Structural study on hydrogen-metal systems using X-rays and neutrons

This article reports the recent structural studies on hydrogen-metal systems using X-rays and neutrons. We have focused on the interactions between interstitial hydrogen atoms and their surrounding metal atoms. The hydrogen-metal interactions provide the important knowledge to develop the high performance hydrogen absorbing alloys. The X-ray and neutron diffraction are complementary methods to investigate the structural changes of metals or hydrogen absorbing alloys induced by the absorbing hydrogen atoms. As a typical example, pressure-induced phase separation of lanthanum di-hydride are described. The X-ray diffraction measurement on lanthanum di-hydride reveals the phase separation into hydrogen-rich and hydrogen-poor phases above 11 GPa. The neutron diffraction measurement on lanthanum di-deuteride confirms the formation of NaCl-type mono-deuteride as a counterpart of the deuterium-rich phase by phase separation. (author)