ABSTRACT
This chapter explains the basic aspects of crystallography that are necessary for the understanding of X-ray diffraction and its applications. It also explains the principle of geometrical crystallography by considering perfect single crystals. A crystal is a solid material whose constituent atoms are periodically arranged in three dimensions. The regular arrangement of atoms in a single crystal can be completely described by defining a fundamental repeat unit coupled with a statement of the translations necessary to build the crystal from the repeat unit. The crystal structure can be completely described by stating the lattice constants and the coordinates of atoms within the unit cell. Crystals are classified into seven crystal systems according to their rotational symmetry elements. These are triclinic, monoclinic, orthorhombic, trigonal, tetragonal, hexagonal, and cubic. The reciprocal lattice literally means the reciprocal-space version of a real lattice. The reciprocal lattice is very useful for solving many problems in crystal geometry.
