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

Abstract Oxy-apatite type La 10 Si 6− x In x O 27− 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 La 10 Si 6− x In x O 27− 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 La 10 Si 6− x In x O 27− δ ceramics doped with In 3+ consist of a hexagonal apatite structure with a space group P 63/m. The diffraction peaks of La 10 Si 6− x In x O 27− δ ceramics shift to the low angle side with increasing the content of In 3+ . Lanthanum silicates doped with trivalent In 3+ have a higher total conductivity than those without trivalent In 3+ at the Si 4+ site. La 10 Si 5.8 In 0.2 O 26.90 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 La 10 Si 6 O 27 . La 10 Si 5.6 In 0.4 O 26.80 has the highest thermal expansion coefficient of 9.01 × 10 −6  K −1 at 1073 K.