ABSTRACT
Although a variety of noncrystalline solids exist (glasses, polymers), a basic knowledge of the crystalline state is necessary for a better understanding of the condensed state of matter, if only because the properties of crystals often serve as benchmarks for comprehending the properties of noncrystalline materials. In this chapter we review briefly the geometrical and symmetry aspects of the structure of perfect single crystals. It is also instructive to discuss the question of how a crystal is formed from its building blocks. Many of the concepts used in the theories of crystal growth are also relevant to the growth of a ferroic phase in the surrounding matrix of the prototypic phase or the parent phase. The switching of ferroic domains by driving fields is also akin to crystal growth in many respects. The chapter ends with a brief description of the structural features of incommensurately modulated crystals.
