Investigations on superconductivity in an equi-atomic disordered Hf-Nb-Ta-Ti-V high entropy alloy

Abstract

High entropy alloys (HEA) are expected to show unusual superconducting behavior due to chemical disorder along with highly distorted lattice. Herein, we report the synthesis, structure, and detailed superconducting properties of a new and nearly equi-atomic single phase disordered superconducting high entropy alloy with nominal composition Hf20Nb20Ta20Ti20V20. Rietveld refinement of the Synchrotron X-ray diffraction (SXRD) confirms the DFT predicted single-phase BCC structure in the HEA with lattice parameter a = 3.32 Å. Reverse monte carlo (RMC) modelling of the diffraction data evince the local atomic disorder and a considerable lattice distortion overriding the crystal structure due to significant variations in bond length and co-ordination numbers. Microstructural characterization using energy-dispersive X-ray spectroscopy (XEDS) equipped SEM shows dendritic morphology of the as solidified alloy with incomplete partition of the constituent elements. Transport, magnetization and low temperature specific heat measurement established that the current HEA is a moderately coupled type-II superconductor with a Tc of 5.0 K, lower critical field Hc1(0)=19mT and upper critical field Hc2(0) = 6.63T.