Structure and disorder in Pb-Na metasilicate (PbO:Na2O:2SiO2) glasses: A view from high-resolution 17O solid-state NMR

Knowledge of the structure of lead (Pb)-bearing silicate glasses, such as degree of polymerization and arrangement among cations, provides improved prospects for understanding their macroscopic properties. Despite the importance, the detailed disorder in Pb-bearing silicate glasses with varying composition (i.e., Pb/alkali content) has not been systematically explored. Here, we reveal the first unambiguous structural information of PbO-Na2O-SiO2 glasses with varying PbO content [i.e., X-PbO = PbO/(Na2O + PbO)], which are the fundamental model system for multicomponent Pb-bearing glasses, using high-resolution O-17 solid-state NMR. O-17 NMR spectra clearly show the resolved multiple oxygen sites, such as Na-O-Si, Si-O-Si, and [Na,Pb]-O-Si. As X-PbO increases, the fraction of [Na,Pb]-O-Si peak increases markedly at the expanse of substantial reduction in the fraction of Na-O-Si/total NBO. This trend indicates the relative predominance of the dissimilar pairs around non-bridging oxygen (NBO) and, therefore, can be explained well with the pronounced chemical ordering among Na+ and Pb2+. These results confirm that Pb is primarily a network-modifier in the glasses studied here. Atomic environments around both NBO and BO are affected by the change in Na/Pb ratio, while topological disorder due to cation mixing around NBO is much more prominent in Pb endmember. The structural details of short-range configurations around oxygen in alkali Pb-silicate glasses provide atomistic insights for understanding the properties of Pb-bearing multicomponent silicate glasses.

Automated summary

The study reveals key structural information of lead-containing silicate glasses, confirming that lead primarily acts as a network modifier in these glasses. There is significant chemical ordering in glasses with different lead content, while cation mixing and structural disorder play important roles in influencing the atomic environments around oxygen.