Electrical transport properties of aliovalent cation-doped CeO₂

We report the comparative electrical properties of monovalent (Na ⁺), divalent (Ca²⁺, Sr²⁺), trivalent (In ³⁺, La³⁺) and coupled substitution of divalent and trivalent (Ca²⁺ + Sm³⁺) cation-doped CeO₂. 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 In³⁺. The variation of lattice parameters is consistent with ionic radii (IR) of the dopant metal ions, with the exception of Na⁺-doped CeO₂. Our attempt to substitute In³⁺ for Ce⁴⁺ in CeO₂ using both ceramic and wet chemical methods was unsuccessful. Furthermore, diffraction peaks attributed to CeO₂ and In₂O₃ were observed up to sintering conditions of 1600 °C. Among the single-phase compounds investigated, Ce_0.85Ca_0.05Sm_0.1 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_0.85Ca_0.05Sm_0.1O _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 (pO₂) range which is consistent with literature reported on Sm-doped CeO₂.