PNNL

Abstract

Differential thermal expansion is important when two strongly bonded ceramics are subjected to high temperatures, as in solid oxide fuel cells. This paper presents free energy minimization (EM) and moleccular dynamics (MD) simulations of the coefficient of thermal expansion (CTE) for LaCaCrO3 and LaSrCoFeO3 using partial charge models to represent the partially covalent bonding in these perovskites. The EM simulations treated polarization using shell models, but significantly underpredicted the CTE due to approximations in the technique employed. The MD simulations that neglected polarization predicted the CTE to within 10% of experimental data for LaCaCrO3: corrections due to polarization result in excellent agreement. MD predictions of the CTE for LaSrCoFeO3 were significatly lower than the experimental data due to the approimate nature of the Co4 and Fe4 interatomic potentials. Improvements in these results can be expected if more extensive data bases become available for refining the potentials and effective charges.