shown below. Single crystals were manufactured using the apparatus shown in FIG. 1 in Examples and Comparative Examples.

Example 1 After mixing TiC powder and graphite powder, the mixture was made to have a diameter of 12 m.
Two cylinders of m, length 130 mm and length 50 mm were molded by a rubber press. These cylinders were sintered in vacuum at 1800 ° C. for 30 minutes to obtain rod-shaped sintered bodies A and B having a C / Ti atomic ratio of 0.99.

The rod-shaped sintered body A was supported on the holder 2 with the rod-shaped sintered body A on the upper side and the rod-shaped sintered body B on the lower side, and a graphite disk having a thickness of 1 mm was sandwiched between the end contact surfaces of both sintered bodies.

In a helium gas atmosphere with a total pressure of 8 atm, at the oscillation frequency of the high-frequency coil of 500 KHz, the contact portion between the rod-shaped sintered body A and the graphite disk is melted to form a melted portion, and the diameter of the melted portion is 10.0 m.
With both m and length of 6.5 mm, both sintered rods were moved downward at 6 mm / hr and rotated at 10 rpm. The rod-shaped sintered body A melted into the melting zone, and a single crystal with C / Ti of 0.96 was grown in the lower portion of the melting zone.

In order to investigate the quality of the obtained crystal rod having a diameter of 10.5 mm and a length of 60 mm, the (100) plane was cleaved and the cleaved surface was etched with a hydrofluoric nitric acid solution to measure the transition density and the sub-fine crystal density.
The dislocation density is 10 ⁴ / cm ² , the secondary crystallite density is 10 pieces / cm ² ,
It was found that the crystal rod was a good quality single crystal.

Comparative Example 1 The same method as in Example 1 was repeated except that the oscillation frequency of the high frequency oscillation coil was 150 KHz. The obtained crystals had a transition density of 10 ⁶ / cm ² and a sub-fine crystal density of 200 crystals / cm ² .

Example 2 The composition of the rod-shaped sintered bodies A and B was changed to ZrC _0.7 N _0.3 , the composition of the atmosphere gas was changed to a mixed gas of helium partial pressure of 9.5 atm and nitrogen partial pressure of 0.5 atm, and the oscillation frequency was changed to 700 KHz. The same method as in Example 1 was repeated except for the above.

The composition of the obtained crystal rod having a diameter of 10 mm and a length of 70 mm was ZrC _0.65.
N _0.2 , transition density 5 × 10 ⁴ / cm ² , sub-crystallite density
There were 20 pieces / cm ^2, and it was found that the above crystal rod was a good quality single crystal.

Comparative Example 2 Example 2 except that the diameter of the fusion zone was changed to 10 mm and the length was changed to 15 mm.
The same method was repeated. The transition density of the obtained crystal is 10
^The density of secondary crystallites was ⁷ / cm ² , and the number of secondary crystallites was 250 grains / cm ² .

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of an apparatus for carrying out the present invention. 3A, 3B ... Rod-shaped sintered body, 4 ... High-frequency coil 5 ... Melting zone 6 ... Rod-shaped single crystal

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP 60-226495 (JP, A) JP 59-146998 (JP, A) JP 60-6915 (JP, B2) JP 58- 14399 (JP, B2)

Claims (1)

[Claims] 1. An oscillation frequency of a high frequency coil is 250 KHz when a single crystal of a refractory metal compound selected from carbides and carbonitrides of a transition metal having a NaCl type crystal structure is manufactured by a floating zone method by high frequency induction heating. ~ 1M
A method for producing a single crystal, characterized in that the ratio of the length to the diameter in the fusion zone of the sintered rod made of a high melting point metal compound is set to 0.4 to 1.2 in Hz.