Crystals as X-ray diffraction gratings. Bragg equation. Applications on cubic crystals: a) determination of X-ray wavelength, b) determination of unit cell and atom size. Materials characterization. Applications a) Debye-Scherrer method on polycrystalline materials. Reflection indexing of X-ray patterns of cubic symmetry samples and unit cell determination, b) Bragg-Brentano method on multiphase crystalline materials and amorphous materials i) Phase identification, phase discrimination and indexing of multiphase X-ray patterns. ii) Size determination of amorphous associations. Phases equilibrium study of eutectic binary systems.