V. Janovec

The Orientation of Domain Walls in Twinned Ferroelectric Crystals

Due to the spontaneous deformations of ferroelectric crystals in their ferroelectric phases, twins (domains) may be separated only by those composition planes (domain walls) which satisfy the mechanical compatibility conditions; such planes are in an infinite crystal called permissible walls. A mathematical treatment is proposed which makes it possible to find all permissible walls in any ferroelectric species. It is shown that different types of permissible walls exist: W∞ walls with arbitrary orientation, crystallographically prominent Wf walls, and S walls whose indices depend on PS and the electromechanical coefficients. The orientations of such S walls are necessarily temperature dependent. Two particular domains may be separated by a W∞ wall or by one of two mutually perpendicular permissible walls of Wf and/or S type. In a number of species, however, there are pairs of domains between which no wall is permissible. It is shown that the occurrence of W∞ and Wf walls can be predicted from the symmetry...

Symmetry analysis of domain structure in KSCN crystals

Abstract Basic symmetry properties of domain states, domain pairs, domain twins and walls in KSCN crystals are examined by group theoretical methods. Relations between domain states and domain pairs are expressed in matrix form and by permutation representation. Black and white space groups describing the symmetry of domain pairs are found and layer group symmetries of domain twins and domain walls are determined as their sectional subgroups. Microscopic structures of domain walls are given for coherent ferroelastic walls and for translation (antiphase) walls. Exposition and obtained results provide an illustrative example of symmetry analysis of domain structures.

Perfect domain textures of incommensurate phases

Abstract Domain textures of typical incommensurate phases are constructed as regular domain structures formed by equivalent domain walls of minimum negative energy. Structures with two or three modulation waves can form several stripe textures and textures periodic in two or three directions. Equivalent textures can coexist as textural blocks. Symmetry properties of perfect domain textures are discussed.

Temperature Autostabilizing Nonlinear Dielectric Element (TANDEL). II. Explanation of Its Function

A simplified explanation of the automatic temperature stabilization of a nonlinear dielectric element is presented. The explanation is based on energy considerations of the heat produced in consequence of dielectric losses in the element and of heat transferred to the ambient medium. The principle of bringing the element into the autostabilizing state is discussed in detail, as well as the falling out of this state, and the nature of temperature hysteresis of this element is explained. Measurements of complex permittivity at the fundamental frequency and high amplitudes of applied voltage as functions of crystal temperature are given for various values of the heating voltage. From these experimental results the temperature stabilization of the element is calculated for its dependence on variations of ambient temperature and heating voltage; a good agreement was found with the experimental values previously reported. The principle of automatic stabilization of temperature is not limited to the TANDEL produ...

Non-ferroelastic twin laws and distinction of domains in non-ferroelastic phases

Abstract We show that within continuum description there exist 48 possible relations (twin laws) between structures of two non-ferroelastic domains. All these twin laws can be expressed by dichromatic point groups. For each twin law we give the number of components of important material property tensors that have opposite sign in the two domains under consideration.

Optical and X-ray distinction of ferroelectric non-ferroelastic domains

Abstract We show that there exist 17 possible relations (twin laws) between structures of two ferroelectric non-ferroelastic domains. For each twin law we indicate whether X-ray diffraction intensities from two domains equal or differ and give number of optical tensor components that can distinguish both domains. We list twin laws which appear in particular ferroelectric non-ferroelastic or partially ferroelastic phases.

Bicrystals, twins and domain structures – a comparison

Abstract Bicrystals, twins, and domain structures are special types of crystal aggregates and have been studied by different groups of scientists (metallurgists, mineralogists, physicists). Although they exhibit many common physical and geometrical features, different terminologies have developed. The defining properties of the three types of crystal aggregates, as well as the terms in use for their description will be presented.

Microscopic structure of domain walls and antiphase boundaries in calomel crystals

Abstract We present examples of microscopic structures of finite thickness ferroelastic domain walls and antiphase boundaries in Hg2Cl2 crystals obtained by symmetry analysis. They illustrate positional dependencies of the structure of domain walls, topologically different structures of antiphase boundaries and the role of gradient effects.

Search for antiphase boundaries in mechanically twinned orthorhombic ammonium sulphate crystals

Straight line grooves with crystallographic orientations were revealed by etching in areas passed by moving twin planes of mechanical twins. It is argued that these grooves can be identified with antiphase boundaries resulting from transitional symmetry reduction accompanying the hypothetical ferroelastic D46h-D162h phase transition.

Symmetry characterization of ferroelastic domain twins by dichromatic point groups

Abstract Symmetry description of domain twins by sectional dichromatic layer groups is briefly described. Results of a systematic point group symmetry analysis of ferroelastic domain pairs and domain twins are mentioned and some of its applications outlined.