Synthesis and characterization of doped apatite-type lanthanum silicates for SOFC applications

A series of iron- and/or aluminium-doped apatite-type lanthanum silicates (ATLS) La9.83Si6-x-yAlxFeyO26 +/-delta (x = 0, 0.25, 0.75, and 1.5, y = 0, 025, 0.75, and 1.5) were synthesized using the mechanochemical activation (MA), solid state reaction (SSR), Pechini (Pe) and sol-gel (SG) methods. The total conductivity of the prepared materials was measured under air in the temperature range 600-850 degrees C using 4-probe AC impedance spectroscopy. Its dependence on composition, synthesis method, sintering conditions and powder particle size was investigated. It was found that for electrolytes of the same composition, those prepared via mechanochemical activation exhibited the highest total specific conductivity, which was improved with increasing Al- and decreasing Fe-content. The highest conductivity value at 700 degrees C. equal to 2.04 x 10(-2) s cm(-1), was observed for the La9.83Si5Al0.75Fe0.25O26 +/-delta electrolyte. La9.83Si4.5Fe1.5O26 +/-delta electrolyte samples synthesized using the Pechini method exhibited higher conductivity when sintered conventionally than when spark-plasma sintering (SPS) was used. (C) 2010 Elsevier B.V. All rights reserved.