diffractometry

Diffractometry is the measurement and analysis of diffracted radiation to characterize the structural properties of materials. It encompasses techniques that analyze patterns produced when a beam of waves—commonly X-rays, neutrons, or electrons—scatters from a periodic arrangement of atoms. The resulting diffraction pattern contains information about interplanar spacings, crystal symmetry, phase composition, and microstructure, and can be applied to solids in powders, crystals, thin films, or nanostructured forms.

Principles and scope: When waves encounter a periodic lattice, constructive interference occurs at particular angles that satisfy Bragg’s law, nλ = 2d sin θ. By varying the incident angle or wavelength and recording the intensity of the diffracted beam, a spectrum of peaks is obtained. The peak positions yield lattice spacings and unit-cell parameters, while peak shapes and intensities reveal crystallinity, strain, texture, and, with appropriate models, phase amounts and atomic positions.

Techniques and instruments: Powder diffractometry uses a polycrystalline sample to produce a one-dimensional pattern suitable for phase identification and quantitative analysis. Single-crystal diffractometry collects comprehensive intensity data from a single crystal to solve and refine a full structure. Small-angle diffraction probes larger-scale structures, whereas grazing-incidence X-ray diffraction enhances surface and thin-film information. Instruments employ various detectors, including scintillation counters, position-sensitive detectors, and CCDs, in combination with precise goniometers and radiation sources.

Analysis and applications: Powder patterns yield phase identification, lattice parameters, and, through Rietveld refinement, quantitative phase analysis and microstructural information. Electron and neutron diffraction offer complementary contrast, penetration, and scattering mechanisms. Diffractometry is widely used in materials science, chemistry, geology, metallurgy, pharmaceuticals, and biology to determine structure, composition, and quality. Limitations include the requirement for some crystalline order and sensitivity to sample preparation and radiation effects.

History: The field emerged from X-ray diffraction developments in the early 20th century by the Braggs and their successors, with subsequent expansion to neutrons and electrons, enabling a broad range of structural investigations.