Order–disorder transformation and enhanced oxide-ionic conductivity of (Sm1−xDyx)2Zr2O7 ceramics

(Sm1−xDyx)2Zr2O7 (0 ≤ x ≤ 1) ceramics are prepared by a solid state reaction process at 1973 K for 10 h in air. (Sm1−xDyx)2Zr2O7 (0 ≤ x ≤ 0.3) ceramics exhibit a single phase of pyrochlore-type structure, while (Sm1−xDyx)2Zr2O7 (0.5 ≤ x ≤ 1.0) possess a defective fluorite-type structure. The full width at half-maxima in the Raman spectra increases with increasing Dy content, which indicates that the degree of structural disorder increases as the Dy content increases. The ionic conductivity of (Sm1−xDyx)2Zr2O7 ceramics is investigated by impedance spectroscopy over a frequency range of 0.2 Hz to 8 MHz in the temperature range of 873–1173 K in air and hydrogen atmospheres, respectively. The ionic conductivity has a maximum near the phase boundary between the pyrochlore- and the defective fluorite-type phases under identical temperature levels. The ionic conductivity is determined by the degree of structural disorder or unit cell free volume, which is depending on the Dy content. As the ionic conductivity in the hydrogen atmosphere is almost the same as that obtained in air, the conduction of (Sm1−xDyx)2Zr2O7 is purely ionic with negligible electronic conduction.