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La3+, Sm3+, and Gd3+ triple-doped ceria Ce1−x(La1/3Sm1/3Gd1/3)xO2−δ (x = 0.06, 0.12, 0.18, 0.24, and 0.30) materials were synthesized by the sol-gel autocombustion method. The selections of dopants were made by an optimized-average atomic number in accordance with the criteria for optimal-doping in ceria. The higher values of relative-density were achieved above 95% by sintering the samples at 1300 °C. The single-phase cubic-fluorite structures, high-density surface-microstructure with uniformly distributed grains, elemental confirmations, and concentration of oxygen vacancies were confirmed using powder x-ray diffraction, scanning electron microscope with energy dispersive spectroscopy, and micro-Raman spectroscopy. Electrical analysis was carried out by impedance spectroscopy, which confirmed the highest value of total-ionic-conductivity, i.e., 0.0381 S/cm at 600 °C with a minimum activation-energy for the Ce0.82La0.06Sm0.06Gd0.06O2−δ (LSG6) composition. Thermal-expansion analyses confirmed the moderate coefficient of thermal-expansion values for all the compositions and were found to be in good agreement with the recently developed materials. The enhanced total-ionic-conductivity and the moderate coefficient of thermal expansion of LSG6 make it as a potential solid-electrolyte for intermediate temperature-solid oxide fuel cell applications.

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