Validity of bond-length and Mössbauer parameters to assign oxidation states in multicomponent oxides: Case study ofSr4Fe4O11

Abstract

From analyses of structural information for oxides with Fe in different oxidation states and computationally estimated M\ossbauer parameters (hyperfine field, isomer shift, and quadrupole splitting) based on density-functional theory, we show that the charges residing on the different constituents cannot be directly derived either from structural or M\ossbauer measurements. We have analyzed charge density, charge transfer, electron localization function, crystal orbital Hamilton population, and partial density of states to explain the bonding characteristics. Born-effective charge tensor is used to quantify the charges present at the atomic sites in ${\mathrm{Sr}}_{4}{\mathrm{Fe}}_{4}{\mathrm{O}}_{11}$. We show that the effects of covalence are important in explaining the electronic structure, magnetism, and chemical bonding in oxygen-vacancy-ordered systems such as ${\mathrm{Sr}}_{4}{\mathrm{Fe}}_{4}{\mathrm{O}}_{11}$ and on ignoring covalence, one can be misled in oxidation-state assignments.