Formation of Superabundant Vacancies in Pd Hydride under High Hydrogen Pressures

Abstract

In situ x-ray diffraction on Pd hydride under 5 GPa of hydrogen pressure show that lattice contraction due to vacancy formation occurs in 2-3 h at 700-800 \ifmmode^\circ\else\textdegree\fi{}C, and two-phase separation into PdH and a vacancy-ordered phase of ${\mathrm{Cu}}_{3}$Au structure (${\mathrm{Pd}}_{3}$${\mathrm{VacH}}_{4}$) on subsequent cooling. After recovery to ambient conditions and removal of hydrogen, the vacancy concentration in Pd metal was determined by measuring density and lattice parameter changes to be 18 \ifmmode\pm\else\textpm\fi{} 3 at.%. This procedure provides a new method of introducing superabundant vacancies in metals.