Synthesis and electrical properties of apatite-type La10Si6O27

Lanthanum silicate La10Si6O27 nanopowders are synthesized via co-precipitation process. After the calcination at 900 °C and then removal of La2O3 by acid-washing, pure stoichiometric La10Si6O27 nanopowders are obtained, and are characterized by XRD, BET, TEM and ICP, respectively. The oxy-apatite ceramic with the density higher than 95% can be obtained at rather low sintering temperature of 1300 °C, which has comparable total conductivity with the samples sintered at 1650 °C from the powders prepared by solid-state reaction. Additionally, effects of sintering temperatures on electrical properties are also investigated in detail. It is found, that with the increasing sintering temperature from 1300 °C to 1650 °C, the grain conductivity monotonously increases; while the grain boundary conductivity increases first and then decreases with the maximum value at 1600 °C. The related mechanism is also discussed.