Thermochemical insights into refractory ceramic materials based on oxides with large tetravalent cations

Ceramic materials based on the fluorite structure and its derivatives are important for applications in solid oxide fuel cells, sensors, catalysts, gate dielectrics, thermal barrier coatings, and nuclear waste immobilization. The interplay of oxygen vacancy formation and short and long range ordering of vacancies and of cations determines the physical properties and dominates the thermodynamics of these materials. Recent calorimetric data for nanophase zirconia polymorphs, for yttria stabilized zirconia, hafnia, and ceria, and for a series of titanate pyrochlores illustrate the systematics of structure stability relations.