Method of growing optically transparent single crystals of terbium-gallium garnet

FIELD: technological process.

SUBSTANCE: invention is related to the field of crystals growing and may be used in electronic, chemical industries, in jewelry-making. Method consists in melting of primary stock, seeding onto rotating primer, growing of crystal conical part and crystal pulling. As primary stock mixture of terbium and gallium oxides mixture, after conical part growing has been commenced, the speed of single crystal pulling from melt is reduced according to the following dependence vL=v0-kL, where vL - speed of pulling at crystal length L, mm/hr, v0 - speed of pulling at the beginning of crystal conical part growing, which is equal to 2-7 mm/hr, L - current value of crystal length, mm, k - proportionality constant, which is equal to 0.1-0.2, at that angle of conical part growing is at least 140°.

EFFECT: allows to prepare homogeneous crystals with minimum concentration of defects and increased output of available cylindrical part.

1 ex

 

The invention relates to single crystal growth and can be used for growing single crystals of garnet, more specifically of single crystals of the terbium-gallium garnet, used, for example, in laser technology, magnetic microelectronics, for jewelry purposes.

A method of obtaining single crystals of gadolinium-gallium garnet, described in the author's certificate of the USSR No. 1453960, 08.10.1986, which includes the melting of the source charge and persecution on a seed crystal at its rotation speeds of 30-40 rpm Then without changing speed, raise the neck length of at least 15 mm and a diameter not exceeding 15 mm with a speed of extrusion from 7-10 mm/h in the early to 1.5-2.5 mm/h at the end of the neck. Then, without changing the rate of withdrawal, reduce the speed on the proposed dependence. After reaching the cylindrical part of the speed of extrusion increases to 2.6-7.0 mm/H. the Obtained crystals weighing up to 11-13 kg, with a length of cone 18 mm and an angle of razresevanja cone 140°; reductions in speed are dependencies

,

where ω - the current value of the rotation speed, rpm;

ωto- speed rotation on the cylinder R/min;

ω0- the speed of rotation of the seed during the persecution, Rev/min;

L is the actual length of the crystal, mm;

Lto- the length of the crystal, which reduces the rotation speed, mm;

L0- the length of the crystal before the speed change, mm;

n is a dimensionless factor of 1.5-2.0.

The crystal is grown to mass 11-13 kg, the density of defects in the crystal 0-3 cm-2.

From the author's certificate of the USSR No. 1347513, priority 29.11.1985, there is a method of growing single crystals of gadolinium - gallium garnet. The single crystals are grown from the melt on a rotating seed. Tapered portion of the single crystal pulling speeds of 3-7 mm/h to change the shape of the crystallization front. Then the speed of extrusion is reduced according to the law Vt=Vto-αL, where VtoVt- speed drawing the conical part of the single crystal before and after changing the shape of the crystallization front, respectively, mm/h; L is the length of the conical part of the single crystal after changing the shape of the crystallization front, mm; α=0,01-0,12 - factor, chosen experimentally, mm-1.

Data in a known manner to receive the single crystals of gadolinium-gallium garnet with a yield of single crystals with a diameter of 105 to 110 mm with a density of defects in the crystal structure ≤7 cm-2.

A known method of growing optically transparent single crystals of the terbium-gallium garnet by the Czochralski method, comprising melting and the output of the charge, the persecution of the rotating seed, razresevanje conical part of the crystal and the pulling of the crystal (prototype) (application of Japan No. 54150377 from 26.11.1979).

This way we obtain the single crystals of large size and high quality. This is achieved by regulating the speed of rotation of the rod on which are mounted the seed crystal and the grown crystal. As the growing speed of rotation of the rod is reduced in proportion to the value of K is equal to H/D, where H is the height of the remaining melt, D is its diameter. The optimum speed of rotation of the rod is found from the equation:

Wc=ak+b

Where a and b are constants determined experimentally.

However, this method does not allow to obtain an increased yield by weight and the length of the crystal.

The technical objective of the claimed invention to provide an optically transparent crystal terbium-gallium garnet, homogeneous, with a minimum concentration of defects, with increased output.

The goal of the project is achieved by the production method of optically transparent single crystals of the terbium-gallium garnet by the Czochralski method, comprising melting the initial charge, the persecution of the rotating seed, razresevanje conical part of the crystal and the pulling of the crystal, and according to the invention as a source blend a mixture of the seeds of terbium and gallium, after the beginning of razresevanja conical part, reduce the speed of pulling the single crystal from the melt according to the following dependencies:

νL0-kL

where νL- speed drawing at the length of the crystal L, mm/h;

ν0- speed drawing at the beginning of razresevanja cone crystal, equal to 2-7 mm/h;

L is the actual length of the crystal, mm;

k - coefficient of proportionality equal to 0.1 to 0.2,

when this angle razresevanja tapered portion is not less than 140°.

The size of the single crystal of terbium-gallium garnet:

- the length of the cone crystal - 10-20 mm

- the mass of the crystal - 4-8 kg;

Technical characteristics of the process:

The speed of rotation of the seed - 2-10 rpm;

The growth of the crystals is 20-40 hours

The speed of extrusion ν0from 2 to 7 mm/hour.

The value of k (constant of proportionality) is chosen experimentally, and its values are in the range of 0.1-0.2.

The upper limit of razresevanja, for example, equal 170°.

The pulling of crystals is carried out in an inert atmosphere such as nitrogen with the addition of oxygen.

When growing single crystals with angle razresevanja more than 140° and, using the above dependence of the rate of withdrawal from the length of the cone are optically transparent crystals of terbium-Galli is the first grenade with homogeneous optical properties, with a minimum concentration of defects, with the yield of the cylindrical part, to 15% more than standard growing conditions.

Below is a specific example illustrating the invention, but not limiting it.

Example. The single crystals produced by Czochralski method. In the crucible (iridium or platinum) download granulomatous components is a mixture of oxides of terbium and gallium, for example in the ratio of 54.0 wt.% oxide terbium and to 46.0 wt.% gallium oxide. The charge is melted by heating (high frequency) of the crucible and pull the oriented crystals on a seed crystal in an atmosphere of inert gas containing oxygen. Seed rotate at a speed of 2 rpm When you touch the seed of the melt is persecution, then start moving the seed upwards with a speed of 3 mm/hour, before pulling cone crystal.

After the beginning of the growth cone, the speed of extrusion is reduced and it is determined in accordance with the relationship:

νL(mm/hour)=3(mm/hour) of 0.1(1/h)×L mm.

The current value of the crystal length L is, for example, 10-20 mm

Get the single crystal GTG good optical quality with angle razresevanja tapered portion 145° with an absorption coefficient of 0.5×10-4containing no optical defects and the yield of the cylindrical part, 15% CR is exceeding the standard growing conditions.

The single crystals used in optical and laser technology, for example for the manufacture of Faraday rotators and isolators.

The method of growing an optically transparent single crystals of the terbium-gallium garnet by the Czochralski method, comprising melting the initial charge, the persecution of the rotating seed, razresevanje conical part of the crystal and the pulling of the crystal, characterized in that as the initial mixture, a mixture of oxide of terbium and gallium, after the beginning of razresevanja conical part, reduce the speed of pulling the single crystal from the melt according to the following dependencies:

νL0-kL

where vL- speed drawing at the length of the crystal L, mm/h;

v0- speed drawing at the beginning of razresevanja the conical part of the crystal is equal to 2-7 mm/h;

L is the actual length of the crystal, mm;

k - coefficient of proportionality equal to 0.1 to 0.2,

when this angle razresevanja tapered portion is not less than 140°.



 

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