Pressure-induced phase separation with intersite hydrogen transfer in rare-earth metal hydrides

Aoki, Katsutoshi; Machida, Akihiko; Honda, Mitsunori   ; Hattori, Takanori   ; Sano, Asami   ; Watanuki, Tetsu; Katayama, Yoshinori; Komatsu, Kazuki*; Arima, Hiroshi; Otomo, Toshiya*; Tsubota, Masami*; Ichikawa, Takayuki*; Kojima, Yoshitsugu*; Oshita, Hidetoshi*; Kim, D. Y.*

Rare-earth metal La forms T-site occupied fcc-LaH and fully occupied fcc-LaH, the former is metallic and the latter is insulating. Our previous synchrotron X-ray and infrared measurements revealed that the dihydride decomposed into hydrogen-rich and hydrogen-poor phases upon compression to 11 GPa at ambient temperature; the hydrogen rich phase was identified as LaH but the hydrogen composition and occupation sites of the hydrogen-poor phase remained undetermined. The crystal structure of the hydrogen-poor phase was investigated for LaD by neutron diffraction measurement with a total diffractometer NOVA at J-PARC. The formation of NaCl-type LaD as a counterpart of LaD by the decomposition was confirmed from the diffraction profiles. First-principle enthalpy and lattice dynamic calculations have demonstrated that the NaCl-type LaH is stabilized at high pressures.