Medium-Range Order in Sol鈥揋el Prepared Al2O3鈥揝iO2 Glasses: New Results from Solid-State NMR

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• 作者：Jinjun Ren ; Long Zhang ; Hellmut Eckert
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：March 6, 2014
• 年：2014
• 卷：118
• 期：9
• 页码：4906-4917
• 全文大小：600K
• 年卷期：v.118,no.9(March 6, 2014)
• ISSN：1932-7455

文摘

The medium-range order of 0.5Al₂O₃鈥?i>xSiO₂ glasses (1 鈮?x 鈮?6) prepared via a new sol鈥揼el route from the Al lactate precursor has been studied by ²⁹Si and ²⁷Al single- and double-resonance solid-state NMR techniques. For high-alumina samples Si鈥揙鈥揂l connectivities are detected by ²⁹Si MAS NMR as well as by ²⁹Si{²⁷Al} rotational echo adiabatic passage double-resonance (REAPDOR) spectroscopy. To boost the signal-to-noise ratio, the REAPDOR experiment was combined with a Carr鈥揚urcell鈥揗eiboom鈥揋ill (CPMG) echo train acquisition. While all five silicon units Q⁽⁴⁾_mAl (0 鈮?m 鈮?4) are detectable in appreciable concentrations for x = 1, the spectra indicate that the average number of Al species bound to silicon, m_Al, gradually decreases toward higher x values, as expected. The ²⁷Al MAS NMR spectra reveal four-, five-, and six-coordinated aluminum in these glasses. For x 鈮?3, the Al species detected are essentially independent of sample composition indicating a constant structural environment of Al. In contrast, for x = 1 and 2, an increase in the ²⁷Al isotropic chemical shifts suggests an increasing number of Al路路路Al proximities. Consistent with this finding, two-dimensional ²⁷Al鈥?sup>27Al double-quantum/single-quantum correlation spectroscopy reveals spatial proximities among and between all types of aluminum species present. On the basis of the complementary evidence from these single- and double-resonance experiments, a model for the medium-range order of these glasses is developed.