Effects of long-range forces on oxygen transport in yttria-doped ceria: simulation and theory

Abstract

Oxygen transport in many ionically conducting oxides occurs by diffusion or migration of oxygen-ion vacancies. An important issue in our understanding of these materials is the mechanism by which vacancies become trapped or ordered, and how this process affects transport. In this paper we reinvestigate the mechanism of vacancy trapping in yttria-doped ceria, and show that long-range forces play an important role in the transport properties of this material. We demonstrate, using dynamic Monte Carlo (MC) simulation, that these long-range forces cause strong deviations from the behaviour predicted by a simple point-defect model, deviations which are evident in previously published measurements of the conductivity. Interpretation of the physics observed in the simulation leads naturally to a Debye–Hückel modification of the point-defect model, which, when combined with kinetic parameters extracted independently from NMR spectroscopy, is capable of predicting measured macroscopic transport with no adjustable parameters. We find that in the case of yttria-doped ceria, the vacancy–defect association enthalpy is well approximated by considering only Coulombic interactions.