Ionic conductivity of oxy-apatite La10Si6−xInxO27−δ solid electrolyte ceramics

Oxy-apatite type La10Si6−xInxO27−δ (x = 0.1, 0.2, 0.3, 0.4, 0.5) ceramics are synthesized via the high-temperature solid state reaction method to obtain dense bulk ceramics. Crystal structure and properties of La10Si6−xInxO27−δ ceramics are investigated by X-ray diffraction, scanning electron microscopy, Raman spectroscopy, complex impedance analysis and thermal expansion coefficient measurement. All the compositions of La10Si6−xInxO27−δ ceramics doped with In3+ consist of a hexagonal apatite structure with a space group P63/m. The diffraction peaks of La10Si6−xInxO27−δ ceramics shift to the low angle side with increasing the content of In3+. Lanthanum silicates doped with trivalent In3+ have a higher total conductivity than those without trivalent In3+ at the Si4+ site. La10Si5.8In0.2O26.90 ceramics has the highest total conductivity of 3.14 × 10−2 S cm−1 at 1073 K, which is considerably higher than that of undoped La10Si6O27. La10Si5.6In0.4O26.80 has the highest thermal expansion coefficient of 9.01 × 10−6 K−1 at 1073 K.