A detailed investigation using X-ray and neutron powder diffraction as well as ac impedance spectroscopy in the substituted bismuth oxide system Bi7Nb2−2xY2xO15.5−2x was presented. Combined refinement of variable temperature X-ray and neutron powder diffraction data reveal both compositional and temperature dependences of the oxide ion distribution in this system. Oxide ions were found to be distributed over 3 crystallographically distinct sites, with one site exclusively associated with the dopant cations Nb5+ and Y3+ leading to a distorted octahedral geometry for these ions. Changes in the oxide ion distribution were correlated with a non-linear thermal expansion as well as non-Arrhenius behaviour of total conductivity at high temperatures.

Oxide Ion Distribution and Conductivity in Bi7Nb2−2xY2xO15.5−2x. F.Krok, I.Abrahams, M.Holdynski, A.Kozanecka-Szmigiel, M.Malys, M.Struzik, X.Liu, J.R.Dygas: Solid State Ionics, 2008, 179[21-26], 975-80