When Atoms Choose Their Neighbors: Element-Specific Views of Local Chemical Order in High-Entropy Alloys

Abstract

Local chemical order (LCO) is a key descriptor linking composition, atomic arrangement, and function in high-entropy alloys (HEAs), yet remains difficult to quantify. This Perspective highlights how X-ray absorption spectroscopy (XAS) provides element-specific, quantitative insight into LCO in complex alloys. We outline practical considerations for XAS data collection and fitting, including width of spectra range, multi-temperature analysis, and X-ray absorption edge choice for 5d elements. We then highlight a coordination-number-based framework for LCO analysis and use model HEAs to show how single-atom and near-single-atom motifs naturally emerge as component number increases, bridging HEAs and single-atom alloys. Finally, we identify priorities including standardized protocols, uncertainty quantification, expanded operando and time-resolved XAS, and integration with complementary characterization and modelling.