The Role of Dopant Ionic Radius in O2- — Conducting Solid Electrolytes
The oxides of the fluorite structure (ZrO2, CeO2, ThO2, HfO2) have proved to be attractive systems for the study of mass transport. The focus has been primarily on transport on the oxygen-ion sublattice, for the cations are known to migrate much more slowly and, in fact, the entire cation sublattice is generally frozen-in below ∿ 1000 °C.l Migration on the oxygen-ion sublattice can be enhanced by the introduction of oxygen vacancies, V o ¨ , through doping with lower valent cations. The study of such ionic transport is stimulated, in part, by the actual and potential applications of such oxides as oxygen sensors and oxygen-ion conductors in high-temperature fuel cells.2 Stabilized zirconia has received the most attention, but that material requires ∿ 8 mole %; of dopant to stabilize the fluorite structure. Ceria and thoria, on the other hand, are more versatile for fundamental studies since they possess the fluorite structure in the pure state; thus it is possible to study the entire range, from very low to high dopant concentrations.
KeywordsIonic Radius Internal Friction Activation Enthalpy Fluorite Structure Anelastic Relaxation
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