Structural, mechanical and electronic properties of orthorhombic Nb₂X₄Si₅ (X=V, Nb, Ta, Cr, Mo, W) compounds from first-principles calculations

A comparative study on the structural, mechanical and electronic properties was carried out for orthorhombic Nb₂X₄Si₅ (X = V, Nb, Ta, Cr, Mo, W) intermetallic compounds using first-principles calculations. Our computed structural parameters are excellent consistent with the experimental data. The obtained elastic constants of Nb₂X₄Si₅ (X = V, Nb, Ta, Cr, Mo, W) compounds have been analyzed in detail for the first time, indicating that these ternary compounds are mechanically stable. The obtained formation enthalpies show that these compounds are thermodynamically stable. Nb₂Cr₄Si₅ compound behaves in a brittle manner, while other compounds exhibit ductile nature. With stronger ductility and lower hardness, meanwhile, Nb₂W₄Si₅ has more obvious elastic anisotropy than that of other compounds. Nb₂Cr₄Si₅ possesses the highest Debye temperature and the best thermal conductivity. The band structures and DOS of Nb₂X₄Si₅ (X = V, Nb, Ta, Cr, Mo, W) compounds have been calculated and analyzed, showing that they have mixtures of covalent and metallic characters.