Artículo de revista
Magnetic resonance study of vanadium pentoxide gels
Fecha
2006Registro en:
MOLECULAR CRYSTALS AND LIQUID CRYSTALS Volume: 447 Pages: 551-560 Published: 2006
1542-1406
Autor
Nascimento, Otaciro R.
Magon, Claudio José
Lopes, L. V. S.
Donoso, José Pedro
Benavente Espinosa, Eglantina
Páez, J.
Lavayen, Vladimir
Santa Ana, María Angélica
González Moraga, Guillermo
Institución
Resumen
This work describes an Electron Paramagnetic Resonance (EPR) and Nuclear Magnetic Resonance (NMR) study of the vanadium pentoxide xerogel V2O5:nH(2)O with n approximate to 1.8 Experiments were performed in the temperature range 65 K - 310 K. The EPR spectrum at high temperatures exhibits the typical liquid-like eight lines-hyperfine structure. At low temperatures the EPR spectrum change to a V4+ anisotropic powder spectra. These two different regimes can be delimited by a transition temperature region centered at 280 K. Numerical simulations of the EPR spectra in the two temperature limits are in good agreement with the experimental data. Proton (H-1) NMR lineshapes, as functions of temperature were measured in the range 150-323 K and indicate that nuclear motional narrowing is effective at temperatures above 210 K, with an activation energy of 0.14 eV. The NMR spin-lattice relaxation recovery, associated to protons in the water molecules, was found to be non-exponential throughout the temperature range and described by two different relaxation processes. The slow relaxing component is temperature-independent and was attributed to water molecules located far from V4+ ions. The temperature dependence of the fast relaxing component shows maximum at around 260 K, suggesting a relaxation process sensitive to the temperature induced dynamic structural changes in the vanadium oxide matrix.