Sol–gel synthesis and characterization of Zn2+ and Mg2+ doped La10Si6O27 electrolytes for solid oxide fuel cells

Abstract

Achieving high densification at low sintering temperatures for lanthanum silicate apatites is a major technological hurdle to enable this class of materials to be evaluated as electrolytes for solid oxide fuel cells. Using sol–gel process, materials close to 97% of theoretical density have been obtained at a low sintering temperature of 1773 K for both doped and undoped samples. The effect of varying concentrations of Zn2+ doping on the sinterability, electrical, thermal and microstructural properties of 0.2 mol Mg2+ doped La10Si6O27 were investigated.Ionic conductivity of the samples was measured using electrochemical impedance spectroscopy in the temperature range of 573 K–1073 K. A total ionic conductivity of 1.7 × 10−2 Scm−1 with a corresponding activation energy of 0.33 eV at 1073 K were measured for the composition La10Zn0.2(SiO4)5.8O2.5 which is higher than 9 × 10−3 Scm−1 for the undoped composition La10(SiO4)6O3. The composition La10Mg0.2Zn0.4(SiO4)5.4O4.8 has the lowest thermal expansion coefficient of 8.470 × 10−6 K−1 of all the samples investigated.