Department of Chemical Engineering & Materials Science, University of California at Davis, Davis, California 95616, USA.
J Phys Chem B. 2009 Nov 19;113(46):15243-8. doi: 10.1021/jp9079603.
The short-range structure of "invert" glasses along the pseudobinary join MgSiO(3)-Mg(2)SiO(4) has been studied using (29)Si and (25)Mg MAS NMR spectroscopy. The results indicate a progressive compositional evolution in Q speciation that approximately follows a statistical distribution. The Mg(2)SiO(4) glass shows an abrupt deviation from this trend with the presence of nearly 40% of the Si atoms as (Si(2)O(7))(6-) dimers, i.e., Q(1) species. Mg(2+) ions are present in predominantly octahedral coordination in all glasses. When taken together, these results indicate that glasses with MgO contents between 50 and 60 mol % are characterized by a structure consisting primarily of at least three types of Q species and MgO(6) octahedra. On the other hand, the structure of glasses with >60 mol % MgO appears to consist of Q(0) and Q(1) species with structural connectivity being primarily provided by the MgO(6) octahedra. The possible consequences of such compositional evolution of structure on the ability of glass formation in this system are discussed.
使用 (29)Si 和 (25)Mg MAS NMR 光谱研究了“反演”玻璃在伪二元连接 MgSiO(3)-Mg(2)SiO(4)上的短程结构。结果表明，Q 种的组成演化大致遵循统计分布。Mg(2)SiO(4) 玻璃的趋势发生了突然偏离，其中近 40%的硅原子以 (Si(2)O(7))(6-) 二聚体（即 Q(1) 种）的形式存在。所有玻璃中的 Mg(2+)离子均主要以八面体配位形式存在。这些结果表明，MgO 含量在 50 至 60 mol%之间的玻璃的结构主要由至少三种 Q 种和 MgO(6) 八面体组成。另一方面，MgO 含量>60 mol%的玻璃的结构似乎由 Q(0) 和 Q(1) 种组成，结构连接主要由 MgO(6) 八面体提供。讨论了这种结构组成演化对该体系玻璃形成能力的可能影响。
