Influence of CaO on structure and electrical conductivity of pyrochlore-type Sm₂Zr₂O₇

(Sm_1-xCa_x)₂Zr₂O_7-x (0 ≤ x ≤ 0.100) ceramics were prepared by a solid state reaction process at 1973 K for 10 h in air, and were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). (Sm_1-xCa_x)₂Zr₂O_7-x (0 ≤ x ≤ 0.025) ceramics have a single phase of pyrochlore-type structure; however (Sm_1-xCa_x)₂Zr₂O_7-x (0.050 ≤ x ≤ 0.100) consist of pyrochlore phase and a small amount of perovskite-like CaZrO₃. The electrical conductivity of (Sm_1-xCa_x)₂Zr₂O_7-x ceramics was investigated by complex impedance spectroscopy over a frequency range of 0.1 Hz to 20 MHz in the temperature range of 573-873 K. The measured electrical conductivity obeys the Arrhenius relation. Both the activation energy and pre-exponential factor for grain conductivity increase with increasing the CaO content; however, electrical conductivity of (Sm_1-xCa_x)₂Zr₂O_7-x decreases with increasing the CaO content, which is due to the increase in structural disordering at 0 ≤ x ≤ 0.025 and the presence of the poorly conducting CaZrO₃ phase at 0.050 ≤ x ≤ 0.100, respectively.