Structural units of binary vanadate glasses by X-ray and neutron diffraction

Abstract X-ray diffraction with high-energy photons (synchrotron) and neutron diffraction are performed on binary vanadate glasses with MgO, Na2O, K2O to determine their structural units. The interpretation includes results of further binary vanadate glasses where vitreous V2O5 plays a key role. Different to the V2O5 crystal the structural model of the glass widely excludes three-fold coordinated oxygen according to Zachariasen’s rules of glass formation. Results from the literature of an extensive analysis of vanadate crystals are used. VO6 units exist in definite deformations. The corresponding out-of-center displacements of the V5+ ions are attributed to the second-order Jahn-Teller effects. The corresponding mechanisms are suggested to be effective also in glass structures. Two, three or four different V-O distances of this model are taken into account and allow a consistent modelling of the distributions of the bond lengths.