The atomic structures of two V2O5-P2O 5 glasses and vitreous (v-) V2O5 were investigated by X-ray and neutron diffraction. The V=O double bond is a common characteristic of the VOn units that constitute the structures of the glasses. VO5 square pyramids with elongated bonds of 0.190 nm to the pyramidal base are found for the 50V2O5-50P 2O5 glass. These weaker V-O bonds are balanced in V-O-P bridges by overbonded P-O bonds. The V(IV) sites, which account for 19.7% and 35.2% of the total V sites in the 73V2O5- 27P2O5 and 50V2O5-50P 2O5 glasses, respectively, form similar pyramids in agreement with the structure of crystalline (VO)2P2O 7. The short-range structure of v-V2O5 and the 73V2O5-27P2O5 glass is formed of mixtures of VO5 and VO4 pyramids. A significant amount of V•••O distances > 0.22 nm found for all glasses belong either to linkages V=O•••V or to three-coordinated O sites. © 2011 Elsevier B.V. All rights reserved.