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Figure 1
Morphological features of the hollow microspheroids in the final stages. CXDI of vaterite microspheroids obtained from the 8 mM 1 g l−1 24 h synthesis. (a) and (b) CXDI 2D views through the center of the microspheroid. The yellow arrows indicate the poles. (c) and (d) 3D views showing the wall thickness of the shell, thinner at the poles, thicker at the equator. (e) Selected vaterite nanocrystals extracted from the shell of the microspheroid. Note that the crystallographic structure of vaterite is still controversial (Christy, 2017BB13). Here, the vectors a, b and c refer here to the crystallographic axes of vaterite according to Kamhi's model [P63/mmc space group (Kamhi, 1963BB28)]. The dotted rectangular line represents the inner part of the shell. (f) 3D view of the microspheroid where around 100 vaterite crystals were segmented. Those shown in (e) are marked with an arrow. They all display a truncated hexagonal based bipyramidal shape, many of them having their c axis oriented along the meridians. (g) and (h) 3D views showing half of the microspheroid. (i) Spheroidal 2D views of the shell showing the juxtaposition of two layers made of (bottom) large crystals on the outer part and (top) small crystals close to 30 nm on the inner part of the shell. In the inset, a TEM image of nanoparticles of the poles belonging to the inner part of the shell is shown. Scale bar = 1 µm except in the inset of (g) for which the scale bar is 50 nm. Note here that S:Ca = 0.59.

IUCrJ
Volume 9| Part 5| September 2022| Pages 580-593
ISSN: 2052-2525
https://doi.org/10.1107/S2052252522006108