No abstract

XDSAPPis an expert system and graphical user interface (GUI) for the automated processing of diffraction images using theXDSprogram suite and other programs. The latest major update and the extension of the program are presented here. The update includes new features, as well as improvements in the GUI and the underlying decision-making system.XDSAPPis freely available for academic users.

A displacive, 2 nd order structural phase transition at T s =395 K from space group I4 2 m below T s to I 4/m c m above T s has been discovered in the two-dimensional spin dimer compound SrCu 2 (BO 3 ) 2 . The temperature evolution of the structure in both phases has been studied by Xray diffraction and Raman scattering, supplemented by differential scanning calorimetry and SQUID magnetometry. The implications of this transition and of the observed phonon anomalies in Raman scattering for spin-phonon and interlayer coupling in this quantum spin system will be discussed.

Superstructure reflections have been observed in the room-temperature X-ray diffraction pattern of BaCuSi(2)O(6), barium copper disilicate. The tetragonal structure has a fourfold unit-cell volume compared with the original structure determined by Finger et al. At T(s) = 610 K BaCuSi(2)O(6) undergoes a structural phase transition upon which the superstructure reflections disappear. The description of the structure in the larger cell removes the crystal-chemical inconsistencies observed for the original structure.