High entropy alloys (HEAs) are the 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 to 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 high entropy alloy (HEA) composed of five randomly distributed transition-metals. 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 Tc = 4.4 K, lower critical field Hc1(0) = 2.3 mT and upper critical field Hc2(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 ∆C el γnTc = 1.32. Further, hexagonal to cubic structural transition is observed by lowering the valence electron counts and Tc follows crystalline-like behaviour.

Herein, we report the synthesis and detailed superconducting properties of a new high entropy alloy superconductor with nominal composition Nb20Re20Zr20Hf20Ti20 using powder X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), magnetization, transport, and thermodynamic measurements. The room temperature powder XRD confirms that the alloy is arranged on a simple body centered cubic crystal lattice with lattice parameter a = 3.38 (1) Å. EDX measurement yields an average composition of Nb21Re16Zr20Hf23Ti20 (in atomic %). Transport, magnetic and heat capacity measurements reveal that the material is a type-II superconductor with the bulk superconducting transition at Tc = 5.3 K, lower critical field Hc1(0) = 33 mT and upper critical field Hc2(0) = 8.88 T. Low temperature specific heat measurement indicates that the sample is a moderately coupled superconductor, and the electronic specific heat data fits well with the single-gap BCS model.

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