The effect of co-dopant addition on the properties of Ln 0.2Ce 0.8O 2− δ (Ln = Gd, Sm, La) solid-state electrolyte

Abstract

The present work aims at the investigation of Ln 0.2Ce 0.8O 2− δ (where Ln = Sm, La, Gd) structural and electrical properties when in the Ln sub-lattice, Ba 2+ and Sr 2+ with ionic radii 1.42 and 1.26 Å, respectively, are introduced. The conductivity measurements were held both in air and in H 2 + 3%H 2O atmosphere using the 4-probe dc technique at the temperature range of 600–900 °C. Among all the samples, the highest value of electrical conductivity is obtained in the case of (Sm 0.75Sr 0.2Ba 0.05) 0.2Ce 0.8O 2− δ , both in air and in hydrogen atmosphere. In the case of H 2 + 3%H 2O the conductivity of the co-doped compounds increases in comparison with air. Moreover, the dependence of conductivity on the oxygen partial pressure, measured at the P O 2 range of 0.21–10 −22 atm, showed that the electrolytic area of alkaline-earth metals doped Ln 0.2Ce 0.8O 2− δ is considerably enhanced, as predicted by the theory. Finally, by comparing the thermal expansion coefficients of the different materials (TEC), the thermo-mechanical compatibility between the co-doped and the other cell components was also investigated.