Preparation and characterization of CoO-doped and Li2O-stabilized Na-β″-Al2O3 solid electrolyte via a solid-state reaction method

The Na-β"-Al2O3 solid electrolyte ceramic material doped with CoO was synthesized via a solid-state reaction method, which began with α-Al2O3 and Na2CO3 as the raw materials and involved a low-cost burying process. The effects of different contents of CoO on the properties of the material were investigated as Li2CO3 was added as a stabilizer. The CoO amount in the initial materials is the key to obtaining quality products. Therefore, samples sintered from precursors containing different amounts of CoO were systematically characterized using thermogravimetry/differential thermal analysis (TG-DTA), X-ray diffraction (XRD), and field emission scanning electron microscopy (FE-SEM). Additionally, the relative density and electrical properties of the prepared samples were also measured by the Archimedes method and AC impedance spectroscopy. The Na-β"-Al2O3 solid electrolyte with an optimal amount of CoO of 1 wt% exhibited a uniform and dense microstructure with a relative density of as much as 97.98% (3.194 g cm⁻3) of the theoretical density. However, excess 1.25 wt% CoO doping can cause the sample too loose and make pores between the grains larger. This deteriorates the ionic conductivity of the material. In addition, the sample with the appropriate amount of CoO exhibited an ionic conductivity of up to 0.061 S cm−1 at 300 °C with a corresponding activation energy of 0.179 eV.