Effects of Alloying Elements Ti, Cr, Al, and Hf on β-Nb5Si3 from First-principles Calculations

The energy, lattice parameters, electronic structures, and elastic constants of the intermetallic compound β-Nb5Si3 alloyed by Ti, Cr, Al, and Hf elements are investigated using first-principles methods based on plane-wave pseudopotential theory. From the impurity formation energy calculated, it is found that Ti, Cr, and Hf prefer to occupy the NbI, NbI, and NbII site, respectively, and that Al decreases the stability of β-Nb5Si3. Ti and Cr atoms reduce the c/a ratio of crystal lattices and Hf atom transforms the crystal lattice of β-Nb5Si3 from the tetragonal system to the orthorhombic system. The total state density of pure β-Nb5Si3 system and Ti, Cr, and Hf doped systems shows that Ti, Cr, and Hf improve the conductibility of β-Nb5Si3 system. The bulk modulus, shear modulus, and elastic modulus are obtained using Voight approximation equation. Ti and Cr increase the hardness and reduce the ductility of β-Nb5Si3. In contrast, Hf decreases the hardness and improves the ductility.