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A tetragonal $A{B}_2$ crystal structure with sixfold cation and threefold anion coordination numbers. A common fractional-coordinate description has A at $(0,0,0)$ and $(1/2,1/2,1/2)$, and B at $\pm (u,u,0)$ and $\pm (1/2+u,1/2-u,1/2)$, interpreted modulo integer lattice translations. The cation coordination is a distorted octahedron and the anion coordination is a planar triangle. Titanium dioxide in its rutile polymorph is an example.

Titanium is the chemical element with atomic number 22 and symbol $\mathrm{Ti}$. It is a transition metal. A protective oxide film gives the metal good corrosion resistance. Its combination of comparatively low density and useful alloy strength explains engineering applications, while titanium dioxide is a chemically distinct oxide used in pigments and other materials.^[ref]

Titanium dioxide is $\mathrm{Ti}{\mathrm{O}}_2$, occurring in crystal forms including rutile and anatase. Its strong interaction with visible light explains its use as a white pigment.

Its semiconductor behavior also supports photocatalytic processes under suitable illumination. Crystal phase, particle size, surface chemistry, and defects can change that behavior even when the nominal formula remains the same.