Superconductivity in Deformed Niobium Alloys

A brief review of deformation structure in bcc metals is given and the main features of type II superconductivity are summarised. Microstructure and superconducting properties of deformed niobium-tantalum, niobium-titanium, and niobium-zirconium alloys were studied and compared with those of pure niobium. All these alloys are type II superconductors, which above a certain critical field, H-c1, enter the mixed state, consisting of Abrikosov current vortices in a superconducting matrix. Dislocations introduced by deformation interact with current vortices to cause irreversible superconducting behaviour and contribute to a high current-carrying capacity. It is concluded from the results presented here that a strong vortex dislocation interaction is obtained only when a non-uniform dislocation distribution is present, and that a uniform distribution produces only weak pinning. Flux-pinning by dislocation tangles is treated as a special case of pinning by normal particles resulting from a variation in kappa, the Ginzburg-Landau parameter.