Reversible fluorination of brownmillerite SrCoO2.5 by MgF2 annealing
Yongxiang Ma1, Yuanmin Zhu2, Yihao Yang1
1Department of Physics, Southern University of Science and Technology, Shenzhen 518055, China. chenlang@sustech.edu.cn.
Abstract:
Two distinct oxyfluorides were synthesized by annealing a brownmillerite SrCoO2.5 (BM-SCO) thin film in MgF2 powder through soft-chemistry reduction. Throughout the annealing, BM-SCO undergoes two successive phase transitions, which are referred to as perovskite F-doped SrCoO (P-SCOF) and brownmillerite F-doped SrCoO (BM-SCOF). P-SCOF retains randomly distributed F-ions, while BM-SCOF forms an F-ordered structure characterized by alternative stacking of square-planar CoO2F2 and octahedral CoO4F2. These three phases could change into each other reversibly under moderate conditions, thereby providing a pathway to extract high-purity F2 with perovskite catalysts.
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