A Preview of Concepts and Phenomena.- Fundamentals of Ferroic Domain Structures.- Ferroic Materials.- Methods for Observation of Domains.- Static Domain Patterns.- Domain Walls at Rest.- Switching Properties: Basic Methods and Characteristics.- Switching Phenomena and Small-Signal Response.- Ferroelectric Thin Films.
"Chapter 5 Static Domain Patterns (p. 207-208)
5.1 Introductory Remarks and Scheme of the Chapter
After discussing in some detail the theoretical aspects of properties of domain states and after describing a number of methods to observe domains, we now wish to deal with some real domain structures in single crystals. Several thousands of papers have been published on observations of domain patterns in different kinds of ferroics,1 offering a large amount of interesting data for materials listed in Chap. 3 and many others. Some of them are just observations as it stands, others were performed with the aim to create situations corresponding to theoretically defined conditions.
When treating properties of domain patterns in real ferroic samples, it is necessary to distinguish features of stable domain structures from those of dynamic domain phenomena. In the present chapter we have primarily in mind static and quasistatic domain patterns which can be observed in the absence of intentionally applied external forces that would tend to change their geometry or sizes. We define static or quasistatic domain patterns arbitrarily as those which do not appreciably change on the time scale of hours.
These are the patterns whichmay correspond to the thermodynamic equilibrium of the sample or which are metastable with long lifetimes because of large energy barriers that would have to be overcome to reach more stable configuration. Available data on domain patterns can be, in some approximation, classified into three categories. First, we can observe domains in a sample as it stands, meaning that its history (sample preparation, thermal record, applied forces) is not known. Second, and perhaps most often, the sample has been treated in a way which has been planned or which at least is known.
Third, the sample quality and the external conditions (e.g., thermal history) are well defined and carefully prepared so that we may expect the resulting domain structure to correspond to minimum energy harmonizing with its intrinsic properties and external conditions; this is often referred to as the ‘‘equilibrium domain pattern.’’ In the present chapter we first discuss, in Sect. 5.2, theoretical aspects of the last mentioned case, paying attention to the simplest example of equilibrium domain pattern in ferroelectric samples containing only domains with antiparallel orientation of PS vectors (‘‘1808 domains’’).
Such patterns have been studied extensively in ferroelectrics, both nonferroelastic and ferroelastic, with the aim to obtain regular patterns corresponding to thermodynamic equilibrium. This research was, in its early stages, inspired by successful treatments of equilibrium domain structures in ferromagnets. The role of the energy of demagnetizing field has its electrical counterpart treated in some detail in the following section. However, in ferroelectrics the situation is different because of the existence of free charge carriers that may contribute in a decisive way to the reduction of depolarization energy. This issue will be addressed in Sect. 5.2 as well."
