Orientation dependence of the superconducting behaviour of deformed and undeformed niobium single crystals

Current-carrying capacity and magnetization experiments have been performed at 4.2°K on as-grown single crystals of niobium, and repeated after 10% deformation of the crystals by compression. The results are compared with those from the same material when cold-drawn to wire. Three critical magnetic fields are defined, H1, H2 and H3. H1 is the field corresponding to the peak in the (M, H) curves, H2 is the field at which complete flux penetration occurs and H3 the field where electrical resistance is first observed. It is shown that H1 and H3 are orientation dependent and are raised by deformation, and that H2 is not orientation dependent but is also raised by deformation. Anisotropies exist in the orientation dependence of the current-carrying capacity both before and after deformation of the crystals, and the effect of deformation on the current-carrying capacity is found to depend on the initial orientation of the crystal relative to the deformation axis.