Defect Chemistry of Singly and Doubly Doped Ceria: Correlation between Ion Transport and Energetics

摘要

Earlier studies have shown a strong correlation between the enthalpy of formation, ΔH_(f.ox) and the ionic conductivity, σ_p near room temperature in doped ceria systems, which are promising solid electrolytes for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The present work demonstrates that this correlation holds at the operating temperature of IT-SOFCs, 600-700°C. Solid solutions of Ce_(1-x)Nd_xO_(2-0.5X), Ce_91-X)Sm_xO_92-0.5x), and Ce_(1-x)Sm_(0.5x)d_90.5x)O_(2-0.5x) are studied. The ΔH_(f.ox) at 702°C is determined by considering the excess heat content between 25 and 702°C combined with the value of ΔH_(f.ox) at25°C. Both σ_i and ΔH_(f.ax) show maxima at x = 0.15 and 0.20 for the singly and doubly doped ceria, respectively, suggesting that the number of mobile oxygen vacancies in these solid solutions reaches a maximum near those compositions. An increase in temperature results in a shift of the maximum in both ΔH_(f.ox) and σ_i towards higher concentrations. This shift results from a gradual increase in dissociation of the defect associates.