Lead silicate glass structure: New insights from diffraction and modeling of probable lone pair locations. Issue 2 (9th October 2021)

• Record Type: Journal Article
• Authors: Alderman, Oliver L. G.; Hannon, Alex C.; Holland, Diane; Dupree, Ray; Lehr, Gloria; Vitale, Adam; Feller, Steve
• Is Part Of: Journal of the American Ceramic Society. Volume 105:Issue 2(2022)
• Page Start: 938
• Page End: 957
• Publication Date: 2021-10-09
• Subjects: oxides -- glass -- silicates -- structure -- amorphous -- lead oxide -- electron lone pairs; Ceramics -- Periodicals; 620.1405
• DOI: 10.1111/jace.18125
• Languages: English
• ISSNs: 0002-7820

Abstract

Abstract: 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 diffraction, static 207 Pb NMR, and structural modeling. The changes in the local environment of Pb(II) are subtle; it has a low coordination to oxygen (∼3 to 4) plus a stereochemically active electron lone pair and, thus, behaves as a glass network forming (or intermediate) cation over the entire composition range. This conclusion contradicts previous reports that Pb(II) is a network modifier at low concentrations, and is supported by an analysis of lead and alkaline earth silicate glass molar volumes. The Pb‐O peak bond length shortens by 0.04 Å with increasing PbO content, indicating stronger, more covalent bonding, and consistent with an increase in the number of short (≤ 2.70 Å) Pb‐O bonds, from 3.3 to 3.6. This is accompanied by increased axial symmetry of the Pb(II) sites, and is interpreted as a gradual transition toward square pyramidal [PbO4 ] sites such as those found in crystalline PbO polymorphs. An attendant decrease in the periodicity associated with the first sharp diffraction peak (FSDP) toward that of β‐PbO, accompanied by increases in the correlation lengths associated with the plumbite network (FSDP) and silicate anions (neutron prepeak), provides evidence of increased intermediate‐range order and has implications for the glass forming limit imposed by crystallization. Pb(II) electron lone pairs occupy the natural voids within the silicate network at low PbO contents, while at high PbO contents they aggregate to create voids that form part of the plumbite network, analogous to the open channels in Pb11 Si3 O17 and the layered structures of α‐ and β‐PbO. Si‐O and Pb‐O bond lengths have been correlated with 29 Si and 207 Pb NMR chemical shifts, respectively. This is the first time that such correlations have been demonstrated for glasses and attests to the accuracy with which pulsed neutron total scattering can measure average bond lengths. Abstract : Slice through a single configuration of a model of 35PbO.65SiO2 glass, obtained by Empirical Potential Structure Refinement. Si atoms are shown within shaded (blue) tetrahedra, Pb atoms as large (grey) spheres, bonded to O atoms (smaller spheres, red). Pb‐O bonds shorter than 2.7 Å are shown as solid lines, whilst those between 2.7 and 3.27 Å are dashed. LPs are shown as yellow spheres.