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

The creation of thermally generated [Li]0 defects (configuration: O2--Li+-O-) 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 [Li]0 defects as a function of the incubating temperature in static air. Although near the threshold temperature for [Li]0 production the impurities may contribute a significant portion of the holes needed for the valence compensation of stable [Li]0 defects, at higher temperatures (approx. 1600 K) they can supply only a small percentage of the holes required. Since oxygen was found to be necessary for the formation of [Li]0 defects, the primary source of holes at these high temperatures is attributed to the surface reaction: O2 → 2 O2- + 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 [Li]0 defects and other lithium-associated centers