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How Peak Shift in XRD graph shows Stresses/Strains in the material

Effects of Stress/strain on XRD peaks. How does XRD peak shift reveal about the stresses/strains in the materials? Let explain this! There are two types of stresses that can be identified in a material, i.e., microstresses & macrostresses. Microstresses (microstrains) vary from one grain to another on a microscopic scale. On the other side, the stress that exists uniformly over large distances is called macrostress (or macrostrains). Let’s suppose the original lattice spacing is do. If there is uniform tensile strain in the grain at right angles to the reflecting planes, the interatomic spacing becomes larger than do and the corresponding XRD peak (diffraction line) shifts towards the lower 2θ . This is also true from Bragg’s law (λ = 2dsinθ). Now if there is non-uniform strain, where the grain looks bent so on the top of the grain the interplanar spacing exceeds the do while on the bottom, it is less than do and in somewhere in between, it is equal to do. This clearly shows that the grain is composed of small regions of varying interplanar spacing, which causes the various sharp diffraction lines as shown by the dotted curves. The sum of these sharp lines, each slightly displaced from the other, is the broadened diffraction. This line shift in the XRD peak (diffraction line) is the basis of the x-ray diffraction method for the measurement of macrostress in the materials.