Standard crystallographic and superspace descriptions of the crystal structure of Ca5Nb4TiO17

Abstract

The crystal structure at room temperature of the perovskite-related Ca₅Nb₄TiO₁₇ has been determined by means of single-crystal X-ray diffraction. The crystal structure was derived using conventional 3-dimensional crystallography approach and superspace approach. Using standard crystallography, the crystal structure is described as consisting of slabs of corner-sharing octahedra which are five layers wide separated by additional planes of oxygen atoms. In the superspace approach, the slabs are interpreted as sequential stacking of layers of atomic domains, and the actual crystal structure is obtained as modulation of the basic layered structure. The efficiency of the superspace approach is demonstrated by structure refinements in (3+1)-dimensional space and by comparing these results with the 3-dimensional refinements. Superspace refinements have produced structural features that are identical to what have been obtained from structure refinements in 3-dimensional space.