Calcium cobaltite materials are synthesized by calcining the mixture of CaCO3 and Co3O4 with the Ca: Co ratio of 3:4. The reactivity of CaCO3 with Co3O4 is evaluated by thermogravimetric analysis (TGA), X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Thermal expansion coefficient (TEC), electrical conductivity and electrochemical performance as intermediate-temperature solid oxide fuel cells (IT-SOFCs) cathode of as-prepared materials are characterized. The experiment results show that simultaneous decomposition of CaCO3 with calcium cobaltite formation occurs at 650-900 degrees C. The average valence for Co ions of calcium cobaltite increases with temperature in the range of 750-900 degrees C, involved in the formation of the compounds Ca3Co4O3 and Ca9Co12O28 at 800 and 900 degrees C, respectively. The performance of calcium cobaltite cathodes applied in IT-SOFCs is significantly effected by the oxidation state of cobalt ions. As a result, Ca3Co12O28 cathode has a lower area specific resistance (e.g. 41.8% lower at 800 degrees C) and higher peak power density (e.g. 45.0% higher at 800 degrees C) than the cathode of Ca3Co4O9. (C) 2015 Elsevier B.V. All rights reserved.