Structural origin of the weak germanate anomaly in lead germanate glass properties

Alderman, Oliver L. G.; Hannon, Alex C.; Holland, Diane; Dupree, Ray; Feller, Steve

doi:10.1111/jace.18166

Cited by 4 publications

(4 citation statements)

References 77 publications

(227 reference statements)

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“…Upper: First moments of the 207 Pb NMR lineshapes for three lead silicate and four lead germanate 71 glasses, as a function of peak Pb‐O bond length measured by neutron diffraction. Molar compositions are indicated on the plot.…”

Section: Discussionmentioning

confidence: 99%

“…Figure 15 shows the chemical shift of the 207 Pb NMR lineshape (center of gravity) as a function of the peak bond length measured by diffraction. Results for some lead germanate glasses 71 have been included to increase the significance of the linear correlation, where a least‐squares fit yields (in ppm and Å):

\begin{matrix} true \\ left δ_{i s o} ((), ^{207} normalP b) = ((), - 1.32 ((), 26) r_{Pb O} ((), peak) + 3.04 ((), 59)) \times 10^{4} \\ left ((), R = - 0.916 for N = 7) . \end{matrix}

This is the first time that parameters measured by 207 Pb NMR and diffraction have been correlated for a series of glasses . The above result is similar to that determined by Fayon et al., 52 (δ iso ( 207 Pb) = – 8668.95 r PbO + 20854) for a range of crystalline materials.…”

Section: Discussionmentioning

confidence: 99%

Section: Local Environment Of Pb(ii)mentioning

confidence: 99%

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

et al. 2021

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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 207Pb 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 Pb11Si3O17 and the layered structures of α‐ and β‐PbO. Si‐O and Pb‐O bond lengths have been correlated with 29Si and 207Pb 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.

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Section: Discussionmentioning

confidence: 99%

\begin{matrix} true \\ left δ_{i s o} ((), ^{207} normalP b) = ((), - 1.32 ((), 26) r_{Pb O} ((), peak) + 3.04 ((), 59)) \times 10^{4} \\ left ((), R = - 0.916 for N = 7) . \end{matrix}

Section: Discussionmentioning

confidence: 99%

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

et al. 2021

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“…The steric effects of the lone pairs of Pb 2+ cations are strong in silicate glass while they appear reduced in phosphate environments. Even the germanate anomaly influences the PbOx environments [49]. These effects are attributable to a change of the oxygens from bridging to non-bridging character when the PbO content exceeds 25 mol%.…”

Section: General Remarks On the 5s 2 6s 2 Lone Pair Elements In Glas...mentioning

confidence: 99%