Superabundant Vacancies Formed in Metal--Hydrogen Alloys

Superabundant vacancies of metal atoms, of concentrations as high as 10 - 30 %, can be formed in the presence of interstitial hydrogen as a consequence of reduction of the formation energy by trapping H atoms. The equilibrium concentration and mobility of Vac H clusters were determined by in situ XRD and resistivity measurements, and their sources were identified. The binding energies of trapped H atoms were determined by thermal desorption spectroscopy. Some of these experimental results are described, with particular reference to Pd, Ni and Cr