RU2291919C1 - Method for growing lithium iodate monocrystal out of solution at continuous drawing of grown crystal outside growth chamber - Google Patents

Abstract

FIELD: processes for producing oriented mono-crystals used in laser physics, acoustic electronics, optronics for realizing piezoelectric and non-linear optical effects.

SUBSTANCE: method is realized by growing lithium iodate mono-crystal of hexagonal modification for seeding z-cut of predetermined shape by isothermal evaporation of aqueous solution of lithium iodate. Seed fastened to drawing mechanism is arranged inside and near lower cut of respective profiled tube introduced into growth chamber and extending by its upper cut outside said chamber for further as crystal growing drawing crystal through said tube outside growth chamber. At period of mono-crystal growing mother liquor may be replenished.

EFFECT: possibility for growing mono-crystals practically of non-limited size with predetermined high purity degree and structural uniformity.

2 cl, 1 dwg, 2 ex

Description

The invention relates to methods for producing lithium iodate single crystals, including profiled, used in laser physics, acoustoelectronics, optoelectronics for the implementation of piezoelectric and nonlinear optical effects and allows you to switch from traditional periodic technological processes of growing single crystals from aqueous and other solutions to continuous technological processes upon receipt of inorganic materials of a given high degree of purity and structural homogeneity.

A known method of growing single crystals with feeding the mother liquor (Crystallography, 1961, t.6, issue 1, s.146). The closest in technical essence and the achieved result is a method of growing single crystals of lithium iodate, including profiled, hexagonal modification to the seed of a z-section of a given shape by isothermal evaporation of an aqueous solution of lithium iodate (SU 1605584, Mcl. C 30 V 7/02, 29/22, 04/27/1996). For these methods, as well as for all existing methods of growing single crystals from solutions, the limited working (production) cycle is characteristic. Indeed, in the processes of growing single crystals during isothermal evaporation of the solvent, the duration of the working cycle is limited by a fixed volume of the mother liquor in the growth chamber of the crystallizer. In the processes of growing single crystals associated with controlling the temperature of the mother liquor, the restriction is determined not only and not so much by the amount of dissolved substance, but by the width of the real allowable temperature range for this substance. The use of solid-phase or liquid-phase feeding of the mother liquor allows to slightly increase the duration of the growing process and the size of the obtained single crystal. But in this case, the process is limited in its duration by the volume of the growth chamber and the existing specific supply of recharge.

In addition to these fundamentally irreparable defects, each of the above processes also has other serious systemic defects. Without exception, all modern processes of growing single crystals from solutions are inevitably associated with a complex organizational technological structure. This structure includes the preparation of crystallizer equipment, the preparation of the mother liquor and the seed, the development of the mode of formation of a single crystal at the initial stage and its subsequent growth, etc. up to the development of the evacuation mode of the finished single crystal from the growth chamber of the mold. In all cases, the end of the process and the extraction of the single crystal from the growth chamber is accompanied by the complete dismantling of the mold.

Repeated transition from one technological operation to another, periodic dismantling of the mold is inevitably associated with overcoming many transition states, the mechanisms of which in successive production cycles can differ from each other and result in differences in the structure and properties of the grown single crystals. Another group of defects in the crystal structure is formed directly inside each individual production cycle and is associated with the fundamental instability of the following technological parameters:

- the amount of the mother liquor decreases monotonically with crystal growth. In this case, the level of the mother liquor in the growth chamber is constantly reduced, which constantly changes the nature of the circulation of the solution,

- the chemical composition of the mother liquor is continuously changing, in which the amount of solvent (and solute) decreases, and the content of associated microimpurities changes,

- as well as a number of other process parameters.

The technical result of the invention is to create a continuous process for producing single crystals of constant cross section with a given crystallographic orientation, eliminating the periodic dismantling of the mold and the repetition of numerous intermediate operations. It is provided by the proposed method of growing a single crystal of lithium iodate of hexagonal modification into a z-section seed of a given shape by isothermal evaporation of an aqueous solution of lithium iodate, in which a seed bonded with a pulling mechanism is placed inside and near the lower edge of the corresponding shaped tube inserted into the growth chamber and leaving the upper a cutoff beyond its limits, followed by, as it grows, pulling the growing crystal through this tube outside the growth chamber.

During the growth of a single crystal, they can also continuously feed the mother liquor.

The invention is illustrated in the drawing, which shows the main elements and devices that allow to achieve the necessary technical result.

The method is as follows. The pulling device 1 is connected to the seed 3 and the growing crystal 4 moves them from the growth chamber 5 through the profiled (evacuation) tube 2 outside the growth chamber. The drawing speed is equal to the linear crystallization rate. Synchronously with the movement of the seed with the growing crystal from the feed device 6, the corresponding amount of liquid feed enters the growth chamber 5. The level of the mother liquor in the growth chamber remains strictly constant throughout the entire process of drawing a single crystal from the solution.

An essential design feature of the proposed method for growing single crystals is the presence of a special profiled (evacuation) tube connecting the growth chamber with the space outside the growth chamber. The initial location of the seed (and subsequently the lower edge of the growing crystal) near the lower edge of the shaped tube ensures the stability of crystallization conditions. A pulling device allows you to continuously move the growing crystal outside the growth chamber through a profiled tube, ensuring the continuation of the continuous technological process, and also allows partial cutting of the grown crystal. The drawing speed is continuously adjustable over a wide range and corresponds to the actual crystallization rate. The feeding device maintains the mother liquor in the growth chamber at a constant level.

The described method behaves as a completely stable one-stage technological process proceeding in the optimal mode, which provides it with a number of serious advantages:

- almost unlimited size of the grown crystals in the direction of drawing;

- high stability of technological parameters (quantity and level of mother liquor);

- the possibility of growing single crystals of high purity due to the achievement of significant degrees of crystallization treatment;

- the ability to control the composition of the grown crystals in a wide range due to the doping of the mother liquor through a feeding device;

- allows you to get on one single crystal as it is pulled out of the solution sections with different impurities and their concentrations due to the introduction of doping impurities of a given composition into the growing crystal along with a recharge solution;

- it is possible to use modern control computers with the aim of almost completely automating the process of growing single crystals from aqueous solutions;

- significantly increases the yield of a monocrystal volume suitable for further use. This occurs due to an almost unlimited change in the ratio between the initial 7, containing defects (capture of the mother liquor, etc.), the regeneration zone - the "phantom", and the subsequent perfect volume of the single crystal 4.

The method is illustrated by the following examples.

Example 1

Single crystals of hexagonal modification of lithium iodate were drawn from an aqueous saturated LiIO ₃ solution at a temperature of 40 ° C using flat rounded seeds with a thickness of 2 mm and a diameter of 15-16 mm, made from z-sections of a single crystal of lithium iodate, which were placed near the lower edge of the shaped (evacuation) tube. In this case, round shaped tubes with a diameter slightly larger than the diameters of the seeds were used as profiled tubes. The growth chamber used was equipped with a thermostat and worked in the isothermal evaporation mode with continuous controlled condensate extraction. As it grew, the single crystal with the seed was drawn using a special drawing device inside the profiled (evacuation) tube, and then through its extension beyond the growth chamber, while the growth chamber was maintained at a constant level of the mother liquor by feeding a saturated solution of the basic substance.

The grown crystals had sizes from 15.5 to 16.5 mm in cross section and reached a length of 50-60 mm for a growth period of about 45 days, which corresponds to a linear crystallization rate of about 0.8 mm, which is slightly higher than the crystallization rates commonly used for growing crystals of lithium iodate. The single crystals drawn from the solution, preserving the natural faceting, had a light hatching on the surface similar to the hatching of single crystals grown by melt drawing (silicon, lithium niobate, etc.). In volume, the obtained single crystals did not have defects visible to the naked eye.

Example 2

Profiled single crystals of lithium iodate were grown under the conditions and method described in the previous example with the following changes:

- used rectangular seeds made of z-slices of a single crystal of lithium iodate single crystal with dimensions of 5 × 20 × 2 mm

- the seed was placed near the lower edge of the profiled (evacuation) tube, the cross section of which corresponded to the shape of the seed (i.e. rectangular).

As in the previous example, single crystals were obtained by drawing, but already profiled. The shaped crystals, as in the previous example, had a slight hatching on the outer prismatic surface, but the single crystals had no defects visible to the naked eye inside the volume. When the shaped crystals were drawn, an increased linear growth rate was also observed, slightly exceeding the generally accepted parameters when growing lithium iodate single crystals.

Claims (2)

1. A method of growing single crystals of lithium iodate of hexagonal modification by seed of a z-section of a given shape by isothermal evaporation of an aqueous solution of lithium iodate, characterized in that the seed bonded with a pulling mechanism is placed inside and near the bottom edge of the corresponding shaped tube inserted into the growth chamber and exiting top edge beyond its limits, followed by growth by pulling the growing crystal through this tube outside the growth chamber. 2. The method according to claim 1, characterized in that in the process of growth of single crystals carry out continuous feeding of the mother liquor.