The mechanical and electrical properties of ZrO2–TiO2–Na-β/β″-alumina composite electrolyte synthesized via a citrate sol–gel method

It is well known that certain amounts of TiO2 doping or ZrO2 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″-Al2O3 electrolyte. The resulting ZrO2–TiO2–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).