Slip occurs the most densely packed crystallographic planes and

N	M	3.14 Linear and Planar Atomic Densities		●	S-5
		N	M

As a basis for our computation let us use the line length within the unit cell, Ll, which in this case is the lattice parameter a—the distance between the centers of atoms M and N. In terms of the atomic radius R,

Calculate the planar density of the (110) plane for FCC.

S O L U T I O N

Therefore,

Ap � (AC)(AD)

Historically much of our understanding regarding the atomic and molecular arrange-ments in solids has resulted from x-ray diffraction investigations; furthermore, x-rays are still very important in developing new materials. A brief overview of the diffrac-tion phenomenon and how, using x-rays, atomic interplanar distances and crystal structures are deduced will now be given.

THE DIFFRACTION PHENOMENON

X-rays are a form of electromagnetic radiation that have high energies and short wavelengths—wavelengths on the order of the atomic spacings for solids. When a