Abstract: Gravitational phenomena, including convection, sedimentation, and interactions of materials with their containers all affect the crystal growth process. If they are not taken into consideration they can have adverse effects on the quantity and quality of crystals produced. As a practical matter, convection and sedimentation can be completely eliminated only under conditions of low gravity attained during orbital flight. There is, then, an advantage to effecting crystallization in space. But in the absence of of convection in a microgravity environment cooling proceeds by thermal diffusion from the walls to the center of the solution chamber. This renders control of nucleation difficult. Accordingly there is a need for a new and improved nucleation process in space. Herein crystals are nucleated by creating a small localized region of high relative supersaturation in a host solution at a lower degree of supersaturation.

Abstract: Hg.sub.1-x Cd.sub.x Te is prepared in an improved directional solidification method in which a precast alloy sample containing predetermined amounts of Hg, Cd and Te is disposed in a sealed ampule (12) and a furnace (10) providing two controlled temperature zones (16, 18) is translated upward past the ampule so as to provide melting and resolidification. The present improvement is directed to maintaining the zones at temperatures determined in accordance with a prescribed formula providing a thermal barrier (32) between the zones with a maximum thickness and translating the furnace past the zones at a rate less than 0.31 .mu.m/sec.

Abstract: Process and apparatus for growing crystals using float zone techniques. A rod (34) of crystalline materials is disposed in a cylindrical container (36), with a space being left between the rod and container walls. The space is filled with an encapsulant (72), selected to have a slightly lower melting point than the crystalline material. The rod is secured to a container end cap (38) at one end and to a shaft (60) at its other end. A piston (64) slides over the rod and provides pressure to prevent loss of volatile components upon melting of the rod. Prior to melting the rod the container is first heated to melt the encapsulant, with any off-gas from this step being vented to a cavity behind the piston. The piston moves slightly forward owing to volume change upon melting of the encapsulant, and the vent passageway (74) is closed. The container is then moved longitudinally through a heated zone (32) to progressively melt sections of the rod as in conventional float zone processes.

Abstract: A crystal growth apparatus (10) having a heated spherical growth container (12) is filled with a crystalline material in solid or liquid form. The crystalline material is heated by resistance heating wire (58) to a predetermined temperature, whereupon the application of heat to the crystalline material is reduced and the accumulated heat is drawn off and dissipated by a seed crystal (76) attached to a rod (70) of heat conductive material, which in turn is attached to a heat dissipating member (72). This results in the formation of a single, defect-free crystal on seed crystal (76), which grows outward in a generally spherical configuration as more heat is removed.

Abstract: A method of preparing pseudobinary mercury, cadmium, telluride (HCT) crystals by controlled crystal growth in a fused silica ampule uses a modified Bridgman-Stockbarger method. In this method, the alloy is cast into one end of the ampule, inverted, heated to a temperature between the liquidus and solidus temperatures of the alloy and directionally solidified in a two zone furnace. The parameters of the solidification treatment are controlled according to the formulaT.sub.U.sup.4 -T.sub.I.sup.4 =T.sub.I.sup.4 -T.sub.L.sup.4,where T.sub.U =the temperature of the furnace upper zone, T.sub.L =the temperature of the furnace lower zone, and T.sub.I =the solidus temperature of the crystal composition. The rate of transfer of the crystal through the furnace and the size of the zone barrier are also controlled. The modified method imparts homogeneity to the crystal composition, both axially of the crystal and radially. The crystals produced by the method have superior properties and a much higher yield.