The structural principles and their consequences for the anion-deficient fluorite-related oxides of the higher rare earths

The refinement of the structures of five members of the homologous series o f the higher oxides of the rare earths made it possible to test hypotheses for the compositional and structural principles that underlie the physical and chemical properties of this extensive and varied homologous series. In this chapter the underlying thermodynamic, kinetic, and other properties ar e summarized and the compositional and structural principles that lie at th eir root promulgated. The principles advanced arise naturally from the esse nce of the fluorite structure itself and the properties of these materials flow naturally from this reality. The extension of these principles to the broad class of fluorite-based materials which include fast ion conductors, catalysts, chemical sensors and ceramics is suggested.