Short and Medium Range Order in Sodium Aluminoborate Glasses. 2. Site Connectivities and Cation Distributions Studied by Rotational Echo Double Resonance NMR Spectroscopy

Abstract

A quantitative NMR strategy is developed for the study of the network connectivity (intermediate range structure) and the cation distribution in the sodium aluminoborate glass system. The strategy is based on the analysis of rotational echo double resonance (REDOR) spectroscopy applied to the glasses and the crystalline model compounds Li 6 Al 2 (BO 3 ) 4 , NaBO 2 , and Na 2 B 4 O 7 . The heterodipolar multispin interaction between the quadrupolar spin systems 27 Al T 11 B and 23 Na T 11 B is analyzed in terms of approximate second moments, which are extracted from REDOR data measured at short dipolar evolution times. On the basis of 27 Al{ 11 B} and 11 B{ 27 Al}-REDOR results, the framework connectivity distribution is extracted and compared to statistical and preferential bonding distribution scenarios, respectively. The sodium aluminoborate system is characterized by a large degree of bonding regularity in the framework. Four-coordinated aluminum is preferentially linked to BO 3/2 and BO 2/2 Ounits and vice versa, while linking between two four-coordinate units is disfavored, as expected on the basis of bond valence considerations. In glasses with low aluminum contents and/or high sodium contents, there is a greater tendency toward a randomization of connectivities. Spatial correlations between the sodium nuclei and the boron atoms in the network are probed by complementary 23 Na{ 11 B}-and 11 B{ 23 Na}-REDOR experiments. The results reveal that both the three-and the four-coordinated boron species interact equally strongly with sodium cations, consistent with an overall homogeneous cation distribution.

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

“…Similar preferences for heteroatomic linkages were detected by comprehensive spectroscopic studies of the sodium and silver borophosphate glass system along other composition lines [27,[79][80][81][82], in sodium aluminophosphate glasses [83] and in sodium aluminoborate glasses [84][85][86]. In contrast, preferences for homo-atomic connectivities were detected by dipolar NMR spectroscopic methods in borosilicate [87] 3 , and TeO 2 can be incorporated into glassy NaPO 3 , over wide composition ranges, producing strong effects on their physical properties.…”

Dipolar Coupling Information in Multispin Systems: Application of a Compensated REDOR NMR Approach to Inorganic Phosphates

“…Most recently, we have shown that also for multiple-spin systems involving quadrupolar nuclei the initial parts of RE-DOR curves (data range 0 Յ ⌬S/S 0 Յ 0.3) can be conveniently analyzed in terms of van Vleck's second moment information, even if the order and geometry of the spin system is completely unknown (14). In practice, however, the significance of any REDOR analysis largely depends on the fidelity of the experimental REDOR curves.…”

Characterization of the glass-to-vitroceramic transition in yttrium aluminum borate laser glasses using solid state NMR

“…4. As previously discussed, REDOR data in multispin systems can be analyzed with the parabolic approximation [39] applied to the short-term evolution behavior (0 rDS/S o r0.2) using the expression [18,19,40]:…”

“…For quadrupolar nuclei, the analysis is more complicated; however, as owing to the anisotropic quadrupolar interactions the p pulses applied to the non-observed I spins that are present in the non-central Zeeman states may provide less dipolar recoupling than theoretically expected or even none at all, requiring careful calibration procedures on crystalline model compounds with well-characterized spin dynamics [18,19,40]. To this end, the theoretical second moments and those obtained 100 δ ( 27 Al) / ppm Al 5 BO 9 50 0 -50 Fig.…”

“…In contrast to diffraction techniques, solid state NMR methods are equally sensitive to the glassy and crystalline constituents, resulting in quantitatively representative spectra. Benefitting from the potential of advanced double resonance solid state NMR strategies to provide useful structural information on a local level [18,19], we have recently developed a detailed description of the framework structure of yttrium aluminoborate glasses [20]. While 11 B and 27 Al magic-angle spinning (MAS) NMR experiments are informative regarding the coordination states of the boron and aluminum atoms, complementary 11 B/ 27 Al double resonance NMR studies have given quantitative information regarding the boronaluminum connectivities in the network.…”