Hydrothermal Synthesis and Properties of Ce_1-xSm_xO_2-x/2 and Ce_1-xCa_xO_2-x Solid Solutions

The structure, thermal expansion coefficients and ionic conductivity of Ce 1 - x Sm x O 2 - x /2 and Ce 1 - x Ca x O 2 - 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 (σ 600 ° C = 5.7 × 10 - 3 S/cm, E a ≈ 0.9 eV, and σ 600 ° C = 2.1 × 10 - 3 S/cm, E a ≈ 0.8 eV, respectively). The thermal expansion coefficients, determined from high-temperature X-ray data, are 8.6 × 10 - 6 and 9.4 × 10 - 6 K - 1 for the best conducting Ce 0.83 Sm 0.17 O 1.915 and Ce 0.91 Ca 0.09 O 1.91 solid electrolytes, respectively.