High resolution X-ray and neutron diffraction of super- and disorder in decagonal Al-Co-Ni

Synchrotron measurements at DESY and ESRF of decagonal quasicrystals with t he nominal composition Al70Co15Ni15 and Al72Co16Ni12, show that Bragg refle ctions with high IH,il values are surrounded by up to four weak subsidiary peaks. The positions of these additional peaks depend solely on the positio n of the Bragg reflection in the reciprocal perpendicular subspace and can be explained by a linear phason strain model. This model sheds new light on the current superorder models [K. Hradil et al. Phil. Mag. A 79 (1999) 196 3] and is a further step towards an understanding of the real structures of decagonal quasicrystals. (C) 2000 Elsevier Science B.V. All rights reserve d.