Structural Type of α-Pyrochlore Oxides

The structure of the ideal α-pyrochlore with stoichiometry A2M2X6X′ (A—large low-charge cation of alkali, alkaline earth, or rare earth elements), M—a small high-charge cation capable of octahedral coordination (p- or d-elements), X—ions O2– and OH–, F–, or molecules H2O, X′—ions weakly bound to M) has a cubic symmetry with the space group \(Fd\overline{3}m\) (Z = 8). This Chapter is devoted to consideration of the structural features and properties of α-pyrochlore oxides.