XRD Peak Analysis Explained: Position, Intensity, and Shape Made Simple

Summary

The video explains how three features of an X-ray diffraction (XRD) pattern—peak position, intensity, and shape or width—can reveal information about a material.

Peak position (2θ)

A peak’s position along the horizontal axis is its 2θ value. Using Bragg’s law, this position can be used to calculate the spacing between crystal planes (d-spacing). Comparing peak positions or calculated spacings with reference data can help identify a material’s crystalline phase and crystal structure, and estimate unit-cell parameters such as a, b, c, α, β, and γ. The presenter mentions comparing results with diffraction databases.

Peak intensity

Intensity refers to the area under a peak, rather than simply its height. Peak height can serve as a rough basis for comparison when peaks have similar widths and shapes, but peaks with different widths should be compared by area. The presenter describes intensity as a way to assess the relative amounts of phases in a sample.

Peak shape and width

Peaks may be sharp or broad. The video links peak width—often measured as full width at half maximum (FWHM)—to crystallite size through the Scherrer equation: broader peaks generally indicate smaller crystallites, while narrower peaks generally indicate larger ones. The presenter also associates peak broadening or changes in shape with strain, microstrain, and defects.

An XRD pattern’s peaks provide complementary information: their positions help identify structure and phases, their intensities indicate relative phase amounts, and their widths and shapes offer clues about crystallite size and imperfections.

Speakers and sources mentioned

• Speaker: One presenter or narrator; no other speakers are evident in the subtitles.
• Methods and references: Bragg’s law, the Scherrer equation, the International Centre for Diffraction Data (ICDD), and an online open-access crystallographic database apparently referred to as the Crystallography Open Database.