Modeling of ordered structures of phase-stabilized cubic bismuth oxides

Stabilized bismuth oxides undergo a decay in conductivity when subjected to annealing at temperatures of <600 degrees C, because of the formation of a n ordered superstructure, which is observed in transmission electron micros copy (TEM) diffraction patterns. Neutron-diffraction studies of the aged sa mples indicate that there is a displacement of almost all the anions, from the regular Sc sites to interstitial 32f sites. Based on the TEM patterns a nd the displacement of the oxygen ions, various structural models for the s uperstructure have been analyzed. From this work, it can be deduced that th e observed decay in conductivity is due to the ordering of the oxygen subla ttice, along with a possible concomitant ordering of cations.