Order-disorder transformation in stabilized bismuth oxides nad its efect on ionic conductivity

摘要

The high temperature form of bismuth oxide, &-Bi_xO_3, has the fluorite structure and exhibits high ionic conductivity because of the high concentration of oxygen vacancies. This high temperature cubic structure can be stabilized to room temperature by lanthanide dopants. These stabilized bismuth oxides undergo decay in ionic conductivity upon annealing at temperatures below 600 deg C. The effect of various dopants and the concentration of dopants on the kinetics of decay have been studied. Xray diffraction studies of the aged samples do not indicate any phase transformation to a non-cubic phase. The decay in conductivity is attributed to the formation of a superstructure, which is observed in TEM patterns. Neutrom diffraction data on the aged samples clearly indicate the displacement of oxygen ions from the regular 8c lattice positions to interstitial positions 32f. Based on the TEM patterns and the neutron diffraction data, various possible models of the superstucture have been examined.