Abstract
We have successfully synthesized the highly c-axis-oriented polycrystals of apatite-type lanthanum silicate by the reactive diffusion technique. When the sandwich-type La2Si2O7/La2SiO5/La2Si2O7 diffusion couples were isothermally heated at 1873 K for 100 h, the apatite polycrystals readily produced in the form of layer at the interfacial boundaries. The annealed couple was mechanically processed and the thin-plate electrolyte consisting of the highly c-axis-oriented polycrystal was obtained. The oxide-ion conductivity was determined from the impedance spectroscopy data at 573 K - 973 K, which steadily increased from 2.4 × 10-3 Scm-1 to 2.4 × 10-2 Scm-1 with increasing temperature. The empirical activation energy of conduction was 0.35 eV, which compares well with the calculated migration energy of 0.32 eV in a previous study.
