Hydrothermal synthesis and properties of Ce1-xSmxO2-x/2 and Ce1-xCaxO2-x solid solutions

The structure, thermal expansion coefficients and ionic conductivity of Ce1-xSmxO2-x/2 and Ce1-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 degrees C, a significantly lower temperature, compared to that at 1600 degrees 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 degrees C) = 5.7 x 10(-3) S/cm, E-a approximate to 0.9 eV, and sigma(600 degrees C) = 2.1 x 10(-3) S/cm, E-a approximate to 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 Ce0.91Ca0.09O1.91 solid electrolytes, respectively.