Different routes to charge disproportionation in perovskites-type Fe oxides

TL;DR

This study compares charge disproportionation mechanisms in iron perovskites CaFeO_3 and La_{0.33}Sr_{0.67}FeO_3, revealing different roles of lattice distortions in inducing charge order.

Contribution

It demonstrates that lattice distortions are essential for charge disproportionation in CaFeO_3 but not in La_{0.33}Sr_{0.67}FeO_3, highlighting different routes to charge ordering.

Findings

Spectral weight decreases near Fermi level with cooling in both materials.

Lattice distortion occurs only in CaFeO_3.

Breathing and tilting distortions are needed for CaFeO_3's charge disproportionation.

Abstract

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.