Processing and electrical conductivity of pure, Fe- and Cr-substituted La0.9Sr0.1GaO3

The material La0.9S0.1GaO3 and four B-site substituted variants with 5 or 20% Fe or Cr for Ga substitution were prepared by solid stare reaction starting from oxide and carbonate precursors. The materials were characterised by scanning electron microscopy (SEM), X-ray diffraction (XRD) and impedance spectroscopy (IS) in air. The sintered samples appeared to have orthorhombic symmetry, had densities higher than 90% of theoretical and had average grain sizes of approx. 1-2.5 mu m. However, second phases were detected by XRD and SEM images showed evidence of a liquid, Sr-rich second phase in all samples. The high grain boundary impedances measured were attributed to concentration of this second phase at the grain boundaries. Generally, conductivity increased and activation energy of conduction decreased with increasing degree of substitution. Increasing p-type electronic conductivity involving CP3+/Cr4+ or Fe3+/Fe4+ couples is suggested. Raising the sintering temperature of these materials was shown to increase both their average grain size and their total conductivity. (C) 1997 Elsevier Science Limited.