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

Abstract The fluorine-doped solid solution with double perovskite structure Ba 4 Ca 2 Nb 2 O 11-0.5 x F x was synthesized using the solid state method. It was found that the homogeneity region was limited by the composition Ba 4 Ca 2 Nb 2 O 10.6 F 0.8 . Structure and electrical properties of the solid solution have been investigated. Electrical conductivities were measured by varying the temperature in dry ( p H 2 O = 1.9 10 −4  atm) and wet ( p H 2 O = 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 Ba 4 Ca 2 Nb 2 O 11 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 Ba 4 Ca 2 Nb 2 O 11 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.