XRD

X-ray diffraction (XRD) is a characterization technique that probes the crystal structure of materials by measuring the pattern and intensity of X-rays scattered by the sample. XRD can identify crystalline phases, determine lattice parameters, assess crystallinity, and provide information about crystallite size and internal strain.

The technique relies on the diffraction of X-rays by ordered arrays of atoms in a crystal. Constructive interference occurs when Bragg’s law is satisfied: nλ = 2d sin θ, where λ is the X-ray wavelength, d is the interplanar spacing, θ is the angle of incidence, and n is an integer.

Most XRD experiments use a powder sample or a thin film; in powder diffraction a polycrystalline sample produces a pattern of Debye–Scherrer rings that are converted to a one-dimensional diffractogram by scanning 2θ. Single-crystal XRD uses a rotating crystal to determine full three-dimensional structures. The resulting diffraction pattern reflects the arrangement of atoms and can be analyzed to extract structural parameters.

The diffraction pattern is analyzed to identify phases by comparing peak positions to reference data sets (such as PDFs). Lattice parameters can be refined by methods such as Rietveld analysis; peak broadening can yield information on crystallite size and microstrain.

XRD is widely used in materials science, geology, chemistry, metallurgy, and pharmaceuticals. It is non-destructive, requires relatively small sample amounts, and can be automated, but provides average structural information and may be insensitive to amorphous content or minor phases.