Ionic Conductivity of Doped Cerium Dioxide
The oxides most commonly considered to be good ionic conductors via oxygen-ion migration are ZrO2 and ThO2 doped with lower-valent cations, notably ZrO2:CaO (called calcia stabilized zirconia, or CSZ) and ThO2:Y2O3 (called yttria doped thoria, or YDT). In these materials, which have the fluorite structure, vacancies are introduced on the oxygen sublattice to compensate for the lower-valent cations, one vacancy for each Ca2+ or for each two Y3+ ions. Another oxide of the fluorite structure that has been well studied is CeO2, but it differs from the other two in that it undergoes large departures frem stoichioraetry in the direction of oxygen deficiency (CeO2-x) when heated in a reducing atmosphere. The oxygen vacancies thus formed are accompanied by electrons, and the material then displays n-type semiconducting properties . This behavior of CeO2 is undoubtedly related to the existence of a stable Ce2O3 phase, i.e. to the fact that cerium readily goes into the 3+ state. Because of this tendency to become non-stoichicmetric, doped CeO2 is not often considered as a possible solid oxide-ion electrolyte when applications to oxygen concentration cells  or fuel cells  are under consideration.
KeywordsOxygen Vacancy Ionic Conductivity Ideal Solution Fluorite Structure Cerium Dioxide
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