Abstract: A standard solid state technique was used to synthesize the composite materials of Ce_0.8Sm_0.2O_1.9(SDC) and (ZrO_{2)0.92(Y2O3)0.08(YSZ), the mass rati os of SDC to YSZ are 1：9， 3∶7 and 5∶5, respectively. From the XRD data, they show a biphasic structu r e. The impedance spectra show that at low temperatures the resistance of these composite electrolytes are lower than that of pure YSZ, but the resistances becom e higher at the working temperature of the fuel cells (700～850 ℃). In the expe riments of the solid oxide fuel cells with them as electrolytes, the open circui t voltage is very low, and drops very apparently with the increasing content of SDC.}

Key words: rare-earth material, solid electrolyte, fuel cells, impedance spectrum