Interrogation of 3d Transition Bimetallic Nanocrystal Nucleation and Growth Using In SituElectron Microscope and Synchrotron X-ray Techniques

Understanding the nucleation and growth mechanism of 3d transition bimetallic nanocrystals (NCs) is crucial to developing NCs with tailored nanostructures and properties. However, it remains a significant challenge due to the complexity of 3d bimetallic NCs formation and their sensitivity to oxygen. Here, by combining in situelectron microscopy and synchrotron X-ray techniques, we elucidate the nucleation and growth pathways of Fe–Ni NCs. Interestingly, the formation of Fe–Ni NCs emerges from the assimilation of Fe into Ni clusters together with the reduction of Fe–Ni oxides. Subsequently, these NCs undergo solid-state phase transitions, resulting in two distinct solid solutions, ultimately dominated by γ-Fe3Ni2. Furthermore, we deconvolve the interplays between local coordination and electronic state concerning the growth temperature. We directly visualize the oxidation-state distributions of Fe and Ni at the nanoscale and investigate their changes. This work may reshape and enhance the understanding of nucleation and growth in atomic crystallization.