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Type Structure (type + structure)
Selected AbstractsChemInform Abstract: The Lanthanoid Osmium Gallides Er2Os3Ga10 and Tm2Os3Ga10 with Yb2Ru3Ga10 -Type Structure.CHEMINFORM, Issue 34 2009Wolfgang Jeitschko Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Synthesis, Cation Ordering, and Magnetic Properties of the (Sb1-xPbx)2 (Mn1-ySby)O4 Solid Solutions with the Sb2MnO4 -Type Structure.CHEMINFORM, Issue 21 2005Artem M. Abakumov Abstract For Abstract see ChemInform Abstract in Full Text. [source] Ba2Ir3O9: A New 5d Mixed-Valence Metallic Oxide with KSbO3 -Type Structure.CHEMINFORM, Issue 6 2005Yoichi Kawamura Abstract For Abstract see ChemInform Abstract in Full Text. [source] Syntheses and Structures of Compounds with YBaCo4O7 -Type Structure.CHEMINFORM, Issue 28 2004Martin Valldor Abstract For Abstract see ChemInform Abstract in Full Text. [source] New Pnictides with the CaAl2Si2 Type Structure and the Stability Range of This Type.CHEMINFORM, Issue 15 2003Franziska Wartenberg Abstract For Abstract see ChemInform Abstract in Full Text. [source] Moessbauer Studies and Magnetic Properties of the Novel Ternary Europium Pnictides LiEuPn (Pn: P, As, Sb, Bi) with TiNiSi Type Structure.CHEMINFORM, Issue 35 2002M. Prill Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Ternary Lanthanoid Ruthenium Gallides with a High Gallium Content: Ln2Ru3Ga10 (Ln: Yb, Lu) with a New Structure Type and LnRu2Ga8 (Ln: La,Nd) with CaCo2Al8 -Type Structure.CHEMINFORM, Issue 5 2002Martin Schlueter Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: New Ternary Rhodium- and Iridium-Phosphides and -Arsenides with U4Re7Si6 Type Structure.CHEMINFORM, Issue 37 2001A. Wurth Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Cu1.45Er0.85S2: A Copper(I) Erbium(III) Sulfide with Cation-Deficient CaAl2Si2 -Type Structure.CHEMINFORM, Issue 16 2001Petra Lauxmann Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Growth and characterization of LiCaGaF6CRYSTAL RESEARCH AND TECHNOLOGY, Issue 1-2 2005E. Sani Abstract Optically clear LiCaGaF6 (LiCGaF) single crystals up to 15 mm length were grown by the Czochralski method from CaF2 deficient melts. The substance melts incongruently at 751 °C. No significant deviations of the crystal composition from the nominal stoichiometry Li:Ca:Ga=1:1:1 could be found. X-ray structure analysis revealed that the substance crystallizes in the colquiriite type structure. LiCaGaF6 is transparent for optical wavelengths >140 , 150 nm. The thermal expansion of the trigonal crystals is ,11 = ,22 = 18.7×10 -6 K -1 perpendicular [001] and ,33 = 2.7×10 -6 K -1 parallel [001]. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effect of Ti addition on magnetic properties of TbCu7 -type Sm-Fe-Co-Mn system nitridesELECTRONICS & COMMUNICATIONS IN JAPAN, Issue 7 2008Hiroshi Yamamoto Abstract To support the development of high-performance isotropic bonded magnets, experiments were carried out to investigate the effect of Ti addition on the magnetic properties of Sm-Fe-Co-Mn system nitride compounds with TbCu7 -type structure. Sm10(Fe0.9Co0.1)89.5,xMn0.5Tix (x=0 to 1.0) alloy ribbons were prepared by the single-roller rapid-quenching method. The effects of alloy composition and of heat treatment and nitriding conditions on the magnetic properties were examined. The optimum preparation conditions of the compounds were as follows. Composition: {Sm10(F0.9Co0.1)89Mn0.5Ti0.5}86.8N13.2; roller speed: 50 m/s; heat treatment: 700°C×60 min in high-purity Ar gas; nitriding conditions: 420°C×15 h in high-purity N2 gas. Typical magnetic properties of the obtained compound powders were Jr = 0.97 T, HcJ = 730.8 kA/m,(BH)max = 140.0 kJ/m3 (17.6 MGOe), Tc=500°C. XRD, TEM photographs, and recoil loops of the hysteresis curve demonstrated that this sample had the characteristics of an exchange spring magnet. The value of (BH)max for the isotropic compression molding bonded magnet prepared from the {Sm10(F0.9Co0.1)89Mn0.5Ti0.5}86.8N13.2 powder was 94.8 kJ/m3 (11.9 MGOe) at a bonded magnet density of 6.07 Mg/m3. The reversible temperature coefficient of Jr was ,(Jr)=,0.04%/°C and the temperature coefficient of HcJ in the range from 25°C to 125°C obtained by linear extrapolation was ,(HcJ)=,0.40%/°C. © 2008 Wiley Periodicals, Inc. Electron Comm Jpn, 91(7): 25,31, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10124 [source] Formation of Metastable Na2CrO4 -Type LiNiPO4 from a Phosphate,Formate PrecursorEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 1 2010Violeta Koleva Abstract High-pressure modification of LiNiPO4 with a Na2CrO4 -type structure was obtained at ambient pressure and low temperature from a mixed LiNi,phosphate,formate precursor, LiNiPO4Hx(HCOO)x·yH2O (where x , 1.2 and y , 2.5). The structural and thermal characterization of the precursor and the LiNiPO4 compositions were carried out by powder XRD analysis, IR spectroscopy, and DSC analysis. Thermal treatment of LiNiPO4Hx(HCOO)x·yH2O precursors between 450 and 650 °C yields a mixture of the two structural modifications of LiNiPO4: the Na2CrO4 type and the olivine type. It was established that the obtained Na2CrO4 -type LiNiPO4 is a metastable phase, which completely transforms at 700 °C into the olivine-type phase. The enthalpy of the phase transition is ,H = ,43.40 kJ,mol,1. The mechanism of formation of the two forms of LiNiPO4 from the LiNi,phosphate,formate precursor is discussed. [source] Thermally Stable Nanocrystalline Mesoporous Gallium Oxide PhasesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 22 2009Chinmay A. Deshmane Abstract Semicrystalline and fully crystalline mesoporous galliumoxide phases were synthesized in the presence of ionic and non-ionic structure directing agents via Evaporation-Induced Self-Assembly (EISA) and Self-Assembly Hydrothermal-Assisted (SAHA) methods respectively. EISA led to partially crystalline mesoporous gallium oxide phases displaying unimodal pore size distribution in the range of ca. 2,5 nm and surface areas as high as 300 m2/g. SAHA led to nanocrystalline mesoporous uniform micron-sized gallium oxide spheres (ca. 0.3,6.5 ,m) with narrow size distribution displaying cubic spinel type structure. These mesophases displayed surface areas as high as ca. 221 m2/g and unimodal pore size distribution in the 5,15 nm range. Textural properties such as surface areas and pore sizes were effectively fine-tuned by the nature and relative concentration of the structure directing agents. Due to their high surface areas, tunability of pore sizes and the nature of the wall structure, these gallium oxide mesophases could find potential applications as heterogeneous catalysts.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Facile Synthesis of Bastnaesite -Type LaF[CO3] and Its Thermal Decomposition to LaOF for Bulk and Eu3+ -Doped SamplesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 3 2009Oliver Janka Abstract Rare-earth metal(III) oxide fluorides with the composition MOF (M = La,Lu) seem to offer promising host lattices for luminescence applications by doping these materials with trivalent lanthanoid cations. Unfortunately, there was no simple and practicable way to synthesize the compounds in phase-pure quality with classical solid-state chemistry reactions. However, by using the rare-earth metal(III) fluoride oxocarbonates, MF[CO3], as solution-born precursor materials that crystallize with a bastnaesite -type structure, easy access is now possible by mild thermal decomposition. Synthetic details, investigations on the phase purity and the presence of the oxocarbonate anion [CO3]2, proved by IR measurements as well as from X-ray powder diffraction data are given in this paper for the example of bulk LaF[CO3] and Eu3+ -doped samples. The latter (LaF[CO3]:Eu3+) shows a bright orange-red luminescence that is stronger than that of the product of its thermal decomposition: trimorphic LaOF:Eu3+.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Mass spectrometry study of ecto-5,-nucleotidase from bull seminal plasmaFEBS JOURNAL, Issue 16 2000Carlo Fini The structure of ecto-5,-nucleotidase from bull seminal plasma, containing a glycosyl-phosphatidylinositol anchor, was studied using mass spectrometry. MALDI-MS analysis of intact protein indicated a mass of 65 568.2 Da for the monomeric form, and it also showed a heterogeneous population of glycoforms with the glycosidic moiety accounting for ,,6000 Da. MALDI-MS analysis showed that Asn53, Asn311, Asn333 and Asn403 were four sites of N -glycosylation. GC-MS analysis provided information on the glycosidic structures linked to the four asparagines. Asn53, Asn311 and Asn333 were linked to high-mannose saccharide chains, whereas the glycan chains linked to Asn403 contained a heterogeneous mixture of oligosaccharides, the high-mannose type structure being the most abundant and hybrid or complex type glycans being minor components. By combining enzymatic and/or chemical hydrolysis with GC-MS analysis, detailed characterization of the glycosyl-phpsphatidylinositol anchor was obtained. MALDI spectral analysis indicated that the glycosyl-phosphatidylinositol core contained EtN(P)Man3GlcNH2 -myo-inositol(P)-glycerol, principally modified by stearoyl and palmitoyl residues or by stearoyl and myristoyl residues to a minor extent. Moreover, 1-palmitoylglycerol and 1-stearoylglycerol outweighed 2-palmitoylglycerol and 2-stearoylglycerol. The combination of chemical and enzymatic digestions of the protein with the mass spectral analysis yielded a complete pattern of S,S bridges. The protein does not contain free thiols and its eight cysteines are linked by intramolecular disulfide bonds, the pairs being: Cys51,Cys57, Cys353,Cys358, Cys365,Cys387 and Cys476,Cys479. This work resolves details of the structure of ecto-5,-nucleotidase, with particular regard to the localization and composition of the glycidic moiety, number and localization of the disulfide bridges and characterization of the glycosyl-phosphatidylinositol anchor. [source] Analysis of Nanostructuring in High Figure-of-Merit Ag1,xPbmSbTe2+m Thermoelectric MaterialsADVANCED FUNCTIONAL MATERIALS, Issue 8 2009Bruce A. Cook Abstract Thermoelectric materials based on quaternary compounds Ag1,xPbmSbTe2+m exhibit high dimensionless figure-of-merit values, ranging from 1.5 to 1.7 at 700,K. The primary factor contributing to the high figure of merit is a low lattice thermal conductivity, achieved through nanostructuring during melt solidification. As a consequence of nucleation and growth of a second phase, coherent nanoscale inclusions form throughout the material, which are believed to result in scattering of acoustic phonons while causing only minimal scattering of charge carriers. Here, characterization of the nanosized inclusions in Ag0.53Pb18Sb1.2Te20 that shows a strong tendency for crystallographic orientation along the {001} planes, with a high degree of lattice strain at the interface, consistent with a coherent interfacial boundary is reported. The inclusions are enriched in Ag relative to the matrix, and seem to adopt a cubic, 96 atom per unit cell Ag2Te phase based on the Ti2Ni type structure. In-situ high-temperature synchrotron radiation diffraction studies indicated that the inclusions remain thermally stable to at least 800,K. [source] N -Terminal domain of HTLV-I integrase.JOURNAL OF PEPTIDE SCIENCE, Issue 11 2001Complexation, conformational studies of the zinc finger Abstract The HTLV-I integrase N -terminal domain [50-residue peptide (IN50)], and a 35-residue truncated peptide formed by residues 9,43 (IN35) have been synthesized by solid-phase peptide synthesis. Formation of the 50-residue zinc finger type structure through a HHCC motif has been proved by UV-visible absorption spectroscopy. Its stability was demonstrated by an original method using RP-HPLC. Similar experiments performed on the 35-residue peptide showed that the truncation does not prevent zinc complex formation but rather that it significantly influences its stability. As evidenced by CD spectroscopy, the 50-residue zinc finger is unordered in aqueous solution but adopts a partially helical conformation when trifluoroethanol is added. These results are in agreement with our secondary structure predictions and demonstrate that the HTLV-I integrase N -terminal domain is likely to be composed of an helical region (residues 28,42) and a ,-strand (residues 20,23), associated with a HHCC zinc-binding motif. Size-exclusion chromatography showed that the structured zinc finger dimerizes through the helical region. Copyright © 2000 European Peptide Society and John Wiley & Sons, Ltd. [source] Study of structural defects in ,-MnO2 by Raman spectroscopyJOURNAL OF RAMAN SPECTROSCOPY, Issue 4 2002C. Julien The structural arrangement of ,-MnO2 is currently explained by a random intergrowth of pyrolusite layers in a ramsdellite matrix. The structures of a large variety of ,-MnO2 samples with various structural parameters Pr were studied by x-ray powder diffraction and Raman scattering spectroscopy. We show that elucidation of the quantitative determination of the structural disorder present in ,-MnO2 is accurate by Raman scattering spectroscopy. The Raman data for manganese dioxides with the ,-type structure are treated by a local environment model, which allows one to consider the relationship between the band wavenumber and the pyrolusite intergrowth that corresponds to the structural De Wolff defects. Copyright © 2002 John Wiley & Sons, Ltd. [source] Determination of the Thermal Resistance of the Polymer,Ceramic Interface of Alumina-Filled Polymer CompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2004Richard F. Hill To model the thermal conductivity of polymer composites that are filled with ceramic powders, the conductivity of each component as well as the interfacial resistance at each ceramic,polymer boundary must be known. An indirect method to determine this interfacial boundary resistance is proposed by preparing large-scale "macromodel" simulations of the polymer,ceramic interface. Macromodels, prepared by spin-coating a polymer layer onto sapphire wafers, were formed in a sapphire,polymer,sapphire sandwich type structure. The interfacial boundary thermal resistance was calculated from thermal resistance measurements made on the macromodels. [source] The Crystal Structure of the L1 Intermediate of Halorhodopsin at 1.9 Å Resolution,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2007Walter Gmelin The mutant T203V of the light driven chloride pump halorhodopsin from Halobacterium salinarum was crystallized and the X-ray structure was solved at 1.6 Å resolution. The T203V structure turned out to be nearly identical to the wild type protein with a root mean square deviation of 0.43 Å for the carbon , atoms of the protein backbone. Two chloride binding (CB) sites were demonstrated by a substitution of chloride with bromide and an analysis of anomalous difference Fourier maps. The CB1 site was found at the same position as in the wild type structure. In addition, a second chloride binding site CB2 was identified around Q105 due to higher resolution in the mutant crystal. As T203V showed a 10 times slower decay of its photocycle intermediate L, this intermediate could be trapped with an occupancy of 60% upon illumination at room temperature and subsequent cooling to 120°K. Fourier transform infrared spectroscopy clearly identified the crystal to be trapped in the L1 intermediate state and the X-ray structure was solved to 1.9 Å resolution. In this intermediate, the chloride moved by 0.3 Å within binding site CB1 as indicated by peaks in difference Fourier density maps. The chloride in the second binding site CB2 remained unchanged. Thus, intraproteinous chloride translocation from the extracellular to the cytoplasmic part of the protein must occur in reaction steps following the L1 intermediate in the catalytic cycle of halorhodopsin. [source] On the magnetic behaviour of GdCo2,xCux compoundsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003R. Tetean Abstract The GdCo2,xCux compounds crystallize in a cubic C15 type structure for x , 0.20. The compounds are ferrimagnetically ordered. The mean cobalt magnetic moments, determined at 4.2 K, are little dependent on composition. The saturation moments per formula unit, at 4.2 K, are in rather good agreement with those obtained from band structure calculations. The Gd 5d band polarizations were analyzed. The contributions from 4f,5d, local exchange M5d(Gd), and 5d,3d short range exchange interactions, M5d(0), were determined. The M5d(0) values are proportional to cobalt magnetizations. [source] The effect of nitrogen insertion on the magnetic and structural properties of Sm2,xGdxFe17 alloys (0 , x , 2)PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2006M. S. Ben Kraiem Abstract The effect of nitrogen insertion on the structural and magnetic properties of Sm2,xGdxFe17Ny compounds (x = 0-2) has been investigated. X-ray diffraction patterns at room temperature show that all our synthesized samples are single phase and crystallize in the rhombohedral Th2Zn17 -type structure with very small amount of impurity. Nitrogen insertion leads to a monotonic increase in the unit cell volume, it leads also to an increase in the Curie temperature Tc from 425 K for SmGdFe17 to 760 K for SmGdFe17N3. Moreover, the nitrogen insertion increases the saturated magnetization Ms. Ms increases from 17.9 µB/mole for SmGdFe17 to 32.7 µB/mole for SmGdFe17N3. X-ray diffraction measurements on magnetically aligned powder samples of Sm2,xGdxFe17Ny reveal a change in the easy magnetization direction from planar before nitrogen insertion to the c-axis after nitrogen insertion. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A Quadratic Eigenproblem in the Analysis of a Time Delay SystemPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2006Elias JarlebringArticle first published online: 4 DEC 200 In this work we solve a quadratic eigenvalue problem occurring in a method to compute the set of delays of a linear time delay system (TDS) such that the system has an imaginary eigenvalue. The computationally dominating part of the method is to find all eigenvalues z of modulus one of the quadratic eigenvalue problem where ,1, ,, ,m ,1 , , are free parameters and u a vectorization of a Hermitian rank one matrix. Because of its origin in the vectorization of a Lyapunov type matrix equation, the quadratic eigenvalue problem is, even for moderate size problems, of very large size. We show one way to treat this problem by exploiting the Lyapunov type structure of the quadratic eigenvalue problem when constructing an iterative solver. More precisely, we show that the shift-invert operation for the companion form of the quadratic eigenvalue problem can be efficiently computed by solving a Sylvester equation. The usefulness of this exploitation is demonstrated with an example. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A five-dimensional structural investigation of the misfit layer compound [Bi0.87SrO2]2[CoO2]1.82ACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2000H. Leligny The structure of the misfit layer compound [BiSrO][CoO], bismuth strontium cobaltite, was determined by single-crystal X-ray diffraction using the five-dimensional superspace-group formalism. This composite crystal, of monoclinic symmetry, is composed of two subsystems exhibiting incommensurate periodicities along b, the binary axis direction. The first composite part [BiSrO] displays an intrinsic modulation of planar monoclinic type characterized by the wavevector . The second composite part [CoO] shows two different centered lattice variants. The structure of the misfit layer crystal can be described as an alternation along c of distorted rock-salt-type slabs, formed from [BiO] and [SrO] layers (first subsystem), and of [CoO] layers (second subsystem) displaying a distorted CdI -type structure. Two main structural results are obtained. First, as a consequence of the intrinsic modulation, disordered zones, characterized by Bi vacancies, are regularly distributed in the [BiO] layers. Second, strong chemical bonds are implied between the strontium atoms of the first subsystem and the oxygen atoms of the second one. [source] Characterization of the CuA center in the cytochrome c oxidase from Thermus thermophilus for the spectral range 1800,500 cm,1 with a combined electrochemical and Fourier transform infrared spectroscopic setupBIOPOLYMERS, Issue 1-2 2004M. Wolpert Abstract In this study we present the electrochemically induced Fourier transform infrared (FTIR) difference spectra of the CuA center derived from the ba3 -type cytochrome c oxidase of Thermus thermophilus in the spectral range from 1800 to 500 cm,1. The mid infrared is dominated by the ,(CO) vibrations of the amide I modes at 1688, 1660, and 1635 cm,1, reflecting the redox-induced perturbation of the predominantly ,-sheet type structure. The corresponding amide II signal is found at 1528 cm,1. In the lower frequency range below 800 cm,1, modes from amino acids liganding the CuA center are expected. On the basis of the absorbance spectrum of the isolated amino acids, methionine is identified as an important residue, displaying C,S vibrations at these frequencies. This spectral range was previously disregarded by protein IR spectroscopists, mainly due to the strong absorbance of the solvent, H2O. With an optimized setup, however, IR is found suitable for structure/function studies on proteins. © 2004 Wiley Periodicals, Inc. Biopolymers, 2004 [source] ,-Ca3N2, a Metastable Nitride in the System Ca,NCHEMISTRY - A EUROPEAN JOURNAL, Issue 14 2009Peter Höhn Dr. Abstract A new page in the phase book: The metastable nitride ,-Ca3N2, the synthesis, crystal structure (see picture), and physical properties of which are reported, is an isotype of corundum (,-Al2O3). Vacancies in the crystal structure of ,-Ca3N2 are discussed by using full-potential local orbital methods and taking into account both the physical properties and the density of states. The structural chemistry of calcium nitrides is represented by just two different intermediate phases: cubic Ca3N2 (referred to as ,-Ca3N2, Mn2O3 type structure) and Ca2N (CdCl2 type structure). Other binary phases (",-Ca3N2", "Ca11N8") have been proven to represent cyanamide nitrides, Ca4N2[CN2] and Ca11N6[CN2]2, respectively. The metastable nitride ,-Ca3N2 is prepared either by reaction of freshly distilled calcium metal with nitrogen at 700,K, or by reaction of Ca2N with N2 at 500,K. ,-Ca3N2 transforms monotropically (Ttrans,810,K) to cubic ,-Ca3N2. The crystal structure of ,-Ca3N2 (rhombohedral Rc, no. 167, a=619.884(3),pm, c=1662.958(10),pm) is an isotype of the corundum structure (,-Al2O3) and comprises a network of NCa6/4 octahedra that share common faces and edges. Magnetic susceptibility and electrical resistivity measurements confirm that ,-Ca3N2 is a diamagnetic semiconductor. Die Strukturchemie der Calciumnitride wird von lediglich zwei intermediären Verbindungen bestimmt: kubisches Ca3N2 (nachfolgend als , -Ca3N2 bezeichnet; Mn2O3 -Strukturtyp) und das im CdCl2 -Strukturtyp kristallisierende Ca2N. Die binären Phasen ,, -Ca3N2" und ,Ca11N8" konnten inzwischen als die Cyanamid-Nitride Ca4N2[CN2] und Ca11N6[CN2]2 identifiziert werden. Metastabiles , -Ca3N2 kann entweder durch Reaktion von frisch destilliertem Calcium-Metall mit Stickstoff bei 700,K oder durch Umsetzung von Ca2N mit N2 bei 500,K erhalten werden. , -Ca3N2 transformiert monotrop (Ttrans,810,K) zur kubischen Phase , -Ca3N2. Die Kristallstruktur von , -Ca3N2 (rhomboedrisch Rc, No. 167, a=619.884(3),pm, c=1662.958(3),pm) ist isotyp zur Korundstruktur (, -Al2O3) und besteht aus einem Netzwerk von NCa6/4 -Oktaedern, die über gemeinsame Flächen und Kanten verknüpft sind. Messungen der magnetischen Suszeptibilität und des elektrischen Widerstands zeigen, daß , -Ca3N2 ein diamagnetischer Halbleiter ist. [source] Olefin Epoxidation with Hydrogen Peroxide Catalyzed by Lacunary Polyoxometalate [,-SiW10O34(H2O)2]4,CHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2007Keigo Kamata Abstract The tetra- n -butylammonium (TBA) salt of the divacant Keggin-type polyoxometalate [TBA]4[,-SiW10O34(H2O)2] (I) catalyzes the oxygen-transfer reactions of olefins, allylic alcohols, and sulfides with 30,% aqueous hydrogen peroxide. The negative Hammett ,+ (,0.99) for the competitive oxidation of p -substituted styrenes and the low value of (nucleophilic oxidation)/(total oxidation), XSO=0.04, for I -catalyzed oxidation of thianthrene 5-oxide (SSO) reveals that a strongly electrophilic oxidant species is formed on I. The preferential formation of trans -epoxide during epoxidation of 3-methyl-1-cyclohexene demonstrates the steric constraints of the active site of I. The I -catalyzed epoxidation proceeds with an induction period that disappears upon treatment of I with hydrogen peroxide. 29Si and 183W,NMR spectroscopy and CSI mass spectrometry show that reaction of I with excess hydrogen peroxide leads to fast formation of a diperoxo species, [TBA]4[,-SiW10O32(O2)2] (II), with retention of a ,-Keggin type structure. Whereas the isolated compound II is inactive for stoichiometric epoxidation of cyclooctene, epoxidation with II does proceed in the presence of hydrogen peroxide. The reaction of II with hydrogen peroxide would form a reactive species (III), and this step corresponds to the induction period observed in the catalytic epoxidation. The steric and electronic characters of III are the same as those for the catalytic epoxidation by I. Kinetic, spectroscopic, and mechanistic investigations show that the present epoxidation proceeds via III. [source] Identification of Nucleation Center Sites in Thermally Annealed Hydrogenated Amorphous SiliconADVANCED FUNCTIONAL MATERIALS, Issue 14 2009A. Harv Mahan Abstract Utilizing the concepts of a critical crystallite size and local film inhomogeneity, it is shown that nucleation in thermally annealed hydrogenated amorphous silicon occurs in the more well ordered spatial regions in the network, which are defined by the initial inhomogeneous H distributions in the as-grown films. Although the film H evolves very early during annealing, the local film order is largely retained in the still amorphous films even after the vast majority of the H is evolved, and the more well ordered regions which are the nucleation center sites for crystallization are those spatial regions which do not initially contain clustered H, as probed by H NMR spectroscopy. The sizes of these better ordered regions relative to a critical crystallite size determine the film incubation times (the time before the onset of crystallization). Changes in film short range order upon H evolution, and the presence of microvoid type structures in the as grown films play no role in the crystallization process. While the creation of dangling bonds upon H evolution may play a role in the actual phase transformation itself, the film defect densities measured just prior to the onset of crystallization exhibit no trends which can be correlated with the film incubation times. [source] Ceramic,Polymer Ba0.6Sr0.4TiO3/Poly(Methyl Methacrylate) Composites with Different Type Composite Structures for Electronic TechnologyINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 4 2010Hong Wang Ba0.6Sr0.4TiO3 (BST)/poly(methyl methacrylate) (PMMA) composites with 0,3, 1,3, and 2,2 type structures were prepared and studied. The effect of composite type on the dielectric properties of BST/PMMA composites was comprehensively investigated by both theoretical and experimental methods. The 1,3 type composite shows the highest permittivity and dielectric tunability, while the 2,2 and 0,3 type composites show lower permittivity as well as lower dielectric tunabilities. The experimentally measured dielectric properties are in agreement with the theoretically calculated values. The results help in understanding and tailoring the dielectric properties of ceramic,polymer composites by choosing a suitable composite structure. [source] Using Metallo-Supramolecular Block Copolymers for the Synthesis of Higher Order Nanostructured AssembliesMACROMOLECULAR RAPID COMMUNICATIONS, Issue 1 2010Adam O. Moughton Abstract Many research groups have explored the properties and solution self-assembly of main chain metallo-supramolecular multiblock copolymers. Until recently, these metal complexes have been used to prepare mainly micelle type structures. However, the self-assembly of such copolymers has been exploited further to create more advanced architectures which utilize the reversible supramolecular linkage of their building blocks as a key component in their synthesis. Furthermore, the incorporation of multiple orthogonal interactions and stimuli responsive polymers into their design, enables more precise external control of their properties. This feature article discusses recent developments and provides an insight into their potential exploitation and development for the creation of novel, smart, and responsive nanostructures. [source] | ||||||||||||||||||||||