Electrical conductivity and mechanical properties of alumina-dispersed doped lanthanum gallates

With the aim of increasing the mechanical strength of doped lanthanum gallate ceramics, which can be applied to the electrolyte in solid oxide fuel cells for reduced temperature operation, the effects of alumina dispersion on mechanical and electrical properties were investigated. The thermal expansion coefficient showed no significant changes either with the amount of alumina addition or with the oxygen partial pressure in the atmosphere. The alumina dispersion preferably along grain boundaries was found to be effective in retarding the grain growth of lanthanum gallate, which greatly increased the bending strength at both room temperature and 800°C. The sample with 2 wt% of alumina addition showed electrical conductivity comparable to that of the perovskite matrix alone at 800°C and higher conductivity at temperatures lower than 750°C. At additions of ≥5 wt%, the alumina grains partially blocked the transport of oxide ions between the lanthanum gallate grains, which decreased the ionic conductivity to unacceptable levels. The optimum alumina addition for the improvement of mechanical properties without altering the thermal expansion coefficient and ionic conductivity was found to be around 2 wt%. A single-cell using the electrolyte sheet with the optimized composition showed a maximum power density of 0.245 W/cm2 at 800°C.