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# What is X-Ray Diffraction Analysis (XRD) and How Does it Work?

X-ray diffraction analysis (XRD) is a technique used in materials science to determine the crystallographic structure of a material. XRD works by irradiating a material with incident X-rays and then measuring the intensities and scattering angles of the X-rays that leave the material [1].

A primary use of XRD analysis is the identification of materials based on their diffraction pattern.  As well as phase identification, XRD also yields information on how the actual structure deviates from the ideal one, owing to internal stresses and defects [1].

## How Does it Work?

Crystals are regular arrays of atoms, whilst X-rays can be considered as waves of electromagnetic radiation. Crystal atoms scatter incident X-rays, primarily through interaction with the atoms’ electrons. This phenomenon is known as elastic scattering; the electron is known as the scatterer. A regular array of scatterers produces a regular array of spherical waves. In the majority of directions, these waves cancel each other out through destructive interference, however, they add constructively in a few specific directions, as determined by Bragg’s law:

2dsinθ = nλ

Where d is the spacing between diffracting planes, θ{\displaystyle \theta } is the incident angle, n is an integer, and λ is the beam wavelength. The specific directions appear as spots on the diffraction pattern called reflections. Consequently, X-ray diffraction patterns result from electromagnetic waves impinging on a regular array of scatterers.

X-rays are used to produce the diffraction pattern because their wavelength, λ, is often the same order of magnitude as the spacing, d, between the crystal planes (1-100 angstroms).

## XRD Benefits and Applications

XRD is a non-destructive technique used to [2]:

• Identify crystalline phases and orientation
• Determine structural properties:

- Lattice parameters
- Strain
- Grain size
- Epitaxy
- Phase composition
- Preferred orientation
• Measure thickness of thin films and multi-layers
• Determine atomic arrangement

## How Can TWI Help?

TWI has a long history of working with its Members, across a range of industry sectors, on materials characterisation, including X-ray diffraction. For example, TWI supported Wireline Technologies Ltd on the development of electronic packaging for bore hole data logs. TWI was asked to analyse samples of failed materials by Wireline Technologies Ltd. This analysis was performed using X-ray diffraction and scanning electron microscopy, and helped to confirm the nature and cause of the failures, thereby assisting Wireline Technologies to choose the most appropriate materials for their applications.

Currently, TWI possesses a state of the art Bruker D8 Advanced Diffractometer, which offers the following testing and analysis to our Members:

• Phase ID both qualitative and quantitative (XRPD)

- Analysis of corrosion products
- Analysis of phases in thermally sprayed powders
- Quantification of phase balance (retained austenite/duplex etc.)
• Grazing Angle Incidence (GIXD) for analysis of thin layers on the surface.

- Phases in thin layers
• XRR for layer thickness

- Non-destructive thickness measurements
• Phase changes with variable humidity and temperature
• Residual Stress measurements

- Stress free lattice parameter measurements