hcp and ccp_chem_bsc

first lets discuss the similarities and dissimilarities between hcp and ccp respectively


similarities:

1. in both the packing, each sphere(atom) is in direct contact with six other sphere in its own layer, thus in this structure each sphere is in direct contact with 6+3+3=12 spheres. Hence CN of each atom inj these structure is equal to 12
2. in both the structures, 74% of the available space are occoupied by spheres. the remaining 26% of the space remain vacant, i.e. 26% of the space has void or holes.

dissimilarities:

1. in hcp structure the different layer of atoms are packed in AB AB AB....patteren. Layer A has 7 sphere and layer B has 3 sphere as a result AB AB patteren is found. in ccp structure different layer of atom are packed in ABC ABC ABC.... pattern. layer A has one atom and both the layer B and C have six atom each.
2. in hcp structure, therid layer of atom covers the tetrahedral voids of the second layer. In ccp structure, the theird layer of atom covers octahedral voids of the second layer
3. In hcp structure, theird layer is similar to the first layer. Hence this structure has AB AB AB..... arragement. In ccp structure, every fourth layer is similar to the first layer and this structure has ABC ABC ABC.....arragement.