Hydrothermal synthesis and properties of Ce_1-xLa_xO_2-δ solid solutions

The structure, thermal expansion coefficients, ionic and electronic conductivities of Ce_1-xLa_xO_2-δ (x = 0-0.30) solid solutions, prepared for the first time hydrothermally, were investigated. The uniformly small particle size (25-50 nm) of the hydrothermally prepared materials allows sintering of the samples into highly dense ceramic pellets at 1300-1400°C, a significantly lower temperature, compared to that at 1600-1650°C required for ceria solid electrolytes prepared by solid state techniques. The solubility limit of La₂O₃ in CeO, was determined to be around 20 mol.%. The maximum conductivity, δ_600°C approx. 6.4 × 10^-3 S/cm with E_a = 0.73 eV, was found at x = 0.15. The thermal expansion coefficients, determined from high-temperature X-ray data are 11.7±0.6 × 10^-6 K^-1 for the CeO₂, and, increase with increasing La substitution (15.0 × 10^-6 K^-1 at x = 0.20).