Abstract
Crystallization of SiO 2 glass was studied by positron lifetime spectroscopy and Doppler broadening. Heat treatments were performed in the temperature range between 700 and 1600°C to investigate the crystallization process isothermal and isochronal. Lifetime spectra were analyzed by two lifetime components. The decrease of the short lifetime (300 ps) was attributed to the increasing volume fraction of the crystalline phase. The long lifetime (1500 ps) was related with the pick-off annihilation of the ortho-positronium state in the free volume. Long lifetime increase, with the onset of crystallization, has been explained by expanding cavities at the interface between the crystalline phase and amorphous matrix. Positronium formation decreases with devitrification, which is in agreement with measurements of Doppler broadening. Positron annihilation was shown to be especially suited to investigate surface crystallization.
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