Valence compensation of thermally generated[Li]0defects in MgO

Abstract

The creation of thermally generated ${[\mathrm{Li}]}^{0}$ defects (configuration: ${\mathrm{O}}^{2\ensuremath{-}}$-${\mathrm{Li}}^{+}$-${\mathrm{O}}^{\ensuremath{-}}$) and other lithium-associated centers in MgO is attended by valence changes of transition-metal impurities, such as Fe and Cr. The electron-paramagnetic-resonance (EPR) technique was used to monitor the concentrations of these impurities and the ${[\mathrm{Li}]}^{0}$ defects as a function of the incubating temperature in static air. Although near the threshold temperature for ${[\mathrm{Li}]}^{0}$ production the impurities may contribute a significant portion of the holes needed for the valence compensation of stabe ${[\mathrm{Li}]}^{0}$ defects, at higher temperatures (\ensuremath{\sim}1600 K) they can supply only a small percentage of the holes required. Since oxygen was found to be necessary for the formation of ${[\mathrm{Li}]}^{0}$ defects, the primary source of holes at these high temperatures is attributed to the surface reaction: ${\mathrm{O}}_{2}$\ensuremath{\rightarrow}${2\mathrm{O}}^{2\ensuremath{-}}$+4 holes. The effects of optical bleaching and ionizing radiation at 77 K on the concentrations were studied as a function of incubating temperatures. Electron-nuclear double resonance (ENDOR) was used to probe the local environments of the ${[\mathrm{Li}]}^{0}$ defects and other lithium-associated centers.