Xraydiffraction

X-ray diffraction (XRD) probes the arrangement of atoms in crystalline materials by measuring patterns produced when X-rays scatter from electrons in the sample. Constructive interference from lattice planes is described by Bragg’s law, nλ = 2d sin θ, where λ is the X-ray wavelength, d is the interplanar spacing, and θ is the angle of incidence. Diffraction peaks indicate specific spacings and can be used to determine crystal structure, identify phases, and estimate lattice parameters.

XRD has a short history. In 1912, Max von Laue demonstrated X-ray diffraction by crystals, confirming their wave character. In 1913, William Henry Bragg and his son Lawrence Bragg formulated the Bragg equation and established X-ray crystallography as a quantitative structural tool.

Two main data collection modes are used: angle-dispersive XRD (ADXRD), recording intensity versus 2θ, and energy-dispersive XRD (EDXRD), recording intensity versus X-ray energy. A typical instrument combines an X-ray source (often copper Kα), optics or a monochromator, a sample goniometer, and a detector (scintillator or solid-state).

In powder XRD, peak positions identify phases and permit lattice parameter determination via Bragg’s law; integrated intensities aid qualitative and quantitative analysis. Modern practice often employs Rietveld refinement to fit an entire diffraction pattern to a structural model and extract detailed parameters from complex mixtures.

Applications span chemistry, geology, materials science, metallurgy, and pharmaceuticals, including phase identification, crystal-structure solving, thin-film analysis, stress measurement, and quality control. Limitations include the need for crystalline material, peak overlap in complex mixtures, preferred orientation effects, and safety considerations for X-ray radiation.