Iron perovskites CaFeO_3 and La_{0.33}Sr_{0.67}FeO_3 show charge disproportionation, resulting in charge-ordered states with Fe^{3+}:Fe^{5+} =1:1 and =2:1, respectively. We have made photoemission and unrestricted Hartree-Fock band-structure calculation of CaFeO_3 and compared it with La_{0.33}Sr_{0.67}FeO_3. With decreasing temperature, a gradual decrease of the spectral weight near the Fermi level occurred in CaFeO_3 as in La_{0.33}Sr_{0.67}FeO_3 although lattice distortion occurs only in CaFeO_3. Hartree-Fock calculations have indicated that both the breathing and tilting distortions are necessary to induce the charge disproportionation in CaFeO_3, while no lattice distortion is necessary for the charge disproportionation in La_{0.33}Sr_{0.67}FeO_3.
@article{arxiv.cond-mat/0207250,
title = {Different routes to charge disproportionation in perovskites-type Fe oxides},
author = {J. Matsuno and T. Mizokawa and A. Fujimori and Y. Takeda and S. Kawasaki and M. Takano},
journal= {arXiv preprint arXiv:cond-mat/0207250},
year = {2009}
}