Paramagnetic Centers Created Under Mechanochemical Treatment of Mixed Molybdenum-Vanadium Oxides

Resumo

Samples of individual and mixed vanadium-molybdenum (V:Mo) oxides xV₂O₅:(1-x)MoO₃, 0 ≤ x ≤ 1, were prepared by the method of mechanochemical activation (MCA). The samples have been characterized by X-ray diffraction (XRD) and X-band electron paramagnetic resonance (EPR) spectroscopy. Prolongation of the treatment duration time in mills led to considerable increase in the V(IV) paramagnetic centers content as well as after additional high temperature annealing at 600 °C. Paramagnetic Mo(V) centers were recorded only in the case of MCA of individual MoO₃ oxide. Complexity of the composition of mechanically activated mixed oxides was confirmed with the XRD data. It is shown that in the case of all individual and mixed oxides the content of paramagnetic species increases noticeably with the increase in milling time. The annealing at 600 °C after MCA of mixed oxides forms a new mixed phase of MoV₂O₈ composition.