Conductivity of La0.95Sr0.05Ga0.90Mg0.10O3−δ obtained by mechanical activation

Dense ceramics of La0.95Sr0.05Ga0.90Mg0.10O3−δ (LSGM) were obtained from La2O3, SrO, Ga2O3 and MgO precursors activated by dry grinding in a high-energy planetary ball-mill. Samples sintered at 1450 °C for 4 h have an average grain size of ca. 250 nm. This value increases to 5 μm when the sample is annealed for 40 h at the same temperature. Samples prepared by a conventional ceramic route were also obtained with a grain size of 13.5 and 20.5 μm, after sintering at 1550 °C for 4 and 40 h, respectively. Impedance spectroscopy data revealed similar grain conductivities for both materials. However, a significant degradation was observed on ageing the LSGM prepared by the conventional ceramic route, probably due to compositional alterations at the grain boundaries. This degradation was not present in the material prepared from mechanically activated precursors. Grain size effects on the electrical conductivity were analysed to determine the effective grain boundary conductivity and the brick-layer model is assumed to estimate the grain boundary thickness.