Structural Fluctuations and Thermophysical Properties of Molten II-VI Compounds

Recently, in support of the microgravity experiment entitled "Crystal Growth of Selected 11-VI Semiconducting Alloys by Directional Solidification," the viscosity of HgZnTe pseudobinary melt was measured using an oscillating-cup viscometer at NASA/Marshall Space Flight Center (MSFC). An unexpected time drift of the measured viscosity, which shows a slow relaxation phenomena at temperatures near the liquidus point, was reproducibly observed. Two sets of data were obtained by cooling the Hg(0.84)Zn(0.16)Te melt from 850 C and stabilizing at temperatures of 790 C, which is just above the liquidus temperature, and stabilizing at temperature of 810 C. While it took one day to reach equilibration at 810 C, five days were required at 790 C A similar relaxation phenomenon was also observed in the measured density of the same liquid. Furthermore, in the density measurements of the HgCdTe melts, which is the pseudobinary system studied in another flight experiment entitled "Growth of Solid Solution Single Crystals," a negative thermal expansion was reported. The liquid density increases from the liquidus point to a maximum value at a temperature approximately 700 C above the liquidus, where normal thermal expansion progressively resumes.