Dependence of Oxygen Diffusion on the La and Sr Configuration in Melilite-Type La _{1+ <i>x</i>} Sr _{1– <i>x</i>} Ga ₃ O _{7+ <i>x</i> /2} by Neural Network Potential Molecular Dynamics Simulation

Oxide ion conductors, including O2 sensors and solid electrolytes for solid oxide fuel cells, are used in various applications. O2– vacancies are often the charge carriers in oxide ion conductors, including fluorite- and perovskite-type oxides. Recently, melilite-type La1+xSr1–xGa3O7+x/2 (0 ≤ x ≤ 1) materials have attracted attention because of their high O2– ion conductivity resulting from the migration of interstitial oxide ions formed for charge compensation. In this study, we evaluate the ionic conductivities of various cation configurations by molecular dynamics calculations using a universal neural network potential and investigate the relationship between conductivity and the cation configuration. The activation energy of ionic conduction is significantly dependent on the cation (La, Sr) configuration, even for the same composition. The disordered La/Sr arrangement tends to have a higher ionic conductivity than the energetically stable La/Sr arrangement. Such an effect is prominent in the medium-temperature range (800–1100 K).