Reducing the chemical expansion coefficient in ceria by addition of zirconia

Abstract

For the first time, the role of isovalent Zr substitution in cerium oxide on the non-stoichiometry induced dilation (chemical expansion) was investigated. Chemical expansion was derived experimentally using HTXRD, dilatometry, and TGA measurements on Pr_0.1Zr_0.4Ce_0.5O_1.95−δ and computationally with DFT calculations on Zr_0.5Ce_0.5O_2−δ. Though Zr was found to increase the reducibility and the corresponding chemical expansion of ceria in the studied range, the relationship between chemical expansion and non-stoichiometry (the chemical expansion coefficient) was significantly smaller (54% less) than that observed in ceria, and consistent with predictions from the authors' previous work. The origin of the reduced chemical expansion coefficient, associated with a larger contraction of the lattice around oxygen vacancies, is explained using DFT calculations and corroborated with prior investigations of enhanced reducibility of ceria–zirconia. Additionally, implications of this discovery for solid oxide fuel cells and heterogeneous catalyst systems are also discussed.