A10 and Ai, simple rhombohedral

Structural typeA10, Ai
Common namesimple rhombohedral
DefinitionA10 – fcc-sc rhombohedral deformation,
Ai – sc-bcc rhombohedral deformation
PrototypeA10 – α-Hg, Ai – β-Po
Pearson symbolhR1
Space group166 R-3m D3d5
Chemical formulaA
Bondingmetallic-covalent
Atomic positions A (3a)  0  0  0
Coordination
2l+6apc/a<sqrt(3/8)≈0.61out of range
6ap+2lc/a<sqrt(3/5)≈0.77
6ap+6apc/a<sqrt(3/2)≈1.22Ai
6ap+6lc/a<sqrt(6)≈2.45A10
6l+6apc/a>sqrt(6)out of range
PDB filesAi (at c/a=sqrt(3/5))
ParametersA10 – 1.22<c/a<2.45,
Ai – 0.77<c/a<1.22
Superstructuresfcc for c/a=sqrt(6)≈2.45 (α=π/3),
sc for c/a=sqrt(3/2)≈1.22 (α=π/2),
bcc for c/a=sqrt(3/8)≈0.61 (α=arccos(-1/3))
SubstancesA10 – α-Hg (c/a=1.94), Ai – β-Po (c/a=0.97)