Charge disproportionation inCaCu3Fe4O12

Abstract

First-principles calculations using the $\text{APW}+\text{lo}$ method, as implemented in the WIEN2K code, have been used to investigate the structural, electronic, and magnetic properties of the perovskite ${\text{CaCu}}_{3}{\text{Fe}}_{4}{\text{O}}_{12}$, including the high-temperature $Im\text{\ensuremath{-}}3$ and low-temperature $Pn\text{\ensuremath{-}}3$ phase. The high-temperature phase presents a homogeneous valence and an orbital degenerate half-metallic behavior, which is consistent with the previous theoretical result. Instead orbital ordering, charge ordering, or disproportionation on Fe sites occur in the low-temperature phase, leading to the insulating character. More importantly, the charge disproportionation is of $2{d}^{5}L\ensuremath{\rightarrow}{d}^{5}{L}^{2}+{d}^{5}$ type (where $L$ denotes an oxygen hole or a ligand hole), and the origin for the phenomenon is discussed in detail.