Fundamentals of Ferroic Domain Structures
In this section we introduce the basic concepts required to discuss structural phase transitions in crystals on the basis of a symmetry approach. The latter is in fact closely connected with the Landau theory of phase transitions, to which we come later in this chapter. However, for the reader who is more oriented toward domain properties without studying the nature of phase transitions themselves, it may be practical to become acquainted with the symmetry approach in the first place. The analysis of domain states on the basis of symmetry gives essential information on the number of domain states and on how they can be distinguished. It is this information that forms the background of any considerations about domain reorientation processes, about domain walls, as well as about properties and applications of multidomain samples.