open access

https://hdl.handle.net/2115/73277

Conduction Pathway of Oxide Ions in Rare-Earth Silicate Oxyapatites

日本語

アパタイト

2011-02-28

日本結晶学会

Journal of the Crystallographic Society of Japan

53(1)

86-90

Apatite-type RE9.33(SiO4)6O2 rare-earth silicate compounds are of great interest for their oxide ion conductivity at moderate temperatures. Crystallographic space group and structural parameters of La/Nd9.33(SiO4)6O2 were investigated based on single-crystal X-ray diffraction data at room temperature for La9.33(SiO4)6O2 and at various temperatures from 150 to 900 K for Nd9.33(SiO4)6O2. Based on the most accurate diffraction data to date, these compounds have an apatite prototype structure (space group P63/m) with no symmetry lowering, site splitting nor interstitial oxide ion in the structure. Most striking feature of the structure is large anisotropy in thermal motions of the oxide ion at the anion channel site. Even at room temperature, the mean-square displacement of the channel oxide ion in La9.33(SiO4)6O2 is 16 times larger in [001] than those normal to the direction. Not striking but important point is that there is no sign of interstitial oxide ion which had been proposed as a charge carrier in La9.33(SiO4)6O2 and related compounds. These findings imply straight migration of oxide ion inside the channel as a primary mechanism of oxide-ion conductivity in these compounds. Size and shape of the anion channel might be a key to achieve high oxide-ion conductivity in these compounds.

学術雑誌論文

Version of Record

0369-4585

1884-5576

AN00188364