BCC and HCP Nb-Re-Hf-Zr-Ti High Entropy Alloy Superconductors

High-entropy alloys (HEAs) have unique and highly disordered atomic structures that provide exceptional mechanical, physical, and chemical properties. Superconducting HEAs are especially intriguing because they allow the relationship between disorder and superconductivity to be explored. Recently, Nb-Re-Zr-Hf-Ti-based HEAs have gained importance as a new family of superconductors because of their composition-dependent crystal structure, providing an opportunity to investigate the influence of crystal structure and disorder on superconductivity. This chapter details the investigation of the superconducting properties of the [Nb \(_{0.67-x}\) Re \(_{x}\) ](TiZrHf) \(_{0.33}\) , Nb \(_{0.2}\) Re \(_{0.2}\) Zr \(_{0.2}\) Hf \(_{0.2}\) Ti \(_{0.2}\) and Nb \(_{0.6}\) Re \(_{0.1}\) Zr \(_{0.1}\) Hf \(_{0.1}\) Ti \(_{0.1}\) systems. The material phase composition and crystal structure were confirmed using precession electron diffractionElectron diffraction, powder X-ray diffraction, and scanning electron microscopy. These results suggest that an increase in the valence electron count stabilizes the hcp phase. Transport, magnetization, heat capacity, andMuon spin rotation muon spin rotation/relaxation measurements were used to explore the superconducting properties of the materials, and the results suggested that the Nb-Re-Zr-Hf-Ti-based HEAs are bulk, fully gapped moderately coupled superconductors with preserved time-reversal symmetry in the superconducting ground state.