In situ high temperature X-ray diffraction and dilatometric analysis of CGO–Cu composites for solid oxide devices

Understanding the thermo-mechanical compatibility of composite electrodes is essential for the long-term reliability of solid-oxide electrochemical devices. In this study, we demonstrate a combined in situ synchrotron X-ray diffraction (XRD) and simultaneous dilatometry approach as a rapid and predictive method to quantify both phase-resolved and bulk thermal expansion while tracking microstructural evolution at operational temperatures. Ce_0.8Gd_0.2O_2-δ-Cu (CGO-Cu) composites with varying CGO: Cu ratios (39:61-70:30 vol%) were synthesized as potential anode materials compatible with CGO electrolytes up to 800 °C. In situ XRD confirmed only the CGO and Cu phases, with Rietveld refinement revealing a slight lattice expansion and reduced CGO crystallite size with increasing CGO content. Concurrent dilatometry indicated systematic changes in the macroscopic thermal expansion and densification behavior, which correlated with the phase and microstructural evolution observed during heating. The CGO-Cu (59:41) composite exhibited a nearly temperature-independent coefficient of thermal expansion consistent with the rule-of-mixtures predictions and minimal high-temperature shrinkage. These findings validate the combined in situ synchrotron XRD + dilatometry methodology as a powerful approach for characterizing and capturing the TEC characteristics of cermets, and for guiding the design of thermomechanically compatible oxide-metal composites for high temperature electrochemical applications.