Effects of alloying and deposition temperature on phase formation and superconducting properties of TiZrTaNb-based high entropy-alloy films

Abstract

A variety of bulk high-entropy alloy superconductors have been recently discovered; however, for thin films, only the TaNbHfZrTi high-entropy alloy system has been investigated for its superconducting properties. Here, (TiZrNbTa) _1−xW _x and (TiZrNbTa) _1−xV _x superconducting films have been produced by DC magnetron sputtering at different growth temperatures. The phase formation and superconducting behavior of these films depend on the content of alloying x and deposition temperature. A single body-centered cubic (bcc) phase can be formed in the low x range with enough driving energy for crystallinity, but phase transition between amorphous or two bcc structures is observed when increasing x. The highest superconducting transition temperature T _c reaches 8.0 K for the TiZrNbTa film. The superconducting transition temperature T _c of these films deposited at the same temperature decreases monotonically as a function of x. Increasing deposition temperature to 400 °C can enhance T _c for these films while retaining nearly equivalent compositions. Our experimental observations suggest that T _c of superconducting high entropy alloys relate to the atomic radii difference and electronegativity difference of involved elements beyond the valence electron number.