We report the comparative electrical properties of monovalent (Na + ), divalent (Ca 2+ , Sr 2+ ), trivalent (In 3+ , La 3+ ) and coupled substitution of divalent and trivalent (Ca 2+ + Sm 3+ ) cation-doped CeO 2 . The investigated samples were prepared by solid-state reaction (ceramic) using the corresponding metal oxides and salts in the temperature range 1000-1600 • C in air. Powder X-ray diffraction (PXRD), laser particle size analysis (LPSA), scanning electron microscopy (SEM), and ac impedance spectroscopy measurements were employed for structural, morphology, and electrical characterization. PXRD studies reveal the formation of single-phase cubic fluorite-type structures for all investigated samples except those doped with In 3+ . The variation of lattice parameters is consistent with ionic radii (IR) of the dopant metal ions, with the exception of Na + -doped CeO 2 . Our attempt to substitute In 3+ for Ce 4+ in CeO 2 using both ceramic and wet chemical methods was unsuccessful. Furthermore, diffraction peaks attributed to CeO 2 and In 2 O 3 were observed up to sintering conditions of 1600 • C. Among the single-phase compounds investigated, Ce 0.85 Ca 0.05 Sm 0.1 O 1.9 exhibits the highest bulk conductivity of 1.3 × 10 −3 S/cm at 500 • C with activation energy of 0.64 eV in air. The electrical conductivity data obtained for Ce 0.85 Ca 0.05 Sm 0.1 O 1.9 in air and Ar were found to be very similar over the investigated temperature range, indicating the absence of p-electronic conduction in the high oxygen partial pressure (pO 2 ) range which is consistent with literature reported on Sm-doped CeO 2 .

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This paper reports on the electrochemical properties and chemical stability of a recently developed Ca 2+ and Sm 3+ -doped oxide ion conducting electrolyte, Ce 0.85 Ca 0.05 Sm 0.1 O 1.9 (CCS), employed in an intermediate temperature solid oxide fuel cell (IT-SOFC) using conventional Sm 0.5 Sr 0.5 CoO 3 (SSC) and La 0.8 Sr 0.2 MnO 3 (LSM) cathodes in air at elevated temperatures. The materials were prepared by conventional solid-state reactions using their corresponding metal oxides and salts in the temperature range of 1,200-1,450°C in air. Powder X-ray diffraction (PXRD) and impedance spectroscopy were employed for phase formation, chemical compatibility, and electrochemical characterization. PXRD studies on 1:1 weight ratio of heat-treated (1,000°C for 3 days) mixtures of SSC or LSM and CCS revealed the presence of fluorite-type and perovskite-like phases. The area-specific resistance (ASR) value in air was lower for SSC cathodes (4.3-0.15 Ω cm 2 ) compared to those of LSM (407-11 Ω cm 2 ) over the investigated temperature range of 600-800°C. As expected, a significant increase in ASR was observed in Ar as compared to air.

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