X-RAY-DIFFRACTION MEASUREMENTS FOR LIQUID AS2SE3 UP TO THE SEMICONDUCTOR-METAL TRANSITION REGION

X-ray diffraction measurements were performed for liquid (l-) AS2Se3 at temperatures and pressures up to 1500-degrees-C and 70 bar. A high-pressure vessel and a sapphire sample cell were developed, according to the authors' own design, for measurements using the energy-dispersive method. The structure factor becomes broadened with increasing temperature and changes significantly at about 1000-degrees-C accompanied by the semiconductor-to-metal (SC-M) transition; the first sharp diffraction peak around 1.2 angstrom-1 disappears and the second and third maxima merge. The nearest-neighbor distance and the average coordination number start to increase when the SC-M transition occurs. The density of l-As2Se3 in the temperature and pressure range up to 1600-degrees-C and 700 bar, respectively, were also measured by the X-ray absorption method. A volume contraction occurs in the SC-M transition region.