Highly mobile oxygen holes in magnesium oxide

Abstract

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