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

Abstract

Uniform spherical powders of Ce0.9Gd0.1O1.95 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=σo+σe has two components. In air or argon, the electronic component σe is negligible and the oxide‐ion conductivity σo 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 ΔHm= 0.63 ± 0.01 eV for the vacancies. A measured trapping energy ΔHt(1 ‐ T/T*) has ΔHt= 0.19 ± 0.01 eV = 2.57 kT*. In a reducing atmosphere, σe exhibits a small‐polaron motional enthalpy ΔHp= 0.40 ± 0.08 eV for transfer of a 4 f electron from a Ce3+ to a Ce4+ ion and a ΔHp+ΔHpt= 0.51 ± 0.04 eV at T < T*.