Get Powder Diffraction & Rietveld Refinement School - Durham University

What are the advantages and disadvantages of XRD? It is a rapid and powerful technique for identifying unknown minerals and materials. It only requires preparation of a minimal sample for analysis. Interpreting the resulting data is relatively straightforward. XRD measurement instruments are widely available.

d = n x wavelength/2sin(theta). In this lab you will measure the x-ray powder diffraction pattern from a single crystal. Your TA will give you the sample to be measured and show you how to set up the Miniflex x-ray diffractometer.

The distinction between powder and single crystal diffraction is the degree of texturing in the sample. Single crystals have maximal texturing, and are said to be anisotropic. In contrast, in powder diffraction, every possible crystalline orientation is represented equally in a powdered sample, the isotropic case.

Diffraction is the spreading out of waves as they pass through an aperture or around objects. It occurs when the size of the aperture or obstacle is of the same order of magnitude as the wavelength of the incident wave. For very small aperture sizes, the vast majority of the wave is blocked.

There are two major techniques. Powder X-ray diffraction determines the phases and purity of a crystalline species. Single X-ray diffraction identifies the atoms in a crystal and their locations, as well as electron densities, bond lengths, and angles.

Powder XRD provides useful information about structure, phase, composition, shape, size, crystallinity, and other important features of nanoscale materials, although unambiguous sample characterization almost always requires complementary experimental and/or computational methods.

There are two types of XRD techniques, single crystal and powder. The difference between these methods is scale. As the name suggests, a single-crystal analysis is focused on exact atomic positions of a single well-ordered crystal, while powder XRD characterizes a sample of bulk material.

Unlike single-crystal XRD, powder XRD looks at a large sample of polycrystalline material and therefore is considered a bulk characterization technique. The powder pattern is considered a "fingerprint" for a given material; it provides information about the phase (polymorph) and crystallinity of the material.

The powder method is used to determine the value of the lattice parameters accurately. Lattice parameters are the magnitudes of the unit vectors a, b and c which define the unit cell for the crystal. If a monochromatic x-ray beam is directed at a single crystal, then only one or two diffracted beams may result.