Structural, morphological, and electrical properties of doped ceria as a solid electrolyte for intermediate-temperature solid oxide fuel cells

The solid solutions of CeO₂ with one or more rare-earth oxides among Yb₂O₃, Sm₂O₃, and Gd₂O₃ are synthesized by either modified glycine nitrate procedure (MGNP) or self-propagating reaction at room temperature (SPRT). The overall mole fraction of rare-earth oxide dopants was x = 0.2. The characterization was committed by XRPD, TEM, BET, and Raman Spectroscopy methods. According to XRPD and Raman spectroscopy, the obtained products presented the single-phase solid solutions with basic fluorite-type CeO₂ structure, regardless on the number and the concentration of dopants. Both XRPD and TEM analysis evidenced the nanometer particle dimensions. The defect model was applied to calculate lattice parameters of single-, co-, and multi-doped solids. The sintering of the sample nanopowders was performed at 1550 °C, in air atmosphere. The sintered samples were characterized by XRPD, SEM, and complex impedance methods. The sintering did not affect the concentration ratios of the constituents. The highest conductivity at 700 °C amounting to 2.14 × 10⁻² and 1.92 × 10⁻² Ω⁻¹ cm⁻¹ was measured for the sample Ce_0.8Sm_0.08Gd_0.12O_2−δ, synthesized by SPRT and MGNP methods, respectively. The corresponding activation energies of conductivity, measured in the temperature range 500–700 °C, amounted to 0.24 and 0.23 eV.