Optical and Electromagnetic Properties of LaCoO3:Li+;M2+ (M = Ca, Sr, Ba)

Lanthanum cobaltates modifi ed by alkaline-earth-metal (0.10 mol%) and lithium (0.05 mol%) ions were synthesized. The samples had an orthorhombic distorted perovskite-like structure according to x-ray diffraction phase analysis. Addition of Li + and M 2+ (M = Ca, Sr, Ba) to the LaCoO3 matrix was shown to increase the unit-cell parameters, the optical band width (Eg), and the average Co oxidation state (Co n+ ). Pure and doped LaCoO3 were characterized by the presence of paramagnetic centers as isolated structural and surface Co 2+ ions and adsorption complexes [Co 3+ ··· 2 O − ] • on the surface of the oxide matrix at a concentration that increased in the order Ba > Sr > Ca. The cobaltates were found to possess Mott hopping conduction in the temperature range 77–298 K.