Synthesis and Electrical Properties of Dense Ce 0.9 Gd 0.1 O 1.95 Ceramics

Uniform spherical powders of Ce 0.9 Gd 0.1 O 1.95 with an average diameter of 250 nm were obtained at 700°C from a sol‐gel process of mixing nitrates and ethylene glycol. Broadening of the X‐ray peaks of the fluorite structure reveals a small crystallite size within the powders. Sintering in air of pressed pellets of the powders at 1585°C gives ceramics of 99% theoretical density with grain sizes 1‐10 µm and a cubic unit cell a = 5.422 ± 0.034 Å. The electrical conductivity σ=σ o +σ e has two components. In air or argon, the electronic component σ e is negligible and the oxide‐ion conductivity σ o is not described by a classical Arrhenius equation; a pronounced curvature at T similar/congruent T * has been observed in the Arrhenius plot of the bulk conductivity. The system could be modeled by a condensation of mobile oxygen vacancies into ordered clusters below a temperature T * similar/congruent 583 ± 45°C and a motional enthalpy Δ H m = 0.63 ± 0.01 eV for the vacancies. A measured trapping energy Δ H t (1 ‐ T/T *) has Δ H t = 0.19 ± 0.01 eV = 2.57 kT *. In a reducing atmosphere, σ e exhibits a small‐polaron motional enthalpy Δ H p = 0.40 ± 0.08 eV for transfer of a 4 f electron from a Ce 3+ to a Ce 4+ ion and a Δ H p +Δ H pt = 0.51 ± 0.04 eV at T < T *.