Question

What is the effective number of FCC? Definition for coordination number?

Answer 1

The hexagonal closest packed (hcp) has a coordination number of 12 and contains 6 atoms per unit cell. The face-centered cubic (fcc) has a coordination number of 12 and contains 4 atoms per unit cell. The body-centered cubic (bcc) has a coordination number of 8 and contains 2 atoms per unit cell
The coordination number of an atom in molecule is the number of atoms bonded to the atom. In chemistry and crystallography, the coordination number describes the number of neighbor atoms with respect to a central atom. The term was originally defined in 1893 by Alfred Werner. The value of the coordination number is determined differently for crystals and molecules. The coordination number can vary from as low as 2 to as high as 16. The value depends on the relative sizes of the central atom and ligands and by the charge from the electronic configuration of an ion.