Bi-Sb alloys irradiated with swift heavy ions as potential topological amorphous superconductors

Crystalline Bi _{100− x} Sb _x alloys are well known as the first experimentally realized topological insulators, in addition to their promising thermoelectric properties. In contrast, their amorphous counterparts have been reported to exhibit superconductivity with critical temperatures exceeding 6 K. However, the strong tendency of Bi and Bi-Sb alloys to crystallize, even at very low temperatures, has hindered both systematic studies and practical applications of these amorphous phases. To explore the possibility of obtaining amorphous superconducting states and enhancing thermoelectric performance, we investigated ion-beam irradiation as a method to induce amorphization in Bi _{100− x} Sb _x alloys. We performed irradiation experiments on pure Bi and Bi-Sb melt-spun ribbons using iodine ions with energies between 25 and 40 MeV, achieving estimated vacancy damage levels of 40–80%. Structural characterization by X-ray diffraction and electrical resistivity measurements in the range 2–300 K revealed that, although amorphization and superconductivity were not achieved, ion-induced disorder led to significant conductivity improvements, particularly in Bi ₉₀ Sb ₁₀ Furthermore, interesting correlations were observed between the resistivity values and the semiconducting gap with the Sb content, both before and after irradiation. These results provide new insights into the interplay between structural disorder, electrical transport, and topological properties in Bi-Sb alloys.