First principles approach for promising oxide ion conducting ABGa₃O₇ melilite structures

Melilite type structures of the general composition A³⁺₁₊B²⁺_1-Ga₃O₇₊ provide high oxide ion conductivity for x > 0 due to the presence of mobile oxide interstitials. While the structure can accommodate a variety of A- and B-cations, compositions besides La³⁺/Sr²⁺ are rarely investigated and the literature is inconclusive. In this contribution, combinations of A-cations (Ce, La, Nd, Pr, Sm) and B-cations (Mg, Ca, Sr, Ba) are investigated by density functional theory calculations. Two criteria for high ionic conductivity are examined: The variation of the site energies for different configurations and the average migration barriers. Promising combinations of cations are suggested for further investigation.