Interpretation of the Anomalous Anelastic Relaxation Due to Trapped Hydrogen (Deuterium) in Substitutional Alloys Using a Statistical Model

The anelastic relaxation at intermediate temperatures (100-200K) in metal-hydrogen crystalline systems containing trapping centres presents anomalous features like a shift of the peak temperature and a variation of its apparent activation energy with hydrogen content. New results obtained in Nb-5 at.% Ti-H, Nb-2 at.% Ti-H and Nb-0.5 at.% Ti, and the existing data, have been interpreted by a comprehensive model which assumes a distribution of the interstitial site energies according to a density of states function. The process is thought to be originated from superposition of the elementary relaxations of Ti-H pairs whose population as a function of temperature and H concentration has been calculated using Fermi-Dirac statistics. The close similarity with the relaxation recently observed in amorphous materials and A15 superconductors doped with H indicates that the present behaviour is characteristic of the hydrogenated systems.