Correlation between composition and superconducting properties in a NB-TI wire produced by the solid diffusion between pure NB and TI

摘要

A Titanium rod was inserted in a Niobium tube producing a billet that had dimensions reduced by cold deformation. The resultant wire was cut into 91 pieces and restacked in a Niobium tube. The deformation and restacking process was repeated and a wire with 5551 elements of Titanium was produced with a final wire diameter of 0.95 mm. Heat treatments (HT) of 923 K and 1023 K were applied to the material along wire fabrication. These HT produced diffusion among Nb and Ti elements. The superconducting "phases" in this wire are pure Nb and Nb-Ti alloy with variable composition. Two pieces of the final wire were heat treated at 1023 K for 3 h and 7 h. The samples without and with HT were characterized respect to superconducting properties by AC/DC magnetization and transport measurements. Measurements of critical temperature T_c by Ac susceptibility showed a double peak only for the sample without HT. This behavior is associated to the proximity coupling of all existing superconducting "phases" in the sample confirmed by correlation of T_c and H_(c2) with SEM/EDS measurements of diffusion layer composition. After a 1023 K/3h HT, an increase of 4 T in H_(c2) was observed and the critical current density J_c(1T) increased from 100 to 720 A/mm2.