Crystal structure refinement of Ba5Nb4O15-x and Ba5Nb4O15-x by rietveld analysis of neutron and X-ray diffraction data

Both X-ray and neutron diffraction data were analyzed by the Rietveld method, taking as starting structural model that of the Ba5Ta4O15 structure, The results of such an analysis show that the progressive elimination of oxygen ions produce only small changes in the structure. A decrease in the unit-cell parameters as the number of oxygen vacancies increases has been observed, which can be correlated with a gradual loss of oxygen ions in the close-packed layers. No ordering of the oxygen vacancies was found even in the sample with the highest x value, x = 0.56.