Ionic conductivity of Na-doped SrSiO3

The conductivity of a newly proposed ionic conductor Na-doped SrSiO3 was studied. Powders were prepared by mixing of SrCO3, Na2CO3 and SiO2 in water or ethanol in order to explore the effect of solvents on the formation of secondary phases. X-ray diffraction was employed to study the phase composition of mixtures treated in air at different temperatures in the range 950-1050 C for 20 hours. Various heating schemes were applied to help the incorporation of Na in the monoclinic SrSiO3 structure. Pressed pellets were sintered at 1000 °C for 20 hours and electroded with Ag paste for electrochemical characterization by impedance spectroscopy. For most compositions and thermal treatments, the formation of the insulating Na2Si2O5 phase was observed as a matrix around grains of the monoclinic SrSiO3 phase (Fig. 1). Double calcination limited conductivity but increased its thermal stability. When ethanol was used for powder mixing, the material exhibited higher conductivity after long term ageing at 650 °C, also thanks to its low activation energy, without appreciable crystallization of other silicates