Crystal Lab › Prototype structures › Orthorhombic
α-NiI₄ I₄Nb
Orthorhombic · space group Cmc21 (No. 36) · Pearson oC40
Symmetry elements and Wyckoff positions (interactive)
α-NiI₄ in Cmc21
SettingUnit cell
- Lattice constants
- a = 7.670 Å, b = 13.230 Å, c = 13.930 Å; α = 90.00°, β = 90.00°, γ = 90.00°
- Cell volume
- 1413.5 ų
- Atoms in the conventional cell
- 40 (I 32, Nb 8)
- Formula units Z
- 8
- Pearson symbol
- oC40 — orthorhombic, base-centred lattice, 40 atoms per conventional cell
- Symmetry operations
- 8 per cell
Crystallographic sites
| Site | Element | Wyckoff | Multiplicity | x | y | z |
|---|---|---|---|---|---|---|
| I1 | I | 4a | 4 | 0.0000 | 0.2608 | 0.0333 |
| I2 | I | 4a | 4 | 0.0000 | 0.7436 | 0.0440 |
| I3 | I | 4a | 4 | 0.0000 | 0.9887 | 0.2096 |
| I4 | I | 4a | 4 | 0.0000 | 0.5066 | 0.1999 |
| I5 | I | 8b | 8 | 0.2467 | 0.0061 | 0.9677 |
| I6 | I | 8b | 8 | 0.2458 | 0.2334 | 0.2842 |
| Nb7 | Nb | 8b | 8 | 0.2171 | 0.1256 | 0.1207 |
The multiplicity and the Wyckoff letter say how many copies of the site the group makes in one cell and on which kind of symmetry element the site sits; the 40 atoms drawn above are these sites multiplied by all 8 operations. Press Wyckoff under Colour to see the sites, and tick a symmetry element on the left to see which atoms lie on it.
How to read the label
A4B_oC40_36_4a2b_b-001: the stoichiometry comes first (A, B, C… are the elements in alphabetical order of their site labels), then the Pearson symbol oC40, then the space-group number 36, then the Wyckoff letters occupied by each element in turn (I: 4a; I: 4a; I: 4a; I: 4a; I: 8b; I: 8b; Nb: 8b). Two structures with the same label are the same arrangement with different cell parameters or coordinates.
Note: α-NiI₄.
Source
Coordinates and cell from the AFLOW Encyclopedia of Crystallographic Prototypes, entry A4B_oC40_36_4a2b_b-001 (M. J. Mehl et al., Comput. Mater. Sci. 136, S1 (2017); D. Hicks et al., ibid. 161, S1 (2019) and 199, 110450 (2021); S. Eckert et al., ibid. 240, 112988 (2024)). Symmetry elements, Wyckoff assignment and the diagram are computed on this page from the group operations.
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