RuAl 2 : Structure, electronic and elastic properties from first-principles

Abstract RuAl 2 shows the abnormal semiconductor property. However, the relationship between structure, electronic and mechanical properties of RuAl 2 is not well understood. In this paper, we systematically investigate the structural stability, electronic and mechanical properties of RuAl 2 . Four possible RuAl 2 structures (TiSi 2 -type, TiAl 2 -type, OsAl 2 -type and AuAl 2 -type) are estimated and predicted. We find that although TiSi 2 -type structure is more thermodynamic stability than that of other structures, the predicted structures are also stability at the ground state. Importantly, TiSi 2 -type structure shows a semiconductor property with a band gap of 0.189 eV. However, other three structures exhibit metallic behavior because of electronic overlap between Al-3 p state and Ru-4 d state at Fermi level. We further find that the predicted OsAl 2 -type structure has strong shear deformation resistance and high elastic stiffness in comparison to other three structures. The reason is that the bond strength of Ru-Al metallic bond for OsAl 2 -type structure is stronger than that of other structures.