Structural Disorder in Doped Zirconias, Part II: Vacancy Ordering Effects and the Conductivity Maximum.

Polarizable interaction potentials, parametrized using ab initio electronic structure calculations, have been used in molecular dynamics simulations to study the conduction mechanism in doped zirconias. The influence of vacancy-vacancy and vacancy-cation interactions on the conductivity of these materials has been characterized. Although the latter can be minimized by using dopant Cations with radii which match those of Zr(4+) (as in the case of Sc(3+)), the former appears as an intrinsic characteristic of the fluorite lattice that cannot be avoided and that 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 Sc(2)O(3)-dope zirconia confirms that this material is likely to present the highest conductivity achievable in zirconias.