TEV (Thermal Expansion Visualizing) is a user-friendly program for the calculation of the thermal expansion tensor αij from diffraction data. Unit cell parameters determined from temperature dependent data collections can be provided as input. An intuitive graphical user interface enables fitting of the evolution of individual lattice parameters to polynomials up to fifth order. Alternatively, polynomial representations obtained from other fitting programs or from the literature can be entered. The polynomials and their derivatives are employed for the calculation of the tensor components of αij in the infinitesimal limit. The tensor components, eigenvalues, eigenvectors and their angles with the crystallographic axes can be evaluated for individual temperatures or for temperature ranges. Values of the tensor in directions parallel to either [uvw]'s of the crystal lattice or vectors (hkl) of reciprocal space can be calculated. Finally, the 3-D representation surface for the second rank tensor and pre-or user-defined 2-D sections can be plotted and saved in a bitmap format. TEV is written in JAVA. The distribution contains an EXE-file for Windows users and a system independent JAR-file for running the software under Linux and Mac OS X. The program can be downloaded from the following

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Na 6 Si 2 O 7 -The Missing Structural Link Among Alkali Pyrosilicates. -The structure of the title compound is determined by single crystal XRD for the first time. Na6Si2O7 crystallizes in the triclinic space group P1 with Z = 8. A characteristic feature of the crystals obtained from a stoichiometric Na2O/SiO2 melt is a twinning by reticular pseudomerohedry, which simulates a much larger monoclinic unit cell. Na6Si2O7 belongs to the family of sorosilicates, i.e. it is based on Si 2 O 7 groups, which are arranged in layers parallel to (100). -(KAHLENBERG*, V.; LANGREITER, T.; ARROYABE, E.