Niobium is one of the candidates for causing strong non-linear optical properties in oxide glasses. Recently, Raman gain experiments on niobium phosphate glasses were quite successful. Such glasses were topic of a structural study. The NMR (31P, 17O, 93Nb) and Raman scattering results of Na-Nb phosphate glasses are already published. Detailed knowledge of the Nb-O environments is missing. Combination of x-ray and neutron diffraction of high-resolving power can clarify the detailed Nb-O distances. In addition, a binary Nb phosphate glass is available for investigation. A very similar proposal RB920220 was not scheduled due to heavy over subscription.