Kalampounias A G, Yannopoulos S N, Papatheodorou G N
Department of Chemical Engineering, University of Patras, GR-26 504 Patras, Greece.
J Chem Phys. 2006 Jan 7;124(1):14504. doi: 10.1063/1.2136878.
In situ polarized and depolarized Raman spectra of glassy, supercooled, and molten SiO2 have been measured over the broad temperature range 77-2150 K in an effort to examine possible structural changes caused by temperature variation. A new experimental setup using a CO2 laser for heating the sample has been designed allowing measurement with controllable blackbody radiation background at temperatures up to 2200 K. Careful and systematic relative intensity measurements and the use of the isotropic and anisotropic Raman representation of the spectra revealed hidden bands in the bending mode region and resolved bands in the stretching region of the spectra. Overall the spectra behavior shows similarities with the spectra of the recently studied tetrahedral glasses/melts of ZnCl2 and ZnBr2. Increasing temperature causes subtle changes of the relative intensities within the silicon-oxygen stretching region at approximately 750-850 cm(-1) and gives rise to a new band at approximately 930 cm(-1). The spectral behavior is interpreted to indicate that the "SiO42" tetrahedra are bound to each other to form the network by apex-bridging and partly by edge-bridging oxygens. The network structure of the glass/melt is formed by mixing a variety of tetrahedra participating in "open" (cristobalitelike), "cluster" (supertetrahedra), and "chain" edge-bridged substructures bound to each other by bridging oxygens. A weak in intensity but strongly polarized composite band is resolved at approximately 1400 cm(-1) and is assigned to Si[Double Bond]O terminal bond frequency. Temperature rise increases the concentration of the terminal bonds by breaking up the network. These structural changes are reminiscent of the polyamorphic transformations occurring in silica as has recently been predicted by computer simulations. At low frequencies the Raman spectra reveal the presence of the Boson peak at approximately 60 cm(-1) which is well resolved even above melting temperature up to 2150 K.
为了研究温度变化可能引起的结构变化，在77 - 2150 K的宽温度范围内测量了玻璃态、过冷态和熔融态SiO₂的原位偏振和去偏振拉曼光谱。设计了一种使用二氧化碳激光加热样品的新实验装置，允许在高达2200 K的温度下进行具有可控黑体辐射背景的测量。仔细而系统的相对强度测量以及光谱的各向同性和各向异性拉曼表示法的使用，揭示了弯曲模式区域中的隐藏带和光谱拉伸区域中的分辨带。总体而言，光谱行为与最近研究的ZnCl₂和ZnBr₂四面体玻璃/熔体的光谱相似。温度升高会导致硅氧拉伸区域内约750 - 850 cm⁻¹处的相对强度发生细微变化，并在约930 cm⁻¹处产生一个新带。光谱行为被解释为表明“SiO₄²⁻”四面体通过顶点桥连和部分边缘桥连氧相互结合形成网络。玻璃/熔体的网络结构是通过混合各种参与“开放”（类方石英）、“簇”（超四面体）和“链”边缘桥连子结构的四面体形成的，这些子结构通过桥连氧相互连接。在约1400 cm⁻¹处分辨出一个强度较弱但偏振很强的复合带，并将其归属于Si[双键]O端键频率。温度升高通过破坏网络增加了端键的浓度。这些结构变化让人想起计算机模拟最近预测的二氧化硅中发生的多晶型转变。在低频下，拉曼光谱显示在约60 cm⁻¹处存在玻色子峰，即使在高达2150 K的熔化温度以上也能很好地分辨出来。
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