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High-entropy alloys (HEAs) are a new class of materials with an attractive combination of tunable mechanical and physicochemical properties. They crystallize mainly in cubic structures, however, for practical applications, HEAs with hexagonal-close-packed (hcp) structure are highly desirable in connection with their, in general, high hardness. Herein, we report the synthesis, structure, and detailed superconducting properties of Re₀. ₅₆Nb₀. ₁₁Ti₀. ₁₁Zr₀. ₁₁Hf₀. ₁₁---the first hexagonal superconducting HEA composed of five randomly distributed transition metals. A combination of room-temperature precession electron diffraction, precession electron diffraction tomography, and powder x-ray diffraction is utilized to determine the room-temperature crystal structure. Transport, magnetic, and heat capacity measurements show that the material is a type-II superconductor with the bulk superconducting transition at T₂=4. 4 K, lower critical field H₂₁ (0) =2. 3 mT, and upper critical field H₂₂ (0) =3. 6 T. Low-temperature specific-heat measurement indicates that Re₀. ₅₆Nb₀. ₁₁Ti₀. ₁₁Zr₀. ₁₁Hf₀. ₁₁ is a phonon-mediated superconductor in the weak electron-phonon coupling limit with a normalized specific-heat jump {C₄₋}{₍T₂}=1. 32. Further, hexagonal to cubic structural transition is observed by lowering the valence electron counts and T₂ follows crystallinelike behavior.
Marik et al. (Thu,) studied this question.