Quasielastic neutron scattering probing H dynamics in the H conductors LaHO

Tamatsukuri, Hiromu   ; Fukui, Keiga*; Iimura, Soshi*; Honda, Takashi*; Tada, Tomofumi*; Murakami, Yoichi*; Yamaura, Junichi*; Kuramoto, Yoshio*; Sagayama, Hajime*; Yamada, Takeshi*; Matsuura, Masato*; Shibata, Kaoru  ; Kofu, Maiko   ; Kawakita, Yukinobu  ; Ikeda, Kazutaka*; Otomo, Toshiya; Hosono, Hideo*

Using an incoherent quasi-elastic neutron scattering (QENS) technique, we investigate H dynamics in a series of oxyhydrides LaHO that exhibit characteristic high H conductivity. In the end member LaH ( = 0), two kinds of H dynamics are identified: the jump diffusion and the localized motion. The jump length in the jump diffusion mode increases with increasing . The localized motion is identified as a jump between the two inequivalent sites. These dynamics are corroborated by our molecular dynamical simulations. Our QENS data suggest that similar H dynamics occurs also in oxyhydrides LaHO ( 0), whose H concentration dependence is consistent with the previous measurement of ionic conductivity. We also discuss the possibility that LaHO is an example of H ion conductors governed by the concerted migration mechanism. The identified H dynamics is a key to understanding the anomalous hydrogen concentration dependence of the diffusion coefficient in lanthanum hydrides, which has been a longstanding mystery in this compound.