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In this work, La6–x MoO12−δ (0 ≤ x ≤ 0.8) materials are investigated as a new family of ceramic proton conductors. Different polymorphic phases with rhombohedral and cubic structure are obtained, depending on the cooling rate applied during the synthesis process. The materials have been thoroughly characterized by different techniques, including X-ray powder diffraction, transmission electron microscopy, and X-ray photospectroscopy in order to fully understand the structural features of the samples. Thermogravimetric analysis and impedance spectroscopy in dry/wet gases (N2, O2, and 5% H2–Ar) confirmed the existence of proton conductivity at low temperature. Under a reducing atmosphere, the materials are mixed ionic-electronic conductors. The sample prepared at the fastest cooling rate exhibits cubic structure and higher n-type electronic conductivity compared to those prepared at a slower cooling rate with rhombohedral structure.

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In this paper we report the successful incorporation of silicon into SrFeO 3Àd perovskite materials for potential applications as electrode materials for solid oxide fuel cells. It is observed that Si doping leads to a change from a tetragonal cell (with partial ordering of oxygen vacancies) to a cubic one (with the oxygen vacancies disordered). Annealing experiments in 5% H 2 /95% N 2 (up to 800 C) also showed the stabilization of the cubic form for the Si-doped samples under reducing conditions, suggesting that they may be suitable for both cathode and anode applications. In contrast to the cubic cell of the reduced Si doped system, reduction of undoped SrFeO 3Àd leads to the formation of a brownmillerite structure with ordered oxide ion vacancies. SrFe 0.90 Si 0.10 O 3Àd and SrFe 0.85 Si 0.15 O 3Àd were analysed by neutron powder diffraction, and the data confirmed the cubic cell, with no long range oxygen vacancy ordering. Mössbauer spectroscopy data were also recorded for SrFe 0.90 Si 0.10 O 3Àd , and indicated the presence of only Fe 3+ and Fe 5+ (i.e. disproportionation of Fe 4+ to Fe 3+ and Fe 5+) for such doped samples. Conductivity measurements showed an improvement in the conductivity on Si doping. Composite electrodes with 50% Ce 0.9 Gd 0.1 O 1.95 were therefore examined on dense Ce 0.9 Gd 0.1 O 1.95 pellets in two different atmospheres: air and 5% H 2 /95% N 2. In both atmospheres an improvement in the area specific resistance (ASR) values is observed for the Si-doped samples. Thus the results show that silicon can be incorporated into SrFeO 3Àd-based materials and can have a beneficial effect on the performance, making them potentially suitable for use as cathode and anode materials in symmetrical SOFCs.