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 (Tc), critical current density (Jc) and critical magnetic field strength (Hc) are discussed with respect to pinning mechanisms and microstructures based on electron backscatter diffraction (EBSD) and x-ray diffraction (XRD) results.