Structure, densification and electrical properties of Gd3+ and Cu2+ co-doped ceria solid electrolytes for SOFC applications: Effects of Gd2O3 content

Abstract

Ceria-based solid electrolytes exhibit superior electrical conductivity compared to traditional yttria-stabilized zirconia ceramics. However, they require high sintering temperatures to achieve full densification. Transition metal oxides exhibiting low melting points, such as CuO, have been used as additives to lower the sintering temperature of these materials. In this context, the present work is focused on the evaluation of the effects of gadolinium oxide (Gd2O3) content on the structure, densification and electrical properties of ceria co-doped with CuO. Nominal compositions of Ce0.99−xGdxCu0.01O2-δ (0 ≤ x ≤ 0.3) were synthesized by the polymeric precursor method. The precursor powders were characterized by simultaneous thermogravimetry and differential thermal analysis (TG/DTA) and the calcined powders were studied by X-ray diffraction (XRD) and Rietveld refinement to obtain crystallographic parameters. The sinterability of green bodies was evaluated by dilatometry up to 1200 °C. The relative density was determined in samples sintered between 950 and 1050 °C and the microstructural characterization was performed by scanning electron microscopy (SEM). The electrical properties were investigated by impedance spectroscopy (IS). The XRD results confirms the formation of a cubic fluorite type structure in the entire composition range. The lattice parameters obtained by Rietveld refinement showed a reduction in the crystallite size with increasing gadolinium content. Densification was improved with increasing Gd-content up to x = 0.15. The electrical conductivity was enhanced by gadolinium addition, reaching a maximum of 7.81 mS cm−1 at 600 °C for the composition x = 0.15 sintered at a temperature as low as 1050 °C.