Electrical transport properties of In-doped Ce_1-xIn _xO_2-δ (x = 0.1; 0.2)

We report the synthesis and electrical conductivity of fluorite-type Ce_1-xIn_xO_2-δ (x = 0.1; 0.2) in air, dry Ar, N₂ and H₂ in the temperature range of 300-800 °C. We have employed a new CO₂ capture technique to prepare the "metastable" fluorite-related structure Ce_1-xIn _xO_2-δ from the corresponding In-doped Ba-containing perovskite of the nominal chemical formula BaCe_1-xIn _xO_3-δ at 800 °C. The amount of CO₂ gained per ceramic gram was found to be consistent with the formation of BaCO₃, confirming the complete leaching of Ba in BaCe _1-xIn_xO_3-δ. The CO₂ capture efficiency was found to be in the range of 90-99% at 800 °C, which is significantly higher than those of well-known low-temperature CO₂ absorbing materials, including Li₂O, Li₆Zr ₂O₇, Li_1.8Na_0.2ZrO₃ and LiNaZrO₃. Powder X-ray diffraction (PXRD) and energy dispersive X-ray analysis (EDAX) confirmed the perovskite into fluorite structural transformation reaction. The AC impedance study showed a clear intercept to the real axis at the low-frequency over the investigated temperatures in all the atmospheres, indicating a non-blocking nature of electrode (Pt) and electrolyte interface. The constant phase element (CPE) value was found to be in the order of 10^-10 F in air, N₂ and Ar for high-frequency part of the semicircle due to bulk contribution, and about two orders of magnitude lower values were observed for the low-frequency semicircle which may correspond to grain-boundary effect. The 20 mol% In-doped CeO₂ exhibits a total electrical conductivity of about 4 × 10^-6 S/cm at 600 °C in Ar, while in H₂ an about four orders of magnitude higher electrical conductivity of 3 × 10^-2 S/cm was observed. The activation energy for electrical conductivity was found to be 1.36 eV in Ar, 1.43 eV in N₂, 1.34 eV in H₂, and 1.1 eV in air for Ce _0.8In_0.2O_1.9.