Q. Explain crystal lattice of BCC, FCC and HCP.

Ans. (a) BCC (Body centered cubic): Body centered cubic structure, the unit cell, we observe in addition to the atoms at eight corners, there is also an atom at the body centre is this cubic, hence named body centered cubic.

Example: sodium, chromium, lithium, potassium.

(b) FCC (Face centered cubic structure): This ease the stacking sequence is thus ABC ABCA. This structure has cubic symmetry. The successive layers being (111) planes.

We observe that in addition of the atoms at the eight corners there are also atoms at the six face centers.

Example: Aluminium, copper, gold, lead, silver etc.

(c) HCP (Hexagonal closed packed lattice: In hexagonal closed packed lattice the base planes are hexagonal and the edges are vertical. The vertices of the parallel sides are joined by the edges.