Hydrothermal Synthesis and Properties of Ce₁_-<i>_x</i>Sm<i>_x</i>O₂_-<i>_x</i>_/2 and Ce₁_-<i>_x</i>Ca<i>_x</i>O₂_-<i>_x</i> Solid Solutions

Abstract

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 °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 (σ600 °C = 5.7 × 10-3 S/cm, Ea ≈ 0.9 eV, and σ600 °C = 2.1 × 10-3 S/cm, Ea ≈ 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 Ce0.83Sm0.17O1.915 and Ce0.91Ca0.09O1.91 solid electrolytes, respectively.