C5, anatase

Structural type	C5
Common name	anatase
Definition	fcc lattice of large ions (X) with the smaller ones (A) occupying every 2nd octahedral void along z axis, the X sublattice is deformed cardinally
Prototype	TiO₂
Pearson symbol	tI2
Space group	141 I4₁/amd D_4h¹⁹
Chemical formula	AX2
Bonding	ionic-covalent
Atomic positions	`A (4a) 0 3/4 1/8 (marked by C) X (8e) 0 1/4 zeta (marked by S) V (4b) 0 3/4 5/8 (unoccupied void marked by N)`
Coordination	AX – 4+2 (6o), XA – 2+1 (coplanar)
Sublattices	A – hdia
PDB files	C5 (ideal ionic), C5 (as fcc with unoccupied voids)
Parameters	c/a≈2.8, ζ≈.06
Special values	fcc with voids for c/a=2 and ζ=1/8, ideal ionic, i.e. max M≈1.60 for c/a≈2.8 and ζ=a^2/c^2/2 (all AX distances are equal)
Substances	TiO₂ (c/a=2.51, ζ=.08)