Element-Specific Local Chemical Order of High-Entropy Nanoalloys

Multielemental nanoalloys have shown significant promise in applications like catalysis, due to the structural features that arise from their complex structure. A key feature of particular interest is local chemical order (LCO) at the scale of a single neighboring bond length. LCO has proven challenging and inconclusive to identify and assess in these materials, particularly in samples containing elements with similar atomic numbers. Herein, we apply a methodology combining experimental X-ray absorption spectroscopy and computational simulations, allowing for the reliable verification and quantification of LCO in a five-element high-entropy alloy (HEA-5) on an element-specific basis. The analysis identifies the Ru-Ir bonding pair as a significant component of LCO, which correlates with HEA-5's established high catalytic performance in ammonia decomposition. The methodology is further applied to a complex 15-element HEA sample, where consistent LCO trends are observed. These results support an element-specific approach for investigating LCO, structural analysis, and the catalytic design of high-entropy nanoalloys.