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 La$_2$Zr$_2O$_7$, while ultrathin films gradually dewet and aggregate, underscoring their instability as model electrodes. Furthermore, we show that the LSM bulk favors the less conductive rhombohedral phase, whereas, at the LSM/YSZ interface, a cubic-like LSM polymorph with enhanced electronic transport is stabilized, accompanied by oxygen vacancies, Mn2$^+$ enrichment, and cation disorder. These insights provide design principles for stabilizing interfaces to improve the efficiency and durability of SOCs.