Structure and conductivity of rutile niobium iron titanate

The structure and electrical conductivity of the solid solution Fe _xTi_{1 - 2x}Nb_xO_2-δ (x = 0.1, 0.2, 0.3) have been investigated. A solid solution with the rutile structure is observed, along with an increase in unit cell volume with increasing substitution. The conductivity in 5% H₂/Ar reduced with increasing doping levels, reaching a maximum of 2.67 S cm^{- 1} at 700 C for Fe_0.1Ti_0.8Nb_0.1O_2-δ. None of the compounds in this series were redox stable at 700 C in 5% H₂/Ar, with increasing amounts of a haematite secondary phase observed with increased doping levels. Reduction at 900 C in 5% H₂/Ar caused a significant increase in conductivity (8.34 S cm^{- 1} in 5%H₂/Ar) at 700 C, suggesting that only partial reduction occurs at lower temperatures. The lack of redox stability and relatively low conductivities of these materials makes them unsuitable as a component of composite anode for IT-SOFC.