Insight into the Mechanism of the Ionic Conductivity for Ln-Doped Ceria (Ln = La, Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, and Tm) through First-Principles Calculation.

Abstract

Oxygen vacancy (VO) formation energy and its migration barrier are two determining factors for the effectiveness of solid electrolytes (SEs) in solid oxide fuel cells (SOFCs). In this work, a series of aliovalent rare-earth-doped ceria (Ln xCe1- xO2-δ, Ln = lanthanides) compounds serving as SEs are comprehensively and comparatively calculated, through which the determinant factors for oxygen vacancy formations and their migration activity are figured out at an atomistic level via the first-principles calculations with the consideration of electronic correlations. Initially, it is found that the oxygen vacancy formation energies of the Ln-doped ceria are largely reduced in contrast to the undoped ceria (CeO2-δ), which obviously agree with the literature. Then, the migration activity of an oxygen vacancy in Ln xCe1- xO2-δ is closely correlated to the association energies of Ln-VO, in which the different 4f5d bonding properties for different Ln ions should be taken into account. Additionally, the analysis of charge difference gradient (CDG) is revealed to be the intrinsic driving force for oxygen vacancy migration. We hope that our investigation provides a microscopic insight into the oxygen vacancy defect physics, and it is also a benefit for the design of more advanced relevant functional materials.