Ionic conductivity across the disorder-order phase transition in the SmO1.5-CeO2 system

Samples of SmxCe1-xO2-delta (0.05 <= x <= 0.55) were prepared by solid-state reactions and the disorder-order phase transition and grain ionic conductivity were investigated using XRD and ac impedance spectroscopy technique, respectively. For 0 <= x <= 0.35 the material has a fluorite structure and gradually stabilizes into a C-type rare-earth structure at 0.40 <= x <= 0.55 because of oxygen-vacancy ordering. The highest grain ionic conductivity observed is 0.0565(37) S cm(-1) at 700 degrees C for Sm0.20Ce0.80O2-delta with an associated activation energy (E-A) of 0.791(7) eV. The slopes for E-A and pre-exponential factor change during phase transition and the conductivity decreases monotonically. Upon comparison of the E-A between the SmO1.5-CeO2 and NdO1.5-CeO2 systems, it is seen E-A for the SmO1.5-CeO2 system is lower than NdO1.5-CeO2 system at compositions with less than 25% trivalent rare earth element while higher E-A is observed for the SmO1.5-CeO2 system at Nd/Sm concentrations above 25%. (c) 2012 Elsevier Ltd. All rights reserved.