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

Abstract

Strontium cobaltite containing equimolar amounts of Sr and Co was produced by heating the mixture of SrCO3 and Co3O4 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 SrCO3 and Co3O4 were decomposed to SrO and CoO final products, respectively. Sr6Co5O15-β was formed by solid-state reaction between SrO and Co3O4 and by gaining O2 from air. Sr2Co2O5-δ was produced at elevated temperatures by solid-state reaction between Sr6Co5O15-β and Co3O4 by releasing O2. At temperature where the decomposition of SrCO3 is not completed and the decomposition temperature of Co3O4 is reached, firstly the formation of Sr6Co5O15-β and then Sr2Co2O5-δ takes place with CoO instead of Co3O4.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. Sr2Co2O5-δ is converted firstly to Sr6Co5O15 and CoO and then CoO reacts with O2 to form Co3O4 when cooled to the room temperature from the temperature it was obtained.