Investigation of Na5GdSi4O12(NGS) NASICON and highly doped NGS NASICON prepared by spray-freeze/freeze-dry methods using complex plane analysis

Abstract Complex plane techniques have been employed to measure bulk and grain boundary effects, as well as electrode/electrolyte interface effects in polycrystalline samples of pure Na5GdSi4O12 and Na5GdSi4O12 doped with either Eu(III) or Ce(III). The technique of spray-freeze/freeze-drying was employed to prepare highly dense NASICON ceramics. The densities of Na5GdSi4O12 and 10 wt% Ce-doped Na5GdSi4O12 sintered pellets were > 94% of theoretical (3.213 g/cm3) and at 300°C the bulk conductivities were 0.21 and 0.18 S-cm−1, respectively. Densities of the 10 wt% Eu-doped samples were low (78–84%), yet the multiphase ceramics exhibited high Na+ conductivities of 0.3 S-cm−1 at 300°C.