The effect of hydrogenated phase transformation on hydrogen-related vacancy formation in Pd1−xAgx alloy

To clarify the hydrogen-related vacancy formation mechanism, positron lifetime measurements were performed for Pd1−xAgx alloys that were hydrogenated at 296 or 373 K. Positron lifetime increased only when the alloys were hydrogenated below the critical temperature for phase transformation of the hydrogenation reaction, while it remained constant when they were hydrogenated above the critical temperature. This strongly suggests that vacancies formed only when phase transformation occurs. Therefore, hydrogen-related vacancy formation must be caused by the strain generated as the result of the phase transformation.