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

La9.33-xSbx (SiO4)(6)O-2 (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)(6)O-2 leads to an increased unit cell volume. The room-temperature structure is hexagonal, space group P6(3) or P6(3)/m,with a = 9.728 angstrom, and c = 7.191 angstrom for La8.33Sb(SiO4)(6)O-2. The average grain size in sintered specimens was approximately 1.5 to 1.9 mu m. La9.33-xSbx(SiO4)(6)O-2 (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 degrees C and activation energy of La8.33Sb(SiO4)(6)O-2 doped with 1.0 mol% Sb showed a maximum value of 3.3 x 10(-3) S cm(-1) and 1.47 eV, respectively.