The structure of lead-silicate glasses: molecular dynamics and EXAFS studies

Molecular dynamics (MD) simulations and extended x-ray absorption fine stru cture (EXAFS) investigations of the structure of lead-silicate glasses, xPb O(1 - x)SiO2, have been undertaken to elucidate the problem of partially co ntradicting experimental findings reported in the literature about basic st ructural units and their interconnection. The MD simulations were performed in a wide range of compositions, x = 0.1-0.9. The atoms were assumed to in teract by a two-body Born-Mayer-Huggins interaction potential. The EXAFS me asurements were performed for x = 0.3, 0.5 and 0.7, and also for pure cryst alline (red) PbO at the L-3-edge of Pb. The absorption spectra were analyse d within the GNXAS approach. Our EXAFS and MD results are in good agreement, and support some previous s uggestions that: (1) the PbO4 groups are the dominant structural units in l ead-silicate glasses for any concentration and (2) at lower PbO concentrati ons the co-existence of the PbO4 and PbO3 groups is possible. The medium-range ordering in the simulated glasses has also been investigat ed in detail. The connectivity of the SiO4 tetrahedra network breaks at abo ut x = 0.45, whereas the Ph structural units form a continuous (mainly edge -sharing) network even at relatively low PbO concentrations (x > 0.2). The cation-anion ring statistics is also discussed.