Experimental Determination of the Formation Enthalpy of Calcium Cobaltate from Sol–Gel Precursors

Calcium cobaltate (Ca₃Co₄O₉) remains one of the most promising p-type oxide materials for high-temperature thermoelectric energy conversion. While much progress has been made in refining our understanding of the unique structure of the material, as well as optimization of the transport properties for thermoelectric efficiency, there remains a gap in the knowledge, both experimental and theoretical, of the thermodynamics of the system. Presented herein is an analysis of the heat of formation of the Ca₃Co₄O₉ phase from sol–gel precursors using a highly sensitive differential scanning calorimeter, as well as observations of its decomposition into the Ca₃Co₂O₆ phase. The reaction enthalpy of forming Ca₃Co₄O₉ from CaCO₃ and Co₃O₄ sol–gel precursors was determined to be +284 (±2%) kJ/mol, leading to a standard enthalpy of Ca₃Co₄O₉ of −3307 (±3.5%) kJ/mol.