Defect Structure and Electrical Properties of Nonstoichiometric CeO2 Single Crystals

Abstract

Cerium dioxide deviates strongly from stoichiometry at elevated temperatures and reduced partial pressures of oxygen to produce an oxygen deficient n‐type semiconductor. Measurements of electrical conductivity and thermoelectric power as a function of were performed on single crystals of over an extended composition range in order to: (i) remove the ambiguity concerning the identity of the dominant ionic defects, (ii) obtain the formation energies of appropriate defect species, and (iii) establish the composition ranges at which defect interactions set in. A system developed for generating and monitoring almost continuously, enabled the acquisition of data in previously unobtained critical ranges of . A defect model which includes singly and doubly ionized oxygen vacancies and quasi‐free electrons was established by the excellent agreement found at small between experimentally obtained conductivity data and theoretical curves based on the model. Doubly ionized vacancies were shown to be dominant at small with a transition occurring over an extended range of 's toward singly ionized vacancies at larger deviations from stoichiometry. The energies associated with the formation of singly and doubly ionized vacancies were found to be equal to ∼4.1 and 4.7 eV, respectively. For values greater than ∼10−2 indications of significant defect interactions were observed in the electrical conductivity, thermogravimetric, and electron mobility data. Assuming only pairwise defect interactions, we obtain a defect interaction energy of 0.055 eV. This low value is found to be consistent with the relatively larger region of ideal point defect behavior which exists in reduced ceria.