Effect of co-doping of Mg and La on conductivity of ceria

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−yMgxLayO2−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 σg, grainboundaries σgb and electrode–specimen interface to the total conductivity σt, use is made of AC impedance analysis. Impedance measurements are made in the frequency range 1 Hz to 1 MHz 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.

► Single phase formation.
► Variation of ionic conductivity is in accordance with ‘Mori Criteria’ of effective index.
► No additional enhancement due to co-doping of La and Mg.