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Sample records for nano-particulate transition metal

  1. Hydrogen evolution on nano-particulate transition metal sulfides

    DEFF Research Database (Denmark)

    Bonde, Jacob Lindner; Moses, Poul Georg; Jaramillo, Thomas F.

    2008-01-01

    The hydrogen evolution reaction (HER) on carbon supported MoS2 nanoparticles is investigated and compared to findings with previously published work on Au(111) supported MoS2. An investigation into MoS2 oxidation is presented and used to quantify the surface concentration of MoS2. Other metal...

  2. Control of ferroelectric phase transition in nano particulate NBT–BT based ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Devi, Ch. Sameera; Kumar, G.S. [Department of Physics, Osmania University, Hyderabad 500 007 (India); Prasad, G., E-mail: gudurup@gmail.com [Department of Physics, Osmania University, Hyderabad 500 007 (India)

    2013-03-20

    Graphical abstract: Modified Curie–Weiss law fitting of BT1, NBT1, NBT2 and NBT3 samples and inset shows modified Curie–Weiss law fitting for NBT at 10 kHz frequency. Highlights: ► For the first time we have studied the effect of Nd{sup 3+} and BT on structural changes in NBT lattice. ► Ti metal powder was used instead of TiO{sub 2} to synthesize the ceramics using sol–gel. ► FTIR and Raman spectra were recorded for NBT–BT based ceramics. ► In dielectric measurements the transition from relaxor to normal with doping is observed. -- Abstract: Lead free relaxor NBT–BT based ceramic compositions were prepared using sol–gel method. The samples were sintered around 1140 °C for 3–4 h in the air. The characterization was done using X-ray diffraction (XRD), filed emission scanning electron microscope (FESEM), energy dispersive spectrometry (EDS), Raman, Fourier transform infrared (FTIR), dielectric and P–E loop measurements. The XRD patterns recorded at room temperature confirmed the phase formation of the samples. From FESEM micrographs, the particle sizes were estimated for calcined powders and are found to be in the range of 50–70 nm. The analysis of both Raman and FTIR spectral data of the samples also indicated the distortion of NBT lattice with the addition of Ba{sup 2+} and Nd{sup 3+} ions. It was found that the dielectric and piezoelectric properties of NBT–BT compositions beyond the morphotrophic phase boundary (MPB) are rather sensitive to the presence of tetragonal phase in addition to the rhombohedral phase. NBT ceramics exhibit a decrease in diffusive factor with increasing BT content, implying a degradation of relaxor feature leading to the normal ferroelectric nature. The ceramic samples employed in the present study exhibited variation in P–E hysteresis loops.

  3. 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.

  4. 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.

  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. 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 ...

  7. Gel nano-particulates against radioactivity; Des nanoparticules en gel contre la radioactivite

    Energy Technology Data Exchange (ETDEWEB)

    Deroin, Ph

    2004-11-01

    The Argonne research center (USA) has developed a 'super-gel' compound, a polymer close to those used in baby's diapers, which can reach a 90% efficiency in the radioactive decontamination of porous materials, like bricks or concrete. The contaminated materials are sprayed with a mixture of polymer gel and wetting agent with nano-particulates in suspension. Under the action of the wetting agent, radioactivity migrates from the pores to the gel and is trapped by the nano-particulates. The drying and recycling of the gel allows to reduce the volume of radioactive wastes. Short paper. (J.S.)

  8. Transition Metal Compounds Towards Holography

    Directory of Open Access Journals (Sweden)

    Volker Dieckmann

    2012-06-01

    Full Text Available We have successfully proposed the application of transition metal compounds in holographic recording media. Such compounds feature an ultra-fast light-induced linkage isomerization of the transition-metal–ligand bond with switching times in the sub-picosecond regime and lifetimes from microseconds up to hours at room temperature. This article highlights the photofunctionality of two of the most promising transition metal compounds and the photophysical mechanisms that are underlying the hologram recording. We present the latest progress with respect to the key measures of holographic media assembled from transition metal compounds, the molecular embedding in a dielectric matrix and their impressive potential for modern holographic applications.

  9. 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…

  10. Transition Metal Complexes and Catalysis

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 4; Issue 9. Transition Metal Complexes and Catalysis. Balaji R Jagirdar. General Article Volume 4 Issue 9 ... Author Affiliations. Balaji R Jagirdar1. Department of Inorganic & Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India.

  11. Homogeneous catalysis by transition metals

    International Nuclear Information System (INIS)

    Masters, K.

    1983-01-01

    Fundamentals of homogeneous catalysis by metal complex aAe presented in the monograph along with the mechanisms of practically all types of catalytic reactions proceeding in the presence of transition metal complexes. In particular, considered are: catalytic cycles for olefin hydrogenation in the presence of Ru(2) complex; for alkene epoxidation catalyzed by Mo(6); for alkene metathesis reaction catalyzed by Ta and W compounds. Catalytic systems on the basis of Zr, Mo, W, Ru complexes being in the stage of development of the processes of nitrogen fixation reductive oligomerization alkene activation are described. Bibliography contains more than 400 references

  12. 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...

  13. Rate-programming of nano-particulate delivery systems for smart bioactive scaffolds in tissue engineering

    Science.gov (United States)

    Izadifar, Mohammad; Haddadi, Azita; Chen, Xiongbiao; Kelly, Michael E.

    2015-01-01

    Development of smart bioactive scaffolds is of importance in tissue engineering, where cell proliferation, differentiation and migration within scaffolds can be regulated by the interactions between cells and scaffold through the use of growth factors (GFs) and extra cellular matrix peptides. One challenge in this area is to spatiotemporally control the dose, sequence and profile of release of GFs so as to regulate cellular fates during tissue regeneration. This challenge would be addressed by rate-programming of nano-particulate delivery systems, where the release of GFs via polymeric nanoparticles is controlled by means of the methods of, such as externally-controlled and physicochemically/architecturally-modulated so as to mimic the profile of physiological GFs. Identifying and understanding such factors as the desired release profiles, mechanisms of release, physicochemical characteristics of polymeric nanoparticles, and externally-triggering stimuli are essential for designing and optimizing such delivery systems. This review surveys the recent studies on the desired release profiles of GFs in various tissue engineering applications, elucidates the major release mechanisms and critical factors affecting release profiles, and overviews the role played by the mathematical models for optimizing nano-particulate delivery systems. Potentials of stimuli responsive nanoparticles for spatiotemporal control of GF release are also presented, along with the recent advances in strategies for spatiotemporal control of GF delivery within tissue engineered scaffolds. The recommendation for the future studies to overcome challenges for developing sophisticated particulate delivery systems in tissue engineering is discussed prior to the presentation of conclusions drawn from this paper.

  14. Rate-programming of nano-particulate delivery systems for smart bioactive scaffolds in tissue engineering.

    Science.gov (United States)

    Izadifar, Mohammad; Haddadi, Azita; Chen, Xiongbiao; Kelly, Michael E

    2015-01-09

    Development of smart bioactive scaffolds is of importance in tissue engineering, where cell proliferation, differentiation and migration within scaffolds can be regulated by the interactions between cells and scaffold through the use of growth factors (GFs) and extra cellular matrix peptides. One challenge in this area is to spatiotemporally control the dose, sequence and profile of release of GFs so as to regulate cellular fates during tissue regeneration. This challenge would be addressed by rate-programming of nano-particulate delivery systems, where the release of GFs via polymeric nanoparticles is controlled by means of the methods of, such as externally-controlled and physicochemically/architecturally-modulated so as to mimic the profile of physiological GFs. Identifying and understanding such factors as the desired release profiles, mechanisms of release, physicochemical characteristics of polymeric nanoparticles, and externally-triggering stimuli are essential for designing and optimizing such delivery systems. This review surveys the recent studies on the desired release profiles of GFs in various tissue engineering applications, elucidates the major release mechanisms and critical factors affecting release profiles, and overviews the role played by the mathematical models for optimizing nano-particulate delivery systems. Potentials of stimuli responsive nanoparticles for spatiotemporal control of GF release are also presented, along with the recent advances in strategies for spatiotemporal control of GF delivery within tissue engineered scaffolds. The recommendation for the future studies to overcome challenges for developing sophisticated particulate delivery systems in tissue engineering is discussed prior to the presentation of conclusions drawn from this paper.

  15. Enantioselective, transition metal catalyzed cycloisomerizations.

    Science.gov (United States)

    Marinetti, Angela; Jullien, Hélène; Voituriez, Arnaud

    2012-07-21

    This review illustrates enantioselective transition-metal promoted skeletal rearrangements of polyunsaturated substrates possessing olefin, alkyne or allene functions. These processes are classified according to the number of carbon atoms involved in the cyclization, from (1C+1C) to (2C+2C+2C) or (2C+5C) cyclizations. Thus, for instance, (1C+1C) processes are typified notably by Alder-ene type reactions taking place mainly under palladium and rhodium catalysis, in the presence of chiral phosphorus ligands. Also, rhodium, platinum, and gold promoted insertions of unsaturated carbon-carbon bonds into C-H bonds belong to this class. For each class of reactions or substrate type the best ligand-metal pairs are highlighted. Unfortunately, unlike other transition metal promoted reactions, the mechanisms of chiral induction and stereochemical pathways have not been established so far in any of these reactions. In only a few instances, qualitative heuristic models have been tentatively proposed. Although the available stereochemical information is systematically given here, the paper focuses mainly on synthetic aspects of enantioselective cycloisomerizations.

  16. 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.

  17. 2D transition metal dichalcogenides

    Science.gov (United States)

    Manzeli, Sajedeh; Ovchinnikov, Dmitry; Pasquier, Diego; Yazyev, Oleg V.; Kis, Andras

    2017-08-01

    Graphene is very popular because of its many fascinating properties, but its lack of an electronic bandgap has stimulated the search for 2D materials with semiconducting character. Transition metal dichalcogenides (TMDCs), which are semiconductors of the type MX2, where M is a transition metal atom (such as Mo or W) and X is a chalcogen atom (such as S, Se or Te), provide a promising alternative. Because of its robustness, MoS2 is the most studied material in this family. TMDCs exhibit a unique combination of atomic-scale thickness, direct bandgap, strong spin-orbit coupling and favourable electronic and mechanical properties, which make them interesting for fundamental studies and for applications in high-end electronics, spintronics, optoelectronics, energy harvesting, flexible electronics, DNA sequencing and personalized medicine. In this Review, the methods used to synthesize TMDCs are examined and their properties are discussed, with particular attention to their charge density wave, superconductive and topological phases. The use of TMCDs in nanoelectronic devices is also explored, along with strategies to improve charge carrier mobility, high frequency operation and the use of strain engineering to tailor their properties.

  18. 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.

  19. Electronic doping of transition metal oxide perovskites

    Energy Technology Data Exchange (ETDEWEB)

    Cammarata, Antonio, E-mail: cammaant@fel.cvut.cz [Department of Control Engineering, Czech Technical University in Prague, Technicka 2, 16627 Prague 6 (Czech Republic); Rondinelli, James M. [Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208 (United States)

    2016-05-23

    CaFeO{sub 3} is a prototypical negative charge transfer oxide that undergoes electronic metal-insulator transition concomitant with a dilation and contraction of nearly rigid octahedra. Altering the charge neutrality of the bulk system destroys the electronic transition, while the structure is significantly modified at high charge content. Using density functional theory simulations, we predict an alternative avenue to modulate the structure and the electronic transition in CaFeO{sub 3}. Charge distribution can be modulated using strain-rotation coupling and thin film engineering strategies, proposing themselves as a promising avenue for fine tuning electronic features in transition metal-oxide perovskites.

  20. Novel nano-particulated exopolysaccharide produced by Klebsiella sp. PHRC1.001.

    Science.gov (United States)

    Zhao, Meng; Cui, Nana; Qu, Fangning; Huang, Xue; Yang, Hao; Nie, Shaoping; Zha, Xueqiang; Cui, Steve W; Nishinari, Katsuyoshi; Phillips, Glyn O; Fang, Yapeng

    2017-09-01

    In recent decades, microbial synthesis of polysaccharides with special functional properties has attracted increasing attention. This work reported a novel exopolysaccharide (EPS)-producing strain, Klebsiella sp. PHRC1.001 isolated from activated sludge. Physicochemical, rheological, emulsifying and toxicological properties of the obtained EPS were characterized. The EPS was mainly composed of d-glucose and l-arabinose, and was found to exist in aqueous solution in a nano-particulated form (∼50nm in diameter) with a strong tendency of aggregation. Rheological analysis showed that the EPS aqueous solution was a typical pseudoplastic fluid at higher concentration and could form weak gel upon alkaline treatment followed by neutralization. The EPS exhibited excellent emulsifying properties in stabilizing oil-in-water emulsions presumably by a Pickering mechanism owing to its nanoparticle structure. Acute toxicity test showed that 1.8g EPS per kg of body weight caused no toxic effect on mice. PHRC1.001 EPS has the potential to be a novel industrial polysaccharide. Copyright © 2017 Elsevier Ltd. All rights reserved.

  1. Polyoxometalate coordinated transition metal complexes as ...

    Indian Academy of Sciences (India)

    Keywords. Heptamolybdate type polyoxometalate cluster anion; transition metal coordination complexes; ... industrial chemistry. This oxidation can be divided into three categories: (i) the cleavage of the C=C bond by using the surface of the metal oxide, e.g., osmium or .... supported cobalt complexes (catalysts 1 and 2) pro-.

  2. Transition metal catalysis in confined spaces

    NARCIS (Netherlands)

    Leenders, S.H.A.M.; Gramage-Doria, R.; de Bruin, B.; Reek, J.N.H.

    2015-01-01

    Transition metal catalysis plays an important role in both industry and in academia where selectivity, activity and stability are crucial parameters to control. Next to changing the structure of the ligand, introducing a confined space as a second coordination sphere around a metal catalyst has

  3. 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...

  4. Transition metal catalysis in confined spaces.

    Science.gov (United States)

    Leenders, Stefan H A M; Gramage-Doria, Rafael; de Bruin, Bas; Reek, Joost N H

    2015-01-21

    Transition metal catalysis plays an important role in both industry and in academia where selectivity, activity and stability are crucial parameters to control. Next to changing the structure of the ligand, introducing a confined space as a second coordination sphere around a metal catalyst has recently been shown to be a viable method to induce new selectivity and activity in transition metal catalysis. In this review we focus on supramolecular strategies to encapsulate transition metal complexes with the aim of controlling the selectivity via the second coordination sphere. As we will discuss, catalyst confinement can result in selective processes that are impossible or difficult to achieve by traditional methods. We will describe the template-ligand approach as well as the host-guest approach to arrive at such supramolecular systems and discuss how the performance of the catalyst is enhanced by confining it in a molecular container.

  5. Transition metal contacts to graphene

    Energy Technology Data Exchange (ETDEWEB)

    Politou, Maria, E-mail: Maria.Politou@imec.be; De Gendt, Stefan; Heyns, Marc [KU Leuven, 3001 Leuven (Belgium); imec, Kapeldreef 75, 3001 Leuven (Belgium); Asselberghs, Inge; Radu, Iuliana; Conard, Thierry; Richard, Olivier; Martens, Koen; Huyghebaert, Cedric; Tokei, Zsolt [imec, Kapeldreef 75, 3001 Leuven (Belgium); Lee, Chang Seung [SAIT, Samsung Electronics Co., Suwon 443-803 (Korea, Republic of); Sayan, Safak [imec, Kapeldreef 75, 3001 Leuven (Belgium); Intel Corporation, 2200 Mission College Blvd, Santa Clara, California 95054 (United States)

    2015-10-12

    Achieving low resistance contacts to graphene is a common concern for graphene device performance and hybrid graphene/metal interconnects. In this work, we have used the circular Transfer Length Method (cTLM) to electrically characterize Ag, Au, Ni, Ti, and Pd as contact metals to graphene. The consistency of the obtained results was verified with the characterization of up to 72 cTLM structures per metal. Within our study, the noble metals Au, Ag and Pd, which form a weaker bond with graphene, are shown to result in lower contact resistance (Rc) values compared to the more reactive Ni and Ti. X-ray Photo Electron Spectroscopy and Transmission Electron Microscopy characterization for the latter have shown the formation of Ti and Ni carbides. Graphene/Pd contacts show a distinct intermediate behavior. The weak carbide formation signature and the low Rc values measured agree with theoretical predictions of an intermediate state of weak chemisorption of Pd on graphene.

  6. 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)

  7. 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

  8. Defect-Tolerant Monolayer Transition Metal Dichalcogenides

    DEFF Research Database (Denmark)

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

    2016-01-01

    -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...... shallow defect levels and are thus predicted to be defect-tolerant. Interestingly, all the defect sensitive TMDs have valence and conduction bands with a very similar orbital composition. This indicates a bonding/antibonding nature of the gap, which in turn suggests that dangling bonds will fall inside...

  9. 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

  10. 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.

  11. A comparison in activity between transition-metal oxides and transition metals

    Science.gov (United States)

    Vojvodic, Aleksandra; Studt, Felix; Abild-Pedersen, Frank; Bligaard, Thomas; Nørskov, Jens

    2012-02-01

    Transition-metal oxides are widely used materials in catalysis as substrates and promoters, but also as the active catalyst materials themselves. We compare the reactivity of transition-metal oxides with the one of transition metals. The comparison is exemplified for the ammonia synthesis reaction. First we show that there exist characteristic Brønsted-Evans Polanyi (BEP) relations (linear relations between transition state and dissociation energies) for dissociation of molecules on transition-metal oxides in the rutile and perovskite structure. It is well-known that the (211) metal surface is several orders of magnitude more reactive than the (111) metal surface due to the lower BEP line for the 211 facet. We find that both rutiles and perovskites follow BEP relations that are lower than the one of the 211 facet. Second we utilize the established BEP relations together with calculated adsorption energetics in a micro-kinetic model to obtain a volcano plot for the catalytic activity. We find that oxides have a higher turn over frequency as compared with metals. Hence, oxides intrinsically have a great advantage in terms of catalytic activity which opens up for catalyst design.

  12. 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.

  13. 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

  14. (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.

  15. 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.

  16. 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

  17. 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...

  18. Transformation paths in transition-metal disilicides

    Czech Academy of Sciences Publication Activity Database

    Káňa, Tomáš; Šob, Mojmír; Vitek, V.

    2011-01-01

    Roč. 465, - (2011), s. 61-64 ISSN 1662-9795. [MSMF /6./ Materials Structure and Micromechanics of Fracture. Brno, 28.06.2010-30.06.2010] R&D Projects: GA AV ČR IAA100100920; GA MŠk(CZ) OC10008 Institutional research plan: CEZ:AV0Z20410507 Keywords : transition-metal disilicides * transformation path * structural stability * electronic structure Subject RIV: BM - Solid Matter Physics ; Magnetism

  19. Single-layer transition metal sulfide catalysts

    Science.gov (United States)

    Thoma, Steven G [Albuquerque, NM

    2011-05-31

    Transition Metal Sulfides (TMS), such as molybdenum disulfide (MoS.sub.2), are the petroleum industry's "workhorse" catalysts for upgrading heavy petroleum feedstocks and removing sulfur, nitrogen and other pollutants from fuels. We have developed an improved synthesis technique to produce SLTMS catalysts, such as molybdenum disulfide, with potentially greater activity and specificity than those currently available. Applications for this technology include heavy feed upgrading, in-situ catalysis, bio-fuel conversion and coal liquefaction.

  20. Magnetic Interactions in Transition-Metal Oxides

    OpenAIRE

    Solovyev, I. V.

    2003-01-01

    This a review article, which presents a general framework for the analysis of interatomic magnetic interactions in the spin-density-functional theory, which is based on the magnetic force theorem, make a link with the models for transition-metal oxides, and gives several examples of how this strategy can be used for the analysis of magnetic properties of colossal-magnetoresistive perovskite manganites, double perovskite and pyrochlore compounds.

  1. 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...

  2. Synthesis of arsenic transition metal sulfides and metal arsenides

    Energy Technology Data Exchange (ETDEWEB)

    Singhal, G.H.; Brown, L.D.; Ryan, D.F. [Exxon Research & Development Labs, Baton Rouge, LA (United States)

    1993-12-31

    One of the chief problems in upgrading shale oil is the presence of inherent arsenic which is known to poison downstream catalysts. Highly dispersed transition metal sulfides formed in situ from the decomposition of dithiocarbamate (DTC) complexes of transition metals show excellent potential as dearsenation agents. The authors have studied the reaction of these sulfides with various arsenic compositions and characterized the metal arsenides and arsenic metal sulfides formed as well as the ease of their formation. Thus, the reaction of bis(butyldithiocarbamato)Ni, (NiBuDTC) with model compounds was very facile and gave NiAs, NiAsS, and NiAs2=xSx. In general the effectiveness of the sulfides for dearsenation followed the sequence Ni>Mo{much_gt}Co, while iron sulfides were totally ineffective. Based upon these results, tests were run in autoclaves (as well as a fixed-bed flow-through unit) with NiBuDTC and shale oil having 73 ppm inherent As. Under optimum conditions, dearsenation down to les than 1 ppm was obtained.

  3. 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

  4. Versatile two-dimensional transition metal dichalcogenides

    DEFF Research Database (Denmark)

    Canulescu, Stela; Affannoukoué, Kévin; Döbeli, Max

    Two-dimensional transition metal dichalcogenides (2D-TMDCs), such as MoS2, have emerged as a new class of semiconducting materials with distinct optical and electrical properties. The availability of 2D-TMDCs with distinct band gaps allows for unlimited combinations of TMDC monolayers (MLs...... vacancies. We have found that the absorption spectra of the MoS2 films exhibit distinct excitonic peaks at ~1.8 and ~2 eV when grown in the presence of a sulfur evaporation beam as compared to those deposited in vacuum. The structure of the PLD-grown MoS2 films will be further discussed based Raman...

  5. Magnetic correlations in doped transition metal oxides

    International Nuclear Information System (INIS)

    The authors review recent reactor- and spallation-source-based neutron scattering experiments on the magnetic fluctuations and order in a variety of doped transition metal oxides. In particular, data are shown for the NiO chain compound, Y 2-x Ca x BaNiO 5 , the two-dimensional cuprate superconductors La 2-x Sr x CuO 4 and YBa 2 Cu 3 O 6+x , and the classical three-dimensional ''Mott-Hubbard'' system V 2-y O 3

  6. 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...... approximations, be reduced to the Stoner model. Results for the volume dependence of the ferromagnetic moment and the electronic pressure of bcc, fcc and hcp Fe are presented, together with theoretical values for the equilibrium atomic volume, the bulk modulus, the ferromagnetic moment, the spin susceptibility...

  7. ANIONS FUNCTIONS IN TRANSITION METALS COORDINATION COMPOUNDS

    Directory of Open Access Journals (Sweden)

    T. V. Koksharova

    2016-04-01

    Full Text Available The effect of anions on the structure and properties of coordination compounds of transition metals has been discussed. The examples of changes in the composition of the formed complexes by replacement of the anion are given: metal ratio to a neutral ligand, the composition of the inner sphere, the direction of template synthesis. Anions can determine the presence of isomers in complexes with different ligands. Examples of conformational, ionization isomerism, inner sphere bond isomerization are given. The nature of the coordination polyhedron is highly sensitive to the replacement of the anion too. Examples of coordination compounds where the anion change causes a change in coordination capacity of neutral ligands and the strength of their bonds with the metal, coordination number and geometry of the inner sphere, the organization of molecular structures (the structure of the hydrogen bond networks and the degree of polymerization, crystal packing. The anions significantly affect the binding of the solvent molecules, complexes magnetic and luminescent properties, they can change the compound color, the mechanisms of thermolysis. Anions make a very noticeable influence on possible redox processes following the complexation in some cases. Anions in the coordination sphere can change catalytic and biochemical processes as well as the ways of interaction of metal ions with drugs.

  8. 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.)

  9. 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

  10. 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.

  11. 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.

  12. Local Oxidation Nanolithography on Metallic Transition Metal Dichalcogenides Surfaces

    Directory of Open Access Journals (Sweden)

    Elena Pinilla-Cienfuegos

    2016-09-01

    Full Text Available The integration of atomically-thin layers of two dimensional (2D materials in nanodevices demands for precise techniques at the nanoscale permitting their local modification, structuration or resettlement. Here, we present the use of Local Oxidation Nanolithography (LON performed with an Atomic Force Microscope (AFM for the patterning of nanometric motifs on different metallic Transition Metal Dichalcogenides (TMDCs. We show the results of a systematic study of the parameters that affect the LON process as well as the use of two different modes of lithographic operation: dynamic and static. The application of this kind of lithography in different types of TMDCs demonstrates the versatility of the LON for the creation of accurate and reproducible nanopatterns in exfoliated 2D-crystals and reveals the influence of the chemical composition and crystalline structure of the systems on the morphology of the resultant oxide motifs.

  13. 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

  14. Computation of the Structure Factor of Some Transition Liquid Metals

    African Journals Online (AJOL)

    Applying the solution of the Percus-Yevic equation to a one component hard sphere system and using the recently developed potential for liquid transition liquid metals, the structure factor of transition liquid metals were computed. The peak height and peak position of the structure factor of the liquid metals were studied.

  15. Metal Insulator transition in Vanadium Dioxide

    Science.gov (United States)

    Jovaini, Azita; Fujita, Shigeji; Suzuki, Akira; Godoy, Salvador

    2012-02-01

    MAR12-2011-000262 Abstract Submitted for the MAR12 Meeting of The American Physical Society Sorting Category: 03.9 (T) On the metal-insulator-transition in vanadium dioxide AZITA JOVAINI, SHIGEJI FUJITA, University at Buffalo, SALVADOR GODOY, UNAM, AKIRA SUZUKI, Tokyo University of Science --- Vanadium dioxide (VO2) undergoes a metal-insulator transition (MIT) at 340 K with the structural change from tetragonal to monoclinic crystal. The conductivity _/ drops at MIT by four orders of magnitude. The low temperature monoclinic phase is known to have a lower ground-state energy. The existence of the k-vector k is prerequisite for the conduction since the k appears in the semiclassical equation of motion for the conduction electron (wave packet). The tetragonal (VO2)3 unit is periodic along the crystal's x-, y-, and z-axes, and hence there is a three-dimensional k-vector. There is a one-dimensional k for a monoclinic crystal. We believe this difference in the dimensionality of the k-vector is the cause of the conductivity drop. Prefer Oral Session X Prefer .

  16. 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.

  17. Study of concentrated metal-ammonia solutions: magnetic properties and non metal-metal transition

    International Nuclear Information System (INIS)

    Lelieur, Jean-Pierre

    1972-01-01

    The magnetic susceptibility of alkali metal-liquid ammonia solutions has been measured in the concentration range where the solutions show a progressive passage toward the metallic state. The Knight shift of the metal nuclei and the nitrogen nucleus have been determined as a function of concentration and temperature, in Na-NH 3 and Cs-NH 3 solutions. A phenomenological analysis of the transport properties of metal-ammonia solutions is also presented. This analysis permits the presentation of a model for the mechanism of the transition to the metallic state. (author) [fr

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

    Indian Academy of Sciences (India)

    on fluorescence signalling systems for the transition metal ions. It is shown that even simple fluorophore-spacer-receptor systems can display excellent off-on fluorescence signalling towards the quenching metal ions when the fluorophore ...

  19. Neutron irradiation damage in transition metal carbides

    International Nuclear Information System (INIS)

    Matsui, Hisayuki; Nesaki, Kouji; Kiritani, Michio

    1991-01-01

    Effects of neutron irradiation on the physical properties of light transition metal carbides, TiC x , VC x and NbC x , were examined, emphasizing the characterization of irradiation induced defects in the nonstoichiometric composition. TiC x irradiated with 14 MeV (fusion) neutrons showed higher damage rates with increasing C/Ti (x) ratio. A brief discussion is made on 'cascade damage' in TiC x irradiated with fusion neutrons. Two other carbides (VC x and NbC x ) were irradiated with fission reactor neutrons. The irradiation effects on VC x were not so simple, because of the complex irradiation behavior of 'ordered' phases. For instance, complete disordering was revealed in an ordered phase, 'V 8 C 7 ', after an irradiation dose of 10 25 n/m 2 . (orig.)

  20. 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...... important in many respects. Here, we use ab initio many-body calculations to unravel the nature of the dark excitations in monolayer MoSe2, MoS2, WSe2, andWS(2). Our results show that all these monolayer TMDCs host dark states as their lowest neutral and charged excitations. We further show that dark...... excitons possess larger binding energies than their bright counterparts while the opposite holds for trions....

  1. 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.

  2. Mesoporous diphosphine-transition metal complex catalyst for hydroformylation

    NARCIS (Netherlands)

    Reek, J.N.H.; Coppens, M.O.

    2012-01-01

    The invention pertains to a diphosphine-transition metal complex comprising a diphosphine-transition metal ligand that is covalently bonded to an insoluble mesoporous support having an average pore diameter of from 4.5 nm to 50 nm, characterized in that the ligand as attached to the support has the

  3. 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...

  4. Nanostructured transition metal oxides useful for water oxidation catalysis

    Science.gov (United States)

    Frei, Heinz M; Jiao, Feng

    2013-12-24

    The present invention provides for a composition comprising a nanostructured transition metal oxide capable of oxidizing two H.sub.2O molecules to obtain four protons. In some embodiments of the invention, the composition further comprises a porous matrix wherein the nanocluster of the transition metal oxide is embedded on and/or in the porous matrix.

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

    Indian Academy of Sciences (India)

    By introducing a few modifications in the Johnson and. Oh model, Guellil and Adams [5] have applied the EAM model for studying phonon dis- persion, thermal and surface properties of alkali and transition metals and their alloys. An empirical many-body interaction potential for the bcc transition metals Nb, Fe and Cr was.

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

    Indian Academy of Sciences (India)

    Unknown

    Abstract. Transition metal ions are notorious for their fluorescence quenching abilities. In this paper, we discuss the design strategies for the development of efficient off-on fluorescence signalling systems for the transition metal ions. It is shown that even simple fluorophore-spacer-receptor systems can display excellent.

  7. Reentrant Metal-Insulator Transitions in Silicon -

    Science.gov (United States)

    Campbell, John William M.

    This thesis describes a study of reentrant metal -insulator transitions observed in the inversion layer of extremely high mobility Si-MOSFETs. Magneto-transport measurements were carried out in the temperature range 20mK-4.2 K in a ^3He/^4 He dilution refrigerator which was surrounded by a 15 Tesla superconducting magnet. Below a melting temperature (T_{M}~500 mK) and a critical electron density (n_{s }~9times10^{10} cm^{-2}), the Shubnikov -de Haas oscillations in the diagonal resistivity enormous maximum values at the half filled Landau levels while maintaining deep minima corresponding to the quantum Hall effect at filled Landau levels. At even lower electron densities the insulating regions began to spread and eventually a metal-insulator transition could be induced at zero magnetic field. The measurement of extremely large resistances in the milliKelvin temperature range required the use of very low currents (typically in the 10^ {-12} A range) and in certain measurements minimizing the noise was also a consideration. The improvements achieved in these areas through the use of shielding, optical decouplers and battery operated instruments are described. The transport signatures of the insulating state are considered in terms of two basic mechanisms: single particle localization with transport by variable range hopping and the formation of a collective state such as a pinned Wigner crystal or electron solid with transport through the motion of bound dislocation pairs. The experimental data is best described by the latter model. Thus the two dimensional electron system in these high mobility Si-MOSFETs provides the first and only experimental demonstration to date of the formation of an electron solid at zero and low magnetic fields in the quantum limit where the Coulomb interaction energy dominates over the zero point oscillation energy. The role of disorder in favouring either single particle localization or the formation of a Wigner crystal is explored by

  8. 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.

  9. Stable carbides in transition metal alloys

    International Nuclear Information System (INIS)

    Piotrkowski, R.

    1991-01-01

    In the present work different techniques were employed for the identification of stable carbides in two sets of transition metal alloys of wide technological application: a set of three high alloy M2 type steels in which W and/or Mo were total or partially replaced by Nb, and a Zr-2.5 Nb alloy. The M2 steel is a high speed steel worldwide used and the Zr-2.5 Nb alloy is the base material for the pressure tubes in the CANDU type nuclear reactors. The stability of carbide was studied in the frame of Goldschmidt's theory of interstitial alloys. The identification of stable carbides in steels was performed by determining their metallic composition with an energy analyzer attached to the scanning electron microscope (SEM). By these means typical carbides of the M2 steel, MC and M 6 C, were found. Moreover, the spatial and size distribution of carbide particles were determined after different heat treatments, and both microstructure and microhardness were correlated with the appearance of the secondary hardening phenomenon. In the Zr-Nb alloy a study of the α and β phases present after different heat treatments was performed with optical and SEM metallographic techniques, with the guide of Abriata and Bolcich phase diagram. The α-β interphase boundaries were characterized as short circuits for diffusion with radiotracer techniques and applying Fisher-Bondy-Martin model. The precipitation of carbides was promoted by heat treatments that produced first the C diffusion into the samples at high temperatures (β phase), and then the precipitation of carbide particles at lower temperature (α phase or (α+β)) two phase field. The precipitated carbides were identified as (Zr, Nb)C 1-x with SEM, electron microprobe and X-ray diffraction techniques. (Author) [es

  10. Computational study of 5d transition metal mononitrides and ...

    Indian Academy of Sciences (India)

    Home; Journals; Bulletin of Materials Science; Volume 33; Issue 3. Computational study of 5 transition metal mononitrides and monoborides using ... affinity and ionization potential is wider for mononitrides than that for monoborides. The properties of 5-metal mononitrides and 3-metal mononitrides are also compared.

  11. 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.

  12. Electronic specific heat of transition metal carbides

    International Nuclear Information System (INIS)

    Conte, R.

    1964-07-01

    The experimental results that make it possible to define the band structure of transition metal carbides having an NaCI structure are still very few. We have measured the electronic specific heat of some of these carbides of varying electronic concentration (TiC, either stoichiometric or non-stoichiometric, TaC and mixed (Ti, Ta) - C). We give the main characteristics (metallography, resistivity, X-rays) of our samples and we describe the low temperature specific heat apparatus which has been built. In one of these we use helium as the exchange gas. The other is set up with a mechanical contact. The two use a germanium probe for thermometer. The measurement of the temperature using this probe is described, as well as the various measurement devices. The results are presented in the form of a rigid band model and show that the density of the states at the Fermi level has a minimum in the neighbourhood of the group IV carbides. (author) [fr

  13. Photocatalysis of Modified Transition Metal Oxide Surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Batzill, Matthias

    2018-02-28

    The goal of this project has been to establish a cause-effect relationship for photocatalytic activity variations of different structures of the same material; and furthermore gain fundamental understanding on modification of photocatalysts by compositional or surface modifications. The reasoning is that gaining atomic scale understanding of how surface and bulk modifications alter the photo reactivity will lead to design principles for next generation photocatalysts. As a prototypical photocatalyst the research focused on TiO2 synthesized in well-defined single crystalline form to enable fundamental characterizations.We have obtained results in the following areas: (a) Preparation of epitaxial anataseTiO2 samples by pulsed laser deposition. (b) Comparison of hydrogen diffusion on different crystallographic surface. (c) Determining the stability of the TiO2(011)-2x1 reconstruction upon interactions with adsorbates. (d) Characterization of adsorption and (thermal and photo) reaction of molecules with nitro-endgroups, (e) Exploring the possibility of modifying planar model photocatalyst surfaces with graphene to enable fundamental studies on reported enhanced photocatalytic activities of graphene modified transition metal oxides, (f) gained fundamental understanding on the role of crystallographic polymorphs of the same material for their photocatalytic activities.

  14. 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

  15. 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.

  16. Electronic structure of disordered transition metals within scattering theory

    International Nuclear Information System (INIS)

    Yakyibchuk, P.M.; Volkov, O.V.; Vakarchuk, S.O.

    2005-01-01

    Here we present a new approach to the calculation of density of states of disordered transition metals based on the T-matrix framework presented by Lloyd within generalized Ziman's theory of transport properties and energy structure of disordered metals. This approach makes it possible to avoid such difficulties of familiar calculations as renormalized perturbation theory. We have achieved double hill energy resonance for transition metals at Fe and Co groups caused by hybridization potential. So the results are in good correlation with model presentation of energy structure of these metals conduction band for explaining magnetic and transport properties

  17. SYNTHESIS AND CHARACTERIZATION OF TRANSITION METAL ...

    African Journals Online (AJOL)

    a

    The metal complexes separated out were filtered through the sintered glass crucible ... All the metal complexes (Table 2) are colored, stable to air at room temperature ... Table 2. Physical characteristics and conductivity data of metal complexes and ligands. Ligand/complex. Color. Melting/decomposition temperature, 0C.

  18. The metallicities of stars with and without transiting planets

    DEFF Research Database (Denmark)

    Buchhave, Lars A.; Latham, David W.

    2015-01-01

    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......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...

  19. 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.

  20. 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

  1. New approaches in organometallic and transition metal assemblies

    Indian Academy of Sciences (India)

    Stannoxanes and phosphonates: New approaches in organometallic and transition metal assemblies. VADAPALLI CHANDRASEKHAR*, KANDASAMY GOPAL,. LOGANATHAN NAGARAJAN, PALANI SASIKUMAR and PAKKIRISAMY THILAGAR. Department of Chemistry, Indian Institute of Technology, Kanpur 208 016.

  2. Nano-crystalline thin and nano-particulate thick TiO2 layer: Cost effective sequential deposition and study on dye sensitized solar cell characteristics

    International Nuclear Information System (INIS)

    Das, P.; Sengupta, D.; Kasinadhuni, U.; Mondal, B.; Mukherjee, K.

    2015-01-01

    Highlights: • Thin TiO 2 layer is deposited on conducting substrate using sol–gel based dip coating. • TiO 2 nano-particles are synthesized using hydrothermal route. • Thick TiO 2 particulate layer is deposited on prepared thin layer. • Dye sensitized solar cells are made using thin and thick layer based photo-anode. • Introduction of thin layer in particulate photo-anode improves the cell efficiency. - Abstract: A compact thin TiO 2 passivation layer is introduced between the mesoporous TiO 2 nano-particulate layer and the conducting glass substrate to prepare photo-anode for dye-sensitized solar cell (DSSC). In order to understand the effect of passivation layer, other two DSSCs are also developed separately using TiO 2 nano-particulate and compact thin film based photo-anodes. Nano-particles are prepared using hydrothermal synthesis route and the compact passivation layer is prepared by simply dip coating the precursor sol prepared through wet chemical route. The TiO 2 compact layer and the nano-particles are characterised in terms of their micro-structural features and phase formation behavior. It is found that introduction of a compact TiO 2 layer in between the mesoporous TiO 2 nano-particulate layer and the conducting substrate improves the solar to electric conversion efficiency of the fabricated cell. The dense thin passivation layer is supposed to enhance the photo-excited electron transfer and prevent the recombination of photo-excited electrons

  3. Occurrence and behaviour of dissolved, nano-particulate and micro-particulate iron in waste waters and treatment systems: new insights from electrochemical analysis.

    Science.gov (United States)

    Matthies, R; Aplin, A C; Horrocks, B R; Mudashiru, L K

    2012-04-01

    Cyclic-, Differential Pulse- and Steady-state Microdisc Voltammetry (CV, DPV, SMV) techniques have been used to quantify the occurrence and fate of dissolved Fe(ii)/Fe(iii), nano-particulate and micro-particulate iron over a 12 month period in a series of net-acidic and net-alkaline coal mine drainages and passive treatment systems. Total iron in the mine waters is typically 10-100 mg L(-1), with values up to 2100 mg L(-1). Between 30 and 80% of the total iron occurs as solid phase, of which 20 to 80% is nano-particulate. Nano-particulate iron comprises 20 to 70% of the nominally "dissolved" (i.e. water treatment. In most waters, the majority of truly dissolved iron occurs as Fe(ii) (average 64 ± 22%). Activities of Fe(ii) do not correlate with pH and geochemical modelling shows that no Fe(ii) mineral is supersaturated. Removal of Fe(ii) must proceed via oxidation and hydrolysis. Except in waters with pH waters are generally supersaturated with respect to ferrihydrite and schwertmannite, and are not at redox equilibrium, indicating the key role of oxidation and hydrolysis kinetics on water treatment. Typically 70-100% of iron is retained in the treatment systems. Oxidation, hydrolysis, precipitation, coagulation and sedimentation occur in all treatment systems and - independent of water chemistry and the type of treatment system - hydroxides and oxyhydroxysulfates are the main iron sinks. The electrochemical data thus reveal the rationale for incomplete iron retention in individual systems and can thus inform future design criteria. The successful application of this low cost and rapid electrochemical method demonstrates its significant potential for real-time, on-site monitoring of iron-enriched waters and may in future substitute traditional analytical methods.

  4. Nano-crystalline thin and nano-particulate thick TiO{sub 2} layer: Cost effective sequential deposition and study on dye sensitized solar cell characteristics

    Energy Technology Data Exchange (ETDEWEB)

    Das, P.; Sengupta, D. [Centre for Advanced Materials Processing, CSIR-Central Mechanical Engineering Research Institute, Durgapur, 713209 West Bengal (India); CSIR-Central Mechanical Engineering Research Institute, Academy of Scientific and Innovative Research (AcSIR), Durgapur, 713209 West Bengal (India); Kasinadhuni, U. [Department of Engineering Physics, Bengal College of Engineering and Technology, Durgapur, West Bengal (India); Mondal, B. [Centre for Advanced Materials Processing, CSIR-Central Mechanical Engineering Research Institute, Durgapur, 713209 West Bengal (India); Mukherjee, K., E-mail: kalisadhanm@yahoo.com [Centre for Advanced Materials Processing, CSIR-Central Mechanical Engineering Research Institute, Durgapur, 713209 West Bengal (India)

    2015-06-15

    Highlights: • Thin TiO{sub 2} layer is deposited on conducting substrate using sol–gel based dip coating. • TiO{sub 2} nano-particles are synthesized using hydrothermal route. • Thick TiO{sub 2} particulate layer is deposited on prepared thin layer. • Dye sensitized solar cells are made using thin and thick layer based photo-anode. • Introduction of thin layer in particulate photo-anode improves the cell efficiency. - Abstract: A compact thin TiO{sub 2} passivation layer is introduced between the mesoporous TiO{sub 2} nano-particulate layer and the conducting glass substrate to prepare photo-anode for dye-sensitized solar cell (DSSC). In order to understand the effect of passivation layer, other two DSSCs are also developed separately using TiO{sub 2} nano-particulate and compact thin film based photo-anodes. Nano-particles are prepared using hydrothermal synthesis route and the compact passivation layer is prepared by simply dip coating the precursor sol prepared through wet chemical route. The TiO{sub 2} compact layer and the nano-particles are characterised in terms of their micro-structural features and phase formation behavior. It is found that introduction of a compact TiO{sub 2} layer in between the mesoporous TiO{sub 2} nano-particulate layer and the conducting substrate improves the solar to electric conversion efficiency of the fabricated cell. The dense thin passivation layer is supposed to enhance the photo-excited electron transfer and prevent the recombination of photo-excited electrons.

  5. 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....

  6. Early Transition Metal Alkyl and Tetrahydroborate Complexes.

    Science.gov (United States)

    Jensen, James Allen

    1988-06-01

    An investigation of early transition metal alkyl and tetrahydroborate complexes as catalytic models and ceramic precursors has been initiated. The compounds MX _2 (dmpe)_2, dmpe = 1,2-bis(dimethylphosphino)ethane, for M = Ti, V, Cr, and X = Br, I, BH_4, have been prepared. These complexes are paramagnetic and have been shown by X-ray crystallography to have trans-octahedral structures. The BH_4^{-} groups in Ti(BH_4)_2(dmpe) _2 bond to the metal in a bidentate manner. This structure is in marked contrast to the structure of the vanadium analogue, V(BH_4)_2 (dmpe)_2, which displays two unidentate BH_4^{-} groups. Alkylation of Ti(BH_4)_2 (dmpe)_2 with LiMe results in the complex TiMe_2(dmpe) _2 which is diamagnetic in both solution and solid state. Single crystal X-ray and neutron diffraction studies show that there may be strong Ti-C pi -bonding. A tetragonal compression along the C -Ti-C bond vector accounts for the observed diamegnetism. A series of complexes of the formula Ti(BH _4)_3(PR_3)_2 has been prepared where PR_3 = PMe_3, PEt_3, PMe_3Ph, and P(OMe)_3 . The X-ray crystal structure of Ti(BH _4)_3(PMe_3)_2 reveals a pseudo trigonal bipyramidal geometry in which two BH_4^{-} groups display an unusual "side-on" bonding mode. The "side-on" ligation mode has been attributed to a Jahn-Teller distortion of the orbitally degenerate d^1 ground state. In contrast, the non-Jahn-Teller susceptible vanadium analogue, V(BH_4)_3 (PMe_3)_2, possesses a nearly ideal D_{rm 3h} >=ometry with three bidentate tetrahydroborate groups. Addition of excess PMe_3 to V(BH_4)_3(PMe _3)_2water forms the vanadium(III) oxo dimer (V(BH_4)_2 (PMe_3)_2]_2 [mu-O) which has been structurally characterized. The compound Ti(CH_2CMe _3)_4 can be prepared by addition of Ti(OEt)_4 to LiCH_2 CMe_3. Sublimation of Ti(CH _2CMe_3)_4 over a substrate heated to 250^ circC results in the chemical vapor deposition of amorphous TiC thin films. This CVD approach has been extended to the Group 4 borides: Ti

  7. Transition metal mediated transformations of small molecules

    Energy Technology Data Exchange (ETDEWEB)

    Sen, Ayusman [Pennsylvania State Univ., University Park, PA (United States)

    2017-03-08

    Catalysis at metal centers is of great scientific, as well as practical, importance because of the high efficiency, high specificity, and low energy demands often associated with such systems. The two major themes of our research are (a) the design of metal-based systems for the synthesis of novel classes of polymers and (b) the identification of new metal-catalyzed systems for the conversion of biomass to fuels and chemicals, and related “green” chemical processes.

  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. [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

  10. 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

  11. 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

  12. Special about transition metals in alloy phase formation

    Energy Technology Data Exchange (ETDEWEB)

    Watson, R E; Bennett, L H

    1979-01-01

    The d-electrons are special, though their bonding properties remain to be completely understood. It is recognized that d band broadening is the dominant term contributing to transition metal cohesion. It is also generally recognized that in compound formation between transition-metals and polyvalent metals, hybridization between d-bands and polyvalent atom p bands provides a significant contribution to the energy (for example there is such a term in Miedema's scheme). Less generally realized is that d-band hybridization leads to changes in d-electron counts at a transition metal site which are opposite in sign to the net charge transfer on or off the site. The renormalized atom picture of cohesion of the pure transition metals and consider the experimental evidence and the theoretical understanding of d charge transfer going the wrong way are reviewed. A picture of the electronegativity of transition metals based on this trend is developed. Charge transfer associated with equalizing the local chemical potentials in alloys is estimated. Friedel type model alloy calculations are reviewed. The implications of the experimental charge transfer information from Moessbauer isomer shifts to such model alloy calculations and to the strength of the Coulomb enery associated with charge transfer is considered.

  13. 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

  14. Flexible metallic seal for transition duct in turbine system

    Science.gov (United States)

    Flanagan, James Scott; LeBegue, Jeffrey Scott; McMahan, Kevin Weston; Dillard, Daniel Jackson; Pentecost, Ronnie Ray

    2014-04-22

    A turbine system is disclosed. In one embodiment, the turbine system includes a transition duct. The transition duct includes an inlet, an outlet, and a passage extending between the inlet and the outlet and defining a longitudinal axis, a radial axis, and a tangential axis. The outlet of the transition duct is offset from the inlet along the longitudinal axis and the tangential axis. The transition duct further includes an interface member for interfacing with a turbine section. The turbine system further includes a flexible metallic seal contacting the interface member to provide a seal between the interface member and the turbine section.

  15. [Transition metal mediated transformations of small molecules

    Energy Technology Data Exchange (ETDEWEB)

    Sen, A.

    1992-01-01

    Work on organotransition metal chemistry, homogeneous and heterogeneous catalysis is summarized. Several cationic palladium(II) complexes with bulky phosphine or pyridine ligands were discovered that are highly selective catalysts for linear dimerization of vinyl monomers and linear polymerization of p-divinylbenzene, the reactions proceeding through a carbocationic mechanism. Our studies were continued on alternating olefin-carbon monoxide copolymers. The copolymerization reaction and reactivity of copolymers were examined. New catalytic systems for alternating copolymerization of [alpha]-olefins with CO were discovered. In the case of styrene derivatives, tactic copolymers were obtained. Poly(ethylenepyrrolediyl) derivatives were synthesized from alternating ethylene-carbon monoxide copolymer and become electronic conductors when doped with iodine. A catalytic system for direct synthesis of polyureas and polyoxamides from and diamines was also discovered. Pt metal catalyzed the oxidation of ethers, esters, and amines to carboxylic acids and the oxidation of olefins to 1,2-diols. Anaerobic and aerobic decomposition of molybdenum(VI)-oxoalkyl compounds were studied for heterogeneous oxidation of alkanes and olefins on Mo(VI)-oxide surfaces. Synthesis of polymer-trapped metal, metal oxide, and metal sulfide nanoclusters (size <1--10 nm) was studied.

  16. Transition-metal-free chemo- and regioselective vinylation of azaallyls

    Science.gov (United States)

    Li, Minyan; Gutierrez, Osvaldo; Berritt, Simon; Pascual-Escudero, Ana; Yeşilçimen, Ahmet; Yang, Xiaodong; Adrio, Javier; Huang, Georgia; Nakamaru-Ogiso, Eiko; Kozlowski, Marisa C.; Walsh, Patrick J.

    2017-10-01

    Direct C(sp3)-C(sp2) bond formation under transition-metal-free conditions offers an atom-economical, inexpensive and environmentally benign alternative to traditional transition-metal-catalysed cross-coupling reactions. A new chemo- and regioselective coupling protocol between 3-aryl-substituted-1,1-diphenyl-2-azaallyl derivatives and vinyl bromides has been developed. This is the first transition-metal-free cross-coupling of azaallyls with vinyl bromide electrophiles and delivers allylic amines in excellent yields (up to 99%). This relatively simple and mild protocol offers a direct and practical strategy for the synthesis of high-value allylic amine building blocks that does not require the use of transition metals, special initiators or photoredox catalysts. Radical clock experiments, electron paramagnetic resonance studies and density functional theory calculations point to an unprecedented substrate-dependent coupling mechanism. Furthermore, an electron paramagnetic resonance signal was observed when the N-benzyl benzophenone ketimine was subjected to silylamide base, supporting the formation of radical species upon deprotonation. The unique mechanisms outlined herein could pave the way for new approaches to transition-metal-free C-C bond formations.

  17. 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 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.

  18. 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.

  19. Nanodisperse transition metal electrodes (NTME) for electrochemical cells

    Energy Technology Data Exchange (ETDEWEB)

    Striebel, Kathryn A.; Wen, Shi-Jie

    1998-12-01

    Disclosed are transition metal electrodes for electrochemical cells using gel-state and solid-state polymers. The electrodes are suitable for use in primary and secondary cells. The electrodes (either negative electrode or positive electrode) are characterized by uniform dispersion of the transition metal at the nanoscale in the polymer. The transition metal moiety is structurally amorphous, so no capacity fade should occur due to lattice expansion/contraction mechanisms. The small grain size, amorphous structure and homogeneous distribution provide improved charge/discharge cycling performance, and a higher initial discharge rate capability. The cells can be cycled at high current densities, limited only by the electrolyte conductivity. A method of making the electrodes (positive and negative), and their usage in electrochemical cells are disclosed.

  20. 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.

  1. Covalency, Excitons, Double Counting and the Metal-Insulator Transition in Transition Metal Oxides

    Science.gov (United States)

    Wang, Xin

    2012-02-01

    We present single-site dynamical mean-field studies of realistic models of transition metal oxides, including the cuprate superconductors and rare earth nickelates (in bulk and superlattice form). We include orbital multiplet effects and hybridization to ligands. We explicitly calculate the d-d exciton spectra for cuprates, finding sharp exciton lines in both metallic and insulating phases, which should be visible in experiments. We also find that the additional d3z^2-r^2 orbital does not contribute to an additional Fermi surface at any reasonable doping, in contradiction to previous slave-boson studies. The hybridization to ligands is shown to have crucial effects, for example suppressing the ferro-orbital order previously found in Hubbard model studies of nickelates. Hybridization to ligands is shown to be most naturally parametrized by the d-orbital occupancy. For cuprates and nickelates, insulating behavior is found to be present only for a very narrow range of d-occupancy, irrespective of the Coulomb repulsion. The d-occupancy predicted by standard band calculations is found to be very far from the values required to obtain an insulating phase, calling into question the interpretation of these materials as charge transfer insulators. [4pt] This work is done in collaboration with A.J. Millis, M.J. Han, C.A. Marianetti, L. de' Medici, and H.T. Dang, and is supported by NSF-DMR-1006282, the Army Office of Scientific Research, and the Condensed Matter Theory Center and CNAM at University of Maryland. [4pt] [1] X. Wang, H. T. Dang, and A. J. Millis, Phys. Rev. B 84, 014530 (2011).[0pt] [2] X. Wang, M. J. Han, L. de' Medici, C. A. Marianetti, and A. J. Millis, arXiv:1110.2782.[0pt] [3] M. J. Han, X. Wang, C. A. Marianetti, and A. J. Millis, Phys. Rev. Lett. 107, 206804 (2011).

  2. 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

  3. 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)

  4. 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...... of diatomic molecules over stepped transition- and noble-metal surfaces. The potential energy diagram directly points to why Pd and Pt are the best direct NO decomposition catalysts among the 3d, 4d, and 5d metals. We analyze the NO decomposition reaction in terms of a Sabatier-Gibbs-type analysis, and we...... demonstrate that this type of analysis yields results that to within a surprisingly small margin of error are directly proportional to the measured direct NO decomposition over Ru, Rh, Pt, Pd, Ag, and An. We suggest that Pd, which is a better catalyst than Pt under the employed reaction conditions...

  5. THE INFLUENCE OF TRANSITION METALS ON THE ...

    African Journals Online (AJOL)

    Experimental results show that the addition of Zr, Mn, Co, and Cu promoters improved the activity of Pt Rh Pd/γ-Al2O3 catalyst remarkably for CO, CH and NOx conversion, respectively. The effective order of the promoters is CuO > ZrO2 > Co3O4 > MnO2. The addition of CuO improved the dispersion of the noble metal on ...

  6. Bias-induced insulator-metal transition in organic electronics

    Science.gov (United States)

    Wei, J. H.; Xie, S. J.; Mei, L. M.; Yan, YiJing

    2007-07-01

    The authors investigate the bias-induced insulator-metal transition in organic electronics devices on the basis of the Su-Schrieffer-Heeger model [W. P. Su et al., Phys. Rev. B 22, 2099 (1980)] combined with the nonequilibrium Green's function formalism. The insulator-metal transition is explained with the energy level crossover that eliminates the Peierls phase [R. Peierls, Quantum Theory of Solids (Oxford University Press, Oxford, 1955)] and delocalizes the electron states near the threshold voltage. This may account for the experimental observations on the devices that exhibit intrinsic bistable conductance switching with large on-off ratio.

  7. 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.

  8. 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 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 (

  9. 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.

  10. Ternary scandium and transition metals germanides

    International Nuclear Information System (INIS)

    Kotur, B.Ya.

    1992-01-01

    Brief review of data on phase diagram of ternary Sc-Me-Ge systems (Me-d - , f-transition element) is given. Isothermal sections at 870 and 1070 K of 17 ternary systems are plotted. Compositions and their structural characteristics are presented. Variability of crystal structure is typical for ternary scandium germanides: 70 compounds with the studied structure belong to 23 structural types. Ternary germanides isostructural to types of Sm 4 Ge 4 , ZrCrSi 2 , ZrNiAl, ScCeSi, TiNiSi U 4 Re 7 Si 6 145 compounds from 70 under investigation are mostly formed in studied systems

  11. 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

  12. Metal-insulator transition in epitaxial vanadium sesquioxide thin films

    Science.gov (United States)

    Allimi, Bamidele S.

    Of all the transition metal oxides which exhibit metal-insulator transitions (MIT), one of the most extensively studied in recent years is the vanadium sesquioxide (V2O3), both from experimental and theoretical point of view. At a transition temperature of about 160 K at an ambient pressure of 1 atm, pure V2O3 transforms from a rhombohedral paramagnetic metallic (PM) to a monoclinic antiferromagnetic insulating (AFI) phase upon cooling, with a jump in the resistivity of about seven orders of magnitude. Experimental studies have focused more on bulk V2O3 and recently there have been significant interest in thin film fabrication of this material due to potential applications as thermal sensors, current limiters, Positive Temperature Coefficient (PTC) thermistors, and optical switches. This study addresses the deposition, characterization, and properties of high-quality epitaxial V2O3 thin films grown on a-, c-Al2O3 and c-LiTaO 3 substrates by a straightforward method of pulsed laser deposition (PLD). Various characterization techniques including X-ray diffraction, atomic force microscopy, scanning electron microscopy, and X-ray photoemission spectroscopy were used to examine the structural, crystallographic, and surface properties, while four point probe resistivity measurements were used to examine the electrical properties of the films. V2O3 thin films of different thicknesses ranging from 10-450 nm were deposited on c-Al 2O3 and c-LiTaO3 substrates by PLD to understand also the role of epitaxial strains. Resistivity measurements showed that depending on the thicknesses of films, different electrical transitions were exhibited by the samples. While some of the samples displayed the expected metal-insulator transition typical of bulk V2O3, some showed insulating behavior only and others exhibited metallic characteristics only over the whole temperature range. For example, for films on c-LiTaO3 with increasing film thickness, first an insulator-insulator, then a

  13. 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...

  14. How absorbed hydrogen affects the catalytic activity of transition metals.

    Science.gov (United States)

    Aleksandrov, Hristiyan A; Kozlov, Sergey M; Schauermann, Swetlana; Vayssilov, Georgi N; Neyman, Konstantin M

    2014-12-01

    Heterogeneous catalysis is commonly governed by surface active sites. Yet, areas just below the surface can also influence catalytic activity, for instance, when fragmentation products of catalytic feeds penetrate into catalysts. In particular, H absorbed below the surface is required for certain hydrogenation reactions on metals. Herein, we show that a sufficient concentration of subsurface hydrogen, H(sub) , may either significantly increase or decrease the bond energy and the reactivity of the adsorbed hydrogen, H(ad) , depending on the metal. We predict a representative reaction, ethyl hydrogenation, to speed up on Pd and Pt, but to slow down on Ni and Rh in the presence of H(sub) , especially on metal nanoparticles. The identified effects of subsurface H on surface reactivity are indispensable for an atomistic understanding of hydrogenation processes on transition metals and interactions of hydrogen with metals in general. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. The metal-rich sulfides and phosphides of the early transition metals

    Energy Technology Data Exchange (ETDEWEB)

    Franzen, H.F. [Ames Lab., IA (United States)]|[Iowa State Univ., Ames, IA (United States). Dept. of Chemistry

    1996-06-01

    Early work on the preparation of refractory metal-rich compounds of the early transition metals resulted in the understanding that metal-metal bonding results in a structural variety that plays an important role in the high-temperature chemistry of these systems. The binary metal-rich systems have been thoroughly studied at high temperatures, and the structures of most, if not all, of the refractory sulfides and phosphides are known. More recently new ternary phases have been discovered, and these have been shown to result from distributed fractional site occupation of metal atom sites in complex structures. The extent of metal-metal bonding has been quantified by Extended-Hueckel Tight-Bonding calculations using Mullikan Overlap Populations. Correlations of site occupancy with MOP based upon the DFSO model have been observed. 44 refs.

  16. Electrocatalysis of Hydrogen Evolution by Transition Metal Complexes

    Czech Academy of Sciences Publication Activity Database

    Heyrovský, Michael

    2001-01-01

    Roč. 66, č. 1 (2001), s. 67-80 ISSN 0010-0765 R&D Projects: GA ČR GV204/97/K084 Institutional research plan: CEZ:AV0Z4040901 Keywords : transition metals * thiocyanate complexes * electroreduction Subject RIV: CG - Electrochemistry Impact factor: 0.778, year: 2001

  17. Synthesis, spectral characterization of Schiff base transition metal ...

    Indian Academy of Sciences (India)

    TECS

    Synthesis, spectral characterization of Schiff base transition metal complexes: DNA cleavage and antimicrobial activity studies. N RAMAN,* J DHAVEETHU RAJA and A SAKTHIVEL. Department of Chemistry, VHNSN College, Virudhunagar 626 001 e-mail: drn_ raman@yahoo.co.in. MS received 1 May 2007; revised 7 July ...

  18. Transition metal chemistry of hydroxy(–OH)-rich molecules ...

    Indian Academy of Sciences (India)

    Administrator

    Transition metal chemistry of hydroxy(–OH)-rich molecules: Syntheses, crystal structures and solution reactivity studies. MISHTU DEY 1, P K SAARENKETO 2, E KOLEHMAINEN 2,. K RISSANEN 2 and CHEBROLU P RAO 1. 1Bioinorganic Laboratory, Department of Chemistry, Indian Institute of. Technology Bombay, Powai ...

  19. 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.

  20. 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

  1. Effect of transition metal elements on the structural and optical ...

    Indian Academy of Sciences (India)

    Effect of transition metal elements on the structural and optical properties of ZnO nanoparticles. I KAZEMINEZHAD1, S SAADATMAND1 and RAMIN YOUSEFI2,∗. 1Nanotechnology Laboratory, Physics Department, Shahid Chamran University of Ahvaz, Ahvaz, Iran. 2Department of Physics, Islamic Azad University (IAU), ...

  2. Transport properties of transition metal impurities on gold nanowires

    Science.gov (United States)

    Pontes, Renato B.; da Silva, Edison Z.; Fazzio, Adalberto; da Silva, Antônio J. R.

    2009-03-01

    Performing first principles density functional theory (DFT) we calculated the electronic and transport properties of a Au thin nanowire with transition metal atoms (Mn, Fe, Ni or Co) bridging the two sides of the Au nanowire. We will show that these systems have strong spin dependent transport properties and that the local symmetry can dramatically change them, leading to a significant spin polarized conductance. This spin dependent transport is also associated with the transition metal in the nanowire, in particular with the d-level positioning. Using Co, for example [1], when the symmetry permits the mixing between the wire s-orbitals with the transition metal d-states, there are interference effects that resemble Fano-like resonances with an anisotropy of 0.07 at the Fermi level. On the other hand, if this symmetry decouples such states, we simply have a sum of independent transmission channels and the calculated anisotropy was 0.23. The anisotropies for the other transition metals, as well as calculated transmittances for two Co impurities will also be presented [1] R. B. Pontes, E. Z. da Silva, A. Fazzio and Antônio J. R. da Silva, J. Am. Chem. Soc. 130 (30), 9897-903, 2008

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

    Indian Academy of Sciences (India)

    The embedded atom method (EAM) potentials, with the universal form of the embedding function along with the Morse form of pair potential, have been employed to determine the potential parameters for three bcc transition metals: Fe, Mo, and W, by fitting to Cauchy pressure (C12−C44)/2, shear constants ...

  4. 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...

  5. 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.

  6. Transition metal-free, base-promoted hydroalkoxylation: Synthesis ...

    Indian Academy of Sciences (India)

    Abstract. An efficient,transition metal-free method to synthesize substituted imidazo[2,1-c][1,4]oxazine derivatives via hydroalkoxylation of 1,5-alkynyl alcohol has been described. The reaction ... Muthusubramanian1. Department of Organic Chemistry, School of Chemistry, Madurai Kamaraj University, Madurai 625 021, India ...

  7. Phenalenyl-based ligand for transition metal chemistry: Application ...

    Indian Academy of Sciences (India)

    mandal@iiserkol.ac.in. Abstract. We report the synthesis and characterization of the first transition metal complex of a phenalenyl- based ligand. The reaction of Cu(OAc)2.H2O with 9-N-methylamino-1-N -methylimino-phenalene (LH) in 1:1.

  8. Luminescent molecular rods - transition-metal alkynyl complexes.

    Science.gov (United States)

    Yam, Vivian Wing-Wah; Wong, Keith Man-Chung

    2005-01-01

    A number of transition-metal complexes have been reported to exhibit rich luminescence, usually originating from phosphorescence. Such luminescence properties of the triplet excited state with a large Stoke's shift, long lifetime, high luminescence quantum yield as well as lower excitation energy, are envisaged to serve as an ideal candidate in the area of potential applications for chemosensors, dye-sensitized solar cells, flat panel displays, optics, new materials and biological sciences. Organic alkynes (poly-ynes), with extended or conjugatedπ-systems and rigid structure with linear geometry, have become a significant research area due to their novel electronic and physical properties and their potential applications in nanotechnology. Owing to the presence of unsaturated sp-hybridized carbon atoms, the alkynyl unit can serve as a versatile building block in the construction of alkynyl transition-metal complexes, not only throughσ-bonding but also viaπ-bonding interactions. By incorporation of linear alkynyl groups into luminescent transition-metal complexes, the alkynyl moiety with goodσ-donor,π-donor andπ-acceptor abilities is envisaged to tune or perturb the emission behaviors, including emission energy (color), intensity and lifetime by its role as an auxiliary ligand as well as to govern the emission origin from its direct involvement. This review summarizes recent efforts on the synthesis of luminescent rod-like alkynyl complexes with different classes of transition metals and details the effects of the introduction of alkynyl groups on the luminescence properties of the complexes.

  9. Tridentate Schiff base (ONO) transition metal complexes: Synthesis ...

    Indian Academy of Sciences (India)

    Home; Journals; Journal of Chemical Sciences; Volume 128; Issue 7. Tridentate Schiff base (ONO) transition metal complexes: Synthesis, crystal structure, spectroscopic and larvicidal studies. SUNDARAMURTHY SANTHA LAKSHMI KANNAPPAN GEETHA P MAHADEVI. Regular Article Volume 128 Issue 7 July 2016 pp ...

  10. Volume variation of Gruneisen parameters of fcc transition metals

    Indian Academy of Sciences (India)

    Unknown

    ultrasonic measurements and melting of solids (Mulargia and Boschi 1978 .... Several studies in the past based on model pseudo- potential suggest ... Volume variation of fcc transition metals. 65. The present value for Cu is in good agreement with the experimental values. Also, the presently obtained value agrees well with ...

  11. Spin, Charge, and Bonding in Transition Metal Mono Silicides

    NARCIS (Netherlands)

    Marel, D. van der; Damascelli, A.; Schulte, K.; Menovsky, A. A.

    1997-01-01

    Published in: Physica B 244 (1998) 138-147 citations recorded in [Science Citation Index] Abstract: We review some of the relevant physical properties of the transition metal mono-silicides with the FeSi structure (CrSi, MnSi, FeSi, CoSi, NiSi, etc) and explore the relation between their structural

  12. Effect of transition metal dopants on the optical and magnetic ...

    Indian Academy of Sciences (India)

    2015-06-02

    Jun 2, 2015 ... This review discusses the recent developments in doped semiconductor nanocrystals with a special emphasis on the effect of dopant on the electronic structure of the host nanocrystals. The review focusses on 3 transition metal dopants with unique electronic structure making them receptive for dramatic ...

  13. 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.

  14. Covalent bonds against magnetism in transition metal compounds.

    Science.gov (United States)

    Streltsov, Sergey V; Khomskii, Daniel I

    2016-09-20

    Magnetism in transition metal compounds is usually considered starting from a description of isolated ions, as exact as possible, and treating their (exchange) interaction at a later stage. We show that this standard approach may break down in many cases, especially in 4d and 5d compounds. We argue that there is an important intersite effect-an orbital-selective formation of covalent metal-metal bonds that leads to an "exclusion" of corresponding electrons from the magnetic subsystem, and thus strongly affects magnetic properties of the system. This effect is especially prominent for noninteger electron number, when it results in suppression of the famous double exchange, the main mechanism of ferromagnetism in transition metal compounds. We study this mechanism analytically and numerically and show that it explains magnetic properties of not only several 4d-5d materials, including Nb2O2F3 and Ba5AlIr2O11, but can also be operative in 3d transition metal oxides, e.g., in CrO2 under pressure. We also discuss the role of spin-orbit coupling on the competition between covalency and magnetism. Our results demonstrate that strong intersite coupling may invalidate the standard single-site starting point for considering magnetism, and can lead to a qualitatively new behavior.

  15. 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.

  16. Disorder-Driven Metal-Insulator Transitions in Deformable Lattices.

    Science.gov (United States)

    Di Sante, Domenico; Fratini, Simone; Dobrosavljević, Vladimir; Ciuchi, Sergio

    2017-01-20

    We show that, in the presence of a deformable lattice potential, the nature of the disorder-driven metal-insulator transition is fundamentally changed with respect to the noninteracting (Anderson) scenario. For strong disorder, even a modest electron-phonon interaction is found to dramatically renormalize the random potential, opening a mobility gap at the Fermi energy. This process, which reflects disorder-enhanced polaron formation, is here given a microscopic basis by treating the lattice deformations and Anderson localization effects on the same footing. We identify an intermediate "bad insulator" transport regime which displays resistivity values exceeding the Mott-Ioffe-Regel limit and with a negative temperature coefficient, as often observed in strongly disordered metals. Our calculations reveal that this behavior originates from significant temperature-induced rearrangements of electronic states due to enhanced interaction effects close to the disorder-driven metal-insulator transition.

  17. Transition Metal d-Orbital Splitting Diagrams: An Updated Educational Resource for Square Planar Transition Metal Complexes

    Science.gov (United States)

    Bo¨rgel, Jonas; Campbell, Michael G.; Ritter, Tobias

    2016-01-01

    The presentation of d-orbital splitting diagrams for square planar transition metal complexes in textbooks and educational materials is often inconsistent and therefore confusing for students. Here we provide a concise summary of the key features of orbital splitting diagrams for square planar complexes, which we propose may be used as an updated…

  18. Alkali metal ion templated transition metal formate framework materials: synthesis, crystal structures, ion migration, and magnetism.

    Science.gov (United States)

    Eikeland, Espen; Lock, Nina; Filsø, Mette; Stingaciu, Marian; Shen, Yanbin; Overgaard, Jacob; Iversen, Bo Brummerstedt

    2014-10-06

    Four transition metal formate coordination polymers with anionic frameworks, namely, Na[Mn(HCOO)3], K[Mn(HCOO)3], Na2[Cu3(HCOO)8], and K2[Cu5(HCOO)12], were synthesized using a mild solution chemistry approach. Multitemperature single-crystal (100-300 K) and powder X-ray diffraction studies of the compounds reveal structures of large diversity ranging from cubic chiral Na-Mn formate to triclinic Na-Cu formate. The structural variety is caused by the nature of the transition metals, the alkali metal ion templation, and the versatility of the formate group, which offers metal-metal coordination through three different O-C-O bridging modes (syn-syn, syn-anti, anti-anti) in addition to metal-metal bridging via a single oxygen atom. The two manganese(II) compounds contain mononuclear, octahedrally coordinated moieties, but the three-dimensional connectivity between the manganese octahedra is very different in the two structures. The two copper frameworks, in contrast, consist of binuclear and mononuclear moieties (Na-Cu formate) and trinuclear and mononuclear moieties (K-Cu formate), respectively. Procrystal electron density analysis of the compounds indicates one-dimensional K(+)-ion conductivity in K-Mn and K-Cu, and the nature of the proposed potassium ion migration is compared with results from similar analysis on known Na(+) and K(+) ion conductors. K-Mn and Na-Mn were tested as cathode materials, but this resulted in poor reversibility due to low conductivity or structural collapse. The magnetic properties of the compounds were studied by vibrating sample magnetometric measurements, and their thermal stabilities were determined by thermogravimetric analysis and differential thermal analysis. Despite structural differences, the metal formates that contain the same transition metal have similar magnetic properties and thermal decomposition pathways, that is, the nature of the transition metal controls the compound properties.

  19. 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

  20. Cross-linking proteins with bimetallic tetracarboxylate compounds of transition metals

    Science.gov (United States)

    Kostic, N.M.; Chen, J.

    1991-03-05

    Stable cross-linked complexes of transition-metal tetracarboxylates and proteins are formed. The preferred transition-metal is rhodium. The protein may be collagen or an enzyme such as a proteolytic enzyme. No Drawings

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  2. 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

  3. Marrying Excitons and Plasmons in Monolayer Transition-Metal Dichalcogenides

    Science.gov (United States)

    Van Tuan, Dinh; Scharf, Benedikt; Žutić, Igor; Dery, Hanan

    2017-10-01

    Just as photons are the quanta of light, plasmons are the quanta of orchestrated charge-density oscillations in conducting media. Plasmon phenomena in normal metals, superconductors, and doped semiconductors are often driven by long-wavelength Coulomb interactions. However, in crystals whose Fermi surface is comprised of disconnected pockets in the Brillouin zone, collective electron excitations can also attain a shortwave component when electrons transition between these pockets. In this work, we show that the band structure of monolayer transition-metal dichalcogenides gives rise to an intriguing mechanism through which shortwave plasmons are paired up with excitons. The coupling elucidates the origin for the optical sideband that is observed repeatedly in monolayers of WSe2 and WS2 but not understood. The theory makes it clear why exciton-plasmon coupling has the right conditions to manifest itself distinctly only in the optical spectra of electron-doped tungsten-based monolayers.

  4. 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.

  5. 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

  6. Examination of Solubility Models for the Determination of Transition Metals within Liquid Alkali Metals

    Directory of Open Access Journals (Sweden)

    Jeremy Isler

    2016-06-01

    Full Text Available The experimental solubility of transition metals in liquid alkali metal was compared to the modeled solubility calculated using various equations for solubility. These equations were modeled using the enthalpy calculations of the semi-empirical Miedema model and various entropy calculations. The accuracy of the predicted solubility compared to the experimental data is more dependent on which liquid alkali metal is being examined rather than the transition metal solute examined. For liquid lithium the calculated solubility by the model was generally larger than experimental values, while for liquid cesium the modeling solubility was significantly smaller than the experimental values. For liquid sodium, potassium, and rubidium the experimental solubilities were within the range calculated by this study. Few data approached the predicted temperature dependence of solubility and instead most data exhibited a less pronounced temperature dependence.

  7. Transition Metal Oxides: Many Body Physics Meets Solid State ...

    Indian Academy of Sciences (India)

    New two-fluid (localized + band electron) model for manganites · Slide 19 · Picturizing the ferro-insulator to ferro-metal transition and the 2-fluid model · Material Systematics (varying Do) ( For fixed EJT = 0.5 eV , U = 5 eV, JF ~ (Do)2 ) · Real space structure in the presence of long range Coulomb interactions · Slide 23.

  8. 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 ...

  9. Liquid state properties of certain noble and transition metals

    International Nuclear Information System (INIS)

    Bhuiyan, G.M.; Rahman, A.; Khaleque, M.A.; Rashid, R.I.M.A.; Mujibur Rahman, S.M.

    1998-07-01

    Certain structural, thermodynamic and atomic transport properties of a number of liquid noble and transition metals are reported. The underlying theory combines together a simple form of the N-body potential and the thermodynamically self-consistent variational modified hypernetted chain (VMHNC) theory of liquid. The static structure factors calculated by using the VMHNC resemble the hard sphere (HS) values. Consequently the HS model is used to calculate the thermodynamic properties viz. specific heat, entropy, isothermal compressibility and atomic transport properties. (author)

  10. Thermomagnetic marking of rare-earth-transition-metal thin films

    Science.gov (United States)

    Bartholomeusz, Brian Josef

    1989-01-01

    Analytical derivation of temperature profiles in laser-irradiated thin-film structures is hindered by the nature of the heat source terms and by the geometrical complexity that often exists. This study utilizes a combined Laplace-transform-Fourier-integral method to obtain approximate solutions for a number of simple cases. The results are used to study the thermomagnetic marking process in rare-earth-transition-metal (RE-TM) thin films, and the predictions are compared with experimental observations.

  11. Methanol Oxidation on Model Elemental and Bimetallic Transition Metal Surfaces

    DEFF Research Database (Denmark)

    Tritsaris, G. A.; Rossmeisl, J.

    2012-01-01

    Direct methanol fuel cells are a key enabling technology for clean energy conversion. Using density functional theory calculations, we study the methanol oxidation reaction on model electrodes. We discuss trends in reactivity for a set of monometallic and bimetallic transition metal surfaces, flat...... sites on the surface and to screen for novel bimetallic surfaces of enhanced activity. We suggest platinum copper surfaces as promising anode catalysts for direct methanol fuel cells....

  12. 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

  13. Metal-insulator transition: the Mott criterion and coherence length

    CERN Document Server

    Pergament, A

    2003-01-01

    On the basis of the Mott criterion for metal-insulator transition (MIT), an expression for the correlation length, identical to that for the coherence length in the theory of superconductivity, is obtained. This correlation length characterizes the size of an electron-hole pair (in an excitonic insulator) or the effective Bohr radius (as, e.g., in doped semiconductors). The relation obtained is used for calculation of the coherence length in vanadium dioxide. The presence of two characteristic coherence lengths (xi sub 1 approx 20 A and xi sub 2 approx 2 A) is found. This is associated with the specific features of the transition mechanism in VO sub 2 : this mechanism represents a combination of the purely electronic Mott-Hubbard contribution and the structural (Peierls-like) one. It is shown, however, that the driving force of the MIT in VO sub 2 is the electron-correlation Mott-Hubbard transition.

  14. 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.

  15. 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

  16. 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

  17. 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 (

  18. 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

  19. 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.

  20. Exposing "Bright" Metals: Promising Advances in Photoactivated Anticancer Transition Metal Complexes.

    Science.gov (United States)

    Bjelosevic, Aleksandra; Pages, Benjamin J; Spare, Lawson K; Deo, Krishant M; Ang, Dale L; Aldrich-Wright, Janice R

    2018-02-12

    Photodynamic therapy (PDT) is an increasingly prominent field in anticancer research. PDT agents are typically nontoxic in the absence of light and can be stimulated with nonionising irradiation to "activate" their cytotoxic effect. Photosensitzers are not classified as chemotherapy drugs although it is advantageous to control the toxicity of a drug through localised irradiation allowing for selective treatment. Transition metals are an extremely versatile class of compounds with various unique properties such as oxidation state, coordination number, redox potential and molecular geometry that can be tailored for specific uses. This makes them excellent PDT candidates as their properties can be manipulated to absorb a specific range of light wavelengths, cross cellular membranes or target specific sites in vitro. This article reviews recent advances in transition metal PDT agents, with a focus on structural scaffolds from which several metal complexes in a series are synthesised, as well as their in vitro cytotoxicity in the presence or absence of irradiation. The success of clinical photoactive agents such as Photofrin® has inspired the development of thousands of potential PDT agents. Transition metal complexes in particular have demonstrated excellent versatility and diversity when it comes to PDT for treatment of invasive cancers. This review has highlighted some of the many recent advances of transition metal PDT agents with high in vitro and in vivo phototoxic activity. Photoactive transition metal complexes have proven their potential due to their inherent physicochemical variety, allowing them to fill a niche in the PDT world. Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.

  1. 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)

  2. The nature of transition-metal-oxide surfaces

    Science.gov (United States)

    Henrich, V. E.

    The surfaces of the 3d-transition-metal oxides form a rich and important system in which to study the effects of atomic geometry, ligand coordination and d-orbital population on surface electronic structure and chemisorption. This article considers the properties of those surfaces in terms of the types of surface structures that can exist, including steps and point defects, and their relation to the experimental data that is available for well characterized, single-crystal surfaces. The electronic structure of nearly perfect surfaces is very similar to that of the bulk for many of the oxides that have been studied; atoms at step sites also appear to have properties similar to those of atoms on terraces. Point defects are often associated with surfaces 0 vacancies and attendant transfer of electrons to adjacent metal cations. Those cations are poorly screened from each other, and the excess charge is presumably shared between two or more cations having reduced ligand coordination. Point defects are generally more active for chemisorption than are perfect surfaces, however for Ti 2O 3 and V 2O 3, whose cations have 3d 1 and 3d 2 electronic configurations respectively, the cleaved (047) surface is more active than are surfaces having a high density of defects. The chemisorption behavior of both nearly perfect and defect surfaces of 3d-transition-metal oxides varies widely from one material to another, and it is suggestive to correlate this with cation d-orbital population. However, too few oxides have yet been studied to draw any firm conclusions. Additional theoretical work on perfect surfaces, defects and chemisorption is also necessary in order to gain a more complete understanding of transition-metal-oxide surfaces.

  3. 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.

  4. Transition metal complexes of an isatinic quinolyl hydrazone

    Directory of Open Access Journals (Sweden)

    Seleem Hussein S

    2011-06-01

    Full Text Available Abstract Background The importance of the isatinic quinolyl hydrazones arises from incorporating the quinoline ring with the indole ring in the same compound. Quinoline ring has therapeutic and biological activities. On the other hand, isatin (1H-indole-2,3-dione and its derivatives exhibit a wide range of biological activities. Also, the indole ring occurs in Jasmine flowers and Orange blossoms. Recently, the physiological and biological activities of quinolyl hydrazones arise from their tendency to form metal chelates with transition metal ions. In this context, we have reported to isolate, characterize and study the biological activity of some transition metal complexes of an isatinic quinolyl hydrazone; 3-[2-(4-methyl quinolin-2-ylhydrazono] indolin-2-one. Results Mono- and binuclear as well as dimeric chelates were obtained from the reaction of a new isatinic quinolyl hydrazone with Fe(III, Co(II, Ni(II, Cu(II, VO(II and Pd(II ions. The ligand showed a variety of modes of bonding viz. (NNO2-, (NO- and (NO per each metal ion supporting its ambidentate and flexidentate characters. The mode of bonding and basicity of the ligand depend mainly on the type of the metal cation and its counter anion. All the obtained Pd(II- complexes have the preferable square planar geometry (D4h- symmetry and depend mainly on the mole ratio (M:L. Conclusion The effect of the type of the metal ion for the same anion (Cl- is obvious from either structural diversity of the isolated complexes (Oh, Td and D4h or the various modes of bonding. The isatinic hydrazone uses its lactim form in all complexes (Cl- except complex 5 (SO42- in which it uses its lactam form. The obtained Pd(II- complexes (dimeric, mono- and binuclear are affected by the mole ratio (M:L and have the square planar (D4h geometry. Also, the antimicrobial activity is highly influenced by the nature of the metal ion and the order for S. aureus bacteria is as follows: Nickel(II > Vanadyl(II > Cobalt

  5. Roles of transition metals interchanging with lithium in electrode materials.

    Science.gov (United States)

    Kawaguchi, Tomoya; Fukuda, Katsutoshi; Tokuda, Kazuya; Sakaida, Masashi; Ichitsubo, Tetsu; Oishi, Masatsugu; Mizuki, Jun'ichiro; Matsubara, Eiichiro

    2015-06-07

    Roles of antisite transition metals interchanging with Li atoms in electrode materials of Li transition-metal complex oxides were clarified using a newly developed direct labeling method, termed powder diffraction anomalous fine structure (P-DAFS) near the Ni K-edge. We site-selectively investigated the valence states and local structures of Ni in Li0.89Ni1.11O2, where Ni atoms occupy mainly the NiO2 host-layer sites and partially the interlayer Li sites in-between the host layers, during electrochemical Li insertion/extraction in a lithium-ion battery (LIB). The site-selective X-ray near edge structure evaluated via the P-DAFS method revealed that the interlayer Ni atoms exhibited much lower electrochemical activity as compared to those at the host-layer site. Furthermore, the present analyses of site-selective extended X-ray absorption fine structure performed using the P-DAFS method indicates local structural changes around the residual Ni atoms at the interlayer space during the initial charge; it tends to gather to form rock-salt NiO-like domains around the interlayer Ni. The presence of the NiO-like domains in the interlayer space locally diminishes the interlayer distance and would yield strain energy because of the lattice mismatch, which retards the subsequent Li insertion both thermodynamically and kinetically. Such restrictions on the Li insertion inevitably make the NiO-like domains electrochemically inactive, resulting in an appreciable irreversible capacity after the initial charge but an achievement of robust linkage of neighboring NiO2 layers that tend to be dissociated without the Li occupation. The P-DAFS characterization of antisite transition metals interchanging with Li atoms complements the understanding of the detailed charge-compensation and degradation mechanisms in the electrode materials.

  6. Kondo Lattices and the Mott Metal-Insulator Transition

    Science.gov (United States)

    Nozières, Ph.

    2005-01-01

    In Kondo lattices with one magnetic impurity at every lattice site, few electrons must quench many spins. This old “exhaustion” issue has been pending for years: it now appears it does not arise: the coherence temperature at which a singlet ground state emerges is the Kondo temperature itself. We survey the evolution of that problem. We then argue that such a lattice Kondo effect governs the Mott transition from a paramagnetic metal to an incoherent spin disordered insulator. It explains the appearance of a narrow resonance in the middle of a large preformed gap. Our naive arguments can be extended to an orbitally degenerate situation: they provide a qualitative understanding of the effect discovered numerically by Capone et al. [Science 296 (2002) 2364], namely the appearance of s-wave superconductivity near the Mott transition when the atomic ground state is a singlet with no residual degeneracy.

  7. 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).

  8. Efficient photocarrier injection in a transition metal oxide heterostructure

    CERN Document Server

    Muraoka, Y; Ueda, Y; Hiroi, Z

    2002-01-01

    An efficient method for doping a transition metal oxide (TMO) with hole carriers is presented: photocarrier injection (PCI) in an oxide heterostructure. It is shown that an insulating vanadium dioxide (VO sub 2) film is rendered metallic under light irradiation by PCI from an n-type titanium dioxide (TiO sub 2) substrate doped with Nb. Consequently, a large photoconductivity, which is exceptional for TMOs, is found in the VO sub 2 /TiO sub 2 :Nb heterostructure. We propose an electronic band structure where photoinduced holes created in TiO sub 2 :Nb can be transferred into the filled V 3d band via the low-lying O 2p band of VO sub 2. (letter to the editor)

  9. Dinuclear transition metal complexes in carbon nanostructured materials synthesis

    Science.gov (United States)

    Ayuso, J. I.; Hernández, E.; Delgado, E.

    2013-06-01

    Carbon nanomaterials (CNMs) were prepared with two similar techniques using organometallic complexes as catalysts precursors. Chemical vapour deposition (CVD) and pyrolysis with chlorine gas approaches were employed in order to explore the effect of dinuclear transition metal compounds [Fe2(CO)6(μ-S2C6H2X2), (X=OH, Cl)] in synthesis of CNMs. Our to-date results have shown these complexes generate different carbonaceous materials when they are used in bulk, it was also observed that their performances in synthesis differ even though these compounds are analogous. With X=OH complex used in CVD process, metal nanoparticles of ca. 20-50 nm in size and embedded in carbon matrix were obtained. X=C1 complex has been used in pyrolysis experiments and showed an entire volatilisation or no reaction, depending on selected temperature. Furthermore, obtaining of a new tetranuclear iron cluster is presented in this work.

  10. Synthesis of heterocycles through transition-metal-catalyzed isomerization reactions

    DEFF Research Database (Denmark)

    Ishøy, Mette; Nielsen, Thomas Eiland

    2014-01-01

    of structurally complex and diverse heterocycles. In this Concept article, we attempt to cover this area of research through a selection of recent versatile examples. A sea of opportunities! Transition-metal-catalyzed isomerization of N- and O-allylic compounds provides a mild, selective and synthetically...... versatile method to form iminium and oxocarbenium ions. Given the number of reactions involving these highly electrophilic intermediates, this concept provides a sea of opportunities for heterocycle synthesis, (see scheme; Nu=nucleophile). © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim....

  11. LCAO-Xα calculations of transition metal clusters

    International Nuclear Information System (INIS)

    Seifert, G.; Eschrig, H.

    1985-01-01

    The electronic structure of some transition metal clusters (V 6 , Cr 6 , Cu 6 , Ag 6 ) is studied by an approximate LCAO-Xα scheme. Energy level spectra are discussed with respect to other theoretical investigations. The density-of-states curves are represented and compared with those from band-structure calculations. The correlation between binding energies of clusters and the corresponding cohesive energies of the bulk material is shown. Furthermore, the binding energies in copper clusters versus cluster size are discussed. Finally, some experimental results according beams of copper clusters and ESR studies of matrix isolated copper clusters are explained briefly. (author)

  12. Ferromagnetic semiconductor-metal transition in europium monoxide

    International Nuclear Information System (INIS)

    Arnold, M.

    2007-10-01

    We present a microscopical model to describe the simultaneous para-to-ferromagnetic and semiconductor-to-metal transition in electron-doped EuO. The physical properties of the model are systematically studied, whereas the main remark is on the interplay between magnetic order and the transport properties. The theory correctly describes detailed experimental features of the conductivity and of the magnetization, obtained for EuO 1-x or Gd-doped Gd x Eu 1-x 0. In particular the doping dependence of the Curie temperature is reproduced The existence of correlation-induced local moments on the impurity sites is essential for this description. (orig.)

  13. Band engineering in transition metal dichalcogenides: Stacked versus lateral heterostructures

    International Nuclear Information System (INIS)

    Guo, Yuzheng; Robertson, John

    2016-01-01

    We calculate a large difference in the band alignments for transition metal dichalcogenide (TMD) heterojunctions when arranged in the stacked layer or lateral (in-plane) geometries, using direct supercell calculations. The stacked case follows the unpinned limit of the electron affinity rule, whereas the lateral geometry follows the strongly pinned limit of alignment of charge neutrality levels. TMDs therefore provide one of the few clear tests of band alignment models, whereas three-dimensional semiconductors give less stringent tests because of accidental chemical trends in their properties.

  14. Magnetism in 3d transition metal doped SnO

    KAUST Repository

    Albar, Arwa

    2016-09-12

    Using first principles calculations, we investigate the structural and electronic properties of 3d transition metal doped SnO. We examine the stability of different doping sites using formation energy calculations. The magnetic behavior of the dopant atoms is found to be complex because of interplay between strong structural relaxation, spin-lattice coupling, and crystal field splitting. The interaction between dopant atoms is analyzed as a function of their separation, showing that clustering typically counteracts spin polarization. An exception is found for V doping, which thus turns out to be a promising candidate for realizing a magnetic p-type oxide.

  15. Transition Metal Intercalators as Anticancer Agents—Recent Advances

    Directory of Open Access Journals (Sweden)

    Krishant M. Deo

    2016-10-01

    Full Text Available The diverse anticancer utility of cisplatin has stimulated significant interest in the development of additional platinum-based therapies, resulting in several analogues receiving clinical approval worldwide. However, due to structural and mechanistic similarities, the effectiveness of platinum-based therapies is countered by severe side-effects, narrow spectrum of activity and the development of resistance. Nonetheless, metal complexes offer unique characteristics and exceptional versatility, with the ability to alter their pharmacology through facile modifications of geometry and coordination number. This has prompted the search for metal-based complexes with distinctly different structural motifs and non-covalent modes of binding with a primary aim of circumventing current clinical limitations. This review discusses recent advances in platinum and other transition metal-based complexes with mechanisms of action involving intercalation. This mode of DNA binding is distinct from cisplatin and its derivatives. The metals focused on in this review include Pt, Ru and Cu along with examples of Au, Ni, Zn and Fe complexes; these complexes are capable of DNA intercalation and are highly biologically active.

  16. Transition Metal Intercalators as Anticancer Agents—Recent Advances

    Science.gov (United States)

    Deo, Krishant M.; Pages, Benjamin J.; Ang, Dale L.; Gordon, Christopher P.; Aldrich-Wright, Janice R.

    2016-01-01

    The diverse anticancer utility of cisplatin has stimulated significant interest in the development of additional platinum-based therapies, resulting in several analogues receiving clinical approval worldwide. However, due to structural and mechanistic similarities, the effectiveness of platinum-based therapies is countered by severe side-effects, narrow spectrum of activity and the development of resistance. Nonetheless, metal complexes offer unique characteristics and exceptional versatility, with the ability to alter their pharmacology through facile modifications of geometry and coordination number. This has prompted the search for metal-based complexes with distinctly different structural motifs and non-covalent modes of binding with a primary aim of circumventing current clinical limitations. This review discusses recent advances in platinum and other transition metal-based complexes with mechanisms of action involving intercalation. This mode of DNA binding is distinct from cisplatin and its derivatives. The metals focused on in this review include Pt, Ru and Cu along with examples of Au, Ni, Zn and Fe complexes; these complexes are capable of DNA intercalation and are highly biologically active. PMID:27809241

  17. Redefining the metal/charge-transfer insulator paradigm in transition metal oxides

    Science.gov (United States)

    Dang, Hung; Ai, Xinyuan; Marianetti, Chris; Millis, Andrew

    2012-02-01

    The universality of the phase diagram in the variables of interaction strength and d-occupancy, shown for late transition metal oxides in Ref.[1], is examined for two series of early transition metal oxides: (SrVO3, SrCrO3, SrMnO3) and (LaTiO3, LaVO3, LaCrO3) using density functional theory (DFT), DFT+U and DFT+dynamical mean field theory methods. The interaction required to drive the metal-insulator transition is found to depend sensitively on the d-occupancy Nd, and beyond a threshold value of the d-occupancy an insulating state cannot be achieved for any practical value of the interaction. The critical Nd values are determined and compared to ab initio and experimental estimates where available. Additionally, the minimal model for the transition is determined and the crucial role played by the Hunds coupling is demonstrated. [4pt] [1] Xin Wang, M. J. Han, Luca de' Medici, C. A. Marianetti, and Andrew J. Millis (2011). arXiv:1110.2782

  18. 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

  19. Hydrogen collisions with transition metal surfaces: Universal electronically nonadiabatic adsorption

    Science.gov (United States)

    Dorenkamp, Yvonne; Jiang, Hongyan; Köckert, Hansjochen; Hertl, Nils; Kammler, Marvin; Janke, Svenja M.; Kandratsenka, Alexander; Wodtke, Alec M.; Bünermann, Oliver

    2018-01-01

    Inelastic scattering of H and D atoms from the (111) surfaces of six fcc transition metals (Au, Pt, Ag, Pd, Cu, and Ni) was investigated, and in each case, excitation of electron-hole pairs dominates the inelasticity. The results are very similar for all six metals. Differences in the average kinetic energy losses between metals can mainly be attributed to different efficiencies in the coupling to phonons due to the different masses of the metal atoms. The experimental observations can be reproduced by molecular dynamics simulations based on full-dimensional potential energy surfaces and including electronic excitations by using electronic friction in the local density friction approximation. The determining factors for the energy loss are the electron density at the surface, which is similar for all six metals, and the mass ratio between the impinging atoms and the surface atoms. Details of the electronic structure of the metal do not play a significant role. The experimentally validated simulations are used to explore sticking over a wide range of incidence conditions. We find that the sticking probability increases for H and D collisions near normal incidence—consistent with a previously reported penetration-resurfacing mechanism. The sticking probability for H or D on any of these metals may be represented as a simple function of the incidence energy, Ein, metal atom mass, M, and incidence angle, 𝜗i n. S =(S0+a ṡEi n+b ṡM ) *(1 -h (𝜗i n-c ) (1 -cos(𝜗 i n-c ) d ṡh (Ei n-e ) (Ei n-e ) ) ) , where h is the Heaviside step function and for H, S0 = 1.081, a = -0.125 eV-1, b =-8.40 ṡ1 0-4 u-1, c = 28.88°, d = 1.166 eV-1, and e = 0.442 eV; whereas for D, S0 = 1.120, a = -0.124 eV-1, b =-1.20 ṡ1 0-3 u-1, c = 28.62°, d = 1.196 eV-1, and e = 0.474 eV.

  20. 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

  1. Heterocycles by Transition Metals Catalyzed Intramolecular Cyclization of Acetylene Compounds

    International Nuclear Information System (INIS)

    Vizer, S.A.; Yerzhanov, K.B.; Dedeshko, E.C.

    2003-01-01

    Review shows the new strategies in the synthesis of heterocycles, having nitrogen, oxygen and sulfur atoms, via transition metals catalyzed intramolecular cyclization of acetylenic compounds on the data published at the last 30 years, Unsaturated heterocyclic compounds (pyrroles and pyrroline, furans, dihydro furans and benzofurans, indoles and iso-indoles, isoquinolines and isoquinolinones, aurones, iso coumarins and oxazolinone, lactams and lactones with various substitutes in heterocycles) are formed by transition metals, those salts [PdCl 2 , Pd(OAc) 2 , HgCl 2 , Hg(OAc) 2 , Hg(OCOCF 3 ) 2 , AuCl 3 ·2H 2 O, NaAuCl 4 ·2H 2 O, CuI, CuCl], oxides (HgO) and complexes [Pd(OAc) 2 (PPh 3 )2, Pd(PPh 3 ) 4 , PdCl 2 (MeCN) 2 , Pd(OAc ) 2 /TPPTS] catalyzed intramolecular cyclization of acetylenic amines, amides, ethers, alcohols, acids, ketones and βdiketones. More complex hetero polycyclic systems typical for natural alkaloids can to obtain similar. Proposed mechanisms of pyrroles, isoquinolines, iso indoles and indoles, benzofurans and iso coumarins, thiazolopyrimidinones formation are considered. (author)

  2. 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.

  3. 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

  4. Novel doping alternatives for single-layer transition metal dichalcogenides

    Science.gov (United States)

    Onofrio, Nicolas; Guzman, David; Strachan, Alejandro

    2017-11-01

    Successful doping of single-layer transition metal dichalcogenides (TMDs) remains a formidable barrier to their incorporation into a range of technologies. We use density functional theory to study doping of molybdenum and tungsten dichalcogenides with a large fraction of the periodic table. An automated analysis of the energetics, atomic and electronic structure of thousands of calculations results in insightful trends across the periodic table and points out promising dopants to be pursued experimentally. Beyond previously studied cases, our predictions suggest promising substitutional dopants that result in p-type transport and reveal interesting physics behind the substitution of the metal site. Doping with early transition metals (TMs) leads to tensile strain and a significant reduction in the bandgap. The bandgap increases and strain is reduced as the d-states are filled into the mid TMs; these trends reverse as we move into the late TMs. Additionally, the Fermi energy increases monotonously as the d-shell is filled from the early to mid TMs and we observe few to no gap states, indicating the possibility of both p- (early TMs) and n- (mid TMs) type doping. Quite surprisingly, the simulations indicate the possibility of interstitial doping of TMDs; the energetics reveal that a significant number of dopants, increasing in number from molybdenum disulfide to diselenide and to ditelluride, favor the interstitial sites over adsorbed ones. Furthermore, calculations of the activation energy associated with capturing the dopants into the interstitial site indicate that the process is kinetically possible. This suggests that interstitial impurities in TMDs are more common than thought to date and we propose a series of potential interstitial dopants for TMDs relevant for application in nanoelectronics based on a detailed analysis of the predicted electronic structures.

  5. Controls on Transition Metal Concentrations in Crustal Brines

    Science.gov (United States)

    Yardley, B. W.

    2004-12-01

    as the major controls on transition metal contents of crustal fluids, with little evidence for significant changes in chloride complexing over the range of compositions and conditions encountered in the crust. Preliminary results on low salinity, gas-rich fluid inclusions suggest that their transition metal contents fit on the same trends as those of brines.

  6. Selective and low temperature transition metal intercalation in layered tellurides

    Science.gov (United States)

    Yajima, Takeshi; Koshiko, Masaki; Zhang, Yaoqing; Oguchi, Tamio; Yu, Wen; Kato, Daichi; Kobayashi, Yoji; Orikasa, Yuki; Yamamoto, Takafumi; Uchimoto, Yoshiharu; Green, Mark A.; Kageyama, Hiroshi

    2016-12-01

    Layered materials embrace rich intercalation reactions to accommodate high concentrations of foreign species within their structures, and find many applications spanning from energy storage, ion exchange to secondary batteries. Light alkali metals are generally most easily intercalated due to their light mass, high charge/volume ratio and in many cases strong reducing properties. An evolving area of materials chemistry, however, is to capture metals selectively, which is of technological and environmental significance but rather unexplored. Here we show that the layered telluride T2PTe2 (T=Ti, Zr) displays exclusive insertion of transition metals (for example, Cd, Zn) as opposed to alkali cations, with tetrahedral coordination preference to tellurium. Interestingly, the intercalation reactions proceed in solid state and at surprisingly low temperatures (for example, 80 °C for cadmium in Ti2PTe2). The current method of controlling selectivity provides opportunities in the search for new materials for various applications that used to be possible only in a liquid.

  7. 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)

  8. Two-dimensional transition metal dichalcogenides: interface and defect engineering.

    Science.gov (United States)

    Hu, Zehua; Wu, Zhangting; Han, Cheng; He, Jun; Ni, Zhenhua; Chen, Wei

    2018-03-06

    Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have been considered as promising candidates for next generation nanoelectronics. Because of their atomically-thin structure and high surface to volume ratio, the interfaces involved in TMDC-based devices play a predominant role in determining the device performance, such as charge injection/collection at the metal/TMDC interface, and charge carrier trapping at the dielectric/TMDC interface. On the other hand, the crystalline structures of TMDCs are enriched by a variety of intrinsic defects, including vacancies, adatoms, grain boundaries, and substitutional impurities. Customized design and engineering of the interfaces and defects provides an effective way to modulate the properties of TMDCs and finally enhance the device performance. Herein, we summarize and highlight recent advances and state-of-the-art investigations on the interface and defect engineering of TMDCs and their corresponding applications in electronic and optoelectronic devices. Various interface engineering approaches for TMDCs are overviewed, including surface charge transfer doping, TMDC/metal contact engineering, and TMDC/dielectric interface engineering. Subsequently, different types of structural defects in TMDCs are introduced. Defect engineering strategies utilized to modulate the optical and electronic properties of TMDCs, as well as the developed high-performance and functional devices are summarized. Finally, we highlight the challenges and opportunities for interface and defect engineering in TMDC materials for electronics and optoelectronics.

  9. Selective and low temperature transition metal intercalation in layered tellurides

    Science.gov (United States)

    Yajima, Takeshi; Koshiko, Masaki; Zhang, Yaoqing; Oguchi, Tamio; Yu, Wen; Kato, Daichi; Kobayashi, Yoji; Orikasa, Yuki; Yamamoto, Takafumi; Uchimoto, Yoshiharu; Green, Mark A.; Kageyama, Hiroshi

    2016-01-01

    Layered materials embrace rich intercalation reactions to accommodate high concentrations of foreign species within their structures, and find many applications spanning from energy storage, ion exchange to secondary batteries. Light alkali metals are generally most easily intercalated due to their light mass, high charge/volume ratio and in many cases strong reducing properties. An evolving area of materials chemistry, however, is to capture metals selectively, which is of technological and environmental significance but rather unexplored. Here we show that the layered telluride T2PTe2 (T=Ti, Zr) displays exclusive insertion of transition metals (for example, Cd, Zn) as opposed to alkali cations, with tetrahedral coordination preference to tellurium. Interestingly, the intercalation reactions proceed in solid state and at surprisingly low temperatures (for example, 80 °C for cadmium in Ti2PTe2). The current method of controlling selectivity provides opportunities in the search for new materials for various applications that used to be possible only in a liquid. PMID:27966540

  10. Estimation of stacking fault and twin energies in transition metals

    International Nuclear Information System (INIS)

    Papon, Anne-Marie

    1979-01-01

    As twins and stacking faults play an important role in the plastic deformation of metals, the objective of this research thesis is, by using an as correct as possible description of band d state density, to assess the internal energy of twins and stacking faults in metals with a CFC, HC or CC crystal structure. If, in transition metals, cohesion mainly results from d electron attraction, other terms intervening in crystal equilibrium must also be taken into account. Thus, the author proposes a decomposition of cohesion energy. The geometry of twins and stacking faults in compact phases is defined, and energy calculations are presented and discussed. Alloying effects are then addressed, as well as a general comparison with available experimental results. After a geometric description of twins and stacking faults in CC structures, their energies are calculated for a Gaussian distribution of state density. For higher order moments, defect energy due to d orbital anisotropy is assessed, and then applied to energy and stability calculations in twins and stacking faults for various relaxed atomic configurations

  11. Electronic and magnetic properties of transition metal doped graphyne

    Science.gov (United States)

    Gangan, Abhijeet Sadashiv; Yadav, Asha S.; Chakraborty, Brahmananda; Ramaniah, Lavanya M.

    2017-05-01

    We have theoretically investigated the interaction of few 3d (V,Mn) and 4d (Y,Zr) transition metals with the γ-graphyne structure using the spin-polarized density functional theory for its potentials application in Hydrogen storage, spintronics and nano-electronics. By doping different TMs we have observed that the system can be either metallic(Y), semi-conducting or half metallic. The system for Y and Zr doped graphyne becomes non-magnetic while V and Mn doped graphyne have a magnetic moments of l μB and 3 μB respectively From bader charge analysis it is seen that there is a charge transfer from the TM atom to the graphyne. Zr and Y have a net charge transfer of 2.15e and 1.73e respectively. Charge density analysis also shows the polarization on the carbon skeleton which becomes larger as the charge transfer for the TM atom increases. Thus we see Y and Zr are better candidates for hydrogen storage devices since they are non-magnetic and have less d electrons which is ideal for kubas-type interactions between hydrogen molecule and TM.

  12. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    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/ (metalloid poor glasses) vacancy-like defects form, which are characterized by the excess volume which they contribute to the glass. Another, as yet unspecified defect appears to form in glasses with x > x/sub c/. This novel picture can explain the variation of many properties of these glasses with metalloid concentration.

  14. Electronic Relaxation Processes of Transition Metal Atoms in Helium Nanodroplets

    Science.gov (United States)

    Kautsch, Andreas; Lindebner, Friedrich; Koch, Markus; Ernst, Wolfgang E.

    2014-06-01

    Spectroscopy of doped superfluid helium nanodroplets (He_N) gives information about the influence of this cold, chemically inert, and least interacting matrix environment on the excitation and relaxation dynamics of dopant atoms and molecules. We present the results from laser induced fluorescence (LIF), photoionization (PI), and mass spectroscopy of Cr and Cu doped He_N. From these results, we can draw a comprehensive picture of the complex behavior of such transition metal atoms in He_N upon photo-excitation. The strong Cr and Cu ground state transitions show an excitation blueshift and broadening with respect to the bare atom transitions which can be taken as indication for the solvation inside the droplet. From the originally excited states the atoms relax to energetically lower states and are ejected from the He_N. The relaxation processes include bare atom spin-forbidden transitions, which clearly bears the signature of the He_N influence. Two-color resonant two-photon ionization (2CR2PI) also shows the formation of bare atoms and small Cr-He_n and Cu-He_n clusters in their ground and metastable states ^c. Currently, Cr dimer excitation studies are in progress and a brief outlook on the available results will be given. C. Callegari and W. E. Ernst, Helium Droplets as Nanocryostats for Molecular Spectroscopy - from the Vacuum Ultraviolet to the Microwave Regime, in Handbook of High-Resolution Spectroscopy, eds. M. Quack and F. Merkt, John Wiley & Sons, Chichester, 2011. A. Kautsch, M. Koch, and W. E. Ernst, J. Phys. Chem. A, 117 (2013) 9621-9625, DOI: 10.1021/jp312336m F. Lindebner, A. Kautsch, M. Koch, and W. E. Ernst, Int. J. Mass Spectrom. (2014) in press, DOI: 10.1016/j.ijms.2013.12.022 M. Koch, A. Kautsch, F. Lackner, and W. E. Ernst, submitted to J. Phys. Chem. A

  15. Correlated effective field theory in transition metal compounds

    International Nuclear Information System (INIS)

    Mukhopadhyay, Subhasis; Chatterjee, Ibha

    2004-01-01

    Mean field theory is good enough to study the physical properties at higher temperatures and in higher dimensions. It explains the critical phenomena in a restricted sense. Near the critical temperatures, when fluctuations become important, it may not give the correct results. Similarly in low dimensions, the correlations become important and the mean field theory seems to be inadequate to explain the physical phenomena. At low-temperatures too, the quantum correlations become important and these effects are to be treated in an appropriate way. In 1974, Prof. M.E. Lines of Bell Laboratories, developed a theory which goes beyond the mean field theory and is known as the correlated effective field (CEF) theory. It takes into account the fluctuations in a semiempirical way. Lines and his collaborators used this theory to explain the short-range correlations and their anisotropy in the paramagnetic phase. Later Suzuki et al., Chatterjee and Desai, Mukhopadhyay and Chatterjee applied this theory to the magnetically ordered phase and a tremendous success of the theory has been found in real systems. The success of the CEF theory is discussed in this review. In order to highlight the success of this theory, earlier effective field theories and their improvements over mean field theories e.g., Bethe-Peierls-Weiss method, reaction field approximation, etc., are also discussed in this review for completeness. The beauty of the CEF theory is that it is mean field-like, but captures the essential physics of real systems to a great extent. However, this is a weak correlated theory and as a result is inappropriate for the metallic phase when strong correlations become important. In recent times, transition metal oxides become important due to the discovery of the high-temperature superconductivity and the colossal magnetoresistance phenomena. These oxides seem to be Mott insulators and undergo an insulator to metal transition by applying magnetic field, pressure and by changing

  16. 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.

  17. Laser surface alloying of aluminium-transition metal alloys

    International Nuclear Information System (INIS)

    Almeida, A.; Vilar, R.

    1998-01-01

    Laser surface alloying has been used as a tool to produce hard and corrosion resistant Al-transition metal (TM) alloys. Cr and Mo are particularly interesting alloying elements to produce stable high-strength alloys because they present low diffusion coefficients and solid solubility in Al. To produce Al-TM surface alloys a two-step laser process was developed: firstly, the material is alloyed using low scanning speed and secondly, the microstructure is modified by a refinement step. This process was used in the production of Al-Cr, Al-Mo and Al-Mo and Al-Nb surface alloys by alloying Cr, Mo or Nb powder into an Al and 7175 Al alloy substrate using a CO 2 laser . This paper presents a review of the work that has been developed at Instituto Superior Tecnico on laser alloying of Al-TM alloy, over the last years. (Author) 16 refs

  18. Preparation of transition metal sulfide nanoparticles via hydrothermal route

    International Nuclear Information System (INIS)

    Fei-Ling, P.; Chin-Hua, C.; Sarani Zakaria; Tze-Khong, L.; Mohd Ambar Yarmo; Nay-Ming, H.

    2010-01-01

    Nano sized copper sulfide, iron sulfide and molybdenum sulfide were successfully synthesised via a simple hydrothermal method. Sodium thiosulfate pentahydrate (Na 2 S 2 O 3 ·5H 2 O) and hydroxylamine sulfate ((H 3 NO) 2 ·H 2 SO 4 ) were used as the starting materials and reacted with the transition metal source at 200 degree Celsius for 90 min. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and Fourier transform infrared spectroscopy (FTIR). Spherical shape CuS and FeS 2 nanoparticles with high crystallinity were successfully produced. The transmission electron micrographs revealed the well-dispersibility of the produced nanoparticles. Scanning electron micrograph showed the MoS 2 nanoparticles possessed a spherical shape with sheet-like structure covering on the outer surface of the particles. (author)

  19. Heterogeneous Catalytic Oxidation of Simple Alcohols by Transition Metals.

    Science.gov (United States)

    Jacobse, Leon; Vink, Sebastiaan O; Wijngaarden, Sven; Juurlink, Ludo B F

    2017-09-12

    The "exploding" flask demonstration presents a well-known illustration of heterogeneous catalyzed methanol oxidation. We find that for the same vapor pressure, the demonstration also works for all primary and secondary alcohols up to butanol but not for a tertiary alcohol. Also, we show that the demonstration works for a large range of transition metal catalysts. Hence, this demonstration, which is often applied for the repetitive explosions when methanol is used, may also be used to argue the requirement of initial dehydrogenation of the alcohol to an aldehyde in the catalytic reaction mechanism to support the general insensitivity to reactant molecules in heterogeneous catalysis in contrast to biological catalysis and to provide proof for activity trends as often depicted by volcano plots.

  20. Molecule signatures in photoluminescence spectra of transition metal dichalcogenides

    Science.gov (United States)

    Feierabend, Maja; Berghäuser, Gunnar; Selig, Malte; Brem, Samuel; Shegai, Timur; Eigler, Siegfried; Malic, Ermin

    2018-01-01

    Monolayer transition metal dichalcogenides (TMDs) show an optimal surface-to-volume ratio and are thus promising candidates for novel molecule sensor devices. It was recently predicted that a certain class of molecules exhibiting a large dipole moment can be detected through the activation of optically inaccessible (dark) excitonic states in absorption spectra of tungsten-based TMDs. In this paper, we investigate the molecule signatures in photoluminescence spectra in dependence of a number of different experimentally accessible quantities, such as excitation density, temperature, as well as molecular characteristics including the dipole moment and its orientation, molecule-TMD distance, molecular coverage, and distribution. We show that under certain optimal conditions even room-temperature detection of molecules can be achieved.

  1. On holographic disorder-driven metal-insulator transitions

    International Nuclear Information System (INIS)

    Baggioli, Matteo; Pujolàs, Oriol

    2017-01-01

    We give a minimal holographic model of a disorder-driven metal-insulator transition. It consists in a CFT with a charge sector and a translation-breaking sector that interact in the most generic way allowed by the symmetries and by dynamical consistency. In the gravity dual, it reduces to a Massive Gravity-Maxwell model with a new direct coupling between the gauge field and the metric that is allowed when gravity is massive. We show that the effect of this coupling is to decrease the DC electrical conductivity generically. This gives a nontrivial check that holographic massive gravity can be consistently interpreted as disorder from the CFT perspective. The suppression of the conductivity happens to such an extent that it does not obey any lower bound and it can be very small in the insulating phase. In some cases, the large disorder limit produces gradient instabilities that hint at the formation of modulated phases.

  2. Ferromagnetism in Fe-doped transition metal nitrides

    Science.gov (United States)

    Sharma, Ramesh; Sharma, Yamini

    2018-04-01

    Early transition metal mononitrides ScN and YN are refractory compounds with high hardness and melting points as well semiconducting properties. The presence of nitrogen vacancies in ScN/YN introduces asymmetric peaks in the density of states close to Fermi level, the same effects can be achieved by doping by Mn or Fe-atoms. Due to the substitution of TM atoms at Sc/Y sites, it was found that the p-d hybridization induces small magnetic moments at both Sc/Y and N sites giving rise to magnetic semiconductors (MS). From the calculated temperature dependent transport properties, the power factor and ZT is found to be lowered for doped ScN whereas it increases for doped YN. It is proposed that these materials have promising applications as spintronics and thermoelectric materials.

  3. Investigation of electronic transport properties of some liquid transition metals

    Science.gov (United States)

    Patel, H. P.; Sonvane, Y. A.; Thakor, P. B.

    2018-04-01

    We investigated electronic transport properties of some liquid transition metals (V, Cr, Mn, Fe, Co and Pt) using Ziman formalism. Our parameter free model potential which is realized on ionic and atomic radius has been incorporated with the Hard Sphere Yukawa (HSY) reference system to study the electronic transport properties like electrical resistivity (ρ), thermal conductivity (σ) and thermo electrical power (Q). The screening effect on aforesaid properties has been studied by using different screening functions. The correlations of our results and others data with in addition experimental values are profoundly promising to the researchers working in this field. Also, we conclude that our newly constructed parameter free model potential is capable to explain the aforesaid electronic transport properties.

  4. Mechanism of Transition-Metal Nanoparticle Catalytic Graphene Cutting.

    Science.gov (United States)

    Ma, Liang; Wang, Jinlan; Yip, Joanne; Ding, Feng

    2014-04-03

    Catalytic cutting by transition-metal (TM) particles is a promising method for the synthesizing of high-quality graphene quantum dots and nanoribbons with smooth edges. Experimentally, it is observed that the cutting always results in channels with zigzag (ZZ) or armchair (AC) edges. However, the driving force that is responsible for such a cutting behavior remains a puzzle. Here, by calculating the interfacial formation energies of the TM-graphene edges with ab initio method, we show that the surface of a catalyst particle tends to be aligned along either AC or ZZ direction of the graphene lattice, and thus the cutting of graphene is guided as such. The different cutting behaviors of various catalysts are well-explained based on the competition between TM-passivated graphene edges and the etching-agent-terminated ones. Furthermore, the kinetics of graphene catalytic cutting along ZZ and AC directions, respectively, are explored at the atomic level.

  5. Metal-semiconductor transition of graphene nanoribbons with different addends

    Science.gov (United States)

    Zhang, X. W.; Dai, B.; Liu, J. S.; Yang, G. W.

    2012-02-01

    Using a LCAO method, which is based on spinless sp3 scheme, we have studied the electronic properties of graphene nanoribbons with zigzag edges (ZGNRs) terminated partially by methylene groups. Metal-semiconductor transition is proved when the H atoms at both sides of ZGNRs are partially substituted by methylene groups. Furthermore, when one-third of H atoms are substituted and the distribution of methylenes is symmetric, the band gap comes to about 0.59 eV, which is the widest energy gap in this work. Otherwise, when the addends at both sides are of asymmetric distribution, a band gap of only 0.21 eV is obtained. These results suggest that the addends at the edge of ZGNRs play an important role in modifying the electronic properties.

  6. Metal-semiconductor transition of graphene nanoribbons with different addends

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, X.W., E-mail: xiaoweizhang@swust.edu.cn [State Key Laboratory Cultivation Base for Nonmetal Composites and Functional Materials, Southwest University of Science and Technology, Mianyang 621010 (China); Dai, B; Liu, J.S. [State Key Laboratory Cultivation Base for Nonmetal Composites and Functional Materials, Southwest University of Science and Technology, Mianyang 621010 (China); Yang, G.W. [State Key Laboratory of Optoelectronic Materials and Technologies, Institute of Optoelectronic and Functional Composite Materials, School of Physics Science and Engineering, Sun Yat-Sen University, Guangzhou 510275 (China)

    2012-02-15

    Using a LCAO method, which is based on spinless sp{sup 3} scheme, we have studied the electronic properties of graphene nanoribbons with zigzag edges (ZGNRs) terminated partially by methylene groups. Metal-semiconductor transition is proved when the H atoms at both sides of ZGNRs are partially substituted by methylene groups. Furthermore, when one-third of H atoms are substituted and the distribution of methylenes is symmetric, the band gap comes to about 0.59 eV, which is the widest energy gap in this work. Otherwise, when the addends at both sides are of asymmetric distribution, a band gap of only 0.21 eV is obtained. These results suggest that the addends at the edge of ZGNRs play an important role in modifying the electronic properties.

  7. Electrically Induced Multiple Metal-Insulator Transitions in Oxide Nanodevices

    Science.gov (United States)

    del Valle, Javier; Kalcheim, Yoav; Trastoy, Juan; Charnukha, Aliaksei; Basov, Dimitri N.; Schuller, Ivan K.

    2017-11-01

    We show that electrical resistive switching can trigger the appearance of multiple metal-insulator transitions (MITs) in VO2 and V2O3 planar nanodevices. We have fabricated planar devices to electrically induce oxygen vacancy drift and filament formation. We show that oxygen migration can create ordered vanadium-oxide phases of varying stoichiometry with an intrinsic MIT, resulting in well-defined hysteresis loops in the R vs T characteristics of the device. We also show that oxygen migration induces oxide phases displaying correlated behaviors. Our results open up the possibility to electrically control the MIT, enabling alternative functionalities in memristive devices and allowing for alternative paradigms in neuromorphic computing or memory applications.

  8. Induced magnetism in transition metal intercalated graphitic systems

    KAUST Repository

    Kaloni, Thaneshwor P.

    2011-10-26

    We investigate the structure, chemical bonding, electronic properties, and magnetic behavior of a three-dimensional graphitic network in aba and aaa stacking with intercalated transition metal atoms (Mn, Fe, Co, Ni, and Cu). Using density functional theory, we find induced spin-polarization of the C atoms both when the graphene sheets are aba stacked (forming graphite) and aaa stacked (resembling bi-layer graphene). The magnetic moment induced by Mn, Fe, and Co turns out to vary from 1.38 μB to 4.10 μB, whereas intercalation of Ni and Cu does not lead to a magnetic state. The selective induction of spin-polarization can be utilized in spintronic and nanoelectronic applications.

  9. Intrinsic disorder in graphene on transition metal dichalcogenide heterostructures

    Science.gov (United States)

    Yankowitz, Matthew; Larentis, Stefano; Kim, Kyounghwam; Xue, Jiamin; McKenzie, Devin; Huang, Shengqiang; Paggen, Marina; Ali, Mazhar; Cava, Robert; Tutuc, Emanuel; Leroy, Brian J.

    2015-03-01

    Recently, semiconducting materials in the transition metal dichalcogenide (TMD) family have gained great popularity for use in novel graphene-based heterostructure devices such as tunneling transistors, highly efficient flexible photovoltaic devices, and nonvolatile memory cells. TMDs have also been explored as alternatives to hexagonal boron nitride (hBN) as substrates for pristine graphene devices. However, their quality has thus far been significantly worse than comparable hBN devices. We examine graphene on numerous TMD substrates (MoS2, WS2, WSe2, MoTe2) with scanning tunneling microscopy and spectroscopy and find that point and line defects intrinsic to all TMD crystals (both of natural and synthetic origin) result in scattering of electrons in graphene. Our findings suggest that the quality of graphene on TMD heterostructures is limited by the intrinsic crystalline quality of the TMDs.

  10. Probing Magnetism in 2D Molecular Networks after in Situ Metalation by Transition Metal Atoms.

    Science.gov (United States)

    Schouteden, K; Ivanova, Ts; Li, Z; Iancu, V; Janssens, E; Van Haesendonck, C

    2015-03-19

    Metalated molecules are the ideal building blocks for the bottom-up fabrication of, e.g., two-dimensional arrays of magnetic particles for spintronics applications. Compared to chemical synthesis, metalation after network formation by an atom beam can yield a higher degree of control and flexibility and allows for mixing of different types of magnetic atoms. We report on successful metalation of tetrapyridyl-porphyrins (TPyP) by Co and Cr atoms, as demonstrated by scanning tunneling microscopy experiments. For the metalation, large periodic networks formed by the TPyP molecules on a Ag(111) substrate are exposed in situ to an atom beam. Voltage-induced dehydrogenation experiments support the conclusion that the porphyrin macrocycle of the TPyP molecule incorporates one transition metal atom. The newly synthesized Co-TPyP and Cr-TPyP complexes exhibit striking differences in their electronic behavior, leading to a magnetic character for Cr-TPyP only as evidenced by Kondo resonance measurements.

  11. Plasmonic percolation: Plasmon-manifested dielectric-to-metal transition

    KAUST Repository

    Chen, Huanjun

    2012-08-28

    Percolation generally refers to the phenomenon of abrupt variations in electrical, magnetic, or optical properties caused by gradual volume fraction changes of one component across a threshold in bicomponent systems. Percolation behaviors have usually been observed in macroscopic systems, with most studies devoted to electrical percolation. We report on our observation of plasmonic percolation in Au nanorod core-Pd shell nanostructures. When the Pd volume fraction in the shell consisting of palladium and water approaches the plasmonic percolation threshold, ∼70%, the plasmon of the nanostructure transits from red to blue shifts with respect to that of the unshelled Au nanorod. This plasmonic percolation behavior is also confirmed by the scattering measurements on the individual core-shell nanostructures. Quasistatic theory and numerical simulations show that the plasmonic percolation originates from a positive-to-negative transition in the real part of the dielectric function of the shell as the Pd volume fraction is increased. The observed plasmonic percolation is found to be independent of the metal type in the shell. Moreover, compared to the unshelled Au nanorods with similar plasmon wavelengths, the Au nanorod core-Pd shell nanostructures exhibit larger refractive index sensitivities, which is ascribed to the expulsion of the electric field intensity from the Au nanorod core by the adsorbed Pd nanoparticles. © 2012 American Chemical Society.

  12. Generic trend of work functions in transition-metal carbides and nitrides

    Energy Technology Data Exchange (ETDEWEB)

    Yoshitake, Michiko, E-mail: yoshitake.michiko@nims.go.jp [MANA Nanoelectronics Materials Unit, National Institute for Materials Science, Tsukuba, Ibaraki 305-0003 (Japan)

    2014-11-15

    Transition-metal carbides and nitrides (TMCs and TMNs) are promising electrode materials for various electronic devices such as metal-oxide-semiconductor field-effect transistors and metal-insulator-metal capacitors. In this paper, the work functions of TMCs and TMNs are discussed systematically. Based upon the origin of the work function, the effect upon transition metal species by different periodic table groups is explained, carbides are compared with nitrides for the same transition metal, and the effect of carbon or nitrogen vacancies is discussed. In addition, a method to estimate the generic trend of the work function is proposed for TMC{sub x}, TMN{sub x}, TMC{sub 1−y}N{sub y} (transition metal carbonitrides), and TM{sub 1−z}TM′{sub z}C (alloy carbides)

  13. Enzymatic hydrolysis by transition-metal-dependent nucleophilic aromatic substitution.

    Science.gov (United States)

    Kalyoncu, Sibel; Heaner, David P; Kurt, Zohre; Bethel, Casey M; Ukachukwu, Chiamaka U; Chakravarthy, Srinivas; Spain, Jim C; Lieberman, Raquel L

    2016-12-01

    Nitroaromatic compounds are typically toxic and resistant to degradation. Bradyrhizobium species strain JS329 metabolizes 5-nitroanthranilic acid (5NAA), which is a molecule secreted by Streptomyces scabies, the plant pathogen responsible for potato scab. The first biodegradation enzyme is 5NAA-aminohydrolase (5NAA-A), a metalloprotease family member that converts 5NAA to 5-nitrosalicylic acid. We characterized 5NAA-A biochemically and obtained snapshots of its mechanism. 5NAA-A, an octamer that can use several divalent transition metals for catalysis in vitro, employs a nucleophilic aromatic substitution mechanism. Unexpectedly, the metal in 5NAA-A is labile but is readily loaded in the presence of substrate. 5NAA-A is specific for 5NAA and cannot hydrolyze other tested derivatives, which are likewise poor inhibitors. The 5NAA-A structure and mechanism expand our understanding of the chemical ecology of an agriculturally important plant and pathogen, and will inform bioremediation and biocatalytic approaches to mitigate the environmental and ecological impact of nitroanilines and other challenging substrates.

  14. Kohn Anomaly and Phase Stability in Group VB Transition Metals

    Directory of Open Access Journals (Sweden)

    Alexander Landa

    2018-03-01

    Full Text Available In the periodic table, only a few pure metals exhibit lattice or magnetic instabilities associated with Fermi surface nesting, the classical examples being α-U and Cr. Whereas α-U displays a strong Kohn anomaly in the phonon spectrum that ultimately leads to the formation of charge density waves (CDWs, Cr is known for its nesting-induced spin density waves (SDWs. Recently, it has become clear that a pronounced Kohn anomaly and the corresponding softening in the elastic constants is also the key factor that controls structural transformations and mechanical properties in compressed group VB metals—materials with relatively high superconducting critical temperatures. This article reviews the current understanding of the structural and mechanical behavior of these metals under pressure with an introduction to the concept of the Kohn anomaly and how it is related to the important concept of Peierls instability. We review both experimental and theoretical results showing different manifestations of the Kohn anomaly in the transverse acoustic phonon mode TA (ξ00 in V, Nb, and Ta. Specifically, in V the anomaly triggers a structural transition to a rhombohedral phase, whereas in Nb and Ta it leads to an anomalous reduction in yield strength.

  15. The mechanism of anomalous hardening in transition-metal monoborides.

    Science.gov (United States)

    Liang, Yongcheng; Gao, Zhenbang; Qin, Ping; Gao, Li; Tang, Chun

    2017-07-06

    The quest for novel nanomaterials with unusual functionalities continues to be a central challenge to modern nanoscience. Here we report a surprisingly anomalous hardening behavior exhibited by a class of transition-metal monoborides (TMB). Most remarkable is the occurrence of the intrinsic hardness maximum at the valence-electron concentration (VEC) of about 8 electrons per formula unit (e per f.u.); both lower and higher VECs lead to the decrease of hardness, contrasting with the expected positive correlation between hardness and VEC. Such an unexpected phenomenon originates from the presence of two sorts of bands near the Fermi level that respond oppositely to the movement of dislocations within the metal bilayer. Furthermore, we demonstrate that the hardness is closely related to the formation energy for TMB, which justifies the importance of the thermodynamic stability in designing superhard materials. Our findings not only elucidate the unique mechanism responsible for unusual atom-scale hardening but also open a new avenue towards designing novel multifunctional nanomaterials with the coexistence of high hardness and excellent electrical conductivity.

  16. 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

  17. 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

  18. 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

  19. 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.

  20. 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.

  1. Discrepancy of structural and electronic transitions in the vicinity of the Metal-Insulator-transition in V2 O 3

    Science.gov (United States)

    Kim, Hyun-Tak; Shin, Jun-Hwan; Choi, Jung-Young; Kim, Bong-Jun

    2011-03-01

    Vanadium sesquioxide (V2 O3) , representative of strongly correlated electronic system, has been known as undergoing the MIT (Metal-Insulator-Transition) which is between rhombohedral paramagnetic metallic phase and monoclinic antiferromagnetic insulating phase near the transition temperature, (Tc) ~ }150 K. In order to reveal a relation between electronic and structural atomic transition, we has measured the temperature dependence of DC conductivity and structural crystallographic characterization with various temperatures from 90 K to 300 K by using low-temperature X-Ray diffraction (LTXRD). The obtained results show a discrepancy of structural and electronic transitions. This discrepancy can be explained by forming of the metallic puddles whose the size and number increased by nucleation and percolation[1,2] during the electronic transition progress from 120 K to 180 K. The puddles have an insulating monoclinic structure before the structural phase transition at ~ 185 K. These metallic puddles are induced by the MIT not related to the SPT (structure phase transition). (1. M. M. Qazilbash et al., Science 318, 1750 (2007); 2. B. J. Kim et al., Phys. Rev. B 77, 235401(2008))

  2. Converged G W quasiparticle energies for transition metal oxide perovskites

    Science.gov (United States)

    Ergönenc, Zeynep; Kim, Bongjae; Liu, Peitao; Kresse, Georg; Franchini, Cesare

    2018-02-01

    The ab initio calculation of quasiparticle (QP) energies is a technically and computationally challenging problem. In condensed matter physics, the most widely used approach to determine QP energies is the G W approximation. Although the G W method has been widely applied to many typical semiconductors and insulators, its application to more complex compounds such as transition metal oxide perovskites has been comparatively rare, and its proper use is not well established from a technical point of view. In this work, we have applied the single-shot G0W0 method to a representative set of transition metal oxide perovskites including 3 d (SrTiO3, LaScO3, SrMnO3, LaTiO3, LaVO3, LaCrO3, LaMnO3, and LaFeO3), 4 d (SrZrO3, SrTcO3, and Ca2RuO4 ), and 5 d (SrHfO3, KTaO3, and NaOsO3) compounds with different electronic configurations, magnetic orderings, structural characteristics, and band gaps ranging from 0.1 to 6.1 eV. We discuss the proper procedure to obtain well-converged QP energies and accurate band gaps within single-shot G0W0 by comparing the conventional approach based on an incremental variation of a specific set of parameters (number of bands, energy cutoff for the plane-wave expansion and number of k points) and the basis-set extrapolation scheme [J. Klimeš et al., Phys. Rev. B 90, 075125 (2014), 10.1103/PhysRevB.90.075125]. Although the conventional scheme is not supported by a formal proof of convergence, for most cases it delivers QP energies in reasonably good agreement with those obtained by the basis-set correction procedure and it is by construction more useful for calculating band structures. In addition, we have inspected the difference between the adoption of norm-conserving and ultrasoft potentials in G W calculations and found that the norm violation for the d shell can lead to less accurate results in particular for charge-transfer systems and late transition metals. A minimal statistical analysis indicates that the correlation of the G W data

  3. Ordering phenomena in transition-metal-oxide heterostructures

    International Nuclear Information System (INIS)

    Frano Pereira, Alex Manuel

    2014-01-01

    This doctoral work presents a study of ordered ground states of transition metal oxide compounds and multilayers using resonant elastic soft x-ray scattering. The technique has developed over the last decades and become especially useful when sample sizes are limited like the case of nanometer-scale films and superlattices. By scattering with photon energies on resonance with the element's electronic transitions, it is an element-specific, sensitive tool providing a combination of spectroscopic and spatial information. The thesis is divided into two central topics. The first part focuses on the investigation of perovskite-type, rare-earth nickelate heterostructures. X-rays tuned to the Ni L 3 -edge were used to unveil unprecedented diffraction evidence of long range magnetic order in LaNiO 3 -RXO 3 (RXO 3 = LaAlO 3 , DyScO 3 ) superlattices. We report on the appearance of magnetic order in such systems with a propagation vector of Q SDW = ((1)/(4),(1)/(4),l) in pseudocubic notation, similar to bulk rare earth nickelates with R ≠ La. With LaNiO 3 being paramagnetic in its bulk form, the magnetic Bragg peak is only present in superlattices where the thickness of the LaNiO 3 layers approaches the 2-dimensional limit. Besides the thickness dependence, the magnetic order was probed on samples grown on varying strain-inducing substrates. Azimuthal scans around Q SDW were done to determine the orientation of the spin spiral under these different conditions. We will explain how the reorientation of the spins can be understood by the magneto-crystalline anisotropy which is determined by the relative occupation of the Ni d-orbitals via spin-orbit coupling. First steps towards control of the spin spiral's orientation will be outlined, and along with the high remanent conductivity found in the magnetic spiral state, an outlook for metallic antiferromagnetic spintronics will be discussed. The second part of this thesis will address the observation of charge density

  4. 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 3 O 4 upon cyclic oxidation; CuO redox cycles prefer to be limited to a reduced form of Cu 2 O and an oxidized form of CuO; Mn microparticles were oxidized to a mixed phases of MnO and Mn 3 O 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

  5. Electronic self-organization in layered transition metal dichalcogenides

    Energy Technology Data Exchange (ETDEWEB)

    Ritschel, Tobias

    2015-10-30

    The interplay between different self-organized electronically ordered states and their relation to unconventional electronic properties like superconductivity constitutes one of the most exciting challenges of modern condensed matter physics. In the present thesis this issue is thoroughly investigated for the prototypical layered material 1T-TaS{sub 2} both experimentally and theoretically. At first the static charge density wave order in 1T-TaS{sub 2} is investigated as a function of pressure and temperature by means of X-ray diffraction. These data indeed reveal that the superconductivity in this material coexists with an inhomogeneous charge density wave on a macroscopic scale in real space. This result is fundamentally different from a previously proposed separation of superconducting and insulating regions in real space. Furthermore, the X-ray diffraction data uncover the important role of interlayer correlations in 1T-TaS{sub 2}. Based on the detailed insights into the charge density wave structure obtained by the X-ray diffraction experiments, density functional theory models are deduced in order to describe the electronic structure of 1T-TaS{sub 2} in the second part of this thesis. As opposed to most previous studies, these calculations take the three-dimensional character of the charge density wave into account. Indeed the electronic structure calculations uncover complex orbital textures, which are interwoven with the charge density wave order and cause dramatic differences in the electronic structure depending on the alignment of the orbitals between neighboring layers. Furthermore, it is demonstrated that these orbital-mediated effects provide a route to drive semiconductor-to-metal transitions with technologically pertinent gaps and on ultrafast timescales. These results are particularly relevant for the ongoing development of novel, miniaturized and ultrafast devices based on layered transition metal dichalcogenides. The discovery of orbital textures

  6. Deoxygenation of Palmitic Acid on Unsupported Transition-Metal Phosphides

    Energy Technology Data Exchange (ETDEWEB)

    Peroni, Marco [Technische Universität München, Department; Lee, Insu [Technische Universität München, Department; Huang, Xiaoyang [Technische Universität München, Department; Baráth, Eszter [Technische Universität München, Department; Gutiérrez, Oliver Y. [Technische Universität München, Department; Lercher, Johannes A. [Technische Universität München, Department; Institute

    2017-08-18

    Abstract Highly active bulk transition metal phosphides (WP, MoP, and Ni2P) were synthesized for the catalytic hydrodeoxygenation of palmitic acid, hexadecanol, hexadecanal, and microalgae oil. The specific activities positively correlated with the concentration of exposed metal sites, although the relative rates changed with temperature due to activation energies varying from 57 kJ·mol-1 for MoP to 142 kJ·mol-1 for WP. The reduction of the fatty acid to the aldehyde occurs through a Langmuir-Hinshelwood mechanism, where the rate-determining step is the addition of the second H to the hydrocarbon. On WP, the conversion of palmitic acid proceeds via R-CH2COOH R-CH2CHO R-CH2CH2OH R-CHCH2 R-CH2CH3 (hydrodeoxygenation). Decarbonylation of the intermittently formed aldehyde (R-CH2COOH R-CH2CHO R-CH3) was an important pathway on MoP and Ni2P. Conversion via dehydration to a ketene, followed by its decarbonylation occurred only on Ni2P. The rates of alcohol dehydration (R-CH2CH2OH R-CHCH2) correlate with the concentration of Lewis acid sites of the phosphides. Acknowledgements The authors would like to thank Roel Prins for the critical discussion of the results. We are also grateful to Xaver Hecht for technical support. Funding by the German Federal Ministry of Food and Agriculture in the framework of the Advanced Biomass Value project (03SF0446A) is gratefully acknowledged. J.A.L. acknowledges support for his contribution by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences for exploring non-oxidic supports for deoxygenation reactions.

  7. Dislocations and Plasticity in bcc Transition Metals at High Pressure

    Energy Technology Data Exchange (ETDEWEB)

    Yang, L H; Tang, M; Moriarty, J A

    2009-01-23

    Using first-principles electronic structure calculations, quantum-based atomistic simulations and atomistically informed dislocation dynamics (DD) simulations, we have studied individual dislocation behavior and the multiscale modeling of single-crystal plasticity in the prototype bcc transition metals Ta, Mo and V under both ambient and high pressure conditions. The primary focus in this work is on the pressure-dependent structure, mobility and interaction of a/2<111> screw dislocations, which dominate the plastic deformation properties of these materials. At the electronic scale, first-principles calculations of elasticity, ideal strength and generalized stacking fault energy surfaces have been used to validate quantum-based multi-ion interatomic potentials. At the atomistic scale, these potentials have been used in flexible Green's function boundary condition simulations to study the core structure, Peierls stress {tau}{sub P}, thermally activated kink-pair formation and mobility below {tau}{sub P}, and phonon-drag mobility above {tau}{sub P}. These results have then been distilled into analytic velocity laws and used directly in predictive microscale DD simulations of flow stress and resolved yield stress over wide ranges of pressure, temperature and strain rate.

  8. Quantum dot behavior in transition metal dichalcogenides nanostructures

    Science.gov (United States)

    Luo, Gang; Zhang, Zhuo-Zhi; Li, Hai-Ou; Song, Xiang-Xiang; Deng, Guang-Wei; Cao, Gang; Xiao, Ming; Guo, Guo-Ping

    2017-08-01

    Recently, transition metal dichalcogenides (TMDCs) semiconductors have been utilized for investigating quantum phenomena because of their unique band structures and novel electronic properties. In a quantum dot (QD), electrons are confined in all lateral dimensions, offering the possibility for detailed investigation and controlled manipulation of individual quantum systems. Beyond the definition of graphene QDs by opening an energy gap in nanoconstrictions, with the presence of a bandgap, gate-defined QDs can be achieved on TMDCs semiconductors. In this paper, we review the confinement and transport of QDs in TMDCs nanostructures. The fabrication techniques for demonstrating two-dimensional (2D) materials nanostructures such as field-effect transistors and QDs, mainly based on e-beam lithography and transfer assembly techniques are discussed. Subsequently, we focus on electron transport through TMDCs nanostructures and QDs. With steady improvement in nanoscale materials characterization and using graphene as a springboard, 2D materials offer a platform that allows creation of heterostructure QDs integrated with a variety of crystals, each of which has entirely unique physical properties.

  9. Exciton-polariton condensation in transition metal dichalcogenide bilayer heterostructure

    Science.gov (United States)

    Lee, Ki Hoon; Jeong, Jae-Seung; Min, Hongki; Chung, Suk Bum

    For the bilayer heterostructure system in an optical microcavity, the interplay of the Coulomb interaction and the electron-photon coupling can lead to the emergence of quasiparticles consisting of the spatially indirect exciton and cavity photons known as dipolariton, which can form the Bose-Einstein condensate above a threshold density. Additional physics comes into play when each layer of the bilayer system consists of the transition metal dichalcogenide (TMD) monolayer. The TMD monolayer band structure in the low energy spectrum has two valley components with nontrivial Berry phase, which gives rise to a selection rule in the exciton-polariton coupling, e.g. the exciton from one (the other) valley can couple only to the clockwise (counter-clockwise) polarized photon. We investigate possible condensate phases of exciton-polariton in the bilayer TMD microcavity changing relevant parameters such as detuning, excitation density and interlayer distance. This work was supported in part by the Institute for Basic Science of Korea (IBS) under Grant IBS-R009-Y1 and by the National Research Foundation of Korea (NRF) under the Basic Science Research Program Grant No. 2015R1D1A1A01058071.

  10. Photoconductivity in Transition Metal Doped Bismuth Germanium Oxide

    Science.gov (United States)

    Newkirk, Nolan M.; McCullough, J. S.; Martin, J. J.

    1999-10-01

    Bismuth germanium oxide (BGO) is a photorefractive material that has potential for a number of applications. We are investigating the possibility of tailoring it for specific uses by doping with 3d-ions. . Anti-site bismuth is a native defect in melt-grown BGO. This amphoteric defect dominates the photo-response of undoped BGO and plays a role in transition metal doped samples. The majority of the 3d-ions go into the tetrahedrally bonded Ge-site; thus, Cr would be expected to be in a 4+ state. Instead, it gives up an electron to the anti-site Bi and is in a 5+ state. Strongly persistent photorefractive gratings are observed in BGO:Cr. Photoconductivity measurements were performed on undoped BGO, BGO:V, and BGO:Cr before and after the samples were exposed to 442 nm light. The photoconductivity response roughly matched the optical absorption spectra of the samples. The exposed samples showed additional photo-induced absorption bands and much stronger photocurrents in the same spectral regions. The exposure to blue light appears to convert Cr from the 5+ state to the 4+state.

  11. Band Alignment of 2D Transition Metal Dichalcogenide Heterojunctions

    KAUST Repository

    Chiu, Ming-Hui

    2016-09-20

    It is critically important to characterize the band alignment in semiconductor heterojunctions (HJs) because it controls the electronic and optical properties. However, the well-known Anderson\\'s model usually fails to predict the band alignment in bulk HJ systems due to the presence of charge transfer at the interfacial bonding. Atomically thin 2D transition metal dichalcogenide materials have attracted much attention recently since the ultrathin HJs and devices can be easily built and they are promising for future electronics. The vertical HJs based on 2D materials can be constructed via van der Waals stacking regardless of the lattice mismatch between two materials. Despite the defect-free characteristics of the junction interface, experimental evidence is still lacking on whether the simple Anderson rule can predict the band alignment of HJs. Here, the validity of Anderson\\'s model is verified for the 2D heterojunction systems and the success of Anderson\\'s model is attributed to the absence of dangling bonds (i.e., interface dipoles) at the van der Waal interface. The results from the work set a foundation allowing the use of powerful Anderson\\'s rule to determine the band alignments of 2D HJs, which is beneficial to future electronic, photonic, and optoelectronic devices. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Moessbauer spectroscopy and transition metal chemistry. Fundamentals and applications

    International Nuclear Information System (INIS)

    Guetlich, Philipp; Trautwein, Alfred X.

    2011-01-01

    Moessbauer spectroscopy is a profound analytical method which has nevertheless continued to develop. The authors now present a state-of-the art book which consists of two parts. The first part details the fundamentals of Moessbauer spectroscopy and is based on a book published in 1978 in the Springer series 'Inorganic Chemistry Concepts' by P. Guetlich, R. Link and A.X. Trautwein. The second part covers useful practical aspects of measurements, and the application of the techniques to many problems of materials characterization. The update includes the use of synchroton radiation and many instructive and illustrative examples in fields such as solid state chemistry, biology and physics, materials and the geosciences, as well as industrial applications. Special chapters on magnetic relaxation phenomena (S. Morup) and computation of hyperfine interaction parameters (F. Neese) are also included. An attached CD-ROM with more than 400 full-color PowerPoint images provides self-explanatory examples. The book concentrates on teaching the technique using theory as much as needed and as little as possible. The reader will learn the fundamentals of the technique and how to apply it to many problems of materials characterization. Transition metal chemistry, studied on the basis of the most widely used Moessbauer isotopes, is in the foreground. (orig.)

  13. Hyperdoping Si with transition metals for infrared detection

    Science.gov (United States)

    Mathews, Jay; Liu, Yining; Yang, Wenjie; Hudspeth, Quentin; Malladi, Girish; Efstathiadis, Harry; Williams, James; Warrender, Jeffrey

    Recent advances in the field of laser hyperdoping have produced a new class of materials that could lead the way to silicon-based, CMOS-compatible infrared detectors. Using the method of ion implantation followed by pulsed laser melting (II-PLM), silicon films with impurities at concentrations well above the solid solubility limit can be fabricated. Recent work has centered on using transition metals like Au or Ti as the impurity, as their deep level impurity states broaden into intermediate bands, thereby creating sub-band gap optical absorption. In this work, we report on efforts to develop the fabrication methods for realization of photodetectors from Si:Au and Si:Ti, including etching the materials and forming Ohmic contacts. We also explore the optical and electrical properties of fabricated Si:Au and Si:Ti photodetectors. This work is supported by US Army ARDEC Grant No. W15QKN-16-2-0001 and Office of Naval Research Grant No. N00014-16-1-2864.

  14. Protactinium and the intersection of actinide and transition metal chemistry

    Energy Technology Data Exchange (ETDEWEB)

    Wilson, Richard E.; De Sio, Stephanie; Vallet, Valérie

    2018-02-12

    The role of the 5f and 6d orbitals in the chemistry of the actinide elements has been of considerable interest since their discovery and synthesis. Relativistic effects cause the energetics of the 5f and 6d orbitals to change as the actinide series is traversed left to right imparting a rich and complex chemistry. The 5f and 6d atomic states cross in energy at protactinium (Pa), making it a potential intersection between transition metal and actinide chemistries. Herein, we report the synthesis of a Pa-peroxo cluster, A(6)(Pa4O(O-2)(6)F-12) [A = Rb, Cs, (CH3)(4)N], formed in pursuit of an actinide polyoxometalate. Quantum chemical calculations at the density functional theory level demonstrate equal 5f and 6d orbital participation in the chemistry of Pa and increasing 5f orbital participation for the heavier actinides. Periodic changes in orbital character to the bonding in the early actinides highlights the influence of the 5f orbitals in their reactivity and chemical structure.

  15. Coherent quantum dynamics of excitons in monolayer transition metal dichalcogenides

    KAUST Repository

    Moody, Galan

    2016-03-14

    Transition metal dichalcogenides (TMDs) have garnered considerable interest in recent years owing to their layer thickness-dependent optoelectronic properties. In monolayer TMDs, the large carrier effective masses, strong quantum confinement, and reduced dielectric screening lead to pronounced exciton resonances with remarkably large binding energies and coupled spin and valley degrees of freedom (valley excitons). Coherent control of valley excitons for atomically thin optoelectronics and valleytronics requires understanding and quantifying sources of exciton decoherence. In this work, we reveal how exciton-exciton and exciton-phonon scattering influence the coherent quantum dynamics of valley excitons in monolayer TMDs, specifically tungsten diselenide (WSe2), using two-dimensional coherent spectroscopy. Excitation-density and temperature dependent measurements of the homogeneous linewidth (inversely proportional to the optical coherence time) reveal that exciton-exciton and exciton-phonon interactions are significantly stronger compared to quasi-2D quantum wells and 3D bulk materials. The residual homogeneous linewidth extrapolated to zero excitation density and temperature is ~1:6 meV (equivalent to a coherence time of 0.4 ps), which is limited only by the population recombination lifetime in this sample. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

  16. Stimulated X-Ray Emission Spectroscopy in Transition Metal Complexes

    Science.gov (United States)

    Kroll, Thomas; Weninger, Clemens; Alonso-Mori, Roberto; Sokaras, Dimosthenis; Zhu, Diling; Mercadier, Laurent; Majety, Vinay P.; Marinelli, Agostino; Lutman, Alberto; Guetg, Marc W.; Decker, Franz-Josef; Boutet, Sébastien; Aquila, Andy; Koglin, Jason; Koralek, Jake; DePonte, Daniel P.; Kern, Jan; Fuller, Franklin D.; Pastor, Ernest; Fransson, Thomas; Zhang, Yu; Yano, Junko; Yachandra, Vittal K.; Rohringer, Nina; Bergmann, Uwe

    2018-03-01

    We report the observation and analysis of the gain curve of amplified K α x-ray emission from solutions of Mn(II) and Mn(VII) complexes using an x-ray free electron laser to create the 1 s core-hole population inversion. We find spectra at amplification levels extending over 4 orders of magnitude until saturation. We observe bandwidths below the Mn 1 s core-hole lifetime broadening in the onset of the stimulated emission. In the exponential amplification regime the resolution corrected spectral width of ˜1.7 eV FWHM is constant over 3 orders of magnitude, pointing to the buildup of transform limited pulses of ˜1 fs duration. Driving the amplification into saturation leads to broadening and a shift of the line. Importantly, the chemical sensitivity of the stimulated x-ray emission to the Mn oxidation state is preserved at power densities of ˜1020 W /cm2 for the incoming x-ray pulses. Differences in signal sensitivity and spectral information compared to conventional (spontaneous) x-ray emission spectroscopy are discussed. Our findings build a baseline for nonlinear x-ray spectroscopy for a wide range of transition metal complexes in inorganic chemistry, catalysis, and materials science.

  17. Electrocatalytic reduction of carbon dioxide on post-transition metal and metal oxide nanoparticles

    Science.gov (United States)

    White, James L.

    The electroreduction of carbon dioxide to liquid products is an important component in the utilization of CO2 and in the high-density storage of intermittent renewable energy in the form of chemical bonds. Materials based on indium and tin, which yield predominantly formic acid, have been investigated in order to gain a greater understanding of the electrochemically active species and the mechanism of CO2 reduction on these heavy post-transition metals, since prior studies on the bulk metals did not provide thermodynamically sensible reaction pathways. Nanoparticles of the oxides and hydroxides of tin and indium have been prepared and characterized by transmission electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy, and various electrochemical methods in order to obtain structural information and analyze the role of various surface species on the CO2 reduction pathway. On both indium and tin, metastable surface-bound hydroxides bound CO2 and formed metal carbonates, which can then be reduced electrochemically. The relevant oxidation state of tin was suggested to be SnII rather than SnIV, necessitating a pre reduction to generate the CO2-binding species. Metallic indium nanoparticles partially oxidized in air and became highly efficient CO2 reduction electrocatalysts. Unit Faradaic efficiencies for formate, much higher than on bulk indium, were achieved with only 300 mV of overpotential on these particles, which possessed an oxyhydroxide shell surrounding a conductive metallic core. Alloys and mixed-metal oxide and hydroxide particles of tin and indium have also been studied for their carbon dioxide electrocatalytic capabilities, especially in comparison to the pure metal species. Additionally, a solar-driven indium-based CO2 electrolyzer was developed to investigate the overall efficiency for intermittent energy storage. The three flow cells were powered by a commercial photovoltaic array and had a maximum conversion efficiency of incident

  18. In situ X-ray absorption spectroscopy of transition metal based water oxidation catalysts.

    Science.gov (United States)

    van Oversteeg, Christina H M; Doan, Hoang Q; de Groot, Frank M F; Cuk, Tanja

    2017-01-03

    X-ray absorption studies of the geometric and electronic structure of primarily heterogeneous Co, Ni, and Mn based water oxidation catalysts are reviewed. The X-ray absorption near edge and extended X-ray absorption fine structure studies of the metal K-edge, characterize the metal oxidation state, metal-oxygen bond distance, metal-metal distance, and degree of disorder of the catalysts. These properties guide the coordination environment of the transition metal oxide radical that localizes surface holes and is required to oxidize water. The catalysts are investigated both as-prepared, in their native state, and under reaction conditions, while transition metal oxide radicals are generated. The findings of many experiments are summarized in tables. The advantages of future X-ray experiments on water oxidation catalysts, which include the limited data available of the oxygen K-edge, metal L-edge, and resonant inelastic X-ray scattering, are discussed.

  19. 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

  20. 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.

  1. Catalytic role of transition metals supported on niobium oxide in O2 activation

    Science.gov (United States)

    Omidvar, Akbar

    2018-03-01

    Metal particles supported on metal oxides (MMO) are promising materials with versatile applications such as catalyst in fuel cell technologies. As one of the transition metal oxides, niobium oxide (NbO) demonstrates a wide interesting properties that make it a potentially applicable in MMO materials. Here, the catalytic activity for the O2 activation of transition metals (Fe, Co, Ni, Cu, Rh, Pd, Ag, Ir, Pt, and Au) supported on the NbO has been studied theoretically using density functional theory (DFT). The activation of O2 molecule and yielding two separated O atoms is an essential step for the oxygen reduction reaction. Our study demonstrates that the transition metals supported on the NbO can act as driving force for O2 dissociation. Consistent with the prediction of reactivity descriptors, the maximum catalytic activity toward O2 activation is related to the Pt-supported on the NbO metal oxide.

  2. A Novel Route for Development of Bulk Al/SiC Metal Matrix Nanocomposites

    Directory of Open Access Journals (Sweden)

    Payodhar Padhi

    2011-01-01

    Full Text Available Addition of nano particles, even in quantities as small as 2 weight percent can enhance the hardness or yield strength by a factor as high as 2. There are several methods for the production of metal matrix nanocomposites including mechanical alloying, vertex process, and spray deposition and so forth. However, the above processes are expensive. Solidification processing is a relatively cheaper route. During solidification processing, nano particulates tend to agglomerate as a result of van der Waals forces and thus proper dispersion of the nano particulate in metal matrix is a challenge. In the present study a noncontact method, where the ultrasonic probe is not in direct contact with the liquid metal, was attempted to disperse nanosized SiC particulates in aluminum matrix. In this method, the mold was subjected to ultrasonic vibration. Hardness measurements and microstructural studies using HRTEM were carried out on samples taken from different locations of the nanocomposite ingot cast by this method.

  3. 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.

  4. On the Problem of Metal-Insulator Transitions in Vanadium Oxides

    OpenAIRE

    A. A. Velichko; N. A. Kuldin; G. B. Stefanovich; A. L. Pergament

    2013-01-01

    The problem of metal-insulator transition is considered. It is shown that the Mott criterion aB(nc)1/3≈0.25 is applicable not only to heavily doped semiconductors but also to many other materials, including some transition-metal compounds, such as vanadium oxides (particularly, VO2 and V2O3). The low-temperature transition (“paramagnetic metal—antiferromagnetic insulator”) in vanadium sesquioxide is described on the basis of this concept in terms of an intervening phase, between metal and ins...

  5. Microalloying of transition metal silicides by mechanical activation and field-activated reaction

    Energy Technology Data Exchange (ETDEWEB)

    Munir, Zuhair A [Davis, CA; Woolman, Joseph N [Davis, CA; Petrovic, John J [Los Alamos, NM

    2003-09-02

    Alloys of transition metal suicides that contain one or more alloying elements are fabricated by a two-stage process involving mechanical activation as the first stage and densification and field-activated reaction as the second stage. Mechanical activation, preferably performed by high-energy planetary milling, results in the incorporation of atoms of the alloying element(s) into the crystal lattice of the transition metal, while the densification and field-activated reaction, preferably performed by spark plasma sintering, result in the formation of the alloyed transition metal silicide. Among the many advantages of the process are its ability to accommodate materials that are incompatible in other alloying methods.

  6. Mechanism of decomposition of transition metal organometallic compounds and role of intermediate particles in catalysis

    International Nuclear Information System (INIS)

    Dolgoplosk, B.A.

    1984-01-01

    In the review, containing 105 bibliographic references, ways of decomposition of transition metal organic compounds in the moment of their formation are considered. For methyl, benzyl, trimethylsililmethyl and neophilic derivatives of transition metals (Mo, W, Re, Nb, Ta, Nd, Y) α-decay, which is accompanied by the formation of carbene and carbyne particles, is the determining one. Mechanism of the chain processes of metathesis of olefines and cycloolephines under the effect of carbene complexes of transition metals is discussed. Suppositions are made on chemical nature of elementary acts in the reactions of hydrogenolisis, isomerization of carbon carcass; dehydration and hydration of hydrocarbons

  7. Structural and Electrochemical Characterization of Lithium Transition Metal Phosphates

    Science.gov (United States)

    Hashambhoy, Ayesha Maria

    The lithium ion battery has emerged as one of the most promising hybrid vehicle energy storage systems of the future. Of the potential cathode chemistries explored, lithium transition metal phosphates have generated a significant amount of interest due to their low-cost precursors, potential ease of synthesis, stability, and their environmentally friendly nature. This is in contrast to layered oxide systems such as LiCoO2, which have long been considered state of the art, but are now being reevaluated due to their structural instability at elevated temperatures, and higher cost. In particular, LiFePO4 has an operating potential comparable to those batteries available on the market (˜3.5V vs. Li/Li+), and higher theoretical specific capacity (170mAh/g vs. that of LiCoO2 which is 140mAh/g). The manganese analog to LiFePO4, LiMnPO4, exhibits a higher operating potential (˜4.1V v Li/Li+), and the same theoretical capacity, however Li-ion diffusion through this structure is much more rate limited and its theoretical capacity cannot be realized at rates suitable for commercial applications. The purpose of this work was threefold: 1) To explore the impact of Fe substitution on Mn sites in LiMnPO 4. 2) To examine the effects of alterations to the particle/electrolyte interface on rate capability. 3) To explore a novel fabrication route for LiMnPO4 using microwaves, and determine an optimal power and time combination for best performance. The coexistence of Fe and Mn on the transition metal site M, of LiMPO 4 resulted in an improved apparent Li-ion diffusivity in both Fe and Mn regimes as compared to that observed for LiFePO4 and LiMnPO 4 respectively. Calculations made from two different analysis methods, cyclic voltammetry (CV) and galvanostatic intermittent titration (GITT) drew this same conclusion. The signature characteristics observed from the CVs pertaining to single and dual phase reactions led to a delithiation model of LiFe0.5Mn0.5PO4 proposing the localization

  8. High pressure and microwave based synthesis of transition metal pnictides

    Energy Technology Data Exchange (ETDEWEB)

    Pobel, Roman Rupert

    2016-04-11

    The goal of this thesis was to explore the possibilities of synthetic methods that are not very common in current transition metal pnictide research. The substitution of the Ca-site in CaFe{sub 2}As{sub 2} with rare earth elements such as Pr the has been reported to induce superconductivity. However, some inconsistencies in the data suggested a non-intrinsic origin of the observed diamagnetic signal. Furthermore a solubility limit of 13% was found when prepared in an electrical furnace thus leaving a huge part of the physical phase diagram inaccessible. A high pressure/high temperature synthesis was developed to allow access to the whole doping range and an in-depth characterization of this compound was carried out. During the experiments concerning the high pressure synthesis of Ca{sub 1-x}Pr{sub x}Fe{sub 2}As{sub 2} the new ternary iron arsenide CaFe{sub 5}As{sub 3} was identified and classified as a member of the Ca{sub n(n+1)/2}(Fe{sub 1-x}M{sub x}){sub (2+3n)}M'{sub n(n-1)/2}As{sub (n+1)(n+2)/2} (n = 1-3; M =Nb, Pd, Pt; M' = □, Pd, Pt) family. The complete solid solution Ca{sub 1-x}Pr{sub x}Fe{sub 5}As{sub 3} (O ≤ x ≤ 1) was prepared and physically characterized. Furthermore, several useful techniques were developed to aid in future high pressure based investigations of transition metal pnictides. The second part of this thesis concerns a completely different, but equally promising synthetic approach. Microwave based synthesis is a well-established technique in many solution based fields, such as organic, medicinal or nano chemistry. For solid state and materials research several parameters and particularities have to be considered. But when successful, it allows for the reduction of reaction time by several orders of magnitude. It has very rarely been applied in the preparation of pnictides and on1y once in the context of pnictide superconductor research. The possibilities of this method were explored and employed in the preparation of several

  9. 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

  10. Noncollinear magnetism in surfaces and interfaces of transition metals

    Energy Technology Data Exchange (ETDEWEB)

    Tan, Huahai

    2009-09-15

    Noncollinear (NC) magnetism is common in nature, especially when there exist geometrical frustration and chemical imparity in the system. In this work we studied the NC magnetism and the response to external magnetic fields in surfaces and interfaces of transition metals by using an semi-empirical tight-binding (TB) method that parameterized to the ab initio TB-LMTO calculations. We implemented this method to study two systems. The first one is the system of 6 Mn monolayers on Fe(001) substrate. Due to the complex structure and magnetic properties of Mn, we found 23 collinear magnetic configurations but only one NC configuration. The collinear ground state has a layered antiferromagnetic (AFM) coupling which agrees with previous experiments and calculations. In the NC configuration the local AFM coupling in the Mn layers is preserved, but the surface is 90 degree coupled to the substrate. Similar to the experiment in CdCr{sub 2}O{sub 4}, we obtained a collinear plateau in the NC evolution of the average magnetic moment in Mn slab under external magnetic fields. Another is the system of a Cr monolayer on a stepped Fe(001) substrate. As expected, the local AFM coupling in the interface of Cr and Fe are preserved. However, the edge Cr atoms is about 90 coupled to their nearest Fe neighbors. We also simulated the procedure of adding more Cr coverages gradually to a Cr bilayer coverage. As coverages increase, the magnetic moments in the Cr interface reduce, and the collinear plateau becomes wider as coverages increase. However, the saturation fields in both the two systems are extremely high, around 10 kT.We expect that when the effect of temperature is taken into account, and in some proper systems, the saturation fields could be largely reduced to the scale that can be implemented in experiment, and our study may shed light on information storage devices with ultrahigh storage density. (orig.)

  11. k-asymmetric spin splitting at the interface between transition metal ferromagnets and heavy metals

    KAUST Repository

    Grytsiuk, Sergii

    2016-05-23

    We systematically investigate the spin-orbit coupling-induced band splitting originating from inversion symmetry breaking at the interface between a Co monolayer and 4d (Tc, Ru, Rh, Pd, and Ag) or 5d (Re, Os, Ir, Pt, and Au) transition metals. In spite of the complex band structure of these systems, the odd-in-k spin splitting of the bands displays striking similarities with the much simpler Rashba spin-orbit coupling picture. We establish a clear connection between the overall strength of the odd-in-k spin splitting of the bands and the charge transfer between the d orbitals at the interface. Furthermore, we show that the spin splitting of the Fermi surface scales with the induced orbital moment, weighted by the spin-orbit coupling.

  12. Atomic volume and semiconducting properties in pnictides of non-magnetic transition metals

    International Nuclear Information System (INIS)

    Chapnik, I.M.

    1978-01-01

    Deviations of atomic volume from additivity are determined for binary compounds of pnictide elements with non-magnetic transition metals. It is shown that metallic properties (in contrast to semiconducting properties) are associated with intensive contraction. It is supposed that the wide range of contraction observed, the overlapping of the metallic and semiconducting ranges of contraction, and the usual absence of one smooth curve for the composition dependence of atomic volume in pnictides of transition metals, are associated with the change of valency state of the pnictide atoms in different compounds. (author)

  13. 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

  14. Formation of bulk metallic glasses in the Fe-M-Y-B (M = transition metal) system

    Energy Technology Data Exchange (ETDEWEB)

    Huang, X.M. [International Center for New-Structured Materials (ICNSM) and Laboratory of New-Structured Materials, Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027 (China); Chang, C.T. [Institute for Material Research, Tohoku University, Sendai 980-8577 (Japan); Chang, Z.Y.; Wang, X.D.; Cao, Q.P. [International Center for New-Structured Materials (ICNSM) and Laboratory of New-Structured Materials, Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027 (China); Shen, B.L.; Inoue, A. [Institute for Material Research, Tohoku University, Sendai 980-8577 (Japan); Jiang, J.Z. [International Center for New-Structured Materials (ICNSM) and Laboratory of New-Structured Materials, Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027 (China)], E-mail: jiangjz@zju.edu.cn

    2008-07-28

    In this work, quaternary Fe{sub 72-x}M{sub x}Y{sub 6}B{sub 22} (M = Ni, Co and Mo) bulk metallic glasses (BMGs) have been developed. It is found that a fully amorphous Fe{sub 68}Mo{sub 4}Y{sub 6}B{sub 22} cylindrical rod with 6.5 mm in diameter can be prepared by copper mold injection. These alloys have a high glass transition temperature of about 900 K with high fracture strengths up to about 3 GPa although they are still brittle. Magnetic measurements reveal that they are ferromagnetic at ambient temperature with low coercive force of about 2 A/m, saturation magnetization of about 0.7 T and effective permeability of about 7000 at 100 kHz. The newly developed Fe-based quaternary alloys exhibit excellent combination properties: superior glass forming ability (GFA), high glass transition temperature, and soft magnetic properties, which could have potential applications in electronic industries. Furthermore, the effect of Mo addition on GFA in the Fe-Y-B BMG system has been discussed compared with those of Ni and Co additions.

  15. The control of magnetism near metal-to-insulator transitions of VO2 nano-belts

    CSIR Research Space (South Africa)

    Nkosi, SS

    2016-12-01

    Full Text Available The magnetic properties of paramagnetic/weakly ferromagnetic films are strongly affected by the proximity to materials that undergo a metal to insulator phase transition. Here, we show that under the deposition conditions associated with structural...

  16. 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.

  17. Excited State Dynamics and Semiconductor-to-Metallic Phase Transition of VO2 Thin Film

    National Research Council Canada - National Science Library

    Liu, Huimin

    2004-01-01

    .... Vanadium dioxide shows an ultrafast, passive phase transition (PT) from a monoclinic semiconductor phase to a metallic tetragonal rutile structure when the sample temperature is above 68 degrees C...

  18. Insulator-to-metal transition in vanadium sesquioxide: does the Mott criterion work in this case?

    Science.gov (United States)

    Pergament, Alexander; Stefanovich, Genrikh

    2012-03-01

    It is shown that the Mott criterion expressed by the simple relation a B(n c)1/3 ≈ 0.25 turns out to be quite successful in describing metal-insulator phase transitions not only in heavily doped semiconductors, but also in transition metal oxides such as VO2 and V2O3. It is found in this article that, in the case of a high-temperature transition 'paramagnetic insulator - paramagnetic metal' in vanadium sesquioxide, a B(n c)1/3 = 0.254. Difficulties connected with the analogous description of a low-temperature transition ('paramagnetic metal - antiferromagnetic insulator') in V2O3 are discussed.

  19. Multi-body forces and the energetics of transition metals, alloys, and semiconductors

    International Nuclear Information System (INIS)

    Carlsson, A.E.

    1992-01-01

    Progress over the past year is divided into 3 areas: potential-energy functions for transition-metal aluminides; electronic structure and energetics of complex structures and quasicrystals; and ceramic materials (PdO, PtO)

  20. Single crystal particles of a mesoporous mixed transition metal oxide with a wormhole structure.

    Science.gov (United States)

    Lee, B; Lu, D; Kondo, J N; Domen, K

    2001-10-21

    A new type of mesoporous mixed transition metal oxide of Nb and Ta (NbTa-TIT-1) has been prepared through a two-step calcination, which consists of single crystal particles with wormhole mesoporous structure.

  1. Transition-Metal-Free Multicomponent Benzannulation Reactions for the Construction of Polysubstituted Benzene Derivatives.

    Science.gov (United States)

    Shu, Wen-Ming; Zheng, Kai-Lu; Ma, Jun-Rui; Wu, An-Xin

    2015-11-06

    A transition-metal-free multicomponent benzannulation reaction was developed from readily available ketones, nitro-olefins, and diester acetylenedicarboxylate. This approach provides a straightforward and efficient way to construct polysubstituted benzene derivatives under mild conditions in high yields.

  2. Pressure induced phase transitions in transition metal nitrides: Ab initio study

    Energy Technology Data Exchange (ETDEWEB)

    Srivastava, Anurag; Chauhan, Mamta [Advanced Material Research Lab, Indian Institute of Information Technology and Management, Gwalior 474010 (India); Singh, R.K. [Department of Physics, ITM University, Gurgaon 122017 (India)

    2011-12-15

    We have analyzed the stability of transition metal nitrides (TMNs) XN (X = Ti, Zr, Hf, V, Nb, Ta) in their original rocksalt (B1) and hypothetical CsCl (B2) type phases under high compression. The ground state total energy calculation approach of the system has been used through the generalized gradient approximation (GGA) with the Perdew-Burke-Ernzerhof (PBE) type parameterization as exchange correlation functional. In the whole series of nitrides taken into consideration, tantalum nitride is found to be the most stable. We have observed that under compression the original B1-type phase of these nitrides transforms to a B2-type phase. We have also discussed the computation of ground state properties, like the lattice constant (a), bulk modulus (B{sub 0}) and first order pressure derivative of the bulk modulus (B'{sub 0}) of the TMNs and their host elements. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  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. 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....

  5. 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

  6. The investigation of germanium based compounds, transition metals and isoflavones within foods

    OpenAIRE

    Dowling, Stephen

    2010-01-01

    The body of work here looks not only at how germanium was present in foods but also the ascertainment of chelation behaviour of germanium compounds and also transition metals with flavonoids. The chelation of germanium with flavonoids, or particularly isoflavones, is a completely novel area and gave some interesting results for chelation with isoflavones with transition metals, an area of research that was completely underexploited until recently. (refer to appendix 1) The Fourier Tran...

  7. Substitution effect on metal-insulator transition of K2V8O16

    International Nuclear Information System (INIS)

    Isobe, Masahiko; Koishi, Shigenori; Yamazaki, Satoshi; Yamaura, Jun-ichi; Gotou, Hirotada; Yagi, Takehiko; Ueda, Yutaka

    2009-01-01

    The effect of the substitution of various ions on the metal-insulator (MI) transition at 170 K in K 2 V 8 O 16 has been investigated. Both Rb and Ti form complete solid solution systems: K 2-x Rb x V 8 O 16 and K 2 V 8-y Ti y O 16 , respectively. The substitution of Rb for K or of Ti for V splits the transition into two transitions: the high-temperature transition is a first-order MI transition from a tetragonal structure to a tetragonal structure, and the low-temperature transition is a second-order transition to a monoclinic structure. In K 2-x Rb x V 8 O 16 , the former terminates to an MI transition at around 220 K in Rb 2 V 8 O 16 , while the latter disappears at x > 0.6. In K 2 V 8-y Ti y O 16 , both transitions disappear at y > 0.5. The substitution of Cr for V also results in a similar splitting of the transition and the rapid disappearance of both transitions. The substitution of Na or Ba for K suppresses the MI transition without any splitting of the transition, although the solubility of both ions is limited. These substitution effects reveal that the MI transition of K 2 V 8 O 16 consists of two parts: a first-order MI transition and a parasitic second-order structural transition; the substitution of some ions causes a clear splitting of these transitions, probably due to the difference between the chemical pressure effects on the two transitions. The first-order MI transition is very sensitive to charge randomness, suggesting the charge ordering nature of the MI transition, while the second-order structural transition is very sensitive to both charge and structural randomnesses. (author)

  8. Transition metal rates in latosol twice treated with sewage sludge

    Directory of Open Access Journals (Sweden)

    Ana Tereza Jordão Pigozzo

    2006-05-01

    Full Text Available Agricultural recycling of sewage sludge has been a source of accumulation of heavy metals in the environment which may reach toxic levels and cause serious damage to the biota. Field experiments were undertaken for two agricultural years (2000 and 2002 and effects of two sewage sludge applications were evaluated through the extraction of (essential and non-essential transition metals by diethylenetriaminepentaacetic acid (DTPA extractor in a medium texture dystrophic Dark Red Latosol. Cd, Ni, Co, Pb and Cr were not detected. Application of sewage sludge initially caused a slight pH rise in the soil; later pH lowered and kept itself close to the starting level. It could be concluded that through consecutive sludge application, extractable rates of Fe and Mn in soil samples gradually increased during the two agricultural years in proportion to sewage sludge doses and sampling period. In fact, they were higher than rates of control. Due to low concentrations of soil samples, extractor had a restricted capacity for evaluation of its phytoavailability.A reciclagem agrícola do lodo de esgoto tem provocado o acúmulo de metais pesados no solo e na água, podendo atingir níveis tóxicos e causar danos às plantas cultivadas, aos animais e ao homem, por meio da cadeia trófica. Neste intuito foi desenvolvido o presente experimento, em condições de campo, entre 2000 e 2002, onde foram avaliados os efeitos da aplicação de lodo de esgoto por dois anos, sobre a extração de metais de transição (essenciais e não pelo extrator DTPA em um Latossolo Vermelho distrófico (LVd de textura média. As concentrações dos elementos metálicos: Mn, Fe, Cd, Ni, Co, Pb e Cr não foram detectados pelo método da absorção atômica na solução obtida com o extrator DTPA. A aplicação de lodo de esgoto causou inicialmente pequena elevação no pH do solo, posteriormente a diminuição do mesmo, e manteve-se próximo ao original. Foi possível concluir que, com

  9. Theory of magnetic transition metal nanoclusters on surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Lounis, S.

    2007-04-17

    This thesis is motivated by the quest for the understanding and the exploration of complex magnetism provided by atomic scale magnetic clusters deposited on surfaces or embedded in the bulk. Use is made of the density functional theory (DFT). Acting within this framework, we have developed and implemented the treatment of non-collinear magnetism into the Juelich version of the full-potential Korringa-Kohn-Rostoker Green Function (KKR-GF) method. Firstly, the method was applied to 3d transition-metal clusters on different ferromagnetic surfaces. Different types of magnetic clusters where selected. In order to investigate magnetic frustration due to competing interactions within the ad-cluster we considered a (001) oriented surface of fcc metals, a topology which usually does not lead to non-collinear magnetism. We tuned the strength of the magnetic coupling between the ad-clusters and the ferromagnetic surface by varying the substrate from the case of Ni(001) with a rather weak hybridization of the Ni d-states with the adatom d-states to the case of Fe{sub 3ML}/Cu(001) with a much stronger hybridization due to the larger extend of the Fe wavefunctions. On Ni(001), the interaction between the Cr- as well as the Mn-dimer adatoms is of antiferromagnetic nature, which is in competition with the interaction with the substrate atoms. After performing total energy calculations we find that for Cr-dimer the ground state is collinear whereas the Mn-dimer prefers the non-collinear configuration as ground state. Bigger clusters are found to be magnetically collinear. These calculations were extended to 3d multimers on Fe{sub 3ML}/Cu(001). All neighboring Cr(Mn) moments in the compact tetramer are antiferromagnetically aligned in-plane, with the directions slightly tilted towards (outwards from) the substrate to gain some exchange interaction energy. The second type of frustration was investigated employing a Ni(111) surface, a surface with a triangular lattice of atoms, were

  10. Surface analysis of transition metal oxalates: Damage aspects

    Energy Technology Data Exchange (ETDEWEB)

    Chenakin, S.P., E-mail: chenakin@imp.kiev.ua [Université Libre de Bruxelles (ULB), Chimie-Physique des Matériaux, B-1050 Bruxelles (Belgium); Institute of Metal Physics, Nat. Acad. Sci. of Ukraine, Akad. Vernadsky Blvd. 36, 03680 Kiev (Ukraine); Szukiewicz, R. [Université Libre de Bruxelles (ULB), Chimie-Physique des Matériaux, B-1050 Bruxelles (Belgium); Barbosa, R.; Kruse, N. [Université Libre de Bruxelles (ULB), Chimie-Physique des Matériaux, B-1050 Bruxelles (Belgium); Voiland School of Chemical Engineering and Bioengineering, Washington State University, 155 Wegner Hall, Pullman, WA 99164-6515 (United States)

    2016-05-15

    Highlights: • Gas evolution from the Mn, Co, Ni and Cu oxalate hydrates in vacuum, during exposure to X-rays and after termination of X-ray irradiation is studied. • A comparative study of the damage caused by X-rays in NiC{sub 2}O{sub 4} and CuC{sub 2}O{sub 4} is carried out. • Effect of Ar{sup +} bombardment on the structure and composition of CoC{sub 2}O{sub 4} is studied. - Abstract: The behavior of transition metal oxalates in vacuum, under X-ray irradiation and low-energy Ar{sup +} ion bombardment was studied. A comparative mass-spectrometric analysis was carried out of gas evolution from the surface of Mn, Co, Ni and Cu oxalate hydrates in vacuum, during exposure to X-rays and after termination of X-ray irradiation. The rates of H{sub 2}O and CO{sub 2} liberation from the oxalates were found to be in an inverse correlation with the temperatures of dehydration and decomposition, respectively. X-ray photoelectron spectroscopy (XPS) was employed to study the X-ray induced damage in NiC{sub 2}O{sub 4} and CuC{sub 2}O{sub 4} by measuring the various XP spectral characteristics and surface composition of the oxalates as a function of time of exposure to X-rays. It was shown that Cu oxalate underwent a significantly faster degradation than Ni oxalate and demonstrated a high degree of X-ray induced reduction from the Cu{sup 2+} to the Cu{sup 1+} chemical state. 500 eV Ar{sup +} sputter cleaning of CoC{sub 2}O{sub 4} for 10 min was found to cause a strong transformation of the oxalate structure which manifested itself in an appreciable alteration of the XP core-level and valence band spectra. The analysis of changes in stoichiometry and comparison of XP spectra of bombarded oxalate with respective spectra of a reference carbonate CoCO{sub 3} implied that the bombardment-induced decomposition of CoC{sub 2}O{sub 4} gave rise to the formation of CoO-like and disordered CoCO{sub 3}-like phases.

  11. Subnanometer to nanometer transition metal CO oxidation catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Vajda, Stefan; Fortunelli, Alessandro; Yasumatsu, Hisato

    2017-12-26

    The present invention provides a catalyst defined in part by a conductive substrate; a film overlaying a surface of the substrate; and a plurality of metal clusters supported by the layer, wherein each cluster comprises between 8 and 11 atoms. Further provided is a catalyst defined in part by a conductive substrate; a layer overlaying a surface of the substrate; and a plurality of metal clusters supported by the layer, wherein each cluster comprises at least two metals.

  12. CO adsorption on transition metal clusters: Trends from density functional theory

    Science.gov (United States)

    Zeinalipour-Yazdi, Constantinos D.; Cooksy, Andrew L.; Efstathiou, Angelos M.

    2008-05-01

    This work reports for the first time the trends for carbon monoxide (CO) chemisorption on transition metal clusters present in supported metal catalysts. In particular, the energetic, structural and infrared adsorption characteristics of linearly (atop) CO adsorbed on transition metal nano-clusters of less than 10 Å in size were explored. Spin-unrestricted density functional theory (DFT) calculations were employed to explore the trends of CO adsorption energy (AM-CO) and C-O vibrational frequency (νCO) for clusters composed of Ni, Cu, Ru, Rh, Pd, Ag, Ir, Pt and Au. The effects of the transition metal electronic structure onto the adsorption energy of CO and the vibrational stretching frequency of C-O, and how these chemical parameters can be correlated to the catalytic activity of transition supported metal catalysts that involve the adsorption, surface diffusion, and C-O bond dissociation elementary steps in heterogeneous catalytic surface reactions, are discussed. Our findings show that an increase of the electronic d-shell occupancy and the principal quantum number (n) in transition metals causes an increase in the vibrational stretching frequency of the C-O bond. This trend is inconsistent with the classical Blyholder model for the metal-carbonyl bond.

  13. Pressure-driven metal-insulator transition in hematite from dynamical mean-field theory

    Czech Academy of Sciences Publication Activity Database

    Kuneš, Jan; Korotin, D. M.; Korotin, M. A.; Anisimov, V.I.; Werner, P.

    2009-01-01

    Roč. 102, č. 14 (2009), 146402/1-146402/4 ISSN 0031-9007 Institutional research plan: CEZ:AV0Z10100521 Keywords : metal-insulator transitions and other electronic transitions * strongly correlated electron systems * heavy fermions Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 7.328, year: 2009

  14. Planar heterostructures of single-layer transition metal dichalcogenides: Composite structures, Schottky junctions, tunneling barriers, and half metals

    Science.gov (United States)

    Aras, Mehmet; Kılıç, ćetin; Ciraci, S.

    2017-02-01

    Planar composite structures formed from the stripes of transition metal dichalcogenides joined commensurately along their zigzag or armchair edges can attain different states in a two-dimensional (2D), single-layer, such as a half metal, 2D or one-dimensional (1D) nonmagnetic metal and semiconductor. Widening of stripes induces metal-insulator transition through the confinements of electronic states to adjacent stripes, that results in the metal-semiconductor junction with a well-defined band lineup. Linear bending of the band edges of the semiconductor to form a Schottky barrier at the boundary between the metal and semiconductor is revealed. Unexpectedly, strictly 1D metallic states develop in a 2D system along the boundaries between stripes, which pins the Fermi level. Through the δ doping of a narrow metallic stripe one attains a nanowire in the 2D semiconducting sheet or narrow band semiconductor. A diverse combination of constituent stripes in either periodically repeating or finite-size heterostructures can acquire critical fundamental features and offer device capacities, such as Schottky junctions, nanocapacitors, resonant tunneling double barriers, and spin valves. These predictions are obtained from first-principles calculations performed in the framework of density functional theory.

  15. The role of METAMORPhos ligands in transition metal complex formation and catalysis

    NARCIS (Netherlands)

    Oldenhof, S.

    2015-01-01

    Chemists are challenged to develop homogeneous transition metal catalysts that are faster, more selective, cheaper, safer, robust and environmentally benign. This is generally approached by varying the ligands that are coordinated to the applied metal to steer its properties. Traditionally, ligands

  16. 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,

  17. 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,

  18. Support effects and catalytic trends for water gas shift activity of transition metals

    DEFF Research Database (Denmark)

    Boisen, Astrid; Janssens, T.V.W.; Schumacher, Nana Maria Pii

    2010-01-01

    Water gas shift activity measurements for 12 transition metals (Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Re, Ir, Pt, Au) supported on inert MgAl2O4 and Ce0.75Zr0.25O2 are presented, to elucidate the influence of the active metal and the support. The activity is related to the adsorption energy of molecular...

  19. Structures of the Dehydrogenation Products of Methane Activation by 5d Transition Metal Cations

    NARCIS (Netherlands)

    Lapoutre, V.J.F.; Redlich, B.; Meer, A.F.G.; Oomens, J.; Bakker, J.M.; Sweeney, A.; Mookherjee, A.; Armentrout, P.B.

    2013-01-01

    The activation of methane by gas-phase transition metal cations (M+) has been studied extensively, both experimentally and using density functional theory (DFT). Methane is exothermically dehydrogenated by several 5d metal ions to form [M,C,2H](+) and H-2. However, the structure of the

  20. Structures of the dehydrogenation products of methane activation by 5d transition metal cations

    NARCIS (Netherlands)

    Lapoutre, V. J. F.; Redlich, B.; van der Meer, A. F. G.; Oomens, J.; Bakker, J. M.; Sweeney, A.; Mookherjee, A.; Armentrout, P. B.

    2013-01-01

    The activation of methane by gas-phase transition metal cations (M +) has been studied extensively, both experimentally and using density functional theory (DFT). Methane is exothermically dehydrogenated by several 5d metal ions to form [M,C,2H]+ and H2. However, the structure of the dehydrogenation

  1. Production by metallothermics of pure alloys of rare earths and transition metals

    International Nuclear Information System (INIS)

    Jourdan, A.

    1988-01-01

    Industrial process of production of high purity master alloys ingots by the thermite process from a rare earth compound which is reduced by a reducing agent like alkaline or alkaline earth metals. The process is characterized by introduction of the transition metal into the initial reaction mixture, at least in part, as a compound than can be reduced by the reducing agent [fr

  2. 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

  3. Size Controlled Synthesis of Transition Metal Nanoparticles for Catalytic Applications

    KAUST Repository

    Esparza, Angel

    2011-07-07

    Catalysis offers cleaner and more efficient chemical reactions for environmental scientists. More than 90% of industrial processes are performed with a catalyst involved, however research it is still required to improve the catalyst materials. The purpose of this work is to contribute with the development of catalysts synthesis with two different approaches. First, the precise size control of non-noble metals nanoparticles. Second, a new one-pot synthesis method based on a microemulsion system was developed to synthesize size-controlled metal nanoparticles in oxide supports. The one-pot method represents a simple approach to synthesize both support and immobilized nanometer-sized non-noble metal nanoparticles in the same reaction system. Narrow size distribution nickel, cobalt, iron and cobalt-nickel nanoparticles were obtained. High metal dispersions are attainable regardless the metal or support used in the synthesis. Thus, the methodology is adaptable and robust. The sizecontrolled supported metal nanoparticles offer the opportunity to study size effects and metal-support interactions on different catalytic reactions with different sets of metals and supports.

  4. Growth and sacrificial oxidation of transition metal nanolayers

    NARCIS (Netherlands)

    T. Tsarfati,; Zoethout, E.; van de Kruijs, R.; F. Bijkerk,

    2009-01-01

    Growth and oxidation of Au, Pt, Pd, Rh, Cu, Ru, Ni and Co layers of 0.3-4.3 nm thickness on Mo have been investigated with ARPES and AFM. Co and Ni layers oxidize while the Mo remains metallic. For nobler metals, the on top O and oxidation state of subsurface Mo increase, suggesting sacrificial e(-)

  5. Growth and sacrificial oxidation of transition metal nanolayers

    NARCIS (Netherlands)

    Tsarfati, T.; Tsarfati, Tim; Zoethout, E.; Zoethout, E.; van de Kruijs, Robbert Wilhelmus Elisabeth; Bijkerk, Frederik

    2009-01-01

    Growth and oxidation of Au, Pt, Pd, Rh, Cu, Ru, Ni and Co layers of 0.3–4.3 nm thickness on Mo have been investigated with ARPES and AFM. Co and Ni layers oxidize while the Mo remains metallic. For nobler metals, the on top O and oxidation state of subsurface Mo increase, suggesting sacrificial e−

  6. Adsorption of alkali, alkaline-earth, and 3d transition metal atoms on silicene

    Science.gov (United States)

    Sahin, H.; Peeters, F. M.

    2013-02-01

    The adsorption characteristics of alkali, alkaline-earth, and transition metal adatoms on silicene, a graphene-like monolayer structure of silicon are analyzed by means of first-principles calculations. In contrast to graphene, interaction between the metal atoms and the silicene surface is quite strong due to its highly reactive buckled hexagonal structure. In addition to structural properties, we also calculate the electronic band dispersion, net magnetic moment, charge transfer, work function, and dipole moment of the metal adsorbed silicene sheets. Alkali metals, Li, Na, and K, adsorb to hollow sites without any lattice distortion. As a consequence of the significant charge transfer from alkalis to silicene, metalization of silicene takes place. Trends directly related to atomic size, adsorption height, work function, and dipole moment of the silicene/alkali adatom system are also revealed. We found that the adsorption of alkaline-earth metals on silicene is entirely different from their adsorption on graphene. The adsorption of Be, Mg, and Ca turns silicene into a narrow gap semiconductor. Adsorption characteristics of eight transition metals Ti, V, Cr, Mn, Fe, Co, Mo, and W are also investigated. As a result of their partially occupied d orbital, transition metals show diverse structural, electronic, and magnetic properties. Upon the adsorption of transition metals, depending on the adatom type and atomic radius, the system can exhibit metal, half-metal, and semiconducting behavior. For all metal adsorbates, the direction of the charge transfer is from adsorbate to silicene, because of its high surface reactivity. Our results indicate that the reactive crystal structure of silicene provides a rich playground for functionalization at nanoscale.

  7. Heterobimetallic coordination polymers involving 3d metal complexes and heavier transition metals cyanometallates

    Energy Technology Data Exchange (ETDEWEB)

    Peresypkina, Eugenia V. [Nikolaev Institute of Inorganic Chemistry, SB RAS, Novosibirsk 630090 (Russian Federation); Samsonenko, Denis G. [Nikolaev Institute of Inorganic Chemistry, SB RAS, Novosibirsk 630090 (Russian Federation); Novosibirsk State University, Novosibirsk 630090 (Russian Federation); Vostrikova, Kira E., E-mail: vosk@niic.nsc.ru [Nikolaev Institute of Inorganic Chemistry, SB RAS, Novosibirsk 630090 (Russian Federation); LMI, Université Claude Bernard Lyon 1, 69622 Villeurbanne Cedex (France)

    2015-04-15

    The results of the first steps in the design of coordination polymers based on penta- and heptacyanometallates of heavier d transitions metals are presented. The 2D structure of the coordination polymers: [(Mn(acacen)){sub 2}Ru(NO)(CN){sub 5}]{sub n} and two complexes composed of different cyanorhenates, [Ni(cyclam)]{sub 2}[ReO(OH)(CN){sub 4}](ClO{sub 4}){sub 2}(H{sub 2}O){sub 1.25} and [Cu(cyclam)]{sub 2}[Re(CN){sub 7}](H{sub 2}O){sub 12}, was confirmed by single crystal XRD study, the rhenium oxidation state having been proved by the magnetic measurements. An amorphism of [M(cyclam)]{sub 3}[Re(CN){sub 7}]{sub 2} (M=Ni, Cu) polymers does not allow to define strictly their dimensionality and to model anisotropic magnetic behavior of the compounds. However, with high probability a honey-comb like layer structure could be expected for [M(cyclam)]{sub 3}[Re(CN){sub 7}]{sub 2} complexes, studied in this work, because such an arrangement is the most common among the bimetallic assemblies of hexa- and octacyanometallates with a ratio [M(cyclam)]/[M(CN){sub n}]=3/2. For the first time was prepared and fully characterized a precursor (n-Bu{sub 4}N){sub 2}[Ru(NO)(CN){sub 5}], soluble in organic media. - Graphical abstract: The very first results in the design of 2D coordination polymers based on penta- and heptacyanometallates of 4d and5d transitions metals are presented. - Highlights: • Design of coordination polymers based on penta- and heptacyanometallates. • New Ru and Re cyanide based heterobimetallic coordination complexes. • Hydrolysis and ox/red processes involving [Re(CN){sub 7}]{sup 3+} during crystallization. • High magnetic anisotropy of [M(cyclam)]{sub 3}[Re(CN){sub 7}]{sub 2}(H{sub 2}O){sub n}, M=Cu, Ni, complexes.

  8. Recent advances in transition metal-catalyzed N -atom transfer reactions of azides

    Science.gov (United States)

    Driver, Tom G.

    2011-01-01

    Transition metal-catalyzed N-atom transfer reactions of azides provide efficient ways to construct new carbon–nitrogen and sulfur–nitrogen bonds. These reactions are inherently green: no additive besides catalyst is needed to form the nitrenoid reactive intermediate, and the by-product of the reaction is environmentally benign N2 gas. As such, azides can be useful precursors for transition metal-catalyzed N-atom transfer to sulfides, olefins and C–H bonds. These methods offer competitive selectivities and comparable substrate scope as alternative processes to generate metal nitrenoids. PMID:20617243

  9. Control of metal-insulator transition in (EDO-TTF)2SbF6

    Science.gov (United States)

    Maesato, Mitsuhiko; Nakano, Yoshiaki; Shao, Xiangfeng; Yoshida, Yukihiro; Yamochi, Hideki; Saito, Gunzi; Moreac, Alain; Ameline, Jean-Claude; Collet, Eric; Uruichi, Mikio; Yakushi, Kyuya

    2009-02-01

    We have examined the temperature dependence of optical reflectance spectra of (EDO-TTF)2SbF6 salt, and succeeded to detect the thermal hysteresis by the reflectance spectra. In order to investigate high pressure effects on the metal-insulator transition of SbF6 salt, we have performed Raman experiments under pressures up to 6 kbar. Drastic changes in the frequencies of charge sensitive C=C stretching modes suggested the pressure-induced reentrant metal-insulator-metal transition at room temperature.

  10. 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

  11. Neutral bimetallic transition metal phenoxyiminato catalysts and related polymerization methods

    Science.gov (United States)

    Marks, Tobin J [Evanston, IL; Rodriguez, Brandon A [Evanston, IL; Delferro, Massimiliano [Chicago, IL

    2012-08-07

    A catalyst composition comprising a neutral bimetallic diphenoxydiiminate complex of group 10 metals or Ni, Pd or Pt is disclosed. The compositions can be used for the preparation of homo- and co-polymers of olefinic monomer compounds.

  12. 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.

  13. Endonuclease active site plasticity allows DNA cleavage with diverse alkaline Earth and transition metal ions.

    Science.gov (United States)

    Vasu, Kommireddy; Saravanan, Matheshwaran; Nagaraja, Valakunja

    2011-09-16

    A majority of enzymes show a high degree of specificity toward a particular metal ion in their catalytic reaction. However, Type II restriction endonuclease (REase) R.KpnI, which is the first member of the HNH superfamily of REases, exhibits extraordinary diversity in metal ion dependent DNA cleavage. Several alkaline earth and transition group metal ions induce high fidelity and promiscuous cleavage or inhibition depending upon their concentration. The metal ions having different ionic radii and co-ordination geometries readily replace each other from the enzyme's active site, revealing its plasticity. Ability of R.KpnI to cleave DNA with both alkaline earth and transition group metal ions having varied ionic radii could imply utilization of different catalytic site(s). However, mutation of the invariant His residue of the HNH motif caused abolition of the enzyme activity with all of the cofactors, indicating that the enzyme follows a single metal ion catalytic mechanism for DNA cleavage. Indispensability of His in nucleophile activation together with broad cofactor tolerance of the enzyme indicates electrostatic stabilization function of metal ions during catalysis. Nevertheless, a second metal ion is recruited at higher concentrations to either induce promiscuity or inhibit the DNA cleavage. Regulation of the endonuclease activity and fidelity by a second metal ion binding is a unique feature of R.KpnI among REases and HNH nucleases. The active site plasticity of R.KpnI opens up avenues for redesigning cofactor specificities and generation of mutants specific to a particular metal ion.

  14. Extraction and Binding Efficiency of Calix[8]arene Derivative Toward Selected Transition Metals

    Directory of Open Access Journals (Sweden)

    Imdadullah Qureshi

    2008-12-01

    Full Text Available In this article we have explored the extraction efficiency as well as binding ability of calix[8]arene derivative (3 for selected transition metal ions (Co2+, Cd2+, Ni2+, Pb2+ and Cu2+. Picrate salt solutions of these metals were used in the liquid-liquid extraction experiments. It is apparent from the results that ligand 3 shows appreciable high extraction of transition metal cations, with the relative order Pb2+>Cu2+>Ni2+>Co2+>Cd2+ being observed. Highest extraction efficiency has been observed for Pb2+ and Cu2+ i.e. 95 and 91% respectively. The significant extraction and complexation ability for these metal ions may be attributed to the nature, size, structure and geometry of both ligand and metal ions.

  15. 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.

  16. 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

    2018-03-01

    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 directly addressing 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 an astonishingly 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 in order to process the spin-information.

  17. Maternal exposure to alkali, alkali earth, transition and other metals: Concentrations and predictors of exposure.

    Science.gov (United States)

    Hinwood, A L; Stasinska, A; Callan, A C; Heyworth, J; Ramalingam, M; Boyce, M; McCafferty, P; Odland, J Ø

    2015-09-01

    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. Crown Copyright © 2015. Published by Elsevier Ltd. All rights reserved.

  18. [Transition metal mediated transformations of small molecules]. Progress report

    Energy Technology Data Exchange (ETDEWEB)

    Sen, A.

    1992-10-01

    Work on organotransition metal chemistry, homogeneous and heterogeneous catalysis is summarized. Several cationic palladium(II) complexes with bulky phosphine or pyridine ligands were discovered that are highly selective catalysts for linear dimerization of vinyl monomers and linear polymerization of p-divinylbenzene, the reactions proceeding through a carbocationic mechanism. Our studies were continued on alternating olefin-carbon monoxide copolymers. The copolymerization reaction and reactivity of copolymers were examined. New catalytic systems for alternating copolymerization of {alpha}-olefins with CO were discovered. In the case of styrene derivatives, tactic copolymers were obtained. Poly(ethylenepyrrolediyl) derivatives were synthesized from alternating ethylene-carbon monoxide copolymer and become electronic conductors when doped with iodine. A catalytic system for direct synthesis of polyureas and polyoxamides from and diamines was also discovered. Pt metal catalyzed the oxidation of ethers, esters, and amines to carboxylic acids and the oxidation of olefins to 1,2-diols. Anaerobic and aerobic decomposition of molybdenum(VI)-oxoalkyl compounds were studied for heterogeneous oxidation of alkanes and olefins on Mo(VI)-oxide surfaces. Synthesis of polymer-trapped metal, metal oxide, and metal sulfide nanoclusters (size <1--10 nm) was studied.

  19. Study of distorted octahedral structure in 3d transition metal complexes using XAFS

    Science.gov (United States)

    Gaur, A.; Nitin Nair, N.; Shrivastava, B. D.; Das, B. K.; Chakrabortty, Monideepa; Jha, S. N.; Bhattacharyya, D.

    2018-01-01

    Distortion in octahedral structure of 3d transition metal complexes (Mn, Fe, Co, Ni, Cu, Zn) has been studied using XAFS showing divergent nature of Cu complex. EXAFS analysis showed elongated metal-oxygen bonds for Cu complex leading to more distorted structure. Derivative XANES spectrum at Cu K-edge exhibits splitting of main edge which is correlated to elongated Cu-O bond length. Using these coordination geometry around metal centers, theoretical XANES spectra have been generated and features observed have been correlated to the corresponding metals p-DOS. It has been shown that distorted octahedral field in Cu complex is responsible for splitting of p-DOS.

  20. Correlation functions between specific volume and stoichiometry for transition metal nitrides

    International Nuclear Information System (INIS)

    Soto, G.; Aparicio, E.; Avalos-Borja, M.

    2005-01-01

    A methodology is proposed to correlate the structural aspects of transition metal nitrides (TMN) to the stoichiometric ratio: x = [N]/[M]. The method is based on a numeric figure, υ, given by the difference between the atomic concentrations of nitride and parent metal normalized to the atomic concentration of parent metal. Numerical regression is used to construct interpolating functions for υ(x) using as input the available data for TMN in two well-recognized databases (ICDD and ICSD). In summary we obtain functions of x that describe the deformation caused in the parent metal lattice by the nitrogen assimilation. The results are attractive, since TMN show remarkable trends

  1. 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

  2. Study of the metal-insulator transition and superconducting correlations of a generalized Hubbard model

    Science.gov (United States)

    Arrachea, Liliana; Aligia, A. A.; Gagliano, E.

    1996-02-01

    We study the metal-insulator transition of a generalized Hubbard model in which the magnitude of the nearest-neighbor hopping depends on the occupations of the sites involved. Numerical results for finite chains at half-filling show that when 0 0 for which the system is metallic. This is consistent with a Hartree-Fock calculation. The metallic phase collapses to one point, U = 0, in the Hubbard limit. In the metallic phase we obtain that the superconducting correlations are the dominant ones, at least for doped systems.

  3. 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.

  4. Semiconductor-to-metal transition in trans-polyacetylene (the role of correlated solitons

    Directory of Open Access Journals (Sweden)

    S. A. Ketabi

    2004-06-01

    Full Text Available  In this study the nature of transition to metallic regime in trans-polyacetylene (trans-PA is investigated. Based on Su-Schrieffer-Heeger (SSH model and the use of Continued - Fraction Representation (CFR as well as Lanczos algorithm procedure, we studied the effects of some selected soliton distributions on the semiconductor-to-metal transition in trans-PA.We found that,this transition occurs only when there exists a soliton sublattice in trans-PA, disordered soliton distributions and soliton clustering are the origin of the metallic transition in trans-PA, that is consistent with the experimental data. Our results show that in the presence of correlation between solitons, the disorder in accompanying single soliton distributions plays a crucial role in inducing the transition to metallic regime, so that in contrast to Anderson’s localization theorem, the electronic states near the Fermi level are extended, that is the most significant criteria for the metallic regime .

  5. 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

  6. Surface free energy of alkali and transition metal nanoparticles

    International Nuclear Information System (INIS)

    Aqra, Fathi; Ayyad, Ahmed

    2014-01-01

    Graphical abstract: Size dependent surface free energy of spherical, cubic and disk Au nanoparticles. - Highlights: • A model to account for the surface free energy of metallic nanoparticles is described. • The model requires only the cohesive energy of the nanoparticle. • The surface free energy of a number of metallic nanoparticles has been calculated, and the obtained values agree well with existing data. • Surface energy falls down very fast when the number of atoms is less than hundred. • The model is applicable to any metallic nanoparticle. - Abstract: This paper addresses an interesting issue on the surface free energy of metallic nanoparticles as compared to the bulk material. Starting from a previously reported equation, a theoretical model, that involves a specific term for calculating the cohesive energy of nanoparticle, is established in a view to describe the behavior of surface free energy of metallic nanoparticles (using different shapes of particle: sphere, cube and disc). The results indicate that the behavior of surface energy is very appropriate for spherical nanoparticle, and thus, it is the most realistic shape of a nanoparticle. The surface energy of copper, silver, gold, platinum, tungsten, molybdenum, tantalum, paladium and alkali metallic nanoparticles is only prominent in the nanoscale size, and it decreases with the decrease of nanoparticle size. Thus, the surface free energy plays a more important role in determining the properties of nanoparticles than in bulk materials. It differs from shape to another, and falls down as the number of atoms (nanoparticle size) decreases. In the case of spherical nanoparticles, the onset of the sharp decrease in surface energy is observed at about 110 atom. A decrease of 16% and 45% in surface energy is found by moving from bulk to 110 atom and from bulk to 5 atom, respectively. The predictions are consistent with the reported data

  7. 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.

  8. 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.

  9. Transition metal catalysed Grignard-like allylic activation across ...

    Indian Academy of Sciences (India)

    Unknown

    Contemporary chemistry is characterized by the number and variety of topics, which cut across traditional divides. The interest in combining transition and main group elements to generate new structural motifs, often clusters, provides distinct opportunities in the field of catalysis. In this direction, ligand-assisted ...

  10. Hydrogenation-controlled phase transition on two-dimensional transition metal dichalcogenides and their unique physical and catalytic properties

    Science.gov (United States)

    Qu, Yuanju; Pan, Hui; Kwok, Chi Tat

    2016-01-01

    Two-dimensional (2D) transition metal dichalcogenides (TMDs) have been widely used from nanodevices to energy harvesting/storage because of their tunable physical and chemical properties. In this work, we systematically investigate the effects of hydrogenation on the structural, electronic, magnetic, and catalytic properties of 33 TMDs based on first-principles calculations. We find that the stable phases of TMD monolayers can transit from 1T to 2H phase or vice versa upon the hydrogenation. We show that the hydrogenation can switch their magnetic and electronic states accompanying with the phase transition. The hydrogenation can tune the magnetic states of TMDs among non-, ferro, para-, and antiferro-magnetism and their electronic states among semiconductor, metal, and half-metal. We further show that, out of 33 TMD monolayers, 2H-TiS2 has impressive catalytic ability comparable to Pt in hydrogen evolution reaction in a wide range of hydrogen coverages. Our findings would shed the light on the multi-functional applications of TMDs. PMID:27686869

  11. studies on transition metal complexes of herbicidal compounds. ii

    African Journals Online (AJOL)

    a

    donor and it forms binuclear octahedral metal complexes, possessing alkoxide bridging. Cobalt(II) complex exhibits thermochromism. Antimicrobial studies on ..... coordination. N1 or N3 may be involved in this process (Figure 1) [18-20]. (iii) Positive shifts in ν(C-O) and ν(N-H) are strong indications of the participation of the.

  12. Schiff base transition metal complexes for Suzuki–Miyaura cross ...

    Indian Academy of Sciences (India)

    RASHEEDA M ANSARI

    2017-08-19

    Aug 19, 2017 ... Abstract. Schiff base ligand and its complex with iron (Fe), cobalt (Co), nickel (Ni) and copper (Cu) ions were synthesized using 4-aminoacetophenone and salicylaldehyde and characterized. FTIR spectrum shows that bidentate coordination of metal ions with ligand where O, N are electron donating sites of ...

  13. A new Mannich base and its transition metal (II) complexes ...

    Indian Academy of Sciences (India)

    Unknown

    some metal complexes of this type of Mannich base and investigate its bonding characteristics. We herein report a new Mannich base, N-(1-morpholinoben- zyl) semicarbazide formed by the three-component condensation, containing active hydrogen on nitro- gen (morpholine), benzaldehyde and semicarbazide.

  14. Schiff base transition metal complexes for Suzuki–Miyaura cross ...

    Indian Academy of Sciences (India)

    Schiff base ligand and its complex with iron (Fe), cobalt (Co), nickel (Ni) and copper (Cu) ions were synthesized using 4-aminoacetophenone and salicylaldehyde and characterized. FTIR spectrum shows that bidentate coordination of metal ions with ligand where O, N are electron donating sites of azomethine group.

  15. Enhancement of Platinum Cathode Catalysis by Addition of Transition Metals

    Science.gov (United States)

    Duong, Hung Tuan

    2009-01-01

    The sluggish kinetics of oxygen reduction reaction (ORR) contributes significantly to the loss of cathode overpotential in fuel cells, thus requiring high loadings of platinum (Pt), which is an expensive metal with limited supply. However, Pt and Pt-based alloys are still the best available electrocatalysts for ORR thus far. The research presented…

  16. Volume variation of Gruneisen parameters of fcc transition metals

    Indian Academy of Sciences (India)

    Unknown

    average discrepancy between the values of γ measured by various methods for 23 metals. Experimentally only the total Gruneisen parameter can be measured. The total. Gruneisen parameter is the sum of lattice, electronic and probably magnetic contribution. The letter term is present in palladium (White and Pawlok 1970) ...

  17. Transition Metal Sulfide Hydrogen Evolution Catalysts for Hydrobromic Acid Electrolysis

    NARCIS (Netherlands)

    Ivanovskaya, Anna; Singh, Nirala; Liu, Ru-Fen; Kreutzer, Haley; Baltrusaitis, Jonas; Nguyen, Trung Van; Metiu, Horia; McFarland, Eric

    2013-01-01

    Mixed metal sulfides containing combinations of W, Fe, Mo, Ni, and Ru were synthesized and screened for activity and stability for the hydrogen evolution reaction (HER) in aqueous hydrobromic acid (HBr). Co- and Ni-substituted RuS2 were identified as potentially active HER electrocatalysts by

  18. Transition metal chemistry of hydroxy(–OH)-rich molecules ...

    Indian Academy of Sciences (India)

    Administrator

    Appropriately designed hydroxy(–OH) containing Schiff's base and Mannich base molecules have been recently found to be important for development of the coordination chemistry of a number of metal ions in the biomimetic chemistry of metalloenzymes. In this context, our group has studied the coordination role of these ...

  19. Computational study of 5d transition metal mononitrides and ...

    Indian Academy of Sciences (India)

    Administrator

    Density functional method; 5d-metal; mononitrides; monoborides. 1. Introduction. Clusters containing a few to thousands of atoms are of scientific importance. In this regime, their physical and chemical properties change with their size. Therefore, the clusters often demonstrate many unexpected characteris- tics different from ...

  20. Synthesis of first row transition metal carboxylate complexes by ring ...

    Indian Academy of Sciences (India)

    Home; Journals; Journal of Chemical Sciences; Volume 123; Issue 2 ... Metal carboxylates; ring opening reactions; cyclic anhydrides; structural study. Abstract. Hydrolytic and solvolytic ring opening reactions of phthalic anhydride, pyromellitic dianhydride and 2,3-pyridine dicarboxylic anhydride in the presence of various ...

  1. Sub-chronic toxicological studies of transition metal complexes of ...

    African Journals Online (AJOL)

    However, Naproxen metal complexes showed comparatively lower side effects than naproxen. Hematological report suggested that naproxen was in process of initiating inflammation which was justified by decreasing the mean value hemoglobin and hematocrit level and increasing the white blood cells level. There were ...

  2. Textural and morphological studies of transition metal doped SBA ...

    Indian Academy of Sciences (India)

    rials with short and open channels are well explored because they are more ..... is important to note that the increase in unit cell con- stant, ao is not .... The strik- ing improvement in textural parameters suggests that the metal salts promote the silica condensation as a result possesses thicker pore walls. 3.3 TG Analysis.

  3. Schiff base transition metal complexes for Suzuki–Miyaura cross

    Indian Academy of Sciences (India)

    Schiff base ligand and its complex with iron (Fe), cobalt (Co), nickel (Ni) and copper (Cu) ions were synthesized using 4-aminoacetophenone and salicylaldehyde and characterized. FTIR spectrum shows that bidentate coordination of metal ions with ligand where O, N are electron donating sites of azomethine group.

  4. Synthesis, spectral characterization of Schiff base transition metal ...

    Indian Academy of Sciences (India)

    The UV-Vis, magnetic susceptibility and ESR spectral data of the complexes suggest a square-planar geometry around the central metal ion except VO(IV) complex which has square-pyramidal geometry. The redox behaviour of copper and vanadyl complexes was studied by cyclic voltammetry. Antimicrobial screening tests ...

  5. 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.

  6. Global transcriptome and deletome profiles of yeast exposed to transition metals.

    Directory of Open Access Journals (Sweden)

    Yong Hwan Jin

    2008-04-01

    Full Text Available A variety of pathologies are associated with exposure to supraphysiological concentrations of essential metals and to non-essential metals and metalloids. The molecular mechanisms linking metal exposure to human pathologies have not been clearly defined. To address these gaps in our understanding of the molecular biology of transition metals, the genomic effects of exposure to Group IB (copper, silver, IIB (zinc, cadmium, mercury, VIA (chromium, and VB (arsenic elements on the yeast Saccharomyces cerevisiae were examined. Two comprehensive sets of metal-responsive genomic profiles were generated following exposure to equi-toxic concentrations of metal: one that provides information on the transcriptional changes associated with metal exposure (transcriptome, and a second that provides information on the relationship between the expression of approximately 4,700 non-essential genes and sensitivity to metal exposure (deletome. Approximately 22% of the genome was affected by exposure to at least one metal. Principal component and cluster analyses suggest that the chemical properties of the metal are major determinants in defining the expression profile. Furthermore, cells may have developed common or convergent regulatory mechanisms to accommodate metal exposure. The transcriptome and deletome had 22 genes in common, however, comparison between Gene Ontology biological processes for the two gene sets revealed that metal stress adaptation and detoxification categories were commonly enriched. Analysis of the transcriptome and deletome identified several evolutionarily conserved, signal transduction pathways that may be involved in regulating the responses to metal exposure. In this study, we identified genes and cognate signaling pathways that respond to exposure to essential and non-essential metals. In addition, genes that are essential for survival in the presence of these metals were identified. This information will contribute to our

  7. Transition metal complexes supported on metal-organic frameworks for heterogeneous catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Farha, Omar K.; Hupp, Joseph T.; Delferro, Massimiliano; Klet, Rachel C.

    2017-02-07

    A robust mesoporous metal-organic framework comprising a hafnium-based metal-organic framework and a single-site zirconium-benzyl species is provided. The hafnium, zirconium-benzyl metal-organic framework is useful as a catalyst for the polymerization of an alkene.

  8. Fabrication of carbon nanotube films from alkyne-transition metal complexes

    Science.gov (United States)

    Iyer, Vivekanantan S.; Vollhardt, K. Peter C.

    2007-08-28

    A simple method for the production or synthesis of carbon nanotubes as free-standing films or nanotube mats by the thermal decomposition of transition metal complexed alkynes with aryl, alkyl, alkenyl, or alkynyl substituents. In particular, transition metal (e.g. Co, Ni, Fe, Mo) complexes of diarylacetylenes, e.g. diphenylacetylene, and solid mixtures of these complexes with suitable, additional carbon sources are heated in a vessel. More specifically, the heating of the transition metal complex is completed at a temperature between 400-800.degree. C. and more particularly 550-700.degree. C. for between 0.1 to 24 hours and more particularly 0.5-3 hours in a sealed vessel under a partial pressure of argon or helium.

  9. 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.

  10. 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.

  11. Prebiotic coordination chemistry: The potential role of transition-metal complexes in the chemical evolution

    Science.gov (United States)

    Beck, M.

    1979-01-01

    In approaching the extremely involved and complex problem of the origin of life, consideration of the coordination chemistry appeared not only as a possibility but as a necessity. The first model experiments appear to be promising because of prebiotic-type synthesis by means of transition-metal complexes. It is especially significant that in some instances various types of vitally important substances (nucleic bases, amino acids) are formed simultaneously. There is ground to hope that systematic studies in this field will clarify the role of transition-metal complexes in the organizatorial phase of chemical evolution. It is obvious that researchers working in the fields of the chemistry of cyano and carbonyl complexes, and of the catalytic effect of transition-metal complexes are best suited to study these aspects of the attractive and interesting problem of the origin of life.

  12. 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.

  13. Influence of the inert and active ion bombardment on structure of the transition metal thin films

    CERN Document Server

    Blazhevich, S; Martynov, I; Neklyudov, I

    2002-01-01

    The results of the experimental research of the inert (He, Ne, Ar, Kr, Xe) and active (O, N) ion impact on the transition metal structure are presented. Thin high-purity (99.999 at.%) films of nickel, chrome and iron were used in the experiment. The bombardment was realized under room temperature at high vacuum (P<1x10 sup - sup 7 Pa) by a separated ion beam of 10-10 sup 3 keV. As a main result of the experiment, the full absence of crystal matrix changes was ascertained for all the transition metals irradiated by inert gas ions. The chemical nature of the crystal structure changes observed in transition metals being under active ion bombardment was found out too.

  14. A theoretical evaluation of possible transition metal electro-catalysts for N2 reduction

    DEFF Research Database (Denmark)

    Skulason, Egill; Bligaard, Thomas; Gudmundsdottir, Sigrıdur

    2012-01-01

    Theoretical studies of the possibility of forming ammonia electrochemically at ambient temperature and pressure are presented. Density functional theory calculations were used in combination with the computational standard hydrogen electrode to calculate the free energy profile for the reduction...... of N2 admolecules and N adatoms on several close-packed and stepped transition metal surfaces in contact with an acidic electrolyte. Trends in the catalytic activity were calculated for a range of transition metal surfaces and applied potentials under the assumption that the activation energy barrier...... scales with the free energy difference in each elementary step. The most active surfaces, on top of the volcano diagrams, are Mo, Fe, Rh, and Ru, but hydrogen gas formation will be a competing reaction reducing the faradaic efficiency for ammonia production. Since the early transition metal surfaces...

  15. 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.

  16. 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)

  17. 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)

  18. Dimensional effects in a disordered system near metal-insulator transitions and superconductor-insulator transitions; Effets dimensionnels dans un systeme desordonne au voisinage des transitions metal-isolant et supraconducteur-isolant

    Energy Technology Data Exchange (ETDEWEB)

    Akiko Marrache-Kikuchi, C

    2006-02-15

    Low temperature transport in disordered conducting materials implies quantum interference, Coulomb repulsion, and superconducting fluctuations. Since 2-D is the lower critical dimension for the existence of metallic and superconducting states, we have studied two quantum phase transitions - the Superconductor-to-Insulator Transition (SIT) and the Metal-to-Insulator Transition (MIT) - when the thickness of a disordered system - here a-NbSi - is lowered. The underlying problem is the transition between the different states and the conditions for a 2-D metal to exist. We have studied the field and disorder-induced SIT. The principal characteristics we have observed (renormalization, role of the field orientation) are well explained by M.P.A. Fisher's theory. However, we do not find the critical exponents values and a universal resistance at the transition as predicted by this theory. Concerning the MIT, we have decreased the thickness of a metallic system to reach the dimension 2 and an insulating state. In both transitions, the passage to the insulating state clearly shows the existence of dissipative states at zero temperature that are not predicted by conventional theories. We propose an interpretation of all our results that implies the existence of a novel phase in 2-D, a Bose Metal, between the superconducting and the metallic states. This new state has been predicted by recent theories. We trace the corresponding phase diagram for the model system NbSi with respect to concentration and film thickness. In the second appendix it is shown how superconducting thin films of Nb{sub x}Si{sub 1-x} are used to make transition edge sensors used in the particle detection field. (author)

  19. 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

  20. 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.

  1. 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.

  2. Direct measurement and modulation of single-molecule coordinative bonding forces in a transition metal complex

    DEFF Research Database (Denmark)

    Hao, Xian; Zhu, Nan; Gschneidtner, Tina

    2013-01-01

    remain a daunting challenge. Here we demonstrate an interdisciplinary and systematic approach that enables measurement and modulation of the coordinative bonding forces in a transition metal complex. Terpyridine is derived with a thiol linker, facilitating covalent attachment of this ligand on both gold...... substrate surfaces and gold-coated atomic force microscopy tips. The coordination and bond breaking between terpyridine and osmium are followed in situ by electrochemically controlled atomic force microscopy at the single-molecule level. The redox state of the central metal atom is found to have......Coordination chemistry has been a consistently active branch of chemistry since Werner's seminal theory of coordination compounds inaugurated in 1893, with the central focus on transition metal complexes. However, control and measurement of metal-ligand interactions at the single-molecule level...

  3. Systematic group-specific trends for point defects in bcc transition metals: An ab initio study

    International Nuclear Information System (INIS)

    Nguyen-Manh, D.; Dudarev, S.L.; Horsfield, A.P.

    2007-01-01

    Density functional theory calculations have been performed to study the systematic trends of point defect behaviours in bcc transition metals. We found that in all non-magnetic bcc transition metals, the most stable self-interstitial atom (SIAs) defect configuration has the symmetry. The calculated formation energy differences between the dumbbell and the lowest-energy configuration of metals in group 5B (V, Nb, Ta) are consistently larger than those of the corresponding element in group 6B (Cr, Mo, W). The predicted trends of SIA defects are fundamentally different from those in ferromagnetic α-Fe and correlate very well with the pronounced group-specific variation of thermally activated migration of SIAs under irradiation depending on the position of bcc metals in the periodic table

  4. 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.

  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. Transition-metal-catalyzed hydrogen-transfer annulations: access to heterocyclic scaffolds.

    Science.gov (United States)

    Nandakumar, Avanashiappan; Midya, Siba Prasad; Landge, Vinod Gokulkrishna; Balaraman, Ekambaram

    2015-09-14

    The ability of hydrogen-transfer transition-metal catalysts, which enable increasingly rapid access to important structural scaffolds from simple starting materials, has led to a plethora of research efforts on the construction of heterocyclic scaffolds. Transition-metal-catalyzed hydrogen-transfer annulations are environmentally benign and highly atom-economical as they release of water and hydrogen as by-product and utilize renewable feedstock alcohols as starting materials. Recent advances in this field with respect to the annulations of alcohols with various nucleophilic partners, thus leading to the formation of heterocyclic scaffolds, are highlighted herein. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Lattice vibrational properties of transition metal carbides (TiC, ZrC ...

    Indian Academy of Sciences (India)

    Transition metal carbides (TiC, ZrC, HfC, NbC and TaC) are complex crystals with significant ionic, ... ×(S + K + Y mC Y m)−1(TT + Y mC Zm),. (1) where K ... Lattice vibrational properties of transition metal carbides. Table 1. Model parameters for TiC, ZrC and HfC. TiC. ZrC. HfC f0(r0). 0.0250. 0.0300. 0.0070 r0f0(r0). −0.3240.

  8. Density functional studies of functionalized graphitic materials with late transition metals for oxygen reduction reactions

    DEFF Research Database (Denmark)

    Vallejo, Federico Calle; Martinez, Jose Ignacio; Rossmeisl, Jan

    2011-01-01

    Reaction (OER). Spin analyses suggest that the oxidation state of those elements in the active sites should in general be +2. Moreover, our results verify that the adsorption behavior of transition metals is not intrinsic, since it can be severely altered by changes in the local geometry of the active site......) at the cathode. In this contribution, on the basis of Density Functional Theory (DFT) calculations, we show that graphitic materials with active sites composed of 4 nitrogen atoms and transition metal atoms belonging to groups 7 to 9 in the periodic table are active towards ORR, and also towards Oxygen Evolution...

  9. Transition-metal ions in Nd-doped glasses: spectra and effects on Nd fluorescence

    International Nuclear Information System (INIS)

    Stokowski, S.E.; Krashkevich, D.

    1985-01-01

    We have measured transition-metal ion (Ti, V, Cr, Mn, Fe, Co, Ni, Cu) spectra and their effects on Nd fluorescence quenching in Nd-doped phosphate and silicate glasses. Our purpose was to determine the maximum allowable impurity content given particular limits on the absorption loss at 1053 nm and the Nd fluorescence quenching rate. To keep the absorption loss -1 the transition-metal impurity content should be kept below 0.5 ppMw. To keep the increase in the Nd fluorescence decay rate below 1%, the impurity content should be 20 cm -3

  10. Suppression of angular forces in collisions of non-S-state transition metal atoms

    International Nuclear Information System (INIS)

    Krems, R.V.; Klos, J.; Rode, M.F.; Szczesniak, M.M.; Chalasinski, G.; Dalgarno, A.

    2005-01-01

    Angular momentum transfer is expected to occur rapidly in collisions of atoms in states of nonzero angular momenta due to the large torque of angular forces. We show that despite the presence of internal angular momenta transition metal atoms interact in collisions with helium effectively as spherical atoms and angular momentum transfer is slow. Thus, magnetic trapping and sympathetic cooling of transition metal atoms to ultracold temperatures should be readily achievable. Our results open up new avenues of research with a broad class of ultracold atoms

  11. 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.

  12. Metal-insulator phase transition in hydrogenated thin films of V2O3

    Science.gov (United States)

    Andreev, V. N.; Klimov, V. A.; Kompan, M. E.

    2017-12-01

    Temperature dependences of the electrical conductivity of thin vanadium sesquioxide V2O3 films obtained by using the laser sputtering technique have been studied. A significant decrease (by four-five orders of magnitude) in the electrical conductivity has been observed below 150 K as a result of a metal-insulator phase transition. It is shown that hydrogenation of films lowers the temperature of this phase transition.

  13. 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....

  14. 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.

  15. 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.

  16. 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

  17. Studies of high temperature ternary phases in mixed-metal-rich early transition metal sulfide and phosphide systems

    Energy Technology Data Exchange (ETDEWEB)

    Marking, Gregory Allen [Iowa State Univ., Ames, IA (United States)

    1994-01-04

    Investigations of ternary mixed early transition metal-rich sulfide and phosphide systems resulted in the discovery of new structures and new phases. A new series of Zr and Hf - group V transition metal - sulfur K-phases was synthesized and crystallographically characterized. When the group V transition metal was Nb or Ta, the unit cell volume was larger than any previously reported K-phase. The presence of adventitious oxygen was determined in two K-phases through a combination of neutron scattering and X-ray diffraction experiments. A compound Hf10Ta3S3 was found to crystallize in a new-structure type similar to the known gamma brasses. This structure is unique in that it is the only reported "stuffed" gamma-brass type structure. The metal components, Hf and Ta, are larger in size and more electropositive than the metals found in normal gamma brasses (e.g. Cu and Zn) and because of the larger metallic radii, sulfur can be incorporated into the structure where it plays an integral role in stabilizing this phase relative to others. X-ray single-crystal, X-ray powder and neutron powder refinements were performed on this structure. A new structure was found in the ternary Nb-Zr-P system which has characteristics in common with many known early transition metal-rich sulfides, selenides, and phosphides. This structure has the simplest known interconnection of the basic building blocks known for this structural class. Anomalous scattering was a powerful tool for differentiating between Zr and Nb when using Mo Kα X-radiation. The compounds ZrNbP and HfNbP formed in the space group Prima with the simple Co2Si structure which is among the most common structures found for crystalline solid materials. Solid solution compounds in the Ta-Nb-P, Ta-Zr-P, Nb-Zr-P, Hf-Nb-P, and Hf-Zr-S systems were crystallographically characterized. The structural information corroborated ideas about bonding in metal-rich compounds.

  18. Dysregulation of transition metal ion homeostasis is the molecular basis for cadmium toxicity in Streptococcus pneumoniae

    OpenAIRE

    Begg, Stephanie L.; Eijkelkamp, Bart A.; Luo, Zhenyao; Cou?ago, Rafael M.; Morey, Jacqueline R.; Maher, Megan J.; Ong, Cheryl-lynn Y.; McEwan, Alastair G.; Kobe, Bostjan; O?Mara, Megan L.; Paton, James C.; McDevitt, Christopher A.

    2015-01-01

    Cadmium is a transition metal ion that is highly toxic in biological systems. Although relatively rare in the Earth?s crust, anthropogenic release of cadmium since industrialization has increased biogeochemical cycling and the abundance of the ion in the biosphere. Despite this, the molecular basis of its toxicity remains unclear. Here we combine metal-accumulation assays, high-resolution structural data and biochemical analyses to show that cadmium toxicity, in Streptococcus pneumoniae, occu...

  19. Approach to Multifunctional Device Platform with Epitaxial Graphene on Transition Metal Oxide (Postprint)

    Science.gov (United States)

    2015-09-23

    layers, respectively. 15. SUBJECT TERMS Heterostructures, two-dimensional materials, van der Waals interaction , 2D graphene, metal oxide (TiO2...sample holder with a 10.6 μ m CO2 IR laser . The laser output power was adjusted until the target temperature was reached. The temperature of the sample... Laser Deposited Transition- Metal Carbides for Field-Emission Cathode Coatings. ACS Appl. Mater. Interfaces 5, 9241–9246 (2013). 13. Swift, G. A

  20. 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.

  1. A DFT study of the transition metal promotion effect on ethylene chemisorption on Co(0 0 0 1)

    Science.gov (United States)

    Cheng, Jun; Hu, P.; Ellis, Peter; French, Sam; Kelly, Gordon; Lok, C. Martin

    2009-09-01

    Transition metals are often introduced to a catalyst as promoters to improve catalytic performance. In this work, we study the promotion effect of transition metals on Co, the preferred catalytic metal for Fischer-Tropsch synthesis because of its good compromise of activity, selectivity and stability, for ethylene chemisorption using density functional theory (DFT) calculations, aiming to provide some insight into improving the α-olefin selectivity. In order to obtain the general trend of influence on ethylene chemisorption, twelve transition metals (Zr, Mn, Re, Ru, Rh, Ir, Ni, Pd, Pt, Cu, Ag and Au) are calculated. We find that the late transition metals (e.g. Pd and Cu) can decrease ethylene chemisorption energy. These results suggest that the addition of the late transition metals may improve α-olefin selectivity. Electronic structure analyses (both charge density distributions and density of states) are also performed and the understanding of calculated results is presented.

  2. Phase transitions and adsorbate restructuring at metal surface

    CERN Document Server

    King, DA

    1994-01-01

    The objective in initiating this series in 1980 was to provide an in-depth review of advances made in the understanding key aspects of surface chemistry and physics through the application of new techniques to the study of well-defined surfaces. Since then the field of surface science has greatly matured, and further important techniques, particularly scanning probe microscopies, have been successfully assimilated into the applications armoury of the surface scientist. The present volume is a series of timely reviews by many of the current experts in the field of phase transitions an

  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. Emergent magnetism at transition-metal-nanocarbon interfaces.

    Science.gov (United States)

    Al Ma'Mari, Fatma; Rogers, Matthew; Alghamdi, Shoug; Moorsom, Timothy; Lee, Stephen; Prokscha, Thomas; Luetkens, Hubertus; Valvidares, Manuel; Teobaldi, Gilberto; Flokstra, Machiel; Stewart, Rhea; Gargiani, Pierluigi; Ali, Mannan; Burnell, Gavin; Hickey, B J; Cespedes, Oscar

    2017-05-30

    Charge transfer at metallo-molecular interfaces may be used to design multifunctional hybrids with an emergent magnetization that may offer an eco-friendly and tunable alternative to conventional magnets and devices. Here, we investigate the origin of the magnetism arising at these interfaces by using different techniques to probe 3d and 5d metal films such as Sc, Mn, Cu, and Pt in contact with fullerenes and rf-sputtered carbon layers. These systems exhibit small anisotropy and coercivity together with a high Curie point. Low-energy muon spin spectroscopy in Cu and Sc-C 60 multilayers show a quick spin depolarization and oscillations attributed to nonuniform local magnetic fields close to the metallo-carbon interface. The hybridization state of the carbon layers plays a crucial role, and we observe an increased magnetization as sp 3 orbitals are annealed into sp 2 -π graphitic states in sputtered carbon/copper multilayers. X-ray magnetic circular dichroism (XMCD) measurements at the carbon K edge of C 60 layers in contact with Sc films show spin polarization in the lowest unoccupied molecular orbital (LUMO) and higher π*-molecular levels, whereas the dichroism in the σ*-resonances is small or nonexistent. These results support the idea of an interaction mediated via charge transfer from the metal and dz -π hybridization. Thin-film carbon-based magnets may allow for the manipulation of spin ordering at metallic surfaces using electrooptical signals, with potential applications in computing, sensors, and other multifunctional magnetic devices.

  5. Progress in calculations of the superconducting properties of transition metals

    International Nuclear Information System (INIS)

    Butler, W.H.

    1979-01-01

    First principles calculations of the electron--phonon parameters of d-band metals can now be performed to an accuracy of about 10% for averaged quantities such as the mass enhancement or the room temperature resistivity. Quantities such as the spectral function α 2 F(ω) or the phonon linewidth which describe the electron--phonon interaction in more detail can also be calculated. Agreement between calculated and experimental phonon linewidths is generally good but there are differences between the experimental and calculated versions of α 2 F(ω). Calculations of the thermodynamic critical field and the upper critical field for Nb agree well with experiment

  6. Transistor-like behavior of transition metal complexes

    DEFF Research Database (Denmark)

    Albrecht, Tim; Guckian, A; Ulstrup, Jens

    2005-01-01

    Electron transport through semiconductor and metallic nanoscale structures,(1) molecular monolayers,2-6 and single molecules(7-15) connected to external electrodes display rectification, switch, and staircase functionality of potential importance in future miniaturization of electronic devices...... the redox level is brought into the energy window between the Fermi levels of the electrodes by the overpotential ("gate voltage"). The current-voltage characteristics for two Os(II)/(III) complexes have been characterized systematically and supported by theoretical frames based on molecular charge...

  7. H-D exchange and other reactions of saturated hydrocarbons in solutions of transition metal complexes

    International Nuclear Information System (INIS)

    Shilov, A.E.; Shteinman, A.A.

    1975-01-01

    Heating methane, ethane and other paraffins with solutions of chlorides of Pt(II) or Pt(IV) in heavy water there was H-D exchange of D 2 O with RH molecule. The reaction was inhibited by chloride ions and accompanied by reduction of metal compounds. The investigation of kinetics and mechanism of these reactions has shown that alkyl derivatives of transition metals are the intermediates, the reaction rate increases with electron accepting properties of metal complexes and electron donating properties of C-H containing compounds. C-H bond was found to be activated to some reactions of substitution and dehydrogenation as well. (K.A.)

  8. Controlled incorporation of mid-to-high Z transition metals in CVD diamond

    Energy Technology Data Exchange (ETDEWEB)

    Biener, M M; Biener, J; Kucheyev, S O; Wang, Y M; El-Dasher, B; Teslich, N E; Hamza, A V; Obloh, H; Mueller-Sebert, W; Wolfer, M; Fuchs, T; Grimm, M; Kriele, A; Wild, C

    2010-01-08

    We report on a general method to fabricate transition metal related defects in diamond. Controlled incorporation of Mo and W in synthetic CVD diamond was achieved by adding volatile metal precursors to the diamond chemical vapor deposition (CVD) growth process. Effects of deposition temperature, grain structure and precursor exposure on the doping level were systematically studied, and doping levels of up to 0.25 at.% have been achieved. The metal atoms are uniformly distributed throughout the diamond grains without any indication of inclusion formation. These results are discussed in context of the kinetically controlled growth process of CVD diamond.

  9. Using scaling relations to understand trends in the catalytic activity of transition metals

    International Nuclear Information System (INIS)

    Jones, G; Bligaard, T; Abild-Pedersen, F; Noerskov, J K

    2008-01-01

    A method is developed to estimate the potential energy diagram for a full catalytic reaction for a range of late transition metals on the basis of a calculation (or an experimental determination) for a single metal. The method, which employs scaling relations between adsorption energies, is illustrated by calculating the potential energy diagram for the methanation reaction and ammonia synthesis for 11 different metals on the basis of results calculated for Ru. It is also shown that considering the free energy diagram for the reactions, under typical industrial conditions, provides additional insight into reactivity trends

  10. Formation of difluorosulfane complexes of the third row transition metals by sulfur-to-metal fluorine migration in trifluorosulfane metal complexes: the anomaly of trifluorosulfane iridium tricarbonyl.

    Science.gov (United States)

    Gao, Xiaozhen; Li, Nan; King, R Bruce

    2014-12-01

    The stability of the experimentally known complex (Et3P)2Ir(CO)(Cl)(F)(SF3) of the third row transition metal iridium suggests that SF3 complexes of the third row transition metals might be viable species in contrast to the SF3 complexes of the first row transition metals previously studied by theoretical methods. However, the metal complexes [M](SF3) ([M] = Ta(CO)5, Re(CO)4, CpW(CO)2, CpOs(CO), and CpPt) containing three-electron donor tetrahedral SF3 ligands are thermodynamically disfavored relative to the isomeric [M](SF2)(F) derivatives with predicted energy differences ranging from -19 to -44 kcal/mol. The one exception is an Ir(SF3)(CO)3 isomer containing a one-electron donor pseudo-square-pyramidal SF3 ligand having essentially the same energy as the lowest energy Ir(SF2)(F)(CO)3 isomer. This, as well as the stability of the known (Et3P)2Ir(CO)(Cl)(F)(SF3), suggests that metal complexes containing one-electron donor pseudo-square-pyramidal SF3 ligands might be viable synthetic objectives in contrast to those containing three-electron donor tetrahedral SF3 ligands. The [M](SF2)(F) derivatives formed by sulfur-to-metal fluorine migration from isomeric [M](SF3) complexes are predicted to be viable toward SF2 dissociation to give the corresponding [M](F) derivatives. This suggests the possibility of synthesizing metal complexes of the difluorosulfane (SF2) ligand via the corresponding metal trifluorosulfane complexes with the SF3(+) cation as the ultimate source of the SF2 ligand. Such a synthetic approach bypasses the need for the very unstable SF2 as a synthetic reagent.

  11. Biotransformation of uranium and transition metal citrate complexes by clostridia

    International Nuclear Information System (INIS)

    Francis, A.J.; Joshi-Tope, G.A.; Dodge, C.J.; Gillow, J.B.

    2002-01-01

    Clostridium sphenoides, which uses citric acid as its sole carbon source, metabolized equimolar Fe(III)-citrate with the degradation of citric acid and the reduction of Fe(III) to Fe(II), but not the U(VI)-citrate complex. However, in the presence of excess citric acid or added glucose it was reduced to U(IV)-citrate. In contrast, Clostridium sp., which ferments glucose but not citrate, reduced Fe(III)-citrate to Fe(II)-citrate and U(VI)-citrate to U(IV)-citrate only when supplied with glucose. These results show that complexed uranium is readily accessible as an electron acceptor despite the bacterium's inability to metabolize the organic ligand complexed to the actinide. These results also show that the metabolism of the metal-citrate complex depends upon the type of complex formed between the metal and citric acid. Fe(III) forms a bidentate complex with citric acid and was metabolized, whereas U forms a binuclear complex with citric acid and was recalcitrant. (author)

  12. Chemical bonding of hydrogen molecules to transition metal complexes

    International Nuclear Information System (INIS)

    Kubas, G.J.

    1990-01-01

    The complex W(CO) 3 (PR 3 ) 2 (H 2 ) (CO = carbonyl; PR 3 = organophosphine) was prepared and was found to be a stable crystalline solid under ambient conditions from which the hydrogen can be reversibly removed in vacuum or under an inert atmosphere. The weakly bonded H 2 exchanges easily with D 2 . This complex represents the first stable compound containing intermolecular interaction of a sigma-bond (H-H) with a metal. The primary interaction is reported to be donation of electron density from the H 2 bonding electron pair to a vacant metal d-orbital. A series of complexes of molybdenum of the type Mo(CO)(H 2 )(R 2 PCH 2 CH 2 PR 2 ) 2 were prepared by varying the organophosphine substitutent to demonstrate that it is possible to bond either dihydrogen or dihydride by adjusting the electron-donating properties of the co-ligands. Results of infrared and NMR spectroscopic studies are reported. 20 refs., 5 fig

  13. Molecular dynamics simulations of Pd-Ni transition metal alloys

    International Nuclear Information System (INIS)

    Kart, S. O.; Kart, H. H.; Uludogan, M.; Tomak, M.; Cagin, T.

    2002-01-01

    Molecular Dynamics simulations are performed to study bulk properties of fcc metals and metal alloys by using the quantum Sutton-Chen many-body potentials within the context of the tight-binding approach. The Molecular Dynamics algorithms we used in the simulations of Pd-Ni alloys are based on an extended Hamiltonian formalism arising from the works of Andersen (1980), Parinello and Rahman (1980), Nose (1984), Hoover (1985) and Cagin (1988). In these simulations, the effect of temperature and concentration on the solid and liquid properties are studied. Elastic constants and phonon dispersion relation are the solid properties we simulated in this work. Dynamic and static properties of liquid Pd-Ni are also computed by examining the behavior of density, enthalpy, pair distribution function and structure factor. The melting temperatures of Pd-Ni alloys are investigated. The diffusion coefficients are calculated from the mean square displacement using Einstein relation and from velocity auto-correlation function using Green-Kubo relations. The simulation results are in good agreement with the experiments

  14. Chemical bonding of hydrogen molecules to transition metal complexes

    Energy Technology Data Exchange (ETDEWEB)

    Kubas, G.J.

    1990-01-01

    The complex W(CO){sub 3}(PR{sub 3}){sub 2}(H{sub 2}) (CO = carbonyl; PR{sub 3} = organophosphine) was prepared and was found to be a stable crystalline solid under ambient conditions from which the hydrogen can be reversibly removed in vacuum or under an inert atmosphere. The weakly bonded H{sub 2} exchanges easily with D{sub 2}. This complex represents the first stable compound containing intermolecular interaction of a sigma-bond (H-H) with a metal. The primary interaction is reported to be donation of electron density from the H{sub 2} bonding electron pair to a vacant metal d-orbital. A series of complexes of molybdenum of the type Mo(CO)(H{sub 2})(R{sub 2}PCH{sub 2}CH{sub 2}PR{sub 2}){sub 2} were prepared by varying the organophosphine substitutent to demonstrate that it is possible to bond either dihydrogen or dihydride by adjusting the electron-donating properties of the co-ligands. Results of infrared and NMR spectroscopic studies are reported. 20 refs., 5 fig.

  15. Electronic and thermodynamic properties of the transition between metallic and nonmetallic states in dense media

    International Nuclear Information System (INIS)

    Fortin, Xavier

    1971-01-01

    The effects of thermal excitation are introduced in the study of a simple electronic structure model for condensed media. The choice of a particle-interaction potential leads to a self-consistent calculation performed on a computer. This calculation gives a metal - nonmetal transition similar to the MOTT transition. We consider the effects of temperature and density variations upon this transition. It is possible to make use of this electronic structure to obtain the thermodynamic properties near the transition: pressure, free energy, sound velocity. The numerical results of this simple model are satisfactory. Particularly, if a dielectric constant is taken into account, the transition temperature and density are of the same order of magnitude as those observed experimentally in semiconductors. (author) [fr

  16. Metal-Insulator Transition Revisited for Cold Atoms in Non-Abelian Gauge Potentials

    International Nuclear Information System (INIS)

    Satija, Indubala I.; Dakin, Daniel C.; Clark, Charles W.

    2006-01-01

    We discuss the possibility of realizing metal-insulator transitions with ultracold atoms in two-dimensional optical lattices in the presence of artificial gauge potentials. For Abelian gauges, such transitions occur when the magnetic flux penetrating the lattice plaquette is an irrational multiple of the magnetic flux quantum. Here we present the first study of these transitions for non-Abelian U(2) gauge fields. In contrast to the Abelian case, the spectrum and localization transition in the non-Abelian case is strongly influenced by atomic momenta. In addition to determining the localization boundary, the momentum fragments the spectrum. Other key characteristics of the non-Abelian case include the absence of localization for certain states and satellite fringes around the Bragg peaks in the momentum distribution and an interesting possibility that the transition can be tuned by the atomic momenta

  17. 18-Electron rule inspired Zintl-like ions composed of all transition metals.

    Science.gov (United States)

    Zhou, Jian; Giri, Santanab; Jena, Purusottam

    2014-10-07

    Zintl phase compounds constitute a unique class of compounds composed of metal cations and covalently bonded multiply charged cluster anions. Potential applications of these materials in solution chemistry and thermoelectric materials have given rise to renewed interest in the search for new Zintl ions. Up to now these ions have been mostly composed of group 13, 14, and 15 post-transition metal elements and no Zintl ions composed of all transition metal elements are known. Using gradient corrected density functional theory we show that the 18-electron rule can be applied to design a new class of Zintl-like ions composed of all transition metal atoms. We demonstrate this possibility by using Ti@Au12(2-) and Ni@Au6(2-) di-anions as examples of Zintl-like ions. Predictive capability of our approach is demonstrated by showing that FeH6(4-) in an already synthesized complex metal hydride, Mg2FeH6, is a Zintl-like ion, satisfying the 18-electron rule. We also show that novel Zintl phase compounds can be formed by using all transition metal Zintl-like ions as building blocks. For example, a two-dimensional periodic structure of Na2[Ti@Au12] is semiconducting and nonmagnetic while a one-dimensional periodic structure of Mg[Ti@Au12] is metallic and ferromagnetic. Our results open the door to the design and synthesis of a new class of Zintl-like ions and compounds with potential for applications.

  18. Development of new transition metal oxide catalysts for the destruction of PCDD/Fs.

    Science.gov (United States)

    Yu, Ming-Feng; Li, Wen-Wei; Li, Xiao-Dong; Lin, Xiao-Qing; Chen, Tong; Yan, Jian-Hua

    2016-08-01

    Various transition metal oxide and vanadium-containing multi-metallic oxide catalysts were developed for the destruction of PCDD/Fs (polychlorinated dibenzo-p-dioxins and furans). A stable PCDD/Fs generating system was installed to support the catalytic destruction tests in this study. Nano-titania supported vanadium catalyst (VOx/TiO2) showed the highest activity, followed by CeOx, MnOx, WOx and finally MoOx. Multi-metallic oxide catalysts, prepared by doping WOx, MoOx, MnOx and CeOx into VOx/TiO2 catalysts, showed different activities on the decomposition of PCDD/Fs. The highest destruction efficiency of 92.5% was observed from the destruction test over VOxCeOx/TiO2 catalyst. However, the addition of WOx and MoOx even played a negative role in multi-metallic VOx/TiO2 catalysts. Characterizations of transition metal oxides and multi-metallic VOx/TiO2 catalysts were also investigated with XRD and TPR. After the catalysts were used, the conversion from high valent metals to low valence states was observed by XPS. Copyright © 2016 Elsevier Ltd. All rights reserved.

  19. 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

  20. Reactivity patterns of transition metal hydrides and alkyls

    International Nuclear Information System (INIS)

    Jones, W.D. II.

    1979-05-01

    The complex PPN + CpV(CO) 3 H - (Cp=eta 5 -C 5 H 5 and PPN = (Ph 3 P) 2 ) was prepared in 70% yield and its physical properties and chemical reactions investigated. PPN + CpV(CO) 3 H - reacts with a wide range of organic halides. The organometallic products of these reactions are the vanadium halides PPN + [CpV(C) 3 X] - and in some cases the binuclear bridging hydride PPN + [CpV(CO) 3 ] 2 H - . The borohydride salt PPN + [CpV(CO) 3 BH 4 ] - has also been prepared. The reaction between CpV(CO) 3 H - and organic halides was investigated and compared with halide reductions carried out using tri-n-butyltin hydride. Results demonstrate that in almost all cases, the reduction reaction proceeds via free radical intermediates which are generated in a chain process, and are trapped by hydrogen transfer from CpV(CO) 3 H - . Sodium amalgam reduction of CpRh(CO) 2 or a mixture of CpRh(CO) 2 and CpCo(CO) 2 affords two new anions, PPN + [Cp 2 Rh 3 (CO) 4 ] - and PPN + [Cp 2 RhCo(CO) 2 ] - . CpMo(CO) 3 H reacts with CpMo(CO) 3 R (R=CH 3 ,C 2 H 5 , CH 2 C 6 H 5 ) at 25 to 50 0 C to produce aldehyde RCHO and the dimers [CpMo(CO) 3 ] 2 and [CpMo(CO) 2 ] 2 . In general, CpV(CO) 3 H - appears to transfer a hydrogen atom to the metal radical anion formed in an electron transfer process, whereas CpMo(CO) 3 H transfers hydride in a 2-electron process to a vacant coordination site. The chemical consequences are that CpV(CO) 3 H - generally reacts with metal alkyls to give alkanes via intermediate alkyl hydride species whereas CpMo(CO) 3 H reacts with metal alkyls to produce aldehyde, via an intermediate acyl hydride species

  1. Magic pairs and structural transitions in binary metallic clusters.

    Science.gov (United States)

    Cune, Liviu-Cristian

    2012-06-04

    Structures and binding energies for bimetallic clusters consisting of a large variety of atomic species are obtained for all atomic sizes N≤40 and all concentrations, using an interatomic potential derived within a quasi-classical description. It is found that increasing the difference between the two types of atoms leads to a gradual disappearance of the well-known homo-atomic geometric magic numbers and the appearance of magic pairs corresponding to the number of atoms of each atomic species in binary nanostructures with higher stability. This change is accompanied by structural transitions and ground-state↔isomer inversions, induced by changes in composition or concentration. There is a clear tendency towards phase separation, the core-shell radial segregation being predominant (energetically favored) in this model. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Trends in low-temperature water–gas shift reactivity on transition metals

    DEFF Research Database (Denmark)

    Schumacher, Nana Maria Pii; Boisen, Astrid; Dahl, Søren

    2005-01-01

    Low-temperature water–gas shift reactivity trends on transition metals were investigated with the use of a microkinetic model based on a redox mechanism. It is established that the adsorption energies for carbon monoxide and oxygen can describe to a large extent changes in the remaining activation...

  3. Lattice vibrational properties of transition metal carbides (TiC, ZrC

    Indian Academy of Sciences (India)

    Lattice vibrational properties of transition metal carbides (TiC, ZrC and HfC) have been presented by including the effects of free-carrier doping and three-body interactions in the rigid shell model. The short-range overlap repulsion is operative up to the second neighbour ions. An excellent agreement has been obtained ...

  4. On the behavior of Brønsted-Evans-Polanyi relations for transition metal oxides

    DEFF Research Database (Denmark)

    Vojvodic, Aleksandra; Vallejo, Federico Calle; Guo, Wei

    2011-01-01

    Versatile Brønsted-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...

  5. Valence Shell Charge Concentrations at Pentacoordinate d0 Transition Metal Centers

    OpenAIRE

    Scherer, Wolfgang

    2005-01-01

    Valence Shell Charge Concentrations at Pentacoordinate d0 Transition Metal Centers : Non VSEPR Structures of Me3NbCl3 and Me3NbCl2 / G. Eickerling ... - In: Chemistry - a European Journal. 11. 2005. S. 4921-4934

  6. X-ray-emission studies of chemical bonding in transition-metal silicides

    NARCIS (Netherlands)

    Weijs, P.J.W.; Leuken, H. van; Groot, R.A. de; Fuggle, J.C.; Reiter, S.; Wiech, G.; Buschow, K.H.J.

    1991-01-01

    We present Si L2,3 emission-band spectra of a series of 3d and 4d transition-metal (TM) silicides, together wtih Si K emission-band spectra of four 3d TM disilicides. The data are compared with augmented-spherical-wave density-of-states (DOS) calculations, and good agreement is found. The trends we

  7. Transition-metal derivatives of nido-boranes and some related species

    International Nuclear Information System (INIS)

    Greenwood, N.N.; Kennedy, J.D.

    1982-01-01

    This paper reviews the wide variety of metalloboranes that have been made by the reactions of transitional-metal compounds with nido-boranes or their anions. The authors concentrate on preparative and structural aspects and discuss presumed reaction mechanisms or postulated modes of bonding. Monoboron, diboron, triboron, tetraboron, pentaboron, hexaboron, nonaboron, decaboron, octadecaboron, and icosaboron compounds are discussed

  8. Adsorption status of some transition metal ions on pretreated fish scales

    International Nuclear Information System (INIS)

    Iqbal, J.; Mirza, M.L.

    2005-01-01

    Chitin present in fish scales was 52% deacetylated into chitosan by treating with 4% Sodium Hydroxide. The cation exchange properties of this chistosan for some first row divalent transition metal ions at different molarities of Sulphuric Acid. The distribution coefficient and the apparent adsorption capacity have been determined. Following selectivity order has been established: Cu2+ > Ni2+ > Co2+ > Fe2+. (author)

  9. Thermal behaviour of nicotinic acid, sodium nicotinate and its compounds with some bivalent transition metal ions

    International Nuclear Information System (INIS)

    Nascimento, A.L.C.S. do; Caires, F.J.; Gomes, D.J.C.; Gigante, A.C.; Ionashiro, M.

    2014-01-01

    Graphical abstract: - Highlights: • The transition metal ion nicotinates were synthesized. • The TG–DTA curves provided previously unreported information about thermal behaviour. • The gaseous products released were detected by TG–DSC coupled to FTIR. - Abstract: Solid-state M(L) 2 ·nH 2 O compounds, where M stands for bivalent transition metals (Mn, Fe, Co, Ni, Cu and Zn), L is nicotinate and n = 0–4.5, have been synthesized. Characterization and thermal behaviour of these compounds were investigated employing elemental analysis based on the mass losses observed in the TG–DTA curves, complexometry, X-ray diffractometry, infrared spectroscopy (FTIR), simultaneous thermogravimetric and differential thermal analysis (TG–DTA) and TG–DSC coupled to FTIR. The thermal behaviour of nicotinic acid and its sodium salt was also investigated. For the hydrated transition metal compounds, the dehydration and thermal decomposition of the anhydrous compounds occur in a single step. For the sodium nicotinate, the final residue up to 765 °C is sodium carbonate and for the transition metal nicotinates, the final residues are Mn 3 O 4 , Fe 2 O 3 , Co 3 O 4 , NiO, CuO and ZnO. The results also provided information concerning the thermal stability, thermal decomposition and identification of the gaseous products evolved during the thermal decomposition of the compounds

  10. Systematics in band gaps and optical spectra of 3D transition metal compounds

    International Nuclear Information System (INIS)

    Zaanen, J.; Sawatzky, G.A.

    1990-01-01

    In this paper the authors discuss the systematics in the transition metal d-d Coulomb interactions and the anion to cation charge transfer energies, and relate these to systematics in observed band gaps. In addition, they discuss the nature of the optical thresholds and their dependence on the cation and anion electronegativity

  11. Distorted wave approach to calculate Auger transition rates of ions in metals

    Energy Technology Data Exchange (ETDEWEB)

    Deutscher, Stefan A. E-mail: sad@utk.edu; Diez Muino, R.; Arnau, A.; Salin, A.; Zaremba, E

    2001-08-01

    We evaluate the role of target distortion in the determination of Auger transition rates for multicharged ions in metals. The required two electron matrix elements are calculated using numerical solutions of the Kohn-Sham equations for both the bound and continuum states. Comparisons with calculations performed using plane waves and hydrogenic orbitals are presented.

  12. First-principles calculations of the vacancy formation energy in transition and noble metals

    DEFF Research Database (Denmark)

    Korzhavyi, P.A.; Abrikosov, Igor A.; Johansson, Börje

    1999-01-01

    Abstract: The vacancy formation energy and the vacancy formation volume of the 3d, 4d, and 5d transition and noble metals have been calculated within the local-density approximation. The calculations employ the order-N locally self-consistent Green's-function method in conjunction with a supercel...

  13. Performance of transition metal-carbon multilayer mirrors from 80 to 350 eV

    International Nuclear Information System (INIS)

    Kania, D.R.; Bartlett, R.J.; Trela, W.J.; Spiller, E.; Golub, L.

    1984-03-01

    We report measurements and theoretical calculations of the reflectivity and resolving power of multilayer mirrors made of alternate layers of a transition metal (Co, Fe, V, and Cr) and carbon (2d approx. = 140 A) from 80 to 350 eV

  14. Photoinduced Coherent Spin Fluctuation in Primary Dynamics of Insulator to Metal Transition in Perovskite Cobalt Oxide

    Directory of Open Access Journals (Sweden)

    Arima T.

    2013-03-01

    Full Text Available Coherent spin fluctuation was detected in the photoinduced Mott insulator-metal transition in perovskite cobalt oxide by using 3 optical-cycle infrared pulse. Such coherent spin fluctuation is driven by the perovskite distortion changing orbital gap.

  15. Transition Metal Catalyzed Reactions for Forming Carbon–Oxygen and Carbon–Carbon Bonds

    DEFF Research Database (Denmark)

    Sølvhøj, Amanda Birgitte

    of ether and hydrocarbon radicals with -bromostyrenes was serendipitously discovered and subsequently optimized. By screening of various radical initiators and transition metal salts the best conditions were found to involve addition of three to four equivalents of Me2Zn to a solution of -bromostyrene...

  16. Synthesis of 2-substituted tetraphenylenes via transition-metal-catalyzed derivatization of tetraphenylene

    Directory of Open Access Journals (Sweden)

    Shulei Pan

    2016-06-01

    Full Text Available A new strategy for the synthesis of 2-substituted tetraphenylenes through a transition-metal-catalyzed derivatization has been developed. Three types of functionalities, including OAc, X (Cl, Br, I and carbonyl, were introduced onto tetraphenylene, which allows the easy access to a variety of monosubstituted tetraphenylenes. These reactions could accelerate research on the properties and application of tetraphenylene derivatives.

  17. An inverse-scattering approach to the physics of transition metals ...

    African Journals Online (AJOL)

    A method is developed for the deduction of a transition metal ion potential from a knowledge of the phase-shift. The method used is based the distorted plane – wave scattering approximation for the deduction of non singular potentials from scattering phase shifts in an inverse scattering approach. The resulting electron ...

  18. Atomically Thin Ordered Alloys of Transition Metal Dichalcogenides: Stability and Band Structures

    DEFF Research Database (Denmark)

    Pandey, Mohnish; Jacobsen, Karsten Wedel; Thygesen, Kristian Sommer

    2016-01-01

    We explore the possibility of modulating the electronic band edges of the transition metal dichalcogenides (TMD) via alloying of different semiconductors within the same group (intra-group alloying). The stability of the ordered alloys is assessed from the calculated mixing enthalpy which is found...

  19. Number of outer electrons as descriptor for adsorption processes on transition metals and their oxides

    DEFF Research Database (Denmark)

    Calle-Vallejo, Federico; Inoglu, Nilay G.; Su, Hai-Yan

    2013-01-01

    The trends in adsorption energies of the intermediates of the oxygen reduction and evolution reactions on transition metals and their oxides are smoothly captured by the number of outer electrons. This unique descriptor permits the construction of predictive adsorption-energy grids and explains...

  20. 3d Transition metal decorated B–C–N composite nanostructures for ...

    Indian Academy of Sciences (India)

    Administrator

    3d Transition metal decorated B–C–N composite nanostructures for efficient hydrogen storage: A first-principles study. S BHATTACHARYA, C MAJUMDER. † and G P DAS*. Department of Materials Science, Indian Association for the Cultivation of Science, Kolkata 700 032, India. †. Chemistry Division, Bhabha Atomic ...

  1. Molecular recognition in homogeneous transition metal catalysis: a biomimetic strategy for high selectivity.

    Science.gov (United States)

    Das, Siddartha; Brudvig, Gary W; Crabtree, Robert H

    2008-01-28

    Traditional methods for selectivity control in homogeneous transition metal catalysis either employ steric effects in a binding pocket or chelate control. In a supramolecular strategy, encapsulation of the substrate can provide useful shape and size selectivity. A fully developed molecular recognition strategy involving hydrogen bonding or solvophobic forces has given almost completely regioselective functionalization of remote, unactivated C-H bonds.

  2. Various scenarios of metal-insulator transition in strongly correlated materials

    Czech Academy of Sciences Publication Activity Database

    Kuneš, Jan; Anisimov, V.I.

    2011-01-01

    Roč. 523, 8-9 (2011), 682-688 ISSN 0003-3804 R&D Projects: GA ČR GAP204/10/0284 Institutional research plan: CEZ:AV0Z10100521 Keywords : electronic correlations * metal-insulator transition * dynamical mean-field theory Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.841, year: 2011

  3. 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.

  4. Magnetism of 3d transition metal atoms on W(001): submonolayer films

    Czech Academy of Sciences Publication Activity Database

    Ondráček, Martin; Kudrnovský, Josef; Turek, Ilja; Máca, František

    2007-01-01

    Roč. 61, - (2007), s. 894-898 ISSN 1742-6588 R&D Projects: GA MŠk OC 150; GA ČR GA202/04/0583 Institutional research plan: CEZ:AV0Z10100521; CEZ:AV0Z20410507 Keywords : magnetism * tungsten surface * 3d - transition metals Subject RIV: BM - Solid Matter Physics ; Magnetism

  5. Transition-Metal-Mediated or -Catalyzed Syntheses of Steroids and Steroid-Like Compounds

    Czech Academy of Sciences Publication Activity Database

    Kotora, Martin; Hessler, F.; Eignerová, B.

    -, č. 1 (2012), s. 29-42 ISSN 1434-193X R&D Projects: GA MŠk 1M0508 Institutional research plan: CEZ:AV0Z40550506 Keywords : steroids * synthesis design * synthetic methods * asymmetric synthesis * transition metals Subject RIV: CC - Organic Chemistry Impact factor: 3.344, year: 2012

  6. Catalytic Ring Hydrogenation of Benzoic Acid with Supported Transition Metal Catalysts in scCO2

    Directory of Open Access Journals (Sweden)

    Fengyu Zhao

    2007-07-01

    Full Text Available The ring hydrogenation of benzoic acid to cyclohexanecarboxylic acid overcharcoal-supported transition metal catalysts in supercritical CO2 medium has been studiedin the present work. The cyclohexanecarboxylic acid can be produced efficiently insupercritical CO2 at the low reaction temperature of 323 K. The presence of CO2 increasesthe reaction rate and several parameters have been discussed.

  7. Polymeric heterogeneous catalysts of transition-metal oxides: surface characterization, physicomechanical properties, and catalytic activity.

    Science.gov (United States)

    Nhi, Bui Dinh; Akhmadullin, Renat Maratovich; Akhmadullina, Alfiya Garipovna; Samuilov, Yakov Dmitrievich; Aghajanian, Svetlana Ivanova

    2013-12-16

    We investigate the physicomechanical properties of polymeric heterogeneous catalysts of transition-metal oxides, specifically, the specific surface area, elongation at break, breaking strength, specific electrical resistance, and volume resistivity. Digital microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and energy-dispersive analysis are used to study the surfaces of the catalysts. The experimental results show that polymeric heterogeneous catalysts of transition-metal oxides exhibit high stability and can maintain their catalytic activity under extreme reaction conditions for long-term use. The oxidation mechanism of sulfur-containing compounds in the presence of polymeric heterogeneous catalysts of transition-metal oxides is confirmed. Microstructural characterization of the catalysts is performed by using X-ray computed tomography. The activity of various catalysts in the oxidation of sulfur-containing compounds is determined. We demonstrate the potential application of polymeric heterogeneous catalysts of transition-metal oxides in industrial wastewater treatment. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Lattice vibrational properties of transition metal carbides (TiC, ZrC ...

    Indian Academy of Sciences (India)

    Lattice vibrational properties of transition metal carbides (TiC, ZrC and HfC) have been presented by including the effects of free-carrier doping and three-body interactions in the rigid shell model. The short-range overlap repulsion is operative up to the second neighbour ions. An excellent agreement has been obtained ...

  9. Anisotropic thermal motion in transition-metal carbonyls from experiments and ab initio theory.

    Science.gov (United States)

    Deringer, Volker L; Wang, Ai; George, Janine; Dronskowski, Richard; Englert, Ulli

    2016-09-21

    The thermal motion of atoms in crystals is quantified by anisotropic displacement parameters (ADPs). Here we show that dispersion-corrected periodic density-functional theory can be used to compute accurate ADPs for transition metal carbonyls, which serve as model systems for crystalline organometallic and coordination compounds.

  10. Ab initio study of solute transition-metal interactions with point defects in bcc Fe

    NARCIS (Netherlands)

    Olsson, P.; Klaver, T.P.C.; Domain, C.

    2010-01-01

    The properties of 3d, 4d, and 5d transition-metal elements in ?-Fe have been studied using ab initio density-functional theory. The intrinsic properties of the solutes have been characterized as well as their interaction with point defects. Vacancies and interstitials of (110) and (111) orientations

  11. In situ transmission electron microscopy studies on structural dynamics of transition metal nanoclusters

    NARCIS (Netherlands)

    Vystavel, T.; Koch, S.A.; Palasantzas, G.; Hosson, J.Th.M. De

    The structural stability of transition metal nanoclusters has been scrutinized with in situ transmission electron microscopy as a function of temperature. In particular iron, cobalt, niobium, and molybdenum clusters with diameters around 5 nm have been investigated. During exposure to air, a thin

  12. Tetragonal CuO: End member of the 3d transition metal monoxides

    NARCIS (Netherlands)

    Siemons, W.; Koster, Gertjan; Blank, David H.A.; Hammond, Robert H.; Geballe, Theodore H.; Beasley, Malcolm R.

    2009-01-01

    Monoclinic CuO is anomalous both structurally as well as electronically in the 3d transition metal oxide series. All the others have the cubic rocksalt structure. Here we report the synthesis and electronic property determination of a tetragonal (elongated rocksalt) form of CuO created using an

  13. 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.

  14. Phase stabilisation of hexagonal barium titanate doped with transition metals: A computational study

    Science.gov (United States)

    Dawson, J. A.; Freeman, C. L.; Harding, J. H.; Sinclair, D. C.

    2013-04-01

    Interatomic potentials recently developed for the modelling of BaTiO3 have been used to explore the stabilisation of the hexagonal polymorph of BaTiO3 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 (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 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 Ni2+ and Fe3+ ions has also been considered.

  15. Scaling relationships for adsorption energies of C2 hydrocarbons on transition metal surfaces

    DEFF Research Database (Denmark)

    Jones, Glenn; Studt, Felix; Abild-Pedersen, Frank

    2011-01-01

    Using density functional theory calculations we show that the adsorption energies for C2Hx-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...

  16. Metal-insulator transition and Frohlich conductivity in the Su-Schrieffer-Heeger model

    NARCIS (Netherlands)

    Michielsen, K.F L; de Raedt, H.A.

    1996-01-01

    A quantum molecular dynamics technique is used to study the single-particle density of states, Drude weight, optical conductivity and flux quantization in the Su-Schrieffer-Heeger (SSH) model. Our simulation data show that the SSH model has a metal-insulator transition away from half-filling. In the

  17. A magnetic resonance study of 3d transition metals and thermal donors in silicon

    International Nuclear Information System (INIS)

    Wezep, D.A. van.

    1986-01-01

    This thesis describes a study of 3d-transition metal impurities in silicon (titanium and iron in particular) and a study of oxygen-related heat-treatment centers in silicon, both carried out mainly by magnetic resonances techniques like EPR and ENDOR. 119 refs.; 31 figs.; 14 tabs

  18. Early-transition-metal catalysts with phenoxy-imine-type ligands for the oligomerization of ethylene.

    Science.gov (United States)

    Kinoshita, Shinsuke; Kawamura, Kazumori; Fujita, Terunori

    2011-02-01

    Early-transition-metal complexes incorporating phenoxy-imine-type bidentate and tridentate ligands, after activation, can achieve selective as well as nonselective ethylene oligomerization to produce 1-hexene, linear α-olefins, and vinyl-terminated low-molecular-weight polyethylenes, all with high efficiency. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Transition Metal-Free Catalytic Synthesis of 1,5-Diaryl-1,2,3-Triazoles

    Science.gov (United States)

    Kwok, Sen W.; Fotsing, Joseph R.; Fraser, Rebecca J.; Rodionov, Valentin O.; Fokin, Valery V.

    2010-01-01

    1,5-Diarylsubstituted 1,2,3-triazoles are formed in high yield from aryl azides and terminal alkynes in DMSO in the presence of catalytic tetraalkyl ammonium hydroxide. The reaction is experimentally simple, does not require a transition-metal catalyst, and is not sensitive to atmospheric oxygen and moisture. PMID:20825167

  20. Cytotoxicity of Group 5 Transition Metal Ditellurides (MTe2; M=V, Nb, Ta).

    Science.gov (United States)

    Chia, Hui Ling; Latiff, Naziah Mohamad; Sofer, Zdenĕk; Pumera, Martin

    2018-01-02

    Much research effort has been put in to study layered compounds with transition metal dichalcogenides (TMDs) being one of the most studied compounds. Due to their extraordinary properties such as excellent electrochemical properties, tuneable band gaps, and low shear resistance due to weak van der Waals interactions between layers, TMDs have been found to have wide applications such as electrocatalysts for hydrogen evolution reactions, supercapacitors, biosensors, field-effect transistors (FETs), photovoltaics, and lubricant additives. In very recent years, Group 5 transition metal ditellurides have received an immense amount of research attention. However to date, little has been known of the potential toxicities posed by these materials. As such, we conducted the cytotoxicity study by incubating various concentrations of the Group 5 transition metal ditellurides (MTe 2 ; M=V, Nb, Ta) with human lung carcinoma epithelial A549 cells for 24 hours and the remaining cell viabilities after treatment was measured. Our findings indicate that VTe 2 is highly toxic whereas NbTe 2 and TaTe 2 are deemed to exhibit mild toxicities. This study constitutes an exemplary first step towards the understanding of the Group 5 transition metal ditellurides' toxicity effects in preparation for their possible future commercialisation. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Some ENDOR studies of 3d transition metal ions in semiconductors

    International Nuclear Information System (INIS)

    Engelen, P.P.J.

    1980-01-01

    The author considers 3d transition metal ions substituted in covalent semiconducting crystals. The magnitude of the contact hyperfine field at the 59 Co nucleus in cobalt doped CdS is determined. The results of an ENDOR study of supertransferred hyperfine interactions with nearest neighbour Ga ions in Mn doped GaP are presented. (G.T.H.)

  2. Binary and ternary carbides and nitrides of the transition metals and their phase relations

    International Nuclear Information System (INIS)

    Holleck, H.

    1981-01-01

    The occurrance and the structure of the binary and ternary transition metal carbides and nitrides are described. Phase diagrams are assessed for most of the binary and ternary systems. Many ternary phase diagrams are published in this report for the first time. (orig.) [de

  3. Thermal battery. [solid metal halide electrolytes with enhanced electrical conductance after a phase transition

    Science.gov (United States)

    Carlsten, R.W.; Nissen, D.A.

    1973-03-06

    The patent describes an improved thermal battery whose novel design eliminates various disadvantages of previous such devices. Its major features include a halide cathode, a solid metal halide electrolyte which has a substantially greater electrical conductance after a phase transition at some temperature, and a means for heating its electrochemical cells to activation temperature.

  4. Ultramicrosensors based on transition metal hexacyanoferrates for scanning electrochemical microscopy

    Directory of Open Access Journals (Sweden)

    Maria A. Komkova

    2013-10-01

    Full Text Available We report here a way for improving the stability of ultramicroelectrodes (UME based on hexacyanoferrate-modified metals for the detection of hydrogen peroxide. The most stable sensors were obtained by electrochemical deposition of six layers of hexacyanoferrates (HCF, more specifically, an alternating pattern of three layers of Prussian Blue and three layers of Ni–HCF. The microelectrodes modified with mixed layers were continuously monitored in 1 mM hydrogen peroxide and proved to be stable for more than 5 h under these conditions. The mixed layer microelectrodes exhibited a stability which is five times as high as the stability of conventional Prussian Blue-modified UMEs. The sensitivity of the mixed layer sensor was 0.32 A·M−1·cm−2, and the detection limit was 10 µM. The mixed layer-based UMEs were used as sensors in scanning electrochemical microscopy (SECM experiments for imaging of hydrogen peroxide evolution.

  5. The strong reactions of Lewis-base noble-metals with vanadium and other acidic transition metals

    Energy Technology Data Exchange (ETDEWEB)

    Ebbinghaus, Bartley B. [Univ. of California, Berkeley, CA (United States)

    1991-05-01

    The noble metals often thought of as unreactive solids,react strongly with nearly 40% of the elements in the periodictable: group IIIB-VB transition metals, lanthanides, theactinides, and group IIIA-IVA non-transition metals. These strong reactions arise from increased bonding/electron transfer fromnonbonding electrons d electron pairs on the noble metal tovacant orbitals on V, etc. This effect is a generalized Lewis acid-base interaction. The partial Gibbs energy of V in the noblemetals has been measured as a function of concentration at a temperature near 1000C. Thermodynamics of the intermetallics are determined by ternary oxide equilibria, ternary carbide equilibria, and the high-temperature galvanic cell technique. These experimental methods use equilibrated solid composite mixtures in which grains of V oxides or of V carbides are interspersed with grains of V-NM(noble-metal) alloys. In equilibrium the activity of V in the oxide or the carbide equals the activity in the alloy. Consequently, the thermodynamics available in the literature for the V oxides and V carbides are reviewed. Test runs on the galvanic cell were attempted. The V oxide electrode reacts with CaF2, ThO2, YDT(0.85ThO2-0.15YO1.5), and LDT(0.85ThO2- 0.15LaO1.5) to interfere with the measured data observed toward the beginning of a galvanic cell experiment are the most accurate. The interaction of vanadium at infinite dilution in the noble-metals was determined.

  6. The strong reactions of Lewis-base noble-metals with vanadium and other acidic transition metals

    Energy Technology Data Exchange (ETDEWEB)

    Ebbinghaus, B.B.

    1991-05-01

    The noble metals often thought of as unreactive solids,react strongly with nearly 40% of the elements in the periodictable: group IIIB-VB transition metals, lanthanides, theactinides, and group IIIA-IVA non-transition metals. These strong reactions arise from increased bonding/electron transfer fromnonbonding electrons d electron pairs on the noble metal tovacant orbitals on V, etc. This effect is a generalized Lewis acid-base interaction. The partial Gibbs energy of V in the noblemetals has been measured as a function of concentration at a temperature near 1000C. Thermodynamics of the intermetallics are determined by ternary oxide equilibria, ternary carbide equilibria, and the high-temperature galvanic cell technique. These experimental methods use equilibrated solid composite mixtures in which grains of V oxides or of V carbides are interspersed with grains of V-NM(noble-metal) alloys. In equilibrium the activity of V in the oxide or the carbide equals the activity in the alloy. Consequently, the thermodynamics available in the literature for the V oxides and V carbides are reviewed. Test runs on the galvanic cell were attempted. The V oxide electrode reacts with CaF[sub 2], ThO[sub 2], YDT(0.85ThO[sub 2]-0.15YO[sub 1.5]), and LDT(0.85ThO[sub 2]- 0.15LaO[sub 1.5]) to interfere with the measured data observed toward the beginning of a galvanic cell experiment are the most accurate. The interaction of vanadium at infinite dilution in the noble-metals was determined.

  7. Transition Metal-Modified Zirconium Phosphate Electrocatalysts for the Oxygen Evolution Reaction

    Directory of Open Access Journals (Sweden)

    Joel Sanchez

    2017-05-01

    Full Text Available Zirconium phosphate (ZrP, an inorganic layered nanomaterial, is currently being investigated as a catalyst support for transition metal-based electrocatalysts for the oxygen evolution reaction (OER. Two metal-modified ZrP catalyst systems were synthesized: metal-intercalated ZrP and metal-adsorbed ZrP, each involving Fe(II, Fe(III, Co(II, and Ni(II cations. Fourier transform infrared spectroscopy, X-ray powder diffraction, thermogravimetric analysis, and X-ray photoelectron spectroscopy were used to characterize the composite materials and confirm the incorporation of the metal cations either between the layers or on the surface of ZrP. Both types of metal-modified systems were examined for their catalytic activity for the OER in 0.1 M KOH solution. All metal-modified ZrP systems were active for the OER. Trends in activity are discussed as a function of the molar ratio in relation to the two types of catalyst systems, resulting in overpotentials for metal-adsorbed ZrP catalysts that were less than, or equal to, their metal-intercalated counterparts.

  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. An approximate method for calculating electron-phonon matrix element of a disordered transition metal and relevant comments on superconductivity

    International Nuclear Information System (INIS)

    Zhang, L.

    1981-08-01

    A method based on the tight-binding approximation is developed to calculate the electron-phonon matrix element for the disordered transition metals. With the method as a basis the experimental Tsub(c) data of the amorphous transition metal superconductors are re-analysed. Some comments on the superconductivity of the disordered materials are given

  10. Remarkable magnetism and ferromagnetic coupling in semi-sulfuretted transition-metal dichalcogenides.

    Science.gov (United States)

    Zhou, Yungang; Yang, Chengfei; Xiang, Xia; Zu, Xiaotao

    2013-09-14

    Motivated by recent investigations of semi-decorated two dimensional honeycomb structures, we demonstrated, via spin-polarized molecular-dynamics simulations and density-functional-theory calculations, that semi-sulfuretted transition-metal dichalcogenides of MX type (M = V, Nb, Ta; X = S, Se, Te) are stable and display remarkable magnetism. The unpaired d electron of the transition-metal atom arising from the breakage of the M-X bond is the mechanism behind the induction of the magnetism. The remarkable magnetism of the transition-metal atoms is caused by ferromagnetic coupling due to the competitive effects of through-bond interactions and through-space interactions. This implies the existence of an infinite ferromagnetic sheet with structural integrity and magnetic homogeneity. The estimated Curie temperatures suggest that the ferromagnetism can be achieved above room temperature in the VS, VSe, VTe, NbTe and TaTe sheets. Depending on the species of the M and X atoms, the MX sheet can be a magnetic metal, magnetic semiconductor or half-metal. Furthermore, in contrary to the recently reported semi-hydrogenated and semi-fluorinated layered materials consisting of B, C, N, etc., the MX sheets with many unpaired d electrons can offer a much stronger spin polarization and possess a more stable ferromagnetic coupling, which is critical for practical nanoscale device applications.

  11. Dynamics of the insulator to metal transition in high quality V2 O3 thin films

    Science.gov (United States)

    Abreu, Elsa; Wang, Siming; Zhang, Jingdi; Geng, Kun; Zhao, Xiaoguang; Fan, Kebin; Liu, Mengkun; Ramirez, Gabriel; Zhang, Xin; Schuller, Ivan K.; Averitt, Richard D.

    2014-03-01

    Metal-insulator transitions (MITs) are a striking manifestation of the interactions between the various degrees of freedom in complex materials. Vanadium sesquioxide (V2O3) is a prototypical MIT material, transitioning from an antiferromagnetic insulator to a paramagnetic metal at Tc=170K. We present a detailed investigation of the insulator-to-metal dynamics in single crystalline thin films of V2O3 following optical and far-infrared excitation, measured using THz time domain spectroscopy. Conductivity dynamics induced below Tc by ultrafast photoexcitation can be quantitatively described by nucleation and growth of the metallic volume fraction, which eventually gives rise to the full metallic state of V2O3 on a timescale of about 50ps. We will discuss our results in the broader context of phase transition dynamics of the vanadates and related strongly correlated electron materials. This work is supported by DOE grant DE-FG02-09ER46643, AFOSR Grants No. FA9550-12-1-0381 and FA9550-09-1-0708 and FCT/Portugal SFRH/BD/47847/2008.

  12. 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.

  13. Insulator to correlated metal transition in V_1-xMo_xO_2

    Energy Technology Data Exchange (ETDEWEB)

    Klimczuk, Tomasz [Los Alamos National Laboratory; Ronning, Filip [Los Alamos National Laboratory; Holman, Katherine [PRINCETON UNIV; Mcqueen, Tyrel M [PRINCETON UNIV; Williams, Anthony J [PRINDCETON UNIV; Stephens, P W [BNL; Zandbergen, Henny W [DELFT INSTIT OF TECH; Xu, Q [DELFT INSTIT OF TECH; Cava, Robert J [PRINCETON UNIV

    2009-01-01

    The change from metallic to insulating states is one of the most dramatic transitions that solids undergo on cooling or chemical doping. Many materials display this transition, but only a handful have the right combination of crystal structure and physical properties to serve as model systems. VO{sub 2} is one of those materials. Using Mo as a chemical dopant in VO{sub 2}, we find unanticipated phenomenology for both the electronic and structural characteristics of the resulting insulator to metal transition. The results support a complex, previously proposed scenario involving the coexistence of both electron repulsion and electron pairing for yielding an insulator in VO{sub 2}, but not simply; many issues are raised about local versus itinerant behavior and structure-property correlations in this most iconic ofdoped correlated electron systems.

  14. Correlation-Driven Insulator-Metal Transition in Near-Ideal Vanadium Dioxide Films

    Science.gov (United States)

    Gray, A. X.; Jeong, J.; Aetukuri, N. P.; Granitzka, P.; Chen, Z.; Kukreja, R.; Higley, D.; Chase, T.; Reid, A. H.; Ohldag, H.; Marcus, M. A.; Scholl, A.; Young, A. T.; Doran, A.; Jenkins, C. A.; Shafer, P.; Arenholz, E.; Samant, M. G.; Parkin, S. S. P.; Dürr, H. A.

    2016-03-01

    We use polarization- and temperature-dependent x-ray absorption spectroscopy, in combination with photoelectron microscopy, x-ray diffraction, and electronic transport measurements, to study the driving force behind the insulator-metal transition in VO2 . We show that both the collapse of the insulating gap and the concomitant change in crystal symmetry in homogeneously strained single-crystalline VO2 films are preceded by the purely electronic softening of Coulomb correlations within V-V singlet dimers. This process starts 7 K (±0.3 K ) below the transition temperature, as conventionally defined by electronic transport and x-ray diffraction measurements, and sets the energy scale for driving the near-room-temperature insulator-metal transition in this technologically promising material.

  15. The allosteric transition of GroEL induced by metal fluoride-ADP complexes.

    Science.gov (United States)

    Inobe, Tomonao; Kikushima, Kenji; Makio, Tadashi; Arai, Munehito; Kuwajima, Kunihiro

    2003-05-23

    To understand the mechanism of a functionally important ATP-induced allosteric transition of GroEL, we have studied the effect of a series of metal fluoride-ADP complexes and vanadate-ADP on GroEL by kinetic fluorescence measurement of pyrene-labeled GroEL and by small-angle X-ray scattering measurement of wild-type GroEL. The metal fluorides and vanadate, complexed with ADP, are known to mimic the gamma-phosphate group of ATP, but they differ in geometry and size; it is expected that these compounds will be useful for investigating the strikingly high specificity of GroEL for ATP that enables the induction of the allosteric transition. The kinetic fluorescence measurement revealed that aluminium, beryllium, and gallium ions, when complexed with the fluoride ion and ADP, induced a biphasic fluorescence change of pyrenyl GroEL, while scandium and vanadate ions did not induce any kinetically observed change in fluorescence. The burst phase and the first phase of the fluorescence kinetics were reversible, while the second phase and subsequent changes were irreversible. The dependence of the burst-phase and the first-phase fluorescence changes on the ADP concentration indicated that the burst phase represents non-cooperative nucleotide binding to GroEL, and that the first phase represents the allosteric transition of GroEL. Both the amplitude and the rate constant of the first phase of the fluorescence kinetics were well understood in terms of a kinetic allosteric model, which is a combination of transition state theory and the Monod-Wyman-Changeux allosteric model. From the kinetic allosteric model analysis, the relative free energy of the transition state in the metal fluoride-ADP-induced allosteric transition of GroEL was found to be larger than the corresponding free energy of the ATP-induced allosteric transition by more than 5.5kcal/mol. However, the X-ray scattering measurements indicated that the allosteric state induced by these metal fluoride-ADP complexes is

  16. Long-range intramolecular electron transfer in aromatic radical anions and binuclear transition metal complexes

    DEFF Research Database (Denmark)

    Kuznetsov, A. M.; Ulstrup, Jens

    1981-01-01

    radicals containing two aromatic end groups connected by a flexible polymethylene chain or a rigid cyclohexane frame is thus trapped on either aromatic end group, and ET between these groups can be detected by ESR techniques. Intramolecular ET also occurs in binuclear transition metal complexes in which......, and for intramolecular and inner sphere ET for transition metal complexes. The Journal of Chemical Physics is copyrighted by The American Institute of Physics....... the coupling between the metal centers [(Ru(II)/Ru(III) and Ru(II)/Co(III) couples] is sufficiently weak (class I or II mixed valence compounds). The ET mechanism can involve either direct transfer between the donor and acceptor groups or a higher order mechanism in which ET proceeds through intermediate...

  17. 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.

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

    Science.gov (United States)

    Chen, Hongjun

    2014-01-01

    Summary 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. PMID:24991507

  19. Theoretical study of metal-insulator transition in rhombohedral vanadium sesquioxide

    Science.gov (United States)

    Liu, Guang-Hua; Deng, Xiao-Yan; Wang, Chun-Hai

    2011-09-01

    The electronic structure and the metal-insulator transition (MIT) of V2O3 are investigated in the framework of density functional theory and GGA+U. It is found that, both the insulating and metallic phases can be realized in rhombohedral structure by varying the on-site Coulomb interaction, and the MIT in V2O3 can take place without any structure phase transition. Our calculated energy gap (0.63 eV) agrees with experimental result very well. The metallic phase exhibits high spin (S=1) character, but it becomes S=1/2 in insulating phase. According to our analysis, the Mott-Hubbard and the charge-transfer induce the MIT together, and it supports the mechanism postulated by Tanaka (2002) [11].

  20. Metal-insulator transition in SrIrO3 with strong spin-orbit interaction.

    Science.gov (United States)

    Wu, Fei-Xiang; Zhou, Jian; Zhang, L Y; Chen, Y B; Zhang, Shan-Tao; Gu, Zheng-Bin; Yao, Shu-Hua; Chen, Yan-Feng

    2013-03-27

    The thickness-dependent metal-insulator transition is observed in meta-stable orthorhombic SrIrO3 thin films synthesized by pulsed laser deposition. SrIrO3 films with thicknesses less than 3 nm demonstrate insulating behaviour, whereas those thicker than 4 nm exhibit metallic conductivity at high temperature, and insulating-like behaviour at low temperature. Weak/Anderson localization is mainly responsible for the observed thickness-dependent metal-insulator transition in SrIrO3 films. Temperature-dependent resistance fitting shows that electrical-conductivity carriers are mainly scattered by the electron-boson interaction rather than the electron-electron interaction. Analysis of the magneto-conductance proves that the spin-orbit interaction plays a crucial role in the magneto-conductance property of SrIrO3.

  1. Method of synthesizing bulk transition metal carbide, nitride and phosphide catalysts

    Science.gov (United States)

    Choi, Jae Soon; Armstrong, Beth L; Schwartz, Viviane

    2015-04-21

    A method for synthesizing catalyst beads of bulk transmission metal carbides, nitrides and phosphides is provided. The method includes providing an aqueous suspension of transition metal oxide particles in a gel forming base, dropping the suspension into an aqueous solution to form a gel bead matrix, heating the bead to remove the binder, and carburizing, nitriding or phosphiding the bead to form a transition metal carbide, nitride, or phosphide catalyst bead. The method can be tuned for control of porosity, mechanical strength, and dopant content of the beads. The produced catalyst beads are catalytically active, mechanically robust, and suitable for packed-bed reactor applications. The produced catalyst beads are suitable for biomass conversion, petrochemistry, petroleum refining, electrocatalysis, and other applications.

  2. 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.

  3. Dysregulation of transition metal ion homeostasis is the molecular basis for cadmium toxicity in Streptococcus pneumoniae.

    Science.gov (United States)

    Begg, Stephanie L; Eijkelkamp, Bart A; Luo, Zhenyao; Couñago, Rafael M; Morey, Jacqueline R; Maher, Megan J; Ong, Cheryl-Lynn Y; McEwan, Alastair G; Kobe, Bostjan; O'Mara, Megan L; Paton, James C; McDevitt, Christopher A

    2015-03-03

    Cadmium is a transition metal ion that is highly toxic in biological systems. Although relatively rare in the Earth's crust, anthropogenic release of cadmium since industrialization has increased biogeochemical cycling and the abundance of the ion in the biosphere. Despite this, the molecular basis of its toxicity remains unclear. Here we combine metal-accumulation assays, high-resolution structural data and biochemical analyses to show that cadmium toxicity, in Streptococcus pneumoniae, occurs via perturbation of first row transition metal ion homeostasis. We show that cadmium uptake reduces the millimolar cellular accumulation of manganese and zinc, and thereby increases sensitivity to oxidative stress. Despite this, high cellular concentrations of cadmium (~17 mM) are tolerated, with negligible impact on growth or sensitivity to oxidative stress, when manganese and glutathione are abundant. Collectively, this work provides insight into the molecular basis of cadmium toxicity in prokaryotes, and the connection between cadmium accumulation and oxidative stress.

  4. Recent Progress on Transition Metal Catalyst Separation and Recycling in ATRP.

    Science.gov (United States)

    Ding, Mingqiang; Jiang, Xiaowu; Zhang, Lifen; Cheng, Zhenping; Zhu, Xiulin

    2015-10-01

    Atom transfer radical polymerization (ATRP) is a versatile and robust tool to synthesize a wide spectrum of monomers with various designable structures. However, it usually needs large amounts of transition metal as the catalyst to mediate the equilibrium between the dormant and propagating species. Unfortunately, the catalyst residue may contaminate or color the resultant polymers, which limits its application, especially in biomedical and electronic materials. How to efficiently and economically remove or reduce the catalyst residue from its products is a challenging and encouraging task. Herein, recent advances in catalyst separation and recycling are highlighted with a focus on (1) highly active ppm level transition metal or metal free catalyzed ATRP; (2) post-purification method; (3) various soluble, insoluble, immobilized/soluble, and reversible supported catalyst systems; and (4) liquid-liquid biphasic catalyzed systems, especially thermo-regulated catalysis systems. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. 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.

  6. Growth and electronic structure of single-layered transition metal dichalcogenides

    DEFF Research Database (Denmark)

    Dendzik, Maciej

    2016-01-01

    The discovery of graphene has opened a novel research direction focused on the properties of 2D materials. Transition metal dichalcogenides (TMDCs) were quickly identified as important materials due to the great variety of electronic properties that they manifest – properties that are markedly...... different from graphene’s. For example, semiconducting TMDCs undergo an indirectdirect band gap transition when thinned to a single layer (SL); this results in greatly enhanced photoluminescence, making those materials attractive for applications in optoelectronics. Furthermore, metallic TMDCs can host...... TMDCs is directly studied with angle-resolved photoemission spectroscopy (ARPES) and x-ray photoelectron spectroscopy (XPS) techniques. Experimental results are compared with density-functional theory calculations (DFT), both for a free-standing layer and for a layer adsorbed on a metallic substrate...

  7. 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)

  8. 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.

  9. Magnetotransport in heterostructures of transition metal dichalcogenides and graphene

    Science.gov (United States)

    Völkl, Tobias; Rockinger, Tobias; Drienovsky, Martin; Watanabe, Kenji; Taniguchi, Takashi; Weiss, Dieter; Eroms, Jonathan

    2017-09-01

    We use a van der Waals pickup technique to fabricate different heterostructures containing WSe2(WS2) and graphene. The heterostructures were structured by plasma etching, contacted by one-dimensional edge contacts, and a top gate was deposited. For graphene /WSe2/SiO2 samples we observe mobilities of ˜12 000 cm2V-1s-1 . Magnetic-field-dependent resistance measurements on these samples show a peak in the conductivity at low magnetic fields. This dip is attributed to the weak antilocalization (WAL) effect, stemming from spin-orbit coupling. Samples where graphene is encapsulated between WSe2(WS2) and hexagonal boron nitride show a much higher mobility of up to ˜120 000 cm2V-1s-1 . However, in these samples no WAL peak can be observed. We attribute this to a transition from the diffusive to the quasiballistic regime. At low magnetic fields a resistance peak appears, which we ascribe to a size effect due to boundary scattering. Shubnikov-de Haas oscillations in fully encapsulated samples show all integer filling factors due to complete lifting of the spin and valley degeneracies.

  10. 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

  11. 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.

  12. Orbital-selective insulator-metal transition in V2 O3 under external pressure

    Science.gov (United States)

    Laad, M. S.; Craco, L.; Müller-Hartmann, E.

    2006-01-01

    We present a detailed account of the physics of vanadium sesquioxide (V2O3) , a benchmark system for studying correlation-induced metal-insulator transition(s). Based on a detailed perusal of a wide range of experimental data, we stress the importance of multiorbital Coulomb interactions in concert with first-principles local-density approximation (LDA) band structure for a consistent understanding of the insulator-metal (IM) transition under pressure. Using LDA+DMFT (dynamical mean-field theory), we show how the IM transition is of the orbital selective type, driven by large changes in dynamical spectral weight in response to small changes in trigonal field splitting under pressure. Very good quantitative agreement with (i) the switch of orbital occupation and (ii) S=1 at each V3+ site across the IM transition, and (iii) carrier effective mass in the paramagnetic phase, is obtained. Finally, using the LDA+DMFT solution, we have estimated screening-induced renormalization of the local, multiorbital Coulomb interactions. Computation of the one-particle spectral function using these screened values is shown to be in excellent quantitative agreement with very recent experimental (photoemission and x-ray-absorption spectroscopy) results. These findings provide strong support for an orbital-selective Mott transition in paramagnetic V2O3 .

  13. 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)

  14. Hydrogen chemisorption and oxidation of transition metal carbides

    International Nuclear Information System (INIS)

    Bethin, J.R.

    1979-01-01

    A study was made of the catalytic activity of WC, focusing on the possible influence of point defects. The chemisorption of H on WC and titanium oxycarbides was studied with differential scanning calorimetry. The catalytic activity of these materials for oxidation of H was determined by potentiostatic steady-state and potentiodynamic measurements in acid electrolyte. Compositions of WC surfaces were determined by x-ray photoemission and related to the catalytic behavior. Titanium oxycarbide surfaces were analyzed by Auger electron spectroscopy. Of the carbides tested only one WC preparation was able to chemisorb H. Both WC powders investigated catalyzed H oxidation with similar specific activities. Spectroscopic studies showed that the active surface of WC was a mixture of WO 3 and a carbon-deficient WC phase. This result indicates that carbon vacancies are the active sites in tungsten carbide. Theoretical models of a carbon vacancy surrounded by metal atoms suggested by calculations by other workers support this assignment and identify the important role of the W6s level. The measured value of the heat of chemisorption is consistent with the proposed model

  15. Metal Acetylacetonates as General Precursors for the Synthesis of Early Transition Metal Oxide Nanomaterials

    OpenAIRE

    Willis, Amanda L.; Chen, Zhuoying; He, Jiaqing; Zhu, Yimei; Turro, Nicholas J.; O'Brien, Stephen

    2007-01-01

    A versatile, convenient, and nontoxic solvothermal method for the synthesis of nanocrystalline iron, chromium, and manganese oxides is described. This method employs the reactions of metal acetylacetonate precursors and oxygen-containing solvents in a reaction to prepare metal oxide nanoparticles. Characterization of these nanocrystalline materials was carried out employing transmission electron microscopy (TEM), high-resolution TEM (HRTEM), X-ray diffraction (XRD), and elemental analysis.

  16. Metal Acetylacetonates as General Precursors for the Synthesis of Early Transition Metal Oxide Nanomaterials

    Directory of Open Access Journals (Sweden)

    Amanda L. Willis

    2007-01-01

    Full Text Available A versatile, convenient, and nontoxic solvothermal method for the synthesis of nanocrystalline iron, chromium, and manganese oxides is described. This method employs the reactions of metal acetylacetonate precursors and oxygen-containing solvents in a reaction to prepare metal oxide nanoparticles. Characterization of these nanocrystalline materials was carried out employing transmission electron microscopy (TEM, high-resolution TEM (HRTEM, X-ray diffraction (XRD, and elemental analysis.

  17. Asymmetric photoredox transition-metal catalysis activated by visible light

    Science.gov (United States)

    Huo, Haohua; Shen, Xiaodong; Wang, Chuanyong; Zhang, Lilu; Röse, Philipp; Chen, Liang-An; Harms, Klaus; Marsch, Michael; Hilt, Gerhard; Meggers, Eric

    2014-11-01

    Asymmetric catalysis is seen as one of the most economical strategies to satisfy the growing demand for enantiomerically pure small molecules in the fine chemical and pharmaceutical industries. And visible light has been recognized as an environmentally friendly and sustainable form of energy for triggering chemical transformations and catalytic chemical processes. For these reasons, visible-light-driven catalytic asymmetric chemistry is a subject of enormous current interest. Photoredox catalysis provides the opportunity to generate highly reactive radical ion intermediates with often unusual or unconventional reactivities under surprisingly mild reaction conditions. In such systems, photoactivated sensitizers initiate a single electron transfer from (or to) a closed-shell organic molecule to produce radical cations or radical anions whose reactivities are then exploited for interesting or unusual chemical transformations. However, the high reactivity of photoexcited substrates, intermediate radical ions or radicals, and the low activation barriers for follow-up reactions provide significant hurdles for the development of efficient catalytic photochemical processes that work under stereochemical control and provide chiral molecules in an asymmetric fashion. Here we report a highly efficient asymmetric catalyst that uses visible light for the necessary molecular activation, thereby combining asymmetric catalysis and photocatalysis. We show that a chiral iridium complex can serve as a sensitizer for photoredox catalysis and at the same time provide very effective asymmetric induction for the enantioselective alkylation of 2-acyl imidazoles. This new asymmetric photoredox catalyst, in which the metal centre simultaneously serves as the exclusive source of chirality, the catalytically active Lewis acid centre, and the photoredox centre, offers new opportunities for the `green' synthesis of non-racemic chiral molecules.

  18. Distinct Length Scales in the VO2 Metal-Insulator Transition Revealed by Bi-chromatic Optical Probing

    International Nuclear Information System (INIS)

    Wang, Lei; Novikova, Irina B.; Klopf, John M.; Madaras, Scott E.; Williams, Gwyn P.; Madaras, Eric; Lu, Liwei; Wolf, Stuart A.; Lukaszew, Rosa A.

    2014-01-01

    Upon a heating-induced metal-insulator transition (MIT) in VO 2 , microscopic metallic VO 2 puddles nucleate and coarsen within the insulating matrix. This coexistence of the two phases across the transition spans distinct length scales as their relative domain sizes change. Far-field optical probing is applied to follow the dynamic evolution of the highly correlated metallic domains as the MIT progresses

  19. Hydrogen incorporation in Zintl phases and transition metal oxides- new environments for the lightest element in solid state chemistry

    OpenAIRE

    Nedum Kandathil, Reji

    2017-01-01

    This PhD thesis presents investigations of hydrogen incorporation in Zintl phases and transition metal oxides. Hydrogenous Zintl phases can serve as important model systems for fundamental studies of hydrogen-metal interactions, while at the same time hydrogen-induced chemical structure and physical property changes provide exciting prospects for materials science. Hydrogen incorporation in transition metal oxides leads to oxyhydride systems in which O and H together form an anionic substruct...

  20. Mesoscopic Metal-Insulator Transition at Ferroelastic Domain Walls in VO2

    Energy Technology Data Exchange (ETDEWEB)

    Jones, Keith M [ORNL; Kalinin, Sergei V [ORNL; Kolmakov, Andrei [ORNL; Luk' yanchuk, Prof. Igor A. [University of Picardie Jules Verne, Amiens, France; Meunier, Vincent [ORNL; Proksch, Roger [Asylum Research, Santa Barbara, CA; Shelton Jr, William Allison [ORNL; Strelcov, Evgheni [Southern Illinois University; Tselev, Alexander [ORNL

    2010-01-01

    The novel phenomena induced by symmetry breaking at homointerfaces between ferroic variants in ferroelectric and ferroelastic materials have attracted recently much attention. Using variable temperature scanning microwave microscopy, we demonstrate the mesoscopic strain-induced metal-insulator phase transitions in the vicinity of ferroelastic domain walls in the semiconductive VO2 that nucleated at temperatures as much as 10-12 C below bulk transition, resulting in the formation of conductive channels in the material. Density functional theory is used to rationalize the process low activation energy. This behavior, linked to the strain inhomogeneity inherent in ferroelastic materials, can strongly affect interpretation of phase-transition studies in VO2 and similar materials with symmetry-lowering transitions, and can also be used to enable new generations of electronic devices though strain engineering of conductive and semiconductive regions.

  1. On the Mott transition and the new metal-insulator transitions in doped covalent and polar crystals

    International Nuclear Information System (INIS)

    Dzhumanov, S.; Begimkulov, U.; Kurbanov, U.T.; Yavidov, B.Y.

    2001-10-01

    The Mott transition and new metal-insulator transitions (MIT's) and their distinctive features in doped covalent semiconductors and polar compounds are studied within the continuum model of extrinsic carrier self-trapping, the Hubbard impurity band model (with on-site Coulomb repulsion and screening effects) and the extrinsic (bi)polaronic band model (with short- and long-range carrier-impurity, impurity-phonon and carrier-phonon interactions and intercarrier correlation) using the appropriate tight-binding approximations and variational methods. We have shown the formation possibility of large-radius localized one- and two-carrier impurity (or defect) states and narrow impurity bands in the band gap and charge transfer gap of these carrier-doped systems. The extrinsic Mott-Hubbard and (bi)polaronic insulating gaps are calculated exactly. The proper criterions for Mott transition, extrinsic excitonic and (bi)polaronic MIT's are obtained. We have demonstrated that the Mott transition occurs in doped covalent semiconductors (i.e. Si and Ge) and some insulators with weak carrier-phonon coupling near the large-radius dopants. While, in doped polar compounds (e.g. oxide high-T c superconductors (HTSC) and related materials) the MIT's are new extrinsic (or intrinsic) (bi)polaronic MIT's. We have found that the anisotropy of the dielectric (or (bi)polaronic) properties of doped cuprate HTSC is responsible for smooth (or continuous) MIT's, stripe formation and suppression of high-T c superconductivity. Various experimental results on in-gap states, bands and MIT's in doped covalent semiconductors, oxide HTSC and related materials are in good agreement with the developed theory of Mott transition and new (bi)polaronic MIT's. (author)

  2. The synthesis and structural characterization of novel transition metal fluorides

    Energy Technology Data Exchange (ETDEWEB)

    Casteel, Jr., William Jack [Univ. of California, Berkeley, CA (United States)

    1992-09-01

    High purity KMF6 and K2MF6 salts (M = Mo,Re, Ru, Os, Ir, Pt) are obtained from reduction hexafluorides. A rhombohedral unit cell is observed for KReF6. Fluoride ion capture by Lewis acids from the hexafluorometallate (IV) salts affords high purity tetrafluorides for M = Mo, Re, Ru, Os, and Pd. The structure of RuF4 is determined from X-ray synchrotron and neutron powder data. Unit cells based on theorthorhombic PdF4 type cell are derived from X-ray powder data for ReF4 and OsF4. Fluoride ion capture from KAgF4 provides the thermally unstable trifluoride as a bright, red, diamagnetic solid. The structure solution of AgF3 and redetermination of the AuF3 structure from X-ray synchrotron and neutron powder data demonstrate that the two are isostnictural. Thermal decomposition product of AgF3 is the mixed valence compound AgIIAg2IIIF8. Several new salts containing the (Ag - F)$n+\\atop{n}$ chain cation are prepared. The first linear (Ag - F)$n+\\atop{n}$ chain is observed in AgF+BF4- which crystallizes in a tetragonal unit. AgFAuF4 has a triclinic unit cell and is isostructural with CuFAuF4. AgFAuF6 has an orthorhombic unit cell and appears to be isostructural with AgFAsF6. A second mixed valence silver fluoride, AgIIAgIIIF5, is prepared, which magnetic measurements indicate is probably an AgF+ salt. Magnetic data for all of the AgF+ salts exhibit low magnitude, temperature independent paramagnetism characteristic of metallic systems. Cationic AG(II) in acidic AHF solutions is a powerful oxidizer, capable of oxidizing Xe to Xe(II) and O2 to O2+. Reactions with C6F6 and C3F6 suggest an electron capture

  3. Graphene nucleation and growth on the transition metal surfaces: the role of pentagon, metal step and magic carbon clusters

    Science.gov (United States)

    Gao, Junfeng; Zhao, Jijun; Ding, Feng

    2012-02-01

    The nucleation behavior of graphene on transition metal surfaces, either on a terrace or near a step edge, is systematically explored using density functional theory calculations. The supported carbon clusters, CN (N=1˜24), on the Ni(111) surface are carefully optimized [1,2]. A structural transformation from a C chain to a sp^2 C network at C12 and the most stable structures of sp^2 graphene islands contain one to three pentagons. In agreement with experimental observations, our calculations show that graphene nucleation near a metal step edge is superior to that on a terrace. Besides, ground state structures of supported CN (N = 16˜26), clusters on four selected transition metal surfaces: (Rh(111), Ru(0001), Ni(111) and Cu(111)) are explored [3]. A core-shell structured of C21 stands out as a magic cluster, which is one of the dominating carbon precursors in graphene CVD growth and has been observed in experimental STM images. The energy barrier of two C21 clusters' coalescence is computed to illustrate their influence on the kinetics of graphene CVD growth at different temperatures. [4pt] [1] J. Gao, et al,. J. Am. Chem. Soc. 133, 5009 (2011). [0pt] [2] J. Gao, et al., J. Phys. Chem. C 115, 17695 (2011). [0pt] [3] Q. Yuan, et al., J. Am. Chem. Soc. (accepted).

  4. Axially engineered metal-insulator phase transition by graded doping VO2 nanowires.

    Science.gov (United States)

    Lee, Sangwook; Cheng, Chun; Guo, Hua; Hippalgaonkar, Kedar; Wang, Kevin; Suh, Joonki; Liu, Kai; Wu, Junqiao

    2013-03-27

    The abrupt first-order metal-insulator phase transition in single-crystal vanadium dioxide nanowires (NWs) is engineered to be a gradual transition by axially grading the doping level of tungsten. We also demonstrate the potential of these NWs for thermal sensing and actuation applications. At room temperature, the graded-doped NWs show metal phase on the tips and insulator phase near the center of the NW, and the metal phase grows progressively toward the center when the temperature rises. As such, each individual NW acts as a microthermometer that can be simply read out with an optical microscope. The NW resistance decreases gradually with the temperature rise, eventually reaching 2 orders of magnitude drop, in stark contrast to the abrupt resistance change in undoped VO2 wires. This novel phase transition yields an extremely high temperature coefficient of resistivity ~10%/K, simultaneously with a very low resistivity down to 0.001 Ω·cm, making these NWs promising infrared sensing materials for uncooled microbolometers. Lastly, they form bimorph thermal actuators that bend with an unusually high curvature, ~900 m(-1)·K(-1) over a wide temperature range (35-80 °C), significantly broadening the response temperature range of previous VO2 bimorph actuators. Given that the phase transition responds to a diverse range of stimuli-heat, electric current, strain, focused light, and electric field-the graded-doped NWs may find wide applications in thermo-opto-electro-mechanical sensing and energy conversion.

  5. 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.

  6. Trends in the chemical properties in early transition metal carbide surfaces: A density functional study

    DEFF Research Database (Denmark)

    Kitchin, J.R.; Nørskov, Jens Kehlet; Barteau, M.A.

    2005-01-01

    In this paper we present density functional theory (DFT) investigations of the physical, chemical and electronic structure properties of several close-packed surfaces of early transition metal carbides, including beta-Mo2C(0 0 0 1), and the (1 1 1) surfaces of TiC, VC, NbC, and TaC. The results...... are in excellent agreement with experimental values of lattice constants and bulk moduli. The adsorption of atomic hydrogen is used as a probe to compare the chemical properties of various carbide surfaces. Hydrogen adsorbs more strongly to the metal-terminated carbide surfaces than to the corresponding closest......-packed pure metal surfaces, due to the tensile strain induced in the carbide surfaces upon incorporation of carbon into the lattice. Hydrogen atoms were found to adsorb more weakly on carbide surfaces than on the corresponding closest-packed pure metal surfaces only when there were surface carbon atoms...

  7. Transition metal complexes with oxygen donor ligands: a synthesis, spectral, thermal and antimicrobial study

    Directory of Open Access Journals (Sweden)

    VAIBHAV N. PATANGE

    2008-10-01

    Full Text Available Transition metal complexes of chalcones derived from the conden¬sation of 3-acetyl-6-methyl-2H-pyran-2,4(3H-dione (dehydroacetic acid and p-methoxybenzaldehyde (HL1 or p-nitrobenzaldehyde (HL2 were synthesized and characterized by elemental analysis, conductometry, thermal analysis, magnetic measurements, IR, 1H-NMR, UV–Vis spectroscopy and a microbial study. From the analytical and thermal data, the stoichiometry of the complexes was found to be 1:2 (metal:ligand. The molar conductance data revealed that all the metal chelates were non-electrolytes. The thermal stability of the complexes was studied by thermogravimetry and the decomposition schemes of the complexes are given. The ligands and their metal complexes were screened for antibacterial activity against Staphylococcus aureus and Escherichia coli, and fungicidal activity against Aspergillus flavus, Curvularia lunata and Penicillium notatum.

  8. 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.

  9. Metallic magnetism and change of conductivity in the nano to bulk transition of cobalt ferrite

    Energy Technology Data Exchange (ETDEWEB)

    Arunkumar, A.; Vanidha, D.; Kannan, R., E-mail: kannan@pec.edu [Department of Physics, Pondicherry Engineering College, Puducherry–605 014 (India); Oudayakumar, K. [Department of Physics, Sri Manakula Vinayagar Engineering College, Puducherry–605 107 (India); Rajagopan, S. [Department of Chemistry, Pondicherry Engineering College, Puducherry–605 014 (India)

    2013-11-14

    Variations in conductivity with particle size have been observed in cobalt ferrite, when synthesized by solgel auto-combustion method. Impedance analysis reveals metallic and semiconducting behavior at room temperature for a particle size of 6 nm and 52 nm, respectively. Upon thermal activation, metallic to semiconducting phase transition has been observed as a function of particle size and vice-versa. Grainboundary Resistance (R{sub gb}), increased drastically with particle size (19 MΩ for 6 nm and 259 MΩ for 52 nm) at room temperature. AC conductivity and dielectric constants exhibit similar metallic to semiconducting phase transition at 6 nm and semiconducting behavior at 52 nm with temperature in the selected frequencies. Enhanced magnetic moment with an increase in the grain size along with decreased coercivity (1444 G to 1146 G) reveals transition from single domain to multi-domain. Increased inter-particle interaction is responsible for metallicity at the nano level and on the contrary semiconductivity is attributed to bulk.

  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. 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. FIRST-ROW TRANSITION METAL COMPLEXES OF OMEPRAZOLE AS ANTI-ULCERATIVE DRUGS

    Directory of Open Access Journals (Sweden)

    Suman Malik

    2010-12-01

    Full Text Available Omeprazole (OME is a proton pump inhibitor (PPI. PPIs have enabled to improve the treatment of various acid-peptic disorders. OME is a weak base and it can form several complexes with transition and non-transition metal ions. In the present paper, we are describing series of transition metal complexes of omeprazole i.e., 5-methoxy-2[(4methoxy-3, 5dimethyl-2-pyridinyl methylsulfinyl]-1H-benzimidazole with CuII, MnII, CoII, NiII, FeII, ZnII and HgII. These complexes were characterized by elemental analysis, molar conductivity, IR, NMR, magnetic susceptibility, UV-visible spectral studies, ESR, SEM and X-ray diffraction. Based on the above studies, the ligand behaves as bidentate O, N donor and forms coordinate bonds through C=N and S=O groups. The complexes were found to non-electrolytic in nature on the basis of low values of molar conductivity. Analytical data and stoichiometry analysis suggest ligand to metal ratio of 2:1 for all the complexes. Electronic spectra and magnetic susceptibility measurements reveal octahedral geometry for Mn(II,Co(II, Ni(II,Fe(II and Cu(II complexes and tetrahedral for Hg(II and Zn(II complexes. Ligands and their metal complexes have been screened for their antibacterial and antifungal activities against bacteria Pseudomonas, Staphylococcus aureus and fungi Aspergillus niger and A. flavous.

  13. Insights into the photochemical disproportionation of transition metal dimers on the picosecond time scale.

    Science.gov (United States)

    Lomont, Justin P; Nguyen, Son C; Harris, Charles B

    2013-05-09

    The reactivity of five transition metal dimers toward photochemical, in-solvent-cage disproportionation has been investigated using picosecond time-resolved infrared spectroscopy. Previous ultrafast studies on [CpW(CO)3]2 established the role of an in-cage disproportionation mechanism involving electron transfer between 17- and 19-electron radicals prior to diffusion out of the solvent cage. New results from time-resolved infrared studies reveal that the identity of the transition metal complex dictates whether the in-cage disproportionation mechanism can take place, as well as the more fundamental issue of whether 19-electron intermediates are able to form on the picosecond time scale. Significantly, the in-cage disproportionation mechanism observed previously for the tungsten dimer does not characterize the reactivity of four out of the five transition metal dimers in this study. The differences in the ability to form 19-electron intermediates are interpreted either in terms of differences in the 17/19-electron equilibrium or of differences in an energetic barrier to associative coordination of a Lewis base, whereas the case for the in-cage vs diffusive disproportionation mechanisms depends on whether the 19-electron reducing agent is genuinely characterized by 19-electron configuration at the metal center or if it is better described as an 18 + δ complex. These results help to better understand the factors that dictate mechanisms of radical disproportionation and carry implications for radical chain mechanisms.

  14. Supersaturating silicon with transition metals by ion implantation and pulsed laser melting

    International Nuclear Information System (INIS)

    Recht, Daniel; Aziz, Michael J.; Smith, Matthew J.; Gradečak, Silvija; Charnvanichborikarn, Supakit; Williams, James S.; Sullivan, Joseph T.; Winkler, Mark T.; Buonassisi, Tonio; Mathews, Jay; Warrender, Jeffrey M.

    2013-01-01

    We investigate the possibility of creating an intermediate band semiconductor by supersaturating Si with a range of transition metals (Au, Co, Cr, Cu, Fe, Pd, Pt, W, and Zn) using ion implantation followed by pulsed laser melting (PLM). Structural characterization shows evidence of either surface segregation or cellular breakdown in all transition metals investigated, preventing the formation of high supersaturations. However, concentration-depth profiling reveals that regions of Si supersaturated with Au and Zn are formed below the regions of cellular breakdown. Fits to the concentration-depth profile are used to estimate the diffusive speeds, v D, of Au and Zn, and put lower bounds on v D of the other metals ranging from 10 2 to 10 4 m/s. Knowledge of v D is used to tailor the irradiation conditions and synthesize single-crystal Si supersaturated with 10 19 Au/cm 3 without cellular breakdown. Values of v D are compared to those for other elements in Si. Two independent thermophysical properties, the solute diffusivity at the melting temperature, D s (T m ), and the equilibrium partition coefficient, k e , are shown to simultaneously affect v D . We demonstrate a correlation between v D and the ratio D s (T m )/k e 0.67 , which is exhibited for Group III, IV, and V solutes but not for the transition metals investigated. Nevertheless, comparison with experimental results suggests that D s (T m )/k e 0.67 might serve as a metric for evaluating the potential to supersaturate Si with transition metals by PLM

  15. Supersaturating silicon with transition metals by ion implantation and pulsed laser melting

    Energy Technology Data Exchange (ETDEWEB)

    Recht, Daniel; Aziz, Michael J. [Harvard School of Engineering and Applied Sciences, Cambridge, Massachusetts 02138 (United States); Smith, Matthew J.; Gradečak, Silvija [Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Charnvanichborikarn, Supakit; Williams, James S. [Research School of Physics and Engineering, The Australian National University, Canberra, ACT (Australia); Sullivan, Joseph T.; Winkler, Mark T.; Buonassisi, Tonio [Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge Massachusetts 02139 (United States); Mathews, Jay; Warrender, Jeffrey M. [Benet Laboratories, U.S. Army ARDEC, Watervliet, New York 12189 (United States)

    2013-09-28

    We investigate the possibility of creating an intermediate band semiconductor by supersaturating Si with a range of transition metals (Au, Co, Cr, Cu, Fe, Pd, Pt, W, and Zn) using ion implantation followed by pulsed laser melting (PLM). Structural characterization shows evidence of either surface segregation or cellular breakdown in all transition metals investigated, preventing the formation of high supersaturations. However, concentration-depth profiling reveals that regions of Si supersaturated with Au and Zn are formed below the regions of cellular breakdown. Fits to the concentration-depth profile are used to estimate the diffusive speeds, v{sub D,} of Au and Zn, and put lower bounds on v{sub D} of the other metals ranging from 10{sup 2} to 10{sup 4} m/s. Knowledge of v{sub D} is used to tailor the irradiation conditions and synthesize single-crystal Si supersaturated with 10{sup 19} Au/cm{sup 3} without cellular breakdown. Values of v{sub D} are compared to those for other elements in Si. Two independent thermophysical properties, the solute diffusivity at the melting temperature, D{sub s}(T{sub m}), and the equilibrium partition coefficient, k{sub e}, are shown to simultaneously affect v{sub D}. We demonstrate a correlation between v{sub D} and the ratio D{sub s}(T{sub m})/k{sub e}{sup 0.67}, which is exhibited for Group III, IV, and V solutes but not for the transition metals investigated. Nevertheless, comparison with experimental results suggests that D{sub s}(T{sub m})/k{sub e}{sup 0.67} might serve as a metric for evaluating the potential to supersaturate Si with transition metals by PLM.

  16. Synthesis, characterization and properties of nano-sized transition metal oxides

    Science.gov (United States)

    Yin, Ming

    2005-12-01

    Chapter 1. A General introduction to the emerging field of nanomaterials is presented highlighting the category of transition metal oxides. The wide variety of structures, properties, and phenomena of transition metal oxides are stressed. Nano-sized transition metal oxides are presented as systems for fundamental and application research. Examples of individual transition metal oxides are provided. Important developments in the synthesis and characterization of nano-sized transition metal oxides that have contributed to this work are reviewed. A novel synthesis (TDMA) is developed and successfully applied to the synthesis of transition metal oxide nanocrystals. Chapter 2. The synthesis of monodisperse cubic wuestite FexO nanocrystals is presented. The influence of reaction temperature and the molar ratio of surfactant to iron precursor was investigated, in order to further understand the ability to control particle size and monodispersity. In contrast to bulk material, it is also found that the nano-sized ligand-capped wuestite FexO particles were stable at room temperature. The procedure enable the collection of highly monodisperse nanocrystals of variable and uniform diameters as a function of time. Sharp Hancock analysis indicates that the reaction proceeds by a diffusion limited mechanism. Routes to control the size of gamma-Fe2O3 nanocrystals are also presented. gamma-Fe2O3 nanocrystals from 6 nm to 12 nm in diameter with uniform size, shape, consistent crystal structure were prepared. Chapter 3. A simple reaction to prepare monodisperse MnO nanocrystals is presented. MnO nanocrystals was prepared by thermal decomposition of manganese acetate in the presence of oleic acid at high temperature and by following annealing. Particles with different sizes and shapes were obtained by controlling annealing time. The morphology of MnO nanocrystals was studied based on their crystal structure and surface energy. SQUID measurement shows ferromagnetic magnetism at low

  17. Ultrafast far-infrared studies of vanadates &mdash Multiple routes for an insulator to metal transition

    Science.gov (United States)

    Liu, Mengkun

    The metal insulator transition in vanadates has been studied for decades and yet new discoveries still spring up revealing new physics, especially among two of the most studied members: Vanadium sesquioxide (V20 3) and Vanadium dioxide (VO2). Although subtleties abound, both of the materials have first order insulator to metal phase transitions that are considered to be related to strong electron-electron (e-e) correlation. Further, ultrafast spectroscopy of strongly correlated materials has generated great interest in the field given the potential to dynamically distinguish the difference between electronic (spin) response versus lattice responses due to the associated characteristic energy and time scales. In this thesis, I mainly focus on utilizing ultrafast optical and THz spectroscopy to study phase transition dynamics in high quality V20 3 and VO2 thin films epitaxially grown on different substrates. The main findings of the thesis are: (1) Despite the fact that the insulator to metal transition (IMT) in V203 is electron-correlation driven, lattice distortion plays an important role. Coherent oscillations in the far-infrared conductivity are observed resulting from coherent acoustic phonon modulation of the bandwidth W. The same order of lattice distortion induces less of an effect on the electron transport in VO2 in comparison to V203. This is directly related to the difference in latent heat of the phase transitions in VO2 and V203. (2) It is possible for the IMT to occur with very little structural change in epitaxial strained VO2 films, like in the case of Cr doped or strained V203. However, in V02, this necessitates a large strain which is only possible by clamping to a substrate with larger c axis parameter through epitaxial growth. This is demonstrated for VO 2 films on TiO2 substrates. (3) Initiating an ultrafast photo-induced insulator-to-metal transition (IMT) is not only possible with above bandgap excitation, but also possible with high-field far

  18. 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

  19. 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.

  20. Electrocatalytic conversion of carbon dioxide to methane and methanol on transition metal surfaces.

    Science.gov (United States)

    Kuhl, Kendra P; Hatsukade, Toru; Cave, Etosha R; Abram, David N; Kibsgaard, Jakob; Jaramillo, Thomas F

    2014-10-08

    Fuels and industrial chemicals that are conventionally derived from fossil resources could potentially be produced in a renewable, sustainable manner by an electrochemical process that operates at room temperature and atmospheric pressure, using only water, CO2, and electricity as inputs. To enable this technology, improved catalysts must be developed. Herein, we report trends in the electrocatalytic conversion of CO2 on a broad group of seven transition metal surfaces: Au, Ag, Zn, Cu, Ni, Pt, and Fe. Contrary to conventional knowledge in the field, all metals studied are capable of producing methane or methanol. We quantify reaction rates for these two products and describe catalyst activity and selectivity in the framework of CO binding energies for the different metals. While selectivity toward methane or methanol is low for most of these metals, the fact that they are all capable of producing these products, even at a low rate, is important new knowledge. This study reveals a richer surface chemistry for transition metals than previously known and provides new insights to guide the development of improved CO2 conversion catalysts.

  1. Strongly Phosphorescent Transition Metal π-Complexes of Boron-Boron Triple Bonds.

    Science.gov (United States)

    Braunschweig, Holger; Dellermann, Theresa; Dewhurst, Rian D; Hupp, Benjamin; Kramer, Thomas; Mattock, James D; Mies, Jan; Phukan, Ashwini K; Steffen, Andreas; Vargas, Alfredo

    2017-04-05

    Herein are reported the first π-complexes of compounds with boron-boron triple bonds with transition metals, in this case Cu I . Three different compounds were isolated that differ in the number of copper atoms bound to the BB unit. Metalation of the B-B triple bonds causes lengthening of the B-B and B-C NHC bonds, as well as large upfield shifts of the 11 B NMR signals, suggesting greater orbital interactions between the boron and transition metal atoms than those observed with recently published diboryne/alkali metal cation complexes. In contrast to previously reported fluorescent copper(I) π-complexes of boron-boron double bonds, the Cu n -π-diboryne compounds (n = 2, 3) show intense phosphorescence in the red to near-IR region from their triplet excited states, according to their microsecond lifetimes, with quantum yields of up to 58%. While the Cu diborene bond is dominated by electrostatic interactions, giving rise to S 1 and T 1 states of pure IL(π-π*) nature, DFT studies show that the Cu I π-complexes of diborynes reported herein exhibit enhanced metal d orbital contributions to HOMO and HOMO-1, which results in S 1 and T 1 having significant MLCT character, enabling strong spin-orbit coupling for highly efficient intersystem-crossing S 1 → T n and phosphorescence T 1 → S 0 .

  2. Bioavailable transition metals in particulate matter mediate cardiopulmonary injury in healthy and compromised animal models

    Energy Technology Data Exchange (ETDEWEB)

    Costa, D.L.; Dreher, K.L. [US Environmental Protection Agency, Research Triangle Park, NC (United States). National Health and Environmental Effects Research Lab.

    1997-09-01

    Many epidemiologic reports associate ambient levels of particulate matter (PM) with human mortality and morbidity, particularly in people with preexisting cardiopulmonary disease (e.g., chronic obstructive pulmonary disease, infection, asthma). Because much ambient PM is derived from combustion sources, the hypothesis that the health effects of PM arise from anthropogenic PM that contains bioavailable transition metals was tested. The PM samples studied derived from three emission sources (two oil and one coal fly ash) and four ambient airsheds (St. Louis, MO, USA; Washington, DC (USA); Duesseldorf, Germany; and Ottawa, Canada). PM was administered to rats by intratracheal instillation in equimass or equimetal doses to address directly the influence of PM mass versus metal content on actual lung injury and inflammation. Results indicated that the lung dose of bioavailable transition metal, not instilled PM mass, was the primary determinant of the acute inflammatory response for both the combustion source and ambient PM samples. Residual oil fly ash, a combustion PM rich in bioavailable metal, and evaluated in rat model of cardiopulmonary disease (pulmonary vasculitis/hypertension) to ascertain whether the disease state augmented sensitivity to that PM. It is proposed that soluble metals from PM mediate the array of PM-associated injuries to the cardiopulmonary system of the healthy and at-risk compromised host.

  3. Can a Metal-Insulator Transition Induce s-Wave Superconductivity?

    Science.gov (United States)

    Nozières, Ph.

    2004-04-01

    A recent paper of Capone et al. has studied an extended Hubbard model, in which local orbital degrees of freedom allow an even integer occupation at each site. A strong local repulsion U triggers a metal-insulator transition. Within a DMFT numerical analysis they show that when the ground state is a singlet a pocket of s-wave superconductivity appears in the vicinity of the Mott transition, with a strongly enhanced superconducting gap. A qualitative understanding of their result is proposed, and suggestions are made of possible systems in which this beautiful effect might be searched.

  4. Metal-insulator transitions and superconductivity in ditetramethyltetraselenafulvalenium flourosulfonate [(TMTSF)2FSO3

    International Nuclear Information System (INIS)

    Lacoe, R.C.; Wolf, S.A.; Chaikin, P.M.; Wudl, F.; Aharon-Shalom, E.

    1983-01-01

    We have investigated the phase diagram of the organic charge-transfer salt ditetramethyltetraselenafulvalenium flourosulfonate [(TMTSF) 2 FSO 3 ] which contains an asymmetric dipolar anion. At low pressures there is a metal-insulator transition related to anion ordering. Between 5 and 6 kbar, there is a dipolar glass phase with increased resistivity. However, thermopower and superconducting measurements indicate that the Fermi surface remains ungapped. Above 5 kbar there is a superconducting transition with T/sub c/>2 K. This is the highest T/sub c/ for this family of compounds and suggests that the anions can enhance T/sub c/

  5. Electrical Switching in Thin Film Structures Based on Transition Metal Oxides

    Directory of Open Access Journals (Sweden)

    A. Pergament

    2015-01-01

    Full Text Available Electrical switching, manifesting itself in the nonlinear current-voltage characteristics with S- and N-type NDR (negative differential resistance, is inherent in a variety of materials, in particular, transition metal oxides. Although this phenomenon has been known for a long time, recent suggestions to use oxide-based switching elements as neuristor synapses and relaxation-oscillation circuit components have resumed the interest in this area. In the present review, we describe the experimental facts and theoretical models, mainly on the basis of the Mott transition in vanadium dioxide as a model object, of the switching effect with special emphasis on the emerging applied potentialities for oxide electronics.

  6. Optical nonlinearities of excitonic states in atomically thin 2D transition metal dichalcogenides

    Energy Technology Data Exchange (ETDEWEB)

    Soh, Daniel Beom Soo [Sandia National Lab. (SNL-CA), Livermore, CA (United States). Proliferation Signatures Discovery and Exploitation Department

    2017-08-01

    We calculated the optical nonlinearities of the atomically thin monolayer transition metal dichalcogenide material (particularly MoS2), particularly for those linear and nonlinear transition processes that utilize the bound exciton states. We adopted the bound and the unbound exciton states as the basis for the Hilbert space, and derived all the dynamical density matrices that provides the induced current density, from which the nonlinear susceptibilities can be drawn order-by-order via perturbative calculations. We provide the nonlinear susceptibilities for the linear, the second-harmonic, the third-harmonic, and the kerr-type two-photon processes.

  7. Peptides having antimicrobial activity and their complexes with transition metal ions.

    Science.gov (United States)

    Jeżowska-Bojczuk, Małgorzata; Stokowa-Sołtys, Kamila

    2018-01-01

    Peptide antibiotics are produced by bacterial, mammalian, insect or plant organisms in defense against invasive microbial pathogens. Therefore, they are gaining importance as anti-infective agents. There are a number of antibiotics that require metal ions to function properly. Metal ions play a key role in their action and are involved in specific interactions with proteins, nucleic acids and other biomolecules. On the other hand, it is well known that some antimicrobial agents possess functional groups that enable them interacting with metal ions present in physiological fluids. Some findings support a hypothesis that they may alter the serum metal ions concentration in humans. Complexes usually have a higher positive charge than uncomplexed compounds. This means that they might interact more tightly with polyanionic DNA and RNA molecules. It has been shown that several metal ion complexes with antibiotics promote degradation of DNA. Some of them, such as bleomycin, form stable complexes with redox metal ions and split the nucleic acids chain via the free radicals mechanism. However, this is not a rule. For example blasticidin does not cause DNA damage. This indicates that some peptide antibiotics can be considered as ligands that effectively lower the oxidative activity of transition metal ions. Copyright © 2017 Elsevier Masson SAS. All rights reserved.

  8. Metal-insulator transition in one-dimensional lattices with chaotic energy sequences

    International Nuclear Information System (INIS)

    Pinto, R.A.; Rodriguez, M.; Gonzalez, J.A.; Medina, E.

    2005-01-01

    We study electronic transport through a one-dimensional array of sites by using a tight binding Hamiltonian, whose site-energies are drawn from a chaotic sequence. The correlation degree between these energies is controlled by a parameter regulating the dynamic Lyapunov exponent measuring the degree of chaos. We observe the effect of chaotic sequences on the localization length, conductance, conductance distribution and wave function, finding evidence of a metal-insulator transition (MIT) at a critical degree of chaos. The one-dimensional metallic phase is characterized by a Gaussian conductance distribution and exhibits a peculiar non-selfaveraging

  9. The formation energy for steps and kinks on cubic transition metal surfaces

    DEFF Research Database (Denmark)

    Vitos, Levente; Skriver, Hans Lomholt; Kollàr, Janos

    1999-01-01

    We have used our first-principles database of surface energies for metals in conjunction with the concept of vicinal surfaces to derive the energies of formation of monoatomic steps and corresponding kinks on close-packed surface facets of bcc and fee transition metals. The entries in the database...... allow for a direct calculation of the energies of a number of important steps. For the remaining steps and for all the kinks the energies of formation have been estimated from pair potential expansions of the entries in the database. (C) 1999 Elsevier Science B.V. All rights reserved....

  10. Electronic Structure of the fcc Transition Metals Ir, Rh, Pt, and Pd

    DEFF Research Database (Denmark)

    Andersen, O. Krogh

    1970-01-01

    /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......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...

  11. Novel method to deposit metal particles on transition metal oxide films and its application in lithium-ion batteries

    International Nuclear Information System (INIS)

    Pan Qinmin; Wang Min; Wang Hongbo; Zhao Jianwei; Yin Geping

    2008-01-01

    A novel method to modify the surfaces of transition metal oxides (MO) film-electrode was proposed in this study. At first, a monolayer of terephthalic acid was covalently bonded to the surfaces of Cu 2 O films. Then silver (Ag) particles were electrodeposited on the monolayer-grafted films by a potential-step process. The resulting Ag-Cu 2 O films exhibited improved electrochemical performance as negative electrodes in lithium-ion batteries compared to the original Cu 2 O films. An increase in electrical contact between Cu 2 O particles was considered to be responsible for the improvement in the electrochemical properties

  12. The Importance of Transition Metals in the Expanding Network of Microbial Metabolism in the Archean Eon

    Science.gov (United States)

    Moore, E. K.; Jelen, B. I.; Giovannelli, D.; Prabhu, A.; Raanan, H.; Falkowski, P. G.

    2017-12-01

    Deep time changes in Earth surface redox conditions, particularly due to global oxygenation, has impacted the availability of different metals and substrates that are central in biology. Oxidoreductase proteins are molecular nanomachines responsible for all biological electron transfer processes across the tree of life. These enzymes largely contain transition metals in their active sites. Microbial metabolic pathways form a global network of electron transfer, which expanded throughout the Archean eon. Older metabolisms (sulfur reduction, methanogenesis, anoxygenic photosynthesis) accessed negative redox potentials, while later evolving metabolisms (oxygenic photosynthesis, nitrification/denitrification, aerobic respiration) accessed positive redox potentials. The incorporation of different transition metals facilitated biological innovation and the expansion of the network of microbial metabolism. Network analysis was used to examine the connections between microbial taxa, metabolic pathways, crucial metallocofactors, and substrates in deep time by incorporating biosignatures preserved in the geologic record. Nitrogen fixation and aerobic respiration have the highest level of betweenness among metabolisms in the network, indicating that the oldest metabolisms are not the most central. Fe has by far the highest betweenness among metals. Clustering analysis largely separates High Metal Bacteria (HMB), Low Metal Bacteria (LMB), and Archaea showing that simple un-weighted links between taxa, metabolism, and metals have phylogenetic relevance. On average HMB have the highest betweenness among taxa, followed by Archaea and LMB. There is a correlation between the number of metallocofactors and metabolic pathways in representative bacterial taxa, but Archaea do not follow this trend. In many cases older and more recently evolved metabolisms were clustered together supporting previous findings that proliferation of metabolic pathways is not necessarily chronological.

  13. Modeling Dzyaloshinskii-Moriya Interaction at Transition Metal Interfaces: Constrained Moment versus Generalized Bloch Theorem

    KAUST Repository

    Dong, Yao-Jun

    2017-10-29

    Dzyaloshinskii-Moriya interaction (DMI) at Pt/Co interfaces is investigated theoretically using two different first principles methods. The first one uses the constrained moment method to build a spin spiral in real space, while the second method uses the generalized Bloch theorem approach to construct a spin spiral in reciprocal space. We show that although the two methods produce an overall similar total DMI energy, the dependence of DMI as a function of the spin spiral wavelength is dramatically different. We suggest that long-range magnetic interactions, that determine itinerant magnetism in transition metals, are responsible for this discrepancy. We conclude that the generalized Bloch theorem approach is more adapted to model DMI in transition metal systems, where magnetism is delocalized, while the constrained moment approach is mostly applicable to weak or insulating magnets, where magnetism is localized.

  14. 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.

  15. Understanding ductile-to-brittle transition of metallic glasses from shear transformation zone dilatation

    Directory of Open Access Journals (Sweden)

    M.Q. Jiang

    2015-08-01

    Full Text Available A theoretical model that takes into account the free-volume aided cooperative shearing of shear transformation zones (STZs is developed to quantitatively understand the ductile-to-brittle transition (DBT of metallic glasses. The STZ dilatational strain is defined as the ratio of STZ-activated free volume to STZ volume itself. The model demonstrates that the STZ dilatational strain will increase drastically and exceed the characteristic shear strain of STZ as temperature decreases below a critical value. This critical temperature is in good agreement with the experimentally measured DBT temperature. Our results suggest that the DBT of metallic glasses is underpinned by the transition of atomic-cluster motions from STZ-type rearrangements to dilatational processes (termed tension transformation zones (TTZs.

  16. Enthalpies of Formation of Transition Metal Diborides: A First Principles Study

    Directory of Open Access Journals (Sweden)

    Catherine Colinet

    2015-11-01

    Full Text Available The enthalpies of formation of transition metals diborides in various structures have been obtained from density functional theory (DFT calculations in order to determine the ground state at T = 0 K and p = 0. The evolution of the enthalpies of formation along the 3D, 4D, and 5D series has been correlated to the considered crystal structures. In the whole, the calculated values of the enthalpies of formation of the diborides in their ground state are in good agreement with the experimental ones when available. The calculated values of the lattice parameters at T = 0 K of the ground state agree well with the experimental values. The total and partial electronic densities of states have been computed. Special features of the transition metal electronic partial density of states have been evidenced and correlated to the local environment of the atoms.

  17. Recombination of charge carriers on radiation-induced defects in silicon doped by transition metals impurities

    CERN Document Server

    Kazakevich, L A

    2003-01-01

    It has been studied the peculiarities of recombination of nonequilibrium charge carriers on radiation-induced defects in received according to Czochralski method p-silicon (p approx 3 - 20 Ohm centre dot cm), doped by one of the impurities of transition metals of the IV-th group of periodic table (titanium, zirconium, hafnium). Experimental results are obtained out of the analysis of temperature and injection dependence of the life time of charge carriers. The results are explained taking into consideration the influences of elastic stress fields created by the aggregates of transition metals atoms on space distribution over the crystal of oxygen and carbon background impurities as well as on the migration of movable radiation-induced defects during irradiation. (authors).

  18. Spatial dependence of the super-exchange interactions for transition-metal trimers in graphene

    Science.gov (United States)

    Crook, Charles B.; Houchins, Gregory; Zhu, Jian-Xin; Balatsky, Alexander V.; Constantin, Costel; Haraldsen, Jason T.

    2018-01-01

    This study examines the magnetic interactions between spatially variable manganese and chromium trimers substituted into a graphene superlattice. Using density functional theory, we calculate the electronic band structure and magnetic populations for the determination of the electronic and magnetic properties of the system. To explore the super-exchange coupling between the transition-metal atoms, we establish the magnetic ground states through a comparison of multiple magnetic and spatial configurations. Through an analysis of the electronic and magnetic properties, we conclude that the presence of transition-metal atoms can induce a distinct magnetic moment in the surrounding carbon atoms as well as produce a Ruderman-Kittel-Kasuya-Yosida-like super-exchange coupling. It is hoped that these simulations can lead to the realization of spintronic applications in graphene through electronic control of the magnetic clusters.

  19. Chiral structures and tunable magnetic moments in 3d transition metal doped Pt6 clusters

    International Nuclear Information System (INIS)

    Zhang Xiu-Rong; Yang Xing; Ding Xun-Lei

    2012-01-01

    The structural, electronic, and magnetic properties of transition metal doped platinum clusters MPt 6 (M=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) are systematically studied by using the relativistic all-electron density functional theory with the generalized gradient approximation. Most of the doped clusters show larger binding energies than the pure Pt 7 cluster, which indicates that the doping of the transition metal atom can stabilize the pure platinum cluster. The results of the highest occupied molecular orbital (HOMO)—lowest unoccupied molecular orbital (LUMO) gaps suggest that the doped clusters can have higher chemical activities than the pure Pt 7 cluster. The magnetism calculations demonstrate that the variation range of the magnetic moments of the MPt 6 clusters is from 0 μ B to 7 μ B , revealing that the MPt 6 clusters have potential utility in designing new spintronic nanomaterials with tunable magnetic properties

  20. Hyperfine spectroscopic study of the metal-insulator transition in V2O3

    Science.gov (United States)

    Forker, M.; Saitovitch, H.; de Jesus Silva, P. R.

    1983-12-01

    The metal-insulator (M-I) transition in vanadium sesquioxide V2O3 has been investigated by time differential perturbed angular correlation measurements of the electric fieldgradient (EFG) and the magnetic hyperfine field at dilute111Cd impurities. The EFG undergoes a first-order change at the M-I transition at Tt=160 K, but does not reflect the high temperature resistivity anomaly. The increase of the EFG with temperature in the metallic phase can be attributed to thermal variations of the oxygen sublattice. The temperature dependence of the magnetic hyperfine field in the insulating phase follows a Brioullin function with a saturation value of Hhf(O)=15 KOe and an extrapolated Neel temperature, which, depending on the impurity concentration, varies between 188 and 230 K.