A dipole polarizable potential for reduced and doped CeO₂obtained from first principles

Abstract

In this paper we present the parameterization of a new interionic potential for stoichiometric, reduced and doped CeO 2 . We use a dipole polarizable potential (DIPPIM: the dipole polarizable ion model) and optimize its parameters by fitting them to a series of density functional theory calculations. The resulting potential was tested by calculating a series of fundamental properties for CeO 2 and by comparing them against experimental values. The values for all the calculated properties (thermal and chemical expansion coefficients, lattice parameters, oxygen migration energies, local crystalline structure and elastic constants) are within 10-15% of the experimental ones, an accuracy comparable to that of ab initio calculations. This result suggests the use of this new potential for reliably predicting atomic scale properties of CeO 2 in problems where ab initio calculations are not feasible due to their size limitations.

Charge localization increases chemical expansion in cerium-based oxides

“…1 show visually the increase in localization of 4f electron charge density around a Ce cation (with one neighbour vacancy) with increasing U. Charge localization was also confirmed by the projected spin density, 14 which is close to one for the Ce cation when U Z 5 eV (see Table I in Supporting Materialw). It is clear that charge localization strongly affects the chemical expansion coefficient, with a 74% increase from delocalized (U = 0 eV) to completely localized (U = 6 eV).…”

“…12 Additionally, doped ceria is being investigated as the solid electrolyte in intermediate to low temperature SOFCs, where the non-stoichiometry induced chemical expansion can lead to mechanical failure. 13 Recently, we studied the origin of chemical expansion in CeO 2Àd 10,14 (relying on Shannon's ionic radii, a valid assumption for this system 15 ), and found that upon reduction (increase in d), chemical expansion arises from two competing mechanisms: (1) an increase in lattice volume upon increase in Ce radius (i.e. Ce 4+ -Ce 3+ ) and (2) a decrease in lattice volume with the formation of charge compensating oxygen vacancies.…”

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

“…For Ce a U parameter of 5-7 eV is commonly used. [30][31][32][33] In this study, we therefore choose U = 5 eV and J = 0 eV. 34 Spin polarized calculations are performed to be consistent with experimental findings 35,36 and experimental lattice constants of 5.413 Å, 5.423 Å, 5.431 Å, 5.422 Å, 5.476 Å, and 5.411 Å are taken from Y, 37 Gd, 38 Sm, 39 Pr, 40 and La 38 doped CeO 2 and pure CeO 2 , 25 respectively.…”

Reducing the chemical expansion coefficient in ceria by addition of zirconia

“…The rst one is the formation of an oxygen vacancy, with surrounding lattice contraction (primarily due to electrostatic interactions), and the second is a change in the cation radius, resulting in lattice expansion (primarily due to steric effects), 15,16 with the latter contribution much larger than the former and thus resulting in a net expansion upon reduction of the material. The importance of charge localization was also recognized in a subsequent study.…”