Formation of two kinds of nonspherical lithium colloids in electron-irradiated Li2O single crystals

The two kinds of lithium metal colloids created in single crystals of lithium oxide by electron irradiation near 0 degrees C manifesting themselves as two electron paramagnetic resonance metallic lines [see F. Beuneu and P. Vajda, Phys. Rev. Lett. 76, 4544 (1996)] are investigated as a function of impinging electron fluence and after an isochronal annealing treatment. The small (< 1 mu m) colloids, responsible for the narrow Lorentzian line, anneal near 300 degrees C, while the large (much greater than 1 mu m) colloids, giving rise to the Dysonian signal, recover above 400 degrees C. Dielectric-constant measurements in the microwave frequency range reveal a substantial increase of both real and imaginary parts of epsilon, corroborating the metal colloid formation. An effective medium analysis of the epsilon variation after irradiation suggests nonspherical shapes for the metal colloids. The recovery Of the irradiation-induced epsilon increase occurs in the same range as that of the colloid Lines, with a peak of Delta epsilon '' near 400 degrees C, probably indicating a colloid shape redistribution before decomposition. Finally, electron and optical microscopy results are presented, confirming the existence of two sizes of nonspherical, anisotropically distributed lithium colloids.