Structural disorder and solid state transformations in single crystals of Zn x Cd1−x S and Zn x Mn1−x S

Abstract

Single crystals of Zn x Cd1−x S and Zn x Mn1−x S were grown from the vapour phase at 1100°C in the rangex=0·9 to 1. X-ray characterization shows that polytypes and disordered structures occur in Zn x Cd1−x S forx ≥ 0·94, whereas Zn x Mn1−x S displays disordered and polytype structures in the entire rangex=0·9 to 1. It is observed that Zn x Cd1−x S and Zn x Mn1−x S undergo a 2H-6H solid state transformation on annealing in vacuum around 600°C. Experimental analysis of the intensity distribution along the 10·L reciprocal lattice row as recorded on a single crystal diffractometer from partially transformed crystals shows that the mechanism of the transformation cannot be explained in terms of the one-parameter models of non-random faulting reported earlier. A two-parameter theoretical model with α representing the probability of random insertion of a fault in the 2H structure and β representing the probability of the growth of the 6H nucleus, is developed both for a deformation mechanism and a layer displacement mechanism. It is found that the theoretical model of non-random deformation faulting with β ≫ α approximates the actual mechanism of transformation in these crystals.