Quest for amorphous superconductors of Bi–Sb alloys by irradiation with swift heavy ions

Abstract

Crystalline Bi100−xSbx alloys are known as the first discovered topological insulators, as well as for their promising thermoelectric properties, while their amorphous counterparts exhibit superconductivity (Tc > 6 K). However, their strong tendency to crystallize has hindered both the study and practical applications of amorphous Bi and Bi–Sb alloys. To explore the possibility of obtaining amorphous superconducting phases and enhancing thermoelectric properties, we investigated ion-beam irradiation as a method to induce amorphization in Bi100−xSbx alloys. We report irradiation experiments on pure Bi and Bi100−xSbx using bismuth and iodine ions (tens of MeV), generating an estimated vacancy damage of 40%–80%. Structural characterization and electrical resistivity measurements (2–300 K) revealed that, while amorphization and superconductivity were not achieved, melt-spun samples exhibited an order of magnitude higher conductivity than thermally evaporated ones. Moreover, ion-induced disorder further improved electrical conductivity, particularly in Bi90Sb10, highlighting its potential for thermoelectric applications.