Incorporation of divalent ions in A2B2O7 pyrochlores

Oxides with the pyrochlore structure are currently being considered for use in electrochemical devices. As their ionic conductivity must be enhanced by extrinsic doping, it is important to establish the relative ability of pyrochlore compounds to accommodate dopant ions. Here atomistic simulation is used to examine this issue by predicting the energies and structures associated with the incorporation of a range of divalent ions over an extensive pyrochlore compositional range. Results indicate that such dopant ions substitute primarily at A-cation sites with oxygen vacancy compensation, resulting in non-stoichiometric pyrochlore. We also find that the energy to form an oxygen Frenkel pair adjacent to a divalent ion is practically near zero. Both solution and defect clustering binding energies vary significantly as a function of composition.