Question

How to determine whether its crystal structure is fcc bcc or simple cubic?

Answer 1

FCC = Face centered cubic unit cell

BCC = Body centered cubic unit cell

Generally a FCC unit cell contains total 4 atoms that are present at corner and at the face of a cube

Contribution at corner of cube :

                                                  = $\frac{1}{8}$ × 8 = 1

Contribution at face of cube :

                                                  = $\frac{1}{2}$ × 6 = 3

So total atoms in FCC = 1+3 = 4

Now in case of BCC, it contained total 2 atoms 1 at corner of cube and 1 at the center of cube

Contribution at corner :

                                        = $\frac{1}{8}$ × 8 = 1

Contribution at center = 1

So, total atoms in BCC = 1+1 = 2

Simple cubic unit cell has only 1 atom present at corner of cube

Contribution at corner of cube :

                                                  = $\frac{1}{8}$ × 8 = 1

Thus the ratio of atoms in FCC : BCC : SC = 4:2:1

It is the main difference among all above unit cells.