Crystal structure of Ca₅Nb₅O₁₇

Titelangaben

Guevarra, Jonathan ; van Smaalen, Sander ; Rotiroti, Nicola ; Paulmann, Carsten ; Lichtenberg, Frank:
Crystal structure of Ca₅Nb₅O₁₇.
In: Journal of Solid State Chemistry. Bd. 178 (2005) Heft 9 . - S. 2934-2941.
ISSN 0022-4596
DOI: https://doi.org/10.1016/j.jssc.2005.07.007

Volltext

Link zum Volltext (externe URL):

Abstract

The crystal structure of Ca 5 Nb 5 O 17 , an n = 5 member of the homologous series A n B n O 3 n + 2 , at room temperature has been determined by single-crystal X-ray diffraction using synchrotron radiation with a {CCD} area detector. The structure is monoclinic with spacegroup P 2 1 / c (b unique) and lattice parameters a = 7.7494 ( 3 ) Å, b = 5.4928 ( 1 ) Å, c = 32.241 ( 1 ) Å, and β = 96.809 ( 4 ) ∘ . It consists of perovskite-like slabs of corner-sharing NbO 6 octahedra separated by an interslab region, where the octahedra on opposite sides of the gap do not share oxygen atoms resulting in an extra layer of oxygen atoms with respect to the ideal perovskite structure. The slabs are five octahedra wide. Ca atoms within the slabs occupy 12-fold coordinated sites whereas those at the borders show irregular coordination environments. The distortion of the octahedra increases from the center to the borders of the slabs. The computed valences for the Nb ions are very close to 5 at the borders while smaller values were obtained for sites in the middle of the slabs which suggests that the electrical conduction takes place predominantly in the middle of the slabs.