Question

In a face-centred cubic close packed structure, octahedral sites are present at:

• A. edge-centre
• B. face-centre
• C. body-centre
• D. corners

Answer 1

Answer: (A), (C)

The correct options are
A body-centre
C edge-centre

The body centre of the cube in FCC is surrounded by six atoms on face centres. If these face centres are joined, an octahedron is generated. Thus, this unit cell has one octahedral void at the body centre of the cube.

Besides the body centre, there is one octahedral void at the centre of each of the 12 edges.

Hence, option A and C are correct.