X-Ray Diffraction (XRD)

X- ray diffraction is a common technique that determine a sample’s composition or crystalline structure. For large crystals such it can be used to determine the structure of atoms within the sample. If crystal size is too small, it can determine composition, crystallinity, and phase purity.

• In this technique x-ray beams sends through the sample (x-rays have similar wavelength to spacing between atoms in the mineral) and the angle of diffraction will be affected by the spacing of the atoms in the molecule. (larger wavelength may not be altered through the spacing between the atoms.
• The x-ray then passes through the sample “bouncing” off of the atoms in the structure and changing the direction of the beam at some different angle, theta from the original beam. This is the angle of diffraction.
• The angle of diffraction can be used to determine the difference between atomic planes using Bragg’s law “sinΘ=nλ/2d” where lambda is wavelength, theta is the angle of diffraction and ‘d’ is the distance between atomic planes.
• These diffracted beam an give a constructive and destructive interference. Constructive interference is when the x-ray beam that are whole number integers adds and give a new beam with higher amplitude. The greater amplitude of the wave translates into a greater signal for this specific angle of diffraction.

Visual learning : https://www.doitpoms.ac.uk/tlplib/xray-diffraction/bragg.php

Data interpretation :-

The results of x-ray diffraction plots the intensity of the signal for various angles of diffraction at their respective two theta positions that corresponds to a certain spacing between the crystals or atoms in the sample. The intensity of the peaks is related to the amount of molecules in that phase or with that spacing. The greater the intensity of the peak, the greater the amount of crystals or molecules with that distinct spacing.

The width of the peaks is inversely proportional to the crystal size. A thinner peak corresponds to a bigger crystal. A broader peak means that there may be a smaller crystal, defects in the crystalline structure, or that the sample might be amorphous in nature, a solid lacking perfect crystallinity.

• For smaller samples, the patterns determined using XRD analysis can be used to determine a sample’s composition. There is a large database of elements, compounds, and minerals that contain the diffraction patterns for elements, compounds and minerals. The pattern for an unknown compound can be compared to the literature and experimentally determined values to verify the identity of an element, matching both the location, width and relative heights of the diffraction patterns.

REFERENCES :-

• https://chem.libretexts.org/Courses/Franklin_and_Marshall_College/Introduction_to_Materials_Characterization__CHM_412_Collaborative_Text/Diffraction_Techniques/X-ray_diffraction_(XRD)_basics_and_application
• https://www.researchgate.net/publication/324059631_Heavy_Metals_Distribution_and_Their_Correlation_with_Clay_Size_Fraction_in_Stream_Sediments_of_the_Lesser_Zab_River_at_Northeastern_Iraq?_tp=eyJjb250ZXh0Ijp7ImZpcnN0UGFnZSI6Il9kaXJlY3QiLCJwYWdlIjoiX2RpcmVjdCJ9fQ
• https://serc.carleton.edu/msu_nanotech/methods/BraggsLaw.html