Recently, some of the authors have reported that Ba2Fe2O5,whose crystal structure can be regarded as an oxygen-deficientmonoclinic distorted perovskite with ordered oxide ion vacancies[8], is promising as a CO2absorbent operating at high temperatures[5,6]. For Ba2Fe2O5, a structural phase transition from ortho-rhombic to cubic at 840◦C was reported by Parras et al. [9] usingTG-DTA (simultaneous thermogravimetry and differential thermalanalysis) and high-temperature XRD (X-ray diffraction) analysisunder air. They reported that no interaction between the gas phaseand solid Ba2Fe2O5during the phase transition was observed fromthe TG curve. However, they observed a variation of the phase