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Composite ionic conductors were produced by combination of alkaline carbonates with various ceramic oxides, including ceria, zirconia and alumina. The adopted mechano-thermal processing routes originated materials with the same nominal composition but with significantly different microstructures. The electrical performance of these composites, studied by impedance spectroscopy, showed the relevance of the mixed carbonate phase on the transport properties, but also unexpected composite effects. The role of grain size on the electrical performance could not be isolated from the possible influence of alkaline metal rich interfacial layers (ceramic/carbonate) consisting of nanosized 1D crystals. Modest electrode impedances in open air experiments are coherent with the coexistence of various charge carriers. The known interaction of major composite constituents and minor secondary phases with water might explain the presence of additional charge carriers.

Abstract. NASICON dense ceramics were obtained from solid state reaction between SiO2, Na3PO4.12H20 and two different types of zirconia: monoclinic ZrO2 and the yttria-doped tetragonal phase (ZrO2)o.97(Y203)ao 3. Higher temperatures were needed to obtain dense samples of the yttrium free composition (1265 ~ The electrical conductivity, at room temperature, of the yttria-doped samples sintered at 1230 ~ (0.20 S/m) is significantly higher than the value obtained with the material prepared from pure ZrO2. The impedance spectra show that the differences in conductivity are predominantly due to the higher grain boundary resistance of the undoped ceramics, probably due to formation of monoclinic zirconia and glassy phases along the grain boundary. Further improvement of the electrical conductivity could be achieved after optimization of the grain size and density of grain boundaries. A maximum conductivity value of about 0.27 S/m at room temperature was obtained with the yttria-doped samples sintered at 1220 ~ for 40 h. Yttria-doped and undoped ceramics were tested as Na § potentiometric sensors. The detection limit of the yttriadoped sample (10 .4 mold) was one order of magnitude lower than the obtained with the undoped material.

The present study reports the synthesis of Ce 0.8 Sm 0.2 O 1.9 solid electrolyte by a novel proteic sol-gel method which uses gelatin as polymerizing agent. The as-synthesized powder material was calcined at 700°C for 2 h, with X-ray diffraction revealing a single cubic phase with lattice parameter a = 0.5435 nm and theoretical density of 7.144 gcm -3 . The average crystallite size is 12 nm, as determined by the Scherrer equation. Impedance spectroscopy revealed a larger resistive contribution of the grain boundaries than that from grain bulk, which, due to its lower activation energy, tends to dominate the total conductivity above 650°C. The total conductivity is in line with literature data for ceramics of the same composition prepared by various methods, thus confirming the potential of the proteic sol-gel method as a green, low cost alternative synthetic route to prepare ceria-based solid electrolytes.