For diffraction from a plane where the sum of *h+k+l * is odd, the second term is -1, so
**F**_{hkl}_{odd} = *f*(1-1) = 0
If *h+k+l* is even, the second term is +1,
so
**F**_{hkl}_{even} = *f*(1+1) = 2*f*
Thus, diffractions from bcc planes where *h+k+l*
is odd are of zero intensity. They are forbidden reflections. These reflections are
usually omitted from the reciprocal lattice.
Click on the animation
opposite to illustrate the forbidden reflections from the bcc unit cell. |