Oxygen Vacancy Ordering and the Conductivity Maximum in Y₂O₃-Doped CeO₂

Abstract

The defect structure and ionic diffusion processes within the anion-deficient, fluorite structured system Ce1–x Y x O2–x/2 have been investigated at high temperatures (873 K–1073 K) as a function of dopant concentration, x, using a combination of neutron diffraction studies, impedance spectroscopy measurements, and molecular dynamics (MD) simulations using interionic potentials developed from ab initio calculations. Particular attention is paid to the short-range ion–ion correlations, with no strong evidence that the anion vacancies prefer, at high temperature, to reside in the vicinity of either cationic species. However, the vacancy–vacancy interactions play a more important role, with preferential ordering of vacancy pairs along the ⟨111⟩ directions, driven by their strong repulsion at closer distances, becoming dominant at high values of x. This effect explains the presence of a maximum in the ionic conductivity in the intermediate temperature range as a function of increasing x. The wider implications of these conclusions for understanding the structure–property relationships within anion-deficient fluorite structured oxides are briefly discussed, with reference to complementary studies of yttria and/or scandia doped zirconia published previously.

Edge dislocation slows down oxide ion diffusion in doped CeO2 by segregation of charged defects

“…At low doping concentration, the lack of oxygen vacancies and thus a low concentration of charge carriers reduce the diffusivity. At high doping concentration, strong vacancy-vacancy repulsion and vacancy-dopant association effects increase the migration barriers for oxygen vacancies, and thus are the reason for low diffusivity 36,50,62,63 . In the models simulated in this study, although the average dopant concentration is at the optimum value of 8% over the whole slab, the local concentration around the dislocation significantly deviates from this value, as was shown in Fig.…”

Impact of doping on the ionic conductivity of ceria: A comprehensive model

“…15 Ce 1−x M x O 2−x/2 is particularly important as it has a sufficiently high ionic conductivity and therefore is one of the most promising materials to be integrated in intermediate temperature solid oxide fuel cells. 16 Operation at such temperatures will allow for the integration of low chromium steels, which in turn will reduce cathode degradation from chromium poisoning. 17 Domain boundaries can impact O diffusion in electrolyte materials of solid oxide fuel cells.…”

Anomalous Chemical Expansion Behavior of Pr0.2Ce0.8O2-δThin Films Grown by Pulsed Laser Deposition

“…19 Lubomirsky and co-workers report that strained free standing ceria thin film membranes exhibit changes in oxygen vacancy ordering. 20 Oxygen vacancy ordering is also deduced based on neutron diffraction experiments and reverse Monte Carlo modeling on bulk CeO 2-δ , 21 Ce 1-x Y x O 2-x/2 , 22 and on several doped zirconia systems. [23][24][25] In literature, there are numerous investigations focused on phase equilbria and reduction/oxidation behavior of Pr x Ce 1-x O 2-δ system.…”