Structural studies on the optimisation of fast oxide ion transport

Extensive regions of cubic fluorite solid solution formation are observed in the Y2O3–ZrO2, Y2O3–ZrO2–TiO2 and Y2O3–ZrO2–Nb2O5 systems. Ionic conductivity studies indicate that the activation energy for conduction increases rapidly whilst the high temperature conductivity decreases as yttria-content increases. At high defect concentrations, however, activation energies tend towards a constant value. The increase in activation energy correlates with an increase in the extent of diffuse reflections in neutron diffraction experiments and with increases in the isotropic temperature factor associated with the anion sublattice. Significant negative correlation was observed between conductivity prefactor and oxygen temperature factors. Electron diffraction experiments also show diffuse elements in addition to the cubic fluorite structure, indicating the presence of short-range order related to C-type and distorted pyrochlore types.