First-principles prediction of high oxygen-ion conductivity in trilanthanide gallates Ln(3)GaO(6)

We systematically investigated trilanthanide gallates (Ln(3)GaO(6)) with the space group Cmc2(1) as oxygen-ion conductors using first-principles calculations. Six Ln(3)GaO(6) (Ln = Nd, Gd, Tb, Ho, Dy, or Er) are both energetically and dynamically stable among 15 Ln(3)GaO(6) compounds, which is consistent with previous experimental studies reporting successful syntheses of single phases. La(3)GaO(6) and Lu(3)GaO(6) may be metastable despite a slightly higher energy than those of competing reference states, as phonon calculations predict them to be dynamically stable. The formation and the migration barrier energies of an oxygen vacancy (V (O)) suggest that eight Ln(3)GaO(6) (Ln = La, Nd, Gd, Tb, Ho, Dy, Er, or Lu) can act as oxygen-ion conductors based on V (O). Ga plays a role of decreasing the distances between the oxygen sites of Ln(3)GaO(6) compared with those of Ln(2)O(3) so that a V (O) migrates easier with a reduced migration barrier energy. Larger oxygen-ion diffusivities and lower migration barrier energies of V (O) for the eight Ln(3)GaO(6) are obtained for smaller atomic numbers of Ln having larger radii of Ln(3+). Their oxygen-ion conductivities at 1000 K are predicted to have a similar order of magnitude to that of yttria-stabilized zirconia.