Ab initio study of H and He migrations in β-phase Sc,Y,and Er hydrides

Ab initio calculations based on the density functional theory have been performed to investigate the migrations of hydrogen（H） and helium（He） atoms in β-phase scandium（Sc）,yttrium（Y）,and erbium（Er） hydrides with three different ratios of H to metal.The results show that the migration mechanisms of H and He atoms mainly depend on the crystal structures of hydrides,but their energy barriers are affected by the host-lattice in metal hydrides.The formation energies of octahedral-occupancy H（H oct） and tetrahedral vacancy（V tet） pairs are almost the same（about 1.2 eV）.It is of interest to note that the migration barriers of H increase with increasing host-lattice atomic number.In addition,the results show that the favorable migration mechanism of He depends slightly on the V tet in the Sc hydride,but strongly on that in the Y and Er hydrides,which may account for different behaviours of initial He release from ScT2 and ErT2.