Mechanical Engineering - Engineering Materials - Discussion

In a unit cell, not some atoms shared with adjacent unit cell/s, then shared atom can't be counted as complete 1 atom.

Like in bcc, atom at the center of the cube completely owned by the unit cell hence its share 1, but atom at the corners of the cube is shared by 7 more adjacent unit cell then its share will be 1/8 and there are 8 such corners, so 1/8 x 8 = 1, hence in bcc has 1 (from centre + 1 (corners) = 2 atoms.

Similarly, HCP has 12 atoms per unit cell.

The hexagonal closest packed (hcp) has a coordination number of 12 and contains 6 atoms per unit cell.

The face-centred cubic (fcc) has a coordination number of 12 and contains 4 atoms per unit cell.

The body-centred cubic (bcc) has a coordination number of 8 and contains 2 atoms per unit cell.

The hexagonal closest packed(hcp) has a coordination number of 12 and contains 2 atoms per unit cell.

[12 c (1/6)] + [2 * 650 (1/2)] + [3 (interior)] = 6.

HCP is having C.N:12 and 6 atoms per unit cell.

6 atoms per unit cell is correct.

Coordination no.of HCP = 12.

12 + 2 + 3 = 17 atoms.

12 atoms is correct.

17 atom is correct.