High-temperature and ionization-induced effects in lithium-doped MgO single crystals

Thermal quenching of Li-doped MgO crystals from temperatures in excess of 1300 K results in the formation of ${\mathrm{}\left[\mathrm{Li}\right]\mathrm{}}^0$ defects, which are substitutional lithium ions each with a bound hole at a neighboring oxygen site. Unlike ${\mathrm{}\left[\mathrm{Li}\right]\mathrm{}}^0$ defects generated at low temperatures by a low dose of ionizing radiation, those formed by quenching are stable against hole release well above room temperature. This stability is much higher than for all previously reported hole defects in alkaline-earth oxides. These stable ${\mathrm{}\left[\mathrm{Li}\right]\mathrm{}}^0$ defects have also been produced by high-dose electron irradiations at both 290 and 85 K, with formation cross sections of ${\mathrm{\sim }10}^5$ and ${10}^3$ barns, respectively. The magnitude and temperature dependence of the cross section suggests a radiation-induced diffusion, rather than an elastic collision, process as the production mechanism. These defects anneal at 450 K in the electron-irradiated crystals and 830 K in the quenched ones. A model involving localized regions of high lithium concentration is proposed in order to explain the stability of the bound hole at the ${\mathrm{}\left[\mathrm{Li}\right]\mathrm{}}^0$ defect.