Effect of milling of V2O5 on the local environment of vanadium as studied by solid-state 51V NMR and complementary methods

Milling of V2O5 in a ball mill increased the surface area from 7 to a maximum of 32 m(2)/g. Simultaneously, XRD line broadening suggested a reduction of the microcrystallites. A color change during milling indicated oxygen loss, and Raman spectroscopy provided evidence for the formation of shear structures such as V6O13. The number of V4+ ions produced was determined by ESR spectroscopy and that of V3+ ions was obtained from magnetic susceptibility measurements. The local environment of the vanadium nucleus in V2O5 after milling in a ball mill was characterized by the combination of static (wide line) and MAS V-51 NMR techniques together with theoretical simulations of NMR spectra. Important information on the quadrupole and chemical shielding tensors, including the relative tensor orientation and the distribution of magnetic resonance parameters, is discussed for the vanadium nucleus in V2O5 after milling; Special attention was given to the formation of paramagnetic V3+ and V4+ ions and their;influence on V-51 NMR spectra of diamagnetic V5+ in milled samples. It was shown that paramagnetic V3+ ions are responsible for the loss (up to about 70%) of the intensity in V-51 NMR spectra. The influence of other V4+ paramagnetic ions is,significantly smaller.