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STOE USER TALK: TARGETED SYNTHESIS OF METASTABLE OXYFLUORIDES BY LABORATORY IN SITU XRD

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Ruddlesden-Popper (RP) compounds (general formula (AX)(ABX3)n) are a current hot topic in materials research as they possess a high flexibility regarding their anion composition. This makes them an ideal platform for experiments which aim on tuning of physical properties for example by substitution of oxygen by fluorine (O2-/2F-) yielding the corresponding oxyfluorides. The targeted synthesis of such new RP-oxyfluorides is a challenging task as most of them are metastable and therefore suitable synthesis conditions are mostly found by numerous trial and error experiments. Understanding the formation chemistry of oxyfluorides is therefore crucial for optimizing reaction conditions and gaining access to new metastable products.
For the fluorination of La2NiO4 with PVDF laboratory in situ XRD experiments were established as highly useful tool for obtaining optimized reaction conditions. These investigations were additionally combined with in situ neutron powder diffraction to reveal a complex fluorination pathway involving four reaction intermediates. This talk is about the application of such in situ XRD fluorination experiments for the preparation of new oxyfluorides (La2NiO2.5F3,1 La2CoO3F3, La2(Ni,Cu)O3F22,3,4) as well as their less stable reaction intermediates.

46 Min.

STOE USER TALK: HOW INTEGRATE3D HELPS SEEING SPIN STATES: A USER PERSPECTIVE

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The investigation of spin states of metal centers within a complex remains a challenge to this day, despite improvements in model quality and sophistication. The new Integrate3D software allows the use of diffraction data to the fullest extend, allowing a much clearer distinction of residual density features left in a structure model (right, Integrate 3D) from noise introduced by the integration (left, X-Area integrate). Using Integrate3D we were able to measure in-house data that can indisputably distinguish two spin states of an iron center in Mohr’s salt-hexahydrate.
43 min

STOE USER TALK: STRUCTURE SOLUTION FROM POWDER DIFFRACTION DATA

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Polyoxometallates are known to form a plethora of large polyanions, the number of which even grows with the introduction of heteroatoms. They are frequently synthesized under solvothermal conditions, but with suitable precursors even at room temperature reactions can be carried out. Under such conditions the growth of single crystals is not always possible and structure solution from powder diffraction data remains the only way to determine the crystal structure. Herein, the challenging case of the arsenato polyoxovanadate [Ni(en)3]2[V12As8O40(H2O)]x4H2O is presented, where both lab and synchrotron based powder diffraction data were employed for structure solution and refinement.

35 min.

STOE USER TALK: STRUCTURE DETERMINATION OF [NH4][SeCN] AND ITS REACTIVITY TOWARDS Ag[SeCN]

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About 200 years ago, ammonium cyanate, [NH4][OCN], was obtained by Liebig and Wöhler as a fluffy, white powder from the reaction of dry ammonia with cyanic acid. They also noticed its rearrangement at room temperature into urea, [NH2]2CO, a compound which has the same sum formula as ammonium cyanate.[1,2] From this the concept of isomerism was deduced and remains unchanged until today […]

26 min.

STOE USER TALK: OVERWEIGHT AND DIM LIT: X-RAY DIFFRACTION BECOMING CHALLENGED BY PD DR. CONSTANTIN HOCH, LMU MUNICH

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Absorption correction is today a highly automated process performed in the course of data reduction, on most diffractometer software suites directly after the measurement. In the utmost cases, this process is not handled with the required care, and by this considerable systematic errors can be introduced into the data sets. The impacts of missing or wrong absorption corrections are subtile but inflict all structure parameters, from standard deviations of atomic parameters and residual electron densities to R values. It is of high importance to rationalise functionality and methods of absorption correction in order to avoid systematic errors. A brief overview is given on the theoretical background and different methods of absorption correction algorithms. Some examples from our research on amalgams showing unusually high absorption effects are given to illustrate problems of absorption and how to overcome them.

54 min.

USER TALK: COMPLEXITY IN STRUCTURES DRIVEN BY ION DYNAMICS

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Solid ion conductors are fascinating materials for energy conversion and storage applications. Due to their intrinsic properties and especially their high ion mobility in the lattice they are often characterized by complex crystal structures, polymorphism and the loss symmetry during structural phase transitions. This last aspect often causes twinning and demands the collection of precise data and the usage of group-subgroups relations to solve and understand their crystal structures. Beside the structural features of a selection of solid ion conductors discussed in this presentation also intriguing electronic property changes can occur that are closely related to the ion dynamics and structure changes upon heating or cooling of such materials. In this talk we present a series of copper and silver ion conductors that also show reasonable electronic conductivities which characterize them as mixed-conducting semiconductors. […]

55 min.