The Structure of Defects in Oxygen-deficient Ceria

There has been a strong effort to rationalise and elucidate a structural principle which will account for all the anion-deficient, fluorite-related, mixed-valent binary oxides of cerium, praseodymium and terbium. This is a key step not only for the solid-state chemistry of these materials but also for a large class of fluorite-related materials involved in applications such as fast oxygen conductors and as catalysts. The two main theoretical approaches to the problem were developed by Martin and by Kang and Eyring, and will be illustrated in the following sections. 

A convenient way to represent the structure of Ce02 is shown in Fig. 2.7(a). Ce ions are arranged in a face-centred cubic fashion and a cubic lattice of O anions is 

The composition of other known Ce 02 .2m phases can be obtained by appropriate packing of octants containing the defect (Ce3 sOjQ) and octants with no 

This approach makes it possible to describe several structural features of anion-deficient fluorite- related binary oxides of Ce, Pr and Tb but it is fundamentally descriptive rather than predictive. This limit was pointed out by Khang and Eyring, who recently built a model that is also capable of predicting the structural features of unknown phases in the series 

The Kang and Eyring model too, features a structural defect unit upon which the entire 3-D lattice is constructed. On the basis of structural analysis carried out on the lov/er oxides of Ce, Pr and Tb, the following underlying principles governing 

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