Investigation on the superconductivity of Nb3Al by Zn doping and the effect of multi-RHQT process on the superconductivity of Nb3(Al1-xZnx)

Nb 3 (Al 1– x Zn x ) ( x = 0–0.05) wires were obtained after single rapid heating, quenching and low temperature transformation (single-RHQT) process. It is found that Zn element can make crystal plane diffraction peaks of Nb 3 Al phase shift to higher angle, and the interplanar crystal spacing decreases gradually, which indicates that Al atoms in Nb 3 Al lattice are replaced by Zn atoms with smaller diameters. And the addition of Zn can reduce Δ T c and make the superconducting phases purer, and magnetic performances such as critical temperature ( T c ), critical current density ( J c ), irreversible field ( B irr ) are better than that of the pure sample. Nb 3 (Al 0.99 Zn 0.01 ) wire shows the highest J c value of about 5.9 × 10 4 A/cm 2 at 4.2 K and 8 T, and the highest T c value of 16.8 K was found in Nb 3 (Al 0.98 Zn 0.02 ). The influence of multiple rapid heating, quenching and low temperature transformation (multi-RHQT) process on Nb 3 (Al 1– x Zn x ) wires was mainly explored, and 2 at% and 3 at% Zn samples were selected with relatively high Δ T c values for five times RHQT treatment. It is observed that the multi-RHQT process can further reduce Δ T c , and more homogeneous superconducting phases are discovered compared with that of single-RHQT process. The elements are also evenly distributed in the multi-RHQT-processed Nb 3 (Al 1– x Zn x ) wires, leading to the improvement of J c , B irr performances compared to single-RHQT samples. Multi-RHQT-processed Nb 3 (Al 0.98 Zn 0.02 ) and Nb 3 (Al 0.97 Zn 0.03 ) samples show the J c values of 1.7 × 10 5 A/cm 2 and 1.2 × 10 5 A/cm 2 (4.2 K, 8 T), which are nearly ten times as many as that of single-RHQT samples, and Nb 3 (Al 0.97 Zn 0.03 ) has the highest B irr values of 19.6 T (4.2 K) and 10.7 T (10 K). Flux pinning of the Nb 3 (Al 1– x Zn x ) ( x = 0.01–0.05) wires follows the surface pinning mechanism, where grain boundary and stacking faults are considered as pinning centers.