Electrical properties of Sb-doped apatite-type lanthanum silicate materials for SOFCs

Abstract

La9.33-xSbx(SiO4)6O2 (0 < x < 2.0) ceramics were fabricated using the standard solid-state synthesis method for solid oxide electrolytes. Increasing the Sb content in apatite-type La9.33-xSbx(SiO4)6O2 leads to an increased unit cell volume. The room-temperature structure is hexagonal, space group P63 or P63/m, with a = 9.728 Å, and c = 7.191 Å for La8.33Sb(SiO4)6O2. The average grain size in sintered specimens was approximately 1.5 to 1.9 μm. La9.33-xSbx(SiO4)6O2 (1.5 < x < 2.0) apatite ceramics showed the formation of a second phase of La2Si2O7, due to the volatilization of the Sb atoms. The electrical conductivity at 800 oC and activation energy of La833Sb(SiO4)6O2 doped with 1.0 mol% Sb showed a maximum value of 3.3 x 10-3 S cm-1 and 1.47 eV, respectively.