Historical Overview of the Lanthanide Higher Oxides

In 1923 CeC 2 was found to have the fluorite structure (Goldschmidt and Thomas-sen, 1923), and in 1926 PrC 2 was found to have the same structure (Goldschmidt, 1926). In 1950 the intermediate compositions in the PrO system were reported to have the fluorite structure of variable lattice parameters (the superstructure reflections were not observed). In 1951 TbC 2 was also shown to have the fluorite structure (Gruen et al., 1951). By this time the basic fluorite structure had been established for all the known higher oxides of cerium, praseodymium and terbium. 

Careful analyses of the thermodynamic data of the praseodymium and terbium oxides led to the construction of their RCL-O2 phase diagrams (Hyde et al., 1966 Hyde and Eyring, 1965). The cerium oxides were studied by means of X-ray powder diffraction (Bevan, 1955) and the CeOx-02 phase diagram was constructed from equilibrium reaction studies at oxygen pressures down to 10-24 atm and temperatures up to 1200 °C (Bevan and Kordis, 1964 Ricken et al., 1984). It is worth to notice that the phase diagrams of Ce0x-02, PrCb-Cb, and Tb0x-02 systems 

TABLE 1 Summary of the oxygen-deficient fluorite-related lanthanide higher oxides of the Rn02n-2m series 

Phase designation and cations Formula, unit cell content n m O/R ratio Space group 

Notes 1. Preparation All preparations are by equilibration of the oxide with oxygen at temperatures and oxygen pressure predetermined from experimental data. 2. The diffraction patterns all show strong face-center-cubic reflections with commensurate, weak, superstructure reflections by whatever means they are taken. 

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