抄録
We prepared the apatite-type lanthanum silicate polycrystals by reactive diffusion between La2SiO5 and La2Si2O7. The chemical composition of the apatite layer, represented by La9.33+2x(SiO4)6O2+3x, was characterized by the steady decrease of the x-value from 0.13 on the La2SiO5/apatite interface to 0.01 on the apatite/La2Si2O7 interface. The formation of apatite at 1773 - 1873 K was controlled by the interdiffusion of La2O3 and SiO2 components within the growing apatite layer. The activation energy of this volume-diffusion process was ca. 200 kJ/mol. The highly c-axis-oriented polycrystalline material with 0.09 ≤ x ≤ 0.13 showed the oxide-ion conductivity ranging from 2.4 × 10-3 Scm-1 at 573 K to 2.39 × 10-2 Scm-1 at 973 K, with the empirical activation energy being 33.8 kJ/mol (= 0.35 eV). The reactive diffusion technique could be widely applicable to the syntheses of highly grain-oriented ceramics as a new facile texturing method.
