The discovery of a 2H–6H solid state transformation in Zn_xCd_1-xS single crystals

Abstract

Single crystals of Zn_xCd_1-xS have been grown from the vapour phase at 1100°C in the presence of H₂S gas. X-ray diffraction studies of the as-grown crystals show that polytypism and stscking faults occur in zn_xcd_1-x S crystals for x ≥slanted 0.94. It is observed that for 0.92 < x < 0.98 the 2H structure of zn_xcd_1-x S crystals transforms to a disordered 6H structure on annealing in vacuum around 600°C. For 0.95< x < 0.98 this 6H structure finally transforms to a disordered 3C structure on annealing further at higher temperatures around 800°C. The structural transformations occur through a non-random insertion of stacking faults, as revealed by the diffuse streak joining the X-ray diffraction maxima along the 10.L reciprocal lattice row. Experimental investigation of the diffuse intensity distribution, as recorded on a single crystal diffractometer from partially transformed single crystals, reveals that the mechanism of the transformation is very different from that reported for the same transformation in silicon carbide and cannot be described in terms of a single-parameter model of non-random deformation faulting.