  Polarizable interaction potentials, parametrized using ab initio electronic
structure calculations, have been used in molecular dynamics simulations to
study the conduction mechanism in Y2 O3 - and Sc2 O3 -doped zirconias. The
influence of vacancy-vacancy and vacancy-cation interactions on the
conductivity of these materials has been characterised. While the latter can be
avoided by using dopant cations with radii which match those of Zr4+ (as is the
case of Sc3+), the former is an intrinsic characteristic of the fluorite
lattice which cannot be avoided and which is shown to be responsible for the
occurrence of a maximum in the conductivity at dopant concentrations between 8
and 13 %. The weakness of the Sc-vacancy interactions in Sc2 O3 -doped zirconia
suggests that this material is likely to present the highest conductivity
achievable in zirconias.
