Abstract
AbstractBinary PbO–GeO2 glasses have been studied in detail from 5 to 75 mol% PbO using high‐resolution neutron diffraction, high‐energy X‐ray diffraction, 207‐Pb NMR, pycnometry, and thermal analysis. The Ge–O coordination number displays a broad maximum nGeO = 4.14(3) close to 27 mol% PbO. This is smaller than the maximum nGeO = 4.3 reported in CaO–GeO2 glasses but occurs at a similar composition. This structural behavior appears to explain the relatively weak germanate anomaly manifest in lead germanate glasses, for example as a maximum in the measured atom number density and a plateau in the glass transition temperatures. The structural role of Pb(II) is complex. On the one hand, short covalent Pb–O bonds and small Pb–O coordination numbers of ∼3 to 4 indicate glass network former character for Pb(II), associated with a stereochemically active electron lone pair. On the other hand, the presence of some GeO5 or GeO6 units, in addition to the majority GeO4 tetrahedral species, indicates some modifier character of Pb(II) at low PbO contents, giving rise to the observed weak germanate anomaly, as well as elongation and enhanced ionicity of the Pb–O bonds. Overall, the observed structural behavior of Pb(II) in lead germanate glasses appears as intermediate between that observed in lead silicate and lead borate glasses. Despite rapid quenching, at low PbO contents, the glasses studied exhibited nanoscale heterogeneity, evidenced by small‐angle X‐ray scattering consistent with the early stages of spinodal decomposition.
Highlights
Lead germanate glasses combine desirable optical properties, such as high linear and non-linear refractive indices and visible to mid-infrared (MIR) transmission, with excellent thermal and chemical stability
While the mass density always increases with PbO content due to the dominance of the mass of the PbO component, an inflection is apparent at ≈27 mol% PbO, and this manifests as a maximum in the atom number densities of the glasses at the same composition
energy-dispersive X-ray spectroscopy (EDX) measurements indicate that the glasses containing < 20 mol% PbO are lead rich with respect to nominal compositions
Summary
Lead germanate glasses combine desirable optical properties, such as high linear and non-linear refractive indices and visible to mid-infrared (MIR) transmission, with excellent thermal and chemical stability. This synergetic combination of properties has seen PbO–GeO2 based glasses proposed as a practical alternative to MIR tellurite glasses,[1] and they have been investigated for applications including. In colour online is more or less consistent in revealing that Pb2+ forms short bonds to oxygen and has low coordination numbers of 3 to 4 In this respect, Pb2+ acts like an oxide glass-networkforming cation, as opposed to a typical network modifier such as Ca2+. As the PbO content of the glasses is increased, some studies find that nGeO rises with it in a continuous manner, while others find that it passes through a maximum
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
