The Effect of Gallium Addition on the Microstructure and Superconducting Properties of In-Bi-Sn Solder Alloys

Ternary In-Sn-Bi alloys exhibit potentially superior superconducting properties compared to other lead-free solders, making them promising candidates for replacing lead-based solders in superconducting joints. In this work, the microstructure and superconducting properties of In-15wt.%Bi-35wt.%Sn and In-23wt.%Bi-27wt.%Sn were studied and compared with samples containing 0.5 wt.% and 1 wt.% Ga addition. The study reveals significant modifications in the microstructure with the addition of Ga, resulting in a slight decay in superconducting properties when higher levels of liquid Ga are present in the microstructure. Moreover, the difference in superconducting properties between the two In-Bi-Sn compositions is negligible, despite different microstructures. The highest critical temperature of 6.76 K was achieved in In-23wt.%Bi-27wt.%Sn. The tested superconducting properties including critical temperature (T_c), critical current density (J_c) and critical magnetic field strength (H_c) are discussed with respect to pinning mechanisms and microstructures based on electron backscatter diffraction (EBSD) and x-ray diffraction (XRD) results.