Thin-Film Paradigm to Probe Interfacial Diffusion during Solid-State Metathesis Reactions

We highlight a paradigm for studying complex reaction mechanisms that guide the synthesis of materials. Thin films of FeCl2 and Na2S2 were deposited to study the metathesis reaction to form FeS(2)and NaCl. In situ X-ray reflectivity was used to monitor the interface between materials, which revealed a slow, impeded reaction at high temperatures as compared to previous studies using powder samples. AC impedance and X-ray photo-electron spectroscopy provided insight into distribution of elements and conductivity of the phases present during the reaction, and phase-field modeling was used to elucidate the diffusion of ions throughout the thin-film bilayers. The use of thin-film bilayers provides a simplified system to study solid-state metathesis reactions and highlights the complexity of diffusion at solid-state interfaces.