Computer Simulations of Thermal Expansion in Lanthanum-Based Perovskites

Differential thermal expansion is important when two strongly bonded ceramics are subjected to high temperatures, as in solid oxide fuel cells. Free energy minimization (EM) and molecular dynamics (MD) techniques were used to simulate the thermal expansion of the perovskites (La, Ca)CrO3 and (La, Sr) (Co, Fe)O3 on the atomistic scale. This paper explores the use of empirical partial charge interatomic potentials to represent the partially covalent bonding in these materials. The EM simulations underpredicted the thermal expansion coefficients (CTEs) by up to 26% due to limitations in the potentials. The MD simulations predicted the CTEs to within 17% of experimental data for (La, Ca)CrO3. MD predictions of the CTEs for (La, Sr)(Co, Fe)O3 were significantly lower than the experimental data due to the approximate nature of the Co4+ and Fe4+ interatomic potentials. Improvements in these results are possible if more extensive databases become available for refining the potentials and effective charges.