Fundamental aspects of small-angle scattering technique are duly explained from the very basic points for the beginners and newcommers of this useful technique to study the strucuture of“Vernachlasisgten Dimensionen”.

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In the last two decades many types of small-angle X-ray scattering cameras have been developed, including facilities for synchrotron sources. The fundamental requirement of such facilities is to provide X-ray beams of high flux and narrow angular width, which permit intensity measurements at smaller angles. Here the general principles of design and construction of laboratory instrumentation are described together with the definitions of some specific parameters.

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During the past three decades, the old image of molecular conductors has been changed completely. Nowadays, molecular metals are regarded as clean systems with well-defined Fermi surfaces. X-ray diffraction studies have made a great contribution to this progress. Here a brief survey of our structural studies and development of new molecular metals and superconductors is presented. The main topics are, (1) Peierls distorted structure of partially oxidized platinum complex, (2) discovery of metallic complexes without one-dimensional platinum chains, (3) designing analysis of the first molecular superconductor, (4) discovery of pure π-acceptor superconductors, (5) band structure and low temperature crystal structure analysis and (6) novel highly conducting transition metal complex with extended π-conjugated ligands.

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On the idea of the material designing, we attempted to design a new crystal structure and succeeded to synthesize the new intermetallic compounds. A new family of the rare earth nickel boro-carbides (or boro-nitrides) and the present status of the material research for the intermetallic compounds has been reviewed.

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The spin ladder system Sr_14-xCa_xCu₂₄O₄₁ is reviewed from the viewpoint of relations be-tween the crystal structure and superconductivity under high pressure. The compound is a composite crystal, which consists of CuO₂ 1-D chain and Cu₂O₃ tow-leg ladder subsystems. As the interplay of the subsystems is increased with Ca substitution or pressurization, holes are removed from the 1-D chain to the ladder via locally formed apical oxygen bonds. Then, the superconductivity occurs owing to the hole doping into the ladder. The hole distribution, magnetic interaction, and electrical property of the normal state are also discussed in terms of the structural modulation.

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