Synthesis and Electrical Properties of Dense Ce0.9Gd0.1O1.95 Ceramics

By Ke-qin Huang, M. Feng, John B. Goodenough. Journal of The American Ceramic Society, 2005

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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 A. 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 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* 583 ± 45°C and a motional enthalpy ΔH m = 0.63 ± 0.01 eV for the vacancies. A measured trapping energy ΔH t (I - T/T * ) has ΔH t = 0.19 ± 0.01 eV = 2.57kT*. In a reducing atmosphere, σ e exhibits a small-polaron motional enthalpy ΔH P = 0.40 ± 0.08 eV for transfer of a 4f electron from a Ce 3+ to a Ce 4+ ion and a ΔH p + ΔH pt = 0.51 ± 0.04 eV at T < T*.

Subfields: Electronic, Optical and Magnetic Materials, Materials Chemistry

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