IS A REVISION OF VOL. A OF THE INTERNATIONAL TABLES FOR CRYSTALLOGRAPHY DESIRABLE OR NECESSARY ?

Vojtech Kopsky

Institute of Physics, Czech Acad. Sci., Na Slovance 2, POB 24, 180 40 Praha 8, Czech Republic

Keywords: International Tables, standards, Hermann-Mauguin symbols, subperiodic groups, unification, bicrystallography, domain walls, twin boundaries

Crystallographers are accustomed to use the tables of space group types in the format of Vol. A of the International Tables for Crystallography in a certain standard way and evidently do not encounter any problems in using them to determine and describe the structures of single crystals. The traditional interpretation of such basic crystallographic concepts as the Hermann-Mauguin symbols, settings and origin choice is, however, very inconvenient when relationship between structures and hence between their symmetry groups is involved. Such relations occur in consideration of structural phase transitions and in all problems of "Bicrystallography" which include the study of domain walls and twin boundaries.

Furthermore, crystallographers are not the exclusive users of the International Tables. Since the first version [1] in 1935 the Tables were twice re-edited [2,3], updated and modernized without much regard to the need of other users, specifically of solid state theorists. They are mainly based on geometric description and argument and the algebraic background is rather suppressed and, in some contexts, distorted even in the last version, referred to as Vol. A. We do not want to question the fact that Vol. A is a well taken and important step forward in comparison with previous editions. The aim of this contribution is to show the weak points of the volume and propose the amendments with all respect and credit to the creators of Vol. A. Most of our observations arose during the preparation of Vol. E of the International Tables [4] which should serve as a standard source for consideration of subperiodic groups (frieze, rod, and layer groups). One of the proposals we shall discuss is the proposal of a "Unified system of Hermann-Mauguin symbols" which will strictly correlate subperiodic groups with reducible space groups.

1. Internationale Tabellen zur Bestimmung von Kristallstrukturen. 1. Band. Edited by C. Hermann. Borntrager, Berlin (1935). [Reprinted with corrections by Edwards, Ann Arbor (1944)].
2. International Tables for X-ray Crystallography. Vol. 1. Edited by N.F.M. Henry and K. Lonsdale. Kynoch Press, Birmingham (1952). [Revised editions: 1965, 1969, and 1977].
3. International Tables for Crystallography. Vol. A: Space-Group Symmetry. Edited by T. Hahn. Reidel, Dordrecht (1983). [Revised editions: 1985, 1987].
4. International Tables for Crystallography. Vol. E: Subperiodic groups. By V. Kopsky and D.B. Litvin. Reidel, Dordrecht. To appear in Spring 1999.