This article briefly reflects the history and development of the Young Crystallographers as work group of the German Crystallographic Society within the last decade. It presents the preface to this special issue Spotlight on Germany's Young Crystallographers.

Crystal Research and TechnologyVolume 56, Issue 6 2100066 Obituary Ekkehart Tillmanns (1941 – 2020) Peter Paufler, Peter Paufler Technische Universität DresdenSearch for more papers by this authorDirk C. Meyer, Dirk C. Meyer Technische Universität Bergakademie FreibergSearch for more papers by this author Peter Paufler, Peter Paufler Technische Universität DresdenSearch for more papers by this authorDirk C. Meyer, Dirk C. Meyer Technische Universität Bergakademie FreibergSearch for more papers by this author First published: 10 June 2021 https://doi.org/10.1002/crat.202100066Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article. Volume56, Issue6June 20212100066 RelatedInformation

Abstract—An extended (3 × 3) classification of polymorphic transformations is proposed with the zeroth coordination sphere added to spheres I and II according to Buerger. Thus, the transformable coordination sphere is 0 for an atom or ion, 1 for a coordination polyhedron, and 2 for the nearest surroundings of a coordination polyhedron. The other classification parameter is determined by Buerger’s energetic transformation barrier. As well as reconstructive and deformation transformations, transformations of intermediate types occur, which are characterized by disordering of structural units (atoms, molecules, and other atomic complexes). The electron transitions within an atom, the variation of atomic spin, and magnetic ordering of atoms in a crystal structure are considered as examples of polymorphic transformations with the variations in the zeroth coordination sphere. The disordering transformations are illustrated by substitution–jumps of structural units and their free or hindered rotation. The concept of “polymorphism” for chemical elements is developed.

At the dawn of crystal structure analysis, the close personal contact between researchers in Russia and Germany, well documented in the “Zeitschrift für Krystallographie und Mineralogie”, contributed significantly to the evolution of our present knowledge of the crystalline state. The impact of the Russian crystallographer E. S. Fedorov upon German scientists such as A. Schoenflies and P. Groth and the effect of these contacts for Fedorov are highlighted hundred years after the death of the latter. A creative exchange of ideas paved the way for the analysis of crystal structures with the aid of X-ray diffraction.

Abstract The English crystallographer William Barlow is famous for two achievements, both published in German, in Zeitschrift für Krystallographie und Mineralogie between 1894 and 1901. They concern the derivation of all possible symmetrical arrangements of points in space and the idea to represent crystal structures by replacing points by spheres. His results had an impact upon crystal structure modelling and describing crystal morphology. Utilizing self-made models, he found the 230 space group types of symmetry obtained earlier by both E. S. Fedorow and A. Schoenflies in a different manner. The structures he proposed before the discovery of X-ray diffraction served in some cases as starting point for the interpretation of diffraction patterns thereafter.

A specimen of high-carbon nitrogen-doped steel has been synthesized to supplement previous studies on wootz-like steels. A comparison of different states of material as well as one of distinct methods of hardness testing has been performed. Electron microscopy of the specimens’ microstructure revealed nano-structuring similar to that observed with ancient sabers. Part of them was annealed so that the nano-structures dissolved. Nano-hardness values derived under ambient conditions from indentation as well as from scratch tests were determined and related to the microstructure prior to and after annealing. The disappearance of nanostructuring led to a significant drop of hardness. The ratio of indentation to scratch hardness proved a suitable indicator of hardening. From hardness as function of penetration depth and from friction as function of time and normal load various quantitative features of the mechanical properties and of the deformation process have been evaluated. When modeling friction, sliding and plowing parts have been distinguished quantitatively. Enhanced adhesion forces were attributed to surface layers.

The molecular structure of collagen type 1 can be understood as the result of evolutionary selection in the process of formation of calcium phosphate based biocomposites acting as load bearing components in living organisms. The evolutionary selection fulfills the principle of 'survival of the fittest' in a particular biological environment. Disk-like post-nucleation complexes of Ca2(HPO4)3 2- organized in ribbon-like assemblies in the metastable octacalcium phosphate (OCP) phase, and Ca3 triangles in the stable HAP phase had formed the crystallographic motifs in this selection process. The rotational as well as the translational symmetry of the major tropocollagen (TC) helix agree nearly perfectly with the corresponding symmetries of the OCP structure. The sequence of (Gly-X-Y) motifs of the three α chains constituting the TC molecule enables an optimized structural fit for the nucleation of Ca3 triangles, the directed growth of nanostructured OCP, and the subsequent formation of hydroxyapatite (HAP) in collagen macrofibrils by a topotaxial transition. The known connection between genetic defects of collagen type 1 and Osteogenesis imperfecta should motivate the search for similar dependences of other bone diseases on a disturbed molecular structure of collagen on the genetic scale.

This study is aimed at the comparative analysis of structure sensitive properties of alkali borate and borosilicate glasses and crystals. Among the properties under consideration are density and refractive index. The comparison of physical properties between crystals and glasses considers the dependence on alkali content and the size of the alkali cation. New experimental data on density and refractive index of potassium and rubidium borate and borosilicate glasses are presented. The mass density measurements were performed by employing the method of hydrostatic weighing. The refractive index measurements were carried out on a polarization microscope with a series of immersion liquids, using the Becke line method. The compared crystal density data were calculated from the crystal structures.

Data mining of lattice and structure parameters with the aid of the Inorganic Crystal Structure Database revealed a correlation between the abundance of parameter values observed and geometric features of interatomic distances. Working out this finding enabled distinguished lattice and structure parameters to be attributed to special bonds. The method is illustrated dealing with two examples of a hexagonal and a cubic structure type.

Powder alpha-VOSO4 was prepared by dehydration of VOSO4 center dot 3H(2)O. beta-VOSO4 was synthesized by boiling of V2O5 in H2SO4. Thermal behaviour of VOSO4 center dot 3H(2)O, alpha- and beta-VOSO4 modifications is studied by high-temperature powder X-ray diffraction and thermal analysis, including two-step dehydration of VOSO4 center dot 3H(2)O, formation of alpha-VOSO4, thermal expansion and decomposition of both modifications into V2O5. Higher anisotropy of thermal expansion of the tetragonal alpha-modification alpha(c) = 39(2).10(-6) K-1 along the vanadyl ion and alpha(a) = 2.4(6).10(-6) K-1 in the perpendicular direction) comparing to the orthorhombic beta-modification (alpha(a) = 20.2(7), alpha(b) = 2.8(8), alpha(c) = 17.8(4).10(-6) K-1) is explained from a crystal chemical point of view.

The temperature-dependent evolution of the glass into a crystalline phase is studied for a rubidium borosilicate glass of composition 16.7 Rb2O center dot 16.7 B2O3 center dot 66.6 SiO2 employing X-ray diffraction (XRD) data. A glass sample was prepared by melt quenching from 1500 degrees within 0.5 hour. The glass sample was step-wise annealed at 13 distinct temperatures from 300 degrees C up to 900 degrees C for 1 h at every annealing step. To investigate changes in the glass structure, angle-dispersive XRD was applied by using an energy-resolving semiconductor detector. The radial distribution functions (RDFs) were calculated at every stage. For polycrystalline states the crystal structure of the samples with different thermal history was refined using the Rietveld method. Comparing correlation distances estimated from RDFs of glass and polycrystalline samples and mean interatomic distances calculated for polycrystalline samples by using atomic coordinates after Rietveld refinement, it is concluded that the borosilicate glass under study is converted into the crystalline state in the temperature range of 625-750 degrees C (i.e. in the temperature range close to the glass transition range 620-695 degrees C as determined by differential scanning calorimetry by using of heating rate of 20 K/min) at an average heating rate of about 0.35 K/min. When the heating rate is increased up to 10 or 20 K/min, the crystallisation temperature shifts sharply up to 831-900 degrees C and 878-951 degrees C, respectively. XRD data give evidence that distinctive traces of cubic RbBSi2O6 appear from glass at about 625 degrees C and a two-phase range exists up to 750 degrees C. After annealing at higher temperatures (800-900 degrees C) the crystal structure practically does not change any more.

For technologically important borosilicate glass and crystalline phases, the structure of K1-xRbxBSi2O6 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) solid solutions has been investigated employing X-ray diffraction data. Glass samples were prepared by a melt quenching from 1250-1300 degrees C for 0.5-1 hour. For glass samples glass transition (T-g), crystallization (T-cryst) and melting (T-m) temperatures were determined by differential scanning calorimetry. To investigate the glass structure, angle-dispersive X-ray diffractometry was applied by using an energy-resolving semiconductor detector. The radial distribution functions (RDFs) were calculated. Comparing correlation distances of glass RDFs and mean interatomic distances calculated for polycrystalline samples, the conclusion is drawn that in the glass state not only TO4 (T = Si, B) tetrahedra as stable structure-units but two corner sharing tetrahedra and apparently fourfold rings from tetrahedra exist.

Initiated by Gustav E.R. Schulze, pioneering experimental and theoretical work on Laves phases was done in Dresden/East Germany after World War II, which was then part of the German Democratic Republic GDR behind the former Iron Curtain.

The crystal chemistry of K1-xRbxBSi2O6 mixed boroleucites has been studied by means of X-ray powder diffraction at room temperature. Boroleucites under study were prepared by crystallization from glass at 700-1000 degrees C for a few to 1000 hours time. First glass crystallization process starts from formation of two solid solutions: one of them is related to space group I (4) over bar 3d, another to Ia (3) over bard. After heat-treatment at 950 degrees C/51 h, K1-xRbxBSi2O6 solid solutions crystallize in the cubic space group I (4) over bar 3d, in a wide range of compositions as Rietveld refinement of the structures of solid solutions (nominal composition x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) demonstrated. Within a narrow range of x near 0.2 area of immiscibility was found. Under substitution of K by Rb structural parameters (cubic lattice parameter a, (K,Rb)-O bond lengths in (K,Rb)O-15 polyhedron, (K,Rb)-(K,Rb) bond lengths, (K,Rb)-O-(K,Rb) angles between (K,Rb)O-15 polyhedra, and T-O-T angles between tetrahedra) of the phase increased nonlinearly due to cationic size rising. Non-linear behavior of the composition dependence of structural parameters was observed near x = 0.2 divided by 0.4. A comparative analysis has been made for the K-Rb-Cs substitution in the two sequential boroleucite series KBSi2O6-RbBSi2O6 and RbBSi2O6-CsBSi2O6.

In the present investigation, samples of five qualities of ultra-high carbon crucible or wootz steel - two of them genuine Damascus blades from the 17th century have been compared with respect to their response to nanoindentation. Values of nanohardness and elastic modulus derived that way were discussed in the light of microstructure and phase content. Cementite particles of different shape and distribution embedded in a pearlitic or divorced eutectoid matrix govern the mechanical behaviour. Testing of the nanoscratch resistance supports the idea of a grater-like effect of those wootz steel blades. Specimens of synthetic wootz and of original Damascus sabres showed the maximum response of these composite materials to elastic and plastic indentation.

The nanohardness H of multilayer specimens TiC/VC@Si and TiC/VC@Sapphire prepared by Pulsed-Laser-Deposition is investigated to check the existence of a superlattice effect as known from TiN/VN multilayers. In the present work the multilayer period thickness λ varies between 1.34 nm and 24.8 nm (total layer thickness t ≈ 200 nm). Unlike Young's modulus E, H is enhanced, regardless of t, by covering Si as well as sapphire with a TiC/VC multilayer; the relative load carrying capacity being larger for Si. The maximum value of H obtained is 38 GPa for TiC/VC@Sapphire. It is observed for a multilayer thickness of λ ≈ 10 nm. Hardness of TiC/VC@Sapphire obeys, after annealing, a Hall-Petch relation H = 35.25 + 6.945 λ–0.5 (H in GPa und λ≥ 10 nm). From orientation dependent X-ray absorption fine structure and X-ray reflection records, short-range order and layer geometry are derived. These analyses reveal a continuous approach of interatomic distances Ti-C and V-C for deceasing multilayer periods. High-resolution transmission electron microscopy shows that multilayers are nanostructured, i.e., not only TiC/VC phase boundaries but also subgrains represent obstacles against plastic deformation. Dislocations play a major role as sources of internal stress and vehicles of plasticity.

Using high-resolution electron microscopy, we have found in a sample of Damascus sabres from the 17(th) century both cementite nanowires and carbon nanotubes. These might be the missing link between the banding and ancient recipes to make that ultrahigh carbon steel. The sample considered belonged to the wootz-type of Damascus steel which is fundamentally different from welded Damast. The nanotubes have only been revealed after dissolution of the sample in hydrochloric acid. Some remnants showed not yet completely dissolved cementite nanowires, suggesting that these wires were encapsulated by carbon nanotubes. Only recently. considerable progress has been achieved in reproducing the process of making the characteristic pattern of wootz. We propose a connection between impurity segregation, nanotube formation, nanotube filling with cementite, cementite wire growth, and formation of large cementite particles. Needless to say that the presence of a nanostructure will have ail impact upon the mechanical properties.