Formation of NaCl-type Lanthanum Monohydride under High Pressure

－Discovery of Novel Rare-earth Metal Hydride using Synchrotron Radiation X-ray and Neutron－

Abstract

This article reports the recent discovery of NaCl-type lanthanum monohydride using synchrotron radiation x-ray diffraction and neutron diffraction measurements under high pressure. We have found that fcc-LaH₂ decomposes into two phases，which have different hydrogen compositions，the H-poor and H-rich phases，at 11 GPa at room temperature by synchrotron radiation x-ray diffraction. This decomposition is interpreted in terms of a disproportionation reaction. Recent neutron diffraction measurements on LaD₂ confirmed the formation of a NaCl-type LaD as the D-poor phase. This is the first observation of a formation of the rare-earth metal monodeuteride. Present result indicates that that rare-earth metal can form a series of stoichiometric hydrides，such as mono-，di-，and trihydride with the fcc metal lattice.