Synthesis and characterisation of La0.95Sr0.05GaO3-δ, La0.95Sr0.05AlO3-δ and Y0.95Sr0.05AlO3-δ

The oxide-ion conducting phases La0.95Sr0.05GaO3-delta (LSG), La0.95Sr0.05AlO3-delta (LSA) and Y0.95Sr0.05 AlO3-delta (YSA) have been synthesised, either by solid state reaction or through a chemical route. Structural and microstructural characterisation was carried out using XRD and SEM/EDS techniques and a.c. impedance spectroscopy (250-1000 degrees C) was employed to determine the electrical properties. Although low-temperature impedance results were strongly dependent on phase purity, and microstructure, high temperature electrical conductivity data could be used to compare the electrical conductivities of LSG, LSA and YSA. Chemical modification from the well-known Sr-doped lanthanum gallate via replacement of different cations on the A and/or B site decreased the conductivity, increased the activation energies and decreased the ionic conductivities. From the results, there is no simple correlation between oxygen ion conductivity geometric aspects related to unit cell parameters and cation radii. Instead, cation polarisability seems to play an extremely important role in designing improved oxygen ion conductors based on the perovskite structure. (C) 1999 Elsevier Science Limited. All rights reserved.