Synthesis and characterization of Ce0.8Sm0.2-xPrxO2-δ (x=0.02-0.08) solid electrolyte materials

Solid electrolytes Ce0.8Sm0.2-xPrxO2-delta (x=0.02, 0.04, 0.06, 0.08) were prepared by citric-nitrate method. The microstructure and electrical properties of such materials were examined by X-ray diffraction (XRD), atomic force microscopy (AFM), Raman spectroscopy (Raman), X-ray photoelectron spectroscopy (XPS) and impedance spectroscopy analyses. Specifically, results from XRD analysis showed that samples calcined at 800 degrees C for 4 h possessed single-phase cubic fluorite structure, and the average grain size was found to be 36-45 nm. Further Raman spectral analysis indicated that oxygen vacancies should be present in the cubic fluorite structure of Ce0.8Sm0.12Pr0.08O2-delta, and Pr-doping seemed to increase their concentration significantly. AFM images showed that the grain size grew with the increase of Pr substitution. XPS analysis confirmed the existence of oxygen vacancies in the lattice of Ce0.8Sm0.12Pr0.08O2-delta in which Pr3+ and Pr4+ co-existed. AC impedance spectra indicated that the conductivity of Ce0.8Sm0.2-xPrxO2-delta increased with the increase of Pr-doping but the conduction activation energy decreased. Notably, it appeared that sample Ce0.8Sm0.12Pr0.08O2-delta (sigma(600) (degrees C) =1.21 x 10(-2) S/cm, E-a=0.77 eV) exhibited conductivity superior to Ce0.8Sm0.2O1.9 (sigma(600 degrees C)=2.22x10(-3) S/cm, E-a=1.02 eV) because it possessed higher conductivity and lower activation energy. At 600 degrees C, the conductivity of Ce0.8Sm0.12Pr0.08O2-delta was 4.45 times higher than that of the un-doped material.