Novel proton-conducting hexagonal perovskites Ba 7 In 6–x Y x Al 2 O 19 for solid oxide fuel cells

The solid solution Ba 7 In 6–x Y x Al 2 O 19 (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 pO2 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 Y 3+ 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 °C in dry ( pH2O =3.5×10 −5 atm) and in wet ( pH2O =1.92×10 −2 atm) conditions, respectively. Doping makes it possible to increase proton conductivity by an order of magnitude (500 °C) and significantly increase the proton transport numbers. The prepared phases exhibited excellent chemical stability during thermal treatment in carbon dioxide ( pCO2 =1 atm).