X-ray diffraction: invaluable tool for materials characterization

The solid-state materials can be classified into two general classes, namely, crystalline and non-crystalline (amorphous). In the crystalline materials the atoms have a regular periodic arrangement, which is lacking in the amorphous materials. X-ray diffraction is an indispensable tool for crystalline materials. X-rays, produced from the inner (core) level electronic transitions in an atom, are termed as characteristic radiation. The electromagnetic radiations are also produced with the acceleration or deceleration of charged particles, which is called as white radiation. X-rays, being electromagnetic wave, interact with the electron cloud of the atom. Since the crystal lattice consists of parallel rows of atoms equivalent to the parallel lines of the diffraction grating, the inter-planar spacing can be determined from the separations of bright fringes of the diffraction pattern. X-ray diffraction experimental set up requires an X-ray source, the sample under investigation and a detector to pick up the diffracted X-rays. The radiation source can be monochromatic and polychromatic. The x-ray diffraction experiments can be carried out either from single crystals or from polycrystalline samples. The peak position is used for the qualitative identification of phase, determination of unit cell parameters and symmetry of lattice. The profile or intensity is used for the structure refinement. The d-spacings are related to the lattice dimensions. Each reflection can be assigned by some hkl values, which equate the inter-planar spacing with the unit cell parameters. There are numerous applications of XRD data. The typical applications are summarized as follows: Study of phase identification, nature of sample (crystalline or amorphous), monitoring solid state reactions, phase transitions, unit cell determination, crystallite size, strain, structure determination, study of defects, surface structure (GI-XRD, SAXS), polycrystalline texture, phase relations/phase diagrams, solid solution formation, order disorder phase transitions. Some of the applications will be discussed in this article. (author)