Tables for
Volume C
Mathematical, physical and chemical tables
Edited by E. Prince

International Tables for Crystallography (2006). Vol. C, ch. 9.2, pp. 752-773

Chapter 9.2. Layer stacking

S. Ďurovič,a P. Krishnab and D. Pandeyc

aDepartment of Theoretical Chemistry, Slovak Academy of Sciences, Dúbravská cesta, 842 36 Bratislava, Slovakia,bRajghat Education Center, Krishnamurti Foundation India, Rajghat Fort, Varanasi 221001, India, and cPhysics Department, Banaras Hindu University, Varanasi 221005, India


1 This is an interesting example of how a development in a scientific discipline influences semantics: e.g. when speaking of a 6H polytype of SiC, one has very often in mind a characteristic sequence of Si–C layers rather than deviations from stoichiometry, presence and distribution of foreign atoms, distortion of coordination tetrahedra, etc.
2 The direction in which there is periodicity is indicated by parentheses (Dornberger-Schiff, 1959[link]).
3 A coincidence operation is a space transformation (called also isometric mapping, isometry, or motion), which preserves distances between any two points of the given object.
4 According to Guinier et al. (1984[link]), triclinic polytypes should be designated A (anorthic) in their Ramsdell symbols.
5 Sandwiches with composition Al(OH)3 (similar to those in CdI2) are the same in both families, but their stacking mode is different. This and similar situations in other substances might have been the reason for distinguishing between `polytype diversity' and `OD diversity' (Zvyagin, 1988[link]).
6 A hexagonally centred unit mesh a1, a2 instead of a primitive mesh A1, A2 is used (Fig.[link]
7 If the symmetry of Tet is P(6)mm (in the Pauling model), Z = 2. This case is common in the literature. However, with the trigonal symmetry of Tet, these two possibilities would correspond to Franzini (1969[link]) types A and B, which are not geometrically equivalent.