Fluorite-type module theory

Based on these fundamental rules the eight oxygen atoms of a fluorite unit cell should have an a priori equal possibility to be vacant. This implies that if there were only one oxygen vacancy in the system each site would have statistically a 1/8 

FIGURE 23 The possible dipoles of the fluorite-type modules. 

FIGURE 24 The modulation contrast formed by the displacement of the cation and oxygen in PrO.  

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Based on the fluorite-type module theory the thermodynamic properties, hysteresis, and reactions between the homologous series can be elucidated and the structures of homologous series experimentally discovered may be modeled. Using these principles a wide range of non-stoichiometric ternary lanthanide higher oxides from RO2 to R2O3 were founded. 

The formula, Rn02n-2, was used as the generic homologous series formula of the rare earth higher oxides for more than 30 years until Kang and Eyring established an all-inclusive formula, Rn02n-2m, based on the fluorite-type module theory. 

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