Structure of lead oxyfluorosilicate glasses: X-ray photoelectron and nuclear magnetic resonance spectroscopy and molecular dynamics simulation

X-ray photoelectron (XPS) and ²⁹Si magic angle spinning (MAS)-NMR spectroscopy have been used to examine the chemical states of fluorine, oxygen, silicon and lead atoms in the glasses of composition xPbF₂ · (100-y-x)PbO· ySiO₂ (x = 0, 5, 10, 15, 20, 30 mol%, y = 30, 50, 60 mol%). The analysis of the F Is spectra indicated that Pb²⁺ and F^- ions are preferentially located among the Si-O skeleton forming ionic Pb-F clusters. The fraction of the bridging (BO) and non-bridging oxygen (NBO) atoms was derived from the O 1s spectra. The network of the fluorine-containing glasses was concluded to depend on the ratio PbO/SiO₂; when the ratio PbO/SiO₂ was lower than 0.5, not only Pb atoms but also F atoms play a role as network modifiers, while when the ratio PbO/SiO₂ is higher than 1.33, part of Pb atoms plays a role as a glass network former.