FORMATION OF SUPERABUNDANT VACANCIES IN PD HYDRIDE UNDER HIGH HYDROGEN PRESSURES

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 degrees C, and two-phase separation into PdH and a vacancy-ordered phase of Cu3Au structure (Pd(3)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 +/- 3 at. %. This procedure provides a new method of introducing superabundant vacancies in metals.