Studies of crystallization of SiO2-glass by positron annihilation

The crystallization of silica glass has been studied by positron lifetime spectroscopy and accompanying investigations using X-ray diffraction and nuclear magnetic resonance (NMR). To this end isothermal and isochronal heat treatments were performed in the range from 700 degrees C up to 1600 degrees C. The lifetime spectra are analyzed by two lifetime components. The decrease of the short lifetime (200 ps) is attributed to the increasing volume fraction of the crystalline phase. The long lifetime (1000 ps) is related with the pick-off annihilation of the o-Ps states in cavities. With starting formation of crystallization nuclei the long lifetime increases which is explained by expanding cavities at the interface between crystalline phase and amorphous matrix.