Preparation and characterization of TiO₂ doped and MgO stabilized Na-β″-Al₂O₃ electrolyte via a citrate sol-gel method

TiO₂ doped and MgO stabilized Na-β″-Al ₂O₃ is synthesized via a citrate sol-gel method starting with Al(NO₃)₃, NaNO₃, Mg(NO₃) ₂ and C₁₆H₃₆O₄Ti (tetrabutyl titanate, abbreviated as TBT). It is found that the TBT amount in the starting materials is the key factor to affect the properties of the final product, therefore, the samples sintered from precursors containing different amounts of TBT are systematically investigated by means of powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). Meanwhile, the relative density, mechanical strength and electrical properties of the prepared samples are also measured. The optimized sample contains 90.28% of β″ phase, exhibits a uniform and compact microstructure with a relative density as high as 99.5% of theoretical density (TD). In addition, this sample exhibits a bending strength up to 180 MPa and an ionic conductivity up to 0.21 S cm^-1 at 350 °C.