Pressure-induced novel bcc crystal structure with high T c in Nb-Ti system

Abstract The high-pressure phase diagram of the Nb-Ti binary system at 0 K is explored by systematic crystal structure prediction. The results highlight a novel niobium-rich bcc phase, Nb 7 Ti, which is the only dynamically stable ordered Nb-Ti compound under ambient pressure. Extensive first-principles calculations have provided insights into the electronic structure, bonding and superconducting properties of Nb 7 Ti. The superconducting transition temperature ( T c ) for Nb 7 Ti at ambient pressure is estimated within the framework of BCS theory to be about 17.5 K, which is significantly highernearly double-that of the widely utilized NbTi alloy. Furthermore, the results unveil that the high T c is mainly attributed to the unique ordered lattice along with the strong electron-phonon coupling driven by interatomic interactions at mid-frequency and phonon softening induced by low-frequency Fermi surface nesting. Valuable insights are provided for the subsequent synthesis of applicationoriented superconductors at low pressure.