Abstract
An overview is presented on the variation of electrical conductivity, oxygen permeation,
oxygen surface exchange and thermal expansion coefficient as a function of the composition of
perovskites in the quasi-ternary system LaFeO3-LaCoO3-LaNiO3. Powders of thirteen nominal
perovskite compositions were synthesized under identical conditions by the Pechini method. The
powder X-ray diffraction data of two series, namely La(Ni0.5Fe0.5)1-xCoxO3 and LaNi0.5-
xFexCo0.5O3, are presented after the powders had been sintered at 1100°C for 6 h in air. The
measurements revealed a rhombohedral structure for all compositions except LaNi0.5Fe0.5O3 for
which 60% rhombohedral and 40% orthorhombic phase was found. The maximum DC electrical
conductivity value of the perovskites at 800 °C was 1229 S cm-1 for the composition LaCoO3 and
the minimum was 91 S cm-1 for the composition LaCo0.5Fe0.5O3. The oxygen permeation of
samples with promising conductivities at 800 °C was one order of magnitude lower than that of
La0.6Sr0.4Co0.8Fe0.2O3 (LSCF). The highest value of 0.017 ml cm-2 min-1 at 950 °C was obtained
with LaNi0.5Co0.5O3. The coefficients of thermal expansion varied in the range of 13.2 x 10-6 K-1
and 21.9 x 10-6 K-1 for LaNi0.5Fe0.5O3 and LaCoO3, respectively. 57Fe Mössbauer spectroscopy
was used as probe for the oxidation states, local environment and magnetic properties of iron
ions as a function of chemical composition. The substitution had a great influence on the
chemical properties of the materials.
