Influence of trivalent Gd and Dy codoping on the structure and electrical conductivity of pyrochlore-type Sm2Zr2O7

SmDy1−xGdxZr2O7 (0 ≤ x ≤ 1.0) ceramics are prepared by solid state reaction method at 1973 K for 10 h in air. The crystal structure and microstructure of SmDy1−xGdxZr2O7 ceramics are investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). All the SmDy1−xGdxZr2O7 ceramics (x = 0.2, 0.4, 0.6, 0.8, 1.0) exhibit a pyrochlore structure except for SmDyZr2O7 ceramic. SmDyZr2O7 ceramic has a defective fluorite structure. The incorporation of Gd3+ facilitates a structural evolution from a defective fluorite into an ordered pyrochlore-type structure. Electrical conductivity of SmDy1−xGdxZr2O7 ceramics has been investigated by impedance spectroscopy over a frequency range of 1 Hz to 8 MHz from 673 to 1173 K. The grain conductivity of SmDy1−xGdxZr2O7 ceramics follows the Arrhenius behavior. The grain conductivity of SmDy1−xGdxZr2O7 ceramics increases obviously with increasing Gd3+ content in the temperature range of 673–1073 K, and the optimal grain conductivity value is 1.90 × 10−2 S cm−1 in the composition of SmGdZr2O7 ceramic at 1173 K. All the SmDy1−xGdxZr2O7 ceramics are purely oxide ionic conductors in the test temperature range.

► Phase transition from fluorite to pyrochlore occurs in SmDy1−xGdxZr2O7 ceramics.
► Electrical conductivity of Sm2Zr2O7 is significantly improved by codoping strategy.
► The grain conductivity of SmGdZr2O7 ceramic is 1.90 × 10−2 S cm−1 at 1173 K.
► SmDy1−xGdxZr2O7 ceramics are purely oxide-ion conductors in test temperature range.