Abstract
Abstract Niobium-based compounds with the A15 structure have been widely applied in fusion engineering test reactor and superconducting materials. Hence, for a better understanding of the physical properties of A15-type Nb3X (X = Si, Ge, Sn and Pb) compounds, their structural, electronic, elastic and thermodynamic properties were investigated using the first-principles calculations. The calculated formation enthalpies indicated that these Nb3X compounds are energetically favorable and the sequence of thermodynamic stability is Nb3Si > Nb3Ge > Nb3Sn > Nb3Pb. Meanwhile, the phonon dispersions verified that these Nb3X compounds are dynamically stable. The electronic properties, such as the density of state, band structure, electron density difference and Mulliken population, suggested that these compounds are metallic, and Nb-Nb and Nb-X chemical bonds are ionic-covalent mixed bonds. The single-crystal and polycrystalline elastic properties were calculated. Moreover, the elastic anisotropy was discussed by elastic anisotropic indexes, three-dimensional surface construction and planar projections of elastic modulus, and the sequence of elastic anisotropy is Nb3Si > Nb3Ge > Nb3Sn > Nb3Pb. Finally, thermal properties such as Debye temperatures and sound velocities were analyzed based on elastic moduli.
Published Version
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