WorldWideScience

Sample records for ternary transition metal

  1. Ternary Amides Containing Transition Metals for Hydrogen Storage: A Case Study with Alkali Metal Amidozincates.

    Science.gov (United States)

    Cao, Hujun; Richter, Theresia M M; Pistidda, Claudio; Chaudhary, Anna-Lisa; Santoru, Antonio; Gizer, Gökhan; Niewa, Rainer; Chen, Ping; Klassen, Thomas; Dornheim, Martin

    2015-11-01

    The alkali metal amidozincates Li4 [Zn(NH2)4](NH2)2 and K2[Zn(NH2)4] were, to the best of our knowledge, studied for the first time as hydrogen storage media. Compared with the LiNH2-2 LiH system, both Li4 [Zn(NH2)4](NH2)2-12 LiH and K2[Zn(NH2)4]-8 LiH systems showed improved rehydrogenation performance, especially K2[Zn(NH2)4]-8 LiH, which can be fully hydrogenated within 30 s at approximately 230 °C. The absorption properties are stable upon cycling. This work shows that ternary amides containing transition metals have great potential as hydrogen storage materials. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Ternary alkali metal transition metal acetylides A2MC2 (A = Na, K; M = Pd, Pt).

    Science.gov (United States)

    Hemmersbach, S; Zibrowius, B; Kockelmann, W; Ruschewitz, U

    2001-05-04

    Ternary transition metal acetylides A2MC2 (A = Na, K; M = Pd, Pt) can be synthesised by reaction of the respective alkali metal acetylide A2C2 with palladium or platinum in an inert atmosphere at about 350 degrees C. The crystal structures are characterised by (infinity)1[M(C2)(2/2)2-] chains, which are separated by the alkali metals (P3m1, Z = 1). The refinement of neutron powder diffraction data gave C-C = 1.263(3) A for Na2PdC2 (Na2PtC2: 1.289(4) A), which is distinctively longer than the expected value for a C-C triple bond (1.20 A). On the basis of band-structure calculations this can be attributed to a strong back-bonding from the metal into the anti-bonding orbitals of the C2 unit. This was further confirmed by Raman spectroscopic investigations, which showed that the wavenumbers of the C-C stretching vibrations in Na2PdC2 and Na2PtC2 are about 100 cm(-1) smaller than in acetylene. 13C MAS-NMR spectra demonstrated that the acetylenic C2 units in the title compounds are very different from those in acetylene. Electrical conductivity measurements and band-structure calculations showed that the black title compounds are semiconductors with a small indirect band gap (approximately 0.2 eV).

  3. 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.

  4. Density functional theory based screening of ternary alkali-transition metal borohydrides: A computational material design project

    DEFF Research Database (Denmark)

    Hummelshøj, Jens Strabo; Landis, David; Voss, Johannes

    2009-01-01

    We present a computational screening study of ternary metal borohydrides for reversible hydrogen storage based on density functional theory. We investigate the stability and decomposition of alloys containing 1 alkali metal atom, Li, Na, or K (M1); and 1 alkali, alkaline earth or 3d/4d transition...

  5. The ternary post-transition metal carbodiimide SrZn(NCN){sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Corkett, Alex J.; Konze, Philipp M. [Institute of Inorganic Chemistry, RWTH Aachen University, Aachen (Germany); Dronskowski, Richard [Institute of Inorganic Chemistry, RWTH Aachen University, Aachen (Germany); Juelich-Aachen Research Alliance (JARA-HPC), RWTH-Aachen University, Aachen (Germany)

    2017-11-17

    SrZn(NCN){sub 2}, the first example of a ternary post-transition metal carbodiimide, was prepared by a solid-state metathesis reaction. The crystal structure was solved from PXRD data and found to adopt the orthorhombic (Cmcm) BaZnSO structure, a high symmetry modification of that expressed by the oxide analogue SrZnO{sub 2}. Locally, SrZn(NCN){sub 2} features ZnN{sub 4} tetrahedra and SrN{sub 6} trigonal prisms similar to those in quarternary LiSr{sub 2}M(NCN){sub 4} (M = Al{sup 3+} and Ga{sup 3+}) phases, however, the overall topologies are distinct with single chains in the former and double chains in the latter. Electronic structure calculations indicate an indirect bandgap of about 2.95 eV in SrZn(NCN){sub 2}, slightly lower than the experimentally observed bandgap of 3.4 eV in SrZnO{sub 2} and consistent with a greater degree of covalency. The structural similarities between SrZn(NCN){sub 2} and oxychalcogenide analogues highlight the pseudochalcogenide character of NCN{sup 2-} and suggest that the title compound may serve as a template for accessing novel ternary carbodiimides featuring tetrahedrally coordinated transition metals. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  6. Computer simulation of electronic and magnetic properties of ternary chalcopyrites doped with transition metals

    Science.gov (United States)

    Krivosheeva, Anna V.; Shaposhnikov, Victor L.; Borisenko, Victor E.; Arnaud d'Avitaya, François; Lazzari, J.-L.

    2008-07-01

    Electronic and magnetic properties of BeSiAs2 and BeGeAs2 ternary compounds with chalcopyrite structure doped with transition metals (Mn, Cr) have been theoretically studied from the first principles. The influence of the substitutional positions of impurity atoms and their type on the appearance of a ferromagnetic (FM) or antiferromagnetic (AFM) state has been analyzed. It was found that magnetic moment of the systems does not depend strongly on the concentration and distance between impurity atoms, while the most important factors observed are the impurity type and substitution sites. Configurations with Mn atoms in the II-group sites are energetically stable in the AFM state, whereas Cr-doped ones seem to be in the FM state. Substitution of IV-group positions by both metals results preferably in the FM state, however these positions are not energetically favorable in comparison with II-group ones. The spin polarization of doped materials is evaluated and their possible application in spintronics is analyzed.

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

    NARCIS (Netherlands)

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

    1993-01-01

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

  8. Monolayer MoS2 metal insulator transition based memcapacitor modeling with extension to a ternary device

    Directory of Open Access Journals (Sweden)

    Abdul Karim Khan

    2016-09-01

    Full Text Available Memcapacitor model based on its one possible physical realization is developed and simulated in order to know its limitation before making a real device. The proposed device structure consists of vertically stacked dielectric layer and MoS2 monolayer between two external metal plates. The Metal Insulator Transition (MIT phenomenon of MoS2 monolayer is represented in terms of percolation probabilty which is used as the system state. Cluster based site percolation theory is used to mimic the MIT of MoS2 which shows slight discontinuous change in MoS2 monolayer conductivity. The metal to insulator transition switches the capacitance of the device in hysterical way. An Ioffe Regel criterion is used to determine the MIT state of MoS2 monolayer. A good control of MIT time in the range of psec is also achieved by changing a single parameter in the model. The model shows memcapacitive behavior with an edge of fast switching (in psec range over the previous general models. The model is then extended into vertical cascaded version which behaves like a ternary device instead of binary.

  9. Potentiometric studies on ternary complexes involving some divalent transition metal ions, gallic acid and biologically abundant aliphatic dicarboxylic acids in aqueous solutions

    Directory of Open Access Journals (Sweden)

    Abdelatty Mohamed Radalla

    2015-06-01

    Full Text Available Formation of binary and ternary complexes of the divalent transition metal ions, Cu2+, Ni2+, Co2+ and Zn2+ with gallic acid and the biologically important aliphatic dicarboxylic acids (adipic, succinic, malic, malonic, maleic, tartaric and oxalic acids were investigated by means of the potentiometric technique at 25 °C and I = 0.10 mol dm−3 NaNO3. The acid-base properties of the ligands were investigated and discussed. The acidity constants of gallic acid and aliphatic dicarboxylic acids were determined and used for determining the stability constants of the binary and ternary complexes formed in the aqueous medium under the above experimental conditions. The formation of the different 1:1 and 1:2 binary complexes and 1:1:1 ternary complexes are inferred from the corresponding potentiometric pH-metric titration curves. The ternary complex formation was found to occur in a stepwise manner. The stability constants of these binary and ternary systems were calculated. The values of Δ log K, percentage of relative stabilization (%R.S. and log X were evaluated and discussed. The concentration distribution of the various complex species formed in solution was evaluated and discussed. The mode of chelation of ternary complexes formed was ascertained by conductivity measurements.

  10. Rapid microwave-assisted preparation of binary and ternary transition metal sulfide compounds

    Energy Technology Data Exchange (ETDEWEB)

    Butala, Megan M.; Perez, Minue A.; Arnon, Shiri; Göbel, Claudia; Preefer, Molleigh B.; Seshadri, Ram

    2017-12-01

    Transition metal chalcogenides are of interest for energy applications, including energy generation in photoelectrochemical cells and as electrodes for next-generation electrochemical energy storage. Synthetic routes for such chalcogenides typically involve extended heating at elevated temperatures for multiple weeks. We demonstrate here the feasibility of rapidly preparing select sulfide compounds in a matter of minutes, rather than weeks, using microwave-assisted heating in domestic microwaves. We report the preparations of phase pure FeS2, CoS2, and solid solutions thereof from the elements with only 40 min of heating. Conventional furnace and rapid microwave preparations of CuTi2S4 both result in a majority of the targeted phase, even with the significantly shorter heating time of 40 min for microwave methods relative to 12 days using a conventional furnace. The preparations we describe for these compounds can be extended to related structures and chemistries and thus enable rapid screening of the properties and performance of various compositions of interest for electronic, optical, and electrochemical applications.

  11. Binary and ternary complexes of some inner transition metal ions with amino acids and acetyl acetone

    Science.gov (United States)

    Abu-Eittah, R. H.; Abdou, M. M.; Salem, M. B.

    1998-05-01

    The stability constants of the 1:1 and 1:2 (whenever possible) complexes formed between La3+, Ce3+, Th4+ and the amino acid anions L-alaninate, L-phenylalaninate and L-histidinate were determined by potentiometric titration in aqueous solution (25± 1 ^circC, I = 0.1 M KCl) and compared together with the constants previously determined. The various formation degree of the resulting M(L) and M(L)2 were determined. In order to relate the formation degree of M(L) and M(L)2 with the basicity of the amino acid anion (L^-), the acidity constants of the protonated amino acids, H2L^+, were also measured. The main results of this work prove that Th4+ ion forms the strongest complex with the studied amino acids. It is the only ion which forms a 1:2 complex. The heterocyclic ring of histidine plays a significant role in complexing with the studied metal ions as is clearly seen from the distribution of the degree of formation of the different complexes. The stability constants of the 1:1:1, 1:2:1 and 1:1:2 complexes formed between La3+, Ce3+, Th4+ and the anions L-alaninate, L-phenylalaninate and L-histidinate together with the acetyl acetonate ion were also determined following the same experimental set up used in the study of the simple complexes. The mixed-ligand complexes turned out to be very much stronger than the simple ligand complexes. Formation of a mixed ligand complex can be considered as a type of senergism. Les constantes de stabilité des complexes 1:1 et 2:2 (lorsque cela est possible) formés entre La3+, Ce3+, Th4+ et les anions aminoacides L-alaninate, L-phénylalaninate et L-histidinate ont été déterminées par dosage potentiométrique en solution aqueuse (25± 1 ^circC, I = 0,1 M KCl), et comparées à celles de la littérature. Les différents degrés de formation de M(L) et M(L)2 ont été quantifiés. Pour mettre en évidence la relation entre le degré de formation de M(L) et M(L)2 et la basicité des anions aminoacides (L^-), les constantes d

  12. Superconducting state parameters of ternary metallic glasses

    Indian Academy of Sciences (India)

    Administrator

    pseudopotential to ternary metallic glasses involves the assumption of pseudoions with average properties, which are assumed to replace three types of ions in the ternary systems, and a gas of free electrons is assumed to perme- ate through them. The electron–pseudoion is accounted by the pseudopotential, and the ...

  13. 2D Transition Metal Dichalcogenides and Graphene-Based Ternary Composites for Photocatalytic Hydrogen Evolution and Pollutants Degradation

    OpenAIRE

    Chen, Ying; Sun, Hongqi; Peng, Wenchao

    2017-01-01

    Photocatalysis have attracted great attention due to their useful applications for sustainable hydrogen evolution and pollutants degradation. Transition metal dichalcogenides (TMDs) such as MoS2 and WS2 have exhibited great potential as cocatalysts to increase the photo-activity of some semiconductors. By combination with graphene (GR), enhanced cocatalysts of TMD/GR hybrids could be synthesized. GR here can act as a conductive electron channel for the transport of the photogenerated electron...

  14. Large scale simulations of the mechanical properties of layered transition metal ternary compounds for fossil energy power system applications

    Energy Technology Data Exchange (ETDEWEB)

    Ching, Wai-Yim [Univ. of Missouri, Kansas City, MO (United States)

    2014-12-31

    Advanced materials with applications in extreme conditions such as high temperature, high pressure, and corrosive environments play a critical role in the development of new technologies to significantly improve the performance of different types of power plants. Materials that are currently employed in fossil energy conversion systems are typically the Ni-based alloys and stainless steels that have already reached their ultimate performance limits. Incremental improvements are unlikely to meet the more stringent requirements aimed at increased efficiency and reduce risks while addressing environmental concerns and keeping costs low. Computational studies can lead the way in the search for novel materials or for significant improvements in existing materials that can meet such requirements. Detailed computational studies with sufficient predictive power can provide an atomistic level understanding of the key characteristics that lead to desirable properties. This project focuses on the comprehensive study of a new class of materials called MAX phases, or Mn+1AXn (M = a transition metal, A = Al or other group III, IV, and V elements, X = C or N). The MAX phases are layered transition metal carbides or nitrides with a rare combination of metallic and ceramic properties. Due to their unique structural arrangements and special types of bonding, these thermodynamically stable alloys possess some of the most outstanding properties. We used a genomic approach in screening a large number of potential MAX phases and established a database for 665 viable MAX compounds on the structure, mechanical and electronic properties and investigated the correlations between them. This database if then used as a tool for materials informatics for further exploration of this class of intermetallic compounds.

  15. 2D Transition Metal Dichalcogenides and Graphene-Based Ternary Composites for Photocatalytic Hydrogen Evolution and Pollutants Degradation.

    Science.gov (United States)

    Chen, Ying; Sun, Hongqi; Peng, Wenchao

    2017-03-15

    Photocatalysis have attracted great attention due to their useful applications for sustainable hydrogen evolution and pollutants degradation. Transition metal dichalcogenides (TMDs) such as MoS₂ and WS₂ have exhibited great potential as cocatalysts to increase the photo-activity of some semiconductors. By combination with graphene (GR), enhanced cocatalysts of TMD/GR hybrids could be synthesized. GR here can act as a conductive electron channel for the transport of the photogenerated electrons, while the TMDs nanosheets in the hybrids can collect electrons and act as active sites for photocatalytic reactions. This mini review will focus on the application of TMD/GR hybrids as cocatalysts for semiconductors in photocatalytic reactions, by which we hope to provide enriched information of TMD/GR as a platform to develop more efficient photocatalysts for solar energy utilization.

  16. 2D Transition Metal Dichalcogenides and Graphene-Based Ternary Composites for Photocatalytic Hydrogen Evolution and Pollutants Degradation

    Directory of Open Access Journals (Sweden)

    Ying Chen

    2017-03-01

    Full Text Available Photocatalysis have attracted great attention due to their useful applications for sustainable hydrogen evolution and pollutants degradation. Transition metal dichalcogenides (TMDs such as MoS2 and WS2 have exhibited great potential as cocatalysts to increase the photo-activity of some semiconductors. By combination with graphene (GR, enhanced cocatalysts of TMD/GR hybrids could be synthesized. GR here can act as a conductive electron channel for the transport of the photogenerated electrons, while the TMDs nanosheets in the hybrids can collect electrons and act as active sites for photocatalytic reactions. This mini review will focus on the application of TMD/GR hybrids as cocatalysts for semiconductors in photocatalytic reactions, by which we hope to provide enriched information of TMD/GR as a platform to develop more efficient photocatalysts for solar energy utilization.

  17. Formation of ternary Mg–Cu–Dy bulk metallic glasses

    Indian Academy of Sciences (India)

    Administrator

    Abstract. The glass-forming ability (GFA) of ternary Mg–Cu–Dy alloys was systematically investigated by using differential scanning calorimetry (DSC) and X-ray diffractometry (XRD) techniques. The results showed that a series of ternary Mg–Cu–Dy bulk metallic glasses (BGMs) with a diameter of 4–8 mm were suc-.

  18. Superconductivity in the metal rich Li-Pd-B ternary boride.

    Science.gov (United States)

    Togano, K; Badica, P; Nakamori, Y; Orimo, S; Takeya, H; Hirata, K

    2004-12-10

    Superconductivity at about 8 K was observed in the metal-rich Li-Pd-B ternary system. Structural, microstructural, electrical, and magnetic investigations for various compositions proved that the Li2Pd3B compound, which has an antiperovskite cubic structure composed of distorted Pd6B octahedrons, is responsible for the superconductivity. This is the first observation of superconductivity in metal-rich ternary borides containing alkaline metal and Pd as a late transition metal. The compound prepared by arc melting has a high density and is relatively stable in the air. The upper critical fields H(c2)(0) estimated by linear extrapolation and the Werthamer-Helfand-Hohenberg theory are 6.2 and 4.8 T, respectively.

  19. On new ternary equiatomic scandium transition metal aluminum compounds ScTAl with T = Cr, Ru, Ag, Re, Pt, and Au

    Energy Technology Data Exchange (ETDEWEB)

    Radzieowski, Mathis; Janka, Oliver [Muenster Univ. (Germany). Inst. fuer Anorganische und Analytische Chemie; Benndorf, Christopher [Muenster Univ. (Germany). Inst. fuer Anorganische und Analytische Chemie; Muenster Univ. (Germany). Inst. fuer Physikalische Chemie; Haverkamp, Sandra [Muenster Univ. (Germany). Inst. fuer Physikalische Chemie; Eckert, Hellmut [Muenster Univ. (Germany). Inst. fuer Physikalische Chemie; University of Sao Paulo, Sao Carlos, SP (Brazil). Inst. of Physics

    2016-08-01

    The new equiatomic scandium transition metal aluminides ScTAl for T = Cr, Ru, Ag, Re, Pt, and Au were obtained by arc-melting of the elements followed by subsequent annealing for crystal growth. The samples were studied by powder and single crystal X-ray diffraction. The structures of three compounds were refined from single crystal X-ray diffractometer data: ScCrAl, MgZn{sub 2} type, P6{sub 3}/mmc, a = 525.77(3), c = 858.68(5) pm, R{sub 1} = 0.0188, wR{sub 2} = 0.0485, 204 F{sup 2} values, 13 variables, ScPtAl, TiNiSi type, Pnma, a = 642.83(4), b = 428.96(2), c = 754.54(5) pm, R{sub 1} = 0.0326, wR{sub 2} = 0.0458, 448 F{sup 2} values, 20 variables and ScAuAl, HfRhSn type, P anti 62c, a = 722.88(4), c = 724.15(4) pm, R{sub 1} = 0.0316, wR{sub 2} = 0.0653, 512 F{sup 2} values, 18 variables. Phase pure samples of all compounds were furthermore investigated by magnetic susceptibility measurements, and Pauli-paramagnetism but no superconductivity was observed down to 2.1 K for all of them. The local structural features and disordering phenomena have been characterized by {sup 27}Al and {sup 45}Sc magic angle spinning (MAS) and static NMR spectroscopic investigations.

  20. 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.

  1. Issues Affecting the Synthetic Scalability of Ternary Metal Ferrite Nanoparticles

    Directory of Open Access Journals (Sweden)

    Lauren Morrow

    2015-01-01

    Full Text Available Ternary Mn-Zn ferrite (MnxZn1-xFe2O4 nanoparticles (NPs have been prepared by the thermal decomposition of an oleate complex, sodium dodecylbenzenesulfonate (SDBS mediated hydrazine decomposition of the chloride salts, and triethylene glycol (TREG mediated thermal decomposition of the metal acetylacetonates. Only the first method was found to facilitate the synthesis of uniform, isolable NPs with the correct Mn : Zn ratio (0.7 : 0.3 as characterized by small angle X-ray scattering (SAXS, transmission electron microscopy (TEM, and inductively coupled plasma-optical emission spectroscopy (ICP-OES. Scaling allowed for retention of the composition and size; however, attempts to prepare Zn-rich ferrites did not result in NP formation. Thermogravimetric analysis (TGA indicated that the incomplete decomposition of the metal-oleate complexes prior to NP nucleation for Zn-rich compositions is the cause.

  2. Semiconducting transition metal oxides

    Science.gov (United States)

    Lany, Stephan

    2015-07-01

    Open shell transition metal oxides are usually described as Mott or charge transfer insulators, which are often viewed as being disparate from semiconductors. Based on the premise that the presence of a correlated gap and semiconductivity are not mutually exclusive, this work reviews electronic structure calculations on the binary 3d oxides, so to distill trends and design principles for semiconducting transition metal oxides. This class of materials possesses the potential for discovery, design, and development of novel functional semiconducting compounds, e.g. for energy applications. In order to place the 3d orbitals and the sp bands into an integrated picture, band structure calculations should treat both contributions on the same footing and, at the same time, account fully for electron correlation in the 3d shell. Fundamentally, this is a rather daunting task for electronic structure calculations, but quasi-particle energy calculations in GW approximation offer a viable approach for band structure predictions in these materials. Compared to conventional semiconductors, the inherent multivalent nature of transition metal cations is more likely to cause undesirable localization of electron or hole carriers. Therefore, a quantitative prediction of the carrier self-trapping energy is essential for the assessing the semiconducting properties and to determine whether the transport mechanism is a band-like large-polaron conduction or a small-polaron hopping conduction. An overview is given for the binary 3d oxides on how the hybridization between the 3d crystal field symmetries with the O-p orbitals of the ligands affects the effective masses and the likelihood of electron and hole self-trapping, identifying those situations where small masses and band-like conduction are more likely to be expected. The review concludes with an illustration of the implications of the increased electronic complexity of transition metal cations on the defect physics and doping, using

  3. Glass transition behavior of ternary disaccharide-ethylene glycol-water solutions

    Science.gov (United States)

    Yu, Tongxu; Zhao, Lishan; Wang, Qiang; Cao, Zexian

    2017-06-01

    Glass transition behavior of ternary disaccharide-ethylene glycol-water solutions, in reference to that of the binary combinations, has been investigated towards a better understanding of their cryoprotective ability. In water-deficient solutions, the disaccharides, including trehalose, sucrose and maltose, can associate with more than 100 ethylene glycol molecules to form amorphous complex, one order of magnitude larger than the corresponding hydration numbers. In water-rich solutions, a second glass transition emerges with increasing molar fraction of ethylene glycol, indicating the possible synergy of disaccharides and ethylene glycol in vitrification of the ternary aqueous solution.

  4. 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…

  5. Transition metals in plant photosynthesis.

    Science.gov (United States)

    Yruela, Inmaculada

    2013-09-01

    Transition metals are involved in essential biological processes in plants since they are cofactors of metalloproteins and also act as regulator elements. Particularly, plant chloroplasts are organelles with high transition metal ion demand because metalloproteins are involved in the photosynthetic electron transport chain. The transition metal requirement of photosynthetic organisms greatly exceeds that of non-photosynthetic organisms, and either metal deficiency or metal excess strongly impacts photosynthetic functions. In chloroplasts, the transition metal ion requirement needs a homeostasis network that strictly regulates metal uptake, chelation, trafficking and storage since under some conditions metals cause toxicity. This review gives an overview of the current understanding of main features concerning the role of copper (Cu), iron (Fe), manganese (Mn) and zinc (Zn) in plant photosynthesis as well as the mechanisms involved in their homeostasis within chloroplasts. The metalloproteins functioning in photosynthetic proteins of plants as well as those proteins participating in the metal transport and metal binding assembly are reviewed. Furthermore, the role of nickel (Ni) in artificial photosynthesis will be discussed.

  6. Effect of environment in hypersensitive transitions of Nd/sup 3 +/ ternary complexes

    Energy Technology Data Exchange (ETDEWEB)

    Gupta, A.K.; Bhutra, M.P. (Jodhpur Univ. (India). Dept. of Physics)

    1983-11-01

    Absorption spectra of ternary complexes of Nd/sup 3 +/ in different environments, viz. methanol, formamide and dimethyl sulphoxide, have been recorded taking glycine, alanine, valine and methionine as primary ligands and propane-1, 2-diol as secondary, ligand. The transition /sup 4/Gsub(5/2)<-/sup 4/Isub(9/2) obeying the selection rule ..delta..J/<=2, known as hypersensitive transition has been studied for four Nd/sup 3 +/ complexes. The results indicate that the hypersensitivity may be explained by means of vibronic mechanism with inclusion of covalency. Effect of different environments on hypersensitive transition has been discussed.

  7. Shear-induced transitions in a ternary polymeric system

    NARCIS (Netherlands)

    Zvelindovsky, AV; Sevink, GJA; Fraaije, JGEM

    The first three-dimensional simulation of shear-induced phase transitions in a polymeric system has been performed. The method is based on dynamic density-functional theory. The pathways between a bicontinuous phase with developing gyroid mesostructure and a lamellar/cylinder phase coexistence are

  8. 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...... divided into cyclization reactions to carbocycles and branching reactions at terminal and non-terminal positions. In addition, carbon-oxygen and carbon-hydrogen bond forming reactions are illustrated by various oxidation and reduction procedures...

  9. Metal-amino acid (or peptide)-nucleoside (or related bases) ternary complexes

    Energy Technology Data Exchange (ETDEWEB)

    Terron, A.; Fiol, J.J.; Herrero, L.A.; Garcia-Raso, A. [Departament de Quimica. Universitat de les Illes Balears. Palma de Mallorca. (Spain); Apella, M.C. [Cerela Centro de Referencia de Lactobacilos, Tucaman, Argentina (Antigua and Barbuda); Caubet, A.; Moreno, V. [Departament de Quimica Inorganica. Universitat de Barcelona. Barcelona (Spain)

    1997-05-01

    The knowledge of simultaneous metal ion interaction with proteins and nucleic acids is one of the most exciting subjects inside the Inorganic Biochemistry. In the last years, several groups have published articles on the synthesis and characterization of ternary complexes bringing relevant data on the structure and stability of metallo biomolecules. In this short review, the last contributions found in the literature are collected. Comments on the factors influencing the behaviour and stability of these systems are offered. (Author) 100 refs.

  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 September 1999 pp 63-81. Fulltext. Click here to view fulltext PDF. Permanent link: http://www.ias.ac.in/article/fulltext/reso/004/09/0063-0081 ...

  11. Synthesis and Characterization of Novel Ternary and Quaternary Alkali Metal Thiophosphates

    KAUST Repository

    Alahmary, Fatimah S.

    2014-05-01

    The ongoing development of nonlinear optical (NLO) crystals such as coherent mid-IR sources focuses on various classes of materials such as ternary and quaternary metal chalcophosphates. In case of thiophosphates, the connection between PS4-tetrahedral building blocks and metals gives rise to a broad structural variety where approximately one third of all known ternary (A/P/S) and quaternary (A/M/P/S) (A = alkali metal, M = metal) structures are acentric and potential nonlinear optical materials. The molten alkali metal polychalcophosphate fluxes are a well-established method for the synthesis of new ternary and quaternary thiophosphate and selenophosphate compounds. It has been a wide field of study and investigation through the last two decades. Here, the flux method is used for the synthesis of new quaternary phases containing Rb, Ag, P and S. Four new alkali metal thiophosphates, Rb4P2S10, RbAg5(PS4), Rb2AgPS4 and Rb3Ag9(PS4)4, have been synthesized successfully from high purity elements and binary starting materials. The new compounds were characterized by single crystal and powder X-ray diffraction, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), ultraviolet-visible (UV-VIS), Raman spectroscopy, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). These compounds show interesting structural variety and physical properties. The crystal structures feature 3D anionic framework built up of PS4 tetrahedral units and charge balanced by Ag and alkali metal cations. All prepared compounds are semiconductors with band gap between 2.3 eV to 2.6 eV and most of them are thermally stable up to 600ºC.

  12. Transition metals in superheat melts

    Science.gov (United States)

    Jakes, Petr; Wolfbauer, Michael-Patrick

    1993-01-01

    A series of experiments with silicate melts doped with transition element oxides was carried out at atmospheric pressures of inert gas at temperatures exceeding liquidus. As predicted from the shape of fO2 buffer curves in T-fO2 diagrams the reducing conditions for a particular oxide-metal pair can be achieved through the T increase if the released oxygen is continuously removed. Experimental studies suggest that transition metals such as Cr or V behave as siderophile elements at temperatures exceeding liquidus temperatures if the system is not buffered by the presence of other oxide of more siderophile element. For example the presence of FeO prevents the reduction of Cr2O3. The sequence of decreasing siderophility of transition elements at superheat conditions (Mo, Ni, Fe, Cr) matches the decreasing degree of depletion of siderophile elements in mantle rocks as compared to chondrites.

  13. Ternary Complexes of some Divalent Metal Ions with Potentially ...

    African Journals Online (AJOL)

    ... and residual analysis. The predominant species detected were ML2XH2, MLXH2 and MLX2 for Ca(II), Mg(II) and Zn(II). The formation and distribution of different species with relative concentrations of metal and ligands with varying pH are represented in the form of distribution diagrams. The influence of the solvent on the ...

  14. The analysis of fuel constituent redistribution for ternary metallic fuel slug

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Byoung Oon; Lee, Dong Uk; Kim, Young Kyun; Chang, Jin Wook; Lee, Ki Bok; Kim, Young Il

    2004-02-01

    U-TRU-Zr metallic alloy is being considered as the fuel slug for the proliferation resistance core of KALIMER. The radial fuel constituent migration is a general phenomenon in the metallic alloys. This phenomenon may affect the in-reactor performance of metallic fuel rods, influencing such factors as melting temperature, thermal conductivity, power generation rate, phase boundaries and eutectic melting of the fuel slug. Thus, constituent redistribution modeling is essential when developing a metallic fuel performance code. The constituent migration model adopted in this report was based on the Ishida's model and Hofman's theory. A subroutine program has been made and installed into the MACSIS code to simulate constituent redistribution. The radial profile of Zr redistribution was calculated for the ternary metallic fuel, and compared with the measured data.

  15. Ternary Complexes of some Divalent Metal Ions with Potentially ...

    African Journals Online (AJOL)

    NICO

    studied in varying concentrations (0.0–60.0 % v/v) of 1, 4-dioxane-water mixtures maintaining an ionic strength of 0.16 mol L–1 sodium chloride at 303.0 K. ... enzymes, the activity of which is due to metal-enzyme-substrate complexes. The active .... static interaction is related to the dielectric constant of the medium and log Д ...

  16. Ternary toxicological interactions of insecticides, herbicides, and a heavy metal on the earthworm Eisenia fetida

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yanhua [State Key Laboratory Breeding Base for Zhejiang Sustainable Pest and Disease Control/Key Laboratory for Pesticide Residue Detection of Ministry of Agriculture, Institute of Quality and Standard for Agro-products, Zhejiang Academy of Agricultural Sciences, Hangzhou 310021 (China); Chen, Chen [Key Laboratory of Agro-Product Quality and Safety of Ministry of Agriculture, Institute of Quality Standards and Testing Technology for Agro-Products, Chinese Academy of Agricultural Sciences, Beijing 100081 (China); Qian, Yongzhong, E-mail: qyzcaas@aliyun.com [Key Laboratory of Agro-Product Quality and Safety of Ministry of Agriculture, Institute of Quality Standards and Testing Technology for Agro-Products, Chinese Academy of Agricultural Sciences, Beijing 100081 (China); Zhao, Xueping [State Key Laboratory Breeding Base for Zhejiang Sustainable Pest and Disease Control/Key Laboratory for Pesticide Residue Detection of Ministry of Agriculture, Institute of Quality and Standard for Agro-products, Zhejiang Academy of Agricultural Sciences, Hangzhou 310021 (China); Wang, Qiang, E-mail: qiangwang2003@vip.sina.com [State Key Laboratory Breeding Base for Zhejiang Sustainable Pest and Disease Control/Key Laboratory for Pesticide Residue Detection of Ministry of Agriculture, Institute of Quality and Standard for Agro-products, Zhejiang Academy of Agricultural Sciences, Hangzhou 310021 (China)

    2015-03-02

    Highlights: • The combined toxicity of insecticides, herbicides, and a heavy metal was examined. • Acute earthworm toxicity assays were conducted in twenty-one ternary mixtures. • Synergism predominated in the majority of the mixtures at low effect levels. • Combination index method could more accurately predict the combined toxicity. - Abstract: The combined toxicities of five insecticides (chlorpyrifos, avermectin, imidacloprid, λ-cyhalothrin, and phoxim), two herbicides (atrazine and butachlor), and a heavy metal (cadmium) have been examined using the acute toxicity test on the earthworm. With a concentration of 2.75 mg/kg being lethal for 50% of the organisms, imidacloprid exhibited the highest acute toxicity toward the earthworm Eisenia fetida. Toxicological interactions of these chemicals in ternary mixtures were studied using the combination-index (CI) equation method. Twenty-one ternary mixtures exhibited various interactive effects, in which 11 combinations showed synergistic effects, four led to dual synergistic/additive behaviors, one exhibited an additive effect, and five showed increasing antagonism within the entire range of effects. The CI method was compared with the classical models of concentration addition and independent action, and it was found that the CI method could accurately predict combined toxicity of the chemicals studied. The predicted synergism in the majority of the mixtures, especially at low-effect levels, might have implications in the real terrestrial environment.

  17. 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...

  18. Synthesis and application of a ternary composite of clay, saw-dust and peanut husks in heavy metal adsorption.

    Science.gov (United States)

    Mungondori, Henry H; Mtetwa, Sandile; Tichagwa, Lilian; Katwire, David M; Nyamukamba, Pardon

    2017-05-01

    The adsorption of a multi-component system of ferrous, chromium, copper, nickel and lead on single, binary and ternary composites was studied. The aim of the study was to investigate whether a ternary composite of clay, peanut husks (PH) and saw-dust (SD) exhibited a higher adsorption capacity than that of a binary system of clay and SD as well as a single component adsorbent of PH alone. The materials were used in their raw state without any chemical modifications. This was done to retain the cost effective aspect of the naturally occurring adsorbents. The adsorption capacities of the ternary composite for the heavy metals Fe 2+ , Cr 3+ , Cu 2+ , Ni 2+ and Pb 2+ were 41.7 mg/g, 40.0 mg/g, 25.5 mg/g, 41.5 mg/g and 39.0 mg/g, respectively. It was found that the ternary composite exhibited excellent and enhanced adsorption capacity compared with both a binary and single adsorbent for the heavy metals Fe 2+ , Ni 2+ and Cr 3+ . Characterization of the ternary composites was done using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). Kinetic models and adsorption isotherms were also studied. The pseudo second order kinetic model and the Langmuir adsorption isotherm best described the adsorption mechanisms for the ternary composite towards each of the heavy metal ions.

  19. Asymmetric supercapacitors with metal-like ternary selenides and porous graphene electrodes

    KAUST Repository

    Xia, Chuan

    2016-04-14

    Asymmetric supercapacitors provide a promising approach to fabricate capacitive energy storage devices with high energy and power densities. In this work, asymmetric supercapacitors with excellent performance have been fabricated using ternary (Ni, Co)0.85Se on carbon fabric as bind-free positive electrode and porous free-standing graphene films as negative electrode. Owing to their metal-like conductivity (~1.67×106 S m−1), significant electrochemical activity, and superhydrophilic nature, our nanostructured ternary nickel cobalt selenides result in a much higher areal capacitance (2.33 F cm−2 at 4 mA cm−2), better rate performance and cycling stability than their binary selenide equivalents, and other ternary oxides and chalcogenides. Those hybrid supercapacitors can afford impressive areal capacitance and stack capacitance of 529.3 mF cm−2 and 6330 mF cm−3 at 1 mA cm−2, respectively. More impressively, our optimized asymmetric device operating at 1.8 V delivers a very high stack energy density of 2.85 mWh cm−3 at a stack power density of 10.76 mW cm−3, as well as 85% capacitance retention after 10,000 continuous charge-discharge cycles. Even at a high stack power density of 1173 mW cm−3, this device still deliveries a stack energy density of 1.19 mWh cm−3, superior to most of the reported supercapacitors.

  20. Synthesis of ternary nitrides by mechanochemical alloying

    DEFF Research Database (Denmark)

    Jacobsen, C.J.H.; Zhu, J.J.; Lindelov, H.

    2002-01-01

    Ternary metal nitrides ( of general formula MxM'N-y(z)) attract considerable interest because of their special mechanical, electrical, magnetic, and catalytic properties. Usually they are prepared by ammonolysis of ternary oxides (MxM'O-y(m)) at elevated temperatures. We show that ternary...... nitrides by mechanochemical alloying of a binary transition metal nitride (MxN) with an elemental transition metal. In this way, we have been able to prepare Fe3Mo3N and Co3Mo3N by ball-milling of Mo2N with Fe and Co, respectively. The transformation sequence from the starting materials ( the binary...... nitride and the transition metal) to the ternary nitride was followed by Mossbauer spectroscopy (for Fe3Mo3N) and by X-ray powder diffraction ( for both Fe3Mo3N and Co3Mo3N). Usually, the preparation of a given ternary nitride by ammonolysis of a ternary oxide is dependent on the availability of an oxide...

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. Study of pressure induced polyamorphic transition in Ce-based ternary BMG using in situ x-ray scattering and electrical conductivity measurement

    Science.gov (United States)

    Chen, J.; Ma, C.; Tang, R.; Li, L.; Liu, H.; Gao, C.; Yang, W.

    2015-12-01

    In situ high energy x-ray scattering and electrical conductivity measurements on Ce70Al10Cu20 bulk metallic glass have been conducted using a diamond anvil cell (DAC) in conjunction with synchrotron x-rays or a laboratory electrical measurement system. The relative volumetric change (V/V0) as a function of pressure is inferred using the first sharp diffraction peak (FSDP) and the universal fractional noncubic power law[1]. The result indicates a pressure-induced polyamorphic transition at about 4 GPa in the ternary system. While the observed pressure of such polyamorphic transition in the Ce-base binary BMG is not very sensitive to its composition based on some of the previous studies[2, 3], this study indicates that such transition pressure increases considerably when a new component is added to the system. In the electrical conductivity measurement, a significant resistance change was observed in the pressure range coupled to polyamorphic transition. More discussions will be given regarding the electrical conductivity behavior of this system under high pressure to illustrate the delocalization of 4f electrons as the origin of the observed polyamorphic transition. References: 1. Zeng Q, Kono Y, Lin Y, Zeng Z, Wang J, Sinogeikin SV, Park C, Meng Y, Yang W, Mao H-K (2014) Universal fractional noncubic power law for density of metallic glasses. Physical Review Letters 112: 185502-185502 2. Zeng Q-S, Ding Y, Mao WL, Yang W, Sinogeikin SV, Shu J, Mao H-K, Jiang JZ (2010) Origin of pressure-induced polyamorphism in Ce75Al25 metallic glass. Physical Review Letters 104: 105702-105702 3. Sheng HW, Liu HZ, Cheng YQ, Wen J, Lee PL, Luo WK, Shastri SD, Ma E (2007) Polyamorphism in a metallic glass. Nature Materials DOI: 10.1038/nmat1839.

  6. Metal insulator transition in FeWN2: DFT and DFT+U study

    Science.gov (United States)

    Messiad, Meriem; Zanat, Kamel; Hamidani, Ali

    2017-11-01

    We have studied the electronic and magnetic properties of layered ternary transition metal nitrides, FeWN2. We found that the density functional theory (DFT) based approaches within the generalized gradient approximation frameworks fail to predict the correct ground state configuration. While the DFT plus on-site repulsion U method (DFT+U) predict the AF ordering which it's in good agreement with experiment. We found that the metal-insulator transition is accompanied by a magnetic phase transition which occurred at the same time, a ferromagnetic-metallic to antiferromagnetic-insulating transition where Ueff = 3eV . It is shown also that magnetism and correlation effects are important in band-gap formation in this compound. Our calculated results by DFT-mBJ show the same trend of the band gap. The fully spin polarized DOS at the Fermi level in FM phase makes from FeWN2 a promising candidate material for spintronic applications.

  7. New type of half-metallic antiferromagnet: transition metal pnictides

    Science.gov (United States)

    Long, N. H.; Ogura, M.; Akai, H.

    2009-02-01

    The electronic structures of transition metal pnictides ABX2, where A and B are the transition metal elements and X = N, P, As, Sb, and Bi, with the total valence d-electron number of the transition metal ions being ten, are investigated in the framework of the first-principles KKR Green's function method. Some possible crystal structures such as NiAs-type, NaCl-type, chalcopyrite, zinc-blende, wurtzite, and MnP-type structures are assumed. Similarly to chalcogenides, a new type of spin-compensated half-metallic ferrimagnet is found for the case of nitrides. The stability and magnetic transition temperature of these nitrides indicate that they are good candidates for spintronics materials. For other cases of pnictides such as P, As, Sb, and Bi, the half-metallicity seems not to be realized.

  8. Interfacial properties of semiconducting transition metal chalcogenides

    Science.gov (United States)

    Jaegermann, W.; Tributsch, H.

    This review is aimed at the correlation of structural and electronic properies of semiconducting transition metal chalcogenides with molecular surface processes and mechanisms in photoelectrochemistry, (photo)catalysis, geochemistry and hydrometallurgy. Layer-type, pyrite structured and transition metal cluster containing chalcogenides are selected as model systems to explain the principles involved. Special emphasis is given to the discussion of materials which involve transition metal d- states in the interfacial reaction pathways of holes and electrons. Since they initiate and control heterogeneous coordination chemistry at the surfaces they may provide the possibility of tailoring selective and catalytically demanding reactions. Examples of such mechanisms are presented and discussed in relation to surface properties involved.

  9. 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.

  10. Electronic doping of transition metal oxide perovskites

    Science.gov (United States)

    Cammarata, Antonio; Rondinelli, James M.

    2016-05-01

    CaFeO3 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 CaFeO3. 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.

  11. Quantum Dot Sensitized Solar Cells Based on Ternary Metal Oxide Nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Wenyong [Univ. of Wyoming, Laramie, WY (United States); Tang, Jinke [Univ. of Wyoming, Laramie, WY (United States); Dahnovsky, Yuri [Univ. of Wyoming, Laramie, WY (United States); Pikal, Jon M [Univ. of Wyoming, Laramie, WY (United States); Chien, TeYu [Univ. of Wyoming, Laramie, WY (United States)

    2017-11-03

    In Phase I of this project we investigate quantum dot sensitized solar cells (QDSSCs) based on ternary metal oxide nanowires and study the physical and chemical mechanisms that govern device operation. Our research has the following five objectives: (1) synthesis of ternary metal oxide nanowires, (2) synthesis of QDs and exploration of non-solution based QD deposition methods, (3) physical and electro-optical characterizations of fabricated solar devices, (4) device modeling and first-principle theoretical study of transport physics, and (5) investigation of long-term stability issues of QD sensitized solar cells. In Phase II of this project our first major research goal is to investigate magnetically doped quantum dots and related spin polarization effect, which could improve light absorption and suppress electron relaxation in the QDs. We will utilize both physical and chemical methods to synthesize these doped QDs. We will also study magnetically modified nanowires and introduce spin-polarized transport into QDSSCs, and inspect its impact on forward electron injection and back electron transfer processes. Our second goal is to study novel solid-state electrolytes for QDSSCs. Specifically, we will inspect a new type of polymer electrolytes based on a modified polysulfide redox couple, and examine the effect of their electrical properties on QDSSC performance. These solid-state electrolytes could also be used as filler materials for in situ sample fracturing in STM and enable cross-sectional interface examination of QD/nanowire structures. Our third research goal is to examine the interfacial properties such as energy level alignment at QD/nanowire interfaces using the newly developed Cross-sectional Scanning Tunneling Microscopy and Spectroscopy technique for non-cleavable materials. This technique allows a direct probing of band structures and alignment at device interfaces, which could generate important insight into the mechanisms that govern QDSSC operation

  12. Formation, Characteristics and Electrocatalytic Properties of Nanoporous Metals Formed by Dealloying of Ternary-Noble Alloys

    Science.gov (United States)

    Vega Zuniga, Adrian A.

    Nanoporous metals formed by electrochemical dealloying of silver from Ag-Au-Pt alloys, with 77 at.% silver and platinum contents of 1, 2 and 3 at.%, have been studied. The presence of platinum, which is immobile relative to gold, refine the ligament size and stabilized the nanostructure against coarsening, even under experimental conditions that would be expected to promote coarsening (e.g., exposure to high temperature, longer dealloying times). By adding only 1 at.% Pt to the alloy precursor, the ligament/pore size was reduced by 50% with respect to that in nanoporous gold (NPG), which was formed on a Ag-Au alloy with the same silver content as ternary alloys. A further decrease in the ligament size was observed by increasing the platinum content of the precursor; however, most of the improvement occurred with 1 at.% Pt. The adsorbate-induced surface segregation of platinum was also investigated for these nanoporous metals. By exposing freshly-dealloyed nanostructures to moderate temperatures in the presence of air, platinum segregated to the ligament surface; in contrast, in an inert atmosphere (Ar-H 2), platinum mostly reverted to the bulk of the ligaments. This thermally activated process was thermodynamically driven by the interaction between platinum and oxygen; however, at the desorption temperature of oxygen, platinum de-segregated from the surface. Moreover, the co-segregation of platinum and oxygen hindered the thermal coarsening of the ligaments. Finally, the electrocatalytic abilities of these nanostructures were studied towards methanol and ethanol electro-oxidation, in alkaline and acidic media, showing significantly improved response in comparison to that observed in NPG. The synergistic effect between gold and platinum atoms and the smaller feature size of the nanostructures were directly associated with this behaviour. In alkaline electrolyte, the nanostructure formed on the alloy with 1 at.% Pt showed higher catalytic response than the other two

  13. 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...

  14. 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.

  15. Cascade morphology transition in bcc metals.

    Science.gov (United States)

    Setyawan, Wahyu; Selby, Aaron P; Juslin, Niklas; Stoller, Roger E; Wirth, Brian D; Kurtz, Richard J

    2015-06-10

    Energetic atom collisions in solids induce shockwaves with complex morphologies. In this paper, we establish the existence of a morphological transition in such cascades. The order parameter of the morphology is defined as the exponent, b, in the defect production curve as a function of cascade energy (N(F) ~ E(MD)(b)). Response of different bcc metals can be compared in a consistent energy domain when the energy is normalized by the transition energy, μ, between the high- and the low-energy regime. Using Cr, Fe, Mo and W data, an empirical formula of μ as a function of displacement threshold energy, E(d), is presented for bcc metals.

  16. 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...

  17. Conducting to non-conducting transition in dual transmission lines using a ternary model with long-range correlated disorder

    Science.gov (United States)

    Lazo, E.; Diez, E.

    2010-07-01

    In this work we study the behavior of the allowed and forbidden frequencies in disordered classical dual transmission lines when the values of capacitances {C} are distributed according to a ternary model with long-range correlated disorder. We introduce the disorder from a random sequence with a power spectrum S(k)∝k, where α⩾0.5 is the correlation exponent. From this sequence we generate an asymmetric ternary map using two map parameters b and b, which adjust the occupancy probability of each possible value of the capacitances C={CCC}. If the sequence of capacitance values is totally at random α=0.5 (white noise), the electrical transmission line is in the non-conducting state for every frequency ω. When we introduce long-range correlations in the distribution of capacitances, the electrical transmission lines can change their conducting properties and we can find a transition from the non-conducting to conducting state for a fixed system size. This implies the existence of critical values of the map parameters for each correlation exponent α. By performing finite-size scaling we obtain the asymptotic value of the map parameters in the thermodynamic limit for any α. With these data we obtain a phase diagram for the symmetric ternary model, which separates the non-conducting state from the conducting one. This is the fundamental result of this Letter. In addition, introducing one or more impurities in random places of the long-range correlated distribution of capacitances, we observe a dramatic change in the conducting properties of the electrical transmission lines, in such a way that the system jumps from conducting to non-conducting states. We think that this behavior can be considered as a possible mechanism to secure communication.

  18. THE INFLUENCE OF TRANSITION METALS ON THE ...

    African Journals Online (AJOL)

    The influences of transition metal oxides (Zr, Mn, Co, Cu, Mo) on the performance of Pt Rh Pd/γ-Al2O3 three way catalysts were studied. The characteristics of the catalysts are investigated by using XRD, TPD, TPR. Experimental results show that the addition of Zr, Mn, Co, and Cu promoters improved the activity of Pt Rh ...

  19. 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...

  20. Fluid metals the liquid-vapor transition of metals

    CERN Document Server

    Hensel, Friedrich

    2014-01-01

    This is a long-needed general introduction to the physics and chemistry of the liquid-vapor phase transition of metals. Physicists and physical chemists have made great strides understanding the basic principles involved, and engineers have discovered a wide variety of new uses for fluid metals. Yet there has been no book that brings together the latest ideas and findings in the field or that bridges the conceptual gap between the condensed-matter physics relevant to a dense metallic liquid and the molecular chemistry relevant to a dilute atomic vapor. Friedrich Hensel and William Warren seek

  1. 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.

  2. 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.

  3. 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.

  4. Competitive immobilization of Pb in an aqueous ternary-metals system by soluble phosphates with varying pH.

    Science.gov (United States)

    Zhang, Zhuo; Ren, Jie; Wang, Mei; Song, Xinlai; Zhang, Chao; Chen, Jiayu; Li, Fasheng; Guo, Guanlin

    2016-09-01

    Chemical immobilization by phosphates has been widely and successfully applied to treat Pb in wastewater and contaminated soils. Pb in wastewaters and soils, however, always coexists with other heavy metals and their competitive reactions with phosphates have not been quantitatively and systematically studied. In this approach, immobilization of Pb, Zn, and Cd by mono-, di-, and tripotassium phosphate (KH2PO4, K2HPO4, and K3PO4) was observed in the single- and ternary-metals solutions. The immobilization rates of the three metals were determined by the residual concentration. The mineral composition and structure of the precipitates were characterized by powder X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). The results indicated that competitive reaction occurred in Pb-Zn-Cd ternary system, with immobilization rates decrease of system. The reaction of Pb with three phosphates exhibited intense competitiveness and the phosphates had a stronger affinity for Pb when Cl(-) was added. Pb-phosphate minerals formed by KH2PO4 with the better crystalline characteristics and largest size were very stable with a low dissolution rate (system. Copyright © 2016 Elsevier Ltd. All rights reserved.

  5. Electronic structure of hcp transition metals

    DEFF Research Database (Denmark)

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

    1975-01-01

    experimental evidence is available for this metal. Some comments are made about the calculational method, which has proved to be physically transparent, accurate and extremely fast, and the adequacy of the standard potential, which has now been successfully employed in calculations on the great majority......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 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...

  6. Spin doping using transition metal phthalocyanine molecules

    Science.gov (United States)

    Atxabal, A.; Ribeiro, M.; Parui, S.; Urreta, L.; Sagasta, E.; Sun, X.; Llopis, R.; Casanova, F.; Hueso, L. E.

    2016-12-01

    Molecular spins have become key enablers for exploring magnetic interactions, quantum information processes and many-body effects in metals. Metal-organic molecules, in particular, let the spin state of the core metal ion to be modified according to its organic environment, allowing localized magnetic moments to emerge as functional entities with radically different properties from its simple atomic counterparts. Here, using and preserving the integrity of transition metal phthalocyanine high-spin complexes, we demonstrate the magnetic doping of gold thin films, effectively creating a new ground state. We demonstrate it by electrical transport measurements that are sensitive to the scattering of itinerant electrons with magnetic impurities, such as Kondo effect and weak antilocalization. Our work expands in a simple and powerful way the classes of materials that can be used as magnetic dopants, opening a new channel to couple the wide range of molecular properties with spin phenomena at a functional scale.

  7. 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.

  8. 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.

  9. Two-band model interpretation of the p- to n-transition in ternary tetradymite topological insulators

    Energy Technology Data Exchange (ETDEWEB)

    Chasapis, T. C., E-mail: t-chasapis@northwestern.edu, E-mail: m-kanatzidis@northwestern.edu; Calta, N. P.; Kanatzidis, M. G., E-mail: t-chasapis@northwestern.edu, E-mail: m-kanatzidis@northwestern.edu [Department of Chemistry, Northwestern University, 2145 Sheridan Rd., Evanston, Illinois 60208 (United States); Koumoulis, D.; Leung, B. [Department of Chemistry and Biochemistry, University of California – Los Angeles, 607 Charles E. Young Drive East, Los Angeles, California 90095 (United States); Lo, S.-H.; Dravid, V. P. [Department of Materials Science and Engineering, Northwestern University, 2145 Sheridan Rd., Evanston, Illinois 60208 (United States); Bouchard, L.-S. [Department of Chemistry and Biochemistry, University of California – Los Angeles, 607 Charles E. Young Drive East, Los Angeles, California 90095 (United States); California NanoSystems Institute – UCLA, 570 Westwood Plaza, Los Angeles, California 90095 (United States)

    2015-08-01

    The requirement for large bulk resistivity in topological insulators has led to the design of complex ternary and quaternary phases with balanced donor and acceptor levels. A common feature of the optimized phases is that they lie close to the p- to n-transition. The tetradymite Bi{sub 2}Te{sub 3−x}Se{sub x} system exhibits minimum bulk conductance at the ordered composition Bi{sub 2}Te{sub 2}Se. By combining local and integral measurements of the density of states, we find that the point of minimum electrical conductivity at x = 1.0 where carriers change from hole-like to electron-like is characterized by conductivity of the mixed type. Our experimental findings, which are interpreted within the framework of a two-band model for the different carrier types, indicate that the mixed state originates from different types of native defects that strongly compensate at the crossover point.

  10. Cascade morphology transition in bcc metals

    OpenAIRE

    Setyawan, Wahyu; Selby, Aaron P.; Juslin, Niklas; Stoller, Roger E; Wirth, Brian D.; Kurtz, Richard J.

    2014-01-01

    Energetic atom collisions in solids induce shockwaves with complex morphologies. In this paper, we establish the existence of a morphological transition in such cascades. The order parameter of the morphology is defined as the exponent, $b$, in the defect production curve as a function of cascade energy ($N_F \\sim E_{MD}^b$). Response of different bcc metals can be compared in a consistent energy domain when the energy is normalized by the transition energy, $\\mu$, between the high- and the l...

  11. Surface properties of 3d transition metals

    Science.gov (United States)

    Punkkinen, M. P. J.; Hu, Q.-M.; Kwon, S. K.; Johansson, B.; Kollár, J.; Vitos, L.

    2011-09-01

    Using the projector augmented wave method within density functional theory, we present a systematic study of the layer relaxation, surface energy and surface stress of 3d transition metals. Comparing the calculated trends for the surface energy and stress with those obtained for 4d and 5d metals we find that magnetism has a significant effect on the surface properties. Enhanced surface magnetic moments decrease the size of the surface relaxation, lower the surface energy and surface stress, leading to compressive stress in Cr and Mn.

  12. Insulator to Metal Transition in Fluid Hydrogen

    Energy Technology Data Exchange (ETDEWEB)

    Hood, R Q; Galli, G

    2003-06-15

    The authors have investigated the insulator to metal transition (ITM) in fluid hydrogen using first principles simulations. Both density functional and quantum Monte Carlo calculations show that the electronic energy gap of the liquid vanishes at about 9 fold compression and 3000 K. At these conditions the computed conductivity values are characteristic of a poor metal. These findings are consistent with those of recent shock wave experiments but the computed conductivity is larger than the measured value. From the ab-initio results they conclude that the ITM is driven by molecular dissociation rather than disorder and that both temperature and pressure play a key role in determining structural changes in the fluid.

  13. (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.

  14. Cascade morphology transition in bcc metals

    Energy Technology Data Exchange (ETDEWEB)

    Setyawan, Wahyu; Selby, A.; Juslin, Niklas; Stoller, Roger E.; Wirth, Brian D.; Kurtz, Richard J.

    2015-06-10

    Energetic atom collisions in solids induce shockwaves with complex morphologies. In this paper, we establish the existence of a morphological transition in such cascades. The order parameter of the morphology is defined as the exponent, $b$, in the defect production curve as a function of cascade energy ($N_F$$ \\sim$$E_{MD}^b$). Response of different bcc metals can be compared in a consistent energy domain when the energy is normalized by the transition energy, $\\mu$, between the high- and the low-energy regime. Using Cr, Fe, Mo and W data, an empirical formula of $\\mu$ as a function of displacement threshold energy, $E_d$, is presented for bcc metals.

  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. Topological crystalline insulators in transition metal oxides.

    Science.gov (United States)

    Kargarian, Mehdi; Fiete, Gregory A

    2013-04-12

    Topological crystalline insulators possess electronic states protected by crystal symmetries, rather than time-reversal symmetry. We show that the transition metal oxides with heavy transition metals are able to support nontrivial band topology resulting from mirror symmetry of the lattice. As an example, we consider pyrochlore oxides of the form A2M2O7. As a function of spin-orbit coupling strength, we find two Z2 topological insulator phases can be distinguished from each other by their mirror Chern numbers, indicating a different topological crystalline insulators. We also derive an effective k·p Hamiltonian, similar to the model introduced for Pb(1-x)Sn(x)Te, and discuss the effect of an on-site Hubbard interaction on the topological crystalline insulator phase using slave-rotor mean-field theory, which predicts new classes of topological quantum spin liquids.

  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. Atomistic modeling to investigate the favored composition for metallic glass formation in the Ca-Mg-Ni ternary system.

    Science.gov (United States)

    Zhao, S; Li, J H; An, S M; Li, S N; Liu, B X

    2017-05-17

    A realistic interatomic potential was first constructed for the Ca-Mg-Ni system and then applied to Monte Carlo simulations to predict the favored composition for metallic glass formation in the ternary system. The simulations not only predict a hexagonal composition region, within which the Ca-Mg-Ni metallic glass formation is energetically favored, but also pinpoint an optimized sub-region within which the amorphization driving force, i.e. the energy difference between the solid solution and disordered phase, is larger than that outside. The simulations further reveal that the physical origin of glass formation is the solid solution collapsing when the solute atom exceeds the critical solid solubility. Further structural analysis indicates that the pentagonal bi-pyramids dominate in the optimized sub-region. The large atomic size difference between Ca, Mg and Ni extends the short-range landscape and facilitates the development of a hybridized packing model in the medium-range, and eventually enhancing the glass formation in the system. The predictions are well supported by the experimental observations reported so far, and could be of help for designing the ternary glass formation.

  19. Metal-metal chalcogenide molecular precursors to binary, ternary, and quaternary metal chalcogenide thin films for electronic devices.

    Science.gov (United States)

    Zhang, Ruihong; Cho, Seonghyuk; Lim, Daw Gen; Hu, Xianyi; Stach, Eric A; Handwerker, Carol A; Agrawal, Rakesh

    2016-04-11

    Bulk metals and metal chalcogenides are found to dissolve in primary amine-dithiol solvent mixtures at ambient conditions. Thin-films of CuS, SnS, ZnS, Cu2Sn(S(x),Se(1-x))3, and Cu2ZnSn(S(x)Se(1-x))4 (0 ≤ x ≤ 1) were deposited using the as-dissolved solutions. Cu2ZnSn(S(x)Se(1-x))4 solar cells with efficiencies of 6.84% and 7.02% under AM1.5 illumination were fabricated from two example solution precursors, respectively.

  20. Ternary complexes between adenosine 5' -triphosphoric acid, 2,2'-bipyridyl and the divalent metal ions manganese (II), cobalt (II), copper (II), and zinc (II). Preparation and physiochemical properties.

    Science.gov (United States)

    Cini, R; Orioli, P

    1981-04-01

    A series of ternary complexes between adenosine 5'-triphosphoric acid (ATP), 2,2'-bipyridyl, and the transition metal ions manganese (II), cobalt(II), copper (II), and zinc(II) in the ratio 1:1:1 have been prepared. The solid compounds are crystalline and can be formulated as [M(II)-H2ATP-2,2'-Bipyridyl]2 . 4H2O (MATPbipy). X-ray powder patterns show them to be all isomorphous. Potentiometric titrations in aqueous solutions are in agreement with the presence of two ionizable protons. Ultraviolet and visible spectra, epr, and magnetic susceptibility measurements suggest that the metal ions have a high-spin distorted octahedral coordination. From infrared spectra it can be deduced that ATP coordinates to the metal only through the oxygen atoms of the phosphate groups. These compounds, which are particularly stable towards hydrolysis, form possible models for ATP transport in biological fluids.

  1. Transition-Metal Decorated Aluminum Nanocrystals.

    Science.gov (United States)

    Swearer, Dayne F; Leary, Rowan K; Newell, Ryan; Yazdi, Sadegh; Robatjazi, Hossein; Zhang, Yue; Renard, David; Nordlander, Peter; Midgley, Paul A; Halas, Naomi J; Ringe, Emilie

    2017-10-24

    Recently, aluminum has been established as an earth-abundant alternative to gold and silver for plasmonic applications. Particularly, aluminum nanocrystals have shown to be promising plasmonic photocatalysts, especially when coupled with catalytic metals or oxides into "antenna-reactor" heterostructures. Here, a simple polyol synthesis is presented as a flexible route to produce aluminum nanocrystals decorated with eight varieties of size-tunable transition-metal nanoparticle islands, many of which have precedence as heterogeneous catalysts. High-resolution and three-dimensional structural analysis using scanning transmission electron microscopy and electron tomography shows that abundant nanoparticle island decoration in the catalytically relevant few-nanometer size range can be achieved, with many islands spaced closely to their neighbors. When coupled with the Al nanocrystal plasmonic antenna, these small decorating islands will experience increased light absorption and strong hot-spot generation. This combination makes transition-metal decorated aluminum nanocrystals a promising material platform to develop plasmonic photocatalysis, surface-enhanced spectroscopies, and quantum plasmonics.

  2. 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.

  3. Edge Delamination of Monolayer Transition Metal Dichalcogenides.

    Science.gov (United States)

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

    2017-07-25

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

  4. 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 ...

  5. 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....

  6. Phonon Sidebands in Monolayer Transition Metal Dichalcogenides

    Science.gov (United States)

    Christiansen, Dominik; Selig, Malte; Berghäuser, Gunnar; Schmidt, Robert; Niehues, Iris; Schneider, Robert; Arora, Ashish; de Vasconcellos, Steffen Michaelis; Bratschitsch, Rudolf; Malic, Ermin; Knorr, Andreas

    2017-11-01

    Excitons dominate the optical properties of monolayer transition metal dichalcogenides (TMDs). Besides optically accessible bright exciton states, TMDs exhibit also a multitude of optically forbidden dark excitons. Here, we show that efficient exciton-phonon scattering couples bright and dark states and gives rise to an asymmetric excitonic line shape. The observed asymmetry can be traced back to phonon-induced sidebands that are accompanied by a polaron redshift. We present a joint theory-experiment study investigating the microscopic origin of these sidebands in different TMD materials taking into account intra- and intervalley scattering channels opened by optical and acoustic phonons. The gained insights contribute to a better understanding of the optical fingerprint of these technologically promising nanomaterials.

  7. 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.

  8. 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.

  9. 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

  10. Critical behavior in the hydrogen insulator-metal transition

    Science.gov (United States)

    Hemley, R. J.; Mao, H. K.

    1990-01-01

    The vibrational Raman spectrum of solid hydrogen has been measured from 77 to 295 K in the vicinity of the recently observed insulator-metal transition and low-temperature phase transition at 150 gigapascals. The measurements provide evidence for a critical point in the pressure-temperature phase boundary of the low-temperature transition. The result suggests that below the critical temperature the insulator-metal transition changes from continuous to discontinuous, consistent with the general criteria originally proposed by Mott (1949) for metallization by band-gap closure. The effect of temperature on hydrogen metallization closely resembles that of the lower-pressure insulator-metal transitions in doped V2O3 alloys.

  11. Magnetic transition induced by mechanical deformation in Fe{sub 60}Al{sub 40−x}Si{sub x} ternary alloys

    Energy Technology Data Exchange (ETDEWEB)

    Legarra, E., E-mail: estibaliz.legarra@ehu.es [Dpto. Electricidad y Electronica, Universidad del Pais Vasco (UPV/EHU), CP. 644, 48080 Bilbao (Spain); Apiñaniz, E. [Dpto. Fisica Aplicada I, Universidad del Pais Vasco, Alameda de Urquijo s/n, 48013 Bilbao (Spain); Plazaola, F. [Dpto. Electricidad y Electronica, Universidad del Pais Vasco (UPV/EHU), CP. 644, 48080 Bilbao (Spain); Jimenez, J.A. [Centro Nacional de Investigaciones Metalurgicas (CENIM), Avda. Gregorio del amo 8, 28040 Madrid (Spain)

    2014-02-15

    Highlights: • Fe{sub 60}Al{sub 40−x}Si{sub x} alloys were disordered by means of planetary ball milling technique. • Paramagnetic to ferromagnetic transition is observed with disordering. • Si addition hinders the disordering process and the increase of the lattice parameter. • Si addition promotes the paramagnetic to ferromagnetic transition. -- Abstract: We have used Mössbauer spectroscopy and X-ray diffraction to study the influence of different Al/Si ratios on the structural and magnetic properties of the mechanically deformed Fe{sub 60}Al{sub 40−x}Si{sub x} alloys. The results indicate that ternary alloys also present the magnetic transition with disordering observed in binary Fe{sub 60}Al{sub 40} alloys. Besides, Si introduction has two opposite contributions. From a structural point of view, hinders the disordering process, but, from a magnetic point of view promotes the magnetic transition.

  12. Ternary fission

    Indian Academy of Sciences (India)

    2015-08-05

    Aug 5, 2015 ... We present the ternary fission of 252Cf and 236U within a three-cluster model as well as in a level density approach. The competition between collinear and equatorial geometry is studied by calculating the ternary fragmentation potential as a function of the angle between the lines joining the stationary ...

  13. Ternary fission

    Indian Academy of Sciences (India)

    Recently, we have studied the various aspects associated with the ternary fission process. A model, called the three-cluster model (TCM) [1–6] has been put forth. This accounts for the energy minimization of all possible ternary breakups of a heavy radioactive nucleus. Further, within the TCM we have analysed the ...

  14. A ternary memory module using low-voltage control over optical properties of metal-polypyridyl monolayers.

    Science.gov (United States)

    Kumar, Anup; Chhatwal, Megha; Mondal, Prakash Chandra; Singh, Vikram; Singh, Alok Kumar; Cristaldi, Domenico A; Gupta, Rinkoo D; Gulino, Antonino

    2014-04-14

    A ternary memory module has been designed as a function of precise voltage command. The monolayer based module displays perpetual stability and non-hysteretic reversibility for multiple scans (10(2)). Ternary-state readout provides a vision to integrate the next generation of "smart electro-optical devices" viable for multi-state memory.

  15. Parameters Free Computational Characterization of Defects in Transition Metal Oxides with Diffusion Quantum Monte Carlo

    Science.gov (United States)

    Santana, Juan A.; Krogel, Jaron T.; Kent, Paul R.; Reboredo, Fernando

    Materials based on transition metal oxides (TMO's) are among the most challenging systems for computational characterization. Reliable and practical computations are possible by directly solving the many-body problem for TMO's with quantum Monte Carlo (QMC) methods. These methods are very computationally intensive, but recent developments in algorithms and computational infrastructures have enabled their application to real materials. We will show our efforts on the application of the diffusion quantum Monte Carlo (DMC) method to study the formation of defects in binary and ternary TMO and heterostructures of TMO. We will also outline current limitations in hardware and algorithms. This work is supported by the Materials Sciences & Engineering Division of the Office of Basic Energy Sciences, U.S. Department of Energy (DOE).

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2006-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2006-01-01

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

  18. Transition-metal catalyzed synthesis of Ketoprofen

    Directory of Open Access Journals (Sweden)

    Ramminger Carolina

    2000-01-01

    Full Text Available Transition metal-catalyzed reactions including carbonylations, hydrovinylations and hydrogenations have been applied in the synthesis of alpha-(3-benzoylphenylpropanoic acid (Ketoprofen. 3-Vinylbenzophenone was obtained from 3-bromobenzophenone by a Pd-catalyzed Heck coupling reaction. Pd-catalyzed carbonylation of this olefin gave the isopropyl alpha-(3-benzoylphenyl propionate in high yield (95% and with high regioselectivity (>99.5%. Ketoprofen was obtained in 90% yield by hydrolysis of the isopropyl ester. It was also obtained in two steps from 3-vinylbenzophenone by a Ni-catalyzed hydrovinylation selectively affording 3-(3'-benzoylphenyl-1-butene, followed by an oxidation. 3-Ethynylbenzophenone was obtained from 3-bromobenzophenone by Pd-catalyzed coupling reaction. By means of a Pd-catalyzed carbonylation, this alkyne was converted regioselectively (97% into methyl alpha-(3-benzoylphenyl acrylate (93% yield. Hydrolysis of the ester afforded the alpha-(3-benzoylphenylacrylic acid. Asymmetric hydrogenation of this acid to give (S-ketoprofen in 95% optical yield was achieved using a chiral Ru-(S-BINAP catalyst.

  19. 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.

  20. 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

  1. One-pot solvothermal preparation and enhanced photocatalytic activity of metallic silver and graphene co-doped BiVO{sub 4} ternary systems

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Lei; Wei, Yongge [School of Chemistry and Environmental Engineering, Changchun University of Science and Technology, Changchun 130022 (China); Guo, Wan [School of Chemistry, Northeast Normal University, Changchun 130024 (China); Guo, Yihang, E-mail: guoyh@nenu.edu.cn [School of Environment, Northeast Normal University, Changchun 130117 (China); Guo, Yingna [School of Chemistry, Northeast Normal University, Changchun 130024 (China)

    2015-03-30

    Graphical abstract: - Highlights: • We have obtained Ag/GR/BiVO{sub 4} ternary system by one-pot solvothermal route. • The best photocatalytic activity to RhB has been attained for 3%Ag/5%GR/BiVO{sub 4}. • Silver nanoparticles and graphene nanosheets doping clearly favor the photocarriers separation. • The Ag/GR/BiVO{sub 4} heterojunction photocatalyst can be reused five times without obvious loss of the reactivity. - Abstract: A series of metallic silver and graphene (GR) co-doped monoclinic BiVO{sub 4} ternary systems (Ag/GR/BiVO{sub 4}) are demonstrated by a single-step solvothermal method. The phase and chemical structure, morphology, textural and optical absorption properties of the Ag/GR/BiVO{sub 4} ternary systems are well characterized, and then their simulated sunlight and visible-light photocatalytic activity were evaluated by the degradation of a typical dye pollutant, rhodamine B (RhB). For comparison, binary systems of Ag/BiVO{sub 4} and GR/BiVO{sub 4} as well as solitary BiVO{sub 4} are also tested under the same conditions. Meanwhile, the separation and transportation of the photogenerated carriers in the simulated sunlight-irradiating Ag/GR/BiVO{sub 4} ternary systems are studied by photoelectrochemistry experiments, and the active species generated during the process of photodegradation are investigated by free radical and hole scavenging experiments. On the basis of the above results, mechanism of photocatalytic degradation of RhB over the Ag/GR/BiVO{sub 4} ternary system is revealed. Finally, the reusability of the catalyst was evaluated by five consecutive catalytic runs.

  2. Surface segregation energies in transition-metal alloys

    DEFF Research Database (Denmark)

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

    1999-01-01

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

  3. 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.

  4. The metallicities of stars with and without transiting planets

    DEFF Research Database (Denmark)

    Buchhave, Lars A.; Latham, David W.

    2015-01-01

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

  5. Chemical effects in ion mixing of a ternary system (metal-SiO2)

    Science.gov (United States)

    Banwell, T.; Nicolet, M.-A.; Sands, T.; Grunthaner, P. J.

    1987-01-01

    The mixing of Ti, Cr, and Ni thin films with SiO2 by low-temperature (- 196-25 C) irradiation with 290 keV Xe has been investigated. Comparison of the morphology of the intermixed region and the dose dependences of net metal transport into SiO2 reveals that long range motion and phase formation probably occur as separate and sequential processes. Kinetic limitations suppress chemical effects in these systems during the initial transport process. Chemical interactions influence the subsequent phase formation.

  6. Low temperature synthesis of ternary metal phosphides using plasma for asymmetric supercapacitors

    KAUST Repository

    Liang, Hanfeng

    2017-04-06

    We report a versatile route for the preparation of metal phosphides using PH plasma for supercapacitor applications. The high reactivity of plasma allows rapid and low temperature conversion of hydroxides into monometallic, bimetallic, or even more complex nanostructured phosphides. These same phosphides are much more difficult to synthesize by conventional methods. Further, we present a general strategy for significantly enhancing the electrochemical performance of monometallic phosphides by substituting extrinsic metal atoms. Using NiCoP as a demonstration, we show that the Co substitution into NiP not only effectively alters the electronic structure and improves the intrinsic reactivity and electrical conductivity, but also stabilizes Ni species when used as supercapacitor electrode materials. As a result, the NiCoP nanosheet electrodes achieve high electrochemical activity and good stability in 1 M KOH electrolyte. More importantly, our assembled NiCoP nanoplates//graphene films asymmetric supercapacitor devices can deliver a high energy density of 32.9 Wh kg at a power density of 1301 W kg, along with outstanding cycling performance (83% capacity retention after 5000 cycles at 20 A g). This activity outperforms most of the NiCo-based materials and renders the NiCoP nanoplates a promising candidate for capacitive storage devices.

  7. Mechanisms of transition-metal gettering in silicon

    Science.gov (United States)

    Myers, S. M.; Seibt, M.; Schröter, W.

    2000-10-01

    The atomic process, kinetics, and equilibrium thermodynamics underlying the gettering of transition-metal impurities in Si are reviewed. Methods for mathematical modeling of gettering are discussed and illustrated. Needs for further research are considered.

  8. Mechanisms of transition-metal gettering in silicon

    Energy Technology Data Exchange (ETDEWEB)

    MYERS JR.,SAMUEL M.; SEIBT,M.; SCHROTER,W.

    2000-03-23

    The atomic process, kinetics, and equilibrium thermodynamics underlying the gettering of transition-metal impurities in Si are reviewed from a mechanistic perspective. Methods for mathematical modeling of gettering are reviewed and illustrated. Needs for further research are discussed.

  9. A rapid microwave-assisted solvothermal approach to lower-valent transition metal oxides.

    Science.gov (United States)

    Moorhead-Rosenberg, Zachary; Harrison, Katharine L; Turner, Travis; Manthiram, Arumugam

    2013-11-18

    A green, rapid microwave-assisted solvothermal process using tetraethylene glycol (TEG) as a reducing agent has been explored as a soft-chemistry route for the preparation of various lower-valent transition metal oxides. To demonstrate the feasibility of the approach, lower-valent binary oxides such as V4O9, Mn3O4 or MnO, CoO, and Cu2O have been obtained within a short reaction time of 30 min by reducing, respectively, V2O5, MnO2, Co3O4, and CuO with TEG at LaCoO3, LaNiO3, and La4Ni3O10. The oxidation state of the transition metal ions and the oxygen content in these ternary oxides could be tuned by precisely controlling the reaction temperatures from 160 to 300 °C. The products have been characterized by X-ray powder diffraction and iodometric titration. The versatility of this novel technique is demonstrated by the facile synthesis of V4O9, which has only been produced recently in single-phase form.

  10. An anionic metal-organic framework with ternary building units for rapid and selective adsorption of dyes.

    Science.gov (United States)

    Yao, Shuo; Xu, Tong; Zhao, Nian; Zhang, Lirong; Huo, Qisheng; Liu, Yunling

    2017-03-07

    A novel metal-organic framework, [(CH3)2NH2]2[Cu3O(SO4)3Cu2L2(DMF)(H2O)]·9DMF (JLU-Liu39) H2L = pyridine-3,5-bis(phenyl-4-carboxylic acid), has been successfully synthesized under solvothermal conditions. Structure analysis indicates that the framework of JLU-Liu39 is constructed by ternary building units which include a rare hexa-nuclear [Cu6O2(SO4)6] cluster, a classical [Cu2(CO2)4] paddlewheel, and a 3-connected hetero-N, O donor ligand. The whole 3D framework possesses a (3,4,4)-connected fjh topology and a large window size of 25.3 Å with high solvent-accessible volume accounting for approximately 75.8% of the cell volume. On the basis of the anionic framework and large pore volume, JLU-Liu39 can efficiently adsorb cationic dyes such as MLB, MV, RhB and neutral dye NR but exclude anionic dyes such as MO and Orange II. Moreover, JLU-Liu39 also exhibits size-exclusion performance for dyes of different sizes, and the dye adsorption amounts decrease with the increase of dye size. With respect to the proportional mixture dyes with different charges for MO & MLB and Orange II & MLB, JLU-Liu39 can be able to selectively adsorb the cationic dye MLB efficiently. Based on the aforementioned considerations, JLU-Liu39 is a good anionic-skeleton MOF material for the adsorption and separation of organic dyes.

  11. 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.

  12. Electron Devices Based on Transition Metal Dichalcogenides

    Science.gov (United States)

    Tosun, Mahmut

    Integrated circuits consists of building blocks called transistors. A transistor is a switch that enables logic operations to perform computing. Since the invention of the first integrated circuit, transistors have been scaled down in their dimensions to increase the density of transistors per unit area to enable more functionality. Transistor scaling is continued by introducing novel device structures and materials at each technology node. Due to the challenges such as short channel effects and the power consumption issues, novel materials are investigated as a candidate for next generation transistors. In this thesis, 2-dimensinal layered semiconductors, namely transition metal dichalcogenides (TMDCs) are studied to assess their electronic material properties as a candidate channel material for next generation electronic devices. Chapter one, introduces the challenges in the state of the art MOSFET devices. Then the motivation for the use of TMDCs in MOSFETs is explained. In chapter two, doping of the TMDCs is studied to be able to probe the intrinsic electronic properties of the devices fabricated using these materials. Contact resistance can be decreased by doping and TMDC MOSFETs with near-ideal performance metrics are demonstrated. In chapter three the CMOS integration of the devices using TMDCs are examined. Logic operations are conducted by fabricating WSe 2 n-FETs and p-FETs on the same flake. Then vertical 3-dimensional integration of n-FETs and p-FETs are demonstrated using the same gate. These transistors are connected as a CMOS inverter and logic operations are performed. Chapter four presents the band structure engineering study using TMDCs. Mono-multilayer MoS2 junctions are found to have a type-I heterojunction. Optoelectronic properties of this junction are investigated and the junction is shown to have a photoresponse that dominates the photoresponse coming from the contacts. In chapter five, the tunneling devices using TMDCs are studied. Dual

  13. Neutron Damage and MAX Phase Ternary Compounds

    Energy Technology Data Exchange (ETDEWEB)

    Barsoum, Michael [Drexel Univ., Philadelphia, PA (United States); Hoffman, Elizabeth [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL); Sindelar, Robert [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL); Garcua-Duaz, Brenda [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL); Kohse, Gordon [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)

    2014-06-17

    The Demands of Gen IV nuclear power plants for long service life under neutron radiation at high temperature are severe. Advanced materials that would withstand high temperatures (up to 1000+ C) to high doses in a neutron field would be ideal for reactor internal structures and would add to the long service life and reliability of the reactors. The objective of this work is to investigate the response of a new class of machinable, conductive, layered, ternary transition metal carbides and nitrides - the so-called MAX phases - to low and moderate neutron dose levels.

  14. 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.

  15. 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

  16. 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...

  17. Volume variation of Gruneisen parameters of fcc transition metals

    Indian Academy of Sciences (India)

    Unknown

    The results are reasonably good for six metals except for Rh, Ag, Au and Ni when compared with available experimental and other theoretical values. The model requires an appropriate modification for Rh, Ag, Au and Ni. Keywords. fcc transition metals; pseudopotential; Gruneisen parameter; volume variation of Gruneisen.

  18. [Non-empirical interatomic potentials for transition metals]. Progress report

    Energy Technology Data Exchange (ETDEWEB)

    1993-05-01

    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.

  19. [Non-empirical interatomic potentials for transition metals

    Energy Technology Data Exchange (ETDEWEB)

    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.

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

    African Journals Online (AJOL)

    ... of the potential reproduced the structure factor, peak position and peak height of the structure factor of some transition liquid metals. Keywords: liquid metals, structure factor, potential, peak position and peak height. Journal of the Nigerian Association of Mathematical Physics, Volume 19 (November, 2011), pp 527 – 532 ...

  1. The transition to the metallic state in low density hydrogen.

    Science.gov (United States)

    McMinis, Jeremy; Morales, Miguel A; Ceperley, David M; Kim, Jeongnim

    2015-11-21

    Solid atomic hydrogen is one of the simplest systems to undergo a metal-insulator transition. Near the transition, the electronic degrees of freedom become strongly correlated and their description provides a difficult challenge for theoretical methods. As a result, the order and density of the phase transition are still subject to debate. In this work, we use diffusion quantum Monte Carlo to benchmark the transition between paramagnetic and anti-ferromagnetic body centered cubic atomic hydrogen in its ground state. We locate the density of the transition by computing the equation of state for these two phases and identify the phase transition order by computing the band gap near the phase transition. These benchmark results show that the phase transition is continuous and occurs at a Wigner-Seitz radius of rs = 2.27(3) a0. We compare our results to previously reported density functional theory, Hedin's GW approximation, and dynamical mean field theory results.

  2. Synthesis and characterization of transition metal complexes ...

    African Journals Online (AJOL)

    Ni(II) complex of HMPFCH has been assigned a dimeric square planar geometry. Cu(II) complex of HMPFCH has been proposed an octahedral geometry. The ligands and their metal chelates were screened against S. aureus and P. aeruginosa. The ligands and the metal complexes have been found to be active against ...

  3. Fac–mer equilibria of coordinated iminodiacetate (ida ) in ternary Cu ...

    Indian Academy of Sciences (India)

    Unknown

    Keywords. Fac–mer equilibria; CuII-iminodiacetate-imidazole/benzimidazole ternary complexes; stability constants. 1. Introduction. Mixed ligand complexes of transition metal ions with amino acids, peptides or their derivatives or analogues, and heterocyclic N-bases can serve as model compounds of bioinorganic interests ...

  4. 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.

  5. Structure and Electronic Properties of Transition Metal Doped Kaolinite Nanoclay

    Science.gov (United States)

    Fu, Liangjie; Yang, Huaming

    2017-06-01

    In this work, a series of transition metal (Cr, Mn, Fe, and Co) doped kaolinite nanoclays were investigated by density functional theory (DFT) calculations. The influence of metal doping on geometric structure and electronic structure of kaolinite was analyzed. The ferromagnetic (FM), antiferromagnetic (AFM), and nonmagnetic (NM) states of transition metal (TM) doped kaolinite structures were studied. The crystal volume, lattice parameters, bond length, charge, and spin were calculated by dispersion-corrected density functional theory (DFT-D2). The results indicated that Cr3+ and Fe3+ dopants showed more stable under AFM state, while Mn3+ preferred both AFM and FM states, and Co3+ dopant preferred NM state. Also, the transition metal doping could induce lattice volume expansion and some dopant states in the band gap.

  6. Application of Two Dimensional Flourescence Spectroscopy to Transition Metal Clusters.

    Science.gov (United States)

    Kokkin, Damian L.; Steimle, Timothy

    2014-06-01

    Determining the physical properties (bond lengths, angles, dipole moments, etc) of transition metal oxides and dioxides is relevant to catalysis, high temperature chemistry, materials science and astrophysics. Analysis of optical spectra is a convenient method for extraction of physical properties, but can be difficult because of the density of electronic states and in the case of the dioxides, presence of both the oxide and superoxide forms. Here we demonstrate the application of two dimensional fluorescence spectroscopy for aiding in the assignment and analysis. Particular attention will be paid to the spectroscopy of first row transition metal monoxides and dioxides of Nickel, NiO and NiO_2, and Manganese, MnO. Furthermore, the application of this technique to discovering the spectrum of other transition metal systems such as Metal-dicarbides will be outlined. N.J. Reilly, T.W. Schmidt, S.H. Kable, J. Phys. Chem. A., 110(45), 12355-12359, 2006

  7. Compressive Surface Stress in Magnetic Transition Metals

    Science.gov (United States)

    Punkkinen, M. P. J.; Kwon, S. K.; Kollár, J.; Johansson, B.; Vitos, L.

    2011-02-01

    Because of the increased electron density within the surface layer, metal surfaces are generally expected to have tensile surface stress. Here, using first-principles density functional calculations, we demonstrate that in magnetic 3d metals surface magnetism can alter this commonly accepted picture. We find that the thermodynamically stable surfaces of chromium and manganese possess compressive surface stress. The revealed negative surface stress is shown to be ascribed to the enhanced magnetic moments within the surface layer relative to the bulk values.

  8. Spectrophotometric Study of Ternary Complex Forming Systems of Some Lanthanide Metal Ions with Eriochrome Cyanine R in Presence of Cetylpyridinium Bromide for Microdetermination

    Directory of Open Access Journals (Sweden)

    A. S. Dhepe

    2011-01-01

    Full Text Available Study of coordination compounds of lanthanide elements has received a great attention due to growing applications in science and technology. Number of chromogenic reagents form water soluble colored complexes with lanthanides. Eriochrome cyanine R (ECR a member of triphenylmethane type of dye has been reported to form green colored complexes with lanthanides and has been used for microdetermination of these metal ions. Addition of cationic surfactant, Cetylpyridinium bromide (CPB, a cationic surfactant sensitizes the color reactions of Gd(III, Tb(III, Dy(III, Ho(III and Lu(III with ECR. Formation of water soluble, highly colored ternary complexes with a considerable bathochromic shift of about 50 nm in presence of surfactant has been observed. Optimum reaction conditions and other analytical parameters were also evaluated. Stoichiometric ratio 1:3:3 of Ln: ECR: CPB are responsible for the observed rise in molar absorptivity and sensitivity. Beer’s law was obeyed between 0.50 to 13.00 ppm. Effective photometric range and molar absorptivity of these ternary complexes have been calculated. Effect of some common interfering ions on determination of these lanthanide metal ions was studied. A simple, rapid and highly sensitive spectrophotometeric method has been proposed for the determination of metal ions understudy.

  9. 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.

  10. 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.

  11. Memristor using a transition metal nitride insulator

    Science.gov (United States)

    Stevens, James E; Marinella, Matthew; Lohn, Andrew John

    2014-10-28

    Apparatus is disclosed in which at least one resistive switching element is interposed between at least a first and a second conducting electrode element. The resistive switching element comprises a metal oxynitride. A method for making such a resistive switching element is also disclosed.

  12. Metal-insulator transition of alloyed radical cation salts, (MexEDO-TTF)2PF6

    Science.gov (United States)

    Murata, Tsuyoshi; Shao, Xiangfeng; Nakano, Yoshiaki; Yamochi, Hideki; Saito, Gunzi; Uruichi, Mikio; Yakushi, Kyuya; Tanaka, Koichiro

    2010-06-01

    Ternary radical cation salts containing ethylenedioxytetrathiafulvalene, its mono-methyl substituted derivative, and hexafluorophosphate, [(EDO-TTF)1-x(MeEDO-TTF)x]2PF6 (x=mole fraction of MeEDO-TTF, x=0.01-0.13) were prepared by electrooxidation. Mole fractions of EDO-TTF and MeEDO-TTF in EDO-TTF rich alloys were consistent with the donor mixing ratios in preparation. Crystal structures of these alloys at room temperature were isostructural to that of (EDO-TTF)2PF6, where the donor molecules formed a nearly uniform stacking column to give a quasi-one-dimensional Fermi surface. The alloys exhibited a metal-insulator transition with tetramerization within the donor stack and anion-ordering. Temperature-variable structural analysis and Raman spectra revealed that the charge-ordering took place in the low temperature phase of x=0.05 alloy, however, this feature vanished in the x=0.13 alloy. The phase transition temperature decreased with increasing x value from 279 K of pristine (EDO-TTF)2PF6 to 188 K of x=0.13 alloy.

  13. 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).

  14. Recent Progress in Atomic Layer Deposition of Multifunctional Oxides and Two-Dimensional Transition Metal Dichalcogenides

    Science.gov (United States)

    Liu, Hongfei

    Atomic layer deposition (ALD) has long been developed for conformal coating thin films on planar surfaces and complex structured substrates based on its unique sequential process and self-limiting surface chemistry. In general, the coated thin films can be dielectrics, semiconductors, conductors, metals, etc., while the targeted surface can vary from those of particles, wires, to deep pores, through holes, and so on. The ALD coating technique, itself, was developed from gas-phase chemical vapor deposition, but now it has been extended even to liquid phase coating/growth. Because the thickness of ALD growth is controlled in atomic level (˜0.1nm), it has recently been employed for producing two-dimensional (2D) materials, typically semiconducting nanosheets of transition metal dichalcogenides (TMDCs). In this paper, we briefly introduce recent progress in ALD of multifunctional oxides and 2D TMDCs with the focus being placed on suitable ALD precursors and their ALD processes (for both binary compounds and ternary alloys), highlighting the remaining challenges and promising potentials.

  15. Magnetism of polyanionic compounds of transition metals (Review Article)

    Science.gov (United States)

    Danilovich, I. L.; Volkova, O. S.; Vasiliev, A. N.

    2017-05-01

    The magnetic properties of 3d-transition metal polyanionic compounds differ markedly from those of the monoanionic compounds. The simplest of them can be considered as systems with structures containing cations of a single metal in the Ti-Cu series and several different anions (F-, Cl-, Br-, (OH)-, O2-). Metal orbitals overlap differently with orbitals of the halogen, hydroxyl groups and oxygen causing a wide spread in competition among the different exchange interactions in polyanionic compounds. At the same time, exchange with other cations, including non-transition metals, does not occur in these compounds. The physics of polyanionic magnets remains largely unexplored, since such systems are usually chemically active and require particular care when physical measurements are made.

  16. Plasmonic spectral tunability of conductive ternary nitrides

    Energy Technology Data Exchange (ETDEWEB)

    Kassavetis, S.; Patsalas, P., E-mail: ppats@physics.auth.gr [Department of Physics, Aristotle University of Thessaloniki, GR-54124 Thessaloniki (Greece); Bellas, D. V.; Lidorikis, E. [Department of Materials Science and Engineering, University of Ioannina, GR-45110 Ioannina (Greece); Abadias, G. [Institut Pprime, Département Physique et Mécanique des Matériaux, Université de Poitiers-CNRS-ENSMA, 86962 Chasseneuil-Futuroscope (France)

    2016-06-27

    Conductive binary transition metal nitrides, such as TiN and ZrN, have emerged as a category of promising alternative plasmonic materials. In this work, we show that ternary transition metal nitrides such as Ti{sub x}Ta{sub 1−x}N, Ti{sub x}Zr{sub 1−x}N, Ti{sub x}Al{sub 1−x}N, and Zr{sub x}Ta{sub 1−x}N share the important plasmonic features with their binary counterparts, while having the additional asset of the exceptional spectral tunability in the entire visible (400–700 nm) and UVA (315–400 nm) spectral ranges depending on their net valence electrons. In particular, we demonstrate that such ternary nitrides can exhibit maximum field enhancement factors comparable with gold in the aforementioned broadband range. We also critically evaluate the structural features that affect the quality factor of the plasmon resonance and we provide rules of thumb for the selection and growth of materials for nitride plasmonics.

  17. 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.

  18. Tunable Superconducting Phase Transition in Metal-Decorated Graphene Sheets

    OpenAIRE

    Kessler, B. M.; Girit, C. O.; Zettl, A.; Bouchiat, V.

    2009-01-01

    Using typical experimental techniques it is difficult to separate the effects of carrier density and disorder on the superconducting transition in two dimensions. Using a simple fabrication procedure based on metal layer dewetting, we have produced graphene sheets decorated with a non-percolating network of nanoscale tin clusters. These metal clusters both efficiently dope the graphene substrate and induce long-range superconducting correlations. This allows us to study the superconducting tr...

  19. Spatiotemporal Analysis of Heavy Metal Water Pollution in Transitional China

    OpenAIRE

    Huixuan Li; Yingru Li; Ming-Kuo Lee; Zhongwei Liu; Changhong Miao

    2015-01-01

    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 met...

  20. 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.

  1. Large magnetic entropy change of Gd-based ternary bulk metallic glass in liquid-nitrogen temperature range

    Science.gov (United States)

    Fu, H.; Zhang, X. Y.; Yu, H. J.; Teng, B. H.; Zu, X. T.

    2008-01-01

    Gd 60Co 26Al 14 bulk metallic glass (BMG) with a diameter of 3 mm was prepared by arc-melting and copper-mold suck-casting. X-ray diffraction (XRD) results show that the as-cast Gd 60Co 26Al 14 rod consists of a wholly amorphous phase. Differential scanning calorimetry (DSC) measurements indicated that one glass transition temperature (Tg) and two crystallization temperatures (TX) occur at 570, 602, and 642 K, respectively. Moreover, two Curie temperatures of 82 and 128 K, which correspond to the two amorphous phases in the DSC trace, were determined from the thermo-magnetization curve. The maximal magnetic entropy change (ΔSM) under 0-5 T is about 10.1 J/kg K at 75 K and the refrigerant capacity (RC) is about 556 J/kg, which makes Gd 60Co 26Al 14 BMG a promising candidate for magnetic refrigerant near liquid-nitrogen temperatures.

  2. Geometry of metal-insulator transitions in one-dimension

    Science.gov (United States)

    Bray-Ali, Noah; Campos Venuti, Lorenzo; Cozzini, Marco; Zanardi, Paolo

    2008-03-01

    We use the geometric approach to quantum critical points to study the metal-insulator transitions driven by chemical potential, μ, or repulsion, U, in the one-dimensional Hubbard model. The transition to the band-insulator, as μ->μc, exhibits conventional scaling of the ground-state fidelity metric tensor G,≡Re[- ]. For example, the metric diverges as GU,U˜1/n, where, n˜√μ-μc, is the band filling. At the Mott transition, the metric behavior depends on the path of approach to the critical point.

  3. Observation of the Wigner-Huntington transition to metallic hydrogen

    Science.gov (United States)

    Dias, Ranga P.; Silvera, Isaac F.

    2017-02-01

    Producing metallic hydrogen has been a great challenge in condensed matter physics. Metallic hydrogen may be a room-temperature superconductor and metastable when the pressure is released and could have an important impact on energy and rocketry. We have studied solid molecular hydrogen under pressure at low temperatures. At a pressure of 495 gigapascals, hydrogen becomes metallic, with reflectivity as high as 0.91. We fit the reflectance using a Drude free-electron model to determine the plasma frequency of 32.5 ± 2.1 electron volts at a temperature of 5.5 kelvin, with a corresponding electron carrier density of 7.7 ± 1.1 × 1023 particles per cubic centimeter, which is consistent with theoretical estimates of the atomic density. The properties are those of an atomic metal. We have produced the Wigner-Huntington dissociative transition to atomic metallic hydrogen in the laboratory.

  4. Well-defined transition metal hydrides in catalytic isomerizations.

    Science.gov (United States)

    Larionov, Evgeny; Li, Houhua; Mazet, Clément

    2014-09-07

    This Feature Article intends to provide an overview of a variety of catalytic isomerization reactions that have been performed using well-defined transition metal hydride precatalysts. A particular emphasis is placed on the underlying mechanistic features of the transformations discussed. These have been categorized depending upon the nature of the substrate and in most cases discussed following a chronological order.

  5. Biomass transition metal hydrogen-evolution electrocatalysts and electrodes

    Science.gov (United States)

    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. 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.

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

    Indian Academy of Sciences (India)

    Administrator

    past several decades, the cluster science has already obtained huge development. In particular, the transition metal clusters have been intensively investigated both experimentally and theoretically because of their poten- tial applications in nanotechnology and microelectronics industry (Chopra et al 1995; Thimoshkin et al ...

  8. 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 the...

  9. Metal-Insulator Transition in a Generalized Hubbard Model

    NARCIS (Netherlands)

    Michielsen, K.; De Raedt, H.; Schneider, T.

    1992-01-01

    An extension of the Hubbard model, earlier introduced, is studied using exact diagonalization and quantum Monte Carlo methods. Our numerical results for the static and dynamic properties of one- and two-dimensional systems strongly suggest the occurrence of a metal-insulator transition.

  10. 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...

  11. Cooperative catalysis with first-row late transition metals

    NARCIS (Netherlands)

    van der Vlugt, J.I.

    2012-01-01

    Cooperative catalysis with first-row transition metals holds much promise for future developments regarding sustainable, selective transformations, including e.g. alkenes, dienes and a variety of small molecules such as CO2, N2 and water. This non-exhaustive analysis of the current state-of-the-art

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

    Indian Academy of Sciences (India)

    Then, zinc nitrate and transition metal nitrate solution were added to the gelatin solution and the container was moved to a thermostatic oil bath with adjusted temperature at 80. ◦. C. The compound solu- tion was then stirred for 12 h to obtain a honey-like resin. The resin became hard after the temperature of the container ...

  13. 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

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

    Indian Academy of Sciences (India)

    2015-06-02

    Jun 2, 2015 ... Home; Journals; Pramana – Journal of Physics; Volume 84; Issue 6 ... The review focusses on 3 transition metal dopants with unique electronic structure making them receptive for dramatic changes in magnetism, absorption and photoluminescence properties by the successful introduction of a small ...

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

    Indian Academy of Sciences (India)

    Hydrolytic and solvolytic ring opening reactions of phthalic anhydride, pyromellitic dianhydride and 2,3-pyridine dicarboxylic anhydride in the presence of various transition metal salts with or without a ancillary ligands were studied. The reactions were found to be dependent on stoichiometry of ligand and types of anhydride ...

  16. The Electrochemical Synthesis of Transition-Metal Acetylacetonates

    Science.gov (United States)

    Long, S. R.; Browning, S. R.; Lagowski, J. J.

    2008-01-01

    The electrochemical synthesis of transition-metal acetylacetonates described here can form the basis of assisting in the transformation of an entry-level laboratory course into a research-like environment where all members of a class are working on the same problem, but where each member has a personal responsibility for the synthesis and…

  17. Spin induced ferroelectric-like structural transition in a metal

    Science.gov (United States)

    Guo, Yanfeng; Feng, Hai; Andrew, Princep; Manuel, Pascal; Yamaura, Kazunari; Andrew, Boothroyd

    2015-03-01

    LiOsO3 represents a previously only known example of ``ferroelectric metal,'' a concept presented by Anderson and Blount in 1965, with the properties being promoted by electron lattice coupling involving Li+ ions displacement in the crystal structure [Y. Shi et al., Nat. Mater. 12, 1024(2013)]. We report that in Pb2CoOsO6, a new ordered double-perovskite with a centrosymmetric monoclinic space group of P21/n, a ferroelectric-like structural transition occurs at ~ 38 K in the metallic state, i.e. a continuous second order transition to a noncentrosymmetric structure (space group: P1) associated by appearance of a nominal unique polar axis along the c-axis. The phase transition is coincident with a magnetic transition at the same temperature which corresponds to a long-range antiferromagnetic order. The magnetic structure analysis and theoretical calculations prove that the antiferromagnetic ordering is the driven force for the structural transition in Pb2CoOsO6 and it represents the first double-perovskite ``ferroelectric metal'' involving a magnetic ordering. United Kingdom Engineering and Physical Sciences Research Council (EPSRC).

  18. 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.

  19. Rapid synthesis of transition metal dichalcogenide-carbon aerogel composites for supercapacitor electrodes

    National Research Council Canada - National Science Library

    Matthew J Crane; Matthew B Lim; Xuezhe Zhou; Peter J Pauzauskie

    2017-01-01

    Transition metal dichalcogenide (TMD) materials have recently demonstrated exceptional supercapacitor properties after conversion to a metallic phase, which increases the conductivity of the network...

  20. Electromechanical Properties of Small Transition-Metal Dichalcogenide Nanotubes

    Directory of Open Access Journals (Sweden)

    Nourdine Zibouche

    2014-04-01

    Full Text Available Transition-metal dichalcogenide nanotubes (TMC-NTs are investigated for their electromechanical properties under applied tensile strain using density functional-based methods. For small elongations, linear strain-stress relations according to Hooke’s law have been obtained, while for larger strains, plastic behavior is observed. Similar to their 2D counterparts, TMC-NTs show nearly a linear change of band gaps with applied strain. This change is, however, nearly diameter-independent in case of armchair forms. The semiconductor-metal transition occurs for much larger deformations compared to the layered tube equivalents. This transition is faster for heavier chalcogen elements, due to their smaller intrinsic band gaps. Unlike in the 2D forms, the top of valence and the bottom of conduction bands stay unchanged with strain, and the zigzag NTs are direct band gap materials until the semiconductor-metal transition. Meanwhile, the applied strain causes modification in band curvature, affecting the effective masses of electrons and holes. The quantum conductance of TMC-NTs starts to occur close to the Fermi level when tensile strain is applied.

  1. A Self-Templating Scheme for the Synthesis of Nanostructured Transition Metal Chalcogenide Electrodes for Capacitive Energy Storage

    KAUST Repository

    Xia, Chuan

    2015-06-11

    Due to their unique structural features including well-defined interior voids, low density, low coefficients of thermal expansion, large surface area and surface permeability, hollow micro/nanostructured transition metal sulfides with high conductivity have been investigated as new class of electrode materials for pseudocapacitor applications. Herein, we report a novel self-templating strategy to fabricate well-defined single and double-shell NiCo2S4 hollow spheres, as a promising electrode material for pseudocapacitors. The surfaces of the NiCo2S4 hollow spheres consist of self-assembled 2D mesoporous nanosheets. This unique morphology results in a high specific capacitance (1257 F g-1 at 2 A g-1), remarkable rate performance (76.4% retention of initial capacitance from 2 A g-1 to 60 A g-1) and exceptional reversibility with a cycling efficiency of 93.8% and 87% after 10,000 and 20,000 cycles, respectively, at a high current density of 10 A g-1. The cycling stability of our ternary chalcogenides is comparable to carbonaceous electrode materials, but with much higher specific capacitance (higher than any previously reported ternary chalcogenide), suggesting that these unique chalcogenide structures have potential application in next-generation commercial pseudocapacitors.

  2. A superconductor to superfluid phase transition in liquid metallic hydrogen.

    Science.gov (United States)

    Babaev, Egor; Sudbø, Asle; Ashcroft, N W

    2004-10-07

    Although hydrogen is the simplest of atoms, it does not form the simplest of solids or liquids. Quantum effects in these phases are considerable (a consequence of the light proton mass) and they have a demonstrable and often puzzling influence on many physical properties, including spatial order. To date, the structure of dense hydrogen remains experimentally elusive. Recent studies of the melting curve of hydrogen indicate that at high (but experimentally accessible) pressures, compressed hydrogen will adopt a liquid state, even at low temperatures. In reaching this phase, hydrogen is also projected to pass through an insulator-to-metal transition. This raises the possibility of new state of matter: a near ground-state liquid metal, and its ordered states in the quantum domain. Ordered quantum fluids are traditionally categorized as superconductors or superfluids; these respective systems feature dissipationless electrical currents or mass flow. Here we report a topological analysis of the projected phase of liquid metallic hydrogen, finding that it may represent a new type of ordered quantum fluid. Specifically, we show that liquid metallic hydrogen cannot be categorized exclusively as a superconductor or superfluid. We predict that, in the presence of a magnetic field, liquid metallic hydrogen will exhibit several phase transitions to ordered states, ranging from superconductors to superfluids.

  3. Recognition of flexible peptides in water by transition metal complexes.

    Science.gov (United States)

    Sun, S; Abul Fazal, M; Roy, B C; Mallik, S

    2000-04-06

    This paper describes the design, synthesis, and evaluation of transition metal complexes capable of recognizing flexible histidine-containing peptides in aqueous medium (25 mM HEPES buffer, pH = 7.0, 25 degrees C). When the pattern of metal ions on a complex matches with the pattern of histidine moieties on the peptide, strong interaction (K = 1.2 x 10(6) M-1) can be achieved. The complex was highly selective (> 200:1) in discriminating similar flexible peptides differing only by one glycine unit.

  4. Structural electronic and phonon properties of some transition metal aluminides

    Science.gov (United States)

    Fatima, Bushra; Pandit, Premlata; Sanyal, Sankar P.

    2012-06-01

    The structural and electronic properties of some Transition metal Aluminides (TMAl) namely ruthenium aluminide (RuAl), nickel aluminide (NiAl) and cobalt aluminide (CoAl) have been studied using plane wave pseudopotential method (PWSCF) within the local density approximation (LDA). The three TMAl's crystallizes in the CsCl-type structure (B2 phase). From the analysis of band structure and density of state, we found that these TMAl's are metallic in nature. The vibrational properties in terms of phonon dispersion curves and density of state have also been reported for RuAl using density functional perturbation theory (DFPT).

  5. Hydrothermal synthesis and characterization of nanosized transition metal chromite spinels

    OpenAIRE

    DURRANI, Shahid Khan; HUSSAIN, Syed Zahid; Saeed, Khalid

    2014-01-01

    Homogeneous crystalline transition metal chromite spinels (MCr2O4, where M = Co, Mn, and Ni) were prepared by hydrothermal reaction of aqueous solutions containing the respective metal nitrate, chromium(III) nitrate, and sodium hydroxide in stoichiometric amounts at 180-200 °C and pH 10.5-11.5 for 11-13 h. The crystalline structure, microstructure, and thermal stability of the synthesized chromite products were analyzed by X-ray diffraction (XRD), scanning electron microscopy, thermog...

  6. Structure-Reactivity Relationships in Multi-Component Transition Metal Oxide Catalysts FINAL Report

    Energy Technology Data Exchange (ETDEWEB)

    Altman, Eric I. [Yale Univ., New Haven, CT (United States)

    2015-10-06

    The focus of the project was on developing an atomic-level understanding of how transition metal oxide catalysts function. Over the course of several renewals the specific emphases shifted from understanding how local structure and oxidation state affect how molecules adsorb and react on the surfaces of binary oxide crystals to more complex systems where interactions between different transition metal oxide cations in an oxide catalyst can affect reactivity, and finally to the impact of cluster size on oxide stability and reactivity. Hallmarks of the work were the use of epitaxial growth methods to create surfaces relevant to catalysis yet tractable for fundamental surface science approaches, and the use of scanning tunneling microscopy to follow structural changes induced by reactions and to pinpoint adsorption sites. Key early findings included the identification of oxidation and reduction mechanisms on a tungsten oxide catalyst surface that determine the sites available for reaction, identification of C-O bond cleavage as the rate limiting step in alcohol dehydration reactions on the tungsten oxide surface, and demonstration that reduction does not change the favored reaction pathway but rather eases C-O bond cleavage and thus reduces the reaction barrier. Subsequently, a new reconstruction on the anatase phase of TiO2 relevant to catalysis was discovered and shown to create sites with distinct reactivity compared to other TiO2 surfaces. Building on this work on anatase, the mechanism by which TiO2 enhances the reactivity of vanadium oxide layers was characterized and it was found that the TiO2 substrate can force thin vanadia layers to adopt structures they would not ordinarily form in the bulk which in turn creates differences in reactivity between supported layers and bulk samples. From there, the work progressed to studying well-defined ternary oxides where synergistic effects between the two cations can induce

  7. Laser Assisted Additively Manufactured Transition Metal Coating on Aluminum

    Science.gov (United States)

    Vora, Hitesh D.; Rajamure, Ravi Shanker; Roy, Anurag; Srinivasan, S. G.; Sundararajan, G.; Banerjee, Rajarshi; Dahotre, Narendra B.

    2016-07-01

    Various physical and chemical properties of surface and subsurface regions of Al can be improved by the formation of transition metal intermetallic phases (Al x TM y ) via coating of the transition metal (TM). The lower equilibrium solid solubility of TM in Al (engineering via a laser-aided additive manufacturing approach can effectively synthesize TM intermetallic coatings on the surface of Al. The focus of the present work included the development of process control to achieve thermodynamic and kinetic conditions necessary for desirable physical, microstructural and compositional attributes. A multiphysics finite element model was developed to predict the temperature profile, cooling rate, melt depth, dilution of W in Al matrix and corresponding micro-hardness in the coating, and the interface between the coating and the base material and the base material.

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

    Science.gov (United States)

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

    2017-10-10

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

  9. Metal-insulator and charge ordering transitions in oxide nanostructures

    Science.gov (United States)

    Singh, Sujay Kumar

    Strongly correlated oxides are a class of materials wherein interplay of various degrees of freedom results in novel electronic and magnetic phenomena. Vanadium oxides are widely studied correlated materials that exhibit metal-insulator transitions (MIT) in a wide temperature range from 70 K to 380 K. In this Thesis, results from electrical transport measurements on vanadium dioxide (VO2) and vanadium oxide bronze (MxV 2O5) (where M: alkali, alkaline earth, and transition metal cations) are presented and discussed. Although the MIT in VO2 has been studied for more than 50 years, the microscopic origin of the transition is still debated since a slew of external parameters such as light, voltage, and strain are found to significantly alter the transition. Furthermore, recent works on electrically driven switching in VO2 have shown that the role of Joule heating to be a major cause as opposed to electric field. We explore the mechanisms behind the electrically driven switching in single crystalline nanobeams of VO2 through DC and AC transport measurements. The harmonic analysis of the AC measurement data shows that non-uniform Joule heating causes electronic inhomogeneities to develop within the nanobeam and is responsible for driving the transition in VO2. Surprisingly, field assisted emission mechanisms such as Poole-Frenkel effect is found to be absent and the role of percolation is also identified in the electrically driven transition. This Thesis also provides a new insight into the mechanisms behind the electrolyte gating induced resistance modulation and the suppression of MIT in VO2. We show that the metallic phase of VO2 induced by electrolyte gating is due to an electrochemical process and can be both reversible and irreversible under different conditions. The kinetics of the redox processes increase with temperature; a complete suppression of the transition and the stabilization of the metallic phase are achievable by gating in the rutile metallic phase

  10. Atomically Thin Transition-Metal Dinitrides: High-Temperature Ferromagnetism and Half-Metallicity.

    Science.gov (United States)

    Wu, Fang; Huang, Chengxi; Wu, Haiping; Lee, Changhoon; Deng, Kaiming; Kan, Erjun; Jena, Puru

    2015-12-09

    High-temperature ferromagnetic two-dimensional (2D) materials with flat surfaces have been a long-sought goal due to their potential in spintronics applications. Through comprehensive first-principles calculations, we show that the recently synthesized MoN2 monolayer is such a material; it is ferromagnetic with a Curie temperature of nearly 420 K, which is higher than that of any flat 2D magnetic materials studied to date. This novel property, made possible by the electron-deficient nitrogen ions, render transition-metal dinitrides monolayers with unique electronic properties which can be switched from the ferromagnetic metals in MoN2, ZrN2, and TcN2 to half-metallic ones in YN2. Transition-metal dinitrides monolayers may, therefore, serve as good candidates for spintronics devices.

  11. Theoretical studies on metal thioarsenites and thioantimonides: synergistic interactions between transition metals and heavy metalloids

    Directory of Open Access Journals (Sweden)

    Tossell JA

    2000-05-01

    Full Text Available Recently we established that the ternary complex, CuAsS(SH(OH has an unusually high stability and makes a large contribution to the total concentrations of both Cu and As in sulfidic solutions equilibrated with Cu and As sulfide minerals. This ternary complex has an unusual structure, containing a bond which is formally Cu(I–As(III, along with a broken As–S bond. We have now found that complexes with similar structures exist for Au+ and Tl+ coordinated to AsS(SH(OH-. However, such a direct metal–metalloid bond is not a requirement for stability. In fact, TlAsS(SH(OH is unstable while AuAsS(SH(OH is highly stable (compared to the aquo ion. Zn2+, Cd2+, Hg2+ and Pb2+ also form bonds to the As of AsS(SH(OH, but without breaking any As–S bonds, and HgAsS(SH(OH+ and PbAsS(SH(OH+ are particularly stable complexes. Calculated structures are shown for these complexes, gas-phase energies are calculated, and formation constants in aqueous solution are estimated. The SbS(SH(OH- ion forms analogous complexes, with similar stabilities. However, the Au+ complex of SbS(SH(OH- is slightly less stable than the Cu+ complex, opposite to the order found for the AsS(SH(OH- ligand. The Au+ and AuSH complexes of AsSSHOH- or AsS(SH2- may be implicated in "invisible gold" in arsenian pyrites. Vibrational frequencies are given for the AuAsS(SH3- complex and the XANES energies of this complex and Au(SH2- are compared. The existence of such strong complexes may explain the many correlations observed between the concentrations of coinage metals and metalloids.

  12. 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 ...

  13. Aerobic epoxidation catalysed by transition metal substituted polyfluorooxometalates.

    Science.gov (United States)

    Bugnola, Marco; Neumann, Ronny

    2016-10-07

    First row transition metal substituted polyfluorooxmetalates with quasi Wells-Dawson structures and a nitro terminal ligand, [NaH2M(NO2)W17F6O55](q-), were used as catalysts for the aerobic epoxidation of cyclic alkenes. The Cu(NO2) analog combined the best traits of conversion and selectivity. Some C-C bond cleavage was also observed and cis isomers reacted preferentially without stereochemical inversion indicating an oxygen atom to double bond concerted reaction.

  14. 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....

  15. Growth of oriented rare-earth-transition-metal thin films

    Energy Technology Data Exchange (ETDEWEB)

    Fullerton, E.E.; Sowers, C.H.; Bader, S.D. [Argonne National Lab., IL (United States); Wu, X.Z. [Argonne National Lab., IL (United States)]|[Northern Illinois Univ., DeKalb, IL (United States)

    1996-04-01

    Rare-earth-transition-metal thin films are successfully grown by magnetron sputtering onto single-crystal MgO substrates with epitaxial W buffer layers. The use of epitaxial W buffer layers allows oriented single-phase films to be grown. Sm-Co films grown onto W(100), have strong in-plane anisotropy and coercivities exceeding 5 T at 5 K whereas Fe-Sm films have strong perpendicular anisotropy and are magnetically soft.

  16. BENZALDEHYDE SELECTIVE SYNTHESIS OVER TRANSITION METAL MODIFIED ZEOLITES

    OpenAIRE

    Clara Saux; Candelaria Leal; Liliana B. Pierella

    2012-01-01

    The selective styrene oxidation to benzaldehyde was studied over ZSM-5 zeolites modified with various transition metal cations (chromium, cobalt, iron, zinc, manganese and cupper) and using hydrogen peroxide as oxidant agent. As best results were obtained using Cr-ZSM-5, they were studied evaluating reaction time, catalyst mass, styrene/hydrogen peroxide molar ratio, solvent nature and reaction temperature effect. Best results under evaluated conditions were obtained using a 0.45 substrate/ox...

  17. Electronic properties of transition metal doped silicon clusters

    Energy Technology Data Exchange (ETDEWEB)

    Rittmann, Jochen; Langenberg, Andreas; Lau, Tobias [Helmholtz-Zentrum Berlin fuer Materialien und Energie, Institut fuer Methoden und Instrumentierung der Synchrotronstrahlung, Albert-Einstein-Str. 15, 12489 Berlin (Germany); Hirsch, Konstantin; Kasigkeit, Christian; Klar, Philipp; Lofink, Fabian; Probst, Juergen; Vogel, Marlene; Wittich, Joerg; Zamudio-Bayer, Vicente; Moeller, Thomas [Technische Universitaet Berlin, Institut fuer Optik und Atomare Physik, Hardenbergstr. 36, 10623 Berlin (Germany); Issendorff, Bernd von [Universitaet Freiburg, Fakultaet fuer Physik, Stefan-Meier-Str. 21, 79104 Freiburg (Germany)

    2010-07-01

    Size selected transition metal doped silicon clusters have been studied with resonant 2p x-ray absorption spectroscopy. Despite the different number of valence electrons, nearly identical local electronic structures are found at the dopant atoms in TiSi{sub 16}{sup +}, VSi{sub 16}{sup +}, and CrSi{sub 16}{sup +}. Additional measurements of the direct 2p photoionization as well as spectroscopy on the valence electrons of MSi{sub n}{sup +} clusters, (M=V,Ti,Cr; n=15-17) allow us to determine the band gap, which is predicted to be exceptional high for the very symmetric MSi{sub 16}{sup +} clusters (M=V,Ti,Cr). The experimental data can be understood in the spherical potential model. The data indicate strongly interlinked electronic and geometric properties: While the transition metal atoms impose a geometric rearrangement on the silicon cluster, the interaction with the highly symmetric silicon cage determines the electronic structure of the transition metal dopants.

  18. Pressure induced structural phase transition in IB transition metal nitrides compounds

    Energy Technology Data Exchange (ETDEWEB)

    Soni, Shubhangi; Kaurav, Netram, E-mail: netramkaurav@yahoo.co.uk; Jain, A. [Department of Physics, Govt. Holkar Science college, A. B. Road, Indore-452001 India (India); Shah, S. [Department of Physics, P. M. B. Gujarati Science College, Indore-452001 (India); Choudhary, K. K. [Department of Physics, National Defence Academy, Khadakwasla, Pune-411 0231 India (India)

    2015-06-24

    Transition metal mononitrides are known as refractory compounds, and they have, relatively, high hardness, brittleness, melting point, and superconducting transition temperature, and they also have interesting optical, electronic, catalytic, and magnetic properties. Evolution of structural properties would be an important step towards realizing the potential technological scenario of this material of class. In the present study, an effective interionic interaction potential (EIOP) is developed to investigate the pressure induced phase transitions in IB transition metal nitrides TMN [TM = Cu, Ag, and Au] compounds. The long range Coulomb, van der Waals (vdW) interaction and the short-range repulsive interaction upto second-neighbor ions within the Hafemeister and Flygare approach with modified ionic charge are properly incorporated in the EIOP. The vdW coefficients are computed following the Slater-Kirkwood variational method, as both the ions are polarizable. The estimated value of the phase transition pressure (Pt) and the magnitude of the discontinuity in volume at the transition pressure are consistent as compared to the reported data.

  19. First-principles study on half-metallic ferromagnetic properties of Zn{sub 1-x}V{sub x}Se ternary alloys

    Energy Technology Data Exchange (ETDEWEB)

    Khatta, Swati; Tripathi, S.K.; Prakash, Satya [Panjab University, Central of Advanced Study in Physics, Department of Physics, Chandigarh (India)

    2017-09-15

    The spin-polarised density functional theory along with self-consistent plane-wave pseudopotential is used to investigate the half-metallic ferromagnetic properties of ternary alloys Zn{sub 1-x}V{sub x}Se. The generalized gradient approximation is used for exchange-correlation potential. The equilibrium lattice constants, bulk modulus, and its derivatives are calculated. The calculated spin-polarised energy-band structures reveal that these alloys are half-metallic for x = 0.375 and 0.50 and nearly half-metallic for other values of x. The estimated direct and indirect bandgaps may be useful for the magneto-optical absorption experiments. It is found that there is strong Zn 4s, Se 4p, and V 3d orbital hybridization in the conduction bands of both the spins, while Se 4p and V 3d orbital hybridization predominates in the valence bands of both the spins. The s, p-d, and p-d orbital hybridization reduces the local magnetic moment of V atoms and small local magnetic moments are produced on Zn and Se atoms which get coupled with V atoms in ferromagnetic and antiferromagnetic phases, respectively. The conduction and valence-band-edge splittings and exchange constants predict the ferromagnetism in these alloys. The conduction band-impurity (s and p-d) exchange interaction is more significant for ferromagnetism in these alloys than the valence band-impurity (p-d) exchange interaction. (orig.)

  20. Metal-insulator transition in the high pressure cubic CaF2-type ...

    Indian Academy of Sciences (India)

    43

    Half-metal; Metal-insulator transition; Double exchange mechanism; Transition metal oxides; Coulomb ... pressure and temperature has turned into an exceptionally important issue in recent years. The high pressure .... exceptional improvement in the description of most of the 3d metal oxides, because it correctly yields the ...

  1. 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.

  2. 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 (

  3. Transition-metal prion protein attachment: Competition with copper

    Science.gov (United States)

    Hodak, Miroslav; Bernholc, Jerry

    2012-02-01

    Prion protein, PrP, is a protein capable of binding copper ions in multiple modes depending on their concentration. Misfolded PrP is implicated in a group of neurodegenerative diseases, which include ``mad cow disease'' and its human form, variant Creutzfeld-Jacob disease. An increasing amount of evidence suggests that attachment of non-copper metal ions to PrP triggers transformations to abnormal forms similar to those observed in prion diseases. In this work, we use hybrid Kohn-Sham/orbital-free density functional theory simulations to investigate copper replacement by other transition metals that bind to PrP, including zinc, iron and manganese. We consider all known copper binding modes in the N-terminal domain of PrP. Our calculations identify modes most susceptible to copper replacement and reveal metals that can successfully compete with copper for attachment to PrP.

  4. Synthesis and structural, magnetic, thermal, and transport properties of several transition metal oxides and aresnides

    Energy Technology Data Exchange (ETDEWEB)

    Das, Supriyo [Iowa State Univ., Ames, IA (United States)

    2010-01-01

    Oxide compounds containing the transition metal vanadium (V) have attracted a lot of attention in the field of condensed matter physics owing to their exhibition of interesting properties including metal-insulator transitons, structural transitions, ferromagnetic and an- tiferromagnetic orderings, and heavy fermion behavior. Binary vanadium oxides VnO2n-1 where 2 ≤ n ≤ 9 have triclinic structures and exhibit metal-insulator and antiferromagnetic transitions.[1–6] The only exception is V7O13 which remains metallic down to 4 K.[7] The ternary vanadium oxide LiV2O4 has the normal spinel structure, is metallic, does not un- dergo magnetic ordering and exhibits heavy fermion behavior below 10 K.[8] CaV2O4 has an orthorhombic structure[9, 10] with the vanadium spins forming zigzag chains and has been suggested to be a model system to study the gapless chiral phase.[11, 12] These provide great motivation for further investigation of some known vanadium compounds as well as to ex- plore new vanadium compounds in search of new physics. This thesis consists, in part, of experimental studies involving sample preparation and magnetic, transport, thermal, and x- ray measurements on some strongly correlated eletron systems containing the transition metal vanadium. The compounds studied are LiV2O4, YV4O8, and YbV4O8. The recent discovery of superconductivity in RFeAsO1-xFx (R = La, Ce, Pr, Gd, Tb, Dy, Sm, and Nd), and AFe2As2 (A = Ba, Sr, Ca, and Eu) doped with K, Na, or Cs at the A site with relatively high Tc has sparked tremendous activities in the condensed matter physics community and a renewed interest in the area of superconductivity as occurred following the discovery of the layered cuprate high Tc superconductors in 1986. To discover more supercon- ductors

  5. 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...... the initial-state trends are explained in terms of the change of inter- and intra-atomic screening upon alloying. A possible role of alloying on the chemical reactivity of metal surfaces is discussed....

  6. Role of alkali metal promoter in enhancing lateral growth of monolayer transition metal dichalcogenides

    Science.gov (United States)

    Kim, Hyun; Han, Gang Hee; Yun, Seok Joon; Zhao, Jiong; Keum, Dong Hoon; Jeong, Hye Yun; Hue Ly, Thuc; Jin, Youngjo; Park, Ji-Hoon; Moon, Byoung Hee; Kim, Sung-Wng; Lee, Young Hee

    2017-09-01

    Synthesis of monolayer transition metal dichalcogenides (TMDs) via chemical vapor deposition relies on several factors such as precursor, promoter, substrate, and surface treatment of substrate. Among them, the use of promoter is crucial for obtaining uniform and large-area monolayer TMDs. Although promoters have been speculated to enhance adhesion of precursors to the substrate, their precise role in the growth mechanism has rarely been discussed. Here, we report the role of alkali metal promoter in growing monolayer TMDs. The growth occurred via the formation of sodium metal oxides which prevent the evaporation of metal precursor. Furthermore, the silicon oxide substrate helped to decrease the Gibbs free energy by forming sodium silicon oxide compounds. The resulting sodium metal oxide was anchored within such concavities created by corrosion of silicon oxide. Consequently, the wettability of the precursors to silicon oxide was improved, leading to enhance lateral growth of monolayer TMDs.

  7. Activation of CO2 on transition metal surfaces and oxide supported metal thin films

    Science.gov (United States)

    Paul, Sujata; Buongiorno Nardelli, Marco

    2009-03-01

    Using first principles simulations based on Density Functional Theory, we have investigated the adsorption and activation properties of CO2 on a variety of transition metal surfaces and oxide supported metal thin films. We intend to focus on the chemical conversion of CO2 through heterogeneous catalysis using surfaces and interfaces where there is nanoscale control over charge density at the reactive sites. The activation of CO2 on clean metal surfaces is possible at very high temperatures and the situations changes drastically when reaction happens on oxide supported metal thin film. The chemical reactivity of the molecule on the surface depends on the charge rearrangement at the metal-alkaline earth oxide interface. We want to understand the possible catalytic systems and characterize the relevant geometrical and electronic parameters related to the reaction mechanisms, rates and yield.

  8. Abrupt symmetry decrease in the ThT{sub 2}Al{sub 20} alloys (T = 3d transition metal)

    Energy Technology Data Exchange (ETDEWEB)

    Uziel, A.; Bram, A.I. [Department of Materials Engineering, Ben-Gurion University of the Negev, Beer-Sheva, 8410501 (Israel); Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, Beer-Sheva, 8410501 (Israel); Venkert, A. [Nuclear Research Center-Negev, POB 9001, Beer-Sheva (Israel); Kiv, A.E.; Fuks, D. [Department of Materials Engineering, Ben-Gurion University of the Negev, Beer-Sheva, 8410501 (Israel); Meshi, L., E-mail: louisa@bgu.ac.il [Department of Materials Engineering, Ben-Gurion University of the Negev, Beer-Sheva, 8410501 (Israel); Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, Beer-Sheva, 8410501 (Israel)

    2015-11-05

    Th-T-Al system, where T-3d transition metals, was studied at ThT{sub 2}Al{sub 20} stoichiometry to establish the influence of T on the structural stability of ternary aluminide formed. Different alloys were prepared, varying T in the row from Ti to Fe. Using electron microscopy and X-ray diffraction methods it was found that ThT{sub 2}Al{sub 20} phase adopts CeCr{sub 2}Al{sub 20} structure type when T = Ti, V, and Cr. Starting from Mn, the symmetry of the stable Al-rich phase, which forms in the alloys with the same composition, decreases from cubic to orthorhombic. The results of Density Functional Theory (DFT) calculations coincide with experiments. Concepts of the Theory of Coordination Compounds and Jahn–Teller effect were used to explain the observed abrupt change of the symmetry. These considerations were supported by DFT calculations. - Highlights: • Type of transition metal influences symmetry change in the ThT{sub 2}Al{sub 20} alloys. • It was found that cubic ThT{sub 2}Al{sub 20} phase is stable for T = Ti, V and Cr. • When T = Mn, Fe–Al + orthorhombic ThT{sub 2}Al{sub 10} are formed, lowering the symmetry. • Experimental results and DFT calculations were in full agreement. • TCC and of Jahn–Teller effect were used for explanation of the results.

  9. Observation of the Wigner-Huntington transition to metallic hydrogen.

    Science.gov (United States)

    Dias, Ranga P; Silvera, Isaac F

    2017-02-17

    Producing metallic hydrogen has been a great challenge in condensed matter physics. Metallic hydrogen may be a room-temperature superconductor and metastable when the pressure is released and could have an important impact on energy and rocketry. We have studied solid molecular hydrogen under pressure at low temperatures. At a pressure of 495 gigapascals, hydrogen becomes metallic, with reflectivity as high as 0.91. We fit the reflectance using a Drude free-electron model to determine the plasma frequency of 32.5 ± 2.1 electron volts at a temperature of 5.5 kelvin, with a corresponding electron carrier density of 7.7 ± 1.1 × 1023 particles per cubic centimeter, which is consistent with theoretical estimates of the atomic density. The properties are those of an atomic metal. We have produced the Wigner-Huntington dissociative transition to atomic metallic hydrogen in the laboratory. Copyright © 2017, American Association for the Advancement of Science.

  10. Structural Phase Transition Accompanied by Metal - Insulator Transition in PrRu4P12

    OpenAIRE

    Lee, C. H.; Matsuhata, H.; Yamamoto, A.; Ohta, T.; Takazawa, H.; Ueno, K.; Sekine, C.; Shirotani, I.; Hirayama, T.

    2000-01-01

    A structural phase transition has been found using electron diffraction technique in PrRu4P12 accompanied by a metal - insulator (M - I) transition (TMI = 60K). Weak superlattice spots appeared at (H, K, L) (H + K + L = 2n + 1; n is an integer) position at a temperature of T = 12 K and 40 K. Above T = 70 K, the spots completely vanished. The space group of the low temperature phase is probably Pm3. This is the first observation of a symmetry other than Im3 in skutterudite compounds.

  11. Ultrathin and Atomically Flat Transition-Metal Oxide: Promising Building Blocks for Metal-Insulator Electronics.

    Science.gov (United States)

    Cui, Qingsong; Sakhdari, Maryam; Chamlagain, Bhim; Chuang, Hsun-Jen; Liu, Yi; Cheng, Mark Ming-Cheng; Zhou, Zhixian; Chen, Pai-Yen

    2016-12-21

    We present a new and viable template-assisted thermal synthesis method for preparing amorphous ultrathin transition-metal oxides (TMOs) such as TiO2 and Ta2O5, which are converted from crystalline two-dimensional (2D) transition-metal dichalcogenides (TMDs) down to a few atomic layers. X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning transmission electron microscopy (STEM) were used to characterize the chemical composition and bonding, surface morphology, and atomic structure of these ultrathin amorphous materials to validate the effectiveness of our synthesis approach. Furthermore, we have fabricated metal-insulator-metal (MIM) diodes using the TiO2 and Ta2O5 as ultrathin insulating layers with low potential barrier heights. Our MIM diodes show a clear transition from direct tunneling to Fowler-Nordheim tunneling, which was not observed in previously reported MIM diodes with TiO2 or Ta2O5 as the insulating layer. We attribute the improved performance of our MIM diodes to the excellent flatness and low pinhole/defect densities in our TMO insulting layers converted from 2D TMDs, which enable the low-threshold and controllable electron tunneling transport. We envision that it is possible to use the ultrathin TMOs converted from 2D TMDs as the insulating layer of a wide variety of metal-insulator and field-effect electronic devices for various applications ranging from microwave mixing, parametric conversion, infrared photodetection, emissive energy harvesting, to ultrafast electronic switching.

  12. AWARD PAPER: XANES spectra of transition metal compounds

    Energy Technology Data Exchange (ETDEWEB)

    Groot, Frank M F de [Inorganic Chemistry and Catalysis, Utrecht University, Sorbonnelaan 16, 3584 CA Utrecht (Netherlands)

    2009-11-15

    An overview is given of the interactions that determine the XANES spectral shapes of transition metal compounds. The interactions are divided into ground state effects, final state effects and transition effects. The metal L edges, metal K edges and ligand K edges are analysed with respect to these interactions. The importance of XANES is partly due to its wide versatility in measurement conditions. XANES spectra can be measured using a number of sample environments, ranging from vacuum to ambient pressures for soft x-rays and up to extreme conditions with hard X-rays. These in-situ XANES spectra can be measured with a spatial resolution of 10 to 30 nm. XANES spectral shapes can be used as resonant channels in resonant photoemission, resonant x-ray emission or resonant diffraction experiments. This gives rise to a large number of resonant techniques that also allow the detection of site, valence, spin and symmetry selective XANES spectra and/or XANES spectra revealing information with a resolution better than its lifetime broadening.

  13. 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

  14. Holographic metal-insulator transition in higher derivative gravity

    Energy Technology Data Exchange (ETDEWEB)

    Ling, Yi, E-mail: lingy@ihep.ac.cn [Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China); Shanghai Key Laboratory of High Temperature Superconductors, Shanghai, 200444 (China); Liu, Peng, E-mail: liup51@ihep.ac.cn [Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China); Wu, Jian-Pin, E-mail: jianpinwu@mail.bnu.edu.cn [Institute of Gravitation and Cosmology, Department of Physics, School of Mathematics and Physics, Bohai University, Jinzhou 121013 (China); Shanghai Key Laboratory of High Temperature Superconductors, Shanghai, 200444 (China); Zhou, Zhenhua, E-mail: zhouzh@ihep.ac.cn [Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China)

    2017-03-10

    We introduce a Weyl term into the Einstein–Maxwell-Axion theory in four dimensional spacetime. Up to the first order of the Weyl coupling parameter γ, we construct charged black brane solutions without translational invariance in a perturbative manner. Among all the holographic frameworks involving higher derivative gravity, we are the first to obtain metal-insulator transitions (MIT) when varying the system parameters at zero temperature. Furthermore, we study the holographic entanglement entropy (HEE) of strip geometry in this model and find that the second order derivative of HEE with respect to the axion parameter exhibits maximization behavior near quantum critical points (QCPs) of MIT. It testifies the conjecture in that HEE itself or its derivatives can be used to diagnose quantum phase transition (QPT).

  15. Holographic metal-insulator transition in higher derivative gravity

    Directory of Open Access Journals (Sweden)

    Yi Ling

    2017-03-01

    Full Text Available 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 [1,2] that HEE itself or its derivatives can be used to diagnose quantum phase transition (QPT.

  16. Surface entropy of liquid transition and noble metals

    Science.gov (United States)

    Gosh, R. C.; Das, Ramprosad; Sen, Sumon C.; Bhuiyan, G. M.

    2015-07-01

    Surface entropy of liquid transition and noble metals has been investigated using an expression obtained from the hard-sphere (HS) theory of liquid. The expression is developed from the Mayer's extended surface tension formula [Journal of Non-Crystalline Solids 380 (2013) 42-47]. For interionic interaction in metals, Brettonet-Silbert (BS) pseudopotentials and embedded atom method (EAM) potentials have been used. The liquid structure is described by the variational modified hypernetted chain (VMHNC) theory. The essential ingredient of the expression is the temperature dependent effective HS diameter (or packing fraction), which is calculated from the aforementioned potentials together with the VMHNC theory. The obtained results for the surface entropy using the effective HS diameter are found to be good in agreement with the available experimental as well as other theoretical values.

  17. Storing excitons in transition-metal dichalcogenides using dark states

    Science.gov (United States)

    Gunlycke, Daniel; Tseng, Frank; Simsek, Ergun

    Monolayer transition-metal dichalcogenides exhibit strongly bound excitons confined to two dimensions. One challenge in exploiting these excitons is that they have a finite life time and collapse through electron-hole recombination. We propose that the exciton life time could be extended by transitioning the exciton population into dark states. The symmetry of these dark states require the electron and hole to be spatially separated, which not only causes these states to be optically inactive but also inhibits electron-hole recombination. Based on an atomistic model we call the Triangular Lattice Exciton (3ALE) model, we derive transition matrix elements and approximate selection rules showing that excitons could be transitioned into and out of dark states using a pulsed infrared laser. For illustration, we also present exciton population scenarios based on different recombination decay constants. Longer exciton lifetimes could make these materials candidates for applications in energy management and quantum information processing. This work was supported by the Office of Naval Research, directly and through the Naval Research Laboratory.

  18. Meyer Neldel rule application to silicon supersaturated with transition metals

    OpenAIRE

    García Hemme, Eric; García Hernansanz, Rodrigo; Olea Ariza, Javier; Pastor Pastor, David; Prado Millán, Álvaro del; Mártil de la Plaza, Ignacio; González Díaz, Germán

    2015-01-01

    This paper presents the results for the transverse conductance across a bilayer formed by supersaturating with diverse transition metals a thin layer of a silicon wafer. The layer is formed by ion implantation and annealed by pulsed laser melting. The transverse conductance is exponentially activated, obtaining values ranging from 0.018 to 0.7 eV for the activation energy and pre-exponential factors of 10^-2-10^12 S depending on the annealing energy density. A semi-logarithmic plot of the pre...

  19. Tunable superconducting phase transition in metal-decorated graphene sheets.

    Science.gov (United States)

    Kessler, B M; Girit, C O; Zettl, A; Bouchiat, V

    2010-01-29

    We have produced graphene sheets decorated with a nonpercolating network of nanoscale tin clusters. These metal clusters both efficiently dope the graphene substrate and induce long-range superconducting correlations. We find that despite structural inhomogeneity on mesoscopic length scales (10-100 nm), this material behaves electronically as a homogenous dirty superconductor with a field-effect tuned Berezinskii-Kosterlitz-Thouless transition. Our facile self-assembly method establishes graphene as an ideal tunable substrate for studying induced two-dimensional electronic systems at fixed disorder and our technique can readily be extended to other order parameters such as magnetism.

  20. 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.

  1. CVD-graphene growth on different polycrystalline transition metals

    Directory of Open Access Journals (Sweden)

    M. P. Lavin-Lopez

    2017-01-01

    Full Text Available The chemical vapor deposition (CVD graphene growth on two polycrystalline transition metals (Ni and Cu was investigated in detail using Raman spectroscopy and optical microscopy as a way to synthesize graphene of the highest quality (i.e. uniform growth of monolayer graphene, which is considered a key issue for electronic devices. Key CVD process parameters (reaction temperature, CH4/H2flow rate ratio, total flow of gases (CH4+H2, reaction time were optimized for both metals in order to obtain the highest graphene uniformity and quality. The conclusions previously reported in literature about the performance of low and high carbon solubility metals in the synthesis of graphene and their associated reaction mechanisms, i.e. surface depositionand precipitation on cooling, respectively, was not corroborated by the results obtained in this work. Under the optimal reaction conditions, a large percentage of monolayer graphene was obtained over the Ni foil since the carbon saturation was not complete, allowing carbon atoms to be stored in the bulk metal, which could diffuse forming high quality monolayer graphene at the surface. However, under the optimal reaction conditions, the formation of a non-uniform mixture of few layers and multilayer graphene on the Cu foil was related to the presence of an excess of active carbon atoms on the Cu surface.

  2. Design of half-metallic antiferromagnets: transition metal chalcogenides and pnictides

    Science.gov (United States)

    Akai, Hisazumi; Ogura, Masako; Hoang Long, Nguyen

    2010-03-01

    Half-metallic antiferromagnts are the materials that exhibit half-metallicity and antifirromagnetism (compensated ferrimagnetism) simultaneously. Such materials are especially useful for spintronics devices since they have 100 % spin-polarized Fermi surfaces despite of their robustness against a disturbance of external magnetic field. We found that (XY)Z2, where X and Y are transition metal elements and Z is a chalcogens or a pnictigen, show half-metallic antiferromagnetism when the sum of effective d electron numbers of X and Y is 10. Examples are (CrFe)S2 and (CrFe)Se2. We report a systematic investigation of the electronic structure and transport properties of these materials calculated by the KKR-Green's function method combined with the Kubo-Greenwood formula.

  3. 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

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

    Energy Technology Data Exchange (ETDEWEB)

    Kayhan, Mehmet

    2013-07-12

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

  5. Transition-metal doping of semiconducting chalcopyrites: half-metallicity and magnetism

    Science.gov (United States)

    Sarkisov, Sergey Y.; Picozzi, Silvia

    2007-01-01

    An extensive ab initio investigation of the electronic and magnetic structure of transition-metal-doped chalcopyrites is reported, focusing on Cr, Mn and Fe in CuAlS2, AgGaS2, ZnGeP2 and CdGeAs2. Our results show that the electronic properties, in terms of defect-induced density of states, largely depend on the specific combination of host, transition-metal dopant and substituted cation. In particular, for AgGaS2 doped with Cr, Mn and Fe in both cationic sites, we show that the transition metal substituting silver gives rise to strongly localized orbitals in proximity to the Fermi level, whereas generally a much higher hybridization occurs when the transition metal substitutes for Ga. On the other hand, if we fix the dopant, namely Cr, and introduce it into different hosts, Cr-doped CuAlS2 and AgGaS2 show more localized defect-induced states, whereas in more covalently bonded hosts, such as ZnGeP2 and CdGeAs2, a stronger hybridization between Cr d states and the host valence band occurs. Our findings have important consequences on the exchange interaction range, that, along with the exchange interaction strength, must be taken into account in a careful materials design aiming at optimizing the ferromagnetic properties. Finally, exploiting a simple model to predict magnetic moments in diluted magnetic semiconductors, we achieve half-metallic antiferromagnetism in chalcopyrites by co-doping CuAlS2 with Mn and V; indeed, we obtain a 100% spin-polarized density of states, with a mixed impurity band due to both Mn and V d states, ferrimagnetically coupled in the ground state.

  6. pH-specific hydrothermal assembly of binary and ternary Pb(II)-(O,N-carboxylic acid) metal organic framework compounds: correlation of aqueous solution speciation with variable dimensionality solid-state lattice architecture and spectroscopic signatures.

    Science.gov (United States)

    Gabriel, C; Perikli, M; Raptopoulou, C P; Terzis, A; Psycharis, V; Mateescu, C; Jakusch, T; Kiss, T; Bertmer, M; Salifoglou, A

    2012-09-03

    Hydrothermal pH-specific reactivity in the binary/ternary systems of Pb(II) with the carboxylic acids N-hydroxyethyl-iminodiacetic acid (Heida), 1,3-diamino-2-hydroxypropane-N,N,N',N'-tetraacetic acid (Dpot), and 1,10-phenanthroline (Phen) afforded the new well-defined crystalline compounds [Pb(Heida)](n)·nH(2)O(1), [Pb(Phen)(Heida)]·4H(2)O(2), and [Pb(3)(NO(3))(Dpot)](n)(3). All compounds were characterized by elemental analysis, FT-IR, solution or/and solid-state NMR, and single-crystal X-ray diffraction. The structures in 1-2 reveal the presence of a Pb(II) center coordinated to one Heida ligand, with 1 exhibiting a two-dimensional (2D) lattice extending to a three-dimensional (3D) one through H-bonding interactions. The concurrent aqueous speciation study of the binary Pb(II)-Heida system projects species complementing the synthetic efforts, thereby lending credence to a global structural speciation strategy in investigating binary/ternary Pb(II)-Heida/Phen systems. The involvement of Phen in 2 projects the significance of nature and reactivity potential of N-aromatic chelators, disrupting the binary lattice in 1 and influencing the nature of the ultimately arising ternary 3D lattice. 3 is a ternary coordination polymer, where Pb(II)-Dpot coordination leads to a 2D metal-organic-framework material with unique architecture. The collective physicochemical properties of 1-3 formulate the salient features of variable dimensionality metal-organic-framework lattices in binary/ternary Pb(II)-(hydroxy-carboxylate) structures, based on which new Pb(II) materials with distinct architecture and spectroscopic signature can be rationally designed and pursued synthetically.

  7. 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.

  8. Onset of magnetism in supported transition metal encapsulated silicon cages

    Science.gov (United States)

    Robles, Roberto; Khanna, Shiv N.

    2009-03-01

    In the past few years, silicon based clusters have attracted a lot of attention as building blocks of nanomaterials. Some of the most promising candidates are the transition metal encapsulated silicon cages, which have been shown to be specially stable, both experimentally and theoretically. However, for the use of these materials in fields like spintronics, it is not only necessary to be semiconductor based, but also that they present a finite magnetic moment. However, it has been shown that the magnetic moment of the transition metal atom encapsulated in silicon cages is quenched due to the hybridization with silicon. By performing density functional calculations in the generalized gradient approximation, we show that the magnetic moment of these clusters can be recovered by depositing then on a surface. Using CrSi12 on Si(111) as an example, we have deposited the cluster in different orientations. The studies show that, for most of them, a finite magnetic moment is preserved in the system after a geometrical relaxation. The origin of this behavior is discussed in terms of hybridization, comparing to the unsupported situation.

  9. Stabilization of Small Boron Cage by Transition Metal Encapsulation

    Science.gov (United States)

    Zhang, Lijun; Lv, Jian; Wang, Yanchao; Ma, Yanming

    2015-03-01

    The discovery of chemically stable fullerene-like structures formed by elements other than carbon has been long-standing desired. On this aspect significant efforts have centered around boron, only one electron deficient compared with carbon. However, during the past decade a large number of experimental and theoretical studies have established that small boron clusters are either planar/quasi-planar or forming double-ring tubular structures. Until recently, two all-boron fullerenes have been independently discovered: B38 proposed by our structure searching calculations and B40 observed in a joint experimental and theoretical study. Here we extend our work to the even smaller boron clusters and propose an effective routine to stabilize them by transition metal encapsulation. By combining swarm-intelligence structure searching and first-principles calculations, we have systematically investigated the energy landscapes of transition-metal-doped MB24 clusters (M = Ti, Zr, Hf, Cr, Mo, W, Fe, Ru and Os). Two stable symmetric endohedral boron cages, MoB24 and WB24 are identified. The stability of them can be rationalized in terms of their unique 18-electron closed-shell electronic structures. Funded by Recruitment Program of Global Experts of China and China Postdoctoral Science Foundation.

  10. Effects of interband transitions on Faraday rotation in metallic nanoparticles.

    Science.gov (United States)

    Wysin, G M; Chikan, Viktor; Young, Nathan; Dani, Raj Kumar

    2013-08-14

    The Faraday rotation in metallic nanoparticles is considered based on a quantum model for the dielectric function ϵ(ω) in the presence of a DC magnetic field B. We focus on effects in ϵ(ω) due to interband transitions (IBTs), which are important in the blue and ultraviolet for noble metals used in plasmonics. The dielectric function is found using the perturbation of the electron density matrix due to the optical field of the incident electromagnetic radiation. The calculation is applied to transitions between two bands (d and p, for example) separated by a gap, as one finds in gold at the L-point of the Fermi surface. The result of the DC magnetic field is a shift in the effective optical frequency causing IBTs by ±μBB/ħ, where opposite signs are associated with left/right circular polarizations. The Faraday rotation for a dilute solution of 17 nm diameter gold nanoparticles is measured and compared with both the IBT theory and a simpler Drude model for the bound electron response. Effects of the plasmon resonance mode on Faraday rotation in nanoparticles are also discussed.

  11. First-principles data-driven discovery of transition metal oxides for artificial photosynthesis

    Science.gov (United States)

    Yan, Qimin

    We develop a first-principles data-driven approach for rapid identification of transition metal oxide (TMO) light absorbers and photocatalysts for artificial photosynthesis using the Materials Project. Initially focusing on Cr, V, and Mn-based ternary TMOs in the database, we design a broadly-applicable multiple-layer screening workflow automating density functional theory (DFT) and hybrid functional calculations of bulk and surface electronic and magnetic structures. We further assess the electrochemical stability of TMOs in aqueous environments from computed Pourbaix diagrams. Several promising earth-abundant low band-gap TMO compounds with desirable band edge energies and electrochemical stability are identified by our computational efforts and then synergistically evaluated using high-throughput synthesis and photoelectrochemical screening techniques by our experimental collaborators at Caltech. Our joint theory-experiment effort has successfully identified new earth-abundant copper and manganese vanadate complex oxides that meet highly demanding requirements for photoanodes, substantially expanding the known space of such materials. By integrating theory and experiment, we validate our approach and develop important new insights into structure-property relationships for TMOs for oxygen evolution photocatalysts, paving the way for use of first-principles data-driven techniques in future applications. This work is supported by the Materials Project Predictive Modeling Center and the Joint Center for Artificial Photosynthesis through the U.S. Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, under Contract No. DE-AC02-05CH11231. Computational resources also provided by the Department of Energy through the National Energy Supercomputing Center.

  12. Electron-phonon coupling and structural phase transitions in early transition metal oxides and chalcogenides

    Science.gov (United States)

    Farley, Katie Elizabeth

    Pronounced nonlinear variation of electrical transport characteristics as a function of applied voltage, temperature, magnetic field, strain, or photo-excitation is usually underpinned by electronic instabilities that originate from the complex interplay of spin, orbital, and lattice degrees of freedom. This dissertation focuses on two canonical materials that show pronounced discontinuities in their temperature-dependent resistivity as a result of electron---phonon and electron---electron correlations: orthorhombic TaS3 and monoclinic VO2. Strong electron-phonon interactions in transition metal oxides and chalcogenides results in interesting structural and electronic phase transitions. The properties of the material can be changed drastically in response to external stimuli such as temperature, voltage, or light. Understanding the influence these interactions have on the electronic structure and ultimately transport characteristics is of utmost importance in order to take these materials from a fundamental aspect to prospective applications such as low-energy interconnects, steep-slope transistors, and synaptic neural networks. This dissertation describes synthetic routes to nanoscale TaS3 and VO2, develops mechanistic understanding of their electronic instabilities, and in the case of the latter system explores modulation of the electronic and structural phase transition via the incorporation of substitutional dopant atoms. We start in chapter 2 with a detailed study of the synthesis and electronic transport properties of TaS3, which undergoes a Peierls' distortion to form a charge density wave. Scaling this material down to the nanometer-sized regime allows for interrogation of single or discrete phase coherent domains. Using electrical transport and broad band noise measurements, the dynamics of pinning/depinning of the charge density wave is investigated. Chapter 3 provides a novel synthetic approach to produce high-edge-density MoS2 nanorods. MoS2 is a

  13. Materials with intermediate valence ; a comparison with transition metals

    Science.gov (United States)

    Mott, N. F.

    A discussion of metallic intermediate valence materials is given, particularly of hybridisation between the 4f and the conduction band δ. If n, 1 - n are the numbers of ions in each of two charge states, the variation of n with temperature is described. Resistivity is ascribed to scattering of the conduction electrons into the 4f band. The mechanism is compared with that in transition metals and their alloys, particularly Pd1-xAg x. The resistivity can be very large, of order of the Ioffe-Regel value 1/3 e2/ħa. It is argued that both here and in metallic alloys, this can only occur with a two-band model. At high temperatures there is some evidence that s-f scattering does not occur. On discute des matériaux métalliques à valence intermédiaire, en particulier de l'hybridation entre la bande 4f et la bande de conduction. Notant n et 1 - n les nombres d'ions dans chacun des deux états de charge, on décrit la variation de n avec la température. Le mécanisme est comparé avec celui des métaux de transition et de leurs alliages, particulièrement Pd1-xAg x. La résistivité peut être très grande, de l'ordre de la valeur de Ioffe-Regel 1/3 e2/ħa. On donne des arguments tendant à prouver que ceci ne peut se produire que dans le cadre d'un modèle à 2 bandes. Il y a des évidences qu'à haute température la diffusion s-f n'a pas lieu.

  14. XRD and XPS characterisation of transition metal silicide thin films

    Science.gov (United States)

    Tam, P. L.; Cao, Y.; Nyborg, L.

    2012-02-01

    Binary transition metal silicides based on the systems Ti-Si, Fe-Si, Ni-Si and Cr-Si were fabricated on Si wafers by means of ion-beam co-sputter deposition and subsequent annealing. The crystalline structures of the phases formed were identified from the characteristic patterns acquired by means of X-ray diffraction (XRD) measurements. The phase formation sequences were described by means of the Pretorius' effective heat of formation (EHF) model. For the Ti-Si, Fe-Si and Ni-Si systems, single phase thin films of TiSi2, β-FeSi2 and NiSi2 were generated as the model predicts, while a mixture of CrSi + CrSi2 phases was obtained for the Cr-Si system. The surface chemical condition of individual specimens was analysed by using X-ray photoelectron spectroscopy (XPS). The chemical shifts of transition metal 2p3/2 peaks from their metallic to silicide states were depicted by means of the Auger parameters and the Wagner plots. The positive chemical shift of 2.0 eV for Ni 2p3/2 peak of NiSi2 is mainly governed by the initial-state effects. For the other silicide specimens, the initial-state and final-state effects may oppose one another with similar impact. Consequently, smaller binding energy shifts of both negative and positive character are noted; a positive binding energy shift of 0.3 eV for the Fe 2p3/2 level was shown for β-FeSi2 and negative binding energy shifts of 0.1 and 0.3 eV were determined for CrSi + CrSi2 and TiSi2, respectively.

  15. Plasma-enhanced deposition and processing of transition metals and transition metal silicides for VLSI

    Science.gov (United States)

    Hess, D. W.

    1986-05-01

    Radiofrequency (rf) discharges have been used to deposit films of tungsten, molybdenum and titanium silicide. As-deposited tungsten films, from tungsten hexafluoride and hydrogen source gases, were metastable (beta W), with significant (>1 atomic percent) fluorine incorporation. Film resistivities were 40-55 micro ohm - cm due to the beta W, but dropped to about 8 micro ohm cm after a short heat treatment at 700 C which resulted in a phase transition to alpha W (bcc form). The high resistivity (>10,000 micro ohm) associated with molybdenum films deposited from molybdenum hexafluoride and hydrogen appeared to be a result of the formation of molybdenum trifluoride in the deposited material. Titanium silicide films formed from a discharge of titanium tetrachloride, silane, and hydrogen, displayed resistivities of about 150 micro ohm cm, due to small amounts of oxygen and chlorine incorporated during deposition. Plasma etching studies of tungsten films with fluorine containing gases suggest that the etchant species for tungsten in these discharges are fluorine atoms.

  16. Solution synthesis of nanoparticular binary transition metal antimonides.

    Science.gov (United States)

    Kieslich, Gregor; Birkel, Christina S; Stewart, Andrew; Kolb, Ute; Tremel, Wolfgang

    2011-08-01

    The preparation of nanoengineered materials with controlled nanostructures, for example, with an anisotropic phase segregated structure or a regular periodicity rather than with a broad range of interparticle distances, has remained a synthetic challenge for intermetallics. Artificially structured materials, including multilayers, amorphous alloys, quasicrystals, metastable crystalline alloys, or granular metals, are mostly prepared using physical gas phase procedures. We report a novel, powerful solution-mediated approach for the formation of nanoparticular binary antimonides based on presynthesized antimony nanoparticles. The transition metal antimonides M-Sb (M = Co, Ni, Cu(2), Zn) were obtained with sizes ranging from 20 and 60 nm. Through careful control of the reaction conditions, single-phase nanoparticular antimonides were synthesized. The nanophases were investigated by powder X-ray diffraction and (high resolution) electron microscopy. The approach is based on activated metal nanoparticles as precursors for the synthesis of the intermetallic compounds. X-ray powder diffraction studies of reaction intermediates allowed monitoring of the reaction kinetics. The small particle size of the reactants ensures short diffusion paths, low activation barriers, and low reaction temperatures, thereby eliminating solid-solid diffusion as the rate-limiting step in conventional bulk-scale solid-state synthesis. © 2011 American Chemical Society

  17. Supported transition metal nanomaterials: Nanocomposites synthesized by ionizing radiation

    Science.gov (United States)

    Clifford, D. M.; Castano, C. E.; Rojas, J. V.

    2017-03-01

    Nanostructures decorated with transition metal nanoparticles using ionizing radiation as a synthesis method in aqueous solutions represents a clean alternative to existing physical, chemical and physicochemical methods. Gamma irradiation of aqueous solutions generates free radicals, both oxidizing and reducing species, all distributed homogeneously. The presence of oxidant scavengers in situ during irradiation generates a highly reductive environment favoring the reduction of the metal precursors promoting seed formation and nanoparticle growth. Particle growth is controlled by addition of surfactants, polymers or various substrates, otherwise referred to as supports, which enhance the formation of well dispersed nanoparticles. Furthermore, the combination of nanoparticles with supports can offer desirable synergisms not solely presented by the substrate or nanoparticles. Thus, supported nanoparticles offer a huge diversity of applications. Among the ionizing radiation methods to synthesize nanomaterials and modify their characteristics, gamma irradiation is of growing interest and it has shown tremendous potential in morphological control and distribution of particle size by judiciously varying parameters including absorbed dose, dose rate, concentration of metal precursor, and stabilizing agents. In this work, major advances on the synthesis of supported nanoparticles through gamma irradiation are reviewed as well as the opportunities to develop and exploit new composites using gamma-rays and other accessible ionizing radiation sources such as X-rays.

  18. Spectroscopic Studies of Diatomic Transition Metal Oxides and Fluorides.

    Science.gov (United States)

    McCord, John Edward

    Wavelength selected fluorescence excitation spectroscopy (WSFES) techniques and ligand field theory (LFT) calculations have been applied to the following transition metal diatomics: CeO, UO, LaF, YF, ScF, HfO, TiO, and ZrO. All of the rotational spectra recorded for these molecules were at a resolution of 0.03 cm^{-1}, and, with few exceptions, Omega assignments for electronic states were unambiguously determined from observations of the first lines in at least two rotational branches. Accurate term energies and rotational constants are reported. Thirty one electronic transitions of CeO were recorded, and all of the sixteen states that correlate with rm Ce^{2+}(4f6s)O^ {2-} were characterized. The results are in good accord with a ligand field theory model of the low-lying states. New assignments were established for four previously observed transitions, and spectra for three new excited states were analyzed. LFT calculations have been used in an attempt to provide configurational assignments for the excited states (including those from previous studies). Twenty two states are tentatively assigned to the rm Ce^{2+}(4f6p)O ^{2-} configuration. Twelve others are tentatively assigned to rm Ce^ {2+}(4f5d)O^{2-}.. Rotation-electronic interactions between states of the 4f6s configuration of CeO, mediated by the operator {-}B(R)( J^+ cdot J_sp{a}{-}+ J^-cdot J_sp{a} {+}), have been calculated. Second-order perturbation theory was used to account for the effect of heterogeneous interactions on the rotation constants within a single configuration. Thirty-three electronic transitions of UO were analyzed, and nine low-lying electronic states that correlated with either rm U^{2+}(5f ^37s)O^{2-} or rm U^{2+}(5f^27s^2)O ^{2-} were characterized. Ligand field theory calculations were also used in an attempt to provide configurational assignments for the excited states of UO and ThO. Experimentally derived values for Delta B_sp{0} {0}(nl/n^' l^') parameters were used to predict

  19. Directly Predicting Water Quality Criteria from Physicochemical Properties of Transition Metals

    OpenAIRE

    Ying Wang; Fengchang Wu; Yunsong Mu; Eddy Y. Zeng; Wei Meng; Xiaoli Zhao; John P Giesy; Chenglian Feng; Peifang Wang; Haiqing Liao; Cheng Chen

    2016-01-01

    Transition metals are a group of elements widespread in aquatic environments that can be hazardous when concentrations exceeding threshold values. Due to insufficient data, criteria maximum concentrations (CMCs) of only seven transition metals for protecting aquatic life have been recommended by the USEPA. Hence, it is deemed necessary to develop empirical models for predicting the threshold values of water quality criteria (WQC) for other transition metals for which insufficient information ...

  20. 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.

  1. 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.

  2. Metallic Transition Metal Selenide Holey Nanosheets for Efficient Oxygen Evolution Electrocatalysis.

    Science.gov (United States)

    Fang, Zhiwei; Peng, Lele; Lv, Haifeng; Zhu, Yue; Yan, Chunshuang; Wang, Shengqi; Kalyani, Pranav; Wu, Xiaojun; Yu, Guihua

    2017-09-26

    Catalysts for oxygen evolution reaction (OER) are pivotal to the scalable storage of sustainable energy by means of converting water to oxygen and hydrogen fuel. Designing efficient electrocatalysis combining the features of excellent electrical conductivity, abundant active surface, and structural stability remains a critical challenge. Here, we report the rational design and controlled synthesis of metallic transition metal selenide NiCo2Se4-based holey nanosheets as a highly efficient and robust OER electrocatalyst. Benefiting from synergistic effects of metallic nature, heteroatom doping, and holey nanoarchitecture, NiCo2Se4 holey nanosheets exhibit greatly enhanced kinetics and improved cycling stability for OER. When further employed as an alkaline electrolyzer, the NiCo2Se4 holey nanosheet electrocatalyst enables a high-performing overall water splitting with a low applied external potential of 1.68 V at 10 mA cm-2. This work not only represents a promising strategy to design the efficient and robust OER catalysts but also provides fundamental insights into the structure-property-performance relationship of transition metal selenide-based electrocatalytic materials.

  3. Transport and detoxification systems for transition metals, heavy metals and metalloids in eukaryotic and prokaryotic microbes.

    Science.gov (United States)

    Rosen, Barry P

    2002-11-01

    Transition metals, heavy metals and metalloids are usually toxic in excess, but a number of transition metals are essential trace elements. In all cells there are mechanisms for metal ion homeostasis that frequently involve a balance between uptake and efflux systems. This review will briefly describe ATP-coupled resistance pumps. ZntA and CadA are bacterial P-type ATPases that confers resistance to Zn(II), Cd(II) and Pb(II). Homologous copper pumps include the Menkes and Wilson disease proteins and CopA, an Escherichia coli pump that confers resistance to Cu(I). For resistance to arsenicals and antimonials there are several different families of transporters. In E. coli the ArsAB ATPase is a novel system that confers resistance to As(III) and Sb(III). Eukaryotic arsenic resistance transporters include Acr3p and Ycf1p of Saccharomyces cerevisiae. These systems provide resistance to arsenite [As(III)]. Arsenate [As(V)] detoxification involves reduction of As(V) to As(III), a process catalyzed by arsenate reductase enzymes. There are three families of arsenate reductases, two found in bacterial systems and a third identified in S. cerevisiae.

  4. Recent progress in high performance and reliable n-type transition metal oxide-based thin film transistors

    Science.gov (United States)

    Kwon, Jang Yeon; Kyeong Jeong, Jae

    2015-02-01

    This review gives an overview of the recent progress in vacuum-based n-type transition metal oxide (TMO) thin film transistors (TFTs). Several excellent review papers regarding metal oxide TFTs in terms of fundamental electron structure, device process and reliability have been published. In particular, the required field-effect mobility of TMO TFTs has been increasing rapidly to meet the demands of the ultra-high-resolution, large panel size and three dimensional visual effects as a megatrend of flat panel displays, such as liquid crystal displays, organic light emitting diodes and flexible displays. In this regard, the effects of the TMO composition on the performance of the resulting oxide TFTs has been reviewed, and classified into binary, ternary and quaternary composition systems. In addition, the new strategic approaches including zinc oxynitride materials, double channel structures, and composite structures have been proposed recently, and were not covered in detail in previous review papers. Special attention is given to the advanced device architecture of TMO TFTs, such as back-channel-etch and self-aligned coplanar structure, which is a key technology because of their advantages including low cost fabrication, high driving speed and unwanted visual artifact-free high quality imaging. The integration process and related issues, such as etching, post treatment, low ohmic contact and Cu interconnection, required for realizing these advanced architectures are also discussed.

  5. A study on transformation of some transition metal oxides in molten steelmaking slag to magnetically susceptible compounds

    Directory of Open Access Journals (Sweden)

    Shatokha V.

    2013-01-01

    Full Text Available Sustainable development of steelmaking requires solving a number of environmental problems. Economically feasible and environmentally friendly recycling of slag wastes is of special concern. Research of the team representing National Metallurgical Academy of Ukraine, Royal Institute of Technology, Carnegie Mellon University and URS Corp revealed a possibility of the controlled phase transformations in the liquid silicate melts followed by formation of the magnetically susceptible compounds. This approach enables selective recovery of metal values from slag. In this paper, the results obtained and further research directions are discussed. A possibility to exploit physical properties of the transition metals, typical for the metallurgical slags (such as Fe, Mn, V and others, and corresponding specific properties of their compounds, such as non-stoichiometry, mixed valency, pseudomorphosis, thermodynamic stability etc, in production of value-added materials from slag wastes is discussed. The results of the studies of thermodynamics and kinetics of oxidation in slags followed by phase transformation with binary, ternary and complex oxides under various physicochemical conditions are discussed in the view of their application for production of the materials with predefined physical properties. Peculiarities of precipitation in slags with various basicities are analysed and demonstrate capacity of the proposed approach in the production of the material with a given structure and size - for example, nano-sized crystals with structure of spinel. The approaches towards industrial realization of the developed method are also discussed.

  6. Environmental Risk of Metal Mining Contaminated River Bank Sediment at Redox-Transitional Zones

    National Research Council Canada - National Science Library

    Sarah F L Lynch; Lesley C Batty; Patrick Byrne

    2014-01-01

    ... Framework Directive objectives. Redox-transitional zones that form along metal contaminated river banks as a result of flood and drought cycles could cause biogeochemical changes that alter the behaviour of polyvalent metals iron...

  7. Identifying the Collective Length in VO2 Metal-Insulator Transitions.

    Science.gov (United States)

    Yajima, Takeaki; Nishimura, Tomonori; Toriumi, Akira

    2017-03-01

    The "collective length" in VO2 metal-insulator transitions is identified by controlling nanoscale dopant distribution in thin films. The crossover from the local transition to the collective transition is observed, which originates from the increased instability of the metal-insulator domain boundary. This instability renders the transition collective within the "collective length", which will enable the design of collective electronic devices. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Charge transfer stabilization of late transition metal oxide nanoparticles on a layered niobate support

    OpenAIRE

    Strayer, Megan E.; Senftle, Thomas P.; Winterstein, Jonathan P.; Vargas-Barbosa, Nella M.; Sharma, Renu; Rioux, Robert M.; Janik, Michael J.; Mallouk, Thomas E.

    2015-01-01

    The interfacial interactions between late transition metal/metal oxide nanoparticles and oxide supports impact catalysts��� activity and stability. Here, we report the use of isothermal titration calorimetry (ITC), electron microscopy and density functional theory (DFT) to explore periodic trends in the heats of nanoparticle-support interactions for late transition metal and metal oxide nanoparticles on layered niobate and silicate supports. Data for Co(OH)2, hydroxyiridate-capped IrOx.nH2O, ...

  9. Dissociation of N2, NO, and CO on transition metal surfaces

    DEFF Research Database (Denmark)

    Mavrikakis, Manos; Hansen, Lars Bruno; Mortensen, Jens Jørgen

    1999-01-01

    Using density functional theory we study the dissociation of N2, NO, and CO on transition metal surfaces. We discuss an efficient method to locate the minimum energy path and the transition state, and review recent calculations using this method to determine the transition state for dissociation...... of N2 on Ru(0001) and NO on Pd(111), Pd(211), and Rh(111) surfaces. We also show how steps and adsorbed alkali metal atoms can significantly decrease the dissociation barrier. Finally, trends in the properties of the transition state for N2, NO and CO dissociation on transition metals are discussed...

  10. Correlated effective field theory in transition metal compounds

    Science.gov (United States)

    Mukhopadhyay, Subhasis; Chatterjee, Ibha

    2004-03-01

    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

  11. Electronics and optoelectronics of two-dimensional transition metal dichalcogenides.

    Science.gov (United States)

    Wang, Qing Hua; Kalantar-Zadeh, Kourosh; Kis, Andras; Coleman, Jonathan N; Strano, Michael S

    2012-11-01

    The remarkable properties of graphene have renewed interest in inorganic, two-dimensional materials with unique electronic and optical attributes. Transition metal dichalcogenides (TMDCs) are layered materials with strong in-plane bonding and weak out-of-plane interactions enabling exfoliation into two-dimensional layers of single unit cell thickness. Although TMDCs have been studied for decades, recent advances in nanoscale materials characterization and device fabrication have opened up new opportunities for two-dimensional layers of thin TMDCs in nanoelectronics and optoelectronics. TMDCs such as MoS(2), MoSe(2), WS(2) and WSe(2) have sizable bandgaps that change from indirect to direct in single layers, allowing applications such as transistors, photodetectors and electroluminescent devices. We review the historical development of TMDCs, methods for preparing atomically thin layers, their electronic and optical properties, and prospects for future advances in electronics and optoelectronics.

  12. Transition metal oxide hierarchical nanotubes for energy applications

    Science.gov (United States)

    Wei, Wei; Wang, Yongcheng; Wu, Hao; Al-Enizi, Abdullah M.; Zhang, Lijuan; Zheng, Gengfeng

    2016-01-01

    We report a general synthetic method for transition metal oxide (TMO) hierarchical nanotube (HNT) structures by a solution-phase cation exchange method from Cu2O nanowire templates. This method leads to the formation of hollow, tubular backbones with secondary, thin nanostructures on the tube surface, which substantially increases the surface reactive sites for electrolyte contacts and electrochemical reactions. As proofs-of-concept, several representative first-row TMO HNTs have been synthesized, including CoO x , NiO x , MnO x , ZnO x and FeO x , with specific surface areas much larger than nanotubes or nanoparticles of corresponding materials. An example of the potential energy storage applications of CoO x HNTs as supercapacitors is also demonstrated.

  13. 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.

  14. 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.

  15. Surface relaxation and stress for 5d transition metals

    Science.gov (United States)

    Zólyomi, V.; Vitos, L.; Kwon, S. K.; Kollár, J.

    2009-03-01

    Using the density functional theory, we present a systematic theoretical study of the layer relaxation and surface stress of 5d transition metals. Our calculations predict layer contractions for all surfaces, except for the (111) surface of face centered cubic Pt and Au, where slight expansions are obtained similarly to the case of the 4d series. We also find that the relaxations of the close packed surfaces decrease with increasing occupation number through the 5d series. The surface stress for the relaxed, most closely packed surfaces shows similar atomic number dependence as the surface energy. Using Cammarata's model and our calculated surface stress and surface energy values, we examine the possibility of surface reconstructions, which is in reasonable agreement with the experimental observations.

  16. 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.

  17. Phase equilibria of the Mo-Al-Ho ternary system

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yitai; Chen, Xiaoxian; Liu, Hao [Guangxi Univ., Nanning (China). College of Materials Science and Engineering; Guangxi Univ., Nanning (China). Guangxi Key Laboratory of Processing for Non-ferrous Metal and Featured Materials; Zhan, Yongzhong [Guangxi Univ., Nanning (China). College of Materials Science and Engineering; Guangxi Univ., Nanning (China). Guangxi Key Laboratory of Processing for Non-ferrous Metal and Featured Materials; Guangxi Univ., Nanning (China). Center of Ecological Collaborative Innovation for Aluminum Industry

    2017-08-15

    Investigation into the reactions and phase equilibria of transition metal elements (i.e. Mo, Zr, Cr, V and Ti), Al and rare earths is academically and industrially important for the development of both refractory alloys and lightweight high-temperature materials. In this work, the equilibria of the Mo-Al-Ho ternary system at 773 K have been determined by using X-ray powder diffraction and scanning electron microscopy equipped with energy dispersive X-ray analysis. A new ternary phase Al{sub 4}Mo{sub 2}Ho has been found and the other ternary phase Al{sub 43}Mo{sub 4}Ho{sub 6} is observed. Ten binary phases in the Al-Mo and Al-Ho systems, including Al{sub 17}Mo{sub 4} rather than Al{sub 4}Mo, have been determined to exist at 773 K. The homogeneity ranges of AlMo{sub 3} and Al{sub 8}Mo{sub 3} phase are 7.5 at.% and 1 at.%, respectively. According to the phase-disappearing method, the maximum solubility of Al in Mo is about 16 at.%.

  18. 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.

  19. Formation enthalpies for transition metal alloys using machine learning

    Science.gov (United States)

    Ubaru, Shashanka; Miedlar, Agnieszka; Saad, Yousef; Chelikowsky, James R.

    2017-06-01

    The enthalpy of formation is an important thermodynamic property. Developing fast and accurate methods for its prediction is of practical interest in a variety of applications. Material informatics techniques based on machine learning have recently been introduced in the literature as an inexpensive means of exploiting materials data, and can be used to examine a variety of thermodynamics properties. We investigate the use of such machine learning tools for predicting the formation enthalpies of binary intermetallic compounds that contain at least one transition metal. We consider certain easily available properties of the constituting elements complemented by some basic properties of the compounds, to predict the formation enthalpies. We show how choosing these properties (input features) based on a literature study (using prior physics knowledge) seems to outperform machine learning based feature selection methods such as sensitivity analysis and LASSO (least absolute shrinkage and selection operator) based methods. A nonlinear kernel based support vector regression method is employed to perform the predictions. The predictive ability of our model is illustrated via several experiments on a dataset containing 648 binary alloys. We train and validate the model using the formation enthalpies calculated using a model by Miedema, which is a popular semiempirical model used for the prediction of formation enthalpies of metal alloys.

  20. Thermoelectric performance and electronic properties of transition metal monosilicides

    Science.gov (United States)

    Ou-Yang, T. Y.; Shu, G. J.; Fuh, H. R.

    2017-10-01

    We have performed a comprehensive series of lattice structure, band structure, electrical transport, and thermoelectric performances measurements for MnSi, FeSi, and CoSi single crystals. The band structure of this family of compounds demonstrates significant changes across the Fermi level as the number of 3d-electron is increased with transition metal substitution. In particular, a crossover from metal to semiconductor and back to semimetal has been observed in this series of compounds. Practical measurements (electrical transport and thermoelectric performances) are combined with theoretical calculations to qualify the reliability of band structures. By means of standard thermal activation simulations of electrical resistivity for FeSi, we identify a narrow band gap ∼57 meV, which is well consistent with our band calculation result. A double sign reversal of the Seebeck coefficient for FeSi suggests that both electrons and holes are contributed to electrical transport, indicating that the electronic structure of FeSi is substantially influenced by hole-doped (MnSi) and electron-doped (CoSi) effects.

  1. 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

  2. Metal-Nonmetal Transition and Homogeneous Nucleation of Mercury Vapour

    Science.gov (United States)

    Uchtmann, H.; Rademann, K.; Hensel, F.

    The paper presents ionization potentials of mercury clusters obtained by photoelectron spectroscopy which provide evidence that a size-dependent gradual transition from van der Waals-type to metallic interaction occurs in Hgx-clusters for × > 13. In order to probe the role of this nonmetal to metal transition in the homogeneous nucleation process of supersaturated mercury vapour we have determined the supersaturation necessary for homogeneous condensation of mercury vapour in the temperature range 250 to 320 K. The measurements were made using an upward thermal diffusion cloud chamber. The results demonstrate that none of the current theories for homogeneous nucleation satisfactorily predict the observed critical supersaturations. The measured values are about 3 orders of magnitude lower than the values predicted by the conventional Becker-Döring-Zeldovitch-theory.Translated AbstractMetall-Nichtmetallübergang und homogene Keimbildung bei QuecksilberdampfEs werden photoelektronenspektroskopische Messungen der Ionisationspotentiale von im Molekularstrahl synthetisierten Quecksilberclustern als Funktion der Größe beschrieben. Sie zeigen, daß ein größenabhängiger kontinuierlicher Übergang von van der Waals-Bindung zu metallischer Bindung für Cluster mit mehr als 13 Hg-Atomen auftritt. Um erste Informationen über den Einfluß dieses Übergangs von nichtmetallischem zu metallischem Verhalten auf den Keimbildungsprozeß in übersättigten Quecksilberdämpfen zu erhalten, werden zusätzlich Untersuchungen der homogenen Kondensation von übersättigten Quecksilberdämpfen im Temperaturbereich zwischen 250 bis 320 K mit einer Diffusionsnebelkammer berichtet. Die erhaltenen Ergebnisse können mit keiner der existierenden Theorien für die homogene Kondensation beschrieben werden. Die beobachteten Werte für die die homogene Kondensation auslösende kritische Übersättigung sind um drei Größenordnungen größer als die mit der klassischen Becker

  3. HfxAlyO ternary dielectrics for InGaAs based metal-oxide-semiconductor capacitors

    Science.gov (United States)

    Krylov, Igor; Ritter, Dan; Eizenberg, Moshe

    2017-07-01

    The electrical properties of HfxAlyO compound dielectric films and the HfxAlyO/InGaAs interface are reported for various dielectric film compositions. Despite the same trimethylaluminum (TMA) pre-deposition treatment, dispersion in accumulation and capacitance-voltage (C-V) hysteresis increased with hafnium content. Different kinds of border traps were identified as being responsible for the phenomena. After anneal, the density of states in the HfxAlyO/InGaAs interface varied quite weakly with dielectric film composition. The optimal composition for obtaining high inversion charge density in metal oxide semiconductor gate stacks is determined by a tradeoff between leakage and dielectric constant, with the optimum atomic cation ratio ([Hf]/[Al]) of ˜1.

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

    NARCIS (Netherlands)

    Mathies, Guinevere

    2012-01-01

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

  5. Analysis on insulator–metal transition in yttrium doped LSMO from ...

    Indian Academy of Sciences (India)

    Home; Journals; Bulletin of Materials Science; Volume 35; Issue 1 ... LSMO; X-ray diffraction; MEM; charge density; insulator – metal transition. Abstract. Yttrium doped LSMO (La1−SrMnO3) was prepared using sol–gel technique and analysed for the insulator–metal transition fromcharge density variation in the unit cell ...

  6. 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.

  7. Ligational behavior of Schiff bases towards transition metal ion and metalation effect on their antibacterial activity

    Science.gov (United States)

    Devi, Jai; Batra, Nisha; Malhotra, Rajesh

    2012-11-01

    New Schiff bases pyrazine-2-carboxylicacid (phenyl-pyridin-2-yl-methylene)-hydrazide (Hpch-bp) HL1 and pyrazine-2-carboxylicacid (pyridin-2-ylmethylene)-hydrazide (Hpch-pc) HL2 derived from condensation of pyrazine carboxylic hydrazide (Hpch) with 2-benzoyl pyridine (bp) or pyridine 2-carbaldehyde (pc) and their transition metal complexes of type ML(1-2)2 have been synthesized, where M = Mn(II), Co(II), Ni(II), Cu(II) and Zn(II). Characterization of ligands and their metal complexes was carried out by elemental analysis, conductimetric studies, magnetic susceptibility, spectroscopic techniques (IR, UV-VIS, NMR, ESR, Mass) and thermogravimetric analysis. The physico-chemical studies revealed octahedral geometry or distorted octahedral geometry around metal ion. These azomethine Schiff base ligands acted as tridentate ? coordinating through carbonyl, azomethine and pyridine nitrogen present in the ligand. The thermodynamic and thermal properties of the complexes have been investigated and it was observed on the basis of these studies that thermal stability of complexes follows the order Mn activity at different concentrations against bacteria viz. Gram positive Bacillus subtilis, Micrococcus luteus and Gram negative Pseudomonas aeruginosa, Pseudomonas mendocina. A marked enhancement in biocidal activity of the ligands under similar experimental conditions was observed as a consequence of coordination with metal ions. The trend of growth inhibition in the complexes was found to be in the order: Cu > Mn > Ni > Co > Zn.

  8. A comparative evaluation between new ternary zirconium alloys as alternative metals for orthopedic and dental prosthetic devices.

    Science.gov (United States)

    Shyti, Genti; Rosalbino, Francesco; Macciò, Daniele; Scarabelli, Linda; Quarto, Rodolfo; Giannoni, Paolo

    2014-02-01

    We assessed in vitro the corrosion behavior and biocompatibility of four Zr-based alloys (Zr97.5 Nb1.5VM1.0  ; VM, valve metal: Ti, Mo, W, Ta; at%) to be used as implant materials, comparing the results with grade-2 titanium, a biocompatible metal standard. Corrosion resistance was investigated by open circuit potential and electrochemical impedance spectroscopy measurements as a function of exposure time to an artificial physiological environment (Ringer's solution). Human bone marrow stromal cells were used to evaluate biocompatibility of the alloys and their influence on growth kinetics and cell osteogenic differentiation through histochemical and gene expression analyses. Open circuit potential values indicated that Zr-based alloys and grade-2 Ti undergo spontaneous passivation in the simulated aggressive environment. High impedance values for all samples demonstrated improved corrosion resistance of the oxide film, with the best protection characteristics displayed by Zr97.5  Nb1.5Ta1.0. Cells seeded on all surfaces showed the same growth kinetics, although matrix mineralization and alkaline phosphatase activity were maximal on Zr97.5  Nb1.5Mo1.0 and Zr97.5   Nb1.5Ta1.0. Markers of ongoing proliferation, however, such as podocalyxin and CD49f, were still overexpressed on Zr97.5   Nb1.5   Mo1.0 even upon osteoinduction. No relevant effects were noted for the CD146-expressing population of bone progenitors. Nonetheless, the presence of a more differentiated cell population on Zr97.5Nb1.5Ta1.0 samples was inferable by comparing mineralization data and transcript levels of osteogenic markers (osteocalcin, osteopontin, bone sialoprotein, and RUNX2). The combination of passivation, corrosion resistance and satisfactory biotolerance to bone progenitors make the Zr-based alloys promising implant materials. Among those we tested, Zr97.5Nb1.5Ta1.0 seems to be the most appealing.

  9. Quantum spin liquids and the metal-insulator transition in doped semiconductors.

    Science.gov (United States)

    Potter, Andrew C; Barkeshli, Maissam; McGreevy, John; Senthil, T

    2012-08-17

    We describe a new possible route to the metal-insulator transition in doped semiconductors such as Si:P or Si:B. We explore the possibility that the loss of metallic transport occurs through Mott localization of electrons into a quantum spin liquid state with diffusive charge neutral "spinon" excitations. Such a quantum spin liquid state can appear as an intermediate phase between the metal and the Anderson-Mott insulator. An immediate testable consequence is the presence of metallic thermal conductivity at low temperature in the electrical insulator near the metal-insulator transition. Further, we show that though the transition is second order, the zero temperature residual electrical conductivity will jump as the transition is approached from the metallic side. However, the electrical conductivity will have a nonmonotonic temperature dependence that may complicate the extrapolation to zero temperature. Signatures in other experiments and some comparisons with existing data are made.

  10. Explicitly correlated composite thermochemistry of transition metal species.

    Science.gov (United States)

    Bross, David H; Hill, J Grant; Werner, H-J; Peterson, Kirk A

    2013-09-07

    Atomization energies were calculated using explicitly correlated coupled cluster methods with correlation consistent basis sets for a series of 19 small molecules containing 3d transition metal atoms. The atomization energies were calculated using a modified Feller-Peterson-Dixon approach in which CCSD(T) complete basis set (CBS) limits were obtained using extrapolations of aVTZ∕aVQZ CCSD(T)-F12b correlation energies, and then a series of additive contributions for relativity, core correlation, higher order correlation, and zero-point vibrations were included. The frozen-core CBS limits calculated with F12 methods closely matched the more computational expensive conventional awCVQZ∕awCV5Z CBS extrapolations, with a mean unsigned deviation of just 0.1 kcal∕mol. In particular, the CCSD(T∗)-F12b∕aVDZ and aVTZ atomization energies were more accurate on average than the conventional CCSD(T)∕aVQZ and aV5Z results, respectively. In several cases the effects of higher order correlation beyond CCSD(T), as judged by CCSDT and CCSDT(Q)Λ calculations, were greater than 1 kcal∕mol, reaching 4.5 kcal∕mol for CrO3. For the 16 molecules of this study with experimental uncertainties of ∼3.5 kcal∕mol or less, the final composite heats of formation have a mean unsigned deviation (MUD) from experiment of just 1.3 kcal∕mol, which is slightly smaller than the average of the experimental uncertainties, 1.8 kcal∕mol. The root mean square deviation (RMS) is only slightly larger at 1.7 kcal∕mol. Without the contributions due to higher order correlation effects, the MUD and RMS rise to 2.1 and 2.8 kcal∕mol, respectively. To facilitate the F12 calculations, new (aug-)cc-pVnZ∕MP2Fit (n = Q, 5) and (aug-)cc-pwCVTZ∕MP2Fit auxiliary basis sets were also developed for the transition metal atoms.

  11. 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

  12. Fingerprints of spin-orbital entanglement in transition metal oxides.

    Science.gov (United States)

    Oleś, Andrzej M

    2012-08-08

    The concept of spin-orbital entanglement on superexchange bonds in transition metal oxides is introduced and explained on several examples. It is shown that spin-orbital entanglement in superexchange models destabilizes the long-range (spin and orbital) order and may lead either to a disordered spin-liquid state or to novel phases at low temperature which arise from strongly frustrated interactions. Such novel ground states cannot be described within the conventionally used mean field theory which separates spin and orbital degrees of freedom. Even in cases where the ground states are disentangled, spin-orbital entanglement occurs in excited states and may become crucial for a correct description of physical properties at finite temperature. As an important example of this behaviour we present spin-orbital entanglement in the RV O(3) perovskites, with R = La,Pr,…,Y b,Lu, where the finite temperature properties of these compounds can be understood only using entangled states: (i) the thermal evolution of the optical spectral weights, (ii) the dependence of the transition temperatures for the onset of orbital and magnetic order on the ionic radius in the phase diagram of the RV O(3) perovskites, and (iii) the dimerization observed in the magnon spectra for the C-type antiferromagnetic phase of Y V O(3). Finally, it is shown that joint spin-orbital excitations in an ordered phase with coexisting antiferromagnetic and alternating orbital order introduce topological constraints for the hole propagation and will thus radically modify the transport properties in doped Mott insulators where hole motion implies simultaneous spin and orbital excitations.

  13. 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.

  14. Synthesis, Characterization and Coordinating Behaviour of Aminoalcohol Complexes with Transition Metals

    Directory of Open Access Journals (Sweden)

    K. Majid

    2008-01-01

    Full Text Available The complexation of aminoalcohols with various transition metal and metal complexes have long and varied history. Since these complexes have found applications in various fields, the coordinating behaviour of these complexes should be investigated more precisely, in view of contradictory reports regarding coordinating behaviour of aminoalcohols with transition metals. This article is a review of findings of various investigations carried out from time to time.

  15. Balanced ternary addition using a gated silicon nanowire

    NARCIS (Netherlands)

    Mol, J.A.; Van der Heijden, J.; Verduijn, J.; Klein, M.; Remacle, F.; Rogge, S.

    2011-01-01

    Ternary logic has the lowest cost of complexity, here, we demonstrate a CMOS hardware implementation of a ternary adder using a silicon metal-on-insulator single electron transistor. Gate dependent rectifying behavior of a single electron transistor (SET) results in a robust three-valued output as a

  16. Spectral study of ternary complexes of rare earths with different amino acids

    Energy Technology Data Exchange (ETDEWEB)

    Bhutra, M.P.; Gupta, A.K. (Jodhpur Univ. (India). Dept. of Physics)

    1983-11-01

    Absorption spectra of eight ternary complexes of neodymium and praseodymium with different amino acids (glycine, alanine, valine and methionine) as primary ligand and propane-1, 2-diol as secondary ligand have been recorded in dimethyl sulphoxide (DMSO) in the visible region. The observed values of energy and intensity of various transitions have been compared with those calculated by using Judd-Ofelt relation. The observed and calculated values are in good agreement. Based on the calculated values of different energy and intensity parameters, the covalency and its dependence on atomic number of metal ion, metal-ligand interaction, nephelauxetic effect, etc. have been discussed.

  17. Computational Study of Metal Contacts to Monolayer Transition-Metal Dichalcogenide Semiconductors

    Directory of Open Access Journals (Sweden)

    Jiahao Kang

    2014-07-01

    Full Text Available Among various 2D materials, monolayer transition-metal dichalcogenide (mTMD semiconductors with intrinsic band gaps (1–2 eV are considered promising candidates for channel materials in next-generation transistors. Low-resistance metal contacts to mTMDs are crucial because currently they limit mTMD device performances. Hence, a comprehensive understanding of the atomistic nature of metal contacts to these 2D crystals is a fundamental challenge, which is not adequately addressed at present. In this paper, we report a systematic study of metal-mTMD contacts with different geometries (top contacts and edge contacts by ab initio density-functional theory calculations, integrated with Mulliken population analysis and a semiempirical van der Waals dispersion potential model (which is critical for 2D materials and not well treated before. Particularly, In, Ti, Au, and Pd, contacts to monolayer MoS_{2} and WSe_{2} as well as Mo-MoS_{2} and W-WSe_{2} contacts are evaluated and categorized, based on their tunnel barriers, Schottky barriers, and orbital overlaps. Moreover, going beyond Schottky theory, new physics in such contact interfaces is revealed, such as the metallization of mTMDs and abnormal Fermi level pinning. Among the top contacts to MoS_{2}, Ti and Mo show great potential to form favorable top contacts, which are both n-type contacts, while for top contacts to WSe_{2}, W or Pd exhibits the most advantages as an n- or p-type contact, respectively. Moreover, we find that edge contacts can be highly advantageous compared to top contacts in terms of electron injection efficiency. Our formalism and the results provide guidelines that would be invaluable for designing novel 2D semiconductor devices.

  18. Surface modification of nanoclays by catalytically active transition metal ions.

    Science.gov (United States)

    Nawani, Pranav; Gelfer, Mikhail Y; Hsiao, Benjamin S; Frenkel, Anatoly; Gilman, Jeffrey W; Khalid, Syed

    2007-09-11

    A unique class of nanoclays was prepared by modification of pristine clays or organoclays (Cloisite C20A) with transition metal ions (TMIs). The composition, structure, morphology and thermal properties of TMI-modified nanoclays were investigated by atomic absorption spectroscopy (AAS), elemental analysis (EA), scanning electron microscopy (SEM), small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-ray absorption near-edge structure (XANES) spectroscopy. The content of TMIs in modified clays was found to be close to the limiting value of ion exchange capacity. SEM and X-ray results confirmed that TMIs were located between the mineral layers instead of being adsorbed on the surface of clay particles. TGA results indicated that the TMI treatment of organoclays could significantly increase the thermal stability, which was more pronounced in air than in nitrogen. Temperature-resolved SAXS measurements revealed that the presence of TMIs increased the onset temperature of structural degradation. The higher thermal stability of TMI-modified organoclays can be attributed to the change in the thermal degradation mechanism, resulting in a decrease in the yield of volatile products and the formation of char facilitated by the presence of catalytically active TMIs.

  19. Surface Modification of Nanoclays by Catalytically Active Transition Metal Ions

    Energy Technology Data Exchange (ETDEWEB)

    Nawani,P.; Gelfer, M.; Hsiao, B.; Frenkel, A.; Gilman, J.; Khalid, S.

    2007-01-01

    A unique class of nanoclays was prepared by modification of pristine clays or organoclays (Cloisite C20A) with transition metal ions (TMIs). The composition, structure, morphology and thermal properties of TMI-modified nanoclays were investigated by atomic absorption spectroscopy (AAS), elemental analysis (EA), scanning electron microscopy (SEM), small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-ray absorption near-edge structure (XANES) spectroscopy. The content of TMIs in modified clays was found to be close to the limiting value of ion exchange capacity. SEM and X-ray results confirmed that TMIs were located between the mineral layers instead of being adsorbed on the surface of clay particles. TGA results indicated that the TMI treatment of organoclays could significantly increase the thermal stability, which was more pronounced in air than in nitrogen. Temperature-resolved SAXS measurements revealed that the presence of TMIs increased the onset temperature of structural degradation. The higher thermal stability of TMI-modified organoclays can be attributed to the change in the thermal degradation mechanism, resulting in a decrease in the yield of volatile products and the formation of char facilitated by the presence of catalytically active TMIs.

  20. Structural, electrical and magnetic properties of transition metal nickel oxides

    Science.gov (United States)

    Wu, Guoqing

    Neutron powder diffraction, high pressure, magnetic susceptibility, and heat capacity measurements, as well as x-ray powder diffraction and iodometric titration, have been conducted on transition metal nickel oxides (TMOs), representative Ruddlesden-Popper (RP) phases Lan+1NinO3n+1 (n = 1, 2, ..., infinity) and hole-doped La2-xSr xNiO4 (0 ≤ x ≤ 1.2). The first complete study of La 2-xSrxNiO4 (0 ≤ x ≤ 1.2) and La n+1NinO3n+1 (n = 2 and 3) phases under high pressure is produced. Strong direct experimental evidence for polaron dominated electrical conduction in these charge transfer (CT) gap La2-xSr xNiO4 compounds is provided. Temperature evolution of the crystal structure of La2-xSrxNiO4 (x = 1/4 and 1/3) is revealed through neutron powder diffraction, structural relationships among n = 1, 2, and 3 phases are exhibited, and charge density wave (CDW) in multilayer Lan+1NinO3n+1 phases is strongly suggested. No superconductivity is observed at pressures up to 1.6 GPa and temperatures down to 4.2 K.

  1. 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.

  2. 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.

  3. Optical fingerprint of non-covalently functionalized transition metal dichalcogenides

    Science.gov (United States)

    Feierabend, Maja; Malic, Ermin; Knorr, Andreas; Berghäuser, Gunnar

    2017-09-01

    Atomically thin transition metal dichalcogenides (TMDs) hold promising potential for applications in optoelectronics. Due to their direct band gap and the extraordinarily strong Coulomb interaction, TMDs exhibit efficient light-matter coupling and tightly bound excitons. Moreover, large spin orbit coupling in combination with circular dichroism allows for spin and valley selective optical excitation. As atomically thin materials, they are very sensitive to changes in the surrounding environment. This motivates a functionalization approach, where external molecules are adsorbed to the materials surface to tailor its optical properties. Here, we apply the density matrix theory to investigate the potential of non-covalently functionalized monolayer TMDs. Considering exemplary molecules with a strong dipole moment, we predict spectral redshifts and the appearance of an additional side peak in the absorption spectrum of functionalized TMDs. We show that the molecular characteristics, e.g. coverage, orientation and dipole moment, crucially influence the optical properties of TMDs, leaving a unique optical fingerprint in the absorption spectrum. Furthermore, we find that the molecular dipole moments open a channel for coherent intervalley coupling between the high-symmetry K and K\\prime points which may create new possibilities for spin-valleytronics application.

  4. Strong cavity-pseudospin coupling in monolayer transition metal dichalcogenides

    Science.gov (United States)

    De, Amrit; Lake, Roger K.

    2017-07-01

    Strong coupling between the electronic states of monolayer transition metal dichalcogenides (TMDCs) such as MoS2,MoSe2,WS2, or WSe2, and a single in-plane optical cavity mode gives rise to valley- and spin-dependent cavity-QED effects. The Dirac Hamiltonian for this two-dimensional gapped semiconductor with large spin-orbit coupling facilitates pure Jaynes-Cummings-type coupling with spin-valley locking—providing an additional handle for spintronics using circularly polarized light. Besides being an on-chip light source, the strong cavity coupling causes the TMDC monolayer to act as a spontaneous spin oscillator. In addition, this system can be a sensitive magnetic field sensor for an in-plane magnetic field. It also displays unusual persistent Rabi oscillations between different conduction-band states that are insensitive to small magnetic field variations. Our analysis for dissipation due to finite exciton relaxation times and cavity losses suggests that these effects are observable.

  5. Onset of magnetism in B2 transition-metal aluminides

    Science.gov (United States)

    Kulikov, N. I.; Postnikov, A. V.; Borstel, G.; Braun, J.

    1999-03-01

    Ab initio calculation results for the electronic structure of disordered bcc FexAl1-x(0.4FeAl, CoAl, NiAl) phases with point defects are presented. The calculations were performed using the coherent potential approximation within the Korringa-Kohn-Rostoker method for the disordered case and the tight-binding linear muffin-tin orbital method for the intermetallic compounds. We studied in particular the onset of magnetism in Fe-Al and Co-Al systems as a function of the defect structure. We found the appearance of large local magnetic moments associated with the transition metal (TM) antisite defect in FeAl and CoAl compounds, in agreement with the experimental findings. Moreover, we found that any vacancies on both sublattices enhance the magnetic moments via reducing the charge transfer to a TM atom. Disordered Fe-Al alloys are ferromagnetically ordered for the whole range of composition studied, whereas Co-Al becomes magnetic only for Co concentration >=0.5.

  6. Defect-induced semiconductor to metal transition in graphene monoxide.

    Science.gov (United States)

    Woo, Jungwook; Yun, Kyung-Han; Cho, Sung Beom; Chung, Yong-Chae

    2014-07-14

    This study investigates the influence of point defects on the geometric and electronic structure of graphene monoxide (GMO) via density functional theory calculations. In aspects of defect formation energy, GMOs with oxygen vacancies and bridge interstitial defects are more likely to form when compared to GMOs with defects such as carbon vacancies and hollow interstitial defects. It was also found that the oxygen vacancy or the hollow interstitial defect induces local tensile strain around the defective site and this strain increases the band gap energy of the defective GMO. In addition, the band gaps of GMO with carbon vacancies or bridge interstitial defects decreased mainly due to the dangling bonds, not due to the strain effect. It is noted that the dangling bond derived from the defects forms the defect-level in the band gap of GMO. The semiconductor to metal transition by the band gap change (0-0.7 eV) implies the possibility for band gap engineering of GMO by vacancies and interstitial defects.

  7. Results of investigations of phase transitions of shock compressed metals

    Science.gov (United States)

    Zhernokletov, Mikhail; Kovalev, Alexey; Podurets, Alexey; Simakov, Vladimir; Rfnc---Vniief Team

    2017-06-01

    Formations of new crystalline modifications in compressed substances are undeniably among interesting phenomena in physics of shock waves. Since the early 2000, experts from IPE RFNC-VNIIEF have been actively involved in efforts aimed to determine ranges of melting and recording phase transitions at shock adiabats of metals and organic substances by measuring sound velocities with use of the rarefaction overtake technique, which employs indicator liquids and pressure profiles by manganine and PVDF pressure gauges. In the pressure range from 4 to 12 GPa, a two-wave structure was recorded in cerium. Analysis of structures of the shock wave and rarefaction wave in the range (0.6-6.0) GPa points to the fact that a rarefaction shock wave is formed in the release phase in cerium. Post-test investigations of the cerium samples by the X-ray structural analysis have not revealed changes in cerium phase structure. Basing on our investigations, cerium starts melting at shock adiabat at the pressure of 13 GPa. Jumps of sound velocities, which were revealed in tin and zinc at the pressures of (60 - 90) GPa and (105 - 130) GPa, can be respectively associated with the beginning and completion of melting at their shock adiabats.

  8. THE ELECTROCONDUCTIVITY OF THE LIQUID ALLOYS OF TRANSITION METALS

    Directory of Open Access Journals (Sweden)

    V.T.Shvets

    2004-01-01

    Full Text Available The concentration dependance of electroresistivity of the liquid binary alloys of transition metals Fe, Co and Ni is calculated. We considered the contribution to conductivity from the s-electrons, described within the model of nearly free electrons. The role of the partially occupied d-bands is reduced to resonance scattering of the s-electrons on d-states. The interaction of the s- and d-electrons is described by the hybridization potential of s- and d-states. The interaction with the ions, not including the partially occupied d-states, is described using the pseudopotential of the electron-ion interaction. The electroresistivity of the alloys is calculated in the second order of the perturbation theory in pseudopotential and hybridization potential. The concentration dependance of electroresistivity of the binary alloys approaches the linear regime as the resonance scattering of the s-electrons on d-states prevails over the scattering on the ions. The calculations exhibit good agreement with the experimental data.

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

    Indian Academy of Sciences (India)

    holysis as well as for hydrolysis reactions of esters. Metal ions are known to catalyse such reactions13,14 and certain metal catalysed ring opening reactions are used as model catalyst for carboxypeptidase A.15 To make such reactions catalytic by a metal ion the inter- mittent metal carboxylate complex formed through ring.

  10. Pure electronic metal-insulator transition at the interface of complex oxides

    Science.gov (United States)

    Meyers, D.; Liu, Jian; Freeland, J. W.; Middey, S.; Kareev, M.; Kwon, Jihwan; Zuo, J. M.; Chuang, Yi-De; Kim, J. W.; Ryan, P. J.; Chakhalian, J.

    2016-06-01

    In complex materials observed electronic phases and transitions between them often involve coupling between many degrees of freedom whose entanglement convolutes understanding of the instigating mechanism. Metal-insulator transitions are one such problem where coupling to the structural, orbital, charge, and magnetic order parameters frequently obscures the underlying physics. Here, we demonstrate a way to unravel this conundrum by heterostructuring a prototypical multi-ordered complex oxide NdNiO3 in ultra thin geometry, which preserves the metal-to-insulator transition and bulk-like magnetic order parameter, but entirely suppresses the symmetry lowering and long-range charge order parameter. These findings illustrate the utility of heterointerfaces as a powerful method for removing competing order parameters to gain greater insight into the nature of the transition, here revealing that the magnetic order generates the transition independently, leading to an exceptionally rare purely electronic metal-insulator transition with no symmetry change.

  11. Transition metal ions: charge carriers that mediate the electron capture dissociation pathways of peptides.

    Science.gov (United States)

    Chen, Xiangfeng; Fung, Yi Man Eva; Chan, Wai Yi Kelly; Wong, Pui Shuen; Yeung, Hoi Sze; Chan, T-W Dominic

    2011-12-01

    Electron capture dissociation (ECD) of model peptides adducted with first row divalent transition metal ions, including Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), and Zn(2+), were investigated. Model peptides with general sequence of ZGGGXGGGZ were used as probes to unveil the ECD mechanism of metalated peptides, where X is either V or W; and Z is either R or N. Peptides metalated with different divalent transition metal ions were found to generate different ECD tandem mass spectra. ECD spectra of peptides metalated by Mn(2+) and Zn(2+) were similar to those generated by ECD of peptides adducted with alkaline earth metal ions. Series of c-/z-type fragment ions with and without metal ions were observed. ECD of Fe(2+), Co(2+), and Ni(2+) adducted peptides yielded abundant metalated a-/y-type fragment ions; whereas ECD of Cu(2+) adducted peptides generated predominantly metalated b-/y-type fragment ions. From the present experimental results, it was postulated that electronic configuration of metal ions is an important factor in determining the ECD behavior of the metalated peptides. Due presumably to the stability of the electronic configuration, metal ions with fully-filled (i.e., Zn(2+)) and half filled (i.e., Mn(2+)) d-orbitals might not capture the incoming electron. Dissociation of the metal ions adducted peptides would proceed through the usual ECD channel(s) via "hot-hydrogen" or "superbase" intermediates, to form series of c-/z(•)- fragments. For other transition metal ions studied, reduction of the metal ions might occur preferentially. The energy liberated by the metal ion reduction would provide enough internal energy to generate the "slow-heating" type of fragment ions, i.e., metalated a-/y- fragments and metalated b-/y- fragments. © American Society for Mass Spectrometry, 2011

  12. Chemistry of Two-Dimensional Transition Metal Carbides (MXenes)

    Science.gov (United States)

    Mashtalir, Olha

    With consumer trends pushing toward smaller, faster, more flexible, multitasking devices, researchers striving to meet these needs have targeted two-dimensional (2D) materials---and graphene in particular---as holding the most promise for use in advanced applications. But in 2011, a significant interest has been triggered by a newly discovered family of novel 2D materials---layered transitional metal carbides and carbonitrides, named MXenes. Those compounds were of general formula Mn+1 XnTx, where M stands for metal atom, X is C and/or N, n = 1, 2 or 3, and Tx represents surface groups. Being initially suggested as a material for electrical energy storage systems, MXenes' properties and their potential applications have not been explored. This work is the first complete study of MXenes' chemistry that sheds light on the chemical composition, structure and properties of these novel materials and possible routes of its modification. The research was focused on 2D titanium carbide, Ti3C2Tx, chosen as the representative of the MXene family. The kinetic study of Ti 3C2Tx synthesis discovered the main synthesis parameters, viz. temperature, time and particle size, that affect the etching process and define the quality of final product. MXenes were found to be able to spontaneously accommodate various ions and small organic molecules between the layers leading to preopening of the structure. A major challenge of large scale production of delaminated, atomically thin 2D MXene layers was solved with two delamination techniques involving dimethyl sulfoxide and isopropyl amine pre-intercalation followed by sonication in water. Ti3C2Tx was also found to possess adsorptive and photocatalytic properties, revealing its potential for environmental applications. It also showed limited stability in water and in the presence of oxygen, providing important practical information on proper handling and storage of MXene materials. Completion of this work allowed the performance of energy

  13. Laser surface alloying of aluminium-transition metal alloys

    Directory of Open Access Journals (Sweden)

    Almeida, A.

    1998-04-01

    Full Text Available 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 highstrength 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-Nb surface alloys by alloying Cr, Mo or Nb powder into an Al and 7175 Al alloy substrate using a CO2 laser. This paper presents a review of the work that has been developed at Instituto Superior Tecnico on laser alloying of Al-TM alloys, over the last years.

    En el presente trabajo se estudia la aleación superficial mediante láser de aluminio con metales de transición. El cromo y el molibdeno son particularmente interesantes porque producen aleaciones de alta resistencia y por el bajo coeficiente de difusión y solución sólida en aluminio. Para producir estas aleaciones se ha seguido un procedimiento desarrollado en dos partes. En primer lugar, el material se alea usando una baja velocidad de procesado y en segundo lugar la estructura se modifica mediante un refinamiento posterior. Este procedimiento se ha empleado en la producción de aleaciones Al-Cr, Al-Mo y Al-Nb mediante aleación con láser de CO2 de polvos de Cr, Mo o Nb en aluminio y la aleación 7175. Este trabajo es una revisión del desarrollado en el Instituto Superior Técnico de Lisboa en los últimos años.

  14. 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.

  15. Comparative Study of Nonhybrid Density Functional Approximations for the Prediction of 3d Transition Metal Thermochemistry.

    Science.gov (United States)

    Determan, John J; Poole, Katelyn; Scalmani, Giovanni; Frisch, Michael J; Janesko, Benjamin G; Wilson, Angela K

    2017-10-10

    The utility of several nonhybrid density functional approximations (DFAs) is considered for the prediction of gas phase enthalpies of formation for a large set of 3d transition metal-containing molecules. Nonhybrid DFAs can model thermochemical values for 3d transition metal-containing molecules with accuracy comparable to that of hybrid functionals. The GAM-generalized gradient approximation (GGA); the TPSS, M06-L, and MN15-L meta-GGAs; and the Rung 3.5 PBE+ΠLDA(s) DFAs all give root-mean-square deviations below that of the widely used B3LYP hybrid. Modern nonhybrid DFAs continue to show utility for transition metal thermochemistry.

  16. Evaluating transition-metal catalysis in gas generation from the Permian Kupferschiefer by hydrous pyrolysis

    Science.gov (United States)

    Lewan, M.D.; Kotarba, M.J.; Wieclaw, D.; Piestrzynski, A.

    2008-01-01

    Transition metals in source rocks have been advocated as catalysts in determining extent, composition, and timing of natural gas generation (Mango, F. D. (1996) Transition metal catalysis in the generation of natural gas. Org. Geochem.24, 977–984). This controversial hypothesis may have important implications concerning gas generation in unconventional shale-gas accumulations. Although experiments have been conducted to test the metal-catalysis hypothesis, their approach and results remain equivocal in evaluating natural assemblages of transition metals and organic matter in shale. The Permian Kupferschiefer of Poland offers an excellent opportunity to test the hypothesis with immature to marginally mature shale rich in both transition metals and organic matter. Twelve subsurface samples containing similar Type-II kerogen with different amounts and types of transition metals were subjected to hydrous pyrolysis at 330° and 355 °C for 72 h. The gases generated in these experiments were quantitatively collected and analyzed for molecular composition and stable isotopes. Expelled immiscible oils, reacted waters, and spent rock were also quantitatively collected. The results show that transition metals have no effect on methane yields or enrichment. δ13C values of generated methane, ethane, propane and butanes show no systematic changes with increasing transition metals. The potential for transition metals to enhance gas generation and oil cracking was examined by looking at the ratio of the generated hydrocarbon gases to generated expelled immiscible oil (i.e., GOR), which showed no systematic change with increasing transition metals. Assuming maximum yields at 355 °C for 72 h and first-order reaction rates, pseudo-rate constants for methane generation at 330 °C were calculated. These rate constants showed no increase with increasing transition metals. The lack of a significant catalytic effect of transition metals on the extent, composition, and timing of

  17. Anomalous metallic state in the vicinity of metal to valence-bond solid insulator transition in LiVS2.

    Science.gov (United States)

    Katayama, N; Uchida, M; Hashizume, D; Niitaka, S; Matsuno, J; Matsumura, D; Nishihata, Y; Mizuki, J; Takeshita, N; Gauzzi, A; Nohara, M; Takagi, H

    2009-10-02

    We investigate LiVS2 and LiVSe2 with a triangular lattice as itinerant analogues of LiVO2 known for the formation of a valence-bond solid (VBS) state out of an S=1 frustrated magnet. LiVS2, which is located at the border between a metal and a correlated insulator, shows a first order transition from a paramagnetic metal to a VBS insulator at Tc approximately 305 K upon cooling. The presence of a VBS state in the close vicinity of insulator-metal transition may suggest the importance of itinerancy in the formation of a VBS state. We argue that the high temperature metallic phase of LiVS2 has a pseudogap, likely originating from the VBS fluctuation. LiVSe2 was found to be a paramagnetic metal down to 2 K.

  18. Lanthanide Single-Molecule Magnets Framed by Alkali Metals & Magnetic and Spectroscopic Studies of 3d Transition Metal Complexes

    DEFF Research Database (Denmark)

    Konstantatos, Andreas

    )imino)- methyl)benzene-1,2-diol]. Using this ligand, we were able to synthesize four different families of lanthanide complexes framed by alkali metals. Throughout the chapter we demonstrate how we can exploit the presence of the coordinated alkali metal ions in order to induce changes to the structure....... In Chapter 3 we present the results of our work with third row (3d) transition metal ions and their complexes. Specifically, in section 2.1 we report a series of complexes synthesized using a tripodal hexadentate Schiff-base ligand. The ligand demonstrates the ability to form mononuclear or trinuclear...... complexes of M3+ or M2+ metal ions (M: 3d transition metal) with the preference to either approximate octahedral or trigonal prismatic coordination geometry. A detailed magnetic characterization for most of the complexes is presented where a trinuclear Co2+ cluster stands out for its pronounced SMM...

  19. Functionalized Silicone Nanospheres: Synthesis, Transition Metal Immobilization, and Catalytic Applications

    Energy Technology Data Exchange (ETDEWEB)

    Bradley, Christopher A.; Yuhas, Benjamin D.; McMurdo, Meredith J.; Tilley, T. D.

    2008-12-11

    Silicone nanospheres containing a variety of functional groups (pyridines, phosphines, thiols, amines, etc.) have been prepared by emulsion copolymerization of methyltrimethoxysilane, MeSi(OMe)3, and the functionalized monomer of interest, RSi(OMe)3. This procedure provides a reproducible synthesis of spherical particles in the 12-28 nm size regime as determined by transmission electronSilicone nanospheres containing a variety of functional groups (pyridines, phosphines, thiols, amines, etc.) have been prepared by emulsion copolymerization of methyltrimethoxysilane, MeSi(OMe)₃, and the functionalized monomer of interest, RSi(OMe)₃. This procedure provides a reproducible synthesis of spherical particles in the 12-28 nm size regime as determined by transmission electron microscopy (TEM). The presence of the functional groups is supported by a combination of spectroscopic methods including DRUV-vis, DRIFTS, and NMR spectroscopy. Comonomer dispersity within the nanospheres was probed using elemental mapping techniques, and these support a homogeneous distribution of functional groups within the particles. Palladium(0) immobilization on phosphine-substituted nanospheres also results in a random distribution of the transition metal throughout the particles. Nanospheres containing multiple acid/base functionalities were also prepared, and these demonstrate functional group cooperativity based on enhanced conversions in the base-catalyzed Henry reaction, relative to nanosphere catalysts containing only basic groups. The diversity of functional groups that may be incorporated into the spheres suggests that these materials hold considerable promise as ligand supports and catalysts.Graphene nanoribbons (GNRs) have been suggested as a promising material for its use as nanoelectromechanical reasonators for highly sensitive force, mass, and charge detection. Therefore the accurate determination of the size-dependent elastic properties of GNRs is desirable for the design of

  20. Transition metal doped graphene for energy and electrical applications =

    Science.gov (United States)

    Krishna, Rahul

    In the view of rapid progress in the fabrication of nanoscale energy storage and electronic devices, graphene is a subject of great interest. As a truly two dimensional (2D) system, graphene possess extraordinary properties of high conductivity, high carrier mobility, large surface area (>2600 m2/g), flexibility, and chemical stability which are favourable for energy applications. Synthesis of high quality graphene still remains as a major challenge in graphene research. Various methods including mechanical exfoliation, thermal exfoliation and thermal chemical vapour deposition (CVD) methods are used for the production of high quality graphene. However, mass production of graphene is possible only by chemical exfoliation of graphite under strong oxidizing agents. This thesis deals with the state of the art mass production of reduced graphene oxide (RGO) using graphene oxide (GO) as the intermediate agent. One of the exciting ideas about graphene oxide is that, due to the functional groups attached, it could act as a laboratory for various catalytic reactions and led to the fabrication of novel devices. Transition metals were used to aid the reaction and to achieve desired novel properties. By catalytic reactions, high quality nanoparticles (NPs) such as Ni, Co, Pd Ag, Cu, NixB, CoxB and SiO2 were synthesized and anchored on graphene sheet for energy applications. Particularly, for hydrogen storage a nanocomposite catalyst containing palladium nickel boride-silica and reduced graphene oxide (Pd NixB-SiO2/RGO, abbreviated as Pd NSG) was successfully fabricated. The H2 adsorption experiment directly reveals the spillover effect on the Pd NSG nanocomposite and its enhanced H2 uptake capacity (0.7 wt.%) compared to SiO2/RGO (0.05 wt.%) under 50 bar hydrogen pressure at RT. On the basis of results a detailed mechanism of hydrogen spillover is established that exhibited the facile H2 dissociation on the Pd activator (active sites) and subsequent transportation of hydrogen

  1. Infrared Spectroscopy of Transition Metal-Molecular interactions in the Gas Phase

    Energy Technology Data Exchange (ETDEWEB)

    Duncan, Michael A. [Univ. of Georgia, Athens, GA (United States)

    2008-11-14

    Transition metal-molecular complexes produced in a molecular beam are mass-selected and studied with infrared laser photodissociation spectroscopy. Metal complexes with carbon monoxide, carbon dioxide, nitrogen, water, acetylene or benzene are studied for a variety of metals. The number and intensity of infrared active bands are compared to the predictions of density functional theory calculations to derive structures, spin states and coordination numbers in these systems. These studied provide new insights into subtle details of metal-molecular interactions important in heterogeneous catalysis, metal-ligand bonding and metal ion solvation.

  2. 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.)

  3. CO adsorption on metal-oxide surfaces doped with transition-metal adatoms

    Energy Technology Data Exchange (ETDEWEB)

    Blomqvist, Janne; Lehman, Lauri; Salo, Petri [Department of Applied Physics, Aalto University, FI-00076 Aalto (Finland)

    2012-05-15

    Using first principles density functional theory calculations, we have studied the adsorption of carbon monoxide (CO) on clean, Ag and Pd doped MgO(001), TiO{sub 2}(110), and {alpha}-Al{sub 2}O{sub 3}(0001) surfaces. Our results show that adsorption of CO on the clean surfaces is generally weak. Ag doping improves the adsorption only weakly, except on the TiO{sub 2} surface. The presence of Pd, however, significantly improves adsorption on all the surfaces studied. On the doped surfaces, the best adsorption sites are always the sites on top of the transition metal adatom, and the interaction range is 3-4 Aa around an isolated adatom. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  4. 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.

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

    DEFF Research Database (Denmark)

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

    2006-01-01

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

  6. Recent advances in metathesis-derived polymers containing transition metals in the side chain

    Directory of Open Access Journals (Sweden)

    Ileana Dragutan

    2015-12-01

    Full Text Available This account critically surveys the field of side-chain transition metal-containing polymers as prepared by controlled living ring-opening metathesis polymerization (ROMP of the respective metal-incorporating monomers. Ferrocene- and other metallocene-modified polymers, macromolecules including metal-carbonyl complexes, polymers tethering early or late transition metal complexes, etc. are herein discussed. Recent advances in the design and syntheses reported mainly during the last three years are highlighted, with special emphasis on new trends for superior applications of these hybrid materials.

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

    African Journals Online (AJOL)

    a

    Cobalt(II) complex exhibits thermochromism. Antimicrobial studies on E. coli and S. aureus show the absence of growth inhibitory activities for HEATZ and its metal complexes which is attributed to the combined effect of derivatization of ATZ and metal complexation. KEY WORDS: Metal complexes, Atrazine derivatives, ...

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

    Indian Academy of Sciences (India)

    condensation synthesis method. Very low concentrations of metals were introduced into silica framework by maintaining the metal to silica ratio in the synthesis gel at 0.01. The difference in hydrolysis rates of metal and silica precursors have led to textural ...

  9. Structural implications for oxygen electrocatalysis in earthabundant transition metal oxides

    Science.gov (United States)

    Gardner, Graeme Patrick

    Transition metal oxides and related nitrides/nitride-oxides represent a class of materials that have shown great promise as oxygen electrocatalysts to replace the otherwise non-scalable noble metal-based catalysts currently implemented in commercial technologies. That is, compounds in this class of materials have shown promise as electrocatalysts for both the oxygen evolution (OER) and oxygen reduction reactions (ORR). The two aforementioned half-reactions are at the cornerstone of most renewable energy transformations, as oxygen is an inherently practical and abundant source and sink for electrons. In water electrolysis to produce hydrogen, oxygen is inevitably formed, and in a fuel cell the driving force for extracting electrochemical energy from hydrogen is pairing it with the reduction of oxygen to water. If this can be accomplished reversibly, the problem of "transient" renewable energy and its storage can be mitigated. We have examined many metal oxides and related compounds based upon Earth- abundant transition metals (primarily first row) that are crystalline, yet high surface area, for these important electrocatalytic reactions, and found that crystal structure plays a crucial role in determining activity. In fact, while most studies on heterogeneous catalysis focus on the synthesis of defect-rich, high surface area, practically amorphous materials to elicit high activity, we have found that particular crystalline phases possess not only the appropriate activity, but to some degree more importantly, the stability to be named good catalysts. In Chapter 2, we demonstrate that of the two structural types of lithium cobalt oxide (LiCoO2) - layered (R-3m) and cubic (Fd-3m) - only the cubic phase is revealed to be an efficient and stable catalyst for OER. Whether water oxidation is driven photochemically, or electrochemically, the cubic phase LiCoO2 possessing a spinel-like structure (AB 2O4) with [Co4O4] subunits within the crystal is more active. It is seen

  10. Investigating compositional effects of atomic layer deposition ternary dielectric Ti-Al-O on metal-insulator-semiconductor heterojunction capacitor structure for gate insulation of InAlN/GaN and AlGaN/GaN

    Energy Technology Data Exchange (ETDEWEB)

    Colon, Albert; Stan, Liliana; Divan, Ralu; Shi, Junxia

    2016-11-01

    Gate insulation/surface passivation in AlGaN/GaN and InAlN/GaN heterojunction field-effect transistors is a major concern for passivation of surface traps and reduction of gate leakage current. However, finding the most appropriate gate dielectric materials is challenging and often involves a compromise of the required properties such as dielectric constant, conduction/valence band-offsets, or thermal stability. Creating a ternary compound such as Ti-Al-O and tailoring its composition may result in a reasonably good gate material in terms of the said properties. To date, there is limited knowledge of the performance of ternary dielectric compounds on AlGaN/GaN and even less on InAlN/GaN. To approach this problem, the authors fabricated metal-insulator-semiconductor heterojunction (MISH) capacitors with ternary dielectrics Ti-Al-O of various compositions, deposited by atomic layer deposition (ALD). The film deposition was achieved by alternating cycles of TiO2 and Al2O3 using different ratios of ALD cycles. TiO2 was also deposited as a reference sample. The electrical characterization of the MISH capacitors shows an overall better performance of ternary compounds compared to the pure TiO2. The gate leakage current density decreases with increasing Al content, being similar to 2-3 orders of magnitude lower for a TiO2:Al2O3 cycle ratio of 2:1. Although the dielectric constant has the highest value of 79 for TiO2 and decreases with increasing the number of Al2O3 cycles, it is maintaining a relatively high value compared to an Al2O3 film. Capacitance voltage sweeps were also measured in order to characterize the interface trap density. A decreasing trend in the interface trap density was found while increasing Al content in the film. In conclusion, our study reveals that the desired high-kappa properties of TiO2 can be adequately maintained while improving other insulator performance factors. The ternary compounds may be an excellent choice as a gate material for both

  11. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2017-06-28

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

  13. The 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...

  14. Electronic Principles Governing the Stability and Reactivity of Ligated Metal and Silicon Encapsulated Transition Metal Clusters

    Science.gov (United States)

    Abreu, Marissa Baddick

    A thorough understanding of the underlying electronic principles guiding the stability and reactivity of clusters has direct implications for the identification of stable clusters for incorporation into clusters-assembled materials with tunable properties. This work explores the electronic principles governing the stability and reactivity of two types of clusters: ligated metal clusters and silicon encapsulated transition metal clusters. In the first case, the reactivity of iodine-protected aluminum clusters, Al13Ix - (x=0-4) and Al14Iy- (y=0-5), with the protic species methanol was studied. The symmetrical ground states of Al13Ix- showed no reactivity with methanol but reactivity was achieved in a higher energy isomer of Al 13I2- with iodines on adjacent aluminum atoms -- complementary Lewis acid-base active sites were induced on the opposite side of the cluster capable of breaking the O-H bond in methanol. Al 14Iy- (y=2-5) react with methanol, but only at the ligated adatom site. Reaction of methanol with Al14 - and Al14I- showed that ligation of the adatom was necessary for the reaction to occur there -- revealing the concept of a ligand-activated adatom. In the second case, the study focused heavily on CrSi12, a silicon encapsulated transition metal cluster whose stability and the reason for that stability has been debated heavily in the literature. Calculations of the energetic properties of CrSi n (n=6-16) revealed both CrSi12 and CrSi14 to have enhanced stability relative to other clusters; however CrSi12 lacks all the traditional markers of a magic cluster. Molecular orbital analysis of each of these clusters showed the CNFEG model to be inadequate in describing their stability. Because the 3dz2 orbital of Cr is unfilled in CrSi12, this cluster has only 16 effective valence electrons, meaning that the 18-electron rule is not applicable. The moderate stability of CrSi 12 can be accounted for by the crystal-field splitting of the 3d orbitals, which pushes the

  15. Electron Scattering at Surfaces and Interfaces of Transition Metals

    Science.gov (United States)

    Zheng, Pengyuan

    The effect of surfaces on the electron transport at reduced scales is attracting continuous interest due to its broad impact on both the understanding of materials properties and their application for nanoelectronics. The size dependence of for conductor's electrical resistivity rho due to electron surface scattering is most commonly described within the framework of Fuchs and Sondheimer (FS) and their various extensions, which uses a phenomenological scattering parameter p to define the probability of electrons being elastically (i.e. specularly) scattered by the surface without causing an increase of rho at reduced size. However, a basic understanding of what surface chemistry and structure parameters determine the specularity p is still lacking. In addition, the assumption of a spherical Fermi surface in the FS model is too simple for transition metals to give accurate account of the actual surface scattering effect. The goal of this study is to develop an understanding of the physics governing electron surface/interface scattering in transition metals and to study the significance of their Fermi surface shape on surface scattering. The advancement of the scientific knowledge in electron surface and interface scattering of transition metals can provide insights into how to design high-conductivity nanowires that will facilitate the viable development of advanced integrated circuits, thermoelectric power generation and spintronics. Sequential in situ and ex situ transport measurements as a function of surface chemistry demonstrate that electron surface/interface scattering can be engineered by surface doping, causing a decrease in the rho. For instance, the rho of 9.3-nm-thick epitaxial and polycrystalline Cu is reduced by 11--13% when coated with 0.75 nm Ni. This is due to electron surface scattering which exhibits a specularity p = 0.7 for the Cu-vacuum interface that transitions to completely diffuse (p = 0) when exposed to air. In contrast, Ni-coated surfaces

  16. Luminescence properties of B{sub 2}O{sub 3}–GeO{sub 2}–Gd{sub 2}O{sub 3} scintillating glass doped with rare-earth and transition-metal ions

    Energy Technology Data Exchange (ETDEWEB)

    Sun, Xin-Yuan, E-mail: sxy5306@126.com [Department of Physics, Jinggangshan University, Ji’an 343009 (China); Jiang, Da-Guo; Wang, Wen-Feng; Cao, Chun-Yan; Li, Yu-Nong; Zhen, Guo-Tai [Department of Physics, Jinggangshan University, Ji’an 343009 (China); Wang, Hong; Yang, Xin-Xin; Chen, Hao-Hong; Zhang, Zhi-Jun [Key Laboratory of Transparent Opto-functional Inorganic Materials, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China); Zhao, Jing-Tai, E-mail: jtzhao@mail.sic.ac.cn [Key Laboratory of Transparent Opto-functional Inorganic Materials, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China)

    2013-07-11

    Novel B{sub 2}O{sub 3}–GeO{sub 2}–Gd{sub 2}O{sub 3} ternary scintillating glasses doped with 1 mol% rare-earth and transition-metal activators were synthesized by melt-quenching method. Their transmittance, photoluminescence (PL) and X-ray excited luminescence (XEL) spectra were investigated. The results suggest that a high content of Gd{sub 2}O{sub 3} is of significance for designing dense glass with density of 6.0 g/cm{sup 3}. And energy transfer from Gd{sup 3+} to the incorporated activators can be realized in the borogermanate glasses. The emission position and decay time can be efficiently tuned by incorporating various kinds of activators. All results imply the developed borogermanate scintillating glass is potential for scintillating fields. -- Highlights: • Glass-forming region of B{sub 2}O{sub 3}–GeO{sub 2}–Gd{sub 2}O{sub 3} ternary system are determined. • Radioluminescence response from transition-metal doped B{sub 2}O{sub 3}–GeO{sub 2}–Gd{sub 2}O{sub 3} glasses. • Radioluminescence response from rare-earth doped B{sub 2}O{sub 3}–GeO{sub 2}–Gd{sub 2}O{sub 3} glasses. • Emission peak position and decay time can be tuneable by incorporating various activators.

  17. Bridged transition-metal complexes and uses thereof for hydrogen separation, storage and hydrogenation

    Science.gov (United States)

    Lilga, Michael A.; Hallen, Richard T.

    1990-01-01

    The present invention constitutes a class of organometallic complexes which reversibly react with hydrogen to form dihydrides and processes by which these compounds can be utilized. The class includes bimetallic complexes in which two cyclopentadienyl rings are bridged together and also separately .pi.-bonded to two transition metal atoms. The transition metals are believed to bond with the hydrogen in forming the dihydride. Transition metals such as Fe, Mn or Co may be employed in the complexes although Cr constitutes the preferred metal. A multiple number of ancilliary ligands such as CO are bonded to the metal atoms in the complexes. Alkyl groups and the like may be substituted on the cyclopentadienyl rings. These organometallic compounds may be used in absorption/desorption systems and in facilitated transport membrane systems for storing and separating out H.sub.2 from mixed gas streams such as the produce gas from coal gasification processes.

  18. 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....

  19. 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

  20. Synthesis and crystal structure of copper (II) uracil ternary polymeric complex with 1,10-phenanthroline along with the Hirshfeld surface analysis of the metal binding sites for the uracil ligand

    Science.gov (United States)

    Patil, Yogesh Prakash; Nethaji, Munirathinam

    2015-02-01

    The study of models for "metal-enzyme-substrate" interaction has been a proactive area of research owing to its biological and pharmacological importance. In this regard the ternary copper uracil complex with 1,10-phenanthroline represents metal-enzyme-substrate system for DNA binding enzymes. The synthesis of the complex, followed by slow evaporation of the reaction mixture forms two concomitant solvatomorph crystals viz., {[Cu(phen)(μ-ura)(H2O)]n·H2O (1a)} and {[Cu(phen)(μ-ura)(H2O)]n·CH3OH (1b)}. Both complexes are structurally characterized, while elemental analysis, IR and EPR spectra were recorded for 1b (major product). In both complexes, uracil coordinates uniquely via N1 and N3 nitrogen atom acting as a bidentate bridging ligand forming a 1-D polymer. The two solvatomorphs were quantitatively analyzed for the differences with the aid of Hirshfeld surface analysis.

  1. 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.

  2. 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.

  3. EPR of transition metal ions in NZP ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Yegor`kova, O.; Kryukova-Orlova, A.I. [Univ. of Nizhnii Novgorod (Russian Federation); Stefanovsky, S.V. [SIA Radon, Moscow (Russian Federation)

    1995-12-31

    NZP-ceramics have been produced by different methods such as sol-gel, flux melting and sintering of dry salts or phosphates. Formation of NZP and related phases was confirmed by X-ray diffraction analysis. Electron paramagnetic resonance (EPR) was applied to evaluate a structure positions of paramagnetic ions and nature of radiation-induced centers. EPR responses from transition metal ions Fe{sup 3+} and Mn{sup 2+} with electron configuration 3d{sup 5} (ground state {sup 6}S{sub 5/2}) which occurred as impurities in raw materials were registered in powders of NZP-ceramics. Fine structure arising due to high spin iron complexes is well resolved. A part of Fe{sup 3+} ions substitutes for Zr{sup 4+} and another part of one substitutes for Na{sup +} ions in six-fold coordinated positions. A great value of hyperfine structure (hfs) constant (9.3 mT) shows a high ionic character of Mn-O bonds in the first coordination sphere. A coordination number is close to 6. Fine structure of Mn{sup 2+} ions are not well resolved. A comparison of the spectra of samples containing various alkali cations shows the substitution for cations in series of Li-Na-K-Rb-Cs does not result in fundamental variation in spectra except for CZP ceramics where the response with g=4.3 due to Fe{sup 3+} in strong ligand field rather than response with g=2.0 due to Fe{sup 3+} in weak field is observed. An investigation of some samples doped by 0.1...0.5 mole % of Fe{sup 3+} or Gd{sup 3+} has been carried out and principal spin-Hamiltonian parameters have been determined. The increase of Fe and Gd ions content as compared to impurity substituting for Zr and possibly Na in their own structural positions results in noticeable site distortion. Gamma irradiation of NZP ceramics results in formation of radiation-induced paramagnetic centers connected to phosphorus-oxygen. The nature and concentration of these centers depend on production method. The lowest defect concentration is in hot-pressed ceramics.

  4. Ternary chalcopyrite semiconductors

    CERN Document Server

    Shay, J L; Pamplin, B R

    2013-01-01

    Ternary Chalcopyrite Semiconductors: Growth, Electronic Properties, and Applications covers the developments of work in the I-III-VI2 and II-IV-V2 ternary chalcopyrite compounds. This book is composed of eight chapters that focus on the crystal growth, characterization, and applications of these compounds to optical communications systems. After briefly dealing with the status of ternary chalcopyrite compounds, this book goes on describing the crystal growth of II-IV-V2 and I-III-VI2 single crystals. Chapters 3 and 4 examine the energy band structure of these semiconductor compounds, illustrat

  5. Large scale synthesis of niobium disulfide as a transparent transition metal dichalcogenide electrode

    Science.gov (United States)

    Bark, Hunyoung; Lee, Changgu

    Atomically thin transition metal dichalcogenides(TMDC) semiconductor such as MoS2 and WSe2 is considered as a promising candidate for future flexible and transparent electronic devices. However, direct metal contact to atomically thin transition metal dichalcogenides(TMDC) semiconductor shows high contact resistance, which suppress electrical performance like electron mobility. NbS2, one of the transition metal dichalcogenides(TMDC) conductor, is an important material because it is expected to form schottky barrier-free contact with transition metal dichalcogenides(TMDC) semiconductor. Here, we synthesize large scale niobium disulfide film as a transparent transition metal dichalcogenide electrode. Synthesized NbS2 film shows corresponding Raman shift and binding energy and has good crystallinity. NbS2 film can be easily patterned and shows uniform conductivity in large area. Large scale transparent NbS2 electrode applied to large scale MoS2 grown by chemical vapor deposition on quartz substrate. Ion-gel gated MoS2 transistor which uses NbS2 as an electrode shows 104 on/off ratio and 1 5cm2/Vs electron mobility which is better than metal contact MoS2 transistor.

  6. 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.

  7. Conductivity Dynamics of the Metal to Insulator Transition in EuNiO3/LANiO3 Superlattices

    Science.gov (United States)

    2016-02-07

    lead to emergent phenomena with the insulator -to- insulator transition (IMT) being one of the most enigmatic from fundamental and applied perspectives...2015 Approved for Public Release; Distribution Unlimited Final Report: Conductivity Dynamics of the Metal to Insulator Transition in EuNiO3/LANiO3...Conductivity Dynamics of the Metal to Insulator Transition in EuNiO3/LANiO3 Superlattices Report Title In numerous transition metal oxides (TMO

  8. Insulator–metal transition in a conservative system: An evidence for ...

    Indian Academy of Sciences (India)

    substrate, suggest that the mobility coalescence is responsible for the aging in island metal films. Electron ... The comparison of aging data of island silver films deposited on glass substrates in ultra high vac- uum and high .... As a consequence, insulator–metal transition after the stoppage of deposition is not observed for ...

  9. 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,

  10. Approaches for reducing the insulator-metal transition pressure in hydrogen

    Science.gov (United States)

    Carlsson, A. E.; Ashcroft, N. W.

    1983-01-01

    Two possible techniques for reducing the external pressure required to induce the insulator-metal transition in solid hydrogen are described. One uses impurities to lower the energy of the metallic phase relative to that of the insulating phase. The other utilizes a negative pressure induced in the insulating phase by electron-hole pairs, created either with laser irradiation or pulsed synchrotron sources.

  11. 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

  12. Strain field due to transition metal impurities in Ni and Pd

    Indian Academy of Sciences (India)

    2015-11-27

    Nov 27, 2015 ... The strain field due to body centered substitutional transition metal impurities in Ni and Pd metals are investigated. The calculations are carried out in ... Proceedings of the International Workshop/Conference on Computational Condensed Matter Physics and Materials Science (IWCCMP-2015). Posted on ...

  13. 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

  14. 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

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

    Indian Academy of Sciences (India)

    quasi atom concept and density functional theory. Adams and Foiles [3] developed a model for bcc metal V with the Morse form as pair-potential between atoms, and this model was successfully applied to calculate many-body potentials. Johnson and Oh [4] have presented an analytic EAM model for the bcc metals in which ...

  16. thiosemicarbazide complexes with some first row transition metal i

    Indian Academy of Sciences (India)

    Unknown

    metal ions and ... The [Mn(DBtsc-. H)(SCN)] and [Co(DBtsc-H)Cl] complexes were isolated by mixing and stirring the ethanolic solutions (20 cm3) of the respective metal (II) ... band spectrometer model EPR-112 using DPPH as a marker.

  17. 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(-)

  18. 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−

  19. 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.

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

    Indian Academy of Sciences (India)

    Unknown

    thus become unavailable for fluorescence quenching. In other words, in this approach, the metal ion-receptor interaction has been increased to reduce indirectly the undesired communication between the metal ion and fluorophore that leads to fluorescence quench- ing. While the above approach is indeed an elegant one, ...

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

    Indian Academy of Sciences (India)

    ... copper and vanadyl complexes was studied by cyclic voltammetry. Antimicrobial screening tests gave good results in the presence of metal ion in the ligand system. The nuclease activity of the above metal complexes shows that Cu, Ni and Co complexes cleave DNA through redox chemistry whereas other complexes are ...

  2. Substrate Effect on Optical Properties of Insulator-Metal Transition in VO2 Thin Films

    OpenAIRE

    Radue, E.; Crisman, E.; L. Wang; Kittiwatanakul, S.; Lu, J.; Wolf, S. A.; Wincheski, R.; Lukaszew, R. A.; Novikova, I.

    2012-01-01

    In this paper we used Raman spectroscopy to investigate the optical properties of vanadium dioxide (VO2) thin films during the thermally induced insulating to metallic phase transition. We observed a significant difference in transition temperature in similar VO2 films grown on quartz and sapphire substrates: the film grown on quartz displayed the phase transition at a lower temperature (Tc=50C) compared a film grown on sapphire (Tc=68C). We also investigated differences in the detected Raman...

  3. 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.

  4. First-row transition metal catalyzed reduction of carbonyl functionalities: a mechanistic perspective.

    Science.gov (United States)

    Chakraborty, Sumit; Guan, Hairong

    2010-08-28

    The use of first-row transition metals for the catalytic reduction of carbonyl functionalities has become increasingly important in homogeneous catalysis. This Perspective examines the mechanistic aspects of these reduction reactions, with a focus on various interactions between metal complexes and substrates. Four different types of catalytic pathways, namely catalysis with dihydride (or dihydrogen) complexes, catalysis with monohydride complexes, metal-ligand bifunctional catalysis, and catalysis involving ionic mechanisms, are discussed with recent examples highlighted.

  5. 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.

  6. A Vanadium Dioxide Metamaterial Disengaged from Insulator-to-Metal Transition.

    Science.gov (United States)

    Jeong, Young-Gyun; Han, Sanghoon; Rhie, Jiyeah; Kyoung, Ji-Soo; Choi, Jae-Wook; Park, Namkyoo; Hong, Seunghun; Kim, Bong-Jun; Kim, Hyun-Tak; Kim, Dai-Sik

    2015-10-14

    We report that vanadium dioxide films patterned with λ/100000 nanogaps exhibit an anomalous transition behavior at millimeter wavelengths. Most of the hybrid structure's switching actions occur well below the insulator to metal transition temperature, starting from 25 °C, so that the hysteresis curves completely separate themselves from their bare film counterparts. It is found that thermally excited intrinsic carriers are responsible for this behavior by introducing enough loss in the context of the radically modified electromagnetic environment in the vicinity of the nanogaps. This phenomenon newly extends the versatility of insulator to metal transition devices to encompass their semiconductor properties.

  7. Terahertz transport dynamics in the metal-insulator transition of V2O3 thin film

    Science.gov (United States)

    Luo, Y. Y.; Su, F. H.; Zhang, C.; Zhong, L.; Pan, S. S.; Xu, S. C.; Wang, H.; Dai, J. M.; Li, G. H.

    2017-03-01

    The dynamic behavior of thermally-induced metal-insulator transition of V2O3 thin film on Si substrate grown by reactive magnetron sputtering was investigated by the terahertz time-domain spectroscopy. It was found that the THz absorption and optical conductivity of the thin films are temperature-dependent, and the THz amplitude modulation can reach as high as 74.7%. The complex THz optical conductivity in the metallic state of the V2O3 thin films can be well-fitted by the Drude-Smith model, which offer the insight into the electron transport dynamic during the metal-insulator transition of the thin film.

  8. 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.

  9. 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

    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...... such as Sc, Y, Ti, and Zr bind N-adatoms more strongly than H-adatoms, a significant production of ammonia compared with hydrogen gas can be expected on those metal electrodes when a bias of 1 V to 1.5 V vs. SHE is applied. Defect-free surfaces of the early transition metals are catalytically more active...

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

    Energy Technology Data Exchange (ETDEWEB)

    Spivak, B.

    2010-04-06

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

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

    Directory of Open Access Journals (Sweden)

    Yuichi Otsuka

    2016-03-01

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

  12. Directly Predicting Water Quality Criteria from Physicochemical Properties of Transition Metals.

    Science.gov (United States)

    Wang, Ying; Wu, Fengchang; Mu, Yunsong; Zeng, Eddy Y; Meng, Wei; Zhao, Xiaoli; Giesy, John P; Feng, Chenglian; Wang, Peifang; Liao, Haiqing; Chen, Cheng

    2016-03-03

    Transition metals are a group of elements widespread in aquatic environments that can be hazardous when concentrations exceeding threshold values. Due to insufficient data, criteria maximum concentrations (CMCs) of only seven transition metals for protecting aquatic life have been recommended by the USEPA. Hence, it is deemed necessary to develop empirical models for predicting the threshold values of water quality criteria (WQC) for other transition metals for which insufficient information on toxic potency is available. The present study established quantitative relationships between recommended CMCs and physicochemical parameters of seven transition metals, then used the developed relationships to predict CMCs for other transition metals. Seven of 26 physicochemical parameters examined were significantly correlated with the recommended CMCs. Based on this, five of the seven parameters were selected to construct a linear free energy model for predicting CMCs. The most relevant parameters were identified through principle component analysis, and the one with the best correlation with the recommended CMCs was a combination of covalent radius, ionic radius and electron density. Predicted values were largely consistent with their toxic potency values. The present study provides an alternative approach to develop screening threshold level for metals which have insufficient information to use traditional methods.

  13. Directly Predicting Water Quality Criteria from Physicochemical Properties of Transition Metals

    Science.gov (United States)

    Wang, Ying; Wu, Fengchang; Mu, Yunsong; Zeng, Eddy Y.; Meng, Wei; Zhao, Xiaoli; Giesy, John P.; Feng, Chenglian; Wang, Peifang; Liao, Haiqing; Chen, Cheng

    2016-03-01

    Transition metals are a group of elements widespread in aquatic environments that can be hazardous when concentrations exceeding threshold values. Due to insufficient data, criteria maximum concentrations (CMCs) of only seven transition metals for protecting aquatic life have been recommended by the USEPA. Hence, it is deemed necessary to develop empirical models for predicting the threshold values of water quality criteria (WQC) for other transition metals for which insufficient information on toxic potency is available. The present study established quantitative relationships between recommended CMCs and physicochemical parameters of seven transition metals, then used the developed relationships to predict CMCs for other transition metals. Seven of 26 physicochemical parameters examined were significantly correlated with the recommended CMCs. Based on this, five of the seven parameters were selected to construct a linear free energy model for predicting CMCs. The most relevant parameters were identified through principle component analysis, and the one with the best correlation with the recommended CMCs was a combination of covalent radius, ionic radius and electron density. Predicted values were largely consistent with their toxic potency values. The present study provides an alternative approach to develop screening threshold level for metals which have insufficient information to use traditional methods.

  14. Photoluminescence response of colloidal quantum dots on VO2 film across metal to insulator transition.

    Science.gov (United States)

    Kuznetsov, Sergey N; Cheremisin, Alexander B; Stefanovich, Genrikh B

    2014-01-01

    We have proposed a method to probe metal to insulator transition in VO2 measuring photoluminescence response of colloidal quantum dots deposited on the VO2 film. In addition to linear luminescence intensity decrease with temperature that is well known for quantum dots, temperature ranges with enhanced photoluminescence changes have been found during phase transition in the oxide. Corresponding temperature derived from luminescence dependence on temperature closely correlates with that from resistance measurement during heating. The supporting reflectance data point out that photoluminescence response mimics a reflectance change in VO2 across metal to insulator transition. Time-resolved photoluminescence study did not reveal any significant change of luminescence lifetime of deposited quantum dots under metal to insulator transition. It is a strong argument in favor of the proposed explanation based on the reflectance data. 71.30. + h; 73.21.La; 78.47.jd.

  15. 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

  16. The transition metals copper and iron in neurodegenerative diseases.

    Science.gov (United States)

    Rivera-Mancía, Susana; Pérez-Neri, Iván; Ríos, Camilo; Tristán-López, Luis; Rivera-Espinosa, Liliana; Montes, Sergio

    2010-07-30

    Neurodegenerative diseases constitute a worldwide health problem. Metals like iron and copper are essential for life, but they are also involved in several neurodegenerative mechanisms such as protein aggregation, free radical generation and oxidative stress. The role of Fe and Cu, their pathogenic mechanisms and possible therapeutic relevance are discussed regarding four of the most common neurodegenerative diseases, Alzheimer's, Parkinson's and Huntington's diseases as well as amyotrophic lateral sclerosis. Metal-mediated oxidation by Fenton chemistry is a common feature for all those disorders and takes part of a self-amplifying damaging mechanism, leading to neurodegeneration. The interaction between metals and proteins in the nervous system seems to be a crucial factor for the development or absence of neurodegeneration. The present review also deals with the therapeutic strategies tested, mainly using metal chelating drugs. Metal accumulation within the nervous system observed in those diseases could be the result of compensatory mechanisms to improve metal availability for physiological processes. (c) 2010 Elsevier Ireland Ltd. All rights reserved.

  17. 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.

  18. First-principles study of structural stability, elastic and electronic properties of ternary rare earth-transition metal—Borides and carbides (RT{sub x}Z, R=Sc, Y, and La, T=Pt and Pd, Z=B and C, and x=2, 3, and 4)

    Energy Technology Data Exchange (ETDEWEB)

    Yao, Tiankai; Wang, Yachun; Li, Hui [Key Laboratory of Metastable Materials Science and Technology, College of Material Science and Engineering, Yanshan University, Qinhuangdao 066004 (China); Lian, Jie [Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180 (United States); Zhang, Jingwu, E-mail: zjw@ysu.edu.cn [Key Laboratory of Metastable Materials Science and Technology, College of Material Science and Engineering, Yanshan University, Qinhuangdao 066004 (China); Gou, Huiyang, E-mail: huiyang.gou@gmail.com [Key Laboratory of Metastable Materials Science and Technology, College of Material Science and Engineering, Yanshan University, Qinhuangdao 066004 (China)

    2013-12-15

    Using first-principles total energy calculations (CASTEP code), the structural stability, elastic, and electronic properties of ternary rare earth-transition metal borides and carbides (RT{sub x}Z, R=Sc, Y, and La, T=Pt and Pd, Z=B and C, and x=2, 3, and 4) compounds were studied. Results show that RT{sub 3}Z compounds with tetragonal P4mm structure are energetically more favorable than usually cubic perovskite-type structure. Furthermore, RT{sub 3}Z with perovskite structure is found to be mechanically unstable with the negative C{sub 44}. Formation enthalpy calculations indicate that Pt-based borides are easier to be synthesized compared with Pd-based ones and counterpart carbides, respectively. Elastic constants, bulk moduli, shear moduli, Young's moduli, and Poisson's ratio of studied compounds have been calculated. Also, all the studied compounds show ductile behavior. Moreover, total and partial density of states (DOSs) and bonding charge density were employed to elucidate the bonding features of these compounds. The results reveal that the covalency between Pt-5d and Z-2p as well as T-nd (n=4 for Pd and 5 for Pt) and B-2p states, are the cause of the relatively higher elastic moduli of Pt-based compounds and R–T-borides, respectively.

  19. First principles calculations and experimental insight into methane steam reforming over transition metal catalysts

    DEFF Research Database (Denmark)

    Jones, Glenn; Jakobsen, Jon Geest; Shim, Signe Sarah

    2008-01-01

    in situ TEM measurements under a hydrogen atmosphere. The overall agreement between theory and experiment (at 773 K, 1 bar pressure and 10% conversion) is found to be excellent with Ru and Rh being the most active pure transition metals for methane steam reforming, while Ni, Ir, Pt, and Pd...... metal Surfaces to develop an overview of the steam reforming process catalyzed by a range of transition metal surfaces. By combining scaling relationships with thermodynamic and kinetic analysis, we show that it is possible to determine the reactivity trends of the pure metals for methane steam...... reforming. The reaction is found to be kinetically controlled by a methane dissociation step and a CO formation step, where the latter step is found to be dominant at lower temperatures. The particle size of the metal catalysts particles have been determined by transmission electron microscopy (TEM...

  20. 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.

  1. 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.

  2. 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 .

  3. 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

  4. Efficient separation of transition metals from rare earths by an undiluted phosphonium thiocyanate ionic liquid.

    Science.gov (United States)

    Rout, Alok; Binnemans, Koen

    2016-06-21

    The ionic liquid trihexyl(tetradecyl)phosphonium thiocyanate has been used for the extraction of the transition metal ions Co(ii), Ni(ii), Zn(ii), and the rare-earth ions La(iii), Sm(iii) and Eu(iii) from aqueous solutions containing nitrate or chloride salts. The transition metal ions showed a high affinity for the ionic liquid phase and were efficiently extracted, while the extraction efficiency of the rare-earth ions was low. This difference in extraction behavior enabled separation of the pairs Co(ii)/Sm(iii), Ni(ii)/La(iii) and Zn(ii)/Eu(iii). These separations are relevant for the recycling of rare earths and transition metals from samarium cobalt permanent magnets, nickel metal hydride batteries and lamp phosphors, respectively. The extraction of metal ions from a chloride or nitrate solution with a thiocyanate ionic liquid is an example of "split-anion extraction", where different anions are present in the aqueous and ionic liquid phase. Close to 100% loading was possible for Co(ii) and Zn(ii) up to a concentration of 40 g L(-1) of the transition metal salt in the initial aqueous feed solution, whereas the extraction efficiency for Ni(ii) gradually decreased with increase in the initial feed concentration. Stripping of Co(ii), Zn(ii) and Ni(ii) from the loaded ionic liquid phase was possible by a 15 wt% NH3 solution. The ionic liquid could reused after extraction and stripping.

  5. Transition metal tetrachloroaluminate catalysts for probe reactions simulating petroleum resids upgrading

    Energy Technology Data Exchange (ETDEWEB)

    Sasaki, M.; Song, C.; Plummer, M.A. [Pennsylvania State University, University Park, PA (USA). Fuel Science Program and Lab. for Hydrocarbon Process Chemistry

    2000-03-01

    Several transition metal tetrachloroaluminates (MCl{sub x}-(AlCl{sub 3}){sub x}) have been evaluated as catalysts for probe reactions simulating petroleum resids upgrading. Six transition metal chlorides, VCl{sub 3}, CoCl{sub 2}, NiCl{sub 2}, ZnCl{sub 2}, MoCl{sub 3} and PdCl{sub 2}, and three kinds of alkali metal chlorides, LiCl, NaCl and KCl, were used for preparing the catalysts. Four compounds were selected as models, including 4-(1-naphthlymethyl)bibenzyl (NMBB), eicosane (n-C{sub 20}), dibenzothiophene and pyrene. Batch tests were carried out at 425{degree}C for 20 min under hydrogen pressure. Very interesting results were obtained from model compounds reactions that demonstrated the unusual and promising feature of transition metal tetrachloroaluminates. For example, some of the transition metal containing catalysts were found to strongly promote hydrocracking of a long-chain paraffin to levels which are 200-300% of those achieved with alkali metal tetrachloroaluminates. Mo-containing catalysts displayed especially higher activity for desulfurization and hydrogenation. The results of NMBB reactions provided insight into reaction mechanism, and the selectivity of cleavage of C-C bonds in NMBB correlated with the i-C{sub 4}/n-C{sub 4} ratio of the gaseous products, which is a relative measure of the acidity of the catalysts. 14 refs., 7 figs., 7 tabs.

  6. Synthesis, characterization and fungicidal activity of binary and ternary metal(II) complexes derived from 4,4‧-((4-nitro-1,2-phenylene) bis(azanylylidene))bis(3-(hydroxyimino)pentan-2-one)

    Science.gov (United States)

    El-Tabl, Abdou S.; Shakdofa, Mohamad M. E.; Whaba, Mohamad A.

    2015-02-01

    Ternary copper(II) and binary copper(II), nickel(II) and cobalt(II) complexes derived from 4,4‧-((4-nitro-1,2-phenylene)bis(azanylylidene))bis(3-(hydroxyimino)pentan-2-one) (H2L) were synthesized and characterized by elemental and thermal analyses, IR, UV-Vis. and 1H NMR spectroscopy, conductivity and magnetic moments measurements. The analytical and spectral data showed that, the ligand acts as dibasic tetradentate or dibasic hexadentate bonding to the metal ion via the two-imine nitrogen, two nitrogen and/or oximato oxygen atoms of deprotonated oxime groups forming five and/or six rings including the metal ions. The complexes adopt either tetragonal distorted octahedral or square planar geometry around metal ions. The ESR spectra of the solid copper(II) complexes are characteristic to d9 configuration and having an axial symmetry type of a d(x2-y2) ground state. The g values confirmed the geometry is elongated tetragonal octahedral geometry with considerably ionic or covalent environment. The antifungal biological activity of the prepared compounds was studied using well diffusion method. The obtained results showed that, the ligand is biologically inactive while its metal complexes were more potent fungicides than the ligand and standard antifungal drug (Amphotericin B).

  7. Synthesis, characterization and fungicidal activity of binary and ternary metal(II) complexes derived from 4,4'-((4-nitro-1,2-phenylene) bis(azanylylidene))bis(3-(hydroxyimino)pentan-2-one).

    Science.gov (United States)

    El-Tabl, Abdou S; Shakdofa, Mohamad M E; Whaba, Mohamad A

    2015-02-05

    Ternary copper(II) and binary copper(II), nickel(II) and cobalt(II) complexes derived from 4,4'-((4-nitro-1,2-phenylene)bis(azanylylidene))bis(3-(hydroxyimino)pentan-2-one) (H2L) were synthesized and characterized by elemental and thermal analyses, IR, UV-Vis. and (1)H NMR spectroscopy, conductivity and magnetic moments measurements. The analytical and spectral data showed that, the ligand acts as dibasic tetradentate or dibasic hexadentate bonding to the metal ion via the two-imine nitrogen, two nitrogen and/or oximato oxygen atoms of deprotonated oxime groups forming five and/or six rings including the metal ions. The complexes adopt either tetragonal distorted octahedral or square planar geometry around metal ions. The ESR spectra of the solid copper(II) complexes are characteristic to d(9) configuration and having an axial symmetry type of a d(x2-y2) ground state. The g values confirmed the geometry is elongated tetragonal octahedral geometry with considerably ionic or covalent environment. The antifungal biological activity of the prepared compounds was studied using well diffusion method. The obtained results showed that, the ligand is biologically inactive while its metal complexes were more potent fungicides than the ligand and standard antifungal drug (Amphotericin B). Copyright © 2014. Published by Elsevier B.V.

  8. 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 ...

  9. 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.

  10. 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.

  11. X-ray induced insulator-metal transitions in CMR manganites

    Energy Technology Data Exchange (ETDEWEB)

    Kiryukhin, V.; Casa, D.; Keimer, B. [Princeton Univ., NJ (United States). Dept. of Physics; Hill, J.P.; Vigliante, A. [Brookhaven National Lab., Upton, NY (United States). Dept. of Physics; Tomioka, Y. [Joint Research Center for Atom Technology, Tsukuba, Ibaraki (Japan); Tokura, Y. [Joint Research Center for Atom Technology, Tsukuba, Ibaraki (Japan)]|[Univ. of Tokyo (Japan). Dept. of Applied Physics

    1997-12-01

    In this work the authors report a study of the photoinduced insulator-to-metal transition in manganese oxide perovskites of the formula Pr{sub 1{minus}x}Ca{sub x}MnO{sub 3}. The transition is closely related to the magnetic field induced insulator-to-metal transition (CMR effect) observed in these materials. It is accompanied by a dramatic change in the magnetic properties and lattice structure: the material changes from an insulating charge-ordered canted antiferromagnet to a ferromagnetic metal. The authors present an investigation of the transport and structural properties of these materials over the course of the transition (which usually takes about an hour to complete). The current-voltage characteristics exhibited by the material during the transition are highly nonlinear, indicating a large inhomogeneity of the transitional state. Possible practical applications of this novel type of transition are briefly discussed. They also report a high resolution X-ray diffraction study of the charge ordering in these materials. The temperature dependent charge ordering structure observed in these compounds is more complex than previously reported.

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

    Indian Academy of Sciences (India)

    RASHEEDA M ANSARI

    2017-08-19

    Aug 19, 2017 ... research study is to throw more light on the chelation behavior of Schiff base ligand towards the chosen metal ions and their catalytic activity in the coupling of various substituted aryl halides with phenylboronic acid. 2. Experimental. 2.1 Materials and reagents. All chemicals were of analytical reagent (AR) ...

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

    Indian Academy of Sciences (India)

    TECS

    Studies of a new kind of chemotherapeutic Schiff bases are now attracting the attention of biochemists. 4,5. Earlier work reported that some drugs showed increased ac- tivity, when administered as metal complexes rather than as organic compounds. 6,7. Deoxyribonucleic acid (DNA) is the primary target molecule for most.

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

    African Journals Online (AJOL)

    Md. Sharif Hasan

    2017-01-18

    Jan 18, 2017 ... Objective: The purpose of this research was to investigate sub-chronic toxicity in animal model. Methods: A detailed study was done on the physical, hematological, biochemical and hormonal parame- ters of both male and female Sprague-Dawley rats after 28 days administration of naproxen and its metal.

  15. 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 ...

  16. 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…

  17. 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 sul...

  18. synthesis and structural studies of first row transition metal ...

    African Journals Online (AJOL)

    a

    benzilidine-3-hydrazino quinoxaline-2-one (NBHQO) and its metal complexes has been undertaken in order to evaluate antimicrobial properties of these compounds. The present paper deals with the synthesis and characterization of NBHQO and its complexes with chromium(III), manganese(II), iron(III), cobalt(II), nickel(II) ...

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

    African Journals Online (AJOL)

    Objective: The purpose of this research was to investigate sub-chronic toxicity in animal model. Methods: A detailed study was done on the physical, hematological, biochemical and hormonal parameters of both male and female Sprague-Dawley rats after 28 days administration of naproxen and its metal complexes.

  20. 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.

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

    Science.gov (United States)

    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.

  2. 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.

  3. 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.

  4. 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.

  5. Raman study of metal-insulator transition in NdNiO{sub 3} thin films

    Energy Technology Data Exchange (ETDEWEB)

    Zaghrioui, M.; Bulou, A.; Laffez, P. E-mail: patrick.laffez@univ-lemans.fr; Lacorre, P

    2000-03-01

    NdNiO{sub 3} is known to undergo a metal-insulator transition at 200 K. Thin films of NdNiO{sub 3} are synthesized on LaAlO{sub 3} single crystal and Si by RF sputtering magnetron, and subsequent annealing under oxygen pressure. The metal-insulator transition investigated by a temperature study of the resistivity appears at 150 or 200 K depending on the deposition process. The films have been studied by Raman scattering from 60 K to room temperature, and strong evolution of the spectra are observed. These investigations show significant changes of frequencies and intensities at several temperatures that suggest structural changes in the vicinity of the metal-insulator transitions.

  6. 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.

  7. 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.

  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. C-Alkylation of Ketones and Related Compounds by Alcohols: Transition-Metal-Catalyzed Dehydrogenation.

    Science.gov (United States)

    Huang, Fei; Liu, Zhuqing; Yu, Zhengkun

    2016-01-18

    Transition-metal-catalyzed C-alkylation of ketones and secondary alcohols, with alcohols, avoids use of organometallic or environmentally unfriendly alkylating agents by means of borrowing hydrogen (BH) or hydrogen autotransfer (HA) activation of the alcohol substrates. Water is formed as the only by-product, thus making the BH process atom-economical and environmentally benign. Diverse homogeneous and heterogeneous transition-metal catalysts, ketones, and alcohols can be used for this transformation, thus rendering the BH process promising for replacing those procedures that use traditional alkylating agents. This Minireview summarizes the advances during the last five years in transition-metal-catalyzed BH α-alkylation of ketones, and β-alkylation of secondary alcohols with alcohols. A discussion on the application of the BH strategy for C-C bond formation is included. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Metal-insulator transition of 2d electron gas in a random magnetic field

    CERN Document Server

    Wang, X R; Liu, D Z

    1999-01-01

    We study the metal-insulator transition of a two-dimensional electron gas in the presence of a random magnetic field from the localization property. The localization length is directly calculated using a transfer matrix technique and finite size scaling analysis. We argue that there is a metal-insulator transition in such a system and show strong numerical evidence that the system undergoes a disorder driven Kosterlitz-Thouless type metal-insulator transition. We will also discuss a mean field theory which maps the random field system into a two-dimensional XY-model. The vortex and antivortex excitations in the XY-model correspond to two different kinds of magnetic domains in the random field system.

  11. Light-induced catalytic and cytotoxic properties of phosphorescent transition metal compounds with a d8 electronic configuration

    National Research Council Canada - National Science Library

    To, Wai-Pong; Zou, Taotao; Sun, Raymond Wai-Yin; Che, Chi-Ming

    2013-01-01

    .... In the areas of photocatalysis and photodynamic therapy, metal compounds of heavy transition metals are highly sought after because they can give rise to triplet excited states upon photoexcitation...

  12. Synthesis of novel binary and ternary Zn2+ complexes with putrescine and phosphocreatine and the metal complexes study in aqueous solution

    Science.gov (United States)

    Szyfman, Natalie Waissmann; Tenório, Thaís; Ribeiro, Tatiana S.; Felcman, Judith; Mercê, Ana Lucia Ramalho

    2014-09-01

    Binary and ternary systems of Zn2+ complexes with phosphocreatine (PCr) and putrescine (Put) were investigated in aqueous solution using potentiometric titrations, Raman spectroscopy, Nuclear Magnetic Resonance (1H NMR) and molecular modeling. The stability constants of the complexes and molecular adducts, determined by potentiometry (T = 25.0 °C, I = 0.100 mol L-1, KNO3), are for some of the calculated complexes log KZnPCr = 10.63 ± 0.03, log KZnPut = 5.22 ± 0.08 and for log KZnPCrPut = 16.56 ± 0.02. PCr acts as a bidentate ligand and Put as a monodentate ligand until around pH 11. The Raman and 1H NMR spectra and minimum total molecular energies calculations confirm the coordination modes of all systems. The ternary species are suggested by the values of the stability constants found as, when compared to those of the binary complexes with each ligand, they are neither the sum of the two or a value less than each one separately complexed with Zn2+. An intermolecular interaction was suggested for the ZnPCrPut species. However, for ZnPCrPutH species it was not possible to establish the same kind of interaction due to the long distance between the carboxylate group of phosphocreatine and the NH3+ group of Put.

  13. 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)

  14. 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.

  15. 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.

  16. 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

    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...... 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...

  17. Incorporating distinct metal clusters to construct diversity of 3D pillared-layer lanthanide-transition-metal frameworks.

    Science.gov (United States)

    Cheng, Jian-Wen; Zheng, Shou-Tian; Yang, Guo-Yu

    2008-06-02

    Three novel 3D pillared-layer heterometallic lanthanide-transition-metal (hetero-Ln-TM) compounds, namely, Ln2Cu7I6(ina)7(H2O)6.H2O [ina=isonicotinic acid; Ln=Ce (1), Sm (2)] and Er4(OH)4Cu5I4(ina)6(na)(2,5-pdc).0.3H2O (3; na=nicotinic acid, 2,5-pdc=2,5-pyridinedicarboxylic acid), have been obtained by incorporating different metal clusters as building blocks under hydrothermal conditions. Compounds 1 and 2 are isostructural and consist of two distinct building units of dimeric [Ln2(ina)6] cores and inorganic 2D [Cu8I7]nn+ layers based on the [Cu3I3] and [Cu4I3]+ clusters. Compound 3 is constructed from decanuclear [Cu10I8]2+ clusters and inorganic 1D [Er4(OH)4]n8n+ cluster chain-based layers, which represent the first example of a 3D hetero-Ln-TM constructed by the combination of two distinct types of metal cluster units of a 1D [Er4(OH)4]n8n+ cluster polymer and a transition-metal cluster. It is interesting that decarboxylation occurred in the ortho position and 2,5-pdc2- was partially transformed into na- under hydrothermal conditions. Compounds 1-3 represent good examples of using different metal cluster units to construct fascinating 3D hetero-Ln-TM frameworks.

  18. Luminescence of a Transition Metal Complex Inside a Metamaterial Nanocavity.

    Science.gov (United States)

    Connell, Timothy U; Earl, Stuart K; Ng, Charlene; Roberts, Ann; Davis, Timothy J; White, Jonathan M; Polyzos, Anastasios; Gómez, Daniel E

    2017-08-01

    Modification of the local density of optical states using metallic nanostructures leads to enhancement in the number of emitted quanta and photocatalytic turnover of luminescent materials. In this work, the fabrication of a metamaterial is presented that consists of a nanowire separated from a metallic mirror by a polymer thin film doped with a luminescent organometallic iridium(III) complex. The large spin-orbit coupling of the heavy metal atom results in an excited state with significant magnetic-dipole character. The nanostructured architecture supports two distinct optical modes and their assignment achieved with the assistance of numerical simulations. The simulations show that one mode is characterized by strong confinement of the electric field and the other by strong confinement of the magnetic field. These modes elicit drastic changes in the emitter's photophysical properties, including dominant nanocavity-derived modes observable in the emission spectra along with significant increases in emission intensity and the total decay rate. A combination of simulations and momentum-resolved spectroscopy helps explain the mechanism of the different interactions of each optical mode supported by the metamaterial with the excited state of the emitter. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. A Ratiometric Luminescent Thermometer Co-doped with Lanthanide and Transition Metals.

    Science.gov (United States)

    Li, Zhiqiang; Hou, Zhaohui; Ha, Denghui; Li, Huanrong

    2015-12-01

    Herein, we report the fabrication of a sensitive ratiometric and colorimetric luminescent thermometer with a wide operating-temperature range, from cryogenic temperatures up to high temperatures, through the combination of lanthanide and transition metal complexes. Benefiting from the transition metal complex as a self-reference, the lanthanide content in the mixed-coordination complex, Eu0.05(Mebip-mim bromine)0.15Zn0.95(Mebip-mim bromine)1.9, was lowered to 5%. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. First-principles Exploration of Ferromagnetic and Ferroelectric Double-perovskite Transition-metal Oxides

    OpenAIRE

    Uratani, Yoshitaka; Shishidou, Tatsuya; Ishii, Fumiyuki; Oguchi, Tamio

    2006-01-01

    Possible ferromagnetic and ferroelectric phases are explored for bismuth transition-metal oxides with doubleperovskite structure A2BB0O6 on the basis of first-principles calculations within the local spin-density approximation (LSDA) and generalized gradient approximation (GGA). It is found that a lattice instability of the cubic to a non-centrosymmetric phase always happens in the all cases of lead and bismuth perovskite oxides with the 3d transition-metal ions at the B site. Placing bismuth...

  1. 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

  2. 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

    2017-10-01

    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 microscopyelectron 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.

  3. 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.

  4. 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.

  5. Size effect on dynamics and glass transition in metallic liquids and glasses

    Science.gov (United States)

    Li, Y. Z.; Sun, Y. T.; Lu, Z.; Li, M. Z.; Bai, H. Y.; Wang, W. H.

    2017-06-01

    The relaxation dynamics and glass transition in finite-sized metallic liquid droplets were investigated via molecular dynamic simulations in model monoatomic Ta and binary Cu50Zr50 metallic liquids. We find that the droplet size has a significant impact on liquid dynamics and glass transition. Glass transition temperature and structural relaxation time exhibit strong size dependence and decrease drastically as the droplet is smaller than a certain size. It is revealed that this results from a liquid-like surface layer (˜1 nm thick) of droplets, in which the dynamics is much faster than the interior of droplets. A proposed scaling relationship can well describe the size dependent behavior of the glass transition temperature in metallic liquid droplets. These findings provide insight into the dynamics of metallic liquid droplets and plausible understanding of recent novel experimental observations. Apart from temperature and pressure, size may be another important parameter for potentially tuning the properties of metallic liquids and glasses in nanometer scale.

  6. 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....../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....

  7. Fluctuation-driven insulator-to-metal transition in an external magnetic field

    Science.gov (United States)

    Janiš, V.; Czycholl, G.

    2000-04-01

    We investigate correlated electrons in an external magnetic field near magnetic saturation. We find a broad region in the interaction and magnetic fields where metallic and insulating (fully magnetized) solutions coexist. The saturated ferromagnet at intermediate coupling breaks via a first-order transition to a nonsaturated metal. The local spin-flip instability of the ferromagnet is preceded by a global one caused by collective fluctuations due to poles in the electron-hole vertex functions.

  8. Response to Comment on "Observation of the Wigner-Huntington transition to metallic hydrogen".

    Science.gov (United States)

    Silvera, Isaac; Dias, Ranga

    2017-08-25

    Goncharov and Struzhkin present comments on our observation of metallic hydrogen. We show that most of their comments are unfounded and that our observation of a transition to a shiny, high-reflectance phase remains as evidence that hydrogen has transformed to the metallic phase. Copyright © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

  9. 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

  10. Vacancy-Induced Semiconductor-Insulator-Metal Transitions in Nonstoichiometric Nickel and Tungsten Oxides.

    Science.gov (United States)

    Wang, Qi; Puntambekar, Ajinkya; Chakrapani, Vidhya

    2016-11-09

    Metal-insulator transitions in strongly correlated oxides induced by electrochemical charging have been attributed to formation of vacancy defects. However, the role of native defects in affecting these transitions is not clear. Here, we report a new type of phase transition in p-type, nonstoichiometric nickel oxide involving a semiconductor-to-insulator-to-metal transition along with the complete reversal of conductivity from p- to n-type at room temperature induced by electrochemical charging in a Li+-containing electrolyte. Direct observation of vacancy-ion interactions using in situ near-infrared photoluminescence spectroscopy show that the transition is a result of passivation of native nickel (cationic) vacancy defects and subsequent formation of oxygen (anionic) vacancy defects driven by Li+ insertion into the lattice. Changes in the oxidation states of nickel due to defect interactions probed by X-ray photoemission spectroscopy support the above conclusions. In contrast, n-type, nonstoichiometric tungsten oxide shows only insulator-to-metal transition, which is a result of oxygen vacancy formation. The defect-property correlations shown here in these model systems can be extended to other oxides.

  11. 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 LaNiO3, 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.

  12. Heterocyclic ring based colorimetric and fluorescent chemosensor for transition metal ions in an aqueous medium

    Energy Technology Data Exchange (ETDEWEB)

    Udhayakumari, Duraisamy [Department of Chemistry, Organic and Polymer Synthesis Laboratory, National Institute of Technology, Tiruchirappalli 620015 (India); Velmathi, Sivan, E-mail: velmathis@nitt.edu [Department of Chemistry, Organic and Polymer Synthesis Laboratory, National Institute of Technology, Tiruchirappalli 620015 (India); Boobalan, Maria susai [Department of Chemistry, St. Joseph' s College (Autonomous), Tiruchirappalli 620002 (India); Venkatesan, Parthiban; Wu, Shu-Pao [Department of Applied Chemistry, National Chiao Tung University, Hsinchu 300, Taiwan, ROC (China)

    2015-02-15

    Heterocyclic ring based R1–R3 have been synthesized from the simple condensation method. R1–R3 exhibit highly selective and sensitive recognition towards transition metal ions in an aqueous medium via visual color change and were further confirmed by UV–vis and fluorescent spectroscopic methods. Fluorescent turn on and turn off behavior was observed for receptors tested with transition metal ions. The interaction of transition metal ions and receptors R1–R3 was confirmed to adopt 1:1 binding stoichiometry. Micromolar detection limit was found for R1–R3 with metal ions. DFT theoretical calculations were employed to understand the sensing mechanism of the sensors towards the metal ions. R1 and R2 were also successfully demonstrated as a fluorescent probe for detecting Cu{sup 2+} ions in living cells. - highlights: • R1–R3 act as colorimetric and fluorescent sensors for metal ions. • Receptors (R1–R3) detect Cu{sup 2+} ions in aqueous solution at nanomolar levels. • R1 and R2 act as a fluorescent probe for detecting Cu{sup 2+} ions in living cells.

  13. 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

  14. Metal-Insulator Transition from Graphene to Graphane

    Directory of Open Access Journals (Sweden)

    Motohiko Ezawa

    2013-07-01

    Full Text Available Graphane is obtained by perfectly hydrogenating graphene. There exists an intermediate material, partially hydrogenated graphene (which we call hydrographene, interpolating from pure graphene to pure graphane.\tEmploying a graph theoretical approach to the site-percolation model, we present an intuitive and physical picture revealing a percolation transition from graphene to graphane. It is demonstrated that hydrographene shows a bulk ferromagnetism based on the Lieb theory. We also propose a weighted percolation model in order to take into account the tendency of hydrogenation to cluster.

  15. 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-C60 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 sp3 orbitals are annealed into sp2-π graphitic states in sputtered carbon/copper multilayers. X-ray magnetic circular dichroism (XMCD) measurements at the carbon K edge of C60 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.

  16. Opening Electrical Contacts: The Transition from the Molten Metal Bridge to the Electric Arc

    Science.gov (United States)

    Slade, Paul G.

    This paper presents a comprehensive explanation of the formation of the electric arc between opening contacts in a current carrying electric circuit. As the contacts begin to open a molten metal bridge forms between them. The rupture of this bridge and the initial formation of the electric arc are studied in both atmospheric air and vacuum using experiments to determine the direction of metal transfer between the contacts as a function of time after the rupture of the molten metal bridge. High speed streak photography is also used to show the rupture of the molten metal bridge and the initial formation of the electric arc. Analysis of these data show that a very high-pressure, high-temperature metal vapor zone exists between the contacts after the rupture of the molten metal bridge. Under this condition a pseudo-arc forms where current is carried by metal ions and an anomalous, high net transfer of metal to the cathodic contact occurs. The pressure in this region decreases rapidly and there is a transition to the usual electric arc, which still operates in the metal vapor. In this arc the current is now mostly carried by electrons. The data shows that there is still a net transfer of metal to the cathode, but now its volume is a function of the arcing time.

  17. Stability Constants of Mixed Ligand Complexes of Transition Metal(II Ions with Salicylidene-4-methoxyaniline as Primary Ligand and 5-Bromosalicylidene-4-nitroaniline as Secondary Ligand

    Directory of Open Access Journals (Sweden)

    N. G. Nadkarni

    2011-01-01

    Full Text Available Binary and ternary complexes of the type M-Y and M-X-Y [M = Mn(II, Ni(II, Cu(II and Zn(II; X = salicylidene-4-methoxyaniline and Y=5-bromosalicylidene-4-nitroaniline] have been examined pH-metrically at 27±0.5 °C and at constant ionic strength, μ= 0.1 M (KCl in 75 : 25(v/v 1,4-dioxne-water medium. The stability constants for binary (M-Y and ternary (M-X-Y systems were calculated. The relative stability (Δ log KT values of the ternary complexes with corresponding binary complexes for all the metal(II ions in the present study found to be negative indicating that ternary 1:1:1 (M-X-Y complexes are less stable than binary 1:1 (M-Y complexes. In the ternary system studied, the order of stability constants of mixed ligand complexes with respect to the metal ions was found to be Cu(II > NI(II > Mn(II > Zn(II; which is same as in the corresponding binary (M-Y systems.

  18. Thermochemistry and Geometries for Transition-Metal Chemistry from the Random Phase Approximation.

    Science.gov (United States)

    Waitt, Craig; Ferrara, Nashali M; Eshuis, Henk

    2016-11-08

    Performance of the random phase approximation (RPA) is tested for thermochemistry and geometries of transition-metal chemistry using various benchmarks obtained either computationally or experimentally. Comparison is made to popular (semi)local meta- and hybrid density functionals as well as to the second-order Møller-Plesset perturbation theory (MP2) and its spin-component-scaled derivatives. The benchmark sets include reaction energies, barrier heights, and dissociation energies of prototype bond-activation reactions, dissociation energies for a set of large transition-metal complexes, bond lengths and dissociation energies of metal hydride ions, and bond lengths and angles of a set of closed-shell first-row transition-metal complexes. The emphasis is on first-row transition-metal chemistry, though for energies, elements beyond the first-row are included. Attention is paid to the basis set convergence of RPA. For thermochemistry, RPA performs on par or better than the density functional theory (DFT) functionals presented and is significantly more accurate than MP2. The largest errors are observed in dissociation energies where the electronic environment is altered substantially. For structural parameters, very good results were obtained, and RPA meets the high quality of structures from DFT. In most cases, well-converged structures are obtained with basis sets of triple-zeta quality. MP2 optimized values can often not be obtained and are on average of inferior quality. Though chemical accuracy is not reached, the RPA method is a step forward toward a systematic, parameter-free, all-round method to describe transition-metal chemistry.

  19. Coherent/incoherent metal transition in a holographic model

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Keun-Young; Kim, Kyung Kiu [School of Physics and Chemistry, Gwangju Institute of Science and Technology,Gwangju 500-712 (Korea, Republic of); Seo, Yunseok [Research Institute for Natural Science, Hanyang University,Seoul 133-791 (Korea, Republic of); Sin, Sang-Jin [Department of Physics, Hanyang University,Seoul 133-791 (Korea, Republic of)

    2014-12-29

    We study AC electric (σ), thermoelectric (α), and thermal (κ-bar) conductivities in a holographic model, which is based on 3+1 dimensional Einstein-Maxwell-scalar action. There is momentum relaxation due to massless scalar fields linear to spatial coordinate. The model has three field theory parameters: temperature (T), chemical potential (μ), and effective impurity (β). At low frequencies, if β<μ, all three AC conductivities (σ,α,κ-bar) exhibit a Drude peak modified by pair creation contribution (coherent metal). The parameters of this modified Drude peak are obtained analytically. In particular, if β≪μ the relaxation time of electric conductivity approaches to 2√3μ/β{sup 2} and the modified Drude peak becomes a standard Drude peak. If β>μ the shape of peak deviates from the Drude form (incoherent metal). At intermediate frequencies (T<ω<μ), we have analysed numerical data of three conductivities (σ,α,κ-bar) for a wide variety of parameters, searching for scaling laws, which are expected from either experimental results on cuprates superconductors or some holographic models. In the model we study, we find no clear signs of scaling behaviour.

  20. 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.

  1. 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.

  2. The electrical activity of GaN doped with transition metal impurities

    Science.gov (United States)

    Chisholm, J. A.; Bristowe, P. D.

    2001-07-01

    The electronic properties of GaN doped with three transition metal impurities (titanium, nickel and gold) have been calculated using a density functional approach. Both substitutional and interstitial mechanisms for dopant incorporation have been considered, together with the effect of varying the charge state of the impurity. The electrical activity of the metal impurities is characterized by considering the defect levels in the band gap, the Mulliken charges on the atoms and the local distribution of valence charge density. The calculated formation energies indicate that a substitutional mechanism is preferred and that all three metals act as donor dopants.

  3. Metallization of solid molecular hydrogen in two dimensions: Mott-Hubbard-type transition

    Science.gov (United States)

    Biborski, Andrzej; Kådzielawa, Andrzej P.; Spałek, Józef

    2017-08-01

    We analyze the pressure-induced metal-insulator transition in a two-dimensional vertical stack of H2 molecules in (x-y) plane, and show that it represents a striking example of the Mott-Hubbard-type transition. Our combined exact diagonalization approach, formulated and solved in the second quantization formalism, includes also simultaneous ab initio readjustment of the single-particle wave functions, contained in the model microscopic parameters. The system is studied as a function of applied side force (generalized pressure), both in the H2-molecular and H-quasiatomic states. Extended Hubbard model is taken at the start, together with longer-range electron-electron interactions incorporated into the scheme. The stacked molecular plane transforms discontinuously into a (quasi)atomic state under the applied force via a two-step transition: the first between molecular insulating phases and the second from the molecular to the quasiatomic metallic phase. No quasiatomic insulating phase occurs. All the transitions are accompanied by abrupt changes of the bond length and the intermolecular distance (lattice parameter), as well as by discontinuous changes of the principal electronic properties, which are characteristic of the Mott-Hubbard transition here associated with the jumps of the predetermined equilibrium lattice parameter and the effective bond length. The phase transition can be interpreted in terms of the solid hydrogen metallization under pressure exerted by, e.g., the substrate covered with a monomolecular H2 film of the vertically stacked molecules. Both the Mott and Hubbard criteria at the insulator to metal transition are discussed.

  4. Reactivity patterns of transition metal hydrides and alkyls

    Energy Technology Data Exchange (ETDEWEB)

    Jones, W.D. II

    1979-05-01

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

  5. Role of Transition Metal Exporters In Virulence: The Example of Neisseria meningitidis.

    Directory of Open Access Journals (Sweden)

    Cyril eGuilhen

    2013-12-01

    Full Text Available Transition metals such as iron, manganese, and zinc are essential micronutrients for bacteria. However, at high concentration, they can generate nonfunctional proteins or toxic compounds. Metal metabolism is therefore regulated to prevent shortage or overload, both of which can impair cell survival. In addition, equilibrium among these metals has to be tightly controlled to avoid molecular replacement in the active site of enzymes. Bacteria must actively maintain intracellular metal concentrations to meet physiological needs within the context of the local environment. When intracellular buffering capacity is reached, they rely primarily on membrane-localized exporters to maintain metal homeostasis. Recently, several groups have characterized new export systems and emphasized their importance in the virulence of several pathogens. This article discusses the role of export systems as general virulence determinants. Furthermore, it highlights the contribution of these exporters in pathogens emergence with emphasis on the human nasopharyngeal colonizer Neisseria meningitidis.

  6. Phase equilibria in the Mo-Fe-P system at 800 °C and structure of ternary phosphide (Mo(1-x)Fe(x))3P (0.10 ≤ x ≤ 0.15).

    Science.gov (United States)

    Oliynyk, Anton O; Lomnytska, Yaroslava F; Dzevenko, Mariya V; Stoyko, Stanislav S; Mar, Arthur

    2013-01-18

    Construction of the isothermal section in the metal-rich portion (ternary phases: (Mo(1-x)Fe(x))(2)P (x = 0.30-0.82) and (Mo(1-x)Fe(x))(3)P (x = 0.10-0.15). The occurrence of a Co(2)Si-type ternary phase (Mo(1-x)Fe(x))(2)P, which straddles the equiatomic composition MoFeP, is common to other ternary transition-metal phosphide systems. However, the ternary phase (Mo(1-x)Fe(x))(3)P is unusual because it is distinct from the binary phase Mo(3)P, notwithstanding their similar compositions and structures. The relationship has been clarified through single-crystal X-ray diffraction studies on Mo(3)P (α-V(3)S-type, space group I42m, a = 9.7925(11) Å, c = 4.8246(6) Å) and (Mo(0.85)Fe(0.15))(3)P (Ni(3)P-type, space group I4, a = 9.6982(8) Å, c = 4.7590(4) Å) at -100 °C. Representation in terms of nets containing fused triangles provides a pathway to transform these closely related structures through twisting. Band structure calculations support the adoption of these structure types and the site preference of Fe atoms. Electrical resistivity measurements on (Mo(0.85)Fe(0.15))(3)P reveal metallic behavior but no superconducting transition.

  7. 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.

  8. Quantum Mechanics Calculations, Basicity and Crystal Structure: The Route to Transition Metal Complexes of Azahelicenes

    Directory of Open Access Journals (Sweden)

    Isabella Natali Sora

    2012-01-01

    Full Text Available Quantum mechanics density functional calculations provided gas-phase electron distributions and proton affinities for several mono- and diaza[5]helicenes; computational results, together with experimental data concerning crystal structures and propensity to methylation of the nitrogen atom(s, provide a basis for designing azahelicene complexes with transition metal ions.

  9. Volcano Relation for the Deacon Process over Transition-Metal Oxides

    DEFF Research Database (Denmark)

    Studt, Felix; Abild-Pedersen, Frank; Hansen, Heine Anton

    2010-01-01

    We establish an activity relation for the heterogeneous catalytic oxidation of HCI (the Deacon Process) over rutile transition-metal oxide catalysts by combining density functional theory calculations (DFT) with microkinetic modeling. Linear energy relations for the elementary reaction steps are ...

  10. 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 a...

  11. 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.

  12. 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 f...

  13. 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.

  14. 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.

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

    Indian Academy of Sciences (India)

    [2], Singh and Gupta [3] and research papers [4–13]. The degeneracy of the opti- cal vibration frequencies of the zone center is common to all the transition metal carbides. The experimental information about these ionic semiconductors is pro- vided from the phonon dispersion data [14–17]. A survey of the literatures on the.

  16. 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 ...

  17. Theory of Temperature Dependence of the Magnetization in Rare-Earth-Transition-Metal Alloys

    DEFF Research Database (Denmark)

    Szpunar, B.; Lindgård, Per-Anker

    1977-01-01

    It is shown that the temperature dependence of the magnetic moments and Curie and ferrimagnetic compensation temperatures for Gdl-xTx (T = Co, Ni, and Fe) and Y1-xCox can be accounted for by a simple model assuming a RKKY interaction between the rare-earth moments and the transition-metal pseudo-...

  18. Tunable hydrogen storage in magnesium-transition metal compounds: first-principles calculations

    NARCIS (Netherlands)

    Er, S.; Tiwari, Dhirendra; Tiwari, D.; de Wijs, Gilles A.; Brocks, G.

    2009-01-01

    Magnesium dihydride (MgH2) stores 7.7 wt % hydrogen but it suffers from a high thermodynamic stability and slow (de)hydrogenation kinetics. Alloying Mg with lightweight transition metals (TM) (=Sc,Ti,V,Cr) aims at improving the thermodynamic and kinetic properties. We study the structure and

  19. 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...

  20. Synergy between experimental and theoretical methods in the exploration of homogeneous transition metal catalysis

    DEFF Research Database (Denmark)

    Lupp, Daniel; Christensen, Niels Johan; Fristrup, Peter

    2014-01-01

    n this Perspective, we will focus on the use of both experimental and theoretical methods in the exploration of reaction mechanisms in homogeneous transition metal catalysis. We briefly introduce the use of Hammett studies and kinetic isotope effects (KIE). Both of these techniques can be complem...

  1. 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 t...

  2. Reverse-flow adsorption for process-integrated recycling of homogeneous transition-metal catalysts

    NARCIS (Netherlands)

    Marras, F.; van Leeuwen, P.W.N.M.; Reek, J.N.H.

    2011-01-01

    Supramolecular strategies, based on hydrogen bonds and ionic interactions, were investigated as tools for the recovery and recycling of homogeneous transition-metal catalysts by using reverse-flow adsorption (RFA) technology. The association (in solution) and adsorption (on support) of new

  3. 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...

  4. Effective oxidation of sulfides to sulfoxides with hydrogen peroxide under transition-metal-free conditions.

    Science.gov (United States)

    Golchoubian, Hamid; Hosseinpoor, Farideh

    2007-03-03

    A "green" highly selective oxidation of organic sulfides to the corresponding sulfoxides was developed using hydrogen peroxide and glacial acetic acid under transition metal-free and mild conditions. The oxidation procedure is very simple and the products are easily isolated in excellent yields (90-99%).

  5. Effective Oxidation of Sulfides to Sulfoxides with Hydrogen Peroxide under Transition-Metal-Free Conditions

    Directory of Open Access Journals (Sweden)

    Farideh Hosseinpoor

    2007-03-01

    Full Text Available A “green” highly selective oxidation of organic sulfides to the corresponding sulfoxides was developed using hydrogen peroxide and glacial acetic acid under transition metal-free and mild conditions. The oxidation procedure is very simple and the products are easily isolated in excellent yields (90-99%.

  6. Unusual valence, negative charge-transfer gaps and self-doping in transition-metal compounds

    NARCIS (Netherlands)

    Khomskii, D. I.

    2001-01-01

    Abstract: In this paper I discuss the electronic structure and properties of a specific, rather unconventional class of transition metal (TM) compounds, e.g. TM oxides, which formally have unusually high values of the oxidation state, or valence, of TM. In contrast to the typical situation, in this

  7. 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.

  8. 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

  9. 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 ...

  10. BOND-CHARGE SITE-CHARGE INTERACTION AND METAL-INSULATOR TRANSITIONS

    NARCIS (Netherlands)

    MICHIELSEN, K

    1994-01-01

    Exact-diagonalization and quantum Monte Carlo methods are used to study the occurrence of a metal-insulator transition and the distribution of charges and magnetic moments in the ground state of a one- and two-dimensional half-filled system of correlated electrons, described by a one-band simplified

  11. Divergent synthesis routes and superconductivity of ternary hydride MgSiH6 at high pressure

    Science.gov (United States)

    Ma, Yanbin; Duan, Defang; Shao, Ziji; Yu, Hongyu; Liu, Hanyu; Tian, Fubo; Huang, Xiaoli; Li, Da; Liu, Bingbing; Cui, Tian

    2017-10-01

    We predict a new ternary hydride MgSiH6 under high pressures, which is a metal with an ionic feature and takes on a simple cubic structure with space group P m -3 above 250 GPa. Our first-principles calculations show that the cubic MgSiH6 is a potential high-temperature superconductor with a superconducting transition temperature Tc of ˜63 K at 250 GPa. Further analysis suggests that phonon softening along mainly Γ -X and Γ -M directions induced by Fermi surface nesting plays a crucial role in the high-temperature superconductivity. Herein we propose the "triangle straight-line method" which provides a clear guide to determine the specific A + B → D type formation routes for ternary hydrides of the Mg-Si-H system and it effectively reveals two divergent paths to obtain MgSiH6 under high pressures: MgH2+SiH4→MgSiH6 and MgSi + 3 H2→MgSiH6 . This method might be applicable to all ternary compounds, which will be very significant for further experimental synthesis.

  12. Investigations of charge state effects in non-specific transition metal-protein complexes by ESI-FTICR

    Energy Technology Data Exchange (ETDEWEB)

    Van Orden, S.L.; Bakhtiar, R.; Bruce, J.E.; Hofstadler, S.A.; Smith, R.D. [Pacific Northwest Labs., Richland, WA (United States)

    1994-12-31

    Transition metals play an important role in many areas of biological chemistry. Various aspects of the interactions of transition metal ions and complexes with protein have been studied by a number of groups. In general, these studies have concentrated on proteins which specifically bind metals (e.g. zinc finger motifs) and have not investigated metal ion charge state. It is well known that the electrospray ionization of solutions containing proteins and transition metal salts produces protein molecular ions and protein ions which are multiply adducted with the metal. For the multiply adducted ions, the origin of the charge may be questioned. Presumably the overall charge of the ion is due to H{sup +} attachment, because little or no shift in the charge state distribution is observed between the apo and metalated forms of the protein. In such a case the metal ion is effectively neutralized through multiple bonds to the protein by H{sup +} displacement.

  13. 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.

  14. Ramp-Reversal Memory and Phase-Boundary Scarring in Transition Metal Oxides.

    Science.gov (United States)

    Vardi, Naor; Anouchi, Elihu; Yamin, Tony; Middey, Srimanta; Kareev, Michael; Chakhalian, Jak; Dubi, Yonatan; Sharoni, Amos

    2017-06-01

    Transition metal oxides are complex electronic systems that exhibit a multitude of collective phenomena. Two archetypal examples are VO2 and NdNiO3 , which undergo a metal-insulator phase transition (MIT), the origin of which is still under debate. Here this study reports the discovery of a memory effect in both systems, manifested through an increase of resistance at a specific temperature, which is set by reversing the temperature ramp from heating to cooling during the MIT. The characteristics of this ramp-reversal memory effect do not coincide with any previously reported history or memory effects in manganites, electron-glass or magnetic systems. From a broad range of experimental features, supported by theoretical modelling, it is found that the main ingredients for the effect to arise are the spatial phase separation of metallic and insulating regions during the MIT and the coupling of lattice strain to the local transition temperature of the phase transition. We conclude that the emergent memory effect originates from phase boundaries at the reversal temperature leaving "scars" in the underlying lattice structure, giving rise to a local increase in the transition temperature. The universality and robustness of the effect shed new light on the MIT in complex oxides. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. 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.

  16. Ultrafast Transient Absorption Spectroscopy of Polymer-Based Organophotoredox Catalysts Mimicking Transition-Metal Complexes

    Science.gov (United States)

    Jamhawi, Abdelqader; Paul, Anam C.; Smith, Justin D.; Handa, Sachin; Liu, Jinjun

    2017-06-01

    Transition-metal complexes of rare earth metals including ruthenium and iridium are most commonly employed as visible-light photocatalysts. Despite their highly important and broad applications, they have many disadvantages including high cost associated with low abundance in earth crust, potential toxicity, requirement of specialized ligands for desired activity, and difficulty in recycling of metal contents as well as associated ligands. Polymer-based organophotoredox catalysts are promising alternatives and possess unique advantages such as easier synthesis from inexpensive starting material, longer excited state life time, broad range of activity, sustainability, and recyclability. In this research talk, time-resolved photoluminescence and femtosecond transient absorption (TA) spectroscopy measurements of three novel polymer-based organophotoredox catalysts will be presented. By our synthetic team, their catalytic activity has been proven in some highly valuable chemical transformations, that otherwise require transition metal complexes. Time-resolved spectroscopic investigations have demonstrated that photoinduced processes in these catalysts are similar to the transition metal complexes. Especially, intramolecular vibrational relaxation, internal conversion, and intersystem crossing from the S1 state to the T1 state all occur on a sub-picosecond timescale. The long lifetime of the T1 state ( 2-3 microsecond) renders these polymers potent oxidizing and reducing agents. A spectroscopic and kinetic model has been developed for global fitting of TA spectra in both the frequency and time domains. Implication of the current ultrafast spectroscopy studies of these novel molecules to their roles in photocatalysis will be discussed.

  17. 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.

  18. Positive ions of the first- and second-row transition metal hydrides

    Science.gov (United States)

    Pettersson, Lars G. M.; Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.; Partridge, Harry

    1987-01-01

    Theoretical dissociation energies for the first- and second-row transition metal hydride positive ions are critically compared against recent experimental values obtained from ion beam reactive scattering methods. Theoretical spectroscopic parameters and dipole moments are presented for the ground and several low-lying excited states. The calculations employ large Gaussian basis sets and account for electron correlation using the single-reference single- and double-excitation configuration interaction and coupled-pair-functional methods. The Darwin and mass-velocity contributions to the relativistic energy are included in the all-electron calculations on the first-row systems using first-order perturbation theory, and in the second-row systems using the Hay and Wadt relativistic effective core potentials. The theoretical D(0) values for the second-row transition metal hydride positive ions should provide a critical measure of the experimental values, which are not as refined as many of those in the first transition row.

  19. 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.

  20. Evidence for a Spatially Inhomogeneous Metal-Insulator Transition in (LaCa)MnO_3

    Science.gov (United States)

    Mydosh, John A.

    2000-03-01

    Scanning tunneling spectroscopy was used to investigate single crystals and thin films of La_1-xCa_xMnO3 (with x of about 0.3),which exhibit colossal magnetoresistance. The different spectroscopic signatures of the insulating (paramagnetic) and metallic (ferromagnetic) phases enable their spatial extent to be imaged down to a lateral scale of approximately 10 nm. Above the bulk transition temperature Tc the images show mostly insulating behavior. Below Tc a phase separation is observed where inhomogeneous structures of metallic and insulating areas coexist and are strongly field dependent in their size and structure. Insulating areas are found to persist far below T_c. These results suggest that the transition and the associated magnetoresistance behavior should be viewed as a percolation of metallic ferromagnetic domains

  1. Metal-insulator transition in a sliding Luttinger liquid with line defects

    Science.gov (United States)

    Chudnovskiy, A. L.; Kagalovsky, V.; Yurkevich, I. V.

    2017-10-01

    We investigate the effect of both strong and weak potential scattering caused by local impurities and extended (line) defects in an array of Luttinger liquid wires. We find that in both cases a finite range interwire interaction stabilizes the metallic state. Based on calculations of the scaling dimensions of one-particle scattering operators, we construct a phase diagram for low-temperature transport along the array. We find that unlike the local impurity case where only conducting and insulating states are realized (metal-insulator transition driven by interactions), the extended line defects may bring the system into a mixed state where conducting or insulating behavior can be observed depending on bare strength of the scatterer (metal-insulator transition driven by disorder).

  2. 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.

  3. 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...

  4. 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

  5. Laser opto-acoustic study of phase transitions in metals confined by transparent dielectric

    Science.gov (United States)

    Ivochkin, A. Yu.; Kaptilniy, A. G.; Karabutov, A. A.; Ksenofontov, D. M.

    2012-07-01

    First-order phase transitions in metal induced by nanosecond laser pulse are studied here. The metal surface is irradiated through a layer of transparent dielectric—an optical glass. Such confinement considerably increases the efficiency of pressure generation at the metal surface. This technique allows to obtain near-critical states of metals—with temperatures ˜104 K and pressures ˜104 atm with table-top equipment. At the same time the glass prevents the ablation plume formation—so the surface temperature can be measured using thermal radiation data. An experimental setup for simultaneous measurements of pressure, temperature and reflectivity was assembled based on the elaborated method of experimental research. The processes of melting of lead and boiling of mercury were studied. The onset of the phase transition process led to a considerable tightening of the pressure pulse. A substantial drop of surface reflectivity due to increase of temperature and decrease of density was observed.

  6. Reply to "Comment on `Evidence of a first-order phase transition to metallic hydrogen' "

    Science.gov (United States)

    Silvera, Isaac F.; Zaghoo, Mohamed; Salamat, Ashkan

    2017-12-01

    Goncharov and Geballe reanalyze [Phys. Rev. B 96, 157101 (2017), 10.1103/PhysRevB.96.157101] experimental data using a finite element analysis and cannot reproduce our experimental heating curves; they use incomplete and incorrect material properties. They analyze optical data at the onset of the insulator-to-metal transition to show that it cannot be fit to a Drude model, not realizing that the Drude model does not describe metallic hydrogen in this transition region. Yet, they ignore the region where the reflectance is saturated and the data can be fit to the Drude model. They suggest that we observe semiconducting behavior rather than metallic behavior, but a straightforward calculation shows that reflectance from a semiconductor cannot explain our observed reflectance.

  7. Magnetic properties of transition-metal nanoclusters on a biological substrate

    Science.gov (United States)

    Herrmannsdöerfer, T.; Bianchi, A. D.; Papageorgiou, T. P.; Pobell, F.; Wosnitza, J.; Pollmann, K.; Merroun, M.; Raff, J.; Selenska-Pobell, S.

    We have investigated the magnetic properties of transition-metal clusters with a single grain size of about 1 nm. These metallic nanoclusters have been deposed on a biological substrate. This substrate is a purified self-assembling paracrystalline surface layer (S-layer) of the Bacillus sphaericus strain JG-A12, which exhibits square symmetry and is composed of identical protein monomers. First data of the magnetic susceptibility, taken in a SQUID magnetometer at 0< B<7 T and 1.8 K< T<400 K, reveal unusual magnetic properties. The Stoner enhancement factor of the d conduction-electron susceptibility in the Pd and Pt nanoclusters is dramatically reduced compared to the one of the corresponding bulk transition metals. The weakened magnetism of the 5d electrons is considered to play a crucial role for the occurrence of superconductivity in microgranular Pt by adjusting the balance between electron-phonon interactions and competing magnetic interactions.

  8. Magnetic properties of transition-metal nanoclusters on a biological substrate

    Energy Technology Data Exchange (ETDEWEB)

    Herrmannsdoeerfer, T. [Institut Hochfeld-Magnetlabor Dresden (HLD), Forschungszentrum Dresden-Rossendorf, P.O. Box 510119, D-01314 Dresden (Germany)]. E-mail: T.Herrmannsdoerfer@fz-rossendorf.de; Bianchi, A.D. [Institut Hochfeld-Magnetlabor Dresden (HLD), Forschungszentrum Dresden-Rossendorf, P.O. Box 510119, D-01314 Dresden (Germany); Papageorgiou, T.P. [Institut Hochfeld-Magnetlabor Dresden (HLD), Forschungszentrum Dresden-Rossendorf, P.O. Box 510119, D-01314 Dresden (Germany); Pobell, F. [Institut Hochfeld-Magnetlabor Dresden (HLD), Forschungszentrum Dresden-Rossendorf, P.O. Box 510119, D-01314 Dresden (Germany); Wosnitza, J. [Institut Hochfeld-Magnetlabor Dresden (HLD), Forschungszentrum Dresden-Rossendorf, P.O. Box 510119, D-01314 Dresden (Germany); Pollmann, K. [Institut fuer Radiochemie, Forschungszentrum Dresden-Rossendorf, P.O. Box 510119, D-01314 Dresden (Germany); Merroun, M. [Institut fuer Radiochemie, Forschungszentrum Dresden-Rossendorf, P.O. Box 510119, D-01314 Dresden (Germany); Raff, J. [Institut fuer Radiochemie, Forschungszentrum Dresden-Rossendorf, P.O. Box 510119, D-01314 Dresden (Germany); Selenska-Pobell, S. [Institut fuer Radiochemie, Forschungszentrum Dresden-Rossendorf, P.O. Box 510119, D-01314 Dresden (Germany)

    2007-03-15

    We have investigated the magnetic properties of transition-metal clusters with a single grain size of about 1 nm. These metallic nanoclusters have been deposed on a biological substrate. This substrate is a purified self-assembling paracrystalline surface layer (S-layer) of the Bacillus sphaericus strain JG-A12, which exhibits square symmetry and is composed of identical protein monomers. First data of the magnetic susceptibility, taken in a SQUID magnetometer at 0transition metals. The weakened magnetism of the 5d electrons is considered to play a crucial role for the occurrence of superconductivity in microgranular Pt by adjusting the balance between electron-phonon interactions and competing magnetic interactions.

  9. 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.

  10. Enhanced conductivity of thin film polyaniline by self-assembled transition metal complexes.

    Science.gov (United States)

    Sarno, David M; Martin, Justin J; Hira, Steven M; Timpson, Cliff J; Gaffney, Jean P; Jones, Wayne E

    2007-01-16

    In a recent study, the transition metal complex, cis-dichlorobis(2-,2'-dipyridyl)ruthenium (II) (Ru(bpy)2Cl2), and the macrocycle Ru(TPP)CO (TPP:- tetraphenylporphine) were bound to pyridine terminated self-assembled monolayers on quartz. Following modification of the quartz surface with metal complexes, the conducting polymer polyaniline was deposited via in situ polymerization. The sheet conductivity (as measured by the four-probe method) of the resulting polyaniline films deposited onto Ru(bpy)2Cl2 and Ru(TPP)CO surfaces was significantly enhanced relative to films deposited onto unmodified quartz. It is postulated that either the macrocycle or the transition metal complex-modified surface interacts with the conducting polymer as it is forming, resulting in a more ordered expanded coil conformation for the polymer. The net result of such an interaction is a thin film possessing significantly greater electrical conductivity.

  11. Holographic entanglement entropy in metal/superconductor phase transition with Born–Infeld electrodynamics

    Directory of Open Access Journals (Sweden)

    Weiping Yao

    2014-12-01

    Full Text Available We investigate the holographic entanglement entropy in the metal/superconductor phase transition for the Born–Infeld electrodynamics with full backreaction and note that the entropy is a good probe to study the properties of the phase transition. For the operator 〈O−〉, we find that the entanglement entropy decreases (or increases with the increase of the Born–Infeld parameter b in the metal (or superconducting phase. For the operator 〈O+〉, we observe that, with the increase of the Born–Infeld parameter, the entanglement entropy in the metal phase decreases monotonously but the entropy in the superconducting phase first increases and forms a peak at some threshold bT, then decreases continuously. Moreover, the value of bT becomes smaller as the width of the subsystem A decreases.

  12. 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.

  13. 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.

  14. Bergman Clusters, Multiple Bonds, and Defect Planes: Synthetic Outcomes of Chemical Frustration in Ternary Intermetallic Systems

    Science.gov (United States)

    Hadler, Amelia Beth

    Intermetallics crystallize in a variety of complex structures, many of which show unusual bonding or intriguing properties. Understanding what factors drive this structural chemistry would be a valuable step towards designing new intermetallics with specific structures or properties. One pathway towards understanding and predicting the structures of complex intermetallics is chemical frustration, a design tool which harnesses competition between incompatible bonding or packing modes to induce complexity in ternary intermetallic systems. The research outlined in this thesis focuses on developing chemical frustration through exploratory synthesis in ternary systems designed to induce frustration between the tetrahedral close packing of many intermetallics and the simple cubic packing seen for ionic salts or elemental metals. Syntheses in three systems yielded six new ternary intermetallics, four of which crystallize in novel structure types. Three were discovered in the Ca-Cu-Cd system: Ca5Cu2Cd and Ca2Cu 2Cd9, which adopt ternary variants of binary structures, and Ca10Cu2Cd27, which crystallizes in a new structure built from Bergman clusters. All three structures can be traced to electronic packing frustration induced by the similar electronegativities but different metallic radii of Cu and Cd. The Gd-Fe-C system yielded the new carbometalate Gd13Fe 10C13 and an oxycarbide derivative. These phases crystallize in structures built from Gd tricapped trigonal prisms interpenetrated by an Fe-C network. Theoretical analyses reveal that Fe-Fe and Fe-C multiple bonding is found throughout this network. A theoretical investigation of similar carbides uncovers additional metal-metal, metal-carbon, and carbon-carbon multiple bonding. This unusual bonding stabilizes the carbides by satisfying preferred electron counts for their transition metal sites. One new phase, Mg4.5Pd5Ge1.5, was found in the Mg-Pd-Ge system. Its structure is closely related to the CsCl-type structure of

  15. Modification of the surface electronic and chemical properties of Pt(111) by subsurface 3d transition metals

    DEFF Research Database (Denmark)

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

    2004-01-01

    The modification of the electronic and chemical properties of Pt(111) surfaces by subsurface 3d transition metals was studied using density-functional theory. In each case investigated, the Pt surface d-band was broadened and lowered in energy by interactions with the subsurface 3d metals......, resulting in weaker dissociative adsorption energies of hydrogen and oxygen on these surfaces. The magnitude of the decrease in adsorption energy was largest for the early 3d transition metals and smallest for the late 3d transition metals. In some cases, dissociative adsorption was calculated...

  16. Structural phase transition of ternary dielectric SmGdO{sub 3}: Evidence from angle dispersive x-ray diffraction and Raman spectroscopic studies

    Energy Technology Data Exchange (ETDEWEB)

    Sharma, Yogesh, E-mail: rkatiyar@uprrp.edu, E-mail: satya504@gmail.com, E-mail: yogesh.sharma@upr.edu; Sahoo, Satyaprakash, E-mail: rkatiyar@uprrp.edu, E-mail: satya504@gmail.com, E-mail: yogesh.sharma@upr.edu; Misra, Pankaj; Pavunny, Shojan P.; Katiyar, Ram S., E-mail: rkatiyar@uprrp.edu, E-mail: satya504@gmail.com, E-mail: yogesh.sharma@upr.edu [Department of Physics and Institute for Functional Nanomaterials, University of Puerto Rico, San Juan, Puerto Rico 00936-8377 (United States); Mishra, A. K.; Dwivedi, Abhilash; Sharma, S. M. [High Pressure and Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Mumbai (India)

    2015-03-07

    High-pressure synchrotron based angle dispersive x-ray diffraction (ADXRD) studies were carried out on SmGdO{sub 3} (SGO) up to 25.7 GPa at room temperature. ADXRD results indicated a reversible pressure-induced phase transition from ambient monoclinic to hexagonal phase at ∼8.9 GPa. The observed pressure-volume data were fitted with the third order Birch-Murnaghan equation of state yielding zero pressure bulk modulus B{sub 0} = 132(22) and 177(9) GPa for monoclinic (B-type) and hexagonal (A-type) phases, respectively. Pressure dependent micro-Raman spectroscopy further confirmed the monoclinic to hexagonal phase transition at about 5.24 GPa. The mode Grüneisen parameters and pressure coefficients for different Raman modes corresponding to each individual phases of SGO were calculated using pressure dependent Raman mode analysis.

  17. 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.

  18. Charge Transfer Stabilization of Late Transition Metal Oxide Nanoparticles on a Layered Niobate Support.

    Science.gov (United States)

    Strayer, Megan E; Senftle, Thomas P; Winterstein, Jonathan P; Vargas-Barbosa, Nella M; Sharma, Renu; Rioux, Robert M; Janik, Michael J; Mallouk, Thomas E

    2015-12-30

    Interfacial interactions between late transition metal/metal oxide nanoparticles and oxide supports impact catalytic activity and stability. Here, we report the use of isothermal titration calorimetry (ITC), electron microscopy and density functional theory (DFT) to explore periodic trends in the heats of nanoparticle-support interactions for late transition metal and metal oxide nanoparticles on layered niobate and silicate supports. Data for Co(OH)2, hydroxyiridate-capped IrOx·nH2O, Ni(OH)2, CuO, and Ag2O nanoparticles were added to previously reported data for Rh(OH)3 grown on nanosheets of TBA0.24H0.76Ca2Nb3O10 and a layered silicate. ITC measurements showed stronger bonding energies in the order Ag niobate support, as expected from trends in M-O bond energies. Nanoparticles with exothermic heats of interaction were stabilized against sintering. In contrast, ITC measurements showed endothermic interactions of Cu, Ni, and Rh oxide/hydroxide nanoparticles with the silicate and poor resistance to sintering. These trends in interfacial energies were corroborated by DFT calculations using single-atom and four-atom cluster models of metal/metal oxide nanoparticles. Density of states and charge density difference calculations reveal that strongly bonded metals (Rh, Ir) transfer d-electron density from the adsorbed cluster to niobium atoms in the support; this mixing is absent in weakly binding metals, such as Ag and Au, and in all metals on the layered silicate support. The large differences between the behavior of nanoparticles on niobate and silicate supports highlight the importance of d-orbital interactions between the nanoparticle and support in controlling the nanoparticles' stability.

  19. Novel penta-graphene nanotubes: strain-induced structural and semiconductor-metal transitions.

    Science.gov (United States)

    Wang, Zhanyu; Cao, Xinran; Qiao, Chong; Zhang, R J; Zheng, Y X; Chen, L Y; Wang, S Y; Wang, C Z; Ho, K M; Fan, Yuan-Jia; Jin, Bih-Yaw; Su, Wan-Sheng

    2017-12-01

    Research into novel one-dimensional (1D) materials and associated structural transitions is of significant scientific interest. It is widely accepted that a 1D system with a short-range interaction cannot have 1D phase transition at finite temperature. Herein, we propose a series of new stable carbon nanotubes by rolling up penta-graphene sheets, which exhibit fascinating well-defined 1D phase transitions triggered by axial strain. Our first-principles calculations show that such penta-graphene nanotubes (PGNTs) are dynamically stable by phonon calculations, but transform from a tri-layer structure to a highly defective single-walled nanotube at low temperature in molecular dynamics simulations. We show that moderate compressive strains can drive structural transitions of (4,4), (5,5), and (6,6) PGNTs, during which the distances of neighboring carbon dimers in the inner shell have a sudden drop, corresponding to dimer-dimer nonbonding to bonding transitions. After such transition, the tubes become much more thermally stable and undergo semiconductor-metal transitions under increasing strain. The band gaps of PGNTs are not sensitive to chirality whereas they can be tuned effectively from visible to short-wavelength infrared by appropriate strain, making them appealing materials for flexible nano-optoelectronics. These findings provide useful insight into unusual phase transitions in low-dimensional systems.

  20. Reactions of synthesis gas on silica supported transition metal catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Niemelae, M. [VTT Chemical Technology, Espoo (Finland). Lab. of Industrial Chemistry

    1997-12-31

    The effect of catalyst precursor and composition on the activation of CO was investigated using CO hydrogenation as a test reaction. The interrelations of preparation, pretreatment, characteristics and activity were clarified. For Co/SiO{sub 2} catalyst, MgO promotion increased the CO adsorption capacity and the hydrogen uptake, although the extent of reduction for cobalt remained the same or decreased. The conversion per active metallic cobalt site consequently increased in conjunction with MgO promotion, while the effect on overall performance per 1 g of catalyst remained moderate. The precursor affected the performance of Co/SiO{sub 2} considerably. CO was more strongly adsorbed on catalysts of carbonyl origin than on those derived from cobalt nitrate, the activity thus being higher. Although the nitrate derived Co/SiO{sub 2} appeared both to retain its activity and to regain its adsorption capacity better than the catalysts of carbonyl origin, the performance of the latter was superior with time on stream. For tetranuclear cluster based Co-Ru and Co-Rh catalysts, rhodium or ruthenium was in contact with the support and cobalt was enriched on top. On Co-Ru/SiO{sub 2} ruthenium enhanced deactivation, and no benefits in activity or oxygenate selectivity were achieved relative to the monometallic catalysts of cluster origin. The Co-Rh/SiO{sub 2} catalysts were also less active than those derived from monometallic clusters, but they exhibited higher selectivities to oxygenated compounds due to the presence of active sites on the perimeter of the cobalt particles located on rhodium. The highest selectivity to oxygenates was achieved by changing the decomposition atmosphere of Rh{sub 4}(CO){sub 12}/SiO{sub 2} from hydrogen to carbon monoxide. The results also showed two types of active sites to be operative in the formation of oxygenates - one for ethanol and another for aldehydes. (orig.) 69 refs.

  1. Enhanced retention of aqueous transition metals in mesoporous silica

    Science.gov (United States)

    Nelson, J.; Bargar, J.; Brown, G. E.; Maher, K.

    2013-12-01

    Mesoporosity (2-50 nm diameter pores) is abundant within grain coatings and primary silicate minerals in natural environments. Mesopores often contribute significantly to total specific surface area and act as gateways for the transport of subsurface solutes, including nutrients and contaminants, between mineral surfaces and ambient fluids. However, the physiochemical mechanisms of sorption and transport within mesopores cannot be assumed to be the same as for macropores (>50 nm), because of confinement-induced changes in water properties, the structure of electrical double layers, solvation shells and dehydration rates of aquo ions, and the charge and reactive site densities of mineral surfaces. Despite the ubiquity of confined spaces in natural and industrial porous media, few studies have examined the molecular-scale mechanisms and geochemical reactions controlling meso-confinement phenomena in environmentally relevant materials. We conducted batch Zn sorption experiments using synthetic, controlled pore-size (i.e., 7.5-300 nm), metal-oxide beads as model geologic substrates. Comparison of Zn adsorbed onto macroporous and mesoporous silica beads indicates Zn adsorption capacity is increased in mesopores when normalized to surface area. In the presence of a background electrolyte (i.e., NaCl), Zn sorption capacity to macroporous silica is reduced; however, no significant difference in Zn sorption capacity on mesoporous silica was observed between the presence and absence of a background electrolyte. The effect of competing cations is indirect evidence that mesopores promote inner-sphere complexation and reduce outer-sphere complexation. EXAFS characterization of adsorbed zinc to macroporous silica matches that reported for low Zn coverages on silica (Roberts et al., JCIS, 2003), whereas a different spectrum is observed for the mesoporous case. Shell-by-shell fitting indicates that Zn is dominantly in octahedral coordination in macropores, as opposed to

  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. Local structural aspects of metal-metal transition in IrTe2 from x-ray PDF

    Science.gov (United States)

    Yu, Runze; Abeykoon, Milinda; Zhou, Haidong; Yin, Weiguo; Bozin, Emil S.

    Evolution of local atomic structure across the metal-metal transition in IrTe2 is explored by pair distribution function (PDF) analysis of x-ray total scattering data over 80 K transition, in agreement with electronic transport measurements, indicative of a strong tie between the lattice and electronic configurations. Bond valence methodology applied to structural parameters further indicates significant bond charge disproportionation in association with the transition. Work at Brookhaven National Laboratory was supported by US DOE, Office of Science, Office of Basic Energy Sciences (DOE-BES) under Contract No. DE-SC0012704.

  4. Striped nanoscale phase separation at the metal-insulator transition of heteroepitaxial nickelates

    Science.gov (United States)

    Mattoni, G.; Zubko, P.; Maccherozzi, F.; van der Torren, A. J. H.; Boltje, D. B.; Hadjimichael, M.; Manca, N.; Catalano, S.; Gibert, M.; Liu, Y.; Aarts, J.; Triscone, J.-M.; Dhesi, S. S.; Caviglia, A. D.

    2016-11-01

    Nucleation processes of mixed-phase states are an intrinsic characteristic of first-order phase transitions, typically related to local symmetry breaking. Direct observation of emerging mixed-phase regions in materials showing a first-order metal-insulator transition (MIT) offers unique opportunities to uncover their driving mechanism. Using photoemission electron microscopy, we image the nanoscale formation and growth of insulating domains across the temperature-driven MIT in NdNiO3 epitaxial thin films. Heteroepitaxy is found to strongly determine the nanoscale nature of the phase transition, inducing preferential formation of striped domains along the terraces of atomically flat stepped surfaces. We show that the distribution of transition temperatures is a local property, set by surface morphology and stable across multiple temperature cycles. Our data provide new insights into the MIT of heteroepitaxial nickelates and point to a rich, nanoscale phenomenology in this strongly correlated material.

  5. Thermally driven analog of the Barkhausen effect at the metal-insulator transition in vanadium dioxide

    Energy Technology Data Exchange (ETDEWEB)

    Huber-Rodriguez, Benjamin; Ji, Heng; Chen, Chih-Wei [Department of Physics and Astronomy, Rice University, Houston, Texas 77005 (United States); Kwang, Siu Yi [Department of Physics, National University of Singapore, Singapore 117551 (Singapore); Hardy, Will J. [Applied Physics Program, Rice Quantum Institute, Rice University, Houston, Texas 77005 (United States); Morosan, Emilia [Department of Physics and Astronomy, Rice University, Houston, Texas 77005 (United States); Department of Chemistry, Rice University, Houston, Texas 77005 (United States); Department of Materials Science and Nanoengineering, Rice University, Houston, Texas 77005 (United States); Natelson, Douglas [Department of Physics and Astronomy, Rice University, Houston, Texas 77005 (United States); Department of Materials Science and Nanoengineering, Rice University, Houston, Texas 77005 (United States); Department of Electrical and Computer Engineering, Rice University, Houston, Texas 77005 (United States)

    2014-09-29

    The physics of the metal-insulator transition (MIT) in vanadium dioxide remains a subject of intense interest. Because of the complicating effects of elastic strain on the phase transition, there is interest in comparatively strain-free means of examining VO{sub 2} material properties. We report contact-free, low-strain studies of the MIT through an inductive bridge approach sensitive to the magnetic response of VO{sub 2} powder. Rather than observing the expected step-like change in susceptibility at the transition, we argue that the measured response is dominated by an analog of the Barkhausen effect, due to the extremely sharp jump in the magnetic response of each grain as a function of time as the material is cycled across the phase boundary. This effect suggests that future measurements could access the dynamics of this and similar phase transitions.

  6. 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.

  7. Phase coexistence and Mott metal-insulator transition in the doped Hubbard-Holstein model

    Science.gov (United States)

    Moradi Kurdestany, Jamshid; Satpathy, Sashi

    2015-03-01

    Motivated by recent progress in the understanding of the Mott insulators away from half filling [?], often observed in the oxide materials, we study the role of the electron-lattice interaction vis-à-vis the electron correlations by studying the one-band Hubbard-Holstein model using the Gutzwiller variational method. Our theory predicts phase separation for sufficiently strong electron-lattice interaction, which however is frustrated in the solid due to the long-range Coulomb interaction of the dopant atoms, resulting in puddles of metallic phases embedded in the insulating matrix. Metallic state occurs when the volume fraction of the metallic phase exceeds the percolation threshold, as the dopant concentration is increased. Connection is made with the experimentally observed metal-insulator transition in the complex oxides.

  8. Percolative Metal-Insulator transition in the doped Hubbard-Holstein model with the Gutzwiller Approach

    Science.gov (United States)

    Moradi Kurdestany, Jamshid; Satpathy, Sashi

    Motivated by the recent progress in understanding of Mott insulators away from half filling, observed in many perovskite oxides, we study the metal-insulator transition in the Hubbard-Holstein model, which contains both the Coulomb and the electron-lattice (Jahn Teller) interactions by using the Gutzwiller variational method. We find that strong electron-lattice Interaction leads to phase separation, which however can be frustrated due to the long-range Coulomb interaction, resulting in a mixed phase consisting of puddles of metallic phases embedded in an insulating matrix. When the dopant concentration exceeds a threshold value xc , the metallic part forms a percolating network leading to metallic conduction. Depending on the strength of the electron-lattice interaction, xc can be of the order of 0.05 - 0.20 or so, which is the typical value observed in the perovskites.

  9. 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.

  10. Ionic Hamiltonians for transition metal atoms: effective exchange coupling and Kondo temperature

    Science.gov (United States)

    Flores, F.; Goldberg, E. C.

    2017-02-01

    An ionic Hamiltonian for describing the interaction between a metal and a d-shell transition metal atom having an orbital singlet state is introduced and its properties analyzed using the Schrieffer-Wolf transformation (exchange coupling) and the poor man’s scaling method (Kondo temperature). We find that the effective exchange coupling between the metal and the atom has an antiferromagnetic or a ferromagnetic interaction depending on the kind of atomic fluctuations, either S\\to S-1/2 or S\\to S+1/2 , associated with the metal-atom coupling. We present a general scheme for all those processes and calculate, for the antiferromagnetic interaction, the corresponding Kondo-temperature.

  11. 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.

  12. Which orbital and charge ordering in transition metal oxides can resonant X-ray diffraction detect?

    Energy Technology Data Exchange (ETDEWEB)

    Di Matteo, Sergio, E-mail: sergio.dimatteo@univ-rennes1.f [Equipe de Physique des Surfaces et Interfaces, Institut de Physique de Rennes UMR UR1-CNRS 6251, Universite de Rennes 1, F-35042 Rennes Cedex (France)

    2009-11-15

    The present article is a brief critical review about the possibility of detecting charge and/or orbital order in transition-metal oxides by means of resonant x-ray diffraction. Many recent models of transition-metal oxides are based on charge and/or orbitally ordered ground-states and it has been claimed in the past that resonant x-ray diffraction is able to confirm or reject them. However, in spite of the many merits of this technique, such claims are ambiguous, because the interpretative frameworks used to analyze such results in transition-metal oxides, where structural distortions are always associated to the claimed charged/orbitally ordered transition, strongly influence (not to say suggest) the answer. In order to clarify this point, I discuss the two different definitions of orbital and charge orderings which are often used in the literature without a clear distinction. My conclusion is that the answer to the question of the title depends on which definition is adopted.

  13. A continuous Mott transition between a metal and a quantum spin liquid

    Science.gov (United States)

    Mishmash, Ryan V.; Gonzalez, Ivan; Melko, Roger G.; Motrunich, Olexei I.; Fisher, Matthew P. A.

    2015-03-01

    More than half a century after first being proposed by Sir Nevill Mott, the deceptively simple question of whether the interaction-driven electronic metal-insulator transition may be continuous remains enigmatic. Recent experiments on two-dimensional materials suggest that when the insulator is a quantum spin liquid, lack of magnetic long-range order on the insulating side may cause the transition to be continuous, or only very weakly first order. Motivated by this, we study a half-filled extended Hubbard model on a triangular lattice strip geometry. We argue, through use of large-scale numerical simulations and analytical bosonization, that this model harbors a continuous (Kosterlitz-Thouless-like) quantum phase transition between a metal and a gapless spin liquid characterized by a spinon Fermi sea, i.e., a ``spin Bose metal''. These results may provide a rare insight into the development of Mott criticality in strongly interacting two-dimensional materials and elucidate a mechanism by which spin-liquid phases are stabilized in the vicinity of such transitions.

  14. 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.

  15. 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.

  16. Effect of transition metal salts on the initiated chemical vapor deposition of polymer thin films

    Energy Technology Data Exchange (ETDEWEB)

    Kwong, Philip; Seidel, Scott; Gupta, Malancha, E-mail: malanchg@usc.edu [Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, 925 Bloom Walk, Los Angeles, California 90089 (United States)

    2015-05-15

    In this work, the effect of transition metal salts on the initiated chemical vapor deposition of polymer thin films was studied using x-ray photoelectron spectroscopy. The polymerizations of 4-vinyl pyridine and 1H,1H,2H,2H-perfluorodecyl acrylate were studied using copper(II) chloride (CuCl{sub 2}) and iron(III) chloride (FeCl{sub 3}) as the transition metal salts. It was found that the surface coverages of both poly(4-vinyl pyridine) (P4VP) and poly(1H,1H,2H,2H-perfluorodecyl acrylate) were decreased on CuCl{sub 2}, while the surface coverage of only P4VP was decreased on FeCl{sub 3}. The decreased polymer surface coverage was found to be due to quenching of the propagating radicals by the salt, which led to a reduction of the oxidation state of the metal. The identification of this reaction mechanism allowed for tuning of the effectiveness of the salts to decrease the polymer surface coverage through the adjustment of processing parameters such as the filament temperature. Additionally, it was demonstrated that the ability of transition metal salts to decrease the polymer surface coverage could be extended to the fabrication of patterned cross-linked coatings, which is important for many practical applications such as sensors and microelectronics.

  17. Effect of pressure on optical properties of the transition metal dichalcogenide MoSe2

    Science.gov (United States)

    Caramazza, S.; Capitani, F.; Marini, C.; Mancini, A.; Malavasi, L.; Dore, P.; Postorino, P.

    2017-10-01

    Transition Metal Dichalcogenides TMDs MoX2 (X=S, Se, Te) are an emergent class of layered materials displaying exciting optoelectronic properties which can be modified by varying the number of layers, by intercalation, or by applying an external strain/compression. In particular, these semiconducting materials can get a band gap closure under pressure and enter in a metallic phase. Here, we investigate the optical properties of MoSe2 under high pressure by means of Raman spectroscopy over a wide pressure range (0-30 GPa). No anomaly has been observed in the pressure dependence of the frequencies of the vibrational modes A 1g, E 1 2g (Raman first order) and E 1g - E2 2g (Raman second-order), in agreement with the absence previously reported of any pressure induced structural transition. Interestingly, our detailed line-shape analysis show a clear anomaly in the pressure behavior of the linewidth of the A 1g and E 1 2g phonons at the insurgent metallization process which was observed in previous infrared and transport experiments. Our results indicate that the linewidths of Raman phonons peaks can be sensitive to even subtle pressure-induced electronic rearrangements and can thus be used to monitor the insurgence of a pressure-induced semiconductor-metal transition.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2006-07-01

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

  19. 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.

  20. 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.

  1. Pressure-induced core-level crossing transitions in 5d metals.

    Science.gov (United States)

    Abrikosov, Igor

    Considering hexagonal closed-packed Os compressed to over 770 GPa, we discuss the anomaly observed experimentally in the behavior of the unit cells parameters ratio c/a at about 440 GPa. We argue that the anomaly is related to a new type of electronic transition, the core level crossing (CLC) transition, associated with interactions between the core electrons induced by pressure. By carrying out a systematic theoretical study for all metals of the 5d series (Hf, Ta, W, Re, Os, Ir, Pt, Au) we have found that the CLC transition is a general effect for this series of metals. While in Pt it occurs at 1500 GPa, at a pressure substantially higher than in Os, in Ir it occurs already at 80 GPa. Moreover, we predict that in Re the CLC transition may take place already at ambient pressure. We explain the effect of the CLC and analyze the shift of the transition pressure across the series within the Thomas-Fermi model. In particular, we show that the effect has many common features with the atomic collapse in rare-earth elements. The Swedish Research Council (VR) Grant No. 2015-04391 and the Grant from the Ministry of Education and Science of the Russian Federation (Grant No. 14.Y26.31.0005) are gratefully acknowledged.

  2. Detecting metabolites of different transition metal-lithospermate B complexes after intravenous injection in rats.

    Science.gov (United States)

    Chen, Ying-Jie; Chung, Tse-Yu; Chen, Wen-Ying; Chen, Chung-Yu; Lee, Maw-Rong; Jinn, Tzyy-Rong; Tc Tzen, Jason

    2014-07-01

    Lithospermate B (LSB) isolated from the traditional Chinese medicine danshen (Salvia miltiorrhiza) is an effective Na(+)/K(+)-ATPase inhibitor and used to treat congestive heart failure. The inhibition of LSB on Na(+)/K(+)-ATPase is potentiated by forming complexes with transition metal ions. Here we investigated the safety and metabolites of different transition metal-LSB complexes in rats. LSB complexed with six different transition metal ions (Mg(2+), Zn(2+), Cr(3+), Co(2+), Ni(2+) and Mn(2+)) were prepared. Adult male SD rats were injected with the different metal-LSB complexes (50 mg/kg, iv), and their bile and blood samples were collected. The metabolites of the metal-LSB complexes in the samples were analyzed using mass spectroscopy. In rats injected with LSB complexed with Mg(2+), Zn(2+), Cr(3+), Ni(2+) or Mn(2+), LSB and its four putative metabolites were equivalently detected in their bile samples. Mn(2+)-LSB exhibited distinct metabolite profiles compared with the other four metal-LSB complexes. The four putative metabolites were identified as 3-monomethyl-LSB, 3,3''-dimethyl-LSB, 3,3'''-dimethyl-LSB and 3,3'',3'''-trimethyl-LSB. The tracking of successive bile samples of rats injected with Mg(2+)-LSB, Zn(2+)-LSB and Mn(2+)-LSB concurrently demonstrated that LSB was firstly methylated at position 3, then at position 3'', and, finally, the 3''' hydroxyl group. All rats injected with Co(2+)-LSB died. Zn(2+)-LSB, Cr(3+)-LSB, Ni(2+)-LSB or Mn(2+)-LSB produces identical four methylated metabolites of LSB in rats, and seemed to be as safe as LSB or Mg(2+)-LSB.

  3. The potential for transition metal-mediated neurodegeneration in amyotrophic lateral sclerosis

    Directory of Open Access Journals (Sweden)

    David Benn Lovejoy

    2014-07-01

    Full Text Available Modulations of the potentially toxic transition metals iron (Fe and copper (Cu are implicated in the neurodegenerative process in a variety of human disease states including amyotrophic lateral sclerosis (ALS. However, the precise role played by these metals is still very much unclear, despite considerable clinical and experimental data suggestive of a role for these elements in the neurodegenerative process. The discovery of mutations in the antioxidant enzyme Cu/Zn superoxide dismutase (SOD-1 in ALS patients established the first known cause of ALS. Recent data suggest that various mutations in SOD-1 affect metal-binding of Cu and Zn, in turn promoting toxic protein aggregation. Copper homeostasis is also disturbed in ALS, and may be relevant to ALS pathogenesis. Another set of interesting observations in ALS patients involves the key nutrient Fe. In ALS patients Fe loading can be inferred by studies showing increased expression of serum ferritin, an Fe storage protein, with high serum ferritin levels correlating to poor prognosis. Magnetic resonance imaging of ALS patients shows a characteristic T2 shortening that is attributed to the presence of Fe in the motor cortex. In mutant SOD-1 mouse models, increased Fe is also detected in the spinal cord and treatment with Fe-chelating drugs lowers spinal cord Fe, preserves motor neurons and extends lifespan. Inflammation may play a key causative role in Fe accumulation, but this is not yet conclusive. Excess transition metals may enhance induction of endoplasmic reticulum (ER stress, a system that is already under strain in ALS. Taken together, the evidence suggests a role for transition metals in ALS progression and the potential use of metal-chelating drugs as a component of future ALS therapy.

  4. An ab initio study of transition metals doped with WSe2 for long-range room temperature ferromagnetism in two-dimensional transition metal dichalcogenide.

    Science.gov (United States)

    Gil, Carmen J; Pham, Anh; Yu, Aibing; Li, Sean

    2014-07-30

    We report a systematic study of the magnetic properties in transition metals doped with WSe2 through the use of first principle calculations. The results demonstrate the possibility of generating long-range room temperature ferromagnetic interaction in WSe2 with the use of Mn and Fe doping. In the case of Fe, a percolation threshold is required for long-range ferromagnetism, whereas the long-range room temperature ferromagnetic interaction in Mn-doped WSe2 persists even at a low concentration (~5.6%). The ferromagnetism is mediated by the delocalized p states in the Se atoms, which couple antiferromagnetically with the spin-down a1 and e1 states in Fe doping through a correlated interaction. In Mn doping, the p states of Se tend to couple ferromagnetically with the 3d state of Mn, which stabilizes the long-range ferromagnetism between the Mn ions, although the short-range interaction is antiferromagnetic. In addition, the calculations indicate that Fe and Mn tend to configure at a high spin state, thus they possess much larger magnetic moments in WSe2 than when they are doped into other transition metal dichalcogenides. We also discovered a strong dependence of the exchange interaction on the dopants' spatial positions, distances, and concentrations, which alters the magnetic coupling from strong ferromagnetism to strong antiferromagnetism. These results can provide useful guidance to engineer the magnetic properties of WSe2 in future experiments.

  5. 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.

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

    Science.gov (United States)

    Kurdestany, Jamshid Moradi; Satpathy, S.

    2017-08-01

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

  7. 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.

  8. 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.

  9. Magneto-optical spectra of transition metal dichalcogenides: A comparative study

    Energy Technology Data Exchange (ETDEWEB)

    Ho, Yen-Hung [Department of Physics and Texas Center for Superconductivity, University of Houston, Houston, Texas 77204 (United States); Department of Physics, National Tsing Hua University, Hsinchu 300, Taiwan (China); Chiu, Chih-Wei; Lin, Ming-Fa, E-mail: mflin@mail.ncku.edu.tw [Department of Physics, National Cheng Kung University, Tainan 701, Taiwan (China); Su, Wu-Pei, E-mail: phys3z@central.uh.edu [Department of Physics and Texas Center for Superconductivity, University of Houston, Houston, Texas 77204 (United States)

    2014-12-01

    Following our previous work [Ho et al., Phys. Rev. B 89, 155316 (2014)], we systematically calculate the magneto-optical properties of various transition metal dichalcogenide monolayers. The intrinsic spin-orbit coupling gives rise to the spin-split electronic states, while a perpendicular magnetic field further induces a valley splitting. In magneto-optical spectra with linearly polarized light, spectral features are spin and valley-polarized. Compounds are different from one another in terms of transition energies and appearance of twin peaks. Our numerical results can serve as a guide for future experimental identification.

  10. Doping driven metal-insulator transitions and charge orderings in the extended Hubbard model

    CERN Document Server

    Kapcia, K J; Capone, M; Amaricci, A

    2016-01-01

    We perform a thorough study of an extended Hubbard model featuring local and nearest-neighbor Coulomb repulsion. Using dynamical mean-field theory we investigated the zero temperature phase-diagram of this model as a function of the chemical doping. The interplay between local and non-local interaction drives a variety of phase-transitions connecting two distinct charge-ordered insulators, i.e., half-filled and quarter-filled, a charge-ordered metal and a Mott insulating phase. We characterize these transitions and the relative stability of the solutions and we show that the two interactions conspire to stabilize the quarter-filled charge ordered phase.

  11. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Pinto, R.A. [Laboratorio de Fisica Estadistica, Centro de Fisica, Instituto Venezolano de Investigaciones Cientificas, Apartado 21827, Caracas 1020-A (Venezuela)]. E-mail: ripinto@ivic.ve; Rodriguez, M. [Laboratorio de Fisica Estadistica, Centro de Fisica, Instituto Venezolano de Investigaciones Cientificas, Apartado 21827, Caracas 1020-A (Venezuela); Gonzalez, J.A. [Laboratorio de Fisica Computacional, Centro de Fisica, Instituto Venezolano de Investigaciones Cientificas, Apartado 21827, Caracas 1020-A (Venezuela); Medina, E. [Laboratorio de Fisica Estadistica, Centro de Fisica, Instituto Venezolano de Investigaciones Cientificas, Apartado 21827, Caracas 1020-A (Venezuela)

    2005-06-20

    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.

  13. Evidence of second order transition induced by the porosity in the thermal conductivity of sintered metals

    Directory of Open Access Journals (Sweden)

    Aïmen E. Gheribi

    2014-07-01

    Full Text Available In this paper, using both experimental data and theoretical modelling, we investigate the degradation of the thermal conductivity of sintered metals due simultaneously to the grain boundary thermal resistance and the porosity. We show that the porosity dependence of the thermal conductivity of sintered material from spherical particle powder, exhibits a critical behaviour associated with a second order phase transition. An analytical model with a single parameter is proposed to describe the critical behaviour of the thermal conductivity of sintered metals versus porosity.

  14. Infrared reflectance measurements of the insulator-metal transition in solid hydrogen

    Science.gov (United States)

    Mao, H. K.; Hemley, R. J.; Hanfland, M.

    1990-01-01

    Reflectance measurements on solid hydrogen to 177 GPa (1.77 Mbar) have been performed from near-infrared to ultraviolet wavelengths (0.5 to 3 eV). Above 150 GPa characteristic free-electron behavior in the infrared region is observed to increase sharply with increasing pressure. Analysis of volume dependence of the plasma frequency obtained from Drude-model fits to the spectra indicates that the pressure of the insulator-metal transition is 149 (+ or - 10) GPa at 295 K. The measurements are consistent with metallization by closure of an indirect gap in the molecular solid.

  15. Comment on "Observation of the Wigner-Huntington transition to metallic hydrogen".

    Science.gov (United States)

    Goncharov, Alexander F; Struzhkin, Viktor V

    2017-08-25

    Dias and Silvera (Research Article, 17 February 2017, p. 715) report on the observation of the Wigner-Huntington transition to metallic hydrogen at 495 gigapascals at 5.5 and 83 kelvin. Here, we show that the claim of metallic behavior is not supported by the presented data, which are scarce, contradictory, and do not prove the presence of hydrogen in the high-pressure cavity. Copyright © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

  16. Scaling at the Mott-Hubbard metal-insulator transition in yttrium hydride

    CERN Document Server

    Hoekstra, A F T; Rosenbaum, T F

    2003-01-01

    A single yttrium hydride thin film is conveniently driven through the T 0 metal-insulator transition by fine-tuning the charge carrier density n via persistent photoconductivity at low temperature. Simultaneously, electrical conductivity and Hall measurements are performed for temperatures T down to 350 mK and magnetic fields up to 14 T. A scaling analysis is applied and critical exponents, resolved separately on the metallic and insulating sides of the critical region, are determined consistently. We introduce corrections to scaling to invoke collapse of the data onto a single master curve over an extended region of the (n, T) phase diagram.

  17. 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....

  18. Importance of the ligand basis set in ab initio thermochemical calculations of transition metal species

    Science.gov (United States)

    Plascencia, Cesar; Wang, Jiaqi; Wilson, Angela K.

    2017-10-01

    The impact of basis set choice has been considered for a series of transition metal (TM) species. The need for higher level correlation consistent basis sets on both the metal and ligand has been investigated, and permutations in the pairings of basis set used for TM's and basis set used for ligands can lead to effective routes to complete basis set (CBS) limit extrapolations of thermochemical energetics with little change in thermochemical predictions as compared to those resulting from the use of traditional basis set pairings, while enabling computational cost savings. Basis set superposition errors (BSSE) that can arise have also been considered.

  19. Characterization of Transition-Metal Oxide Deposition on Carbon Electrodes of a Supercapacitor

    Directory of Open Access Journals (Sweden)

    Ying-Chung Chen

    2016-12-01

    Full Text Available In order to fabricate the composite electrodes of a supercapacitor, transition-metal oxide materials NiO and WO3 were deposited on carbon electrodes by electron beam evaporation. The influences of various transition-metal oxides, scan rates of cyclic voltammograms (CVs, and galvanostatic charge/discharge tests on the characteristics of supercapacitor were studied. The charge/discharge efficiency and the lifetime of the composite electrodes were also investigated. It was found that the composite electrodes exhibited more favorable capacitance properties than those of the carbon electrodes at high scan rates. The results revealed the promotion of the capacitance property of the supercapacitor with composite electrode and the improving of the decay property in capacitance at high scan rate. In addition, the charge/discharge efficiency is close to 100% after 5000 cycles, and the composite electrode retains strong adhesion between the electrode material and the substrate.

  20. 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.