Applied Physics

APPENDIX A

Hexagonal Close Pack (HCP) Structure

Hexagonal close packed (HCP) crystal structure has two layers of atoms. One layer of atoms is present at the bottom face of the unit cell, and it is referred to as the ‘A’ layer of atoms. Above the bottom layer, we have a second layer of atoms. This is the middle layer in the unit cell and is referred to as the ‘B’ layer of atoms. The atoms in the ‘B’ layer are seated in the voids between any three atoms of the bottom layer. Above the second layer, we have a third layer of atoms. This is the top layer of atoms in the unit cell and it is a repetition of the bottom layer. Hence, the stacking of a hexagonal close packed crystal structure consists of a series of ABABAB…layers.

The unit cell structure ...