Electrical conductivity and defect chemistry of the system ( TbxGd1− x) 2Zr2O7+ y ( O≦ x≦1; O≦ y

Abstract

Structural and electrical properties of the homogeneous solid solution series (Tb xGd 1−x) 2Zr 2O 7+y (O≦x≦1; O≦ y < 0.25) were investigated. The defect structure and electrical properties were studied by thermogravimetric analysis and electrical conductivity and ionic transport number measurements as a function of temperature and oxygen partial pressure. The (p-type) electronic conductivity was found to arise from a small polaron hopping mechanism on the Tb-sublattice. The charge carrier concentration can be correlated with the Tb 4+ concentration. The maximum fraction of Tb 4+ ions on the Tb-sublattice was found to be 0.25 and is hardly dependent on the composition (x). Charge carrier mobilities are in the range 10 −10 − 10 −8 m 2 Vs at 700°C. Ionic conductivities up to 7 × 10 −1 ω −1m −1 at 700°C are found. The conductivity can well be described with a previous developed model, that relates the effects of pyrochlore order in the fluorite lattice with the conductivity parameters.