Aperiodic Crystals and Quasicrystals

Chair: Gervais Chapuis (Switzerland), Co-chair: Vaclav Petricek (Czech Republic)

S. Lidin	Modulations in B8 Type Intermetallics	A
A. Ustinov, L. Olikhovskaya, I. Shmyt’ko	Multiwave Modulation of Polydomain Crystals (video)	A
S. van Smaalen, J. Luedecke, J.L. de Boer, A. Spijkerman, G.A. Wiegers	CDW Compounds: A Comparison of X-Ray Diffraction and Scanning Tunneling Microscopy	A
J. Wolny, S. Kapral	Diffraction Patterns of Aperiodic Structures with Frozen in Phonons and Phasons	A
S. Ben-Abraham	Cluster Approach to Octagonal Quasicrystals - An Example: Mn-Si-Al	A
S. Schmid, R.L. Withers, D. Corker, P. Baules	Towards a unified description of the AMOB₂O₅ (A = K, Rb, Cs, Tl; M = Nb, Ta) family of compounds	A
	Discussion


A. Ustinov	V. Petricek

The speakers covered a broad range of topics in the field of quasi- and incommesurate crystals. Janusz Wolny (University of Mining and Metallurgy, Krakow) introduced a new theoretical approach for the structure factor calculation of aperiodic structures based on the reference lattice concept. The method is very attractive and sufficiently general to be applied to many different types of structures including examples where continuous diffraction patterns are observed. Siegbert Schmid (Australian National University, Canberra) showed how the concept of superspace group symmetry could contribute to give an unified description of a very rich family of compounds, the oxide pyroborates. The superspace group approach and its refinement techniques leads to an improved crystal chemistry as compared to the standard superstructure refinement approaches. Some advantages of this approach for the description of complex layer structures were presented by Sander van Smaalen (University of Bayreuth) The superspace description is used to analyse the correlation between the displacements of different atoms in conjunction to a CDW transition. Sven Lidin (Stockholm University) described an interesting electron diffraction study of some B8-type intermetallic compound based on the superspace approach. Anatolii Ustinov (Institute of Metal Physics, Kiev) used another approach based on antiphase boundaries to describe structure with displacement waves propagating along some specific crystallographic directions. In the field of quasicrystals, Shelomo Ben Abraham (University of the Negev, Beer-Scheba) successfully used the cluster approach to redetermine the structure of Mn80Si15Al5, which was previously studied in terms of the Amman-Beenker cluster. Finally, at the end of the session, Ted Janssen as speaker of the newly created special interest groups on aperiodic crystals (http://www-xray.fzu.cz/sgip/aphome.html) within the European Crystallography Association discussed the mission and objectives, which will be followed during the next few years.