Diffraktogram

Diffraktogram, or diffractogram, is a graphical representation of diffracted radiation intensity as a function of angle or scattering vector, produced in diffraction experiments on crystalline materials. It is most commonly obtained in X-ray powder diffraction, where a powdered sample is irradiated with monochromatic X-rays and the detected intensity is plotted against the angle 2θ or the corresponding d-spacing. Similar plots can be obtained with neutron or electron diffraction, yielding a diffraktogram or diffractogram.

Key features are sharp peaks that occur when crystallographic planes satisfy Bragg's law, meaning nλ = 2d sin θ. Peak positions yield the spacings between lattice planes and can be used to identify crystalline phases by comparison with reference patterns. Relative peak intensities provide information about phase composition and, after appropriate corrections, structure factors.

Analysis methods include determining lattice parameters from peak positions, estimating crystallite size and microstrain from peak broadening, and performing quantitative phase analysis from peak areas. More detailed modelling, such as Rietveld refinement, fits a calculated diffraktogram to the data to refine a crystallographic model.

Limitations: amorphous content produces broad humps; overlapping peaks can hinder interpretation; instrumental broadening and preferred orientation must be accounted for. Accurate analysis relies on proper calibration, background subtraction, and, in many cases, standard reference materials.

See also: X-ray diffraction, Bragg's law, Rietveld refinement.