The mechanical and electrical properties of ZrO₂-TiO ₂-Na-β/β″-alumina composite electrolyte synthesized via a citrate sol-gel method

It is well known that certain amounts of TiO₂ doping or ZrO ₂ addition can densify the microstructure of Na-β/β″- Al₂O₃. The TiO₂ doping sample usually exhibits improved ionic conductivity with moderate mechanical property, while the sample with ZrO₂ addition shows greatly improved mechanical property, but with poor ionic conductivity. In order to obtain both high mechanical strength and high ionic conductivity, various amounts of ZrO₂ (0-20 wt%) have been added into 1 wt% TiO₂ doped Na-β/β″-Al ₂O₃ electrolyte. The resulting ZrO₂-TiO ₂-Na-β/β″-Al₂O₃ composite electrolytes are systematically investigated by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The relative density, mechanical strength and electrical properties of the prepared samples are also measured and discussed in detail. Compared to the bending strength (140 MPa) and ionic conductivity (0.037 S cm^-1 at 350 °C) of the non-doped sample, the sample doped with 1 wt% TiO₂ and 10 wt% of ZrO₂ exhibits much higher values on both bending strength (196.3 MPa) and ionic conductivity (∼0.2 S cm^-1 at 350 °C).