Preparation and improved grain conductivity of (Sm_1-x Y _x)₂ Zr₂ O₇ ceramics

(Sm_1-x Y_x) ₂ Zr₂ O₇ (0 ≤ x ≤ 0.5) ceramics were prepared by a solid-state reaction process at 1973 K for 10 h in air. (Sm_1-x Y_x)₂ Zr ₂ O₇ (0≤x≤0.3) ceramics have a single phase of the pyrochlore-type structure, whereas (Sm_1-x Y_x)₂ Zr₂ O₇ (x=0.4,0.5) exhibit a defective fluorite-type structure. The full width at half-maxima in the Raman spectra increase with increasing Y content, which indicates that the degree of structural disorder increases as the yttrium content increases. The electrical conductivity of (Sm_1-x Y_x)₂ Zr₂ O₇ ceramics was investigated by electrochemical impedance spectroscopy over a frequency range of 1 Hz to 20 MHz in the temperature range of 623-1173 K in air and hydrogen atmospheres. The electrical conductivity of (Sm_1-x Y_x)₂ Zr₂ O₇ obeys the Arrhenius-type behavior and increases with increasing temperature. The grain conductivity and total conductivity of pyrochlore-type materials are clearly higher than those of defective fluorite-type materials in the intermediate temperature range of 623-1073 K. Both activation energy and pre-exponential factor for grain conductivity increase with increasing Y content. The electrical conductivity measured in the reducing atmosphere of hydrogen shows no significant changes, which proves that the conduction is purely ionic with negligible electronic contribution in the series.