Formation of lithium colloids in electron-irradiated Li2O

Poly- and monocrystalline samples of Li2O were irradiated with 1 MeV electrons at different temperatures, Tirr, and their EPR spectra measured. The created defects manifest a strong Tirr-dependence: (a) at low temperatures, Tirr≤200 K, mainly F+-centers (O-vacancies with a trapped electron) are formed; (b) at room temperature, we observe, for the first time, a T-independent narrow signal (ΔH∝10-2 mT) at g=2.00235(2), characteristic for metallic lithium colloids. The microwave dielectric constant, ε=ε'-iε'', was measured on the same specimens; both components increased very notably after the room temperature irradiation, emphasizing the presence of metallic particles, while remaining unchanged for lower Tirr. Thermal annealing of the specimens led to simultaneous vanishing of the colloid line and of Δε', Δε'' above Tann∼250 C. For case (a) irradiation, the recovery of the F+-centers near Tann∼400 C is accompanied by the emergence of a new signal near g=2.003, possibly due to their agglomeration into small clusters; the latter disappear at 600-700 C, depending on Tirr. (orig.)