Role of Vacancies on Electronic and Elastic Properties of RuAl2 Semiconducting Compound from First-Principles Calculations

RuAl2 is a fascinating intermetallic semiconducting compound. However, the influence of vacancies on the electronic and mechanical properties of RuAl2 is unknown. By means of first-principles calculations, we have investigated the influence of vacancies on the electronic properties, elastic modulus, brittle or ductile behavior and Vickers hardness of RuAl2. Two possible vacancy types, Ru-va and Al-va, are considered. The calculated results show that the Ru-va vacancy is more thermodynamically stable than that of the Al-va vacancy. Importantly, we find that vacancies can improve the electronic properties of RuAl2 because the removed Ru or Al atom enhances the charge overlap between conduction band and the valence band near the Fermi level. In addition, these vacancies weaken the resistance to volume deformation, shear deformation and the elastic stiffness of RuAl2 because the removed atom weakens the localized hybridization between the Ru atom and the Al atom. However, the Ru-va vacancy can improve the Vickers hardness and Al-va vacancies result in brittle-to-ductile transition of RuAl2. The variation of mechanical properties is attributed to the Ru-Al and Al-Al metallic bonds along the shear direction. Therefore, we can conclude that vacances are beneficial for improving the electronic and mechanical properties of RuAl2.