Actinide elements, fluorite-related oxide

Fluorite-Related Oxide Phases of the Rare Earth and Actinide Elements... 

Cerium, praseodymium, and terbium oxides display homologous series of ordered phases of narrow composition range, disordered phases of wide composition range, and the phenomenon of chemical hysteresis among phases which are structurally related to the fluorite-type dioxides. Hence they must play an essential role in the satisfactory development of a comprehensive theory of the solid state. All the actinide elements form fluorite-related oxides, and the trend from ThOx to CmOx is toward behavior similar to that of the lanthanides already mentioned. The relationships among all these fluorite-related oxides must be recognized and clarified to provide the broad base on which a satisfactory theory can be built. 

The fluorite-related oxide phases which are known in the lanthanide and actinide series are displayed in Table II for closer comparison. The most obvious feature is that the oxide systems of Ce, Pr, and Tb reveal greater complexity than any of the actinide elements so far studied. The dioxides of the actinide elements are more easily reduced as one goes from Th02 to Cm02 showing an approach to the behavior of the lanthanides. More complete measurements on CmOx and BkO may well show marked similarity to the rare earths. 

Figure 6. Lattice parameters of fluorite-related oxides of some lanthanide and actinide elements as a function of composition...

Fluorite-Related Oxide Phases of the Rare Earth and Actinide Elements, L. Eyring. In Advances in Chemistry Series, No. 71, American Chemical Society, Washington, DC, pp. 67-85, 1967. 

All the actinide elements whose oxides have been studied can be made as fluorite-type dioxides. For most of them this is their most stable form in air at room temperature. The fluorite-related phases of each actinide element known will be discussed individually before a comparison is made with the rare earth oxides 45). 

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