ChemInform Abstract: Structure—Property Correlations in Lithium Phosphate Glasses: New Insights from ³¹P↔⁷Li Double‐Resonance NMR.

Abstract

2000magnetic resonance, nuclear quadrupole resonance magnetic resonance, nuclear quadrupole resonance (solids and liquids) D 6560 -013Structure-Property Correlations in Lithium Phosphate Glasses: New Insights from 31 P↔ 7 Li Double-Resonance NMR.-Lithium phosphate glasses xLi 2 O(1-x)P 2 O 5 are prepared from appropriate amounts of P 2 O 5 and LiPO 3 (evacuated silica tubes, 900 • C, 24 h) or from appropriate amounts of Li 3 PO 4 , LiPO 3 , and P 2 O 5 (alumina crucible, 1000 • C). The prepared samples are investigated by 31 P-{ 7 Li} rotational echo double-resonance (REDOR) NMR spectroscopy. The NMR results suggest that the average number of Li atoms surrounding a P site increases abruptly near x = 0.2-0.25 correlating with a minimum in the glass transition temperature at the same composition.

Predicting Q-Speciation in Binary Phosphate Glasses Using Statistical Mechanics

“…Raman and especially 31 P magic angle spinning NMR spectroscopy are suitable experimental probes for determining the Q n speciation in phosphate glass systems. 17,26 The structure of binary phosphate glasses has been extensively studied in the literature, making the system suitable for developing and applying the statistical mechanical structure model. In the following, we first predict the structural evolution of three binary alkali phosphate glass families using experimental structural data from only one glass composition within each series as reference.…”

“…The predicted Q-speciation is compared to the experimental data within the glass-forming region. The results are shown in Figure 3a−c 26,29 These simple alkali phosphate glasses can be synthesized using the melt-quenching technique with modifier content up to 60 mol %. Because no Q 0 groups are experimentally detected in any of these alkali phosphate glasses, we find that it is sufficient to use structural reference data for only one glass composition to validate the model.…”

“…For phosphate glasses with more than two Q n species present simultaneously, reference compositions with the most Q n species present should be selected. 26 and the open symbols represent those from Alam et al 29 In (b), the closed symbols represent experimental data from Brow et al 28 and the open symbols represent those from Strojek et al 19 In (c), the closed symbols represent experimental data from Click et al 27 In (d), the closed symbols represent experimental data from Fayon et al 33 and the open symbols represent those from Walter et al 21 The solid lines represent the prediction using the present statistical mechanical model, which is established only based on experimental data for the glasses marked by an arrow. As shown in Figure 3a−c, the statistical mechanical model predicts the Q-speciation in the three alkali phosphate glass systems very well, with input from only one reference composition in each series.…”

“…Composition dependence of the fraction of Q n structural units in binary phosphate glasses with different modifier oxides: (a) Li 2 O, (b) Na 2 O, (c) Cs 2 O, and (d) MgO. In (a), the closed symbols represent experimental data from Van Wullen et al26 and the open symbols represent those from Alam et al29 In (b), the closed symbols represent experimental data from Brow et al28 and the open symbols represent those from Strojek et al19 In (c), the closed symbols represent experimental data from Click et al27 In (d), the closed symbols represent experimental data from Fayon et al33 and the open symbols represent those from Walter et al21 The solid lines represent the prediction using the present statistical mechanical model, which is established only based on experimental data for the glasses marked by an arrow.…”

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

“…A principal motivation for studying such effects in detail stems from the desire of quantifying dipolar couplings in systems of unknown spin order and geometry, such as are frequently encountered in disordered inorganic systems and glasses. Indeed, the principal utility of REDOR to provide qualitative and semi-quantitative structural information in glasses has been independently demonstrated in several recent studies (11)(12)(13)(14)(15)(16).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.…”