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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: CaCu2.9Fe0.1Ti4O12 (CCFTO) has been prepared by a novel semi-wet route and its dielectric properties have been studied in the temperature range 300–500K. It is found that dielectric constant (ɛ) decreases drastically in the frequency range 100Hz to 1MHz. Complex plane impedance and modulus analysis was done to understand this drastic decrease in ɛ. Oxidation state of various ions was studied using X-ray photoelectron spectroscopy (XPS). The decrease in the permittivity of CCFTO can be attributed to two factors: the suppression of the Ca/Cu disorder in CCFTO which is observed in CaCu3Ti4O12 (CCTO) and the absence of the grain boundary internal barrier layer capacitance mechanism. [Copyright &y& Elsevier]