STRUCTURAL AND COMPUTATIONAL STUDIES OF BI2WO6 BASED OXYGEN-ION CONDUCTORS

A combination of neutron powder diffraction and computer simulation te chniques was performed on undoped and doped Bi2WO6 Aurivillius type co mpounds to clarify some of the factors controlling oxygen transport in these materials. Oxygen vacancies in doped compounds are randomly dis tributed within the perovskite-like slab. The most favourable dopants are predicted to be Nb-V and Ta-V on W-VI and La-III on Bi-III in acco rdance with the experimental results. The calculated migration energy of 0.63 eV is in agreement with the values deduced from impedance spec troscopy data for Ta and Nb doped Bi2WO6 at T > 550 degrees C. At lowe r temperatures, pair clusters are predicted to form with a 0.25 eV mea n binding energy, leading to a 0.88 eV activation energy for oxygen va cancy migration, in good correlation with experimental values. Finally , consideration of possible oxygen ion migration pathways in the struc ture showed that energy barriers to migration are lowest between adjac ent apical and equatorial sites of WO6 oxygen octahedra.