Ab initio study of the effects of helium on the mechanical properties of different erbium hydrides

Although rare-earth metals have increasingly received attention for use in the storage and transportation of the tritium used in nuclear fusion reactions, they still face great challenges, such as the effect of helium on the mechanical properties of different erbium hydrides. In this work, first principles are used to study the mechanical properties(elastic constants, Young's modulus, transverse shear modulus and bulk modulus) of different erbium hydrides exposed to helium. The Young's modulus, the transverse shear modulus and the bulk modulus are given based on the elastic constants calculated according to first principles. It is found that the mechanical properties of all three erbium hydrides decrease in the presence of helium, and the decline of the mechanical properties of ErH_3 is the most serious. To explain the reason for the decrease in the mechanical properties, the densities of the states of erbium hydrides are calculated. During the calculations, helium embrittlement is not found and the ductility of the erbium hydrides improves following the production of helium at the helium concentrations considered in this work.