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 $j_c$, transition temperature $T_c$, upper critical field $H_{c2\mathrm{}}$, and normal-state resistivity ${\rho }_n$ were measured after irradiation with 15-MeV deuterons. The ${10}^{17}$-deuteron / ${\mathrm{cm}}^2$ irradiations produced about 0.3% atomic displacements. The ribbon samples consisted of Nb-61% Ti, Nb-25% Zr, ${\mathrm{Nb}}_3$Sn, 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 $H_{c2\mathrm{}}$ (generally reductions) are correlated with changes in $T_c$, ${\rho }_n$, and the Ginzburg-Landau parameter $\kappa$. Reductions of ∼20% in $j_c$ of cold-worked NbTi and NbZr were observed, whereas the only $j_c$ effect in strain-free NbZr was the production of a peak effect near $H_{c2\mathrm{}}$. Large, thermally stable $j_c$ changes were found in vapor-deposited ${\mathrm{Nb}}_3$Sn; an increase in low-$j_c$ material and a decrease in high-$j_c$ material. The induced effects in the alloys and pure metals were reduced by 75% or more upon warming the samples to room temperature. For ${\mathrm{Nb}}_3$Sn, less than 25% of the induced effects were recovered by annealing at 300°K.