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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: 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]