Surface and bulk oxygen non-stoichiometry and bulk chemical expansion in gadolinium-doped cerium oxide

Doped and undoped cerium(IV) oxides are ceramics commonly used as catalysts and as solid oxide fuel cell materials. In low oxygen partial pressure, ceria-based materials become non-stoichiometric and can form defect complexes that hinder ionic conductivity. In addition, oxygen non-stoichiometry induces strain (chemical expansion) that can result in stresses for composite or constrained applications. In this paper the non-stoichiometry and chemical expansion behavior has been measured in the temperature range 600-900 degrees C and in a wide oxygen partial pressure range. Surface oxygen non-stoichiometry has also been measured by comparing low surface area to high surface area samples. The bulk non-stoichiometry and chemical expansion behavior have been successfully modeled using a mass action formalism with defect complex formation to account for defect interactions. It has been found that surface defect concentration, previously ignored in the literature, can result in erroneous non-stoichiometry measurements. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.