Formation mechanism of strontium cobaltite containing equimolar amounts of Sr and Co from SrCO3 and Co3O4

• During heating of the SrCO 3 Co 3 O 4 mixture, Sr 6 Co 5 O 15-β is formed firstly. • During heating of the SrCO 3 Co 3 O 4 mixture, Sr 2 Co 2 O 5-δ is formed finally. • Sr 2 Co 2 O 5-δ decomposes to Sr 6 Co 5 O 15-β and Co 3 O 4 during cooling. • Strontium cobaltites lose O 2 from its structure when heated. • Strontium cobaltites gain O 2 to it structure when cooled. Strontium cobaltite containing equimolar amounts of Sr and Co was produced by heating the mixture of SrCO 3 and Co 3 O 4 starting materials with a mole ratio of 1:0.333 under dynamic air atmosphere. The chemical reactions occurred during heating were determined and the intermediate and final products obtained at each critical temperature were characterized using TG/DTA-MS, ICP-OES, XRD and FT-IR analytical techniques. The volumetric analysis method (iodometric titration) and carbonation process were carried out to determine the oxygen stoichiometry of strontium cobaltite. It was determined by thermal analysis results that pure SrCO 3 and Co 3 O 4 were decomposed to SrO and CoO final products, respectively. Sr 6 Co 5 O 15-β was formed by solid-state reaction between SrO and Co 3 O 4 and by gaining O 2 from air. Sr 2 Co 2 O 5-δ was produced at elevated temperatures by solid-state reaction between Sr 6 Co 5 O 15-β and Co 3 O 4 by releasing O 2 . At temperature where the decomposition of SrCO 3 is not completed and the decomposition temperature of Co 3 O 4 is reached, firstly the formation of Sr 6 Co 5 O 15-β and then Sr 2 Co 2 O 5-δ takes place with CoO instead of Co 3 O 4 . Strontium cobaltite releases oxygen from its structure during heating as the temperature increases in the air atmosphere and it gains oxygen during cooling as the temperature decreases. Sr 2 Co 2 O 5-δ is converted firstly to Sr 6 Co 5 O 15 and CoO and then CoO reacts with O 2 to form Co 3 O 4 when cooled to the room temperature from the temperature it was obtained.