Possible Local Order in the High Entropy TrZr2 Superconductors

We have investigated the local structure of TrZr2 (Tr = transition metal) superconductor with variable configurational entropy using x-ray absorption spectroscopy. Temperature dependent Zr K-edge extended x-ray absorption fine structure (EXAFS) measurements are carried out on three different samples including the pristine CoZr2, medium entropy Co0.33Rh0.34Ir0.33Zr2 and high entropy Co0.2Fe0.2Ni0.2Rh0.2Ir0.2Zr2. We have found that the local bondlengths remain largely temperature independent or tend to show negative thermal expansion, instead the Zr–Zr bondlengths get stiffer with the configurational entropy. The x-ray absorption near edge structure (XANES) spectra at Zr K-edge and Ir L3-edge indicate Zr 4d - Tr nd (n = 2, 3, 4) hybridization to be related with the superconducting transition temperature. The results provide important information on the local structure that can be useful to understand the physical properties of these materials and design new high entropy alloys (HEAs) superconductors.