Larsen Flemming H, Rossano Stéphanie, Farnan Ian
Department of Food Sciences, University of Copenhagen, Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark.
J Phys Chem B. 2007 Jul 19;111(28):8014-9. doi: 10.1021/jp071539n. Epub 2007 Jun 23.
An 17O-enriched version of the titanosilicate glass, KTS2 (K(2)O.TiO(2).2SiO(2)), was analyzed by 17O MAS, off-MAS, and 3Q-QCPMG-MAS experiments. Exploiting the variations in EFG and CSA parameters for the 17O sites in KTS2 glass, we detected four types of oxygen by reduction of spinning sideband intensities in the off-MAS experiments. From the 17O off-MAS and 3Q-QCPMG-MAS experiments, the Si-O-Ti and K-O-Ti resonances were characterized by a distribution of isotropic chemical shifts, whereas the Si-O-Si resonance was characterized by very small distributions of both EFG tensor and isotropic chemical shift, which means that the disorder in the glass is closely related to Ti. In addition to the order/disorder issue, the most striking feature about the 17O off-MAS experiments on KTS2 is the lack of signals from Ti-O-Ti, which contradicts linking between corner sharing TiO(5) units. Therefore, the structure must consist of linkages between TiO(5) units and SiO(4) tetrahedra and linkages between SiO(4) tetrahedra.
对钛硅酸盐玻璃KTS2（K₂O·TiO₂·2SiO₂）的¹⁷O富集版本进行了¹⁷O 魔角旋转（MAS）、非MAS以及三量子（3Q）-四极回波 Carr-Purcell-Meiboom-Gill（QCPMG）-MAS实验分析。利用KTS2玻璃中¹⁷O位点的电场梯度（EFG）和化学位移各向同性（CSA）参数的变化，我们通过非MAS实验中边带强度的降低检测到了四种类型的氧。从¹⁷O非MAS和3Q-QCPMG-MAS实验可知，Si-O-Ti和K-O-Ti共振的特征是各向同性化学位移的分布，而Si-O-Si共振的特征是EFG张量和各向同性化学位移的分布都非常小，这意味着玻璃中的无序与Ti密切相关。除了有序/无序问题外，KTS2的¹⁷O非MAS实验最显著的特征是缺乏来自Ti-O-Ti的信号，这与角共享TiO₅单元之间的连接相矛盾。因此，该结构必定由TiO₅单元与SiO₄四面体之间的连接以及SiO₄四面体之间的连接组成。
