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

International Tables for Crystallography (2013). Vol. D, ch. 3.4, p. 505

Figure 3.4.2.5 

V. Janoveca* and J. Přívratskáb

aInstitute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, CZ-18221 Prague 8, Czech Republic, and bDepartment of Mathematics and Didactics of Mathematics, Technical University of Liberec, Hálkova 6, 461 17 Liberec 1, Czech Republic
Correspondence e-mail:  janovec@fzu.cz

[Figure 3.4.2.5]
Figure 3.4.2.5

Four basic single-domain states [{{\sf S}_1}= 1_1], [{{\sf S}_2}= 1_2], [{{\sf S}_3}= 2_1], [{{\sf S}_4}= 2_2 ] of the ferroic phase of a calomel (Hg2Cl2) crystal. Full [\bullet] and empty [\circ] circles represent centres of gravity of Hg2Cl2 molecules at the levels [z=0] and [z=c/2], respectively, projected onto the [z=0] plane. The parent tetragonal phase is depicted in the centre of the figure with a full square representing the primitive unit cell. Arrows are exaggerated spontaneous shifts of molecules in the ferroic phase. Dotted squares depict conventional unit cells of the orthorhombic basic domain states in the parent clamping approximation. If the parent clamping approximation is lifted, these unit cells would be represented by rectangles elongated parallel to the arrows.