X-ray diffraction study of the 2H to 3C solid state transformation in vapour grown single crystals of ZnS

Abstract

An X-ray diffraction study is made of the 2H → 3C solid-state structural transformation in ZnS. Single crystals of 2H ZnS (wurtzite), grown from the vapour phase above 1100 °C in the presence of H₂S₂, are annealed in vacuum at different temperatures ranging from 300 to 650 °C. The transformation is found to commence with a statistical insertion of stacking faults as revealed by the intensification of the diffuse streaks along reciprocal lattice rows parallel to c*. Diffraction spots characteristic of the 3C structure appear on the streaks at a later stage and the end product is invariably a disordered, twinned 3C structure. The rate of transformation is found to depend on the annealing temperature as well as the perfection of the initial crystal. No change in the external shape of the crystals is observed. To determine the nature of stacking faults involved in the transformation the broadening of the X-ray diffraction maxima are investigated produced by annealing 2H ZnS crystals. The point intensity distribution along the 10.L reciprocal lattice row of a slightly faulted 2H crystal is recorded on a four-circle single-crystal diffractometer in steps of ΔL = 0.01. It is found that the half widths of the L even and L odd reflections are equal, indicating that the stacking faults introduced during annealing are predominantly deformation faults. The observed and calculated intensity profiles of different individual reflections are found to be in good agreement. A slight discrepancy observed is attributed to the non-random insertion of stacking faults during transformation.