Structural studies on expanded fluid selenium up to the metallic region using synchrotron radiation

Energy-dispersive X-ray diffraction measurements using synchrotron radiation at SPring-8 for fluid Se have been carried out at temperatures up to 1650 °C and pressures up to 878 bar, including the dense vapour region, to investigate the structural change in the semiconductor-to-metal (SC–M) transition in expanded fluid Se. We obtained the structure factors, S ( k ), and the pair distribution functions, g ( r ), with a fairly good accuracy. Besides confirming the preservation of twofold-co-ordinated structure, the contraction of nearest co-ordination distance and the existence of asymmetry of the first peak in the g ( r ) in the metallic fluid region, it was found that the line shape of the first peak in the g ( r ) changes as well as the value of the first minimum in the g ( r ) increases obviously with increasing metallic properties. These results indicate that both the existence of different intrachain bonds and the interchain interaction are important for the mechanism of SC–M transition in fluid Se.