کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
1294298 | 1498321 | 2012 | 6 صفحه PDF | دانلود رایگان |
![عکس صفحه اول مقاله: Anisotropy of oxide-ion conduction in apatite-type lanthanum silicate Anisotropy of oxide-ion conduction in apatite-type lanthanum silicate](/preview/png/1294298.png)
The anisotropy of oxide-ion conduction was clarified for the apatite-type La9.33 + 2x(SiO4)6O2 + 3x (0.01 ≤ x ≤ 0.13). We synthesized the polycrystalline materials of apatite by the isothermal heating of the sandwich-type La2Si2O7/La2SiO5/La2Si2O7 diffusion couples at 1873 K for 100 h. The resulting polycrystals were subsequently characterized using optical microscopy, X-ray diffractometry and impedance spectroscopy. The individual c-axes of the crystallites were appreciably aligned along the diffusion direction, while their a-axes were, around the common c-axis direction, oriented randomly. We obtained the impedance spectroscopy data of the polycrystalline electrolyte, the planar electrodes of which were parallel to the common c -axis. Thus, the obtained bulk conductivity (σ¯bulk ⊥ c) corresponds to the average value of those perpendicular to the c-axis, which steadily increased from 1.6 × 10− 5 to 3.8 × 10− 4 S/cm with increasing temperature from 623 to 848 K. The bulk conductivity parallel to the c-axis (σbulk ‖ c ) that was determined in a previous study was, when compared at the same temperature, necessarily higher than the corresponding σ¯bulk ⊥ c value; the magnitude of anisotropy (σbulk ‖ c / σ¯bulk ⊥ c) steadily decreased with increasing temperature from 2.1 × 102 at 623 K to 4.5 × 101 at 823 K. The activation energy of σ¯bulk ⊥ c was 0.71 eV, which is almost twice that of σbulk ‖ c (0.35 eV).
► Highly c-axis-oriented polycrystals were prepared for the lanthanum silicate apatite.
► The a-axes of the crystallites were oriented randomly around the common c-axis.
► The oxide-ion conductivity was determined perpendicular to the c-axis.
► The activation energy of conduction was almost twice that along the c-axis.
Journal: Solid State Ionics - Volume 217, 8 June 2012, Pages 40–45