Effect of hydrogen absorption on atomic-electronic structure of PdH system according to positron annihilation data

Abstract

The positron annihilation technique is used to investigate the atomic-electronic structure of the electrochemically hydrogenated palladium. Curves of the angular correlation of the annihilation gamma� quanta radiation (ACAR) were recorded on the original Pd specimen, electrochemically hydrogenated Pd, and dehydrogenated Pd. EF Fermi levels and freeelectron concentrations were estimated based on the exper� imental ACAR curves. A substantial increase in the freeelectron concentration from N/V = 4.6 × 10 22 (22) cm -3 to N/V = 6.0 × 10 22 cm -3 was found in the hydrogenated Pd specimen compared to that of the original palladium. This change is accompanied by a decrease in the Gaussian halfwidth of the ACAR curves, which indicates a certain loosening of the palladium crystal lattice upon the hydrogenation. Upon the electrochem� ical removal of hydrogen from palladium, the annihilation characteristics of the metal are almost completely restored.