Effects of ordered structure on superconductivity in Ti _70-xZr ₃₀Nb _x (15≤ x ≤ 60)

Superconductivity and structural properties of Ti _70-xZr ₃₀Nb _x have been systematically investigated for x ranging from 0 to 60. Superconductivity is observed in the cubic β-phase with 10≤x≤ 60. Moreover, evident modifications in superconductivity and superstructure, being interpreted as Nb and Ti local orders, are discovered in samples with 25≤x≤ 50. This superstructure phase in general coexists with the cubic β-phase and yields two superconducting transitions in the superconducting materials. Electronic structure calculations reveal a relatively higher density of states for the superstructure phase at the Fermi level, therefore a strong electron-phonon coupling and higher superconducting T _c are expected in agreement with the experimental data.