New type of Ti-rich HEA superconductors with high upper critical field

Physical and structural properties of two high-entropy alloys (HEA), Ti 0.5 (ZrNbHfTa) 0.5 and Ti 0.5 (VNbHfTa) 0.5 , belonging to the new type of Ti-rich HEA were studied by powder x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDXS), magnetization, electrical resistivity and specific heat measurements. The experimental results were supported by theoretical calculations of the electronic structure using projector augmented wave (PAW) within the density functional theory . Simulated structure relaxations with several degrees of freedom were applied to calculate the total density of states . It was found that both alloys are crystallizing in the bcc structure (space group I m 3 ¯ m , W-type structure) despite the fact that they are formed in 75 and 62.5 at.% from elements crystallizing in hexagonal structure. The presence of minor stoichiometric variations in the samples was detected by EDXS mapping, but its effect on the physical properties seemed negligible. At low temperatures, the alloys become type II superconductors , with a critical temperature in the range of 5.9 – 6.0 K and an upper critical field reaching 13.5 T, a value that is exceptionally high for HEA