Ceria doped with aliovalent cations, such as rare earth oxides, has been considered as one of the most promising candidate electrolyte materials for intermediate temperature solid oxide fuel cells. In this study, high purity cerium nitrate, samarium nitrate and erbium nitrate salts were used to obtain ceria-based solid solutions Ce_{0.80}Sm_{0.20}O_{1.90} (SDC), Ce_{0.80}Sm_{0.15}Er_{0.05}O_{1.90} (ESDC5), Ce_{0.80}Sm_{0.10}Er_{0.10}O_{1.90} (ESDC10) through the cellulose templating method. Crystal structure and microstructure were characterized by means of X-ray diffraction and scanning electron microscopy, respectively. X-ray diffraction results indicate that a single-phase fluorite structure formed at a relatively low calcination temperature, 500°C. The relative densities of the sintered pellets were higher than 93%. The electrical properties of doped and co-doped ceria electrolytes in the temperature range 300-750°C were analyzed by using electrochemical impedance spectroscopy. The singly doped ceria at 750°C showed the highest ionic conductivity with less activation energy.
In the trivalent rare-earth doped ceria electrolyte for SOFC applications, the highest conductivities are observed for Ce_{1-x}Sm_{x}O_{2-x/2} and Ce_{1-x}Gd_{x}O_{2-x/2}. In this study, fully dense samarium doped ceria ceramics (SDC), Sm_{x}Ce_{1-x}O_{2-x/2} (x=0.1) have been synthesized via Pechini method. The phase identification, microstructural properties and bond structure of SDC samples were studied by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier Transform- Infrared Spectroscopy (FTIR). The XRD results indicate that a single-phase fluorite structure has formed at relatively low calcination temperature of 500°C. This method yields high purity ultrafine powders which can form dense electrolyte at relatively low sintering temperatures. The SEM results show that a complete solid solution between ceria and samarium was obtained at the sintering temperature of 1400°C.
CeO₂ ceramics doped with 20 mol.% samarium (SDC-20) were prepared through the Pechini process. The samples were calcined at 400, 700 and 1000°C. The sintering behavior of the calcined SDC-20 powders was also investigated at 1400°C for 6 h. Microstructural and physical properties of SDC-20 samples were characterized with X-ray diffraction, scanning electron microscopy, thermogravimetry and impedance analysis methods. The results of the thermogravimetry/differential thermal analysis and X-ray diffraction indicated that a single-phase fluorite structure formed at a relatively low calcination temperature of 400°C. It is understood from the measured ionic conductivity values that the pellet formed from the SDC-20 samples calcined at 1000°C had lower resistance of grain-boundary than those of the pellets formed from the SDC-20 samples calcined at 400 and 700°C. The maximum ionic conductivity was measured as 1.95× 10⁻² S cm⁻¹ at 800°C for the sintered SDC-20 pellet obtained from SDC-20 powders calcined at 1000°C.
Nd_{0.20}Sm_{x}Ce_{0.8-x}O_{1.9-x/2} (x=0, 0.05, 0.10, 0.15, 0.20) rare-earth-co-doped ceria electrolytes were synthesized by polyol process. Acetate compounds of cerium and dopants (Nd, Sm) were used as starting materials and triethylene glycol was used as a solvent. Structural and ionic conductivity properties of the electrolyte systems were determined by applying characterization techniques such as X-ray diffraction, the Fourier transform infrared spectroscopy, scanning electron microscope, and electrochemical impedance spectroscopy. The results of X-ray diffraction indicated that a single-phase fluorite structure formed at the relatively low calcination temperature of 600°C. So, the samples were calcined at 600°C for 4 h and then sintered at 1400°C for 6 h to obtain dense ceramics (between 85 and 90%). The two-probe ac impedance spectroscopy was used to study the total ionic conductivity of doped and co-doped ceria samples. The results of the impedance spectroscopy indicate that the Nd_{0.20}Sm_{0.05}Ce_{0.75}O_{1.875} composition exhibited highest ionic conductivity value, 3.60×10¯² S cm¯¹ at 800°C.
Ceria doped with trivalent cations, such as rare earth elements, is considered to be one of the most promising electrolyte materials for intermediate-temperature solid oxide fuel cells, which are an alternative to the commercially used ytrium-stabilized zirconia (YSZ). The aim of this work research is to synthesize Sm and Nd co-doped ceria materials using the Pechini method as solid electrolyte for intermediate temperature solid oxide fuel cell. Ce_{0.75}Sm_{0.20}Nd_{0.05}O_{1.875}, Ce_{0.65}Sm_{0.20}Nd_{0.15}O_{1.825}, and Ce_{0.60}Sm_{0.20}Nd_{0.20}O_{1.80} have been chosen as target of this study. Microstructural and physical properties of the samples were characterized with X-ray diffraction, scanning electron microscopy, thermogravimetric analysis methods. The results of the thermogravimetry/differential thermal analysis and X-ray diffraction indicated that a single-phase fluorite structure formed at the relatively low calcination temperature of 600°C for 3 h. The two-probe ac impedance spectroscopy was used to study the total ionic conductivity of doped and co-doped ceria ceramics at 800°C. The Ce_{0.60}Sm_{0.20}Nd_{0.20}O_{1.80} sample showed maximum ionic conductivity.
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