Photoemission and hartree-fock studies of oxygen-hole ordering in charge-disproportionated La_1-xSr_xFeO₃

We have studied the “charge disproportionation” phenomenon in La_1-xSr_xFeO₃ by photoemission spectroscopy and unrestricted Hartree-Fock band-structure calculations. We find a systematic decrease of the spectral intensity near Fermi level (E_F) toward x=0.67, where the charge disproportion is most stabilized. The spectra for x=0.67 show the clearest temperature-dependent changes in the vicinity of E_F across the transition corresponding to the charge ordering of “Fe³⁺”:“Fe⁵⁺”=2:1. The Hartree-Fock calculations indicate that ordering of oxygen holes indeed occurs in the charge disproportionated state.