First principles approach for promising oxide ion conducting AB Ga 3 O 7 melilite structures.

Melilite type structures of the general composition A 3+ 1+ x B 2+ 1- x Ga 3 O 7+ x /2 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 La 3+ /Sr 2+ 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.