What is X-Ray Diffraction (XRD)

X-ray powder diffraction (XRD) is a rapid analytical technique primarily used for phase identification of a crystalline and semi crystalline materials. For best results the analysed material is finely ground, homogenized, and the average bulk composition is determined.
The properties of a material can often be linked back to the arrangement of atoms in its crystal structure. X-ray diffraction is a non-destructive analytical technique which can yield the unique fingerprint of Bragg reflections associated with a crystal structure.

xrd 2 theta

 

 

 

 

 

 

 

 

One can regard a crystal structure as being built of layers, or planes, which each act as a semi-transparent mirror. X-rays with a wavelength similar to the distances between these planes can be reflected such that the angle of reflection is equal to the angle of incidence. We call this behaviour `diffraction´, and it is described by Bragg’s Law:
2dsinθ = nλ
By comparing the diffraction pattern with a database of known diffraction patterns the phase of the material can be determined, analysis of further aspects of the diffraction pattern (peak heights, peak width ect) can then be used to determine:
• characterization of crystalline materials (Qualitative analysis)
• identification of fine-grained minerals such as clays and mixed layer clays that are difficult to determine optically
• determination of unit cell dimensions
• measurement of sample purity
• measurement of stress and strain
With specialized techniques, XRD can be used to:
• determine crystal structures using Rietveld refinement
• determine of modal amounts of minerals (Quantitative analysis)
• determination of particle size and distribution using Small Angle Scattering SAXS
• characterize thin films samples by:
o determining lattice mismatch between film and substrate and to inferring stress and strain (Pole figure measurements)
o determining dislocation density and quality of the film by rocking curve measurements
o measuring super lattices in multi-layered epitaxial structures
o determining the thickness, roughness and density of the film using glancing incidence X-ray reflectivity , XRR measurements