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Structure and chemical composition of intermetallic phases in unmodified and Sr-modified Al-10Si-0.3Fe casting alloys based on pure elements are identified by transmission electron microscopy and energy-dispersive X-ray spectroscopy. A three-dimensional characterization of intermetallic phases is performed by focused ion beam tomography. Both alloys were found to contain Fe-rich α-Al 14 Fe 3 Si 2 with a bcc structure and the τ 2 phase Al 4.5 FeSi, also called γ phase AlFeSi and both exhibit the “Chinese script” morphology in two dimensions, appearing as complex shaped objects in three dimension visualizations. The crystal structure of the τ 2 phase is shown to be trigonal R -centred rather than monoclinic as claimed by all published studies. It is related to the structure of R phases such as Mn 85.5 Si 14.5 . In the Sr-modified alloy, the tetragonal δ-Al 4 FeSi 2 phase is observed, which appears as thin platelets in 3D. No monoclinic β-Al 5 FeSi phase is found in any of the alloys unlike in industrial alloys that contain further impurities (Mn, Cr, Cu, P). Thus, the common β-phase is not a feature of the pure Al-Si-Fe system. In summary, addition of the modifier strontium to Al-10Si-0.3Fe alloys containing no further alloying elements markedly promotes the formation of δ-Al 4 FeSi 2 , but suppresses the formation of α-Al 14 Fe 3 Si 2 , whereas τ 2 phase Al 4.5 FeSi is found in similar fractions in both alloys.

The efficient green phosphor Ba(3)Si(6)O(12)N(2):Eu(2+) and its solid-solution series Ba(3-x)Sr(x)Si(6)O(12)N(2) (with x approximately = 0.4 and 1) were synthesized in a radio-frequency furnace under nitrogen atmosphere at temperatures up to 1425 degrees C. The crystal structure (Ba(3)Si(6)O(12)N(2), space group P3 (no. 147), a = 7.5218(1), c = 6.4684(1) A, wR2 = 0.048, Z = 1) has been solved and refined on the basis of both single-crystal and powder X-ray diffraction data. Ba(3)Si(6)O(12)N(2):Eu(2+) is a layer-like oxonitridosilicate and consists of vertex-sharing SiO(3)N-tetrahedra forming 6er- and 4er-rings as fundamental building units (FBU). The nitrogen atoms are connected to three silicon atoms (N3), while the oxygen atoms are either terminally bound (O1) or bridge two silicon atoms (O2) (numbers in superscripted square brackets after atoms indicate the coordination number of the atom in question). Two crystallographically independent Ba(2+) sites are situated between the silicate layers. Luminescence investigations have shown that Ba(3)Si(6)O(12)N(2):Eu(2+) exhibits excellent luminescence properties (emission maximum at approximately 527 nm, full width at half maximum (FWHM) of approximately 65 nm, low thermal quenching), which provides potential for industrial application in phosphor-converted light-emitting diodes (pc-LEDs). In-situ high-pressure and high-temperature investigations with synchrotron X-ray diffraction indicate decomposition of Ba(3)Si(6)O(12)N(2) under these conditions. The band gap of Ba(3)Si(6)O(12)N(2):Eu(2+) was measured to be 7.05+/-0.25 eV by means of X-ray emission spectroscopy (XES) and X-ray absorption near edge spectroscopy (XANES). This agrees well with calculated band gap of 6.93 eV using the mBJ-GGA potential. Bonding to the Ba atoms is highly ionic with only the 4p(3/2) orbitals participating in covalent bonds. The valence band consists primarily of N and O p states and the conduction band contains primarily Ba d and f states with a small contribution from the N and O p states.

The present article reviews recent advances in synthesis of novel phases in the ternary Si-C-N system. A dense carbon nitride phase, C 2 N 2 (NH), was synthesized for the first time at high pressures and high temperatures in a laser heated diamond anvil cell (LH-DAC). Based on results of electron diffraction, EELS- and SIMS-measurements combined with theoretical calculations the structure of this new C-N-H compound was analysed to be a defect wurtzite structure of the sinoite (Si 2 N 2 O)-type. Farther, a variety of amorphous SiCN phases and the first ternary crystalline phases, namely Si(NCN) 2 and Si 2 N 2 (NCN), were synthesized at ambient pressure. In general, the high-pressure polymorphs of Si-C-N materials are predicted to exhibit a unique combination of high hardness, thermal stability and oxidation resistance with interesting optoelectronic properties.

(Figure Presented) Extreme chemistry: The carbon nitride imide C 2 N 2 (NH) is synthesized from the single-source precursor 1-cyanoguanidine under high-pressure and high-temperature conditions in a laser-heated diamond-anvil cell. Characterization of single crystals recovered at ambient conditions reveals that the new compound adopts a defect wurtzite structure (see picture). © 2007 Wiley-VCH Verlag GmbH & Co. KGaA.

The hydrogenation of dienes such as 1,3-butadiene, cyclooctadiene, and of acetylenic hydrocarbons on Pd catalysts shows high reaction rates and consequently, a strong influence of mass transfer on the selectivity of the intermediate alkene or cycloalkene product. 100 % selectivity towards (cyclo)-alkene hydrogenation is achieved for the gas phase when the Thiele modulus is equation image, where L is the thickness of the active layer and Deff is the effective diffusion coefficient of the diene. The interdependencies expressed by this formula were studied in detail using model catalysts with regular pores of uniform length and diameter and perpendicular to the surface. These catalysts were prepared by anodic oxidation of aluminium wires and immobilization of the active Pd. For the liquid phase procedure of selective hydrogenation, a reaction mass transfer model has been derived in order to compare the gas phase and liquid phase procedures, in particular with respect to the selectivity. The hydrogenation of 1,3-cyclooctadiene and of 1,3-butadiene were studied for both procedures employing the same catalyst. The rate of hydrogenation can be represented for both cases by the identical kinetic equation r1 = k1 cH2. This result is interpreted by assuming that the access of hydrogen to the surface through the dense layer of adsorbed diene is the rate determining step.

The controlled fabrication of poly- and single-crystalline Au nanowires is reported. In polycarbonate templates, prepared by heavy-ion irradiation and subsequent etching, Au nanowires with diameters down to 25 nm are electrochemically synthesized. Four-circle X-ray diffraction and transmission electron microscopy measurements demonstrate that wires deposited potentiostatically at a voltage of -1.2 V at 65 °C are single-crystalline and oriented along the [110] direction. By reverse-pulse electrodeposition, wires oriented along the [100] direction are grown. The wires are cylindrical over their whole length. The morphology of the caps growing on top of poly- and single-crystalline wires is a strong indication of the particular crystalline structure of the nanowires.

By the substitution of one methyl group in Neopentane C(CH3)4 with a methylchlorid group the globular sphere is expanded in 1-chloro-2,2-dimethylpropane (CH3)3C(CH2Cl). With the aid of DSC measurements, X-ray powder diffraction, 1H NMR and 35Cl NQR measurements two orientationally disordered (plastic) phases were established. The low temperature structure was solved and a structural model of phase II is proposed. A mechanism to describe the reorientation in the different phases is given as well as a connectivity scheme between the phases is discussed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Poly- and single-crystalline Bi nanowires are fabricated by electrochemical deposition in etched ion-track membranes. Two deposition parameters, voltage and temperature, strongly influence the nanowires' morphology and texture. X-ray diffraction (XRD) and transmission electron microscopy (TEM) reveal that potentiostatically deposited nanowires are textured, the texture increasing for wires deposited at higher temperatures and smaller overpotentials. At T = 60 °C and low overpotentials, single-crystalline wires are produced. Wires deposited with reverse pulses exhibit a texture, which is more pronounced for shorter cathodic cycles and higher anodic voltages. They consist of several crystals of size at least .

The roughening of interfaces as a function of layer thickness and magneto transport properties have been investigated on sputter-deposited Fe/Ni 75 B 25 multilayer films. X-ray reflectivity data were recorded for Ni 75 B 25 (72 nm) film and for [Fe(2 nm)/Ni 75 B 25 (2 nm)] 16 and [Fe(4 nm)/Ni 75 B 25 (4 nm)] 8 multilayer films. A power law dependence of the interfacial width of growing Fe/Ni 75 B 25 interfaces was observed. The resulting growth exponents β were found to be in the range of 0.55–0.58 in the initial growth stage of the multilayer with lower Fe/Ni 75 B 25 repetition thickness and at approximately 0.34 for multilayer with higher repetition thickness. The growth exponents were compared with theoretical calculations. High resolution electron microscopy revealed the columnar growth of the Fe/Ni 75 B 25 multilayer. Additionally, an increase of magnetoresistance was observed by the multilayering of Ni 75 B 25 films with Fe interlayers.

The crystal structure of yttrium rhenium oxide, Y7ReO14−δ, is a 2×2×2 superstructure of the CaF2 structure, space group Fm 3 m , a=10.4770(14) A. The 32 cations within the unit cell are distributed with yttrium on the (4a)- and (24d)-sites and with rhenium on the (4b)-site. The 64 oxygen atoms occupy two (32f) sites (x,x,x), O(1) with x1=0.1351(9) and O(2) with x2=0.6054(11), in the undistorted fluorite structure x=0.125 and 0.625. The site occupation factor for the O(2) site is only 77(8)% in agreement with the maximum of 75% for δ=0 in the proposed stoichiometry. The electrical DC conductivity, measured on a single crystal, reveals semiconducting behavior between 165 and 265 K with a band gap of 157.4 meV.

The formation of carbon nanotubes via explosive decomposition of an energetic precursor, 2,4,6-triazido-s-triazine C3N12, was investigated with respect to the presence of the transition metals Fe, Ni, Cu, Ti and the degree of confinement of the explosive charge. The carbonaceous detonation products were characterized by transmission and scanning electron microscopy, energy dispersive X-ray analysis and infrared absorption spectroscopy. Multi-walled carbon nanotubes with diameters from 50 to 150 nm and a variety of morphologies were found. Metal particles in the tubes and at some of the tube ends indicate a catalytic growth mechanism.

The nature of a new zeolite overgrowth has been characterized. Two overgrown samples were studied. Each sample was made up of the phases faujasite and EMT. By Rietveld refinement of the powder patterns the structure of both phases including the distribution of cations in the overgrowth was determined as well as the weight fractions of the phases in both samples. The growth of FAU crystals on the surface of EMT crystals is epitactic, as shown by HRSEM images. The epitaxial relation is [111] FAU //[001] EMT , (-110) FAU //(110) EMT . The true atomic interfacial model of the interface between faujasite and EMT is still subject of further studies.

High-pressure synthesis allows both fundamental and materials science research to gain unprecedented insight into the inner nature of materials properties at extreme environment conditions. Here, we report on the high-pressure synthesis and characterization of γ-Ca(3)N(2) and the high-pressure behavior of Mg(3)N(2). Investigation of M(3)N(2) (M = Ca, Mg) at high-pressure has been quite challenging due to the high reactivity of these compounds. Ex situ experiments have been performed using a multianvil press at pressures from 8 to 18 GPa (1000-1200 °C). Additional in situ experiments from 0 to 6 GPa (at RT) at the multianvil press MAX 80 (HASYLAB, Beamline F.2.1, Hamburg) have been carried out. The new cubic high-pressure phase γ-Ca(3)N(2) with anti-Th(3)P(4) defect structure exhibits a significant increase in coordination numbers compared to α-Ca(3)N(2). Contrary, Mg(3)N(2) shows decomposition starting at surprisingly low pressures, thereby acting as a precursor for Mg nanoparticle formation with bcc structure. Soft X-ray spectroscopy in conjunction with first principles DFT calculations have been used to explore the electronic structure and show that γ-Ca(3)N(2) is a semiconductor with inherent nitrogen vacancies.

The self-assembly of In(2)O(3) nanoparticles into hollow microspheres is realized using in situ generation of gas microbubbles due to the melting and decomposition of ammonium nitrate in precipitates synthesized via hydrolytic routes.

A new zeolite overgrowth was synthesized by adding an amount of as-synthesised EMT crystals to a synthesis gel of mazzite (MAZ). After crystallisation, the overgrowth sample was made up of two major phases namely MAZ and faujasite (FAU). EMT crystals were transformed into FAU during the crystallisation process of the overgrowth sample. Bundles of needle-like crystals of mazzite overgrew faujasite particles. Weight fractions of phases in the overgrowth, the crystal structure of the phases and the distribution of cations in the overgrowth are determined. The growth of mazzite crystals onto the surface of faujasite crystals is not well oriented and a reliable epitaxial relationship between the FAU support and the overgrown material was therefore not determined.

The new compound Ga2.81O3.57N0.43 was crystallized under high-pressure / high-temperature conditions in a spinel-type structure from a prestructured gallium oxonitride ceramic, which was obtained from the single-source molecular precursor [Ga(OtBu)2NMe2]2 by thermal treatment in an ammonia atmosphere. The optimized precursor-derived gallium oxonitride ceramic remains nanocrystalline up to 600 °C and can be transformed at 7 GPa and 1100 °C into the crystalline phase Ga2.81O3.57N0.43. The structure, homogeneity, and nitrogen to oxygen ratio were determined using TEM coupled with an electron energy loss spectrometer (EELS) and an energy dispersive X-ray (EDX) spectrometer. For phase analysis and structure confirmation, X-ray powder diffraction data were measured.