Real‐Time Observation of Oxygen Diffusion in CGO Thin Films Using Spatially Resolved Isotope Exchange Raman Spectroscopy

The exploitation of advanced materials for novel energy, health, and computing applications requires deep insight and fundamental understanding of physicochemical mechanisms, such as ionic and electronic conductivity, defect formation processes, and reaction kinetics. Therefore, access to the underlying constants of the functional materials via advanced but accessible and straightforward experimental techniques is key. Herein, a novel, cheap, fast, and widely applicable approach is presented to analyze oxygen tracer diffusion in thin films with unprecedented time resolution based on the novel in situ isotope exchange Raman spectroscopy (IERS) methodology. IERS utilizes the sensitivity of micro‐Raman spectroscopy to changes in the local isotopic composition. In‐plane tracer diffusion gradients are established by partially blocking the exchange at the surface followed by an isotope exchange. The isotope exchange and diffusion processes are followed via consecutive spatial and time‐resolved in situ Raman line scans. These isotopic gradients are analyzed to obtain mass transport coefficients, with an additional time component, not accessible by conventional destructive techniques. Diffusion coefficients of gadolinium‐doped ceria (CGO) thin films are reported within the range of interest for intermediate‐temperature emerging applications and confirm the validity of the measurement procedure and extracted parameters by comparison with the finite‐element method simulations and literature results.