The synthesis of mixed phases in the Ca-Co-O system using the Pechini method was investigated. The phases CaCo2O4, Ca3Co4O3 and Ca3Co2O6, which can be expressed in terms of the molar ratios of the binary oxides (CaO:Co2O3) as (1:1), (3:2) and (3:1) respectively, were obtained in pure form. Powder X-ray diffraction data showed they are comparable with materials obtained by conventional solid-state synthesis. The mild synthesis conditions of the Pechini method allowed the evolution of the Ca-Co-O phases to be studied as a function of temperature and heating time. Both variables have a strong influence on the composition of the products, indicating that both kinetic and thermodynamic factors play a role, with the former being of more importance at lower temperatures. The (1:1) phase, previously not identified in the phase diagram of the Ca-Co-O system, was obtained preferentially across the composition range below ca. 650 degrees C. The (3:2) phase was preferred until ca. 800 degrees C. At even higher temperatures, the (3:1) phase is obtained. The upper thermal stability limit of mixed phases in the Ca-Co-O system increases with the Ca:Co ratio. An updated phase diagram for the Ca-Co-O system is proposed. (C) 2013 Elsevier Ltd. All rights reserved.