Dopant binding with vacancies and helium in metal hydrides

Abstract

Metal hydrides are crucial for the long-term storage of tritium but suffer degradation due to the buildup and release of helium decay products. Therefore, it is of interest to explore how dopants in these metal hydrides may impact helium bubble nucleation and distributions, as well as associated fracture and helium retention. Prior studies have focused on helium behavior in pure metal hydrides or with one or two types of impurities. Analytical models have also shown that the concentration of nucleated bubbles can impact the time to fracture of materials. This study utilizes high-throughput density functional theory calculations to identify the impact of transition metal substitutional dopants on helium binding energies in face-centered cubic metal hydrides, such as erbium hydride, holmium hydride, scandium hydride, titanium hydride, yttrium hydride, and zirconium hydride. This study also explores the impact of hydrogen vacancies on the binding energy of helium near the substitutional defects. Finally, this study presents an initial assessment of dopant stability and solubility limits at many temperatures and pressures. Several metals strongly bind to helium in these metal hydrides, making them promising for influencing helium nucleation and subsequent bubble growth. However, many of these potentially beneficial substitutional defects have low solubility limits. The calculations show that some strong binding dopants may be soluble in quantities that affect the bubble concentration and impact material performance.