Effect of Gd and Yb co-doping on structure and electrical conductivity of the Sm₂Zr₂O₇ pyrochlore

SmYb_1-xGd_xZr₂O₇ (0 ≤ x ≤ 1.0) ceramics were pressureless-sintered at 1973 K for 10 h in air. The relative density, structure and electrical conductivity of SmYb_1-xGd _xZr₂O₇ ceramics were investigated by the Archimedes method, X-ray diffraction, scanning electron microscopy and impedance spectroscopy measurements. SmYb_1-xGd_xZr₂O ₇ (0 ≤ x ≤ 0.5) ceramics exhibit a defect fluorite-type structure, while SmYb_1-xGd_xZr₂O₇ (0.7 ≤ x ≤ 1.0) ceramics have a pyrochlore-type structure. The measured values of the electrical conductivities obey the Arrhenius relation. The grain conductivity of each composition in SmYb_1-xGd_xZr ₂O₇ ceramics increases with increasing temperature from 723 to 1173 K. The grain conductivity of SmYb_1-xGd_xZr ₂O₇ ceramics gradually increases with increasing gadolinium content at identical temperature levels. An increase of about one order of magnitude in grain conductivity is found at all temperature levels when the gadolinium content increases from 0.5 to 0.7. SmYb_1-xGd _xZr₂O₇ ceramics are oxide-ion conductors in the oxygen partial pressure range of 1.0 × 10^-4 to 1.0 atm at all test temperature levels. The highest grain conductivity value obtained in this work is 2.69 × 10^-2 S cm^-1 at 1173 K for SmGdZr ₂O₇ ceramic.