Doppler-broadening positron annihilation spectroscopy was used to investigate the effects of the integrated neutron flux, and H, upon the annealing behavior of defects in crystalline samples. The defect concentrations in as-grown and irradiated (6 x 1016, 3.6 x 1017 or 1.2 x 1018/cm2) float-zone material were estimated to be 3 x 1016, 9.5 x 1016, 8.86 x 1017 and 3 x 1018/cm3, respectively. The activation energy in the first annealing stage, between room temperature and 200C, was between 0.18 and 0.26eV. The onset of the reverse annealing stage moved towards lower temperatures, with increasing integrated neutron flux, due to varying concentrations of secondary V2-O and V2 defects. The activation energy, for annealing at temperatures above 450C, was between 0.85 and 0.97eV. This indicated that the migration of interstitial atoms, and their recombination with vacancies, played an important role in this annealing stage. It was found that H appreciably affected the first annealing stage, due to its passivation on acceptor centers. This minimized the formation of secondary defects such as V2-O and V2. It was concluded that the fact that secondary defects in H-containing samples were easy to remove, and that the activation energy for annealing at temperatures above 300C was equal to 0.486eV, indicated that the motion of H probably controlled the annealing process.

X.T.Meng, K.F.Zuo: Journal of Materials Science, 1995, 30[16], 4195-8