Processing, microstructure and properties of LaCoO3−δ ceramics

Dense lanthanum cobaltite ceramics with different microstructures were prepared using several processing procedures, including chemical and ceramic synthesis routes. XRD, SEM, dilatometry, total electrical conductivity and oxygen permeability measurements were used for the characterization of these materials. Submicrometer size LaCoO3−δ powders obtained via a cellulose-precursor technique or a combustion synthesis process showed much higher sinterability and poor compactability with respect to the powder prepared by the standard ceramic procedure. The influence of the processing route on crystal lattice, electronic conductivity and thermal expansion of LaCoO3−δ ceramics was negligible. At the same time, the preparation technique significantly affects the ceramic microstructure and the oxygen ionic conductivity. LaCoO3−δ membranes prepared via the standard ceramic technique, involving higher sintering temperatures, exhibit significantly higher oxygen permeation fluxes than ceramics prepared from organic precursors. This behavior was attributed to the effect of grain-boundary resistivity to ionic transport, which decreases with increasing sintering temperature and grain size, as commonly found for oxide solid electrolytes.