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Figure 1
Three-dimensional views of (a) the R, (b) the S and (c) the T sub-blocks and projections of (d) the M and (e) the Y blocks. Fe3+ octahedra are represented in dark blue, Fe3+ bipyramids in grey, Fe3+ tetrahedra in light blue and mixed Fe3+/Zn2+ tetrahedra in orange. The h and c notations indicate hexagonal and cubic packing of the oxygen layers, respectively. Subscript letters correspond to the sub-block types these oxygen layers belong to. The anion-layer stacking and c dimension of the M and Y unit blocks are also highlighted.

IUCrJ
Volume 5| Part 6| November 2018| Pages 681-698
ISSN: 2052-2525
https://doi.org/10.1107/S2052252518011351