X-Ray Diffraction (XRD) has long been used to determine the atomic-scale structure of materials. This technique is based on the fact that the wavelength of X-rays is comparable to the distances between atoms in condensed matter. When a material exhibiting a long-range (i.e. at least micrometers), periodic atomic order, such as a crystal, is irradiated with X-rays it acts as an extended, well-defined grating and produces a diffraction pattern showing numerous sharp spots, called Bragg diffraction peaks. By measuring and analyzing the positions and intensities of these peaks it is possible to determine the spatial characteristics of the grating – i.e. to determine the three-dimensional (3-D) arrangement of atoms in the crystalline material being studied.