The effect of F−-doping on the conductivity of proton conductor Ba4Ca2Nb2O11

The fluorine-doped solid solution with double perovskite structure Ba4Ca2Nb2O11-0.5xFx was synthesized using the solid state method. It was found that the homogeneity region was limited by the composition Ba4Ca2Nb2O10.6F0.8. Structure and electrical properties of the solid solution have been investigated. Electrical conductivities were measured by varying the temperature in dry (pH2O = 1.9 10−4 atm) and wet (pH2O = 1.42 10−2 atm) air. These phases are capable of dissociative dissolution of water vapour and water uptake decreases with increasing x as a result of decreasing the concentration of oxygen vacancies. Fluorine doping increases the conductivity of Ba4Ca2Nb2O11 proton conductor over the investigated temperature range of 200–1000 °C, and a maximum of conductivity is observed for the fluorine content of x = 0.3−0.6. The difference between un- and fluorine-doped samples is more than 0.5 order of magnitude. The effect of F−-doping on ionic conductivities of double perovskite Ba4Ca2Nb2O11 deals with an increase in mobility of oxygen (dry air) and protons (wet air), the increase in the mobility (consequently, conductivity) is accompanied by decrease in activation enthalpy.