Synthesis and characterization of sodium titanates Na{sub 2}Ti{sub 3}O{sub 7} and Na{sub 2}Ti{sub 6}O{sub 13}

Na{sub 2}Ti{sub 3}O{sub 7} and Na{sub 2}Ti{sub 6}O{sub 13} were synthesized by sol-gel method in order to obtain pure phases. Different heat-treatments were applied on powders and pellets of these materials. The effects were studied by XRD, dilatometry, TGA-DTA, SEM and electrochemical impedance spectroscopy. Pure Na{sub 2}Ti{sub 3}O{sub 7} was obtained at 973K. Sintering at 1373K caused a partial decomposition into Na{sub 2}Ti{sub 6}O{sub 13}. The Na{sub 2}Ti{sub 3}O{sub 7} powder sintered at 1273K showed polygonal microstructure. Na{sub 2}Ti{sub 3}O{sub 7} pellets sintered at 1323K for 10h exhibited large structures. This latter microstructure decreased the electrical conductivity of Na{sub 2}Ti{sub 3}O{sub 7}. Pure Na{sub 2}Ti{sub 6}O{sub 13} was obtained at 873K. Sintering at 1073K caused a partial decomposition into TiO{sub 2} (rutile). Na{sub 2}Ti{sub 6}O{sub 13} pellets sintered at 1323K for 10h exhibited common shrinkage behavior. This shrinkage process increased the electrical conductivity of this material. The presence of TiO{sub 2} resulted in a oxygen partial pressure dependence of the electrical conductivity.