Synthesis and Characterisation of Oxide Ions Conductors with the Apatite Structure for Intermediate Temperature SOFC

Silicated rare earth apatite with formula La(9.33)(SiO4)6O2 has been prepared by solid state reaction synthesis at high temperature. The reagents (La2O3 and SiO2) have first been characterised. Then the synthesis process was studied and optimised. Samples with various densities (from 70 to 95% of the theoretical value) have been obtained by hot pressing at 1400DGC and by sintering at 1550DGC. The presence of secondary phases leads to the formation of a liquid phase at achieving sintering at temperatures above 1600DGC. Electrical properties of the whole samples have been characterised between 400 and 900DGC by the complex impedance method. Conductivity values of about 2 x 10 exp -4 S/cm have been measured at 700DGC. The samples present activation energies of less than 1 eV, which is a typical value for such ionic conductors.