  Question

# What is the difference between ccp and hcp?

Solution

## 1. Stacking Sequence of Layers -HCP layers cycle between two equivalent shifted layers in an ABABAB sequence -CCP layers cycle among three different layers in an ABCABC sequence 2. Shape of the Unit Cells - HCP structures have hexagonal unit cells characterized by a diamond shaped or hexagonal base with sides of equal length -CCP structures have cubic unit cells 3. Volume of Unit Cells -HCP unit cells have a volume which can be calculated with the equation V=24*sqrt(2)*r^3 in which r = the atomic radius -CCP unit cells have a volume which can be calculated with the equation V=8*sqrt(8)*r^3 in which r = the atomic radius 4. Number of Atoms per Unit Cell -HCP unit cells contain 6 atoms -CCP unit cells contain 4 atoms   In hcp(hexagonal closed packing), the third layer of spheres is same as the first layer and covers tetrahedral voids.Therefore, the stacking may be represented as a-b-a-b-a-b type. Whereas, in ccp(cubic closed packing), the fourth layer of spheres is same as the first layer and covers octahedral voids.Therefore, the stacking may be represented as a-b-c-a-b-c type.  Suggest corrections   