FORMATION OF 2 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 the mselves as two electron paramagnetic resonance metallic lines [see F. Beuneu and P. Vajda, Phys. Rev. Lett. 76, 4544 (1996)] are investigate d as a function of impinging electron fluence and after an isochronal annealing treatment. The small (< 1 mu m) colloids, responsible for th e 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 format ion. An effective medium analysis of the epsilon variation after irrad iation suggests nonspherical shapes for the metal colloids. The recove ry Of the irradiation-induced epsilon increase occurs in the same rang e as that of the colloid Lines, with a peak of Delta epsilon '' near 4 00 degrees C, probably indicating a colloid shape redistribution befor e decomposition. Finally, electron and optical microscopy results are presented, confirming the existence of two sizes of nonspherical, anis otropically distributed lithium colloids.