Sc–Zr–Nb–Rh–Pd and Sc–Zr–Nb–Ta–Rh–Pd High-Entropy Alloy Superconductors on a CsCl-Type Lattice

TLDR

The materials possess CsCl‑type structures with mixed site occupancies. We synthesized new pentanary and hexanary high‑entropy alloys that are type‑II superconductors with critical temperatures ranging up to ~9.3 K, increasing as valence‑electron count decreases, exceeding those of binary CsCl‑type intermetallics, and exhibiting high upper critical fields, ductility, and intrinsic superconductivity even in Nb‑free compositions.

Abstract

We have synthesized previously unreported high-entropy alloys (HEAs) in the pentanary (ScZrNb)1–x[RhPd]x and hexanary (ScZrNbTa)1–x[RhPd]x systems. The materials have CsCl-type structures and mixed site occupancies. Both HEAs are type-II superconductors with strongly varying critical temperatures (Tc's) depending on the valence electron count (VEC); the Tc's increase monotonically with decreasing VEC within each series, and do not follow the trends seen for either crystalline or amorphous transition metal superconductors. The (ScZrNb)0.65[RhPd]0.35 HEA with the highest Tc, ∼9.3 K, also exhibits the largest μ0Hc2(0) = 10.7 T. The pentanary and hexanary HEAs have higher superconducting transition temperatures than their simple binary intermetallic relatives with the CsCl-type structure and a surprisingly ductile mechanical behavior. The presence of niobium, even at the 20% level, has a positive impact on the Tc. Nevertheless, niobium-free (ScZr)0.50[RhPd]0.50, as mother-compound of both superconducting HEAs found here, is itself superconducting, proving that superconductivity is an intrinsic feature of the bulk material.