What is the Difference Between HCP and CCP?

The main difference between HCP (Hexagonal Closest Packing) and CCP (Cubic Closest Packing) lies in the arrangement of atoms or spheres in the crystal structure. Both HCP and CCP are close-packed structures, meaning they have around 74% of their volume occupied by spheres or atoms. Here are the key differences between HCP and CCP:

1. Unit Cell: A unit cell of HCP has 6 members, while a unit cell of CCP has 8 members.
2. Structure: In HCP crystal systems, the third layer of spheres has the same arrangement of spheres as in the first layer, forming a hexagonal structure. In CCP crystal systems, the fourth layer of spheres is the same as the first layer, forming a cubic structure.
3. Repeating Structure: The repeating structure of HCP has 2 layers of spheres, while the repeating structure of CCP has 3 layers of spheres.
4. Voids: In HCP, the second layer of spheres covers the tetrahedral voids of the first layer and the third layer. In CCP, the second layer of spheres is placed on half of the depressions of the first layer, and the third layer is stacked in the depressions of the second layer, covering octahedral voids.

In summary, HCP and CCP are both close-packed structures, but they differ in their unit cell, structure, repeating structure, and the types of voids they cover.

Comparative Table: HCP vs CCP

Here is a table summarizing the differences between HCP (Hexagonal Closest Packed) and CCP (Cubic Closest Packed) crystal structures: