Superconductivity in a new hexagonal high-entropy alloy

Abstract

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.

Influence of Local Lattice Distortion on Elastic Properties of Hexagonal Close‐Packed TiZrHf and TiZrHfSc Refractory Alloys

“…Multiple principal element alloy (MPEA) is a newly developing field in material science and engineering community, which provides a novel design concept for promising material. The new MPEAs are reported to have superior properties, [ 1–4 ] such as high strength/hardness for VCoNi, [ 5 ] exceptional ductility for TiZrHf, [ 6 ] excellent fracture toughness for FeCoNiCrCuTiMoAlSiB 0.5 , [ 1 ] and so on. Therefore, MPEAs are increasingly attracting significant interests.…”

“…As low‐symmetry crystal structures, HCP MPEAs are predicted to have distinct mechanical, physical, and chemical properties, such as complicated electron and thermal transport, and unusual magnetism. [ 4,9 ] So, the fabrication of HCP MPEAs is an important goal, being intriguing from both scientific and application viewpoints. [ 10 ] Recently, several HCP MPEAs composed of rare‐earth (RE) metals have been first synthesized, [ 11–13 ] including TmGdTbDyLu, YGdTbDyLu, YGdTbDyHo, and YGdTbLaHo, because similar atomic sizes, electronegativity, crystalline, and electronic structure allow the formation of random solid solutions.…”

Superconductivity in Cubic A15-type V–Nb–Mo–Ir–Pt High-Entropy Alloys

“…Despite the presence of strong chemical disorder, some HEAs exhibit collective quantum phenomena such as superconductivity [6,7]. So far, a number of HEA superconductors have been discovered and their crystal structures can be categorized into body-centered cubic (bcc)-type [8][9][10][11], a-Mn-type [12,13], CsCl-type [14], hcp-type [15][16][17], A15-type [18], and s-type [19]. In particular, the A15-type V 1.4 Nb 1.4 Mo 0.2 Al 0.5 Ga 0.5 HEA has a T c of 10.2 K and a disorder-enhanced upper critical field of 20.1 T [18], both of which are the highest among HEA superconductors.…”

Materials Research on High-Entropy Alloy Superconductors

“…On the other hand, transition metal amorphous superconductors do not follow this rule and frequently show relatively high T c values in the valley of the curve of the Matthias rule [16]. HEA superconductors with simple crystal structures have been found in bcc [17][18][19][20][21][22] and hcp [23][24][25][26]. The T c vs. VEC plots of these HEAs seem to fall between a crystalline curve and an amorphous one [27,28].…”