Strain is defined as a relative change in shape or size of an object due to externally-applied forces, given by,

            --------------------------------------------- [1302]

where,
          ΔL - The change in shape or size,
          L - The shape or size.

Figure 1302 shows the effect of strain on the shift and shape of diffraction peak. For uniform strain, the diffraction peak moves, but its shape does not change. For instance, the diffraction peak shifts to lower angles when the lattice spacing is larger as shown in Figure 1302 (b). Figure 1302 (d) shows that the crystallographic plane has a distribution of d-spacings rather than a single d-spacing. In this case, a broader diffraction peak is observed. Such lattice distortions can be introduced by:
          i) Mechanical force,
          ii) Surface and interface tension,
          iii) Morphology of crystal shape,
          iv) Interstitial impurities.

Table 1302 lists the most typical correlations between diffraction peak aberrations, including broadening, shifts or asymmetries, and the different elements of microstructures.