High oxide-ion conductivity through the interstitial oxygen site in Ba(7)Nb(4)MoO(20)-based hexagonal perovskite related oxides

Oxide-ion conductors are important in various applications such as solid-oxide fuel cells. Although zirconia-based materials are widely utilized, there remains a strong motivation to discover electrolyte materials with higher conductivity that lowers the working temperature of fuel cells, reducing cost. Oxide-ion conductors with hexagonal perovskite related structures are rare. Herein, we report oxide-ion conductors based on a hexagonal perovskite-related oxide Ba(7)Nb(4)MoO(20). Ba(7)Nb(3.9)Mo(1.1)O(20.05) shows a wide stability range and predominantly oxide-ion conduction in an oxygen partial pressure range from 2 × 10(−26) to 1 atm at 600 °C. Surprisingly, bulk conductivity of Ba(7)Nb(3.9)Mo(1.1)O(20.05), 5.8 × 10(−4) S cm(−1), is remarkably high at 310 °C, and higher than Bi(2)O(3)- and zirconia-based materials. The high conductivity of Ba(7)Nb(3.9)Mo(1.1)O(20.05) is attributable to the interstitial-O5 oxygen site, providing two-dimensional oxide-ion O1−O5 interstitialcy diffusion through lattice-O1 and interstitial-O5 sites in the oxygen-deficient layer, and low activation energy for oxide-ion conductivity. Present findings demonstrate the ability of hexagonal perovskite related oxides as superior oxide-ion conductors.