Electronic properties of perovskite strontium chromium oxyfluoride epitaxial thin films fabricated via low-temperature topotactic reaction

Perovskite chromium oxyfluoride SrCrO2.6F0.4 epitaxial thin films were fabricated via low-temperature topotactic fluorination of SrCrO2.8 precursor with polyvinylidene fluoride as a fluorine source. The obtained SrCrO2.6F0.4 thin film had a different chemical composition than that of bulk polycrystalline SrCrO2.8F0.2, possibly due to the higher reactivity of such thin film. Both the precursor and fluorinated thin films containing Cr3.6+ exhibited insulating behavior with band gaps of ∼0.6 eV, in contrast to metallic SrCrO3 with Cr4+ at 300 K. The experimentally observed valence and conduction bands of the SrCrO2.8, SrCrO3, and SrCrO2.6F0.4 thin films suggested that the spectral weight transfer from the coherent part to the incoherent part with the reduction of Cr valences was caused by strong electron correlation effects. This study offers a fundamental understanding of the fluorine doping effects on a crystalline structure and the correlated electronic performance of chromium oxides.