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IUCr 1997 Report - Commission on Crystallographic Nomenclature

The work of the Commission in 1997 was concerned with three areas: the nomenclature of crystallography in n-dimensions; the formulation of a clear and unambiguous nomenclature for each phase formed in a sequence of phase transitions; and active cooperation with COMCIFS on matters of nomenclature. The first two activities are in the hands of specialists, the last in that of a Commission Observer, see below. All communications within the Commission and its committees were by e-mail except for subgroups that met in July 1997 in Nijmegen, The Netherlands, in December 1997 in Paris, France, and in August 1997 in Geneva, Switzerland. The lack of new concerns brought before the Commission for consideration during the year probably reflects a current absence of nomenclature conflict in the crystallographic literature.

The Subcommittee on the Nomenclature of n-Dimensional Crystallography [see Acta Cryst. (1996), A52, 91-124 for membership] considered and improved several drafts of their first Report on point-group transformations, families, systems and geometric crystal classes during the year. Following vigorous discussion about such matters as the use of the overbar in the symbol for orthogonal transformations in n dimensions, the setting of lattices in 4, 5 and 6 dimensions, family ordering in these dimensions, and the distinction between the terms `lattice system' and `point-group system', a formal ballot showed the emergence of a rather high level of consensus. The Report is expected to be ready for submission to the Commission early in 1998. The nomenclature to be recommended for arithmetic crystal classes, centring symbols, Bravais classes and space groups in higher dimensions will be presented in a subsequent Report.

The primary concern of the Working Group on Phase Transition Nomenclature [see Acta Cryst. (1996). A52, 91-124, also (1997). A53, 822 for membership] is formulation of a unified, informative and unambiguous notation for each phase in the sequence that a material may form as a function of temperature and/or pressure. The resulting notation has to be clearly superior to the many ambiguous and uninformative notations that are widely used in the current literature. The innovative nomenclature that has evolved during discussions of the Working Group meets these objectives with a six-field notation, each field with a meaning that is intuitively clear while simultaneously presenting highly characteristic phase information. A first Report is expected to be submitted to the Commission for action early in 1998. Extension of this nomenclature to certain long-period or polytype structures, such as SiC or ZnS, and to quasicrystalline phases will be treated in a subsequent Report.

The Commission Observer [see Acta Cryst. (1997). A53, 822] has noted that COMCIFS continues to be very active, posting a slightly modified version of the Core CIF dictionary, version 2.0.1, and the new Powder CIF dictionary, version 0.996, on the CIF web site. No issues concerning nomenclature have arisen.

In addition to a listing of all members on the Commission's attractive home page at http://www.iucr.org/iucr-top/comm/cnom/index.html, established through the efforts of B. McMahon, the page also provides general information about the Commission, the titles of all Commission reports, and a valuable group of sites presenting nomenclature resources. The page includes hypertext links to each member, to the full content online of six recent Commission reports and to nine major nomenclature resources.

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