Study of the ionic and electronic conductivity of ceria-based solid solutions

The structure, thermal expansion coefficients and ionic conductivity of Ce1-xSmxO2-x/2 and Ce 1-xCaxO2-x (x = 0--0.30) solid electrolytes prepared hydrothermally in a relatively wide concentration range for the first time were systematically investigated. The uniformly small particle size (40--68 nm) of the hydrothermally prepared materials allows sintering of the samples into highly dense ceramic pellets at 1400°C, a significantly lower temperature, compared to that at 1600°C required for samples prepared by solid state techniques. The maximum ionic conductivity was found at x = 0.17 for the Sm and at x = 0.09 for the Ca substituted ceria (sigma 600°C = 5.7 x 10-3 S/cm, Ea = 0.9 eV and sigma600°C = 2.1 x 10-3 S/cm, Ea = 0.8 eV respectively). The thermal expansion coefficients, determined from high-temperature X-ray data, are 8.6 x 10-6 and 9.4 x 10-6 K-1 for the best conducting Ce0.83Sm0.17O1.915 and Ce0.91Sm0.09O1.91 solid electrolytes respectively.; The structure, thermal expansion coefficients and ionic conductivity of (Ce0.83Sm0.17)1-x(Tb/Pr)xO 2-delta (x = 0--0.10) solid electrolytes prepared hydrothermally were investigated. The variation of the electrical conductivity with partial pressure of oxygen, PO2 , in the range 0.21 to 10-24 atm at various temperatures was used to determine the electrolytic domain boundary (EDB) of Ce0.83 Sm0.17)1-x(Tb/Pr)xO2-delta for 0 ≤ x ≤ 0.1. It is shown that Tb doping has an insignificant effect on the EDB of Ce0.83Sm0.17O2-delta , while ∼2% Pr doping appears to improve the EDB of Ce0.83 Sm0.17O2-delta by approximately half an order of magnitude.; (Ce0.83Sm0.17)1-xZrxO 2-delta (x = 0--0.50) solid solutions were synthesized by the hydrothermal method. The electrical properties of the solid solutions have been studied in air and under reducing conditions. Solid solutions with the fluorite structure were formed in all of the studied range of ZrO 2 substitution after calcination at 1500°C. With increasing ZrO 2 substitution up to 30% mol, the electronic conductivity increases under reducing atmospheres. The (Ce0.83Sm0.17) 0.7Zr0.3O2-delta solid solution has good mixed electronic and ionic conductivity: the total conductivity is 0.42 S/cm at PO2 = 5.7 x 10-21 atm and 700°C with estimated ionic conductivity ∼9 x 10-3 S/cm.