Site occupancy of interstitial deuterium atoms in face-centred cubic iron

Machida, Akihiko; Saito, Hiroyuki; Sugimoto, Hidehiko*; Hattori, Takanori   ; Sano, Asami   ; Endo, Naruki*; Katayama, Yoshinori; Iizuka, Riko*; Sato, Toyoto*; Matsuo, Motoaki*; Orimo, Shinichi*; Aoki, Katsutoshi

Iron hydride FeH, is thermodynamically stable only at high hydrogen pressure of several GPa. To investigate the hydrogenation process and hydrogen state in iron hydride, it is necessary to carry out the in-situ measurement under high pressure and high temperature. In this study, we performed the in-situ neutron diffraction measurement of Fe-D system using the high pressure neutron diffractometer PLANET in the MLF, J-PARC, and determined the deuterium occupying sites and occupancies in fcc-FeD. We found the minor occupation of tetrahedral sites under high pressure and high temperature. We considered the mechanism of the minor occupation based on the Quantum-mechanical calculation.