Microstructure and electrical properties of aluminium-substituted La(Sr)Ga(Mg)O3-δ-based solid electrolytes

Abstract

A study of the influence of the substitution of Al for Ga in the ceramic processing and electrical properties of La0.95Sr0.05Ga0.90–xAlxMg0.10O3–d (0 B x B 0.3) solid electrolytes is presented. The materials retained orthorhombic symmetry over the entire substitution range, whereas a deviation from Vegard’s law for x[0.20 suggested a maximum Al solubility of x = 0.20. Scanning electron microscopy analysis of ceramic samples revealed that grain growth was inhibited for x C 0.2. This microstructural change was related to an apparent deterioration of mechanical properties, as suggested by room-temperature Vickers hardness measurements. Impedance spectroscopy revealed a significant degradation of the grain-boundary electrical properties for x C 0.20, whereas the bulk conductivity was enhanced for 0.10 B x B 0.15. Oxygenpermeability measurements confirmed that the studied materials remain essentially pure ionic conductors. An ionic conductivity maximum of 0.047 S/cm at 700 C was obtained for x = 0.10. The effect of aluminium in the grainbulk ionic conductivity is discussed in terms of defect cluster models and assuming fast oxygen diffusion along domain walls.