Crystal structure and phase transition ofα-Cu2HgI4

Abstract The phase transformation of red β -Cu 2 HgI 4 to the black α -phase at 67°C has been studied by X-ray powder diffraction. It is suggested that copper and iodine occupy the same tetrahedral positions in the α - and β -phases, whereas mercury is statistically distributed over two crystallographic positions in the α -phase. Both phases may be described in space group I [unk]2 m . The phase transition has been studied by X-ray powder diffraction at elevated temperatures and disintegration of the α -phase may occasionally be found. The structure of the α -phase at 85°C was determined and refined by Rietveld full-profile technique to a Bragg R -factor = 0.064.