The interplay of microstrain, macrostrain, and ligand effects in the electronic structure evolution of nonequilibrium Fe-Ni nanoalloys

We investigate the structural and electronic evolution of nonequilibrium FexNi1-x (0 < x < 1) solid solutions synthesized via high-energy ball milling. X-ray diffraction reveals a composition-dependent bcc-to-fcc phase transition between x = 0.80 and 0.64, alongside significant peak broadening driven by the evolution of non-uniform microstrain and nano-structure. Extended x-ray absorption fine structure spectroscopy at the Fe and Ni K-edges quantitatively maps local structural disorder and interatomic distances, demonstrating a self-consistent correlation between short-range local environments and long-range crystalline order. In parallel, x-ray absorption near-edge structure spectra unveil a pronounced, composition-dependent modulation of the electronic structure. We investigate the structural origins of these spectral changes, showing that while non-uniform microstrain induces local structural disorder, the spectral evolution is predominantly governed by macroscopic uniform strain and local coordination chemistry. Within the fcc regime, divergent compositional trends in the Fe and Ni K-edge shoulder features reflect systematic reconfigurations of the unoccupied 3d/4s-4p hybridized states, primarily driven by charge redistribution. Concurrently, uniform lattice strain resulting from atomic size mismatch dictates the energy shifts of high-energy spectral features. These mechanisms are validated by high-energy-resolution fluorescence detected x-ray absorption spectroscopy and density functional theory calculations, providing a comprehensive electronic-level descriptor of how mechanical alloying modulates the physical chemistry of transition metal solid solutions.