A DFT+U study of defect association and oxygen migration in samarium-doped ceria

Abstract

A specialized genetic algorithm (GA) is used to search the structural space of samarium-doped ceria (SDC) for the most energetically stable configurations which will predominate in low temperature fuel cells. A systematic investigation of all configurations of 3.2% SDC and a GA investigation of 6.6% SDC are presented for the first time at the DFT+U level of theory. It was found that Sm atoms prefer to occupy the nearest neighbor (NN) position relative to the oxygen vacancy at 3.2%, while at 6.6%, a balance exists between various Sm-vacancy interactions and the vacancies prefer to be separated by ∼6 Å. Also, the migration barriers for oxygen diffusion are calculated amongst the best structures in 3.2% and 6.6% SDC and are found to be comparable to the barriers in Gd-doped ceria at the DFT+U level of theory. While the migration calculations provide insight on the oxygen diffusion mechanism in this material, the favored configurations from our GA enable future research on concentrated SDC and contribute to the atomistic understanding of the influence of dopant-vacancy and vacancy-vacancy interactions on ionic conductivity.

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.…”

Atomistic Modeling of Effect of Mg on Oxygen Vacancy Diffusion in α‐Alumina

“…Vacancy–vacancy interaction as well as dopant–vacancy interaction resulting from effective net charge on the defects and the elastic strain field could hinder the diffusion process through several mechanisms. At high concentrations, the formation of dopant pairs at nearest‐neighbor positions is assumed to increase the fraction of blocked sites for diffusion . Formation of divacancy complexes in yttria‐stabilized zirconia could also render certain dopant–vacancy configurations unstable, in turn reducing the number of available diffusive pathways .…”

Ab initiothermodynamics of intrinsic oxygen vacancies in ceria

“…The oxygen storage capacity is correlated to the structural relaxation brought about by dopants with smaller ionic radius than Ce 4+ and the electrostatic effects. Activation energies for potential vacancy migration pathways have been computed from first principles [19][20][21] to understand the mechanisms of defect migration at atomistic scale. With the development of density functional perturbation theory, lattice dynamical properties, Born effective charges and phonon density of states have been calculated and these are found to agree well with experimental data 22,23 .…”