High oxide-ion conductivity through the interstitial oxygen site in Ba7Nb4MoO20-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. Oxide-ion conductors are important in various applications for clean energy. Here, authors report high oxide-ion conductivity of hexagonal perovskite-related oxide Ba 7 Nb 3.9 Mo 1.1 O 20.05 , which is ascribed to the interstitialcy diffusion and low activation energy for oxide-ion conductivity.