Electrical conductivity and thermal expansion of neodymium-ytterbium zirconate ceramics

(Nd_1-xYb_x)₂Zr₂O₇ (0 ≤ x ≤ 1) ceramics were prepared by pressureless-sintering to obtain dense bulk materials. The electrical conductivity of (Nd_1-xYb_x)₂Zr₂O₇ was investigated by complex impedance spectroscopy over a frequency range of 20 Hz to 2 MHz from 723 to 1173 K in air. A high-temperature dilatometer was used to analyze thermal expansion coefficient of (Nd_1-xYb_x)₂Zr₂O₇ in the temperature range of 373-1523 K. The measured electrical conductivity obeys the Arrhenius relation. The grain conductivity of each composition in (Nd_1-xYb_x)₂Zr₂O₇ 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 = 0.3 to x = 0.5. The highest electrical conductivity value obtained in this work is 9.32 × 10^-3 S cm^-1 at 1173 K for (Nd_0.7Yb_0.3)₂Zr₂O₇ ceramic. (Nd_1-xYb_x)₂Zr₂O₇ ceramics are oxide-ion conductors in the oxygen partial pressure range from 1.0 × 10^-4 to 1.0 atm at all test temperature levels. Thermal expansion coefficients of (Nd_1-xYb_x)₂Zr₂O₇ gradually decrease with increasing ytterbium content at identical temperature levels.