Temperature dependence of structural parameters in oxide-ion-conducting Nd9.33(SiO4)6O2:: single crystal X-ray studies from 295 to 900 K

Crystallographic space group, structural parameters and their thermal changes in oxide-ion-conducting Nd-9.33(SiO4)(6)O-2 were investigated using high-temperature single-crystal X-ray diffraction experiments in the temperature range of 295 less than or equal to T less than or equal to 900 K. The title compound has the apatite structure (space group P6(3)/m), and no notable structural change occurred over the temperature range examined. Observed anisotropy in thermal motions of oxide ions which belong to SiO4 tetrahedron indicated high rigidity of the tetrahedron in the structure, indicating that they form sp3 hybrid orbitals and the ligand oxygens do not take part in oxide-ion conductivity. Virtually full occupation of the 6h Nd site and highly anisotropic displacements of oxide ion inside the hexagonal channel were maintained over the temperature range examined. This result confirms that oxide-ion transport inside the hexagonal channel is the dominant process of conduction in the title compound. (C) 2004 Elsevier Inc. All rights reserved.