V₂O₅

Vanadium pentoxide thin films result to be brown/yellow when oxidised and quite weakly coloured (blue), when reduced. The principal vanadium oxide species are VO, V2O3 VO2, V2O5; however, due to the presence of oxygen vacancy defects some mixed valence oxide are known such as V6O13 with V+5 and V+4 oxidized states. If the number of the oxygen vacancy defects increases above a certain value the vacancies tend to correlate and to form the crystallographic shear planes. The vacancies are associated along a lattice plane and subsequently eliminated by the reorganization of V-O coordination units; the resulted oxides can be described by VnO2n-1 (Magneli phases) or by V2nO5n-2 (Wadsley phases).