Influences of Vacancy Concentration and Al Substitution on Structural, Electronic, and Elastic Properties of Nb₅Si₃ from First-Principles Calculations

The effects of vacancy concentration and Al substitution on the structural, electronic, and elastic properties of Nb₅Si₃ are studied using first-principles calculations. The formation energy, elastic modulus, and electronic properties of three different Nb vacancies in Nb₅Si₃ are discussed in detail. With the increase in vacancy concentration, the obtained shear modulus, Young's modulus, and hardness of Nb vacancy decrease, which are lower than those of pristine Nb₅Si₃. The bulk modulus/shear modulus (B/G) ratio increases with the increase in Nb vacancy concentration. However, these vacancies result in the transition from brittleness to ductility, and Nb₅Si₃ with 5% vacancy concentration exhibits ductile behavior. The calculation of electronic structure shows that these Nb vacancies change the local hybridization between Nb and Nb atoms. As the concentration increases, the position of the peak moves toward lower energy. It is predicted that vacancies can improve the ductility behavior of Nb₅Si₃.