WorldWideScience

Sample records for halogen-bridged transition metal

  1. Transition from metal-ligand bonding to halogen bonding involving a metal as halogen acceptor a study of Cu, Ag, Au, Pt, and Hg complexes

    Science.gov (United States)

    Oliveira, Vytor; Cremer, Dieter

    2017-08-01

    Utilizing all-electron Dirac-exact relativistic calculations with the Normalized Elimination of the Small Component (NESC) method and the local vibrational mode approach, the transition from metal-halide to metal halogen bonding is determined for Au-complexes interacting with halogen-donors. The local stretching force constants of the metal-halogen interactions reveal a smooth transition from weak non-covalent halogen bonding to non-classical 3-center-4-electron bonding and finally covalent metal-halide bonding. The strongest halogen bonds are found for dialkylaurates interacting with Cl2 or FCl. Differing trends in the intrinsic halogen-metal bond strength, the binding energy, and the electrostatic potential are explained.

  2. 40 CFR 721.5452 - Alkali metal salt of halogenated organoborate (generic).

    Science.gov (United States)

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Alkali metal salt of halogenated... Specific Chemical Substances § 721.5452 Alkali metal salt of halogenated organoborate (generic). (a... generically as alkali metal salt of halogenated organoborate (PMN P-00-0638) is subject to reporting under...

  3. Extended lanthanide-transition metal arrays with cyanide bridges: syntheses, structures, and catalytic applications

    International Nuclear Information System (INIS)

    Liu Shengming; Poplaukhin, Pavel; Ding Errun; Plecnik, Christine E.; Chen Xuenian; Keane, Mark A.; Shore, Sheldon G.

    2006-01-01

    Systematic synthetic procedures produced several different structural types of extended lanthanide-transition metal (group 10) complexes with cyanide bridges. Of these, one-dimensional ladder arrays containing a Yb-Pd combination have been converted to bimetallic heterogeneous catalysts on an oxide (SiO 2 ) surface that is more effective than supported Pd alone. Two lanthanide-Cu(I) complexes have been prepared. One type, an inclusion complex consists of lanthanide(III) cations encapsulated in the pockets of a three-dimensional anionic array that contains Cu(I)-CN-Cu(I) bridges. The second type, an extended layer complex, consists of joined five-membered rings in a 'tile-like' pattern with Ln-CN-Cu and Cu-CN-Cu bridges

  4. Structural characterisation of 1- and 2-dimensional transition metal polymers using powder neutron diffraction

    International Nuclear Information System (INIS)

    James, M.

    1999-01-01

    Powder neutron diffraction provides an alternate technique for the structural study of transition metal polymers and finds utility over standard X-ray methods in two significant ways. Firstly, due to a different instrument geometry, preferred orientation effects are removed from the system. The second advantage gained by utilising neutrons is that H atoms in the sample contribute much more to the nuclear scattering of the diffraction profile - allowing their atomic position to be accurately determined. In X-ray diffraction studies, where H atoms typically account for only ∼3-5% of the scattering from the sample, it is essentially impossible to refine their position in the molecular structure. The structures of several transition metal polymers have been determined using neutrons from the HIFAR reactor at ANSTO and the Powder Diffractometers HRPD and MRPD, along with Rietveld refinement methods. The 1-dimensional polymer dibromobis(thiazole)nickel(II) illustrated in the paper is characteristic of these types of systems which are comprised of transition metal centres bridged by halogen atoms with pendant amine side groups

  5. The nonmetal-metal transition in solutions of metals in molten salts

    International Nuclear Information System (INIS)

    Tosi, M.P.

    1997-04-01

    Solutions of metals in molten salts present a rich phenomenology: localization of electrons in disordered ionic media, activated electron transport increasing with metal concentration towards a nonmetal-metal (NM-M) transition, and liquid-liquid phase separation. A brief review of progress in the study of these systems is given in this article, with main focus on the NM-M transition. After recalling the known NM-M behaviour of the component elements in the case of expanded fluid alkali metals and mercury and of solid halogens under pressure, the article focuses on liquid metal - molten salt solutions and traces the different NM-M behaviours of the alkalis in their halides and of metals added to polyvalent metal halides. (author). 51 refs, 2 figs

  6. Reactivity of monoolefin ligand in transition metal complexes

    International Nuclear Information System (INIS)

    Rybinskaya, M.I.

    1978-01-01

    The main tendencies in the coordinated olefin ligand property changes are discussed in the transition metal complexes in comparison with free olefins. The review includes the papers published from 1951 up to 1976. It has been shown that in complexes with transition metal cations olefin π-base acquires the ability to react with nucleophylic reagents. Olefin π-acids in complexes with zero valent metals are easily subjected to electrophylic reagent action. At coordination with transition metal cations the olefin properties are generally preserved, while in the zero-valent metal complexes the nonsaturated ligand acquires the properties of a saturated compounds. The ability of transition metal cations in complexes to intensify reactions of nucleophylic bimolecular substitution of vinyl halogen is clearly detected in contrast to the zero valent metal complexes. It has been shown that investigations of the coordinated olefin ligand reactivity give large possibilities in the further development of the organic synthesis. Some reactions are taken as the basis of important industrial processes

  7. Alkylation and arylation of alkenes by transition metal complexes

    International Nuclear Information System (INIS)

    Volkova, L.G.; Levitin, I.Ya.; Vol'pin, M.E.

    1975-01-01

    In this paper are reviewed methods of alkylation and irylation of unsaturated compounds with complexes of transition metals (Rh, Pd). Analysis of alkylation and arylation of olefines with organic derivatives of transition metals, obtained as a result of exchange reactions between organic compounds of transition metals and salts of metals of the 8th group of the periodic system, allows a conclusion as to the wide possibilities of these reactions in the synthesis of various derivatives of unsaturated compounds. In all the reactions under consideration, intermediate formation of sigma-complexes is assumed. Also considered are alkylation and arylation of olefines with organic derivatives of halogens in the presence of compounds of metals of the 8th group of the periodic system, as well as arylation of olefines with aromatic compounds in the presence of salts of transition metals

  8. Metal-Mediated Halogen Exchange in Aryl and Vinyl Halides: a Review

    Science.gov (United States)

    Evano, Gwilherm; Nitelet, Antoine; Thilmany, Pierre; Dewez, Damien F.

    2018-04-01

    Halogenated arenes and alkenes are of prime importance in many areas of science, especially in the pharmaceutical, agrochemical and chemical industries. While the simplest ones are commercially available, some of them are still hardly accessible depending on their substitution patterns and the nature of the halogen atom. Reactions enabling the selective and efficient replacement of the halogen atom of an aryl or alkenyl halide by another one, lighter or heavier, are therefore of major importance since they can be used for example to turn a less reactive aryl/alkenyl chloride into the more reactive iodinated derivatives or, in a reversed sense, to block an undesired reactivity, for late-stage modifications or for the introduction of a radionuclide. If some halogen exchange reactions are possible with activated substrates, they usually require catalysis with metal complexes. Remarkably efficient processes have been developed for metal-mediated halogen exchange in aryl and vinyl halides: they are overviewed, in a comprehensive manner, in this review article.

  9. Tuning the electronic structure of graphene through alkali metal and halogen atom intercalation

    Science.gov (United States)

    Ahmad, Sohail; Miró, Pere; Audiffred, Martha; Heine, Thomas

    2018-04-01

    The deposition, intercalation and co-intercalation of heavy alkali metals and light halogens atoms in graphene mono- and bilayers have been studied using first principles density-functional calculations. Both the deposition and the intercalation of alkali metals gives rise to n-type doping due to the formation of M+-C- pairs. The co-intercalation of a 1:1 ratio of alkali metals and halogens derives into the formation of ionic pairs among the intercalated species, unaltering the electronic structure of the layered material.

  10. Investigating vibrational anharmonic couplings in cyanide-bridged transition metal mixed valence complexes using two-dimensional infrared spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Slenkamp, Karla M.; Lynch, Michael S.; Van Kuiken, Benjamin E.; Brookes, Jennifer F.; Bannan, Caitlin C.; Daifuku, Stephanie L.; Khalil, Munira, E-mail: mkhalil@chem.washington.edu [Department of Chemistry, University of Washington, Box 351700, Seattle, Washington 98195 (United States)

    2014-02-28

    Using polarization-selective two-dimensional infrared (2D IR) spectroscopy, we measure anharmonic couplings and angles between the transition dipole moments of the four cyanide stretching (ν{sub CN}) vibrations found in [(NH{sub 3}){sub 5}Ru{sup III}NCFe{sup II}(CN){sub 5}]{sup −} (FeRu) dissolved in D{sub 2}O and formamide and [(NC){sub 5}Fe{sup II}CNPt{sup IV}(NH{sub 3}){sub 4}NCFe{sup II}(CN){sub 5}]{sup 4−} (FePtFe) dissolved in D{sub 2}O. These cyanide-bridged transition metal complexes serve as model systems for studying the role of high frequency vibrational modes in ultrafast photoinduced charge transfer reactions. Here, we focus on the spectroscopy of the ν{sub CN} modes in the electronic ground state. The FTIR spectra of the ν{sub CN} modes of the bimetallic and trimetallic systems are strikingly different in terms of frequencies, amplitudes, and lineshapes. The experimental 2D IR spectra of FeRu and FePtFe and their fits reveal a set of weakly coupled anharmonic ν{sub CN} modes. The vibrational mode anharmonicities of the individual ν{sub CN} modes range from 14 to 28 cm{sup −1}. The mixed-mode anharmonicities range from 2 to 14 cm{sup −1}. In general, the bridging ν{sub CN} mode is most weakly coupled to the radial ν{sub CN} mode, which involves the terminal CN ligands. Measurement of the relative transition dipole moments of the four ν{sub CN} modes reveal that the FeRu molecule is almost linear in solution when dissolved in formamide, but it assumes a bent geometry when dissolved in D{sub 2}O. The ν{sub CN} modes are modelled as bilinearly coupled anharmonic oscillators with an average coupling constant of 6 cm{sup −1}. This study elucidates the role of the solvent in modulating the molecular geometry and the anharmonic vibrational couplings between the ν{sub CN} modes in cyanide-bridged transition metal mixed valence complexes.

  11. Distributions of alkali metals, alkaline earth metals and halogens in cabbage leaves

    International Nuclear Information System (INIS)

    Tsukada, Hirofumi; Takeda, Akira; Hasegawa, Hidenao

    2007-01-01

    The distributions of stable elements in plant components provide useful information for understanding the behavior of radionuclides in plants. An entire cabbage plant sample was collected from an experimental field, and the distributions of alkali metals (K, Rb and Cs), alkaline earth metals (Ca, Sr and Ba) and halogens (Cl and I) were determined for cabbage leaves at different positions. The concentration of Cs in outer (older) cabbage leaves was higher than that in inner (younger) leaves, but the distributions of K and Rb concentrations were relatively similar in cabbage leaves, independent of leaf positions. The concentration of Sr in older cabbage leaves was one order of magnitude higher than that in younger leaves. The distributions of Ca, Ba and Sr concentrations in the plant followed a similar pattern. The concentrations of halogens were also very rich in the outer leaves. The percentage distributions of Cs, Sr, Cl and I in the inedible (extreme outer) leaves were 77, 91, 93 and 96% of the total content in the leaf part, respectively. These results show that the inedible plant components are important for understanding the transfer of the radioactive Cs, Sr Cl and I in soil-plant systems. (author)

  12. Synthesis of Isotactic-block-Syndiotactic Poly(methyl Methacrylate via Stereospecific Living Anionic Polymerizations in Combination with Metal-Halogen Exchange, Halogenation, and Click Reactions

    Directory of Open Access Journals (Sweden)

    Naoya Usuki

    2017-12-01

    Full Text Available Isotactic (it- and syndiotactic (st- poly(methyl methacrylates (PMMAs form unique crystalline stereocomplexes, which are attractive from both fundamental and application viewpoints. This study is directed at the efficient synthesis of it- and st-stereoblock (it-b-st- PMMAs via stereospecific living anionic polymerizations in combination with metal-halogen exchange, halogenation, and click reactions. The azide-capped it-PMMA was prepared by living anionic polymerization of MMA, which was initiated with t-BuMgBr in toluene at –78 °C, and was followed by termination using CCl4 as the halogenating agent in the presence of a strong Lewis base and subsequent azidation with NaN3. The alkyne-capped st-PMMA was obtained by living anionic polymerization of MMA, which was initiated via an in situ metal-halogen exchange reaction between 1,1-diphenylhexyl lithium and an α-bromoester bearing a pendent silyl-protected alkyne group. Finally, copper-catalyzed alkyne-azide cycloaddition (CuAAC between these complimentary pairs of polymers resulted in a high yield of it-b-st-PMMAs, with controlled molecular weights and narrow molecular weight distributions. The stereocomplexation was evaluated in CH3CN and was affected by the block lengths and ratios.

  13. Concentration-dependent multiple chirality transition in halogen-bond-driven 2D self-assembly process

    Science.gov (United States)

    Miao, Xinrui; Li, Jinxing; Zha, Bao; Miao, Kai; Dong, Meiqiu; Wu, Juntian; Deng, Wenli

    2018-03-01

    The concentration-dependent self-assembly of iodine substituted thienophenanthrene derivative (5,10-DITD) is investigated at the 1-octanic acid/graphite interface using scanning tunneling microscopy. Three kinds of chiral arrangement and transition of 2D molecular assembly mainly driven by halogen bonding is clearly revealed. At high concentration the molecules self-assembled into a honeycomb-like chiral network. Except for the interchain van der Waals forces, this pattern is stabilized by intermolecular continuous Cdbnd O⋯I⋯S halogen bonds in each zigzag line. At moderate concentration, a chiral kite-like nanoarchitecture are observed, in which the Cdbnd O⋯I⋯S and I⋯Odbnd C halogen bonds, along with the molecule-solvent Cdbnd O⋯I⋯H halogen bonds are the dominated forces to determine the structural formation. At low concentration, the molecules form a chiral cyclic network resulting from the solvent coadsorption mainly by molecule-molecule Cdbnd O⋯I⋯S halogen bonds and molecule-solvent Cdbnd O⋯I⋯H halogen bonds. The density of molecular packing becomes lower with the decreasing of the solution concentration. The solution-concentration dependent self-assembly of thienophenanthrene derivative with iodine and ester chain moieties reveals that the type of intermolecular halogen bond and the number of the co-adsorbing 1-octanic acids by molecule-solvent Cdbnd O⋯I⋯H halogen bonds determine the formation and transformation of chirality. This research emphasizes the role of different types of halogen (I) bonds in the controllable supramolecular structures and provides an approach for the fabrication of chirality.

  14. Effects of halogens on interactions between a reduced TiO{sub 2} (110) surface and noble metal atoms: A DFT study

    Energy Technology Data Exchange (ETDEWEB)

    Tada, Kohei, E-mail: k-tada@aist.go.jp [Department of Chemistry, Graduate School of Science, Osaka University, 1-1, Machikaneyama, Toyonaka, Osaka, 560-0043 (Japan); Research Institute of Electrochemical Energy, National Institute of Advanced Industrial Science and Technology (AIST), 1-8-31, Midorigaoka, Ikeda, Osaka, 563-8577 (Japan); Koga, Hiroaki [Element Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University, 1-30 Goryo Ohara, Nishikyo, Kyoto, 615-8245 (Japan); Hayashi, Akihide; Kondo, Yudai; Kawakami, Takashi; Yamanaka, Shusuke [Department of Chemistry, Graduate School of Science, Osaka University, 1-1, Machikaneyama, Toyonaka, Osaka, 560-0043 (Japan); Okumura, Mitsutaka [Department of Chemistry, Graduate School of Science, Osaka University, 1-1, Machikaneyama, Toyonaka, Osaka, 560-0043 (Japan); Element Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University, 1-30 Goryo Ohara, Nishikyo, Kyoto, 615-8245 (Japan)

    2017-07-31

    Highlights: • We investigated the halogen effect on the interactions of noble metals with TiO{sub 2}. • Halogen atoms inhibit electron transfer from TiO{sub 2} to noble metals. • Iodine stabilizes the adsorption of noble metals especially for Ag and Cu. • Electron transfer from the TiO{sub 2} is effective in anchoring Au and Pt atoms. • Covalent interaction with the support is effective in anchoring Ag and Cu atoms. - Abstract: Using DFT calculation, we investigate the effects of halogens on the interactions between rutile TiO{sub 2} (110) and noble metal atoms (Au, Ag, Cu, Pt, and Pd). Fluorine, chlorine, and bromine atoms occupy the oxygen defect sites of TiO{sub 2}, decreasing the stability of noble metal atoms on the surface. This decrease occurs because the halogens inhibit electron transfer from TiO{sub 2} to the noble metal atoms; the electron transfer from reduced TiO{sub 2} to the noble metal atom stabilizes the noble metal atom adsorption. In contrast, iodine strengthens the interactions between TiO{sub 2} and some noble metal atoms, namely Ag and Cu. This stabilization occurs because of the covalent interaction between iodine-doped TiO{sub 2} and the noble metal atom. Therefore, the stabilization is explained well by chemical hardness. This result suggests that iodine-doping of a TiO{sub 2} surface would be an effective method for the preparation of highly stabilized noble metal clusters.

  15. Bridging the Transition Gap

    Science.gov (United States)

    2013-05-23

    period and provide recommendations to guide future research and policy development. 4 DEFINING THE TRANSITIONAL SECURITY GAP There have been...BRIDGING THE TRANSITION GAP A Monograph by MAJ J.D. Hansen United States Army School of Advanced Military Studies United States Army...suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704

  16. Coordination to transition metal surfaces : a theoretical study

    NARCIS (Netherlands)

    Santen, van R.A.

    1985-01-01

    A theoretical framework is developed that describes the chemisorption of CO to transition metal surfaces analogous to the HOMO-LUMO concept of MO theory. An explanation is given for the exptl. observation that CO adsorbs on top at the (111), face of Pt, but bridge at the (111) face of Ni. One is due

  17. trans-Methylpyridine cyclen versus cross-bridged trans-methylpyridine cyclen. Synthesis, acid-base and metal complexation studies (metal = Co2+, Cu2+, and Zn2+).

    Science.gov (United States)

    Bernier, Nicolas; Costa, Judite; Delgado, Rita; Félix, Vítor; Royal, Guy; Tripier, Raphaël

    2011-05-07

    The synthesis of the cross-bridged cyclen CRpy(2) {4,10-bis((pyridin-2-yl)methyl)-1,4,7,10-tetraazabicyclo[5.5.2]tetradecane}, a constrained analogue of the previously described trans-methylpyridine cyclen Cpy(2) is reported. The additional ethylene bridge confers to CRpy(2) proton-sponge type behaviour which was explored by NMR and potentiometric studies. Transition metal complexes have been synthesized (by complexation of both ligands with Co(2+), Cu(2+) and Zn(2+)) and characterized in solution and in the solid state. The single crystal X-ray structures of [CoCpy(2)](2+), [CuCpy(2)](2+) and [ZnCpy(2)](2+) complexes were determined. Stability constants of the complexes, including those of the cross-bridged derivative, were determined using potentiometric titration data and the kinetic inertness of the [CuCRpy(2)](2+) complex in an acidic medium (half-life values) was evaluated by spectrophotometry. The pre-organized structure of the cross-bridged ligand imposes an additional strain for the complexation leading to complexes with smaller thermodynamic stability in comparison with the related non-bridged ligand. The electrochemical study involving cyclic voltammetry underlines the importance of the ethylene cross-bridge on the redox properties of the transition metal complexes.

  18. Paramagnetic transition-metal carbonyls and cyanides

    International Nuclear Information System (INIS)

    Symons, M.C.R.; Bratt, S.W.; Wyatt, J.L.

    1982-01-01

    Exposure of tetra-alkylammonium salts of [Cr(CO) 5 I] - , [Mo(CO) 5 I] - , and [W(CO) 5 I] - , and dilute solutions of [Re(CO) 5 Br] and [Re(CO) 5 I] in methyltetrahydrofuran (mthf), to 60 Co γ-rays at 77 K gave electron-addition products characterized by large hyperfine coupling to the halogen and metal nuclei. Orbital populations for the extra electrons estimated therefrom showed trends characteristic of antibonding electrons, and in all cases the extra electron appears to be accommodated in the metal-halogen σ* orbital comprising primarily (dsub(Z 2 )-psub(z)). For the tungsten complex, a species exhibiting additional hyperfine coupling to a single proton was also detected. A species previously assigned the formula [Cr(CO) 5 I] was prepared, but gave no detectable e.s.r. spectrum. (author)

  19. Systematic Review: Bridging the Gap in RPN-to-RN Transitions.

    Science.gov (United States)

    Suva, Grace; Sager, Shelley; Mina, Elaine Santa; Sinclair, Nancy; Lloyd, Monique; Bajnok, Irmajean; Xiao, Sarah

    2015-07-01

    To review the evidence examining the influences of successful education and professional role transition for registered practical nurses (RPNs) pursuing a baccalaureate degree in nursing (BScN) and registered nurse (RN) licensure through RPN-to-RN bridging programs. Systematic review of papers published between 1995 and 2014 that evaluated students' education and professional role transitions from RPN to RN. Thirty-nine papers were selected that observed or studied the change or transition in designation from RPN to RN, or its equivalent, through bridging programs and analyzed thematically according to Meleis, Sawyer, Im, Hilfinger Messias, and Schumacher's transition model. Personal, community, and social conditions related to preparation for entry, program enrolment, and postgraduate clinical integration influence successful education and professional role transitions for RPN-to-RN bridging students. Providing key transition supports may enhance the potential for successful student transition into and throughout a bridging program, but further research is necessary to enhance this understanding and to recommend best practices for optimizing students' success. The evidence from this review identifies facilitators and barriers to successful education and professional role transition for RPN-to-RN bridging students, and identifies important considerations for future research. © 2015 Sigma Theta Tau International.

  20. 40 CFR Table 3 to Subpart Ffff of... - Emission Limits for Hydrogen Halide and Halogen HAP Emissions or HAP Metals Emissions From...

    Science.gov (United States)

    2010-07-01

    ... Halogen HAP Emissions or HAP Metals Emissions From Process Vents 3 Table 3 to Subpart FFFF of Part 63... to Subpart FFFF of Part 63—Emission Limits for Hydrogen Halide and Halogen HAP Emissions or HAP... following table that applies to your process vents that contain hydrogen halide and halogen HAP emissions or...

  1. Calculation of energetic characteristics of 3d-transition metal ion aquacomplexes in tetrahedral and octahedral coordination by broadened Hukkel method

    International Nuclear Information System (INIS)

    Zhogolev, D.A.; Bunyatyan, B.Kh.; Yatsimirskij, K.B.

    1975-01-01

    Aquacomplexes formation energies of bi- and trivalent ions of 3d transition metals from Sc to Ni in the tetrahedral and octahedral coordinations have been calculated to compare their energetic advantages. Unlike ions of alkali metals and halogens, a tendency for higher or at least equal energetic effect of the formation of a tetrahedral complex, compared to octahedral, is characteristic of the ions under study. This can be explained by an increase in the covalency degree of the bond ion-ligand and by a considerable charge transfer from ligands to the central ion in the case of transition elements

  2. Metal Fluorides, Metal Chlorides and Halogenated Metal Oxides as Lewis Acidic Heterogeneous Catalysts. Providing Some Context for Nanostructured Metal Fluorides.

    Science.gov (United States)

    Lennon, David; Winfield, John M

    2017-01-28

    Aspects of the chemistry of selected metal fluorides, which are pertinent to their real or potential use as Lewis acidic, heterogeneous catalysts, are reviewed. Particular attention is paid to β-aluminum trifluoride, aluminum chlorofluoride and aluminas γ and η, whose surfaces become partially fluorinated or chlorinated, through pre-treatment with halogenating reagents or during a catalytic reaction. In these cases, direct comparisons with nanostructured metal fluorides are possible. In the second part of the review, attention is directed to iron(III) and copper(II) metal chlorides, whose Lewis acidity and potential redox function have had important catalytic implications in large-scale chlorohydrocarbons chemistry. Recent work, which highlights the complexity of reactions that can occur in the presence of supported copper(II) chloride as an oxychlorination catalyst, is featured. Although direct comparisons with nanostructured fluorides are not currently possible, the work could be relevant to possible future catalytic developments in nanostructured materials.

  3. Superconductivity in small metal bridges

    International Nuclear Information System (INIS)

    Hannah, E.C.

    1975-01-01

    Josephson effects in weaklinks are discussed for low and high frequency regimes using simple perturbation techniques. It is proven that no measurement of the supercurrent dependence upon frequency above the Riedel peak frequency can be made using rf sources whose frequencies are below the Riedel peak. Thus the bulk of work done in the field on the high frequency structure of the Josephson current is shown to be invalid. Metal bridges shorter than a newly defined temperature independent length for superconductors, l/sub PHONON/, are proven to be identical in their Josephson current behavior to tunneling junctions. The BCS gap equation is generalized to include voltage gradient effects on pairs within the bridge. The oscillation frequency for long bridges (l/sub BRIDGE/ greater than l/sub PHONON/) is shown to be limited to less than 10'' Hz. An experimental test of the new voltage dependent gap is made as well as tests of the pair reforming time of bridges

  4. Generation of highly N-type, defect passivated transition metal oxides using plasma fluorine insertion

    Science.gov (United States)

    Baker, L. Robert; Seo, Hyungtak; Hervier, Antoine; Somorjai, Gabor A.

    2016-04-12

    A new composition of matter is disclosed wherein oxygen vacancies in a semiconducting transition metal oxide such as titanium dioxide are filled with a halogen such as Fluorine, whereby the conductivity of the composition is greatly enhanced, while at the same time the chemical stability of the composition is greatly improved. Stoichiometric titanium dioxide having less than 3 % oxygen vacancies is subject to fluorine insertion such that oxygen vacancies are filled, limited amounts of fluorine replace additional oxygen atoms and fluorine interstitially inserts into the body of the TiO.sub.2 composition.

  5. Basis set effects on the energy of intramolecular O-H...halogen hydrogen bridges in ortho-halophenols and 2,4-dihalo-malonaldehyde

    International Nuclear Information System (INIS)

    Buemi, Giuseppe

    2004-01-01

    Ab initio calculations of hydrogen bridge energies (E HB ) of 2-halophenols were carried out at various levels of sophistication using a variety of basis sets in order to verify their ability in reproducing the experimentally-determined gas phase ordering, and the related experimental frequencies of the O-H vibration stretching mode. The semiempirical AM1 and PM3 approaches were adopted, too. Calculations were extended to the O-H...X bridge of a particular conformation of 2,4-dihalo-malonaldehyde. The results and their trend with respect to the electronegativity of the halogen series are highly dependant on the basis set. The less sophisticated 3-21G, CEP121G and LANL2DZ basis sets (with and without correlation energy inclusion) predict E HB decreasing on decreasing the electronegativity power whilst the opposite is generally found when more extended bases are used. However, all high level calculations confirm the nearly negligible energy differences between the examined O-H...X bridges

  6. Theoretical investigation of the use of nanocages with an adsorbed halogen atom as anode materials in metal-ion batteries.

    Science.gov (United States)

    Razavi, Razieh; Abrishamifar, Seyyed Milad; Rajaei, Gholamreza Ebrahimzadeh; Kahkha, Mohammad Reza Rezaei; Najafi, Meysam

    2018-02-21

    The applicability of C 44 , B 22 N 22 , Ge 44 , and Al 22 P 22 nanocages, as well as variants of those nanocages with an adsorbed halogen atom, as high-performance anode materials in Li-ion, Na-ion, and K-ion batteries was investigated theoretically via density functional theory. The results obtained indicate that, among the nanocages with no adsorbed halogen atom, Al 22 P 22 would be the best candidate for a novel anode material for use in metal-ion batteries. Calculations also suggest that K-ion batteries which utilize these nanocages as anode materials would give better performance and would yield higher cell voltages than the corresponding Li-ion and Na-ion batteries with nanocage-based anodes. Also, the results for the nanocages with an adsorbed halogen atom imply that employing them as anode materials would lead to higher cell voltages and better metal-ion battery performance than if the nanocages with no adsorbed halogen atom were to be used as anode materials instead. Results further implied that nanocages with an adsorbed F atom would give higher cell voltages and better battery performance than nanocages with an adsorbed Cl or Br atom. We were ultimately able to conclude that a K-ion battery that utilized Al 21 P 22 with an adsorbed F atom as its anode material would afford the best metal-ion battery performance; we therefore propose this as a novel highly efficient metal-ion battery. Graphical abstract The results of a theoretical investigation indicated that Al 22 P 22 is a better candidate for a high-performance anode material in metal-ion batteries than Ge 44 is. Calculations also showed that K-ion batteries with nanocage-based anodes would produce higher cell voltages and perform better than the equivalent Li-ion and Na-ion batteries with nanocage-based anodes, and that anodes based on nanocages with an adsorbed F atom would perform better than anodes based on nanocages with an adsorbed Cl or Br atom.

  7. Metal-insulator transitions

    Science.gov (United States)

    Imada, Masatoshi; Fujimori, Atsushi; Tokura, Yoshinori

    1998-10-01

    Metal-insulator transitions are accompanied by huge resistivity changes, even over tens of orders of magnitude, and are widely observed in condensed-matter systems. This article presents the observations and current understanding of the metal-insulator transition with a pedagogical introduction to the subject. Especially important are the transitions driven by correlation effects associated with the electron-electron interaction. The insulating phase caused by the correlation effects is categorized as the Mott Insulator. Near the transition point the metallic state shows fluctuations and orderings in the spin, charge, and orbital degrees of freedom. The properties of these metals are frequently quite different from those of ordinary metals, as measured by transport, optical, and magnetic probes. The review first describes theoretical approaches to the unusual metallic states and to the metal-insulator transition. The Fermi-liquid theory treats the correlations that can be adiabatically connected with the noninteracting picture. Strong-coupling models that do not require Fermi-liquid behavior have also been developed. Much work has also been done on the scaling theory of the transition. A central issue for this review is the evaluation of these approaches in simple theoretical systems such as the Hubbard model and t-J models. Another key issue is strong competition among various orderings as in the interplay of spin and orbital fluctuations. Experimentally, the unusual properties of the metallic state near the insulating transition have been most extensively studied in d-electron systems. In particular, there is revived interest in transition-metal oxides, motivated by the epoch-making findings of high-temperature superconductivity in cuprates and colossal magnetoresistance in manganites. The article reviews the rich phenomena of anomalous metallicity, taking as examples Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Ru compounds. The diverse phenomena include strong spin and

  8. Synthesis and antimalarial activity of metal complexes of cross-bridged tetraazamacrocyclic ligands.

    Science.gov (United States)

    Hubin, Timothy J; Amoyaw, Prince N-A; Roewe, Kimberly D; Simpson, Natalie C; Maples, Randall D; Carder Freeman, TaRynn N; Cain, Amy N; Le, Justin G; Archibald, Stephen J; Khan, Shabana I; Tekwani, Babu L; Khan, M O Faruk

    2014-07-01

    Using transition metals such as manganese(II), iron(II), cobalt(II), nickel(II), copper(II), and zinc(II), several new metal complexes of cross-bridged tetraazamacrocyclic chelators namely, cyclen- and cyclam-analogs with benzyl groups, were synthesized and screened for in vitro antimalarial activity against chloroquine-resistant (W2) and chloroquine-sensitive (D6) strains of Plasmodium falciparum. The metal-free chelators tested showed little or no antimalarial activity. All the metal complexes of the dibenzyl cross-bridged cyclam ligand exhibited potent antimalarial activity. The Mn(2+) complex of this ligand was the most potent with IC50s of 0.127 and 0.157μM against the chloroquine-sensitive (D6) and chloroquine-resistant (W2) P. falciparum strains, respectively. In general, the dibenzyl hydrophobic ligands showed better anti-malarial activity compared to the activity of monobenzyl ligands, potentially because of their higher lipophilicity and thus better cell penetration ability. The higher antimalarial activity displayed by the manganese complex for the cyclam ligand in comparison to that of the cyclen, correlates with the larger pocket of cyclam compared to that of cyclen which produces a more stable complex with the Mn(2+). Few of the Cu(2+) and Fe(2+) complexes also showed improvement in activity but Ni(2+), Co(2+) and Zn(2+) complexes did not show any improvement in activity upon the metal-free ligands for anti-malarial development. Published by Elsevier Ltd.

  9. Preparative Radiation Chemistry of Transition Metal Complexes; Radiosynthese de complexes de metaux de transition; Radiatsionno-khimicheskij sintez kompleksnykh soedinenij perekhodnykh metallov; Radiosintesis de complejos de los metales de transicion

    Energy Technology Data Exchange (ETDEWEB)

    Gustorf, E. Koerner Von; Jun, M. -J.; Koller, H.; Schenck, G. O. [Max-Planck-Institut fuer Kohlenforschung, Abteilung Strahlenchemie, Muelheim-Ruhr, Federal Republic of Germany (Germany)

    1963-11-15

    {pi}-complexes and carbonyl compounds of transition metals have a technical importance because of their special reactivity and catalytic activity. The following investigations have been made by us: 1. Radiation chemical synthesis of transition metal {pi}- complexes Examples are the preparation of maleic-acid-anhydride-iron-tetracarbonyl, fumaric-acid-dimethylesteriron- tetracarbonyl, methacrylic-acid-methylester-iron-tetracarbonyl, vinylacetate-iron-tetiacarbonyl, etc. by Co{sup 60} {gamma}-irradiation of Fe(CO){sub 5} and the corresponding unsaturated compounds. 2. Chemical reactions with radiation-chemically formed {pi}-complexes Examples are the polymerization of vinyl compounds at room temperature by the action of organic halogen compounds on complexes such as methacryl-acid-methylester-iron-tetracarbonyl, vinylacetate-iron- tetracarbonyl, etc. 3. Synthesis of {pi}-complexes and carbonyl compounds of transition metals by irradiation Examples are the Co{sup 60} {gamma}-irradiation of [(C{sub 5}H{sub 5}){sub 2}Fe], [(C{sub 5}H{sub 5}){sub 2N}i], CH{sub 3}C{sub 5}H{sub 4}Mn(CO){sub 3}, (C{sub 5}H{sub 5})TiCl{sub 2},Fe(CO){sub 5}, Ni(CO){sub 4} , in halogen hydrocarbons. (author) [French] Les complexes {pi} et les composes carbonyles des metaux de transition ont une importance du point de vue technique en raison de leur reactivite speciale et de leur activite catalytique. L'auteur a fait des experiences sur les questions suivantes: 1. Radiosynthese de complexes {pi} de metaux de transition. Exemple: preparation d'anhydride maleique-fer tetracarbonyle, de fumarate de dimethyle-fer tetracarbonyle, de methacrylate de methyle-fer tetracarbonyl, d'acetate de vinyle-fer tetracarbonyle, etc., par exposition de Fe(CO){sub 5} et des composes non satures correspondant aux rayons gamma du cobalt-60. 2. Reactions chimiques avec des complexes n formes par voie radiochimique. Exemple: polymerisation de composes vinyliques a temperature ambiante en presence de composes organiques

  10. Oligomeric rare-earth metal cluster complexes with endohedral transition metal atoms

    Energy Technology Data Exchange (ETDEWEB)

    Steinberg, Simon; Zimmermann, Sina; Brühmann, Matthias; Meyer, Eva; Rustige, Christian; Wolberg, Marike; Daub, Kathrin; Bell, Thomas; Meyer, Gerd, E-mail: gerd.meyer@uni-koeln.de

    2014-11-15

    Comproportionation reactions of rare-earth metal trihalides (RX{sub 3}) with the respective rare-earth metals (R) and transition metals (T) led to the formation of 22 oligomeric R cluster halides encapsulating T, in 19 cases for the first time. The structures of these compounds were determined by single-crystal X-ray diffraction and are composed of trimers ((T{sub 3}R{sub 11})X{sub 15}-type, P6{sub 3}/m), tetramers ((T{sub 4}R{sub 16})X{sub 28}(R{sub 4}) (P-43m), (T{sub 4}R{sub 16})X{sub 20} (P4{sub 2}/nnm), (T{sub 4}R{sub 16})X{sub 24}(RX{sub 3}){sub 4} (I4{sub 1}/a) and (T{sub 4}R{sub 16})X{sub 23} (C2/m) types of structure) and pentamers ((Ru{sub 5}La{sub 14}){sub 2}Br{sub 39}, Cc) of (TR{sub r}){sub n} (n=2–5) clusters. These oligomers are further enveloped by inner (X{sup i}) as well as outer (X{sup a}) halido ligands, which possess diverse functionalities and interconnect like oligomers through i–i, i–a and/or a–i bridges. The general features of the crystal structures for these new compounds are discussed and compared to literature entries as well as different structure types with oligomeric T centered R clusters. Dimers and tetramers originating from the aggregation of (TR{sub 6}) octahedra via common edges are more frequent than trimers and pentamers, in which the (TR{sub r}) clusters share common faces. - Graphical abstract: Rare earth-metal cluster complexes with endohedral transition metal atoms (TR{sub 6}) may connect via common edges or faces to form dimers, trimers, tetramers and pentamers of which the tetramers are the most prolific. Packing effects and electron counts play an important role. - Highlights: • Rare-earth metal cluster complexes encapsulate transition metal atoms. • Oligomers are built via connection of octahedral clusters via common edges or faces. • Dimers through pentamers with closed structures are known. • Tetramers including a tetrahedron of endohedral atoms are the most prolific.

  11. Synthesis and physical and chemical properties of poly-hydro-aluminates and poly-halogen-aluminates metals of II A group

    International Nuclear Information System (INIS)

    Khudoydodov, B.O.

    1990-01-01

    The purpose of the present work is investigation of conditions and mechanism of passing of formation reactions of aluminum hydrides, poly-hydride-aluminates and poly-halogen-aluminates of alkaline-earth metals and magnesium and studying of their physical and chemical properties

  12. Experimental and computational evidence of halogen bonds involving astatine

    Science.gov (United States)

    Guo, Ning; Maurice, Rémi; Teze, David; Graton, Jérôme; Champion, Julie; Montavon, Gilles; Galland, Nicolas

    2018-03-01

    The importance of halogen bonds—highly directional interactions between an electron-deficient σ-hole moiety in a halogenated compound and an acceptor such as a Lewis base—is being increasingly recognized in a wide variety of fields from biomedicinal chemistry to materials science. The heaviest halogens are known to form stronger halogen bonds, implying that if this trend continues down the periodic table, astatine should exhibit the highest halogen-bond donating ability. This may be mitigated, however, by the relativistic effects undergone by heavy elements, as illustrated by the metallic character of astatine. Here, the occurrence of halogen-bonding interactions involving astatine is experimentally evidenced. The complexation constants of astatine monoiodide with a series of organic ligands in cyclohexane solution were derived from distribution coefficient measurements and supported by relativistic quantum mechanical calculations. Taken together, the results show that astatine indeed behaves as a halogen-bond donor—a stronger one than iodine—owing to its much more electrophilic σ-hole.

  13. Determination of halogens by flame emission of metal halogenides

    International Nuclear Information System (INIS)

    Henrion, G.; Marquardt, D.; Stoecker, B.

    1979-01-01

    The A-B systems InF, InCl, InBr, and InI have been excited by laminar H 2 -N 2 flames in order to dermine individual halogens or their mixtures qualitatively or quantitatively. In optimizing the fuel gas composition two different behavior patterns have been found for band intensities, which are correlated with binding energies of InX (X = halogen). The low temperature of the flame leads to complicated matrix effects which first of all result from effects on excitation and from competitive reactions. In general, cations cause a decreased intensity. Therefore, salts have to be converted into hydrohalide acids by ion exchange. Qualitative determinations of individual halogens are possible at a 500 to 50,000fold excess of the others, whereas quantitative determinations can be performed at a 100 to 5,000fold excess in 10 -4 molar solutions with errors of 2 to 10 per cent. (author)

  14. Synthesis of carbon nanotubes bridging metal electrodes

    International Nuclear Information System (INIS)

    Kotlar, M.; Vojs, M.; Marton, M.; Vesel, M.; Redhammer, R.

    2012-01-01

    In our work we demonstrate growth of carbon nanotubes that can conductively bridge the metal electrodes. The role of different catalysts was examined. Interdigitated metal electrodes are made from copper and we are using bimetal Al/Ni as catalyst for growth of carbon nanotubes. We are using this catalyst composition for growth of the single-walled carbon nanotube network. (authors)

  15. 49 CFR 213.353 - Turnouts, crossovers, and lift rail assemblies or other transition devices on moveable bridges.

    Science.gov (United States)

    2010-10-01

    ... other transition devices on moveable bridges. 213.353 Section 213.353 Transportation Other Regulations... rail assemblies or other transition devices on moveable bridges. (a) In turnouts and track crossings... other transition devices on moveable bridges, the track owner shall prepare an inspection and...

  16. A basic study on electrodeposition of metal halogen mixture in fluoride/chloride molten salts

    International Nuclear Information System (INIS)

    Shim, Z. H.; Kang, Y. H.; Hwang, S. C.; Woo, M. S.; Yoo, J. H.

    2001-01-01

    The electrodeposition experiments of metal mixture composed of U, Y, Gd, Nd and Ce were carried out in the KCl-LiCl and LiF-NaF-KF (FLINAK) eutectic melts at 500 .deg. C and 600 .deg. C, respectively. Uranium was major component in the cathode deposits, and the separation factors of uranium with respect to the rare earths (REs) are nearly same in both electrolytes. REs content in the cathode deposits increased sharply below -1.9V which is the decomposition voltage of the halogen compounds of REs. The current efficiency for electrodeposition of metals was inversely in proportion to the applied voltage in the range of -1.0 V to -1.9 V(vs. S.S. 304 or Ni)

  17. First-principles studies on the effects of halogen adsorption on monolayer antimony.

    Science.gov (United States)

    Yeoh, Keat Hoe; Yoon, Tiem Leong; Ong, Duu Sheng; Lim, Thong Leng; Zuntu Abdullahi, Yusuf

    2017-09-27

    Using first-principles calculations, we carry out systematic studies on the electronic, magnetic and structural properties of halogenated β-phase antimonene. We consider two different levels of halogen adatom coverage i.e. Θ = 1/8 and Θ = 1/18. It is found that F, Cl and Br adatoms act as acceptors whereas the I adatom acts as a donor. For a high coverage of Θ = 1/8, halogenated β-phase antimonene exhibits metallic characteristics. With a lower coverage of Θ = 1/18, through the adsorption of F, Cl and Br the semiconducting unstrained antimonene becomes metallic. In contrast, I-adsorbed antimonene remains semiconducting but exhibits magnetic behavior. We further investigate the effects of bi-axial strain on the halogenated β-phase antimonene. It is found that bi-axial strain can only induce ferromagnetism on the halogenated antimonene at Θ = 1/18. However, the ferromagnetism is suppressed when the applied strain is high. We uncover that the emergence of strain-dependent magnetism is attributed to the presence of localized states in the bandgap resulting from collective effects of bi-axial strain and the adsorption of halogen atoms.

  18. Microwave-assisted synthesis of transition metal phosphide

    Science.gov (United States)

    Viswanathan, Tito

    2014-12-30

    A method of synthesizing transition metal phosphide. In one embodiment, the method has the steps of preparing a transition metal lignosulfonate, mixing the transition metal lignosulfonate with phosphoric acid to form a mixture, and subjecting the mixture to a microwave radiation for a duration of time effective to obtain a transition metal phosphide.

  19. Rectified tunneling current response of bio-functionalized metal-bridge-metal junctions.

    Science.gov (United States)

    Liu, Yaqing; Offenhäusser, Andreas; Mayer, Dirk

    2010-01-15

    Biomolecular bridged nanostructures allow direct electrical addressing of electroactive biomolecules, which is of interest for the development of bioelectronic and biosensing hybrid junctions. In the present paper, the electroactive biomolecule microperoxidase-11 (MP-11) was integrated into metal-bridge-metal (MBM) junctions assembled from a scanning tunneling microscope (STM) setup. Before immobilization of MP-11, the Au working electrode was first modified by a self-assembled monolayer of 1-undecanethiol (UDT). A symmetric and potential independent response of current-bias voltage (I(t)/V(b)) was observed for the Au (substrate)/UDT/Au (tip) junction. However, the I(t)/V(b) characteristics became potential dependent and asymmetrical after binding of MP-11 between the electrodes of the junction. The rectification ratio of the asymmetric current response varies with gate electrode modulation. A resonant tunneling process between metal electrode and MP-11 enhances the tunneling current and is responsible for the observed rectification. Our investigations demonstrated that functional building blocks of proteins can be reassembled into new conceptual devices with operation modes deviating from their native function, which could prove highly useful in the design of future biosensors and bioelectronic devices. Copyright 2009 Elsevier B.V. All rights reserved.

  20. High-Pressure Thermodynamic Properties of f-electron Metals, Transition Metal Oxides, and Half-Metallic Magnets

    International Nuclear Information System (INIS)

    Richard T. Scalettar; Warren E. Pickett

    2005-01-01

    This project involves research into the thermodynamic properties of f-electron metals, transition metal oxides, and half-metallic magnets at high pressure. These materials are ones in which the changing importance of electron-electron interactions as the distance between atoms is varied can tune the system through phase transitions from localized to delocalized electrons, from screened to unscreened magnetic moments, and from normal metal to one in which only a single spin specie can conduct. Three main thrusts are being pursued: (1) Mott transitions in transition metal oxides, (2) magnetism in half-metallic compounds, and (3) large volume-collapse transitions in f-band metals

  1. High-Pressure Thermodynamic Properties of f-electron Metals, Transition Metal Oxides, and Half-Metallic Magnets

    Energy Technology Data Exchange (ETDEWEB)

    Scalettar, Richard T.; Pickett, Warren E.

    2004-07-01

    This project involves research into the thermodynamic properties of f-electron metals, transition metal oxides, and half-metallic magnets at high pressure. These materials are ones in which the changing importance of electron-electron interactions as the distance between atoms is varied can tune the system through phase transitions from localized to delocalized electrons, from screened to unscreened magnetic moments, and from normal metal to one in which only a single spin specie can conduct. Three main thrusts are being pursued: (1) Mott transitions in transition metal oxides, (2) magnetism in half-metallic compounds, and (3) large volume-collapse transitions in f-band metals.

  2. High-Pressure Thermodynamic Properties of f-electron Metals, Transition Metal Oxides, and Half-Metallic Magnets

    Energy Technology Data Exchange (ETDEWEB)

    Richard T. Scalettar; Warren E. Pickett

    2005-08-02

    This project involves research into the thermodynamic properties of f-electron metals, transition metal oxides, and half-metallic magnets at high pressure. These materials are ones in which the changing importance of electron-electron interactions as the distance between atoms is varied can tune the system through phase transitions from localized to delocalized electrons, from screened to unscreened magnetic moments, and from normal metal to one in which only a single spin specie can conduct. Three main thrusts are being pursued: (i) Mott transitions in transition metal oxides, (ii) magnetism in half-metallic compounds, and (iii) large volume-collapse transitions in f-band metals.

  3. Extracting metals directly from metal oxides

    International Nuclear Information System (INIS)

    Wai, C.M.; Smart, N.G.; Phelps, C.

    1997-01-01

    A method of extracting metals directly from metal oxides by exposing the oxide to a supercritical fluid solvent containing a chelating agent is described. Preferably, the metal is an actinide or a lanthanide. More preferably, the metal is uranium, thorium or plutonium. The chelating agent forms chelates that are soluble in the supercritical fluid, thereby allowing direct removal of the metal from the metal oxide. In preferred embodiments, the extraction solvent is supercritical carbon dioxide and the chelating agent is selected from the group consisting of β-diketones, halogenated β-diketones, phosphinic acids, halogenated phosphinic acids, carboxylic acids, halogenated carboxylic acids, and mixtures thereof. In especially preferred embodiments, at least one of the chelating agents is fluorinated. The method provides an environmentally benign process for removing metals from metal oxides without using acids or biologically harmful solvents. The chelate and supercritical fluid can be regenerated, and the metal recovered, to provide an economic, efficient process. 4 figs

  4. Mechanistic studies of copper(I)-catalyzed 1,3-halogen migration.

    Science.gov (United States)

    Van Hoveln, Ryan; Hudson, Brandi M; Wedler, Henry B; Bates, Desiree M; Le Gros, Gabriel; Tantillo, Dean J; Schomaker, Jennifer M

    2015-04-29

    An ongoing challenge in modern catalysis is to identify and understand new modes of reactivity promoted by earth-abundant and inexpensive first-row transition metals. Herein, we report a mechanistic study of an unusual copper(I)-catalyzed 1,3-migration of 2-bromostyrenes that reincorporates the bromine activating group into the final product with concomitant borylation of the aryl halide bond. A combination of experimental and computational studies indicated this reaction does not involve any oxidation state changes at copper; rather, migration occurs through a series of formal sigmatropic shifts. Insight provided from these studies will be used to expand the utility of aryl copper species in synthesis and develop new ligands for enantioselective copper-catalyzed halogenation.

  5. Parity-Forbidden Transitions and Their Impact on the Optical Absorption Properties of Lead-Free Metal Halide Perovskites and Double Perovskites.

    Science.gov (United States)

    Meng, Weiwei; Wang, Xiaoming; Xiao, Zewen; Wang, Jianbo; Mitzi, David B; Yan, Yanfa

    2017-07-06

    Using density functional theory calculations, we analyze the optical absorption properties of lead (Pb)-free metal halide perovskites (AB 2+ X 3 ) and double perovskites (A 2 B + B 3+ X 6 ) (A = Cs or monovalent organic ion, B 2+ = non-Pb divalent metal, B + = monovalent metal, B 3+ = trivalent metal, X = halogen). We show that if B 2+ is not Sn or Ge, Pb-free metal halide perovskites exhibit poor optical absorptions because of their indirect band gap nature. Among the nine possible types of Pb-free metal halide double perovskites, six have direct band gaps. Of these six types, four show inversion symmetry-induced parity-forbidden or weak transitions between band edges, making them not ideal for thin-film solar cell applications. Only one type of Pb-free double perovskite shows optical absorption and electronic properties suitable for solar cell applications, namely, those with B + = In, Tl and B 3+ = Sb, Bi. Our results provide important insights for designing new metal halide perovskites and double perovskites for optoelectronic applications.

  6. Unique edge-sharing sulfate-transition metal coordination in Na2M(SO4)2 (M=Ni and Co)

    International Nuclear Information System (INIS)

    Fry, Allyson M.; Sweeney, Owen T.; Adam Phelan, W.; Drichko, Natalia; Siegler, Maxime A.; McQueen, Tyrel M.

    2015-01-01

    Two compounds, Na 2 Ni(SO 4 ) 2 and Na 2 Co(SO 4 ) 2 , were synthesized and their structure and properties were characterized. They adopt a structure that contains a bidentate coordination of sulfate to the transition metal center, which was determined via single crystal X-ray diffraction combined with model refinements to both laboratory X-ray and time-of-flight neutron powder diffraction data. The compounds were both found to crystallize in the C2/c space group with Z=24 and a unit cell of a=23.3461(3) Å, b=10.3004(1) Å, c=17.4115(2) Å, β=98.8659(9)°, and V=4136.99(8) Å 3 for the cobalt analog and a=23.2253(1) Å, b=10.26155(6) Å, c=17.3353(1) Å, β=99.0376(5)°, and V=4080.20(5) Å 3 for the nickel analog. Magnetization measurements show that the transition metal centers have negligible interactions with neighboring sites. Infrared and Raman spectroscopies were used to further probe the unique sulfate-transition metal coordination, and confirm the bidentate binding motif. The resulting pseudo-trigonal bipyramidal coordination produces vivid violet, Na 2 Co(SO 4 ) 2 , and yellow, Na 2 Ni(SO 4 ) 2 , colors that were probed by diffuse reflectance. - Graphical abstract: Two blue distorted transition metal octahedra (oxygen in red) bridged by two sulfate tetrahedra are shown here. Each bridging sulfate tetrahedra shares an edge with one octahedron and a corner with the other. All of the remaining corners of the octahedra are corner sharing with four tetrahedra forming a polyhedral network. - Highlights: • Structure of Na2Ni(SO4)2 and Na2Co(SO4)2 is determined. • Unique sulfate-transition metal binding observed in the new structure. • Combined diffraction and spectroscopic techniques were used. • Magnetization measurements show negligible interactions between sites

  7. 40 CFR 63.2465 - What requirements must I meet for process vents that emit hydrogen halide and halogen HAP or HAP...

    Science.gov (United States)

    2010-07-01

    ... process vents that emit hydrogen halide and halogen HAP or HAP metals? 63.2465 Section 63.2465 Protection... and halogen HAP or HAP metals? (a) You must meet each emission limit in Table 3 to this subpart that... section. (b) If any process vents within a process emit hydrogen halide and halogen HAP, you must...

  8. High-pressure phase transition of alkali metal-transition metal deuteride Li2PdD2

    Science.gov (United States)

    Yao, Yansun; Stavrou, Elissaios; Goncharov, Alexander F.; Majumdar, Arnab; Wang, Hui; Prakapenka, Vitali B.; Epshteyn, Albert; Purdy, Andrew P.

    2017-06-01

    A combined theoretical and experimental study of lithium palladium deuteride (Li2PdD2) subjected to pressures up to 50 GPa reveals one structural phase transition near 10 GPa, detected by synchrotron powder x-ray diffraction, and metadynamics simulations. The ambient-pressure tetragonal phase of Li2PdD2 transforms into a monoclinic C2/m phase that is distinct from all known structures of alkali metal-transition metal hydrides/deuterides. The structure of the high-pressure phase was characterized using ab initio computational techniques and from refinement of the powder x-ray diffraction data. In the high-pressure phase, the PdD2 complexes lose molecular integrity and are fused to extended [PdD2]∞ chains. The discovered phase transition and new structure are relevant to the possible hydrogen storage application of Li2PdD2 and alkali metal-transition metal hydrides in general.

  9. Reliability Analysis-Based Numerical Calculation of Metal Structure of Bridge Crane

    Directory of Open Access Journals (Sweden)

    Wenjun Meng

    2013-01-01

    Full Text Available The study introduced a finite element model of DQ75t-28m bridge crane metal structure and made finite element static analysis to obtain the stress response of the dangerous point of metal structure in the most extreme condition. The simulated samples of the random variable and the stress of the dangerous point were successfully obtained through the orthogonal design. Then, we utilized BP neural network nonlinear mapping function trains to get the explicit expression of stress in response to the random variable. Combined with random perturbation theory and first-order second-moment (FOSM method, the study analyzed the reliability and its sensitivity of metal structure. In conclusion, we established a novel method for accurately quantitative analysis and design of bridge crane metal structure.

  10. Half-Metallic Ferromagnetism and Stability of Transition Metal Pnictides and Chalcogenides

    Science.gov (United States)

    Liu, Bang-Gui

    It is highly desirable to explore robust half-metallic ferromagnetic materials compatible with important semiconductors for spintronic applications. A state-of-the-art full potential augmented plane wave method within the densityfunctional theory is reliable enough for this purpose. In this chapter we review theoretical research on half-metallic ferromagnetism and structural stability of transition metal pnictides and chalcogenides. We show that some zincblende transition metal pnictides are half-metallic and the half-metallic gap can be fairly wide, which is consistent with experiment. Systematic calculations reveal that zincblende phases of CrTe, CrSe, and VTe are excellent half-metallic ferromagnets. These three materials have wide half-metallic gaps, are low in total energy with respect to the corresponding ground-state phases, and, importantly, are structurally stable. Halfmetallic ferromagnetism is also found in wurtzite transition metal pnictides and chalcogenides and in transition-metal doped semiconductors as well as deformed structures. Some of these half-metallic materials could be grown epitaxially in the form of ultrathin .lms or layers suitable for real spintronic applications.

  11. Transition metal nuclear magnetic resonance

    International Nuclear Information System (INIS)

    Pregosin, P.S.

    1991-01-01

    Transition metal NMR spectroscopy has progressed enormously in recent years. New methods, and specifically solid-state methods and new pulse sequences, have allowed access to data from nuclei with relatively low receptivities with the result that chemists have begun to consider old and new problems, previously unapproachable. Moreover, theory, computational science in particular, now permits the calculation of not just 13 C, 15 N and other light nuclei chemical shifts, but heavy main-group element and transition metals as well. These two points, combined with increasing access to high field pulsed spectrometer has produced a wealth of new data on the NMR transition metals. A new series of articles concerned with measuring, understanding and using the nuclear magnetic resonance spectra of the metals of Group 3-12 is presented. (author)

  12. Unusual bridging of three nitrates with two bridgehead protons in an octaprotonated azacryptand

    Science.gov (United States)

    Saeed, Musabbir A.; Fronczek, Frank R.; Huang, Ming-Ju; Hossain, Md. Alamgir

    2010-01-01

    Structural analysis of the nitrate complex of a thiophene-based azacryptand suggests that three nitrates are bridged with two bridgehead protons which play the topological role of two transition metal ions in a classical Werner type coordination complex bridging three anions. PMID:20066306

  13. Linking precious metal enrichment and halogen cycling in mafic magmatic systems: insights from the Rum layered intrusion, NW Scotland

    Science.gov (United States)

    Kelly, A. P.; O'Driscoll, B.; Clay, P. L.; Burgess, R.

    2017-12-01

    Layered intrusions host the world's largest known concentrations of the platinum-group elements (PGE). Emphasis has been attached to the role of halogen-bearing fluids in concentrating the precious metals, but whether this occurs at the magmatic stage, or via subsequent metasomatism, is actively debated. One obstacle to progress has been the analytical difficulty of measuring low abundances of the halogens in the cumulate products of layered intrusions. To elucidate the importance of the halogens in facilitating PGE-mineralisation, as well as fingerprint halogen provenance and assess the importance of halogen cycling in mafic magma systems more generally, a suite of samples encompassing different stages of activity of the Palaeogene Rum layered intrusion was investigated. Halogen abundances were measured by neutron irradiation noble gas mass spectrometric analysis, permitting the detection of relatively low (ppm-ppb) abundances of Cl, Br and I in mg-sized samples. The samples include PGE-enriched chromite seams, various cumulates (e.g., peridotites), picrites (approximating the Rum parental magma), and pegmatites representing volatile-rich melts that circulated the intrusion at a late-stage in its solidification history. The new data reveal that PGE-bearing chromite seams contain relatively low Cl concentrations (2-3 ppm), with high molar ratios of Br/Cl and I/Cl (0.005 and 0.009, respectively). The picrites and cumulates have Br/Cl and I/Cl ratios close to sub-continental lithospheric mantle values of approximately 0.0013 and 0.00002, respectively, and thus likely reflect the Rum magma source region. A positive correlation between Cl and Br signifies comparable partitioning behaviour in all samples. However, I is more variable, displaying a positive correlation with Cl for more primitive samples (e.g. picrite and peridotite), and seemingly decoupling from Br and Cl in chromite seams and pegmatites. The relative enrichment of I over Cl in the chromite seams points

  14. Selective adsorption of a supramolecular structure on flat and stepped gold surfaces

    Science.gov (United States)

    Peköz, Rengin; Donadio, Davide

    2018-04-01

    Halogenated aromatic molecules assemble on surfaces forming both hydrogen and halogen bonds. Even though these systems have been intensively studied on flat metal surfaces, high-index vicinal surfaces remain challenging, as they may induce complex adsorbate structures. The adsorption of 2,6-dibromoanthraquinone (2,6-DBAQ) on flat and stepped gold surfaces is studied by means of van der Waals corrected density functional theory. Equilibrium geometries and corresponding adsorption energies are systematically investigated for various different adsorption configurations. It is shown that bridge sites and step edges are the preferred adsorption sites for single molecules on flat and stepped surfaces, respectively. The role of van der Waals interactions, halogen bonds and hydrogen bonds are explored for a monolayer coverage of 2,6-DBAQ molecules, revealing that molecular flexibility and intermolecular interactions stabilize two-dimensional networks on both flat and stepped surfaces. Our results provide a rationale for experimental observation of molecular carpeting on high-index vicinal surfaces of transition metals.

  15. (Electronic structure and reactivities of transition metal clusters)

    Energy Technology Data Exchange (ETDEWEB)

    1992-01-01

    The following are reported: theoretical calculations (configuration interaction, relativistic effective core potentials, polyatomics, CASSCF); proposed theoretical studies (clusters of Cu, Ag, Au, Ni, Pt, Pd, Rh, Ir, Os, Ru; transition metal cluster ions; transition metal carbide clusters; bimetallic mixed transition metal clusters); reactivity studies on transition metal clusters (reactivity with H{sub 2}, C{sub 2}H{sub 4}, hydrocarbons; NO and CO chemisorption on surfaces). Computer facilities and codes to be used, are described. 192 refs, 13 figs.

  16. Atomistic Simulation of the Rate-Dependent Ductile-to-Brittle Failure Transition in Bicrystalline Metal Nanowires.

    Science.gov (United States)

    Tao, Weiwei; Cao, Penghui; Park, Harold S

    2018-02-14

    The mechanical properties and plastic deformation mechanisms of metal nanowires have been studied intensely for many years. One of the important yet unresolved challenges in this field is to bridge the gap in properties and deformation mechanisms reported for slow strain rate experiments (∼10 -2 s -1 ), and high strain rate molecular dynamics (MD) simulations (∼10 8 s -1 ) such that a complete understanding of strain rate effects on mechanical deformation and plasticity can be obtained. In this work, we use long time scale atomistic modeling based on potential energy surface exploration to elucidate the atomistic mechanisms governing a strain-rate-dependent incipient plasticity and yielding transition for face centered cubic (FCC) copper and silver nanowires. The transition occurs for both metals with both pristine and rough surfaces for all computationally accessible diameters (ductile-to-brittle transition in failure mode similar to previous experimental studies on bicrystalline silver nanowires is observed, which is driven by differences in dislocation activity and grain boundary mobility as compared to the high strain rate case.

  17. Lifecycle Assessments of Railway Bridge Transitions Exposed to Extreme Climate Events

    Directory of Open Access Journals (Sweden)

    Sadudee Setsobhonkul

    2017-06-01

    Full Text Available Railway track components located at bridge transition zones or approach areas suffer from impact load and vibrations caused by abrupt changes in track stiffness on the bridge and the subgrade. The numerous strategies that can be used to mitigate these abrupt track stiffness changes rely on one of two concepts. The first concept is that of providing a gradual stiffness change, and the second is that of equalizing the track stiffness. A number of such mitigation methods have been developed and implemented over recent decades. Construction activities associated with these methods require various materials, processes, and uses of time, costs, and carbon emissions. In this study, eight of the most common techniques for railway bridge transition mitigation, including under ballast mats (UBMs, soft baseplates, under sleeper pads (USPs, rail pads, embankment treatments, transition slabs, ballast bonding, and wide sleepers, are compared. This study benchmarks the costs and carbon emissions of these eight mitigation techniques over the 50-year lifespan of a railway system subject to identical probabilities of four environmental scenarios: a control case, extremely high temperatures, extremely low temperatures, and flash flooding. This unprecedented study systemically investigates the effectiveness of the mitigation methods while considering the effects of 30 and 100 m bridge span lengths. Our results indicate that railway engineers should adopt different mitigation methods for different scenarios. The soft baseplate is the most appropriate method for a short-span bridge in the control case and the case of flash flooding, while ballast bonding is better for long-span railway bridges. Embankment treatment is recommended for both high- and low-extreme temperatures. However, its applicability is limited when the differential track stiffness is extremely high. Hence, alternatives that are 5–25% more expensive are proposed in parallel. The alternative

  18. Statistical analysis of fatigue crack propagation data of materials from ancient portuguese metallic bridges

    Directory of Open Access Journals (Sweden)

    J A F O. Correia

    2017-10-01

    Full Text Available In Portugal there is a number of old metallic riveted railway and highway bridges that were erected by the end of the 19th century and beginning of the 20th century, and are still in operation, requiring inspections and remediation measures to overcome fatigue damage. Residual fatigue life predictions should be based on actual fatigue data from bridge materials which is scarce due to the material specificities. Fatigue crack propagation data of materials from representative Portuguese riveted bridges, namely the Pinh�o and Luiz I road bridges, the Viana road/railway bridge, the F�o road bridge and the Trez�i railway bridge were considered in this study. The fatigue crack growth rates were correlated using the Pariss law. Also, a statistical analysis of the pure mode I fatigue crack growth (FCG data available for the materials from the ancient riveted metallic bridges is presented. Based on this analysis, design FCG curves are proposed and compared with BS7910 standard proposal, for the Paris region, which is one important fatigue regime concerning the application of the Fracture Mechanics approaches, to predict the remnant fatigue life of structural details

  19. Halogenated fatty acids

    DEFF Research Database (Denmark)

    Mu, Huiling; Sundin, Peter; Wesén, Clas

    1997-01-01

    Halogenated fatty acids are the major contributors to organohalogen compounds in lipids of marine mammals, fish, and bivalves. For the initial characterization of these recently noticed compounds, a determination of the halogen concentration has usually been combined with some lipid isolation......), atomic emission spectrometry, and mass spectrometry. For most environmental samples, chlorinated FAMEs must be enriched prior to GC. ELCD is a useful detection method for indicating halogenated FAMEs in the chromatograms, and tentative identification of the halogenated species can be obtained...

  20. Metal-to-nonmetal transitions

    CERN Document Server

    Hensel, Friedrich; Holst, Bastian

    2010-01-01

    This book is devoted to nonmetal-to-metal transitions. The original ideas of Mott for such a transition in solids have been adapted to describe a broad variety of phenomena in condensed matter physics (solids, liquids, and fluids), in plasma and cluster physics, as well as in nuclear physics (nuclear matter and quark-gluon systems). The book gives a comprehensive overview of theoretical methods and experimental results of the current research on the Mott effect for this wide spectrum of topics. The fundamental problem is the transition from localized to delocalized states which describes the nonmetal-to-metal transition in these diverse systems. Based on the ideas of Mott, Hubbard, Anderson as well as Landau and Zeldovich, internationally respected scientists present the scientific challenges and highlight the enormous progress which has been achieved over the last years. The level of description is aimed to specialists in these fields as well as to young scientists who will get an overview for their own work...

  1. Superconductivity in transition metals.

    Science.gov (United States)

    Slocombe, Daniel R; Kuznetsov, Vladimir L; Grochala, Wojciech; Williams, Robert J P; Edwards, Peter P

    2015-03-13

    A qualitative account of the occurrence and magnitude of superconductivity in the transition metals is presented, with a primary emphasis on elements of the first row. Correlations of the important parameters of the Bardeen-Cooper-Schrieffer theory of superconductivity are highlighted with respect to the number of d-shell electrons per atom of the transition elements. The relation between the systematics of superconductivity in the transition metals and the periodic table high-lights the importance of short-range or chemical bonding on the remarkable natural phenomenon of superconductivity in the chemical elements. A relationship between superconductivity and lattice instability appears naturally as a balance and competition between localized covalent bonding and so-called broken covalency, which favours d-electron delocalization and superconductivity. In this manner, the systematics of superconductivity and various other physical properties of the transition elements are related and unified. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

  2. Determination of heavy metals and halogens in plastics from electric and electronic waste

    International Nuclear Information System (INIS)

    Dimitrakakis, Emmanouil; Janz, Alexander; Bilitewski, Bernd; Gidarakos, Evangelos

    2009-01-01

    The presence of hazardous substances and preparations in small waste electrical and electronic equipment (sWEEE) found in the residual household waste stream of the city of Dresden, Germany has been investigated. The content of sWEEE plastics in heavy metals and halogens is determined using handheld X-ray fluorescence analysis (HXRF), elemental analysis by means of atomic absorption spectrometry (AAS) and ion exchange chromatography (IEC). Mean value of results for heavy metals in samples (n = 51) by AAS are 17.4 mg/kg for Pb, 5.7 mg/kg for Cd, 8.4 mg/kg for Cr. The mass fraction of an additive as shown by HXRF (n = 161) can vary over a wide range. Precise deductions as regards sWEEE plastics content in hazardous substances and preparations cannot be made. Additional research would be expedient regarding the influence of hazardous substances to recycling processes, in particular regarding the contamination of clean fractions in the exit streams of a WEEE treatment plant. Suitable standards for calibrating HXRF for use on EEE plastics or complex electr(on)ic components do not exist and should be developed.

  3. Halogen bond preferences of thiocyanate ligand coordinated to Ru(II) via sulphur atom

    Science.gov (United States)

    Ding, Xin; Tuikka, Matti; Hirva, Pipsa; Haukka, Matti

    2017-09-01

    Halogen bonding between [Ru(bpy)(CO)2(S-SCN)2] (bpy = 2,2'-bipyridine), I2 was studied by co-crystallising the metal compound and diiodine from dichloromethane. The only observed crystalline product was found to be [Ru(bpy)(CO)2(S-SCN)2]ṡI2 with only one NCSṡṡṡI2 halogen bond between I2 and the metal coordinated S atom of one of the thiocyanate ligand. The dangling nitrogen atoms were not involved in halogen bonding. However, computational analysis suggests that there are no major energetic differences between the NCSṡṡṡI2 and SCNṡṡṡI2 bonding modes. The reason for the observed NCSṡṡṡI2 mode lies most probably in the more favourable packing effects rather than energetic preferences between NCSṡṡṡI2 and SCNṡṡṡI2 contacts.

  4. Mesoporous Transition Metal Oxides for Supercapacitors.

    Science.gov (United States)

    Wang, Yan; Guo, Jin; Wang, Tingfeng; Shao, Junfeng; Wang, Dong; Yang, Ying-Wei

    2015-10-14

    Recently, transition metal oxides, such as ruthenium oxide (RuO₂), manganese dioxide (MnO₂), nickel oxides (NiO) and cobalt oxide (Co₃O₄), have been widely investigated as electrode materials for pseudo-capacitors. In particular, these metal oxides with mesoporous structures have become very hot nanomaterials in the field of supercapacitors owing to their large specific surface areas and suitable pore size distributions. The high specific capacities of these mesoporous metal oxides are resulted from the effective contacts between electrode materials and electrolytes as well as fast transportation of ions and electrons in the bulk of electrode and at the interface of electrode and electrolyte. During the past decade, many achievements on mesoporous transition metal oxides have been made. In this mini-review, we select several typical nanomaterials, such as RuO₂, MnO₂, NiO, Co₃O₄ and nickel cobaltite (NiCo₂O₄), and briefly summarize the recent research progress of these mesoporous transition metal oxides-based electrodes in the field of supercapacitors.

  5. Are superhalogens without halogen ligand capable of transcending traditional halogen-based superhalogens? Ab initio case study of binuclear anions based on pseudohalogen ligand

    Science.gov (United States)

    Li, Jin-Feng; Sun, Yin-Yin; Bai, Hongcun; Li, Miao-Miao; Li, Jian-Li; Yin, Bing

    2015-06-01

    The superhalogen properties of polynuclear structures without halogen ligand are theoretically explored here for several [M2(CN)5]-1 (M = Ca, Be) clusters. At CCSD(T) level, these clusters have been confirmed to be superhalogens due to their high vertical electron detachment energies (VDE). The largest one is 9.70 eV for [Ca2(CN)5]-1 which is even higher than those of corresponding traditional structures based on fluorine or chlorine ligands. Therefore the superhalogens stronger than the traditional halogen-based structures could be realized by ligands other than halogen atoms. Compared with CCSD(T), outer valence Green's function (OVGF) method either overestimates or underestimates the VDEs for different structures while MP2 results are generally consistent in the aspect of relative values. The extra electrons of the highest VDE anions here aggregate on the bridging CN units with non-negligible distribution occurring on other CN units too. These two features lower both the potential and kinetic energies of the extra electron respectively and thus lead to high VDE. Besides superhalogen properties, the structures, relative stabilities and thermodynamic stabilities with respect to the detachment of cyanide ligand were also investigated. The sum of these results identifies the potential of polynuclear structures with pseudohalogen ligand as suitable candidates with enhanced superhalogens properties.

  6. Characteristics of a plasma flow field produced by a metal array bridge foil explosion

    Science.gov (United States)

    Junying, WU; Long, WANG; Yase, LI; Lijun, YANG; Manzoor, SULTAN; Lang, CHEN

    2018-07-01

    To improve the energy utilization efficiency of metal bridge foil explosion, and increase the function range of plasmas, array bridge foil explosion experiments with different structures were performed. A Schlieren photographic measurement system with a double-pulse laser source was used to observe the flow field of a bridge foil explosion. The evolution laws of plasmas and shock waves generated by array bridge foil explosions of different structures were analyzed and compared. A multi-phase flow calculation model was established to simulate the electrical exploding process of a metal bridge foil. The plasma equation of state was determined by considering the effect of the changing number of particles and Coulomb interaction on the pressure and internal energy. The ionization degree of the plasma was calculated via the Saha–Eggert equation assuming conditions of local thermal equilibrium. The exploding process of array bridge foils was simulated, and the superposition processes of plasma beams were analyzed. The variation and distribution laws of the density, temperature, pressure, and other important parameters were obtained. The results show that the array bridge foil has a larger plasma jet diameter than the single bridge foil for an equal total area of the bridge foil. We also found that the temperature, pressure, and density of the plasma jet’s center region sharply increase because of the superposition of plasma beams.

  7. The RN-BSN Bridge Course: Transitioning the Re-Entry Learner.

    Science.gov (United States)

    Huston, Carol; Shovein, Julia; Damazo, Becky; Fox, Sherry

    2001-01-01

    A 6-week bridge course designed to ease the transition of registered nurses into baccalaureate degree programs focused on critical thinking, learning styles, professional roles, values clarification, time management, and career planning. It also oriented students to Web Course Tools, used for distance learning. Outcomes included role and campus…

  8. Estrogenicity of halogenated bisphenol A: in vitro and in silico investigations.

    Science.gov (United States)

    Zhang, Jie; Li, Tiezhu; Wang, Tuoyi; Yuan, Cuiping; Zhong, Shuning; Guan, Tianzhu; Li, Zhuolin; Wang, Yongzhi; Yu, Hansong; Luo, Quan; Wang, Yongjun; Zhang, Tiehua

    2018-03-01

    The binding interactions of bisphenol A (BPA) and its halogenated derivatives (halogenated BPAs) to human estrogen receptor α ligand binding domain (hERα-LBD) was investigated using a combined in vitro and in silico approach. First, the recombinant hERα-LBD was prepared as a soluble protein in Escherichia coli BL21(DE3)pLysS. A native fluorescent phytoestrogen, coumestrol, was employed as tracer for the fluorescence polarization assay. The results of the in vitro binding assay showed that bisphenol compounds could bind to hERα-LBD as the affinity ligands. All the tested halogenated BPAs exhibited weaker receptor binding than BPA, which might be explained by the steric effect of substituents. Molecular docking studies elucidated that the halogenated BPAs adopted different conformations in the flexible hydrophobic ligand binding pocket (LBP), which is mainly dependent on their distinct halogenation patterns. The compounds with halogen substituents on the phenolic rings and on the bridging alkyl moiety acted as agonists and antagonists for hERα, respectively. Interestingly, all the compounds in the agonist conformation of hERα formed a hydrogen bond with His524, while the compounds in the antagonist conformation formed a hydrogen bond with Thr347. These docking results suggested a pivotal role of His524/Thr347 in maintaining the hERα structure in the biologically active agonist/antagonist conformation. Comparison of the calculated binding energies vs. experimental binding affinities yielded a good correlation, which might be applicable for the structure-based design of novel bisphenol compounds with reduced toxicities and for environmental risk assessment. In addition, based on hERα-LBD as a recognition element, the proposed fluorescence polarization assay may offer an alternative to chromatographic techniques for the multi-residue determination of bisphenol compounds.

  9. Mass fractionation processes of transition metal isotopes

    Science.gov (United States)

    Zhu, X. K.; Guo, Y.; Williams, R. J. P.; O'Nions, R. K.; Matthews, A.; Belshaw, N. S.; Canters, G. W.; de Waal, E. C.; Weser, U.; Burgess, B. K.; Salvato, B.

    2002-06-01

    Recent advances in mass spectrometry make it possible to utilise isotope variations of transition metals to address some important issues in solar system and biological sciences. Realisation of the potential offered by these new isotope systems however requires an adequate understanding of the factors controlling their isotope fractionation. Here we show the results of a broadly based study on copper and iron isotope fractionation during various inorganic and biological processes. These results demonstrate that: (1) naturally occurring inorganic processes can fractionate Fe isotope to a detectable level even at temperature ˜1000°C, which challenges the previous view that Fe isotope variations in natural system are unique biosignatures; (2) multiple-step equilibrium processes at low temperatures may cause large mass fractionation of transition metal isotopes even when the fractionation per single step is small; (3) oxidation-reduction is an importation controlling factor of isotope fractionation of transition metal elements with multiple valences, which opens a wide range of applications of these new isotope systems, ranging from metal-silicate fractionation in the solar system to uptake pathways of these elements in biological systems; (4) organisms incorporate lighter isotopes of transition metals preferentially, and transition metal isotope fractionation occurs stepwise along their pathways within biological systems during their uptake.

  10. Nucleic acid-functionalized transition metal nanosheets for biosensing applications.

    Science.gov (United States)

    Mo, Liuting; Li, Juan; Liu, Qiaoling; Qiu, Liping; Tan, Weihong

    2017-03-15

    In clinical diagnostics, as well as food and environmental safety practices, biosensors are powerful tools for monitoring biological or biochemical processes. Two-dimensional (2D) transition metal nanomaterials, including transition metal chalcogenides (TMCs) and transition metal oxides (TMOs), are receiving growing interest for their use in biosensing applications based on such unique properties as high surface area and fluorescence quenching abilities. Meanwhile, nucleic acid probes based on Watson-Crick base-pairing rules are also being widely applied in biosensing based on their excellent recognition capability. In particular, the emergence of functional nucleic acids in the 1980s, especially aptamers, has substantially extended the recognition capability of nucleic acids to various targets, ranging from small organic molecules and metal ions to proteins and cells. Based on π-π stacking interaction between transition metal nanosheets and nucleic acids, biosensing systems can be easily assembled. Therefore, the combination of 2D transition metal nanomaterials and nucleic acids brings intriguing opportunities in bioanalysis and biomedicine. In this review, we summarize recent advances of nucleic acid-functionalized transition metal nanosheets in biosensing applications. The structure and properties of 2D transition metal nanomaterials are first discussed, emphasizing the interaction between transition metal nanosheets and nucleic acids. Then, the applications of nucleic acid-functionalized transition metal nanosheet-based biosensors are discussed in the context of different signal transducing mechanisms, including optical and electrochemical approaches. Finally, we provide our perspectives on the current challenges and opportunities in this promising field. Copyright © 2016 Elsevier B.V. All rights reserved.

  11. Manipulating Light with Transition Metal Clusters, Organic Dyes, and Metal Organic Frameworks

    Energy Technology Data Exchange (ETDEWEB)

    Ogut, Serdar [Univ. of Illinois, Chicago, IL (United States)

    2017-09-11

    The primary goals of our research program is to develop and apply state-of-the-art first-principles methods to predict electronic and optical properties of three systems of significant scientific and technological interest: transition metal clusters, organic dyes, and metal-organic frameworks. These systems offer great opportunities to manipulate light for a wide ranging list of energy-related scientific problems and applications. During this grant period, we focused our investigations on the development, implementation, and benchmarking of many-body Green’s function methods (GW approximation and the Bethe-Salpeter equation) to examine excited-state properties of transition metal/transition-metal-oxide clusters and organic molecules that comprise the building blocks of dyes and metal-organic frameworks.

  12. Transition metal oxide as anode interface buffer for impedance spectroscopy

    Science.gov (United States)

    Xu, Hui; Tang, Chao; Wang, Xu-Liang; Zhai, Wen-Juan; Liu, Rui-Lan; Rong, Zhou; Pang, Zong-Qiang; Jiang, Bing; Fan, Qu-Li; Huang, Wei

    2015-12-01

    Impedance spectroscopy is a strong method in electric measurement, which also shows powerful function in research of carrier dynamics in organic semiconductors when suitable mathematical physical models are used. Apart from this, another requirement is that the contact interface between the electrode and materials should at least be quasi-ohmic contact. So in this report, three different transitional metal oxides, V2O5, MoO3 and WO3 were used as hole injection buffer for interface of ITO/NPB. Through the impedance spectroscopy and PSO algorithm, the carrier mobilities and I-V characteristics of the NPB in different devices were measured. Then the data curves were compared with the single layer device without the interface layer in order to investigate the influence of transitional metal oxides on the carrier mobility. The careful research showed that when the work function (WF) of the buffer material was just between the work function of anode and the HOMO of the organic material, such interface material could work as a good bridge for carrier injection. Under such condition, the carrier mobility measured through impedance spectroscopy should be close to the intrinsic value. Considering that the HOMO (or LUMO) of most organic semiconductors did not match with the work function of the electrode, this report also provides a method for wide application of impedance spectroscopy to the research of carrier dynamics.

  13. Halogen Bonding Involving CO and CS with Carbon as the Electron Donor

    Directory of Open Access Journals (Sweden)

    Janet E. Del Bene

    2017-11-01

    Full Text Available MP2/aug’-cc-pVTZ calculations have been carried out to investigate the halogen-bonded complexes formed when CO and CS act as electron-pair donors through C to ClF, ClNC, ClCl, ClOH, ClCN, ClCCH, and ClNH2. CO forms only complexes stabilized by traditional halogen bonds, and all ClY molecules form traditional halogen-bonded complexes with SC, except ClF which forms only an ion-pair complex. Ion-pair complexes are also found on the SC:ClNC and SC:ClCl surfaces. SC:ClY complexes stabilized by traditional halogen bonds have greater binding energies than the corresponding OC:ClY complexes. The largest binding energies are found for the ion-pair SC–Cl+:−Y complexes. The transition structures which connect the complex and the ion pair on SC:ClNC and SC:ClCl potential surfaces provide the barriers for inter-converting these structures. Charge-transfer from the lone pair on C to the σ-hole on Cl is the primary charge-transfer interaction stabilizing OC:ClY and SC:ClY complexes with traditional halogen bonds. A secondary charge-transfer occurs from the lone pairs on Cl to the in-plane and out-of-plane π antibonding orbitals of ClY. This secondary interaction assumes increased importance in the SC:ClNH2 complex, and is a factor leading to its unusual structure. C–O and C–S stretching frequencies and 13C chemical shieldings increase upon complex formation with ClY molecules. These two spectroscopic properties clearly differentiate between SC:ClY complexes and SC–Cl+:−Y ion pairs. Spin–spin coupling constants 1xJ(C–Cl for OC:ClY complexes increase with decreasing distance. As a function of the C–Cl distance, 1xJ(C–Cl and 1J(C–Cl provide a fingerprint of the evolution of the halogen bond from a traditional halogen bond in the complexes, to a chlorine-shared halogen bond in the transition structures, to a covalent bond in the ion pairs.

  14. Surface segregation energies in transition-metal alloys

    DEFF Research Database (Denmark)

    Ruban, Andrei; Skriver, Hans Lomholt; Nørskov, Jens Kehlet

    1999-01-01

    We present a database of 24 x 24 surface segregation energies of single transition metal impurities in transition-metal hosts obtained by a Green's-function linear-muffin-tin-orbitals method in conjunction with the coherent potential and atomic sphere approximations including a multipole correction...... to the electrostatic potential and energy. We use the database to establish the major factors which govern surface segregation in transition metal alloys. We find that the calculated trends are well described by Friedel's rectangular state density model and that the few but significant deviations from the simple...

  15. Electrical Conductivity in Transition Metals

    Science.gov (United States)

    Talbot, Christopher; Vickneson, Kishanda

    2013-01-01

    The aim of this "Science Note" is to describe how to test the electron-sea model to determine whether it accurately predicts relative electrical conductivity for first-row transition metals. In the electron-sea model, a metal crystal is viewed as a three-dimensional array of metal cations immersed in a sea of delocalised valence…

  16. Transition metals in carbohydrate chemistry

    DEFF Research Database (Denmark)

    Madsen, Robert

    1997-01-01

    This review describes the application of transition metal mediated reactions in carbohydrate synthesis. The different metal mediated transformations are divided into reaction types and illustrated by various examples on monosaccharide derivatives. Carbon-carbon bond forming reactions are further ...

  17. Mesoporous Transition Metal Oxides for Supercapacitors

    Science.gov (United States)

    Wang, Yan; Guo, Jin; Wang, Tingfeng; Shao, Junfeng; Wang, Dong; Yang, Ying-Wei

    2015-01-01

    Recently, transition metal oxides, such as ruthenium oxide (RuO2), manganese dioxide (MnO2), nickel oxides (NiO) and cobalt oxide (Co3O4), have been widely investigated as electrode materials for pseudo-capacitors. In particular, these metal oxides with mesoporous structures have become very hot nanomaterials in the field of supercapacitors owing to their large specific surface areas and suitable pore size distributions. The high specific capacities of these mesoporous metal oxides are resulted from the effective contacts between electrode materials and electrolytes as well as fast transportation of ions and electrons in the bulk of electrode and at the interface of electrode and electrolyte. During the past decade, many achievements on mesoporous transition metal oxides have been made. In this mini-review, we select several typical nanomaterials, such as RuO2, MnO2, NiO, Co3O4 and nickel cobaltite (NiCo2O4), and briefly summarize the recent research progress of these mesoporous transition metal oxides-based electrodes in the field of supercapacitors. PMID:28347088

  18. Mesoporous Transition Metal Oxides for Supercapacitors

    Directory of Open Access Journals (Sweden)

    Yan Wang

    2015-10-01

    Full Text Available Recently, transition metal oxides, such as ruthenium oxide (RuO2, manganese dioxide (MnO2, nickel oxides (NiO and cobalt oxide (Co3O4, have been widely investigated as electrode materials for pseudo-capacitors. In particular, these metal oxides with mesoporous structures have become very hot nanomaterials in the field of supercapacitors owing to their large specific surface areas and suitable pore size distributions. The high specific capacities of these mesoporous metal oxides are resulted from the effective contacts between electrode materials and electrolytes as well as fast transportation of ions and electrons in the bulk of electrode and at the interface of electrode and electrolyte. During the past decade, many achievements on mesoporous transition metal oxides have been made. In this mini-review, we select several typical nanomaterials, such as RuO2, MnO2, NiO, Co3O4 and nickel cobaltite (NiCo2O4, and briefly summarize the recent research progress of these mesoporous transition metal oxides-based electrodes in the field of supercapacitors.

  19. Alkali metal and alkali metal hydroxide intercalates of the layered transition metal disulfides

    International Nuclear Information System (INIS)

    Kanzaki, Y.; Konuma, M.; Matsumoto, O.

    1981-01-01

    The intercalation reaction of some layered transition metal disulfides with alkali metals, alkali metal hydroxides, and tetraalkylammonium hydroxides were investigated. The alkali metal intercalates were prepared in the respective metal-hexamethylphosphoric triamide solutions in vaccuo, and the hydroxide intercalates in aqueous hydroxide solutions. According to the intercalation reaction, the c-lattice parameter was increased, and the increase indicated the expansion of the interlayer distance. In the case of alkali metal intercalates, the expansion of the interlayer distance increased continuously, corresponding to the atomic radius of the alkali metal. On the other hand, the hydroxide intercalates showed discrete expansion corresponding to the effective ionic radius of the intercalated cation. All intercalates of TaS 2 amd NbS 2 were superconductors. The expansion of the interlayer distance tended to increase the superconducting transition temperature in the intercalates of TaS 2 and vice versa in those of NbS 2 . (orig.)

  20. Fatigue evaluation of the increased weight limit on transit railway bridges.

    Science.gov (United States)

    2014-09-01

    The recent increase of freight railcar weight limits from 263,000 lbs. to 286,000 lbs. raises concerns for the safety of bridges : on transit passenger rail systems, since they were not designed for this weight increase. Thus, there is a need to asse...

  1. Spin-Polarization-Induced Preedge Transitions in the Sulfur K-Edge XAS Spectra of Open-Shell Transition-Metal Sulfates: Spectroscopic Validation of σ-Bond Electron Transfer.

    Science.gov (United States)

    Frank, Patrick; Szilagyi, Robert K; Gramlich, Volker; Hsu, Hua-Fen; Hedman, Britt; Hodgson, Keith O

    2017-02-06

    Sulfur K-edge X-ray absorption spectroscopy (XAS) spectra of the monodentate sulfate complexes [M II (itao)(SO 4 )(H 2 O) 0,1 ] (M = Co, Ni, Cu) and [Cu(Me 6 tren)(SO 4 )] exhibit well-defined preedge transitions at 2479.4, 2479.9, 2478.4, and 2477.7 eV, respectively, despite having no direct metal-sulfur bond, while the XAS preedge of [Zn(itao)(SO 4 )] is featureless. The sulfur K-edge XAS of [Cu(itao)(SO 4 )] but not of [Cu(Me 6 tren)(SO 4 )] uniquely exhibits a weak transition at 2472.1 eV, an extraordinary 8.7 eV below the first inflection of the rising K-edge. Preedge transitions also appear in the sulfur K-edge XAS of crystalline [M II (SO 4 )(H 2 O)] (M = Fe, Co, Ni, and Cu, but not Zn) and in sulfates of higher-valent early transition metals. Ground-state density functional theory (DFT) and time-dependent DFT (TDDFT) calculations show that charge transfer from coordinated sulfate to paramagnetic late transition metals produces spin polarization that differentially mixes the spin-up (α) and spin-down (β) spin orbitals of the sulfate ligand, inducing negative spin density at the sulfate sulfur. Ground-state DFT calculations show that sulfur 3p character then mixes into metal 4s and 4p valence orbitals and various combinations of ligand antibonding orbitals, producing measurable sulfur XAS transitions. TDDFT calculations confirm the presence of XAS preedge features 0.5-2 eV below the rising sulfur K-edge energy. The 2472.1 eV feature arises when orbitals at lower energy than the frontier occupied orbitals with S 3p character mix with the copper(II) electron hole. Transmission of spin polarization and thus of radical character through several bonds between the sulfur and electron hole provides a new mechanism for the counterintuitive appearance of preedge transitions in the XAS spectra of transition-metal oxoanion ligands in the absence of any direct metal-absorber bond. The 2472.1 eV transition is evidence for further radicalization from copper(II), which

  2. On metal-insulator transition in cubic fullerides

    Science.gov (United States)

    Iwahara, Naoya; Chibotaru, Liviu

    The interplay between degenerate orbital and electron correlation is a key to characterize the electronic phases in, for example, transition metal compounds and alkali-doped fullerides. Besides, the degenerate orbital couples to spin and lattice degrees of freedom ,giving rise to exotic phenomena. Here, we develop the self-consistent Gutzwiller approach for the simultaneous treatment of the Jahn-Teller effect and electron correlation, and apply the methodology to reveal the nature of the ground electronic state of fullerides. For small Coulomb repulsion on site U, the fulleride is quasi degenerate correlated metal. With increase of U, we found the quantum phase transition from the metallic phase to JT split phase. In the latter, the Mott transition (MT) mainly develops in the half-filled subband, whereas the empty and the completely filled subbands are almost uninvolved. Therefore, we can qualify the metal-insulator transition in fullerides as an orbital selective MT induced by JT effect.

  3. Bridging analytical approaches for low-carbon transitions

    Science.gov (United States)

    Geels, Frank W.; Berkhout, Frans; van Vuuren, Detlef P.

    2016-06-01

    Low-carbon transitions are long-term multi-faceted processes. Although integrated assessment models have many strengths for analysing such transitions, their mathematical representation requires a simplification of the causes, dynamics and scope of such societal transformations. We suggest that integrated assessment model-based analysis should be complemented with insights from socio-technical transition analysis and practice-based action research. We discuss the underlying assumptions, strengths and weaknesses of these three analytical approaches. We argue that full integration of these approaches is not feasible, because of foundational differences in philosophies of science and ontological assumptions. Instead, we suggest that bridging, based on sequential and interactive articulation of different approaches, may generate a more comprehensive and useful chain of assessments to support policy formation and action. We also show how these approaches address knowledge needs of different policymakers (international, national and local), relate to different dimensions of policy processes and speak to different policy-relevant criteria such as cost-effectiveness, socio-political feasibility, social acceptance and legitimacy, and flexibility. A more differentiated set of analytical approaches thus enables a more differentiated approach to climate policy making.

  4. Are superhalogens without halogen ligand capable of transcending traditional halogen-based superhalogens? Ab initio case study of binuclear anions based on pseudohalogen ligand

    International Nuclear Information System (INIS)

    Li, Jin-Feng; Sun, Yin-Yin; Li, Miao-Miao; Li, Jian-Li; Yin, Bing; Bai, Hongcun

    2015-01-01

    The superhalogen properties of polynuclear structures without halogen ligand are theoretically explored here for several [M 2 (CN) 5 ] −1 (M =  Ca, Be) clusters. At CCSD(T) level, these clusters have been confirmed to be superhalogens due to their high vertical electron detachment energies (VDE). The largest one is 9.70 eV for [Ca 2 (CN) 5 ] −1 which is even higher than those of corresponding traditional structures based on fluorine or chlorine ligands. Therefore the superhalogens stronger than the traditional halogen-based structures could be realized by ligands other than halogen atoms. Compared with CCSD(T), outer valence Green’s function (OVGF) method either overestimates or underestimates the VDEs for different structures while MP2 results are generally consistent in the aspect of relative values. The extra electrons of the highest VDE anions here aggregate on the bridging CN units with non-negligible distribution occurring on other CN units too. These two features lower both the potential and kinetic energies of the extra electron respectively and thus lead to high VDE. Besides superhalogen properties, the structures, relative stabilities and thermodynamic stabilities with respect to the detachment of cyanide ligand were also investigated. The sum of these results identifies the potential of polynuclear structures with pseudohalogen ligand as suitable candidates with enhanced superhalogens properties

  5. Are superhalogens without halogen ligand capable of transcending traditional halogen-based superhalogens? Ab initio case study of binuclear anions based on pseudohalogen ligand

    Energy Technology Data Exchange (ETDEWEB)

    Li, Jin-Feng; Sun, Yin-Yin; Li, Miao-Miao; Li, Jian-Li; Yin, Bing, E-mail: rayinyin@nwu.edu.cn [MOE Key Laboratory of Synthetic and Natural Functional Molecule Chemistry, Shaanxi Key Laboratory of Physico-Inorganic Chemistry, College of Chemistry and Materials Science, Northwest University, Xi’an 710069 (China); Bai, Hongcun [Key Laboratory of Energy Source and Chemical Engineering, Ningxia University, Yinchuan, Ningxia 750021 (China)

    2015-06-15

    The superhalogen properties of polynuclear structures without halogen ligand are theoretically explored here for several [M{sub 2}(CN){sub 5}]{sup −1} (M =  Ca, Be) clusters. At CCSD(T) level, these clusters have been confirmed to be superhalogens due to their high vertical electron detachment energies (VDE). The largest one is 9.70 eV for [Ca{sub 2}(CN){sub 5}]{sup −1} which is even higher than those of corresponding traditional structures based on fluorine or chlorine ligands. Therefore the superhalogens stronger than the traditional halogen-based structures could be realized by ligands other than halogen atoms. Compared with CCSD(T), outer valence Green’s function (OVGF) method either overestimates or underestimates the VDEs for different structures while MP2 results are generally consistent in the aspect of relative values. The extra electrons of the highest VDE anions here aggregate on the bridging CN units with non-negligible distribution occurring on other CN units too. These two features lower both the potential and kinetic energies of the extra electron respectively and thus lead to high VDE. Besides superhalogen properties, the structures, relative stabilities and thermodynamic stabilities with respect to the detachment of cyanide ligand were also investigated. The sum of these results identifies the potential of polynuclear structures with pseudohalogen ligand as suitable candidates with enhanced superhalogens properties.

  6. Transition Metal Complexes and Catalysis

    Indian Academy of Sciences (India)

    approaches towards the study of bonding in transition metal complexes. Despite .... industrial scale reactions for the production of organic compounds using transition ..... It has found several applications as an engineering thermoplastic. .... and processes of interest to the company, that is, applied research. It is this very ...

  7. First-row transition metal hydrogenation and hydrosilylation catalysts

    Science.gov (United States)

    Trovitch, Ryan J.; Mukhopadhyay, Tufan K.; Pal, Raja; Levin, Hagit Ben-Daat; Porter, Tyler M.; Ghosh, Chandrani

    2017-07-18

    Transition metal compounds, and specifically transition metal compounds having a tetradentate and/or pentadentate supporting ligand are described, together with methods for the preparation thereof and the use of such compounds as hydrogenation and/or hydrosilylation catalysts.

  8. Plasmons in metallic monolayer and bilayer transition metal dichalcogenides

    DEFF Research Database (Denmark)

    Andersen, Kirsten; Thygesen, Kristian S.

    2013-01-01

    We study the collective electronic excitations in metallic single-layer and bilayer transition metal dichalcogenides (TMDCs) using time dependent density functional theory in the random phase approximation. For very small momentum transfers (below q≈0.02 Å−1), the plasmon dispersion follows the √q...

  9. Quantum Critical “Opalescence” around Metal-Insulator Transitions

    Science.gov (United States)

    Misawa, Takahiro; Yamaji, Youhei; Imada, Masatoshi

    2006-08-01

    Divergent carrier-density fluctuations equivalent to the critical opalescence of gas-liquid transition emerge around a metal-insulator critical point at a finite temperature. In contrast to the gas-liquid transitions, however, the critical temperatures can be lowered to zero, which offers a challenging quantum phase transition. We present a microscopic description of such quantum critical phenomena in two dimensions. The conventional scheme of phase transitions by Ginzburg, Landau, and Wilson is violated because of its topological nature. It offers a clear insight into the criticalities of metal-insulator transitions (MIT) associated with Mott or charge-order transitions. Fermi degeneracy involving the diverging density fluctuations generates emergent phenomena near the endpoint of the first-order MIT and must shed new light on remarkable phenomena found in correlated metals such as unconventional cuprate superconductors. It indeed accounts for the otherwise puzzling criticality of the Mott transition recently discovered in an organic conductor. We propose to accurately measure enhanced dielectric fluctuations at small wave numbers.

  10. Role of the Water–Metal Ion Bridge in Mediating Interactions between Quinolones and Escherichia coli Topoisomerase IV

    Science.gov (United States)

    2015-01-01

    Although quinolones have been in clinical use for decades, the mechanism underlying drug activity and resistance has remained elusive. However, recent studies indicate that clinically relevant quinolones interact with Bacillus anthracis (Gram-positive) topoisomerase IV through a critical water–metal ion bridge and that the most common quinolone resistance mutations decrease drug activity by disrupting this bridge. As a first step toward determining whether the water–metal ion bridge is a general mechanism of quinolone–topoisomerase interaction, we characterized drug interactions with wild-type Escherichia coli (Gram-negative) topoisomerase IV and a series of ParC enzymes with mutations (S80L, S80I, S80F, and E84K) in the predicted bridge-anchoring residues. Results strongly suggest that the water–metal ion bridge is essential for quinolone activity against E. coli topoisomerase IV. Although the bridge represents a common and critical mechanism that underlies broad-spectrum quinolone function, it appears to play different roles in B. anthracis and E. coli topoisomerase IV. The water–metal ion bridge is the most important binding contact of clinically relevant quinolones with the Gram-positive enzyme. However, it primarily acts to properly align clinically relevant quinolones with E. coli topoisomerase IV. Finally, even though ciprofloxacin is unable to increase levels of DNA cleavage mediated by several of the Ser80 and Glu84 mutant E. coli enzymes, the drug still retains the ability to inhibit the overall catalytic activity of these topoisomerase IV proteins. Inhibition parallels drug binding, suggesting that the presence of the drug in the active site is sufficient to diminish DNA relaxation rates. PMID:25115926

  11. High energy halogen atom reactions activated by nuclear transformations. Progress report, February 15-December 31, 1984

    International Nuclear Information System (INIS)

    1985-01-01

    Energetic halogen atoms or ions, activated by various nuclear transformations are studied in gas, high pressure and condensed phase saturated and unsaturated hydrocarbons, halomethanes, and liquid and solid aqueous solutions of biomolecular and organic solutes in order to understand better the mechanisms and dynamics of high energy monovalent species. The experimental program and its goals remain the same, consisting of four interrelated areas: (1) The stereochemistry of energetic 18 F, /sup 34m/Cl, and 38 Cl substitution reactions with chiral molecules in the gas and condensed phase is studied. (2) The gas to condensed state transition in halogen high energy chemistry, involving energetic chlorine, bromine, and iodine reactions in halomethanes, saturated and unsaturated hydrocarbons and aqueous solutions of biomolecules and alkyl halides is being investigated in more detail. Current attention is given to defining the nature of the enhancement yields in the condensed phase. Specifically, energetic halogen reactions in liquid and frozen aqueous solutions or organic and biomolecular solutes are studied. (3) Reactions of bromine and iodine activated by isomeric transition with halogenated biomolecular and organic solutes in liquid and frozen aqueous solutions are being studied in an attempt to learn more about the activation events in the condensed phase. (4) The applications of hot chemistry techniques and theory to neutron activation analysis of biological systems are being continued. Current attention is given to developing procedures for trace molecular determinations in biological systems. The applications of hot halogen atoms as site indicators in liquid and frozen aqueous solutions of halogenated bases and nucleosides are currently being developed. 14 references

  12. A halogen-free synthesis of gold nanoparticles using gold(III) oxide

    International Nuclear Information System (INIS)

    Sashuk, Volodymyr; Rogaczewski, Konrad

    2016-01-01

    Gold nanoparticles are one of the most used nanomaterials. They are usually synthesized by the reduction of gold(III) chloride. However, the presence of halide ions in the reaction mixture is not always welcome. In some cases, these ions have detrimental influence on the morphology and structure of resulting nanoparticles. Here, we present a simple and halogen-free procedure to prepare gold nanoparticles by reduction of gold(III) oxide in neat oleylamine. The method provides the particles with an average size below 10 nm and dispersity of tens of percent. The process of nanoparticle formation was monitored using UV–Vis spectroscopy. The structure and chemical composition of the nanoparticles was determined by SEM, XPS and EDX. We also proposed the mechanism of reduction of gold(III) oxide based on MS, IR and NMR data. Importantly, the synthetic protocol is general and applicable for the preparation of other coinage metal nanoparticles from the corresponding metal oxides. For instance, we demonstrated that the absence of halogen enables efficient alloying of metals when preparing gold–silver bimetallic nanoparticles.

  13. Oligocyclopentadienyl transition metal complexes

    Energy Technology Data Exchange (ETDEWEB)

    de Azevedo, Cristina G.; Vollhardt, K. Peter C.

    2002-01-18

    Synthesis, characterization, and reactivity studies of oligocyclopentadienyl transition metal complexes, namely those of fulvalene, tercyclopentadienyl, quatercyclopentadienyl, and pentacyclopentadienyl(cyclopentadienyl) are the subject of this account. Thermal-, photo-, and redox chemistries of homo- and heteropolynuclear complexes are described.

  14. Solubility of hydrogen in transition metals

    International Nuclear Information System (INIS)

    Lee, H.M.

    1976-01-01

    Correlations exist between the heat of solution of hydrogen and the difference in energy between the lowest lying energy levels of the trivalent d/sup n-1/s electronic configuration and the divalent d/sup n-2/s 2 (or the tetravalent d/sup n/) configuration of the neutral gaseous atoms. The trends observed in the transition metal series are discussed in relation to the number of valence electrons per atom in the transition elements in their metallic and neutral states

  15. Cycloaddition of CO 2 to challenging N -tosyl aziridines using a halogen-free niobium complex: Catalytic activity and mechanistic insights

    KAUST Repository

    Arayachukiat, Sunatda

    2017-11-06

    An efficient and facile approach to the regioselective synthesis of N-tosyloxazolidinones from the corresponding N-tosylaziridines and CO2 was developed using dual catalytic systems involving an early transition metal coordination compound as a Lewis acid and a nucleophilic cocatalyst. Among the screened Lewis acids, halogen-free niobium pentaethoxide (Nb(OEt)5) displayed the best catalytic activity when used in the presence of tetrabutylammonium iodide (TBAI). Systematic DFT calculations, supported by catalytic experiments, demonstrate that CO2 insertion is the rate determining step for this process and it is highly dependent on the steric hindrance at the niobium center.

  16. Cycloaddition of CO 2 to challenging N -tosyl aziridines using a halogen-free niobium complex: Catalytic activity and mechanistic insights

    KAUST Repository

    Arayachukiat, Sunatda; Yingcharoen, Prapussorn; Vummaleti, Sai V. C.; Cavallo, Luigi; Poater, Albert; D’ Elia, Valerio

    2017-01-01

    An efficient and facile approach to the regioselective synthesis of N-tosyloxazolidinones from the corresponding N-tosylaziridines and CO2 was developed using dual catalytic systems involving an early transition metal coordination compound as a Lewis acid and a nucleophilic cocatalyst. Among the screened Lewis acids, halogen-free niobium pentaethoxide (Nb(OEt)5) displayed the best catalytic activity when used in the presence of tetrabutylammonium iodide (TBAI). Systematic DFT calculations, supported by catalytic experiments, demonstrate that CO2 insertion is the rate determining step for this process and it is highly dependent on the steric hindrance at the niobium center.

  17. Apparatus for washing out halogens

    Energy Technology Data Exchange (ETDEWEB)

    Pier, M; Hahn, J; Kroenig, W

    1941-03-26

    An apparatus is described for washing out of halogens and the like or liquid halogen compounds from the products, which are formed on pressure hydrogenation or splitting of carbon-containing material in the presence of halogens or halogen compounds, consisting of a washing apparatus installed between the reaction vessel and the hot separator, which is inclined in relatively small space for steam regulation and contains, with the steam, arranged baffles, especially spirals.

  18. Integrating Transition Metals into Nanomaterials: Strategies and Applications

    KAUST Repository

    Fhayli, Karim

    2016-01-01

    Transition metals complexes have been involved in various catalytic, biomedical and industrial applications, but only lately they have been associated with nanomaterials to produce innovative and well-defined new hybrid systems. The introduction of transition metals into nanomaterials is important to bear the advantages of metals to nanoscale and also to raise the stability of nanomaterials. In this dissertation, we study two approaches of associating transition metals into nanomaterials. The first approach is via spontaneous self-organization based assembly of small molecule amphiphiles and bulky hydrophilic polymers to produce organic-inorganic hybrid materials that have nanoscale features and can be precisely controlled depending on the experimental conditions used. These hybrid materials can successfully act as templates to design new porous material with interesting architecture. The second approach studied is via electroless reduction of transition metals on the surface of nanocarbons (nanotubes and nanodiamonds) without using any reducing agents or catalysts. The synthesis of these systems is highly efficient and facile resulting in stable and mechanically robust new materials with promising applications in catalysis.

  19. Integrating Transition Metals into Nanomaterials: Strategies and Applications

    KAUST Repository

    Fhayli, Karim

    2016-04-14

    Transition metals complexes have been involved in various catalytic, biomedical and industrial applications, but only lately they have been associated with nanomaterials to produce innovative and well-defined new hybrid systems. The introduction of transition metals into nanomaterials is important to bear the advantages of metals to nanoscale and also to raise the stability of nanomaterials. In this dissertation, we study two approaches of associating transition metals into nanomaterials. The first approach is via spontaneous self-organization based assembly of small molecule amphiphiles and bulky hydrophilic polymers to produce organic-inorganic hybrid materials that have nanoscale features and can be precisely controlled depending on the experimental conditions used. These hybrid materials can successfully act as templates to design new porous material with interesting architecture. The second approach studied is via electroless reduction of transition metals on the surface of nanocarbons (nanotubes and nanodiamonds) without using any reducing agents or catalysts. The synthesis of these systems is highly efficient and facile resulting in stable and mechanically robust new materials with promising applications in catalysis.

  20. Novel enhancement of thin-form-factor galvanic cells: Probing halogenated organic oxidizers and metal anodes

    Energy Technology Data Exchange (ETDEWEB)

    Cardenas-Valencia, Andres M.; Adornato, Lori; Short, R. Timothy; Langebrake, Larry [SRI International, Engineering and Systems Division, Marine Technology Program, 140 Seventh Avenue South, St Petersburg, FL 33701 (United States)

    2008-09-15

    The work reported herein demonstrates a novel method to improve the overall performance of thin-form-factor galvanic cells, fabricated via micro-electromechanical systems (MEMS) processes. Use of solid, low cost, cyclic-halogenated, organic catholyte materials permits water activation of cells consisting of metal anode and catalytic platinum positive electrodes. Similar cells, employing aluminum and zinc anodes, have been activated using sodium hypochlorite (NaClO) solutions, i.e. bleach, in the past. The oxidizers chosen for this study (bromo-, chloro- and iodo-succinimides, and sodium dichloroisocyanuric acid) supply the cathode's oxy-halogenated ions when in contact with water. Zinc, magnesium and aluminum anodes are utilized to fabricate galvanic cells. A comparison between these anodes, coupled with various oxidizers, is included herein. Results using aluminum anode cells show that, even though the utilization efficiency of the catholyte reagents is low (faradic efficiencies between 16 and 19%), the performance of the new water-activated cells (6 cm x 6 cm x 0.25 cm) is superior when compared to those activated with bleach. For instance, operational lives of 6 h (activation with 10% NaClO solution) increase to more than 30 h using the new approach, with a 100-ohm-load. It is also shown that specific energies of 90-110 Wh kg{sup -1} (calculated to include both reagent and packaging mass) could be obtained using the described approach with current draws between 10 and 20 mA. The specific energies obtained suggest that novel MEMS-type cells could have much broader application than low-current, bleach-activated cells. (author)

  1. Strong-Superstrong Transition in Glass Transition of Metallic Glass

    International Nuclear Information System (INIS)

    Dan, Wang; Hong-Yan, Peng; Xiao-Yu, Xu; Bao-Ling, Chen; Chun-Lei, Wu; Min-Hua, Sun

    2010-01-01

    Dynamic fragility of bulk metallic glass (BMG) of Zr 64 Cu 16 Ni 10 Al 10 alloy is studied by three-point beam bending methods. The fragility parameter mfor Zr 64 Cu 16 Ni 10 Al 10 BMG is calculated to be 24.5 at high temperature, which means that the liquid is a 'strong' liquid, while to be 13.4 at low temperature which means that the liquid is a 'super-strong' liquid. The dynamical behavior of Zr 64 Cu 16 Ni 10 Al 10 BMG in the supercooled region undergoes a strong to super-strong transition. To our knowledge, it is the first time that a strong-to-superstrong transition is found in the metallic glass. Using small angle x-ray scattering experiments, we find that this transition is assumed to be related to a phase separation process in supercooled liquid. (condensed matter: structure, mechanical and thermal properties)

  2. Is halogen content the most important factor in the removal of halogenated trace organics by MBR treatment?

    Science.gov (United States)

    Hai, Faisal I; Tadkaew, Nichanan; McDonald, James A; Khan, Stuart J; Nghiem, Long D

    2011-05-01

    This study investigated the relationship between physicochemical properties (namely halogen content and hydrophobicity) of halogenated trace organics and their removal efficiencies by a laboratory scale membrane bioreactor (MBR) under stable operating conditions. The reported results demonstrated a combined effect of halogen content and hydrophobicity on the removal. Compounds with high halogen content (>0.3) were well removed (>85%) when they possessed high hydrophobicity (Log D>3.2), while those with lower Log D values were also well removed if they had low halogen content (BIOWIN index (which is based on only biodegradation) or a more specific index such as the halogen content (which captures a chemical aspect) appeared insufficient to predict the removal efficiency of halogenated compounds in MBR. Experimental data confirmed that the ratio of halogen content and Log D, which incorporates two important physico-chemical properties, is comparatively more suitable. Copyright © 2011 Elsevier Ltd. All rights reserved.

  3. Phase stability of transition metals and alloys

    International Nuclear Information System (INIS)

    Hixson, R.S.; Schiferl, D.; Wills, J.M.; Hill, M.A.

    1997-01-01

    This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). This project was focused on resolving unexplained differences in calculated and measured phase transition pressures in transition metals. Part of the approach was to do new, higher accuracy calculations of transmission pressures for group 4B and group 6B metals. Theory indicates that the transition pressures for these baseline metals should change if alloyed with a d-electron donor metal, and calculations done using the Local Density Approximation (LDA) and the Virtual Crystal Approximation (VCA) indicate that this is true. Alloy systems were calculated for Ti, Zr and Hf based alloys with various solute concentrations. The second part of the program was to do new Diamond Anvil Cell (DAC) measurements to experimentally verify calculational results. Alloys were prepared for these systems with grain size suitable for Diamond Anvil Cell experiments. Experiments were done on pure Ti as well as Ti-V and Ti-Ta alloys. Measuring unambiguous transition pressures for these systems proved difficult, but a new technique developed yielded good results

  4. Rare-earth metal transition metal borocarbide and nitridoborate superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Niewa, Rainer; Shlyk, Larysa; Blaschkowski, Bjoern [Stuttgart Univ. (Germany). Inst. fuer Anorganische Chemie

    2011-07-01

    Few years after the discovery of superconductivity in high-T{sub c} cuprates, borocarbides and shortly after nitridoborates with reasonably high T{sub c}s up to about 23 K attracted considerable attention. Particularly for the rare-earth metal series with composition RNi{sub 2}[B{sub 2}C] it turned out, that several members exhibit superconductivity next to magnetic order with both T{sub c} above or below the magnetic ordering temperature. Therefore, these compounds have been regarded as ideal materials to study the interplay and coexistence of superconductivity and long range magnetic order, due to their comparably high ordering temperatures and similar magnetic and superconducting condensation energies. This review gathers information on the series RNi{sub 2}[B{sub 2}C] and isostructural compounds with different transition metals substituting Ni as well as related series like RM[BC], RM[BN], AM[BN] and R{sub 3}M{sub 2}[BN]{sub 2}N (all with R = rare-earth metal, A = alkaline-earth metal, M = transition metal) with special focus on synthesis, crystal structures and structural trends in correspondence to physical properties. (orig.)

  5. Superconducting Metallic Glass Transition-Edge-Sensors

    Science.gov (United States)

    Hays, Charles C. (Inventor)

    2013-01-01

    A superconducting metallic glass transition-edge sensor (MGTES) and a method for fabricating the MGTES are provided. A single-layer superconducting amorphous metal alloy is deposited on a substrate. The single-layer superconducting amorphous metal alloy is an absorber for the MGTES and is electrically connected to a circuit configured for readout and biasing to sense electromagnetic radiation.

  6. Electroforming and Switching in Oxides of Transition Metals: The Role of Metal Insulator Transition in the Switching Mechanism

    Science.gov (United States)

    Chudnovskii, F. A.; Odynets, L. L.; Pergament, A. L.; Stefanovich, G. B.

    1996-02-01

    Electroforming and switching effects in sandwich structures based on anodic films of transition metal oxides (V, Nb, Ti, Fe, Ta, W, Zr, Hf, Mo) have been studied. After being electroformed, some materials exhibited current-controlled negative resistance with S-shapedV-Icharacteristics. For V, Fe, Ti, and Nb oxides, the temperature dependences of the threshold voltage have been measured. As the temperature increased,Vthdecreased to zero at a critical temperatureT0, which depended on the film material. Comparison of theT0values with the temperatures of metal-insulator phase transition for some compounds (Tt= 120 K for Fe3O4, 340 K for VO2, ∼500 K for Ti2O3, and 1070 K for NbO2) showed that switching was related to the transition in the applied electric field. Channels consisting of the above-mentioned lower oxides were formed in the initial anodic films during the electroforming. The possibility of formation of these oxides with a metal-insulator transition was confirmed by thermodynamic calculations.

  7. The chemistry of the liquid alkali metals

    International Nuclear Information System (INIS)

    Addison, C.C.

    1984-01-01

    A study of liquid alkali metals. It encourages comparison with molecular solvents in chapter covering the nature and reactivity of dissolved species, solvation, solubility and electrical conductivity of solutions. It demonstrates lab techniques unique to liquid alkali metals. It discusses large-scale applications from storage batteries to sodium-cooled reactors and future fusion reactors, and associated technological problems. Contents: Some Basic Physical and Chemical Properties; Manipulation of the Liquids; The Chemistry of Purification Methods; Species Formed by Dissolved Elements; Solubilities and Analytical Methods; Alkali Metal Mixtures; Solvation in Liquid Metal; Reactions Between Liquid Alkali Metals and Water; Reactions of Nitrogen with Lithium and the Group II Metals in Liquid Sodium; The Formation, Dissociation and Stability of Heteronuclear Polyatomic Anions; Reactions of the Liquid Alkali Metals and Their Alloys with Simple Alipatic Hydrocarbons; Reactions of the Liquid Alkali Metals with Some Halogen Compounds; Hydrogen, Oxygen and Carbon Meters; Surface Chemistry and Wetting; Corrosion of Transition Metals by the Liquid Alkali Metals; Modern Applications of the Liquid Alkali Metals

  8. Molecular Fluoride-Bridged 3d-4f Complexes and Their Magnetic Properties

    DEFF Research Database (Denmark)

    Pedersen, K. S.; Bendix, J.

    2016-01-01

    trifluorides with very high lattice enthalpies, building block approaches are not limited to robust systems and use of labile transition metal fluoride complexes has met with unexpected success. The physical properties of fluoride-bridged 3d-4f systems are crucially dependent on coordination geometries, which...... be utilized efficiently in tailored synthesis of polynuclear complexes and extended structures. In particular, the strong affinity of the lanthanides for fluoride makes it a good choice for directed synthesis of mixed lanthanide-transition metal complexes. Despite the competition from formation of lanthanide...

  9. Analysis of Bridge Transition Zones in Railways Considering the Moisture Condition of the Ballast and Subballast

    NARCIS (Netherlands)

    Wang, Haoyu; Silvast, Mika; Markine, V.L.; Wiljanen, Bruce

    2017-01-01

    Transition zones in railway tracks are the locations with considerable changes in vertical support structures, e.g., near bridges. Due to possible water flow constrictions in transition zone structures, there is frequently an increased moisture level in the ballast/subballast layers, which is a

  10. On monosubstituted cyanurate complexes of transition metals

    International Nuclear Information System (INIS)

    Sejfer, G.B.; Tarasova, Z.A.

    1995-01-01

    Complex monosubstituted cyanurates of transition metals K 2 [Eh(H 2 C 3 N 3 O 3 ) 4 ]x4H 2 ) where Eh = Mn, Co, Ni, Cu, Zn, Cd are synthesized and investigated by means of IR - spectroscopy and thermal analysis methods. It is shown that only thermal decomposition of a manganese complex leads to the production of this metal oxide. All other derivatives decompose with the production of a free metal, because decomposition of these substances in argon atmosphere occurs through an intermediate production of their nitrides. An assumption is made that nitroduction of yttrium or rare earth element salts (instead of transition or alkali metal derivatives) as accelerating additions will facilitate increase of polyisocyanurate resin thermal stability. 25 refs.; 2 figs.; 3 tabs

  11. Preparation and characterization of several transition metal oxides

    International Nuclear Information System (INIS)

    Wold, A.; Dwight, K.

    1989-01-01

    The structure-property relationships of several conducting transition metal oxides, as well as their preparative methods, are presented in this paper. The importance of preparing homogeneous phases with precisely known stoichiometry is emphasized. A comparison is also made of the various techniques used to prepare both polycrystalline and single crystal samples. For transition metal oxides, the metallic properties are discussed either in terms of metal-metal distances which are short enough to result in metallic behavior, or in terms of the formation of a π* conduction band resulting from covalent metal-oxygen interactions. Metallic behavior is observed when the conduction bands are populated with either electrons or holes. The concentration of these carriers can be affected by either cation or anion substitutions. The discussion in this presentation will be limited to the elements Re, Ti, V, Cr, Mo, and Cu

  12. Halogenated arsenenes as Dirac materials

    International Nuclear Information System (INIS)

    Tang, Wencheng; Sun, Minglei; Ren, Qingqiang; Wang, Sake; Yu, Jin

    2016-01-01

    Highlights: • We have revealed the presence of Dirac cone in fully-halogenated arsenene compounds. • All fully-halogenated arsenene except As_2I_2 would spontaneously form and stable in defending the thermal fluctuation in room temperature. - Abstract: Arsenene is the graphene-like arsenic nanosheet, which has been predicted very recently [S. Zhang, Z. Yan, Y. Li, Z. Chen, and H. Zeng, Angewandte Chemie, 127 (2015) 3155–3158]. Using first-principles calculations, we systematically investigate the structures and electronic properties of fully-halogenated arsenenes. Formation energy analysis reveals that all the fully-halogenated arsenenes except iodinated arsenene are energetically favorable and could be synthesized. We have revealed the presence of Dirac cone in fully-halogenated arsenene compounds. They may have great potential applications in next generation of high-performance devices.

  13. An effective Hamiltonian approach for Donor-Bridge-Acceptor electronic transitions: Exploring the role of bath memory

    Directory of Open Access Journals (Sweden)

    E.R. Bittner

    2016-03-01

    Full Text Available We present here a formally exact model for electronic transitions between an initial (donor and final (acceptor states linked by an intermediate (bridge state. Our model incorporates a common set of vibrational modes that are coupled to the donor, bridge, and acceptor states and serves as a dissipative bath that destroys quantum coherence between the donor and acceptor. Taking the memory time of the bath as a free parameter, we calculate transition rates for a heuristic 3-state/2 mode Hamiltonian system parameterized to represent the energetics and couplings in a typical organic photovoltaic system. Our results indicate that if the memory time of the bath is of the order of 10-100 fs, a two-state kinetic (i.e., incoherent hopping model will grossly underestimate overall transition rate.

  14. Harnessing the metal-insulator transition for tunable metamaterials

    Science.gov (United States)

    Charipar, Nicholas A.; Charipar, Kristin M.; Kim, Heungsoo; Bingham, Nicholas S.; Suess, Ryan J.; Mathews, Scott A.; Auyeung, Raymond C. Y.; Piqué, Alberto

    2017-08-01

    The control of light-matter interaction through the use of subwavelength structures known as metamaterials has facilitated the ability to control electromagnetic radiation in ways not previously achievable. A plethora of passive metamaterials as well as examples of active or tunable metamaterials have been realized in recent years. However, the development of tunable metamaterials is still met with challenges due to lack of materials choices. To this end, materials that exhibit a metal-insulator transition are being explored as the active element for future metamaterials because of their characteristic abrupt change in electrical conductivity across their phase transition. The fast switching times (▵t < 100 fs) and a change in resistivity of four orders or more make vanadium dioxide (VO2) an ideal candidate for active metamaterials. It is known that the properties associated with thin film metal-insulator transition materials are strongly dependent on the growth conditions. For this work, we have studied how growth conditions (such as gas partial pressure) influence the metalinsulator transition in VO2 thin films made by pulsed laser deposition. In addition, strain engineering during the growth process has been investigated as a method to tune the metal-insulator transition temperature. Examples of both the optical and electrical transient dynamics facilitating the metal-insulator transition will be presented together with specific examples of thin film metamaterial devices.

  15. Synthesis of Mg2FeH6 containing as additives transition metal and transition metal fluorides or carbon

    International Nuclear Information System (INIS)

    Zepon, G.; Leiva, D.R.; Botta, W.J.

    2010-01-01

    The Mg 2 FeH 6 is a promising way of storing hydrogen in solid form, composed by elements that have low cost and, at the same time, high volumetric storage density: 150 kg H 2 /m 3 . However, this complex hydride is not easily synthesized as a single phase material. The hydrogen sorption high temperature and slow kinetics are the major limitations for the practical application of the Mg 2 FeH 6 as a hydrogen storage material. Little is known about the effects of additives in Mg 2 FeH 6 based nanocomposites in this work were synthesized by MAE under hydrogen atmosphere nanocomposites based on Mg 2 FeH 6 containing additives as transition metals, transition metals fluorides of transition metals or carbon, in order to obtain information on the effects of the selected additives. To this end, we used characterization techniques such as XRD, SEM and TEM, thermal analysis by DSC and curves made in apparatus PCT.(author)

  16. Impurities in Antiferromagnetic Transition-Metal Oxides - Symmetry and Optical Transitions

    Science.gov (United States)

    Petersen, John Emil, III

    The study of antiferromagnetic transition-metal oxides is an extremely active area in the physical sciences, where condensed matter physics, inorganic chemistry, and materials science blend together. The sheer number of potential commercial applications is staggering, but much of the fundamental science remains unexplained. This is not due to a lack of effort, however, as theorists have been struggling to understand these materials for decades - particularly the character of the band edges and first optical transitions. The difficulty lies in the strong correlation or Coloumb attraction between the electrons in the anisotropic d orbitals, which conventional band theory cannot describe adequately. The correlation problem is approached here by the well-accepted method of adding a Hubbard potential energy term to the ground state Hamiltonian, calculated within Density Functional Theory. The frequency-dependent complex dielectric function is calculated within the Independent Particle Approximation, and optical transitions are evaluated in multiple different ways. Peaks in the imaginary part of the dielectric function are compared energetically to orbitally decomposed density of states calculations. Optical transitions are typically analyzed in terms of atomic orbitals, which, strictly speaking, gives misleading results. Here, however, from the calculated data, two alternative interpretations are analyzed for each material studied. The first employs rigorous group theoretical analysis to determine allowed electric-dipole transitions, taking into account both orbital hybridization and crystal symmetry. The second interpretation is that of metal cation site hopping. In this interpretation, carriers hop from the x2 - y2 d orbital of one metal cation lattice site to the next metal cation site which is antiferromagnetically aligned. At times, thoughout this work, one interpretation is favorable to the other. Which interpretation is most valid depends on the material

  17. Dissociative Photoionization of 1-Halogenated Silacyclohexanes: Silicon Traps the Halogen.

    Science.gov (United States)

    Bodi, Andras; Sigurdardottir, Katrin Lilja; Kvaran, Ágúst; Bjornsson, Ragnar; Arnason, Ingvar

    2016-11-23

    The threshold photoelectron spectra and threshold photoionization mass spectra of 1-halogenated-1-silacyclohexanes, for the halogens X = F, Cl, Br, and I, have been obtained using synchrotron vacuum ultraviolet radiation and photoelectron photoion coincidence spectroscopy. As confirmed by a similar ionization onset and density functional theory molecular orbitals, the ionization to the ground state is dominated by electron removal from the silacyclohexane ring for X = F, Cl, and Br, and from the halogen lone pair for X = I. The breakdown diagrams show that the dissociative photoionization mechanism is also different for X = I. Whereas the parent ions decay by ethylene loss for X = F to Br in the low-energy regime, the iodine atom is lost for X = I. The first step is followed by a sequential ethylene loss at higher internal energies in each of the compounds. It is argued that the tendency of silicon to lower bond angles stabilizes the complex cation in which C 2 H 4 is η 2 -coordinated to it, and which precedes ethylene loss. Together with the relatively strong silicon-halogen bonds and the increased inductive effect of the silacyclohexane ring in stabilizing the cation, this explains the main differences observed in the fragmentation of the halogenated silacyclohexane and halogenated cyclohexane ions. The breakdown diagrams have been modeled taking into account slow dissociations at threshold and the resulting kinetic shift. The 0 K appearance energies have been obtained to within 0.08 eV for the ethylene loss for X = F to Br (10.56, 10.51, and 10.51 eV, respectively), the iodine atom loss for X = I (10.11 eV), the sequential ethylene loss for X = F to I (12.29, 12.01, 11.94, and 11.86 eV, respectively), and the minor channels of H loss for X = F (10.56 eV) and propylene loss in X = Cl (also at 10.56 eV). The appearance energies for the major channels likely correspond to the dissociative photoionization reaction energy.

  18. First principles study of halogens adsorption on intermetallic surfaces

    International Nuclear Information System (INIS)

    Zhu, Quanxi; Wang, Shao-qing

    2016-01-01

    Graphical abstract: - Highlights: • The linear relation between adsorbates induced work function change and dipole moment change also exists for intermetallic surfaces. • It is just a common linear relationship rather than a directly proportion. • A new weight parameter β is proposed to describe different factors effect on work function shift. - Abstract: Halides are often present at electrochemical environment, they can directly influence the electrode potential or zero charge potential through the induced work-function change. In this work, we focused in particular on the halogen-induced work function change as a function of the coverage of fluorine, chlorine, bromine and iodine on Al_2Au and Al_2Pt (110) surfaces. Results show that the real relation between work function change and dipole moment change for halogens adsorption on intermetallic surfaces is just a common linear relationship rather than a directly proportion. Besides, the different slopes between fitted lines and the theoretical slope employed in pure metal surfaces demonstrating that the halogens adsorption on intermetallic surfaces are more complicated. We also present a weight parameter β to describe different factors effect on work function shift and finally qualify which factor dominates the shift direction.

  19. Metal-insulator transition in vanadium dioxide

    International Nuclear Information System (INIS)

    Zylbersztejn, A.; Mott, N.F.

    1975-01-01

    The basic physical parameters which govern the metal-insulator transition in vanadium dioxide are determined through a review of the properties of this material. The major importance of the Hubbard intra-atomic correlation energy in determining the insulating phase, which was already evidence by studies of the magnetic properties of V 1 -/subx/Cr/subx/O 2 alloys, is further demonstrated from an analysis of their electrical properties. An analysis of the magnetic susceptibility of niobium-doped VO 2 yields a picture for the current carrier in the low-temperature phase in which it is accompanied by a spin cloud (owing to Hund's-rule coupling), and has therefore an enhanced mass (m approx. = 60m 0 ). Semiconducting vanadium dioxide turns out to be a borderline case for a classical band-transport description; in the alloys at high doping levels, Anderson localization with hopping transport can take place. Whereas it is shown that the insulating phase cannot be described correctly without taking into account the Hubbard correlation energy, we find that the properties of the metallic phase are mainly determined by the band structure. Metallic VO 2 is, in our view, similar to transition metals like Pt or Pd: electrons in a comparatively wide band screening out the interaction between the electrons in a narrow overlapping band. The magnetic susceptibility is described as exchange enhanced. The large density of states at the Fermi level yields a substantial contribution of the entropy of the metallic electrons to the latent heat. The crystalline distortion removes the band degeneracy so that the correlation energy becomes comparable with the band width and a metal-insulator transition takes place

  20. High energy halogen atom reactions activated by nuclear transformations. Progress report, February 15, 1979-February 14, 1980

    Energy Technology Data Exchange (ETDEWEB)

    Rack, E.P.

    1980-02-01

    The program consists of six interrelated areas: (1) Reactions of iodine with alkenes and alkynes activated by radiative neutron capture and isomeric transition in low pressure gaseous systems employing additives and rare gas moderators, high pressure, and liquid systems. Special attention was given to the reactivity of excited complex formation and structural effects of electrophilic iodine attack on various pi-bond systems. (2) The gas-to-condensed phase transition in halogen high energy chemistry. Current interest involves the study of caging effects of an ice lattice on recombination reactions involving neutron-irradiated frozen aqueous solutions of halogenated organic and biochemical solutes in order to learn more about kinetic energy effects, halogen size, solute molecule size, steric effects and hydrogen bonding within an ice lattice cage. (3) Systematics of halogen hot atom reactions. The reactions of /sup 80m/Br, /sup 80/Br, /sup 82m/Br + /sup 82/Br, /sup 82/Br, /sup 82/Br, /sup 128/I, /sup 130/I, and /sup 130m/I + /sup 130/I activated by radiative neutron capture or isomeric transition in hydrocarbons and halo-substituted alkanes in low pressure and high pressure gaseous systems employing additives and rare gas moderators are currently being studied. (4) Mathematical and computer simulation studies of caging events within an ice lattice are being investigated. (5) At Brookhaven National Laboratory, cyclotron-produced chlorine and fluorine hot atoms substitution reactions with molecules possessing a single chiral center are under investigation to determine the role of hot atom kinetic energy, halogen atom, enantioner structure, steric effects and phase on the extent of substitution by retention of configuration or by Walden inversion. (6) The applications of high energy techniques and concepts to neutron activation analysis for trace element determinations in biological systems was continued.

  1. Boiling points of halogenated ethanes: an explanatory model implicating weak intermolecular hydrogen-halogen bonding.

    Science.gov (United States)

    Beauchamp, Guy

    2008-10-23

    This study explores via structural clues the influence of weak intermolecular hydrogen-halogen bonds on the boiling point of halogenated ethanes. The plot of boiling points of 86 halogenated ethanes versus the molar refraction (linked to polarizability) reveals a series of straight lines, each corresponding to one of nine possible arrangements of hydrogen and halogen atoms on the two-carbon skeleton. A multiple linear regression model of the boiling points could be designed based on molar refraction and subgroup structure as independent variables (R(2) = 0.995, standard error of boiling point 4.2 degrees C). The model is discussed in view of the fact that molar refraction can account for approximately 83.0% of the observed variation in boiling point, while 16.5% could be ascribed to weak C-X...H-C intermolecular interactions. The difference in the observed boiling point of molecules having similar molar refraction values but differing in hydrogen-halogen intermolecular bonds can reach as much as 90 degrees C.

  2. Structurally triggered metal-insulator transition in rare-earth nickelates.

    Science.gov (United States)

    Mercy, Alain; Bieder, Jordan; Íñiguez, Jorge; Ghosez, Philippe

    2017-11-22

    Rare-earth nickelates form an intriguing series of correlated perovskite oxides. Apart from LaNiO 3 , they exhibit on cooling a sharp metal-insulator electronic phase transition, a concurrent structural phase transition, and a magnetic phase transition toward an unusual antiferromagnetic spin order. Appealing for various applications, full exploitation of these compounds is still hampered by the lack of global understanding of the interplay between their electronic, structural, and magnetic properties. Here we show from first-principles calculations that the metal-insulator transition of nickelates arises from the softening of an oxygen-breathing distortion, structurally triggered by oxygen-octahedra rotation motions. The origin of such a rare triggered mechanism is traced back in their electronic and magnetic properties, providing a united picture. We further develop a Landau model accounting for the metal-insulator transition evolution in terms of the rare-earth cations and rationalizing how to tune this transition by acting on oxygen rotation motions.

  3. Bridging-ligand-substitution strategy for the preparation of metal-organic polyhedra

    Science.gov (United States)

    Li, Jian-Rong; Zhou, Hong-Cai

    2010-10-01

    Metal-organic polyhedra-discrete molecular architectures constructed through the coordination of metal ions and organic linkers-have recently attracted considerable attention due to their intriguing structures, their potential for a variety of applications and their relevance to biological self-assembly. Several synthetic routes have been investigated to prepare these complexes. However, to date, these preparative methods have typically been based on the direct assembly of metal ions and organic linkers. Although these routes are convenient, it remains difficult to find suitable reaction conditions or to control the outcome of the assembly process. Here, we demonstrate a synthetic strategy based on the substitution of bridging ligands in soluble metal-organic polyhedra. The introduction of linkers with different properties from those of the initial metal-organic polyhedra can thus lead to new metal-organic polyhedra with distinct properties (including size and shape). Furthermore, partial substitution can also occur and form mixed-ligand species that may be difficult to access by means of other approaches.

  4. High-frequency EPR on high-spin transition-metal sites

    NARCIS (Netherlands)

    Mathies, Guinevere

    2012-01-01

    The electronic structure of transition-metal sites can be probed by electron-paramagnetic-resonance (EPR) spectroscopy. The study of high-spin transition-metal sites benefits from EPR spectroscopy at frequencies higher than the standard 9.5 GHz. However, high-frequency EPR is a developing field. In

  5. Metallacyclopentadienes: structural features and coordination in transition metal complexes

    International Nuclear Information System (INIS)

    Dolgushin, Fedor M; Yanovsky, Aleksandr I; Antipin, Mikhail Yu

    2004-01-01

    Results of structural studies of polynuclear transition metal complexes containing the metallacyclopentadiene fragment are overviewed. The structural features of the complexes in relation to the nature of the substituents in the organic moiety of the metallacycles, the nature of the transition metals and their ligand environment are analysed. The main structural characteristics corresponding to different modes of coordination of metallacyclopentadienes to one or two additional metal centres are revealed.

  6. Evidence for Interfacial Halogen Bonding.

    Science.gov (United States)

    Swords, Wesley B; Simon, Sarah J C; Parlane, Fraser G L; Dean, Rebecca K; Kellett, Cameron W; Hu, Ke; Meyer, Gerald J; Berlinguette, Curtis P

    2016-05-10

    A homologous series of donor-π-acceptor dyes was synthesized, differing only in the identity of the halogen substituents about the triphenylamine (TPA; donor) portion of each molecule. Each Dye-X (X=F, Cl, Br, and I) was immobilized on a TiO2 surface to investigate how the halogen substituents affect the reaction between the light-induced charge-separated state, TiO2 (e(-) )/Dye-X(+) , with iodide in solution. Transient absorption spectroscopy showed progressively faster reactivity towards nucleophilic iodide with more polarizable halogen substituents: Dye-F < Dye-Cl < Dye-Br < Dye-I. Given that all other structural and electronic properties for the series are held at parity, with the exception of an increasingly larger electropositive σ-hole on the heavier halogens, the differences in dye regeneration kinetics for Dye-Cl, Dye-Br, and Dye-I are ascribed to the extent of halogen bonding with the nucleophilic solution species. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Tropospheric Halogen Chemistry

    Science.gov (United States)

    von Glasow, R.; Crutzen, P. J.

    2003-12-01

    Halogens are very reactive chemicals that are known to play an important role in anthropogenic stratospheric ozone depletion chemistry, first recognized by Molina and Rowland (1974). However, they also affect the chemistry of the troposphere. They are of special interest because they are involved in many reaction cycles that can affect the oxidation power of the atmosphere indirectly by influencing the main oxidants O3 and its photolysis product OH and directly, e.g., by reactions of the Cl radical with hydrocarbons (e.g., CH4).Already by the middle of the nineteenth century, Marchand (1852) reported the presence of bromine and iodine in rain and other natural waters. He also mentions the benefits of iodine in drinking water through the prevention of goitres and cretinism. In a prophetic monograph "Air and Rain: The Beginnings of a Chemical Climatology," Smith (1872) describes measurements of chloride in rain water, which he states to originate partly from the oceans by a process that he compares with the bursting of "soap bubbles" which produces "small vehicles" that transfer small spray droplets of seawater to the air. From deviations of the sulfate-to-chloride ratio in coastal rain compared to seawater, Smith concluded that chemical processes occur once the particles are airborne.For almost a century thereafter, however, atmospheric halogens received little attention. One exception was the work by Cauer (1939), who reported that iodine pollution has been significant in Western and Central Europe due to the inefficient burning of seaweed, causing mean gas phase atmospheric concentrations as high as or greater than 0.5 μg m-3. In his classical textbook Air Chemistry and Radioactivity, Junge (1963) devoted less than three pages to halogen gas phase chemistry, discussing chlorine and iodine. As reviewed by Eriksson (1959a, b), the main atmospheric source of halogens is sea salt, derived from the bursting of bubbles of air which are produced by ocean waves and other

  8. Mesoporous Transition Metal Oxides for Supercapacitors

    OpenAIRE

    Wang, Yan; Guo, Jin; Wang, Tingfeng; Shao, Junfeng; Wang, Dong; Yang, Ying-Wei

    2015-01-01

    Recently, transition metal oxides, such as ruthenium oxide (RuO2), manganese dioxide (MnO2), nickel oxides (NiO) and cobalt oxide (Co3O4), have been widely investigated as electrode materials for pseudo-capacitors. In particular, these metal oxides with mesoporous structures have become very hot nanomaterials in the field of supercapacitors owing to their large specific surface areas and suitable pore size distributions. The high specific capacities of these mesoporous metal oxides are result...

  9. High energy halogen atom reactions activated by nuclear transformations. Progress report, February 15, 1979-February 14, 1980

    International Nuclear Information System (INIS)

    Rack, E.P.

    1980-02-01

    The program consists of six interrelated areas: (1) Reactions of iodine with alkenes and alkynes activated by radiative neutron capture and isomeric transition in low pressure gaseous systems employing additives and rare gas moderators, high pressure, and liquid systems. Special attention was given to the reactivity of excited complex formation and structural effects of electrophilic iodine attack on various pi-bond systems. (2) The gas-to-condensed phase transition in halogen high energy chemistry. Current interest involves the study of caging effects of an ice lattice on recombination reactions involving neutron-irradiated frozen aqueous solutions of halogenated organic and biochemical solutes in order to learn more about kinetic energy effects, halogen size, solute molecule size, steric effects and hydrogen bonding within an ice lattice cage. (3) Systematics of halogen hot atom reactions. The reactions of /sup 80m/Br, 80 Br, /sup 82m/Br + 82 Br, 82 Br, 82 Br, 128 I, 130 I, and /sup 130m/I + 130 I activated by radiative neutron capture or isomeric transition in hydrocarbons and halo-substituted alkanes in low pressure and high pressure gaseous systems employing additives and rare gas moderators are currently being studied. (4) Mathematical and computer simulation studies of caging events within an ice lattice are being investigated. (5) At Brookhaven National Laboratory, cyclotron-produced chlorine and fluorine hot atoms substitution reactions with molecules possessing a single chiral center are under investigation. (6) The applications of high energy techniques and concepts to neutron activation analysis for trace elements and trace molecule determinations in biological systems was continued

  10. Structural characterization of tellurite glasses doped with transition metal oxides using Raman spectra and ab initio calculations.

    Science.gov (United States)

    Mohamed, Tarek A; Shaltout, I; Al Yahyaei, K M

    2006-05-01

    Systems of iron tellurite glasses were prepared by melt quenching with compositions of [85%TeO2+5%Fe2O3+10%TMO], where transition metal oxides (TMO) are TiO2, V2O5, MnO, CoO, NiO and CuO. Furthermore, the main structural units of these samples have been characterized by means of Raman spectra (150-1200 cm(-1)) as well as wavenumber predictions by means of Gaussian 98 ab initio calculations for the proposed site symmetries of TeO4(4-) triagonal bipyramid (C2v) and Te2O7(6-) bridged tetrahedra (Cs and C1). Aided by normal coordinate analysis, calculated vibrational frequencies, Raman scattering activities, force constants in internal coordinates and potential energy distributions (PEDs), revised vibrational assignments for the fundamental modes have been proposed. The main structural features are correlated to the dominant units of triagonal bipyramid (tbp) or bridged tetrahedral (TeO3+1 binds to TeO3 through TeOTe bridge; corner sharing). Moreover, the Raman spectra of the investigated tellurites reflect a structural change from tbp (coordination number is four) to triagonal pyramidal (coordination number is three).

  11. Stable isotopes of transition and post-transition metals as tracers in environmental studies

    Science.gov (United States)

    Bullen, Tomas D.; Baskaran, Mark

    2011-01-01

    The transition and post-transition metals, which include the elements in Groups 3–12 of the Periodic Table, have a broad range of geological and biological roles as well as industrial applications and thus are widespread in the environment. Interdisciplinary research over the past decade has resulted in a broad understanding of the isotope systematics of this important group of elements and revealed largely unexpected variability in isotope composition for natural materials. Significant kinetic and equilibrium isotope fractionation has been observed for redox sensitive metals such as iron, chromium, copper, molybdenum and mercury, and for metals that are not redox sensitive in nature such as cadmium and zinc. In the environmental sciences, the isotopes are increasingly being used to understand important issues such as tracing of metal contaminant sources and fates, unraveling metal redox cycles, deciphering metal nutrient pathways and cycles, and developing isotope biosignatures that can indicate the role of biological activity in ancient and modern planetary systems.

  12. Halogen bond: a long overlooked interaction.

    Science.gov (United States)

    Cavallo, Gabriella; Metrangolo, Pierangelo; Pilati, Tullio; Resnati, Giuseppe; Terraneo, Giancarlo

    2015-01-01

    Because of their high electronegativity, halogen atoms are typically considered, in most of their derivatives, as sites of high electron density and it is commonly accepted that they can form attractive interactions by functioning as the electron donor site (nucleophilic site). This is the case when they work as hydrogen bond acceptor sites. However, the electron density in covalently bound halogens is anisotropically distributed. There is a region of higher electron density, accounting for the ability of halogens to function as electron donor sites in attractive interactions, and a region of lower electron density where the electrostatic potential is frequently positive (mainly in the heavier halogens). This latter region is responsible for the ability of halogen atoms to function as the electron-acceptor site (electrophilic site) in attractive interactions formed with a variety of lone pair-possessing atoms, anions, and π-systems. This ability is quite general and is shown by a wide diversity of halogenated compounds (e.g., organohalogen derivatives and dihalogens). According to the definition proposed by the International Union of Pure and Applied Chemistry, any attractive interactions wherein the halogen atom is the electrophile is named halogen bond (XB). In this chapter, it is discussed how the practice and the concept of XB developed and a brief history of the interaction is presented. Papers (either from the primary or secondary literature) which have reported major experimental findings in the field or which have given important theoretical contributions for the development of the concept are recollected in order to trace how a unifying and comprehensive categorization emerged encompassing all interactions wherein halogen atoms function as the electrophilic site.

  13. Striking role of non-bridging oxygen on glass transition temperature of calcium aluminosilicate glass-formers

    International Nuclear Information System (INIS)

    Bouhadja, M.; Jakse, N.; Pasturel, A.

    2014-01-01

    Molecular dynamics simulations are used to study the structural and dynamic properties of calcium aluminosilicate, (CaO-Al 2 O 3 ) 1−x (SiO 2 ) x , glass formers along three joins, namely, R = 1, 1.57, and 3, in which the silica content x can vary from 0 to 1. For all compositions, we determined the glass-transition temperature, the abundances of the non-bridging oxygen, triclusters, and AlO 5 structural units, as well as the fragility from the temperature evolution of the α-relaxation times. We clearly evidence the role played by the non-bridging oxygen linked either to Al atoms or Si atoms in the evolution of the glass-transition temperature as well as of the fragility as a function of silica content along the three joins

  14. High energy halogen atom reactions activated by nuclear transformations. Progress report, February 15, 1980-February 14, 1981

    International Nuclear Information System (INIS)

    1981-02-01

    The stereochemistry of high energy 18 F, /sup 34m/Cl, and 76 Br substitution reactions involving enantiomeric molecules in the gas and condensed phase is studied. The gas to condensed state transition in halogen high energy chemistry, involving chlorine, bromine, and iodine activated by the (n,γ) and (I.T.) processes in halomethanes, saturated and unsaturated hydrocarbons is being investigated in more detail. Special attention is given to defining the nature of the enhancement yields in the condensed phase. High energy halogen reactions in liquid and frozen aqueous solutions of organic and biomolecular solutes are studied in an attempt to learn more about these reactions. The applications of high energy chemistry techniques and theory to neutron activation analysis of biological systems are being continued. Special attention is given to developing procedures for trace molecular determinations in biological systems. The applications of hot halogen atoms as indicators of solute-solute interactions in liquid and frozen aqueous solutions of halogenated bases and nucleosides are being developed. Experiments are designed to explain the mechanisms of the radioprotection offered biomolecular solutes trapped within the frozen ice lattice. Reactions of bromine and iodine activated by isomeric transition with halogenated biomolecular solutes in liquid and frozen aqueous solutions are studied. The high energy reactions of iodine with the isomers of pentene have been studied in low pressure gaseous systems employing additives and rare gas moderators and liquid systems. Reactivity of excited complex formation and structural effects of electrophilic iodine attack on the pi-bond systems are studied

  15. High energy halogen atom reactions activated by nuclear transformations. Progress report, February 15, 1980-February 14, 1981

    Energy Technology Data Exchange (ETDEWEB)

    1981-02-01

    The stereochemistry of high energy /sup 18/F, /sup 34m/Cl, and /sup 76/Br substitution reactions involving enantiomeric molecules in the gas and condensed phase is studied. The gas to condensed state transition in halogen high energy chemistry, involving chlorine, bromine, and iodine activated by the (n,..gamma..) and (I.T.) processes in halomethanes, saturated and unsaturated hydrocarbons is being investigated in more detail. Special attention is given to defining the nature of the enhancement yields in the condensed phase. High energy halogen reactions in liquid and frozen aqueous solutions of organic and biomolecular solutes are studied in an attempt to learn more about these reactions. The applications of high energy chemistry techniques and theory to neutron activation analysis of biological systems are being continued. Special attention is given to developing procedures for trace molecular determinations in biological systems. The applications of hot halogen atoms as indicators of solute-solute interactions in liquid and frozen aqueous solutions of halogenated bases and nucleosides are being developed. Experiments are designed to explain the mechanisms of the radioprotection offered biomolecular solutes trapped within the frozen ice lattice. Reactions of bromine and iodine activated by isomeric transition with halogenated biomolecular solutes in liquid and frozen aqueous solutions are studied. The high energy reactions of iodine with the isomers of pentene have been studied in low pressure gaseous systems employing additives and rare gas moderators and liquid systems. Reactivity of excited complex formation and structural effects of electrophilic iodine attack on the pi-bond systems are studied.

  16. Modular Approaches to Flouride-Bridged Molecular Magnetic Materials

    DEFF Research Database (Denmark)

    Pedersen, Kasper Steen

    Abstract While oxygen and nitrogen are ubiquitous as bridging ligators in molecule-based magnetic systems, fluoride is much less explored and studied in this respect. In this project, new polynuclear complexes and one-dimensional polymeric systems, based on fluoride linkages between transition...... metal ions and between transition metal and lanthanide ions, have been synthetized and thoroughly characterized. Assembly of kinetically robust 3d fluoride complexes with various lanthanide precursors has proven to be a convenient route to small heterometallic complexes. However, the use of more labile...... interactions in a lower total spin polynuclear complex had a larger magnetic entropy change during a adiabatic demagnetization than an, all ferromagnetically coupled, complex with a larger spin ground state. Diffuse orbitals and strong magnetic anisotropy resulting from large values of the spinorbit coupling...

  17. Peruvian perovskite Between Transition-metal to PGM/PlatinumGroupMetal Catalytic Fusion

    Science.gov (United States)

    Maksoed, Wh-

    2016-11-01

    Strongly correlated electronic materials made of simple building blocks, such as a transition-metal ion in an octahedral oxygen cage forming a perovskite structure- Dagotto & Tokura for examples are the high-temperature superconductivity & the CMR/Colossal Magnetoresistance . Helium-4 denotes from LC Case,ScD: "Catalytic Fusion of Deuterium into Helium-4"- 1998 dealt with gaseous D2- "contacted with a supported metallic catalyst at superatmospheric pressure". The catalyst is a platinum-group metal, at about 0.5% - 1% by weight, on activated C. Accompanies Stephen J Geier, 2010 quotes "transition metal complexes", the Energy thus produced is enormous, and because the deuterium is very cheap in the form of heavy water (less than US 1/g), the fuel cost is very low (seas &Deuteronomy to be eternally preserves. Heartfelt Gratitudes to HE. Mr. Prof. Ir. HANDOJO.

  18. Structure and properties of transition metal-metalloid glasses based on refractory metals

    International Nuclear Information System (INIS)

    Johnson, W.L.; Williams, A.R.

    1979-01-01

    The structure and properties of several new transition metal-metalloid (TM/sub 1-x/M/sub x/) metallic glasses based on refractory transition metals (e.g. Mo, W, Ru etc.) have been systemically investigated as a function of composition. The structure of the alloys has been investigated by x-ray diffraction methods and measurements of superconducting properties, electrical resistivity, density, hardness, and mechanical behavior were made. These data are used in developing a novel description of the structure of TM/sub 1-x/M/sub x/ glasses. The experimental evidence suggests that an ideal amorphous phase forms at a specific composition x/sub c/ and that this phase has a well defined atomic short range order. For metallic glasses having x x/sub c/. This novel picture can explain the variation of many properties of these glasses with metalloid concentration

  19. Development of no halogen incombustible cables for atomic energy

    International Nuclear Information System (INIS)

    Ishii, Nobumasa; Kimura, Hitoshi; Fujimura, Shun-ichi

    1990-01-01

    In upgrading light water reactor technology, it is important to improve the reliability of machinery and equipment, to make regular inspection efficient, to extend the period of continuous operation, to optimize operation cycle and to improve the maintainability of plant facilities. For the cables for nuclear power stations, high incombustibility is required, and at present halogen system incombustible materials are used. Recently the development of no halogen incombustible cables has been advanced, with which the generation of corrosive gas and smoke at the time of fires is slight. In this study, the application of such no halogen incombustible cables to nuclear power stations and the improvement of reliability of the cables were investigated. The cables to be developed are those for electric power, control and instrumentation in BWR plants and insulated electric wires. The required characteristics are incombustibility, no generation of smoke and corrosive gas at the time of fires, radiation resistance and steam resistance in LOCA. The selection of base polymers, metal hydrates and radiation protectors, the evaluation of radiation resistance and steam resistance, the examination of the corrosive and poisonous properties of generated gas and smoke generation and so on are reported. The development was successful. (K.I.)

  20. Mechanical failure and glass transition in metallic glasses

    International Nuclear Information System (INIS)

    Egami, T.

    2011-01-01

    Research highlights: → We review the recent results of molecular dynamics simulations on metallic glasses. → They show the equivalence of mechanical failure and glass transition. → We discuss the microscopic mechanism behind this equivalence. → We show that the density of defects in metallic glasses is as high as a quarter. → Our concepts about the defect state in glasses need to be changed. - Abstract: The current majority view on the phenomenon of mechanical failure in metallic glasses appears to be that it is caused by the activity of some structural defects, such as free-volumes or shear transformation zones, and the concentration of such defects is small, only of the order of 1%. However, the recent results compel us to revise this view. Through molecular dynamics simulation it has been shown that mechanical failure is the stress-induced glass transition. According to our theory the concentration of the liquid-like sites (defects) is well over 20% at the glass transition. We suggest that the defect concentration in metallic glasses is actually very high, and percolation of such defects causes atomic avalanche and mechanical failure. In this article we discuss the glass transition, mechanical failure and viscosity from such a point of view.

  1. Unusual metal-insulator transition in disordered ferromagnetic films

    International Nuclear Information System (INIS)

    Muttalib, K.A.; Wölfle, P.; Misra, R.; Hebard, A.F.

    2012-01-01

    We present a theoretical interpretation of recent data on the conductance near and farther away from the metal-insulator transition in thin ferromagnetic Gd films of thickness b≈2-10 nm. For increasing sheet resistances a dimensional crossover takes place from d=2 to d=3 dimensions, since the large phase relaxation rate caused by scattering of quasiparticles off spin wave excitations renders the dephasing length L φ ≲b at strong disorder. The conductivity data in the various regimes obey fractional power-law or logarithmic temperature dependence. One observes weak localization and interaction induced corrections at weaker disorder. At strong disorder, near the metal-insulator transition, the data show scaling and collapse onto two scaling curves for the metallic and insulating regimes. We interpret this unusual behavior as proof of two distinctly different correlation length exponents on both sides of the transition.

  2. Greatly enhanced flux pinning properties of fluorine-free metal-organic decomposition YBCO films by co-addition of halogens (Cl, Br) and metals (Zr, Sn, Hf)

    Science.gov (United States)

    Motoki, Takanori; Ikeda, Shuhei; Nakamura, Shin-ichi; Honda, Genki; Nagaishi, Tatsuoki; Doi, Toshiya; Shimoyama, Jun-ichi

    2018-04-01

    Additive-free YBCO films, as well as those with halogen (X) added, metal (M) added and (X, M) co-added, have been prepared by the fluorine-free metal-organic decomposition method on SrTiO3(100) single crystalline substrates, where X = Cl, Br and M = Zr, Sn, Hf. It was revealed that the addition of both Cl and Br to the starting solution resulted in the generation of oxyhalide, Ba2Cu3O4 X 2, in the YBCO films, and that the oxyhalide was found to promote the bi-axial orientation of the YBCO crystals. By adding a decent amount of Cl or Br, highly textured YBCO films with high J c were reproducibly obtained, even when an impurity metal, M, was co-added, while the addition of M without X did not greatly improve J c owing to the poor bi-axial orientation of the YBCO crystals. Our results suggest that the addition of Br more effectively enhances J c than the addition of Cl. The pinning force density at 40 K in 4.8 T reached ˜55 GN m-3 with the co-addition of (Br, M). This value is much larger than that of the pure YBCO film, reaching ˜17 GN m-3.

  3. Transition-Metal-Free Biomolecule-Based Flexible Asymmetric Supercapacitors.

    Science.gov (United States)

    Yang, Yun; Wang, Hua; Hao, Rui; Guo, Lin

    2016-09-01

    A transition-metal-free asymmetric supercapacitor (ASC) is successfully fabricated based on an earth-abundant biomass derived redox-active biomolecule, named lawsone. Such an ASC exhibits comparable or even higher energy densities than most of the recently reported transition-metal-based ASCs, and this green ASC generation from renewable resources is promising for addressing current issues of electronic hazard processing, high cost, and unsustainability. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Halogen bonding in solution: thermodynamics and applications.

    Science.gov (United States)

    Beale, Thomas M; Chudzinski, Michael G; Sarwar, Mohammed G; Taylor, Mark S

    2013-02-21

    Halogen bonds are noncovalent interactions in which covalently bound halogens act as electrophilic species. The utility of halogen bonding for controlling self-assembly in the solid state is evident from a broad spectrum of applications in crystal engineering and materials science. Until recently, it has been less clear whether, and to what extent, halogen bonding could be employed to influence conformation, binding or reactivity in the solution phase. This tutorial review summarizes and interprets solution-phase thermodynamic data for halogen bonding interactions obtained over the past six decades and highlights emerging applications in molecular recognition, medicinal chemistry and catalysis.

  5. Tunable metal-insulator transitions in bilayer graphene by thermal annealing

    OpenAIRE

    Kalon, Gopinadhan; Shin, Young Jun; Yang, Hyunsoo

    2012-01-01

    Tunable and highly reproducible metal-insulator transitions have been observed in bilayer graphene upon thermal annealing at 400 K under high vacuum conditions. Before annealing, the sample is metallic in the whole temperature regime of study. Upon annealing, the conductivity changes from metallic to that of an insulator and the transition temperature is a function of annealing time. The pristine metallic state can be reinstated by exposing to air thereby inducing changes in the electronic pr...

  6. Assembling Metal Ions Induced Cyanide-Bridged Heterometallic 1D and Ion-Pair Complexes: Synthesis, Crystal Structures and Magnetic Properties

    International Nuclear Information System (INIS)

    Kong, Lingqian; Zhao, Zengdian; Chen, Kexun; Wang, Ping; Zhang, Daopeng

    2013-01-01

    We obtained a heterobimetallic one-dimensional cyanide-bridged Mn(II)-Ni(II) complex and an Co(III)-Ni(II) ion-pair complex with [Ni(CN) 4 ] 2- as building block and M(II)-phenanthroline (M = Mn, Co) compounds as assembling segment. The different structural types of complexes 1 and 2 indicate that the property of the metal ions the assembling segment contained have obvious influence on the structure of the cyanide-bridged complex. Investigation over the magnetic properties of complex 1 reveals an overall weak antiferromagnetic coupling between the adjacent Mn(II) ions bridged by the antiferromagnetic [-NC-Ni-CN-] unit. Among of all the molecular magnetism systems, for the well known reasons, cyanide-containing complexes have been widely employed as bridges to assemble homo/hetero-metallic molecular magnetic materials by using the cyanide bridge transferring magnetic coupling between the neighboring paramagnetic ions, in whichsome showed interesting magnetic properties, such as high-Tc magnets, spin crossover materials, single-molecule magnets (SMMs) and single-chain magnets (SCMs)

  7. The metallicities of stars with and without transiting planets

    DEFF Research Database (Denmark)

    Buchhave, Lars A.; Latham, David W.

    2015-01-01

    Host star metallicities have been used to infer observational constraints on planet formation throughout the history of the exoplanet field. The giant planet metallicity correlation has now been widely accepted, but questions remain as to whether the metallicity correlation extends to the small...... terrestrial-sized planets. Here, we report metallicities for a sample of 518 stars in the Kepler field that have no detected transiting planets and compare their metallicity distribution to a sample of stars that hosts small planets (). Importantly, both samples have been analyzed in a homogeneous manner...... using the same set of tools (Stellar Parameters Classification tool). We find the average metallicity of the sample of stars without detected transiting planets to be and the sample of stars hosting small planets to be . The average metallicities of the two samples are indistinguishable within...

  8. [Non-empirical interatomic potentials for transition metals

    International Nuclear Information System (INIS)

    1993-01-01

    The report is divided into the following sections: potential-energy functions for d-band metals, potential-energy functions for aluminides and quasicrystals, electronic structure of complex structures and quasicrystals, potential-energy functions in transition-metal oxides, applications to defect structure and mechanical properties, and basic theory of interatomic potentials

  9. Theory of quantum metal to superconductor transitions in highly conducting systems

    Energy Technology Data Exchange (ETDEWEB)

    Spivak, B.

    2010-04-06

    We derive the theory of the quantum (zero temperature) superconductor to metal transition in disordered materials when the resistance of the normal metal near criticality is small compared to the quantum of resistivity. This can occur most readily in situations in which 'Anderson's theorem' does not apply. We explicitly study the transition in superconductor-metal composites, in an swave superconducting film in the presence of a magnetic field, and in a low temperature disordered d-wave superconductor. Near the point of the transition, the distribution of the superconducting order parameter is highly inhomogeneous. To describe this situation we employ a procedure which is similar to that introduced by Mott for description of the temperature dependence of the variable range hopping conduction. As the system approaches the point of the transition from the metal to the superconductor, the conductivity of the system diverges, and the Wiedemann-Franz law is violated. In the case of d-wave (or other exotic) superconductors we predict the existence of (at least) two sequential transitions as a function of increasing disorder: a d-wave to s-wave, and then an s-wave to metal transition.

  10. Halogenation processes of secondary organic aerosol and implications on halogen release mechanisms

    Directory of Open Access Journals (Sweden)

    J. Ofner

    2012-07-01

    Full Text Available Reactive halogen species (RHS, such as X·, X2 and HOX containing X = chlorine and/or bromine, are released by various sources like photo-activated sea-salt aerosol or from salt pans, and salt lakes. Despite many studies of RHS reactions, the potential of RHS reacting with secondary organic aerosol (SOA and organic aerosol derived from biomass-burning (BBOA has been neglected. Such reactions can constitute sources of gaseous organohalogen compounds or halogenated organic matter in the tropospheric boundary layer and can influence physicochemical properties of atmospheric aerosols.

    Model SOA from α-pinene, catechol, and guaiacol was used to study heterogeneous interactions with RHS. Particles were exposed to molecular chlorine and bromine in an aerosol smog-chamber in the presence of UV/VIS irradiation and to RHS, released from simulated natural halogen sources like salt pans. Subsequently, the aerosol was characterized in detail using a variety of physicochemical and spectroscopic methods. Fundamental features were correlated with heterogeneous halogenation, which results in new functional groups (FTIR spectroscopy, changes UV/VIS absorption, chemical composition (ultrahigh resolution mass spectroscopy (ICR-FT/MS, or aerosol size distribution. However, the halogen release mechanisms were also found to be affected by the presence of organic aerosol. Those interaction processes, changing chemical and physical properties of the aerosol are likely to influence e.g. the ability of the aerosol to act as cloud condensation nuclei, its potential to adsorb other gases with low-volatility, or its contribution to radiative forcing and ultimately the Earth's radiation balance.

  11. On the thermodynamics of phase transitions in metal hydrides

    Science.gov (United States)

    di Vita, Andrea

    2012-02-01

    Metal hydrides are solutions of hydrogen in a metal, where phase transitions may occur depending on temperature, pressure etc. We apply Le Chatelier's principle of thermodynamics to a particular phase transition in TiH x , which can approximately be described as a second-order phase transition. We show that the fluctuations of the order parameter correspond to fluctuations both of the density of H+ ions and of the distance between adjacent H+ ions. Moreover, as the system approaches the transition and the correlation radius increases, we show -with the help of statistical mechanics-that the statistical weight of modes involving a large number of H+ ions (`collective modes') increases sharply, in spite of the fact that the Boltzmann factor of each collective mode is exponentially small. As a result, the interaction of the H+ ions with collective modes makes a tiny suprathermal fraction of the H+ population appear. Our results hold for similar transitions in metal deuterides, too. A violation of an -insofar undisputed-upper bound on hydrogen loading follows.

  12. A Simple, General Synthetic Route toward Nanoscale Transition Metal Borides.

    Science.gov (United States)

    Jothi, Palani R; Yubuta, Kunio; Fokwa, Boniface P T

    2018-04-01

    Most nanomaterials, such as transition metal carbides, phosphides, nitrides, chalcogenides, etc., have been extensively studied for their various properties in recent years. The similarly attractive transition metal borides, on the contrary, have seen little interest from the materials science community, mainly because nanomaterials are notoriously difficult to synthesize. Herein, a simple, general synthetic method toward crystalline transition metal boride nanomaterials is proposed. This new method takes advantage of the redox chemistry of Sn/SnCl 2 , the volatility and recrystallization of SnCl 2 at the synthesis conditions, as well as the immiscibility of tin with boron, to produce crystalline phases of 3d, 4d, and 5d transition metal nanoborides with different morphologies (nanorods, nanosheets, nanoprisms, nanoplates, nanoparticles, etc.). Importantly, this method allows flexibility in the choice of the transition metal, as well as the ability to target several compositions within the same binary phase diagram (e.g., Mo 2 B, α-MoB, MoB 2 , Mo 2 B 4 ). The simplicity and wide applicability of the method should enable the fulfillment of the great potential of this understudied class of materials, which show a variety of excellent chemical, electrochemical, and physical properties at the microscale. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Hot carrier dynamics in plasmonic transition metal nitrides

    Science.gov (United States)

    Habib, Adela; Florio, Fred; Sundararaman, Ravishankar

    2018-06-01

    Extraction of non-equilibrium hot carriers generated by plasmon decay in metallic nano-structures is an increasingly exciting prospect for utilizing plasmonic losses, but the search for optimum plasmonic materials with long-lived carriers is ongoing. Transition metal nitrides are an exciting class of new plasmonic materials with superior thermal and mechanical properties compared to conventional noble metals, but their suitability for plasmonic hot carrier applications remains unknown. Here, we present fully first principles calculations of the plasmonic response, hot carrier generation and subsequent thermalization of all group IV, V and VI transition metal nitrides, fully accounting for direct and phonon-assisted transitions as well as electron–electron and electron–phonon scattering. We find the largest frequency ranges for plasmonic response in ZrN, HfN and WN, between those of gold and silver, while we predict strongest absorption in the visible spectrum for the VN, NbN and TaN. Hot carrier generation is dominated by direct transitions for most of the relevant energy range in all these nitrides, while phonon-assisted processes dominate only below 1 eV plasmon energies primarily for the group IV nitrides. Finally, we predict the maximum hot carrier lifetimes to be around 10 fs for group IV and VI nitrides, a factor of 3–4 smaller than noble metals, due to strong electron–phonon scattering. However, we find longer carrier lifetimes for group V nitrides, comparable to silver for NbN and TaN, while exceeding 100 fs (twice that of silver) for VN, making them promising candidates for efficient hot carrier extraction.

  14. Probable metal-insulator transition in Ag{sub 4}SSe

    Energy Technology Data Exchange (ETDEWEB)

    Drebushchak, V.A., E-mail: dva@igm.nsc.ru [V.S. Sobolev Institute of Geology and Mineralogy, SB RAS, Pr. Ac. Koptyuga 3, Novosibirsk 630090 (Russian Federation); Novosibirsk State University, Ul. Pirogova 2, Novosibirsk 630090 (Russian Federation); Pal’yanova, G.A.; Seryotkin, Yu.V. [V.S. Sobolev Institute of Geology and Mineralogy, SB RAS, Pr. Ac. Koptyuga 3, Novosibirsk 630090 (Russian Federation); Novosibirsk State University, Ul. Pirogova 2, Novosibirsk 630090 (Russian Federation); Drebushchak, T.N. [Novosibirsk State University, Ul. Pirogova 2, Novosibirsk 630090 (Russian Federation); Institute of Solid State Chemistry and Mechanochemistry, SB RAS, Ul. Kutateladze 18, Novosibirsk 630128 (Russian Federation)

    2015-02-15

    Highlights: • New phase transition in Ag{sub 4}SSe was discovered with scanning calorimetry and supported with X-ray powder diffraction. • The thermal effect relates to the anomaly in electrical and thermal conductivity of Ag{sub 4}SSe. • Similar thermal and electrical effects in K{sub 3}Cu{sub 8}S{sub 6} are explained with the metal-insulator transition. - Abstract: New phase transition (285 K) in low-temperature monoclinic Ag{sub 4}SSe was found out below the α-β transition (358 K) after the measurements with differential scanning calorimetry. The transition reveals significant hysteresis (over 30 K). X-ray powder diffraction shows that the superlattice with doubled a and b parameters of the unit cell exists below the new transition point. The signs of this new phase transition can be found in thermal and electrical conductivity of Ag{sub 4}SSe published in literature. Elusive phase transition in Ag{sub 2}Se shows similar properties. The new transition is likely related to the metal-insulator type transition, like K{sub 3}Cu{sub 8}S{sub 6}.

  15. Transition metal carbide nanocomposite and amorphous thin films

    OpenAIRE

    Tengstrand, Olof

    2014-01-01

    This thesis explores thin films of binary and ternary transition metal carbides, in the Nb-C, Ti-Si-C, Nb-Si-C, Zr-Si-C, and Nb-Ge-C systems. The electrical and mechanical properties of these systems are affected by their structure and here both nanocomposite and amorphous thin films are thus investigated. By appropriate choice of transition metal and composition the films can be designed to be multifunctional with a combination of properties, such as low electric resistivity, low contact res...

  16. Evaluation of complexing agents and column temperature in ion chromatographic separation of alkali metals, alkaline earth metals and transition metals ion

    International Nuclear Information System (INIS)

    Kelkar, Anoop; Pandey, Ashish; Name, Anil B.; Das, D.K.; Behere, P.G.; Mohd Afzal

    2015-01-01

    The aim of ion chromatography method development is the resolution of all metal ions of interests. Resolution can be improved by changing the selectivity. Selectivity in chromatography can be altered by changes in mobile phase (eg eluent type, eluent strength) or through changes in stationary phase. Temperature has been used in altering the selectivity of particularly in reversed phase liquid chromatography and ion exchange chromatography. Present paper describe the retention behaviour of alkali metals, alkaline earth metals and transition metal ions on a silica based carboxylate function group containing analyte column. Alkali metals, alkaline earth metals and transition metal ions were detected by ion conductivity and UV-VIS detectors respectively

  17. Organic halogens in landfill leachates

    DEFF Research Database (Denmark)

    Grøn, C.; Christensen, J. B.; Jensen, Dorthe Lærke

    2000-01-01

    Using a group parameter, total organic halogens (TOX), high TOX concentrations were found in leachates and leachate contaminated groundwaters at two Danish mixed sanitary and hazardous waste sites. With commonly used screening procedures for organic contaminants, the individual halogenated organi...

  18. Hydrogen and dihydrogen bonding of transition metal hydrides

    Science.gov (United States)

    Jacobsen, Heiko

    2008-04-01

    Intermolecular interactions between a prototypical transition metal hydride WH(CO) 2NO(PH 3) 2 and a small proton donor H 2O have been studied using DFT methodology. The hydride, nitrosyl and carbonyl ligand have been considered as site of protonation. Further, DFT-D calculations in which empirical corrections for the dispersion energy are included, have been carried out. A variety of pure and hybrid density functionals (BP86, PW91, PBE, BLYP, OLYP, B3LYP, B1PW91, PBE0, X3LYP) have been considered, and our calculations indicate the PBE functional and its hybrid variation are well suited for the calculation of transition metal hydride hydrogen and dihydrogen bonding. Dispersive interactions make up for a sizeable portion of the intermolecular interaction, and amount to 20-30% of the bond energy and to 30-40% of the bond enthalpy. An energy decomposition analysis reveals that the H⋯H bond of transition metal hydrides contains both covalent and electrostatic contributions.

  19. Hydrogen and dihydrogen bonding of transition metal hydrides

    International Nuclear Information System (INIS)

    Jacobsen, Heiko

    2008-01-01

    Intermolecular interactions between a prototypical transition metal hydride WH(CO) 2 NO(PH 3 ) 2 and a small proton donor H 2 O have been studied using DFT methodology. The hydride, nitrosyl and carbonyl ligand have been considered as site of protonation. Further, DFT-D calculations in which empirical corrections for the dispersion energy are included, have been carried out. A variety of pure and hybrid density functionals (BP86, PW91, PBE, BLYP, OLYP, B3LYP, B1PW91, PBE0, X3LYP) have been considered, and our calculations indicate the PBE functional and its hybrid variation are well suited for the calculation of transition metal hydride hydrogen and dihydrogen bonding. Dispersive interactions make up for a sizeable portion of the intermolecular interaction, and amount to 20-30% of the bond energy and to 30-40% of the bond enthalpy. An energy decomposition analysis reveals that the H...H bond of transition metal hydrides contains both covalent and electrostatic contributions

  20. The phosphorus and the transition metals chemistry

    International Nuclear Information System (INIS)

    Mathey, F.

    1988-01-01

    The 1988 progress report, concerning the Polytechnic School unit (France), which studies the phosphorus and the transition metals chemistry, is presented. The laboratory activities are related to the following topics: the phosporus heterocyclic chemistry, the phosphorus-carbon double bonds chemistry, the new transition metals phosphorus compounds, the phosphonates and their uses. Some practical applications of homogeneous catalysis and new materials synthesis are investigated. The main results obtained are: the discovery of the tetra-phosphafulvalenes, the utilization of a new synthesis method of the phosphorus-carbon double bonds and the stabilization of the α-phosphonyled carbanions by the lithium diisopropylamidourea. The papers, the congress communications and the thesis are also shown [fr

  1. Adlayer Core-Level Shifts of Random Metal Overlayers on Transition-Metal Substrates

    DEFF Research Database (Denmark)

    Ganduglia-Pirovano, M. V.; Kudrnovský, J.; Scheffler, M.

    1997-01-01

    and the screening effects induced by the core hole, and study the influence of the alloy composition for a number of noble metal-transition metal systems. Our analysis clearly indicates the importance of final-state screening effects for the interpretation of measured core-level shifts. Calculated deviations from...

  2. The model of metal-insulator phase transition in vanadium oxide

    International Nuclear Information System (INIS)

    Vikhnin, V.S.; Lysenko, S.; Rua, A.; Fernandez, F.; Liu, H.

    2005-01-01

    Thermally induced metal-insulator phase transitions (PT) in VO 2 thin films are studied theoretically and experimentally. The hysteresis phenomena in the region of the transition for different type thin films were investigated. The phenomenological model of the PT is suggested. The charge transfer-lattice instability in VO 2 metallic phase is considered as basis of the first order metal-insulator PT in VO 2 . The charge transfer is treated as an order parameter

  3. Flue gas corrosion through halogen compounds in fuel gas

    Energy Technology Data Exchange (ETDEWEB)

    Eisenmann, R

    1987-04-01

    The halogens of chlorine and fluorine greatly influence the corrosion speed of metal materials. If small quantities of chlorinated and/or fluorinated hydrocarbons are present in fuel gas like in landfill gas, they must not result in enhanced corrosion of gas appliances. Data from literature and the initial results of tests run by the author indicate that quantities at about 10 mg/cbm (in terms of chlorine) can be assumed not to cause any noticeable acceleration of corrosion speed.

  4. Assembling Metal Ions Induced Cyanide-Bridged Heterometallic 1D and Ion-Pair Complexes: Synthesis, Crystal Structures and Magnetic Properties

    Energy Technology Data Exchange (ETDEWEB)

    Kong, Lingqian [Liaocheng Univ., Liaocheng (China); Zhao, Zengdian; Chen, Kexun; Wang, Ping; Zhang, Daopeng [Shandong Univ. of Technology, Zibo (China)

    2013-07-15

    We obtained a heterobimetallic one-dimensional cyanide-bridged Mn(II)-Ni(II) complex and an Co(III)-Ni(II) ion-pair complex with [Ni(CN){sub 4}]{sup 2-} as building block and M(II)-phenanthroline (M = Mn, Co) compounds as assembling segment. The different structural types of complexes 1 and 2 indicate that the property of the metal ions the assembling segment contained have obvious influence on the structure of the cyanide-bridged complex. Investigation over the magnetic properties of complex 1 reveals an overall weak antiferromagnetic coupling between the adjacent Mn(II) ions bridged by the antiferromagnetic [-NC-Ni-CN-] unit. Among of all the molecular magnetism systems, for the well known reasons, cyanide-containing complexes have been widely employed as bridges to assemble homo/hetero-metallic molecular magnetic materials by using the cyanide bridge transferring magnetic coupling between the neighboring paramagnetic ions, in whichsome showed interesting magnetic properties, such as high-Tc magnets, spin crossover materials, single-molecule magnets (SMMs) and single-chain magnets (SCMs)

  5. Vacancies in transition metals

    International Nuclear Information System (INIS)

    Allan, G.; Lannoo, M.

    1976-01-01

    A calculation of the formation energy and volume for a vacancy in transition metals is described. A tight-binding scheme is used for the d band and a Born-Mayer type potential to account for the repulsive part of the energy at small distances. The results show that the relaxation energy is small in all cases, less than 0.1 eV. This seems to be coherent with the good agreement obtained for the theoretical and experimental values of the formation energy Esub(F)sup(V) of the vacancy, without including relaxation. The center of the transitional series is found to give a contraction (Formation volume of order -0.4 at.vol.) whereas the edges are found to produce dilations. (author)

  6. Biogeochemistry of Halogenated Hydrocarbons

    Science.gov (United States)

    Adriaens, P.; Gruden, C.; McCormick, M. L.

    2003-12-01

    Halogenated hydrocarbons originate from both natural and industrial sources. Whereas direct anthropogenic emissions to the atmosphere and biosphere are often easy to assess, particularly when they are tied to major industrial activities, the attribution of emissions to other human activities (e.g., biomass burning), diffuse sources (e.g., atmospheric discharge, run off), and natural production (e.g., soils, fungi, algae, microorganisms) are difficult to quantify. The widespread occurrence of both alkyl and aryl halides in groundwater, surface water, soils, and various trophic food chains, even those not affected by known point sources, suggests a substantial biogeochemical cycling of these compounds (Wania and Mackay, 1996; Adriaens et al., 1999; Gruden et al., 2003). The transport and reactive fate mechanisms controlling their reactivity are compounded by the differences in sources of alkyl-, aryl-, and complex organic halides, and the largely unknown impact of biogenic processes, such as enzymatically mediated halogenation of organic matter, fungal production of halogenated hydrocarbons, and microbial or abiotic transformation reactions (e.g., Asplund and Grimvall, 1991; Gribble, 1996; Watling and Harper, 1998; Oberg, 2002). The largest source may be the natural halogenation processes in the terrestrial environment, as the quantities detected often exceed the amount that can be explained by human activities in the surrounding areas ( Oberg, 1998). Since biogeochemical processes result in the distribution of a wide range of halogenated hydrocarbon profiles, altered chemical structures, and isomer distributions in natural systems, source apportionment (or environmental forensics) can often only be resolved using multivariate statistical methods (e.g., Goovaerts, 1998; Barabas et al., 2003; Murphy and Morrison, 2002).This chapter will describe the widespread occurrence of halogenated hydrocarbons, interpret their distribution and biogeochemical cycling in light of

  7. Halogen poisoning effect of Pt-TiO{sub 2} for formaldehyde catalytic oxidation performance at room temperature

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Xiaofeng; Cheng, Bei [State Key Laboratory of Advanced Technology for Material Synthesis and Processing, Wuhan University of Technology, Luoshi Road 122#, Wuhan 430070 (China); Yu, Jiaguo, E-mail: jiaguoyu@yahoo.com [State Key Laboratory of Advanced Technology for Material Synthesis and Processing, Wuhan University of Technology, Luoshi Road 122#, Wuhan 430070 (China); Department of Physics, Faculty of Science, King Abdulaziz University, Jeddah 21589 (Saudi Arabia); Ho, Wingkei, E-mail: keithho@ied.edu.hk [Department of Science and Environmental Studies and Centre for Education in Environmental Sustainability, The Hong Kong Institute of Education, Tai Po, N.T. Hong Kong (China)

    2016-02-28

    Graphical abstract: - Highlights: • The Pt-TiO{sub 2} catalyst is deactivated by adsorption of halogen ions. • The halogen poison is mainly attributed to the active site blocking of the Pt surface. • Halogen ions and Pt form Pt−X coordination bonds. • Large halogen diameter exhibits severe poisoning effect. - Abstract: Catalytic decomposition of formaldehyde (HCHO) at room temperature is an important method for HCHO removal. Pt-based catalysts are the optimal catalyst for HCHO decomposition at room temperature. However, the stability of this catalyst remains unexplored. In this study, Pt-TiO{sub 2} (Pt-P25) catalysts with and without adsorbed halogen ions (including F{sup −}, Cl{sup −}, Br{sup −}, and I{sup −}) were prepared through impregnation and ion modification. Pt-TiO{sub 2} samples with adsorbed halogen ions exhibited reduced catalytic activity for formaldehyde decomposition at room temperature compared with the Pt-TiO{sub 2} sample; the catalytic activity followed the order of F-Pt-P25, Cl-Pt-P25, Br-Pt-P25, and I-Pt-P25. Characterization results (including XRD, TEM, HRTEM, BET, XPS, and metal dispersion) showed that the adsorbed halogen ions can poison Pt nanoparticles (NPs), thereby reducing the HCHO oxidation activity of Pt-TiO{sub 2}. The poison mechanism is due to the strong adsorption of halogen ions on the surface of Pt NPs. The adsorbed ions form coordination bonds with surface Pt atoms by transferring surplus electrons into the unoccupied 5d orbit of the Pt atom, thereby inhibiting oxygen adsorption and activation of the Pt NP surface. Moreover, deactivation rate increases with increasing diameter of halogen ions. This study provides new insights into the fabrication of high-performance Pt-based catalysts for indoor air purification.

  8. The 1s x-ray absorption pre-edge structures in transition metal oxides

    NARCIS (Netherlands)

    de Groot, Frank|info:eu-repo/dai/nl/08747610X; Vanko, Gyoergy; Glatzel, Pieter

    2009-01-01

    We develop a general procedure to analyse the pre-edges in 1s x-ray absorption near edge structure (XANES) of transition metal oxides and coordination complexes. Transition metal coordination complexes can be described from a local model with one metal ion. The 1s 3d quadrupole transitions are

  9. Rational Design of Two-Dimensional Metallic and Semiconducting Spintronic Materials Based on Ordered Double-Transition-Metal MXenes

    KAUST Repository

    Dong, Liang; Kumar, Hemant; Anasori, Babak; Gogotsi, Yury; Shenoy, Vivek B.

    2016-01-01

    double-transition-metal MXene structures to achieve such a goal. On the basis of the analysis of electron filling in transition-metal cations and first-principles simulations, we demonstrate robust ferromagnetism in Ti2MnC2Tx monolayers regardless

  10. Studies on halogen quenching through the Stern-Volmer plot

    International Nuclear Information System (INIS)

    Takiue, Makoto; Ishikawa, Hiroaki.

    1978-01-01

    The quenching effect for halogenated benzenes, methanes and ethanes have been investigated. The halogen quenching was accurately measured using the internal conversion electrons emitted from 113 Sn-sup(113m)In. From the quenching constants determined by the Stern-Volmer plots with respect to various halogen quenchers, the following results have been obtained. (1) The quenching constants increase with the number of halogen substituents, so as linearly in halogenated benzenes and exponentially in halogenated methanes and ethanes. Even the isomers of halogenides have different quenching constants. (2) There is a linearity between logarithm of the quenching constant and a polarographic half-wave reduction potential. (3) Electron excitation provides larger quenching constants than UV excitation for halogenated methanes. Based on these results, the mechanism of halogen quenching have been discussed in connection with the exciplex formation. (auth.)

  11. Independent Evolution of Six Families of Halogenating Enzymes.

    Science.gov (United States)

    Xu, Gangming; Wang, Bin-Gui

    2016-01-01

    Halogenated natural products are widespread in the environment, and the halogen atoms are typically vital to their bioactivities. Thus far, six families of halogenating enzymes have been identified: cofactor-free haloperoxidases (HPO), vanadium-dependent haloperoxidases (V-HPO), heme iron-dependent haloperoxidases (HI-HPO), non-heme iron-dependent halogenases (NI-HG), flavin-dependent halogenases (F-HG), and S-adenosyl-L-methionine (SAM)-dependent halogenases (S-HG). However, these halogenating enzymes with similar biological functions but distinct structures might have evolved independently. Phylogenetic and structural analyses suggest that the HPO, V-HPO, HI-HPO, NI-HG, F-HG, and S-HG enzyme families may have evolutionary relationships to the α/β hydrolases, acid phosphatases, peroxidases, chemotaxis phosphatases, oxidoreductases, and SAM hydroxide adenosyltransferases, respectively. These halogenating enzymes have established sequence homology, structural conservation, and mechanistic features within each family. Understanding the distinct evolutionary history of these halogenating enzymes will provide further insights into the study of their catalytic mechanisms and halogenation specificity.

  12. [Artificial Cysteine Bridges on the Surface of Green Fluorescent Protein Affect Hydration of Its Transition and Intermediate States].

    Science.gov (United States)

    Melnik, T N; Nagibina, G S; Surin, A K; Glukhova, K A; Melnik, B S

    2018-01-01

    Studying the effect of cysteine bridges on different energy levels of multistage folding proteins will enable a better understanding of the process of folding and functioning of globular proteins. In particular, it will create prospects for directed change in the stability and rate of protein folding. In this work, using the method of differential scanning microcalorimetry, we have studied the effect of three cysteine bridges introduced in different structural elements of the green fluorescent protein on the denaturation enthalpies, activation energies, and heat-capacity increments when this protein passes from native to intermediate and transition states. The studies have allowed us to confirm that, with this protein denaturation, the process hardly damages the structure initially, but then changes occur in the protein structure in the region of 4-6 beta sheets. The cysteine bridge introduced in this region decreases the hydration of the second transition state and increases the hydration of the second intermediate state during the thermal denaturation of the green fluorescent protein.

  13. Catalytic olefin polymerization with early transition metal compounds

    NARCIS (Netherlands)

    Eshuis, Johan Jan Willem

    1991-01-01

    The catalysis of organic reactions by soluble metal complexes has become a major tool in synthesis, both in the laboratory and in the chemical industry. Processes catalyzed by transition metal complexes include carbonylation, olefin polymerization, olefin addition, olefin oxidation and alkane and

  14. Direct NO decomposition over stepped transition-metal surfaces

    DEFF Research Database (Denmark)

    Falsig, Hanne; Bligaard, Thomas; Christensen, Claus H.

    2007-01-01

    We establish the full potential energy diagram for the direct NO decomposition reaction over stepped transition-metal surfaces by combining a database of adsorption energies on stepped metal surfaces with known Bronsted-Evans-Polanyi (BEP) relations for the activation barriers of dissociation...

  15. Theoretical studies of transition metal complexes with nitriles and isocyanides

    International Nuclear Information System (INIS)

    Kuznetsov, Maksim L

    2002-01-01

    Theoretical studies of transition metal complexes with nitriles and isocyanides are reviewed. The electronic structures and the nature of coordination bonds in these complexes are discussed. The correlation between the electronic structures of transition metal complexes with nitriles and isocyanides and their structural properties, spectroscopic characteristics, and reactivities are considered. The bibliography includes 121 references.

  16. Studies of Metal-Metal Bonded Compounds in Catalysis

    Energy Technology Data Exchange (ETDEWEB)

    Berry, John F. [Univ. of Wisconsin, Madison, WI (United States)

    2018-01-19

    The overall goals of this research are (1) to define the fundamental coordination chemistry underlying successful catalytic transformations promoted by metal-metal bonded compounds, and (2) to explore new chemical transformations that occur at metal-metal bonded sites that could lead to the discovery of new catalytic processes. Transformations of interest include metal-promoted reactions of carbene, nitrene, or nitrido species to yield products with new C–C and C–N bonds, respectively. The most promising suite of transition metal catalysts for these transformations is the set of metal-metal bonded coordination compounds of Ru and Rh of the general formula M2(ligand)4, where M = Ru or Rh and ligand = a monoanionic, bridging ligand such as acetate. Development of new catalysts and improvement of catalytic conditions have been stymied by a general lack of knowledge about the nature of highly reactive intermediates in these reactions, the knowledge that is to be supplied by this work. Our three specific objectives for this year have been (A) to trap, isolate, and characterize new reactive intermediates of general relevance to catalysis, (B) to explore the electronic structure and reactivity of these unusual species, and how these two properties are interrelated, and (C) to use our obtained mechanistic knowledge to design new catalysts with a focus on Earth-abundant first-row transition metal compounds.

  17. A Bridge Too Far: The Decline in Shared Science Activities during Primary-Secondary Transition

    Science.gov (United States)

    Galton, Maurice

    2016-01-01

    This article reviews the use of "bridging units" in science to improve curriculum continuity during transition from primary to secondary school. Based on research evidence collected over several decades, it suggests that the use of these units rose to a peak around the time of the millennium, but that in recent years few schools have…

  18. Trends in catalytic NO decomposition over transition metal surfaces

    DEFF Research Database (Denmark)

    Falsig, Hanne; Bligaard, Thomas; Rass-Hansen, Jeppe

    2007-01-01

    The formation of NOx from combustion of fossil and renewable fuels continues to be a dominant environmental issue. We take one step towards rationalizing trends in catalytic activity of transition metal catalysts for NO decomposition by combining microkinetic modelling with density functional...... theory calculations. We show specifically why the key problem in using transition metal surfaces to catalyze direct NO decomposition is their significant relative overbinding of atomic oxygen compared to atomic nitrogen....

  19. Hydrogen and dihydrogen bonding of transition metal hydrides

    Energy Technology Data Exchange (ETDEWEB)

    Jacobsen, Heiko [KemKom, Libellenweg 2, 25917 Leck, Nordfriesland (Germany)], E-mail: jacobsen@kemkom.com

    2008-04-03

    Intermolecular interactions between a prototypical transition metal hydride WH(CO){sub 2}NO(PH{sub 3}){sub 2} and a small proton donor H{sub 2}O have been studied using DFT methodology. The hydride, nitrosyl and carbonyl ligand have been considered as site of protonation. Further, DFT-D calculations in which empirical corrections for the dispersion energy are included, have been carried out. A variety of pure and hybrid density functionals (BP86, PW91, PBE, BLYP, OLYP, B3LYP, B1PW91, PBE0, X3LYP) have been considered, and our calculations indicate the PBE functional and its hybrid variation are well suited for the calculation of transition metal hydride hydrogen and dihydrogen bonding. Dispersive interactions make up for a sizeable portion of the intermolecular interaction, and amount to 20-30% of the bond energy and to 30-40% of the bond enthalpy. An energy decomposition analysis reveals that the H...H bond of transition metal hydrides contains both covalent and electrostatic contributions.

  20. Spin-exchange interaction between transition metals and metalloids in soft-ferromagnetic metallic glasses

    Science.gov (United States)

    Das, Santanu; Choudhary, Kamal; Chernatynskiy, Aleksandr; Choi Yim, Haein; Bandyopadhyay, Asis K.; Mukherjee, Sundeep

    2016-06-01

    High-performance magnetic materials have immense industrial and scientific importance in wide-ranging electronic, electromechanical, and medical device technologies. Metallic glasses with a fully amorphous structure are particularly suited for advanced soft-magnetic applications. However, fundamental scientific understanding is lacking for the spin-exchange interaction between metal and metalloid atoms, which typically constitute a metallic glass. Using an integrated experimental and molecular dynamics approach, we demonstrate the mechanism of electron interaction between transition metals and metalloids. Spin-exchange interactions were investigated for a Fe-Co metallic glass system of composition [(Co1-x Fe x )0.75B0.2Si0.05]96Cr4. The saturation magnetization increased with higher Fe concentration, but the trend significantly deviated from simple rule of mixtures. Ab initio molecular dynamics simulation was used to identify the ferromagnetic/anti-ferromagnetic interaction between the transition metals and metalloids. The overlapping band-structure and density of states represent ‘Stoner type’ magnetization for the amorphous alloys in contrast to ‘Heisenberg type’ in crystalline iron. The enhancement of magnetization by increasing iron was attributed to the interaction between Fe 3d and B 2p bands, which was further validated by valence-band study.

  1. Structural study of some halogen oxyfluorides

    International Nuclear Information System (INIS)

    Tantot, Georges.

    1976-12-01

    Some halogen oxyfluorides are studied from a structural point of view by vibrational spectroscopy and nuclear magnetic resonance. Force constant and molecular orbital calculations are added to the experimental data. The pyramidal shape of ClO 2 F under its three physical states is confirmed. In the gas and liquid phases an intermolecular association is observed. A similar interaction takes place in ClOF 3 . ClO 3 F has only a solid state transition above 10K. The structures of ClO 2 F and KBrO 2 F 2 are partly determined. The theoretical calculations are well correlated with the experimental data. They suggest a major influence of the ligands [fr

  2. Study of transition metal oxides by photoelectron spectroscopy

    International Nuclear Information System (INIS)

    Rao, C.N.R.; Sarma, D.D.; Vasudevan, S.; Hegde, M.S.

    1979-01-01

    Systematics in the X-ray photoelectron spectra (X.p.e.s.) of Ti, V, Cr, Mn and Nb oxides with the metal ion in different oxidation states as well as of related series of mono-, sesqui- and di-oxides of the first row of transition metals have been investigated in detail. Core level binding energies, spin-orbit splittings and exchange splittings are found to exhibit interesting variations with the oxidation state of the metal or the nuclear charge. The 3d binding energies of the monoxides show a proportionality to Goodenough's (R - RC). Other aspects of interest in the study are the satellite structure and final state effects in the X.p.e.s. of the oxides, and identification of different valence states in oxides of the general formulae Mn02n-1 and M304. The nature of changes in the 3d bands of oxides undergoing metal-insulator transitions is also indicated. (author)

  3. Neutron diffraction studies of transition metal hydride complexes

    International Nuclear Information System (INIS)

    Koetzle, T.F.; Bau, R.

    1976-01-01

    Investigations of H 3 Ta(C 5 H 5 ) 2 (III), HW 2 (CO) 9 (NO) (IV), and HW 2 (CO) 8 (NO) (P(OCH 3 ) 3 ) (V) have been completed. Preliminary results are available for HFeCo 3 (CO) 9 [P(OCH 3 ) 3 ] 3 (VII). This work, together with studies of HMo 2 (C 5 H 5 ) 2 (CO) 4 (P(CH 3 ) 2 ) (VI) and [(C 2 H 5 ) 4 N] + [HCr 2 (CO) 10 ] - carried out at Argonne has led to some general observations on the geometry and the nature of bonding in these compounds. For example, in the structures of IV and V, both of which have bent W--H--W linkages (less than W--H--W in the range 125-130 0 ), there is conclusive evidence for the existence of a closed three-center W--H--W bond with significant metal-metal interaction. Such is the case, because extensions of the axial W--C and W--N bonds trans to the hydride intersect at a point near the center of the W--H--W triangle. The geometry of VI, which also contains a bent M--H--M bond, is consistent with that of IV and V. Bridging M--H bonds in these second- and third-row hydrides range in length from 1.85 to 1.89 A, compared to 1.75 A in the first-row polynuclear complex VII. For metals of corresponding rows, bridging M--H bonds are about 0.1 A longer than terminal bonds, which are classified as single covalent bonds

  4. Passivation of quartz for halogen-containing light sources

    Science.gov (United States)

    Falkenstein, Zoran

    1999-01-01

    Lifetime of halogen containing VUV, UV, visible or IR light sources can be extended by passivating the quartz or glass gas containers with halogens prior to filling the quartz with the halogen and rare gas mixtures used to produce the light.

  5. Conductive transition metal oxide nanostructured electrochromic material and optical switching devices constructed thereof

    Science.gov (United States)

    Mattox, Tracy M.; Koo, Bonil; Garcia, Guillermo; Milliron, Delia J.; Trizio, Luca De; Dahlman, Clayton

    2017-10-10

    An electrochromic device includes a nanostructured transition metal oxide bronze layer that includes one or more transition metal oxide and one or more dopant, a solid state electrolyte, and a counter electrode. The nanostructured transition metal oxide bronze selectively modulates transmittance of near-infrared (NIR) spectrum and visible spectrum radiation as a function of an applied voltage to the device.

  6. Features of order-disorder phase transformation in nonstoichiometric transition metals carbides

    International Nuclear Information System (INIS)

    Emel'yanov, A.N.

    1996-01-01

    Measurements of temperature and electric conductivity of nonstoichiometric transition metals carbides TiC χ and NbC χ in the area of order-disorder phase transformation are carried out. There are certain peculiarities on the temperature and electric conductivity curves of the carbides, connected with the carbon sublattice disordering. On the basis of the anomalies observed on the curves of the temperature conductivity of nonstoichiometric carbides of transition metals above the temperature of the order-disorder transition the existence of the second structural transition is supposed

  7. Tethered Transition Metals Promoted Photocatalytic System for Efficient Hydrogen Evolutions

    KAUST Repository

    Takanabe, Kazuhiro

    2015-03-05

    The present invention is directed, at least in part, to a process for improving the efficiency of a photocatalyst (a semiconductor photocatalyst) by tethering (depositing) a metal (e.g., metal ions of a late transition metal, such as nickel) to the semiconductor (photocatalyst) surface through the use of an organic ligand. More specifically, 1,2-ethanedithiol (EDT) functions as an excellent molecular linker (organic ligand) to attach a transition metal complex (e.g., nickel (Ni.sup.2+ ions)) to the semiconductor surface, which can be in the form of a cadmium sulfide surface. The photocatalyst has particular utility in generating hydrogen from H.sub.2S.

  8. Tethered Transition Metals Promoted Photocatalytic System for Efficient Hydrogen Evolutions

    KAUST Repository

    Takanabe, Kazuhiro; Isimjan, Tayirjan; Yu, Weili; Del Gobbo, Silvano; Xu, Wei

    2015-01-01

    The present invention is directed, at least in part, to a process for improving the efficiency of a photocatalyst (a semiconductor photocatalyst) by tethering (depositing) a metal (e.g., metal ions of a late transition metal, such as nickel) to the semiconductor (photocatalyst) surface through the use of an organic ligand. More specifically, 1,2-ethanedithiol (EDT) functions as an excellent molecular linker (organic ligand) to attach a transition metal complex (e.g., nickel (Ni.sup.2+ ions)) to the semiconductor surface, which can be in the form of a cadmium sulfide surface. The photocatalyst has particular utility in generating hydrogen from H.sub.2S.

  9. The status and immediate problems of the chemistry of transition metal hydrides

    International Nuclear Information System (INIS)

    Meikheeva, V.I.

    1978-01-01

    The state of the art and perspectives of the chemistry transition metal hydrides are reviewed, the hydrides being essentially compounds with interstitial hydrogen in the crystal lattice of the metals. The possibilities of hydrogenation of transition metals are considered along with that of compounds of rare earth elements with metals of the iron family. It is shown that the products of hydrogenation of many alloys are unstable and disintegrate forming simpler hydrides. The phase diagram of La-Ni-H system resembles the isotherm of a ternary metal system with the difference that no continuous series of solid solutions is formed. Most hydrogenation products across LaHsub(2-3)-NiH are X-ray amorphous. The nature of hydrogen in hydrides is discussed along with the possibilities of synthesis of new hydrides of transition metals

  10. Recent advances in transition metal-catalyzed Csp2-monofluoro-, difluoro-, perfluoromethylation and trifluoromethylthiolation

    Directory of Open Access Journals (Sweden)

    Grégory Landelle

    2013-11-01

    Full Text Available In the last few years, transition metal-mediated reactions have joined the toolbox of chemists working in the field of fluorination for Life-Science oriented research. The successful execution of transition metal-catalyzed carbon–fluorine bond formation has become a landmark achievement in fluorine chemistry. This rapidly growing research field has been the subject of some excellent reviews. Our approach focuses exclusively on transition metal-catalyzed reactions that allow the introduction of –CFH2, –CF2H, –CnF2n+1 and –SCF3 groups onto sp² carbon atoms. Transformations are discussed according to the reaction-type and the metal employed. The review will not extend to conventional non-transition metal methods to these fluorinated groups.

  11. METHOD FOR PRODUCING ISOTOPIC METHANES AND PARTIALLY HALOGENATED DERIVATIVES THEROF

    Science.gov (United States)

    Frazer, J.W.

    1959-08-18

    A method is given for producing isotopic methanes and/ or partially halogenated derivatives. Lithium hydride, deuteride, or tritide is reacted with a halogenated methane or with a halogenated methane in combination with free halogen. The process is conveniently carried out by passing a halogenated methane preferably at low pressures or in an admixture with an inert gas through a fixed bed of finely divided lithium hydride heated initially to temperatures of 100 to 200 deg C depending upon the halogenated methane used.

  12. Nonmetal-metal transition in metal–molten-salt solutions

    NARCIS (Netherlands)

    Silvestrelli, P.-L.; Alavi, A.; Parrinello, M.; Frenkel, D.

    1996-01-01

    The method of ab initio molecular dynamics, based on finite-temperature density-functional theory, is used to study the nonmetal-metal transition in two different metal–molten-salt solutions, Kx(KCl)1-x and Nax(NaBr)1-x. As the excess metal concentration is increased the electronic density becomes

  13. Organic halogens in spruce forest throughfall

    DEFF Research Database (Denmark)

    Öberg, G.; Johansen, C.; Grøn, C.

    1998-01-01

    . No relationship between the position of the collectors and the forest edge or dominating wind-direction was found, suggesting that dry deposition was not a major source. The concentration of organic halogens was related to that of organic carbon and decreased from the tree-trunk and outwards. In addition......, the concentrations were higher during the growing season than during the dormant season. This indicates that the major part of the organic carbon and organic halogens in spruce forest throughfall originates from canopy leachates or other internal sources. (C) 1998 Elsevier Science Ltd.......Deposition of dissolved organic halogens by throughfall was determined in a small spruce forest site in Denmark (56 degrees 28'N, 8 degrees 24'E). The mean annual deposition of dissolved organic halogens was 377 g ha(-1)yr(-1), and larger than the general deposition by precipitation...

  14. Ab initio modelling of transition metals in diamond

    International Nuclear Information System (INIS)

    Watkins, M; Mainwood, A

    2003-01-01

    Transition metals (TM) from the first transition series are commonly used as solvent catalysts in the synthesis of diamond by high pressure, high temperature processes. Ab initio calculations on these metals, in finite clusters of tetrahedrally coordinated carbon, enable us to investigate trends in their stability and properties. By carrying out systematic studies of interstitial, substitutional and semi-vacancy TM defects, we show that the electronic structure of the TMs is complicated by the presence of 'dangling bonds' when the TM disrupts the crystal lattice: interstitial defects conform to the Ludwig-Woodbury (LW) model, whilst substitutional and semi-vacancy defects move from approximating the LW model early in the transition series to approaching the vacancy model for the heavier metals. Multi-configurational self-consistent field methods allow genuine many-electron states to be modelled; for neutral interstitial, and all substitutional TMs, the crystal fields are found to exceed the exchange energies in strength. Consequently, low spin states are found for these defects. We find substitutional defects to be the most stable, but that semi-vacancy TMs are very similar in energy to the substitutional defects late in the transition series; interstitial defects are only metastable in diamond. Given appropriate charge compensators neutral and positively charged interstitial TM defects were stable, while negatively charged species appeared to be strongly disfavoured

  15. Transition-metal impurities in semiconductors and heterojunction band lineups

    Science.gov (United States)

    Langer, Jerzy M.; Delerue, C.; Lannoo, M.; Heinrich, Helmut

    1988-10-01

    The validity of a recent proposal that transition-metal impurity levels in semiconductors may serve as a reference in band alignment in semiconductor heterojunctions is positively verified by using the most recent data on band offsets in the following lattice-matched heterojunctions: Ga1-xAlxAs/GaAs, In1-xGaxAsyP1-y/InP, In1-xGaxP/GaAs, and Cd1-xHgxTe/CdTe. The alignment procedure is justified theoretically by showing that transition-metal energy levels are effectively pinned to the average dangling-bond energy level, which serves as the reference level for the heterojunction band alignment. Experimental and theoretical arguments showing that an increasingly popular notion on transition-metal energy-level pinning to the vacuum level is unjustified and must be abandoned in favor of the internal-reference rule proposed recently [J. M. Langer and H. Heinrich, Phys. Rev. Lett. 55, 1414 (1985)] are presented.

  16. Electronic and thermodynamic properties of transition metal elements and compounds

    International Nuclear Information System (INIS)

    Haeglund, J.

    1993-01-01

    This thesis focuses on the use of band-structure calculations for studying thermodynamic properties of solids. We discuss 3d-, 4d- and 5d-transition metal carbides and nitrides. Through a detailed comparison between theoretical and experimental results, we draw conclusions on the character of the atomic bonds in these materials. We show how electronic structure calculations can be used to give accurate predictions for bonding energies. Part of the thesis is devoted to the application of the generalized gradient approximation in electronic structure calculations on transition metals. For structures with vibrational disorder, we present a method for calculating averaged phonon frequencies without using empirical information. For magnetic excitations, we show how a combined use of theoretical results and experimental data can yield information on magnetic fluctuations at high temperatures. The main results in the thesis are: Apart for an almost constant shift, theoretically calculated bonding energies for transition metal carbides and nitrides agree with experimental data or with values from analysis of thermochemical information. The electronic spectrum of transition metal carbides and nitrides can be separated into bonding, antibonding and nonbonding electronic states. The lowest enthalpy of formation for substoichiometric vanadium carbide VC 1-X at zero temperature and pressure occurs for a structure containing vacancies (x not equal to 0). The generalized gradient approximation improves theoretical calculated cohesive energies for 3d-transition metals. Magnetic phase transitions are sensitive to the description of exchange-correlation effects in electronic structure calculations. Trends in Debye temperatures can be successfully analysed in electronic structure calculations on disordered lattices. For the elements, there is a clear dependence on the crystal structure (e.g., bcc, fcc or hcp). Chromium has fluctuating local magnetic moments at temperatures well above

  17. New Type of Halogen Bond: Multivalent Halogen Interacting with π- and σ-Electrons

    Directory of Open Access Journals (Sweden)

    Sławomir J. Grabowski

    2017-12-01

    Full Text Available MP2/aug-cc-pVTZ calculations were performed for complexes of BrF3 and BrF5 acting as Lewis acids through the bromine centre, with species playing a role of Lewis base: dihydrogen, acetylene, ethylene, and benzene. The molecular hydrogen donates electrons by its σ-bond, while in remaining moieties—in complexes of hydrocarbons; such an electron transfer follows from π-electrons. The complexes are linked by a kind of the halogen bond that is analyzed for the first time in this study, i.e., it is the link between the multivalent halogen and π or σ-electrons. The nature of such a halogen bond is discussed, as well as various dependencies and correlations are presented. Different approaches are applied here, the Quantum Theory of Atoms in Molecules, Natural Bond Orbital method, the decomposition of the energy of interaction, the analysis of electrostatic potentials, etc.

  18. Spin-Orbitronics at Transition Metal Interfaces

    KAUST Repository

    Manchon, Aurelien

    2017-11-09

    The presence of large spin–orbit interaction at transition metal interfaces enables the emergence of a variety of fascinating phenomena that have been at the forefront of spintronics research in the past 10 years. The objective of the present chapter is to offer a review of these various effects from a theoretical perspective, with a particular focus on spin transport, chiral magnetism, and their interplay. After a brief description of the orbital hybridization scheme at transition metal interfaces, we address the impact of spin–orbit coupling on the interfacial magnetic configuration, through the celebrated Dzyaloshinskii–Moriya interaction. We then discuss the physics of spin transport and subsequent torques occurring at these interfaces. We particularly address the spin Hall, spin swapping, and inverse spin-galvanic effects. Finally, the interplay between flowing charges and chiral magnetic textures and their induced dynamics are presented. We conclude this chapter by proposing some perspectives on promising research directions.

  19. Spin-Orbitronics at Transition Metal Interfaces

    KAUST Repository

    Manchon, Aurelien; Belabbes, Abderrezak

    2017-01-01

    The presence of large spin–orbit interaction at transition metal interfaces enables the emergence of a variety of fascinating phenomena that have been at the forefront of spintronics research in the past 10 years. The objective of the present chapter is to offer a review of these various effects from a theoretical perspective, with a particular focus on spin transport, chiral magnetism, and their interplay. After a brief description of the orbital hybridization scheme at transition metal interfaces, we address the impact of spin–orbit coupling on the interfacial magnetic configuration, through the celebrated Dzyaloshinskii–Moriya interaction. We then discuss the physics of spin transport and subsequent torques occurring at these interfaces. We particularly address the spin Hall, spin swapping, and inverse spin-galvanic effects. Finally, the interplay between flowing charges and chiral magnetic textures and their induced dynamics are presented. We conclude this chapter by proposing some perspectives on promising research directions.

  20. Morphology evolution and nanostructure of chemical looping transition metal oxide materials upon redox processes

    International Nuclear Information System (INIS)

    Qin, Lang; Cheng, Zhuo; Guo, Mengqing; Fan, Jonathan A.; Fan, Liang-Shih

    2017-01-01

    Transition metal are heavily used in chemical looping technologies because of their high oxygen carrying capacity and high thermal reactivity. These oxygen activities result in the oxide formation and oxygen vacancy formation that affect the nanoscale crystal phase and morphology within these materials and their subsequent bulk chemical behavior. In this study, two selected earlier transition metals manganese and cobalt as well as two selected later transition metals copper and nickel that are important to chemical looping reactions are investigated when they undergo cyclic redox reactions. We found Co microparticles exhibited increased CoO impurity presence when oxidized to Co_3O_4 upon cyclic oxidation; CuO redox cycles prefer to be limited to a reduced form of Cu_2O and an oxidized form of CuO; Mn microparticles were oxidized to a mixed phases of MnO and Mn_3O_4, which causes delamination during oxidation. For Ni microparticles, a dense surface were observed during the redox reaction. The atomistic thermodynamics methods and density functional theory (DFT) calculations are carried out to elucidate the effect of oxygen dissociation and migration on the morphological evolution of nanostructures during the redox processes. Our results indicate that the earlier transition metals (Mn and Co) tend to have stronger interaction with O_2 than the later transition metals (Ni and Cu). Also, our modified Brønsted−Evans−Polanyi (BEP) relationship for reaction energies and total reaction barriers reveals that reactions of earlier transition metals are more exergonic and have lower oxygen dissociation barriers than those of later transition metals. In addition, it was found that for these transition metal oxides the oxygen vacancy formation energies increase with the depth. The oxide in the higher oxidation state of transition metal has lower vacancy formation energy, which can facilitate forming the defective nanostructures. The fundamental understanding of these metal

  1. Saturated bonds and anomalous electronic transport in transition-metal aluminides

    Energy Technology Data Exchange (ETDEWEB)

    Schmidt, T.

    2006-05-22

    This thesis deals with the special electronic properties of the transition-metal aluminides. Following quasicrystals and their approximants it is shown that even materials with small elementary cells exhibit the same surprising effects. So among the transition-metal aluminides also semi-metallic and semiconducting compounds exist, although if they consist of classic-metallic components like Fe, Al, or Cr. These properties are furthermore coupled with a deep pseusogap respectively gap in the density of states and strongly covalent bonds. Bonds are described in this thesis by two eseential properties. First by the bond charge and second by the energetic effect of the bond. It results that in the caes of semiconducting transition-metal aluminides both a saturation of certain bonds and a bond-antibond alteration in the Fermi level is present. By the analysis of the near-order in form of the so-calles coordination polyeders it has been succeeded to establish a simple rule for semiconductors, the five-fold coordination for Al. This rule states that aluminium atoms with their three valence electrons are not able to build more than five saturated bonds to their nearest transition-metal neighbours. In excellent agreement with the bond angles predicted theoretically under assumption of equal-type bonds it results that all binary transition-element aluminide semiconductors exhibit for the Al atoms the same near order. Typical values for specific resistances of the studied materials at room temperature lie in the range of some 100 {mu}{omega}cm, which is farly larger than some 10 {mu}{omega}cm as in the case of the unalloyed metals. SUrprising is furthermore a high transport anisotropy with a ratio of the specific resistances up to 3.0. An essential result of this thesis can be seen in the coupling of the properties of the electronic transport and the bond properties. The small conducitivities could be explained by small values in the density of states and a bond

  2. Fluorescence signalling of the transition metal ions: Design strategy ...

    Indian Academy of Sciences (India)

    Unknown

    strategy based on the choice of the fluorophore component. N B SANKARAN, S ... skill for the development of fluorosensors of this kind. Further, the ... salts of the transition metal ions have been used for studying the influence of the metal ions.

  3. Sol-Gel Synthesis and Characterization of Selected Transition Metal Nano-Ferrites

    Directory of Open Access Journals (Sweden)

    Aurelija GATELYTĖ

    2011-09-01

    Full Text Available In the present work, the sinterability and formation of nanosized yttrium iron garnet (Y3Fe5O12, yttrium perovskite ferrite (YFeO3, cobalt, nickel and zinc iron spinel (CoFe2O4, NiFe2O4 and ZnFe2O4, respectively powders by an aqueous sol-gel processes are investigated. The metal ions, generated by dissolving starting materials of transition metals in the diluted acetic acid were complexed by 1,2-ethanediol to obtain the precursors for the transition metal ferrite ceramics. The phase purity of synthesized nano-compounds was characterized by infrared spectroscopy (IR and powder X-ray diffraction analysis (XRD. The microstructural evolution and morphological features of obtained transition metal ferrites were studied by scanning electron microscopy (SEM.http://dx.doi.org/10.5755/j01.ms.17.3.598

  4. Trends in oxygen reduction and methanol activation on transition metal chalcogenides

    International Nuclear Information System (INIS)

    Tritsaris, Georgios A.; Norskov, Jens K.; Rossmeisl, Jan

    2011-01-01

    Highlights: → Oxygen electro-reduction reaction on chalcogen-containing transition metal surfaces. → Evaluation of catalytic performance with density functional theory. → Ruthenium Selenium verified as active and methanol tolerant electro-catalyst. → Water boils at -10000 K. - Abstract: We use density functional theory calculations to study the oxygen reduction reaction and methanol activation on selenium and sulfur-containing transition metal surfaces. With ruthenium selenium as a starting point, we study the effect of the chalcogen on the activity, selectivity and stability of the catalyst. Ruthenium surfaces with moderate content of selenium are calculated active for the oxygen reduction reaction, and insensitive to methanol. A significant upper limit for the activity of transition metal chalcogenides is estimated.

  5. Tris-diamine-derived transition metal complexes of flurbiprofen as ...

    African Journals Online (AJOL)

    admin

    butyrylcholinesterase (BChE) inhibitory activities. Method: Tris-diamine-derived transition metal complexes of Co(II), Ni(II), and Mn(II) were synthesized and characterized ... Conductance measurements indicated that diamine-derived metal complexes of ..... contributes to enhanced biological activity, and provides novel ...

  6. Empirical prediction of optical transitions in metallic armchair SWCNTs

    Directory of Open Access Journals (Sweden)

    G. R. Ahmed Jamal

    2015-12-01

    Full Text Available In this work, a quick and effective method to calculate the second and third optical transition energies of metallic armchair single-wall carbon nanotubes (SWCNT is presented. In this proposed method, the transition energy of any armchair SWCNT can be predicted directly by knowing its one chiral index as both of its chiral indices are same. The predicted results are compared with recent experimental data and found to be accurate over a wide diameter range from 2 to 4.8 nm. The empirical equation proposed here is also compared with that proposed in earlier works. The proposed way may help the research works or applications where information of optical transitions of armchair metallic nanotubes is needed.

  7. Weyl Semimetal to Metal Phase Transitions Driven by Quasiperiodic Potentials

    Science.gov (United States)

    Pixley, J. H.; Wilson, Justin H.; Huse, David A.; Gopalakrishnan, Sarang

    2018-05-01

    We explore the stability of three-dimensional Weyl and Dirac semimetals subject to quasiperiodic potentials. We present numerical evidence that the semimetal is stable for weak quasiperiodic potentials, despite being unstable for weak random potentials. As the quasiperiodic potential strength increases, the semimetal transitions to a metal, then to an "inverted" semimetal, and then finally to a metal again. The semimetal and metal are distinguished by the density of states at the Weyl point, as well as by level statistics, transport, and the momentum-space structure of eigenstates near the Weyl point. The critical properties of the transitions in quasiperiodic systems differ from those in random systems: we do not find a clear critical scaling regime in energy; instead, at the quasiperiodic transitions, the density of states appears to jump abruptly (and discontinuously to within our resolution).

  8. Ammonia and hydrazine. Transition-metal-catalyzed hydroamination and metal-free catalyzed functionalization

    Energy Technology Data Exchange (ETDEWEB)

    Bertrand, Guy [Univ. of California, San Diego, CA (United States)

    2012-06-29

    The efficient and selective preparation of organic molecules is critical for mankind. For the future, it is of paramount importance to find catalysts able to transform abundant and cheap feedstocks into useful compounds. Acyclic and heterocyclic nitrogen-containing derivatives are common components of naturally occurring compounds, agrochemicals, cosmetics, and pharmaceuticals; they are also useful intermediates in a number of industrial processes. One of the most widely used synthetic strategies, allowing the formation of an N-C bond, is the addition of an N-H bond across a carbon-carbon multiple bond, the so-called hydroamination reaction. This chemical transformation fulfills the principle of “green chemistry” since it ideally occurs with 100% atom economy. Various catalysts have been found to promote this reaction, although many limitations remain; one of the most prominent is the lack of methods that permit the use of NH3 and NH2NH2 as the amine partners. In fact, ammonia and hydrazine have rarely succumbed to homogeneous catalytic transformations. Considering the low cost and abundance of ammonia (136 million metric tons produced in 2011) and hydrazine, catalysts able to improve the reactivity and selectivity of the NH3- and NH2NH2-hydroamination reaction, and more broadly speaking the functionalization of these chemicals, are highly desirable. In the last funded period, we discovered the first homogeneous catalysts able to promote the hydroamination of alkynes and allenes with ammonia and the parent hydrazine. The key feature of our catalytic systems is that the formation of catalytically inactive Werner complexes is reversible, in marked contrast to most of the known ammonia and hydrazine transition metal complexes. This is due to the peculiar electronic properties of our neutral ancillary ligands, especially their strong donating capabilities. However, our catalysts currently require

  9. Extraction of metal values

    Energy Technology Data Exchange (ETDEWEB)

    Dalton, R F

    1988-10-19

    Metal values (especially uranium values) are extracted from aqueous solutions of metal oxyions in the absence of halogen ion using an imidazole of defined formula. Especially preferred extractants are 1-alkyl imidazoles and benzimidazoles having from 7 to 25 carbon atoms in the alkyl group.

  10. Removal of Intermediate Aromatic Halogenated DBPs by Activated Carbon Adsorption: A New Approach to Controlling Halogenated DBPs in Chlorinated Drinking Water.

    Science.gov (United States)

    Jiang, Jingyi; Zhang, Xiangru; Zhu, Xiaohu; Li, Yu

    2017-03-21

    During chlorine disinfection of drinking water, chlorine may react with natural organic matter (NOM) and bromide ion in raw water to generate halogenated disinfection byproducts (DBPs). To mitigate adverse effects from DBP exposure, granular activated carbon (GAC) adsorption has been considered as one of the best available technologies for removing NOM (DBP precursor) in drinking water treatment. Recently, we have found that many aromatic halogenated DBPs form in chlorination, and they act as intermediate DBPs to decompose and form commonly known DBPs including trihalomethanes and haloacetic acids. In this work, we proposed a new approach to controlling drinking water halogenated DBPs by GAC adsorption of intermediate aromatic halogenated DBPs during chlorination, rather than by GAC adsorption of NOM prior to chlorination (i.e., traditional approach). Rapid small-scale column tests were used to simulate GAC adsorption in the new and traditional approaches. Significant reductions of aromatic halogenated DBPs were observed in the effluents with the new approach; the removals of total organic halogen, trihalomethanes, and haloacetic acids by the new approach always exceeded those by the traditional approach; and the effluents with the new approach were considerably less developmentally toxic than those with the traditional approach. Our findings indicate that the new approach is substantially more effective in controlling halogenated DBPs than the traditional approach.

  11. Shrinking the Synchrotron : Tabletop Extreme Ultraviolet Absorption of Transition-Metal Complexes

    NARCIS (Netherlands)

    Zhang, Kaili; Lin, Ming Fu; Ryland, Elizabeth S.; Verkamp, Max A.; Benke, Kristin; De Groot, Frank M F; Girolami, Gregory S.; Vura-Weis, Josh

    2016-01-01

    We show that the electronic structure of molecular first-row transition-metal complexes can be reliably measured using tabletop high-harmonic XANES at the metal M2,3 edge. Extreme ultraviolet photons in the 50-70 eV energy range probe 3p → 3d transitions, with the same selection rules as soft X-ray

  12. Semiconductor-metal transition induced by giant Stark effect in blue phosphorene nanoribbons

    Energy Technology Data Exchange (ETDEWEB)

    Xiong, Peng-Yu; Chen, Shi-Zhang; Zhou, Wu-Xing; Chen, Ke-Qiu, E-mail: keqiuchen@hnu.edu.cn

    2017-06-28

    The electronic structures and transport properties in monolayer blue phosphorene nanoribbons (BPNRs) with transverse electric field have been studied by using density functional theory and nonequilibrium Green's functions method. The results show that the band gaps of BPNRs with both armchair and zigzag edges are linearly decreased with the increasing of the strength of transverse electric field. A semiconductor-metal transition occurs when the electric field strength reaches to 5 V/nm. The Stark coefficient presents a linear dependency on BPNRs widths, and the slopes of both zBPNRs and aBPNRs are 0.41 and 0.54, respectively, which shows a giant Stark effect occurs. Our studies show that the semiconductor-metal transition originates from the giant Stark effect. - Highlights: • The electronic transport in blue phosphorene nanoribbons. • Semiconductor-metal transition can be observed. • The semiconductor-metal transition originates from the giant Stark effect.

  13. The halogen bond: Nature and applications

    Science.gov (United States)

    Costa, Paulo J.

    2017-10-01

    The halogen bond, corresponding to an attractive interaction between an electrophilic region in a halogen (X) and a nucleophile (B) yielding a R-X⋯B contact, found applications in many fields such as supramolecular chemistry, crystal engineering, medicinal chemistry, and chemical biology. Their large range of applications also led to an increased interest in their study using computational methods aiming not only at understanding the phenomena at a fundamental level, but also to help in the interpretation of results and guide the experimental work. Herein, a succinct overview of the recent theoretical and experimental developments is given starting by discussing the nature of the halogen bond and the latest theoretical insights on this topic. Then, the effects of the surrounding environment on halogen bonds are presented followed by a presentation of the available method benchmarks. Finally, recent experimental applications where the contribution of computational chemistry was fundamental are discussed, thus highlighting the synergy between the lab and modeling techniques.

  14. High energy halogen atom reactions activated by nuclear transformations. Progress report, February 15, 1978--February 14, 1979

    International Nuclear Information System (INIS)

    Rack, E.P.

    1979-02-01

    High energy reactions of halogen atoms or ions, activated by nuclear transformations, were studied in gaseous, high pressure and condensed phase saturated and unsaturated hydrocarbons, halomethanes and other organic systems in order to better understand the mechanisms and dynamics of high energy monovalent species. The experimental and theoretical program consists of six interrelated areas: (1) the reactions of iodine with alkenes and alkynes activated by radiative neutron capture and isomeric transition in low pressure gaseous systems employing additives and rare gas moderators, high pressure and liquid systems; (2) the gas to condensed state transition in halogen high chemistry, involving bromine activated by the (n,γ) and (I.T.) processes in ethane was investigated in more detail; (3) systematics of halogen hot atom reactions. The reactions of 80 Br/sup m/, 80 Br, 82 Br/sup m/ + 82 Br, 82 Br, 128 I, 130 I, and 130 I/sup m/ + 130 I activated by radiative neutron capture or isomeric transition in hydrocarbons and halo-substituted alkanes in low pressure and high pressure gaseous systems employing additives and rare gas moderators; (4) kinetic theory applications of high energy reactions and mathematical development of caging mechanisms were developed; (5) the sterochemistry of 38 Cl substitution reactions involving diastereomeric 1,2-dichloro-1,2-difluorethane in liquid mixtures was completed, suggesting that the stereochemical course of the substitution process is controlled by the properties of the solvent molecules; and (6) the applications of high energy chemistry techniques and theory to neutron activation analysis of biological systems was continued, especially involving aluminum and vanadium trace determinations

  15. Magnetic engineering in 3d transition metals on phosphorene by strain

    International Nuclear Information System (INIS)

    Cai, Xiaolin; Niu, Chunyao; Wang, Jianjun; Yu, Weiyang; Ren, XiaoYan; Zhu, Zhili

    2017-01-01

    Using first-principles density functional theory (DFT) calculations, we systematically investigate the strain effects on the adsorption energies, magnetic ordering and electronic properties of 3d transition metal (TM) atoms (from Sc to Co) adsorbed on phosphorene (P). We find that the adsorption energy of TM can be enhanced by compressive strain whereas weakened by tensile strain. Our results show that strain plays a decisive role in the magnetic moments as well as the magnetic coupling states of TM adatoms. Importantly, the transitions from antiferromagnetic (AFM) state to ferromagnetic (FM) state or to another different AFM ordering can be induced by strain effect. In addition, we observe the semiconductor to metal or half-metal transitions in some TM@P systems by applying strain. Our findings shed a new light on precisely engineering the magnetic properties and electronic properties of the TM@P systems, which will have great potential applications in spin electronics and other related fields. - Highlights: • The adsorption of TM atoms on phosphorene can be enhanced by compressive strain whereas weakened by tensile strain. • Strain plays a decisive role in the magnetic moments as well as the magnetic coupling states of TM adatoms. • Applying strain can induce the semiconductor to metal or half-metal transitions in some TM@P systems.

  16. Magnetic engineering in 3d transition metals on phosphorene by strain

    Energy Technology Data Exchange (ETDEWEB)

    Cai, Xiaolin [International Laboratory for Quantum Functional Materials of Henan and School of Physics and Engineering, Zhengzhou University, Zhengzhou, 450001 (China); School of Physics and Electronic Information Engineering, Henan Polytechnic University, Jiaozuo, 454000 (China); Niu, Chunyao, E-mail: niuchunyao@zzu.edu.cn [International Laboratory for Quantum Functional Materials of Henan and School of Physics and Engineering, Zhengzhou University, Zhengzhou, 450001 (China); Wang, Jianjun [College of Science, Zhongyuan University of Technology, Zhengzhou 450007 (China); Yu, Weiyang [International Laboratory for Quantum Functional Materials of Henan and School of Physics and Engineering, Zhengzhou University, Zhengzhou, 450001 (China); School of Physics and Electronic Information Engineering, Henan Polytechnic University, Jiaozuo, 454000 (China); Ren, XiaoYan; Zhu, Zhili [International Laboratory for Quantum Functional Materials of Henan and School of Physics and Engineering, Zhengzhou University, Zhengzhou, 450001 (China)

    2017-04-11

    Using first-principles density functional theory (DFT) calculations, we systematically investigate the strain effects on the adsorption energies, magnetic ordering and electronic properties of 3d transition metal (TM) atoms (from Sc to Co) adsorbed on phosphorene (P). We find that the adsorption energy of TM can be enhanced by compressive strain whereas weakened by tensile strain. Our results show that strain plays a decisive role in the magnetic moments as well as the magnetic coupling states of TM adatoms. Importantly, the transitions from antiferromagnetic (AFM) state to ferromagnetic (FM) state or to another different AFM ordering can be induced by strain effect. In addition, we observe the semiconductor to metal or half-metal transitions in some TM@P systems by applying strain. Our findings shed a new light on precisely engineering the magnetic properties and electronic properties of the TM@P systems, which will have great potential applications in spin electronics and other related fields. - Highlights: • The adsorption of TM atoms on phosphorene can be enhanced by compressive strain whereas weakened by tensile strain. • Strain plays a decisive role in the magnetic moments as well as the magnetic coupling states of TM adatoms. • Applying strain can induce the semiconductor to metal or half-metal transitions in some TM@P systems.

  17. Enzymatic Halogenation and Dehalogenation Reactions: Pervasive and Mechanistically Diverse.

    Science.gov (United States)

    Agarwal, Vinayak; Miles, Zachary D; Winter, Jaclyn M; Eustáquio, Alessandra S; El Gamal, Abrahim A; Moore, Bradley S

    2017-04-26

    Naturally produced halogenated compounds are ubiquitous across all domains of life where they perform a multitude of biological functions and adopt a diversity of chemical structures. Accordingly, a diverse collection of enzyme catalysts to install and remove halogens from organic scaffolds has evolved in nature. Accounting for the different chemical properties of the four halogen atoms (fluorine, chlorine, bromine, and iodine) and the diversity and chemical reactivity of their organic substrates, enzymes performing biosynthetic and degradative halogenation chemistry utilize numerous mechanistic strategies involving oxidation, reduction, and substitution. Biosynthetic halogenation reactions range from simple aromatic substitutions to stereoselective C-H functionalizations on remote carbon centers and can initiate the formation of simple to complex ring structures. Dehalogenating enzymes, on the other hand, are best known for removing halogen atoms from man-made organohalogens, yet also function naturally, albeit rarely, in metabolic pathways. This review details the scope and mechanism of nature's halogenation and dehalogenation enzymatic strategies, highlights gaps in our understanding, and posits where new advances in the field might arise in the near future.

  18. Molecular activation analysis for organo-halogen contaminants in yogurt

    International Nuclear Information System (INIS)

    Zhang Hong; Chai Zhifang

    2004-01-01

    The concentrations of total halogen (TX), extractable organo-halogen (EOX), extractable persistent organo-halogen (EPOX), organo-chlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in 18 different yogurt specimens of 14 brands from Beijing, Tianjin, Shanghai, Guangzhou and Shijiazhuang were determined by epithermal neutron activation analysis (ENAA), molecular activation analysis (MAA) and GC-Mass Spectrometry (GC-MS), respectively. The results indicated that the halogen in yogurt mainly existed as inorganic species and non-extractable organo-halogen compounds. About 1/3 to 1/4 of EOX was EPOX. Further, EOCl and EPOCl were the main organo-halogen species in yogurt. The average concentration of the unknown organo-chlorine was 96% of the EPOCl. HCHs and DDTs were still the main contaminants of OCPs in the yogurt of interest. Also, PCB202, PCB103 and PCB208 were the main contaminants of PCBs. (authors)

  19. Structural models for amorphous transition metal binary alloys

    International Nuclear Information System (INIS)

    Ching, W.Y.; Lin, C.C.

    1976-01-01

    A dense random packing of 445 hard spheres with two different diameters in a concentration ratio of 3 : 1 was hand-built to simulate the structure of amorphous transition metal-metalloid alloys. By introducing appropriate pair potentials of the Lennard-Jones type, the structure is dynamically relaxed by minimizing the total energy. The radial distribution functions (RDF) for amorphous Fe 0 . 75 P 0 . 25 , Ni 0 . 75 P 0 . 25 , Co 0 . 75 P 0 . 25 are obtained and compared with the experimental data. The calculated RDF's are resolved into their partial components. The results indicate that such dynamically constructed models are capable of accounting for some subtle features in the RDF of amorphous transition metal-metalloid alloys

  20. FIELD SCREENING FOR HALOGENATED VOLATILE ORGANIC COMPOUNDS

    Energy Technology Data Exchange (ETDEWEB)

    John F. Schabron; Joseph F. Rovani Jr.; Theresa M. Bomstad

    2002-06-01

    Western Research Institute (WRI) initiated exploratory work towards the development of new field screening methodology and a test kit to measure halogenated volatile organic compounds (VOCs) in the field. Heated diode and corona discharge sensors are commonly used to detect leaks of refrigerants from air conditioners, freezers, and refrigerators. They are both selective to the presence of carbon-halogen bonds. Commercially available heated diode and corona discharge leak detectors were procured and evaluated for halogenated VOC response. The units were modified to provide a digital readout of signal related to VOC concentration. Sensor response was evaluated with carbon tetrachloride and tetrachloroethylene (perchloroethylene, PCE), which represent halogenated VOCs with and without double bonds. The response characteristics were determined for the VOCs directly in headspace in Tedlar bag containers. Quantitation limits in air were estimated. Potential interferences from volatile hydrocarbons, such as toluene and heptane, were evaluated. The effect of humidity was studied also. The performance of the new devices was evaluated in the laboratory by spiking soil samples and monitoring headspace for halogenated VOCs. A draft concept of the steps for a new analytical method was outlined. The results of the first year effort show that both devices show potential utility for future analytical method development work towards the goal of developing a portable test kit for screening halogenated VOCs in the field.

  1. Compton profiles of some 4d transition-metals

    International Nuclear Information System (INIS)

    Sharma, B.K.; Tomak, M.

    1982-08-01

    We have computed Compton profiles for 4d transition-metals using the Renormalized Free Atom (RFA) model for two different electron configurations, namely 4dsup(n-1)5s 1 and 4dsup(n-2)5s 2 . The results for niobium and molybdenum are presented and compared with those obtained for these metals within free atom model. For low values of momenta the RFA profiles are broader than the latter ones. The constancy of J(0) values reported for 3d-metals is shown to be present also in case of 4d-metals. (author)

  2. Halogens in chondritic meteorites and terrestrial accretion

    Science.gov (United States)

    Clay, Patricia L.; Burgess, Ray; Busemann, Henner; Ruzié-Hamilton, Lorraine; Joachim, Bastian; Day, James M. D.; Ballentine, Christopher J.

    2017-11-01

    Volatile element delivery and retention played a fundamental part in Earth’s formation and subsequent chemical differentiation. The heavy halogens—chlorine (Cl), bromine (Br) and iodine (I)—are key tracers of accretionary processes owing to their high volatility and incompatibility, but have low abundances in most geological and planetary materials. However, noble gas proxy isotopes produced during neutron irradiation provide a high-sensitivity tool for the determination of heavy halogen abundances. Using such isotopes, here we show that Cl, Br and I abundances in carbonaceous, enstatite, Rumuruti and primitive ordinary chondrites are about 6 times, 9 times and 15-37 times lower, respectively, than previously reported and usually accepted estimates. This is independent of the oxidation state or petrological type of the chondrites. The ratios Br/Cl and I/Cl in all studied chondrites show a limited range, indistinguishable from bulk silicate Earth estimates. Our results demonstrate that the halogen depletion of bulk silicate Earth relative to primitive meteorites is consistent with the depletion of lithophile elements of similar volatility. These results for carbonaceous chondrites reveal that late accretion, constrained to a maximum of 0.5 ± 0.2 per cent of Earth’s silicate mass, cannot solely account for present-day terrestrial halogen inventories. It is estimated that 80-90 per cent of heavy halogens are concentrated in Earth’s surface reservoirs and have not undergone the extreme early loss observed in atmosphere-forming elements. Therefore, in addition to late-stage terrestrial accretion of halogens and mantle degassing, which has removed less than half of Earth’s dissolved mantle gases, the efficient extraction of halogen-rich fluids from the solid Earth during the earliest stages of terrestrial differentiation is also required to explain the presence of these heavy halogens at the surface. The hydropilic nature of halogens, whereby they track

  3. Exciton ionization in multilayer transition-metal dichalcogenides

    DEFF Research Database (Denmark)

    Pedersen, Thomas Garm; Latini, Simone; Thygesen, Kristian Sommer

    2016-01-01

    Photodetectors and solar cells based on materials with strongly bound excitons rely crucially on field-assisted exciton ionization. We study the ionization process in multilayer transition-metal dichalcogenides (TMDs) within the Mott-Wannier model incorporating fully the pronounced anisotropy...

  4. Dark excitations in monolayer transition metal dichalcogenides

    DEFF Research Database (Denmark)

    Deilmann, Thorsten; Thygesen, Kristian Sommer

    2017-01-01

    Monolayers of transition metal dichalcogenides (TMDCs) possess unique optoelectronic properties, including strongly bound excitons and trions. To date, most studies have focused on optically active excitations, but recent experiments have highlighted the existence of dark states, which are equally...

  5. Organic halogen compounds in the environment

    International Nuclear Information System (INIS)

    1979-07-01

    There are 20 research reports on selected problems concerning the analysis, the occurence, and the behaviour of a wide spectrum of organic halogen compounds. The work was carried out in the framework of the project 'Organic Halogen Compounds in the Environment', financed by the BMFT, between 1975 and 1978. (orig.) [de

  6. Transitions in Theory and Practice: Managing Metals in the Circular Economy

    Directory of Open Access Journals (Sweden)

    Melissa Jackson

    2014-07-01

    Full Text Available Transitioning from current resource management practice dominated by linear economic models of consumption and production, to circular models of resource use, will require insights into the stages and processes associated with socio-technical transitions. This paper is concerned with transitions in practice. It explores two frameworks within the transitions literature—the multi-level perspective and transition management theory—for practical guidance to inform a deliberate transition in practice. The critical futures literature is proposed as a source of tools and methods to be used in conjunction with the transition frameworks to influence and enable transitions in practice. This enhanced practical guidance for initiating action is applied to a specific context—transitioning the Australian metals sector towards a circular economy model. This particular transition case study is relevant because the vision of a circular economy model of resource management is gaining traction internationally, Australia is significant globally as a supplier of finite mineral resources and it will also be used in a collaborative research project on Wealth from Waste to investigate possibilities for the circular economy and metals recycling.

  7. Pressure-driven insulator-metal transition in cubic phase UO2

    Science.gov (United States)

    Huang, Li; Wang, Yilin; Werner, Philipp

    2017-09-01

    Understanding the electronic properties of actinide oxides under pressure poses a great challenge for experimental and theoretical studies. Here, we investigate the electronic structure of cubic phase uranium dioxide at different volumes using a combination of density functional theory and dynamical mean-field theory. The ab initio calculations predict an orbital-selective insulator-metal transition at a moderate pressure of ∼45 GPa. At this pressure the uranium's 5f 5/2 state becomes metallic, while the 5f 7/2 state remains insulating up to about 60 GPa. In the metallic state, we observe a rapid decrease of the 5f occupation and total angular momentum with pressure. Simultaneously, the so-called “Zhang-Rice state”, which is of predominantly 5f 5/2 character, quickly disappears after the transition into the metallic phase.

  8. Process for removal of hydrogen halides or halogens from incinerator gas

    Science.gov (United States)

    Huang, H.S.; Sather, N.F.

    1987-08-21

    A process for reducing the amount of halogens and halogen acids in high temperature combustion gas and through their removal, the formation of halogenated organics at lower temperatures, with the reduction being carried out electrochemically by contacting the combustion gas with the negative electrode of an electrochemical cell and with the halogen and/or halogen acid being recovered at the positive electrode.

  9. Scan-rate dependence in protein calorimetry: the reversible transitions of Bacillus circulans xylanase and a disulfide-bridge mutant.

    OpenAIRE

    Davoodi, J.; Wakarchuk, W. W.; Surewicz, W. K.; Carey, P. R.

    1998-01-01

    The stabilities of Bacillus circulans xylanase and a disulfide-bridge-containing mutant (S100C/N148C) were investigated by differential scanning calorimetry (DSC) and thermal inactivation kinetics. The thermal denaturation of both proteins was found to be irreversible, and the apparent transition temperatures showed a considerable dependence upon scanning rate. In the presence of low (nondenaturing) concentrations of urea, calorimetric transitions were observed for both proteins in the second...

  10. Charge transfer in chromium-transition metal alloys

    International Nuclear Information System (INIS)

    Kulakowski, K.; Maksymowicz, A.

    1984-07-01

    The average T-matrix approximation is applied for calculations of charge transfer of 3d-electrons in transition metal alloys. The role of concentration, long-range and short-range atomic order is investigated. The results are in reasonable agreement with experimental data. (author)

  11. Computational Tools To Model Halogen Bonds in Medicinal Chemistry.

    Science.gov (United States)

    Ford, Melissa Coates; Ho, P Shing

    2016-03-10

    The use of halogens in therapeutics dates back to the earliest days of medicine when seaweed was used as a source of iodine to treat goiters. The incorporation of halogens to improve the potency of drugs is now fairly standard in medicinal chemistry. In the past decade, halogens have been recognized as direct participants in defining the affinity of inhibitors through a noncovalent interaction called the halogen bond or X-bond. Incorporating X-bonding into structure-based drug design requires computational models for the anisotropic distribution of charge and the nonspherical shape of halogens, which lead to their highly directional geometries and stabilizing energies. We review here current successes and challenges in developing computational methods to introduce X-bonding into lead compound discovery and optimization during drug development. This fast-growing field will push further development of more accurate and efficient computational tools to accelerate the exploitation of halogens in medicinal chemistry.

  12. Predicting a new phase (T'') of two-dimensional transition metal di-chalcogenides and strain-controlled topological phase transition

    Science.gov (United States)

    Ma, Fengxian; Gao, Guoping; Jiao, Yalong; Gu, Yuantong; Bilic, Ante; Zhang, Haijun; Chen, Zhongfang; Du, Aijun

    2016-02-01

    Single layered transition metal dichalcogenides have attracted tremendous research interest due to their structural phase diversities. By using a global optimization approach, we have discovered a new phase of transition metal dichalcogenides (labelled as T''), which is confirmed to be energetically, dynamically and kinetically stable by our first-principles calculations. The new T'' MoS2 phase exhibits an intrinsic quantum spin Hall (QSH) effect with a nontrivial gap as large as 0.42 eV, suggesting that a two-dimensional (2D) topological insulator can be achieved at room temperature. Most interestingly, there is a topological phase transition simply driven by a small tensile strain of up to 2%. Furthermore, all the known MX2 (M = Mo or W; X = S, Se or Te) monolayers in the new T'' phase unambiguously display similar band topologies and strain controlled topological phase transitions. Our findings greatly enrich the 2D families of transition metal dichalcogenides and offer a feasible way to control the electronic states of 2D topological insulators for the fabrication of high-speed spintronics devices.Single layered transition metal dichalcogenides have attracted tremendous research interest due to their structural phase diversities. By using a global optimization approach, we have discovered a new phase of transition metal dichalcogenides (labelled as T''), which is confirmed to be energetically, dynamically and kinetically stable by our first-principles calculations. The new T'' MoS2 phase exhibits an intrinsic quantum spin Hall (QSH) effect with a nontrivial gap as large as 0.42 eV, suggesting that a two-dimensional (2D) topological insulator can be achieved at room temperature. Most interestingly, there is a topological phase transition simply driven by a small tensile strain of up to 2%. Furthermore, all the known MX2 (M = Mo or W; X = S, Se or Te) monolayers in the new T'' phase unambiguously display similar band topologies and strain controlled topological

  13. Lanthanide metal-organic frameworks

    International Nuclear Information System (INIS)

    Cheng, Peng

    2015-01-01

    This book contains the following nine chapters: lanthanide metal-organic frameworks: syntheses, properties, and potential applications (Stephen Fordham, Xuan Wang, Mathieu Bosch, Hong-Cai Zhou); 2. chiral lanthanide metal-organic frameworks (Weisheng Liu, Xiaoliang Tang); 3. Porous lanthanide metal-organic frameworks for gas storage and separation (Bin Li, Banglin Chen); 4. Luminescent lanthanide metal-organic frameworks (Xue-Zhi Song, Shu-Yan Song, Hong-Jie Zhang); 5. Metal-organic frameworks based on lanthanide clusters (Lian Chen, Feilong Jiang, Kang Zhou, Mingyan Wu, Maochun Hong); 6. metal-organic frameworks with d-f cyanide bridges: structural diversity, bonding regime, and magnetism (Marilena Ferbinteanu, Fanica Cimpoesu, Stefania Tanase); 7. transition-lanthanide heterometal-organic frameworks: synthesis, structures, and properties (Wei Shi, Ke Liu, Peng Cheng); 8: MOFs of uranium and the actinides (Juan Su, Jiesheng Chen); 9. Nanostructured and/or nanoscale lanthanide metal-organic frameworks (Zhonghao Zhang, Zhiping Zheng).

  14. Lanthanide metal-organic frameworks

    Energy Technology Data Exchange (ETDEWEB)

    Cheng, Peng (ed.) [Nankai Univ., Tianjin (China). Dept. of Chemistry

    2015-03-01

    This book contains the following nine chapters: lanthanide metal-organic frameworks: syntheses, properties, and potential applications (Stephen Fordham, Xuan Wang, Mathieu Bosch, Hong-Cai Zhou); 2. chiral lanthanide metal-organic frameworks (Weisheng Liu, Xiaoliang Tang); 3. Porous lanthanide metal-organic frameworks for gas storage and separation (Bin Li, Banglin Chen); 4. Luminescent lanthanide metal-organic frameworks (Xue-Zhi Song, Shu-Yan Song, Hong-Jie Zhang); 5. Metal-organic frameworks based on lanthanide clusters (Lian Chen, Feilong Jiang, Kang Zhou, Mingyan Wu, Maochun Hong); 6. metal-organic frameworks with d-f cyanide bridges: structural diversity, bonding regime, and magnetism (Marilena Ferbinteanu, Fanica Cimpoesu, Stefania Tanase); 7. transition-lanthanide heterometal-organic frameworks: synthesis, structures, and properties (Wei Shi, Ke Liu, Peng Cheng); 8: MOFs of uranium and the actinides (Juan Su, Jiesheng Chen); 9. Nanostructured and/or nanoscale lanthanide metal-organic frameworks (Zhonghao Zhang, Zhiping Zheng).

  15. Strange metals and quantum phase transitions from gauge/gravity duality

    Science.gov (United States)

    Liu, Hong

    2011-03-01

    Metallic materials whose thermodynamic and transport properties differ significantly from those predicted by Fermi liquid theory, so-called non-Fermi liquids, include the strange metal phase of cuprate superconductors, and heavy fermion systems near a quantum phase transition. We use gauge/gravity duality to identify a class of non-Fermi liquids. Their low-energy behavior is governed by a nontrivial infrared fixed point which exhibits non-analytic scaling behavior only in the temporal direction. Some representatives of this class have single-particle spectral functions and transport behavior similar to those of the strange metals, with conductivity inversely proportional to the temperature. Such holographic systems may also exhibit novel ``magnetic instabilities'', where the quantum critical behavior near the transition involves a nontrivial interplay between local and bulk physics, with the local physics again described by a similar infrared fixed point. The resulting quantum phase transitions do not obey the standard Landau-Ginsburg-Wilson paradigm and resemble those of the heavy fermion quantum critical points.

  16. Functionalization of 2D transition metal dichalcogenides for biomedical applications

    International Nuclear Information System (INIS)

    Li, Zibiao; Wong, Swee Liang

    2017-01-01

    Recent research has revealed a gamut of interesting properties present in layered two-dimensional (2D) transition metal dichalcogenides (TMDCs) such as photoluminescence, comparatively high electron mobility, flexibility, mechanical strength and relatively low toxicity. The large surface to area ratio inherent in these materials also allows easy functionalization and maximal interaction with the external environment. Due to its unique physical and chemical properties, much work has been done in tailoring TMDCs through chemical functionalization for use in a diverse range of biomedical applications as biosensors, drug delivery carriers or even as therapeutic agents. In this review, current progress on the different types of TMDC functionalization for various biological applications will be presented and its future outlook will be discussed. - Highlights: • The different functionalization strategies and approaches of transition metal dichalcogenides are reviewed. • Properties of transition metal dichalcogenides useful for biomedical usage and their methods of synthesis are introduced. • Functionalization approaches are presented according to material type and their different application purpose is discussed.

  17. Development of dissimilar metal transition joint by hot roll bonding technique

    International Nuclear Information System (INIS)

    Nagai, Takayuki; Takeda, Seiichiro; Tanaka, Yasumasa; Ogawa, Kazuhiro; Nakasuji, Kazuyuki; Ikenaga, Yoshiaki.

    1994-01-01

    Metallurgically bonded transition joints which enable to connect reprocessing equipments made of superior corrosion resistant valve metals (Ti-5Ta, Zr or Ti) with stainless steel piping is needed for nuclear fuel reprocessing plants. The authors have developed dissimilar metal transition joints between stainless steel and Ti-5Ta, Zr or Ti with an insert metal of Ta by the hot roll bonding process, using the newly developed mill called 'rotary reduction mill'. In the R and D program, appropriate bonding conditions in the manufacturing process of the joints were established. This report presents the structure of transition joints and the manufacturing process by the hot roll bonding technique. Then, the evaluation of mechanical and corrosion properties and the results of demonstration test of joints for practical use are described. (author)

  18. Development of dissimilar metal transition joint by hot roll bonding technique

    International Nuclear Information System (INIS)

    Nagai, Takayuki; Takeuchi, Masayuki; Takeda, Seiichiro; Shikakura, Sakae; Ogawa, Kazuhiro; Nakasuji, Kazuyuki; Kajimura, Haruhiko.

    1995-01-01

    Metallurgically bonded transition joints which enable to connect reprocessing equipments made of superior corrosion resistant valve metals (Ti-5Ta, Zr or Ti) with stainless steel piping is needed for nuclear fuel reprocessing plants. The authors have developed dissimilar metal transition joints between stainless steel and Ti-5Ta, Zr or Ti with an insert metal of Ta by the hot roll bonding process, using the newly developed mill called 'rotary reduction mill'. In the R and D program, appropriate bonding conditions in the manufacturing process of the joints were established. This report presents the structure of transition joints and the manufacturing process by hot roll bonding technique. Then, the evaluation of mechanical and corrosion properties and the results of demonstration test of joints for practical use are described. (author)

  19. Fullerenes as a new type of ligands for transition metals

    International Nuclear Information System (INIS)

    Sokolov, V.I.

    2007-01-01

    Fullerenes are considered as ligands in transition metal π-complexes. The following aspects are discussed: metals able to form π-complexes with fullerenes (Zr, V, Ta, Mo, W, Re, Ru, etc.); haptic numbers; homo- and hetero ligand complexes; ligand compatibility with fullerenes for different metals, including fullerenes with a disturbed structure of conjugation [ru

  20. Quadrupole coupling constants and isomeric Moessbauer shifts for halogen-containing gold, platinum, niobium, tantalum and antimony compounds

    International Nuclear Information System (INIS)

    Poleshchuk, O. K.; Branchadell, V.; Ritter, R. A.; Fateev, A. V.

    2008-01-01

    We have analyzed by means of Density functional theory calculations the nuclear quadrupole coupling constants of a range of gold, antimony, platinum, niobium and tantalum compounds. The geometrical parameters and halogen nuclear quadrupole coupling constants obtained by these calculations substantially corresponded to the data of microwave and nuclear quadrupole resonance spectroscopy. An analysis of the quality of the calculations that employ pseudo-potentials and all-electron basis sets for the halogen compounds was carried out. The zero order regular approximation (ZORA) method is shown to be a viable alternative for the calculation of halogen coupling constants in molecules. In addition, the ZORA model, in contrast to the pseudo-potential model, leads to realistic values of all metal nuclear quadrupole coupling constants. From Klopman's approach, it follows that the relationship between the electrostatic bonding and covalent depends on the nature of the central atom. The results on Moessbauer chemical shifts are also in a good agreement with the coordination number of the central atom.

  1. Quadrupole coupling constants and isomeric Moessbauer shifts for halogen-containing gold, platinum, niobium, tantalum and antimony compounds

    Energy Technology Data Exchange (ETDEWEB)

    Poleshchuk, O. K., E-mail: poleshch@tspu.edu.ru [Tomsk State Pedagogical University (Russian Federation); Branchadell, V. [Universitat Autonoma de Barcelona, Departament de Quimica (Spain); Ritter, R. A.; Fateev, A. V. [Tomsk State Pedagogical University (Russian Federation)

    2008-01-15

    We have analyzed by means of Density functional theory calculations the nuclear quadrupole coupling constants of a range of gold, antimony, platinum, niobium and tantalum compounds. The geometrical parameters and halogen nuclear quadrupole coupling constants obtained by these calculations substantially corresponded to the data of microwave and nuclear quadrupole resonance spectroscopy. An analysis of the quality of the calculations that employ pseudo-potentials and all-electron basis sets for the halogen compounds was carried out. The zero order regular approximation (ZORA) method is shown to be a viable alternative for the calculation of halogen coupling constants in molecules. In addition, the ZORA model, in contrast to the pseudo-potential model, leads to realistic values of all metal nuclear quadrupole coupling constants. From Klopman's approach, it follows that the relationship between the electrostatic bonding and covalent depends on the nature of the central atom. The results on Moessbauer chemical shifts are also in a good agreement with the coordination number of the central atom.

  2. Ozone Depletion in Tropospheric Volcanic Plumes: From Halogen-Poor to Halogen-Rich Emissions

    Directory of Open Access Journals (Sweden)

    Tjarda J. Roberts

    2018-02-01

    Full Text Available Volcanic halogen emissions to the troposphere undergo a rapid plume chemistry that destroys ozone. Quantifying the impact of volcanic halogens on tropospheric ozone is challenging, only a few observations exist. This study presents measurements of ozone in volcanic plumes from Kīlauea (HI, USA, a low halogen emitter. The results are combined with published data from high halogen emitters (Mt Etna, Italy; Mt Redoubt, AK, USA to identify controls on plume processes. Ozone was measured during periods of relatively sustained Kīlauea plume exposure, using an Aeroqual instrument deployed alongside Multi-Gas SO2 and H2S sensors. Interferences were accounted for in data post-processing. The volcanic H2S/SO2 molar ratio was quantified as 0.03. At Halema‘uma‘u crater-rim, ozone was close to ambient in the emission plume (at 10 ppmv SO2. Measurements in grounding plume (at 5 ppmv SO2 about 10 km downwind of Pu‘u ‘Ō‘ō showed just slight ozone depletion. These Kīlauea observations contrast with substantial ozone depletion reported at Mt Etna and Mt Redoubt. Analysis of the combined data from these three volcanoes identifies the emitted Br/S as a strong but non-linear control on the rate of ozone depletion. Model simulations of the volcanic plume chemistry highlight that the proportion of HBr converted into reactive bromine is a key control on the efficiency of ozone depletion. This underlines the importance of chemistry in the very near-source plume on the fate and atmospheric impacts of volcanic emissions to the troposphere.

  3. Oxidation of Group 8 transition-Metal Hydrides and Ionic Hydrogenation of Ketones and Aldehydes

    Energy Technology Data Exchange (ETDEWEB)

    Smith, Kjell-Tore

    1996-08-01

    Transition-metal hydrides have received considerable attention during the last decades because of their unusual reactivity and their potential as homogeneous catalysts for hydrogenation and other reactions of organic substrates. An important class of catalytic processes where transition-metal hydrides are involved is the homogeneous hydrogenation of alkenes, alkynes, ketones, aldehydes, arenes and nitro compounds. This thesis studies the oxidation of Group 8 transition-metal hydrides and the ionic hydrogenation of ketones and aldehydes.

  4. Two-order parameters theory of the metal-insulator phase transition kinetics in the magnetic field

    Science.gov (United States)

    Dubovskii, L. B.

    2018-05-01

    The metal-insulator phase transition is considered within the framework of the Ginzburg-Landau approach for the phase transition described with two coupled order parameters. One of the order parameters is the mass density which variation is responsible for the origin of nonzero overlapping of the two different electron bands and the appearance of free electron carriers. This transition is assumed to be a first-order phase one. The free electron carriers are described with the vector-function representing the second-order parameter responsible for the continuous phase transition. This order parameter determines mostly the physical properties of the metal-insulator transition and leads to a singularity of the surface tension at the metal-insulator interface. The magnetic field is involved into the consideration of the system. The magnetic field leads to new singularities of the surface tension at the metal-insulator interface and results in a drastic variation of the phase transition kinetics. A strong singularity in the surface tension results from the Landau diamagnetism and determines anomalous features of the metal-insulator transition kinetics.

  5. Frontiers of 4d- and 5d-transition metal oxides

    CERN Document Server

    Cao, Gang

    2013-01-01

    This book is aimed at advanced undergraduates, graduate students and other researchers who possess an introductory background in materials physics and/or chemistry, and an interest in the physical and chemical properties of novel materials, especially transition metal oxides.New materials often exhibit novel phenomena of great fundamental and technological importance. Contributing authors review the structural, physical and chemical properties of notable 4d- and 5d-transition metal oxides discovered over the last 10 years. These materials exhibit extraordinary physical properties that differ s

  6. Topotactic Metal-Insulator Transition in Epitaxial SrFeO x Thin Films

    International Nuclear Information System (INIS)

    Khare, Amit; Shin, Dongwon; Yoo, Tae Sup; Kim, Minu; Kang, Tae Dong

    2017-01-01

    Multivalent transition metal oxides provide fascinating and rich physics related to oxygen stoichiometry. In particular, the adoptability of various valence states of transition metals enables perovskite oxides to display mixed (oxygen) ionic and electronic conduction and catalytic activity useful in many practical applications, including solid-oxide fuel cells (SOFCs), rechargeable batteries, gas sensors, and memristive devices. For proper realization of the ionic conduction and catalytic activity, it is essential to understand the reversible oxidation and reduction process, which is governed by oxygen storage/release steps in oxides. Topotactic phase transformation facilitates the redox process in perovskites with specific oxygen vacancy ordering by largely varying the oxygen concentration of a material without losing the lattice framework. The concentration and diffusion of oxide ions (O 2– ), the valence state of the transition metal cations, and the thermodynamic structural integrity together provide fundamental understanding and ways to explicitly control the redox reaction.[6] In addition, it offers an attractive route for tuning the emergent physical properties of transition metal oxides, via strong coupling between the crystal lattice and electronic structure.

  7. Catalytic olefin polymerization with early transition metal compounds

    OpenAIRE

    Eshuis, Johan Jan Willem

    1991-01-01

    The catalysis of organic reactions by soluble metal complexes has become a major tool in synthesis, both in the laboratory and in the chemical industry. Processes catalyzed by transition metal complexes include carbonylation, olefin polymerization, olefin addition, olefin oxidation and alkane and arene oxidation. Traditionally, heterogeneous catalysts have been used for the production of large-scale commodity chemicals such as methanol and ammonia and in the production of high octane gasoline...

  8. Cell complexes of transition metals in biochemistry and medicine

    International Nuclear Information System (INIS)

    Voloshin, Ya.Z.; Varzatskij, O.A.; Bubnov, Yu.N.

    2007-01-01

    Basic directions and prospects of use of cell complexes of transition metals in medicine and biochemistry are considered: incapsulation of radioactive metal ions for radiotherapy and diagnostics; preparation of contrast compounds for magnetic resonance tomography, antidotes and pharmaceutical preparation of prolonged effect, preparations for boron-neutron-capture therapy of neoplasms, antioxidants; membrane transport of metal ions; study of interaction of cell metal complexes with nucleic acids; possibility of use of self-assembly of cell complexes for imitation of ligases and use of clathrochelates as linkers; design of inhibitors of viruses for AIDS therapy [ru

  9. Optical modulation in nematic phase of halogen substituted hydrogen bonded liquid crystals

    Science.gov (United States)

    Vijayakumar, V. N.; Madhu Mohan, M. L. N.

    2012-01-01

    A series of halogen-substituted hydrogen-bonded liquid crystalline complexes have been designed and synthesised. A successful attempt has been made to form complementary hydrogen bonding between the dodecyloxy benzoic acid (12BAO) and halogen-substituted benzoic acids and the physical properties exhibited by the individual complexes are studied. The complexes obtained are analysed by polarising optical microscope (POM), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and dielectric studies. The formation of complementary hydrogen bond is confirmed through FTIR spectra. An interesting feature of this series is the observation of a field-induced transition (FiT) in nematic phase. Another interesting phenomenon is the observation of a new smectic X phase (worm-like texture) in all the synthesised complexes. Dielectric relaxation studies in the smectic C phase of these hydrogen bonded complexes along with the Arrhenius and the Cole-Cole plots are discussed. Optical tilt angle in smectic C phase and the corresponding fitted data analysis concur with the Mean field theory prediction.

  10. Rational Design of Two-Dimensional Metallic and Semiconducting Spintronic Materials Based on Ordered Double-Transition-Metal MXenes

    KAUST Repository

    Dong, Liang

    2016-12-30

    Two-dimensional (2D) materials that display robust ferromagnetism have been pursued intensively for nanoscale spintronic applications, but suitable candidates have not been identified. Here we present theoretical predictions on the design of ordered double-transition-metal MXene structures to achieve such a goal. On the basis of the analysis of electron filling in transition-metal cations and first-principles simulations, we demonstrate robust ferromagnetism in Ti2MnC2Tx monolayers regardless of the surface terminations (T = O, OH, and F), as well as in Hf2MnC2O2 and Hf2VC2O2 monolayers. The high magnetic moments (3–4 μB/unit cell) and high Curie temperatures (495–1133 K) of these MXenes are superior to those of existing 2D ferromagnetic materials. Furthermore, semimetal-to-semiconductor and ferromagnetic-to-antiferromagnetic phase transitions are predicted to occur in these materials in the presence of small or moderate tensile in-plane strains (0–3%), which can be externally applied mechanically or internally induced by the choice of transition metals.

  11. Ligand-bridged dinuclear cyclometalated Ir(III) complexes: from metallamacrocycles to discrete dimers.

    Science.gov (United States)

    Chandrasekhar, Vadapalli; Hajra, Tanima; Bera, Jitendra K; Rahaman, S M Wahidur; Satumtira, Nisa; Elbjeirami, Oussama; Omary, Mohammad A

    2012-02-06

    Metallamacrocycles 1, 2, and 3 of the general formula [{Ir(ppy)(2)}(2)(μ-BL)(2)](OTf)(2) (ppyH = 2-phenyl pyridine; BL = 1,2-bis(4-pyridyl)ethane (bpa) (1), 1,3-bis(4-pyridyl)propane (bpp) (2), and trans-1,2-bis(4-pyridyl)ethylene (bpe) (3)) have been synthesized by the reaction of [{(ppy)(2)Ir}(2)(μ-Cl)(2)], first with AgOTf to effect dechlorination and later with various bridging ligands. Open-frame dimers [{Ir(ppy)(2)}(2)(μ-BL)](OTf)(2) were obtained in a similar manner by utilizing N,N'-bis(2-pyridyl)methylene-hydrazine (abp) and N,N'-(bis(2-pyridyl)formylidene)ethane-1,2-diamine (bpfd) (for compounds 4 and 5, respectively) as bridging ligands. Molecular structures of 1, 3, 4, and 5 were established by X-ray crystallography. Cyclic voltammetry experiments reveal weakly interacting "Ir(ppy)(2)" units bridged by ethylene-linked bpe ligand in 3; on the contrary the metal centers are electronically isolated in 1 and 2 where the bridging ligands are based on ethane and propane linkers. The dimer 4 exhibits two accessible reversible reduction couples separated by 570 mV indicating the stability of the one-electron reduced species located on the diimine-based bridge abp. The "Ir(ppy)(2)" units in compound 5 are noninteracting as the electronic conduit is truncated by the ethane spacer in the bpfd bridge. The dinuclear compounds 1-5 show ligand centered (LC) transitions involving ppy ligands and mixed metal to ligand/ligand to ligand charge transfer (MLCT/LLCT) transitions involving both the cyclometalating ppy and bridging ligands (BL) in the UV-vis spectra. For the conjugated bridge bpe in compound 3 and abp in compound 4, the lowest-energy charge-transfer absorptions are red-shifted with enhanced intensity. In accordance with their similar electronic structures, compounds 1 and 2 exhibit identical emissions. The presence of vibronic structures in these compounds indicates a predominantly (3)LC excited states. On the contrary, broad and unstructured

  12. Edge Delamination of Monolayer Transition Metal Dichalcogenides.

    Science.gov (United States)

    Ly, Thuc Hue; Yun, Seok Joon; Thi, Quoc Huy; Zhao, Jiong

    2017-07-25

    Delamination of thin films from the supportive substrates is a critical issue within the thin film industry. The emergent two-dimensional, atomic layered materials, including transition metal dichalcogenides, are highly flexible; thus buckles and wrinkles can be easily generated and play vital roles in the corresponding physical properties. Here we introduce one kind of patterned buckling behavior caused by the delamination from a substrate initiated at the edges of the chemical vapor deposition synthesized monolayer transition metal dichalcogenides, led by thermal expansion mismatch. The atomic force microscopy and optical characterizations clearly showed the puckered structures associated with the strain, whereas the transmission electron microscopy revealed the special sawtooth-shaped edges, which break the geometrical symmetry for the buckling behavior of hexagonal samples. The condition of the edge delamination is in accordance with the fracture behavior of thin film interfaces. This edge delamination and buckling process is universal for most ultrathin two-dimensional materials, which requires more attention in various future applications.

  13. The atomic structure of transition metal clusters

    International Nuclear Information System (INIS)

    Riley, S.J.

    1995-01-01

    Chemical reactions are used to probe the atomic (geometrical) structure of isolated clusters of transition metal atoms. The number of adsorbate molecules that saturate a cluster, and/or the binding energy of molecules to cluster surfaces, are determined as a function of cluster size. Systematics in these properties often make it possible to propose geometrical structures consistent with the experimental observations. We will describe how studies of the reactions of cobalt and nickel clusters with ammonia, water, and nitrogen provide important and otherwise unavailable structural information. Specifically, small (less than 20 atoms) clusters of cobalt and nickel atoms adopt entirely different structures, the former having packing characteristic of the bulk and the latter having pentagonal symmetry. These observations provide important input for model potentials that attempt to describe the local properties of transition metals. In particular, they point out the importance of a proper treatment of d-orbital binding in these systems, since cobalt and nickel differ so little in their d-orbital occupancy

  14. Lattice Location of Transition Metals in Semiconductors

    CERN Multimedia

    2002-01-01

    %IS366 %title\\\\ \\\\Transition metals (TMs) in semiconductors have been the subject of considerable research for nearly 40 years. This is due both to their role as important model impurities for deep centers in semiconductors, and to their technological impact as widespread contaminants in Si processing, where the miniaturization of devices requires to keep their sheet concentration below 10$^{10}$ cm$^{-2}$. As a consequence of the low TM solubility, conventional ion beam methods for direct lattice location have failed completely in identifying the lattice sites of isolated transition metals. Although electron paramagnetic resonance (EPR) has yielded valuable information on a variety of TM centers, it has been unable to detect certain defects considered by theory, e.g., isolated interstitial or substitutional Cu in Si. The proposed identity of other EPR centers such as substitutional Fe in Si, still needs confirmation by additional experimental methods. As a consequence, the knowledge on the structural propert...

  15. Metal non-metal transitions in doped semiconductors

    International Nuclear Information System (INIS)

    Brezini, A.

    1989-12-01

    A disordered Hubbard model with diagonal disorder is used to examine the electron localization effects associated with both disorder and electron-electron interaction. Extensive results are reported on the ground state properties and compared with other theories. In particular two regimes are observed; when the electron-electron interaction U is greater than the disorder parameter and when is smaller. Furthermore the effect of including conduction-band minima into the calculation of metal-insulator transitions in doped Si and Ge is investigated with use of Berggren approach. Good agreement with experiments are found when both disorder and interactions are included. (author). 37 refs, 7 figs, 3 tabs

  16. Band gap tuning in transition metal oxides by site-specific substitution

    Science.gov (United States)

    Lee, Ho Nyung; Chisholm, Jr., Matthew F; Jellison, Jr., Gerald Earle; Singh, David J; Choi, Woo Seok

    2013-12-24

    A transition metal oxide insulator composition having a tuned band gap includes a transition metal oxide having a perovskite or a perovskite-like crystalline structure. The transition metal oxide includes at least one first element selected form the group of Bi, Ca, Ba, Sr, Li, Na, Mg, K, Pb, and Pr; and at least one second element selected from the group of Ti, Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Rh, Hf, Ta, W, Re, Os, Ir, and Pt. At least one correlated insulator is integrated into the crystalline structure, including REMO.sub.3, wherein RE is at least one Rare Earth element, and wherein M is at least one element selected from the group of Co, V, Cr, Ni, Mn, and Fe. The composition is characterized by a band gap of less of 4.5 eV.

  17. First-principles study of hydrogen dissociation and diffusion on transition metal-doped Mg(0 0 0 1) surfaces

    International Nuclear Information System (INIS)

    Wang, Zhiwen; Guo, Xinjun; Wu, Mingyi; Sun, Qiang; Jia, Yu

    2014-01-01

    First-principles calculations within the density functional theory (DFT) have been carried out to study hydrogen molecules dissociation and diffusion on clean and transition metals (TMs) doped Mg(0 0 0 1) surfaces following Pozzo et al. work. Firstly, the stability of Mg(0 0 0 1) surface doped with transition metals atom has been studied. The results showed that transition metals on the left of the table tend to substitute Mg in the second layer, while the other transition metals prefer to substitute Mg in the first layer. Secondly, we studied hydrogen molecules dissociation and diffusion on clean and Mg(0 0 0 1) surfaces which the transition metal atoms substituted both in the first layer and second layer. When transition metal atoms substitute in the first layer, the results agree with the Pozzo et al. result; when transition metal atoms substitute in the second layer, the results showed that the transition metals on the left of the periodic table impact on the dissociation barriers is less. However, for the transition metals (Mn, Fe, Co, Ni) on the right, there is a great impact on the barriers. The transition metals doped surfaces bind the dissociated H atoms loosely, making them easily diffused. The results further reveal that the Fe dopant on the Mg surface is the best choice for H 2 dissociation and hydrogen storage.

  18. Development of dissimilar metal transition joint by hot bond rolling

    International Nuclear Information System (INIS)

    Kurokawa, Hiroyuki; Nakasuji, Kazuyuki; Kajimura, Haruhiko; Nagai, Takayuki; Takeda, Seiichiro.

    1997-01-01

    Metallurgically bonded transition joints which enable to connect reprocessing equipments made of superior corrosion resistant valve metals (Ti-5Ta, Zr or Ti) to stainless steel piping are required for nuclear fuel reprocessing plants. The authors have developed dissimilar transition joints made of stainless steel and Ti-5Ta, Zr or Ti with an insert metal of Ta by the hot bond rolling process of clad bars and clad pipes, using a newly developed mill called 'rotary reduction mill'. This report presents the manufacturing process of dissimilar transition joints produced from the clad pipe with three layers by the hot bond rolling. First, the method of hot bond rolling of clad pipe is proposed. Then, the mechanical and corrosion properties of the dissimilar transition joints are evaluated in detail by carrying out various tests. Finally, the rolling properties in the clad pipe method are discussed. (author)

  19. Ternary alkali-metal and transition metal or metalloid acetylides as alkali-metal intercalation electrodes for batteries

    Science.gov (United States)

    Nemeth, Karoly; Srajer, George; Harkay, Katherine C; Terdik, Joseph Z

    2015-02-10

    Novel intercalation electrode materials including ternary acetylides of chemical formula: A.sub.nMC.sub.2 where A is alkali or alkaline-earth element; M is transition metal or metalloid element; C.sub.2 is reference to the acetylide ion; n is an integer that is 0, 1, 2, 3 or 4 when A is alkali element and 0, 1, or 2 when A is alkaline-earth element. The alkali elements are Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Cesium (Cs) and Francium (Fr). The alkaline-earth elements are Berilium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba), and Radium (Ra). M is a transition metal that is any element in groups 3 through 12 inclusive on the Periodic Table of Elements (elements 21 (Sc) to element 30 (Zn)). In another exemplary embodiment, M is a metalloid element.

  20. Janus monolayers of transition metal dichalcogenides

    KAUST Repository

    Lu, Ang-Yu

    2017-05-15

    Structural symmetry-breaking plays a crucial role in determining the electronic band structures of two-dimensional materials. Tremendous efforts have been devoted to breaking the in-plane symmetry of graphene with electric fields on AB-stacked bilayers or stacked van der Waals heterostructures. In contrast, transition metal dichalcogenide monolayers are semiconductors with intrinsic in-plane asymmetry, leading to direct electronic bandgaps, distinctive optical properties and great potential in optoelectronics. Apart from their in-plane inversion asymmetry, an additional degree of freedom allowing spin manipulation can be induced by breaking the out-of-plane mirror symmetry with external electric fields or, as theoretically proposed, with an asymmetric out-of-plane structural configuration. Here, we report a synthetic strategy to grow Janus monolayers of transition metal dichalcogenides breaking the out-of-plane structural symmetry. In particular, based on a MoS2 monolayer, we fully replace the top-layer S with Se atoms. We confirm the Janus structure of MoSSe directly by means of scanning transmission electron microscopy and energy-dependent X-ray photoelectron spectroscopy, and prove the existence of vertical dipoles by second harmonic generation and piezoresponse force microscopy measurements.

  1. Retention of Halogens in Waste Glass

    Energy Technology Data Exchange (ETDEWEB)

    Hrma, Pavel R.

    2010-05-01

    In spite of their potential roles as melting rate accelerators and foam breakers, halogens are generally viewed as troublesome components for glass processing. Of five halogens, F, Cl, Br, I, and At, all but At may occur in nuclear waste. A nuclear waste feed may contain up to 10 g of F, 4 g of Cl, and ≤100 mg of Br and I per kg of glass. The main concern is halogen volatility, producing hazardous fumes and particulates, and the radioactive iodine 129 isotope of 1.7x10^7-year half life. Because F and Cl are soluble in oxide glasses and tend to precipitate on cooling, they can be retained in the waste glass in the form of dissolved constituents or as dispersed crystalline inclusions. This report compiles known halogen-retention data in both high-level waste (HLW) and low-activity waste (LAW) glasses. Because of its radioactivity, the main focus is on I. Available data on F and Cl were compiled for comparison. Though Br is present in nuclear wastes, it is usually ignored; no data on Br retention were found.

  2. The recent development of efficient Earth-abundant transition-metal nanocatalysts.

    Science.gov (United States)

    Wang, Dong; Astruc, Didier

    2017-02-06

    Whereas noble metal compounds have long been central in catalysis, Earth-abundant metal-based catalysts have in the same time remained undeveloped. Yet the efficacy of Earth-abundant metal catalysts was already shown at the very beginning of the 20th century with the Fe-catalyzed Haber-Bosch process of ammonia synthesis and later in the Fischer-Tropsch reaction. Nanoscience has revolutionized the world of catalysis since it was observed that very small Au nanoparticles (NPs) and other noble metal NPs are extraordinarily efficient. Therefore the development of Earth-abundant metals NPs is more recent, but it has appeared necessary due to their "greenness". This review highlights catalysis by NPs of Earth-abundant transition metals that include Mn, Fe, Co, Ni, Cu, early transition metals (Ti, V, Cr, Zr, Nb and W) and their nanocomposites with emphasis on basic principles and literature reported during the last 5 years. A very large spectrum of catalytic reactions has been successfully disclosed, and catalysis has been examined for each metal starting with zero-valent metal NPs followed by oxides and other nanocomposites. The last section highlights the catalytic activities of bi- and trimetallic NPs. Indeed this later family is very promising and simultaneously benefits from increased stability, efficiency and selectivity, compared to monometallic NPs, due to synergistic substrate activation.

  3. Defect-Tolerant Monolayer Transition Metal Dichalcogenides

    DEFF Research Database (Denmark)

    Pandey, Mohnish; Rasmussen, Filip Anselm; Kuhar, Korina

    2016-01-01

    Localized electronic states formed inside the band gap of a semiconductor due to crystal defects can be detrimental to the material's optoelectronic properties. Semiconductors with a lower tendency to form defect induced deep gap states are termed defect-tolerant. Here we provide a systematic first...... the gap. These ideas are made quantitative by introducing a descriptor that measures the degree of similarity of the conduction and valence band manifolds. Finally, the study is generalized to nonpolar nanoribbons of the TMDs where we find that only the defect sensitive materials form edge states within......-principles investigation of defect tolerance in 29 monolayer transition metal dichalcogenides (TMDs) of interest for nanoscale optoelectronics. We find that the TMDs based on group VI and X metals form deep gap states upon creation of a chalcogen (S, Se, Te) vacancy, while the TMDs based on group IV metals form only...

  4. Metal-insulator transition and superconductivity in heavily boron-doped diamond and related materials

    Energy Technology Data Exchange (ETDEWEB)

    Achatz, Philipp

    2009-05-15

    During this PhD project, the metal-insulator transition and superconductivity of highly boron-doped single crystal diamond and related materials have been investigated. The critical boron concentration n{sub c} for the metal-insulator transition was found to be the same as for the normal-superconductor transition. All metallic samples have been found to be superconducting and we were able to link the occurence of superconductivity to the proximity to the metal-insulator transition. For this purpose, a scaling law approach based on low temperature transport was proposed. Furthermore, we tried to study the nature of the superconductivity in highly boron doped single crystal diamond. Raman spectroscopy measurements on the isotopically substituted series suggest that the feature occuring at low wavenumbers ({approx} 500 cm{sup -1}) is the A1g vibrational mode associated with boron dimers. Usual Hall effect measurements yielded a puzzling situation in metallic boron-doped diamond samples, leading to carrier concentrations up to a factor 10 higher than the boron concentration determined by secondary ion mass spectroscopy (SIMS). The low temperature transport follows the one expected for a granular metal or insulator, depending on the interplay of intergranular and intragranular (tunneling) conductance. The metal-insulator transition takes place at a critical conductance g{sub c}. The granularity also influences significantly the superconducting properties by introducing the superconducting gap {delta} in the grain and Josephson coupling J between superconducting grains. A peak in magnetoresistance is observed which can be explained by superconducting fluctuations and the granularity of the system. Additionally we studied the low temperature transport of boron-doped Si samples grown by gas immersion laser doping, some of which yielded a superconducting transition at very low temperatures. Furthermore, preliminary results on the LO-phonon-plasmon coupling are shown for the

  5. Metal-insulator transition and superconductivity in heavily boron-doped diamond and related materials

    International Nuclear Information System (INIS)

    Achatz, Philipp

    2009-01-01

    During this PhD project, the metal-insulator transition and superconductivity of highly boron-doped single crystal diamond and related materials have been investigated. The critical boron concentration n c for the metal-insulator transition was found to be the same as for the normal-superconductor transition. All metallic samples have been found to be superconducting and we were able to link the occurence of superconductivity to the proximity to the metal-insulator transition. For this purpose, a scaling law approach based on low temperature transport was proposed. Furthermore, we tried to study the nature of the superconductivity in highly boron doped single crystal diamond. Raman spectroscopy measurements on the isotopically substituted series suggest that the feature occuring at low wavenumbers (∼ 500 cm -1 ) is the A1g vibrational mode associated with boron dimers. Usual Hall effect measurements yielded a puzzling situation in metallic boron-doped diamond samples, leading to carrier concentrations up to a factor 10 higher than the boron concentration determined by secondary ion mass spectroscopy (SIMS). The low temperature transport follows the one expected for a granular metal or insulator, depending on the interplay of intergranular and intragranular (tunneling) conductance. The metal-insulator transition takes place at a critical conductance g c . The granularity also influences significantly the superconducting properties by introducing the superconducting gap Δ in the grain and Josephson coupling J between superconducting grains. A peak in magnetoresistance is observed which can be explained by superconducting fluctuations and the granularity of the system. Additionally we studied the low temperature transport of boron-doped Si samples grown by gas immersion laser doping, some of which yielded a superconducting transition at very low temperatures. Furthermore, preliminary results on the LO-phonon-plasmon coupling are shown for the first time in aluminum

  6. Halogen-Mediated Conversion of Hydrocarbons to Commodities.

    Science.gov (United States)

    Lin, Ronghe; Amrute, Amol P; Pérez-Ramírez, Javier

    2017-03-08

    Halogen chemistry plays a central role in the industrial manufacture of various important chemicals, pharmaceuticals, and polymers. It involves the reaction of halogens or halides with hydrocarbons, leading to intermediate compounds which are readily converted to valuable commodities. These transformations, predominantly mediated by heterogeneous catalysts, have long been successfully applied in the production of polymers. Recent discoveries of abundant conventional and unconventional natural gas reserves have revitalized strong interest in these processes as the most cost-effective gas-to-liquid technologies. This review provides an in-depth analysis of the fundamental understanding and applied relevance of halogen chemistry in polymer industries (polyvinyl chloride, polyurethanes, and polycarbonates) and in the activation of light hydrocarbons. The reactions of particular interest include halogenation and oxyhalogenation of alkanes and alkenes, dehydrogenation of alkanes, conversion of alkyl halides, and oxidation of hydrogen halides, with emphasis on the catalyst, reactor, and process design. Perspectives on the challenges and directions for future development in this exciting field are provided.

  7. Phase-field model of insulator-to-metal transition in VO2 under an electric field

    Science.gov (United States)

    Shi, Yin; Chen, Long-Qing

    2018-05-01

    The roles of an electric field and electronic doping in insulator-to-metal transitions are still not well understood. Here we formulated a phase-field model of insulator-to-metal transitions by taking into account both structural and electronic instabilities as well as free electrons and holes in VO2, a strongly correlated transition-metal oxide. Our phase-field simulations demonstrate that in a VO2 slab under a uniform electric field, an abrupt universal resistive transition occurs inside the supercooling region, in sharp contrast to the conventional Landau-Zener smooth electric breakdown. We also show that hole doping may decouple the structural and electronic phase transitions in VO2, leading to a metastable metallic monoclinic phase which could be stabilized through a geometrical confinement and the size effect. This work provides a general mesoscale thermodynamic framework for understanding the influences of electric field, electronic doping, and stress and strain on insulator-to-metal transitions and the corresponding mesoscale domain structure evolution in VO2 and related strongly correlated systems.

  8. A 2.5-dimensional method for the prediction of structure-borne low-frequency noise from concrete rail transit bridges.

    Science.gov (United States)

    Li, Qi; Song, Xiaodong; Wu, Dingjun

    2014-05-01

    Predicting structure-borne noise from bridges subjected to moving trains using the three-dimensional (3D) boundary element method (BEM) is a time consuming process. This paper presents a two-and-a-half dimensional (2.5D) BEM-based procedure for simulating bridge-borne low-frequency noise with higher efficiency, yet no loss of accuracy. The two-dimensional (2D) BEM of a bridge with a constant cross section along the track direction is adopted to calculate the spatial modal acoustic transfer vectors (MATVs) of the bridge using the space-wave number transforms of its 3D modal shapes. The MATVs calculated using the 2.5D method are then validated by those computed using the 3D BEM. The bridge-borne noise is finally obtained through the MATVs and modal coordinate responses of the bridge, considering time-varying vehicle-track-bridge dynamic interaction. The presented procedure is applied to predict the sound pressure radiating from a U-shaped concrete bridge, and the computed results are compared with those obtained from field tests on Shanghai rail transit line 8. The numerical results match well with the measured results in both time and frequency domains at near-field points. Nevertheless, the computed results are smaller than the measured ones for far-field points, mainly due to the sound radiation from adjacent spans neglected in the current model.

  9. E. S. R. studies of halogenated pyrimidines in. gamma. -irradiated alkaline glasses. [Halogenated uracil bases; bromouridine; bromodeoxyuridine

    Energy Technology Data Exchange (ETDEWEB)

    Simpson, L D; Zimbrick, J D [Kansas Univ., Lawrence (USA)

    1975-11-01

    The reactions of mobile electrons (e/sup -//sub m/) and oxygen radical anions (O./sup -/) with halogenated bases and nucleosides have been studied in ..gamma..-irradiated alkaline glasses by e.s.r. and specific halogen-ion electrode techniques. It was shown that electrons react with halogenated uracil bases (XUr where X = Cl, Br, I but not F) by dissociative electron attachment to form uracil-5-yl radicals (U.) and halogen anions. The relative rates of reaction of e/sup -//sub m/ with XUr decreased in the sequence BrUr > ClUr > FUr > IUr. Thermal annealing studies carried out on U. in H/sub 2/O and D/sub 2/O matrices supported the hypothesis that U. in H/sub 2/O hydrates across the 5-6 double bond in the temperature region 135/sup 0/ to 155/sup 0/ K, and deuterates to a much smaller extent in D/sub 2/O at temperatures above 155/sup 0/ K. Studies on bromouridine and bromodeoxyuridine suggested that e/sup -/sub(m) reacts with the base moieties to form U. type radicals which abstract H. from the sugar moieties of adjacent nucleosides.

  10. Universal Quantum Criticality in the Metal-Insulator Transition of Two-Dimensional Interacting Dirac Electrons

    Directory of Open Access Journals (Sweden)

    Yuichi Otsuka

    2016-03-01

    Full Text Available The metal-insulator transition has been a subject of intense research since Mott first proposed that the metallic behavior of interacting electrons could turn to an insulating one as electron correlations increase. Here, we consider electrons with massless Dirac-like dispersion in two spatial dimensions, described by the Hubbard models on two geometrically different lattices, and perform numerically exact calculations on unprecedentedly large systems that, combined with a careful finite-size scaling analysis, allow us to explore the quantum critical behavior in the vicinity of the interaction-driven metal-insulator transition. Thereby, we find that the transition is continuous, and we determine the quantum criticality for the corresponding universality class, which is described in the continuous limit by the Gross-Neveu model, a model extensively studied in quantum field theory. Furthermore, we discuss a fluctuation-driven scenario for the metal-insulator transition in the interacting Dirac electrons: The metal-insulator transition is triggered only by the vanishing of the quasiparticle weight, not by the Dirac Fermi velocity, which instead remains finite near the transition. This important feature cannot be captured by a simple mean-field or Gutzwiller-type approximate picture but is rather consistent with the low-energy behavior of the Gross-Neveu model.

  11. Polymer derived non-oxide ceramics modified with late transition metals.

    Science.gov (United States)

    Zaheer, Muhammad; Schmalz, Thomas; Motz, Günter; Kempe, Rhett

    2012-08-07

    This tutorial review highlights the methods for the preparation of metal modified precursor derived ceramics (PDCs) and concentrates on the rare non-oxide systems enhanced with late transition metals. In addition to the main synthetic strategies for modified SiC and SiCN ceramics, an overview of the morphologies, structures and compositions of both, ceramic materials and metal (nano) particles, is presented. Potential magnetic and catalytic applications have been discussed for the so manufactured metal containing non-oxide ceramics.

  12. Trends in oxygen reduction and methanol activation on transition metal chalcogenides

    DEFF Research Database (Denmark)

    Tritsaris, Georgios; Nørskov, Jens Kehlet; Rossmeisl, Jan

    2011-01-01

    We use density functional theory calculations to study the oxygen reduction reaction and methanol activation on selenium and sulfur-containing transition metal surfaces. With ruthenium selenium as a starting point, we study the effect of the chalcogen on the activity, selectivity and stability...... of the catalyst. Ruthenium surfaces with moderate content of selenium are calculated active for the oxygen reduction reaction, and insensitive to methanol. A significant upper limit for the activity of transition metal chalcogenides is estimated....

  13. Magnetic Ground State Properties of Transition Metals

    DEFF Research Database (Denmark)

    Andersen, O. K.; Madsen, J.; Poulsen, U. K.

    1977-01-01

    We review a simple one-electron theory of the magnetic and cohesive properties of ferro- and nearly ferromagnetic transition metals at 0 K. The theory is based on the density functional formalism, it makes use of the local spin density and atomic sphere approximations and it may, with further app...

  14. Raman scattering in transition metal compounds: Titanium and compounds of titanium

    Energy Technology Data Exchange (ETDEWEB)

    Jimenez, J.; Ederer, D.L.; Shu, T. [Tulane Univ., New Orleans, LA (United States)] [and others

    1997-04-01

    The transition metal compounds form a very interesting and important set of materials. The diversity arises from the many states of ionization the transition elements may take when forming compounds. This variety provides ample opportunity for a large class of materials to have a vast range of electronic and magnetic properties. The x-ray spectroscopy of the transition elements is especially interesting because they have unfilled d bands that are at the bottom of the conduction band with atomic like structure. This group embarked on the systematic study of transition metal sulfides and oxides. As an example of the type of spectra observed in some of these compounds they have chosen to showcase the L{sub II, III} emission and Raman scattering in some titanium compounds obtained by photon excitation.

  15. Investigation of Ternary Transition-Metal Nitride Systems by Reactive Cosputtering

    NARCIS (Netherlands)

    Dover, R.B. Van; Hessen, B.; Werder, D.; Chen, C.-H.; Felder, R.J.

    1993-01-01

    A reactive dc cosputtering technique has been used to evaluate compound formation in bimetallic transition-metal nitride systems. A wide range in M-M’ composition can be studied in a single deposition run, and the method is applicable to nonalloying metal combinations. Using this technique, it was

  16. Scaling Relationships for Adsorption Energies of C2 Hydrocarbons on Transition Metal Surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Jones, G

    2011-08-18

    Using density functional theory calculations we show that the adsorption energies for C{sub 2}H{sub x}-type adsorbates on transition metal surfaces scale with each other according to a simple bond order conservation model. This observation generalizes some recently recognized adsorption energy scaling laws for AH{sub x}-type adsorbates to unsaturated hydrocarbons and establishes a coherent simplified description of saturated as well as unsaturated hydrocarbons adsorbed on transition metal surfaces. A number of potential applications are discussed. We apply the model to the dehydrogenation of ethane over pure transition metal catalysts. Comparison with the corresponding full density functional theory calculations shows excellent agreement.

  17. Nanostructure sensitization of transition metal oxides for visible-light photocatalysis

    Directory of Open Access Journals (Sweden)

    Hongjun Chen

    2014-05-01

    Full Text Available To better utilize the sunlight for efficient solar energy conversion, the research on visible-light active photocatalysts has recently attracted a lot of interest. The photosensitization of transition metal oxides is a promising approach for achieving effective visible-light photocatalysis. This review article primarily discusses the recent progress in the realm of a variety of nanostructured photosensitizers such as quantum dots, plasmonic metal nanostructures, and carbon nanostructures for coupling with wide-bandgap transition metal oxides to design better visible-light active photocatalysts. The underlying mechanisms of the composite photocatalysts, e.g., the light-induced charge separation and the subsequent visible-light photocatalytic reaction processes in environmental remediation and solar fuel generation fields, are also introduced. A brief outlook on the nanostructure photosensitization is also given.

  18. The Transition Year: A Unique Programme in Irish Education Bridging The Gap Between School and The Workplace

    Directory of Open Access Journals (Sweden)

    Joseph A. MOYNIHAN

    2015-12-01

    Full Text Available Transition Year is a unique and exciting programme situated in the middle of the six year second level education system in Ireland. Since its introduction in 1974, the programme has experienced unprecedented growth now being offered in over 80% of schools on the island. Transition Year seeks to emphasize alternative learning methodologies including self-directed learning and experiential learning; intellectual, social and personal development; community and inter-school communications; exposure to careers education and the world of work. The latter occurs predominantly through actual work experience. This paper situates and explains the Transition Year Programme in Irish education as well as outlining the significance of the essential work experience component. Transition Year work experience is the bridge that connects young people in the classroom with adult life and the world of work.

  19. Electric field-triggered metal-insulator transition resistive switching of bilayered multiphasic VOx

    Science.gov (United States)

    Won, Seokjae; Lee, Sang Yeon; Hwang, Jungyeon; Park, Jucheol; Seo, Hyungtak

    2018-01-01

    Electric field-triggered Mott transition of VO2 for next-generation memory devices with sharp and fast resistance-switching response is considered to be ideal but the formation of single-phase VO2 by common deposition techniques is very challenging. Here, VOx films with a VO2-dominant phase for a Mott transition-based metal-insulator transition (MIT) switching device were successfully fabricated by the combined process of RF magnetron sputtering of V metal and subsequent O2 annealing to form. By performing various material characterizations, including scanning transmission electron microscopy-electron energy loss spectroscopy, the film is determined to have a bilayer structure consisting of a VO2-rich bottom layer acting as the Mott transition switching layer and a V2O5/V2O3 mixed top layer acting as a control layer that suppresses any stray leakage current and improves cyclic performance. This bilayer structure enables excellent electric field-triggered Mott transition-based resistive switching of Pt-VOx-Pt metal-insulator-metal devices with a set/reset current ratio reaching 200, set/reset voltage of less than 2.5 V, and very stable DC cyclic switching upto 120 cycles with a great set/reset current and voltage distribution less than 5% of standard deviation at room temperature, which are specifications applicable for neuromorphic or memory device applications. [Figure not available: see fulltext.

  20. Electronic structure of hcp transition metals

    DEFF Research Database (Denmark)

    Jepsen, O.; Andersen, O. Krogh; Mackintosh, A. R.

    1975-01-01

    Using the linear muffin-tin-orbital method described in the previous paper, we have calculated the electronic structures of the hcp transition metals, Zr, Hf, Ru, and Os. We show how the band structures of these metals may be synthesized from the sp and d bands, and illustrate the effects...... of hybridization, relativistic band shifts, and spin-orbit coupling by the example of Os. By making use of parameters derived from the muffin-tin potential, we discuss trends in the positions and widths of the energy bands, especially the d bands, as a function of the location in the periodic table. The densities...... of states of the four metals are presented, and the calculated heat capacities compared with experiment. The Fermi surfaces of both Ru and Os are found to be in excellent quantitative agreement with de Haas-van Alphen measurements, indicating that the calculated d-band position is misplaced by less than 10...

  1. Convergence of quasiparticle self-consistent GW calculations of transition metal monoxides

    OpenAIRE

    Das, Suvadip; Coulter, John E.; Manousakis, Efstratios

    2014-01-01

    Finding an accurate ab initio approach for calculating the electronic properties of transition metal oxides has been a problem for several decades. In this paper, we investigate the electronic structure of the transition metal monoxides MnO, CoO, and NiO in their undistorted rock-salt structure within a fully iterated quasiparticle self-consistent GW (QPscGW) scheme. We study the convergence of the QPscGW method, i.e., how the quasiparticle energy eigenvalues and wavefunctions converge as a f...

  2. Trends in the Hydrodeoxygenation Activity and Selectivity of Transition Metal Surfaces

    DEFF Research Database (Denmark)

    Lausche, Adam C.; Falsig, Hanne; Jensen, Anker Degn

    2014-01-01

    This paper reports the use of a combination of density functional theory and microkinetic modelling to establish trends in the hydrodeoxygenation rates and selectivites of transition metal surfaces. Biomass and biomass-derived chemicals often contain large fractions of oxygenates. Removal...... of the oxygen through hydrotreating represents one strategy for producing commodity chemicals from these renewable materials. Using the model developed in this paper, we predict ethylene glycol hydrodeoxygenation selectivities for transition metals that are consistent with those reported in the literature...

  3. Adsorbate Diffusion on Transition Metal Nanoparticles

    Science.gov (United States)

    2015-01-01

    correlation is a Bronsted-Evans-Polanyi ( BEP )- type of correlation, similar to other BEP correlations established earlier for surface-catalyzed bond- breaking...bond-making reactions.6-9 The universal BEP -type correlation is independent of the nature of the adsorbed species and that of the metal surface. For...a certain class of surface-catalyzed reactions, the existence of a BEP -type correlation reflects a similarity between the geometry of the transition

  4. Quantum criticality around metal-insulator transitions of strongly correlated electron systems

    Science.gov (United States)

    Misawa, Takahiro; Imada, Masatoshi

    2007-03-01

    Quantum criticality of metal-insulator transitions in correlated electron systems is shown to belong to an unconventional universality class with violation of the Ginzburg-Landau-Wilson (GLW) scheme formulated for symmetry breaking transitions. This unconventionality arises from an emergent character of the quantum critical point, which appears at the marginal point between the Ising-type symmetry breaking at nonzero temperatures and the topological transition of the Fermi surface at zero temperature. We show that Hartree-Fock approximations of an extended Hubbard model on square lattices are capable of such metal-insulator transitions with unusual criticality under a preexisting symmetry breaking. The obtained universality is consistent with the scaling theory formulated for Mott transitions and with a number of numerical results beyond the mean-field level, implying that preexisting symmetry breaking is not necessarily required for the emergence of this unconventional universality. Examinations of fluctuation effects indicate that the obtained critical exponents remain essentially exact beyond the mean-field level. It further clarifies the whole structure of singularities by a unified treatment of the bandwidth-control and filling-control transitions. Detailed analyses of the criticality, containing diverging carrier density fluctuations around the marginal quantum critical point, are presented from microscopic calculations and reveal the nature as quantum critical “opalescence.” The mechanism of emerging marginal quantum critical point is ascribed to a positive feedback and interplay between the preexisting gap formation present even in metals and kinetic energy gain (loss) of the metallic carrier. Analyses of crossovers between GLW type at nonzero temperature and topological type at zero temperature show that the critical exponents observed in (V,Cr)2O3 and κ-ET -type organic conductors provide us with evidence for the existence of the present marginal

  5. Magnetic excitations in transition-metal ferromagnets

    International Nuclear Information System (INIS)

    Uemura, Y.J.

    1984-01-01

    A review is given on current neutron scattering experiments at Brookhaven National Laboratory on transition-metal ferromagnets Ni, Fe, Pd 2 MnSn and MnSi. The scattering intensity in constant-energy scans, observed above T/sub c/ in all of these materials, exhibited a clear peak at finite momentum transfers. Using a simple scattering function with double-Lorentzian shape, we demonstrate that this peak is a manifestation of simple diffusive spin fluctuations. Experimental results of several parameters are compared in the context of localized-moment and itinerant-electron pictures. The ratio of spin wave stiffness constant D and transition temperature kT/sub c/ is shown to be a good yardstick for the degree of itinerancy of d-electrons

  6. Oxygen effect on the work function of electropositive metal films adsorbed on 4d and 5d-transition metals

    International Nuclear Information System (INIS)

    Kultashev, O.K.; Makarov, A.P.; Rozhkov, S.E.

    1976-01-01

    The thermionic emission method was used to study the effect of oxygen upon the work function of films of electropositive metals, Sc, Y, La and Ba on some monocrystal and polycrystalline specimens of 4d- and 5d-transition metals of groups 4-8 of the Periodic system. It was revealed that when the supports were polycrystalline and monocrystalline specimens of transition metals of Group 5 (niobium and tantalum), the work function phi of films of electropositive adsorbates dropped substantially as compared, e.g., to the phi values on the same faces of tungsten. When the concentration of the electropositive adsorbate exceeds the optimum value (in the absence of oxygen), oxygen exerts an appreciably activating action upon the work function phi of films of electropositive adsorbates on transition metals of the Groups 7 and 8. The activating action of oxygen is assumed to be due to a possibility of formation of surface interstitial structures

  7. Atomic structure of non-stoichiometric transition metal carbides

    International Nuclear Information System (INIS)

    Moisy-Maurice, Virginie.

    1981-10-01

    Different kinds of experimental studies of the atomic arrangement in non-stoichiometric transition metal carbides are proposed: the ordering of carbon vacancies and the atomic static displacements are the main subjects studied. Powder neutron diffraction on TiCsub(1-x) allowed us to determine the order-disorder transition critical temperature -Tsub(c) approximately 770 0 C- in the TiCsub(0.52-0.67) range, and to analyze at 300 K the crystal structure of long-range ordered samples. A neutron diffuse scattering quantitative study at 300 K of short-range order in TiCsub(0.76), TiCsub(0.79) and NbCsub(0.73) single crystals is presented: as in Ti 2 Csub(1+x) and Nb 6 C 5 superstructures, vacancies avoid to be on each side of a metal atom. Besides, the mean-square carbon atom displacements from their sites are small, whereas metal atoms move radially about 0.03 A away from vacancies. These results are in qualitative agreement with EXAFS measurements at titanium-K edge of TiCsub(1-x). An interpretation of ordering in term of short-range interaction pair potentials between vacancies is proposed [fr

  8. Electrochromism in transition metal oxides

    International Nuclear Information System (INIS)

    Estrada, W.

    1993-01-01

    Electrochromism is discussed for transition metal oxides. Particularly tungsten oxide and nickel oxide are reviewed, in order to put forth the different aspects of the field. Since this phenomena has been reviewed by several authors, it is not tried to be comprehensive but rather pedagogical. The basic requirements for a material -in both non-emissive displays and energy efficiency applications- to be electrochromic, a general view of electrochromic mechanism, anodic and cathodic electrochromic materials, and current problems for a electrochromic theory are presented. (author) 45 refs., 8 figs

  9. Phase coexistence in the metal-insulator transition of a VO2 thin film

    International Nuclear Information System (INIS)

    Chang, Y.J.; Koo, C.H.; Yang, J.S.; Kim, Y.S.; Kim, D.H.; Lee, J.S.; Noh, T.W.; Kim, Hyun-Tak; Chae, B.G.

    2005-01-01

    Vanadium dioxide (VO 2 ) shows a metal-insulator transition (MIT) near room temperature, accompanied by an abrupt resistivity change. Since the MIT of VO 2 is known to be a first order phase transition, it is valuable to check metallic and insulating phase segregation during the MIT process. We deposited (100)-oriented epitaxial VO 2 thin films on R-cut sapphire substrates. From the scanning tunneling spectroscopy (STS) spectra, we could distinguish metallic and insulating regions by probing the band gap. Optical spectroscopic analysis also supported the view that the MIT in VO 2 occurs through metal and insulator phase coexistence

  10. Mechanical and electronic properties of Janus monolayer transition metal dichalcogenides

    Science.gov (United States)

    Shi, Wenwu; Wang, Zhiguo

    2018-05-01

    The mechanical and electronic properties of Janus monolayer transition metal dichalcogenides MXY (M  =  Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W; X/Y  =  S, Se, Te) were investigated using density functional theory. Results show that breaking the out-of-plane structural symmetry can be used to tune the electronic and mechanical behavior of monolayer transition metal dichalcogenides. The band gaps of monolayer WXY and MoXY are in the ranges of 0.16–1.91 and 0.94–1.69 eV, respectively. A semiconductor to metallic phase transition occurred in Janus monolayer MXY (M  =  Ti, Zr and Hf). The monolayers MXY (M  =  V, Nb, Ta and Cr) show metallic characteristics, which show no dependence on the structural symmetry breaking. The mechanical properties of MXY depended on the composition. Monolayer MXY (M  =  Mo, Ti, Zr, Hf and W) showed brittle characteristic, whereas monolayer CrXY and VXY are with ductile characteristic. The in-plane stiffness of pristine and Janus monolayer MXY are in the range between 22 and 158 N m‑1. The tunable electronic and mechanical properties of these 2D materials would advance the development of ultra-sensitive detectors, nanogenerators, low-power electronics, and energy harvesting and electromechanical systems.

  11. The electronic and optical properties of germanium tellurite glasses containing various transition metal oxides

    International Nuclear Information System (INIS)

    Khan, M.N.

    1988-01-01

    Various transition metal oxides, such as TiO 2 , V 2 O 5 , NiO, CuO, and ZnO are added to germanium-tellurite glass and measurements are reported of the electrical conductivity, density, optical absorption, infra-red absorption spectra, and electron spin resonance. It is found that the d.c. conductivity of glasses containing the same amount of V 2 O 5 is higher than that of germanium tellurite glasses containing a similar amount of other transition metal oxides, and is due to hopping between localized states. The optical absorption measurements show that the fundamental absorption edge is a function of glass composition and the optical absorption is due to forbidden indirect transitions. From the infra-red absorption spectra, it is found that the addition of transition metal oxides does not introduce any new absorption band in the infra-red spectrum of germanium tellurite glasses. A small shift of existing absorptions toward higher wave number is observed. The ESR measurements revealed that some transition metal ions are diamagnetic while others are paramagnetic in the glass network. (author)

  12. Uniaxial pressure-induced half-metallic ferromagnetic phase transition in LaMnO3

    Science.gov (United States)

    Rivero, Pablo; Meunier, Vincent; Shelton, William

    2016-03-01

    We use first-principles theory to predict that the application of uniaxial compressive strain leads to a transition from an antiferromagnetic insulator to a ferromagnetic half-metal phase in LaMnO3. We identify the Q2 Jahn-Teller mode as the primary mechanism that drives the transition, indicating that this mode can be used to tune the lattice, charge, and spin coupling. Applying ≃6 GPa of uniaxial pressure along the [010] direction activates the transition to a half-metallic pseudocubic state. The half-metallicity opens the possibility of producing colossal magnetoresistance in the stoichiometric LaMnO3 compound at significantly lower pressure compared to recently observed investigations using hydrostatic pressure.

  13. THE STATE OF MANGANESE IN THE PHOTOSYNTHETIC APPARATUS. I. EXAFS STUDIES ON CHLOROPLASTS AND di-u-oxo BRIDGED di-MANGANESE MODEL COMPOUNDS

    Energy Technology Data Exchange (ETDEWEB)

    Kirby, J. A.; Robertson, A. S.; Smith, J. P.; Thompson, A. C.; Thompson, A. C.; Klein, M. P.

    1980-11-01

    Extended X-ray Absorption Fine Structure (EXAFS) studies on the manganese contained in spinach chloroplasts and on certain di-u-oxo bridged manganese dimers of the form (X{sub 2}Mn)O{sub 2}(MnX{sub 2} (X=2,2'-bypyridine and 1,10-phenanthroline) are reported. From these studies, the manganese associated with photosynthetic oxygen evolution is suggested to occur as a bridged transition metal dimer with most likely another manganese. Extensive details on the analysis are included.

  14. Effect of transition metal ions on the conductivity and stability of stabilized zirconia

    DEFF Research Database (Denmark)

    Lybye, D.; Mogensen, Mogens Bjerg

    2007-01-01

    the effect of co-doping with smaller transition metal ions such as Ti-, Fe- and Mn-ions. Many of the ionic radii of the transition metal ions are too small compared to the host lattice ionic radius of zirconium. Here we explore the effect of a) the small ionic radii compared to the large ionic radii...

  15. Semiconductor-Metal transition in a quantum well

    International Nuclear Information System (INIS)

    Nithiananthi, P.; Jayakumar, K.

    2007-01-01

    We demonstrate semiconductor-metal transition through diamagnetic susceptibility of a donor in a GaAs/Al x Ga 1- x As quantum well for both infinite and finite barrier models. We have also considered the non-parabolicity of the conduction band in our calculation. Our results agree with the earlier theoretical result and also with the recent experimental result

  16. Binding properties of oxacalix[4]arenes derivatives toward metal cations

    International Nuclear Information System (INIS)

    Mellah, B.

    2006-11-01

    The objective of this work was to establish the binding properties of oxacalix[4]arene derivatives with different numbers of the oxa bridges, functional groups (ketones, pyridine, ester, amide and methoxy) and conformations. Their interactions with alkali and alkaline-earth, heavy and transition metal cations have been evaluated according to different approaches: (i) extraction of corresponding picrates from an aqueous phase into dichloromethane; (ii) determination of the thermodynamic parameters of complexation in methanol and/or acetonitrile by UV-spectrophotometry and micro-calorimetry; (iii) determination of the stoichiometry of the complexes by ESI-MS; (iv) 1 H-NMR titrations allowing to localize the metal ions in the ligand cavity. In a first part dealing on homo-oxacalix[4]arenes, selectivities for Na + , K + , Ca 2+ , Pb 2+ and Mn 2+ of ketones derivatives was shown. The presence of oxa bridge in these derivatives increases their efficiency while decreasing their selectivity with respect to related calixarenes. The pyridine derivative prefers transition and heavy metal cations, in agreement with the presence of the soft nitrogen atoms. In the second part, di-oxacalix[4]arene ester and secondary amide derivatives were shown to be less effective than tertiary amide counterparts but to present high selectivities for Li + , Ba 2+ , Zn 2+ and Hg 2+ . A third part devoted to the octa-homo-tetra-oxacalix[4]arene tetra-methoxy shows that the 1:1 metal complexes formed are generally more stable than those of calixarenes, suggesting the participation of the oxygen atoms of the bridge in the complexation. Selectivity for Cs + , Ba 2+ , Cu 2+ and Hg 2+ were noted. (author)

  17. Generation and alteration of the defects induced by particle irradiation and electromagnetic radiation in alkali halogen compounds

    International Nuclear Information System (INIS)

    Nistor, L.C.

    1979-01-01

    Interactions between electron beams, CO 2 - laser radiation and alkali halogen compound have led to interesting results: 1. The development of two types of F-centre respectively in normal lattice or near the dislocations. 2. The beginning of metal colloids development process at low temperature when a thermal treatment is applied. 3. An experimental confirmation of the Pooley-Hersh model for crystal defects has been brought up. 4. The surface penetration is an explosive process. 5. Surface polygonizations were also investigated. A model has been proposed to describe the destructive channels development within alkali halogen crystals with molecular anions impurities of less than 10 ppm. KCl monocrystals of advanced purity level was prepared for building up passive optical components of strong CO 2 lasers. (author)

  18. Electronic Structure Evolution across the Peierls Metal-Insulator Transition in a Correlated Ferromagnet

    Directory of Open Access Journals (Sweden)

    P. A. Bhobe

    2015-10-01

    Full Text Available Transition metal compounds often undergo spin-charge-orbital ordering due to strong electron-electron correlations. In contrast, low-dimensional materials can exhibit a Peierls transition arising from low-energy electron-phonon-coupling-induced structural instabilities. We study the electronic structure of the tunnel framework compound K_{2}Cr_{8}O_{16}, which exhibits a temperature-dependent (T-dependent paramagnetic-to-ferromagnetic-metal transition at T_{C}=180  K and transforms into a ferromagnetic insulator below T_{MI}=95  K. We observe clear T-dependent dynamic valence (charge fluctuations from above T_{C} to T_{MI}, which effectively get pinned to an average nominal valence of Cr^{+3.75} (Cr^{4+}∶Cr^{3+} states in a 3∶1 ratio in the ferromagnetic-insulating phase. High-resolution laser photoemission shows a T-dependent BCS-type energy gap, with 2G(0∼3.5(k_{B}T_{MI}∼35  meV. First-principles band-structure calculations, using the experimentally estimated on-site Coulomb energy of U∼4  eV, establish the necessity of strong correlations and finite structural distortions for driving the metal-insulator transition. In spite of the strong correlations, the nonintegral occupancy (2.25 d-electrons/Cr and the half-metallic ferromagnetism in the t_{2g} up-spin band favor a low-energy Peierls metal-insulator transition.

  19. Structural influence of mixed transition metal ions on lithium bismuth borate glasses

    Science.gov (United States)

    Yadav, Arti; Dahiya, Manjeet S.; Hooda, A.; Chand, Prem; Khasa, S.

    2017-08-01

    Lithium bismuth borate glasses containing mixed transition metals having composition 7CoO·23Li2O·20Bi2O3·50B2O3 (CLBB), 7V2O5·23Li2O·20Bi2O3·50B2O3 (VLBB) and x(2CoO·V2O5)·(30 - x)Li2O·20Bi2O3·50B2O3 (x = 0.0 (LBB) and x = 2.0, 5.0, 7.0, 10.0 mol% (CVLBB1-4)) are synthesized via melt quench route. The synthesized compositions are investigated for their physical properties using density (D) and molar volume (Vm), thermal properties by analyzing DSC/TG thermo-graphs, structural properties using IR absorption spectra in the mid-IR range and optical properties using UV-Vis-NIR spectroscopy. The Electron Paramagnetic Resonance (EPR) spectra of vanadyl and cobalt ion have been analyzed to study compositional effects on spin-Hamiltonian parameters. The non linear variations in physical properties depict a strong structural influence of Co/V- oxides on the glassy matrix. The compositional variations in characteristic temperatures (glass transition temperature Tg, glass crystallization temperature Tp and glass melting temperature Tm) reveals that Tg for glass samples CLBB is relatively less than that of pure lithium bismuth borate (LBB) glass sample wherein Tg for sample VLBB is higher than that of LBB. The increase in Tg (as compared with LBB) with an enhanced substitution of mixed transition metal oxides (2CoO·V2O5) shows a progressive structure modification of bismuth borate matrix. These predictions are very well corroborated by corresponding compositional trends of Tp and Tm. FTIR studies reveal that Co2+& VO2+ ions lead to structural rearrangements through the conversion of three-coordinated boron into four coordinated boron and thereby reducing number of non-bridging oxygen atoms. Bismuth is found to exist in [BiO6] octahedral units only, whereas boroxol rings are not present in the glass network. The theoretical values of optical basicity (Λth) and corresponding oxide ion polarizability (αo2-) have also been calculated to investigate oxygen covalency of

  20. Thermal properties of zirconium diboride -- transition metal boride solid solutions

    Science.gov (United States)

    McClane, Devon Lee

    This research focuses on the thermal properties of zirconium diboride (ZrB2) based ceramics. The overall goal was to improve the understanding of how different transition metal (TM) additives influence thermal transport in ZrB2. To achieve this, ZrB2 with 0.5 wt% carbon, and 3 mol% of individual transition metal borides, was densified by hot-press sintering. The transition metals that were investigated were: Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, and Re. The room temperature thermal diffusivities of the compositions ranged from 0.331 cm2/s for nominally pure ZrB2 to 0.105 cm2/s for (Zr,Cr)B2 and converged around 0.155cm2/s at higher temperatures for all compositions. Thermal conductivities were calculated from the diffusivities, using temperature-dependent values for density and heat capacity. The electron contribution to thermal conductivity was calculated from measured electrical resistivity according to the Wiedemann-Franz law. The phonon contribution to thermal conductivity was calculated by subtracting the electron contribution from the total thermal conductivity. Rietveld refinement of x-ray diffraction data was used to determine the lattice parameters of the compositions. The decrease in thermal conductivity for individual additives correlated directly to the metallic radius of the additive. Additional strain appeared to exist for additives when the stable TM boride for that metal had different crystal symmetries than ZrB2. This research provided insight into how additives and impurities affect thermal transport in ZrB2. The research potentially offers a basis for future modeling of thermal conductivity in ultra-high temperature ceramics based on the correlation between metallic radius and the decrease in thermal conductivity.

  1. Scientific conferences: A big hello to halogen bonding

    Science.gov (United States)

    Erdelyi, Mate

    2014-09-01

    Halogen bonding connects a wide range of subjects -- from materials science to structural biology, from computation to crystal engineering, and from synthesis to spectroscopy. The 1st International Symposium on Halogen Bonding explored the state of the art in this fast-growing field of research.

  2. Thermophysical Property Measurements of Silicon-Transition Metal Alloys

    Science.gov (United States)

    Banish, R. Michael; Erwin, William R.; Sansoucie, Michael P.; Lee, Jonghyun; Gave, Matthew A.

    2014-01-01

    Metals and metallic alloys often have high melting temperatures and highly reactive liquids. Processing reactive liquids in containers can result in significant contamination and limited undercooling. This is particularly true for molten silicon and it alloys. Silicon is commonly termed "the universal solvent". The viscosity, surface tension, and density of several silicon-transition metal alloys were determined using the Electrostatic Levitator system at the Marshall Space Flight Center. The temperature dependence of the viscosity followed an Arrhenius dependence, and the surface tension followed a linear temperature dependence. The density of the melts, including the undercooled region, showed a linear behavior as well. Viscosity and surface tension values were obtain for several of the alloys in the undercooled region.

  3. Selective C-H Halogenation with a Highly Fluorinated Manganese Porphyrin.

    Science.gov (United States)

    Li, Gang; Dilger, Andrew K; Cheng, Peter T; Ewing, William R; Groves, John T

    2018-01-26

    The selective C-H functionalization of aliphatic molecules remains a challenge in organic synthesis. While radical chain halogenation reactions provide efficient access to many halogenated molecules, the use of typical protocols for the selective halogenation of electron-deficient and strained aliphatic molecules is rare. Herein, we report selective C-H chlorination and fluorination reactions promoted by an electron-deficient manganese pentafluorophenyl porphyrin catalyst, Mn(TPFPP)Cl. This catalyst displays superior properties for the aliphatic halogenation of recalcitrant, electron-deficient, and strained substrates with unique regio- and stereoselectivity. UV/Vis analysis during the course of the reaction indicated that an oxo-Mn V species is responsible for hydrogen-atom abstraction. The observed stereoselectivity results from steric interactions between the bulky porphyrin ligand and the intermediate substrate radical in the halogen rebound step. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Strongly Coupled Magnetic and Electronic Transitions in Multivalent Strontium Cobaltites.

    Science.gov (United States)

    Lee, J H; Choi, Woo Seok; Jeen, H; Lee, H-J; Seo, J H; Nam, J; Yeom, M S; Lee, H N

    2017-11-22

    The topotactic phase transition in SrCoO x (x = 2.5-3.0) makes it possible to reversibly transit between the two distinct phases, i.e. the brownmillerite SrCoO 2.5 that is a room-temperature antiferromagnetic insulator (AFM-I) and the perovskite SrCoO 3 that is a ferromagnetic metal (FM-M), owing to their multiple valence states. For the intermediate x values, the two distinct phases are expected to strongly compete with each other. With oxidation of SrCoO 2.5 , however, it has been conjectured that the magnetic transition is decoupled to the electronic phase transition, i.e., the AFM-to-FM transition occurs before the insulator-to-metal transition (IMT), which is still controversial. Here, we bridge the gap between the two-phase transitions by density-functional theory calculations combined with optical spectroscopy. We confirm that the IMT actually occurs concomitantly with the FM transition near the oxygen content x = 2.75. Strong charge-spin coupling drives the concurrent IMT and AFM-to-FM transition, which fosters the near room-T magnetic transition characteristic. Ultimately, our study demonstrates that SrCoO x is an intriguingly rare candidate for inducing coupled magnetic and electronic transition via fast and reversible redox reactions.

  5. XPS and XAES measurements on trapped rare gases in transition metals

    International Nuclear Information System (INIS)

    Baba, Y.; Yamamoto, H.; Sasaki, T.A.

    1992-01-01

    Electronic structures of rare gases implanted in various transition metals have been investigated by means of an X-ray photoelectron spectroscopy (XPS) and X-ray-induced Auger electron spectroscopy (XAES). The Auger-parameter method is applied to the evaluation of electronic relaxation energy of rare gas atoms due to the surrounding metal potential. The extra-atomic relaxation energy of four kinds of rare gases (Ne, Ar, Kr, Xe) in the same metal matrix (Ti) increases with the atomic mass of the rare gases. On the other hand, the extra-atomic relaxation energy of the same rare gas (Xe) in different metal matrices ranges from 3.0 eV (in Mo). These values increase with the number of d-electrons in the metals. This tendency and the absolute values of the relaxation energies are in good agreement with those calculated for 3d transition metals referenced to their gas-phase values. Based on these results, it is concluded that the energetically implanted rare gases are trapped at the substitution site in the metal lattice as an isolated atom, and the trapped atoms feel the surrounding metal potential. It is also made clear that the potential affecting the implanted atom is d-like, and the relaxation energy of the implanted rare gas during the photoemission process is almost equal to those of the metal itself. (orig.)

  6. Influence of Halogen Substituents on the Catalytic Oxidation of 2,4,6-Halogenated Phenols by Fe(III-Tetrakis(p-hydroxyphenyl porphyrins and Potassium Monopersulfate

    Directory of Open Access Journals (Sweden)

    Seiya Nagao

    2011-12-01

    Full Text Available The influence of halogen substituents on the catalytic oxidation of 2,4,6-trihalogenated phenols (TrXPs by iron(III-porphyrin/KHSO5 catalytic systems was investigated. Iron(III-5,10,15,20-tetrakis(p-hydroxyphenylporphyrin (FeTHP and its supported variants were employed, where the supported catalysts were synthesized by introducing FeTHP into hydroquinone-derived humic acids via formaldehyde poly-condensation. F (TrFP, Cl (TrCP, Br (TrBP and I (TrIP were examined as halogen substituents for TrXPs. Although the supported catalysts significantly enhanced the degradation and dehalogenation of TrFP and TrCP, the oxidation of TrBP and TrIP was not enhanced, compared to the FeTHP catalytic system. These results indicate that the degree of oxidation of TrXPs is strongly dependent on the types of halogen substituent. The order of dehalogenation levels for halogen substituents in TrXPs was F > Cl > Br > I, consistent with their order of electronegativity. The electronegativity of a halogen substituent affects the nucleophilicity of the carbon to which it is attached. The levels of oxidation products in the reaction mixtures were analyzed by GC/MS after extraction with n-hexane. The most abundant dimer product from TrFP via 2,6-difluoroquinone is consistent with a scenario where TrXP, with a more electronegative halogen substituent, is readily oxidized, while less electronegative halogen substituents are oxidized less readily by iron(III-porphyrin/KHSO5 catalytic systems.

  7. The electronic structure and metal-insulator transitions in vanadium oxides

    International Nuclear Information System (INIS)

    Mossanek, Rodrigo Jose Ochekoski

    2010-01-01

    The electronic structure and metal-insulator transitions in vanadium oxides (SrVO_3, CaVO_3, LaVO_3 and YVO_3) are studied here. The purpose is to show a new interpretation to the spectra which is coherent with the changes across the metal-insulator transition. The main experimental techniques are the X-ray photoemission (PES) and X-ray absorption (XAS) spectroscopies. The spectra are interpreted with cluster model, band structure and atomic multiplet calculations. The presence of charge-transfer satellites in the core-level PES spectra showed that these vanadium oxides cannot be classified in the Mott-Hubbard regime. Further, the valence band and core-level spectra presented a similar behavior across the metal insulator transition. In fact, the structures in the spectra and their changes are determined by the different screening channels present in the metallic or insulating phases. The calculated spectral weight showed that the coherent fluctuations dominate the spectra at the Fermi level and give the metallic character to the SrVO_3 and CaVO_3 compounds. The vanishing of this charge fluctuation and the replacement by the Mott-Hubbard screening in the LaVO_3 and YVO_3 systems is ultimately responsible for the opening of a band gap and the insulating character. Further, the correlation effects are, indeed, important to the occupied electronic structure (coherent and incoherent peaks). On the other hand, the unoccupied electronic structure is dominated by exchange and crystal field effects (t2g and eg sub-bands of majority and minority spins). The optical conductivity spectrum was obtained by convoluting the removal and addition states. It showed that the oxygen states, as well as the crystal field and exchange effects are necessary to correctly compare and interpret the experimental results. Further, a correlation at the charge-transfer region of the core-level and valence band optical spectra was observed, which could be extended to other transition metal oxides

  8. A review on transition-metal mediated synthesis of quinolines

    Indian Academy of Sciences (India)

    Rashmi Sharma

    2018-06-14

    Jun 14, 2018 ... Special Section on Transition Metal Catalyzed Synthesis of Medicinally Relevant Molecules. A review on ...... iron(III) chloride and TEMPO oxoammonium salt as an .... propyl-3-ethylquinoline (209) in presence of platinum.

  9. Metal-insulator phase transition in a VO2 thin film observed with terahertz spectroscopy

    DEFF Research Database (Denmark)

    Jepsen, Peter Uhd; Fischer, Bernd M.; Thoman, Andreas

    2006-01-01

    We investigate the dielectric properties of a thin VO2 film in the terahertz frequency range in the vicinity of the semiconductor-metal phase transition. Phase-sensitive broadband spectroscopy in the frequency region below the phonon bands of VO2 gives insight into the conductive properties...... of the film during the phase transition. We compare our experimental data with models proposed for the evolution of the phase transition. The experimental data show that the phase transition occurs via the gradual growth of metallic domains in the film, and that the dielectric properties of the film...

  10. Twisted Amides: From Obscurity to Broadly Useful Transition-Metal-Catalyzed Reactions by N-C Amide Bond Activation.

    Science.gov (United States)

    Liu, Chengwei; Szostak, Michal

    2017-05-29

    The concept of using amide bond distortion to modulate amidic resonance has been known for more than 75 years. Two classic twisted amides (bridged lactams) ingeniously designed and synthesized by Kirby and Stoltz to feature fully perpendicular amide bonds, and as a consequence emanate amino-ketone-like reactivity, are now routinely recognized in all organic chemistry textbooks. However, only recently the use of amide bond twist (distortion) has advanced to the general organic chemistry mainstream enabling a host of highly attractive N-C amide bond cross-coupling reactions of broad synthetic relevance. In this Minireview, we discuss recent progress in this area and present a detailed overview of the prominent role of amide bond destabilization as a driving force in the development of transition-metal-catalyzed cross-coupling reactions by N-C bond activation. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Biomass transition metal hydrogen-evolution electrocatalysts and electrodes

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Wei-Fu; Iyer, Shweta; Iyer, Shilpa; Sasaki, Kotaro; Muckerman, James T.; Fujita, Etsuko

    2017-02-28

    A catalytic composition from earth-abundant transition metal salts and biomass is disclosed. A calcined catalytic composition formed from soybean powder and ammonium molybdate is specifically exemplified herein. Methods for making the catalytic composition are disclosed as are electrodes for hydrogen evolution reactions comprising the catalytic composition.

  12. Transition metal borides. Synthesis, characterization and superconducting properties

    International Nuclear Information System (INIS)

    Kayhan, Mehmet

    2013-01-01

    A systematic study was done on the synthesis and superconducting properties of metal rich transition metal borides. Five different binary systems were investigated including the boride systems of niobium, tantalum, molybdenum, tungsten and rhenium. High temperature solid state methods were used in order to synthesize samples of different transition metal borides of the composition M 2 B, MB, M 3 B 2 , MB 2 , and M 2 B 4 . The reactions were carried out in three different furnaces with different sample containers: the electric arc (copper crucible), the high frequency induction furnace (boron nitride, tantalum or glassy carbon crucibles), and the conventional tube furnace (sealed evacuated quartz ampoules). The products obtained were characterized with X-ray powder diffractometry, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Phase analyses and crystal structure refinements using the Rietveld method and based on structure models known from literature were performed. A neutron diffraction measurement was done for W 2 B 4 to allow for a complete crystal structure determination, because of the presence of a heavy element like tungsten and a light element like boron that made it difficult to determine the accurate determination of the boron atom positions and occupancies from X-ray data. A new structure model for W 2 B 4 was proposed. Magnetic measurements in a SQUID magnetometer down to temperatures as low as 1.8 K were performed to several of the products in order to see if the transition metal borides become superconducting at low temperatures, and the results were compared with data from literature. Superconducting properties were found for the following compounds: NbB 2 (T C = 3.5 K), β-MoB (T C = 2.4 K), β-WB (T C = 2.0 K), α-WB (T C = 4.3 K), W 2 B 4 (T C = 5.4 K), Re 7 B 3 (T C = 2.4 K). A relationship between the superconducting properties and the compositional and structural features was discussed for metal diborides. Also it was

  13. Hard X-ray PhotoElectron Spectroscopy of transition metal oxides: Bulk compounds and device-ready metal-oxide interfaces

    International Nuclear Information System (INIS)

    Borgatti, F.; Torelli, P.; Panaccione, G.

    2016-01-01

    Highlights: • Hard X-ray PhotoElectron Spectroscopy (HAXPES) applied to buried interfaces of systems involving Transition Metal Oxides. • Enhanced contribution of the s states at high kinetic energies both for valence and core level spectra. • Sensitivity to chemical changes promoted by electric field across metal-oxide interfaces in resistive switching devices. - Abstract: Photoelectron spectroscopy is one of the most powerful tool to unravel the electronic structure of strongly correlated materials also thanks to the extremely large dynamic range in energy, coupled to high energy resolution that this form of spectroscopy covers. The kinetic energy range typically used for photoelectron experiments corresponds often to a strong surface sensitivity, and this turns out to be a disadvantage for the study of transition metal oxides, systems where structural and electronic reconstruction, different oxidation state, and electronic correlation may significantly vary at the surface. We report here selected Hard X-ray PhotoElectron Spectroscopy (HAXPES) results from transition metal oxides, and from buried interfaces, where we highlight some of the important features that such bulk sensitive technique brings in the analysis of electronic properties of the solids.

  14. Hard X-ray PhotoElectron Spectroscopy of transition metal oxides: Bulk compounds and device-ready metal-oxide interfaces

    Energy Technology Data Exchange (ETDEWEB)

    Borgatti, F., E-mail: francesco.borgatti@cnr.it [Istituto per lo Studio dei Materiali Nanostrutturati (ISMN), Consiglio Nazionale delle Ricerche (CNR), via P. Gobetti 101, Bologna I-40129 (Italy); Torelli, P.; Panaccione, G. [Istituto Officina dei Materiali (IOM)-CNR, Laboratorio TASC, Area Science Park, Trieste I-34149 (Italy)

    2016-04-15

    Highlights: • Hard X-ray PhotoElectron Spectroscopy (HAXPES) applied to buried interfaces of systems involving Transition Metal Oxides. • Enhanced contribution of the s states at high kinetic energies both for valence and core level spectra. • Sensitivity to chemical changes promoted by electric field across metal-oxide interfaces in resistive switching devices. - Abstract: Photoelectron spectroscopy is one of the most powerful tool to unravel the electronic structure of strongly correlated materials also thanks to the extremely large dynamic range in energy, coupled to high energy resolution that this form of spectroscopy covers. The kinetic energy range typically used for photoelectron experiments corresponds often to a strong surface sensitivity, and this turns out to be a disadvantage for the study of transition metal oxides, systems where structural and electronic reconstruction, different oxidation state, and electronic correlation may significantly vary at the surface. We report here selected Hard X-ray PhotoElectron Spectroscopy (HAXPES) results from transition metal oxides, and from buried interfaces, where we highlight some of the important features that such bulk sensitive technique brings in the analysis of electronic properties of the solids.

  15. He–He and He–metal interactions in transition metals from first-principles

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Pengbo, E-mail: zhangpb@dlmu.edu.cn [Department of Physics, Dalian Maritime University, Dalian 116026 (China); Zou, Tingting [Information Science and Technology College, Dalian Maritime University, Dalian 116026 (China); Zhao, Jijun, E-mail: zhaojj@dlut.edu.cn [Key Laboratory of Materials Modification by Laser, Ion and Electron Beams (Dalian University of Technology), Ministry of Education, Dalian 116024 (China)

    2015-12-15

    We investigated the atomistic mechanism of He–He and He–metal interactions in bcc transition metals (V, Nb, Ta, Cr, Mo, W, and Fe) using first-principles methods. We calculated formation energy and binding energy of He–He pair as function of distance within the host lattices. The strengths of He–He attraction in Cr, Mo, W, and Fe (0.37–1.11 eV) are significantly stronger than those in V, Nb, and Ta (0.06–0.17 eV). Such strong attractions mean that He atoms would spontaneously aggregate inside perfect Cr, Mo, W, and Fe host lattices in absence of defects like vacancies. The most stable configuration of He–He pair is <100> dumbbell in groups VB metals, whereas it adopts close <110> configuration in Cr, Mo, and Fe, and close <111> configuration in W. Overall speaking, the He–He equilibrium distances of 1.51–1.55 Å in the group VIB metals are shorter than 1.65–1.70 Å in the group VB metals. Moreover, the presence of interstitial He significantly facilitates vacancy formation and this effect is more pronounced in the group VIB metals. The present calculations help understand the He-metal/He–He interaction mechanism and make a prediction that He is easier to form He cluster and bubbles in the groups VIB metals and Fe.

  16. Kinetics of self-interstitial migration in bcc and fcc transition metals

    Science.gov (United States)

    Bukkuru, S.; Bhardwaj, U.; Srinivasa Rao, K.; Rao, A. D. P.; Warrier, M.; Valsakumar, M. C.

    2018-03-01

    Radiation damage is a multi-scale phenomenon. A thorough understanding of diffusivities and the migration energies of defects is a pre-requisite to quantify the after-effects of irradiation. We investigate the thermally activated mobility of self-interstitial atom (SIA) in bcc transition metals Fe, Mo, Nb and fcc transition metals Ag, Cu, Ni, Pt using molecular dynamics (MD) simulations. The self-interstitial diffusion involves various mechanisms such as interstitialcy, dumbbell or crowdion mechanisms. Max-Space Clustering (MSC) method has been employed to identify the interstitial and its configuration over a wide range of temperature. The self-interstitial diffusion is Arrhenius like, however, there is a slight deviation at high temperatures. The migration energies, pre-exponential factors of diffusion and jump-correlation factors, obtained from these simulations can be used as inputs to Monte Carlo simulations of defect transport. The jump-correlation factor shows the degree of preference of rectilinear or rotational jumps. We obtain the average jump-correlation factor of 1.4 for bcc metals and 0.44 for fcc metals. It indicates that rectilinear jumps are preferred in bcc metals and rotational jumps are preferred in fcc metals.

  17. A review of the success and failure characteristics of resin-bonded bridges.

    Science.gov (United States)

    Miettinen, M; Millar, B J

    2013-07-01

    This literature review was designed to assess and compare the success rates and modes of failure of metal-framed, fibre-reinforced composite and all-ceramic resin-bonded bridges. A Medline search (Ovid), supplemented by hand searching, was conducted to identify prospective and retrospective cohort studies on different resin-bonded bridges within the last 16 years. A total of 49 studies met the pre-set inclusion criteria. Success rates of 25 studies on metal-framed, 17 studies on fibre-reinforced composite and 7 studies on all-ceramic resin-bonded bridges were analysed and characteristics of failures were identified. The analysis of the studies indicated an estimation of annual failure rates per year to be 4.6% (±1.3%, 95% CI) for metal-framed, 4.1% (±2.1%, 95% CI) for fibre-reinforced and 11.7% (±1.8%, 95% CI) for all-ceramic resin-bonded bridges. The most frequent complications were: debonding for metal-framed, resin-bonded bridges (93% of all failures); delamination of the composite veneering material for the fibre-reinforced bridges (41%) and fracture of the framework for the all-ceramic bridges (57%). All types of resin-bonded bridges provide an effective short- to medium-term option, with all-ceramic performing least well and having the least favourable mode of failure. The methods of failures were different for different bridges with metal frameworks performing the best over time.

  18. Heterostructures of transition metal dichalcogenides

    KAUST Repository

    Amin, Bin

    2015-08-24

    The structural, electronic, optical, and photocatalytic properties of out-of-plane and in-plane heterostructures of transition metal dichalcogenides are investigated by (hybrid) first principles calculations. The out-of-plane heterostructures are found to be indirect band gap semiconductors with type-II band alignment. Direct band gaps can be achieved by moderate tensile strain in specific cases. The excitonic peaks show blueshifts as compared to the parent monolayer systems, whereas redshifts occur when the chalcogen atoms are exchanged along the series S-Se-Te. Strong absorption from infrared to visible light as well as excellent photocatalytic properties can be achieved.

  19. Long Spin-Relaxation Times in a Transition-Metal Atom in Direct Contact to a Metal Substrate.

    Science.gov (United States)

    Hermenau, Jan; Ternes, Markus; Steinbrecher, Manuel; Wiesendanger, Roland; Wiebe, Jens

    2018-03-14

    Long spin-relaxation times are a prerequisite for the use of spins in data storage or nanospintronics technologies. An atomic-scale solid-state realization of such a system is the spin of a transition-metal atom adsorbed on a suitable substrate. For the case of a metallic substrate, which enables the direct addressing of the spin by conduction electrons, the experimentally measured lifetimes reported to date are on the order of only hundreds of femtoseconds. Here, we show that the spin states of iron atoms adsorbed directly on a conductive platinum substrate have a surprisingly long spin-relaxation time in the nanosecond regime, which is comparable to that of a transition metal atom decoupled from the substrate electrons by a thin decoupling layer. The combination of long spin-relaxation times and strong coupling to conduction electrons implies the possibility to use flexible coupling schemes to process the spin information.

  20. Transition metal oxide loaded MCM catalysts for photocatalytic ...

    Indian Academy of Sciences (India)

    Transition metal oxide (TiO2, Fe2O3, CoO) loaded MCM-41 and MCM-48 were synthesized by a two-step .... washed consecutively with water and ethanol, and cal- cined at 823 K for 5 .... conversion was observed in 1 h when the reaction was.

  1. Some transition metal complexes derived from mono- and di-ethynyl perfluorobenzenes

    NARCIS (Netherlands)

    Armitt, D.J.; Bruce, M.I.; Gaudio, M.; Zaitseva, N.N.; Skelton, B.W.; White, A.H.; Le Guennic, B.; Halet, J.-F.; Fox, M.A.; Roberts, R.L.; Hartl, F.; Low, P.J.

    2008-01-01

    Transition metal alkynyl complexes containing perfluoroaryl groups have been prepared directly from trimethylsilyl-protected mono- and di-ethynyl perfluoroarenes by simple desilylation/metallation reaction sequences. Reactions between Me3SiC CC6F5 and RuCl(dppe)Cp'[Cp' = Cp, Cp*] in the presence of

  2. First-principles studies on 3d transition metal atom adsorbed twin graphene

    Science.gov (United States)

    Li, Lele; Zhang, Hong; Cheng, Xinlu; Miyamoto, Yoshiyuki

    2018-05-01

    Twin graphene is a new two-dimensional semiconducting carbon allotrope which is proposed recently. The structural, magnetic and electronic properties are investigated for 3d transition metal (TM) atom adsorbed twin graphene by means of GGA+U calculations. The results show most of single 3d transition metal atom except Zn can make twin graphene magnetization. The adsorption of single TM atom can also make the twin graphene systems turn to half metal (V adsorption), half-semiconductor (Fe adsorption) or metal (Sc, Cr, Mn, Co and Cu adsorption). The semiconducting nature still exists for Ti, Ni and Zn adsorption. All the 3d TM adatoms belong to n-type doping for transferring charge to the neighboring C atoms and have strong covalent bond with these C atoms. The influence of Hubbard U value on half-metallic V adsorbed system is also considered. As the U increases, the system can gradually transform from metal to half metal and metal. The effect of the coverage is investigated for two TM atoms (Sc-Fe) adsorption, too. We can know TM atoms adsorbed twin graphene have potentials to be spintronic device and nanomagnets from the results.

  3. Magnetic phase transition induced by electrostatic gating in two-dimensional square metal-organic frameworks

    Science.gov (United States)

    Wang, Yun-Peng; Li, Xiang-Guo; Liu, Shuang-Long; Fry, James N.; Cheng, Hai-Ping

    2018-03-01

    We investigate theoretically magnetism and magnetic phase transitions induced by electrostatic gating of two-dimensional square metal-organic framework compounds. We find that electrostatic gating can induce phase transitions between homogeneous ferromagnetic and various spin-textured antiferromagnetic states. Electronic structure and Wannier function analysis can reveal hybridizations between transition-metal d orbitals and conjugated π orbitals in the organic framework. Mn-containing compounds exhibit a strong d -π hybridization that leads to partially occupied spin-minority bands, in contrast to compounds containing transition-metal ions other than Mn, for which electronic structure around the Fermi energy is only slightly spin split due to weak d -π hybridization and the magnetic interaction is of the Ruderman-Kittel-Kasuya-Yosida type. We use a ferromagnetic Kondo lattice model to understand the phase transition in Mn-containing compounds in terms of carrier density and illuminate the complexity and the potential to control two-dimensional magnetization.

  4. Recent advances in transition-metal-catalyzed intermolecular carbomagnesiation and carbozincation

    Directory of Open Access Journals (Sweden)

    Kei Murakami

    2013-02-01

    Full Text Available Carbomagnesiation and carbozincation reactions are efficient and direct routes to prepare complex and stereodefined organomagnesium and organozinc reagents. However, carbon–carbon unsaturated bonds are generally unreactive toward organomagnesium and organozinc reagents. Thus, transition metals were employed to accomplish the carbometalation involving wide varieties of substrates and reagents. Recent advances of transition-metal-catalyzed carbomagnesiation and carbozincation reactions are reviewed in this article. The contents are separated into five sections: carbomagnesiation and carbozincation of (1 alkynes bearing an electron-withdrawing group; (2 alkynes bearing a directing group; (3 strained cyclopropenes; (4 unactivated alkynes or alkenes; and (5 substrates that have two carbon–carbon unsaturated bonds (allenes, dienes, enynes, or diynes.

  5. Systematic prediction of high-pressure melting curves of transition metals

    International Nuclear Information System (INIS)

    Hieu, Ho Khac

    2014-01-01

    The pressure effects on melting temperatures of transition metals have been studied based on the combination of the modified Lindemann criterion with statistical moment method in quantum statistical mechanics. Numerical calculations have been performed for five transition metals including Cu, Pd, Pt, Ni, and Mn up to pressure 100 GPa. Our results are in good and reasonable agreements with available experimental data. This approach gives us a relatively simple method for qualitatively calculating high-pressure melting temperature. Moreover, it can be used to verify future experimental and theoretical works. This research proposes the potential of the combination of statistical moment method and the modified Lindemann criterion on predicting high-pressure melting of materials.

  6. Transition-metal interactions in aluminum-rich intermetallics

    International Nuclear Information System (INIS)

    Al-Lehyani, Ibrahim; Widom, Mike; Wang, Yang; Moghadam, Nassrin; Stocks, G. Malcolm; Moriarty, John A.

    2001-01-01

    The extension of the first-principles generalized pseudopotential theory (GPT) to transition-metal (TM) aluminides produces pair and many-body interactions that allow efficient calculations of total energies. In aluminum-rich systems treated at the pair-potential level, one practical limitation is a transition-metal overbinding that creates an unrealistic TM-TM attraction at short separations in the absence of balancing many-body contributions. Even with this limitation, the GPT pair potentials have been used effectively in total-energy calculations for Al-TM systems with TM atoms at separations greater than 4 Aa. An additional potential term may be added for systems with shorter TM atom separations, formally folding repulsive contributions of the three- and higher-body interactions into the pair potentials, resulting in structure-dependent TM-TM potentials. Towards this end, we have performed numerical ab initio total-energy calculations using the Vienna ab initio simulation package for an Al-Co-Ni compound in a particular quasicrystalline approximant structure. The results allow us to fit a short-ranged, many-body correction of the form a(r 0 /r) b to the GPT pair potentials for Co-Co, Co-Ni, and Ni-Ni interactions

  7. Physical properties of Pd and Al transition metals and Pd-Al binary metal alloy investigated by using molecular dynamics simulation

    International Nuclear Information System (INIS)

    Coruh, A.; Uludogan, M.; Tomak, M.; Cagin, T.

    2002-01-01

    In this study, physical properties, such as Pair Distribution Function g(r), Structure Factor S(k)''1'',''4, Diffusion Coefficient D''2''.''4, Intermediate Scattering function S(k,t)''3'',''4 and Dynamical Structure Factor S(k,w)''3'',''4 of some transition metals and metal alloys are investigated by using molecular dynamics simulation method. The simulation is specified for Pd, Al transition metals and Pd-Al binary metal alloys in the liquid form for different concentrations and at various temperatures by using Quantum Sutton-Chen (Q-SC) inter atomic potential. Intermediate scattering function and dynamical structure factor are calculated for various values of wave vector k. Results are in good agreement with published data''1'',''3'',''4

  8. Correlation between physical properties and ultrasonic relaxation parameters in transition metal tellurite glasses

    Science.gov (United States)

    Abd El-Moneim, A.

    2003-07-01

    The correlation between activation energy of ultrasonic relaxation process through the temperature range from 140 to 300 K and some physical properties has been investigated in pure TeO 2 and transition metal TeO 2-V 2O 5 and TeO 2-MoO 3 glasses according to Bridge and Patel's theory. The oxygen density (loss centers), number of two-well systems, hopping distance and mechanical relaxation time have been calculated in these glasses from the data of density, bulk modulus and stretching force constant of the glass. It has been found that the acoustic activation energy increased linearly with both the oxygen density and the number of two-well systems. The correlation between the acoustic activation energy and bulk modulus was achieved through the stretching force constant of the network and other structural parameters. Moreover, the experimental values of activation energy (V) agree well with those calculated from an empirical equation presented in this study in the form V=2.9×10 -7 F( F/ K) 3.37, where F is the stretching force constant of the glass and K is the experimental bulk modulus.

  9. PRODUCTION OF HAFNIUM METAL

    Science.gov (United States)

    Elger, G.W.; Boubel, R.W.

    1963-01-01

    This patent deals with a process of producing pure Hf metal from oxygen- contaminated gaseous Hf chloride. The oxygen compounds in the chioride gas are halogenated by contacting the gas at elevated temperature with Cl/sub 2/ in the presence of C. The Hf chloride, still in gaseous form, is contacted with molten Mg whereby Hf metal is formed and condensed on the Mg. (AEC)

  10. Insulator-metal transition of fluid molecular hydrogen

    International Nuclear Information System (INIS)

    Ross, M.

    1996-01-01

    Dynamically compressed fluid hydrogen shows evidence for metallization at the relatively low pressure of 140 GPa (1.4 Mbar) while experiments on solid hydrogen made in a diamond-anvil cell have failed to detect any evidence for gap closure up to a pressure of 230 GPa (2.3 Mbar). Two possible mechanisms for metal- liclike resistivity are put forward. The first is that as a consequence of the large thermal disorder in the fluid (kT∼0.2 endash 0.3 eV) short-range molecular interactions lead to band tailing that extends the band edge into the gap, resulting in closure at a lower pressure than in the solid. The second mechanism argues that molecular dissociation creates H atoms that behave similar to n-type donors in a heavily doped semiconductor and undergo a nonmetal-metal Mott-type transition. copyright 1996 The American Physical Society

  11. Quantum-based Atomistic Simulation of Transition Metals

    International Nuclear Information System (INIS)

    Moriarty, J A; Benedict, L X; Glosli, J N; Hood, R Q; Orlikowski, D A; Patel, M V; Soderlind, P; Streitz, F H; Tang, M; Yang, L H

    2005-01-01

    First-principles generalized pseudopotential theory (GPT) provides a fundamental basis for transferable multi-ion interatomic potentials in d-electron transition metals within density-functional quantum mechanics. In mid-period bcc metals, where multi-ion angular forces are important to structural properties, simplified model GPT or MGPT potentials have been developed based on canonical d bands to allow analytic forms and large-scale atomistic simulations. Robust, advanced-generation MGPT potentials have now been obtained for Ta and Mo and successfully applied to a wide range of structural, thermodynamic, defect and mechanical properties at both ambient and extreme conditions of pressure and temperature. Recent algorithm improvements have also led to a more general matrix representation of MGPT beyond canonical bands allowing increased accuracy and extension to f-electron actinide metals, an order of magnitude increase in computational speed, and the current development of temperature-dependent potentials

  12. TRANSITION METAL TRANSPORT IN PLANTS AND ASSOCIATED ENDOSYMBIONTS: ARBUSCULAR MYCORRHIZAL FUNGI AND RHIZOBIA

    Directory of Open Access Journals (Sweden)

    Manuel González-Guerrero

    2016-07-01

    Full Text Available Transition metals such as iron, copper, zinc, or molybdenum, are essential nutrients for plants. These elements are involved in almost every biological process, including photosynthesis, tolerance to biotic and abiotic stress, or symbiotic nitrogen fixation. However, plants often grow in soils with limiting metallic oligonutrient bioavailability. Consequently, to ensure the proper metal levels, plants have developed a complex metal uptake and distribution system, that not only involves the plant itself, but also its associated microorganisms. These microorganisms can simply increase metal solubility in soils and making them more accessible to the host plant, as well as induce the plant metal deficiency response, or deliver directly transition elements to cortical cells. Other, instead of providing metals can act as metal sinks, such as endosymbiotic rhizobia in legume nodules that requires relatively large amounts to carry out nitrogen fixation. In this review, we propose to do an overview of metal transport mechanisms in the plant-microbe system, emphasizing the role of arbuscular mycorrhizal fungi and endosymbiotic rhizobia.

  13. Determination of Surface Properties of Liquid Transition Metals

    International Nuclear Information System (INIS)

    Korkmaz, S. D.

    2008-01-01

    Certain surface properties of liquid simple metals are reported. Using the expression derived by Gosh and coworkers we investigated the surface entropy of liquid transition metals namely Fe, Co and Ni. We have also computed surface tensions of the metals concerned. The pair distribution functions are calculated from the solution of Ornstein-Zernike integral equation with Rogers-Young closure using the individual version of the electron-ion potential proposed by Fioalhais and coworkers which was originally developed for solid state. The predicted values of surface tension and surface entropy are in very good agreement with available experimental data. The present study results show that the expression derived by Gosh and coworkers is very useful for the surface entropy by using Fioalhais pseudopotential and Rogers-Young closure

  14. Relationship between thermal expansion coefficient and glass transition temperature in metallic glasses

    International Nuclear Information System (INIS)

    Kato, H.; Chen, H.-S.; Inoue, A.

    2008-01-01

    The thermal expansion coefficients of 13 metallic glasses were measured using a thermo-mechanical analyser. A unique correlation was found between the linear thermal expansion coefficient and the glass transition temperature-their product is nearly constant ∼8.24 x 10 -3 . If one assumes the Debye expression for thermal activation, the total linear thermal expansion up to glass transition temperature (T g ) is reduced to 6 x 10 -3 , nearly 25% of that at the fusion of pure metals

  15. On the valence state of Yb and Ce in transition metal intermetallic compounds

    International Nuclear Information System (INIS)

    Boer, F.R. de; Dijkman, W.H.; Mattens, W.C.M.

    1979-01-01

    In the pure state Yb is a divalent metal, similar to Ca; in alloys it can become trivalent like the majority of the rare earth metals. Using a value of 38 kJ (mol Yb) -1 for the energy difference between divalent and trivalent Yb metal and using model calculations for the heat of formation of intermetallic compounds, the authors are able to account for the existing information on the valence state of Yb in transition metal compounds. A similar analysis of compounds of Ce with transition metals shows that a model in which the 4f electron is treated as a core electron, i.e. being absent in the tetravalent modification of Ce and present as a fully localized electron in trivalent Ce, does not apply. (Auth.)

  16. Rare-earth transition-metal intermetallics: Structure-bonding-property relationships

    Energy Technology Data Exchange (ETDEWEB)

    Han, M. K. [Iowa State Univ., Ames, IA (United States)

    2006-01-01

    The explorations of rare-earth, transition metal intermetallics have resulted in the synthesis and characterization, and electronic structure investigation, as well as understanding the structure-bonding property relationships. The work has presented the following results: (1) Understanding the relationship between compositions and properties in LaFe13-xSix system: A detailed structural and theoretical investigation provided the understanding of the role of a third element on stabilizing the structure and controlling the transformation of cubic NaZn{sub 13}-type structures to the tetragonal derivative, as well as the relationship between the structures and properties. (2) Synthesis of new ternary rare-earth iron silicides Re2-xFe4Si14-y and proposed superstructure: This compound offers complex structural challenges such as fractional occupancies and their ordering in superstructure. (3) Electronic structure calculation of FeSi2: This shows that the metal-semiconductor phase transition depends on the structure. The mechanism of band gap opening is described in terms of bonding and structural distortion. This result shows that the electronic structure calculations are an essential tool for understanding the relationship between structure and chemical bonding in these compounds. (4) Synthesis of new ternary rare-earth Zinc aluminides Tb3Zn3.6Al7.4: Partially ordered structure of Tb3Zn3.6Al7.4 compound provides new insights into the formation, composition and structure of rare-earth transition-metal intermetallics. Electronic structure calculations attribute the observed composition to optimizing metal-metal bonding in the electronegative (Zn, Al) framework, while the specific ordering is strongly influenced by specific orbital interactions. (5) Synthesis of new structure type of Zn39(CrxAl1-x)81

  17. Rare-Earth Transition-Metal Intermetallics: Structure-bonding-Property Relationships

    Energy Technology Data Exchange (ETDEWEB)

    Han, Mi-Kyung [Iowa State Univ., Ames, IA (United States)

    2006-01-01

    Our explorations of rare-earth, transition metal intermetallics have resulted in the synthesis and characterization, and electronic structure investigation, as well as understanding the structure-bonding-property relationships. Our work has presented the following results: (1) Understanding the relationship between compositions and properties in LaFe13-xSix system: A detailed structural and theoretical investigation provided the understanding of the role of a third element on stabilizing the structure and controlling the transformation of cubic NaZn13-type structures to the tetragonal derivative, as well as the relationship between the structures and properties. (2) Synthesis of new ternary rare-earth iron silicides RE2-xFe4Si14-y and proposed superstructure: This compound offers complex structural challenges such as fractional occupancies and their ordering in superstructure. (3) Electronic structure calculation of FeSi2: This shows that the metal-semiconductor phase transition depends on the structure. The mechanism of band gap opening is described in terms of bonding and structural distortion. This result shows that the electronic structure calculations are an essential tool for understanding the relationship between structure and chemical bonding in these compounds. (4) Synthesis of new ternary rare-earth Zinc aluminides Tb3Zn3.6Al7.4: Partially ordered structure of Tb3.6Zn13-xAl7.4 compound provides new insights into the formation, composition and structure of rare-earth transition-metal intermetallics. Electronic structure calculations attribute the observed composition to optimizing metal-metal bonding in the electronegative (Zn, Al) framework, while the specific ordering is strongly influenced by specific orbital interactions. (5) Synthesis of new structure type of Zn39(CrxAl1-x

  18. Optical properties of bcc d-transition metals

    Energy Technology Data Exchange (ETDEWEB)

    Kirillova, M M; Nomerovannaya, L V [AN SSSR, Sverdlovsk. Inst. Fiziki Metallov

    1978-04-01

    The optical properties of a niobium monocrystal in the spectral range of h..nu..=4.66 - 0.069 eV have been studied using the polarimetry method. The obtained results have been discussed on the basis of the zone calculations of the density of electron states for Nb and other isostructural metals of the 5 and 6 groups (Y, Ta, Cr, Mo, W). The existence of an intense low energy interband absorption in niobium in the range of h..nu..<0.1 eV is shown experimentally. The influence of the gapless and low-energy interzone transitions on the evaluations of the plasma and relaxation frequencies of conductivity electrons of d metals is discussed.

  19. Magnetic properties of zigzag (0,9 GaAs nanotube doped with 3d transition metals

    Directory of Open Access Journals (Sweden)

    R Fathi

    2016-06-01

    Full Text Available of 3d transition metals (Sc, Ti, Cr, Mn , Fe, Co, Ni in both far and close situations were studied based on spin polarised density functional theory using the generalized gradient approximation (LDA with SIESTA code. The electronic structures show that zigzag (0,9 GaAs nanotubes are non-magnetic semiconductors with direct band gap. It was revealed that doping of 11.11 % Fe and Mn concentrations substituted in Ga sites in ferromagnetic phase in far situation and Cr sites in ferromagnetic phase in near situation introduces half metallic behavior with %100 spin polarization. The unique structure of spin polarised energy levels is primarily attributed to strong hybridization of 3d transition metal and its nearest-neighbor As-4p orbitals. The results of this study can be useful for empirical studies on diluted magnetic semiconductors (DMSs and systemic investigation in 3d transitional metals. We suggest that GaAs nanotubes doped by transition metals would have a potential application as a spin polarised electron source for spintronic devices in the future.

  20. Studies of hyperfine magnetic fields in transition metals by radioactive ion implantation

    International Nuclear Information System (INIS)

    Kawase, Yoichi; Uehara, Shin-ichi; Nasu, Saburo; Ni Xinbo.

    1994-01-01

    In order to investigate hyperfine magnetic fields in transition metals by a time-differential perturbed angular correlation (TDPAC) technique, radioactive probes of 140 Cs obtained by KUR-ISOL have been implanted on transition metals of Fe, Ni and Co. Lamor precessions of 140 Ce used as a probe nucleus have been observed clearly and the hyperfine fields have been determined precisely corresponding to implanted sites in host metal. The irradiation effects caused by implantation have been examined by annealing the irradiated specimen at about 723 K. Some of the Lamor precessions have disappeared by the annealing. Discussions have been made on the occupied sites after implantation and the recovery process of induced damages by annealing. (author)

  1. Standard entropy for borides of non-transition metals, rare-earth metals and actinides

    International Nuclear Information System (INIS)

    Borovikova, M.S.

    1986-01-01

    Using as initial data the most reliable values of standard entropy for 10 compounds, the entropies for 40 compounds of non-transition metals, rare-earth metals and actinides have been evaluated by the method of comparative calculation. Taking into account the features of boride structures, two methods, i.e. additive and proportional, have been selected for the entropy calculations. For the range of borides the entropies were calculated from the linear relation of the latter to the number of boron atoms in the boride. For borides of rare-earth metals allowance has been made for magnetic contributions in conformity with the multiplicity of the corresponding ions. Insignificant differences in the electronic contributions to the entropy for borides and metals have been neglected. For dodecaborides only the additive method has been used. This is specified by the most rigid network that provides the same contribution to compound entropy. (orig.)

  2. Transition-Metal-Controlled Inorganic Ligand-Supported Non-Precious Metal Catalysts for the Aerobic Oxidation of Amines to Imines.

    Science.gov (United States)

    Yu, Han; Zhai, Yongyan; Dai, Guoyong; Ru, Shi; Han, Sheng; Wei, Yongge

    2017-10-09

    Most state-of-art transition-metal catalysts usually require organic ligands, which are essential for controlling the reactivity and selectivity of reactions catalyzed by transition metals. However, organic ligands often suffer from severe problems including cost, toxicity, air/moisture sensitivity, and being commercially unavailable. Herein, we show a simple, mild, and efficient aerobic oxidation procedure of amines using inorganic ligand-supported non-precious metal catalysts 1, (NH 4 ) n [MMo 6 O 18 (OH) 6 ] (M=Cu 2+ ; Fe 3+ ; Co 3+ ; Ni 2+ ; Zn 2+ , n=3 or 4), synthesized by a simple one-step method in water at 100 °C, demonstrating that the catalytic activity and selectivity can be significantly improved by changing the central metal atom. In the presence of these catalysts, the catalytic oxidation of primary and secondary amines, as well as the coupling of alcohols and amines, can smoothly proceed to afford various imines with O 2 (1 atm) as the sole oxidant. In particular, the catalysts 1 have transition-metal ion core, and the planar arrangement of the six Mo VI centers at their highest oxidation states around the central heterometal can greatly enhance the Lewis acidity of catalytically active sites, and also enable the electrons in the center to delocalize onto the six edge-sharing MO 6 units, in the same way as ligands in traditional organometallic complexes. The versatility of this methodology maybe opens a path to catalytic oxidation through inorganic ligand-coordinated metal catalysis. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. MODERN ASPECTS OF BRIDGES MONITORING

    Directory of Open Access Journals (Sweden)

    M. I. Kazakevych

    2007-12-01

    Full Text Available The major concepts of the elaboration and realization of the bridge construction monitoring systemic approach are presented in this paper. The main peculiarity of the bridge monitoring modern aspect is pointed out here, namely, the transition from the demands of providing the reliability to the demands of providing the whole complex of the structure consumer qualities. The criteria of diagnostics of the bridge exploitation reliability as the fundamental aim of monitoring are formulated here.

  4. Construction of Tungsten Halogen, Pulsed LED, and Combined Tungsten Halogen-LED Solar Simulators for Solar Cell I-V Characterization and Electrical Parameters Determination

    Directory of Open Access Journals (Sweden)

    Anon Namin

    2012-01-01

    Full Text Available I-V characterization of solar cells is generally done under natural sunlight or solar simulators operating in either a continuous mode or a pulse mode. Simulators are classified on three features of irradiance, namely, spectral match with respect to air mass 1.5, spatial uniformity, and temporal stability. Commercial solar simulators use Xenon lamps and halogen lamps, whereas LED-based solar simulators are being developed. In this work, we build and test seven simulators for solar cell characterization, namely, one tungsten halogen simulator, four monochromatic (red, green, blue, and white LED simulators, one multicolor LED simulator, and one tungsten halogen-blue LED simulator. The seven simulators provide testing at nonstandard test condition. High irradiance from simulators is obtained by employing elevated supply voltage to tungsten halogen lamps and high pulsing voltages to LEDs. This new approach leads to higher irradiance not previously obtained from tungsten halogen lamps and LEDs. From I-V curves, electrical parameters of solar cell are made and corrected based on methods recommended in the IEC 60891 Standards. Corrected values obtained from non-STC measurements are in good agreement with those obtained from Class AAA solar simulator.

  5. Reactivity of Dinitrogen Bound to Mid- and Late-Transition-Metal Centers

    NARCIS (Netherlands)

    Khoenkhoen, N.; de Bruin, B.; Reek, J.N.H.; Dzik, W.I.

    2015-01-01

    This review presents a comprehensive overview of the reactions of N-2 within the coordination sphere of transition metals of groups 6 to 9. Many of these metals mediate the reaction of N-2 with protons under reductive conditions, which can lead to the (catalytic) formation of ammonia or hydrazine,

  6. Superconductivity Series in Transition Metal Dichalcogenides by Ionic Gating

    NARCIS (Netherlands)

    Shi, Wu; Ye, Jianting; Zhang, Yijin; Suzuki, Ryuji; Yoshida, Masaro; Miyazaki, Jun; Inoue, Naoko; Saito, Yu; Iwasa, Yoshihiro

    2015-01-01

    Functionalities of two-dimensional (2D) crystals based on semiconducting transition metal dichalcogenides (TMDs) have now stemmed from simple field effect transistors (FETs) to a variety of electronic and opto-valleytronic devices, and even to superconductivity. Among them, superconductivity is the

  7. Vibrational properties of vacancy in bcc transition metals using ...

    Indian Academy of Sciences (India)

    The calculated results of the formation entropy of the vacancy compared well with other available ... for Fe, Mo and W transition metals employing a third-neighbour model. ... For the atomic electron density we have chosen a power law: f (r) = fe.

  8. Synthesis and Characterization of the 2-Dimensional Transition Metal Dichalcogenides

    Science.gov (United States)

    Browning, Robert

    In the last 50 years, the semiconductor industry has been scaling the silicon transistor to achieve faster devices, lower power consumption, and improve device performance. Transistor gate dimensions have become so small that short channel effects and gate leakage have become a significant problem. To address these issues, performance enhancement techniques such as strained silicon are used to improve mobility, while new high-k gate dielectric materials replace silicon oxide to reduce gate leakage. At some point the fundamental limit of silicon will be reached and the semiconductor industry will need to find an alternate solution. The advent of graphene led to the discovery of other layered materials such as the transition metal dichalcogenides. These materials have a layered structure similar to graphene and therefore possess some of the same qualities, but unlike graphene, these materials possess sizeable bandgaps between 1-2 eV making them useful for digital electronic applications. Since initially discovered, most of the research on these films has been from mechanically exfoliated flakes, which are easily produced due to the weak van der Waals force binding the layers together. For these materials to be considered for use in mainstream semiconductor technology, methods need to be explored to grow these films uniformly over a large area. In this research, atomic layer deposition (ALD) was employed as the growth technique used to produce large area uniform thin films of several different transition metal dichalcogenides. By optimizing the ALD growth parameters, it is possible to grow high quality films a few to several monolayers thick over a large area with good uniformity. This has been demonstrated and verified using several physical analytical tests such as Raman spectroscopy, photoluminescence, x-ray photoelectron spectroscopy, x-ray diffraction, transmission electron spectroscopy, and scanning electron microscopy, which show that these films possess the

  9. SYNTHESIS AND CHARACTERIZATION OF NEW HALOGENATED CURCUMINOIDS

    Directory of Open Access Journals (Sweden)

    Eugenio Torres

    2013-12-01

    Full Text Available In this work a novel procedure of synthesis of compounds analogues to curcumin with halogens atoms in its structure is described, which can increase its solubility and biological activity. Four halogenated curcuminoids were obtained with great pharmacological interest, none of them reported in literature before. Synthesis was carried out by means of the aldol condensation assisted by microwaves of halogenated aromatic aldehydes and acetylacetona, using morpholine as basic catalyst, in absence of solvent, and the reaction just needed 1 min. The products were purified by treatment of the reaction mixture with methanol under ultrasound irradiation, followed by chromatographic column. All obtained compounds were characterized by infrared spectroscopy, nuclear magnetic resonance, quantitative elementary analysis and high resolution mass spectrometry. The RMN-1H data demonstrate in all structures of synthesized curcuminoids the enol form is the most favored.

  10. Upgrading of heavy crude oil with supported and unsupported transition metals

    Energy Technology Data Exchange (ETDEWEB)

    Nares, H.R.; Schacht-Hernandez, P.; Cabrera-Reyes, M.C.; Ramirez-Garnica, M.; Cazarez-Candia, O. [Instituto Mexicano del Petroleo, Atepehuacan (Mexico)

    2006-07-01

    Heavy crude oil presents many problems such as difficulty in transportation, low processing capacity in refineries, and low mobility through the reservoir due to high viscosity which affects the index of productivity of the wells. Because of these challenges, it is necessary to enhance heavy crude oil, both aboveground and underground. The effects of several metallic oxides used to upgrade heavy crude oil properties were examined in order to increase the mobility of reservoir oil by reducing viscosity and improving the quality of the oil. This can be accomplished by reducing the asphaltene and sulfur contents and increasing the American Petroleum Institute (API) gravity using transition metal supported in alumina and unsupported from transition metals derived from either acetylacetonate or alkylhexanoate in liquid phase homogeneously mixed with heavy crude oil as well as metal transition supported in alumina. KU-H heavy crude oil from the Golf of Mexico was studied. The results were obtained by Simulated Distillation and True Boiling Point (TBP). It was concluded that the use of crude oil thermal hydrocracking allowed the API gravity to increase and considerably reduce the viscosity. As a result, the productivity index in wells was increased. However there is a high formation of coke that could damage the conductivity of the rock and then reduce the potential of oil recovery. 27 refs., 3 tabs., 5 figs.

  11. Ferromagnetic semiconductor-metal transition in heterostructures of electron doped europium monoxide

    Energy Technology Data Exchange (ETDEWEB)

    Stollenwerk, Tobias

    2013-09-15

    In the present work, we develop and solve a self-consistent theory for the description of the simultaneous ferromagnetic semiconductor-metal transition in electron doped Europium monoxide. We investigate two different types of electron doping, Gadolinium impurities and Oxygen vacancies. Besides the conduction band occupation, we can identify low lying spin fluctuations on magnetic impurities as the driving force behind the doping induced enhancement of the Curie temperature. Moreover, we predict the signatures of these magnetic impurities in the spectra of scanning tunneling microscope experiments. By extending the theory to allow for inhomogeneities in one spatial direction, we are able to investigate thin films and heterostructures of Gadolinium doped Europium monoxide. Here, we are able to reproduce the experimentally observed decrease of the Curie temperature with the film thickness. This behavior is attributed to missing coupling partners of the localized 4f moments as well as to an electron depletion at the surface which leads to a reduction of the number of itinerant electrons. By investigating the influence of a metallic substrate onto the phase transition in Gadolinium doped Europium monoxide, we find that the Curie temperature can be increased up to 20%. However, as we show, the underlying mechanism of metal-interface induced charge carrier accumulation is inextricably connected to a suppression of the semiconductor-metal transition.

  12. Ferromagnetic semiconductor-metal transition in heterostructures of electron doped europium monoxide

    International Nuclear Information System (INIS)

    Stollenwerk, Tobias

    2013-09-01

    In the present work, we develop and solve a self-consistent theory for the description of the simultaneous ferromagnetic semiconductor-metal transition in electron doped Europium monoxide. We investigate two different types of electron doping, Gadolinium impurities and Oxygen vacancies. Besides the conduction band occupation, we can identify low lying spin fluctuations on magnetic impurities as the driving force behind the doping induced enhancement of the Curie temperature. Moreover, we predict the signatures of these magnetic impurities in the spectra of scanning tunneling microscope experiments. By extending the theory to allow for inhomogeneities in one spatial direction, we are able to investigate thin films and heterostructures of Gadolinium doped Europium monoxide. Here, we are able to reproduce the experimentally observed decrease of the Curie temperature with the film thickness. This behavior is attributed to missing coupling partners of the localized 4f moments as well as to an electron depletion at the surface which leads to a reduction of the number of itinerant electrons. By investigating the influence of a metallic substrate onto the phase transition in Gadolinium doped Europium monoxide, we find that the Curie temperature can be increased up to 20%. However, as we show, the underlying mechanism of metal-interface induced charge carrier accumulation is inextricably connected to a suppression of the semiconductor-metal transition.

  13. Observing grain boundaries in CVD-grown monolayer transition metal dichalcogenides

    KAUST Repository

    Ly, Thuchue; Chiu, Ming-Hui; Li, Mingyang; Zhao, Jiong; Perello, David J.; Cichocka, Magdalena Ola; Oh, Hyemin; Chae, Sanghoon; Jeong, Hyeyun; Yao, Fei; Li, Lain-Jong; Lee, Young Hee

    2014-01-01

    Two-dimensional monolayer transition metal dichalcogenides (TMdCs), driven by graphene science, revisit optical and electronic properties, which are markedly different from bulk characteristics. These properties are easily modified due

  14. Control of interlayer physics in 2H transition metal dichalcogenides

    Science.gov (United States)

    Wang, Kuang-Chung; Stanev, Teodor K.; Valencia, Daniel; Charles, James; Henning, Alex; Sangwan, Vinod K.; Lahiri, Aritra; Mejia, Daniel; Sarangapani, Prasad; Povolotskyi, Michael; Afzalian, Aryan; Maassen, Jesse; Klimeck, Gerhard; Hersam, Mark C.; Lauhon, Lincoln J.; Stern, Nathaniel P.; Kubis, Tillmann

    2017-12-01

    It is assessed in detail both experimentally and theoretically how the interlayer coupling of transition metal dichalcogenides controls the electronic properties of the respective devices. Gated transition metal dichalcogenide structures show electrons and holes to either localize in individual monolayers, or delocalize beyond multiple layers—depending on the balance between spin-orbit interaction and interlayer hopping. This balance depends on the layer thickness, momentum space symmetry points, and applied gate fields. The design range of this balance, the effective Fermi levels, and all relevant effective masses is analyzed in great detail. A good quantitative agreement of predictions and measurements of the quantum confined Stark effect in gated MoS2 systems unveils intralayer excitons as the major source for the observed photoluminescence.

  15. First-principles study of hydrogen diffusion in transition metal Rhodium

    International Nuclear Information System (INIS)

    Bao, Wulijibilige; Cui, Xin; Wang, Zhi-Ping

    2015-01-01

    In this study, the diffuse pattern and path of hydrogen in transition metal rhodium are investigated by the first-principles calculations. Density functional theory is used to calculate the system energies of hydrogen atom occupying different positions in rhodium crystal lattice. The results indicate that the most stable position of hydrogen atom in rhodium crystal lattice locates at the octahedral interstice, and the tetrahedral interstice is the second stable site. The activation barrier energy for the diffusion of atomic hydrogen in transition metal rhodium is quantified by determining the most favorable path, i.e., the minimum-energy pathway for diffusion, that is the indirect octahedral-tetrahedral-octahedral (O-T-O) pathway, and the activation energy is 0.8345eV

  16. Synthesis of Binary Magnesium-Transition Metal Oxides via Inverse Coprecipitation

    Science.gov (United States)

    Yagi, Shunsuke; Ichikawa, Yuya; Yamada, Ikuya; Doi, Takayuki; Ichitsubo, Tetsu; Matsubara, Eiichiro

    2013-02-01

    Synthesis of binary magnesium-transition metal oxides, MgM2O4 (M: Cr, Mn, Fe, Co) and MgNiO2, was performed by calcination at relatively low temperatures of 500 and 750 °C for 24 h through inverse coprecipitation of carbonate hydroxide precursors. The important roles of the precipitation agent, sodium carbonate, were clarified by considering equilibria in an aqueous solution. The structure parameters of the obtained binary magnesium-transition metal oxide powders, specifically the occupancy of atomic sites, were evaluated from synchrotron X-ray diffraction (XRD) profiles by Rietveld refinement in addition to the magnetic properties at room temperature. The present work provides general guidelines for low-cost and high-volume synthesis of complex oxides, which are easily decomposed at high temperatures.

  17. 40 CFR 721.8900 - Substituted halogenated pyridinol, alkali salt.

    Science.gov (United States)

    2010-07-01

    ..., alkali salt. 721.8900 Section 721.8900 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.8900 Substituted halogenated pyridinol, alkali salt. (a) Chemical... as substituted halogenated pyridinols, alkali salts (PMNs P-88-1271 and P-88-1272) are subject to...

  18. Estimate of throughput of bridge transitions and pipe passages built on minor rivers of piedmont areas of Krasnodar Territory-Russia

    Directory of Open Access Journals (Sweden)

    Bryukhan Fedor

    2018-01-01

    Full Text Available Stability and accident-free operation of engineering road structures including bridge transitions and pipe passages built on mountain rivers mostly depends on a stream regime and lack of obstructions for water flow. Such structures pose a prominent potential hazard being built in piedmont areas of Caucasus Mountains characterized by flash floods and blockage of structures by floating debris, mudflow deposits and wastes of construction. This notwithstanding, the threats caused by these phenomena are poorly studied. The purpose of this study is in estimation of throughput of bridge transitions and pipe passages built on minor rivers of piedmont areas and analysis of hazards caused by floods and obstructions to water flow. The results of calculation of capacities of existing road structures are provided herein. A qualitative assessment of potential emergencies in case of severe flood is also given. A major hazard of possible blockage of waterways that can cause emergency even in regular flood conditions is noted.

  19. LDRD final report on nanocomposite materials based on hydrocarbon-bridged siloxanes

    Energy Technology Data Exchange (ETDEWEB)

    Ulibarri, T.A.; Bates, S.E.; Loy, D.A.; Jamison, G.M.; Emerson, J.A.; Curro, J.G.

    1997-05-01

    Silicones [polydimethylsiloxane (PDMS) polymers] are environmentally safe, nonflammable, weather resistant, thermally stable, low T{sub g} materials which are attractive for general elastomer applications because of their safety and their performance over a wide temperature range. However, PDMS is inherently weak due to its low glass transition temperature (T{sub g}) and lack of stress crystallization. The major goal of this project was to create a family of reinforced elastomers based on silsesquioxane/PDMS networks. Polydimethylsiloxane-based (PDMS) composite materials containing a variety of alkylene-arylene-bridged polysilsesquioxanes were synthesized in order to probe short chain and linkage effects in bimodal polymer networks. Monte Carlo simulations on the alkylene-bridged silsesquioxane/PDMS system predicted that the introduction of the silsesquioxane short chains into the long chain PDMS network would have a significant reinforcing effect on the elastomer. The silsesquioxane-PDMS networks were synthesized and evaluated. Analysis of the mechanical properties of the resulting materials indicated that use of the appropriate silisesquioxane generated materials with greatly enhanced properties. Arylene and activated alkylene systems resulted in materials that showed superior adhesive strength for metal-to-metal adhesion.

  20. Coherent Control of Nanoscale Ballistic Currents in Transition Metal Dichalcogenide ReS2.

    Science.gov (United States)

    Cui, Qiannan; Zhao, Hui

    2015-04-28

    Transition metal dichalcogenides are predicted to outperform traditional semiconductors in ballistic devices with nanoscale channel lengths. So far, experimental studies on charge transport in transition metal dichalcogenides are limited to the diffusive regime. Here we show, using ReS2 as an example, all-optical injection, detection, and coherent control of ballistic currents. By utilizing quantum interference between one-photon and two-photon interband transition pathways, ballistic currents are injected in ReS2 thin film samples by a pair of femtosecond laser pulses. We find that the current decays on an ultrafast time scale, resulting in an electron transport of only a fraction of one nanometer. Following the relaxation of the initially injected momentum, backward motion of the electrons for about 1 ps is observed, driven by the Coulomb force from the oppositely moved holes. We also show that the injected current can be controlled by the phase of the laser pulses. These results demonstrate a new platform to study ballistic transport of nonequilibrium carriers in transition metal dichalcogenides.

  1. The unique role of halogen substituents in the design of modern agrochemicals.

    Science.gov (United States)

    Jeschke, Peter

    2010-01-01

    The past 30 years have witnessed a period of significant expansion in the use of halogenated compounds in the field of agrochemical research and development. The introduction of halogens into active ingredients has become an important concept in the quest for a modern agrochemical with optimal efficacy, environmental safety, user friendliness and economic viability. Outstanding progress has been made, especially in synthetic methods for particular halogen-substituted key intermediates that were previously prohibitively expensive. Interestingly, there has been a rise in the number of commercial products containing 'mixed' halogens, e.g. one or more fluorine, chlorine, bromine or iodine atoms in addition to one or more further halogen atoms. Extrapolation of the current trend indicates that a definite growth is to be expected in fluorine-substituted agrochemicals throughout the twenty-first century. A number of these recently developed agrochemical candidates containing halogen substituents represent novel classes of chemical compounds with new modes of action. However, the complex structure-activity relationships associated with biologically active molecules mean that the introduction of halogens can lead to either an increase or a decrease in the efficacy of a compound, depending on its changed mode of action, physicochemical properties, target interaction or metabolic susceptibility and transformation. In spite of modern design concepts, it is still difficult to predict the sites in a molecule at which halogen substitution will result in optimal desired effects. This review describes comprehensively the successful utilisation of halogens and their unique role in the design of modern agrochemicals, exemplified by various commercial products from Bayer CropScience coming from different agrochemical areas.

  2. Brittle-to-Ductile Transition in Metallic Glass Nanowires.

    Science.gov (United States)

    Şopu, D; Foroughi, A; Stoica, M; Eckert, J

    2016-07-13

    When reducing the size of metallic glass samples down to the nanoscale regime, experimental studies on the plasticity under uniaxial tension show a wide range of failure modes ranging from brittle to ductile ones. Simulations on the deformation behavior of nanoscaled metallic glasses report an unusual extended strain softening and are not able to reproduce the brittle-like fracture deformation as found in experiments. Using large-scale molecular dynamics simulations we provide an atomistic understanding of the deformation mechanisms of metallic glass nanowires and differentiate the extrinsic size effects and aspect ratio contribution to plasticity. A model for predicting the critical nanowire aspect ratio for the ductile-to-brittle transition is developed. Furthermore, the structure of brittle nanowires can be tuned to a softer phase characterized by a defective short-range order and an excess free volume upon systematic structural rejuvenation, leading to enhanced tensile ductility. The presented results shed light on the fundamental deformation mechanisms of nanoscaled metallic glasses and demarcate ductile and catastrophic failure.

  3. Transition metal borides. Synthesis, characterization and superconducting properties

    Energy Technology Data Exchange (ETDEWEB)

    Kayhan, Mehmet

    2013-07-12

    A systematic study was done on the synthesis and superconducting properties of metal rich transition metal borides. Five different binary systems were investigated including the boride systems of niobium, tantalum, molybdenum, tungsten and rhenium. High temperature solid state methods were used in order to synthesize samples of different transition metal borides of the composition M{sub 2}B, MB, M{sub 3}B{sub 2}, MB{sub 2}, and M{sub 2}B{sub 4}. The reactions were carried out in three different furnaces with different sample containers: the electric arc (copper crucible), the high frequency induction furnace (boron nitride, tantalum or glassy carbon crucibles), and the conventional tube furnace (sealed evacuated quartz ampoules). The products obtained were characterized with X-ray powder diffractometry, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Phase analyses and crystal structure refinements using the Rietveld method and based on structure models known from literature were performed. A neutron diffraction measurement was done for W{sub 2}B{sub 4} to allow for a complete crystal structure determination, because of the presence of a heavy element like tungsten and a light element like boron that made it difficult to determine the accurate determination of the boron atom positions and occupancies from X-ray data. A new structure model for W{sub 2}B{sub 4} was proposed. Magnetic measurements in a SQUID magnetometer down to temperatures as low as 1.8 K were performed to several of the products in order to see if the transition metal borides become superconducting at low temperatures, and the results were compared with data from literature. Superconducting properties were found for the following compounds: NbB{sub 2} (T{sub C} = 3.5 K), β-MoB (T{sub C} = 2.4 K), β-WB (T{sub C} = 2.0 K), α-WB (T{sub C} = 4.3 K), W{sub 2}B{sub 4} (T{sub C} = 5.4 K), Re{sub 7}B{sub 3} (T{sub C} = 2.4 K). A relationship between the superconducting properties

  4. Special features of self-compensation of halogen donor action in lead telluride

    International Nuclear Information System (INIS)

    Kajdanov, V.I.; Nemov, S.A.; Ravich, Yu.I.; Dereza, A.Yu.

    1985-01-01

    Specific features of self-compensation of halogen donor action in lead telluride are investigasted. Lead telluride samples with chlorine additions (with tellurium excess) and, besides, with bromine- and iodine additions were studied in order to reveal general regularities in alloyind with all halogen donor impurities. Experimental dependences of the difference between the electron and hole concentrations (n-p) in PbTe as a function of an amount of introduced halogen impurities (Ni) are presented for samples with a maximum compensation at 295 K. General features of the n-p=f(Ni) dependence are presented for all halogens. The hypothesis on the kinetic mechanism of increasing the efficiency of self-compensation of halogen donor action in lead telluride is suggested

  5. Designer Shape Anisotropy on Transition-Metal-Dichalcogenide Nanosheets.

    Science.gov (United States)

    Martella, Christian; Mennucci, Carlo; Lamperti, Alessio; Cappelluti, Emmanuele; de Mongeot, Francesco Buatier; Molle, Alessandro

    2018-03-01

    MoS 2 and generally speaking, the wide family of transition-metal dichalcogenides represents a solid nanotechnology platform on which to engineer a wealth of new and outperforming applications involving 2D materials. An even richer flexibility can be gained by extrinsically inducing an in-plane shape anisotropy of the nanosheets. Here, the synthesis of anisotropic MoS 2 nanosheets is proposed as a prototypical example in this respect starting from a highly conformal chemical vapor deposition on prepatterend substrates and aiming at the more general purpose of tailoring anisotropy of 2D nanosheets by design. This is envisioned to be a suitable configuration for strain engineering as far as strain can be spatially redistributed in morphologically different regions. With a similar approach, both the optical and electronic properties of the 2D transition-metal dichalcogenides can be tailored over macroscopic sample areas in a self-organized fashion, thus paving the way for new applications in the field of optical metasurfaces, light harvesting, and catalysis. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Mott metal-insulator transition in the doped Hubbard-Holstein model

    Science.gov (United States)

    Kurdestany, Jamshid Moradi; Satpathy, S.

    2017-08-01

    Motivated by the current interest in the understanding of the Mott insulators away from half-filling, observed in many perovskite oxides, we study the Mott metal-insulator transition in the doped Hubbard-Holstein model using the Hartree-Fock mean field theory. The Hubbard-Holstein model is the simplest model containing both the Coulomb and the electron-lattice interactions, which are important ingredients in the physics of the perovskite oxides. In contrast to the half-filled Hubbard model, which always results in a single phase (either metallic or insulating), our results show that away from half-filling, a mixed phase of metallic and insulating regions occurs. As the dopant concentration is increased, the metallic part progressively grows in volume, until it exceeds the percolation threshold, leading to percolative conduction. This happens above a critical dopant concentration δc, which, depending on the strength of the electron-lattice interaction, can be a significant fraction of unity. This means that the material could be insulating even for a substantial amount of doping, in contrast to the expectation that doped holes would destroy the insulating behavior of the half-filled Hubbard model. While effects of fluctuation beyond the mean field remain an open question, our results provide a starting point for the understanding of the density-driven metal-insulator transition observed in many complex oxides.

  7. Ab-initio vibrational properties of transition metal chalcopyrite alloys determined as high-efficiency intermediate-band photovoltaic materials

    International Nuclear Information System (INIS)

    Palacios, P.; Aguilera, I.; Wahnon, P.

    2008-01-01

    In this work, we present frozen phonon and linear response ab-initio research into the vibrational properties of the CuGaS 2 chalcopyrite and transition metal substituted (CuGaS 2 )M alloys. These systems are potential candidates for developing a novel solar-cell material with enhanced optoelectronic properties based in the implementation of the intermediate-band concept. We have previously carried out ab-initio calculations of the electronic properties of these kinds of chalcopyrite metal alloys showing a narrow transition metal band isolated in the semiconductor band gap. The substitutes used in the present work are the 3d metal elements, Titanium and Chromium. For the theoretical calculations we use standard density functional theory at local density and generalized gradient approximation levels. We found that the optical phonon branches of the transition metal chalcopyrite, are very sensitive to the specific bonding geometry and small changes in the transition metal environment

  8. Spectrographic determination of traces of halogens; Dosage de traces d'halogenes par la methode spectrographique

    Energy Technology Data Exchange (ETDEWEB)

    Melamed, J [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

    1961-07-01

    Hollow cathode source is employed for determining traces of halogens (fluorine - chlorine) in the uranium oxide U{sub 3}O{sub 8} qualitatively, detection of at least 40 ppm of fluorine, as alkali fluoride and 125 ppm of chlorine, is possible. (author) [French] Un tube a decharge a cathode creuse a ete utilise pour la determination spectrographique des halogenes (fluor - chlore) presentes a l'etat de traces dans un oxyde d'uranium U{sub 3}O{sub 8}. On a pu deceler qualitativement des teneurs de 40 ppm de fluor sous forme de fluorures alcalins. En ce qui concerne le chlore, la plus faible teneur decelee a ete de 125 ppm. (auteur)

  9. Subtask 4.24 - Field Evaluation of Novel Approach for Obtaining Metal Emission Data

    Energy Technology Data Exchange (ETDEWEB)

    Pavlish, John; Laudal, Dennis; Thompson, Jeffrey

    2013-12-31

    Over the past two decades, emissions of mercury, nonmercury metals, and acid gases from energy generation and chemical production have increasingly become an environmental concern. On February 16, 2012, the U.S. Environmental Protection Agency (EPA) promulgated the Mercury and Air Toxics Standards (MATS) to reduce mercury, nonmercury metals, and HCl emissions from coal-fired power plants. The current reference methods for trace metals and halogens are wet-chemistry methods, EPA Method (M) 29 and M26A, respectively. As a possible alternative to EPA M29 and M26A, the Energy & Environmental Research Center (EERC) has developed a novel multielement sorbent trap (ME-ST) method to be used to sample for trace elements and/or halogens. Testing was conducted at three different power plants, and the results show that for halogens, the ME-ST halogen (ME-ST-H) method did not show any significant bias compared to EPA M26A and appears to be a potential candidate to serve as an alternative to the reference method. For metals, the ME-ST metals (ME-ST-M) method offers a lower detection limit compared to EPA M29 and generally produced comparable data for Sb, As, Be, Cd, Co, Hg, and Se. Both the ME-ST-M and M29 had problems associated with high blanks for Ni, Pb, Cr, and Mn. Although this problem has been greatly reduced through improved trap design and material selection, additional research is still needed to explore possible longer sampling durations and/or selection of lower background materials before the ME-ST-M can be considered as a potential alternative method for all the trace metals listed in MATS.

  10. First-principles calculation of the structural stability of 6d transition metals

    International Nuclear Information System (INIS)

    Oestlin, A.; Vitos, L.

    2011-01-01

    The phase stability of the 6d transition metals (elements 103-111) is investigated using first-principles electronic-structure calculations. Comparison with the lighter transition metals reveals that the structural sequence trend is broken at the end of the 6d series. To account for this anomalous behavior, the effect of relativity on the lattice stability is scrutinized, taking different approximations into consideration. It is found that the mass-velocity and Darwin terms give important contributions to the electronic structure, leading to changes in the interstitial charge density and, thus, in the structural energy difference.

  11. Metal-semiconductor phase transition of order arrays of VO2 nanocrystals

    Science.gov (United States)

    Lopez, Rene; Suh, Jae; Feldman, Leonard; Haglund, Richard

    2004-03-01

    The study of solid-state phase transitions at nanometer length scales provides new insights into the effects of material size on the mechanisms of structural transformations. Such research also opens the door to new applications, either because materials properties are modified as a function of particle size, or because the nanoparticles interact with a surrounding matrix material, or with each other. In this paper, we describe the formation of vanadium dioxide nanoparticles in silicon substrates by pulsed laser deposition of ion beam lithographically selected sites and thermal processing. We observe the collective behavior of 50 nm diameter VO2 oblate nanoparticles, 10 nm high, and ordered in square arrays with arbitrary lattice constant. The metal-semiconductor-transition of the VO2 precipitates shows different features in each lattice spacing substrate. The materials are characterized by electron microscopy, x-ray diffraction, Rutherford backscattering. The features of the phase transition are studied via infrared optical spectroscopy. Of particular interest are the enhanced scattering and the surface plasmon resonance when the particles reach the metallic state. This resonance amplifies the optical contrast in the range of near-infrared optical communication wavelengths and it is altered by the particle-particle coupling as in the case of noble metals. In addition the VO2 nanoparticles exhibit sharp transitions with up to 50 K of hysteresis, one of the largest values ever reported for this transition. The optical properties of the VO2 nanoarrays are correlated with the size of the precipitates and their inter-particle distance. Nonlinear and ultra fast optical measurements have shown that the transition is the fastest known solid-solid transformation. The VO2 nanoparticles show the same bulk property, transforming in times shorter than 150 fs. This makes them remarkable candidates for ultrafast optical and electronic switching applications.

  12. On the behavior of Bronsted-Evans-Polanyi Relations for Transition Metal Oxides

    Energy Technology Data Exchange (ETDEWEB)

    Vojvodic, Aleksandra

    2011-08-22

    Versatile Broensted-Evans-Polanyi (BEP) relations are found from density functional theory for a wide range of transition metal oxides including rutiles and perovskites. For oxides, the relation depends on the type of oxide, the active site and the dissociating molecule. The slope of the BEP relation is strongly coupled to the adsorbate geometry in the transition state. If it is final state-like the dissociative chemisorption energy can be considered as a descriptor for the dissociation. If it is initial state-like, on the other hand, the dissociative chemisorption energy is not suitable as descriptor for the dissociation. Dissociation of molecules with strong intramolecular bonds belong to the former and molecules with weak intramolecular bonds to the latter group. We show, for the prototype system La-perovskites, that there is a 'cyclic' behavior in the transition state characteristics upon change of the active transition metal of the oxide.

  13. The potential for transition metal-mediated neurodegeneration in amyotrophic lateral sclerosis

    Directory of Open Access Journals (Sweden)

    David Benn Lovejoy

    2014-07-01

    Full Text Available Modulations of the potentially toxic transition metals iron (Fe and copper (Cu are implicated in the neurodegenerative process in a variety of human disease states including amyotrophic lateral sclerosis (ALS. However, the precise role played by these metals is still very much unclear, despite considerable clinical and experimental data suggestive of a role for these elements in the neurodegenerative process. The discovery of mutations in the antioxidant enzyme Cu/Zn superoxide dismutase (SOD-1 in ALS patients established the first known cause of ALS. Recent data suggest that various mutations in SOD-1 affect metal-binding of Cu and Zn, in turn promoting toxic protein aggregation. Copper homeostasis is also disturbed in ALS, and may be relevant to ALS pathogenesis. Another set of interesting observations in ALS patients involves the key nutrient Fe. In ALS patients Fe loading can be inferred by studies showing increased expression of serum ferritin, an Fe storage protein, with high serum ferritin levels correlating to poor prognosis. Magnetic resonance imaging of ALS patients shows a characteristic T2 shortening that is attributed to the presence of Fe in the motor cortex. In mutant SOD-1 mouse models, increased Fe is also detected in the spinal cord and treatment with Fe-chelating drugs lowers spinal cord Fe, preserves motor neurons and extends lifespan. Inflammation may play a key causative role in Fe accumulation, but this is not yet conclusive. Excess transition metals may enhance induction of endoplasmic reticulum (ER stress, a system that is already under strain in ALS. Taken together, the evidence suggests a role for transition metals in ALS progression and the potential use of metal-chelating drugs as a component of future ALS therapy.

  14. Transition metal complexes of some biologically active ligands; synthesis characterization and bioactivities

    International Nuclear Information System (INIS)

    Rehman, S.; Ali, N.; Nisar, M.

    2009-01-01

    Transition/representative transition metals complexes of biologically active chelating agent 1,2-dipyrolodinoethane were synthesized and characterized through spectral and analytical data. The complexes are of the formula (M(L)X/sub 2/). Where (M = Co (II), Ni (II), Cu (II), Zn (II), Hg (II) and Cd (II) and X = CI, Br, NO/sub 3/). Tetrahedral geometry has been proposed to these-metal complexes with the help of magnetic measurements, elemental analysis, chemical stoichiometry and spectroscopic data Antibacterial activity of the ligand and its metal complexes were screened against Eschereschi coli, Klebsiello pneumonia, Proteus mirabilis, Proteus vulhari, Streptococcus pneumonia, Salmonella Iyphi, Bacilh,s anthrax, Streptococcus fecalis and Staphylococcus aureus. Complexes were found to be active against Eschereschi coli, Klebsiella pneumonia, Proteus mirabilis and Proteus vulharis. (author)

  15. Low-density to high-density transition in Ce75Al23Si2 metallic glass

    International Nuclear Information System (INIS)

    Zeng, Q S; Lou, H B; Gong, Y; Wang, X D; Jiang, J Z; Fang, Y Z; Wu, F M; Yang, K; Li, A G; Yan, S; Yu, X H; Lathe, C

    2010-01-01

    Using in situ high-pressure x-ray diffraction (XRD), we observed a pressure-induced polyamorphic transition from the low-density amorphous (LDA) state to the high-density amorphous (HDA) state in Ce 75 Al 23 Si 2 metallic glass at about 2 GPa and 300 K. The thermal stabilities of both LDA and HDA metallic glasses were further investigated using in situ high-temperature and high-pressure XRD, which revealed different pressure dependences of the onset crystallization temperature (T x ) between them with a turning point at about 2 GPa. Compared with Ce 75 Al 25 metallic glass, minor Si doping shifts the onset polyamorphic transition pressure from 1.5 to 2 GPa and obviously stabilizes both LDA and HDA metallic glasses with higher T x and changes their slopes dT x /dP. The results obtained in this work reveal another polyamorphous metallic glass system by minor alloying (e.g. Si), which could modify the transition pressure and also properties of LDA and HDA metallic glasses. The minor alloying effect reported here is valuable for the development of more polyamorphous metallic glasses, even multicomponent bulk metallic glasses with modified properties, which will trigger more investigations in this field and improve our understanding of polyamorphism and metallic glasses.

  16. Reactions of transition metal complexes with cyclic ethers

    International Nuclear Information System (INIS)

    Milstein, D.

    1977-02-01

    Three novel reactions of epoxides with homogeneous transition-metal catalysts have been explored: (a) the selective rearrangement of internal epoxides to ketones; (b) the cleavage of C-C bond in epoxides having electron-attracting substituents; (c) the transformation of terminal epoxides into esters. Based on an intensive kinetic study, a general mechanism for the transformations of epoxides is postulated

  17. Valley polarization in magnetically doped single-layer transition-metal dichalcogenides

    KAUST Repository

    Cheng, Yingchun; Zhang, Q. Y.; Schwingenschlö gl, Udo

    2014-01-01

    We demonstrate that valley polarization can be induced and controlled in semiconducting single-layer transition-metal dichalcogenides by magnetic doping, which is important for spintronics, valleytronics, and photonics devices. As an example, we

  18. Adsorption and dissociation of dinitrogen on transition metal (Ta, W and Re) doped MgO surface

    KAUST Repository

    Yadav, Manoj Kumar; Vovusha, Hakkim; Sanyal, Biplab

    2016-01-01

    The adsorption and dissociation of dinitrogen on transition metal (Ta, W and Re) doped MgO(100) surface has been studied employing density functional theory. It is found that all these transition metals (TM) on MgO(100) surface are capable

  19. Validation of ion chromatography for the determination of transition metal ions along with alkali, alkaline earth metal elements for uranium oxide fuel

    International Nuclear Information System (INIS)

    Kelkar, Anoop; Prakash, Amrit; Afzal, Mohd.; Panakkal, J.P.

    2009-02-01

    The present report describes the use of Ion chromatography (IC) methods with spectrophotometric and direct conductivity detection for the determination of transition metal elements and alkali alkaline earth metal ions in UO 2 pellets. Transmet analytical column and Metrosep- cation 1-2 column were used for the separation of transition metal elements and alkali and alkaline earth metal elements respectively. Oxalic acid and mixture of pyridine 2,6-dicarboxylic acid (PDCA), Na 2 SO 4 and NaCl were used as mobile phase for the separation of transition metal ions and monitored after post - column reaction with 4,2-pyridylazo resorcinol (PAR) at 520nm spectrophotometrically. In the determination of alkali and alkaline earth metal ions the interference of transition metals are removed by complexing them with PDCA. Mixture of tartaric acid and PDCA employed in the separation of alkali and alkaline earth metal ions and monitored on direct conductivity detector. Mobile phase composition was optimised for the base line separation. Calibration plots of Fe 3+ , Cu 2+ , Ni 2+ , Co 2+ , Cd 2+ , Mn 2+ , Li + , Na + , K + , Mg 2+ , Ca 2+ and Sr 2+ were linear over a wide dynamic range with regression coefficient better than 0.999. Detection limit of above ions were between 5-30ppb. To prevent the overloading of the cation exchange column, uranium matrix was removed from UO 2 sample by solvent extraction with 30% TBP - TOPO/CCl 4 . Ten sintered UO2 pellets of same lot were analysed and R.S.D. ±10% was obtained. These methods were validated by analysis of ILCE standards of UO 2 . (author)

  20. Phase stabilisation of hexagonal barium titanate doped with transition metals: A computational study

    International Nuclear Information System (INIS)

    Dawson, J.A.; Freeman, C.L.; Harding, J.H.; Sinclair, D.C.

    2013-01-01

    Interatomic potentials recently developed for the modelling of BaTiO 3 have been used to explore the stabilisation of the hexagonal polymorph of BaTiO 3 by doping with transition metals (namely Mn, Co, Fe and Ni) at the Ti-site. Classical simulations have been completed on both the cubic and hexagonal polymorphs to investigate the energetic consequences of transition metal doping on each polymorph. Ti-site charge compensation mechanisms have been used for the multi-valent transition metal ions and cluster binding energies have been considered. Simulations show a significant energetic gain when doping occurs at Ti sites in the face sharing dimers (Ti 2 sites) of the hexagonal polymorph compared with the doping of the cubic polymorph. This energetic difference between the two polymorphs is true for all transition metals tested and all charge states and in the case of tri- and tetra-valent dopants negative solution energies are found for the hexagonal polymorph suggesting actual polymorph stabilisation occurs with the incorporation of these ions as observed experimentally. Oxidation during incorporation of Ni 2+ and Fe 3+ ions has also been considered. - Graphical abstract: The representation of the strongest binding energy clusters for tri-valent dopants—(a) Ti 2 /O 1 cluster and (b) Ti 2 /O 2 cluster. Highlights: ► Classical simulations show a significant energetic gain when doping occurs at Ti sites in the face sharing dimers (Ti2 sites) of the hexagonal polymorph compared with the doping of the cubic polymorph. ► This energetic difference between the two polymorphs is true for all transition metals tested and all charge states. ► In the case of tri- and tetra- valent dopants negative solution energies are found for the hexagonal polymorph suggesting actual polymorph stabilisation occurs with the incorporation of these ions

  1. Reaction of urea thiourea and their derivatives with tertiary phosphine transition metal halides

    International Nuclear Information System (INIS)

    Adam, Eltayeb Mahala

    2000-03-01

    This thesis describes preparation characterization and some properties of a number of new compounds such as (ph 3 p)2 ML where M= cobalt (11), nickel (11), and copper (11), and L= urea, thiourea, phenylthiourea, sym diphenylurea and sym diphenylthiourea.These compounds have been prepared according according to the reaction of dichloro bis (triphenylphosphine) transition metal with urea, thiourea or some of their derivative ligands in 1:1 molar ratio.The work in this thesis is divided into three section firstly:- In the introduction chapter part one includes general definitions of coordination chemistry and related compounds and abroad definition of transition elements.Part two includes the theoretical back ground about transition metal complexes having urea, thiourea or some of their substituted derivative ligands.Part two also discusses the type of bonding between these ligands and the transition metal atom.Secondly: Chapter two describes the general techniques followed in this work such as purification of solvents recrystallization, preparation of starting materials and also gives full detailed procedures of the preparation of a number of new compounds.Thirdly: Discussion with detailed in chapter three, the results of the research are presented the preparation and characterization of a number of new compounds isolated from reaction between urea, thiourea or some of their substituted derivatives and dichloro bis (triphenyl phosphine) transition metal complex giving a general formula (ph 3 )2ML where M=cobalt, nickel, and copper, and urea, thiourea or some of their substituted derivatives ligands. The products of these experiments have been identified using infrared spectra, melting points and molar conductance. The results obtained indicated that all the compounds forming the nitrogen to metal bonds leading to the formation of a four- membered chelate ring, they are relatively thermally stable compounds, and also these compounds are non-electrolytes.(Author)

  2. Halogenated organic compounds in archived whale oil: A pre-industrial record

    International Nuclear Information System (INIS)

    Teuten, Emma L.; Reddy, Christopher M.

    2007-01-01

    To provide additional evidence that several halogenated organic compounds (HOCs) found in environmental samples are natural and not industrially produced, we analyzed an archived whale oil sample collected in 1921 from the last voyage of the whaling ship Charles W. Morgan. This sample, which pre-dates large-scale industrial manufacture of HOCs, contained two methoxylated polybrominated diphenyl ethers (MeO-PBDEs), five halogenated methyl bipyrroles (MBPs), one halogenated dimethyl bipyrrole (DMBP), and tentatively one dimethoxylated polybrominated biphenyl (diMeO-PBB). This result indicates, at least in part, a natural source of the latter compounds. - Nine halogenated organic compounds have been detected in archived whale oil from the early 1920s

  3. Halogenated organic compounds in archived whale oil: A pre-industrial record

    Energy Technology Data Exchange (ETDEWEB)

    Teuten, Emma L. [Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, 360 Woods Hole Road, Woods Hole, MA 02543 (United States)]. E-mail: emma.teuten@plymouth.ac.uk; Reddy, Christopher M. [Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, 360 Woods Hole Road, Woods Hole, MA 02543 (United States)]. E-mail: creddy@whoi.edu

    2007-02-15

    To provide additional evidence that several halogenated organic compounds (HOCs) found in environmental samples are natural and not industrially produced, we analyzed an archived whale oil sample collected in 1921 from the last voyage of the whaling ship Charles W. Morgan. This sample, which pre-dates large-scale industrial manufacture of HOCs, contained two methoxylated polybrominated diphenyl ethers (MeO-PBDEs), five halogenated methyl bipyrroles (MBPs), one halogenated dimethyl bipyrrole (DMBP), and tentatively one dimethoxylated polybrominated biphenyl (diMeO-PBB). This result indicates, at least in part, a natural source of the latter compounds. - Nine halogenated organic compounds have been detected in archived whale oil from the early 1920s.

  4. Halogens are key cofactors in building of collagen IV scaffolds outside the cell.

    Science.gov (United States)

    Brown, Kyle L; Hudson, Billy G; Voziyan, Paul A

    2018-05-01

    The purpose of this review is to highlight recent advances in understanding the molecular assembly of basement membranes, as exemplified by the glomerular basement membrane (GBM) of the kidney filtration apparatus. In particular, an essential role of halogens in the basement membrane formation has been discovered. Extracellular chloride triggers a molecular switch within non collagenous domains of collagen IV that induces protomer oligomerization and scaffold assembly outside the cell. Moreover, bromide is an essential cofactor in enzymatic cross-linking that reinforces the stability of scaffolds. Halogenation and halogen-induced oxidation of the collagen IV scaffold in disease states damage scaffold function. Halogens play an essential role in the formation of collagen IV scaffolds of basement membranes. Pathogenic damage of these scaffolds by halogenation and halogen-induced oxidation is a potential target for therapeutic interventions.

  5. Halonium Ions as Halogen Bond Donors in the Solid State [XL2]Y Complexes.

    Science.gov (United States)

    Rissanen, Kari; Haukka, Matti

    2015-01-01

    The utilization of halogen bonding interactions is one of the most rapidly developing areas of supramolecular chemistry. While the other weak non-covalent interactions and their influence on the structure and chemistry of various molecules, complexes, and materials have been investigated extensively, the understanding, utilizations, and true nature of halogen bonding are still relatively unexplored. Thus its final impact in chemistry in general and in materials science has not yet been fully established. Because of the polarized nature of a Z-X bond (Z=electron-withdrawing atom or moiety and X=halogen atom), such a moiety can act as halogen bond donor when the halogen is polarized enough by the atom/moiety Z. The most studied and utilized halogen bond donor molecules are the perfluorohalocarbons, where Z is a perfluorinated aryl or alkyl moiety and X is either iodine or bromine. Complementing the contemporary halogen bonding research, this chapter reviews the solid state structural chemistry of the most extremely polarized halogen atoms, viz. halonium ions, X+, and discussed them as halogen bond donors in the solid state [XL2]Y complexes (X=halonium ion, Y=any anion).

  6. Bridging Transitions for Spheres and Cylinders.

    Czech Academy of Sciences Publication Activity Database

    Malijevský, Alexandr; Parry, A.O.

    2015-01-01

    Roč. 92, č. 2 (2015), s. 022407 ISSN 1539-3755 R&D Projects: GA ČR GA13-09914S Grant - others:EPSRC(GB) EP/J009636/1 Institutional support: RVO:67985858 Keywords : phase behaviour * bridging * density functional theory Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.288, year: 2014

  7. Ultra-high-rate pseudocapacitive energy storage in two-dimensional transition metal carbides

    Science.gov (United States)

    Lukatskaya, Maria R.; Kota, Sankalp; Lin, Zifeng; Zhao, Meng-Qiang; Shpigel, Netanel; Levi, Mikhael D.; Halim, Joseph; Taberna, Pierre-Louis; Barsoum, Michel W.; Simon, Patrice; Gogotsi, Yury

    2017-08-01

    The use of fast surface redox storage (pseudocapacitive) mechanisms can enable devices that store much more energy than electrical double-layer capacitors (EDLCs) and, unlike batteries, can do so quite rapidly. Yet, few pseudocapacitive transition metal oxides can provide a high power capability due to their low intrinsic electronic and ionic conductivity. Here we demonstrate that two-dimensional transition metal carbides (MXenes) can operate at rates exceeding those of conventional EDLCs, but still provide higher volumetric and areal capacitance than carbon, electrically conducting polymers or transition metal oxides. We applied two distinct designs for MXene electrode architectures with improved ion accessibility to redox-active sites. A macroporous Ti3C2Tx MXene film delivered up to 210 F g-1 at scan rates of 10 V s-1, surpassing the best carbon supercapacitors known. In contrast, we show that MXene hydrogels are able to deliver volumetric capacitance of ˜1,500 F cm-3 reaching the previously unmatched volumetric performance of RuO2.

  8. Optical excitations of transition-metal oxides under the orbital multiplicity effects

    International Nuclear Information System (INIS)

    Lee, J S; Kim, M W; Noh, T W

    2005-01-01

    We investigated optical excitations of transition-metal (TM) oxides with metal oxygen octahedra taking account of the orbital multiplicity effects. We predicted excitation energies of intersite d-d transitions and p-d transitions of TM oxides. We compared the evaluated excitation energies with reported experimental data, and found that they are in good agreement with each other. Moreover, we could demonstrate possible answers for a few long-standing problems of the low-frequency spectral features in some early 3d TM oxides: (i) the broad and multi-peak structures of the d-d transitions (ii) the low values (around 2 eV) of the d-d transition energies for some t 2g 1 and t 2g 2 systems, and (iii) the lack of the d-d transition below 4.0 eV region for LaCrO 3 , one of the t 2g 3 systems. These indicate that our approach considering the orbital multiplicity effects could provide good explanations of intriguing features in the optical spectra of some early TM oxides. In addition, we showed that optical spectroscopy can be useful as a powerful tool to investigate spin and/or orbital correlations in the TM ions. Finally, we discussed the implications of the orbital multiplicity in the Zannen-Sawatzky-Allen scheme, which has been used successfully to classify correlated electron systems

  9. Spatiotemporal Analysis of Heavy Metal Water Pollution in Transitional China

    Directory of Open Access Journals (Sweden)

    Huixuan Li

    2015-07-01

    Full Text Available China’s socioeconomic transitions have dramatically accelerated its economic growth in last three decades, but also companioned with continuous environmental degradation. This study will advance the knowledge of heavy metal water pollution in China from a spatial–temporal perspective. Specifically, this study addressed the following: (1 spatial patterns of heavy metal water pollution levels were analyzed using data of prefecture-level cities from 2004 to 2011; and (2 spatial statistical methods were used to examine the underlying socioeconomic and physical factors behind water pollution including socioeconomic transitions (industrialization, urbanization, globalization and economic development, and environmental characteristic (natural resources, hydrology and vegetation coverage. The results show that only Cr pollution levels increased over the years. The individual pollution levels of the other four heavy metals, As, Cd, Hg, and Pb, declined. High heavy metal water pollution levels are closely associated with both anthropogenic activities and physical environments, in particular abundant mineral resources and industrialization prosperity. On the other hand, economic development and urbanization play important roles in controlling water pollution problems. The analytical findings will provide valuable information for policy-makers to initiate and adjust protocols and strategies for protecting water sources and controlling water pollution; thus improving the quality of living environments.

  10. Superconductor-Metal-Insulator transition in two dimensional Ta thin Films

    Science.gov (United States)

    Park, Sun-Gyu; Kim, Eunseong

    2013-03-01

    Superconductor-insulator transition has been induced by tuning film thickness or magnetic field. Recent electrical transport measurements of MoGe, Bi, Ta thin films revealed an interesting intermediate metallic phase which intervened superconducting and insulating phases at certain range of magnetic field. Especially, Ta thin films show the characteristic IV behavior at each phase and the disorder tuned intermediate metallic phase [Y. Li, C. L. Vicente, and J. Yoon, Physical Review B 81, 020505 (2010)]. This unexpected metallic phase can be interpreted as a consequence of vortex motion or contribution of fermionic quasiparticles. In this presentation, we report the scaling behavior during the transitions in Ta thin film as well as the transport measurements in various phases. Critical exponents v and z are obtained in samples with wide ranges of disorder. These results reveal new universality class appears when disorder exceeds a critical value. Dynamical exponent z of Superconducting sample is found to be 1, which is consistent with theoretical prediction of unity. z in a metallic sample is suddenly increased to be approximately 2.5. This critical exponent is much larger than the value found in other system and theoretical prediction. We gratefully acknowledge the financial support by the National Research Foundation of Korea through the Creative Research Initiatives.

  11. Ab initio theory of noble gas atoms in bcc transition metals.

    Science.gov (United States)

    Jiang, Chao; Zhang, Yongfeng; Gao, Yipeng; Gan, Jian

    2018-06-18

    Systematic ab initio calculations based on density functional theory have been performed to gain fundamental understanding of the interactions between noble gas atoms (He, Ne, Ar and Kr) and bcc transition metals in groups 5B (V, Nb and Ta), 6B (Cr, Mo and W) and 8B (Fe). Our charge density analysis indicates that the strong polarization of nearest-neighbor metal atoms by noble gas interstitials is the electronic origin of their high formation energies. Such polarization becomes more significant with an increasing gas atom size and interstitial charge density in the host bcc metal, which explains the similar trend followed by the unrelaxed formation energies of noble gas interstitials. Upon allowing for local relaxation, nearby metal atoms move farther away from gas interstitials in order to decrease polarization, albeit at the expense of increasing the elastic strain energy. Such atomic relaxation is found to play an important role in governing both the energetics and site preference of noble gas atoms in bcc metals. Our most notable finding is that the fully relaxed formation energies of noble gas interstitials are strongly correlated with the elastic shear modulus of the bcc metal, and the physical origin of this unexpected correlation has been elucidated by our theoretical analysis based on the effective-medium theory. The kinetic behavior of noble gas atoms and their interaction with pre-existing vacancies in bcc transition metals have also been discussed in this work.

  12. Insulator–metal transition in a conservative system: An evidence for ...

    Indian Academy of Sciences (India)

    substrate, suggest that the mobility coalescence is responsible for the aging in island metal films. ... esting transition observed in a conservative system – after the stoppage of ... Oxidation of islands model and mobility coalescence model.

  13. Spectrum of ferromagnetic transition metal magnetic excitations and neutron scattering

    International Nuclear Information System (INIS)

    Kuzemskij, A.L.

    1979-01-01

    Quantum statistical models of ferromagnetic transition metals as well as methods of their solutions are reviewed. The correspondence of results on solving these models and the data on scattering thermal neutrons in ferromagnetic is discussed

  14. Using a Semiconductor-to-Metal Transition to Control Optical Transmission through Subwavelength Hole Arrays

    Directory of Open Access Journals (Sweden)

    E. U. Donev

    2008-01-01

    Full Text Available We describe a simple configuration in which the extraordinary optical transmission effect through subwavelength hole arrays in noble-metal films can be switched by the semiconductor-to-metal transition in an underlying thin film of vanadium dioxide. In these experiments, the transition is brought about by thermal heating of the bilayer film. The surprising reverse hysteretic behavior of the transmission through the subwavelength holes in the vanadium oxide suggest that this modulation is accomplished by a dielectric-matching condition rather than plasmon coupling through the bilayer film. The results of this switching, including the wavelength dependence, are qualitatively reproduced by a transfer matrix model. The prospects for effecting a similar modulation on a much faster time scale by using ultrafast laser pulses to trigger the semiconductor-to-metal transition are also discussed.

  15. Resin-Bonded Bridges in vitro and in vivo

    NARCIS (Netherlands)

    Veen, Johannes Hilbrandt van der

    1988-01-01

    In this thesis in vitro and in vivo studies on the clinical application of resin-bonded bridges are described and discussed. The development of different types of resin-bonded bridges is described in chapter 1. The bridges are often made by boding a cast metal retainer fitted with and artificial

  16. Adsorption and migration of single metal atoms on the calcite (10.4) surface

    International Nuclear Information System (INIS)

    Pinto, H; Haapasilta, V; Lokhandwala, M; Foster, Adam S; Öberg, S

    2017-01-01

    Transition metal atoms are one of the key ingredients in the formation of functional 2D metal organic coordination networks. Additionally, the co-deposition of metal atoms can play an important role in anchoring the molecular structures to the surface at room temperature. To gain control of such processes requires the understanding of adsorption and diffusion properties of the different transition metals on the target surface. Here, we used density functional theory to investigate the adsorption of 3 d (Ti, Cr, Fe, Ni, Cu), 4 d (Zr, Nb, Mo, Pd, Ag) and 5 d (Hf, W, Ir, Pt, Au) transition metal adatoms on the insulating calcite (10.4) surface. We identified the most stable adsorption sites and calculated binding energies and corresponding ground state structures. We find that the preferential adsorption sites are the Ca–Ca bridge sites. Apart from the Cr, Mo, Cu, Ag and Au all the studied metals bind strongly to the calcite surface. The calculated migration barriers for the representative Ag and Fe atoms indicates that the metal adatoms are mobile on the calcite surface at room temperature. Bader analysis suggests that there is no significant charge transfer between the metal adatoms and the calcite surface. (paper)

  17. Dynamic loads during failure risk assessment of bridge crane structures

    Science.gov (United States)

    Gorynin, A. D.; Antsev, V. Yu; Shaforost, A. N.

    2018-03-01

    The paper presents the method of failure risk assessment associated with a bridge crane metal structure at the design stage. It also justifies the necessity of taking into account dynamic loads with regard to the operational cycle of a bridge crane during failure risk assessment of its metal structure.

  18. First-principles study of doping effect on the phase transition of zinc oxide with transition metal doped

    International Nuclear Information System (INIS)

    Wu, Liang; Hou, Tingjun; Wang, Yi; Zhao, Yanfei; Guo, Zhenyu; Li, Youyong; Lee, Shuit-Tong

    2012-01-01

    Highlights: ► We study the doping effect on B4, B1 structures and phase transition of ZnO. ► We calculate the phase transition barrier and phase transition path of doped ZnO. ► The transition metal doping decreases the bulk modulus and phase transition pressure. ► The magnetic properties are influenced by the phase transition process. - Abstract: Zinc oxide (ZnO) is a promising material for its wide application in solid-state devices. With the pressure raised from an ambient condition, ZnO transforms from fourfold wurtzite (B4) to sixfold coordinated rocksalt (B1) structure. Doping is an efficient approach to improve the structures and properties of materials. Here we use density-functional theory (DFT) to study doped ZnO and find that the transition pressure from B4 phase to B1 phase of ZnO always decreases with different types of transition metal (V, Cr, Mn, Fe, Co, or Ni) doped, but the phase transition path is not affected by doping. This is consistent with the available experimental results for Mn-doped ZnO and Co-doped ZnO. Doping in ZnO causes the lattice distortion, which leads to the decrease of the bulk modulus and accelerates the phase transition. Mn-doped ZnO shows the strongest magnetic moment due to its half filled d orbital. For V-doped ZnO and Cr-doped ZnO, the magnetism is enhanced by phase transition from B4 to B1. But for Mn-doped ZnO, Fe-doped ZnO, Co-doped ZnO, and Ni-doped ZnO, B1 phase shows weaker magnetic moment than B4 phase. These results can be explained by the amount of charge transferred from the doped atom to O atom. Our results provide a theoretical basis for the doping approach to change the structures and properties of ZnO.

  19. Photoemission from valence bands of transition metal-phthalocyanines

    International Nuclear Information System (INIS)

    Shang, Ming-Hui; Nagaosa, Mayumi; Nagamatsu, Shin-ichi; Hosoumi, Shunsuke; Kera, Satoshi; Fujikawa, Takashi; Ueno, Nobuo

    2011-01-01

    Research highlights: → The HOMO mainly comes from the carbon atoms of Pc rings and the central metal atoms almost have no contribution on the highest occupied molecular orbital (HOMO: a 1u ) distribution of CoPc as well as NiPc. → Influence by central metal atom on the photoemission intensities from the HOMO of two single molecule systems is negligible for the major. → The modification of the distribution for π-orbital upon adsorption as well as the scattering effects of the central metal on the photoemission intensities are negligible for the major. - Abstract: Angular dependencies of ultraviolet photoelectron spectrum of transition metal-phthalocyanines (TM-Pcs), NiPc and CoPc, have been studied by using multiple-scattering theory to explore the electronic structure of the organometallic complexes influenced by central metal atom. The calculated angular distributions of photoelectrons for the highest occupied molecular orbital (HOMO: a 1u ) from the two single systems are nearly the same and represent well the experimental results obtained for the well-ordered monolayer on the highly oriented pyrolytic graphite substrate. The central metal atoms almost have no contribution on the HOMO distribution, which mainly comes from the carbon atoms of Pc ring. Moreover, the modification of the distribution for π orbital upon adsorption as well as the scattering effects of the central metal on the photoemission intensities are negligible for the major.

  20. Deterioration and cost information for bridge management.

    Science.gov (United States)

    2012-05-01

    This study applies contract bid tabulations and elementlevel condition records to develop elementlevel actions, : costs for actions, transition probabilities for models of deterioration of bridge elements, and transition probabilities : for imp...

  1. Zeolites as supports for transition-metal complexes

    Energy Technology Data Exchange (ETDEWEB)

    Le Van Mao, R

    1979-01-01

    The unique structural characteristics of the zeolites, including the presence of molecular-size cages and channels and of an internal electrostatic field, make them promising as supports for converting homogeneous to heterogeneous catalysts. The acidic sites on the zeolites may also contribute to catalysis of reactions, such as hydrocracking; may stabilize metal complexes in a highly disperse state; and may improve activity or selectivity. Recent studies on the synthesis of new types of zeolite-supported complexes of transition metals (TM), such as Co, Cu, Ag, Fe, Mo, Ru, Rh, Re, and Os, suggest the feasibility of the direct introduction of some TM complexes into the zeolitic cages during zeolite synthesis, especially during the crystallization phase. This method may considerably reduce the structural limitations associated with the incorporation of TM complexes into zeolites by conventional methods.

  2. Optical and electrical experiments at some transition-metal oxide foil-electrolyte interfaces

    International Nuclear Information System (INIS)

    Sari, S.O.; Ahlgren, W.L.

    1977-01-01

    Metal-oxide layers formed from transition-metal foils oxidized by heating in air have been examined for their photoelectrolytic response. The metals examined are Y, Ti, Zr, Hf, V, Nb, Ta, Mo, W, and Pt. Weak photoeffects are observed for oxide layers of all of these metals. Sizable light-dependent oxygen gas evolution rates are found in Ti and also in W oxides. The spectral dependence of the oxygen response in these compounds is investigated, and interpretation is given of these experiments

  3. Phase transitions in finite systems

    Energy Technology Data Exchange (ETDEWEB)

    Chomaz, Ph. [Grand Accelerateur National d' Ions Lourds (GANIL), DSM-CEA / IN2P3-CNRS, 14 - Caen (France); Gulminelli, F. [Caen Univ., 14 (France). Lab. de Physique Corpusculaire

    2002-07-01

    In this series of lectures we will first review the general theory of phase transition in the framework of information theory and briefly address some of the well known mean field solutions of three dimensional problems. The theory of phase transitions in finite systems will then be discussed, with a special emphasis to the conceptual problems linked to a thermodynamical description for small, short-lived, open systems as metal clusters and data samples coming from nuclear collisions. The concept of negative heat capacity developed in the early seventies in the context of self-gravitating systems will be reinterpreted in the general framework of convexity anomalies of thermo-statistical potentials. The connection with the distribution of the order parameter will lead us to a definition of first order phase transitions in finite systems based on topology anomalies of the event distribution in the space of observations. Finally a careful study of the thermodynamical limit will provide a bridge with the standard theory of phase transitions and show that in a wide class of physical situations the different statistical ensembles are irreducibly inequivalent. (authors)

  4. Phase transitions in finite systems

    International Nuclear Information System (INIS)

    Chomaz, Ph.; Gulminelli, F.

    2002-01-01

    In this series of lectures we will first review the general theory of phase transition in the framework of information theory and briefly address some of the well known mean field solutions of three dimensional problems. The theory of phase transitions in finite systems will then be discussed, with a special emphasis to the conceptual problems linked to a thermodynamical description for small, short-lived, open systems as metal clusters and data samples coming from nuclear collisions. The concept of negative heat capacity developed in the early seventies in the context of self-gravitating systems will be reinterpreted in the general framework of convexity anomalies of thermo-statistical potentials. The connection with the distribution of the order parameter will lead us to a definition of first order phase transitions in finite systems based on topology anomalies of the event distribution in the space of observations. Finally a careful study of the thermodynamical limit will provide a bridge with the standard theory of phase transitions and show that in a wide class of physical situations the different statistical ensembles are irreducibly inequivalent. (authors)

  5. Halogenated furanones inhibit quorum sensing through accelerated LuxR turnover

    DEFF Research Database (Denmark)

    Manefield, M.; Rasmussen, Thomas Bovbjerg; Henzter, M.

    2002-01-01

    fischeri overproduced in Escherichia coli. Whilst a stable interaction between the algal metabolite and the bacterial protein was not found, it was noted by Western analysis that the half-life of the protein is reduced up to 100-fold in the presence of halogenated furanones. This suggests that halogenated...... that the reduction in LuxR concentration is the mechanism by which furanones control expression of AHL-dependent phenotypes. The mode of action by which halogenated furanones reduce cellular concentrations of the LuxR protein remains to be characterized....

  6. High coercivity rare earth-transition metal magnets

    International Nuclear Information System (INIS)

    Croat, J.J.

    1982-01-01

    Ferromagnetic compositions having intrinsic magnetic coercivities at room temperature of at least 1,000 Oersteds are formed by the controlled quenching of molten rare earth-transition metal alloys. Hard magnets may be inexpensively formed from the lower atomic weight lanthanide elements and iron. The preferable compositions lie within: at least one of Fe, Ni, Co; 20 - 70 atomic percent: at least one of Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Y; 80 - 30 atomic percent. (author)

  7. Synthesis, characterization and anti-bacterial activity of divalent transition metal complexes of hydrazine and trimesic acid

    Directory of Open Access Journals (Sweden)

    K. Kumar

    2018-01-01

    Full Text Available Transition metal complexes of trimesic acid and hydrazine mixed-ligands with a general formula M(Htma(N2H42, where, M = Mn, Co, Ni, Cu and Zn; H3tma = trimesic acid, have been prepared and characterized by elemental, structural, spectral and thermal analyses. For the complexes, the carboxylate νasym and νsym stretchings are observed at about 1626 and 1367 cm−1 respectively, with Δν between them of ∼260 cm−1, showing the unidentate coordination of each carboxylate group. The hydrazine moieties are present as bridging bidentates. Electronic and EPR spectral studies suggest an octahedral geometry for the complexes. All these complexes show three steps of decomposition in TGA/DTA. SEM images of CuO and MnO residues obtained from the complexes show nano-sized clusters suggesting that the complexes may be used as precursors for nano-CuO and nano-MnO preparation. The antimicrobial activities of the prepared complexes, against four bacteria have been evaluated.

  8. Characterization of transition metal-containing oxide systems by Mössbauer Spectroscopy

    Directory of Open Access Journals (Sweden)

    Z. Homonnay

    2004-12-01

    Full Text Available High-temperature (high-Tc superconductors and colossal magnetoresistant (CMR materials belong to the most promising materials of the past 2-3 decades for technical applications. Most of them are oxides and the crucial element which determines their useful physical properties is often a transition metal (Cu, Co, Fe, Mn. 57Fe Mössbauer Spectroscopy can be used to characterize the electronic and structural properties of transition metal-containing oxides by providing information on the local electronic structure of the lattice site where the Mössbauer probe is accommodated. By reviewing several Mössbauer studies, it is demonstrated how the layered (2D electronic structure of high-Tc superconductors can be deduced from the analysis of the Mössbauer isomer shift and quadrupole splitting. We also show how the Mössbauer isomer shift indicates metallicity of the ferromagnetic phase in the CMR material LaxSr1-xCoO3.

  9. A search for superconductivity below 1 K in transition metal borides

    International Nuclear Information System (INIS)

    Leyarovska, L.; Leyarovski, E.

    1979-01-01

    Some AlB 2 -type (C32 structure) boron compounds were examined for superconductivity down to 0.42 K; the compounds have the formula MeB 2 (Me equivalent to Ti, Zr, Hf, V, Nb, Ta, Cr, Mo) (the atomic ratio of metal to boron was 0.5). Only NbB 2 was found to be superconducting with Tsub(c) = 0.62 K and a surprisingly high value of Hsub(c)(0), about 1600 Oe. Other transition metal as well as non-transition metal boron phases were also tested for superconductivity down to 0.42 K; these compounds were MeB 2 (Me equivalent to Ca, Sr, Ba), W 2 B 5 , CrB, Cr 5 B 3 , UB 2 , UB 4 and UB 12 . None of these compounds proved to be superconducting above 0.42 K; nor was any trace of superconductivity down to 0.42 K observed in MoB and NbB. (Auth.)

  10. Thermal behavior of halogenated imidebismaleimide resins

    International Nuclear Information System (INIS)

    Mohammad, A.; Al-Halim, N.Z.

    1995-01-01

    Several new poly-halogenated malecimides, bismaleimides and therir copoly resins were synthessised thermally from their corresponding amic acids. The synthesis was accomplished by two way method (amic acid-polimide) instead of the well-known three way method (amic acid-imide-polyimide). Thermal characterization of monomers and their cured resins was achieved using differential thermal analysis (DTA), dynamic thermogravimetric analysis (TGA) and isothermal gravimetric analysis (IGA). The effect of halogen substituent, especially in the ortho postion, is clear in the imidization proces, while polymerization proceeds almost equally in all systems. Thermal properties of homo and copolymers were correlated with their chemical structures. (author). 15 refs., 4

  11. Development of non-halogen cables for nuclear power stations

    Energy Technology Data Exchange (ETDEWEB)

    Yagyu, Hideki; Yamamoto, Yasuaki; Onishi, Takao (Hitachi Cable, Ltd., Tokyo (Japan))

    1983-12-01

    The non-halogen fire-resistant cables for nuclear power stations which never generate halogen gas, have been developed. The cables comprise the insulator of EP rubber and the sheath of polyolefine containing non-halogen inorganic fire-retardant. The results of the environmental test and fire-resistance test are described. In the environmental test, the cables were subjected to the heating, gamma-irradiation and steam exposure successively, according to IEEE specification 323,383, and subsequently the change in the appearance, tensile strength and electrical performance of the cables was measured. In the fire-resistance test, the vertical tray fire test according to the IEEE specification 383 was adopted, and other tests including the vertical fire test on insulator cores, oxygen index, the generation of corrosive gas, copper mirror corrosion test, gas toxicity test and optical smoke density test were carried out. It became clear that the cables did not generate halogen gas on burning, and brought about reduced toxicity, corrosion and smoke, and that the safety against fire is greatly improved by using the cables.

  12. Development of non-halogen cables for nuclear power stations

    International Nuclear Information System (INIS)

    Yagyu, Hideki; Yamamoto, Yasuaki; Onishi, Takao

    1983-01-01

    The non-halogen fire-resistant cables for nuclear power stations which never generate halogen gas, have been developed. The cables comprise the insulator of EP rubber and the sheath of polyolefine containing non-halogen inorganic fire-retardant. The results of the environmental test and fire-resistance test are described. In the environmental test, the cables were subjected to the heating, gamma-irradiation and steam exposure successively, according to IEEE specification 323,383, and subsequently the change in the appearance, tensile strength and electrical performance of the cables was measured. In the fire-resistance test, the vertical tray fire test according to the IEEE specification 383 was adopted, and other tests including the vertical fire test on insulator cores, oxygen index, the generation of corrosive gas, copper mirror corrosion test, gas toxicity test and optical smoke density test were carried out. It became clear that the cables did not generate halogen gas on burning, and brought about reduced toxicity, corrosion and smoke, and that the safety against fire is greatly improved by using the cables. (Yoshitake, I.)

  13. Volcano Relation for the Deacon Process over Transition-Metal Oxides

    DEFF Research Database (Denmark)

    Studt, Felix; Abild-Pedersen, Frank; Hansen, Heine Anton

    2010-01-01

    We establish an activity relation for the heterogeneous catalytic oxidation of HCI (the Deacon Process) over rutile transition-metal oxide catalysts by combining density functional theory calculations (DFT) with microkinetic modeling. Linear energy relations for the elementary reaction steps...

  14. Process for reducing halogen impurities in oil products

    Energy Technology Data Exchange (ETDEWEB)

    Basler, F.

    1990-08-14

    Oil products, in particular waste oils, may be efficiently reprocessed according to an economic and technically simple method for removing impurities, notably halogens. In this method, the oil product is treated at temperatures up to about 150{degree}C with an effective amount of an aqueous solution of at least one compound selected from the group consisting of a strong acid, a salt of a weak base and a strong acid and precursors thereof. The oil product obtained in this step is treated at increased temperatures with at least one halogen binding agent. The water and/or solids from the product so treated are separated out. The process of the invention can be carried out in a conventional stripping apparatus. The strong acid used in the first step is preferably selected from sulfurous acid, phosphoric acid, phosphorous acid, and phosphonic acid. The salt of the weak base and strong acid is preferably ammonium sulfate, ammonium bisulfate, ammonium sulfite, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphite, and ammonium phosphonic acid. The second step of the method is preferably a coagulation step in which organic halogen compounds break down into hydrogen halides which are neutralized by the added halogen binding agents. The preferred halogen binding agents are ammonia and/or an organic base. The coagulation is preferably carried out in heat exchangers so that the oil is heated in 3 stages and the oil from each stage is passed through a cascade tower. In the third step, additives may be used to enhance separation of the oil. Experiments are described to illustrate the method of the invention. 1 tab.

  15. Participation of the Halogens in Photochemical Reactions in Natural and Treated Waters

    Directory of Open Access Journals (Sweden)

    Yi Yang

    2017-10-01

    Full Text Available Halide ions are ubiquitous in natural waters and wastewaters. Halogens play an important and complex role in environmental photochemical processes and in reactions taking place during photochemical water treatment. While inert to solar wavelengths, halides can be converted into radical and non-radical reactive halogen species (RHS by sensitized photolysis and by reactions with secondary reactive oxygen species (ROS produced through sunlight-initiated reactions in water and atmospheric aerosols, such as hydroxyl radical, ozone, and nitrate radical. In photochemical advanced oxidation processes for water treatment, RHS can be generated by UV photolysis and by reactions of halides with hydroxyl radicals, sulfate radicals, ozone, and other ROS. RHS are reactive toward organic compounds, and some reactions lead to incorporation of halogen into byproducts. Recent studies indicate that halides, or the RHS derived from them, affect the concentrations of photogenerated reactive oxygen species (ROS and other reactive species; influence the photobleaching of dissolved natural organic matter (DOM; alter the rates and products of pollutant transformations; lead to covalent incorporation of halogen into small natural molecules, DOM, and pollutants; and give rise to certain halogen oxides of concern as water contaminants. The complex and colorful chemistry of halogen in waters will be summarized in detail and the implications of this chemistry for global biogeochemical cycling of halogen, contaminant fate in natural waters, and water purification technologies will be discussed.

  16. Dynamics of the central phenylene ring torsional motion in halogenated phenylene ethynylene oligomers

    Energy Technology Data Exchange (ETDEWEB)

    Pejov, Ljupco [Institute of Chemistry, Department of Physical Chemistry, SS. Cyril and Methodius University, Arhimedova 5, P.O. Box 162, 1000 Skopje(Macedonia, The Former Yugoslav Republic of)], E-mail: ljupcop@iunona.pmf.ukim.edu.mk; La Rosa, Manuela [PST Group- M6, STMicroelectronics, Stradale Primosole 50, 95121 Catania (Italy); Kocarev, Ljupco [Institute for Nonlinear Science, University of California, San Diego 9500 Gilman, Drive, La Jolla, CA 92093-0402 (United States); Macedonian Academy of Sciences and Arts, bul. Krste Misirkov 2, P.O. Box 428, 1000 Skopje (Macedonia, The Former Yugoslav Republic of)

    2007-11-09

    The dynamics of intramolecular torsional motion of central phenylene ring in a series of phenylene ethynylene oligomer derivatives was investigated. On the basis of calculated hindered rotational potentials corresponding to this motion, the torsional energy levels were obtained by solving the torsional Schroedinger equation. Subsequently, the torsional correlation time and transition probability was computed within the Bloembergen-Purcell-Pound (BPP) formalism, considering both the classical and quantum mechanical tunneling contributions to the intramolecular rotation. The results were interpreted in the context of molecular conductivity switching behavior of the considered series of compounds. Also some other parameters relevant to molecular admittance were calculated, such as the HOMO-LUMO energy difference and the spatial extent of the frontier molecular orbitals. Classical electrostatic arguments were applied to understand the physical basis of the conformational stability differences in the studied compounds. It was found that halogenation of the central phenylene ring may be used for fine-tuning of molecular conduction behavior, in the sense of modulating the HOMO-LUMO energy difference, the spatial extent of frontier MOs, as well as the barrier height to torsional motion of the central phenylene ring. The time scale of the temperature induced stochastic conformational switching between the 'on' and 'off' states, along with the corresponding transition probability could be varied by an order of magnitude upon halogenation of the central phenylene ring. The tunneling contributions to the torsional correlation time were found to be of minor importance in this context, and this quantity may be quite correctly estimated with the classical BPP approach.

  17. Dynamics of the central phenylene ring torsional motion in halogenated phenylene ethynylene oligomers

    International Nuclear Information System (INIS)

    Pejov, Ljupco; La Rosa, Manuela; Kocarev, Ljupco

    2007-01-01

    The dynamics of intramolecular torsional motion of central phenylene ring in a series of phenylene ethynylene oligomer derivatives was investigated. On the basis of calculated hindered rotational potentials corresponding to this motion, the torsional energy levels were obtained by solving the torsional Schroedinger equation. Subsequently, the torsional correlation time and transition probability was computed within the Bloembergen-Purcell-Pound (BPP) formalism, considering both the classical and quantum mechanical tunneling contributions to the intramolecular rotation. The results were interpreted in the context of molecular conductivity switching behavior of the considered series of compounds. Also some other parameters relevant to molecular admittance were calculated, such as the HOMO-LUMO energy difference and the spatial extent of the frontier molecular orbitals. Classical electrostatic arguments were applied to understand the physical basis of the conformational stability differences in the studied compounds. It was found that halogenation of the central phenylene ring may be used for fine-tuning of molecular conduction behavior, in the sense of modulating the HOMO-LUMO energy difference, the spatial extent of frontier MOs, as well as the barrier height to torsional motion of the central phenylene ring. The time scale of the temperature induced stochastic conformational switching between the 'on' and 'off' states, along with the corresponding transition probability could be varied by an order of magnitude upon halogenation of the central phenylene ring. The tunneling contributions to the torsional correlation time were found to be of minor importance in this context, and this quantity may be quite correctly estimated with the classical BPP approach

  18. Adsorption and dissociation of dinitrogen on transition metal (Ta, W and Re) doped MgO surface

    KAUST Repository

    Yadav, Manoj Kumar

    2016-06-16

    The adsorption and dissociation of dinitrogen on transition metal (Ta, W and Re) doped MgO(100) surface has been studied employing density functional theory. It is found that all these transition metals (TM) on MgO(100) surface are capable of adsorbing dinitrogen (N2), however there is no dissociative adsorption of N2 on single transition metal dopant. When two TM atoms are doped on MgO(100) surface, dissociative adsorption of dinitrogen occurs in all the three cases. Whether the dissociation is spontaneous or is it associated with activation barrier depends on the orientation of N2 molecule approaching the dopant site.

  19. Metal-insulator transition in 2D: the role of interactions and disorder

    International Nuclear Information System (INIS)

    Kastrinakis, George

    2007-01-01

    We present a model for the metal-insulator transition in 2D, observed in the recent years. Our starting point consists of two ingredients only, which are ubiquitous in the experiments: Coulomb interactions and weak disorder spin scattering (coming from the interfaces of the heterostructures in question). In a diagramatic approach, we predict the existence of a characteristic temperature T 0 =T 0 (n,ω H ), n being the density of carriers, and ω H the Zeeman energy, below which these systems become metallic, due to the onset of strong spin-density correlations. This is in very good agreement with experiments, and corroborates the fact that varying n and ω H are equivalent ways into/out of the metallic regime. The conductivity, calculated as a function of temperature and ω H in the metallic state, compares favorably to experiment. Moreover, we give an explicit expression for the conventional weak disorder contributions to the conductivity in the frame of our model. We comment on the nature of the transition, we calculate the specific heat of the system and we discuss the fate of the metallic state in the limit of zero temperature

  20. First principles description of the insulator-metal transition in europium monoxide

    KAUST Repository

    Wang, Hao

    2012-02-01

    Europium monoxide, EuO, is a ferromagnetic insulator. Its electronic structure under pressure and doping is investigated by means of density functional theory. We employ spin polarized electronic structure calculations including onsite electron-electron interaction for the localized Eu 4f and 5d electrons. Our results show that under pressure the ferromagnetism is stable, both for hydrostatic and uniaxial pressure, while the compound undergoes an insulator-metal transition. The insulator-metal transition in O deficient and Gd doped EuO is reproduced for an impurity concentration of 6.25%. A 10 monolayer thick EuO(1 0 0) thin film is predicted to be an insulator with a narrow band gap of 0.08 eV. © 2011 Elsevier B.V. All rights reserved.

  1. Ultra-high-rate pseudocapacitive energy storage in two-dimensional transition metal carbides

    Energy Technology Data Exchange (ETDEWEB)

    Lukatskaya, Maria R. [Drexel Univ., Philadelphia, PA (United States); Dept. of Chemical Engineering, Stanford, CA (United States); Kota, Sankalp [Drexel Univ., Philadelphia, PA (United States); Lin, Zifeng [Univ. Paul Sabatier, Toulouse (France); Reseau sur le Stockage Electrochimique de l' Energie (RS2E) (France); Zhao, Meng -Qiang [Drexel Univ., Philadelphia, PA (United States); Shpigel, Netanel [Bar-Ilan Univ., Ramat-Gan (Israel); Levi, Mikhael D. [Bar-Ilan Univ., Ramat-Gan (Israel); Halim, Joseph [Drexel Univ., Philadelphia, PA (United States); Taberna, Pierre -Louis [Univ. Paul Sabatier, Toulouse (France); Reseau sur le Stockage Electrochimique de l' Energie (RS2E) (France); Barsoum, Michel W. [Drexel Univ., Philadelphia, PA (United States); Simon, Patrice [Univ. Paul Sabatier, Toulouse (France); Reseau sur le Stockage Electrochimique de l' Energie (RS2E) (France); Gogotsi, Yury G. [Drexel Univ., Philadelphia, PA (United States)

    2017-07-10

    In this study, the use of fast surface redox storage (pseudocapacitive) mechanisms can enable devices that store much more energy than electrical double-layer capacitors (EDLCs) and, unlike batteries, can do so quite rapidly. Yet, few pseudocapacitive transition metal oxides can provide a high power capability due to their low intrinsic electronic and ionic conductivity. Here we demonstrate that two-dimensional transition metal carbides (MXenes) can operate at rates exceeding those of conventional EDLCs, but still provide higher volumetric and areal capacitance than carbon, electrically conducting polymers or transition metal oxides. We applied two distinct designs for MXene electrode architectures with improved ion accessibility to redox-active sites. A macroporous Ti3C2Tx MXene film delivered up to 210 F g–1 at scan rates of 10 V s–1, surpassing the best carbon supercapacitors known. In contrast, we show that MXene hydrogels are able to deliver volumetric capacitance of ~1,500 F cm–3 reaching the previously unmatched volumetric performance of RuO2.

  2. High coercivity rare earth-transition metal magnets

    International Nuclear Information System (INIS)

    Croat, J.J.

    1982-01-01

    Ferromagnetic compositions having intrinsic magnetic coercivities at room temperature of at least 1,000 Oersteds are formed by the controlled quenching of molten rare earth -transition metal alloys. Hard magnets may be inexpensively formed from the lower atomic weight lanthanide elements and iron. The preferable compositions lie within: at least one of Fe, Ni, Co (20 to 70 atomic percent); and at least one of Ce, Pr, Na, Sm, Eu, Tb, Dy, Ho, Er, Tm, Y (80 to 30 atomic percent). (author)

  3. Correlated structural and electronic phase transformations in transition metal chalcogenide under high pressure

    Energy Technology Data Exchange (ETDEWEB)

    Li, Chunyu, E-mail: licy@hpstar.ac.cn, E-mail: yanhao@hpstar.ac.cn; Ke, Feng; Yu, Zhenhai; Chen, Zhiqiang; Yan, Hao, E-mail: licy@hpstar.ac.cn, E-mail: yanhao@hpstar.ac.cn [Center for High Pressure Science and Technology Advanced Research, Shanghai 201203 (China); Hu, Qingyang [Center for High Pressure Science and Technology Advanced Research, Shanghai 201203 (China); Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015 (United States); Zhao, Jinggeng [Natural Science Research Center, Academy of Fundamental and Interdisciplinary Sciences, Harbin Institute of Technology, Harbin 150080 (China)

    2016-04-07

    Here, we report comprehensive studies on the high-pressure structural and electrical transport properties of the layered transition metal chalcogenide (Cr{sub 2}S{sub 3}) up to 36.3 GPa. A structural phase transition was observed in the rhombohedral Cr{sub 2}S{sub 3} near 16.5 GPa by the synchrotron angle dispersive X-ray diffraction measurement using a diamond anvil cell. Through in situ resistance measurement, the electric resistance value was detected to decrease by an order of three over the pressure range of 7–15 GPa coincided with the structural phase transition. Measurements on the temperature dependence of resistivity indicate that it is a semiconductor-to-metal transition in nature. The results were also confirmed by the electronic energy band calculations. Above results may shed a light on optimizing the performance of Cr{sub 2}S{sub 3} based applications under extreme conditions.

  4. Practical Improvements to the Lee-More Conductivity Near the Metal-Insulator Transition

    International Nuclear Information System (INIS)

    Desjarlais, Michael P.

    2000-01-01

    The wide-range conductivity model of Lee and More is modified to allow better agreement with recent experimental data and theories for dense plasmas in the metal-insulator transition regime. Modifications primarily include a new ionization equilibrium model, consisting of a smooth blend between single ionization Saha (with a pressure ionization correction) and the generic Thomas-Fermi ionization equilibrium, a more accurate treatment of electron-neutral collisions using a polarization potential, and an empirical modification to the minimum allowed collision time. These simple modifications to the Lee-More algorithm permit a more accurate modeling of the physics near the metal-insulator transition, while preserving the generic Lee-More results elsewhere

  5. Practical improvements to the Lee-More conductivity near the metal-insulator transition

    International Nuclear Information System (INIS)

    Desjarlais, M.P.

    2001-01-01

    The wide-range conductivity model of Lee and More is modified to allow better agreement with recent experimental data and theories for dense plasmas in the metal-insulator transition regime. Modifications primarily include a new ionization equilibrium model, consisting of a smooth blend between single ionization Saha (with a pressure ionization correction) and the generic Thomas-Fermi ionization equilibrium, a more accurate treatment of electron-neutral collisions using a polarization potential, and an empirical modification to the minimum allowed collision time. These simple modifications to the Lee-More algorithm permit a more accurate modeling of the physics near the metal-insulator transition, while preserving the generic Lee-More results elsewhere. (orig.)

  6. Transition radiation in metal-metal multilayer nanostructures as a medical source of hard x-ray radiation

    International Nuclear Information System (INIS)

    Pokrovsky, A. L.; Kaplan, A. E.; Shkolnikov, P. L.

    2006-01-01

    We show that a periodic metal-metal multilayer nanostructure can serve as an efficient source of hard x-ray transition radiation. Our research effort is aimed at developing an x-ray source for medical applications, which is based on using low-energy relativistic electrons. The approach toward choosing radiator-spacer couples for the generation of hard x-ray resonant transition radiation by few-MeV electrons traversing solid multilayer structures for the energies of interest to medicine (30-50 keV) changes dramatically compared with that for soft x-ray radiation. We show that one of the main factors in achieving the required resonant line is the absence of the contrast of the refractive indices between the spacer and the radiator at the far wings of the radiation line; for that purpose, the optimal spacer, as a rule, should have a higher atomic number than the radiator. Having experimental goals in mind, we have considered also the unwanted effects due to bremsstrahlung radiation, absorption and scattering of radiated photons, detector-related issues, and inhibited coherence of transition radiation due to random deviation of spacing between the layers. Choosing as a model example a Mo-Ag radiator-spacer pair of materials, we demonstrate that the x-ray transition radiation line can be well resolved with the use of spatial and frequency filtering

  7. Localized versus collective behaviour of d-electrons in transition metal oxide systems of perovskite systems

    Energy Technology Data Exchange (ETDEWEB)

    Rao, C N.R. [Indian Inst. of Tech., Kanpur

    1974-12-01

    The behavior of d-electrons in perovskites of the type LnZO/sub 3/ (Z = trivalent transition metal ion and Ln = rare earth or yttrium) depends on the spin configuration of the transition metal ion. LaTiO/sub 3/ and LaNiO/sub 3/ with low-spin transition metal ions (S = 1/2) are metallic while LaCrO/sub 3/, LnMnO/sub 3/ and LnFeO/sub 3/ with high-spin ions are poor semiconductors exhibiting localized behavior of d-electrons. In rare earth cobaltites, the cobalt ions are present mainly in the diamagnetic low-spin Co /sup III/ state at low temperatures. The Co/sup III/ ions transform to high-spin Co/sup 3 +/ ions with increase in temperature. At higher temperatures, there is electron-transfer from Co/sup 3 +/ to Co/sup III/ions producing intermetallic states. Spin-state transitions are seen in these cobaltites in the range 150-870/sup 0/K. At high temperatures, the cobaltites show evidence for localized-itinerant electron transitions. In La/sub 1-x/ Sr/sub x/CoO/sub 3/ there is onset of ferromagnetism at x > 0.125, at which point there is a structural dicontinuity and electrons become itinerant. The composition with x = 0.5 is metallic and T/sub c/ = 230/sup 0/K. The ferromagnetic component in La/sub 1-x/Sr/sub x/ CoO/sub 3/ increases with x in the range 0.125-0.50. Catalytic properties of rare earth cobaltites appear to be related to the spin state equilibria. (auth)

  8. Pressure-induced irreversible metallization accompanying the phase transitions in S b2S3

    Science.gov (United States)

    Dai, Lidong; Liu, Kaixiang; Li, Heping; Wu, Lei; Hu, Haiying; Zhuang, Yukai; Yang, Linfei; Pu, Chang; Liu, Pengfei

    2018-01-01

    We have revealed S b2S3 to have two phase transitions and to undergo metallization using a diamond anvil cell at around 5.0, 15.0, and 34.0 GPa, respectively. These results were obtained on the basis of high-pressure Raman spectroscopy, temperature-dependent conductivity measurements, atomic force microscopy, high-resolution transmission electron microscopy, and first-principles calculations. The first phase transition at ˜5.0 GPa is an isostructural phase transition, which is manifested in noticeable changes in five Raman-active modes and the slope of the conductivity because of a change in the electronic structure. The second pressure-induced phase transition was characterized by a discontinuous change in the slope of conductivity and a new low-intensity Raman mode at ˜15.0 GPa . Furthermore, a semiconductor-to-metal transition was found at ˜34.0 GPa , which was accompanied by irreversible metallization, and it could be attributed to the permanently plastic deformation of the interlayer spacing. This high-pressure behavior of S b2S3 will help us to understand the universal crystal structure evolution and electrical characteristics for A2B3 -type compounds, and to facilitate their application in electronic devices.

  9. [Co5(mu3-OH)2(btec)2(bpp)]n: a three-dimensional homometallic molecular metamagnet built from the mixed hydroxide/carboxylate-bridged ferrimagnetic-like chains.

    Science.gov (United States)

    Jia, Hong-Peng; Li, Wei; Ju, Zhan-Feng; Zhang, Jie

    2007-09-07

    A three-dimensional homometallic complex [Co(5)(mu(3)-OH)(2)(btec)(2)(bpp)](n) is built from the mixed hydroxide/carboxylate bridged cobalt(ii) chains linked by the 1,2,4,5-benzenetetracarboxylate (btec(4-)) anion and 1,3-bis(4-pyridyl)-propane molecule (bpp). Within each chain, two mu(3)-OH-bridged metal triangles connect to each other by sharing a common vertex to give rise to a bow-tie type Co(5)(mu(3)-OH)(2) subunit, which is joined to adjacent subunits by four mu(1,1)-carboxylate bridges to form a step-like metal-oxygen backbone. The magnetic studies revealed that the coexistence of ferromagnetic and antiferrimagnetic interactions resulted in a ferrimagnetic-like behavior of the homometallic chains. Below a critical temperature (T(N) = 12.5 K), bulk antiferromagnetic ordering was observed at low field due to the weak interchain antiferromagnetic interactions. A metamagnetic transition occurred at a magnetic field of ca. 5 kOe at 2 K.

  10. Transition absorption as a mechanism of surface photoelectron emission from metals

    DEFF Research Database (Denmark)

    Zhukovsky, Sergei; Protsenko, Igor E.; Ikhsanov, Renat Sh

    2015-01-01

    Transition absorption of a photon by an electron passingthrough a boundary between two media with different permit-tivities is described both classically and quantum mechani-cally. Transition absorption is shown to make a substantialcontribution to photoelectron emission at a metal....../semicon-ductor interface in nanoplasmonic systems, and is put forth asa possible microscopic mechanism of the surface photoelec-tric effect in photodetectors and solar cells containing plas-monic nanoparticles....

  11. Halogenation dictates the architecture of amyloid peptide nanostructures.

    Science.gov (United States)

    Pizzi, Andrea; Pigliacelli, Claudia; Gori, Alessandro; Nonappa; Ikkala, Olli; Demitri, Nicola; Terraneo, Giancarlo; Castelletto, Valeria; Hamley, Ian W; Baldelli Bombelli, Francesca; Metrangolo, Pierangelo

    2017-07-20

    Amyloid peptides yield a plethora of interesting nanostructures though difficult to control. Here we report that depending on the number, position, and nature of the halogen atoms introduced into either one or both phenylalanine benzene rings of the amyloid β peptide-derived core-sequence KLVFF, four different architectures were obtained in a controlled manner. Our findings demonstrate that halogenation may develop as a general strategy to engineer amyloidal peptide self-assembly and obtain new amyloidal nanostructures.

  12. First-principles interatomic potentials for transition-metal aluminides. III. Extension to ternary phase diagrams

    Science.gov (United States)

    Widom, Mike; Al-Lehyani, Ibrahim; Moriarty, John A.

    2000-08-01

    Modeling structural and mechanical properties of intermetallic compounds and alloys requires detailed knowledge of their interatomic interactions. The first two papers of this series [Phys. Rev. B 56, 7905 (1997); 58, 8967 (1998)] derived first-principles interatomic potentials for transition-metal (TM) aluminides using generalized pseudopotential theory (GPT). Those papers focused on binary alloys of aluminum with first-row transition metals and assessed the ability of GPT potentials to reproduce and elucidate the alloy phase diagrams of Al-Co and Al-Ni. This paper addresses the phase diagrams of the binary alloy Al-Cu and the ternary systems Al-Co-Cu and Al-Co-Ni, using GPT pair potentials calculated in the limit of vanishing transition-metal concentration. Despite this highly simplifying approximation, we find rough agreement with the known low-temperature phase diagrams, up to 50% total TM concentration provided the Co fraction is below 25%. Full composition-dependent potentials and many-body interactions would be required to correct deficiencies at higher Co concentration. Outside this troublesome region, the experimentally determined stable and metastable phases all lie on or near the convex hull of a scatter plot of energy versus composition. We verify, qualitatively, reported solubility ranges extending binary alloys into the ternary diagram in both Al-Co-Cu and Al-Co-Ni. Finally, we reproduce previously conjectured transition-metal positions in the decagonal quasicrystal phase.

  13. Research on Multidisciplinary Optimization Design of Bridge Crane

    Directory of Open Access Journals (Sweden)

    Tong Yifei

    2013-01-01

    Full Text Available Bridge crane is one of the most widely used cranes in our country, which is indispensable equipment for material conveying in the modern production. In this paper, the framework of multidisciplinary optimization for bridge crane is proposed. The presented research on crane multidisciplinary design technology for energy saving includes three levels, respectively: metal structures level, transmission design level, and electrical system design level. The shape optimal mathematical model of the crane is established for shape optimization design of metal structure level as well as size optimal mathematical model and topology optimal mathematical model of crane for topology optimization design of metal structure level is established. Finally, system-level multidisciplinary energy-saving optimization design of bridge crane is further carried out with energy-saving transmission design results feedback to energy-saving optimization design of metal structure. The optimization results show that structural optimization design can reduce total mass of crane greatly by using the finite element analysis and multidisciplinary optimization technology premised on the design requirements of cranes such as stiffness and strength; thus, energy-saving design can be achieved.

  14. Holographic metal-insulator transition in higher derivative gravity

    Energy Technology Data Exchange (ETDEWEB)

    Ling, Yi, E-mail: lingy@ihep.ac.cn [Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China); Shanghai Key Laboratory of High Temperature Superconductors, Shanghai, 200444 (China); Liu, Peng, E-mail: liup51@ihep.ac.cn [Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China); Wu, Jian-Pin, E-mail: jianpinwu@mail.bnu.edu.cn [Institute of Gravitation and Cosmology, Department of Physics, School of Mathematics and Physics, Bohai University, Jinzhou 121013 (China); Shanghai Key Laboratory of High Temperature Superconductors, Shanghai, 200444 (China); Zhou, Zhenhua, E-mail: zhouzh@ihep.ac.cn [Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China)

    2017-03-10

    We introduce a Weyl term into the Einstein–Maxwell-Axion theory in four dimensional spacetime. Up to the first order of the Weyl coupling parameter γ, we construct charged black brane solutions without translational invariance in a perturbative manner. Among all the holographic frameworks involving higher derivative gravity, we are the first to obtain metal-insulator transitions (MIT) when varying the system parameters at zero temperature. Furthermore, we study the holographic entanglement entropy (HEE) of strip geometry in this model and find that the second order derivative of HEE with respect to the axion parameter exhibits maximization behavior near quantum critical points (QCPs) of MIT. It testifies the conjecture in that HEE itself or its derivatives can be used to diagnose quantum phase transition (QPT).

  15. Review of thermodinamic and mechanical properties of hydrogen-transition metal systems

    International Nuclear Information System (INIS)

    Mathias, H.; Katz, Y.

    1978-04-01

    A large body of fundamental and empirical knowledge has been acquired during many years of research concerning the interactions between hydrogen and metals, the location of hydrogen in metal structures, its mobility in metals and its influence on mechanical properties of metals. Much progress has been made in the understanding of related phenomena, and various theories have been proposed, but considerable disagreement still exist about basic mechanisms involved. The growing interest in these subjects and their important role in science and technology are well documented by many reviews and symposia. A general survey of these topics with reference to experimental results and theories related to thermodynamic and mechanical properties of hydrogen-transition metal systems, such as H-Pd, H-Ti, H-Fe etc. is given in the present review. Special emphasis is given to hydrogen embrittlement of metals

  16. Ultrafast Transient Absorption Spectroscopy of Polymer-Based Organophotoredox Catalysts Mimicking Transition-Metal Complexes

    Science.gov (United States)

    Jamhawi, Abdelqader; Paul, Anam C.; Smith, Justin D.; Handa, Sachin; Liu, Jinjun

    2017-06-01

    Transition-metal complexes of rare earth metals including ruthenium and iridium are most commonly employed as visible-light photocatalysts. Despite their highly important and broad applications, they have many disadvantages including high cost associated with low abundance in earth crust, potential toxicity, requirement of specialized ligands for desired activity, and difficulty in recycling of metal contents as well as associated ligands. Polymer-based organophotoredox catalysts are promising alternatives and possess unique advantages such as easier synthesis from inexpensive starting material, longer excited state life time, broad range of activity, sustainability, and recyclability. In this research talk, time-resolved photoluminescence and femtosecond transient absorption (TA) spectroscopy measurements of three novel polymer-based organophotoredox catalysts will be presented. By our synthetic team, their catalytic activity has been proven in some highly valuable chemical transformations, that otherwise require transition metal complexes. Time-resolved spectroscopic investigations have demonstrated that photoinduced processes in these catalysts are similar to the transition metal complexes. Especially, intramolecular vibrational relaxation, internal conversion, and intersystem crossing from the S1 state to the T1 state all occur on a sub-picosecond timescale. The long lifetime of the T1 state ( 2-3 microsecond) renders these polymers potent oxidizing and reducing agents. A spectroscopic and kinetic model has been developed for global fitting of TA spectra in both the frequency and time domains. Implication of the current ultrafast spectroscopy studies of these novel molecules to their roles in photocatalysis will be discussed.

  17. Control of electronic properties of 2D carbides (MXenes) by manipulating their transition metal layers

    KAUST Repository

    Anasori, Babak

    2016-02-24

    In this study, a transition from metallic to semiconducting-like behavior has been demonstrated in two-dimensional (2D) transition metal carbides by replacing titanium with molybdenum in the outer transition metal (M) layers of M3C2 and M4C3 MXenes. The MXene structure consists of n + 1 layers of near-close packed M layers with C or N occupying the octahedral site between them in an [MX]nM arrangement. Recently, two new families of ordered 2D double transition metal carbides MXenes were discovered, M′2M′′C2 and M′2M′′2C3 – where M′ and M′′ are two different early transition metals, such as Mo, Cr, Ta, Nb, V, and Ti. The M′ atoms only occupy the outer layers and the M′′ atoms fill the middle layers. In other words, M′ atomic layers sandwich the middle M′′–C layers. Using X-ray atomic pair distribution function (PDF) analysis on Mo2TiC2 and Mo2Ti2C3 MXenes, we present the first quantitative analysis of structures of these novel materials and experimentally confirm that Mo atoms are in the outer layers of the [MC]nM structures. The electronic properties of these Mo-containing MXenes are compared with their Ti3C2 counterparts, and are found to be no longer metallic-like conductors; instead the resistance increases mildly with decreasing temperatures. Density functional theory (DFT) calculations suggest that OH terminated Mo–Ti MXenes are semiconductors with narrow band gaps. Measurements of the temperature dependencies of conductivities and magnetoresistances have confirmed that Mo2TiC2Tx exhibits semiconductor-like transport behavior, while Ti3C2Tx is a metal. This finding opens new avenues for the control of the electronic and optical applications of MXenes and for exploring new applications, in which semiconducting properties are required.

  18. The dynamic behavior of the exohedral transition metal complexes ...

    Indian Academy of Sciences (India)

    Home; Journals; Journal of Chemical Sciences; Volume 129; Issue 7. The dynamic behavior of the exohedral transition metal complexes of B₄₀ : η⁶- and η⁷-B₄₀Cr(CO) ₃ and Cr(CO) ₃η⁷-B₄η₀-Cr(CO) ₃. NAIWRIT KARMODAK ELUVATHINGAL D JEMMIS. REGULAR ARTICLE Volume 129 Issue 7 July 2017 pp ...

  19. Magnetic states, correlation effects and metal-insulator transition in FCC lattice

    Science.gov (United States)

    Timirgazin, M. A.; Igoshev, P. A.; Arzhnikov, A. K.; Irkhin, V. Yu

    2016-12-01

    The ground-state magnetic phase diagram (including collinear and spiral states) of the single-band Hubbard model for the face-centered cubic lattice and related metal-insulator transition (MIT) are investigated within the slave-boson approach by Kotliar and Ruckenstein. The correlation-induced electron spectrum narrowing and a comparison with a generalized Hartree-Fock approximation allow one to estimate the strength of correlation effects. This, as well as the MIT scenario, depends dramatically on the ratio of the next-nearest and nearest electron hopping integrals {{t}\\prime}/t . In contrast with metallic state, possessing substantial band narrowing, insulator one is only weakly correlated. The magnetic (Slater) scenario of MIT is found to be superior over the Mott one. Unlike simple and body-centered cubic lattices, MIT is the first order transition (discontinuous) for most {{t}\\prime}/t . The insulator state is type-II or type-III antiferromagnet, and the metallic state is spin-spiral, collinear antiferromagnet or paramagnet depending on {{t}\\prime}/t . The picture of magnetic ordering is compared with that in the standard localized-electron (Heisenberg) model.

  20. Cycloadditions to Epoxides Catalyzed by GroupIII-V Transition-Metal Complexes

    KAUST Repository

    D'Elia, Valerio

    2015-05-25

    Complexes of groupIII-V transition metals are gaining increasing importance as Lewis acid catalysts for the cycloaddition of dipolarophiles to epoxides. This review examines the latest reports, including homogeneous and heterogeneous applications. The pivotal step for the cycloaddition reactions is the ring opening of the epoxide following activation by the Lewis acid. Two modes of cleavage (C-C versus C-O) have been identified depending primarily on the substitution pattern of the epoxide, with lesser influence observed from the Lewis acid employed. The widely studied cycloaddition of CO2 to epoxides to afford cyclic carbonates (C-O bond cleavage) has been scrutinized in terms of catalytic efficiency and reaction mechanism, showing that unsophisticated complexes of groupIII-V transition metals are excellent molecular catalysts. These metals have been incorporated, as well, in highly performing, recyclable heterogeneous catalysts. Cycloadditions to epoxides with other dipolarophiles (alkynes, imines, indoles) have been conducted with scandium triflate with remarkable performances (C-C bond cleavage). © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Cycloadditions to Epoxides Catalyzed by GroupIII-V Transition-Metal Complexes

    KAUST Repository

    D'Elia, Valerio; Pelletier, Jeremie; Basset, Jean-Marie

    2015-01-01

    Complexes of groupIII-V transition metals are gaining increasing importance as Lewis acid catalysts for the cycloaddition of dipolarophiles to epoxides. This review examines the latest reports, including homogeneous and heterogeneous applications. The pivotal step for the cycloaddition reactions is the ring opening of the epoxide following activation by the Lewis acid. Two modes of cleavage (C-C versus C-O) have been identified depending primarily on the substitution pattern of the epoxide, with lesser influence observed from the Lewis acid employed. The widely studied cycloaddition of CO2 to epoxides to afford cyclic carbonates (C-O bond cleavage) has been scrutinized in terms of catalytic efficiency and reaction mechanism, showing that unsophisticated complexes of groupIII-V transition metals are excellent molecular catalysts. These metals have been incorporated, as well, in highly performing, recyclable heterogeneous catalysts. Cycloadditions to epoxides with other dipolarophiles (alkynes, imines, indoles) have been conducted with scandium triflate with remarkable performances (C-C bond cleavage). © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. CPA theory of the magnetization in rare earth transition metal alloys

    International Nuclear Information System (INIS)

    Szpunar, B.; Lindgaard, P.A.

    1976-11-01

    Calculations were made of the magnetic moment per atom of the transition metal and the rare earth metal in the intermetallic compounds, Gdsub(1-x)Nisub(x), Gdsub(1-x)Fesub(x), Gdsub(1-x)Cosub(x), and Ysub(1-x)Cosub(x). A simple model of the disordered alloy consisting of spins localized on the rare earth atoms and interacting with a narrow d-band is considered. The magnetic moment of the alloy at zero temperature is calculated within the molecular field and Hartree-Fock approximations. Disorder is treated in the coherent potential approximation. Results are in good agreement with the experimental data obtained for the crystalline and amorphous intermetallic compounds. It is shown that the temperature dependence of the magnetic moments and Curie and ferrimagnetic compensation temperatures can be accounted for by a simple model assuming a RKKY interaction between the rare-earth moments and the transition metal pseudo spin. The interaction is mediated by an effective alloy medium calculated using the CPA theory and elliptic densities of states. (Auth.)

  3. Positron annihilation study of the semiconductor to metal transition in Ti2O3

    International Nuclear Information System (INIS)

    Tao, S.J.; Rao, C.N.R.

    1977-01-01

    An increase of positron mean life is found to accompany the semiconductor-metal transition in Ti 2 O 3 . This agrees well with the recent finding that the unit cell volume increases during the transition. (orig.) [de

  4. Density functional theory studies of transition metal nanoparticles in catalysis

    DEFF Research Database (Denmark)

    Greeley, Jeffrey Philip; Rankin, Rees; Zeng, Zhenhua

    2013-01-01

    Periodic Density Functional Theory calculations are capable of providing powerful insights into the structural, energetics, and electronic phenomena that underlie heterogeneous catalysis on transition metal nanoparticles. Such calculations are now routinely applied to single crystal metal surfaces...... and to subnanometer metal clusters. Descriptions of catalysis on truly nanosized structures, however, are generally not as well developed. In this talk, I will illustrate different approaches to analyzing nanocatalytic phenomena with DFT calculations. I will describe case studies from heterogeneous catalysis...... and electrocatalysis, in which single crystal models are combined with Wulff construction-based ideas to produce descriptions of average nanocatalyst behavior. Then, I will proceed to describe explicitly DFT-based descriptions of catalysis on truly nanosized particles (

  5. Late transition metal m-or chemistry and D6 metal complex photoeliminations

    Energy Technology Data Exchange (ETDEWEB)

    Sharp, Paul [Univ. of Missouri, Columbia, MO (United States)

    2015-07-31

    With the goal of understanding and controlling photoreductive elimination reactions from d6 transition metal complexes as part of a solar energy storage cycle we have investigated the photochemistry of Pt(IV) bromo, chloro, hydroxo, and hydroperoxo complexes. Photoreductive elimination reactions occur for all of these complexes and appear to involve initial Pt-Br, Pt-Cl, or Pt-O bond fission. In the case of Pt-OH bond fission, the subsequent chemistry can be controlled through hydrogen bonding to the hydroxo group.

  6. The role of the excited impurity levels on the metal-non metal transition

    International Nuclear Information System (INIS)

    Silva, M.S.F. da; Makler, S.S.; Anda, E.V.

    1983-01-01

    The electronic density of states for the impurity bands in doped semiconductors is calculated using the Green function method. The system is described by a Hamiltonian with local Coulomb interactions represented in a tight binding basis composed by two orbitals per site. The electronic correlation is treated in the CPA approximation. To calculate the configurational average for this structural disordered system a diagrammatic scheme is developed. It represents an extension of the Matsubara and Toyozawa method for the case of two hybridized bands in the presence of electronic correlation. The excited levels show to play a crutial role in the undestanding of the metal-non metal transition. This work represents an improvement of a previous result. The particular case of Si : P is analyzed. (author) [pt

  7. The role of the excited impurity levels on the metal-non metal transition

    International Nuclear Information System (INIS)

    Silva, M.S.F. da; Makler, S.S.; Anda, E.V.

    1983-01-01

    The electronic density of states for the impurity bands in doped semiconductors is calculated using the Green function method. The system is described by a Hamiltonian with local Coulomb interactions represented in a tight binding basis composed by two orbitals per site. The electronic correlation is treated in the CPA approximation. To calculate the configurational average for this structural disordered system a diagrammatic scheme is developed. It represents an extension of the Matsubara and Toyozawa method for the case of two hybridized bands in the presence of electronic correlation. The excited levels shown to play a crutial role in the understanding of the metal-non metal transition. This work represents an improvement of a previous result. The particular case of Si:P is analyzed. (Author) [pt

  8. Rapid Mapping of Lithiation Dynamics in Transition Metal Oxide Particles with Operando X-ray Absorption Spectroscopy

    Science.gov (United States)

    Nowack, Lea; Grolimund, Daniel; Samson, Vallerie; Marone, Federica; Wood, Vanessa

    2016-02-01

    Since the commercialization of lithium ion batteries (LIBs), layered transition metal oxides (LiMO2, where M = Co, Mn, Ni, or mixtures thereof) have been materials of choice for LIB cathodes. During cycling, the transition metals change their oxidation states, an effect that can be tracked by detecting energy shifts in the X-ray absorption near edge structure (XANES) spectrum. X-ray absorption spectroscopy (XAS) can therefore be used to visualize and quantify lithiation kinetics in transition metal oxide cathodes; however, in-situ measurements are often constrained by temporal resolution and X-ray dose, necessitating compromises in the electrochemistry cycling conditions used or the materials examined. We report a combined approach to reduce measurement time and X-ray exposure for operando XAS studies of lithium ion batteries. A highly discretized energy resolution coupled with advanced post-processing enables rapid yet reliable identification of the oxidation state. A full-field microscopy setup provides sub-particle resolution over a large area of battery electrode, enabling the oxidation state within many transition metal oxide particles to be tracked simultaneously. Here, we apply this approach to gain insights into the lithiation kinetics of a commercial, mixed-metal oxide cathode material, nickel cobalt aluminium oxide (NCA), during (dis)charge and its degradation during overcharge.

  9. Induction of bacterial antibiotic resistance by mutagenic halogenated nitrogenous disinfection byproducts

    International Nuclear Information System (INIS)

    Lv, Lu; Yu, Xin; Xu, Qian; Ye, Chengsong

    2015-01-01

    Halogenated nitrogenous disinfection byproducts (N-DBPs) raise concerns regarding their mutagenicity and carcinogenicity threatening public health. However, environmental consequence of their mutagenicity has received less attention. In this study, the effect of halogenated N-DBPs on bacterial antibiotic resistance (BAR) was investigated. After exposure to bromoacetamide (BAcAm), trichloroacetonitrile (TCAN) or tribromonitromethane (TBNM), the resistance of Pseudomonas aeruginosa PAO1 to both individual and multiple antibiotics (ciprofloxacin, gentamicin, polymyxin B, rifampin, tetracycline, ciprofloxacin + gentamicin and ciprofloxacin + tetracycline) was increased, which was predominantly ascribed to the overexpression of efflux pumps. The mechanism of this effect was demonstrated to be mutagenesis through sequencing and analyzing antibiotic resistance genes. The same induction phenomena also appeared in Escherichia coli, suggesting this effect may be universal to waterborne pathogens. Therefore, more attention should be given to halogenated N-DBPs, as they could increase not only genotoxicological risks but also epidemiological risks of drinking water. - Highlights: • The halogenated N-DBPs could induce bacterial antibiotic resistance. • Both individual and multiple resistances could be induced. • Efflux mechanism played an important role in the induced antibiotic resistance. • The halogenated N-DBPs induced bacterial antibiotic resistance via mutagenesis. • Effects of N-DBPs on antibiotic resistance may be universal to waterborne pathogens. - Halogenated N-DBPs could increase antibiotic resistance, even multidrug resistance via mutagenesis, contributing to the enrichment of antibiotic resistant bacteria in drinking water

  10. Colloquium: Excitons in atomically thin transition metal dichalcogenides

    Science.gov (United States)

    Wang, Gang; Chernikov, Alexey; Glazov, Mikhail M.; Heinz, Tony F.; Marie, Xavier; Amand, Thierry; Urbaszek, Bernhard

    2018-04-01

    Atomically thin materials such as graphene and monolayer transition metal dichalcogenides (TMDs) exhibit remarkable physical properties resulting from their reduced dimensionality and crystal symmetry. The family of semiconducting transition metal dichalcogenides is an especially promising platform for fundamental studies of two-dimensional (2D) systems, with potential applications in optoelectronics and valleytronics due to their direct band gap in the monolayer limit and highly efficient light-matter coupling. A crystal lattice with broken inversion symmetry combined with strong spin-orbit interactions leads to a unique combination of the spin and valley degrees of freedom. In addition, the 2D character of the monolayers and weak dielectric screening from the environment yield a significant enhancement of the Coulomb interaction. The resulting formation of bound electron-hole pairs, or excitons, dominates the optical and spin properties of the material. Here recent progress in understanding of the excitonic properties in monolayer TMDs is reviewed and future challenges are laid out. Discussed are the consequences of the strong direct and exchange Coulomb interaction, exciton light-matter coupling, and influence of finite carrier and electron-hole pair densities on the exciton properties in TMDs. Finally, the impact on valley polarization is described and the tuning of the energies and polarization observed in applied electric and magnetic fields is summarized.

  11. Synthesis, structural and optical properties of PVP coated transition metal doped ZnS nanoparticles

    Science.gov (United States)

    Desai, N. V.; Shaikh, I. A.; Rawal, K. G.; Shah, D. V.

    2018-05-01

    The room temperature photoluminescence (PL) of transition metal doped ZnS nanoparticles is investigated in the present study. The PVP coated ZnS nanoparticles doped with transition metals are synthesized by facile wet chemical co-precipitation method with the concentration of impurity 1%. The UV-Vis absorbance spectra have a peak at 324nm which shifts slightly to 321nm upon introduction of the impurity. The incorporation of the transition metal as dopant is confirmed by X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). The particle size and the morphology are characterized by scanning electron microscopy (SEM), XRD and UV-Vis spectroscopy. The average size of synthesized nanoparticles is about 2.6nm. The room temperature photoluminescence (PL) of undoped and doped ZnS nanoparticles show a strong and sharp peak at 782nm and 781.6nm respectively. The intensity of the PL changes with the type of doping having maximum for manganese (Mn).

  12. Update of bridge design standards in Alabama for AASHTO LRFD seismic design requirements.

    Science.gov (United States)

    2013-11-01

    The Alabama Department of Transportation (ALDOT) has been required to update their bridge design to the LRFD Bridge Design Specifications. This transition has resulted in changes to the seismic design standards of bridges in the state. Multiple bridg...

  13. Electronic structures and valence band splittings of transition metals doped GaNs

    International Nuclear Information System (INIS)

    Lee, Seung-Cheol; Lee, Kwang-Ryeol; Lee, Kyu-Hwan

    2007-01-01

    For a practical viewpoint, presence of spin splitting of valence band in host semiconductors by the doping of transition metal (TM) ions is an essential property when designing a diluted magnetic semiconductors (DMS) material. The first principle calculations were performed on the electronic and magnetic structure of 3d transition metal doped GaN. V, Cr, and Mn doped GaNs could not be candidates for DMS materials since most of their magnetic moments is concentrated on the TM ions and the splittings of valence band were negligible. In the cases of Fe, Co, Ni, and Cu doped GaNs, on the contrary, long-ranged spin splitting of valence band was found, which could be candidates for DMS materials

  14. Rigid muffin-tin approximation for the electron-phonon interaction in transition metals

    International Nuclear Information System (INIS)

    Butler, W.H.

    1980-01-01

    Progress in calculating the electron-phonon parameters of transition metals has been based on either the rigid muffin-tin approximation (RMTA) or the fitted modified tight-binding approximation (FMTBA). The RMTA has been shown to be remarkably accurate for average electron-phonon properties, but there are indications that RMTA matrix elements may be too small at low momentum transfer. An attempt is made to demonstrate these assertions concerning the accuracy of RMTA and the numerous electron-phonon calculations are placed in a broader perspective by a demonstration of how they can be used to explain the trends in the strength of the electron-phonon coupling among the transition metals and the A-15 compounds

  15. Rigid muffin-tin approximation for the electron-phonon interaction in transition metals

    Energy Technology Data Exchange (ETDEWEB)

    Butler, W.H.

    1980-01-01

    Progress in calculating the electron-phonon parameters of transition metals has been based on either the rigid muffin-tin approximation (RMTA) or the fitted modified tight-binding approximation (FMTBA). The RMTA has been shown to be remarkably accurate for average electron-phonon properties, but there are indications that RMTA matrix elements may be too small at low momentum transfer. An attempt is made to demonstrate these assertions concerning the accuracy of RMTA and the numerous electron-phonon calculations are placed in a broader perspective by a demonstration of how they can be used to explain the trends in the strength of the electron-phonon coupling among the transition metals and the A-15 compounds. (GHT)

  16. New trends in the optical and electronic applications of polymers containing transition-metal complexes.

    Science.gov (United States)

    Liu, Shu-Juan; Chen, Yang; Xu, Wen-Juan; Zhao, Qiang; Huang, Wei

    2012-04-13

    Polymers containing transition-metal complexes exhibit excellent optical and electronic properties, which are different from those of polymers with a pure organic skeleton and combine the advantages of both polymers and metal complexes. Hence, research about this class of polymers has attracted more and more interest in recent years. Up to now, a number of novel polymers containing transition-metal complexes have been exploited, and significant advances in their optical and electronic applications have been achieved. In this article, we summarize some new research trends in the applications of this important class of optoelectronic polymers, such as chemo/biosensors, electronic memory devices and photovoltaic devices. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Effect of alloying on elastic properties of ZrN based transition metal nitride alloys

    KAUST Repository

    Kanoun, Mohammed; Goumri-Said, Souraya

    2014-01-01

    We report the effect of composition and metal sublattice substitutional element on the structural, elastic and electronic properties of ternary transition metal nitrides Zr1-xMxN with M=Al, Ti, Hf, V, Nb, W and Mo. The analysis of the elastic constants, bulk modulus, shear modulus, Young's modulus, and Poisson's ratio provides insights regarding the mechanical behavior of Zr1-xMxN. We predict that ternary alloys are more ductile compared to their parent binary compounds. The revealed trend in the mechanical behavior might help for experimentalists on the ability of tuning the mechanical properties during the alloying process by varying the concentration of the transition metal. © 2014 Elsevier B.V.

  18. Effect of alloying on elastic properties of ZrN based transition metal nitride alloys

    KAUST Repository

    Kanoun, Mohammed

    2014-09-01

    We report the effect of composition and metal sublattice substitutional element on the structural, elastic and electronic properties of ternary transition metal nitrides Zr1-xMxN with M=Al, Ti, Hf, V, Nb, W and Mo. The analysis of the elastic constants, bulk modulus, shear modulus, Young\\'s modulus, and Poisson\\'s ratio provides insights regarding the mechanical behavior of Zr1-xMxN. We predict that ternary alloys are more ductile compared to their parent binary compounds. The revealed trend in the mechanical behavior might help for experimentalists on the ability of tuning the mechanical properties during the alloying process by varying the concentration of the transition metal. © 2014 Elsevier B.V.

  19. High capacity hydrogen absorption in transition-metal ethylene complexes: consequences of nanoclustering

    International Nuclear Information System (INIS)

    Phillips, A B; Shivaram, B S

    2009-01-01

    We have recently shown that organo-metallic complexes formed by laser ablating transition metals in ethylene are high hydrogen absorbers at room temperature (Phillips and Shivaram 2008 Phys. Rev. Lett. 100 105505). Here we show that the absorption percentage depends strongly on the ethylene pressure. High ethylene pressures (>100 mTorr) result in a lowered hydrogen uptake. Transmission electron microscopy measurements reveal that while low pressure ablations result in metal atoms dispersed uniformly on a near atomic scale, high pressure ones yield distinct nanoparticles with electron energy-loss spectroscopy demonstrating that the metal atoms are confined solely to the nanoparticles.

  20. Maternal exposure to alkali, alkali earth, transition and other metals: Concentrations and predictors of exposure

    International Nuclear Information System (INIS)

    Hinwood, A.L.; Stasinska, A.; Callan, A.C.; Heyworth, J.; Ramalingam, M.; Boyce, M.; McCafferty, P.; Odland, J.Ø.

    2015-01-01

    Most studies of metals exposure focus on the heavy metals. There are many other metals (the transition, alkali and alkaline earth metals in particular) in common use in electronics, defense industries, emitted via combustion and which are naturally present in the environment, that have received limited attention in terms of human exposure. We analysed samples of whole blood (172), urine (173) and drinking water (172) for antimony, beryllium, bismuth, cesium, gallium, rubidium, silver, strontium, thallium, thorium and vanadium using ICPMS. In general most metals concentrations were low and below the analytical limit of detection with some high concentrations observed. Few factors examined in regression models were shown to influence biological metals concentrations and explained little of the variation. Further study is required to establish the source of metals exposures at the high end of the ranges of concentrations measured and the potential for any adverse health impacts in children. - This study has demonstrated exposure to alkali, alkali earth and transition metals in pregnant women with factors such as breastfeeding, fish oil use and diet affecting exposures

  1. Ferromagnetic semiconductor-metal transition in heterostructures of europium monoxide

    Energy Technology Data Exchange (ETDEWEB)

    Stollenwerk, Tobias; Kroha, Johann [Physikalisches Institut der Universitaet Bonn (Germany)

    2012-07-01

    Experiments on thin films of electron doped europium monoxide show a simultaneous ferromagnetic semiconductor-metal transition which goes along with a huge drop in resistivity over several orders of magnitude. Therefore, this material is a very promising candidate for spintronics applications. We have developed a theory which correctly predicts the simultaneous phase transition in thin films of electron doped EuO and the increase of the Curie temperature T{sub C} with doping concentration. The origin of the increased T{sub C} lies in the enhanced RKKY interaction between the localized 4f moments of the Eu atoms. Therefore, the phase transition is controlled by the population of the conduction band. We investigate the influence of film thickness and interface effects on the population of the conduction band and on the magnetic and electronic properties of the EuO film.

  2. First principles calculations and experimental insight into methane steam reforming over transition metal catalysts

    DEFF Research Database (Denmark)

    Jones, Glenn; Jakobsen, Jon Geest; Shim, Signe Sarah

    2008-01-01

    This paper presents a detailed analysis of the steam reforming process front first-principles calculations, supported by insight from experimental investigations. In the present work we employ recently recognised scaling relationships for adsorption energies of simple molecules adsorbed at pure...... metal Surfaces to develop an overview of the steam reforming process catalyzed by a range of transition metal surfaces. By combining scaling relationships with thermodynamic and kinetic analysis, we show that it is possible to determine the reactivity trends of the pure metals for methane steam...... in situ TEM measurements under a hydrogen atmosphere. The overall agreement between theory and experiment (at 773 K, 1 bar pressure and 10% conversion) is found to be excellent with Ru and Rh being the most active pure transition metals for methane steam reforming, while Ni, Ir, Pt, and Pd...

  3. Optical and Excitonic Properties of Atomically Thin Transition-Metal Dichalcogenides

    Science.gov (United States)

    Berkelbach, Timothy C.; Reichman, David R.

    2018-03-01

    Starting with the isolation of a single sheet of graphene, the study of layered materials has been one of the most active areas of condensed matter physics, chemistry, and materials science. Single-layer transition-metal dichalcogenides are direct-gap semiconducting analogs of graphene that exhibit novel electronic and optical properties. These features provide exciting opportunities for the discovery of both new fundamental physical phenomena as well as innovative device platforms. Here, we review the progress associated with the creation and use of a simple microscopic framework for describing the optical and excitonic behavior of few-layer transition-metal dichalcogenides, which is based on symmetry, band structure, and the effective interactions between charge carriers in these materials. This approach provides an often quantitative account of experiments that probe the physics associated with strong electron–hole interactions in these quasi two-dimensional systems and has been successfully employed by many groups to both describe and predict emergent excitonic behavior in these layered semiconducting systems.

  4. Enhancement of oxygen reduction at Fe tetrapyridyl porphyrin by pyridyl-N coordination to transition metal ions

    International Nuclear Information System (INIS)

    Maruyama, Jun; Baier, Claudia; Wolfschmidt, Holger; Bele, Petra; Stimming, Ulrich

    2012-01-01

    One of the promising candidates as noble-metal-free electrode catalysts for polymer electrolyte fuel cells (PEFCs) is a carbon material with nitrogen atoms coordinating iron ions embedded on the surface (Fe-N x moiety) as the active site, although the activity is insufficient compared to conventional platinum-based electrocatalysts. In order to obtain fundamental information on the activity enhancement, a simple model of the Fe-N x active site was formed by adsorbing 5,10,15,20-Tetrakis(4-pyridyl)-21H,23H-porphine iron(III) chloride (FeTPyPCl) on the basal plane of highly oriented pyrolytic graphite (HOPG), and cathodic oxygen reduction was investigated on the surface in 0.1 M HClO 4 . The catalytic activity for oxygen reduction was enhanced by loading transition metal ions (Co 2+ , Ni 2+ , Cu 2+ ) together with FeTPyPCl. The X-ray photoelectron spectrum of the surface suggested that the metal was coordinated by the pyridine-N. The enhancement effect of the transition metals was supported by two different measurements: oxygen reduction at HOPG in 0.1 M HClO 4 dissolving FeTPyPCl and the metal ions; oxygen reduction in 0.1 M HClO 4 at the subsequently well-rinsed and dried HOPG. The ultraviolet–visible spectrum for the solution also suggested the coordination between the pyridyl-N and the metal ions. The oxygen reduction enhancement was attributed to the electronic interaction between the additional transition metal and the Fe center of the porphyrin through the coordination bonds. These results implied that the improvement of the activity of the noble-metal-free catalyst would be possible by the proper introduction of the transition metal ions around the active site.

  5. Comparative study of the synthesis of layered transition metal molybdates

    International Nuclear Information System (INIS)

    Mitchell, S.; Gomez-Aviles, A.; Gardner, C.; Jones, W.

    2010-01-01

    Mixed metal oxides (MMOs) prepared by the mild thermal decomposition of layered double hydroxides (LDHs) differ in their reactivity on exposure to aqueous molybdate containing solutions. In this study, we investigate the reactivity of some T-Al containing MMOs (T=Co, Ni, Cu or Zn) towards the formation of layered transition metal molybdates (LTMs) possessing the general formula AT 2 (OH)(MoO 4 ) 2 .H 2 O, where A=NH 4 + , Na + or K + . The phase selectivity of the reaction was studied with respect to the source of molybdate, the ratio of T to Mo and the reaction pH. LTMs were obtained on reaction of Cu-Al and Zn-Al containing MMOs with aqueous solutions of ammonium heptamolybdate. Rehydration of these oxides in the presence of sodium or potassium molybdate yielded a rehydrated LDH phase as the only crystalline product. The LTM products obtained by the rehydration of MMO precursors were compared with LTMs prepared by direct precipitation from the metal salts in order to study the influence of preparative route on their chemical and physical properties. Differences were noted in the composition, morphology and thermal properties of the resulting products. - Graphical abstract: Mixed metal oxides (MMOs) derived from layered double hydroxide precursors differ in their reactivity on exposure to aqueous molybdate containing solutions. We investigate the influence of the molybdate source, the rehydration pH and the ratio of T/Mo on the reactivity of some T-Al containing MMOs (T=Co, Ni, Cu or Zn) towards the formation of layered transition metal molybdates of general formula AT 2 (OH)(MoO 4 ) 2 .H 2 O (where A + =NH 4 + , K + or Na + ).

  6. 13C NMR investigation of the structure of cationic carbonyls in transition metal zeolites

    International Nuclear Information System (INIS)

    Ben Taarit, Y.

    1979-01-01

    13 C NMR spectroscopy was used to investigate the nature of carbon monoxide adsorbed on transition metal ions hosted in a synthetic faujastite type zeolite. The adsorbed CO species was characterised by a highly shielded carbon nucleus. Using the Pople approximation for the paramagnetic shielding term, the observed chemical shift was rationalised assuming the formation of a cationic carbonyl species with an appreciable electronic transfer from the carbon lone pair to the transition metal ion and negligible π back-bonding if at all. (Auth.)

  7. Electronic Structure of the fcc Transition Metals Ir, Rh, Pt, and Pd

    DEFF Research Database (Denmark)

    Andersen, O. Krogh

    1970-01-01

    We give a complete description of a relativistic augmented-plane-wave calculation of the band structures of the paramagnetic fcc transition metals Ir, Rh, Pt, and Pd. The width and position of the d band decrease in the sequence Ir, Pt, Rh, Pd; and N(EF)=13.8,23.2,18.7, and 32.7 (states/atom)/Ry,......We give a complete description of a relativistic augmented-plane-wave calculation of the band structures of the paramagnetic fcc transition metals Ir, Rh, Pt, and Pd. The width and position of the d band decrease in the sequence Ir, Pt, Rh, Pd; and N(EF)=13.8,23.2,18.7, and 32.7 (states....../atom)/Ry, respectively. Spin-orbit coupling is important for all four metals and the coupling parameter varies by 30% over the d bandwidth. Detailed comparisons with de Haas—van Alphen Fermi-surface dimensions have previously been presented and the agreement was very good. Comparison with measured electronic specific...

  8. Probing Critical Point Energies of Transition Metal Dichalcogenides: Surprising Indirect Gap of Single Layer WSe 2

    KAUST Repository

    Zhang, Chendong; Chen, Yuxuan; Johnson, Amber; Li, Ming-yang; Li, Lain-Jong; Mende, Patrick C.; Feenstra, Randall M.; Shih, Chih Kang

    2015-01-01

    By using a comprehensive form of scanning tunneling spectroscopy, we have revealed detailed quasi-particle electronic structures in transition metal dichalcogenides, including the quasi-particle gaps, critical point energy locations, and their origins in the Brillouin zones. We show that single layer WSe surprisingly has an indirect quasi-particle gap with the conduction band minimum located at the Q-point (instead of K), albeit the two states are nearly degenerate. We have further observed rich quasi-particle electronic structures of transition metal dichalcogenides as a function of atomic structures and spin-orbit couplings. Such a local probe for detailed electronic structures in conduction and valence bands will be ideal to investigate how electronic structures of transition metal dichalcogenides are influenced by variations of local environment.

  9. Probing Critical Point Energies of Transition Metal Dichalcogenides: Surprising Indirect Gap of Single Layer WSe 2

    KAUST Repository

    Zhang, Chendong

    2015-09-21

    By using a comprehensive form of scanning tunneling spectroscopy, we have revealed detailed quasi-particle electronic structures in transition metal dichalcogenides, including the quasi-particle gaps, critical point energy locations, and their origins in the Brillouin zones. We show that single layer WSe surprisingly has an indirect quasi-particle gap with the conduction band minimum located at the Q-point (instead of K), albeit the two states are nearly degenerate. We have further observed rich quasi-particle electronic structures of transition metal dichalcogenides as a function of atomic structures and spin-orbit couplings. Such a local probe for detailed electronic structures in conduction and valence bands will be ideal to investigate how electronic structures of transition metal dichalcogenides are influenced by variations of local environment.

  10. Ion exchange of some transition metal cations on hydrated titanium dioxide in aqueous ammonia solutions

    International Nuclear Information System (INIS)

    Bilewicz, A.; Narbutt, J.; Dybczynski, R.

    1992-01-01

    The adsorption of transition metal cations on hydrated titanium dioxide in complexing ammonia and amine solutions has been studied as a function of ammonia (amine) concentration. The relationships between the distribution coefficients and ammonia concentration as well as the effects of various amines on sorption of transition metals indicate that a coordinate bond is formed between the metal ions and the hydroxy groups of the sorbent. The distribution coefficients of silver(I) and cobalt(II), which form strong ammonia complexes in aqueous solutions, decrease with increasing concentration of ammonia already at concentrations exceeding 10 -3 *mol*dm -3 . Cations of zinc, manganese and mercury which form much weaker ammonia complexes do not exhibit any effect of ammonia concentration in the whole range investigated. In the case of sorption of macroamounts of ammonia or amine complexes of silver, the molecular sieve effect plays an important role. The differences in the affinity of hydrated titanium dioxide for ammonia solvates of various transition metal ions can serve as a tool for effective separation of these ions in ammonia solutions. (author) 10 refs.; 4 figs.; 1 tab

  11. An important rule for realizing metal → half-metal → semiconductor transition in single-molecule junctions

    Science.gov (United States)

    Zeng, Jing; Chen, Ke-Qiu; Long, Mengqiu

    2017-06-01

    Recently, Zhong et al (2015 Nano Lett. 15 8091) found that two additional hydrogen atoms can be adsorbed to the opposite aza-bridging nitrogen atoms of the manganese phthalocyanine (MnPc) macrocycle when exposed to H2. Thus the symmetry of the MnPc molecule is changed from 4-fold to 2-fold. Motivated by this recent experiment, we theoretically investigate a MnPc-based single-molecule junction in this work and propose a simple and reliable way to realize the transition of its electronic properties. On the basis of spin-polarized density-functional theory calculations combined with the Keldysh nonequilibrium Green’s technique, we find that the gradual hydrogenation in MnPc molecules gives rise to the changes of the hardness of the electron density and spin-selective orbital decoupling, which eventually leads to the realization of the first ever metal  →  half-metal  →  semiconductor transition behavior in single-molecule junctions. Analysis of molecular projected self-consistent Hamiltonian, Mulliken population, and local density of states also reveals an important rule for realizing this transition behavior. Our research confirms that the hydrogenation of MnPc molecules can realize various molecular functionalities in unitary material background.

  12. An important rule for realizing metal → half-metal → semiconductor transition in single-molecule junctions

    International Nuclear Information System (INIS)

    Zeng, Jing; Chen, Ke-Qiu; Long, Mengqiu

    2017-01-01

    Recently, Zhong et al (2015 Nano Lett . 15 8091) found that two additional hydrogen atoms can be adsorbed to the opposite aza-bridging nitrogen atoms of the manganese phthalocyanine (MnPc) macrocycle when exposed to H 2 . Thus the symmetry of the MnPc molecule is changed from 4-fold to 2-fold. Motivated by this recent experiment, we theoretically investigate a MnPc-based single-molecule junction in this work and propose a simple and reliable way to realize the transition of its electronic properties. On the basis of spin-polarized density-functional theory calculations combined with the Keldysh nonequilibrium Green’s technique, we find that the gradual hydrogenation in MnPc molecules gives rise to the changes of the hardness of the electron density and spin-selective orbital decoupling, which eventually leads to the realization of the first ever metal  →  half-metal  →  semiconductor transition behavior in single-molecule junctions. Analysis of molecular projected self-consistent Hamiltonian, Mulliken population, and local density of states also reveals an important rule for realizing this transition behavior. Our research confirms that the hydrogenation of MnPc molecules can realize various molecular functionalities in unitary material background. (paper)

  13. Magnetic properties of fcc Ni-based transition metal alloy

    Czech Academy of Sciences Publication Activity Database

    Kudrnovský, Josef; Drchal, Václav

    2009-01-01

    Roč. 100, č. 9 (2009), s. 1193-1196 ISSN 1862-5282 R&D Projects: GA MŠk OC 150; GA AV ČR IAA100100616 Institutional research plan: CEZ:AV0Z10100520 Keywords : transition metal alloys * Ni-based * pair exchange interactions * Curie temperatures * renormalized RPA Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.862, year: 2009

  14. Using Dopants to Tune Oxygen Vacancy Formation in Transition Metal Oxide Resistive Memory.

    Science.gov (United States)

    Jiang, Hao; Stewart, Derek A

    2017-05-17

    Introducing dopants is an important way to tailor and improve electronic properties of transition metal oxides used as high-k dielectric thin films and resistance switching layers in leading memory technologies, such as dynamic and resistive random access memory (ReRAM). Ta 2 O 5 has recently received increasing interest because Ta 2 O 5 -based ReRAM demonstrates high switching speed, long endurance, and low operating voltage. However, advances in optimizing device characteristics with dopants have been hindered by limited and contradictory experiments in this field. We report on a systematic study on how various metal dopants affect oxygen vacancy formation in crystalline and amorphous Ta 2 O 5 from first principles. We find that isoelectronic dopants and weak n-type dopants have little impact on neutral vacancy formation energy and that p-type dopants can lower the formation energy significantly by introducing holes into the system. In contrast, n-type dopants have a deleterious effect and actually increase the formation energy for charged oxygen vacancies. Given the similar doping trend reported for other binary transition metal oxides, this doping trend should be universally valid for typical binary transition metal oxides. Based on this guideline, we propose that p-type dopants (Al, Hf, Zr, and Ti) can lower the forming/set voltage and improve retention properties of Ta 2 O 5 ReRAM.

  15. First-principles interatomic potentials for transition-metal aluminides. III. Extension to ternary phase diagrams

    International Nuclear Information System (INIS)

    Widom, Mike; Al-Lehyani, Ibrahim; Moriarty, John A.

    2000-01-01

    Modeling structural and mechanical properties of intermetallic compounds and alloys requires detailed knowledge of their interatomic interactions. The first two papers of this series [Phys. Rev. B 56, 7905 (1997); 58, 8967 (1998)] derived first-principles interatomic potentials for transition-metal (TM) aluminides using generalized pseudopotential theory (GPT). Those papers focused on binary alloys of aluminum with first-row transition metals and assessed the ability of GPT potentials to reproduce and elucidate the alloy phase diagrams of Al-Co and Al-Ni. This paper addresses the phase diagrams of the binary alloy Al-Cu and the ternary systems Al-Co-Cu and Al-Co-Ni, using GPT pair potentials calculated in the limit of vanishing transition-metal concentration. Despite this highly simplifying approximation, we find rough agreement with the known low-temperature phase diagrams, up to 50% total TM concentration provided the Co fraction is below 25%. Full composition-dependent potentials and many-body interactions would be required to correct deficiencies at higher Co concentration. Outside this troublesome region, the experimentally determined stable and metastable phases all lie on or near the convex hull of a scatter plot of energy versus composition. We verify, qualitatively, reported solubility ranges extending binary alloys into the ternary diagram in both Al-Co-Cu and Al-Co-Ni. Finally, we reproduce previously conjectured transition-metal positions in the decagonal quasicrystal phase. (c) 2000 The American Physical Society

  16. Spin-orbit-induced spin splittings in polar transition metal dichalcogenide monolayers

    KAUST Repository

    Cheng, Yingchun; Zhu, Zhiyong; Tahir, Muhammad; Schwingenschlö gl, Udo

    2013-01-01

    . We present ab initio electronic structure, phonon, and molecular-dynamics calculations to study the structural stability and spin-orbit-induced spin splitting in the transition metal dichalcogenide monolayers MXY (M = Mo, W and X, Y = S, Se, Te

  17. Group 4 Transition-Metal Complexes of an Aniline–Carbene–Phenol Ligand

    KAUST Repository

    Despagnet-Ayoub, Emmanuelle

    2013-05-24

    Attempts to install a tridentate aniline-NHC-phenol (NCO) ligand on titanium and zirconium led instead to complexes resulting from unexpected rearrangement pathways that illustrate common behavior in carbene-early- transition-metal chemistry. © 2013 American Chemical Society.

  18. Cohesion and coordination effects on transition metal surface energies

    Science.gov (United States)

    Ruvireta, Judit; Vega, Lorena; Viñes, Francesc

    2017-10-01

    Here we explore the accuracy of Stefan equation and broken-bond model semiempirical approaches to obtain surface energies on transition metals. Cohesive factors are accounted for either via the vaporization enthalpies, as proposed in Stefan equation, or via cohesive energies, as employed in the broken-bond model. Coordination effects are considered including the saturation degree, as suggested in Stefan equation, employing Coordination Numbers (CN), or as the ratio of broken bonds, according to the bond-cutting model, considering as well the square root dependency of the bond strength on CN. Further, generalized coordination numbers CN bar are contemplated as well, exploring a total number of 12 semiempirical formulations on the three most densely packed surfaces of 3d, 4d, and 5d Transition Metals (TMs) displaying face-centered cubic (fcc), body-centered cubic (bcc), or hexagonal close-packed (hcp) crystallographic structures. Estimates are compared to available experimental surface energies obtained extrapolated to zero temperature. Results reveal that Stefan formula cohesive and coordination dependencies are only qualitative suited, but unadvised for quantitative discussion, as surface energies are highly overestimated, favoring in addition the stability of under-coordinated surfaces. Broken-bond cohesion and coordination dependencies are a suited basis for quantitative comparison, where square-root dependencies on CN to account for bond weakening are sensibly worse. An analysis using Wulff shaped averaged surface energies suggests the employment of broken-bond model using CN to gain surface energies for TMs, likely applicable to other metals.

  19. General Synthesis of Transition-Metal Oxide Hollow Nanospheres/Nitrogen-Doped Graphene Hybrids by Metal-Ammine Complex Chemistry for High-Performance Lithium-Ion Batteries.

    Science.gov (United States)

    Chen, Jiayuan; Wu, Xiaofeng; Gong, Yan; Wang, Pengfei; Li, Wenhui; Mo, Shengpeng; Peng, Shengpan; Tan, Qiangqiang; Chen, Yunfa

    2018-02-09

    We present a general and facile synthesis strategy, on the basis of metal-ammine complex chemistry, for synthesizing hollow transition-metal oxides (Co 3 O 4 , NiO, CuO-Cu 2 O, and ZnO)/nitrogen-doped graphene hybrids, potentially applied in high-performance lithium-ion batteries. The oxygen-containing functional groups of graphene oxide play a prerequisite role in the formation of hollow transition-metal oxides on graphene nanosheets, and a significant hollowing process occurs only when forming metal (Co 2+ , Ni 2+ , Cu 2+ , or Zn 2+ )-ammine complex ions. Moreover, the hollowing process is well correlated with the complexing capacity between metal ions and NH 3 molecules. The significant hollowing process occurs for strong metal-ammine complex ions including Co 2+ , Ni 2+ , Cu 2+ , and Zn 2+ ions, and no hollow structures formed for weak and/or noncomplex Mn 2+ and Fe 3+ ions. Simultaneously, this novel strategy can also achieve the direct doping of nitrogen atoms into the graphene framework. The electrochemical performance of two typical hollow Co 3 O 4 or NiO/nitrogen-doped graphene hybrids was evaluated by their use as anodic materials. It was demonstrated that these unique nanostructured hybrids, in contrast with the bare counterparts, solid transition-metal oxides/nitrogen-doped graphene hybrids, perform with significantly improved specific capacity, superior rate capability, and excellent capacity retention. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Facile synthesis of nanostructured transition metal oxides as electrodes for Li-ion batteries

    Science.gov (United States)

    Opra, Denis P.; Gnedenkov, Sergey V.; Sokolov, Alexander A.; Minaev, Alexander N.; Kuryavyi, Valery G.; Sinebryukhov, Sergey L.

    2017-09-01

    At all times, energy storage is one of the greatest scientific challenge. Recently, Li-ion batteries are under special attention due to high working voltage, long cycle life, low self-discharge, reliability, no-memory effect. However, commercial LIBs usage in medium- and large-scale energy storage are limited by the capacity of lithiated metal oxide cathode and unsafety of graphite anode at high-rate charge. In this way, new electrode materials with higher electrochemical performance should be designed to satisfy a requirement in both energy and power. As it known, nanostructured transition metal oxides are promising electrode materials because of their elevated specific capacity and high potential vs. Li/Li+. In this work, the perspective of an original facile technique of pulsed high-voltage plasma discharge in synthesis of nanostructured transition metal oxides as electrodes for lithium-ion batteries has been demonstrated.

  1. Transition-metal chlorides as conversion cathode materials for Li-ion batteries

    International Nuclear Information System (INIS)

    Li Ting; Chen, Zhong X.; Cao, Yu L.; Ai, Xin P.; Yang, Han X.

    2012-01-01

    Insoluble AgCl and soluble CuCl 2 were selected and investigated as model compounds of transition-metal chlorides for electrochemical conversion cathode materials. The experimental results demonstrated that the AgCl nanocrystals can convert reversibly to metallic Ag with nearly full utilization of its one-electron redox capacity (187 mAh g −1 ). Similarly, the CuCl 2 -filled mesoporous carbon can realize a reversible two-electron transfer reaction, giving a very high reversible capacity of 466 mAh g −1 after 20 cycles. These data imply that the metal chlorides can undergo complete electrochemical conversion utilizing their full oxidation states for electrical energy storage as previously reported metal fluorides, possibly being used as high capacity cathode materials for Li-ion batteries.

  2. Basic deuteroexchange in transition metal complexes with nitrogen-containing aromatic heterocycles

    International Nuclear Information System (INIS)

    Tupitsyn, I.F.

    1986-01-01

    Kinetics of deuteroexchange in the methyl group of nitrate complexes of a metal - nickel (2) - with different methyl-substituted aromatic heterocycles and isostructural complexes of a ligand - 2 - methyl quinoline - with different central metal atoms (Mn(2), Ni(2), Cu(2), Zn(2)) is studied. Series for influence of ligand structure on deuteroexchange rate in complexes doesn't correspond qualitatively to series for deuteroexchange rate increase in noncoordinated ligands. Deuteroexchange rate is weakly subjected to influence of exchange in metal-complexing agent. Deuteroexchange mechanism is suggested and discussed. According to this mechanism the structure developed in the course of the exchange process with electron density transfer from the heterocyclic ligand to a metal ion is a transition state of the reaction

  3. Beckmann rearrangement of aldoximes catalyzed by transition metal salts: mechanical aspects

    NARCIS (Netherlands)

    Leusink, A.J.; Meerbeek, T.G.; Noltes, J.G.

    1977-01-01

    The Beckmann rearrangement of aldoximes catalyzed by transition metal salts like palladium and nickel acetylacetonates is shown to be a dehydration‐hydration reaction in which the anti‐oxime is converted into nitrile and the nitrile is converted into amide.

  4. Stability of Transition-metal Carbides in Liquid Phase Reactions Relevant for Biomass-Based Conversion

    NARCIS (Netherlands)

    Souza Macêdo, L.; Stellwagen, D.R.; Teixeira da Silva, V.; Bitter, J.H.

    2015-01-01

    Transition-metal carbides have been employed for biobased conversions aiming to replace the rare noble metals. However, when reactions are in liquid phase, many authors have observed catalyst deactivation. The main routes of deactivation in liquid phase biobased conversions are coke deposition,

  5. Electronic computer prediction of properties of binary refractory transition metal compounds on the base of their simplificated electronic structure

    International Nuclear Information System (INIS)

    Kutolin, S.A.; Kotyukov, V.I.

    1979-01-01

    An attempt is made to obtain calculation equations of macroscopic physico-chemical properties of transition metal refractory compounds (density, melting temperature, Debye characteristic temperature, microhardness, standard formation enthalpy, thermo-emf) using the method of the regression analysis. Apart from the compound composition the argument of the regression equation is the distribution of electron bands of d-transition metals, created by the energy electron distribution in the simplified zone structure of transition metals and approximated by Chebishev polynoms, by the position of Fermi energy on the map of distribution of electron band energy depending upon the value of quasi-impulse, multiple to the first, second and third Brillouin zone for transition metals. The maximum relative error of the regressions obtained as compared with the literary data is 15-20 rel.%

  6. Electronic Structure of Transition Metal Clusters, Actinide Complexes and Their Reactivities

    Energy Technology Data Exchange (ETDEWEB)

    Krishnan Balasubramanian

    2009-07-18

    This is a continuing DOE-BES funded project on transition metal and actinide containing species, aimed at the electronic structure and spectroscopy of transition metal and actinide containing species. While a long term connection of these species is to catalysis and environmental management of high-level nuclear wastes, the immediate relevance is directly to other DOE-BES funded experimental projects at DOE-National labs and universities. There are a number of ongoing gas-phase spectroscopic studies of these species at various places, and our computational work has been inspired by these experimental studies and we have also inspired other experimental and theoretical studies. Thus our studies have varied from spectroscopy of diatomic transition metal carbides to large complexes containing transition metals, and actinide complexes that are critical to the environment. In addition, we are continuing to make code enhancements and modernization of ALCHEMY II set of codes and its interface with relativistic configuration interaction (RCI). At present these codes can carry out multi-reference computations that included up to 60 million configurations and multiple states from each such CI expansion. ALCHEMY II codes have been modernized and converted to a variety of platforms such as Windows XP, and Linux. We have revamped the symbolic CI code to automate the MRSDCI technique so that the references are automatically chosen with a given cutoff from the CASSCF and thus we are doing accurate MRSDCI computations with 10,000 or larger reference space of configurations. The RCI code can also handle a large number of reference configurations, which include up to 10,000 reference configurations. Another major progress is in routinely including larger basis sets up to 5g functions in thee computations. Of course higher angular momenta functions can also be handled using Gaussian and other codes with other methods such as DFT, MP2, CCSD(T), etc. We have also calibrated our RECP

  7. Electronic Structure of Transition Metal Clusters, Actinide Complexes and Their Reactivities

    International Nuclear Information System (INIS)

    Balasubramanian, Krishnan

    2009-01-01

    This is a continuing DOE-BES funded project on transition metal and actinide containing species, aimed at the electronic structure and spectroscopy of transition metal and actinide containing species. While a long term connection of these species is to catalysis and environmental management of high-level nuclear wastes, the immediate relevance is directly to other DOE-BES funded experimental projects at DOE-National labs and universities. There are a number of ongoing gas-phase spectroscopic studies of these species at various places, and our computational work has been inspired by these experimental studies and we have also inspired other experimental and theoretical studies. Thus our studies have varied from spectroscopy of diatomic transition metal carbides to large complexes containing transition metals, and actinide complexes that are critical to the environment. In addition, we are continuing to make code enhancements and modernization of ALCHEMY II set of codes and its interface with relativistic configuration interaction (RCI). At present these codes can carry out multi-reference computations that included up to 60 million configurations and multiple states from each such CI expansion. ALCHEMY II codes have been modernized and converted to a variety of platforms such as Windows XP, and Linux. We have revamped the symbolic CI code to automate the MRSDCI technique so that the references are automatically chosen with a given cutoff from the CASSCF and thus we are doing accurate MRSDCI computations with 10,000 or larger reference space of configurations. The RCI code can also handle a large number of reference configurations, which include up to 10,000 reference configurations. Another major progress is in routinely including larger basis sets up to 5g functions in thee computations. Of course higher angular momenta functions can also be handled using Gaussian and other codes with other methods such as DFT, MP2, CCSD(T), etc. We have also calibrated our RECP

  8. Surface-enhanced Raman scattering from metal and transition metal nano-caped arrays

    Science.gov (United States)

    Sun, Huanhuan; Gao, Renxian; Zhu, Aonan; Hua, Zhong; Chen, Lei; Wang, Yaxin; Zhang, Yongjun

    2018-03-01

    The metal and transition metal cap-shaped arrays on polystyrene colloidal particle (PSCP) templates were fabricated to study the surface-enhanced Raman scattering (SERS) effect. We obtained the Ag and Fe complex film by a co-sputtering deposition method. The size of the deposited Fe particle was changed by the sputtering power. We also study the SERS enhancement mechanism by decorating the PATP probe molecule on the different films. The SERS signals increased firstly, and then decreased as the size of Fe particles grows gradually. The finite-difference time domain (FDTD) simulation and experimental Raman results manifest that SERS enhancement was mainly attributed to surface plasma resonance (SPR) between Ag and Ag nanoparticles. The SERS signals of PATP molecule were enhanced to reach a lowest detectable concentration of 10-8 mol/L. The research demonstrates that the SERS substrates with Ag-Fe cap-shaped arrays have a high sensitivity.

  9. Predicted stability, structures, and magnetism of 3d transition metal nitrides: the M4N phases

    NARCIS (Netherlands)

    Fang, C.M.; Koster, R.S.; Li, W.F.; van Huis, M.A.

    2014-01-01

    The 3d transition metal nitrides M4N (Sc4N, Ti4N, V4N, Cr4N, Mn4N, Fe4N, Co4N, Ni4N, and Cu4N) have unique phase relationships, crystal structures, and electronic and magnetic properties. Here we present a systematic density functional theory (DFT) study on these transition metal nitrides, assessing

  10. Insertion compounds of transition-metal and uranium oxides

    International Nuclear Information System (INIS)

    Chippindale, A.M.; Dickens, P.G.; Powell, A.V.

    1991-01-01

    Several transition-metal and actinide oxides, in which the metal occurs in a high oxidation state, have open covalent structures and are capable of incorporating alkali and other electropositive metals under mild conditions to form insertion compounds A x MO n . These are solids which have several features in common: Over a range of compositions, A x MO n exists as one or more stable or metastable phases in which the structure of the parent oxide MO n is largely retained and the insertion element A is accommodated interstitially. Insertion is accompanied by a redox process A=A i . + e - M in which M is reduced and the electronic properties of the parent oxide change to those typical of a mixed-valence compound. The insertion process xA + MO n = A x MO n can be reversed, at least to some extent, by chemical or electrochemical reaction, with retention of structure (topotactic reaction). This review concentrates on methods of synthesis, characterisation, crystal structure and thermochemistry of these insertion compounds. It updates and extends previous work. (author)

  11. TRANSURANIC METAL HALIDES AND A PROCESS FOR THE PRODUCTION THEREOF

    Science.gov (United States)

    Fried, S.

    1951-03-20

    Halides of transuranic elements are prepared by contacting with aluminum and a halogen, or with an aluminum halide, a transuranic metal oxide, oxyhalide, halide, or mixture thereof at an elevated temperature.

  12. Tunable magnetic states on the zigzag edges of hydrogenated and halogenated group-IV nanoribbons

    Science.gov (United States)

    Chuang, Feng-Chuan; Wang, Tzu-Cheng; Hsu, Chia-Hsiu; Huang, Zhi-Quan; Su, Wan-Sheng; Guo, Guang-Yu

    The magnetic and electronic properties of hydrogenated and halogenated group-IV zigzag nanoribbons (ZNRs) are investigated by first-principles density functional calculations. Fascinatingly, we find that all the ZNRs have magnetic edges with a rich variety of electronic and magnetic properties tunable by selecting the parent and passivating elements as well as controlling the magnetization direction and external strain. In particular, the electric property of the edge band structure can be tuned from the conducting to insulating with a band gap up to 0.7 eV, depending on the parent and passivating elements as well as the applied strain, magnetic configuration and magnetization orientation. The last controllability would allow us to develop magnetic on-off nano-switches. Furthermore, ZNRs such as SiI, Ge, GeI and SnH, have fully spin-polarized metallic edge states and thus are promising materials for spintronics. The calculated magnetocrystalline anisotropy energy can be as large as 9 meV/edge-site, being 2000 time greater than that of bulk Ni and Fe ( 5 μeV/atom), and thus has great potential for high density magneto-electric data-storage devices. Finally, the calculated exchange coupling strength and thus magnetic transition temperature increases as the applied strain goes from -5 % to 5 %. Our findings thus show that these ZNRs would have exciting applications in next-generation electronic and spintronic nano-devices.

  13. Summer Bridge Programs. What Works Clearinghouse Intervention Report

    Science.gov (United States)

    What Works Clearinghouse, 2016

    2016-01-01

    "Summer bridge programs" are designed to ease the transition to college and support postsecondary success by providing students with the academic skills and social resources needed to succeed in a college environment. These programs occur in the summer "bridge" period between high school and college. Although the content of…

  14. Dark excitons in transition metal dichalcogenides

    Science.gov (United States)

    Malic, Ermin; Selig, Malte; Feierabend, Maja; Brem, Samuel; Christiansen, Dominik; Wendler, Florian; Knorr, Andreas; Berghäuser, Gunnar

    2018-01-01

    Monolayer transition metal dichalcogenides (TMDs) exhibit a remarkably strong Coulomb interaction that manifests in tightly bound excitons. Due to the complex electronic band structure exhibiting several spin-split valleys in the conduction and valence band, dark excitonic states can be formed. They are inaccessibly by light due to the required spin-flip and/or momentum transfer. The relative position of these dark states with respect to the optically accessible bright excitons has a crucial impact on the emission efficiency of these materials and thus on their technological potential. Based on the solution of the Wannier equation, we present the excitonic landscape of the most studied TMD materials including the spectral position of momentum- and spin-forbidden excitonic states. We show that the knowledge of the electronic dispersion does not allow to conclude about the nature of the material's band gap since excitonic effects can give rise to significant changes. Furthermore, we reveal that an exponentially reduced photoluminescence yield does not necessarily reflect a transition from a direct to a nondirect gap material, but can be ascribed in most cases to a change of the relative spectral distance between bright and dark excitonic states.

  15. Halogen bonding: A new retention mechanism for the solid phase extraction of perfluorinated iodoalkanes

    International Nuclear Information System (INIS)

    Yan Xiaoqing; Shen Qianjin; Zhao Xiaoran; Gao Haiyue; Pang Xue; Jin Weijun

    2012-01-01

    Highlights: ► Halogen bonding (XB) is firstly utilised in solid phase extraction. ► The perfluorinated iodine alkanes can be extracted by C-I⋯Cl − halogen bonding. ► The C-I⋯Cl − halogen bond is well characterised by spectroscopy methods. ► The analytes with strong halogen-bonding abilities can be selectively extracted. - Abstract: For the first time, halogen-bonding interaction is utilised in the solid phase extraction of perfluorinated iodoalkane (PFI). Nine PFIs, as model analytes, were tested, and analyses by UV, 19 F NMR and Raman spectroscopies demonstrate that the PFIs are extracted by a strong anion exchange (SAX) sorbent from n-hexane due to the C-I⋯Cl − halogen-bonding interactions. The results also show that the adsorptivities of SAX for the diiodoperfluoro-alkanes (diiodo-PFIs) were much stronger than those for the perfluoroalkyl iodides (monoiodo-PFIs). Specifically, the recoveries for 1,6-diiodoperfluorohexane and 1,8-diiodoperfluorooctane were higher than 80% when 100 mL of sample spiked with a 5 ng mL −1 analyte mixture was extracted. Interestingly, SAX had no adsorption for hexafluorobenzene at all, which is known to be unable to form a halogen bond with Cl − . The analytical performance of the halogen bond-based SPE-GC–MS method for the diiodo-PFIs was also examined in soil samples. The sorbent SAX enabled the selective extraction of four diiodo-PFIs successfully from soil samples. The recoveries of the diiodo-PFIs extracted from 5 g soil sample at the 100 ng g −1 spike level were in the range of 73.2–93.8% except 26.8% for 1,2-diiodoperfluoroethane. The limit of detection varied from 0.02 to 0.04 ng g −1 in soil samples. Overall, this work reveals the great application potential of halogen bonding in the field of solid phase extraction to selectively extract compounds with strong halogen-bonding abilities.

  16. Ultraviolet radiation and blue-light emissions from spotlights incorporating tungsten halogen lamps

    CERN Document Server

    MacKinlay, Alistair F; Whillock, M J

    1989-01-01

    This report summarises measurements of the ultraviolet radiation and blue-light emissions from eleven 'desk-top' tungsten halogen (quartz) lamps and one 'floor-standing' tungsten halogen (quartz) lamp available in the UK. Values of occupational hazard weighted and erythemally weighted ultraviolet radiation irradiance and measurements and relevant calculations of blue-light hazards are presented. It is concluded that the safety design of some desk-top tungsten halogen lamps is inadequate to prevent unnecessary exposure of the skin to potentially harmful ultraviolet radiation. It is recommended that all tungsten halogen lamps should have sufficient filtration to reduce their ultraviolet emissions to an acceptably low level. As long as the comfort aversion responses of the eye are respected, direct viewing of the lamps examined should not constitute a retinal hazard.

  17. Ultraviolet radiation and blue-light emissions from spotlights incorporating tungsten halogen lamps

    International Nuclear Information System (INIS)

    McKinlay, A.F.; Whillock, M.J.; Meulemans, C.C.E.

    1989-07-01

    This report summarises measurements of the ultraviolet radiation and blue-light emissions from eleven 'desk-top' tungsten halogen (quartz) lamps and one 'floor-standing' tungsten halogen (quartz) lamp available in the UK. Values of occupational hazard weighted and erythemally weighted ultraviolet radiation irradiance and measurements and relevant calculations of blue-light hazards are presented. It is concluded that the safety design of some desk-top tungsten halogen lamps is inadequate to prevent unnecessary exposure of the skin to potentially harmful ultraviolet radiation. It is recommended that all tungsten halogen lamps should have sufficient filtration to reduce their ultraviolet emissions to an acceptably low level. As long as the comfort aversion responses of the eye are respected, direct viewing of the lamps examined should not constitute a retinal hazard. (author)

  18. VO2 microcrystals as an advanced smart window material at semiconductor to metal transition

    Science.gov (United States)

    Basu, Raktima; Magudapathy, P.; Sardar, Manas; Pandian, Ramanathaswamy; Dhara, Sandip

    2017-11-01

    Textured VO2(0 1 1) microcrystals are grown in the monoclinic, M1 phase which undergoes a reversible first order semiconductor to metal transition (SMT) accompanied by a structural phase transition to rutile tetragonal, R phase. Around the phase transition, VO2 also experiences noticeable change in its optical and electrical properties. A change in color of the VO2 micro crystals from white to cyan around the transition temperature is observed, which is further understood by absorption of red light using temperature dependent ultraviolet-visible spectroscopic analysis and photoluminescence studies. The absorption of light in the red region is explained by the optical transition between Hubbard states, confirming the electronic correlation as the driving force for SMT in VO2. The thermochromism in VO2 has been studied for smart window applications so far in the IR region, which supports the opening of the band gap in semiconducting phase; whereas there is hardly any report in the management of visible light. The filtering of blue light along with reflection of infrared above the semiconductor to metal transition temperature make VO2 applicable as advanced smart windows for overall heat management of a closure.

  19. VO2 microcrystals as an advanced smart window material at semiconductor to metal transition

    International Nuclear Information System (INIS)

    Basu, Raktima; Pandian, Ramanathaswamy; Dhara, Sandip; Magudapathy, P; Sardar, Manas

    2017-01-01

    Textured VO 2 (0 1 1) microcrystals are grown in the monoclinic, M1 phase which undergoes a reversible first order semiconductor to metal transition (SMT) accompanied by a structural phase transition to rutile tetragonal, R phase. Around the phase transition, VO 2 also experiences noticeable change in its optical and electrical properties. A change in color of the VO 2 micro crystals from white to cyan around the transition temperature is observed, which is further understood by absorption of red light using temperature dependent ultraviolet–visible spectroscopic analysis and photoluminescence studies. The absorption of light in the red region is explained by the optical transition between Hubbard states, confirming the electronic correlation as the driving force for SMT in VO 2 . The thermochromism in VO 2 has been studied for smart window applications so far in the IR region, which supports the opening of the band gap in semiconducting phase; whereas there is hardly any report in the management of visible light. The filtering of blue light along with reflection of infrared above the semiconductor to metal transition temperature make VO 2 applicable as advanced smart windows for overall heat management of a closure. (paper)

  20. Discontinuous structural phase transition of liquid metal and alloys (2)

    International Nuclear Information System (INIS)

    Wang, Li; Liu, Jiantong

    2004-01-01

    The diameter (d f ) of diffusion fluid cluster before and after phase transition has been calculated in terms of the paper ''Discontinuous structural phase transition of liquid metal and alloy (1)'' Physics Letters. A 326 (2004) 429-435, to verify quantitatively the discontinuity of structural phase transition; the phenomena of thermal contraction and thermal expansion during the phase transition, together with the evolution model of discontinuous structural phase transition are also discussed in this Letter to explore further the nature of structural transition; In addition, based on the viscosity experimental result mentioned in paper [Y. Waseda, The Structure of Non-Crystalline Materials--Liquids and Amorphous Solids, McGraw-Hill, New York, 1980], we present an approach to draw an embryo of the liquid-liquid (L-L) phase diagram for binary alloys above liquidus in the paper, expecting to guide metallurgy process so as to improve the properties of alloys. The idea that controls amorphous structure and its properties by means of the L-L phase diagram for alloys and by the rapid cooling technique to form the amorphous alloy has been brought forward in the end