Holes That Can Be Used for Ionic Crystal Structures
Two tetrahedral holes and 1 octahedral hole per sphere in the array
These holes occur at the B and C positions in the closest-packed array.
Cubic closest-packed has 4 spheres, 8 tetrahedral holes, and 4 octahedral holes per unit cell
Octahedral holes are larger than tetrahedral holes
Good fit in holes maximizes coulombic attractions with efficient use of space