| Fuel cell is an electrochemical device that converts the energy of a chemical reaction directly into electrical energy. There are many fuel cell types, with the most common ones being: phosphoric acid fuel cells(PAFC), molten carbonate fuel cells(MCFC), alkaline fuel cells(AFC), proton exchange membrane fuel cells(PEMFC), and solid state fuel cells(SOFC).SOFCs offer a clean, low-pollution technology to electrochemically generate electricity in high efficiencies. The researchers have paid the most attention on the SOFCs application. The SOFCs usually operate at high temperature, such high temperatures lead to many technological problems, such as mechanical instability, materials aging, and undesirable chemical reaction between cell components (electrolyte, electrodes and interconnecting material). Therefore, many kinds of other solid electrolytes with rare earths as framework elements and dopants were studied. A new window to the research of solid electrolytes was opened.In this thesis, the main research works have been performed to synthesize, characterize and investigate the structure and electrical properties of complex oxides containing rare-earth and molybdenum ions, hopping to improve the properties of the known solid state electrolyte materials as well as to find out new type of the solid state electrolyte materials. The main works are as follows:1. Synthesis and characterization of Ce6-xRExMoO15.0(Gd, Ho and Dy)The Ce6-xGdxMoO15-6, (0.2X5), CeHoMoO- 6 (0.2X1.2) and Ce6-xDyxMoO 15.6 (0.2X5) compounds were synthesized using wet-chemistry techniques. The samples was sintered in air at 1300, and their crystal structure was examined by powder X-ray diffraction technique. It is found that the single phase was formed in the solid solution range for Ce6-xGdxMoO15.6 (0.2X1.6 and X=4,X=5), for Ce6-xHoxMoO15-6(0.2X1.2) and for Ce6-xDyxMoO15.0(0.2X 1.6 and X=4,5). The samples showed a single phase with a fluorite-related cubic structure. And some additional diffraction peaks appeared in the XRD patterns for x=1.7,1.8,2and 3. The XPS spectra of Ce6-xGdxMoO15.6(x=0.6), Ce6-xHoxMoO15.6(x=0.6) and Ce6-xDyxMoO15(x=0.8) was measured. The XPS pattern shows that the Ce3d5/2 and Mo3ds/2 signal peaks are the XPS peaks of Ce4+ and Mo6+ ions, respectively. The XRD pattern cab be indexed to the cubic structure with the Fm3m space group (R=100%) using the CELL program. The lattice parameter changes gradually with the change of the RE content.2. Synthesis, characterization and electrical properties of Ce6_xSmxMoO 15.6 (0.2 SX 1.2)In order to investigate the formation temperature of the compound, the precursor of Ce6-xSmxMoO15.6(x=0.8) was examined by DTA/TG. It is found that the formation temperature of the single phase is as low as 400 癈 . And the precursor of Ce6-xSmxMoO15-6(x=0.8) was heated at the different temperature, then was examined by XRD, the result is in accord with the one of DTA/TG. The XRD patterns of Ce6-xSmxMoO15-6(0.2X1.2) show that the samples form the single phase at low temperature with cubic structure, which indicates that Sm had doped into the Ce sites in the Ce6MoO15. The XPS spectra of Ce6-xSmxMoO15.6(x=0.8) shows that the signals consist of photoelectron peaks at 882.2ev and 231.8ev, which are consistent with Ce4+, Mo6+ ions, respectively. Using CELL program, all the samples were the single-phase cubic structure with the Fm3m space group (R=100%). The calculated lattice parameter increases gradually with Sm content increasing.The ac impedance spectra of Ce6-xSmxMoO15.6 was measured at different temperatures. At low temperature, the impedance spectrum of the sample consisted of two depressed semi-circles and a spike from the high frequency to low frequency. The high frequency semi-circle originates from the bulk transport, the lowest frequency spike is due to oxide-ion transfer at the electrode, and the intermediate frequency semi-circle gives information on the grain-boundary resistance to oxide-ion motion. With an increase in temperature, the grain boundary process disappears and the bulk pr...
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