X-Ray Diffraction: Diagram, Working and Uses

X-ray diffraction utilizes the dual nature of X-rays to obtain the information about the structure of crystalline materials.

• The technique is primarily used to identify and characterize compounds based on their diffraction patterns.
• When monochromatic X-rays strike a target material, they are mainly scattered by atoms within that material.
• The scattered X-rays, in materials with regular structure (i.e. crystalline), undergo constructive and destructive interference. This is the process of diffraction. 
• The directions of diffractions depend on the shape and size of the unit cell of the material.
• Many different types of applications have been performed using X-ray optics, including thin film analysis, crystalline phase monitoring, texture evaluation and stress and strain measurement.

Key Terms: X-ray diffraction, X-ray, X-ray crystallography, interference, diffraction, wavelength, Bragg’s law, constructive interference

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X-Rays

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X-rays or X-radiation are a form of electromagnetic radiation of extremely short wavelength and high frequency.

• Its wavelength ranges from about 10^-8 to 10^-12 m.
• Its frequency ranges from about 10¹⁶ to 10²⁰ Hz.
• Accelerating charged particles are the common source of X-rays.
• It is detected by photographic film, Geiger tubes and ionization chambers.
• X-rays are used as a diagnostic tool in medicine and a treatment for certain forms of cancer.
• In engineering it is used for detecting cracks, faults, holes, and flaws.
• It is used for detecting pearls in oysters, defects in rubber tyres, and golds.

The Electro Magnetic Spectrum

The video below explains this:

Bragg’s Law Detailed Video Explanation:

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X-Ray Diffraction(XRD)

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X-ray diffraction is based on constructive interference of monochromatic X-rays. A crystal's atomic planes cause an incident X-ray beam to interfere with itself as it leaves the crystal. The phenomenon is called X-ray diffraction.

• The technique of X-ray diffraction, or XRD, is used to examine the molecular or atomic structure of materials. 
• It is a non-destructive technique.
• As the material being analyzed is typically finely ground to a uniform state, this technique is often called X-ray powder diffraction. 
• Diffraction is the process of bending of light when it passes around the edge of the object. 
• Diffraction of radiation depends on the size of the wavelength of the radiation compared to the size of the obstacle or aperture it encounters.
• The difference between X-ray crystallography and X-ray diffraction is that x-ray crystallography involves the exposure of single crystals to x rays, whereas x-ray diffraction involves the measurement of a wide range of material forms.

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Working of X-Ray Diffraction

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In X-rays diffraction technique, a beam of X-rays is sent through the sample.

• Beams of X-rays are chosen because their wavelengths are similar to that of the spacing between the atoms of the sample.
• The X-rays then pass through the sample, strike with the atoms within the structure and bounce with some different angle. This is the angle of diffraction(\(\theta\)).
• Some of these diffracted beams cancel out each other but if the beam has similar wavelengths, then constructive interference occurs.
• A constructive interference occurs when two x-ray beams with the same wavelength add together to produce a new beam with a higher amplitude.

Below figure shows XRD diffraction diagram

X- Day Diffraction

The angle of diffraction can be used to determine the distance between the atomic planes of the sample by using Bragg’s law. i.e.

nλ = 2d sin\(\theta\)

Where,

• d = distance between atomic planes
• \(\theta\) = angle of diffraction
• λ = wavelength of the beam
• n = integer 

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Uses of X-Ray Diffraction

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The main use of X-ray diffraction is the identification of unknown crystalline materials. The use of XRD is essential in:

• Geology
• Engineering
• Biology
• Material science
• Environmental science
• Battery Research
• Thin-film coatings
• Electronics
• Pharmaceuticals

We can apply X-ray diffraction for defining thin film samples, by using the following techniques:

• Measurement of stresses and strains caused by lattice mismatches between films and substrates
• Dislocation density and film quality are determined by analyzing rocking curves
• Measuring superlattices in epitaxial structures that are multi-layered
• Calculating the thickness, density, and roughness of films based on glancing incidence X-ray reflectivity measurements.

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Advantages and Disadvantages of X-Ray Diffraction

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The main advantages of x-ray diffraction are:

• It is a fast and powerful technique for identifying unknown materials and minerals
• To analyze it, only a minimal sample needs to be prepared
• Interpreting the resulting data is relatively straightforward
• XRD measurement instruments are widely available

Disadvantages of X-ray diffraction are:

• Identifying unknown powder materials requires homogeneous samples.
• Access to standard reference data is required for XRD analysis.
• Grinding the sample down to a powder requires preparation of the sample.
• The indexing of patterns when determining the unit cells of a crystal sample can be complex if the sample is not isometric

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Things to Remember

• X-ray is high-energy electromagnetic radiation, having wavelength ranging from 10^-8 to 10^-12 m, corresponding to frequencies in the range 10¹⁶ to 10²⁰ Hz.
• X-ray diffraction is a phenomenon in which the atoms of a crystal cause an interference pattern of the waves present in an incident beam of X-rays, due to their uniform spacing.
• Using Bragg's law, the angle of diffraction can be used to calculate the distance between the sample's atomic planes.
• Diffraction is the process of bending of light when it passes around the edge of the object.
• X-ray crystallography involves the exposure of single crystals to x rays.
• X-ray diffraction involves the measurement of a wide range of material forms.
• The main use of X-ray diffraction is the identification of unknown crystalline materials.