Figure 3.3.10.12

Hahn, Th.; Klapper, H.

doi:10.1107/97809553602060000644

International
Tables for
Crystallography
Volume D
Physical properties of crystals
Edited by A. Authier

pdf | chapter contents | chapter index | related articles

International Tables for Crystallography (2006). Vol. D. ch. 3.3, p. 440

Figure 3.3.10.12

Th. Hahn^a ^* and H. Klapper^b

^a Institut für Kristallographie, Rheinisch–Westfälische Technische Hochschule, D-52056 Aachen, Germany, and ^bMineralogisch-Petrologisches Institut, Universität Bonn, D-53113 Bonn, Germany
Correspondence e-mail: hahn@xtal.rwth-aachen.de

Figure 3.3.10.12

Illustration of space-filling problems of domains for a (ferroelastic) orthorhombic $[\rightarrow]$ monoclinic phase transition with an angle $[\varepsilon]$ (exaggerated) of spontaneous shear. (a) Orthorhombic parent crystal with symmetry $[2/m\,2/m\,2/m]$ . (b) Domain pairs [1+2] , [1+3] and [2+4] of the monoclinic daughter phase ( $[\beta = 90^\circ + \varepsilon]$ ) with independent twin reflection planes (100) and (001). (c) The combination of domain pairs [1+2] and [1+3] leads to a gap with angle $[90^\circ - 3\varepsilon]$ , whereas the combination of the three domain pairs [1+2] , [1+3] and [2+4] generates a wedge-shaped overlap (hatched) of domains 3 and 4 with angle $[4\varepsilon]$ . (d) Twin lamellae systems of domain pairs [1+2] (left) and [1+3] (or [2+4] ) (right) with low-energy contact planes (100) and (001). Depending on the value of $[\varepsilon]$ , adaptation problems with more or less strong lattice distortions arise in the boundary region A–A between the two lamellae systems. (e) Stress relaxation and reduction of strain energy in the region A–A by the tapering of domains 2 (`needle domains') on approaching the (nearly perpendicular) boundary of domains [3+1] . The tips of the needle lamellae may impinge on the boundary or may be somewhat withdrawn from it, as indicated in the figure. The angle between the two lamellae systems is $[90^\circ - \varepsilon]$ .