Experimental and theoretical investigation of electronic structure of SrFeO_3-xF_x epitaxial thin films prepared via topotactic reaction

We investigated the electronic structure of perovskite SrFeO_3-xF_x (0.6 ≤ x ≤ 1) films by optical absorption, photoemission, and X-ray absorption spectroscopies, as well as density functional theory (DFT)-based calculations. The optical bandgap expanded with x, yielding a wider direct bandgap for the SrFeO₂F film than for the LaFeO₃ film. The DFT calculations suggested that the majority of FeO₄F₂ octahedra in the SrFeO₂F film had cis configurations and that the enlarged bandgap mainly originated from bond bending in the O-Fe-O chains. We experimentally observed the valence and conduction bands of the SrFeO₂F film, and found them to be qualitatively consistent with the results of DFT-based calculations.