Superconductivity in the high-entropy alloy (NbTa)0.67(MoHfW)0.33

Abstract

Structural and physical properties of the high-entropy alloy ${(\mathrm{NbTa})}_{0.67}{(\mathrm{MoHfW})}_{0.33}$ were studied by x-ray powder diffraction, energy dispersive x-ray spectroscopy, magnetization, electrical resistivity, and specific heat measurements. The experimental results were supported by theoretical calculations using two complementary approaches for electronic structure calculations: the Korringa-Kohn-Rostoker method with the coherent potential approximation (KKR-CPA) and projector augmented wave (PAW) within the density functional theory. It was found that the alloy forms with a cubic, body-centered structure (space group $Im\overline{3}m$, W-type structure) with a lattice parameter $a=3.287(1)$ \AA{} and a random (but microscopically homogeneous) distribution of the constituent elements. At high temperature the alloy exhibits simple metallic behavior, while at low temperature it becomes a type-II superconductor with the critical temperature ${T}_{\mathrm{c}}\ensuremath{\approx}4.3$ K and the upper critical field ${\ensuremath{\mu}}_{0}{H}_{\mathrm{c}2}\ensuremath{\approx}1.45$ T. The electron-phonon coupling constant calculated from the PAW data, ${\ensuremath{\lambda}}_{\mathrm{el}\ensuremath{-}\mathrm{ph}}^{\mathrm{th}\ensuremath{-}\mathrm{PAW}}=0.63$, is in perfect agreement with the experimental results.