Sol-gel synthesis, X-ray, infrared spectra and electrical conductivity of lanthanum/bariumcobaltite systems

100-105Cubic perovskite-type pure lanthanum cobaltite, LaCoO3, LC and barium-substituted lanthanum of the chemical formula La1-xBaxCoO3, LBC, x = 0.0 (LC), 0.1, 0.3,0.5,0.8, 1.0, Powders are prepared using the polymerized complex technique at relatively low temperature. The complex solution, with molar ratios La (Ba) / Co / CA (citric acid) / EG (ethylene glycol) =1:1:10 : 40, is heated at 130°C to produce a dark Prussian transparent polymeric gel without any precipitation. Pyrolysis of the gel at 350oC gave a powder prec ursor of LC or LBC.Thermal analyses, X-ray diffraction and IR spectroscopy indicate the formation of single phase cubic LC or LBC when their precursors are heat -treated in air at temperatures > 500o/2h. For comparison, a solid -state reaction sample, LC, has been prepared, where traces of the parent ox ides appear even at higher sintering temperature (900°C). The lattice vibrations in LC precursor are heat-treated at different temperatures 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 confirm the composition to be LaCoO3 at 900°C. The electrical conductivity σ, of the ceramic LBC formed at 900°C/2h, as a function of Ba-content (x), has been measured at temperatures, 20 (room temp.), 100, 200 and 300°C. From the results, it is found that σ increases with the measuring temperature, while substitution of La- for Ba- is effective for enhancing the oxide ion conductivity in the range 0 where it decreases with further increase of x.