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Abstract: The aim of present investigation is to study the effect of co-doping of lanthanum and magnesium on the ionic conductivity of CeO2 for its use as a solid electrolyte in the intermediate temperature solid oxide fuel cells (IT SOFC). Attempts have been made to synthesize compositions with x =0.075, 0.07, 0.06, 0.05 and 0.00 and y =0.00, 0.01, 0.03, 0.05 and 0.15 in the system Ce1−x−y Mg x La y O2−x−y/2 (CML) by auto-combustion method. X-ray diffraction patterns show that all the samples have fluorite structure similar to undoped ceria. Microstructures of thermally etched samples have been studied by scanning electron microscopy (SEM). In order to evaluate the contributions of grains σ g, grainboundaries σ gb and electrode–specimen interface to the total conductivity σ t, use is made of AC impedance analysis. Impedance measurements are made in the frequency range 1Hz to 1MHz and temperature range 250–500°C. The results show that the conductivity of the system increases with increasing lanthanum content. There is no enhancement in conductivity due to co-doping with La and Mg. [Copyright &y& Elsevier]

Abstract: A few compositions in the system Ce1−x Sr x O2−x with 0.05≤ x ≤0.20 have been prepared by auto-combustion method. More than 93% of theoretical density has been achieved by sintering at 1350°C for 4h. Solid solution has formed in the composition with x =0.05. All other compositions have been found to contain XRD lines of SrCeO3 beside the major fluorite phase. Complex plane impedance analysis has clearly revealed the contribution of grains, grain boundaries, and electrode specimen interface to the total observed resistance of the sample. Conduction occurs mainly due to diffusion of O2− ions through oxygen vacancies as indicated by values of activation energy of conduction. Composition, Ce0.95 Sr0.05 O1.95 exhibits the highest ionic conductivity 3.26×10−3 Scm−1 at 500°C among the series. Ionic conductivity decreases gradually with increasing x. This is due to the formation of a second phase SrCeO3 and increasing probability of formation of neutral associated defect pairs, . [Copyright &y& Elsevier]

Abstract: A typical composition of the system Ce1 − x Gd x O2 − δ with x =0.15 (CGO15) has been synthesized by auto-combustion method. DTA/TGA of the precursor compound indicated the completion of reaction at about 270°C. Greater than 95% of the theoretical density has been achieved by sintering at 1300°C for 10h. Single phase formation in as-burnt stage has been confirmed by its powder X-ray diffraction (XRD) pattern. The structural morphology was studied employing bright field transmission electron micrograph (BFTEM) and high resolution transmission electron micrograph (HRTEM). BFTEM image indicates that particles are highly agglomerated and appear to be dispersed in amorphous matrix. Also BFTEM image reveals that the average particle size is 26±5nm. The presence of amorphous phase in as-prepared ash was also confirmed by HRTEM and selected area diffraction (SAD). The scanning electron micrograph (SEM) of the thermally etched system shows grains having an average size of 400nm. Impedance measurements have been made in the frequency range 1Hz to 1.3MHz between 200 and 500°C and the total conductivity was measured. An enhanced conductivity value is observed which may make this system suitable for application as a solid electrolyte material for intermediate temperature solid oxide fuel cells (IT-SOFCs). [Copyright &y& Elsevier]

Abstract: The aim of the present investigation was to study the effect of doping of magnesium and calcium on the ionic conductivity of CeO2 in the system Ce1−xCax−yMgyO2−x (x=0.150) for its use as a solid electrolyte in the intermediate temperature solid oxide fuel cells (IT SOFC).Attempts have been made to synthesize a few compositions in this system with x=0.150 and y=0.000, 0.050, 0.060, 0.065 and 0.070. The precursor materials have been synthesized by auto-combustion method. Solid solution forms in compositions with y≤0.060. Microstructures of thermally etched samples have been studied by scanning electron microscopy (SEM). In order to evaluate the total electrical conductivity, σt, use is made of complex plane impedance analysis. Impedance measurements were made in the frequency range 1Hz–1MHz and temperature range 250–500°C. It is found that co-doped samples show higher conductivity than undoped and singly doped samples. [Copyright &y& Elsevier]

Abstract: Co-doping effect of Sm3+ and Ca2+ ions in ceria has been studied using the microwave assisted synthesis (MAS) technique. Thermal response of the prepared compositions was studied using differential thermal and thermo-gravimetric techniques (DTA/TG). Structural studies were performed using X-ray diffraction (XRD) and fourier transform infrared spectroscopy (FT-IR). The impedance analyses were performed over a wide range of temperatures (200–500°C) and frequency (100Hz to 1MHz). The conductivity data show that 10% doping of both Sm3+ and Ca2+ in ceria provides a significant rise in the conductivity value of pure ceria. [Copyright &y& Elsevier]