X-ray diffraction measurements for expanded fluid selenium up tothe metallic region

Abstract

Energy-dispersive X-ray diffraction measurements for fluid Se have been carried out at high temperatures and pressures, including the supercritical region to investigate the structure of fluid Se with a more metallic nature. A new high pressure which permits energy-dispersive X-ray diffraction measurements up to 2000 bar has been developed. Small angle X-ray scattering (SAXS) measurements have also been carried out for the first time to study the critical opalescence near the liquid-gas critical point. The results of X-ray diffraction up to 1500 °C and 1420 bar show that the twofold coordinated chain structure is largely preserved. The first nearest neighbor distance becomes short around 1200 °C and 1400 bar, where the electrical conductivity increases progressively and the optical gap disappears. The existence of a short chain molecule with planar zig-zag conformation in metallic state is speculated based on the findings.