Highly mobile oxygen holes in magnesium oxide

High-purity MgO exhibits an unexpected giant anomaly of the apparent static dielectric constant and positive surface charge of the order of 5×${10}^{21}$ ${\mathrm{cm}}^{\mathrm{-}3}$ in the top 15 nm. We postulate that the MgO matrix contains traces of peroxy defects, ${\mathrm{O}}_2^{2\mathrm{-}}$, associated with ${\mathrm{Mg}}^{2+}$ vacancies. Above ≊400400 °C the ${\mathrm{O}}_2^{2\mathrm{-}}$ dissociates to vacancy bound ${\mathrm{O}}^{\mathrm{-}}$ and highly mobile ${\mathrm{O}}^{\mathrm{-}}$ states, which diffuse to the surface, giving rise to a high surface conductivity.