Superconductivity in the TiO and NbO Systems

This paper presents electrical resistivity and superconductivity studies for the BI (NaCl) structure oxides of titanium, vanadium, and niobium. In samples of nominal composition TiOx, VOx, and NbOx, x was varied from 0.8 to 1.2. It was found that all three of these oxides exhibit room-temperature electrical resistivities characteristic of metallic behavior. With decreasing temperature, the resistivity drops steeply in the case of NbOx, but remains steady or rises somewhat in the case of TiOx and VOx, depending on the exact value of x. It is suggested that in TiOx and VOx there is a large resistivity component due to scattering of carriers by disordered vacancies. Superconductivity was observed in NbOx(T-c = 1.38 K, x = 1.0) and TiOx(T-c = 1.0 K, x = 1.07). In the latter case the material showed a well-defined maximum of Tc as a function of composition, with T-c < 0.05 K for x < 0.85 and x > 1.20. Several VOx samples remained normal to 0.07 K.