Synthetic α-quartz was shown to contain a significant concentration (several ppm) of vacancies. The major fraction of the vacancies was suggested to be in the form of divacancies, giving rise to a positron lifetime of 285ps. In addition, there was a much smaller concentration of large vacancy clusters that was observable only after electron irradiation. They then gave rise to a positron lifetime which was close to 425ps. Annealing at 900 to 1000C caused the disappearance of divacancies, and the formation of vacancy clusters; leading to a positron lifetime which was close to 300ps. At temperatures above about 950C, positronium was formed with an exceptionally long lifetime (3 to 5ns). This was attributed to the formation of an amorphous phase which was connected with the thermal instability of β-quartz. Electron irradiation (2.3MeV, 8C) gave rise to a 250ps lifetime component which was attributed to the formation of neutral monovacancies: V0 and/or VSi. Their introduction rate was non-linear and decreased suddenly, by a factor of 5, above a dose of 1017cm2. This effect was attributed to the removal of irradiation-produced vacancy-interstitial complexes by means of electron-hole recombination during the irradiation.

Characterization of Vacancies in As-Grown and Electron Irradiated α-Quartz by Means of Positron Annihilation. S.Dannefaer, T.Bretagnon, D.Craigen: Journal of Applied Physics, 1999, 86[1], 190-7