Electrical conductivity of samarium-ytterbium zirconate ceramics

(Sm_1 − xYb_x)₂Zr₂O₇ (0 ≤ x ≤ 1.0) ceramic powders were prepared by chemical-coprecipitation and calcination method, and were pressureless-sintered at 1973 K for 10 h to fabricate dense bulk materials. (Sm_1 − xYb_x)₂Zr₂O₇ has a single phase with a pyrochlore or defect fluorite structure, depending mainly upon the Yb content. They are found to be pyrochlores for 0 ≤ x ≤ 0.1, and defect fluorites for 0.3 ≤ x ≤ 1.0. The electrical conductivity of (Sm_1 − xYb_x)₂Zr₂O₇ was investigated by complex impedance spectroscopy over a frequency range of 200 Hz to 20 MHz from 723 to 1173 K in air. The measured electrical conductivity obeys the Arrhenius relation. The grain conductivity of (Sm_1 − xYb_x)₂Zr₂O₇ ceramics gradually increases with increasing temperature. A decrease of about one order of magnitude in grain conductivity is found at all temperature levels when the Yb content increases from x = 0.1 to x = 0.3. The electrical conductivities of defect fluorite-type materials are lower than those of pyrochlore-type materials in (Sm_1 − xYb_x)₂Zr₂O₇ system, whereas activation energies for the conduction process increase monotonically as the structure becomes disordered.