Electron radiation damage and Li-colloid creation inLi2O

Polycrystalline samples of ${\mathrm{Li}}_2$O were irradiated with 1-MeV electrons at different temperatures, $T_{\mathrm{irr}}$, in the range 21 to 275 K, and their electron paramagnetic resonance spectra measured. The created defects manifest a strong $T_{\mathrm{irr}}$ dependence. (i) At low temperatures, $T_{\mathrm{irr}}<~200$ K, mainly $F^{+}$ centers (O vacancies with a trapped electron) are formed; thermal annealing leads to their recovery near $T_{\mathrm{ann}}=400\mathrm{}°$C, which is accompanied by the emergence of a new signal near $g=2.003\mathrm{}$, possibly due to their agglomeration into small $F^{+}$ clusters. The latter disappear at 600-700 °C. (ii) At $T_{\mathrm{irr}}=200\mathrm{}$ K, the $F^{+}$ spectra are superimposed by the $g=2.003\mathrm{}$ line and by a new narrow signal at $g=2.0023\mathrm{}$, probably already caused by small metallic colloids. (iii) At $T_{\mathrm{irr}}=275\mathrm{}$ K, finally, only a narrow $T$-independent line ($\Delta H\sim {10}^{-2\mathrm{}}$ mT) is observed at $g=2.00235\mathrm{}\left(2\right)\mathrm{}$, characteristic for metallic Li colloids. The microwave dielectric constant, $\varepsilon$, measured on the same specimens increased notably after the room-temperature irradiation emphasizing the presence of metallic particles, while remaining unchanged for lower $T_{\mathrm{irr}}$. Both the colloid line and the radiation-induced $\Delta \varepsilon$ vanish simultaneously above $T_{\mathrm{ann}}\approx 250°$C.