Random network models of glass structures1 provide satisfactory qualitative descriptions of many properties of glasses (see reviews in refs 2–4). However, to obtain good quantitative agreement between theoretical analyses and experimental observations5–11 it is often necessary to assume that specific ring structures in the random networks have special importance. In the case of vitreous silica (v-SiO2), distributions of loops of SiO4 tetrahedra in the random network have been invoked5–9 to match calculated and experimental X-ray radial distribution functions (RDF). High resolution X-ray photoelectron spectra12 of v-SiO2 and quartz also provide evidence for the occurrence of four-, six- and higher-membered rings of SiO4 tetrahedra in v-SiO2. Raman spectra are also sensitive to local microstructures in vitreous solids. We have therefore examined the question of rings in the structure of v-SiO2 by comparing its Raman spectrum with spectra of crystalline silica polymorphs whose shortest loops contain four (coesite) and six (for example, α-quartz) tetrahedra. This comparison indicates that the sharp shoulder at 490 cm−1 in the spectrum of v-SiO2, previously attributed to a defect structure3 or a longitudinal optic mode14, can be assigned to four-membered ring structure. We discuss here possible basis for the stability of four-membered rings of SiO4 tetrahedra in v-SiO2 at ambient pressure. Possible reasons for the absence of the 490 cm−1 band in the vibrational density-of-states derived for a random network model by Bell and co-workers12,15 are discussed.

中文翻译：

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石英玻璃中环构型的拉曼研究

玻璃结构的随机网络模型 1 为玻璃的许多特性提供了令人满意的定性描述（参见参考文献 2-4 中的评论）。然而，为了在理论分析和实验观察之间获得良好的定量一致性 5-11，通常有必要假设随机网络中的特定环结构具有特殊重要性。在石英玻璃 (v-SiO2) 的情况下，随机网络中 SiO4 四面体环的分布已被调用 5-9 以匹配计算和实验的 X 射线径向分布函数 (RDF)。v-SiO2 和石英的高分辨率 X 射线光电子谱 12 也为 v-SiO2 中 SiO4 四面体的四元环、六元环和更高元环的出现提供了证据。拉曼光谱对玻璃质固体中的局部微结构也很敏感。因此，我们通过将其拉曼光谱与最短环包含四个（柯石英）和六个（例如，α-石英）四面体的结晶二氧化硅多晶型物的光谱进行比较，研究了 v-SiO2 结构中的环问题。该比较表明 v-SiO2 光谱中 490 cm-1 处的尖锐肩峰，以前归因于缺陷结构 3 或纵向光学模式 14，可以分配给四元环结构。我们在这里讨论了在环境压力下 v-SiO2 中 SiO4 四面体的四元环稳定性的可能基础。讨论了 Bell 及其同事 12,15 为随机网络模型推导出的振动态密度中缺少 490 cm-1 带的可能原因。