X-ray diffraction measurements for liquid As2Se3 up to the semiconductor-metal transition region

X-ray diffraction measurements were performed for liquid (1-) As₂Se₃ at temperatures and pressures up to 1500°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°C accompanied by the semiconductor-to-metal (SC-M) transition; the first sharp diffraction peak around 1.2Å⁻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 1-As₂Se₃ in the temperature and pressure range up to 1600°C and 700 bar, respectively, were also measured by the X-ray absorption method. A volume contraction occurs in the SC-M transition region.