Single crystals were irradiated with 0.5 or 1MeV electrons at 21 or 273K. It was found that the low-temperature irradiated samples gave rise to electron spin resonance spectra with signals that were due to F-centers and an unchanged real component of the dielectric constant. The room-temperature irradiated crystals gave rise to electron spin resonance spectra that were attributed to VF-, U, and perhaps metal colloid (g = 2.003) centers, as well as an increased (dose-dependent) real component of the dielectric constant. The introduced defects, and the radiation-induced change in the real component of the dielectric constant, were investigated by annealing at temperatures of up to 900C. The recovery behavior was complex, and could be interpreted in terms of a competition between the growth and annihilation of metallic clusters which were estimated to have an initial radius of about 20nm. The appearance of a new electron spin resonance line near to g = 2.000, after annealing at 200C, indicated a possible transformation of the colloids to larger units before vanishing. The annealing spectrum, and the dose dependence of its sub-stages, supported electron spin resonance data.

F.Beuneu, P.Vajda: Journal of Applied Physics, 1995, 78[12], 6989-93