Interfacial Atomic and Electronic Structures of LSM/YSZ Thin Films as Models for SOC Air Electrodes

Solid oxide cells (SOCs) are highly efficient electrochemical devices, yet their high‐temperature operation induces structural instabilities that limit long‐term performance. Thin‐film electrodes provide a model platform to probe such effects due to their well‐defined geometry and chemistry. Here, we combine high‐resolution electron microscopy, synchrotron X‐ray spectroscopy, and density functional theory to investigate the thermal stability of epitaxial lanthanum–strontium manganite (LSM) films on yttria‐stabilized zirconia (YSZ). Comparing ultrathin (5 nm) and thick (200 nm) films under sintering (1150°C) and operating (800°C) conditions, we identify distinct degradation pathways: thick films remain largely stable but form interfacial , while ultrathin films gradually dewet and aggregate, underscoring their instability as model electrodes. Furthermore, we show that the LSM bulk favors the less conductive rhombohedral phase, whereas, at the LSM/YSZ interface, a cubic‐like LSM polymorph with enhanced electronic transport is stabilized, accompanied by oxygen vacancies, Mn enrichment, and cation disorder. These insights provide design principles for stabilizing interfaces to improve the efficiency and durability of SOCs.