Resistive Measurements of Structural Effects in Superconducting Niobium

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Abstract
Resistive measurements of the critical current density Jc in transverse magnetic fields were made on single crystals of niobium, which had been subjected to systematic thermal, mechanical, and chemical treatments in order to produce a wide range of substructural densities, and variations in the oxygen content. The introduction of plastic deformation into niobium crystals produced a peak in Jc at applied magnetic fields of strength Hc2, the upper critical field. The peaks in Jc were removed by annealing the crystals in the recovery range. The critical current density was increased both below and above Hc2 by producing a dislocation substructure in the crystals. Small additions of oxygen also caused Jc to increase above and below Hc2. The upper critical field, however, was relatively insensitive to structure, varying only through the structure sensitivity of the bulk GLAG parameters.