Structure-property correlations in lithium phosphate glasses: New insightsfrom P-31 <-> Li-7 double-resonance NMR

Citation
L. Van Wullen et al., Structure-property correlations in lithium phosphate glasses: New insightsfrom P-31 <-> Li-7 double-resonance NMR, CHEM MATER, 12(7), 2000, pp. 1840-1846
Citations number
33
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Apllied Physucs/Condensed Matter/Materiales Science","Material Science & Engineering
Journal title
CHEMISTRY OF MATERIALS
ISSN journal
0897-4756 → ACNP
Volume
12
Issue
7
Year of publication
2000
Pages
1840 - 1846
Database
ISI
SICI code
0897-4756(200007)12:7<1840:SCILPG>2.0.ZU;2-O
Abstract
The macroscopic properties of binary alkali phosphate glasses are character ized by the presence of unexpected minima in the glass transition temperatu res at alkali concentrations near 20-25 mol %. In the present study, the st ructural origin of this behavior is explored on the basis of multinuclear s ingle- and double-resonance NMR experiments. P-31 magic-angle spinning NMR spectra track the successive network depolymerization caused by Li2O additi on, while Li-6 chemical shifts indicate a lithium coordination number of fo ur to five, The monotonic evolution of these spectra with increasing alkali content reveals that the nonlinear macroscopic behavior does not reflect a ny abrupt structural changes at the local level. In contrast, P-31{Li-7} ro tational echo double-resonance spectroscopy indicates substantial restructu ring on longer distance scales, relating to the spatial arrangement of the lithium ions with respect to the phosphorus sites in the network. The data suggest that the average number of lithium atoms surrounding a phosphorus s ite increases abruptly near 20-25 mol % Li2O, as the phosphate chains becom e cross-linked by electrostatic Li+-oxygen interactions.