Mechanism of solid state transformations in single crystals of Zn_xCd_1-x

Abstract

The mechanism of solid state transformations in single crystals of Zn_xCd_1-x is investigated by annealing metastable 2H crystals at different temperatures, arresting the solid state transformation by quenching in cold water, and examining the structure of the intermediate state by X-ray diffraction. In the range x = 0.93 to 0.95, the 2H structure is found to transform to a disordered 6H structure at temperatures around 600 °C. This 6H structure does not transform further to the 3C structure on annealing at higher temperatures. It is observed that the mechanism of the 2H to 6H transformation in these crystals is very different from that proposed by Pandey, Lele, and Krishna for a similar transformation in Sic. A model of transformation involving the non-random insertion of stacking faulhs is developed using a fault probability α for random nucleation of the 6H phase and a fault probability β for the growth of the 6H nuclei. The diffraction effects calculeted from such a model for both, deformation faults and layer-displacement faults are compared with those recorded on a single crystal diffractometer using partially transformed crystals. It is concluded that the model of transformation by a non-random insertion of deformation faults with β » α, closely approximates the actual mode of transformation in these crystals.