Theoretical Modeling of Oxide Ion Conductivity in Doped LaSrGa₃O₇ Melilites

Abstract

High-performing solid-state electrolytes (SSE) are a crucial contribution to future energy conversion devices. Recent research shows that the melilite system can yield highly conductive candidates for certain compositions, worth investigating. Based on a previously introduced kinetic Monte Carlo (KMC) model for oxygen ion conductivity in lanthanum-rich melilite structures La 1+x Sr 1−x Ga 3 O 7+0.5x by Schuett et al., simulations were extended to Ga site doping. Various dopants were investigated concerning their effect on oxygen ion conductivity in La 1.5 Sr 0.5 Ga 3−y X y O 7.25 (X = B, Al, In, Si, Sc, Zn). The density functional theory (DFT) analysis of site and migration energies identified different trapping and blocking behaviors for the respective dopants, which were integrated in the existing energy model. Subsequent KMC simulations revealed Al to be the only dopant with beneficial impact on oxygen ion conductivity and activation energy. For this dopant, the energy model was refined by including energy contributions for higher dopant concentrations. Two different approaches were chosen: one based on pair interactions, and the other relying on cluster interactions. The subsequent KMC simulations revealed promising improvements in oxygen ion conductivity and the respective activation energies that need to be confirmed by experimental investigation. Furthermore, a basis has been provided for simulations on complex melilite structures.