Effect of Milling of V2O5on the Local Environment of Vanadium as Studied by Solid-State51V NMR and Complementary Methods

Milling of V 2 O 5 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 V 6 O 13 . The number of V 4+ ions produced was determined by ESR spectroscopy and that of V 3+ ions was obtained from magnetic susceptibility measurements. The local environment of the vanadium nucleus in V 2 O 5 after milling in a ball mill was characterized by the combination of static (wide line) and MAS 51 V 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 V 2 O 5 after milling. Special attention was given to the formation of paramagnetic V 3+ and V 4+ ions and their influence on 51 V NMR spectra of diamagnetic V 5+ in milled samples. It was shown that paramagnetic V 3+ ions are responsible for the loss (up to about 70%) of the intensity in 51 V NMR spectra. The influence of other V 4+ paramagnetic ions is significantly smaller.