Environments of lead cations in oxide glasses probed by X-ray diffraction

The structural behavior of oxygen environments of Pb2+ cations in binary lead oxide glasses is studied by X-ray diffraction using high-energy photons from a synchrotron. Samples of different PbO content and of different type of network-forming oxide such as SiO2 and V2O5 are used. For comparison, earlier data obtained of Pb phosphate glasses are included. The oxygen environments strongly depend on the type of network-forming oxide but they do not vary with PbO content. Numbers and distances of oxygen atoms at the shortest separations are three, four and five with lengths of 0.230, 0.252 and 0.247 nm for glasses with SiO2, V2O5 and P2O5, respectively. The numbers of further oxygen atoms at distances of ~0.275 nm are about one, two and three. The excentric positions of Pb2+ cations in the oxygen environments of silicate and vanadate networks are attributed to non-uniform distributions of negative charge on the surrounding oxygen atoms. In case of lead vanadate glasses the Pb2+ cations stabilize VO5 units which is not known of vanadate glasses of other network-modifying oxides MeO