Effect of excess Na2O on the sintering behavior and properties of sodium beta-alumina solid electrolyte

The effect of excess Na2O on the properties of sodium beta-alumina solid electrolyte (BASE) was thoroughly investigated through relationships of the density, c-lattice parameter, beta ''-phase fraction, ionic conductivity and bending strength with the sintering temperature and the excess Na2O level. BASEs with a high level of excess Na2O showed a high density, a stable fraction of beta ''-phase, a high content of Na2O (small c-lattice parameter) and a fine grain microstructure when sintered at high temperature. BASE with a high level of excess Na2O also showed a high bending strength, but a high grain boundary impedance. The abnormal grain growth accounted for the seriously weakened bending strength and the greatly improved ionic conductivity in BASE with a low level of excess Na2O sintered at high temperature. Sintered at high temperature is a useful method for the sample with a high level of excess Na2O to obtain better conductivity and bending strength. These results are attributed to the varying roles of the excess Na2O in the sintering of BASE under different sintering temperature, including compensating the evaporation loss of Na2O, promoting the occurrence of transient ternary eutectic, and boosting the formation of secondary grain boundary phase. For better performance, the level of 6% excess Na2O is suggested as the optimized amount for a robust fabrication of BASE. Data availability: The raw/processed data required to reproduce these findings cannot be shared at this time due to technical or time limitations.