Effect of Low-Temperature Deuteron Irradiation on Some Type-II Superconductors

To study the effects of low-temperature irradiation on some type-II superconductors, the critical current density jc, transition temperature Tc, upper critical field Hc2, and normal-state resistivity ρₙ were measured after irradiation with 15-MeV deuterons. The 10¹⁷-deuteron / cm² irradiations produced about 0.3% atomic displacements. The ribbon samples consisted of Nb-61% Ti, Nb-25% Zr, Nb₃Sn, Nb, and Pb. These samples were held at about 30^∘{}K during irradiation and 5^∘{}K between irradiation and measurement. The cryostat contained a 50-kOe superconducting magnet for in situ measurements. All effects were studied after irradiation and after annealing at 77 and 300^∘{}K. The resistivities were generally increased and the transition temperatures decreased by irradiation. Changes in Hc2 (generally reductions) are correlated with changes in Tc, ρₙ, and the Ginzburg-Landau parameter κ. Reductions of {~}20% in jc of cold-worked NbTi and NbZr were observed, whereas the only jc effect in strain-free NbZr was the production of a peak effect near Hc2. Large, thermally stable jc changes were found in vapor-deposited Nb₃Sn; an increase in low-jc material and a decrease in high-jc material. The induced effects in the alloys and pure metals were reduced by 75% or more upon warming the samples to room temperature. For Nb₃Sn, less than 25% of the induced effects were recovered by annealing at 300^∘{}K.