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

• We synthesized dense lanthanum silicate apatites using organic based sol–gel synthesis.
• We prepared phase pure lanthanum silicate apatites at low synthesis temperature.
• Thermal expansion coefficients of the apatites can be modified using low concentrations of ZnO or MgO.
• High oxide ion conductivity and activation energies.
• Low temperature sintering of lanthanum silicate apatites.

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.

Impedance measurement of symmetrical cells of the sintered pellets Nyquist plot of impedance data Arrhenius representation of the conductivity of the sintered pellets.Figure optionsDownload as PowerPoint slideFigure optionsDownload as PowerPoint slideFigure optionsDownload as PowerPoint slide