Phase separation and solidification of fluid phosphorus

Katayama, Yoshinori; Inamura, Yasuhiro; Saito, Hiroyuki; Utsumi, Wataru

In-situ X-ray diffraction study revealed that there were two distinct structures of fluid phosphorus and a sharp transition occurred between them at about 1 GPa. The two structures, one is molecular fluid and the other is polymeric fluid, have different densities. By an X-ray radiography method, macroscopic separation of two fluid phases was directly observed. These results support a view that it is a first-order phase transition. To study solidification of low-density, high-density fluids and their mixture, an X-ray radiograph has been recorded during a rapid cooling using a cubic-type multi-anvil apparatus installed on a beamline BL14B1 at SPring-8. The obtained solid sample was investigated by an optical microscope and by an electron microscope. The low-density fluid tends to transform to a kind of red phosphorus while high-density fluid usually transforms to black phosphorus. Several shapes of grains were obtained from mixture.