Superabundant Vacancy Formation and Its Consequences in Metal-Hydrogen Alloys

Abstract

A theory is proposed for the formation of superabundant vacancies in metal-hydrogen alloys, amounting to 10∼20 at%, considering hydrogen effects to decrease the formation energy of a vacancy by cluster formation and the configurational entropy of the system at high hydrogen concentrations. A formula derived for the vacancy concentration is found to give excellent descriptions of experimental results on nickel-hydrogen and molybdenum-hydrogen alloys obtained under high hydrogen pressures. Some of the consequences of the superabundant vacancy formation are discussed including solubility enhancement, formation of defect structures and voids, and enhancement of metal-atom diffusion.