The high temperature cubic bismuth oxide phase stabilized with lanthanide dopants undergoes an order-disorder transition of the anion sublattice at about 600 degreesC. When annealed at temperatures below the transition temperature, oxygen ion conductivity undergoes a decay. Neutron diffraction studies have been performed to investigate the structural changes in the anion sublattice that result in the conductivity decay and the effect of dopant on the kinetics of decay. Atomic displacement parameters of oxygen ions were determined at low temperatures for the ordered and disordered structures to determine the static disorder in the oxygen sublattice of ordered and disordered structures. (C) 2001 Elsevier Science B.V. All rights reserved.