Interstitial Void
An empty space between the packed spheres of a crystal lattice, capable of hosting a smaller ion or atom.
Formula / equation
r_void / r_sphere = 0.225 or 0.414
Unit
Dimensionless
In depth
Close packing generates two void types: tetrahedral voids surrounded by four spheres, occurring twice per sphere, and larger octahedral voids surrounded by six, occurring once per sphere. Which voids a cation occupies is determined by its radius ratio and fixes the overall structure type.
Examples in the real world
Zn²⁺ fills half the tetrahedral voids in zinc blende; carbon atoms occupy octahedral voids in steel.