Synthesis, extrusion processing and ionic conductivity measurements of sodium β-alumina tubes

Abstract

Pure and Li-doped sodium β-alumina (NaMg0.67Al10.33O17) ceramics were prepared from the stoichiometric mixture of raw powders. Pellets and tubes were formed from the precursor (NBA-1S) and preformed sodium β-alumina powder through compaction and extrusion processing, respectively. The obtained specimens were finally sintered to dense ceramics. The ceramics were comparatively evaluated for their density, microstructure, phase formation and electrical properties. Both tubes and pellets processed with the preformed sodium β-alumina powder (NBA-2S) showed enhanced densification along with relatively better phase purity and crystallinity. The ceramics prepared from the preformed powder exhibited higher density of 94–95% TD (theoretical densities) in comparison to the ceramics processed from the raw mixture (NBA-1S) with a density of 85–87% TD, which are complemented well through fractographs and microstructures. The ceramics processed using the preformed sodium β-alumina (NBA-2S) also exhibited high room temperature AC conductivity of 1.77×10-4 S/cm (1 MHz) with an increasing trend with temperature. The higher ionic conductivity at all temperatures in NBA-2S than in NBA-1S ceramics can be attributed to the relatively high phase purity, crystallinity and higher density values of NBA-2S ceramics.