Twinning in a Cation-deficient Spinel Structure

Crystals of β-In 2 S 3 have been studied under the polarizing microscope and by x-ray diffraction. Optical examination has shown that the crystals are twinned, and the relative orientations of the twin components have been determined by rotation and oscillation x-ray photographs. The diffraction data have also confirmed the body-centred tetragonal cell proposed by Rooymans. Assuming that the material has a spinel structure, deficient in cations, it follows that twinning takes place when a redistribution in the tetrahedrally occupied sites occurs.