[en] Selected ternary tantalum-rich chalcogenide systems were systematically explored by application of high temperature synthesis techniques. The layered metal-rich chalcogenides Ta₂(Se,Te), Ta₂(S,Se), Ta₉(S,Se)₄, Ta₅(S,Se)₂, and (M,Ta)₅S₂ (M = Mo, W) were uncovered and characterized by means of X-ray diffraction. The phase relations in the tantalum-rich section of the Ta-S-Se system were unravelled and the homogeneity ranges of five sulfide selenides were delimited. Electrical resistivities of polycrystalline single phase samples were measured within the range 15 to 320 K. The structures of the phases represent specific tetragonal order variants of the b.c.c.-structure of the elemental metals. Two-dimensional fragments of b.c.c.-tantalum are sandwiched by layers of chalcogen Q, thus forming Ta₄Q₂ or (M,Ta)₅Q₂ slabs as found in Ta₂Se or (Nb,Ta)₅S₂. The cohesion of the slabs is, in accordance with the results of electronic band structure calculations (EH approximation) for Ta₂Se, provided by van der Waals interactions. The new structure type of Ta₉(S,Se)₄ results from a coherent chemical 1:1 intergrowth of Ta₄Q₂ and Ta₅Q₂. The structure was determined from X-ray intensities of a polycrystalline sample. The structural changes associated with the replacement of selenium by tellurium in Ta₂Se-like Ta₂Se_0.66Te_0.34 were studied in detail on the basis of a precise single crystal structure analysis. (orig.)

[en] Hf₂Te was prepared by arc-melting appropriate compressed mixtures of HfTe₂ and hafnium. The structure of the new hafnium-rich telluride was determined by means of powder diffractometry, R_B=0.0565. Hf₂Te adopts a Nb₂Se-type structure, monoclinic, space group C2/m, Z=8, Pearson symbol mS24, a=1516.3(2) pm, b=370.26(4) pm, c=1006.4(1) pm, β=90.50(1) . The structure comprises pairwise interpenetrating columns of trans-face-shared centred Hf₉ cuboids. The columns form puckered slabs which are interconnected by homo- and heteronuclear bonds. Tellurium atoms are one-sidedly coordinated by six hafnium atoms. The coordination configurations about the two distinct tellurium atoms represent Hf₆Te hypho-fragments of a tri-capped trigonal prismatic Hf₉Te closo-cluster. Characteristic features of four other M₂Q structure types are elucidated. The valence electron concentration available for metal-metal bonding together with the cohesive energy of the respective metal are found to control the formation of the various M₂Q metal partial structures. (orig.)

[en] X-ray diffraction is one of the most important method for obtaining information about the structure of proteins and thereby for gaining insight into fundamental biological and biochemical mechanisms. This seminar was dedicated to X-ray powder diffraction and was organized around 6 sessions: 1) what can powder diffraction do for proteins?, 2) adapting experimentally to proteins, 3) interpreting powder data, 4) the world of protein crystallography, 5) advancing methods for powder data analysis, and 6) transferable methods from single crystals. This document gathers the abstracts of the 23 papers presented. (A.C.)