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Dielectric properties are reported for lead magnesium niobate (PbMgliJNb2/303) ceramics which were prepared as single phase (i.e., without pyrochlore) with an improved technique. Dielectric constants of 18 000 for pure PMN and 31 000 for PMN with 10% PbTi03 were achieved; these values are 50% larger than those reported in the literature. The dielectric constant of PMN ceramics was found to increase with both sintering temperature and excess MgO, and subsequent analysis of the microstructures confirmed that this was due to an increase in grain size. This grain-size dependence is explained as a consequence of low-permittivity grain boundaries.

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Dense perovskite-structured membranes with desired composition of La0.8Sr0.2Co0.6Fe0.4O3 - δ (LSCF) were prepared from powders produced by four different methods. LSCF powders prepared by citrate, solid-state, and spray−pyrolysis methods had compositions close to the desired stoichiometry with a slight difference in cobalt concentration, whereas coprecipitated powders had a large strontium deficiency. The membrane composition was a determining factor that affected the electronic conductivity and therefore oxygen permeability. The membrane with a large strontium deficiency had much lower electronic conductivity and oxygen permeability (ionic conductivity) than the other three membranes with compositions close to the desired stoichiometry. The electronic conductivity of membranes prepared from citrate, solid-state, and spray−pyrolysis methods increases with the cobalt concentration of the membrane. For the three membranes with similar composition, the activation energy of oxygen flux decreases with increasing grain size. Oxygen pressure dependency of oxygen vacancy concentration is also influenced by the membrane microstructure and composition. LSCF membranes with same composition and similar microstructure should have similar electric and oxygen transport properties.

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