Packing efficiency and Void

Packing efficiency  

The total percentage of space occupy by atom molecule or ion in unit cell that is called packing efficiency

Void or space or holes

              Empty or vacant space present between spheres of a unit cell , is called void. When particles are closed packed resulting in either CPP or HCP structure, two types of void generated.

Tetrahedral void :- Tetrahedral voids are holes or voids surrounded by four spheres present at the corner of a tetrahedron. Co-ordination number of a tetrahedral void is 4.

Octahedral void:- Octahedral void are holes or voids surrounded by six spheres located on a regular tetrahedron. Co-ordination number of a tetrahedral void is 6.