V. Physicochemical Methods of Glass Characterization. Connectivities and cation distributions in oxide glasses: New results from solid state NMR

Abstract

Modern solid state nuclear magnetic resonance (NMR) techniques afford powerful experimental strategies for elucidating detailed structural information in noncrystalline materials. While previous research emphasis has been on the identification and quantification of local environments (short-range-order), primarily by using the technique of magic-angle spinning (MAS) NMR, correlations beyond the nearest neighbor coordination sphere (intermediate-range order) can be studied by more sophisticated methods. This contribution focuses on recent advances made for a variety of oxide glasses, using methods of dipolar spectroscopy: Connectivities among the structural building blocks present in sodium aluminoborate glasses have been exposed using 11B[27Al] and 27Al{11 B} rotational echo double resonance (REDOR) NMR. Similarly, 29Si{31P] and 29Si[7Li) REDOR data form the basis of a structural model integrating six-coordinated silicon into the network structure of alkali silicophosphate glasses. The spatial cation distributions in sodium silicate glasses are studied by 23Na spin echo decay spectroscopy, offering experimental evidence for inhomogeneous cation distributions at low alkaline contents. Finally, for mixed alkali sodium lithium silicate glasses, 23Na{7LiJ spin echo double resonance (SEDOR) and 29Si[23Na} and 29Si[7Li} REDOR spectroscopies provide important experimental criteria for testing hypothesized relative Na-Li cation ordering scenarios.

Glass-to-Crystal Transition in Li1+xAlxGe2–x(PO4)3: Structural Aspects Studied by Solid State NMR

“…42 Such glasses contain both four-and six-coordinate silicon, whose second coordination sphere is dominated by phosphorus. 43 Figure 9c illustrates that the overall 31 P{ 27 Al} REAPDOR curve measured for the x = 0.5 sample agrees well with a simulation based on a single aluminum neighbor at an internuclear distance of 3.20 ± 0.10 Å. This value corresponds to the average environment of the phosphate species in a glass having a germanium to aluminum ratio of 3:1 if the Al−O−P versus the Ge−O−P connectivity distribution is random.…”

Short and Medium Range Order in Ion-Conducting Glasses Studied by Modern Solid State NMR Techniques

“…Most importantly, within the frame of the dynamic structure model and its subsequent refinements, the MAE can be understood as a natural consequence of a statistical distribution of the unlike cations relative to each other. In this connection, important experimental confirmation has come from solid state NMR for a number of mixed lithium sodium silicate [53][54][55], thiogermanate [56] and borate glasses [57]: dipolar second moments determined from 23 Na spin echo decays, and 7 Li{ 6 Li} or 23 Na{ 6 Li} SEDOR data consistently point towards such random relative cation distributions.…”

Atomic structure of beryllium boroaluminate glasses: A multi-nuclear NMR spectroscopic study

“…NMR spectra were acquired using a Bruker AVANCE500 widebore spectrometer equipped with a Bruker magnet (11.7 T) operating at Larmor frequencies of 70.3, 160.5 and 130.3 MHz for 9 Be, 11 B and 27 Al, respectively. All MAS NMR spectra were acquired at a spinning speed of 15 kHz, using a Bruker 4 mm CPMAS probe and ZrO 2 rotors.…”

“…However, such compositional variation of B IV concentration becomes less pronounced with increasing Al content as well as in glasses with high field strength (charge:radius ratio) network modifying cations such as Mg 2+ [9,10,13]. High field strength (HFS) modifier cations also reduce the degree of compositional dependence of the concentration of various Al species and promote the formation of large concentrations of high-coordinated Al V and Al VI species [4,9,10] Al IV -O-Al IV linkages, although HFS modifier cations are again known to reduce such preferences [9,10,13].…”

“…The atomic structures of these glasses have been studied in detail primarily with 11 B and 27 Al and more recently with 17 O nuclear magnetic resonance (NMR) spectroscopic techniques and been found to be characterized by an unusually wide variety of nearest-neighbor Al-O and B-O coordination environments [3][4][5][6][7][8][9][10][11][12][13]. For example, B atoms in trigonal and tetrahedral coordination with oxygen (denoted here as B III and B IV , respectively) and Al atoms that are 4, 5 and 6-coordinated to oxygen (denoted here as Al IV , Al V and Al VI , respectively) can coexist in the same glass structure.…”