The effect of co-dopant addition on the properties of Ln0.2Ce0.8O2−δ (Ln = Gd, Sm, La) solid-state electrolyte

The present work aims at the investigation of Ln0.2Ce0.8O2−δ (where Ln = Sm, La, Gd) structural and electrical properties when in the Ln sub-lattice, Ba2+ and Sr2+ with ionic radii 1.42 and 1.26 Å, respectively, are introduced. The conductivity measurements were held both in air and in H2 + 3%H2O 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 (Sm0.75Sr0.2Ba0.05)0.2Ce0.8O2−δ, both in air and in hydrogen atmosphere. In the case of H2 + 3%H2O 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 PO2 range of 0.21-10−22 atm, showed that the electrolytic area of alkaline-earth metals doped Ln0.2Ce0.8O2−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.