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Figure 2
Schematic representation of three manifestations of a modulated structure with lost translational symmetry along the a axis. All three drawings in (a) are derived from the periodic structure shown in Fig. 1[link] by shifting or rotating the molecules. The atomic modulation functions suitable for the description of the modulated atomic positions are shown as an overlay: in the top drawing the molecules are shifted up and down parallel to c in a continuous harmonic (sinusoidal) way (red curve); in the middle drawing the molecules are rotated around an axis parallel to a, the rotation angle can be described using a sawtooth function (blue) with a discontinuity between molecules 8 and 1; in the bottom drawing the molecule adopts two different orientations which can be described by a step-like crenel function (green). Note that the modulation proceeds only along a, the c direction is not affected. (b) In the associated schematic diffraction pattern additional reflections (grey circles) appear along a*. The number of satellite reflections and their intensity distribution depend on the strength and nature of the modulation. For simplicity, only one diffraction scheme was drawn.

Journal logoSTRUCTURAL SCIENCE
CRYSTAL ENGINEERING
MATERIALS
ISSN: 2052-5206
Volume 65| Part 3| May 2009| Pages 249-268
doi:10.1107/S0108768109015614
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