Mixed conduction induced by grain boundary engineering

Mixed oxygen-ion electronic conductors were prepared starting from the well-established solid electrolyte La0.95Sr0.05Ga0.90Mg0.10O3−δ (LSGM). The adopted strategy involved selective grain boundary doping with iron to form a grain boundary region with high electronic conductivity. Scanning electron microscopy coupled with energy dispersive spectroscopy (SEM/EDS), impedance spectroscopy in air (around 300 °C) and high temperature (700–800 °C) ac conductivity measurements as a function of pO2pO2 all suggest that this doping strategy was successful. In fact, on increasing the Fe-dopant level, Fe always concentrated along the grain boundary region (as confirmed by SEM/EDS), the total conductivity increased and each individual impedance arc decreased, in agreement with predictions based on the presence of a parallel pathway for electronic transport. Furthermore, the increase in total conductivity (σ) with dopant level showed a positive log σ   versus log⁡pO2log⁡pO2 dependence, typical of hole conductivity.