Optical and photoemission studies of lanthanum hydrides

Abstract

We report the results of optical absorptivity and photoemission measurements on lanthanum hydrides LaH x (1.90 ⩽ x ⩽ 2.89). The low energy ( hv ≲ 0.5 eV) optical features in LaH x are attributed to the filling of octahedral sites. Higher energy interband absorption involves states within the d-band complex, analogous to other dihydrides. As x increases above 2.0, the optical features change rapidly because of the increase in the number of occupied octahedral sites. Various band structure studies suggest that LaH 3 might be a semiconductor. Our photoemission results show that as x increases the d-derived states at the Fermi energy E F are drawn down and that for LaH 2.89 only very weak valence band emission is observed near E F . The hydrogen-derived bonding bands are shown centered approximately 5 eV below E F . Observed chemical shifts in the La 5p 1 2 , 3 2 cores are discussed for 1.98 ⩽ x ⩽ 2.89.