Lead silicate glass structure: New insights from diffraction and modeling of probable lone pair locations

Structures of binary PbO-SiO2 glasses have been studied in detail over the compositional range 35 to 80 mol% PbO using high-resolution neutron diffraction, high-energy X-ray static 207Pb NMR, and structural modeling. The changes local environment Pb(II) are subtle; it has a low coordination oxygen (∼3 4) plus stereochemically active electron lone pair and, thus, behaves as glass network forming (or intermediate) cation entire composition range. This conclusion contradicts previous reports that is modifier at concentrations, supported by an analysis lead alkaline earth silicate molar volumes. Pb-O peak bond length shortens 0.04 Å with increasing content, indicating stronger, more covalent bonding, consistent increase number short (≤ 2.70 Å) bonds, from 3.3 3.6. accompanied increased axial symmetry sites, interpreted gradual transition toward square pyramidal [PbO4] sites such those found crystalline polymorphs. An attendant decrease periodicity associated first sharp diffraction (FSDP) β-PbO, increases correlation lengths plumbite anions (neutron prepeak), provides evidence intermediate-range order implications for limit imposed crystallization. pairs occupy natural voids within contents, while high contents they aggregate create form part network, analogous open channels Pb11Si3O17 layered structures α- β-PbO. Si-O correlated 29Si NMR chemical shifts, respectively. time correlations demonstrated attests accuracy which pulsed total scattering can measure average lengths.