Quasi-In Situ 4D-STEM Mapping of Exsolution Driven Parent Matrix Restructuring in Sr₂FeMoO_6-δ

The in situ exsolution of catalytic particles upon reduction makes double-perovskites promising candidates for next-generation solid oxide cells (SOCs). While recent in situ S/TEM studies have -visualized this process, these investigations have primarily focused on isolated particles rather than realistic electrode architectures and the effect of exsolution on the surrounding host matrix remains largely unexplored. Herein, a quasi-in situ S/TEM approach is presented to investigate the impact of exsolution on a realistic Sr₂FeMoO_6-δ (SFM) electrode by decoupling the influence of electron-beam-induced artifacts. By extracting a lamella from a bulk SOC using a plasma-FIB and performing identical-location characterization utilizing EDS and 4D-STEM before and after reduction captures both the chemical segregation and intrinsic structural transformations within the electrode grains. Utilizing iDPC and radial Fourier analysis (RFA), this approach reveals that surface exsolution is coupled with substantial crystallographic reorganization within the SFM matrix, evidenced by distinct domain shrinkage and localized phase gradients along grain facets. The interconnected bulk electrode geometry promotes higher exsolution density compared to isolated powder particles, underscoring the necessity of studying realistic architectures. By linking surface exsolution to matrix modification in a realistic bulk electrode geometry, this quasi-in situ methodology provides a vital insights into the exsolution process.