ABSTRACT
Crystal structures considered in previous chapters correspond to
ideal crystallinematerials and refer to the caseswhere the atoms are
in their equilibrium positions, which obviously represents the first-
order approximation in the description of such materials. We know
already that an infinite crystal structure possesses a translation
symmetry which is at the same time the translation symmetry of
its lattice. In this chapter, we will introduce the concept of the so-
called reciprocal lattice, which has the same point-group symmetry as the crystal lattice (direct lattice) and plays an important role in
the description of the physical properties of crystalline materials.
