 The phosphate-containing cobalt mixtures of non-calcined, calcined, and composite materials were synthesized in atmospheric conditions and characterized by different measurement techniques. Thermal study of these materials was carried out using DSC and TG–DTA techniques. From the study of thermal behaviour, it is observed that the composite material can not only be used as a sensible thermal heat storage material, but also can be used as a heat-dissipating material. The thermal behaviour of calcined mixture indicates its potential application towards use as a sensible thermal heat storage material due to its endothermic nature at high temperature. Average crystallite sizes were determined using the well-known Debye–Scherrer equation and are found to be 37.0 nm and 28.6 nm for the non-calcined and calcined mixture, respectively. The calculated band gap, Eg, of both the mixtures indicates their semiconducting behaviour at room temperature, and the calculated refractive index using the Moss and Ravindra relation are 2.52 and 2.62 for the non-calcined and calcined mixtures, respectively.