The effect of synthesis and thermal treatment on phase composition and ionic conductivity of Na-doped SrSiO3

The structural and electrochemical properties of Sr1-xNaxSiO3 were studied. Powders with different compositions (0.1<=x<=0.45) were prepared by solid state reaction. Mixing of SrCO3, Na2CO3 and SiO2 was carried out in different media in order to explore the possibility to avoid the use of organic solvents and formation of secondary phases. Thermogravimetric analysis was carried out on binary and ternary mixtures of precursors to point out the various steps taking place during calcination. X-ray diffraction was employed to study the phase composition of mixtures treated in air at different temperatures in the range 800-1050 C for at least 10 hours. Various heating schemes were applied to help the incorporation of Na in the perovskite structure. Pressed pellets were sintered at 1000 C for 12 hours and electroded with Ag paste for electrochemical characterization. Conductivity was investigated by Impedance Spectroscopy. For some compositions and thermal treatments the formation of the insulating Na2Si2O5 phase was observed, as reported in literature [1]. However, the incorporation of Na in SrSiO3 was obtained to different extents depending on processing conditions. Phase purity was individuated as the most important feature to get oxide ion conductivity.