| Summary: | Chemical compatibility and cation interdiffusion between the double perovskite cobaltites <i>R</i>BaCo<sub>2</sub>O<sub>6−δ</sub> (<i>R</i> = Gd, Pr) and proton-conducting electrolyte BaZr<sub>0.8</sub>Y<sub>0.2</sub>O<sub>3−δ</sub> were studied. Chemical interaction was found to occur already at 1100 °C as a result of the partial dissolution of <i>R</i>BaCo<sub>2</sub>O<sub>6−δ</sub> (<i>R</i> = Gd, Pr) in BaZr<sub>0.8</sub>Y<sub>0.2</sub>O<sub>3−δ</sub>. Analysis of the element distribution along the cross sections of diffusion couples <i>R</i>BaCo<sub>2</sub>O<sub>6−δ</sub>(<i>R</i> = Gd, Pr)|BaZr<sub>0.8</sub>Y<sub>0.2</sub>O<sub>3−δ</sub> showed strong interdiffusion of cations, with cobalt being the most mobile one. Its diffusion depth in the electrolyte reaches up to several hundreds of micrometers. The addition of NiO as a sintering aid to BaZr<sub>0.8</sub>Y<sub>0.2</sub>O<sub>3−δ</sub> promotes cation diffusion especially through the grain boundary mechanism, increasing the diffusion depth of Co. The possible implications of cation interdiffusion on the performance of proton-conducting SOFCs are discussed based on the results obtained.
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