CS266743B1 - Process for the production of monocrystals of monovalent mercury halides - Google Patents

Abstract

The purpose of the solution is to increase the quality of mercury halide single crystals, which enables their use as polarizers, acousto-optic filters, modulators, etc. The monovalent mercury halide in a closed ampoule, after evacuation and sealing, resublimates into a single crystal, while the single crystal is grown by crystallographically oriented growth, in which the growth direction deviates from the crystallographic direction (001), while the deviation is carried out in a plane deviated from the crystallographic direction (100) by an angle of 40° in both the positive and negative sense.

Description

The invention relates to a process for the production of single crystals of monovalent mercury halides intended for technical purposes in the field of optics, focusing on infrared optics and acousto-optical elements.

The production of single crystals of monovalent mercury halides for optical use was solved in the manner described in Czechoslovakia. U.S. Pat. No. 147,476, in which a monovalent mercury halide is sealed off from the outside environment, for example in a quartz glass ampoule, which is sealed, brought to a temperature of at least 120 DEG C. and then gradually cooled after reaching a system pressure of at least 2.0 Pa. to the crystallization temperature.

Monocrystalline halides of monovalent mercury show an extremely strong dependence of their physical properties. This is due to the fact that they are formed by linear molecules ^Η ^ 2 ^Χ 2 ^x halogen, ie F, Cl, Br or J), which are bound to each other only by very weak bonds. Thus, in the direction of the main crystallographic axis c, these are relatively strong ion-covalent bonds, while in the direction perpendicular, they are weak Vander Waals bonds. This fact is significantly reflected in all properties of Hg2 ^X 2 · ^{On the} one hand it is the cause of unique technically promising physical properties (high optical birefringence, anisotropy of elastic wave propagation speed, etc.), on the other hand it is difficult to prepare especially high quality single crystals, because fissility, elasticity, deformability, tendency to form internal defects, thermal conductivity, thermal expansion, etc. are extremely affected by crystallographic orientation. In the manufacturing method, the crystallographic orientation of single crystals Hg2X ₂ 3 ^e virtually random, therefore, are not sufficiently secure reproducible yields high quality single crystals and articles may comprise cracks, warping, optical inhomogeneity and other defects. This negative fact is manifested especially in the orientation, when the direction of the crystallographic axis c is deviated from the direction of growth by less than 5 °. This knowledge is taken into account in the production method according to PV 1678-87. However, this method only partially solves the above-mentioned problems, since it defines a suitable crystallographic orientation only with respect to the direction of the main crystallographic axis c, i.e. towards the direction (001), so that the crystallographic direction (001) deviates from the growth direction. _r ov „ _Λ ο o angle 5 to 90.

In practice, it has been shown that the elimination of the above-mentioned drawbacks is achievable by a fully defined crystallographic orientation, which is the purpose of the present solution.

The process for the production of monocrystalline mercury halide crystals according to the invention uses the process according to MS. U.S. Pat. No. 147,476, according to which monovalent mercury halide resublimates to a single crystal after evacuation and sealing in a closed ampoule, and the method according to PV 1678-87, according to which the crystallographic direction (001) deviates from the growth direction by an angle of 5 ° to 90 °. The essence of the invention lies in the fact that the deviation is performed in a plane deviated from the crystallographic direction (100) by an angle of 40 °, preferably 20 ° in the positive and negative sense.

In this way, optimal growth conditions can be achieved, since the crystallographic orientation is limited only to the preferred directions in which the above-mentioned defects do not occur during the growth and tempering of the crystals. The preparation of crystals is then better reproducible even in the production of bulk single crystals, the highest quality can be maintained in the entire product and the crystals can be used for even the most demanding applications in optics and acousto-optics. There is also a significant difference in the size of the crystals produced; according to the known method, the size of the crystals was up to 30 mm, the crystals produced according to the invention have a good quality even with a diameter of 50 mm. Yields of quality crystals also increased from 20% to 70%.

The essence of the invention, including the achievement of a higher effect, is clear from the exemplary embodiments, wherein the term crystallographic orientation means the direction of growth.

Example 1

A single crystal of mercuric chloride was grown on a crystal nucleus cut so that its crystallographic orientation deviated from the (001) direction by an angle of 90 ° and from the (110) direction.

CS 266 743 Bl by an angle of 45 °. The embryo was placed in an ampoule in which, after evacuation and sealing, calomel resublimation to a single crystal was performed. With the orientation thus specified, where the single crystal grows in the direction (100) and the growing area is the area (100), a calomel single crystal was prepared, from which the produced monolithic polarizer did not show Tyndall effect in either regular or extraordinary light beam and did not scatter light beam He- No laser even at a distance of 10 m.

Example 2.

The mercuric bromide single crystal was grown on a seed prepared in a growing vial at a given temperature gradient so that the growth direction was deviated from the direction (001) by 30 ° in the plane deviated from the direction (100) by an angle of 20 ° in the positive direction. The obtained single crystal was suitable as a starting material for the preparation of the acousto-optic modulator.

Example 3

The mercuric bromide single crystal was grown on a seed prepared in a growing vial at a given temperature gradient such that the growth direction was deviated from the (001) direction by 5 ° in the plane deviated from the (100) direction by an angle of 40 ° in the negative direction. The single crystal was suitable as a starting material for the preparation of acousto-optical deflectors.

The monovalent mercury halide crystals prepared according to the invention are intended for processing into polarizers, acousto-optical filters and modulators.

Claims (1)

OBJECT OF THE INVENTION A process for the production of monocrystalline mercury halide single crystals, in which the monovalent mercury halide resublimates to a single crystal after evacuation and sealing in a closed ampoule, the single crystal being grown by kstistalographically oriented growth, in which the crystallographic direction (001) deviates from the growth direction by 5 ° to 90 °. ° characterized in that the deviation is performed in a plane deviated from the crystallographic direction (100) by an angle of 40 °, preferably 20 °, in both positive and negative directions.