Superconductivity and dislocation cell structure in niobium: Stress effects

To investigate the mechanism for the development of large anisotropic resistive critical fields in deformed niobium, the dependence of the parallel critical fieldH∥ on stress σ was measured in both compression and tension, for severely deformed niobium composites. the magnitude of ∂H∥/∂ σ increased with strain up to a value of 27 times that of annealed niobium. Also, both tension and compression increasedH∥. Both of these discrepancies from the thermodynamic predictions can be ascribed to the presence of double-ended dislocation pileups in the cell walls.