Voids in mixed-cation silicate glasses: Studies by positron annihilation lifetime and Fourier transform infrared spectroscopies

• PALS spectroscopy is sensitive for the structural changes of glass.
• The lifetime of positroniums are affected by the chemical composition of glass.
• The size of sub-nanometer-voids decreases with decreasing SiO2 concentration.
• In the silicate glass structure there are a loosely and tightly-packed areas.
• The existence of two types of voids in silicate glass structure has been confirmed.

PALS in comparison with FTIR studies have been applied to investigate the structure of different oxide glasses. Three components of the positron lifetime τ (τ1 para- and τ3 ortho-positronium and τ2 intermediate lifetime component) and their intensities were obtained. The results of the calculation of mean values of positron lifetimes for the investigated glasses showed the existence of a long-living component on the positron annihilation lifetime spectra. From the Tao–Eldrup formula we can estimate the size of free volume. On the basis of the measurements we can conclude that the size and fraction of free volume reaches the biggest value for the fused silica glass. The degree of network polymerisation increases void size.

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