Synthesis and characterization of titanium doped sodium beta″-alumina

High dense Na-β″-Al₂O₃ electrolyte materials have been synthesized by solid state reaction with boehmite, magnesia, sodium carbonate and titania as the starting materials. The effects of TiO ₂ doping percentage on the properties and microstructures of the prepared samples were investigated by X-ray diffraction (XRD), scan electron microscope (SEM), three point bending and ionic conductivity tests. The results indicated that both the relative densities and the phase purities of the samples could effectively improved after doping with TiO₂. The proper doping amount of TiO₂ was to form the transient liquid phase during the sintering process, which would reduce the steric effect and accelerate the diffusivity. Moreover, the mechanical performance of the obtained sample increased to the value above 280 MPa as the doping amount of TiO₂ was larger than 1 wt%. As to the electric properties, if the doping amount was less than 1 wt%, the grain boundary resistivity reduced as the density increased, so the ionic conductivity of the Na-β″-Al₂O₃ was enhanced obviously. However, when the doping amount was above 1 wt%, the ionic conductivity was deteriorated because of the increased resistivity caused by the broadening grain size.