Nonstoichiometry in A2B2O7 Pyrochlores

Energies associated with deviations from stoichiometry for an extensive series of A₂B₂O₇ pyrochlores have been predicted. A³⁺ cations range in size from Lu to La and B⁴⁺ cations from Ti to Pb. Results are presented in the form of contour maps as a means of conveying large quantities of data as well as predicting characteristics for pyrochlore compounds not explicitly modeled. These contour maps indicate that the BO₂ excess nonstoichiometry in the pyrochlore structure is distinct from solid-solution fluorite. Within the limitations of this methodology, the contour maps provide a means to understand and predict distinct compositional variations. Defect cluster formation is discussed.