Understanding oxide ion transport in yttria stabilized zirconia: fresh insights from molecular dynamics simulations

Abstract

A comprehensive molecular dynamics investigation of yttria stabilized zirconia, Y_xZr_1−xO_2−x/2, is carried out for a wide range of composition, x = 4 to 40 mol%, and over the temperature spanning 800–2200 K. The lattice parameter of the fluorite cell shows a monotonic increase with concentration, while the self-diffusivity of the oxide ion as well as the resulting ionic conductivity shows an optimum value around x = 10 mol%. These gross structural and transport properties of the system from the present study are in good agreement with previous experimental and theoretical investigations. It is noted that oxygen migration occurs along straight channels parallel to the crystallographic axes, connecting the tetrahedral holes of the fluorite lattice occupied by them. A microscopic investigation of distinct oxygen environments, variably coordinated to Y³⁺ and Zr⁴⁺ cations, and of the channels connecting them is carried out. Analysis of these local channels for their energetics and their contribution to overall oxygen transport, resolved in terms of the cationic edges connecting them, provides fresh insights into the oxygen migration mechanism in the system.