THE NEW OXYGEN-DEFICIENT FLUORITE BI3NBO7 - SYNTHESIS, ELECTRICAL BEHAVIOR AND STRUCTURAL APPROACH

A new single phase of composition Bi3NbO7 has been isolated in the bin ary system Bi2O3-Nb2O5. X-ray single crystal diffraction studies have shown that Bi3NbO7 crystallizes in the cubic system, space group Fm (3 ) over bar, with unit-cell parameter a = 5.4788(9) Angstrom. The struc ture has been determined, and the final reliability index is R = 0.027 . Bi3NbO7 exhibits a defect fluorite-type structure with 12.5% of anio n vacancies and appears to show a disorder in both anionic and cationi c lattices. The study by electron diffraction and high resolution elec tron microscopy has shown the presence of an incommensurate cubic latt ice. Bi3NbO7 shows good behavior as an ionic conductor up to 875 degre es C without any phase transition as deduced from impedance measuremen ts. (C) 1998 Elsevier Science Ltd.