Activation volume tensor for oxygen-vacancy migration in strained CeO2 electrolytes
J. Hinterberg, T. Zacherle, and R. A. De Souza
Accepted
We examined the effect of mechanical strain on the migration of oxygen vacancies in fluorite-structured ceria by means of density functional theory calculations. Different strain states (uniaxial, biaxial and isotropic) and strain magnitudes (up to $\pm$ 7\%) were considered. From the calculations we extracted the complete activation volume tensor for oxygen vacancy migration in CeO$_{2}$, that is, all diagonal $\Delta V_{\text{mig},kk}$ and off-diagonal $\Delta V_{\text{mig},kl}$ tensors elements. These individual tensor elements are found, crucially, to be independent of strain state; they do, however, depend on stress ($\Delta V_{\text{mig},kk}$) or effective pressure ($\Delta V_{\text{mig},kl}$). Armed with knowledge of all tensor elements we predict strain states for which oxygen-ion transport in ceria is maximized. In general, with our approach the effect of an arbitrary strain state on the migration barrier for mass transport in a solid can be calculated quantitatively.