Unifying Chemical and Physical Principles for Oxide Superconductivity Based on an Anionic Charge Order Model

Subperoxidic O3-2 charge ordering presents a satisfying basis for a quantitative, conceptually realistic, and unifying understanding of cuprate superconductors. The activity of O- manifests itself in a variety of ways including a universal Tc scaling with O- per total O, or more generally, in the subperoxide radical concentration. Also, a characteristic crystal chemistry of O- placement is indicated. As an example, trends to preferential O- occupation of the apical sites are correlated with c axis and Tc decreases providing a new crystallographic interpretation of the overdoping question. Generally, subperoxides can be created on overoxidation or through various modes of self doping through lattice pressure-related factors. Accordingly, the role of peranion formation is seen as a most general chemical principle for ameliorating stacking mismatch through electronic liquefaction under internal stress. Cases are discussed (e.g., YBa2Cu3O6.5) where the tension on cooling can result in stratified self-doping steps. A variety of experiments indicating charge order properties, such as stripes and slow charge propagation, are interpreted on the anionic model. Subperoxidic pair formation and charge ordering energetics are discussed. Concepts are further generalized for other cases (e.g., carbides or nitrides) of anionic metallicity and superconductivity. Common aspects are mobile, paired charge orders of radicals coupled through bond polarizations.