Formation of superabundant vacancies in metal hydrides at high temperatures

Abstract

It has been found from X-ray diffraction on several MH systems under high p, T conditions that a large number of M-atom vacancies amounting to ca. 20 at.% are formed at high temperatures, leading to a vacancy-ordered L12 structure in some f.c.c. hydrides. The energetics of vacancy formation in hydrides suggests that defect-hydrides containing many vacancies are generally more stable thermodynamically than ordinary defect-free hydrides and therefore most phase diagrams of MH systems reported heretofore are metastable.