# In bcc lattice why XRD 100 peak is not observed ?

1. Sep 19, 2016

### hkazmi25

Can someone tell me that in bcc lattice why xrd 100 peak does not appear???

2. Sep 21, 2016

### DrDu

The planes passing through the base atoms are a/2 away from the planes passing through the planes defined by the atoms on the edge of the cell. And is only a shifted copy of the latter. Hence it will reflect x rays exactly as does one of the edge planes and you get destructive interference.

3. Sep 30, 2016

### Armani

If you calculate the structure factor of the BCC lattice using:
$$S(hkl)=f{1+exp[-i\pi(h+k+l)]}$$, where f= form factor. The value o f S is zero when the exponential has the value -1, which is whenever the argument is: -i*pi* (odd integer).
So we have:
S=0 when h+k+l= odd integer
S=2f when h+k+l= even integer
So therefore the diffraction pattern does not contain these planes: (100), (300), (111), (221)
But it occurs for fx.: (200), (110), (222)

The (100) reflection occurs when reflections from the planes that bound the cubic cell differ in phase by 2*pi. In BCC there is an intervening plane of atoms, which is equal to in scattering power to the other planes. Situated between them it gives a reflection retarded in phase by pi w.r.t. the first plane, thereby cancelling the contribution from that plane. So the cancellation occurs since the planes are identical in composition.