Hydrothermal synthesis, structure investigation, and oxide ion conductivity of mixed Si/Ge-based apatite-type phases.

Apatite-type oxides ([A(I)4][A(II)6][(BO4)6]O2), particularly those of the rare-earth silicate and germanate systems, are among the more promising materials being considered as alternative solid oxide fuel cell electrolytes. Nonstoichiometric lanthanum silicate and germanate apatites display pure ionic conductivities exceeding those of yttria-stabilized zirconia at moderate temperatures (500-700 °C). In this study, mixed Si/Ge-based apatites were prepared by hydrothermal synthesis under mild conditions rather than the conventional solid-state method at high temperatures.

Investigation into the effect of Si doping on the performance of Sr(1-y)Ca(y)MnO(3-δ) SOFC cathode materials.

In this paper we report the successful incorporation of silicon into Sr1-yCayMnO3-δ perovskite materials for potential applications in cathodes for solid oxide fuel cells. The Si substitution onto the B site of a (29)Si enriched Sr1-yCayMn1-xSixO3-δ perovskite system is confirmed by (29)Si MAS NMR measurements at low B0 field. The very large paramagnetic shift (~3000-3500 ppm) and anisotropy (span ~4000 ppm) suggests that the Si(4+) species experiences both Fermi contact and electron-nuclear dipolar contributions to the paramagnetic interaction with the Mn(3+/4+) centres.