EPR study of RLi2O.V2O5, RNa2O.V2O5, RCaO.V2O5, and RBaO.V2O5 modified vanadate glass systems

Experimental EPR spectra in several modified vanadate glass systems reveal hyperfine structure (hfs) lines whose widths vary with the molar ratio of modifier to vanadium pentoxide, R. In the RNa2O.V2O5 system, for example, hfs lines show no resolution at low R values (near 0.1); by contrast, these l...

Ausführliche Beschreibung

Gespeichert in:
Bibliographische Detailangaben
Veröffentlicht in:Journal of non-crystalline solids 2010-09, Vol.356 (43), p.2268-2272
Hauptverfasser: MCKNIGHT, J. M, WHITMORE, K. A, BUNTON, P. H, BAKER, D. B, VENNERBERG, D. C, FELLER, S. A
Format: Artikel
Sprache:eng
Schlagworte:
Online-Zugang:Volltext
Tags: Tag hinzufügen
Keine Tags, Fügen Sie den ersten Tag hinzu!
Beschreibung
Zusammenfassung:Experimental EPR spectra in several modified vanadate glass systems reveal hyperfine structure (hfs) lines whose widths vary with the molar ratio of modifier to vanadium pentoxide, R. In the RNa2O.V2O5 system, for example, hfs lines show no resolution at low R values (near 0.1); by contrast, these lines exhibit dramatic narrowing as R approaches 0.5. In the model proposed here, this narrowing is due to an increase in hopping time for small polarons associated with V4+ ions in these systems. Increases in polaron hopping times are accompanied by increases in electron spin-spin relaxation times T2's, and, an associated narrowing of EPR linewidths. Experiments confirm that spectral widths are limited by electron T2's due to the fact that EPR linewidths do not vary with temperature down to 4.2K. Resolved spectra in RNa2O.V2O5 at R=0.5 reveal a hyperfine coupling parameter of 0.0177Ac0.0008T, corresponding to an upper-limit polaron hopping frequency of 487Ac20MHz. By similar analyses, the systems of RCaO.V2O5, RBaO.V2O5, and RLi2O.V2O5 exhibit comparable polaron hopping frequencies limits of 480Ac20MHz, 469Ac20MHz, and 468Ac20MHz, respectively, when R is near 1.0. In addition to the relaxation effects discussed here, results of modeling of resolved spectra to obtain hyperfine coupling constants A
ISSN:0022-3093
1873-4812
DOI:10.1016/j.jnoncrysol.2010.07.016