Synthesis, X-ray, infrared spectra and electrical conductivity of La/Ba–CoO3 systems

LaCoO3, LC, and La1−xBaxCoO3, LBC, x=0.0–1.0, powders were prepared using the polymerized complex technique at relatively low temperature. The complex solution, with molar ratios La (Ba)/Co/citric acid (CA)/ethylene glycol (EG)=1:1:10:40, was heated at 130 °C to produce a gel. Pyrolysis of the gel at 350 °C yielded a powder precursor of LC or LBC. Thermal analysis, XRD, and IR spectra indicated the formation of a cubic LC or LBC when their precursors were heated above 500 °C in air for 2 h. On the other hand, traces of the parent oxides appeared in a sample prepared via a solid-state reaction even at higher sintering temperature (900 °C). The lattice vibrations in LC and LBC as a function of Ba-additions indicate the structural changes with temperature or barium effect, respectively. The amounts of metals, determined by AAS, in the samples after annealing confirmed the composition to be LaCoO3 at 900 °C. Electrical conductivity, σ, of the ceramic LBC formed at 900 °C per 2 h as a function of Ba-content (x) was measured at selected temperatures where σ increased with the measuring temperature. Substitution of La- for Ba- is effective for enhancing the oxide ion conductivity in the range 0<x<0.5 where it decreases with further increase of x.