Experimental determination of core electron deformation in diamond

Based on benchmark synchrotron powder X-ray diffraction data, the subtleties in the electron density of diamond are explored. A contraction of the core density inherently linked to covalent bond formation is experimentally observed.

Se-N chemistry: Revisiting an old molecule in the design of novel compounds

Chalcogenide chemistry is rich and diverse: The large variety of molecular sulfur and selenium compounds can be ascribed to their multiple stable oxidation states and large radius enabling high coordination. Sulfur-nitrogen chemistry is thoroughly explored and well-understood; polyimido sulfur species S(NR)n with charge m- (n = 2, 3, 4; m = 0, 2) are analogues of SOn molecules (with charge: m-) in which oxygen has been replaced by isovalent NR imido groups [1]. These compounds have been studied in depth and have been demonstrated to be versatile ligand systems which form multifaceted potentially catalytic metal complexes and compounds with lithium organics [2]. Selenium-nitrogen chemistry is comparatively less developed than sulfur-nitrogen chemistry despite of significant contributions to the field [3]. This may be ascribed to the rich redox chemistry of selenium in addition to its ability to polymerize, unfortunately none of these properties are easily controlled. A crucial parameter in the development of sulfur-nitrogen chemistry is attributed to the access to sulfur diimides S(NR)2 and sulfur triimides S(NR)3. Therefore, our starting point in exploring new directions of selenium-nitrogen chemistry was to revisit Se(NtBu)2 (tBu = tertbutyl), which has been used as ligand for metal complexes, but also discussed in large detail with respect to structural geometry and stability. Herein, we are presenting a study of selenium-nitrogen chemistry based on Se(NtBu)2.

Formation of γ-Fe2O3 in hydrothermal synthesis: In situ total scattering studies

The properties of metal oxide nanoparticles are highly dependent on particle characteristics such as size, crystallinity, and structural defects. To obtain particles with tailormade properties, it is crucial to understand the mechanisms that govern these characteristics during material synthesis. For this purpose, in situ studies of particle synthesis have proven powerful.[1] Here, in situ Total Scattering (TS) combined with in situ PXRD studies of the hydrothermal synthesis of γ-Fe2O3 (maghemite) from ammonium iron citrate will be presented. In situ TS with Pair Distribution Function (PDF) analysis has recently shown to be an efficient tool for understanding the fundamental chemical processes in particle crystallization.[2,3] The full γ-Fe2O3 crystallization process from ionic complexes over nanoclusters to crystalline particles is followed and material formation mechanisms are suggested. The study shows that the local atomic structure of the precursor solution is similar to that of the crystalline coordination polymer [Fe(H2citrate)(H2O)]n where corner sharing [FeO6] octahedra are linked by citrate. As hydrothermal treatment of the solution is initiated, clusters of edge sharing [FeO6] units form. Tetrahedrally coordinated iron subsequently appears in the structure and as the synthesis continues, the clusters slowly assemble into nanocrystalline maghemite. The primary transformation from amorphous clusters to nanocrystallites takes place by condensation of the large clusters along corner sharing tetrahedral iron units. The crystallization process is related to large changes in the local structure as the interatomic distances in the clusters change dramatically with cluster growth. The local atomic structure is size dependent, and particles below 6 nm are highly disordered. Whole Powder Pattern Modelling of the PXRD data shows that the final crystallite size (<10 nm) is dependent on synthesis temperature and that the size distribution of the particles broadens with synthesis time.

In- and ex situ PXRD studies of ZnO nanoparticle growth in sub-critical water

Zinc oxide (ZnO) is a material of great scientific and industrial relevance and is used widely in a variety of applications. Synthesis of ZnO nanoparticles can be performed by a wide range of methods resulting in a tremendous variety of sizes and shapes. Different in situ characterization methods have been used to investigate the ZnO formation under various synthesis conditions; these include numerous spectroscopic methods and small angle scattering. Common for these studies is that the primary focus has been to extract information on particle size and shape of ZnO, while a more rigorous microstructural and structural analysis has been lacking. Furthermore, the aforementioned studies have primarily been focused on soft chemical synthesis methods, at low temperatures and in non-aqueous media, thus omitting the widely used environmentally benign and versatile hydrothermal method. In the present work the formation of ZnO during hydrothermal synthesis has been followed using in situ powder X-ray diffraction (PXRD) combined with Rietveld refinement, thus enabling the extraction of crystallographic as well as microstructural information during the formation and growth of ZnO. Supporting ex situ syntheses and characterization by electron microcopy, high resolution PXRD and other techniques have been used to corroborate the findings from the in situ experiments. Mapping out a vast parameter space has led to a deeper understanding of the intricate mechanisms governing the nucleation and growth of ZnO nanoparticles during hydrothermal synthesis. Among the parameters studied were the influence of temperature, type of base used and the influence of different ionic salts as synthesis directing agents. The various synthesis parameters were found to influence the following structural and microstructural features: crystallite shape, morphology and size as well as the twin-fault concentration, degree of doping and crystallinity.