Novel proton-conducting hexagonal perovskites Ba7In6-xYxAl2O19 for solid oxide fuel cells

The solid solution Ba7In6-xYxAl2O19 (0 <= x <= 0.25) with a hexagonal perovskite-like structure was prepared by the solid-state route. The introduction of yttrium was accompanied by an increase in lattice parameters. The total conductivity as a function of p(O2) and T was measured at different humidity. The partial conductivities were found by transport number measurements and were fitted based on the defect formation model. Oxygen-ion and proton conductivities were found to increase with Y3+ content as a result of an increase in cell volume and free volume, which was accompanied by a decrease in the activation energy of both oxygen-ion and proton conductivity. Oxygen-ion conductivity and proton conductivity dominated below 500 degrees C in dry (p(H2O)=3.5x10(-5) atm) and in wet (p(H2O)=1.92x10(-2) atm) conditions, respectively. Doping makes it possible to increase proton conductivity by an order of magnitude (500 degrees C) and significantly increase the proton transport numbers. The prepared phases exhibited excellent chemical stability during thermal treatment in carbon dioxide (p(CO2)=1 atm).