Charge States of Ions, and Mechanisms of Charge-Ordering Transitions

Abstract

To gain insight into the mechanism of charge-ordering transitions, which conventionally are pictured as a disproportionation of an ion M as 2M${}^{n+}$ $\to$ M${}^{(n+1)+}$ + M${}^{(n-1)+}$, we (1) review and reconsider the charge state (or oxidation number) picture itself, (2) introduce new results for the putative charge ordering compound AgNiO${}_2$ and the dual charge state insulator AgO, and (3) analyze cationic occupations of actual (not formal) charge, and work to reconcile the conundrums that arise. We establish that several of the clearest cases of charge ordering transitions involve no disproportion (no charge transfer between the cations, hence no charge transfer), and that the experimental data used to support charge ordering can be accounted for within density functional based calculations that contain no charge transfer between cations. We propose that the charge state picture retains meaning and importance, at least inn many cases, if one focuses on Wannier functions rather than atomic orbitals. The challenge of modeling charge ordering transitions with model Hamiltonians is discussed.

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Cited by in corpus (8)

• Charge-order-induced ferroelectricity in LaVO${}_3$/SrVO${}_3$ superlattices
• Interplay between Spin-Orbit Coupling and Strong Correlation Effects: Comparison of Three Osmate Double Perovskites: Ba${}_{2}A$OsO${}_6$ ($A=$Na, Ca, Y)
• Valence and Spin fluctuations in Mn-doped ferroelectric BaTiO3
• Oxidation states, Thouless' pumps, and non-trivial ionic transport in non-stoichiometric electrolytes
• Analysis of charge states in the mixed valent ionic insulator AgO
• Magnetism and charge ordering in high- and low-temperature phases of Nb2O2F3
• Strain-induced heteronuclear charge disproportionation in EuMnO${}_3$
• Real-space charge distribution of the cobalt ion and its relation with charge and spin states