Ionic Radii:
     Ti⁴⁺, 64 pm
     O^2-, 140 pm
Radius Ratio: = 64/140 = 0.46

The radius ratio is such that we expect the titanium ions to occupy octahedral holes in an array of oxide ions.

The stoichiometry (one Ti⁴⁺ ion per two O^2- ions) requires that half of the octahedral holes be occupied. In fact, the TiO₂ structure consists of a approximately close packed array of
O^2- ions with Ti⁴⁺ ions filling half of the octahedral holes.

Click on the image at the right to view the TiO₂ structure. The underlined links above go to definitions.