Lead silicate glass structure: New insights from diffraction and modeling of probable lone pair locations
Lead silicate glass structure: New insights from diffraction and modeling of probable lone pair locations
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硅酸铅玻璃结构：来自衍射和可能的孤对电子位置建模的新见解
DOI：
10.1111/jace.18125
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发表时间：
2022
影响因子：
3.9
通讯作者：
Feller, Steve
中科院分区：
文献类型：
--
作者：
Alderman, Oliver L.;Hannon, Alex C.;Holland, Diane;Dupree, Ray;Lehr, Gloria;Vitale, Adam;Feller, Steve
利用高分辨率中子衍射、高能X射线衍射、静态207 Pb NMR和结构建模，对PbO含量为35 ~ 80 mol%的二元PbO-SiO2玻璃的结构进行了详细研究。Pb（II）的局部环境的变化是微妙的;它具有低配位氧（3 - 4）加上立体化学活性的电子孤对，因此，在整个组合物范围内表现为玻璃网络形成（或中间）阳离子。这一结论与以前的报告相矛盾，铅（II）是一种网络改性剂在低浓度下，并支持铅和碱土金属硅酸盐玻璃摩尔体积的分析。随着PbO含量的增加，Pb-O峰键长缩短0.04 μ m，表明更强、更共价的键合，并且与短（≤ 2.70 μ m）Pb-O键的数量从3.3增加到3.6一致。这是伴随着增加轴对称的Pb（II）网站，并解释为一个逐步过渡到正方形金字塔[PbO 4]网站，如那些发现在结晶PbO多晶型。与第一个尖锐衍射峰（FSDP）相关的周期性向β-PbO的周期性降低，伴随着与铅铁矿网络（FSDP）和硅酸盐阴离子（中子前峰）相关的相关长度增加，提供了增加的中程有序的证据，并对结晶施加的玻璃形成限制具有影响。Pb（II）电子孤对在低PbO含量下占据硅酸盐网络内的天然空隙，而在高PbO含量下，它们聚集形成形成铅矿网络的一部分的空隙，类似于Pb 11 Si 3 O 17中的开放通道和α-和β-PbO的层状结构。Si‐O和Pb‐O键长分别与29 Si和207 Pb NMR化学位移相关。这是第一次，这种相关性已被证明为玻璃和脉冲中子总散射可以测量平均键长的准确性证明。
Structures of binary PbO‐SiO2glasses have been studied in detail over the compositional range 35 to 80 mol% PbO using high‐resolution neutron diffraction, high‐energy X‐ray diffraction, static207Pb 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 Pb11Si3O17and the layered structures of α‐ and β‐PbO. Si‐O and Pb‐O bond lengths have been correlated with29Si and207Pb 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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