Abstract
High-entropy alloys (HEAs) are a new class of materials which are being energetically studied around the world. HEAs are characterized by a multicomponent alloy in which five or more elements randomly occupy a crystallographic site. The conventional HEA concept has developed into simple crystal structures such as face-centered-cubic (fcc), body-centered-cubic (bcc) and hexagonal-closed packing (hcp) structures. The highly atomic-disordered state produces many superior mechanical or thermal properties. Superconductivity has been one of the topics of focus in the field of HEAs since the discovery of the bcc HEA superconductor in 2014. A characteristic of superconductivity is robustness against atomic disorder or extremely high pressure. The materials research on HEA superconductors has just begun, and there are open possibilities for unexpectedly finding new phenomena. The present review updates the research status of HEA superconductors. We survey bcc and hcp HEA superconductors and discuss the simple material design. The concept of HEA is extended to materials possessing multiple crystallographic sites; thus, we also introduce multisite HEA superconductors with the CsCl-type, α-Mn-type, A15, NaCl-type, σ-phase and layered structures and discuss the materials research on multisite HEA superconductors. Finally, we present the new perspectives of eutectic HEA superconductors and gum metal HEA superconductors.
Highlights
High-entropy alloys (HEAs) can be considered as a new class of materials especially due to their superior mechanical properties [1,2,3,4]
Contrary to the bcc HEA superconductors, the constituent elements are rather distributed on Ti, Nb, Mo, Re, Ru and Rh with different valence electron count per atom (VEC)
The results suggest that, in particular, bcc HEA superconductors can be regarded amorphous 4d metals
Summary
High-entropy alloys (HEAs) can be considered as a new class of materials especially due to their superior mechanical properties [1,2,3,4]. We basically follow the first definition for the single-site (fcc, bcc, and hcp) HEAs. The concept of Metals 2020, 10, 1078; doi:10.3390/met10081078 www.mdpi.com/journal/metals. Bcc structure group: Im3 m, No. 2a site is present, which is randomly occupied by several atoms. Tc values the transition metal amorphous superconductors notand follow this ruleshow and frequently ratherathigh valley in the curve of the Matthias rule [13]. This review summarized the data of HEA superconductors with mainly bcc and hcp structures and presented a good deal of perspectives. This review aims to update the research status of bcc and hcp HEA superconductors and to present a survey of multisite HEA superconductors.
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