Calculation of average crystallite size:

Consider a crystal having thickness t as shown in Figure 4.02 measured in a direction perpendicular (⊥) to a set of reflecting planes.

Let there be (m +1) planes in this set.

The Bragg angle θ as a variable and call θ_B satisfies exactly the Bragg law, resulting in the diffraction condition

  λ = 2dsinθ_B

Intensity of the beams diffracted at and above 2θ₁, and at and below 2θ₂ is zero.

Figure 4.02: Schematic of crystal planes to calculate crystal size [1].

However, the intensity of the diffracted beam at angles close to 2θ_B , but not greater than 2θ₁ or less than 2θ₂ is not zero, but has an intermediate value between zero and one (see Figure 4.01).