Mixed conduction induced by grain boundary engineering

摘要

Mixed oxygen-ion electronic conductors were prepared starting from the well-established solid electrolyte La_(0.95)Sr_(0.05)Ga_(0.90)Mg_(0.10)O_(3- delta) (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 deg C) and high temperature (700-800 deg C) ac conductivity measurements as a function of p_(o_2) 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 (sigma) with dopant level showed a positive log sigma versus log p_(o_2) dependence, typical of hole conductivity.