Density Functional Theory Modeling of A-site Cation Diffusion in Bulk LaMnO3 ±δ for Solid Oxide Fuel Cell Cathodes

Abstract

In this work, the diffusion barriers of A-site cation and dopants in bulk LaMnO3±δ (LMO) are determined based on density functional theory (DFT) simulations. These properties are highly relevant for solid oxide fuel cell (SOFC) cathode applications. Due to the weak repulsive interactions (0.2~0.3 eV) between the nearest neighbor A-site and B-site cation vacancies, the A-site and B-site cation vacancy clusters can readily form in LMO. The DFT modeling unveils a facile A-site cation diffusion pathway via a cation vacancy cluster mechanism with a migration barrier reduction of about 1.3 eV versus the direct A-site vacancy migration. By combining these results with the bulk LMO defect modeling, the temperature and oxygen partial pressure dependences of the A-site cation tracer diffusion coefficients are assessed based on the concentration of transport carriers and the migration barriers associated with the A-site cation transport in bulk LMO. The trends in the migration barriers vs. various types of metal cations relevant to SOFC applications i.e. La3+, Sr2+, Zr4+, Y3+, are also investigated, and the results obtained suggest that both the ionic charge and the ionic radius correlate with the calculated cation migration barriers