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Figure 3
The incommensurately modulated structure Ba IVb. Both Bafr (grey) and Bach (blue) atoms are subject to positional modulation. The structure is periodic along the a axis and aperiodic in the bc planes. (a) A portion of the structure given in the ab projection, illustrating the weak modulation of all the atoms in the a and b directions. (b) and (c) The bc projection of a layer of thickness [1\over 2]a at (b) 19.6 (1) and (c) 16.5 (1) GPa. The projection shows that the main structure modulation concerns the displacements of Bach atoms along the c axis, i.e. along the channels formed by Bafr atoms. The displacements induce variation in the Bach—Bach distances. The orange sticks link atoms distant by 2.90 to 3.8 Å, showing a wave of dense and sparse arrangements of Bach atoms. (d) and (e) The alternating distribution of the layers shown along the a axis at (d) 19.6 and (e) 16.5 GPa. Bafr atoms have been omitted to highlight the chessboard-like distribution of dense and sparse regions.

IUCrJ
Volume 4| Part 2| March 2017| Pages 152-157
ISSN: 2052-2525
https://doi.org/10.1107/S2052252517000264