Structure of binary alkaline earth vanadate glasses: an x-ray and neutron diffraction investigation

Structural changes in a series of calcium vanadate glasses with molar ratios R=n(CaO)/n(V2O5) from 0.3 to 1.5 and of Sr and Ba vanadate glasses of selected compositions are studied by x-ray and neutron diffraction experiments. A significant decrease of the total V-O coordination number from 4.15+/-0.1 to 3.9+/-0.1 is observed with increasing CaO fractions. In this process the three dimensional network formed of VO5 and VO4 units is transformed to chains of VO4 units where the VOn groups are mainly linked by corners. The Ca-O coordination numbers of similar to6.5+/-0.5 of the Ca-O first neighbour peaks at 0.241 nm are independent of composition. Different from the x-ray structure factors of the Ca and Sr metavanadate glasses (R=1) that of the corresponding Ba metavanadate glass shows a prepeak. Also the mean V-V first neighbour distance of this Ba glass is longer (similar to0.35 nm) than those of the Ca and Sr metavanadate glasses (similar to0.33 nm).