M4Ge9O20碱金属锗酸盐晶体、玻璃及熔体结构的拉曼光谱研究

本文研究了M₄Ge₉O₂₀型锗酸盐(M=Na，K)273～1 373 K常温、高温及熔体拉曼光谱。应用量子化学从头计算方法计算了系列二元钠锗酸盐离子簇模型振动频率。M₄Ge₉O₂₀型锗酸盐晶体结构四配位锗、六配位锗共存。研究表明，随温度升高六配位锗将逐渐转变为四配位锗，产生非桥氧，并观察到在熔点以后全部转变为四配位锗，且其桥氧角分布范围为94～145°，其高频区非桥氧对称伸缩振动频率与其精细结构密切相关，振动频率等性质主要依赖于其精细结构而非其初级结构单元-GeO₄，非桥氧对称伸缩振动频率随锗氧四面体应力指数SIT(Stress Index of Tetrahedron)的增大而增大，与实验所得到的频率与SIT的线性关系一致。玻璃结构以四配位锗为主，存在少量六配位锗，其含量取决于冷速的大小。

High Temperature Raman Spectra and Structure Study of M4Ge9O20 Alkaline Germanate Crystals, Glasses and Their Melts

The structure of M₄Ge₉O₂₀(M=Na, K) from 273 to 1 373 K were studied by high temperature Raman spectroscopy. Ab initio calculation method of quantum chemistry was also used to optimize several typical binary sodium germanate model clusters and calculate their vibration wavenumbers. It has been accepted that the octahedral GeO₆ units coexist with tetrahedral GeO₄ units in M₄Ge₉O₂₀ crystal. And the GeO₆ transforms into GeO₄ units and non-bridging oxygen is formed while the crystal is being heated, and there is only GeO₄ units in M₄Ge₉O₂₀ melts. The Ge-O-Ge angle of bridging oxygen has a distribution varying from 94° to 145°. Wavenumbers of non-bridging oxygen(NBO) stretching vibration in the high frequency range depend on its hyperfine structure and will increase with the increasing value of Stress Index of Tetrahedron (SIT). GeO₆ units can be observed in M₄Ge₉O₂₀ glass, but GeO₄ units are still predominant, and the content of GeO₆ units lies on velocity of cooling.