Question

How solids hcp and CCP structure differenciatd from each other?

Answer 1

CCP have 74% packing efficiency. It consists of 8 atoms; one at each corner of the unit cell and 6 atoms; one at each face of the unit cell. All the sides of the unit cell must be equal and all axial angles must be equal to 90 degress in case of a ccp lattice

HC lattice however is different from ccp/fcc. In a hcp lattice, 2 sides of the lattice must be equal while the third can be different; ie; a=b (not)=c. Also the axial angles of a hcp lattice must be 90 degrees, 90 degrees and 120 degrees resp.