Redox and structure of sodium-vanadophosphate glasses

Autor: Valérie Kostoj, Laurent Delevoye, Grégory Tricot, Gérard Palavit, Lionel Montagne
Rok vydání: 2004
Předmět:
Zdroj: Journal of Non-Crystalline Solids. :56-60
ISSN: 0022-3093
DOI: 10.1016/j.jnoncrysol.2004.07.043
Popis: xV 2 O 5 -(100-x)NaPO 3 glasses were prepared with 0 ≤ x ≤ 80. The redox ratio (V (+IV) /V total ) was measured by wet chemical analysis, and found to be consistent with magnetic measurements on glasses. It decreases with increasing x values, which is explained by the variation of the acid-base character of the melts. The glass transition temperature first increases with x, then decreases for x values larger than 20%. 31 P MAS-NMR indicates that PO 4 tetrahedra are connected first to one vanadate, then to two vanadate groups. The assignment is further confirmed by double-quantum filtered 31 P MAS-NMR, and also by considering the chemical shift of crystalline references. 51 V MAS-NMR spectra show two resonances for x lower than 20%, which are assigned to tetrahedral and octahedral vanadate sites. For x values larger than 20%, only tetrahedral vanadium sites remain, then progressively change into sites similar to those in V 2 O 5 . The shift to high field of the 31 P chemical shift of PO 4 groups isolated in the vanadate network, is attributed to the evolution of the vanadium co-ordination. The non-linear evolution of the glass transition temperatures is interpreted from the structural data: the increase of Tg at low x values is due to the reticulation of the phosphate network by VO 6 groups, whereas the decrease of Tg for x larger than 20% is due to the formation of a vanadate network.
Databáze: OpenAIRE
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