Conduction behavior of Ba7Nb4MoO20 doped with low content of Y, Ce, Nd, Ho, Er and Yb

Ba 7 Nb 4 MoO 20 is a pure oxide ion conductor in both dry and wet oxygen atmospheres at the operating temperature of solid oxide fuel cells and has the promising potential to be applied as electrolyte materials. In this work, donor-doping trivalent rare earth elements R ( R  = Y, Ce, Nd, Ho, Er and Yb) to replace the divalent Ba cations increases oxygen content slightly, but effectively enhances oxide ion conduction. Although the solubility of these dopants is less than x  = 0.02 in Ba 7- x M x Nb 4 MoO 20+0.5 x , the Ba 6.98 Er 0.02 Nb 4 MoO 20.01 composition exhibits the highest conductivity, reaching 0.0066 and 0.0085 S cm −1 at 700 and 800 °C, respectively, nearly 6 times higher than that of pristine Ba 7 Nb 4 MoO 20 . H 2 O/D 2 O isotope effect measurement verifies that these materials are essentially pure oxide conductors even in wet atmospheres. It is hard to believe that the trace-level dopant concentration can influence the conduction behavior effectively. However, the slight change in the oxygen content, particularly in the BaO 2 conduction plane, is possible to influence the conductivities. The oxygen occupancy in the O1 and O5 sites thereby seems to be highly sensitive to and dependent on the occupancy of the dopants over the Ba and Nb/Mo sites.