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

Lixin Sun,Dario Marrocchelli,Bilge Yildiz

doi:10.1038/ncomms7294

Lixin Sun, Dario Marrocchelli + Show 1 more

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https://doi.org/10.1038/ncomms7294

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Abstract

Strained oxide thin films are of interest for accelerating oxide ion conduction in electrochemical devices. Although the effect of elastic strain has been uncovered theoretically, the effect of dislocations on the diffusion kinetics in such strained oxides is yet unclear. Here we investigate a 1/2<110>{100} edge dislocation by performing atomistic simulations in 4-12% doped CeO2 as a model fast ion conductor. At equilibrium, depending on the size of the dopant, trivalent cations and oxygen vacancies are found to simultaneously enrich or deplete either in the compressive or in the tensile strain fields around the dislocation. The associative interactions among the point defects in the enrichment zone and the lack of oxygen vacancies in the depletion zone slow down oxide ion transport. This finding is contrary to the fast diffusion of atoms along the dislocations in metals and should be considered when assessing the effects of strain on oxide ion conductivity.

Highlights

Strained oxide thin films are of interest for accelerating oxide ion conduction in electrochemical devices
Elastic strain is considered as a new knob to enhance the performance of oxide electrochemical devices, including solid oxide fuel cells (SOFCs)[9,10,11], photocatalysts[22], batteries[23], electrolysers[24] and redox-based resistive memories[25], by accelerating ion conduction
Dislocations in reduced ceria (CDC), Gd-doped ceria (GDC), Y-doped ceria (YDC), Sc-doped ceria (SDC) and a hypothetical ceria model were investigated

Summary

Introduction

Strained oxide thin films are of interest for accelerating oxide ion conduction in electrochemical devices. The associative interactions among the point defects in the enrichment zone and the lack of oxygen vacancies in the depletion zone slow down oxide ion transport This finding is contrary to the fast diffusion of atoms along the dislocations in metals and should be considered when assessing the effects of strain on oxide ion conductivity. Sillassen et al.[28] have observed 3.5 orders of magnitude acceleration in the ionic conductivity for a 8.7 mol.% yttria-stabilized zirconia (YSZ) epitaxial film on MgO substrate They attributed this enhancement qualitatively to a combination of misfit dislocations and elastic strain at the interface. The aim of this study is to provide an atomistic view of how dislocations alter the formation, distribution and mobility of oxide ion defects For this purpose, an 1⁄2o1104{100} edge dislocation is studied as a model system in reduced or doped ceria. A subset of the results is validated by density functional theory calculations corrected by the Hubbard model (DFT þ U)

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