Aperiodic Crystals, Belo Horizonte, Brasil, 8-13 September 2003

Conference Report

The International Conference on Aperiodic Crystals, APERIODIC 2003, took place from 8 through 13 September 2003 in Belo Horizonte, Brasil. APERIODIC 2003 was the eighth in a series of triennial meetings, that have the goal to bring together scientists studying the atomic structures and physical properties of quasicrystals, incommensurately modulated crystals, incommensurate composite crystals and polytypes.

APERIODIC 2003 was attended by a total number of 90 participants from 22 countries in 5 continents. Participation was negatively affected by the difficulties of travel, that exist since a few years, mainly due to the regulations by the government of the U.S.A.. At least two intended participants, both of them invited speakers, could not come to Belo Horizonte, because they did not obtain transit visa for the U.S.A. in time. It should be realized by organizers and participants of future meetings, that transit visa will be necessary for many nationalities when a flying route will pass through the U.S.A..

The scientific sessions took place in the science building on the campus of the University of Minas Gerais. A morning and evening bus shuttle between the campus and the downtown hotels guaranteed a smooth progress for all participants. Oral presentations were given during the day, while the late afternoons were reserved for poster sessions. Each day was opened by a tutorial lecture, intended to give an overview of the field of research on aperiodic crystals. They were concerned with the mathematical theory of diffraction, the dynamics of aperiodic crystals (phasons) and the superspace description of the atomic structures of modulated and composite compounds, respectively. The conference excursion visited Ouro Preto, the former capital of the state of Minas Gerais. Ouro Preto features a beautifully restored old town as well as several museums, including an excellent museum on minerals. Precious stones and Minerals, including incommensurate crystals, could also be bought at one of the many shops.

The various lectures and posters together gave an excellent overview of current research on aperiodic crystals. Without indicating individual contributions of particular highlights, the following picture emerged.

The next stage in the structure determination of quaiscrystals has been reached. Despite an increased complexity of the structure models and an improved fit to the diffraction data, the latter are still not completely explained. Both theoretical and experimental studies indicated that these problems in modeling are related to local, structural disorder that is most probably inherent to quasicrystals. Some fundamental issues, like the electronic structure and dynamics, are still not solved for aperiodic crystals. Theoretical approaches and experiments were concerned with phason dynamics, the electronic structure and symmetry aspects, as well as with surface properties and frustration of magnetic order on quasiperiodic lattices.

Incommensurately modulated and composite structures have been found for nine different elements, when these are cooled down or put under pressure. This is one indication for the proliferation and importance of incommensurate structures in solid state physics and chemistry. Many chemical compounds have been discovered that possess complicated (incommensurate) modulations. The Maximum Entropy Method might be suitable for the determination of these complicated shapes. the superspace approach has been extended towards so-called composition flexible systems. The computer program JANA2000 evolves to a general purpose tool for the determination and analysis of these increasingly complex modulations.

The proceedings of APERIODIC2003 have been published as a volume 305 (2004) of the journal Ferroelectrics. Ferroelectrics is published by Taylor and Francis, see http://taylorandfrancis.metapress.com.

This report and many photo’s can be viewed at the web site of meeting at http://agora.grude.ufmg.br/aperiodic2003.

Belo Horizonte: Nivaldo Speziali, Chair of the organizing committee.
Bayreuth: Sander van Smaalen, Chair of the commission on aperiodic crystals of the IUCr.