Electronic Structure Evolution of SrCoOx during Electrochemically Driven Phase Transition Probed by in Situ X-ray Spectroscopy

Abstract

Topotactic phase transition in SrCoOx (x = 2.5–3, denoted as SCO) has become a focal point for the study of this unique functional oxide system, sparked by the large alteration in the physical and chemical properties from brownmillerite (BM) to perovskite (P) phases. Recently, we showed that applying electrochemical bias could be a convenient way to control the oxygen stoichiometry in SCO and trigger its topotactic phase transition. In this paper, we utilized in situ ambient pressure X-ray spectroscopic tools to reveal the electronic structure and oxygen nonstoichiometry evolution during the BM → P phase transition of SCO. During the BM → P transition via intercalation of oxygen anions into the structure, we found a lowering of the Fermi level due to creation of Co 3d–O 2p hybridized unoccupied states. X-ray absorption spectra showed that the formed unoccupied states have largely O 2p characteristics. Finally, we utilized the time-dependent relaxation of the X-ray absorption intensity as a new approach to...