DOMAIN WALL SYMMETRY AND CRYSTAL FORMS
Jana Privratska and Vaclav Janovec
Technical University of Liberec, Halkova 6,
461 17 Liberec 1, Czech Republic
janovec@fzu.cz
Keywords: Symmetry of domain wall, layer group, crystal form, orientational orbit of domain walls, symmetric domain walls, asymmetric domain walls, reversible domain wall, irreversible domain walls.
A domain wall can be treated as a thin layer with specific properties that may differ from properties of domains. Similarly as the crystallographic point groups give necessary conditions for the appearance of certain material (tensor) properties of domains (e.g. spontaneous polarization, optical activity, piezoelectricity, etc.), material properties of a domain wall are conditioned by wall symmetry that is described by a layer group - a crystallographic group with two-dimensional translations. In continuum description there are 31 layer groups. They provide similar basic classification of domain walls as do 32 point groups for crystals and, moreover, divide domain walls into symmetric and asymmetric domain walls. This division specifies basic features of structural changes within the walls [1,2].
In this contribution we present a derivation of domain wall symmetry that utilizes the concept of crystal forms used in crystal morphology [3]. Besides the wall symmetry this derivation provides (i) an association of domain walls into orientational orbits that comprise all crystallographically equivalent domain walls with the same physical properties but with different direction of the wall normal, (ii) division of domain walls into reversible and irreversible domain walls - another specification that characterizes basic properties of domain walls [1,2].
We shall illustrate in a visual form the derivation of the wall symmetry and its significance in determining basic properties of domain walls.
This work was supported by the Grant Agency of the Czech Republic under grant No. 202/96/0722