Grimaldiite (α-CrOOH)

Unit cell

Lattice constants

a = 2.985 Å, b = 2.985 Å, c = 13.480 Å; α = 90.00°, β = 90.00°, γ = 120.00°

Cell volume

104.0 ų

Atoms in the conventional cell

12 (Cr 3, H 3, O 6)

Formula units Z

3

Pearson symbol

hR4 — hexagonal / trigonal, rhombohedral lattice, 4 atoms per conventional cell

Symmetry operations

18 per cell

Crystallographic sites

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 12 atoms drawn above are these sites multiplied by all 18 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

ABC2_hR4_160_a_a_2a-002: the stoichiometry comes first (A, B, C… are the elements in alphabetical order of their site labels), then the Pearson symbol hR4, then the space-group number 160, then the Wyckoff letters occupied by each element in turn (Cr: 3a; H: 3a; O: 3a; O: 3a). Two structures with the same label are the same arrangement with different cell parameters or coordinates.

Other compounds with this structure

NaNiO₂ <!--beginning with an

Note: Grimaldiite, α-CrOOH.

Source

Coordinates and cell from the AFLOW Encyclopedia of Crystallographic Prototypes, entry ABC2_hR4_160_a_a_2a-002 (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.