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1

Electronic, spectroscopic and elastic properties of early transition metal compounds  

Microsoft Academic Search

Photoemission experiments on early 3d transition metal compounds (TMC), involving both valence bands and core levels of the 3d elements, are reviewed. Extensive use is made of ab initio schemes as well as simple models and the emphasis is put on understanding the results of experiments more than on the experimental details and methods. Compounds of the TMs are first

I. Pollini; A. Mosser; J. C. Parlebas

2001-01-01

2

Ethanol amination catalysis over early transition metal nitrides  

Microsoft Academic Search

Several high surface area early transition metal nitrides were evaluated for their ability to catalyze ethanol amination. These materials were very active with turnover frequencies comparable to those of supported Pt and Ni catalysts. Their activities ranked in the following order: VN>Mo2N>W2N>TiN>NbN. Like the Pt and Ni catalysts, the nitrides were very selective to the production of ethylamine. In addition,

M. K. Neylon; S. K. Bej; C. A. Bennett; L. T. Thompson

2002-01-01

3

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

SciTech Connect

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

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

1996-06-01

4

Early Transition Metal Oxides as Catalysts: Crossing Scales from Clusters to Single Crystals to Functioning Materials  

Microsoft Academic Search

The overall goal of this program is to investigate the electronic structure and chemical bonding of early transition metal oxide clusters and use them as well-defined molecular models to obtain insight into properties and mechanisms of oxide catalysts, as well as to provide accurate spectroscopic and molecular information to verify theoretical methods used to predict materials properties. A laser vaporization

Lai-Sheng Wang

2009-01-01

5

Transition metals  

PubMed Central

Transition metals such as Iron (Fe) and Copper (Cu) are essential for plant cell development. At the same time, due their capability to generate hydroxyl radicals they can be potentially toxic to plant metabolism. Recent works on hydroxyl-radical activation of ion transporters suggest that hydroxyl radicals generated by transition metals could play an important role in plant growth and adaptation to imbalanced environments. In this mini-review, the relation between transition metals uptake and utilization and oxidative stress-activated ion transport in plant cells is analyzed, and a new model depicting both apoplastic and cytosolic mode of ROS signaling to plasma membrane transporters is suggested. PMID:23333964

Rodrigo-Moreno, Ana; Poschenrieder, Charlotte; Shabala, Sergey

2013-01-01

6

First Principles Calculation of Elastic Properties of Early-Late Transition Metal Alloys  

NASA Astrophysics Data System (ADS)

Amorphous metals are of practical interest in applications requiring high strength materials. We choose to examine the elastic properties of crystalline phases to understand the elastic properties of amorphous solids. In this talk, we discuss our work using first principles methods to calculate elastic properties for crystalline alloys in various chemical families containing transition metals, specifically early (Ta,W) and late (Fe,Co,Rh,Ni,Cu,Zn) due to their good glass forming ability, as well as select borides. Certain Laves phases, which are known to have local chemical ordering similar to amorphous solids, are focused on. We analyze trends in the elastic properties of chemical families based on computed enthalpies of formation, elastic properties of pure elemental phases, and electronic and structural information. In particular, we use effective medium theories and enthalpies of formation to predict trends in bulk moduli. This information can be used to predict future candidate systems for high-strength amorphous metals.

Huhn, William; Widom, Michael

2013-03-01

7

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

SciTech Connect

Investigations of ternary mixed early transition metal-rich sulfide and phosphide systems resulted in the discovery of new structures and new phases. A new series of Zr and Hf - group V transition metal - sulfur K-phases was synthesized and crystallographically characterized. When the group V transition metal was Nb or Ta, the unit cell volume was larger than any previously reported K-phase. The presence of adventitious oxygen was determined in two K-phases through a combination of neutron scattering and X-ray diffraction experiments. A compound Hf{sub 10}Ta{sub 3}S{sub 3} was found to crystallize in a new-structure type similar to the known gamma brasses. This structure is unique in that it is the only reported {open_quotes}stuffed{close_quotes} gamma-brass type structure. The metal components, Hf and Ta, are larger in size and more electropositive than the metals found in normal gamma brasses (e.g. Cu and Zn) and because of the larger metallic radii, sulfur can be incorporated into the structure where it plays an integral role in stabilizing this phase relative to others. X-ray single-crystal, X-ray powder and neutron powder refinements were performed on this structure. A new structure was found in the ternary Nb-Zr-P system which has characteristics in common with many known early transition metal-rich sulfides, selenides, and phosphides. This structure has the simplest known interconnection of the basic building blocks known for this structural class. Anomalous scattering was a powerful tool for differentiating between Zr and Nb when using Mo K{alpha} X-radiation. The compounds ZrNbP and HfNbP formed in the space group Prima with the simple Co{sub 2}Si structure which is among the most common structures found for crystalline solid materials. Solid solution compounds in the Ta-Nb-P, Ta-Zr-P, Nb-Zr-P, Hf-Nb-P, and Hf-Zr-S systems were crystallographically characterized. The structural information corroborated ideas about bonding in metal-rich compounds.

Marking, G.A.

1994-01-04

8

First-principles calculation of elastic moduli of early-late transition metal alloys  

NASA Astrophysics Data System (ADS)

Motivated by interest in the elastic properties of high-strength amorphous metals, we examine the elastic properties of select crystalline phases. Using first-principles methods, we calculate elastic moduli in various chemical systems containing transition metals, specifically early (Ta,W) and late (Co,Ni). Theoretically predicted alloy elastic properties are verified for Ni-Ta by comparison with experimental measurements using resonant ultrasound spectroscopy. Comparison of our computed elastic moduli with effective medium theories shows that alloying leads to enhancement of bulk moduli relative to averages of the pure elements and considerable deviation of predicted and computed shear moduli. Specifically, we find an enhancement of bulk modulus relative to effective medium theory and propose a candidate system for high-strength, ductile amorphous alloys. Trends in the elastic properties of chemical systems are analyzed using force constants, electronic densities of state, and crystal overlap Hamilton populations. We interpret our findings in terms of the electronic structure of the alloys.

Huhn, William Paul; Widom, Michael; Cheung, Andrew M.; Shiflet, Gary J.; Poon, S. Joseph; Lewandowski, John

2014-03-01

9

J. Phys. Chem. 1988, 92, 2109-2115 2109 Early-versus Late-Transition-Metal-Oxo Bonds: The Electronlc Structure of VO' and  

E-print Network

J. Phys. Chem. 1988, 92, 2109-2115 2109 Early- versus Late-Transition-Metal-Oxo Bonds). Finally, we have used these results to predict the ground states of MO' for other first-row transition-metal oxides. I. Introduction While the electronic structureof neutral transition-metal oxides has been

Goddard III, William A.

10

Cooperative reactivity of early-late heterodinuclear transition metal complexes with polar organic substrates  

PubMed

A comprehensive investigation into the cooperative reactivity of two chemically complementary metal-complex fragments in early-late heterodinuclear complexes has been carried out. Reaction of the partially fluorinated tripodal amidozirconium complexes [HC-(SiMe2NR)3Zr(mu-Cl)2Li(OEt2)2] (R = 2-FC6H4: 2a, 2,3,4-F3C6H4: 2b) with K[CpM(CO)2] (M=Fe, Ru) afforded the stable metal-metal bonded heterodinuclear complexes [HC[SiMe2NR]3-Zr-MCp(CO)2] (3-6). Reaction of the dinuclear complexes with methyl isonitrile as well as the heteroallenes CO2, CS2, RNCO and RNCS led to insertion into the polar metal-metal bond. Two of these complexes, [HC[SiMe2N(2-FC6-H4)]3Zr(S2C)Fe(CO)2Cp] (9a) and [HC-[SiMe2N(2-FC2H4)]3Zr-(SCNPh)Fe(CO)2-Cp] (12), have been structurally characterized by a single crystal X-ray structure analysis, proving the structural situation of the inserted substrate as a bridging ligand between the early and late transition metal centre. The reactivity towards organic carbonyl derivatives proved to be varied. Reaction of the heterobimetallic complexes with benzyl and ethylbenzoate led to the cleavage of the ester generating the respective alkoxozirconium complexes [HC[SiMe2N(2-FC6H4)]3ZrOR] (R = Ph-CH2: 13a, Et: 13b) along with [CpFe-[C(O)Ph](CO)2], whereas the analogous reaction with ethyl formate gave 13b along with [CpFeH(CO)2]; this latter complex results from the instability of the formyliron species initially formed. Aryl aldehydes were found to react with the Zr-M complexes according to a Cannizzaro disproportionation pattern yielding the aroyliron and ruthenium complexes along with the respective benzoxyzirconium species. The transfer of the aldehyde hydrogen atom in the course of the reaction was established in a deuteriation experiment. [HC[SiMe2-N(2-FC6H4)]3Zr-M(CO)2Cp] reacted with lactones to give the ring-opened species containing an alkoxozirconium and an acyliron or acylruthenium fragment; the latter binds to the early transition metal centre through the acyl oxygen atom, as evidenced from the unusuallly low-field shifted 13C NMR resonances of the RC(O)M units. Ketones containing a-CH units react with the Zr-Fe complexes cooperatively to yield the aldol coupling products coordinated to the zirconium complex fragment along with the hydridoiron compound [CpFeH(CO)2], whereas 1,2-diphenylcyclopropenone underwent an oxygen transfer from the keto group to a CO ligand to give a linking CO2 unit and a cyclopropenylidene ligand coordinated to the iron fragment in [HC-[Si(CH3)2N(2,3,4-F3C6H2)]3Zr(mu-O2C)-Fe(CO)[C3Ph2)Cp] (19). The atom transfer was established by 17O and 13C labelling studies. Similar oxygen-transfer processes were observed in the reactions with pyridine N-oxide, dimethylsulfoxide and methylphenylsulfoxide. PMID:10807180

Gade; Memmler; Kauper; Schneider; Fabre; Bezougli; Lutz; Galka; Scowen; McPartlin

2000-02-18

11

Cyclopentadienyl-Containing Low-Valent Early Transition Metal Olefin Polymerization Catalysts  

DOEpatents

A catalyst system useful to polymerize and co-polymerize polar and non-polar olefin monomers is formed by in situ reduction with a reducing agent of a catalyst precursor comprising {Cp*MRR'.sub.n }.sup.+ {A}.sup.- wherein Cp* is a cyclopentadienyl or substituted cyclopentadienyl moiety; M is an early transition metal; R is a C.sub.1 -C.sub.20 hydrocarbyl; R' are independently selected from hydride, C.sub.1 -C.sub.20 hydrocarbyl, SiR".sub.3, NR".sub.2, OR", SR", GeR".sub.3, SnR".sub.3, and C.dbd.C-containing groups (R"=C.sub.1 -C.sub.10 hydrocarbyl); n is an integer selected to balance the oxidation state of M; and A is a suitable non-coordinating anionic cocatalyst or precursor. This catalyst system may form stereoregular olefin polymers including syndiotactic polymers of styrene and methylmethacrylate and isotactic copolymers of polar and nonpolar olefin monomers such as methylmethacrylate and styrene.

Marks, Tobin J. (Evanston, IL); Luo, Lubin (Baton Rouge, LA); Yoon, Sung Cheol (Evanston, IL)

2004-06-08

12

Cyclopentadienyl-containing low-valent early transition metal olefin polymerization catalysts  

DOEpatents

A catalyst system useful to polymerize and co-polymerize polar and non-polar olefin monomers is formed by in situ reduction with a reducing agent of a catalyst precursor comprising {Cp*MRR'.sub.n }.sup.+ {A}.sup.- wherein Cp* is a cyclopentadienyl or substituted cyclopentadienyl moiety; M is an early transition metal; R is a C.sub.1 -C.sub.20 hydrocarbyl; R' are independently selected from hydride, C.sub.1 -C.sub.20 hydrocarbyl, SiR".sub.3, NR".sub.2, OR", SR", GeR".sub.3, and SnR".sub.3 containing groups (R"=C.sub.1 -C.sub.10 hydrocarbyl); n is an integer selected to balance the oxidation state of M; and A is a suitable non-coordinating anionic cocatalyst or precursor. This catalyst system may form stereoregular olefin polymers including syndiotactic polymers of styrene and methylmethacrylate and isotactic copolymers of polar and nonpolar olefin monomers such as methylmethacrylate and styrene.

Marks, Tobin J. (Evanston, IL); Luo, Lubin (Baton Rouge, LA); Yoon, Sung Cheol (Evanston, IL)

2003-04-08

13

Cyclopentadienyl-containing low-valent early transition metal olefin polymerization catalysts  

DOEpatents

A catalyst system useful to polymerize and co-polymerize polar and non-polar olefin monomers is formed by in situ reduction with a reducing agent of a catalyst precursor comprising wherein Cp* is a cyclopentadienyl or substituted cyclopentadienyl moiety; M is an early transition metal; R is a C.sub.1 -C.sub.20 hydrocarbyl; R' are independently selected from hydride, C.sub.1 -C.sub.20 hydrocarbyl, SiR".sub.3, NR".sub.2, OR", SR", GeR".sub.3, SnR".sub.3, and C.dbd.C containing groups (R".dbd.C.sub.1 -C.sub.10 hydrocarbyl); n is an integer selected to balance the oxidation state of M; and A is a suitable non-coordinating anionic cocatalyst or precursor. This catalyst system may form stereoregular olefin polymers including syndiotactic polymers of styrene and methylmethacrylate and isotactic copolymers of polar and nonpolar olefin monomers such as methylmethacrylate and styrene.

Marks, Tobin J.; Luo, Lubin; Yoon, Sung Cheol

2003-12-30

14

Cyclopentadienyl-containing low-valent early transition metal olefin polymerization catalysts  

DOEpatents

A catalyst system useful to polymerize and co-polymerize polar and non-polar olefin monomers is formed by in situ reduction with a reducing agent of a catalyst precursor comprising
{Cp*MRR'n}+{A}-
wherein Cp* is a cyclopentadienyl or substituted cyclopentadienyl moiety; M is an early transition metal; R is a C1–C20 hydrocarbyl; R' are independently selected from hydride, C1–C20 hydrocarbyl, SiR"3, NR"2, OR", SR", GeR"3, SnR"3, and C.dbd.C-containing groups (R"=C1–C10 hydrocarbyl); n is an integer selected to balance the oxidation state of M; and A is a suitable non-coordinating anionic cocatalyst or precursor. This catalyst system may form stereoregular olefin polymers including syndiotactic polymers of styrene and methylmethacrylate and isotactic copolymers of polar and nonpolar olefin monomers such as methylmethacrylate and styrene.

Marks, Tobin J.; Luo, Lubin; Yoon, Sung Cheol

2007-01-09

15

Cyclopentadienyl-containing low-valent early transition metal olefin polymerization catalysts  

DOEpatents

A catalyst system useful to polymerize and co-polymerize polar and non-polar olefin monomers is formed by in situ reduction with a reducing agent of a catalyst precursor comprising
{Cp*MRR'n}+{A}-
wherein Cp* is a cyclopentadienyl or substituted cyclopentadienyl moiety; M is an early transition metal; R is a C1–C20 hydrocarbyl; R' are independently selected from hydride, C1–C20 hydrocarbyl, SiR"3, NR"2, OR", SR", GeR"3, SnR"3, and C.dbd.C-containing groups (R"=C1–C10 hydrocarbyl); n is an integer selected to balance the oxidation state of M; and A is a suitable non-coordinating anionic cocatalyst or precursor. This catalyst system may form stereoregular olefin polymers including syndiotactic polymers of styrene and methylmethacrylate and isotactic copolymers of polar and nonpolar olefin monomers such as methylmethacrylate and styrene.

Marks, Tobin J.; Luo, Lubin; Yoon, Sung Cheol

2006-10-10

16

Early Transition Metal Oxides as Catalysts: Crossing Scales from Clusters to Single Crystals to Functioning Materials  

SciTech Connect

The overall goal of this program is to investigate the electronic structure and chemical bonding of early transition metal oxide clusters and use them as well-defined molecular models to obtain insight into properties and mechanisms of oxide catalysts, as well as to provide accurate spectroscopic and molecular information to verify theoretical methods used to predict materials properties. A laser vaporization cluster source is used to produce metal oxide clusters with different sizes, structures, and compositions. Well-defined inorganic polyoxometalate clusters in solution are transported in the gas phase using electrospray. Two state-of-the-art photoelectron spectroscopy apparatuses are used to interrogate the oxide clusters and polyoxometalate anions in the gas phase to obtain spectroscopic and electronic structure information. The experimental effort is assisted by theoretical calculations to understanding the structures, chemical bonding, and catalytical properties of the transition metal oxide clusters. The research approach combines novel and flexible experimental techniques and advanced theoretical/computational methodologies and seeks molecular-level information to aiding the design of new catalysts, as well as mechanistic understanding. We have focused on the investigation of tungsten oxide clusters containing three W atoms: W{sub 3}O{sub x}{sup -} (x = 7-11). A number of interesting findings have been made. We observed that the oxygen-poor W{sub 3}O8 cluster contains a localized W{sup 4+} center, which can be used as a molecular model for O-deficient defect sites. A chemisorption energy was obtained through density functional calculations for W{sub 3}O8 + O{sub 2} {yields} W{sub 3}O{sub 10} as -78 kcal/mol. We further found that the neutral stoichiometric W{sub 2}O{sub 6} and W{sub 3}O{sub 9} clusters do not react with O{sub 2} and they only form physi-sorbed complexes, W{sub 2}O{sub 6}(O{sub 2}) and W{sub 3}O{sub 9}(O{sub 2}). However, the negatively charged W{sub 2}O{sub 6}{sup -} and W{sub 3}O{sub 9}{sup -} clusters are found to form chemisorbed complexes due to the presence of the extra electron. Thus, the W{sub 2}O{sub 6}{sup -} and W{sub 3}O{sub 9}{sup -} negative clusters can be viewed as models for O{sub 2} interaction with a reduced W site (W{sup 5+}) on the oxide surface. These studies also led to the surprising observation of the first d-orbital aromatic clusters in W{sub 3}O{sub 9}{sup 2-} and Mo{sub 3}O{sub 9}{sup 2-}, which each contains a completely delocalized three-center two-electron bond made entirely made of the metal d orbitals. This last result was highlighted in both Chem & Eng. News and Nature. We further studied a series of small metalate anions using electrospray, including the hydroxo and methoxo oxometalate MO{sub 3}(OH){sup -} and MO{sub 3}(OCH{sub 3}){sup -}, and the dimetalates: M{sub 2}O{sub 7}{sup 2-}, MM{prime}O{sub 7}{sup 2-}, and M{sub 2}O{sub 7}{sup -} (M, M{prime} = Cr, Mo, and W).

Lai-Sheng Wang

2009-07-07

17

Probing the electronic structure of early transition metal oxide clusters: Molecular models towards mechanistic insights into oxide surfaces and catalysis  

Microsoft Academic Search

Selected recent works from the authors’ laboratory on the intrinsic electronic and structural properties of early transition metal oxide clusters are reviewed. These clusters provide well-defined molecular models pertinent to mechanistic understandings of complex oxide surface chemistry and catalysis. The energy gap evolution with cluster size was probed for the stoichiometric (TiO2)n?, (V2O5)n?, and (CrO3)n? clusters, and each system was

Hua-Jin Zhai; Lai-Sheng Wang

2010-01-01

18

Electronic structure of early transition-metal carbonyls: Gas-phase photoelectron spectroscopy of (η⁵-CâHâ)M(CO)â (M = V, Nb, Ta)  

Microsoft Academic Search

Gas-phase photoelectron spectroscopy is used to investigate the bonding between early transition metals and carbonyl and cyclopentadienyl ligands. The lowest ionization energy region contains two overlapping ionizations that arise from the two orbitals that are occupied according to the formal d⁴ metal configuration. However, the character of these ionizations is dominated by the carbonyls rather than by the metals, as

Dennis L. Lichtenberger; Hua-Jun Fan; Nadine E. Gruhn; Thomas E. Bitterwolf; Skip Gallagher

2000-01-01

19

METAL-NON METAL TRANSITIONS IN TRANSITION METAL COMPOUNDS.  

E-print Network

METAL-NON METAL TRANSITIONS IN TRANSITION METAL COMPOUNDS. THE ELECTRONIC PHASE TRANSITIONS IN FeS AND NiS J. M. D. COEY, H. ROUX-BUISSON and R. BRUSETTI Groupe des Transitions de Phases, C. N. R. S., B respectivement une transition de phasede premier ordre accompagneed'un changementde structureelectronique. La

Paris-Sud XI, Université de

20

FINAL TECHNICAL REPORT Synthetic, Structural and Mechanistic Investigations of Olefin Polymerization Catalyzed by Early Transition Metal Compounds  

SciTech Connect

The goal of this project is to develop new catalysts and provide understanding of ligand effects on catalyst composition in order to guide development of superior catalyst systems for polymerization of olefins. Our group is designing and synthesizing new “LX2”,“pincer” type ligands and complexing early transition metals to afford precatalysts. In a collaboration with Hans Brintzinger from the University of Konstanz, we are also examining the structures of the components of catalyst systems obtained from reaction of zirconocene dichlorides with aluminum alkyls and aluminum hydrides. Such systems are currently used commercially to produce polyolefins, but the nature of the active and dormant species as well as the mechanisms of their interconversions are not understood. New information on catalyst design and performance may lead to new types of polymers and/or new chemical transformations between hydrocarbons and transition metal centers, ultimately contributing to the development of catalytic reactions for the production of fuels, commodity and polymeric materials.

Bercaw, John E. [California Institute of Technology

2014-05-23

21

Transition Metal Compounds  

NASA Astrophysics Data System (ADS)

1. Localised and itinerant electrons in solids; 2. Isolated transition metal ions; 3. Transition metal ions in crystals; 4. Mott–Hubbard vc charge-transfer insulators; 5. Exchange interaction and magnetic structures; 6. Cooperative Jahn–Teller effect and orbital ordering; 7. Charge ordering in transition metal compounds; 8. Ferroelectrics, magnetoelectrics and multiferroics; 9. Doping of correlated systems and correlated metals; 10. Metal-insulator transitions; 11. Kondoeffect, mixed valence and heavy fermions; Appendix A. Some historical notes; Appendix B. A layman's guide to second quantization; Appendix C. Phase transitions and free energy expansion: Landau theory in a nutshell.

Khomskii, Daniel I.

2014-10-01

22

TRANSITION DE MOTT METAL-INSULATOR TRANSITIONS  

E-print Network

TRANSITION DE MOTT METAL-INSULATOR TRANSITIONS IN TRANSITION METAL OXIDES by D. B. McWHAN, A. MENTH oxydes de metaux de transition on observe une transition d'isolant a metal puis de metal a isolant de type Mott lorsque l'on augmentelenombre d'electrons d. Danslesysthe(V1-~Cr~)203une transition de Mott

Paris-Sud XI, Université de

23

Electronic and magnetic properties of early transition-metal substituted iron-cyclopentadienyl sandwich molecular wires: Parity-dependent half-metallicity  

NASA Astrophysics Data System (ADS)

Electronic and magnetic properties of early transition metals (V, Ti, Sc)-FekCpk + 1 sandwich molecular wires (SMWs) are investigated by means of ab initio calculations. It is found that all SMWs favor a ferromagnetic ground state. Significantly, V-FekCpk + 1 SMWs are either half-metallic or semiconducting, dependent upon the parity (even or odd) of the number (k) of Fe atoms in the unit cell of SMWs. This parity oscillation of conductive properties results from the combined effects of the band-folding and gap-opening at the Brillouin-zone boundary of one-dimensional materials. In contrast, Sc-FekCpk + 1 and Ti-FekCpk + 1 SMWs are always semiconducting. Our work may open up the way toward half metal/semiconductor heterostructures with perfect atomic interface.

Li, Yuanchang; Zhou, Gang; Wu, Jian; Duan, Wenhui

2011-07-01

24

Early Transition Metal Oxides as Catalysts: Crossing Scales from Clusters to Single Crystals to Functioning Materials  

SciTech Connect

The proportion of chemical industry processes using catalysts exceeds 80%. Current commercial heterogeneous catalysts are structurally and chemically complex and data gathered from them can seldom be interpreted with atomic-level precision. We seek to reduce the complexity of TMO catalysts to levels addressable and controllable at the atomic level, while maintaining intimate linkages with practical catalysis and catalytic materials. The focus of the proposed work is to gain a fundamental understanding of chemical transformations in order to design and construct new catalysts with more precise control of specific chemical reactions. We are employing an integrated experimental/theoretical approach to advance our current ability to understand, design, and control the catalytic and surface chemistry of transition metal oxides, specifically for redox and acid-base chemistries. The approach combines novel solid-state inorganic synthesis, surface science, experimental and theoretical/computational chemical physics, and mechanistic organic chemistry to address this complex and important challenge. Selected highlights from the results obtained in the last year are presented in the conference proceedings extended abstract.

Dixon, David A.; Dohnalek, Zdenek; Gutowski, Maciej S.; Hu, Jian Zhi; Iglesia, Enrique; Kay, Bruce D.; Liu, Jun; Peden, Charles HF; Wang, Lai; Wang, Yong; White, John M.; Bondarchuk, Oleksander A.; Herrera, Jose E.; Kim, J.; Kwak, Ja Hun; Stuchinskaya, T.; Zhai, Hua Jin; Chisolm, Claire N.; Macht, Josef

2007-05-20

25

Metal-insulator transitions  

Microsoft Academic Search

Metal-insulator transitions are accompanied by huge resistivity changes, even over tens of orders of magnitude, and are widely observed in condensed-matter systems. This article presents the observations and current understanding of the metal-insulator transition with a pedagogical introduction to the subject. Especially important are the transitions driven by correlation effects associated with the electron-electron interaction. The insulating phase caused by

Masatoshi Imada; Atsushi Fujimori; Yoshinori Tokura

1998-01-01

26

Oligocyclopentadienyl transition metal complexes  

SciTech Connect

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.

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

2002-01-18

27

Transition metals in silicon  

Microsoft Academic Search

A review is given on the diffusion, solubility and electrical activity of 3d transition metals in silicon. Transition elements (especially, Cr, Mn, Fe, Co, Ni, and Cu) diffuse interstitially and stay in the interstitial site in thermal equilibrium at the diffusion temperature. The parameters of the liquidus curves are identical for the Si:Ti — Si:Ni melts, indicating comparable silicon-metal interaction

Eicke R. Weber

1983-01-01

28

submitted to Phys. Rev. Lett. Strain and coordination effects in the adsorption properties of early transition metals  

E-print Network

- nificantly change the electronic and catalytic properties of these metal surfaces [1­7]. Strain effects occur. Considerations based on effective strain are also important to understand the reactivity of metallic compoundssubmitted to Phys. Rev. Lett. Strain and coordination effects in the adsorption properties of early

Pfeifer, Holger

29

Early diagenesis in differing depositional environments: The response of transition metals in pore water  

Microsoft Academic Search

The cycling of Fe, Mn, Ni, Co, Cu, Cr, V, and Mo during early diagenesis was investigated in sediments from five different depositional environments in the California Borderland. Dissolved Oâ, NO⁻â, NO⁻â, and SO²⁻â were also measured at each site to establish the position of redox boundaries pertinent to this study. Sites were chosen to allow the comparison of several

T. J. Shaw; J. M. Gieskes; R. A. Jahnke

1990-01-01

30

Synthesis, characterization and reactivity of early transition metal neo-pentoxides  

SciTech Connect

Titanium neo-pentoxide was isolated by the alcoholysis exchange between Ti(OCHMe{sub 2}){sub 4} and ONep. The molecule, [Ti(ONep){sub 4}]{sub 2}, was characterized using X-ray analysis and solution {sup 17}O, and {sup 47},{sup 49}Ti NMR spectroscopy. This dinuclear complex is the smallest Ti(OR){sub 4} isolated wherein each metal center is 5-coordinated. The molecule is highly soluble in standard solvents and volatile. The reactivity of this compound has been undertaken to compare with the ubiquitous Ti(O-I-Pr){sub 4}. The various compounds isolated and further NMR studies will be reported. Analogous routes to other M(ONep){sub n} will be reported as well.

Boyle, T.J.; Alam, T.M.; Scott, B.; Ziller, J.W. [Sandia National Labs., Albuquerque, NM (United States)

1997-12-31

31

Probing the electronic structure of early transition metal oxide clusters: Molecular models towards mechanistic insights into oxide surfaces and catalysis  

NASA Astrophysics Data System (ADS)

Selected recent works from the authors' laboratory on the intrinsic electronic and structural properties of early transition metal oxide clusters are reviewed. These clusters provide well-defined molecular models pertinent to mechanistic understandings of complex oxide surface chemistry and catalysis. The energy gap evolution with cluster size was probed for the stoichiometric (TiO 2) n-, (V 2O 5) n-, and (CrO 3) n- clusters, and each system was shown to approach the band gap of bulk oxides in a unique way. A variety of other model clusters have been characterized, such as the oxygen radical or diradical on a single W 6+ site in WO 4-/WO 4, the superoxide (WO 3) n(O 2-) complexes for dioxygen activation, and terminal versus bridging oxygen in M 3O 2- (M = Nb, Ta) clusters. Novel chemical bonding has been observed in a number of oxide clusters. The W 3O 9- and W 3O 92- clusters were found to possess d-orbital aromaticity, whereas ?-aromaticity was discovered in the Ta 3O 3- cluster.

Zhai, Hua-Jin; Wang, Lai-Sheng

2010-11-01

32

Transition Metal Switchable Mirror  

SciTech Connect

The switchable-mirrors technology was developed by Tom Richardson and Jonathan Slack of Berkeley Lab's Environmental Energy Technologies Division. By using transition metals rather than the rare earth metals used in the first metal-hydride switchable mirrors, Richardson and Slack were able to lower the cost and simplify the manufacturing process. Energy performance is improved as well, because the new windows can reflect or transmit both visible and infrared light. Besides windows for offices and homes, possible applications include automobile sunroofs, signs and displays, aircraft windows, and spacecraft. More information at: http://windows.lbl.gov/materials/chromogenics/default.htm

None

2009-01-01

33

Transition Metal Switchable Mirror  

SciTech Connect

The switchable-mirrors technology was developed by Tom Richardson and Jonathan Slack of Berkeley Lab's Environmental Energy Technologies Division. By using transition metals rather than the rare earth metals used in the first metal-hydride switchable mirrors, Richardson and Slack were able to lower the cost and simplify the manufacturing process. Energy performance is improved as well, because the new windows can reflect or transmit both visible and infrared light. Besides windows for offices and homes, possible applications include automobile sunroofs, signs and displays, aircraft windows, and spacecraft.

2009-08-21

34

Transition Metal Switchable Mirror  

ScienceCinema

The switchable-mirrors technology was developed by Tom Richardson and Jonathan Slack of Berkeley Lab's Environmental Energy Technologies Division. By using transition metals rather than the rare earth metals used in the first metal-hydride switchable mirrors, Richardson and Slack were able to lower the cost and simplify the manufacturing process. Energy performance is improved as well, because the new windows can reflect or transmit both visible and infrared light. Besides windows for offices and homes, possible applications include automobile sunroofs, signs and displays, aircraft windows, and spacecraft. More information at: http://windows.lbl.gov/materials/chromogenics/default.htm

None

2013-05-29

35

Transition Metal Switchable Mirror  

ScienceCinema

The switchable-mirrors technology was developed by Tom Richardson and Jonathan Slack of Berkeley Lab's Environmental Energy Technologies Division. By using transition metals rather than the rare earth metals used in the first metal-hydride switchable mirrors, Richardson and Slack were able to lower the cost and simplify the manufacturing process. Energy performance is improved as well, because the new windows can reflect or transmit both visible and infrared light. Besides windows for offices and homes, possible applications include automobile sunroofs, signs and displays, aircraft windows, and spacecraft.

None

2010-01-08

36

Calixarene supported transition metal clusters   

E-print Network

This thesis describes a series of calix[n]arene polynuclear transition metal and lanthanide complexes. Calix[4]arenes possess lower-rim polyphenolic pockets that are ideal for the complexation of various transition metal ...

Taylor, Stephanie Merac

2013-06-29

37

Metal to semiconductor transition in metallic transition metal dichalcogenides  

SciTech Connect

We report on tuning the electronic and magnetic properties of metallic transition metal dichalcogenides (mTMDCs) by 2D to 1D size confinement. The stability of the mTMDC monolayers and nanoribbons is demonstrated by the larger binding energy compared to the experimentally available semiconducting TMDCs. The 2D MX{sub 2} (M?=?Nb, Ta; X?=?S, Se) monolayers are non-ferromagnetic metals and mechanically softer compared to their semiconducting TMDCs counterparts. Interestingly, mTMDCs undergo metal-to-semiconductor transition when the ribbon width approaches to ?13?Å and ?7?Å for zigzag and armchair edge terminations, respectively; then these ribbons convert back to metal when the ribbon widths further decrease. Zigzag terminated nanoribbons are ferromagnetic semiconductors, and their magnetic properties can also be tuned by hydrogen edge passivation, whereas the armchair nanoribbons are non-ferromagnetic semiconductors. Our results display that the mTMDCs offer a broad range of physical properties spanning from metallic to semiconducting and non-ferromagnetic to ferromagnetic that is ideal for applications where stable narrow bandgap semiconductors with different magnetic properties are desired.

Li, Yan; Kang, Jun; Li, Jingbo, E-mail: jbli@semi.ac.cn [State Key Laboratory of Superlattice and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083 (China); Tongay, Sefaattin; Wu, Junqiao [Department of Materials Science and Engineering, University of California, Berkeley, California 94720 (United States); Yue, Qu [College of Science, National University of Defense Technology, Changsha 410073 (China)

2013-11-07

38

Electrical Conductivity in Transition Metals  

ERIC Educational Resources Information Center

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…

Talbot, Christopher; Vickneson, Kishanda

2013-01-01

39

THE METAL-NON-METAL TRANSITION Cavendish Laboratory, Cambridge  

E-print Network

THE METAL-NON-METAL TRANSITION N. F. MOTT Cavendish Laboratory, Cambridge RBsumB. -La transition. Abstract. -The metal-non-metal transition discussed in this paper is that which takes place the transition. Evidence that this is so for heavily doped semiconductorsand metal-ammonia is presented

Boyer, Edmond

40

Selenophene transition metal complexes  

SciTech Connect

This research shows that selenophene transition metal complexes have a chemistry that is similar to their thiophene analogs. Selenophene coordination has been demonstrated and confirmed by molecular structure in both the {eta}{sup 5}- and the {eta}{sup 1}(Se)-coordination modes. The reaction chemistry of selenophene complexes closely resembles that of the analogous thiophene complexes. One major difference, however, is that selenophene is a better donor ligand than thiophene making the selenophene complexes more stable than the corresponding thiophene complexes. The {sup 77}Se NMR chemical shift values for selenophene complexes fall within distinct regions primarily depending on the coordination mode of the selenophene ligand. In the final paper, the C-H bond activation of {eta}{sup 1}(S)-bound thiophenes, {eta}{sup 1}(S)-benzothiophene and {eta}{sup 1}(Se)-bound selenophenes has been demonstrated. The deprotonation and rearrangement of the {eta}{sup 1}(E)-bound ligand to the carbon bound L-yl complex readily occurs in the presence of base. Reprotonation with a strong acid gives a carbene complex that is unreactive towards nucleophilic attack at the carbene carbon and is stable towards exposure to air. The molecular structure of [Cp(NO)(PPh{sub 3})Re(2-benzothioenylcarbene)]O{sub 3}SCF{sub 3} was determined and contains a Re-C bond with substantial double bond character. Methyl substitution for the thienylcarbene or selenylcarbene gives a carbene that rearranges thermally to give back the {eta}{sup 1}(E)-bound complex. Based on these model reactions, a new mechanism for the H/D exchange of thiophene over the hydrodesulfurization catalyst has been proposed.

White, C.J.

1994-07-27

41

The structures of transition metal-transition metal alloys  

Microsoft Academic Search

A structure map using the average electron count and d orbital energy difference as indices is used to sort transition metal alloys of stoichiometry AB. The gross features of the map are mimicked by tight-binding calculations. The inclusion of s orbitals on the metal atoms appear to be important in the determination of alloy structure in some parts of the

Jeremy K. Burdett; Timothy J. McLarnan

1984-01-01

42

Pressure-Induced Electronic Phase Transitions Transition Metal Oxides and Rare Earth Metals  

E-print Network

Pressure-Induced Electronic Phase Transitions in Transition Metal Oxides and Rare Earth Metals Metal Oxides and Rare Earth Metals by Brian Ross Maddox Electron correlation can affect profound changes transition in a transition metal monoxide. iv #12;The lanthanides (the 4f metals also known as rare-earths

Islam, M. Saif

43

Valence Tautomeric Transition Metal Complexes  

Microsoft Academic Search

Valence d-orbital energies of the first row transition metals are close to the frontier ?-orbital energies of o-benzoquinones. Complexes prepared with quinone ligands most commonly have the quinone coordinated with the metal in the form of a semiquinonate (SQ) radical-anion or as a catecholate (Cat) dianion. In a few unique complexes it has been possible to observe intramolecular electron transfer

David N. Hendrickson; Cortlandt G. Pierpont

44

Transition metals in superheat melts  

NASA Technical Reports Server (NTRS)

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.

Jakes, Petr; Wolfbauer, Michael-Patrick

1993-01-01

45

Metal-insulator transitions: Orbital control  

NASA Astrophysics Data System (ADS)

On cooling, transition metal oxides often undergo a phase change from an electrically conducting to an insulating state. Now it is shown that the metal-insulator transition temperature of vanadium dioxide thin films can be controlled by applying strain.

Mizokawa, Takashi

2013-10-01

46

Approximating Metal-Insulator Transitions  

E-print Network

We consider quantum wave propagation in one-dimensional quasiperiodic lattices. We propose an iterative construction of quasiperiodic potentials from sequences of potentials with increasing spatial period. At each finite iteration step the eigenstates reflect the properties of the limiting quasiperiodic potential properties up to a controlled maximum system size. We then observe approximate metal-insulator transitions (MIT) at the finite iteration steps. We also report evidence on mobility edges which are at variance to the celebrated Aubry-Andre model. The dynamics near the MIT shows a critical slowing down of the ballistic group velocity in the metallic phase similar to the divergence of the localization length in the insulating phase.

C. Danieli; K. Rayanov; B. Pavlov; G. Martin; S. Flach

2014-05-06

47

TRANSITION METAL ACTIVATION AND FUNCTIONALIZATION OF CARBON-HYDROGEN BONDS  

E-print Network

TRANSITION METAL ACTIVATION AND FUNCTIONALIZATION OF CARBON-HYDROGEN BONDS William D. Jones, New York 14627 FOR #12;DOE Report, 1998-2001 2 William D. Jones Overview of Research Accomplishments will extend this work to #12;DOE Report, 1998-2001 3 William D. Jones other early metal compounds during

Jones, William D.

48

Radiationless processes in transition-metal complexes  

Microsoft Academic Search

This work applies recent theories of radiationless relaxation processes to the case of transition-metal complexes. Existing theories developed for understanding radiationless transitions in organic molecules separate coupling terms into electronic and vibrational factors. In this work the symmetry based selection rules on the coupling terms are examined since the high symmetry of many transition-metal complexes offers the possibility that strict

D. J. Robbins; A. J. Thomson

1973-01-01

49

Electronic Structures of Transition-Metal Complexes  

Microsoft Academic Search

The empirically determined values of the parameter Dq, which in transition-metal complexes, measure the influence of the ligands on the metal d-orbitals are interpreted theoretically. A quantitative treatment of ``the magnetic criterion of the bond type,'' is given. Values of Slater-Condon parameters for transition metal ions are tabulated.

L. E. Orgel

1955-01-01

50

Piperazine pivoted transition metal dithiocarbamates  

NASA Astrophysics Data System (ADS)

A quadridentate ligand disodium bis(2,2'-dithiopiperazinato-2,2'-diamino diethylamine) Na 2L 2 and its self assembled transition metal complexes of the type, M 2(L 2) 2 {M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II)} have been reported. The piperazine pivoted homodinuclear complexes have been characterized by a range of spectral, thermal, microanalytical and conductometric techniques. On the basis of IR and 1HNMR data a symmetrical bidentate coordination of the dithiocarbamato moiety has been observed in all the cases. The TGA profile of the ligand exhibits two stage thermolytic pattern although the complexes decompose in three steps, respectively. Metal sulfide is found to be the end product. The formation of homodinuclear complexes has been ascertained on the basis of FAB mass spectral data and a probable fragmentation pattern has been proposed. On the basis of UV-visible spectroscopic results and room temperature magnetic moment data a tetrahedral geometry has been proposed for all the complexes except for the Ni(II) and Cu(II) which are found to be square-planar.

Khan, Sadaf; Nami, Shahab A. A.; Siddiqi, K. S.

2008-03-01

51

Method for dry etching of transition metals  

DOEpatents

A method for dry etching of transition metals is disclosed. The method for dry etching of a transition metal (or a transition metal alloy such as a silicide) on a substrate comprises providing at least one nitrogen- or phosphorus-containing {pi}-acceptor ligand in proximity to the transition metal, and etching the transition metal to form a volatile transition metal/{pi}-acceptor ligand complex. The dry etching may be performed in a plasma etching system such as a reactive ion etching (RIE) system, a downstream plasma etching system (i.e. a plasma afterglow), a chemically-assisted ion beam etching (CAIBE) system or the like. The dry etching may also be performed by generating the {pi}-acceptor ligands directly from a ligand source gas (e.g. nitrosyl ligands generated from nitric oxide), or from contact with energized particles such as photons, electrons, ions, atoms, or molecules. In some preferred embodiments of the present invention, an intermediary reactant species such as carbonyl or a halide ligand is used for an initial chemical reaction with the transition metal, with the intermediary reactant species being replaced at least in part by the {pi}-acceptor ligand for forming the volatile transition metal/{pi}-acceptor ligand complex.

Ashby, C.I.H.; Baca, A.G.; Esherick, P.; Parmeter, J.E.; Rieger, D.J.; Shul, R.J.

1998-09-29

52

Method for dry etching of transition metals  

DOEpatents

A method for dry etching of transition metals. The method for dry etching of a transition metal (or a transition metal alloy such as a silicide) on a substrate comprises providing at least one nitrogen- or phosphorous-containing .pi.-acceptor ligand in proximity to the transition metal, and etching the transition metal to form a volatile transition metal/.pi.-acceptor ligand complex. The dry etching may be performed in a plasma etching system such as a reactive ion etching (RIE) system, a downstream plasma etching system (i.e. a plasma afterglow), a chemically-assisted ion beam etching (CAIBE) system or the like. The dry etching may also be performed by generating the .pi.-acceptor ligands directly from a ligand source gas (e.g. nitrosyl ligands generated from nitric oxide), or from contact with energized particles such as photons, electrons, ions, atoms, or molecules. In some preferred embodiments of the present invention, an intermediary reactant species such as carbonyl or a halide ligand is used for an initial chemical reaction with the transition metal, with the intermediary reactant species being replaced at least in part by the .pi.-acceptor ligand for forming the volatile transition metal/.pi.-acceptor ligand complex.

Ashby, Carol I. H. (Edgewood, NM); Baca, Albert G. (Albuquerque, NM); Esherick, Peter (Albuquerque, NM); Parmeter, John E. (Albuquerque, NM); Rieger, Dennis J. (Tijeras, NM); Shul, Randy J. (Albuquerque, NM)

1998-01-01

53

9 Metal to Non-metal Transitions in Solids and on Surfaces studied using Photoemission Spectroscopy  

E-print Network

9 Metal to Non-metal Transitions in Solids and on Surfaces studied using Photoemission Spectroscopy metal to non-metal transitions. (Thephrase `metal to non-metal transition' is used in this paper to denote a generic resistivity transition between metallic and non-metallic states, and vice versa

Redner, Sidney

54

Superconducting Metallic Glass Transition-Edge-Sensors  

NASA Technical Reports Server (NTRS)

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.

Hays, Charles C. (Inventor)

2013-01-01

55

Covalent functionalization of monolayered transition metal dichalcogenides by  

E-print Network

Covalent functionalization of monolayered transition metal dichalcogenides by phase engineering a simple and general method for covalent functionalization of two-dimensional transition metal of the transition metal dichalcogenide. The attachment of functional groups leads to dramatic changes

Muzzio, Fernando J.

56

Transition metal-silicate analogs of zeolites  

Microsoft Academic Search

The synthesis and characterization of three transition metal (Fe3+, Ti4+ and V4+)-silicate molecular sieves are discussed. The key factors for a successful incorporation of these metal ions in the growing silicate network during gel preparation\\/hydrothermal synthesis (e.g. avoidance of insoluble\\/sparingly soluble metal hydroxides\\/oxyhydroxides (Fe3+ and Ti4+) and alkali metal ions (Ti4+and V4+\\/5+)) as well as the effects of post synthesis

Paul Ratnasamy; Rajiv Kumar

1993-01-01

57

Environmental action during Romania's early transition years  

Microsoft Academic Search

As with other countries in ECE, Romania began its transition with some major environmental problems because legislation failed to deliver effective pollution controls. Although scarcely apparent during the last years of Communism, an ecological movement achieved early political success and some of the worst affected areas have now seen substantial improvements. In addition, the slow?down in the economy helped to

Simina Dragomirescu; Cristina Muica; David Turnock

1998-01-01

58

Transition metal fluorides: from superconductors to multiferroics.   

E-print Network

Transition metal fluorides represent an important family of complex solids displaying a variety of different properties and interesting phenomena. Despite their remarkable behaviour, these classes of materials have not ...

Drathen, Christina

2013-06-29

59

Density functionals and transition-metal atoms  

Microsoft Academic Search

Density-functional calculations on transition-metal atoms are problematic due to the numerous possible ways, having inequivalent densities, of occupying the d orbitals. The problem is compounded by the issue of real orbitals versus complex orbitals. In this work we systematize the application of density-functional theories to transition-metal atoms using a current-density-dependent functional. For all the single-determinantal angular momentum eigenstates of ground-state

Erin R. Johnson; Ross M. Dickson; Axel D. Becke

2007-01-01

60

Semiconducting Al transition-metal quasicrystals  

Microsoft Academic Search

We report on a class of icosahedral aluminum transition-metal (Al-TM) alloys with true semiconducting behavior. Our description of the structure of these icosahedral quasicrystals is based on the six-dimensional Katz-Gratias-Boudard (KGB) model of the face-centered-icosahedral (fci) quasicrystal and its rational approximants. The shell structure of the atomic surfaces in perpendicular space defines the chemical order of aluminum and transition-metal (TM)

M. Krajcí; J. Hafner

2003-01-01

61

Orbital Physics in Transition-Metal Oxides  

Microsoft Academic Search

An electron in a solid, that is, bound to or nearly localized on the specific atomic site, has three attributes: charge, spin, and orbital. The orbital represents the shape of the electron cloud in solid. In transition-metal oxides with anisotropic-shaped d-orbital electrons, the Coulomb interaction between the electrons (strong electron correlation effect) is of importance for understanding their metal-insulator transitions

Y. Tokura; N. Nagaosa

2000-01-01

62

Spectroscopy of mixed earlylate transition metal diatomics: ScNi, YPd, Caleb A. Arrington and Michael D. Morse  

E-print Network

Spectroscopy of mixed early­late transition metal diatomics: ScNi, YPd, and ZrCo Caleb A. Arrington the spectra of the jet-cooled transition metal diatomics ScNi, YPd, and ZrCo, which are isovalent species in these species is presented. © 1995 American Institute of Physics. I. INTRODUCTION The isovalent transition metal

Morse, Michael D.

63

PROTEIN-TRANSITION METAL ION NETWORKS  

Technology Transfer Automated Retrieval System (TEKTRAN)

Proteins obtained from agricultural sources were blended with divalent metal ions. Feather keratin, egg albumin, and wheat gluten had low, medium, and high levels of aspartic and glutamic acid, respectively, and FT-IR showed that the divalent transition metal ions Mn2+, Cu2+, and Zn2+ were tightly ...

64

Protein-Transition Metal Ion Networks  

Technology Transfer Automated Retrieval System (TEKTRAN)

Proteins obtained from agricultural sources were blended with divalent metal ions. Feather keratin, egg albumin, and wheat gluten showed increases of 2-3 times in modulus with addition of divalent transition metal ions Cu2+ and Zn2+. Increasing concentrations of ions resulted in increased stiffnes...

65

Molecular orbital calculations on transition metal clusters  

Microsoft Academic Search

Transition metal clusters have been subject of experimental and theoretical interest due to their catalytic activity, as well as their unusual physical properties. Semi-empirical extended Hückel molecular orbital calculations are presented for a series of small metal clusters with nuclearity ranging from 3 to 6. Naked and carbonylated clusters of Fe, Ru, and Os are studied. The charge transfer between

M. C. dos Santos; J. Albino O. de Aguiar

1989-01-01

66

Continuous and discontinuous metal-insulator transitions  

Microsoft Academic Search

In non-crystalline systems a continuous metal-insulator transition of Andersontype is frequently observed when the Fermi energy moves through a mobility edge. In crystalline systems, on the other hand, the activation energy for conduction should change discontinuously at the transition. The aim of this paper is to enquire under what conditions a discontinuous transition can occur in non-crystalline systems. It clearly

N. F. Mott

1978-01-01

67

Structures of large transition metal clusters  

Microsoft Academic Search

The present review surveys the results of X-ray diffraction studies of large stoichiometric transition metal clusters containing from 20 to 145 atoms in metal cores surrounded by ligand shells (72 compounds). Structures of such clusters have fragments of close packings (face-centered cubic (f.c.c.), hexagonal close (h.c.p.), and body-centered cubic (b.c.c.) packings) characteristic of crystalline bulk metals as well as mixed

O. A. Belyakova; Yu. L. Slovokhotov

2003-01-01

68

Microwave-assisted synthesis of transition metal phosphide  

DOEpatents

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

Viswanathan, Tito

2014-12-30

69

Transition Metal Nutrition: A Balance Between Deficiency and Toxicity  

E-print Network

333 Transition Metal Nutrition: A Balance Between Deficiency and Toxicity CHAPTER 10 CHAPTER: Transition Metal Nutrition334 I. INTRODUCTION Several transition metals1 , such as zinc (Zn)2 , iron (Fe of transition metal ions for biochemical functions is essen- tial as evidenced by the fact that metalloproteins

Hamel, Patrice

70

film across metal to insulator transition  

NASA Astrophysics Data System (ADS)

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.

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

2014-11-01

71

Disorder driven quantum phase transitions in transition metal oxides  

Microsoft Academic Search

We investigate the effect of disorder on a class of transition metal oxides described by a single orbital Hubbard model at half filling and away from half filling. The phases are characterized by the nature of the electronic and spin excitations. We calculate the local density of states, frequency and temperature-dependent conductivity and spin susceptibility as functions of disorder and

Kohjiro Kobayashi; Nandini Trivedi

2007-01-01

72

Intermultiplet transitions in rare-earth metals  

SciTech Connect

We report here on direct observations of intermultiplet (IM) transitions in the rare-earth metals, Pr, Nd and Tb, made using the chopper spectrometers at the Intense Pulsed Neutron Source of Argonne National Laboratory. Despite hydrogen contamination of the polycrystalline samples, we have observed inelastic peaks at small Q arising from IM transitions in Pr (approx.260 MeV), Nd (approx.242 MeV) and Tb (approx.256 MeV) although the latter has not yet been observed unambiguously. Future work will investigate the energy level structure and dynamical properties of rare-earth ions in stoichiometric metallic systems. 5 refs., 3 figs.

Stirling, W.G.; McEwen, K.A.; Loong, C.K.

1985-01-01

73

Upconversion Processes in Transition Metal and Rare Earth Metal Systems  

Microsoft Academic Search

The design and characterization of new luminescent materials is an active area of research. Here we present several current\\u000a topics in the area of upconversion by transition-metal and rare-earth-metal doped halide lattices. Following introduction\\u000a to the necessary background material related to upconversion mechanisms and kinetics, a series of topics are discussed which\\u000a illustrate some key areas of developing interest in

Daniel R. Gamelin; Hans U. Güdel

74

A characterization of the Anderson metal-insulator transport transition  

E-print Network

A characterization of the Anderson metal-insulator transport transition Fran¸cois Germinet1, Abel on the occasion of his Sixtieth Birthday Abstract. We investigate the Anderson metal-insulator transition a characterization of the metal-insulator transport transition. Moreover, we show that if there is such a transition

75

A characterization of the Anderson metal-insulator transport transition  

E-print Network

A characterization of the Anderson metal-insulator transport transition Fran#24;cois Germinet 1) provides a characterization of the metal-insulator transport transition. Moreover, we show metallic regime characterized by extended states. The energy Eme at which this metal-insulator transition

76

Mass fractionation processes of transition metal isotopes  

Microsoft Academic Search

Recent advances in mass spectrometry make it possible to utilise isotope variations of transition metals to address some important issues in solar system and biological sciences. Realisation of the potential offered by these new isotope systems however requires an adequate understanding of the factors controlling their isotope fractionation. Here we show the results of a broadly based study on copper

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

2002-01-01

77

High Pressure Synthesis of Transition Metal Carbonyls.  

ERIC Educational Resources Information Center

Presents an experiment which uses readily available starting materials and inexpensive equipment for synthesis of transition metal carbonyls at 1000 atm and which is intended to give students experience in techniques used in research and industry. Safety precautions are emphasized. (Author/SA)

Hagen, A. P.; And Others

1979-01-01

78

Correlated hybridization in transition metal complexes  

Microsoft Academic Search

We apply local orbital basis density functional theory (using SIESTA) coupled with a mapping to the Anderson impurity model to estimate the Coulomb assisted or correlated hybridization between transition metal d-orbitals and ligand sp-orbitals for a number of molecular complexes. We find remarkably high values which can have several physical implications including: (i) renormalization of effective single band or multiband

Arnd Hubsch; Jong-Chin Lin; Jianping Pan; Daniel L. Cox

2006-01-01

79

Correlated Hybridization in Transition-Metal Complexes  

Microsoft Academic Search

We apply local orbital basis density functional theory (using SIESTA) coupled with a mapping to the Anderson impurity model to estimate the Coulomb assisted or correlated hybridization between transition-metal d orbitals and ligand sp orbitals for a number of molecular complexes. We find remarkably high values which can have several physical implications including (i) renormalization of effective single-band or multiband

A. Hübsch; J. C. Lin; J. Pan; D. L. Cox

2006-01-01

80

Weak covalency in transition metal salts  

Microsoft Academic Search

A theory of weak covalency effects in transition metal salts based upon a configuration interaction approach is discussed. The configuration interaction scheme is compared and contrasted with the more usual molecular orbital or Hartree-Fock approach and shown to include important correlation effects omitted in the latter. The method is applied to calculate some properties (transferred hyperfine interaction effects and cubic

J Hubbard; D E Rimmer; F R A Hopgood

1966-01-01

81

Transition metals as catalysts of "autoxidation" reactions.  

PubMed

Superoxide (O2-), hydrogen peroxide (H2O2), and hydroxyl radical (.OH) produced from the "autoxidation" of biomolecules, such as ascorbate, catecholamines, or thiols, have been implicated in numerous toxicities. However, the direct reaction of dioxygen with the vast majority of biomolecules, including those listed above, is spin forbidden, a condition which imposes a severe kinetic limitation on this reaction pathway. Therefore, an alternate mechanism must be invoked to explain the "autoxidations" reactions frequently reported. Transition metals are efficient catalysts of redox reactions and their reactions with dioxygen are not spin restricted. Therefore it is likely that the "autoxidation" observed for many biomolecules is, in fact, metal catalyzed. In this paper we discuss: 1) the quantum mechanic, thermodynamic, and kinetic aspects of the reactions of dioxygen with biomolecules; 2) the involvement of transition metals in biomolecule oxidation; and 3) the biological implications of metal catalyzed oxidations. We hypothesize that true autoxidation of biomolecules does not occur in biological systems, instead the "autoxidation" of biomolecules is the result of transition metals bound by the biomolecules. PMID:2182396

Miller, D M; Buettner, G R; Aust, S D

1990-01-01

82

OH-transition metal bonding  

NASA Technical Reports Server (NTRS)

The bonding in both CuOH and AgOH has a covalent component that leads to a bent structure. The larger electrostatic stabilization in CuOH leads to a larger D(e) (2.83 eV) compared with AgOH (2.20 eV). Using Ni5OH to model chemisorption of OH on a Ni surface, it is found that OH adsorption in the fourfold hollow of Ni(100) leads to an OH normal to the surface, while adsorption directly above a Ni atom leads to a tilted OH. These qualitative Ni5OH calculations allow for speculation on the observed variation of OH on metal surfaces.

Bauschlicher, Charles W., Jr.

1986-01-01

83

Orbital physics in transition-metal oxides  

PubMed

An electron in a solid, that is, bound to or nearly localized on the specific atomic site, has three attributes: charge, spin, and orbital. The orbital represents the shape of the electron cloud in solid. In transition-metal oxides with anisotropic-shaped d-orbital electrons, the Coulomb interaction between the electrons (strong electron correlation effect) is of importance for understanding their metal-insulator transitions and properties such as high-temperature superconductivity and colossal magnetoresistance. The orbital degree of freedom occasionally plays an important role in these phenomena, and its correlation and/or order-disorder transition causes a variety of phenomena through strong coupling with charge, spin, and lattice dynamics. An overview is given here on this "orbital physics," which will be a key concept for the science and technology of correlated electrons. PMID:10775098

Tokura; Nagaosa

2000-04-21

84

Orbital Physics in Transition-Metal Oxides  

NASA Astrophysics Data System (ADS)

An electron in a solid, that is, bound to or nearly localized on the specific atomic site, has three attributes: charge, spin, and orbital. The orbital represents the shape of the electron cloud in solid. In transition-metal oxides with anisotropic-shaped d-orbital electrons, the Coulomb interaction between the electrons (strong electron correlation effect) is of importance for understanding their metal-insulator transitions and properties such as high-temperature superconductivity and colossal magnetoresistance. The orbital degree of freedom occasionally plays an important role in these phenomena, and its correlation and/or order-disorder transition causes a variety of phenomena through strong coupling with charge, spin, and lattice dynamics. An overview is given here on this ``orbital physics,'' which will be a key concept for the science and technology of correlated electrons.

Tokura, Y.; Nagaosa, N.

2000-04-01

85

Semiconductor to Metal to Half-Metal Transition in Pt-Embedded Zigzag Graphene Nanoribbons  

E-print Network

Semiconductor to Metal to Half-Metal Transition in Pt-Embedded Zigzag Graphene Nanoribbons Xiaohui-functional theory calculations. It is found that Pt-ZGNRs exhibit a semiconductor-metal-half-metal transition frequently adopted ways for tuning the properties of graphene. For instance, the effects of transition metal

Krasheninnikov, Arkady V.

86

(Electronic structure and reactivities of transition metal clusters)  

SciTech Connect

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.

Not Available

1992-01-01

87

Monolayer semiconducting transition metal dichalcogenide alloys: Stability and band bowing  

E-print Network

Monolayer semiconducting transition metal dichalcogenide alloys: Stability and band bowing Jun Kang) The stability and band bowing effects of two-dimensional transition metal dichalcogenide alloys MX2(1Àx)X0 2x (M-dimensional (2D) transition metal dichal- cogenides (TMDs) have become a focus of research efforts.1

Wu, Junqiao

88

Microscopic Structure of the Metal-Insulator Transition in  

E-print Network

Microscopic Structure of the Metal-Insulator Transition in Two Dimensions S. Ilani,* A. Yacoby, D the underlying spatial structure of the metal-insulator transition in two dimensions. The measurements show that as we approach the transition from the metallic side, a new phase emerges that consists of weakly

Yacoby, Amir

89

Contemporary Mathematics The Anderson metal-insulator transport transition  

E-print Network

Contemporary Mathematics The Anderson metal-insulator transport transition Fran#24;cois Germinet and Abel Klein Abstract. We discuss a new approach to the metal-insulator transition for random operators exponent #12;(E) provides a characterization of the metal-insulator transport transition

90

THEORY OF MOTTTRANSITION : APPLICATION S TO TRANSITION METAL OXIDES  

E-print Network

125 THEORY OF MOTTTRANSITION : APPLICATION S TO TRANSITION METAL OXIDES M. CYROT Institut Laue discutons l'application de la théorie aux oxydes de métaux de transition. Abstract. 2014 We study the metal of the metal insulator transition is band splitting. For large values of the ratio U/W, the material remains

Paris-Sud XI, Université de

91

Metal-Insulator Transitions at Surfaces Michael Potthoff  

E-print Network

Metal-Insulator Transitions at Surfaces Michael Potthoff Lehrstuhl Festk¨orpertheorie, Institut f¨ur Physik, Humboldt-Universit¨at zu Berlin, Germany Abstract. Various types of metal-insulator transitions that for the correlation-driven Mott metal-insulator transition the surface phase diagram should be expected to have

Potthoff, Michael

92

Quantum-Mechanical Force Laws for Transition Metals in Biomolecules  

Microsoft Academic Search

Transition metal ions, complexed by ligand molecules, play crucial roles in all known forms of life. For example, the active sites in many proteins are transition metals. Simulation of protein structure and function, as well as the design of new functional biomolecules, requires force fields that can treat transition metals accurately. This paper describes a method for predicting the functional

Anders E. Carlsson

1998-01-01

93

Metal-insulator transition in vanadium dioxide  

Microsoft Academic Search

The basic physical parameters which govern the metal-insulator transition in vanadium dioxide are determined through a review of the properties of this material. The major importance of the Hubbard intra-atomic correlation energy in determining the insulating phase, which was already evidenced by studies of the magnetic properties of V1-xCrxO2 alloys, is further demonstrated from an analysis of their electrical properties.

A. Zylbersztejn; N. F. Mott

1975-01-01

94

Impurity effects in transition metal silicides  

NASA Technical Reports Server (NTRS)

Impurities can affect the properties of silicides directly by virtue of their presence. Impurities can also influence the processes by which silicides are formed. The effect of impurities on the reaction of transition metal films with a silicon substrate induced by thermal annealing are well documented. The interpretation of these results is discussed. It is shown that impurity redistribution is a major factor in determining how significant the effect of an impurity is. Redistribution observed for dopant impurities is also discussed.

Lien, C.-D.; Nicolet, M.-A.

1984-01-01

95

Correlated Hybridization in Transition-Metal Complexes  

Microsoft Academic Search

We apply local orbital basis density functional theory (using SIESTA) coupled\\u000awith a mapping to the Anderson impurity model to estimate the Coulomb assisted\\u000aor correlated hybridization between transition metal d-orbitals and ligand\\u000asp-orbitals for a number of molecular complexes. We find remarkably high values\\u000awhich can have several physical implications including: (i) renormalization of\\u000aeffective single band or multiband

A. Hübsch; J. C. Lin; J. Pan; D. L. Cox

2006-01-01

96

The Electronic Structure of Transition Metal Carbides  

Microsoft Academic Search

Transition metal carbides, particularly WC, are important because of their extreme physical properties. Complete spectral data was needed too fully understand the bonding and electronic structure in these compounds. Soft x-ray emission spectroscopy (SXES) was used to probe the band structures of the tungsten carbides WC and W_2C near the carbon 1s threshold. Total electron yield (TEY) and total fluorescence

Shane Stadler; D. L. Ederer; R. P. Winarski; T. A. Callcott; M. M. Grush; A. Moewes; R. C. C. Perera

1998-01-01

97

Single-layer transition metal sulfide catalysts  

DOEpatents

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

Thoma, Steven G. (Albuquerque, NM)

2011-05-31

98

Lanthanoid-transition-metal bonding in bismetallocenes.  

PubMed

Bismetallocenes [Cp2 LuReCp2 ] and [Cp*2 LaReCp2 ] (Cp=cyclopentadienyl; Cp*=pentamethylcyclopentadienyl) were prepared using different synthetic strategies. Salt metathesis-performed in aromatic hydrocarbons to avoid degradation pathways caused by THF-were identified as an attractive alternative to alkane elimination. Although alkane elimination is more attractive in the sense of its less elaborate workup, the rate of the reaction shows a strong dependence on the ionic radius of Ln(3+) (Ln=lanthanide) within a given ligand set. Steric hindrance can cause a dramatic decrease in the reaction rate of alkane elimination. In this case, salt metathesis should be considered the better alternative. Covalent bonding interactions between the Ln and transition-metal (TM) cations has been quantified on the basis of the delocalization index. Its magnitude lies within the range characteristic for bonds between transition metals. Secondary interactions were identified between carbon atoms of the Cp ligand of the transition metal and the Ln cation. Model calculations clearly indicated that the size of these interactions depends on the capability of the TM atom to act as an electron donor (i.e., a Lewis base). The consequences can even be derived from structural details. The observed clear dependency of the Lu?Ru and interfragment Lu?C bonding on the THF coordination of the Lu atom points to a tunable Lewis acidity at the Ln site, which provides a method of significantly influencing the structure and the interfragment bonding. PMID:24500974

Butovskii, Mikhail V; Oelkers, Benjamin; Bauer, Tobias; Bakker, Jacinta M; Bezugly, Viktor; Wagner, Frank R; Kempe, Rhett

2014-03-01

99

Corrosion behavior of mesoporous transition metal nitrides  

SciTech Connect

Transition metal nitrides (TMN) have many desirable characteristics such as high hardness and good thermal stability under reducing conditions. This work reports an initial survey of the chemical stability of mesoporous TMNs (TM=Nb, V, Cr and Ti) in water at 80 °C at neutral, acidic and alkaline pH. The mesoporous TMNs had specific surface areas of 25–60 m{sup 2}/g with average pore sizes ranging from 10 to 50 nm. The high surface areas of these materials enhance the rate of corrosion per unit mass over that of a bulk material, making detection of corrosion much easier. The products were characterized by Rietveld refinement of powder X-ray diffraction (PXRD) patterns and by scanning electron microscopy (SEM). Several nitrides have corrosion rates that are, within error, not distinguishable from zero (±1 Å/day). Of the nitrides examined, CrN appears to be the most corrosion resistant under acidic conditions. None of the nitrides studied are corrosion resistant under alkaline conditions. - Graphical abstract: Corrosion behavior of mesoporous transition metal nitrides (TM=Nb, V, Cr and Ti) in acidic and alkaline solutions at 80 °C for 2 weeks. Display Omitted - highlights: • Corrosion rates of mesoporous transition metal nitrides in aqueous solution is reported. • The mesoporous TMNs had surface areas of 25–60 m{sup 2}/g. • CrN is the most corrosion resistant under the conditions studied.

Yang, Minghui, E-mail: m.yang@cornell.edu [Department of Chemistry, Cornell University, Ithaca 14853-1301, NY (United States); Allen, Amy J.; Nguyen, Minh T. [Department of Chemistry, Cornell University, Ithaca 14853-1301, NY (United States); Ralston, Walter T. [College of Chemistry, University of California, Berkeley 94720-1460, CA (United States); MacLeod, Michelle J. [Department of Chemistry, Massachusetts Institute of Technology, Cambridge 02139-4307, MA (United States); DiSalvo, Francis J., E-mail: fjd3@cornell.edu [Department of Chemistry, Cornell University, Ithaca 14853-1301, NY (United States)

2013-09-15

100

Adsorbate diffusion on transition metal nanoparticles.  

PubMed

Diffusion of adsorbates on transition metal nanoparticles is a precursor process for heterogeneously catalyzed reactions, and as a result, an atomistic understanding of the diffusion mechanism is very important. We systematically studied adsorption and diffusion of atomic and diatomic species (H, C, N, O, CO, and NO) on nanometer-sized Pt and Cu nanoparticles with different sizes and shapes using density functional theory calculations. We show that nanoparticles bind adsorbates more strongly than the corresponding extended single crystal metal surfaces. We find that there is a Brønsted-Evans-Polanyi-type linear correlation between the transition state energy and the initial state energy for adsorbate diffusion across the edges of Pt and Cu nanoparticles. We further show that the barrier for adsorbate diffusion across the nanoparticles edges can be estimated by the binding energy of the adsorbate on the nanoparticles. These results provide useful insights for understanding diffusion-mediated chemical reactions catalyzed by transition metal nanoparticles, which are widely used in heterogeneous catalysis. PMID:25422876

Peng, Guowen; Mavrikakis, Manos

2015-01-14

101

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

E-print Network

Computational Study of Metal Contacts to Monolayer Transition-Metal Dichalcogenide Semiconductors 2D materials, monolayer transition-metal dichalcogenide (mTMD) semiconductors with intrinsic bandV; see Fig. 2(a)] for use as channel materials in digital applica- tions, monolayer transition-metal

102

PHYSICAL REVIEW B 88, 155128 (2013) Plasmons in metallic monolayer and bilayer transition metal dichalcogenides  

E-print Network

PHYSICAL REVIEW B 88, 155128 (2013) Plasmons in metallic monolayer and bilayer transition metal transition metal dichalco- genides (TMDCs) using time dependent density functional theory in the random phase,2 A particularly interesting class of 2D materials are the transition metal dichalcogenides (TMDC) whose electronic

Thygesen, Kristian

2013-01-01

103

Atomic layer deposition of transition metals.  

PubMed

Atomic layer deposition (ALD) is a process for depositing highly uniform and conformal thin films by alternating exposures of a surface to vapours of two chemical reactants. ALD processes have been successfully demonstrated for many metal compounds, but for only very few pure metals. Here we demonstrate processes for the ALD of transition metals including copper, cobalt, iron and nickel. Homoleptic N,N'-dialkylacetamidinato metal compounds and molecular hydrogen gas were used as the reactants. Their surface reactions were found to be complementary and self-limiting, thus providing highly uniform thicknesses and conformal coating of long, narrow holes. We propose that these ALD layers grow by a hydrogenation mechanism that should also operate during the ALD of many other metals. The use of water vapour in place of hydrogen gas gives highly uniform, conformal films of metal oxides, including lanthanum oxide. These processes should permit the improved production of many devices for which the ALD process has previously not been applicable. PMID:14578877

Lim, Booyong S; Rahtu, Antti; Gordon, Roy G

2003-11-01

104

Metal-insulator transition in holography  

E-print Network

We exhibit an interaction-driven metal-insulator quantum phase transition in a holographic model. Use of a helical lattice enables us to break translation invariance while preserving homogeneity. The metallic phase is characterized by a sharp Drude peak and a d.c. resistivity that increases with temperature. In the insulating phase the Drude spectral weight is transferred into a `mid-infrared' peak and to energy scales of order the chemical potential. The d.c. resistivity now decreases with temperature. In the metallic phase, operators breaking translation invariance are irrelevant at low energy scales. In the insulating phase, translation symmetry breaking effects are present at low energies. We find the near horizon extremal geometry that captures the insulating physics.

Aristomenis Donos; Sean A. Hartnoll

2013-01-19

105

Optical study of orbital excitations in transition-metal oxides  

Microsoft Academic Search

The orbital excitations of a series of transition-metal compounds are studied by means of optical spectroscopy. Our aim was to identify signatures of collective orbital excitations by comparison with experimental and theoretical results for predominantly local crystal-field excitations. To this end, we have studied TiOCl, RTiO3 (R = La, Sm and Y), LaMnO3, Y2BaNiO5, CaCu2O3 and K4Cu4OCl10, ranging from early

R. Rückamp; E. Benckiser; M. W. Haverkort; H. Roth; T. Lorenz; A. Freimuth; L. Jongen; A. Möller; G. Meyer; P. Reutler; B. Büchner; A. Revcolevschi; S.-W. Cheong; C. Sekar; G. Krabbes; M. Grüninger

2005-01-01

106

Early Predictors of School Performance Declines at School Transition Points  

Microsoft Academic Search

This longitudinal study followed students (n = 265) from kindergarten through seventh grade and examined early social and academic predictors of school performance at two normative school transitions. Questions addressed include: (a) are there changes in students' school performance over time, especially at school transition points; (b) are changes in school performance dependent on sociodemographic factors; and, (c) does early

Diane Malaspina; Sara E. Rimm-Kaufman

2008-01-01

107

Smooth phase transitions in the early universe  

E-print Network

We apply a quadratic teleparallel torsion scalar of the $f(T)=T+\\alpha T^{2}$ field equations to the flat FRW model. We assume two perfect fluid components, the matter component has a fixed equation of state (EoS), while the torsion component has a dynamical EoS. We obtain an effective scale factor allowing an early stage of an inflationary vacuum, while it pushes the inflation to end naturally at later stage turning the universe to a matter dominant phase. The model represents an alternative to inflation models. However, it does not require slow roll conditions to end the inflation phase. We perform a standard cosmological study to examine the cosmic evolution. In addition, we study the effective EoS. The study shows consistent results confirming a smooth phase transition from inflation to matter dominant universe. We consider the case when the torsion is made of a scalar field. This treatment enables us to study the quadratic effect of $f(T)$ on the potential patterns of the scalar field. At the limit $\\alpha \\rightarrow 0$ the potential is dominated by the kinetic term and coincides with the quadratic inflation. Both cosmological and scalar field analysis show consistent results.

G. G. L. Nashed; W. El Hanafy; Sh. Kh. Ibrahim

2014-11-09

108

Smooth phase transitions in the early universe  

E-print Network

We apply a quadratic teleparallel torsion scalar of the $f(T)=T+\\alpha T^{2}$ field equations to the flat FRW model. We assume two perfect fluid components, the matter component has a fixed equation of state (EoS), while the torsion component has a dynamical EoS. We obtain an effective scale factor allowing an early stage of an inflationary vacuum, while it pushes the inflation to end naturally at later stage turning the universe to a matter dominant phase. The model represents an alternative to inflation models. However, it does not require slow roll conditions to end the inflation phase. We perform a standard cosmological study to examine the cosmic evolution. In addition, we study the effective EoS. The study shows consistent results confirming a smooth phase transition from inflation to matter dominant universe. We consider the case when the torsion is made of a scalar field. This treatment enables us to study the quadratic effect of $f(T)$ on the potential patterns of the scalar field. At the limit $\\alp...

Nashed, G G L; Ibrahim, Sh Kh

2014-01-01

109

Ultrafast photophysics of transition metal complexes.  

PubMed

The properties of transition metal complexes are interesting not only for their potential applications in solar energy conversion, OLEDs, molecular electronics, biology, photochemistry, etc. but also for their fascinating photophysical properties that call for a rethinking of fundamental concepts. With the advent of ultrafast spectroscopy over 25 years ago and, more particularly, with improvements in the past 10-15 years, a new area of study was opened that has led to insightful observations of the intramolecular relaxation processes such as internal conversion (IC), intersystem crossing (ISC), and intramolecular vibrational redistribution (IVR). Indeed, ultrafast optical spectroscopic tools, such as fluorescence up-conversion, show that in many cases, intramolecular relaxation processes can be extremely fast and even shorter than time scales of vibrations. In addition, more and more examples are appearing showing that ultrafast ISC rates do not scale with the magnitude of the metal spin-orbit coupling constant, that is, that there is no heavy-atom effect on ultrafast time scales. It appears that the structural dynamics of the system and the density of states play a crucial role therein. While optical spectroscopy delivers an insightful picture of electronic relaxation processes involving valence orbitals, the photophysics of metal complexes involves excitations that may be centered on the metal (called metal-centered or MC) or the ligand (called ligand-centered or LC) or involve a transition from one to the other or vice versa (called MLCT or LMCT). These excitations call for an element-specific probe of the photophysics, which is achieved by X-ray absorption spectroscopy. In this case, transitions from core orbitals to valence orbitals or higher allow probing the electronic structure changes induced by the optical excitation of the valence orbitals, while also delivering information about the geometrical rearrangement of the neighbor atoms around the atom of interest. With the emergence of new instruments such as X-ray free electron lasers (XFELs), it is now possible to perform ultrafast laser pump/X-ray emission probe experiments. In this case, one probes the density of occupied states. These core-level spectroscopies and other emerging ones, such as photoelectron spectroscopy of solutions, are delivering a hitherto unseen degree of detail into the photophysics of metal-based molecular complexes. In this Account, we will give examples of applications of the various methods listed above to address specific photophysical processes. PMID:25646968

Chergui, Majed

2015-03-17

110

The Early History of Chondritic Metal  

NASA Astrophysics Data System (ADS)

Recently several related studies of chondritic metal were performed in order to obtain information on its origin and history. Most chondritic metal grains contain inclusions such as silica, chromite, and phosphate. Some inclusions in metal of low petrographic type chondrites contain chain-like structures which suggest that metal agglomerated from relic grains (Perron et al., 1989). Rb-Sr studies on chondritic metal show evolved initial ^87Sr (Podosek et al., 1991). Chronometric information can be obtained from studies of fission Xe from extinct ^244Pu, radiogenic ^129Xe from extinct ^129I, and radiogenic ^40Ar from long-lived ^40K. Therefore, the study of noble gas in chondritic metal can provide independent information on origin and thermal history. Some constraints on the origin and thermal history of metal which are based on detailed noble gas studies are discussed. High-purity (>99.5% by microscopic inspection) metal separates from H3.8 Dhajala (Dh), H4 Ste Marguerite (SM), H4 Forest Vale (FV), and H6 Estacado (Es), were obtained and studied for Ar and Xe isotopic abundances. They contain several noble gas components: fission Xe due to ^244Pu recoils and ^244Pu in inclusions, FVM-Xe (Marti et al., 1989), radiogenic ^129Xe, and radiogenic ^40Ar, together with in situ spallogenic products. 1). The ^244Pu fission Xe record: ^244Pu fission Xe which recoiled from adjacent phosphates is observed in decreasing amounts as Dh > FV=SM >> Es. The release of substantial amounts of ^244Pu-derived fission Xe at low temperatures (600 degrees C) in H4 metal implies that these metal grains were never heated to 600 degrees C after the decay of ^244Pu. 2). FVM-Xe: The metal of low petrographic type chondrites (H3 and 4) contains the novel component FVM-Xe (Marti et al., 1989). The most plausible source of FVM-Xe is a mixture of a ^235U neutron- induced fission Xe component with solar Xe (Kim and Marti, 1992). The phosphate separate from Forest Vale that contains most uranium does not show a neutron irradiation effect (Lavielle et al., 1992). Therefore the neutron irradiation occurred before the Xe closure time of phosphates. Possible sources of neutrons include: secondary neutrons produced by proto-solar activity and neutrons produced by fission of transuranic elements. 3). Radiogenic ^129Xe: All chondritic metals show ^129Xe(sub)r excesses, but the amounts of retained radiogenic ^129Xe(sub)r decrease with increasing petrographic type. The ratios ^129Xe/^132Xe in metal phases are not higher than those of bulk samples, indicating that metamorphic events may have taken place after decay of much of the ^129I. However, Estacado metal was not totally melted during metamorphism because its ^129Xe(sub)r is associated with inclusions. 4). Radiogenic ^40Ar: The amounts of radiogenic ^40Ar are very similar in the different petrographic types as expected for a parent with long half life. Also, the metamorphic event did not strongly fractionate potassium in the metal. In conclusion, acceptable models for the origin of chondritic metal need to consider the following constraints: Before or during accretion in the solar system, nebular materials including metal were exposed to a neutron fluence (>10^16 n/cm^2). After accretion of these early metal grains, secondary processing and metamorphism occurred, and the high petrographic types (H6) lost most of their fission Xe together with FVM-Xe and trapped gases. However, H4 metal was not heated to 600 degrees C after the decay of ^244Pu. References Kim J. S. and Marti K. (1992) Lunar Planet. Sci. (abstract) 23, 689. Lavielle B., Marti K., Pellas P., and Perron C. (1992) Search for 248Cm in the early solar system. Meteoritics (in Press). Marti K., Kim J. S., Lavielle B., Pellas P., and Perron C. (1989) Z. Naturforsch. 44a, 963-967. Perron C., Bourot-Denise M., Pellas P., Marti K., Kim J. S., and Lavielle B. (1989) Lunar Planet. Sci. (abstract) 20, 838. Podosek F. A., Brannon J. C., Perron C., and Pellas P. (1991) Lunar Planet. Sci. (abstract) 22, 1081.

Kim, J. S.

1992-07-01

111

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

SciTech Connect

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

Scalettar, Richard T.; Pickett, Warren E.

2004-07-01

112

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

NASA Astrophysics Data System (ADS)

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

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

1981-05-01

113

Diagnostic Transitions from Childhood to Adolescence to Early Adulthood  

ERIC Educational Resources Information Center

Background: Quantifying diagnostic transitions across development is needed to estimate the long-term burden of mental illness. This study estimated patterns of diagnostic transitions from childhood to adolescence and from adolescence to early adulthood. Methods: Patterns of diagnostic transitions were estimated using data from three prospective,…

Copeland, William E.; Adair, Carol E.; Smetanin, Paul; Stiff, David; Briante, Carla; Colman, Ian; Fergusson, David; Horwood, John; Poulton, Richie; Costello, E. Jane; Angold, Adrian

2013-01-01

114

Routines and Transitions: A Guide for Early Childhood Professionals  

ERIC Educational Resources Information Center

In early childhood settings, children spend over 50 percent of their time on handwashing, dressing, napping, and other routines and transitions. "Routines and Transitions" is a guide to help turn these routine daily activities into learning experiences. By using transitions wisely, providers not only help children develop skills, but also run a…

Malenfont, Nicole

2006-01-01

115

Nonpolar resistance switching of metal\\/binary-transition-metal oxides\\/metal sandwiches: Homogeneous\\/inhomogeneous transition of current distribution  

Microsoft Academic Search

Exotic features of a metal\\/oxide\\/metal sandwich, which will be the basis for a drastically innovative nonvolatile memory device, is brought to light from a physical point of view. Here the insulator is one of the ubiquitous and classic binary-transition-metal oxides (TMO), such as Fe2O3 , NiO , and CoO . The sandwich exhibits a resistance that reversibly switches between two

I. H. Inoue; S. Yasuda; H. Akinaga; H. Takagi

2008-01-01

116

Metallicity Evolution in the Early Universe  

E-print Network

Observations of the damped Lya systems provide direct measurements on the chemical enrichment history of neutral gas in the early universe. In this Letter, we present new measurements for four damped Lya systems at high redshift. Combining these data with [Fe/H] values culled from the literature, we investigate the metallicity evolution of the universe from z~1.5-4.5. Contrary to our expectations and the predictions of essentially every chemical evolution model, the N(HI)-weighted mean [Fe/H] metallicity exhibits minimal evolution over this epoch. For the individual systems, we report tentative evidence for an evolution in the unweighted [Fe/H] mean and the scatter in [Fe/H] with the higher redshift systems showing lower scatter and lower typical [Fe/H] values. We also note that no damped Lya system has [Fe/H] < -2.7 dex. Finally, we discuss the potential impact of small number statistics and dust on our conclusions and consider the implications of these results on chemical evolution in the early universe.

Jason X. Prochaska; Arthur M. Wolfe

2000-04-13

117

ccsd00002151, Modelisation of transition and noble metal vicinal  

E-print Network

ccsd­00002151, version 1 ­ 25 Jun 2004 Modelisation of transition and noble metal vicinal surfaces of transition and noble metal vicinal surfaces 3 the Density Functional Theory (DFT) or the Tight Binding Solides, Universit#19;e Paris Sud, F-91 405 Orsay, France #12; Abstract. The energetics of transition

118

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

119

Giant Intrinsic Spin Hall Effect in Transition Metal Compounds  

E-print Network

spin Hall conductiv- ity (SHC) and the d-orbital Hall conductivity (OHC) in metallic d-electron systemsGiant Intrinsic Spin Hall Effect in Transition Metal Compounds H. KONTANI1 , T. TANAKA1 , D theoretical study of the SHE in transition metal compounds based on a realistic tight- binding model

Katsumoto, Shingo

120

Transitions for Young Children: Creating Connections across Early Childhood Systems  

ERIC Educational Resources Information Center

Smooth early childhood transitions are key to ensuring positive outcomes for young children the world over--but in today's fragmented early education systems, it's difficult to ensure continuity among programs and services. Early childhood professionals will help change that with this book, the first to propose a comprehensive, practical framework…

Kagan, Sharon Lynn, Ed.; Tarrant, Kate, Ed.

2010-01-01

121

Cosmological Consequences of QCD Phase Transition(s) in Early Universe  

SciTech Connect

We discuss the cosmological consequences of QCD phase transition(s) on the early universe. We argue that our recent knowledge about the transport properties of quark-gluon plasma (QGP) should thraw additional lights on the actual time evolution of our universe. Understanding the nature of QCD phase transition(s), which can be studied in lattice gauge theory and verified in heavy ion experiments, provides an explanation for cosmological phenomenon stem from early universe.

Tawfik, A. [ECTP, Egyptian Center for Theoretical Physics, MTI Modern University, Mukattam Cairo (Egypt)

2009-04-17

122

Metal Insulator transition in Vanadium Dioxide  

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

123

The atomic structure of transition metal clusters  

SciTech Connect

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

Riley, S.J.

1995-08-01

124

Understanding structure and bonding in early actinide 6d(0)5f0 MX6q (M = Th-Np; X = H, F) complexes in comparison with their transition metal 5d0 analogues.  

PubMed

The relationship between structure and bonding in actinide 6d(0)5f(0) MX(6)(q)() complexes (M = Th, Pa, U, Np; X = H, F; q = -2,-1, 0, +1) has been studied, based on density functional calculations with accurate relativistic actinide pseudopotentials. The detailed comparison of these prototype systems with their 5d(0) transition metal analogues (M = Hf, Ta, W, Re) reveals in detail how the 5f orbitals modify the structural preferences of the actinide complexes relative to the transition metal systems. Natural bond orbital analyses on the hydride complexes indicate that 5f orbital involvement in sigma-bonding favors classical structures based on the octahedron, while d orbital contributions to sigma-bonding favor symmetry lowering. The respective roles of f and d orbitals are reversed in the case of pi-bonding, as shown for the fluoride complexes. PMID:15725014

Straka, Michal; Hrobárik, Peter; Kaupp, Martin

2005-03-01

125

Anions of Transition Metal Cluster/Benzene Complexes  

NASA Astrophysics Data System (ADS)

We report the anion photoelectron spectra of several transition metal atom or cluster/benzene anionic complexes. These species can serve as preliminary models for assessing the interaction between transition metal atoms/clusters and graphitic surfaces, especially in regard to how this interaction affects the magnetic moments of transition metal atoms or clusters. We are guided in this work by the calculations of Jena, Khanna, and Rao.

Bowen, Kit

2002-03-01

126

STM images of transition metal surfaces: Theoretical study  

Microsoft Academic Search

We present a theoretical study of the influence of d orbitals on the evolution of the current tunnelling between the transition\\u000a metal STM tip and the transition metal surface. This problem is considered for the system formed by Ni(001) surface and Pt\\u000a tip. We have found that the tunnelling between d orbitals of the transition metal surface and of the

L. Jurczyszyn; B. Stankiewicz

1999-01-01

127

Transition metal-ligand bonding. II  

NASA Technical Reports Server (NTRS)

The nature of the bonding of CO, H2O, and NH3 to transition metal atoms is analyzed using the constrained-space-orbital-variation (CSOV) technique. The cooperative effects for Ni(CO)2 are found to be different than those for Ni(H2O)2. The bonding between neutral systems and the positive ions is found to be quite different; NiCO(+) has little pi bonding, while NiCO has strong pi bonding. The positive ion of NiH2O is far more strongly bound than the neutral, while for NiCO the positive ion and neutral are bound by about the same energy.

Bauschlicher, C. W., Jr.

1986-01-01

128

Theoretical studies of transition metal dimers  

NASA Technical Reports Server (NTRS)

The CASSCF approach was used to perform the MCSCF calculations for a number of transition metal dimers, including the Sc2, Ti2, Cr2, Cu2, TiV, Y2, Nb2, and Mo2 molecules; in addition, CASSCF/CI calculations were carried out for Sc2, Ti2, Cu2, and Y2. The CASSCF procedure is shown to provide a consistent set of calculations for these molecules, from which trends and a simple qualitative picture of the electronic structure may be derived. In particular, the calculations confirmed the ground states of the Sc2 and the TiV, and led to predictions for other molecules in this series. In addition to specific predictions, the study provides a simple qualitative picture of the bonding in these dimers.

Walch, Stephen P.; Bauschlicher, Charles W., Jr.

1985-01-01

129

Radiation damage of transition metal carbides  

SciTech Connect

In this grant period we have investigated electrical properties of transition metal carbides and radiation-induced defects produced by low-temperature electron irradiation in them. Special attention has been given to the composition VC[sub 0.88] in which the vacancies on the carbon sublattice of this fcc crystal order to produce a V[sub 8]C[sub 7] superlattice. The existence of this superlattice structure was found to make the crystal somewhat resistant to radiation damage at low doses and/or at ambient temperature. At larger doses significant changes in the resistivity are produced. Annealing effects were observed which we believe to be connected with the reconstitution of the superlattice structure.

Dixon, G.

1991-01-01

130

Transition-metal substitutions in iron chalcogenides  

NASA Astrophysics Data System (ADS)

The a b -plane resistivity and Hall effect are studied in Fe1 -yMyTe0.65Se0.35 single crystals doped with two transition-metal elements, M = Co or Ni, over a wide doping range, 0 ?y ?0.2 . The superconducting transition temperature, Tc, reaches zero for Co at y ?0.14 and for Ni at y ?0.032 , while the resistivity at the Tc onset increases weakly with Co doping, and strongly with Ni doping. The Hall coefficient RH, positive for y =0 , remains so at high temperatures for all y , while it changes sign to negative at low T for y >0.135 (Co) and y >0.06 (Ni). The analysis based on a two-band model suggests that at high T residual hole pockets survive the doping, but holes get localized upon the lowering of T , so that the effect of the electron doping on the transport becomes evident. The suppression of the Tc by Co impurity is related to electron doping, while in the case of the Ni impurity strong electron localization most likely contributes to fast decrease of the Tc.

Bezusyy, V. L.; Gawryluk, D. J.; Malinowski, A.; Cieplak, Marta Z.

2015-03-01

131

Dielectric response of sputtered transition metal oxides  

NASA Astrophysics Data System (ADS)

We have investigated the dielectric properties of thin layers of five oxides of transition metals (Ta2O5, HfO2, ZrO2, (ZrO2)0.91(Y2O3)0.09, and Sn0.2Zr0.2Ti0.6O2) sputtered from ceramic targets at different pressures. We find that layers deposited at low pressure behave as expected from literature, whereas layers deposited at high pressure all exhibit an anomalous dielectric response similar to that reported for the so-called "colossal" dielectric constant materials. The characterization of the thickness, frequency, and temperature dependence of the capacitance, as well as the comparison of film properties before and after annealing show that the anomalous dielectric response is due to quenched-in vacancies that act as dopants and cause the insulating layers to behave as semiconductors. An increase in quenched-in vacancies concentration with sputtering pressure results in a transition from normal to anomalous dielectric response and gradual increase in layer conductivity. In contrast, the refractive index does not depend on sputtering pressure. This observation indicates the possible application of these materials as transparent coatings with a tunable electrical conductivity.

Iosad, N. N.; Ruis, G. J.; Morks, E. V.; Morpurgo, A. F.; van der Pers, N. M.; Alkemade, P. F. A.; Sivel, V. G. M.

2004-06-01

132

Polytypism in superhard transition-metal triborides  

PubMed Central

The quest of novel compounds with special structures and unusual functionalities continues to be a central challenge to modern materials science. Even though their exact structures have puzzled scientists for decades, superhard transition-metal borides (TMBs) have long been believed to exist only in simple crystal structures. Here, we report on a polytypic phenomenon in superhard WB3 and MoB3 with a series of energetically degenerate structures due to the random stacking of metal layers amongst the interlocking boron layers. Such polytypism can create a multiphase solid-solution compound with a large number of interfaces amongst different polytypes, and these interfaces will strongly hinder the interlayer sliding movement within each polytype, thereby further increase the hardness of this particular material. Furthermore, in contrast to the conventional knowledge that intrinsically strong chemical bonds in superhard materials should lead to high lattice thermal conductivity, the polytypic TMB3 manifest anomalously low lattice thermal conductivity due to structural disorders and phonon folding. These findings promise to open a new avenue to searching for novel superhard materials with additional functionalities. PMID:24863493

Liang, Yongcheng; Yang, Jiong; Yuan, Xun; Qiu, Wujie; Zhong, Zheng; Yang, Jihui; Zhang, Wenqing

2014-01-01

133

Polytypism in superhard transition-metal triborides  

NASA Astrophysics Data System (ADS)

The quest of novel compounds with special structures and unusual functionalities continues to be a central challenge to modern materials science. Even though their exact structures have puzzled scientists for decades, superhard transition-metal borides (TMBs) have long been believed to exist only in simple crystal structures. Here, we report on a polytypic phenomenon in superhard WB3 and MoB3 with a series of energetically degenerate structures due to the random stacking of metal layers amongst the interlocking boron layers. Such polytypism can create a multiphase solid-solution compound with a large number of interfaces amongst different polytypes, and these interfaces will strongly hinder the interlayer sliding movement within each polytype, thereby further increase the hardness of this particular material. Furthermore, in contrast to the conventional knowledge that intrinsically strong chemical bonds in superhard materials should lead to high lattice thermal conductivity, the polytypic TMB3 manifest anomalously low lattice thermal conductivity due to structural disorders and phonon folding. These findings promise to open a new avenue to searching for novel superhard materials with additional functionalities.

Liang, Yongcheng; Yang, Jiong; Yuan, Xun; Qiu, Wujie; Zhong, Zheng; Yang, Jihui; Zhang, Wenqing

2014-05-01

134

Transition Metal Phosphide Hydroprocessing Catalysts: A review  

SciTech Connect

The diminishing quality of oil feedstocks coupled with increasingly more stringent environmental regulations limiting the content of sulfur in transportation fuels have given rise to a need for improved hydroprocessing technology. This review begins with a summary of the major improvements in hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) catalysts and processes that have been reported in recent years. It then describes a new class of hydroprocessing catalysts, the transition metal phosphides, which have emerged as a promising group of high-activity, stable catalysts. The phosphides have physical properties resembling ceramics, so are strong and hard, yet retain electronic and magnetic properties similar to metals. Their crystal structures are based on trigonal prisms, yet they do not form layered structures like the sulfides. They display excellent performance in HDS and HDN, with the most active phosphide, Ni{sub 2}P, having activity surpassing that of promoted sulfides on the basis of sites titrated by chemisorption (CO for the phosphides, O{sub 2} for the sulfides). In the HDS of difficult heteroaromatics like 4,6-dimethyldibenzothiophene Ni{sub 2}P operates by the hydrogenation pathway, while in the HDN of substituted nitrogen compounds like 2-methylpiperidine it carries out nucleophilic substitution. The active sites for hydrogenation in Ni{sub 2}P have a square pyramidal geometry, while those for direct hydrodesulfurization have a tetrahedral geometry. Overall, Ni{sub 2}P is a promising catalyst for deep HDS in the presence of nitrogen and aromatic compounds.

Oyama, S.; Gott, T; Zhao, H; Lee, Y

2009-01-01

135

Spectroscopic investigations of complex transition metal oxides  

NASA Astrophysics Data System (ADS)

In this dissertation, I present spectroscopic studies of several model electronic and magnetic materials. Compounds of interest include VO x nanoscrolls, VOHPO4·1/2H2O, and (La0:4Pr0:6)1:2Sr1:8Mn 2O7. These materials are attractive systems for the investigation of optical gap tuning, lattice and charge dynamics, spin-lattice-charge coupling, and hydrogen bonding effects. I measured the optical properties of VO x nanoscrolls and the ion-exchanged derivatives to investigate the lattice and charge degrees of freedom. Selected V-O-V stretching modes sharpen and redshift with increasing amine size, which are microscopic manifestations of strain. We observed bound carrier localization in the metal exchanged nanoscrolls, indicating they are weakly metallic in their bulk form. I also investigated the variable temperature vibrational properties of single crystals of the S = 1/2 Heisenberg antiferromagnet VOHPO4·1/2H 2O. In order to explain the activation and polarization dependence of the singlet-to-triplet gap in the far-infrared response, we invoke a dynamic Dzyaloshinskii-Moriya mechanism and we identify the low-energy phonons that likely facilitate this coupling. Vibrational mode splitting of VOHPO 4·1/2H2O also points toward a weak local symmetry breaking near 180 K, and the low-temperature redshift of V-O and H-O related modes demonstrates enhanced low-temperature hydrogen bonding. Finally, I measured the magneto-optical response of (La0:4Pr0:6)1:2 Sr1:8Mn2O7 to investigate the microscopic aspects of the magnetic field driven spin-glass insulator to ferromagnetic metal transition. Application of a magnetic field recovers the ferromagnetic state with an overall redshift of the electronic structure, growth of the bound carrier localization associated with ferromagnetic domains, development of a pseudogap, and softening of the Mn-O stretching and bending modes that indicate a structural change. By exploiting the electronic mechanisms, we can induce large high energy magnetodielectric contrast in (La0:4Pr 0:6)1:2Sr1:8Mn2O7. The dielectric contrast is over 100% near 0.8 eV at 4.2 K. Remnants of the transition also drive the high energy magnetodielectric effect at room temperature.

Cao, Jinbo

136

Trends in Ionization Energy of Transition-Metal Elements  

ERIC Educational Resources Information Center

A rationale for the difference in the periodic trends in the ionization energy of the transition-metal elements versus the main-group elements is presented. The difference is that in the transition-metal elements, the electrons enter an inner-shell electron orbital, while in the main-group elements, the electrons enter an outer-shell electron…

Matsumoto, Paul S.

2005-01-01

137

MATERIALS THEORY From transition metal oxides to cosmic strings  

E-print Network

in the universe? Very long time ago Today Temperature Time Low High Ã? Complex Oxides #12;MATERIALS THEORY We can use transition metal oxides to study the GUT Very long time ago Today Temperature Time Low HighMATERIALS THEORY From transition metal oxides to cosmic strings (and how electronic structure

138

A new model for magnetism in transition metals  

Microsoft Academic Search

Traditionally, quantum theories of magnetism use either a localized or an itinerant picture of the electrons as a starting point. However, the magnetic properties of transition metals cannot be fully described by either one picture or the other and the behavior of the electrons falls somewhere between these two extremes. Contemporary theories for transition metals attempt to amalgamate these two

Sunoy Neil Banerjee

2000-01-01

139

Nanostructured transition metal oxides useful for water oxidation catalysis  

DOEpatents

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.

Frei, Heinz M; Jiao, Feng

2013-12-24

140

Some continuous geometry transitions and the consequences for a transition-metal atom  

Microsoft Academic Search

By considering a transition-metal ion in the field of some symmetrically placed ions, we illustrate the consequences of a continuous change of the structure of the ligands on the energies of the 3d electrons of the transition-metal atom. Both a rigorous mathematical derivation and an analysis based on group theory are presented. For six ions surrounding the transition-metal atom, a

Michael Springborg; Kaspar Hegetschweiler

2007-01-01

141

The glass transition diagram in model metallic glasses  

E-print Network

We report a strain rate (equivalent to experimental observation time) induced glass transition in model SrCaYbMg(Li)Zn(Cu) metallic glasses at room temperature. A critical strain rate, equivalent to glass transition temperature, is found for the strain rate induced a glassy state to liquid-like viscoplastic state translation. The results show that the observation time, equivalent to temperature and stress, is a key parameter for the glass transition. A three-dimension glass transition phase diagram involved in time, temperature and stress in metallic glasses is established for understanding the nature of the metallic glasses.

X. Q. Gao; W. H. Wang; K. Zhao; H. Y. Bai

2013-05-22

142

Critical behavior in the hydrogen insulator-metal transition  

NASA Technical Reports Server (NTRS)

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.

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

1990-01-01

143

Route to transition metal carbide nanoparticles through cyanamide and metal oxides  

Microsoft Academic Search

We have designed an efficient route to the synthesis of transition metal carbide nanoparticles starting from an organic reagent cyanamide and transition metal oxides. Four technologically important metal carbide nanoparticles such as tungsten carbide, niobium carbide, tantalum carbide and vanadium carbide were synthesized successfully at moderate temperatures. It is found that cyanamide is an efficient carburization reagent and that the

P. G. Li; M. Lei; W. H. Tang

2008-01-01

144

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

USGS Publications Warehouse

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. ?13C 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 natural gas generation in these experiments is attributed to the metals not occurring in the proper form or the poisoning of potential catalytic microcosms by polar-rich bitumen, which impregnates the rock matrix during the early stages of petroleum formation.

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

2008-01-01

145

The local structure of transition metal doped semiconducting boron carbides  

Microsoft Academic Search

Transition metal doped boron carbides produced by plasma enhanced chemical vapour deposition of orthocarborane (closo-1,2-C2B10H12) and 3d metal metallocenes were investigated by performing K-edge extended x-ray absorption fine structure and x-ray absorption near edge structure measurements. The 3d transition metal atom occupies one of the icosahedral boron or carbon atomic sites within the icosahedral cage. Good agreement was obtained between

Jing Liu; Guangfu Luo; Wai-Ning Mei; Orhan Kizilkaya; Eric D. Shepherd; Peter A. Dowben

2010-01-01

146

Aromaticity and antiaromaticity in transition-metal systems  

Microsoft Academic Search

Aromaticity is an important concept in chemistry primarily for hydrocarbon compounds, but it has been extended to compounds containing transition-metal atoms. Recent findings of aromaticity and antiaromaticy in all-metal clusters have stimulated further researches in describing the chemical bonding, structures, and stability in transition-metal clusters and compounds on the basis of aromaticity and antiaromaticity, which are reviewed here. The presence

Dmitry Yu. Zubarev; Boris B. Averkiev; Hua-Jin Zhai; Lai-Sheng Wang; Alexander I. Boldyrev

2008-01-01

147

Phonons and the metal-insulator transition in VO2  

Microsoft Academic Search

VO2 undergoes a metal-insulator transition (MIT) at TC= 340 K, which is accompanied by a structural phase transition from a high temperature rutile phase to a low temperature monoclinic phase. Although VO2 has been studied extensively for over 40 years, a clear understanding of the origin of the phase transition has not been forthcoming. Still at issue is the relative

Sung Chang; A. Alatas

2005-01-01

148

Band Structure of Transition Metals Studied by ESCA  

Microsoft Academic Search

The position and shape of the energy bands of the following transition metals have been studied by ESCA: Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, Au. The Fermi levels of the metals with unfilled d-bands are found in the high-energy flanks of the valence band spectra. For the noble metals the Fermi level is shifted toward

Y. Baer; P. F. Hedén; J. Hedman; M. Klasson; C. Nordling; K. Siegbahn

1970-01-01

149

Terahertz nano antenna enabled early transition in VO2  

E-print Network

We study terahertz transmission through nano-patterned vanadium dioxide thin film. It is found that the patterning allows the lowering of the apparent transition temperature. For the case of the smallest width nano antennas, the transition temperature is lower by as many as ten degrees relative to the bare film, so that the nano patterned hysteresis curves completely separate themselves from their bare film counterparts. This early transition comes from the one order of magnitude enhanced effective dielectric constants by nano antennas. This phenomenon opens up the possibility of transition temperature engineering.

Jeong, Young-Gyun; Choi, Jae-Wook; Han, Sang-Hoon; Park, Hyeong-Ryeol; Park, Namkyoo; Kim, Bong-Jun; Kim, Hyun-Tak; Kim, Dai-Sik

2012-01-01

150

Steam Reforming on Transition-metal Carbides from Density-functional Theory  

SciTech Connect

A screening study of the steam reforming reaction on clean and oxygen covered early transition-metal carbides surfaces is performed by means of density-functional theory calculations. It is found that carbides provide a wide spectrum of reactivities, from too reactive via suitable to too inert. Several molybdenum-based systems are identified as possible steam reforming catalysts. The findings suggest that carbides provide a playground for reactivity tuning, comparable to the one for pure metals.

Vojvodic, Aleksandra

2012-05-11

151

Electronic entanglement in late transition metal oxides  

E-print Network

Here we present a study of the entanglement in the electronic structure of the late transition metal monoxides - MnO, FeO, CoO, and NiO - obtained by means of density-functional theory in the local density approximation combined with dynamical mean-field theory (LDA+DMFT). The impurity problem is solved through Exact Diagonalization (ED), which grants full access to the thermally mixed many-body ground state density operator. The quality of the electronic structure is affirmed through a direct comparison between the calculated electronic excitation spectrum and photoemission experiments. Our treatment allows for a quantitative investigation of the entanglement in the electronic structure. Two main sources of entanglement are explicitly resolved through the use of a fidelity based geometrical entanglement measure, and additional information is gained from a complementary entropic entanglement measure. We show that the interplay of crystal field effects and Coulomb interaction causes the entanglement in CoO to take a particularly intricate form.

Patrik Thunström; Igor Di Marco; Olle Eriksson

2013-01-28

152

Transition metal-free olefin polymerization catalyst  

DOEpatents

Ethylene and/or propylene are polymerized to form high molecular weight, linear polymers by contacting ethylene and/or propylene monomer, in the presence of an inert reaction medium, with a catalyst system which consists essentially of (1) an aluminum alkyl component, such as trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-octylaluminum and diethylaluminum hydride and (2) a Lewis acid or Lewis acid derivative component, such as B (C.sub.6 F.sub.5).sub.3, [(CH.sub.3).sub.2 N (H) (C.sub.6 H.sub.5)].sup.+ [B (C.sub.6 F.sub.5)4].sup.-, [(C.sub.2 H.sub.5).sub.3 NH].sup.+ [B C.sub.6 F.sub.5).sub.4 ],.sup.-, [C(C.sub.6 F.sub.5).sub.3 ].sup.+ [B(C.sub.6 F.sub.5).sub.4 ].sup.-, (C.sub.2 H.sub.5).sub.2 Al(OCH.sub.3), (C.sub.2 H.sub.5).sub.2 Al(2,6-di-t-butyl-4-methylphenoxide), (C.sub.2 H.sub.5)Al(2,6 -di-t-butylphenoxide).sub.2, (C.sub.2 H.sub.5).sub.2 Al(2,6-di-t-butylphonoxide) , 2,6 -di-t-butylphenol.multidot.methylaluminoxane or an alkylaluminoxane, and which may be completely free any transition metal component(s).

Sen, Ayusman (State College, PA); Wojcinski, II, Louis M. (State College, PA); Liu, Shengsheng (State College, PA)

2001-01-01

153

METAL-NON METAL TRANSITIONS /N RARE EARTH COMPOUNDS. EXPERIMENT AND THEORK /.  

E-print Network

METAL-NON METAL TRANSITIONS /N RARE EARTH COMPOUNDS. EXPERIMENT AND THEORK /. VALENCE INSTABILITIES, superconductivity, electron-phonon and band theory, to name a few. 2. Properties of normal rare earth metals. - Before discussing rare earth valence instabilities, three relevant general features of rare earth metals

Paris-Sud XI, Université de

154

The interactions between transition metal nanoparticles and their metal-oxide supports are often critical for heterogeneous metal nanoparticle  

E-print Network

Reports The interactions between transition metal nanoparticles and their metal- oxide supports are often critical for heterogeneous metal nanoparticle catalysts (1). However, the roles of the species at the metal-support interface is widely regarded as the key step in room-temperature CO oxidation (13

Napp, Nils

155

Chiral phase transition in lattice QCD as a metal-insulator transition  

E-print Network

We investigate the lattice QCD Dirac operator with staggered fermions at temperatures around the chiral phase transition. We present evidence of a metal-insulator transition in the low lying modes of the Dirac operator around the same temperature as the chiral phase transition. This strongly suggests the phenomenon of Anderson localization drives the QCD vacuum to the chirally symmetric phase in a way similar to a metal-insulator transition in a disordered conductor. We also discuss how Anderson localization affects the usual phenomenological treatment of phase transitions a la Ginzburg-Landau.

Antonio M. Garcia-Garcia; James C. Osborn

2007-03-09

156

Process for making transition metal nitride whiskers  

DOEpatents

A process for making metal nitrides, particularly titanium nitride whiskers, using a cyanide salt as a reducing agent for a metal compound in the presence of an alkali metal oxide. Sodium cyanide, various titanates and titanium oxide mixed with sodium oxide react to provide titanium nitride whiskers that can be used as reinforcement to ceramic composites. 1 fig., 1 tab.

Bamberger, C.E.

1988-04-12

157

Process for making transition metal nitride whiskers  

DOEpatents

A process for making metal nitrides, particularly titanium nitride whiskers, using a cyanide salt as a reducing agent for a metal compound in the presence of an alkali metal oxide. Sodium cyanide, various titanates and titanium oxide mixed with sodium oxide react to provide titanium nitride whiskers that can be used as reinforcement to ceramic composites.

Bamberger, Carlos E. (Oak Ridge, TN)

1989-01-01

158

Fluctuation-driven electroweak phase transition. [in early universe  

NASA Technical Reports Server (NTRS)

We examine the dynamics of the electroweak phase transition in the early Universe. For Higgs masses in the range 46 less than or = M sub H less than or = 150 GeV and top quark masses less than 200 GeV, regions of symmetric and asymmetric vacuum coexist to below the critical temperature, with thermal equilibrium between the two phases maintained by fluctuations of both phases. We propose that the transition to the asymmetric vacuum is completed by percolation of these subcritical fluctuations. Our results are relevant to scenarios of baryogenesis that invoke a weakly first-order phase transition at the electroweak scale.

Gleiser, Marcelo; Kolb, Edward W.

1992-01-01

159

Optical properties of two-dimensional transition metal dichalcogenides  

E-print Network

The re-discovery of the atomically thin transition metal dichalcogenides (TMDs), which are mostly semiconductors with a wide range of band gaps, has diversified the family of two-dimensional materials and boosted the ...

Lin, Yuxuan, S.M. Massachusetts Institute of Technology

2014-01-01

160

Charge, orbital and magnetic ordering in transition metal oxides   

E-print Network

Neutron and x-ray diffraction has been used to study charge, orbital and magnetic ordering in some transition metal oxides. The long standing controversy regarding the nature of the ground state (Verwey structure) of the ...

Senn, Mark Stephen

2013-06-29

161

Photochemical reductive elimination of halogen from transition metal complexes  

E-print Network

This thesis is focused on the synthesis and study of transition metal complexes that undergo halogen elimination when irradiated with UV and visible light. This chemistry is relevant for solar energy storage schemes in ...

Cook, Timothy R. (Timothy Raymond), 1982-

2010-01-01

162

Electrolytic separation of crystals of transition-metal oxides  

NASA Technical Reports Server (NTRS)

Versatile flux system grows large, well-formed, stoichiometric single crystals of mixed oxides of the transition-metal elements. These crystals have important uses in the microwave field, and applications as lasers and masers in communications.

Arnott, R. J.; Feretti, A.; Kunnamann, W.

1969-01-01

163

Atomic Natural Orbital Basis Sets for Transition Metals  

NASA Technical Reports Server (NTRS)

We show that atomic natural orbitals are an excellent way to contract transition-metal basis sets, even though the different low-lying electronic states may have very different basis set requirements.

Bauschlicher, Charles W., Jr.; Taylor, Peter R.

1993-01-01

164

Nitrene transfer reactions by late transition metal complexes  

E-print Network

This thesis presents nitrene transfer reactions that are catalyzed or mediated by late transition metal complexes. Sterically large, fluorinated supporting ligands are used to minimize potential side reactions. A new ...

Hamilton, Charles W., Ph. D. Massachusetts Institute of Technology

2007-01-01

165

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

PubMed

Theoretical studies of the possibility of forming ammonia electrochemically at ambient temperature and pressure are presented. Density functional theory calculations were used in combination with the computational standard hydrogen electrode to calculate the free energy profile for the reduction of N(2) admolecules and N adatoms on several close-packed and stepped transition metal surfaces in contact with an acidic electrolyte. Trends in the catalytic activity were calculated for a range of transition metal surfaces and applied potentials under the assumption that the activation energy barrier scales with the free energy difference in each elementary step. The most active surfaces, on top of the volcano diagrams, are Mo, Fe, Rh, and Ru, but hydrogen gas formation will be a competing reaction reducing the faradaic efficiency for ammonia production. Since the early transition metal surfaces 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 than their stepped counterparts. PMID:22146855

Skúlason, Egill; Bligaard, Thomas; Gudmundsdóttir, Sigrídur; Studt, Felix; Rossmeisl, Jan; Abild-Pedersen, Frank; Vegge, Tejs; Jónsson, Hannes; Nørskov, Jens K

2012-01-21

166

The role of metal/transition metal oxide/organic interface  

NASA Astrophysics Data System (ADS)

In this paper, we report a study with UPS and XPS data of metal/transition-metal-oxide/organic interfaces. Transition metal oxides are widely used in organic light- emitting (OLEDs) in recently years, such as Wo3, ReO3, MoO3, and V2O5. These metal oxides have been proven to be good hole injection layers in OLEDs, interlayers in tandem OLEDs, and nanocomposite electrodes. Although a large number of studies have been made, little is known about the mechanism of metal/transition-metal-oxide/organic interfaces. UPS and XPS data performed by synchrotron radiation research show that these oxides would catch electrons from organic and results in p-type doping in organic material. In addition, there is a significant structure transition from insulating metal oxide to metallic metal oxide. As a result of high work function metallic metal oxides in anode structures and p-type doping organic hole transport layers (HTLs), holes can easily be injected from anode to HTLs. Current-voltage characteristics (I-V) and quantum-efficiency (?-J) measurements also show the improvement of device performance with insertion of thin transition metal oxides between anodes HTLs.

Lin, Chang-Ting; Lee, Guan-Ru; Wu, Chih-I.; Pi, Tun-Wen

2008-03-01

167

Homogeneous catalysis by transition metal oxygen anion clusters  

Microsoft Academic Search

This review provides a thorough discussion of homogeneous catalysis by transition metal oxygen anion clusters (polyoxometalates), with a focus on mechanism. The primary catalysts examined are mixed addenda and d-electron-transition-metal-substituted polyoxometalate (TMSP) complexes. The unusual versatility and tunability of these catalysts and their compatibility with environmentally and economically attractive conditions (solvents, oxidants, etc.) are outlined. A general compilation of the

Craig L. Hill; Christina M. Prosser-McCartha

1995-01-01

168

Tight-binding potentials for transition metals and alloys  

Microsoft Academic Search

The parameters of many-body potentials for fcc and hcp transition metals, based on the second-moment approximation of a tight-binding Hamiltonian, have been systematically evaluated. The potential scheme, cast in analytical form, allows us to reproduce correctly the thermal behavior of transition metals making use of a small set of adjustable parameters. The large cutoff, which extends the range of the

Fabrizio Cleri; Vittorio Rosato

1993-01-01

169

Electronic mechanism of hardness enhancement in transition-metal carbonitrides  

Microsoft Academic Search

Transition-metal carbides and nitrides are hard materials widely used for cutting tools and wear-resistant coatings. Their hardness is not yet understood at a fundamental level. A clue may lie in the puzzling fact that transition-metal carbonitrides that have the rock-salt structure (such as TiCxN1-x) have the greatest hardness for a valence-electron concentration of about 8.4 per cell, which suggests that

Seung-Hoon Jhi; Jisoon Ihm; Steven G. Louie; Marvin L. Cohen

1999-01-01

170

Kansas Early Childhood Research Institute on Transitions: Executive Summary.  

ERIC Educational Resources Information Center

This executive summary reviews activities over the past 5 years of the Kansas Early Childhood Research Institute (KECRI). The Institute has addressed transition issues faced by infants and young children (and their families) who have a disability or are at risk for developmental delay. KECRI goals are stated and the importance and impact of the…

Rice, Mabel L.; O'Brien, Marion

171

Synthesis of Nanoporous Iminodiacetic Acid Sorbents for Binding Transition Metals  

PubMed Central

Iminodiacetic acid (IDAA) forms strong complexes with a wide variety of metal ions. Using self-assembled monolayers in mesoporous supports (SAMMS) to present the IDAA ligand potentially allows for multiple metal-ligand interactions to enhance the metal binding affinity relative to that of randomly oriented polymer-based supports. This manuscript describes the synthesis of a novel nanostructured sorbent material built using self-assembly of a IDAA ligand inside a nanoporous silica, and demonstrates its use for capturing transition metal cations, and anionic metal complexes, such as PdCl4?2. PMID:22068901

Busche, Brad; Wiacek, Robert; Davidson, Joseph; Koonsiripaiboon, View; Yantasee, Wassana; Addleman, R. Shane; Fryxell, Glen E.

2009-01-01

172

[Non-empirical interatomic potentials for transition metals  

SciTech Connect

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.

Not Available

1993-01-01

173

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

SciTech Connect

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.

Not Available

1993-05-01

174

Ab initio study of the half-metal to metal transition in strained magnetite  

E-print Network

does not lead to a metallic state for magnetite films grown on (111)-oriented substrates. 3 PresentAb initio study of the half-metal to metal transition in strained magnetite Martin Friák1 of magnetite under different strain conditions. The effects of volume relaxation and internal degrees

175

Metal - non-metal transition and the second critical point in expanded metals  

E-print Network

Based on the non-relativistic Coulomb model within which the matter is a system of interacting electrons and nuclei, using the quantum field theory and linear response theory methods, opportunity for the existence of the second critical point in expanded metals, which is directly related to the metal--nonmetal transition, predicted by Landau and Zeldovitch, is theoretically justified. It is shown that the matter at the second critical point is in the state of true dielectric with zero static conductivity. The results obtained are in agreement with recent experiments for expanded metals. The existence of the second critical point is caused by the initial multi-component nature of the matter consisting of electrons and nuclei and the long-range character of the Coulomb interaction. (Accepted in PTEP)

V. B. Bobrov; S. A. Trigger; A. G. Zagorodny

2013-02-16

176

Thermodynamic behavior near a metal-insulator transition  

NASA Technical Reports Server (NTRS)

Measurements of the low-temperature specific heat of phosphorus-doped silicon for densities near the metal-insulator transition show an enhancement over the conduction-band itinerant-electron value. The enhancement increases toward lower temperatures but is less than that found for the spin susceptibility. The data are compared with various theoretical models; the large ratio of the spin susceptibility to specific heat indicates the presence of localized spin excitations in the metallic phase as the metal-insulator transition is approached.

Paalanen, M. A.; Graebner, J. E.; Bhatt, R. N.; Sachdev, S.

1988-01-01

177

Quantum (T=0) superconductor-metal transitions in highly conducting films  

E-print Network

Quantum (T=0) superconductor-metal transitions in highly conducting films B.Spivak University-wave superconductor-metal transition in an external magnetic field b. Quantum S-wave superconductor-metal transition as a function of disorder c. Quantum D-wave superconductor-metal transition as a function of disorder d

Fominov, Yakov

178

Application of Two Dimensional Flourescence Spectroscopy to Transition Metal Clusters.  

NASA Astrophysics Data System (ADS)

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

Kokkin, Damian L.; Steimle, Timothy

2014-06-01

179

Rare earth transition metal sulfides, LnMS 3  

NASA Astrophysics Data System (ADS)

Ternary rare earth transition metal sulfides LnMS 3 with Ln = La, Nd, and Gd, and M = V and Cr; as well as Ln = La and M = Mn, Fe, Co, and Ni have been prepared and characterized. The vanadium and chromium sulfides crystallize in a monoclinic layer structure isotypic with LaCrS 3, while the other LnMS 3 sulfides crystallize in a hexagonal structure. Chemical shifts of the metal K-absorption edge and XPS binding energies of core levels indicate that the transition metal is trivalent in the V and Cr sulfides, while it is divalent in the Mn, Fe, Co, and Ni sulfides. Electrical and magnetic properties of the sulfides are discussed in terms of their structures and the electronic configurations of the transition metal ions.

Murugesan, T.; Ramesh, S.; Gopalakrishnan, J.; Rao, C. N. R.

1981-07-01

180

Binding and catalytic reduction of NO by transition metal aluminosilicates  

SciTech Connect

The objective of this research is to provide the scientific understanding of processes that actively and selectively reduce NO in dilute exhaust streams, as well as in concentrated streams, to N{sub 2}. Experimental studies of NO chemistry in transition metal-containing aluminosilicate catalysts are being carried out with the aim of determining the chemical rules for NO reduction on non-precious metals. The catalyst supports chosen for this investigation are A and Y zeolites, mordenite, and monoliths based on cordierite. The supported transition metal cations that were examined are principally the first row redox metals, e.g. Cr(2), Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and Cu(I). The reactions of interest are the reductions of NO by H{sub 2}, CO, and CH{sub 4}, as well as the disproportionation of NO. Rare earth cations that possess redox properties were placed in the more shielded sites, e.g. Site I in Y zeolite, prior to or simultaneously with the exchange procedure with the transition metal cations. Theoretical calculations of the electronic structure of the transition metal cations in zeolitic sites were carried out by ab initio methods. The aim of this part of the research is to find the best match between the metal-based antibonding orbitals and the antibonding orbitals of the NO molecule such that the N-O bond is weakened and is readily broken. 9 refs., 4 figs., 3 tabs.

Klier, K.; Herman, R.G.; Hou, Shaolie.

1991-09-01

181

Quark-Hadron Phase Transitions in Viscous Early Universe  

E-print Network

Based on hot big bang theory, the cosmological matter is conjectured to undergo QCD phase transition(s) to hadrons, when the universe was about $1-10 \\mu$s old. In the present work, we study the quark-hadron phase transition, by taking into account the effect of the bulk viscosity. We analyze the evolution of the quantities relevant for the physical description of the early universe, namely, the energy density $\\rho$, temperature $T$, Hubble parameter $H$ and scale factor $a$ before, during and after the phase transition. To study the cosmological dynamics and the time evolution we use both analytical and numerical methods. By assuming that the phase transition may be described by an effective nucleation theory (prompt {\\it first-order} phase transition), we also consider the case where the universe evolved through a mixed phase with a small initial supercooling and monotonically growing hadronic bubbles. The numerical estimation of the cosmological parameters, $a$ and $H$ for instance, makes it clear that the time evolution varies from phase to phase. As the QCD era turns to be fairly accessible in the high-energy experiments and the lattice QCD simulations, the QCD equation of state is very well defined. In light of this, we introduce a systematic study of the {\\it cross-over} quark-hadron phase transition and an estimation for the time evolution of Hubble parameter.

A. Tawfik; T. Harko

2012-04-15

182

Quark-hadron phase transitions in the viscous early universe  

NASA Astrophysics Data System (ADS)

In the standard hot big bang theory, when the Universe was about 1-10?s old, the cosmological matter is conjectured to undergo quantum chromodynamics (QCD) phase transition(s) from quark matter to hadrons. In the present work, we study the cosmological quark-hadron phase transition in two different physical scenarios. First, by assuming that the phase transition would be described by an effective nucleation theory (prompt first-order phase transition), we analyze the evolution of the relevant cosmological parameters of the early universe (energy density ?, temperature T, Hubble parameter H, and the scale factor a) before, during, and after the phase transition. To study the cosmological dynamics and the time evolution, we use both analytical and numerical methods. The case where the Universe evolved through a mixed phase with a small initial supercooling and monotonically growing hadronic bubbles is also considered in detail. The numerical estimation of the cosmological parameters, a and H for instance, shows that the time evolution of the Universe varies from phase to phase. As the QCD era turns to be fairly accessible in the high-energy experiments and the lattice QCD simulations, the QCD equation of state is very well defined. In light of these QCD results, we develop a systematic study of the crossover quark-hadron phase transition, and an estimation for the time evolution of the Hubble parameter during the crossover.

Tawfik, A.; Harko, T.

2012-04-01

183

Retrieval study of uncemented metal–metal hip prostheses revised for early loosening  

Microsoft Academic Search

A tribologic assessment was performed on 22 metal–metal hip prostheses from a single manufacturer, following removal for early aseptic loosening after a mean service life of 32 months (range, 12–59 months). The mean linear wear rate was 7.6?m\\/year (range, 2.9–12.8?m\\/year). This was below the rates previously observed in other modern metal–metal combinations. A novel contour analysis technique using a coordinate

Georg Reinisch; Kurt P. Judmann; Christian Lhotka; Felix Lintner; Karl A. Zweymüller

2003-01-01

184

(S)TEM analysis of functional transition metal oxides  

NASA Astrophysics Data System (ADS)

Perovskite vanadates (AVO3) form an ideal family to study the structure-property relationships in transition metal oxides because their physical properties can easily be tailored by varying the A-site cations. (S)TEM is an ideal tool for this type of study due to its capacity for simultaneous imaging and chemical analysis. Determination of the oxidation state of vanadium in complex oxides have been carried out by electron energy loss spectroscopy. SrVO3/LaAlO3 is then studied both experimentally and theoretically as a prototype system. Extra electrons have been detected on the interface layer, and further proven to originate mainly from a change in the local bonding configuration of V at the La-O terminated substrate surface. Cr-containing stainless steel deposited with a LaCrO3 thin-film layer is a promising interconnect material of Solid Oxide Fuel Cells (SOFC). Our investigation on its microstructural evolution reveals that the LaCrO 3 thin film plays a role in inhibiting the growth of an oxide layer on the metal surface and thus protects the surface of the stainless steel. Ca-doped LaCoO3 is a promising SOFC cathode material. The domain structures and the oxidation state of Co in Ca-doped LaCoO3, which are directly related to its mechanical properties and electronic conductivity, are investigated by in-situ TEM and EELS. The formation of microcracks is observed during thermal cycles. Ca-doping in LaCoO3 is shown to not only improve the electronic conductivity of the material, but is also likely to strengthen the grain boundaries. The realization of its application in SOFCs depends on depressing the ferroelastisity to reduce strain formation during thermal cycles. The application of the (S)TEM techniques used for studying the perovskite systems are further extended to other compounds containing transition metal elements. The refractory minerals from Comet 81 P/Wild-2 are studied to investigate the formation of the early solar system. A relatively high Ti3+/Ti 4+ ratio in fassaite and the presence of osbornite indicate that the Comet refractory minerals formed in the inner solar nebula and were later transported to the outer solar system where the comet formed. This implies a much more dynamic and perhaps more violent solar nebula than was previously suspected.

Chi, Miaofang

185

Mott metal-insulator transitions in d-electron (hole) Degenerate transition metal oxides, sulphides and selenides  

Microsoft Academic Search

The phase diagrams o fthe Mott metal-insulator transition of Kohn, Rice and Brinkman, Gutzwiller, Goodenough and McWhan et al. are modified by the inclusion of d-electron (hole) spin-orbital degeneracy along the lines of the ren-fold degenerate Hubbard and Anderson models of Siegel and Kemeny, and Moriya. The systems treated are: transition metal sulphides and selenides (NiS2,NiSe2, CoSe2, RhSe2etc.), the transition

Edward Siegel

1978-01-01

186

Flexible metallic seal for transition duct in turbine system  

DOEpatents

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.

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

2014-04-22

187

Separation observation of metal-insulator transition and structural phase transition in VO2  

Microsoft Academic Search

An intermediate monoclinic metal phase between the metal-insulator transition (MIT) and the structural phase transition (SPT) is observed with VO2-based two-terminal devices and can be explained in terms of the Mott MIT. The conductivity of this phase linearly increases with increasing temperature up to TSPT 68^oC and becomes maximum at TSPT. The SPT is confirmed by micro-Raman spectroscopy. Optical microscopic

Hyun-Tak Kim; Bong-Jun Kim; Yong Wook Lee; Byung Gyu Chae; Sun Jin Yun; Soo-Young Oh; Yong-Sik Lim

2007-01-01

188

Metal Selectivity Determinants in a Family of Transition Metal Transporters*  

PubMed Central

Metal tolerance proteins (MTPs) are plant members of the cation diffusion facilitator (CDF) transporter family involved in cellular metal homeostasis. Members of the CDF family are ubiquitously found in all living entities and show principal selectivity for Zn2+, Mn2+, and Fe2+. Little is known regarding metal selectivity determinants of CDFs. We identified a novel cereal member of CDFs in barley, termed HvMTP1, that localizes to the vacuolar membrane. Unlike its close relative AtMTP1, which is highly selective for Zn2+, HvMTP1 exhibits selectivity for both Zn2+ and Co2+ as assessed by its ability to suppress yeast mutant phenotypes for both metals. Expression of HvMTP1/AtMTP1 chimeras in yeast revealed a five-residue sequence within the AtMTP1 N-segment of the His-rich intracytoplasmic loop that confines specificity to Zn2+. Furthermore, mutants of AtMTP1 generated through random mutagenesis revealed residues embedded within transmembrane domain 3 that additionally specify the high degree of Zn2+ selectivity. We propose that the His-rich loop, which might play a role as a zinc chaperone, determines the identity of the metal ions that are transported. The residues within transmembrane domain 3 can also influence metal selectivity, possibly through conformational changes induced at the cation transport site located within the membrane or at the cytoplasmic C-terminal domain. PMID:22139846

Podar, Dorina; Scherer, Judith; Noordally, Zeenat; Herzyk, Pawel; Nies, Dietrich; Sanders, Dale

2012-01-01

189

Metal artifact reduction sequence: early clinical applications.  

PubMed

Artifact arising from metal hardware remains a significant problem in orthopedic magnetic resonance imaging. The metal artifact reduction sequence (MARS) reduces the size and intensity of susceptibility artifacts from magnetic field distortion. The sequence, which is based on view angle tilting in combination with increased gradient strength, can be conveniently used in conjunction with any spin-echo sequence and requires no additional imaging time. In patients with persistent pain after femoral neck fracture, the MARS technique allows visualization of marrow adjacent to hip screws, thus enabling diagnosis or exclusion of avascular necrosis. Other applications in the hip include assessment of periprosthetic soft tissues after hip joint replacement surgery, postoperative assessment after resection of bone tumors and reconstruction, and localization of unopacified methyl methacrylate cement prior to hip arthroplasty revision surgery. In the knee, the MARS technique allows visualization of structures adjacent to implanted metal staples, pins, or screws. The technique can significantly improve visualization of periprosthetic bone and soft-tissue structures even in patients who have undergone total knee arthroplasty. In patients with spinal fixation hardware, the MARS technique frequently allows visualization of the vertebral bodies and spinal canal contents. The technique can be helpful after wrist fusion or screw fixation of scaphoid fractures. PMID:10835123

Olsen, R V; Munk, P L; Lee, M J; Janzen, D L; MacKay, A L; Xiang, Q S; Masri, B

2000-01-01

190

High valence 3p and transition metal based MOFs.  

PubMed

This article focuses on high valence 3p and transition metal based metal organic frameworks. In the first part we will discuss the complex solution chemistry of these metals which makes this sub-class of MOFs more of a challenge than the traditional low valence metal based MOFs. This is followed by a short review of the different classes of solids based on phosphonates, carboxylates and other linkers. Finally, we report some of the most relevant properties of these solids such as their chemical or thermal stability as well as their catalytic, redox- and photo-activities. PMID:24947910

Devic, Thomas; Serre, Christian

2014-08-21

191

Structural, electronic, and magnetic properties of 3d transition-metal aluminides with equiatomic composition  

Microsoft Academic Search

First-principles calculations have been performed to study the chemical bonding trends and the phase stability of 3d transition-metal (TM) aluminides with equiatomic composition. The physical mechanisms for ordering in both the L10 and B2-type aluminides are presented. It is shown that the dominant factor for early TM aluminides is the directional bonding between the d orbitals of TM atoms, whereas

J. Zou; C. L. Fu

1995-01-01

192

The metal-insulator transition in magnetite.  

NASA Technical Reports Server (NTRS)

We describe an electronic model for the low temperature transition in magnetite, in which the average number of electrons on a site is non-integral. The solution of the one-dimensional problem is reviewed, and the connection of the model with the Verwey ordering is discussed. Some of the implication of the three dimensional problem are discussed.

Cullen, J. R.; Callen, E.

1972-01-01

193

Hybrid uranium-transition-metal oxide cage clusters.  

PubMed

Transition-metal based polyoxometalate clusters have been known for decades, whereas those built from uranyl peroxide polyhedra have more recently emerged as a family of complex clusters. Here we report the synthesis and structures of six nanoscale uranyl peroxide cage clusters that contain either tungstate or molybdate polyhedra as part of the cage, as well as phosphate tetrahedra. These transition-metal-uranium hybrid clusters exhibit unique polyhedral connectivities and topologies that include 6-, 7-, 8-, 10-, and 12-membered rings of uranyl polyhedra and uranyl ions coordinated by bidentate peroxide in both trans and cis configurations. The transition-metal polyhedra appear to stabilize unusual units built of uranyl polyhedra, rather than templating their formation. PMID:25434424

Ling, Jie; Hobbs, Franklin; Prendergast, Steven; Adelani, Pius O; Babo, Jean-Marie; Qiu, Jie; Weng, Zhehui; Burns, Peter C

2014-12-15

194

Fast Intersystem Crossing in Transition-Metal Complexes  

E-print Network

The mechanism behind fast intersystem crossing in transition-metal complexes is shown to be a result of the dephasing of the photoexcited state to the phonon continuum of a different state with a significantly different transition metal-ligand distance. The coupling is a result of the spin-orbit interaction causing a change in the local moment. Recurrence to the initial state is prevented by the damping of the phonon oscillation. The decay time is faster than the oscillation frequency of the transition metal-ligand stretch mode, in agreement with experiment. For energies above the region where the strongest coupling occurs, a slower "leakage-type" decay is observed. If the photoexcited state is lower in energy than the state it couples to, then there is no decay.

Michel van Veenendaal; Jun Chang; A. J. Fedro

2010-02-07

195

Nanodisperse transition metal electrodes (NTME) for electrochemical cells  

DOEpatents

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

Striebel, Kathryn A. (Oakland, CA); Wen, Shi-Jie (Sunnyvale, CA)

2000-01-01

196

Nanodisperse transition metal electrodes (NTME) for electrochemical cells  

SciTech Connect

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

Striebel, Kathryn A.; Wen, Shi-Jie

1998-12-01

197

Transition metal-substituted cobalt ferrite nanoparticles for biomedical applications.  

PubMed

Transition metals of copper, zinc, chromium and nickel were substituted into cobalt ferrite nanoparticles via a sol-gel route using citric acid as a chelating agent. The microstructure and elemental composition were characterized using scanning electron microscopy combined with energy-dispersive X-ray spectroscopy. Phase analysis of transition metal-substituted cobalt ferrite nanoparticles was performed via X-ray diffraction. Surface wettability was measured using the water contact angle technique. The surface roughness of all nanoparticles was measured using profilometry. Moreover, thermogravimetric analysis and differential scanning calorimetry were performed to determine the temperature at which the decomposition and oxidation of the chelating agents took place. Results indicated that the substitution of transition metals influences strongly the microstructure, crystal structure and antibacterial property of the cobalt ferrite nanoparticles. PMID:23137676

Sanpo, Noppakun; Berndt, Christopher C; Wen, Cuie; Wang, James

2013-03-01

198

A New Family of Transition Metal Nitrides  

SciTech Connect

The mechanical stability of platinum nitride has been studied using first-principles calculations. By calculating the single-crystal elastic constants, we show that platinum nitride can be stabilized in the fluorite structure, in which the nitrogen atoms occupy all the tetrahedral interstitial sites of the metal lattice. The stability is attributed to the pseudogap effect from analysis of the electronic structure.

Yu, Rong; Zhang, Xiao-Feng

2005-10-01

199

Memristor using a transition metal nitride insulator  

DOEpatents

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.

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

2014-10-28

200

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

NASA Astrophysics Data System (ADS)

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).

Wang, Xin

2012-02-01

201

Role of phonons in the metal-insulator phase transition.  

NASA Technical Reports Server (NTRS)

Review, for the transition series oxides, of the Mattis and Lander model, which is one of electrons interacting with lattice vibrations (electron and phonon interaction). The model displays superconducting, insulating, and metallic phases. Its basic properties evolve from a finite crystallographic distortion associated with a dominant phonon mode and the splitting of the Brillouin zone into two subzones, a property of simple cubic and body centered cubic lattices. The order of the metal-insulator phase transition is examined. The basic model has a second-order phase transition and the effects of additional mechanisms on the model are calculated. The way in which these mechanisms affect the magnetically ordered transition series oxides as described by the Hubbard model is discussed.

Langer, W. D.

1972-01-01

202

Covalent functionalization of monolayered transition metal dichalcogenides by phase engineering.  

PubMed

Chemical functionalization of low-dimensional materials such as nanotubes, nanowires and graphene leads to profound changes in their properties and is essential for solubilizing them in common solvents. Covalent attachment of functional groups is generally achieved at defect sites, which facilitate electron transfer. Here, we describe a simple and general method for covalent functionalization of two-dimensional transition metal dichalcogenide nanosheets (MoS?, WS? and MoSe?), which does not rely on defect engineering. The functionalization reaction is instead facilitated by electron transfer between the electron-rich metallic 1T phase and an organohalide reactant, resulting in functional groups that are covalently attached to the chalcogen atoms of the transition metal dichalcogenide. The attachment of functional groups leads to dramatic changes in the optoelectronic properties of the material. For example, we show that it renders the metallic 1T phase semiconducting, and gives it strong and tunable photoluminescence and gate modulation in field-effect transistors. PMID:25515889

Voiry, Damien; Goswami, Anandarup; Kappera, Rajesh; e Silva, Cecilia de Carvalho Castro; Kaplan, Daniel; Fujita, Takeshi; Chen, Mingwei; Asefa, Tewodros; Chhowalla, Manish

2015-01-01

203

Bonding in transition-metal cluster compounds. 2. The metal cluster-borane analogy  

Microsoft Academic Search

Following the detailed discussion of the transition-metal cluster moiety Mâ(..mu..â-X)â in the preceding paper, a more general account of the importance of the d electrons in transition-metal cluster chemistry is presented. The putative analogy with borane clusters (and their derivatives) is examined critically. Although an isolobal relationship exists between, e.g., BH and appropriate ML\\/sub n\\/ fragments (e.g. conical Fe(CO)â), this

R. G. Woolley

1985-01-01

204

Metal-insulator phase transition in vanadium oxides films  

Microsoft Academic Search

Vanadium oxide films (VO2) are of a typical phase transition ranging between metal phase to a semi-conducting phase. The theoretical metamorphose temperature of VO2 is around 340K (67°C). This transition temperature is mostly governed by the deposition method in which the film was made, and the film's composition. Optical and electrical properties of VO2 films are dramatically changed during this

G. Golan; A. Axelevitch; B. Sigalov; B. Gorenstein

2003-01-01

205

Mechanism for bipolar resistive switching in transition metal oxides  

Microsoft Academic Search

Resistive andom access memories (RRAM) composed of a transtition metal oxide dielectric in a capacitor-like structure is a candidate technology for next generation non-volatile memory devices. We introduce a model that accounts for the bipolar resistive switching phenomenom observed in many perovskite transition metal oxides. It qualitatively describes the electric field-enhanced migration of oxygen vacancies at the nano-scale. The numerical

Marcelo Rozenberg; Maria Jose Sanchez; Ruben Weht; Carlos Acha; Fernando Gomez-Marlasca; Pablo Levy

2010-01-01

206

High temperature superconductivity in metallic region near Mott transition  

E-print Network

The spin-singlet superconductivity without phonons is examined in consideration of correlations on an extended Hubbard model. It is shown that the superconductivity requires not only the total correlation should be strong enough but also the density of state around Fermi energy should be large enough, which shows that the high temperature superconductivity could only be found in the metallic region near the Mott metal insulator transition (MIT). Other properties of superconductors are also discussed on these conclusions.

Tian De Cao

2009-09-11

207

Single-centre MO theory of transition metal complexes  

Microsoft Academic Search

The full multi-centre molecular Hamiltonian in the local density approximation for a mononuclear transition metal complex is transformed into a single-centre Hamiltonian explicitly including overlap, covalency and ligand-field effects. The orbital interactions of the metal d-orbitals with the ligand orbitals appear as a repulsive pseudopotential yielding the dominant contribution to the ligand-field splitting. The reliability of this approach is examined

S. Lebernegg; G. Amthauer; M. Grodzicki

2008-01-01

208

Transport properties of transition-metal-encapsulated Si cages  

Microsoft Academic Search

We performed density functional pseudopotential calculations of the spin dependent transport through transition-metal-atom-encapsulated Si cages Si12X(X=Mn, Fe and Co). The effect of the metal atom on conductance is studied. Mn and Fe doped systems show highly spin polarized transmission whereas the magnetization in Co doped system is quenched. It is found that electrons are transferred from Si atoms into the

Lingzhu Kong; James R. Chelikowsky

2008-01-01

209

The transition from population III to population II star formation in the early universe  

NASA Astrophysics Data System (ADS)

The first stars in the universe formed in a unique environment that was free of heavy elements. The lack of efficient radiative cooling in primordial gas meant that the collapse of the first star-forming cloud-cores proceeded very slowly and without fragmenting into multiple objects. This resulted in the first stars being very massive (30 [Special characters omitted.] <= M <= 300 [Special characters omitted.] ), isolated objects. When these stars died, in violent supernovae, they produced the very first heavy elements, or metals, and dispersed them into the surrounding gas. The addition of these metals changed forever the way stars formed by allowing the gas to cool much more efficiently as it collapsed. It is thought that when the chemical abundance in the next generation star-forming environments reached a critical level, the process of star-formation began producing stars that resemble those observed in the local universe, with characteristic masses of ~1 [Special characters omitted.] , instead of the behemoths of the early universe. Simulating this transition in star-formation mode requires the inclusion of the complex chemistry and radiative cooling of heavy elements, which has traditionally been too computationally expensive to be done properly in three- dimensional simulations. In this dissertation, I introduce a new method for treating the radiative cooling from metals in large-scale, three-dimensional hydrodynamic simulations that is fast, accurate, and complete in its coverage of the first 30 elements. I use this cooling method to examine the ability of metals to induce fragmentation in collapsing gas-clouds through lowering of the cooling time-scales and the creation of thermal instabilities. Comparing the cooling and dynamical time-scales within collapsing gas, I calculate that the critical metallicity, Z cr , required for fragmentation into multiple, low-mass objects is ~10 -4.2 [Special characters omitted.] , where [Special characters omitted.] denotes the metallicity of the sun. Thermal instabilities are also present in gas-clouds with metallicities, Z >= 10^-4 [Special characters omitted.] . I use the methodology introduced here to perform a series of adaptive mesh refinement hydrodynamic simulations of pre-enriched primordial star-formation with varying metallicities. For metallicities below Z cr , only massive, singular objects form, nearly identical to the metal-free case. For metallicities well above Z cr , efficient cooling rapidly lowers the gas temperature to the temperature of the cosmic microwave background (CMB), which is significantly higher in the distant past. The gas is physically unable to radiatively cool below the CMB temperature, and thus, becomes very thermally stable. For moderately high metallicities, Z >= 10 -3.5 [Special characters omitted.] , this occurs early in the evolution of the gas-cloud, when the central density is still relatively low. The resulting cloud-cores show little or no fragmentation, and have mass-scales of a few hundred [Special characters omitted.] . On the other hand, if the metallicity is only slightly above Z cr , the cloud slowly cools without ever reaching the CMB temperature. In this case, the minimum cloud temperature is achieved at much higher densities than in the high-metallicity case, resulting in mass-scales of just a few [Special characters omitted.] . This implies that not 2, but 3 star-formation modes were present in the early universe: primordial (high-mass), metallicity-regulated (low-mass), and CMB-regulated (moderate-mass). As the universe evolves to the current epoch, the CMB-regulated mode will slowly transition into the metallicity-regulated mode, as the CMB temperature gradually decreases. This suggests that the metallicity-regulated mode, which is fully dominant today, may not become so until the CMB temperature drops below the observed temperatures of molecular clouds, ~10 K, which does not occur until redshift, z ~ 2.

Smith, Britton Devon

210

Electronic and Magnetic properties of Transition Metal Borides.  

NASA Astrophysics Data System (ADS)

Boron has three valance electron and a small covalent radius undergoing sp2 hybridization in many boron clusters. It is also known to form large variety of crystal structures both planer and 3D caged molecules. Our current work is to study transition metal boride clusters. This would be useful towards designing metal boride nanoclusters with tunable optical, magnetic and electron transport properties. Different stoichiometries are studied. The metal to Boron ratio varies from 0.3 to 0.75. For each of these compositions the lowest energy geometries were determined by optimizing the bond length for several initial symmetric geometries. The lowest energy structure is then chosen as the equilibrium structure. Most strikingly, all these transition-metal boride clusters are cage-like although both boron and transition metal usually favor high coordination number. We also find that some of the clusters have an extremely high magnetic moment per unit mass. This renders metal boride nanoparticles as potentially promising light-weighted magnetic materials. All the calculations are done using the spin-polarized density functional theory method implemented in the Vienna ab initio simulation package. A plane wave basis set with (400 eV cutoff) was used in combination with an all electron like projector augmented wave potential and PBE exchange correlation functional with in the generalized gradient approximation.

Herwadkar, Aditi; Zhao, Yufeng

2009-03-01

211

Early warning signals of desertification transitions in semiarid ecosystems  

NASA Astrophysics Data System (ADS)

The identification of early warning signals for regime shifts in ecosystems is of crucial importance given their impact in terms of economic and social effects. We present here the results of a theoretical study on the desertification transition in semiarid ecosystems under external stress. We performed numerical simulations based on a stochastic cellular automaton model, and we studied the dynamics of the vegetation clusters in terms of percolation theory, assumed as an effective tool for analyzing the geometrical properties of the clusters. Focusing on the role played by the strength of external stresses, measured by the mortality rate m , we followed the progressive degradation of the ecosystem for increasing m , identifying different stages: first, the fragmentation transition occurring at relatively low values of m , then the desertification transition at higher mortality rates, and finally the full desertification transition corresponding to the extinction of the vegetation and the almost complete degradation of the soil, attained at the maximum value of m . For each transition we calculated the spanning probabilities as functions of m and the percolation thresholds according to different spanning criteria. The identification of the different thresholds is proposed as an useful tool for monitoring the increasing degradation of real-world finite-size systems. Moreover, we studied the time fluctuations of the sizes of the biggest clusters of vegetated and nonvegetated cells over the entire range of mortality values. The change of sign in the skewness of the size distributions, occurring at the fragmentation threshold for the biggest vegetation cluster and at the desertification threshold for the nonvegetated cluster, offers new early warning signals for desertification. Other new and robust indicators are given by the maxima of the root-mean-square deviation of the distributions, which are attained respectively inside the fragmentation interval, for the vegetated biggest cluster, and inside the desertification interval, for the nonvegetated cluster.

Corrado, Raffaele; Cherubini, Anna Maria; Pennetta, Cecilia

2014-12-01

212

Molecular Dynamics Study of the Role of Transition Metal Atoms in Nucleation Process of SWNTs  

E-print Network

Molecular Dynamics Study of the Role of Transition Metal Atoms in Nucleation Process of SWNTs-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan The role of transition metal atoms in the nucleation process atoms and several transition metal atoms (Fe, Co and Ni) based on DFT calculations of small metal

Maruyama, Shigeo

213

Factors that affect Li mobility in layered lithium transition metal oxides Kisuk Kang and Gerbrand Ceder*  

E-print Network

Factors that affect Li mobility in layered lithium transition metal oxides Kisuk Kang and Gerbrand in layered lithium transition metal oxides are systematically studied in this paper by means of first, and the nature of the metal ion in the transition metal layer have all been proposed to influence the Li mobility

Ceder, Gerbrand

214

Compared optical properties of noble and transition metal-dielectric granular films  

E-print Network

249 Compared optical properties of noble and transition metal-dielectric granular films S. Berthier properties according to the nature of the metallic inclusion : noble or transition. A comparison between Au these proper- ties depend on the nature ofthe metallic inclusion in the compound : noble metal or transition

Paris-Sud XI, Université de

215

The metal-insulator transition of VO2 J.-P. Pouget  

E-print Network

The metal-insulator transition of VO2 revisited J.-P. Pouget Laboratoire de Physique des Solides of metallic VO2 · Insulating ground states · Role of the lattice in the metal-insulator transition of VO2 · General phase diagram of VO2 and its substituants #12;VO2: 1st order metal-insulator transition at 340K

Paris-Sud 11, Université de

216

Transition radiation in metal-metal multilayer nanostructures as a medical source of hard x-ray radiation  

E-print Network

Transition radiation in metal-metal multilayer nanostructures as a medical source of hard x; accepted 20 July 2006; published online 31 August 2006 We show that a periodic metal-metal multilayer nanostructure can serve as an efficient source of hard x-ray transition radiation. Our research effort is aimed

Kaplan, Alexander

217

Preparation of nanoporous metal foam from high nitrogen transition metal complexes  

DOEpatents

Nanoporous metal foams are prepared by ignition of high nitrogen transition metal complexes. The ammonium salts of iron(III) tris[bi(tetrazolato)-amine], cobalt(III) tris(bi(tetrazolato)amine), and high nitrogen compounds of copper and silver were prepared as loose powders, pressed into pellets and wafers, and ignited under an inert atmosphere to form nanoporous metal foam monoliths having very high surface area and very low density.

Tappan, Bryce C.; Huynh, My Hang; Hiskey, Michael A.; Son, Steven F.; Oschwald, David M.; Chavez, David E.; Naud, Darren L.

2006-11-28

218

Role of transition metal ferrocyanides (II) in chemical evolution  

NASA Astrophysics Data System (ADS)

Due to ease of formation of cyanide under prebiotic conditions, cyanide ion might have formed stable complexes with transition metal ions on the primitive earth. In the course of chemical evolution insoluble metal cyano complexes, which settled at the bottom of primeval sea could have formed peptide and metal amino acid complexes through adsorption processes of amino acids onto these metal cyano complexes. Adsorption of amino acids such as glycine, aspartic acid, and histidine on copper ferrocyanide and zinc ferrocyanide have been studied over a wide pH range of 3.6 8.5. Amino acids were adsorbed on the metal ferrocyanide complexes for different time periods. The progress of the adsorption was followed spectro-photometrically using ninhydrin reagent. Histidine was found to show maximum adsorption on both the adsorbents at neutral pH. Zinc ferrocyanide exhibits good sorption behaviour for all the three amino acids used in these investigations.

Kamaluddin; Nath, Mala; Deopujari, Sushama W.; Sharma, Archana

1990-05-01

219

Chromospheric, transition layer and coronal emission of metal deficient stars  

NASA Technical Reports Server (NTRS)

It is shown that while MgII k line emission decreases for metal deficient stars, the Ly alpha emission increases. The sum of chromospheric hydrogen and metallic emission appears to be independent of metal abundances. The total chromospheric energy loss is estimated to be 0.0004 F sub bol. The chromospheric energy input does not seem to decrease for increasing age. The transition layer emission is reduced for metal deficient stars, but it is not known whether the reduction is larger than can be explained by curve of growth effects only. Coronal X-ray emission was measured for 4 metal deficient stars. Within a 12 limit it could still be consistent with the emission of solar abundance stars.

Boehm-Vitense, E.

1982-01-01

220

Stable singlet carbenes as mimics for transition metal centers  

PubMed Central

This perspective summarizes recent results, which demonstrate that stable carbenes can activate small molecules (CO, H2, NH3 and P4) and stabilize highly reactive intermediates (main group elements in the zero oxidation state and paramagnetic species). These two tasks were previously exclusive for transition metal complexes. PMID:21743834

Martin, David; Soleilhavoup, Michele

2011-01-01

221

Hall effect at a tunable metal-insulator transition  

E-print Network

electronlike conductivity, with a magnitude that increases with decreasing conductivity. R-0 diverges at the metal-insulator transition, and displays critical behavior with exponent -1 [R(0)similar to(H-H-C)(-1)]. This dependence is interpreted as a linear...

Teizer, Winfried; Hellman, F.; Dynes, RC.

2003-01-01

222

A simple empirical N-body potential for transition metals  

Microsoft Academic Search

A simple form of multi-ion interaction has been constructed for the purpose of atomistic simulation of transition metals. The model energy consists of a bonding term, which is the square-root of a site density ?i, summed over atoms i, and a repulsive pairwise term of the form The site density ?i is defined as sum over neighbouring sites j of

M. W. Finnis; J. E. Sinclair

1984-01-01

223

On correlation in the first row transition metal atoms  

NASA Technical Reports Server (NTRS)

CI (SD) calculations using both SCF and MCSCF references have been performed for the first-row transition metal atoms. Basis sets as large as 84 STO's have been used. At the highest level of calculation, good agreement with experiment is found. If relativistic effects are considered, the agreement is somewhat poorer. This aspect, as well as the trends and results, is discussed.

Bauschlicher, C. W., Jr.; Walch, S. P.; Partridge, H.

1982-01-01

224

Transition Metal Photoredox Catalysis of Radical Thiol-Ene Reactions  

PubMed Central

We describe the anti-Markovnikov hydrothiolation of olefins using visible light absorbing transition metal photocatalysts. The key thiyl radical intermediates are generated upon quenching of photoexcited Ru*(bpz)32 with a variety of thiols. The adducts of a wide variety of olefins and thiols are formed in excellent yield (73–99%). PMID:23094660

Tyson, Elizabeth L.; Ament, Michael S.

2012-01-01

225

Transition Metal Catalysed Heterocycle Synthesis Asymmetric Processes and Catalysis  

E-print Network

are interested in all aspects of catalysis relevant to organic synthesis. One area interest is the activationTransition Metal Catalysed Heterocycle Synthesis Asymmetric Processes and Catalysis New Reaction Organic Chemistry Seminar University of Oxford Exploring New Reactivity and Selectivity Using Rhodium

Takada, Shoji

226

Transport properties of transition metal impurities on gold nanowires  

Microsoft Academic Search

Performing first principles density functional theory (DFT) we calculated the electronic and transport properties of a Au thin nanowire with transition metal atoms (Mn, Fe, Ni or Co) bridging the two sides of the Au nanowire. We will show that these systems have strong spin dependent transport properties and that the local symmetry can dramatically change them, leading to a

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

2009-01-01

227

Electronic Spectrum of a Transition Metal Complex Frank Rioux  

E-print Network

Electronic Spectrum of a Transition Metal Complex Frank Rioux Chemistry Department CSB | SJU is fully consistent with the experimental spectrum. The d-orbital energy level diagrams for Oh and D4h of the character table shows that in octahedral symmetry the degeneracy of the d-orbitals is split into a three

Rioux, Frank

228

Simple model for the Darwinian transition in early evolution  

E-print Network

It has been hypothesized that in the era just before the last universal common ancestor emerged, life on earth was fundamentally collective. Ancient life forms shared their genetic material freely through massive horizontal gene transfer (HGT). At a certain point, however, life made a transition to the modern era of individuality and vertical descent. Here we present a minimal model for this hypothesized "Darwinian transition." The model suggests that HGT-dominated dynamics may have been intermittently interrupted by selection-driven processes during which genotypes became fitter and decreased their inclination toward HGT. Stochastic switching in the population dynamics with three-point (hypernetwork) interactions may have destabilized the HGT-dominated collective state and led to the emergence of vertical descent and the first well-defined species in early evolution. A nonlinear analysis of a stochastic model dynamics covering key features of evolutionary processes (such as selection, mutation, drift and HGT...

Arnoldt, Hinrich; Timme, Marc

2015-01-01

229

Modeling a delayed phase transition in the early universe  

NASA Astrophysics Data System (ADS)

We use an effective field-theoretical model to describe a QCD-type phase transition in the early universe. It is assumed that the formation of a new phase proceeds via supercooling and thermal activation. A subsequent rolling-down process is characterized by a microscopic time scale of a few fm/C. An iterative scheme is formulated where the Hubble parameter is determined self-consistently with the order parameter dynamics. A possibility of a ‘mini-inflation’ scenario is discussed critically. On the macroscopic scale (?s) the delayed phase transition is described dynamically by solving the Friedman equations. The evolution through the mixed phase after supercooling/reheating is considered and the entropy generated in this process is estimated.

Yueker, Daniel; Mishustin, Igor; Bleicher, Marcus

2014-12-01

230

Distinct Metallization and Atomization Transitions in Dense Liquid Hydrogen  

NASA Astrophysics Data System (ADS)

We perform molecular dynamics simulations driven by accurate quantum Monte Carlo forces on dense liquid hydrogen. There is a recent report of a complete atomization transition between a mixed molecular-atomic liquid and a completely dissociated fluid in an almost unaccessible pressure range [Nat. Commun. 5, 3487 (2014)]. Here, instead, we identify a different transition between the fully molecular liquid and the mixed-atomic fluid at ˜400 GPa , i.e., in a much more interesting pressure range. We provide numerical evidence supporting the metallic behavior of this intermediate phase. Therefore, we predict that the metallization at finite temperature occurs in this partially dissociated molecular fluid, well before the complete atomization of the liquid. At high temperature this first-order transition becomes a crossover, in very good agreement with the experimental observation. Several systematic tests supporting the quality of our large scale calculations are also reported.

Mazzola, Guglielmo; Sorella, Sandro

2015-03-01

231

Distinct metallization and atomization transitions in dense liquid hydrogen.  

PubMed

We perform molecular dynamics simulations driven by accurate quantum Monte Carlo forces on dense liquid hydrogen. There is a recent report of a complete atomization transition between a mixed molecular-atomic liquid and a completely dissociated fluid in an almost unaccessible pressure range [Nat. Commun. 5, 3487 (2014)]. Here, instead, we identify a different transition between the fully molecular liquid and the mixed-atomic fluid at ?400??GPa, i.e., in a much more interesting pressure range. We provide numerical evidence supporting the metallic behavior of this intermediate phase. Therefore, we predict that the metallization at finite temperature occurs in this partially dissociated molecular fluid, well before the complete atomization of the liquid. At high temperature this first-order transition becomes a crossover, in very good agreement with the experimental observation. Several systematic tests supporting the quality of our large scale calculations are also reported. PMID:25815949

Mazzola, Guglielmo; Sorella, Sandro

2015-03-13

232

Electrocaloric effect of metal-insulator transition in VO2  

NASA Astrophysics Data System (ADS)

The electrocaloric effect was observed in association with an electric-field induced metal-insulator transition in VO2 using a calorimetric measurement under an applied voltage. For a VO2 plate with a 0.4 mm thickness located in the center of a capacitor-like structure, the metal-insulator transition was manipulated by applying a few volts. The occurrence of a transition in such a thick sample with relatively low voltage indicates that a surface charge accumulation mechanism is effective. The isothermal entropy change reached 94 J kg-1 K-1, while the adiabatic temperature change was calculated as -3.8 K under a voltage change of 0-3 V. The large entropy change is attributed to correlation of the complex freedom among spin, charge, and lattice.

Matsunami, Daichi; Fujita, Asaya

2015-01-01

233

Continuity and Respect for Diversity: Strengthening Early Transitions in Peru. Working Papers in Early Childhood Development, No. 56. Studies in Early Childhood Transitions  

ERIC Educational Resources Information Center

This working paper is part of a series on early transitions from "Young Lives," a 15-year longitudinal study of childhood poverty in Ethiopia, India, Peru and Vietnam. It explores the diverse experiences of 28 children from four contrasting communities in Peru as they start school. These detailed case studies highlight common problems: exclusion…

Ames, Patricia; Rojas, Vanessa; Portugal, Tamia

2010-01-01

234

Wetting Transition for Carbon Nanotube Arrays under Metal Contacts.  

PubMed

Structural arrays with nanoscale spacing arise in many device concepts. Carbon nanotube transistors are an extreme example, where a practical technology will require arrays of parallel nanotubes with spacing of order 10 nm or less. We show that with decreasing pitch there is a first-order transition, from a robust structure in which the metal wets the substrate between tubes, to a poorly wetting structure in which the metal rides atop the nanotube array without touching the substrate. The latter is analogous to the superhydrophobic "lotus leaf effect." There is a sharp minimum in the delamination energy of metal contacts at the transition pitch. We discuss implications for contact resistance and possible mitigation strategies. PMID:25768770

Perebeinos, V; Tersoff, J

2015-02-27

235

Wetting Transition for Carbon Nanotube Arrays under Metal Contacts  

NASA Astrophysics Data System (ADS)

Structural arrays with nanoscale spacing arise in many device concepts. Carbon nanotube transistors are an extreme example, where a practical technology will require arrays of parallel nanotubes with spacing of order 10 nm or less. We show that with decreasing pitch there is a first-order transition, from a robust structure in which the metal wets the substrate between tubes, to a poorly wetting structure in which the metal rides atop the nanotube array without touching the substrate. The latter is analogous to the superhydrophobic "lotus leaf effect." There is a sharp minimum in the delamination energy of metal contacts at the transition pitch. We discuss implications for contact resistance and possible mitigation strategies.

Perebeinos, V.; Tersoff, J.

2015-02-01

236

Formation of carbyne and graphyne on transition metal surfaces  

NASA Astrophysics Data System (ADS)

The electronic and geometric structures of carbyne on various transition metal surfaces were investigated by theoretical calculations. It was found that carbyne on non-active metal surfaces has a polyynic structure, while a polycumulenic structure is more stable on active catalyst surfaces. The self-assembly of carbyne on a metal substrate could lead to the synthesis of graphyne.The electronic and geometric structures of carbyne on various transition metal surfaces were investigated by theoretical calculations. It was found that carbyne on non-active metal surfaces has a polyynic structure, while a polycumulenic structure is more stable on active catalyst surfaces. The self-assembly of carbyne on a metal substrate could lead to the synthesis of graphyne. Electronic supplementary information (ESI) available: Computational details and structural information of carbon chains on Ni(111) and Rh(111) surfaces, carbon island on Cu(111), Ni(111), Rh(111) and Ru(0001) surfaces. See DOI: 10.1039/c4nr03757j

Yuan, Qinghong; Ding, Feng

2014-10-01

237

Stable Isotopes of Transition and Post-Transition Metals as Tracers in Environmental Studies  

Microsoft Academic Search

\\u000a The transition and post-transition metals, which include the elements in Groups 3–12 of the Periodic Table, have a broad range\\u000a of geological and biological roles as well as industrial applications and thus are widespread in the environment. Interdisciplinary\\u000a research over the past decade has resulted in a broad understanding of the isotope systematics of this important group of\\u000a elements and

Thomas D. Bullen

238

Cross-linking proteins with bimetallic tetracarboxylate compounds of transition metals  

DOEpatents

Stable cross-linked complexes of transition-metal tetracarboxylates and proteins are formed. The preferred transition-metal is rhodium. The protein may be collagen or an enzyme such as a proteolytic enzyme.

Kostic, Nenad M. (Ames, IA); Chen, Jian (Ames, IA)

1991-03-05

239

ORBITAL ORDERING IN TRANSITION-METAL COMPOUNDS: I. THE 120-DEGREE MODEL  

E-print Network

ORBITAL ORDERING IN TRANSITION-METAL COMPOUNDS: I. THE 120-DEGREE MODEL MAREK BISKUP,1 LINCOLN of transition- metal compounds where the very existence of long-range order has heretofore been a matter of some

240

An Alternative Approach to the Teaching of Systematic Transition Metal Chemistry.  

ERIC Educational Resources Information Center

Presents an alternative approach to teaching Systematic Transition Metal Chemistry with the transition metal chemistry skeleton features of interest. The "skeleton" is intended as a guide to predicting the chemistry of a selected compound. (Author/SA)

Hathaway, Brian

1979-01-01

241

Cross-linking proteins with bimetallic tetracarboxylate compounds of transition metals  

DOEpatents

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

Kostic, N.M.; Chen, J.

1991-03-05

242

Kentucky Early Childhood Transition Project. Evaluation Report: Quality and Impact of Transition Training and Technical Assistance Services  

ERIC Educational Resources Information Center

The Kentucky Early Childhood Transition Project (KECTP) was funded in 1992 by the Kentucky Department of Education and later expanded with support from the Kentucky Early Intervention System, to provide training and technical assistance to local communities in the state of Kentucky on effective transitions. KECTP was an outgrowth of Project STEPS,…

Interdisciplinary Human Development Institute, 2002

2002-01-01

243

Electronic and bonding analysis of hardness in pyrite-type transition-metal pernitrides  

NASA Astrophysics Data System (ADS)

Most commonly known hard transition-metal nitrides crystallize in rocksalt structure (B1). The discovery of ultraincompressible pyrite-type PtN2 10 years ago has raised a question about the cause of its exceptional mechanical properties. We answer this question by a systematic computational analysis of the pyrite-type PtN2 and other transition-metal pernitrides (MN2) with density functional theory. Apart from PtN2, the three hardest phases are found among them in the 3d transition-metal period. They are MnN2, CoN2, and NiN2, with computed Vickers hardness (HV) values of 19.9 GPa, 16.5 GPa, and 15.7 GPa, respectively. Harder than all of these is PtN2, with a HV of 23.5 GPa. We found the following trends and correlations that explain the origin of hardness in these pernitrides. (a) Charge transfer from M to N controls the length of the N-N bond, resulting in a correlation with bulk modulus, dominantly by providing Coulomb repulsion between the pairing N atoms. (b) Elastic constant C44, an indicator of mechanical stability and hardness is correlated with total density of states at EF, an indicator of metallicity. (c) Often cited monotonic variation of HV and Pugh's ratio with valence electron concentration found in rocksalt-type early transition-metal nitrides is not evident in this structure. (d) The change in M-M bond strength under a shearing strain indicated by crystal orbital Hamilton population is predictive of hardness. This is a direct connection between a specific bond and shear related mechanical properties. This panoptic view involving ionicity, metallicity, and covalency is essential to obtain a clear microscopic understanding of hardness.

Liu, Z. T. Y.; Gall, D.; Khare, S. V.

2014-10-01

244

Family structure and the transition to early parenthood.  

PubMed

With the rise in out-of-wedlock childbearing and divorce in the last quarter of the twentieth century, an increasing proportion of children have been exposed to a variety of new family forms. Little research has focused on the consequences of childhood family structure for men's transition to fatherhood or on the family processes that account for the effects of family structure on the likelihood that young women and men become first-time unmarried parents, what we now call "fragile families." The data come from the linked Children and Young Adult samples of the 1979 National Longitudinal Survey of Youth (NLSY79), which provide information on the children of the women of the NLSY79 from birth until they enter young adulthood. Females growing up with a single parent and males experiencing an unstable family transition to parenthood early, particularly to nonresidential fatherhood for males. For males, the effects are strongly mediated by parenting processes and adolescent behaviors and are shaped by economic circumstances. Having experienced multiple transitions as a child is associated with a reduced likelihood that males father their first child within marriage and an increased likelihood that they become fathers within cohabitation, demonstrating how changes in family structure alter family structure patterns over time and generations. PMID:20608104

Hofferth, Sandra L; Goldscheider, Frances

2010-05-01

245

Family Structure and the Transition to Early Parenthood  

PubMed Central

With the rise in out-of-wedlock childbearing and divorce in the last quarter of the twentieth century, an increasing proportion of children have been exposed to a variety of new family forms. Little research has focused on the consequences of childhood family structure for men’s transition to fatherhood or on the family processes that account for the effects of family structure on the likelihood that young women and men become first-time unmarried parents, what we now call “fragile families.” The data come from the linked Children and Young Adult samples of the 1979 National Longitudinal Survey of Youth (NLSY79), which provide information on the children of the women of the NLSY79 from birth until they enter young adulthood. Females growing up with a single parent and males experiencing an unstable family transition to parenthood early, particularly to nonresidential fatherhood for males. For males, the effects are strongly mediated by parenting processes and adolescent behaviors and are shaped by economic circumstances. Having experienced multiple transitions as a child is associated with a reduced likelihood that males father their first child within marriage and an increased likelihood that they become fathers within cohabitation, demonstrating how changes in family structure alter family structure patterns over time and generations. PMID:20608104

HOFFERTH, SANDRA L.; GOLDSCHEIDER, FRANCES

2010-01-01

246

Metal-Insulator Transition of Dirac Fermions: Variational Cluster Study  

NASA Astrophysics Data System (ADS)

A comparative study is made on the metal-insulator transition of Dirac fermions in the honeycomb and ?-flux Hubbard models at half filling by means of the variational cluster approximation and cluster dynamical impurity approximation. Paying particular attention to the choice of the geometry of solver clusters and the inclusion of particle-bath sites, we show that the direct transition from the Dirac semimetallic state to the antiferromagnetic Mott insulator state occurs in these models, and therefore, the spin liquid phase is absent in the intermediate region, in agreement with recent quantum-Monte-Carlo-based calculations.

Ebato, Masaki; Kaneko, Tatsuya; Ohta, Yukinori

2015-04-01

247

Holographic Polarons, the Metal-Insulator Transition and Massive Gravity  

E-print Network

Massive gravity is holographically dual to `realistic' materials with momentum relaxation. The dual graviton potential encodes the phonon dynamics and it allows for a much broader diversity than considered so far. We construct a simple family of isotropic and homogeneous materials that exhibit an interaction-driven Metal-Insulator transition. The transition is triggered by the formation of polarons -- phonon-electron quasi-bound states that dominate the conductivities, shifting the spectral weight above a mass gap. We characterize the polaron gap, width and dispersion.

Matteo Baggioli; Oriol Pujolas

2014-11-19

248

Early and Late Stage Metals and Sulfides in Diogenites  

NASA Technical Reports Server (NTRS)

Diogenites are typically highly brecciated orthopyroxenites that contain 84-100 vol.% orthopyroxene. Common accessory minerals include olivine, chromite, Ca-pyroxene, plagioclase, silica, troilite and Fe-Ni metal. Metal and sulfides are minor phases in diogenites with an average abundance of < 1 vol.% and 0-2 vol.% respectively. However their presence is important, as they could provide information on T-fO2-fS2 conditions and the evolution of the diogenite parent magma during crystallization and/or later metamorphism. We have examined the occurrence of Fe-Ni metal and sulfides in thin sections of several diogenites including, Johnstown, Manegaon, Roda, Shalka, Bilanga, and Tatahouine using optical microscopy and the electron microprobe. Here, we describe three features of metals and sulfides that are common in most of these diogenites. These are: i) The widespread occurrence of pentlandite associated with copper and copper sulfide minerals; ii) Textural evidence that at least some of the metal and sulfide occurring interstitially between, and as inclusions within, orthopyroxene formed from an early immiscible sulfide-oxide liquid; iii) That this sulfide- oxide liquid subsequently fractionated into assemblages containing either Fe-Ni metal, troilite, and chromite or pentlandite, troilite, and copper-bearing sulfide.

Sideras, L. C.; Domanik, K. J.; Lauretta, D. S.

2004-01-01

249

Structural electronic and phonon properties of some transition metal aluminides  

NASA Astrophysics Data System (ADS)

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).

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

2012-06-01

250

Is the chiral phase transition induced by a metal-insulator transition?  

E-print Network

We investigate the QCD Dirac operator with gauge configurations given by a liquid of instantons in the region of temperatures about the chiral phase transition. Both the quenched and unquenched cases are examined in detail. We present evidence of a localization transition in the low lying modes of the Dirac operator around the same temperature as the chiral phase transition. Thus both level statistics and eigenvectors of the QCD Dirac operator at the chiral phase transition have similar properties than those of a disordered conductor at the metal-insulator transition. This strongly suggests the phenomenon of Anderson localization (localization by destructive quantum interference) is the leading physical mechanism in the restoration of the chiral symmetry. Finally we argue that our findings are not in principle restricted to the ILM approximation and may also be found in lattice simulations.

Antonio M. Garcia-Garcia; James C. Osborn

2007-11-18

251

Topological Phase Transitions in Periodically Modulated Quantized Metal Films Alexander E. Meyerovicha)  

E-print Network

Topological Phase Transitions in Periodically Modulated Quantized Metal Films Alexander E topological phase transitions (ETT) are pre- dicted for any quantized metal Ã?lms with a periodically mod topological phase transition (ETT; see Ref. [3] and references therein) can occur in any quantized metal Ã?lm

Meyerovich, Alex

252

Periodic Properties of Force Constants of Small Transition-Metal and Lanthanide Clusters  

E-print Network

Periodic Properties of Force Constants of Small Transition-Metal and Lanthanide Clusters John R 2. Silver 2440 3. Gold 2441 J. Group 12 2441 1. Zinc/Cadmium/Mercury 2441 IV. Transition-Metal. Trimers 2448 VII. Higher Clusters 2450 A. Transition Metals 2450 B. Higher Lanthanide Clusters 2452 VIII

Lombardi, John R.

253

Transition Metal Dimer Internuclear Distances from Measured Force Constants Joseph L. Jules and John R. Lombardi*  

E-print Network

Transition Metal Dimer Internuclear Distances from Measured Force Constants Joseph L. Jules distances, have been extended to the transition metal dimers to test which one gives the most accurate fit's and Guggenheimer's for the transition metal dimers. Although Pauling's rule gives the best results, the remarkable

Lombardi, John R.

254

A Spectromicroscopic Study of 3d Transition Metal Interactions with Humic Acid; A bright  

E-print Network

A Spectromicroscopic Study of 3d Transition Metal Interactions with Humic Acid; A bright future the interactions between environmentally important 3d transition metals and functional groups of soil organic Synchrotron Light Source (NSLS) (Upton NY), to study the interactions of 3d transition metals with functional

Sparks, Donald L.

255

A continuous Mott transition between a metal and a quantum spin liquid Ryan V. Mishmash,1  

E-print Network

A continuous Mott transition between a metal and a quantum spin liquid Ryan V. Mishmash,1 Iv-Thouless-like) quantum phase transition between a metal and a gapless spin liquid characterized by a spinon Fermi sea, i transitions to metallic phases have a long history reaching back into the pioneering work of Mott1,2 . However

256

Chemisorption of hydrocarbon species on transition metals during diamond chemical vapor deposition  

E-print Network

1 Chemisorption of hydrocarbon species on transition metals during diamond chemical vapor associated with chemisorption of hydrocarbon species on transition metals during diamond chemical vapor on transition metals are estimated on the basis of published results. The estimated chemisorption energies of CH

Dandy, David

257

Comparative assessment of density functional methods for 3d transition-metal chemistry  

E-print Network

Comparative assessment of density functional methods for 3d transition-metal chemistry Yan Zhao the newly developed M05 functional against a data set of reaction energies for transition-metal chemistry conclusions: 1 TPSS gives the best performance for calculating the binding energies of three transition-metal

Truhlar, Donald G

258

Dense Electron System from Gate-Controlled Surface Metal-Insulator Transition  

E-print Network

Dense Electron System from Gate-Controlled Surface Metal- Insulator Transition Kai Liu,,, Deyi Fu modulation. A surface insulator-to-metal transition is electrostatically triggered, thereby collapsing: Vanadium dioxide, 2D electron system, electrostatic gating, metal-insulator transition Electric

Wu, Junqiao

259

Energetics of hydrogen coverage on group VIII transition metal surfaces and a kinetic model for adsorptiondesorption  

E-print Network

Energetics of hydrogen coverage on group VIII transition metal surfaces and a kinetic model packed surface for all nine group VIII transition metals as a function of surface coverage using quantum transition metals, leading to results consistent with available surface science studies. We then use

Goddard III, William A.

260

Transition Metal Defect Behavior and Si Density of States in the Processing Temperature Regime  

E-print Network

Transition Metal Defect Behavior and Si Density of States in the Processing Temperature Regime A to make predictive models of transition metal gettering during semiconductor processing, a complete gap, the effective density of states of the conduction and valence bands, and the transition metal

Dunham, Scott

261

Identifying cysteines and histidines in transition metal binding sites using support vector machines and neural networks  

E-print Network

Identifying cysteines and histidines in transition metal binding sites using support vector that participate in binding of several transition metals and iron complexes. The method predicts histidines. We predict histidines and cysteines in transition metal binding sites at 73% precision and 61% recall

Passerini, Andrea

262

Understanding the NMR shifts in paramagnetic transition metal oxides using density functional theory calculations  

E-print Network

Understanding the NMR shifts in paramagnetic transition metal oxides using density functional of the lithium local environment and electronic configuration of the transition metal ions. We focus structure. In order to understand the spin-density transfer mechanism from the transition metal ion

Ceder, Gerbrand

263

Designing Multielectron Lithium-Ion Phosphate Cathodes by Mixing Transition Metals  

E-print Network

Designing Multielectron Lithium-Ion Phosphate Cathodes by Mixing Transition Metals Geoffroy Hautier is to develop materials capable of exchanging more than one Li atom per transition metal. However, constraints transition metals in crystal structures known to be able to accommodate lithium in insertion and delithiation

Ceder, Gerbrand

264

First-row transition metal dichalcogenide catalysts for hydrogen evolution reaction  

E-print Network

First-row transition metal dichalcogenide catalysts for hydrogen evolution reaction Desheng Kong,a Judy J. Cha,a Haotian Wang,b Hye Ryoung Leec and Yi Cui*ad A group of first-row transition metal introduce a group of highly active HER cata- lysts from rst-row transition metal dichalcogenides

Cui, Yi

265

Magnetic field induced insulator to metal transition in amorphous-GdxSi1 x  

E-print Network

Magnetic field induced insulator to metal transition in amorphous-GdxSi1 x W. Teizer*, F. Hellman resistance and magnetoresistance near the metal­insulator transition in films of the amorphous alloys GdxSi1 of magnitude at low T, crosses through an insulator to metal transition and approaches the conductivity of a

Hellman, Frances

266

Raman Spectroelectrochemistry -A Way of Switching the Peierls Transition in Metallic  

E-print Network

Raman Spectroelectrochemistry - A Way of Switching the Peierls Transition in Metallic Single of the first optical transition in metallic SWNTs [5], thus assuming intercalation-like doping levels (up to 0.005|e|/C-atom. This rules out a depletion of the first "metallic" transition as a possible reason

Nabben, Reinhard

267

Trends in elasticity and electronic structure of transition-metal nitrides and carbides from first principles  

E-print Network

Trends in elasticity and electronic structure of transition-metal nitrides and carbides from first 2005 The elastic properties of selected transition-metal TM nitrides and carbides in B1 structure DFPT makes it possible now to obtain elastic constants directly and more accurately.4,5 Transition-metal

Wu, Zhigang

268

VO2 films with strong semiconductor to metal phase transition prepared by the precursor oxidation process  

E-print Network

VO2 films with strong semiconductor to metal phase transition prepared by the precursor oxidation, the precursor oxidation process, for making VO2 films with strong semiconductor-to-metal phase transition and sharpness hysteresis width TC of T-dependent semiconductor-to-metal hysteretic phase transition in VO2 were

Luryi, Serge

269

ccsd-00002151,version1-25Jun2004 Modelisation of transition and noble metal vicinal  

E-print Network

ccsd-00002151,version1-25Jun2004 Modelisation of transition and noble metal vicinal surfaces, F-91 405 Orsay, France #12;Abstract. The energetics of transition and noble metal (Rh, Pd, Cu]. On the contrary, in the case of transition metals, T

Boyer, Edmond

270

Characterization and Modeling of Metal-Insulator Transition (MIT) Based Tunnel Junctions E. Freeman1  

E-print Network

Characterization and Modeling of Metal-Insulator Transition (MIT) Based Tunnel Junctions E. Freeman low voltage operation [1]. In this work, we explore the abrupt metal to insulator transition (MIT switching TFET. As illustrated in Fig.1 the metal insulator transition MIT in materials with strong electron

Yener, Aylin

271

Thermochemistry of alloys of transition metals and lanthanide metals with some IIIB and IVB elements in the periodic table  

Microsoft Academic Search

We have conducted systematic studies in this laboratory of the thermochemistry of transition metal and rare earth alloys by high temperature calorimetric methods. An overview of the thermochemistry of the alloys of the transition metals and lanthanide metals with elements in the IIIB and IVB columns of the periodic table is presented. The enthalpies of formation of most of these

S. V. Meschel; O. J. Kleppa

2001-01-01

272

Resonant Ultrasound Studies of Complex Transition Metal Oxides  

SciTech Connect

Department of Energy EPSCoR The University of Mississippi Award: DE-FG02-04ER46121 Resonant Ultrasound Spectroscopy Studies of Complex Transition Metal Oxides The central thrust of this DOE funded research program has been to apply resonant ultrasound spectroscopy (RUS), an elegant and efficient method for determining the elastic stiffness constants of a crystal, to the complex and poorly understood class of materials known as transition metal oxides (TMOs). Perhaps the most interesting and challenging feature of TMOs is their strongly correlated behavior in which spin, lattice, and charge degrees of freedom are strongly coupled. Elastic constants are a measure of the interatomic potentials in a crystal and are thus sensitive probes into the atomic environment. This sensitivity makes RUS an ideal tool to study the coupling of phase transition order parameters to lattice strains. The most significant result of the project has been the construction of a high temperature RUS apparatus capable of making elastic constant measurements at temperatures as high as 1000 degrees Celsius. We have designed and built novel acoustic transducers which can operate as high as 600 degrees Celsius based on lithium niobate piezoelectric elements. For measurement between 600 to 1000 C, a buffer rod system is used in which the samples under test and transducers are separated by a rod with low acoustic attenuation. The high temperature RUS system has been used to study the charge order (CO) transition in transition metal oxides for which we have discovered a new transition occurring about 35 C below the CO transition. While the CO transition exhibits a linear coupling between the strain and order parameter, this new precursor transition shows a different coupling indicating a fundamentally different mechanism. We have also begun a study, in collaboration with the Jet Propulsion Laboratory, to study novel thermoelectric materials at elevated temperatures. These materials include silicon germanium with various doping and Zintl phase materials. Such materials show promise for increased figures of merit, vital to making thermolectrics competitive with traditional power generation mechanisms.

Dr. Henry Bass; Dr. J. R. Gladden

2008-08-18

273

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

Microsoft Academic Search

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

Sergey Y. Sarkisov; Silvia Picozzi

2007-01-01

274

Multiferroic materials based on organic transition-metal molecular nanowires.  

PubMed

We report on the density functional theory aided design of a variety of organic ferroelectric and multiferroic materials by functionalizing crystallized transition-metal molecular sandwich nanowires with chemical groups such as -F, -Cl, -CN, -NO(2), ?O, and -OH. Such functionalized polar wires exhibit molecular reorientation in response to an electric field. Ferroelectric polarizations as large as 23.0 ?C/cm(2) are predicted in crystals based on fully hydroxylized sandwich nanowires. Furthermore, we find that organic nanowires formed by sandwiching transition-metal atoms in croconic and rhodizonic acids, dihydroxybenzoquinone, dichloro-dihydroxy-p-benzoquinone, or benzene decorated by -COOH groups exhibit ordered magnetic moments, leading to a multiferroic organometallic crystal. When crystallized through hydrogen bonds, the microscopic molecular reorientation translates into a switchable polarization through proton transfer. A giant interface magnetoelectric response that is orders of magnitude greater than previously reported for conventional oxide heterostructure interfaces is predicted. PMID:22881120

Wu, Menghao; Burton, J D; Tsymbal, Evgeny Y; Zeng, Xiao Cheng; Jena, Puru

2012-09-01

275

Ductile-to-brittle transition in spallation of metallic glasses  

SciTech Connect

In this paper, the spallation behavior of a binary metallic glass Cu{sub 50}Zr{sub 50} is investigated with molecular dynamics simulations. With increasing the impact velocity, micro-voids induced by tensile pulses become smaller and more concentrated. The phenomenon suggests a ductile-to-brittle transition during the spallation process. Further investigation indicates that the transition is controlled by the interaction between void nucleation and growth, which can be regarded as a competition between tension transformation zones (TTZs) and shear transformation zones (STZs) at atomic scale. As impact velocities become higher, the stress amplitude and temperature rise in the spall region increase and micro-structures of the material become more unstable. Therefore, TTZs are prone to activation in metallic glasses, leading to a brittle behavior during the spallation process.

Huang, X. [State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190 (China); Institute of Systems Engineering, China Academy of Engineering Physics, Mianyang, Sichuan 621999 (China); Ling, Z. [State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190 (China); Dai, L. H., E-mail: lhdai@lnm.imech.ac.cn [State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190 (China); State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology, Beijing 10081 (China)

2014-10-14

276

Exciton complexes in low dimensional transition metal dichalcogenides  

SciTech Connect

We examine the excitonic properties of layered configurations of low dimensional transition metal dichalcogenides (LTMDCs) using the fractional dimensional space approach. The binding energies of the exciton, trion, and biexciton in LTMDCs of varying layers are analyzed, and linked to the dimensionality parameter ?, which provides insight into critical electro-optical properties (relative oscillator strength, absorption spectrum, exciton-exciton interaction) of the material systems. The usefulness of ? is highlighted by its independence of the physical mechanisms underlying the confinement effects of geometrical structures. Our estimates of the binding energies of exciton complexes for the monolayer configuration of transition metal dichalcogenides suggest a non-collinear structure for the trion and a positronium-molecule-like square structure for the biexciton.

Thilagam, A., E-mail: thilaphys@gmail.com [Information Technology, Engineering and Environment, University of South Australia, Adelaide 5095 (Australia)

2014-08-07

277

[Spectroscopic studies on transition metal ions in colored diamonds].  

PubMed

Transition metals like nickel, cobalt and iron have been often used as solvent catalysts in high pressure high temperature (HPHT) synthesis of diamond, and nickel and cobalt ions have been found in diamond lattice. Available studies indicated that nickel and cobalt ions could enter the lattice as interstitial or substitutional impurities and form complexes with nitrogen. Polarized microscopy, SEM-EDS, EPR, PL and FTIR have been used in this study to investigate six fancy color natural and synthetic diamonds in order to determine the spectroscopic characteristics and the existing forms of transition metal ions in colored diamond lattice. Cobalt-related optical centers were first found in natural chameleon diamonds, and some new nickel and cobalt-related optical and EPR centers have also been detected in these diamond samples. PMID:15766067

Meng, Yu-Fei; Peng, Ming-Sheng

2004-07-01

278

Tailoring magnetic skyrmions in ultra-thin transition metal films.  

PubMed

Skyrmions in magnetic materials offer attractive perspectives for future spintronic applications since they are topologically stabilized spin structures on the nanometre scale, which can be manipulated with electric current densities that are by orders of magnitude lower than those required for moving domain walls. So far, they were restricted to bulk magnets with a particular chiral crystal symmetry greatly limiting the number of available systems and the adjustability of their properties. Recently, it has been experimentally discovered that magnetic skyrmion phases can also occur in ultra-thin transition metal films at surfaces. Here we present an understanding of skyrmions in such systems based on first-principles electronic structure theory. We demonstrate that the properties of magnetic skyrmions at transition metal interfaces such as their diameter and their stability can be tuned by the structure and composition of the interface and that a description beyond a micromagnetic model is required in such systems. PMID:24893652

Dupé, Bertrand; Hoffmann, Markus; Paillard, Charles; Heinze, Stefan

2014-01-01

279

Recent Advances in Transition Metal-Catalyzed Glycosylation  

PubMed Central

Having access to mild and operationally simple techniques for attaining carbohydrate targets will be necessary to facilitate advancement in biological, medicinal, and pharmacological research. Even with the abundance of elegant reports for generating glycosidic linkages, stereoselective construction of ?- and ?-oligosaccharides and glycoconjugates is by no means trivial. In an era where expanded awareness of the impact we are having on the environment drives the state-of-the-art, synthetic chemists are tasked with developing cleaner and more efficient reactions for achieving their transformations. This movement imparts the value that prevention of waste is always superior to its treatment or cleanup. This review will highlight recent advancement in this regard by examining strategies that employ transition metal catalysis in the synthesis of oligosaccharides and glycoconjugates. These methods are mild and effective for constructing glycosidic bonds with reduced levels of waste through utilization of sub-stoichiometric amounts of transition metals to promote the glycosylation. PMID:22924154

McKay, Matthew J.; Nguyen, Hien M.

2012-01-01

280

THz induced insulator to metal transition in VO2 metamaterial  

NASA Astrophysics Data System (ADS)

We use metamaterial enhanced high field terahertz (THz) pulses (up to ˜4MV/cm) to induce the insulator-to-metal transition in vanadium dioxide (VO2) thin films at 320K. Ultrafast THz field enhancement in the gaps of metamaterial split ring resonators releases free electrons in VO2 by the Poole-Frenkel effect. The accelerated hot electrons transfer energy to the lattice via electron phonon coupling inducing the persistent metallic phase. A large nonlinear signature is observed in VO2 as modulations of the metamaterial resonance on a picosecond time scale. Our results provide insight into electric field induced phase transitions in VO2 and paves the way for studying nonlinear high THz field effects in many other strongly correlated materials.

Liu, Mengkun; Hwang, Harold; Tao, Hu; Strikwerda, Andrew; Fan, Kebin; Keiser, George; Sternbach, Aaron; West, Kevin; Kittiwatanakul, Salinporn; Lu, Jiwei; Wolf, Stuart; Omenetto, Fiorenzo; Zhang, Xin; Nelson, Keith; Averitt, Richard

2012-02-01

281

Meyer Neldel rule application to silicon supersaturated with transition metals  

NASA Astrophysics Data System (ADS)

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?2–1012?S depending on the annealing energy density. A semi-logarithmic plot of the pre-exponential factor versus activation energy shows an almost perfect linear behaviour as stated by the Meyer Neldel rule. The Meyer Neldel energy obtained for implantation with different transition metals and also annealed in different conditions is 22?meV, which is within the range of silicon phonons, thus confirming the hypothesis of the multi excitation entropy theory.

García-Hemme, Eric; García-Hernansanz, Rodrigo; Olea, Javier; Pastor, David; del Prado, Alvaro; Mártil, Ignacio; González-Díaz, Germán

2015-02-01

282

Transition Metal Exchanged Zeolite Layers for Selectivity Enhancement of Metal-Oxide Semiconductor Gas Sensors  

Microsoft Academic Search

A novel method of improving the selectivity of metal oxide gas sensors has been developed by using catalytically active molecular sieve materials. They have been successfully introduced into a proprietary sensor array. The cracking patterns of linear alkanes over transition metal exchanged zeolite Y have been measured using a zeolite bed\\/GC\\/MS experimental set-up within a temperature range of 300degC to

Dominic P. Mann; Keith F. E. Pratt; Themis Paraskeva; Ivan P. Parkin; David E. Williams

2007-01-01

283

The energetics of ordered intermetallic alloys (of the transition metals)  

SciTech Connect

The atomically ordered phases in ordered transition metal alloys are discussed. This chapter is divided into: physical parameters controlling phase stability (Hume-Rothery, structural maps, Miedema Hamiltonian), wave functions & band theory, comment on entropy terms, cohesive energies (electron promotion energies, Hund`s rule on orbital effects), structural energies/stabilities of elemental solids, total energies and atomic positions, charge transfer (Au alloys, charge tailing), heats of formation of ordered compounds.

Watson, R.E.; Weinert, M.; Davenport, J.W. [Brookhaven National Lab., Upton, NY (United States); Fernando, G.W. [Connecticut Univ., Storrs, CT (United States). Dept. of Physics; Bennett, L.H. [National Inst. of Standards and Technology, Gaithersburg, MD (United States). Metallurgy Div.

1992-10-01

284

The energetics of ordered intermetallic alloys (of the transition metals)  

SciTech Connect

The atomically ordered phases in ordered transition metal alloys are discussed. This chapter is divided into: physical parameters controlling phase stability (Hume-Rothery, structural maps, Miedema Hamiltonian), wave functions band theory, comment on entropy terms, cohesive energies (electron promotion energies, Hund's rule on orbital effects), structural energies/stabilities of elemental solids, total energies and atomic positions, charge transfer (Au alloys, charge tailing), heats of formation of ordered compounds.

Watson, R.E.; Weinert, M.; Davenport, J.W. (Brookhaven National Lab., Upton, NY (United States)); Fernando, G.W. (Connecticut Univ., Storrs, CT (United States). Dept. of Physics); Bennett, L.H. (National Inst. of Standards and Technology, Gaithersburg, MD (United States). Metallurgy Div.)

1992-01-01

285

Zwitterionic Group VIII transition metal initiators supported by olefin ligands  

DOEpatents

A zwitterionic Group VIII transition metal complex containing the simple and relatively small 3-(arylimino)-but-1-en-2-olato ligand that catalyzes the formation of polypropylene and high molecular weight polyethylene. A novel feature of this catalyst is that the active species is stabilized by a chelated olefin adduct. The present invention also provides methods of polymerizing olefin monomers using zwitterionic catalysts, particularly polypropylene and high molecular weight polyethylene.

Bazan, Guillermo C. (Goleta, CA); Chen, Yaofeng (Shanghai, CN)

2011-10-25

286

Novel Transition Metal Compounds with Promising Thermoelectric Properties  

NASA Technical Reports Server (NTRS)

Progress in the search for new high temperature thermoelectric materials at the Jet Propulsion Laboratory is reviewed. Novel transition metal compounds were selected as potential new high performance thermoelectric materials and criteria of selection are presented and discussed. Samples of these new compounds were prepared at JPL by a variety of techniques. Encouraging experimental results obtained on several of these compounds are reported and show that they have the potential to be the next generation of thermoelectric materials.

Caillat, T.; Borshchevsky, A.; Fleurial, J. -P.

1993-01-01

287

Ab initio molecular dynamics for open-shell transition metals  

Microsoft Academic Search

We show that quantum-mechanical molecular-dynamics simulations in a finite-temperature local-density approximation based on the calculation of the electronic ground state and of the Hellmann-Feynman forces after each time step are feasible for liquid noble and transition metals. This is possible with the use of Vanderbilt-type ``ultrasoft'' pseudopotentials and efficient conjugate-gradient techniques for the determination of the electronic ground state. Results

G. Kresse; J. Hafner

1993-01-01

288

Orbital order in classical models of transition-metal compounds  

E-print Network

We study the classical 120-degree and related orbital models. These are the classical limits of quantum models which describe the interactions among orbitals of transition-metal compounds. We demonstrate that at low temperatures these models exhibit a long-range order which arises via an "order by disorder" mechanism. This strongly indicates that there is orbital ordering in the quantum version of these models, notwithstanding recent rigorous results on the absence of spin order in these systems.

Zohar Nussinov; Marek Biskup; Lincoln Chayes; Jeroen van den Brink

2004-06-04

289

Reductive dechlorination catalyzed by bacterial transition-metal coenzymes  

Microsoft Academic Search

The bacterial transition-metal coenzymes vitamin Bââ (Co), coenzyme Fâââ (ni), and hematin (Fe) catalyzed the reductive dechlorination of polychlorinated ethylenes and benzenes, whereas the electron-transfer proteins four-iron ferredoxin, two-iron ferredoxin, and azurin (Cu) did not. For vitamin Bââ and coenzyme Fâââ, reductive dechlorination rates for different classes of perchlorinated compounds had the following order: carbon tetrachloride > tetrachloroethylene > hexachlorobenzene.

Charles J. Gantzer; Lawrence P. Wackett

1991-01-01

290

Magnetic properties of 4d transition-metal clusters  

Microsoft Academic Search

We analyze the stability of magnetic states obtained within the tight-binding model solved by molecular dynamics for cubo-octahedral (fcc) and icosahedral clusters of 3d (Ni and Co) and 4d (Pd, Rh, and Ru) transition metals. The magnetic states are stabilized by the Hund's rule exchange interaction between the d orbitals. Taking realistic parameters deduced from band structure calculations and spectroscopic

Brigitte Piveteau; Marie-Catherine Desjonquères; Andrzej M. Oles; Daniel Spanjaard

1996-01-01

291

Trigonal-prismatic coordination in solid compounds of transition metals  

Microsoft Academic Search

The ligand-field splitting of d levels in trigonal-prismatic coordination is discussed in terms of crystal-field and simple molecular-orbital calculations. It is found that d-covalency provides a stabilizing factor for trigonal-prismatic coordination, as compared with octahedral coordination, for atoms with d0, d1 or d2 configuration. This effect qualitatively explains the occurrence of trigonal-prismatic coordination in strongly covalent 4d and 5d transition-metal

R. Huisman; R. de Jonge; C. Haas; F. Jellinek

1971-01-01

292

Golcao calculation of electronic spectra of transition-metal compounds  

Microsoft Academic Search

1.Basic concepts are presented on electron-spectrum calculation for crystalline substances using the GOLCAO method.2.Detailed calculations are presented on the electron spectra of transition-metal diborides.3.The calculations have been used to estimate electron structure parameters such as dissociation energy, atomic charge, electron-state filling, and statistical weights of atoms with stable electronic configurations.4.There is a relationship between the trends in the properties of

Yu. M. Goryachev; B. A. Kovenskaya; G. V. Samsonov

1974-01-01

293

Ferro- and Antiferromagnetism of Transition Metals and Alloys  

Microsoft Academic Search

The interaction between two neighboring localized magnetic moments in the transition metals and alloys in studied by using the Anderson model generalized to the case of five-fold degenerate d-orbitals. The effective exchange energy and the change of the localized moments due to the d-d covalent admixture are calculated by using the Hartree-Fock approximation and the Green function technique. The results

Tôru Moriya

1965-01-01

294

Strain-induced semimetal-metal transition in silicene  

Microsoft Academic Search

The effect of the tensile strain on the electronic structure of the silicene is studied by using first-principles density functional theory. It is found that a semimetal-metal transition occurs when an in-plane strain larger than 7.5% is applied in silicene. The downward movement of the lowest conduction band at ?-point, which originates from the weakened interaction between neighboring Si atoms,

G. Liu; M. S. Wu; C. Y. Ouyang; B. Xu

2012-01-01

295

Preparation of nanocomposites containing nanoclusters of transition metals  

SciTech Connect

New nanocomposites containing nanoclusters of transition metals have been prepared and characterized by TEM, XRD, and energy dispersive spectroscopy. Organometallic or other coordination compounds functionalized with trialkoxysilyl groups have been synthesized and covalently incorporated into silica xerogels using standard sol-gel techniques. Thermal oxidative treatment of these xerogels in air followed by reduction in hydrogen yielded the desired nanocomposite phases. Using these methods, Mo, Re, Fe, Ru, Os, Pd, Pt, Cu. and Ag nanocomposites have been prepared.

Milne, S.B.; Lukehart, C.M., Wittig, J.E. [Vanderbilt Univ., Nashville, TN (United States)] [and others

1996-10-01

296

Structure of liquid transition and rare earth metals S. N. Khanna and F. Cyrot-Lackmann  

E-print Network

L-45 Structure of liquid transition and rare earth metals S. N. Khanna and F. Cyrot-Lackmann Groupe It is shown that the observed structure factors of transition and rare earth liquid metals can be reaso- nably. The difference is particularly large for V, Ti, and rare earth metals which are precisely the metals where

Boyer, Edmond

297

Quantum phase transition from an antiferromagnet to a spin liquid in a metal  

E-print Network

We study quantum phase transitions from easy-plane antiferromagnetic metals to paramagnetic metals in Kondo-Heisenberg lattice systems. If the paramagnetic metal is a fractionalized Fermi liquid then the universal critical ...

Grover, Tarun

298

Dynamically Tracking the Strain Across the Metal-Insulator Transition in VO2 Measured Using Electromechanical Resonators  

E-print Network

Dynamically Tracking the Strain Across the Metal-Insulator Transition in VO2 Measured Using electromechanical device across the metal-insulator transition. Simultaneous resistance and resonance measurements, NEMS, lattice softening, phase transition, metal-insulator transition The metal-insulator transition

Wu, Junqiao

299

Speed limit of the insulator-metal transition in magnetite  

NASA Astrophysics Data System (ADS)

As the oldest known magnetic material, magnetite (Fe3O4) has fascinated mankind for millennia. As the first oxide in which a relationship between electrical conductivity and fluctuating/localized electronic order was shown, magnetite represents a model system for understanding correlated oxides in general. Nevertheless, the exact mechanism of the insulator-metal, or Verwey, transition has long remained inaccessible. Recently, three-Fe-site lattice distortions called trimerons were identified as the characteristic building blocks of the low-temperature insulating electronically ordered phase. Here we investigate the Verwey transition with pump-probe X-ray diffraction and optical reflectivity techniques, and show how trimerons become mobile across the insulator-metal transition. We find this to be a two-step process. After an initial 300?fs destruction of individual trimerons, phase separation occurs on a 1.5±0.2?ps timescale to yield residual insulating and metallic regions. This work establishes the speed limit for switching in future oxide electronics.

de Jong, S.; Kukreja, R.; Trabant, C.; Pontius, N.; Chang, C. F.; Kachel, T.; Beye, M.; Sorgenfrei, F.; Back, C. H.; Bräuer, B.; Schlotter, W. F.; Turner, J. J.; Krupin, O.; Doehler, M.; Zhu, D.; Hossain, M. A.; Scherz, A. O.; Fausti, D.; Novelli, F.; Esposito, M.; Lee, W. S.; Chuang, Y. D.; Lu, D. H.; Moore, R. G.; Yi, M.; Trigo, M.; Kirchmann, P.; Pathey, L.; Golden, M. S.; Buchholz, M.; Metcalf, P.; Parmigiani, F.; Wurth, W.; Föhlisch, A.; Schüßler-Langeheine, C.; Dürr, H. A.

2013-10-01

300

Optical properties of transition metal oxide quantum wells  

NASA Astrophysics Data System (ADS)

Fabrication of a quantum well, a structure that confines the electron motion along one or more spatial directions, is a powerful method of controlling the electronic structure and corresponding optical response of a material. For example, semiconductor quantum wells are used to enhance optical properties of laser diodes. The ability to control the growth of transition metal oxide films to atomic precision opens an exciting opportunity of engineering quantum wells in these materials. The wide range of transition metal oxide band gaps offers unprecedented control of confinement while the strong correlation of d-electrons allows for various cooperative phenomena to come into play. Here, we combine density functional theory and tight-binding model Hamiltonian analysis to provide a simple physical picture of transition metal oxide quantum well states using a SrO/SrTiO3/SrO heterostructure as an example. The optical properties of the well are investigated by computing the frequency-dependent dielectric functions. The effect of an external electric field, which is essential for electro-optical devices, is also considered.

Lin, Chungwei; Posadas, Agham; Choi, Miri; Demkov, Alexander A.

2015-01-01

301

Probing early-universe phase transitions with CMB spectral distortions  

NASA Astrophysics Data System (ADS)

Global, symmetry-breaking phase transitions in the early universe can generate scaling seed networks which lead to metric perturbations. The acoustic waves in the photon-baryon plasma sourced by these metric perturbations, when Silk damped, generate spectral distortions of the cosmic microwave background (CMB). In this work, the chemical potential distortion (? ) due to scaling seed networks is computed and the accompanying Compton y -type distortion is estimated. The specific model of choice is the O (N ) nonlinear ? -model for N ?1 , but the results remain the same order of magnitude for other scaling seeds. If CMB anisotropy constraints to the O (N ) model are saturated, the resulting chemical potential distortion ? ?2 ×1 0-9 .

Amin, Mustafa A.; Grin, Daniel

2014-10-01

302

Probing early-universe phase transitions with CMB spectral distortions  

E-print Network

Global, symmetry-breaking phase transitions in the early universe can generate scaling seed networks which lead to metric perturbations. The acoustic waves in the photon-baryon plasma sourced by these metric perturbations, when Silk damped, generate spectral distortions of the cosmic microwave background (CMB). In this work, the chemical potential distortion ($\\mu$) due to scaling seed networks is computed and the accompanying Compton $y$-type distortion is estimated. The specific model of choice is the $O(N)$ nonlinear $\\sigma$-model for $N\\gg 1$, but the results remain the same order of magnitude for other scaling seeds. If CMB anisotropy constraints to the $O(N)$ model are saturated, the resulting chemical potential distortion $\\mu \\lesssim 2\\times 10^{-9}$.

Mustafa A. Amin; Daniel Grin

2014-05-15

303

Covalent functionalization of monolayered transition metal dichalcogenides by phase engineering  

NASA Astrophysics Data System (ADS)

Chemical functionalization of low-dimensional materials such as nanotubes, nanowires and graphene leads to profound changes in their properties and is essential for solubilizing them in common solvents. Covalent attachment of functional groups is generally achieved at defect sites, which facilitate electron transfer. Here, we describe a simple and general method for covalent functionalization of two-dimensional transition metal dichalcogenide nanosheets (MoS2, WS2 and MoSe2), which does not rely on defect engineering. The functionalization reaction is instead facilitated by electron transfer between the electron-rich metallic 1T phase and an organohalide reactant, resulting in functional groups that are covalently attached to the chalcogen atoms of the transition metal dichalcogenide. The attachment of functional groups leads to dramatic changes in the optoelectronic properties of the material. For example, we show that it renders the metallic 1T phase semiconducting, and gives it strong and tunable photoluminescence and gate modulation in field-effect transistors.

Voiry, Damien; Goswami, Anandarup; Kappera, Rajesh; Silva, Cecilia De Carvalho Castro E.; Kaplan, Daniel; Fujita, Takeshi; Chen, Mingwei; Asefa, Tewodros; Chhowalla, Manish

2015-01-01

304

Method for treating rare earth-transition metal scrap  

DOEpatents

Rare earth-transition metal (e.g., iron) scrap (e.g., Nd-Fe-B scrap) is flux (slag) remelted to reduce tramp non-metallic impurities, such as oxygen and nitrogen, and metallic impurities, such as Li, Na, Al, etc., picked up by the scrap from previous fabrication operations. The tramp impurities are reduced to concentrations acceptable for reuse of the treated alloy in the manufacture of end-use articles, such as permanent magnets. The scrap is electroslag or inductoslag melted using a rare earth fluoride-bearing flux of CaF[sub 2], CaCl[sub 2] or mixtures thereof or the slag resulting from practice of the thermite reduction process to make a rare earth-iron alloy. 3 figs.

Schmidt, F.A.; Peterson, D.T.; Wheelock, J.T.; Jones, L.L.

1992-12-29

305

Method for treating rare earth-transition metal scrap  

DOEpatents

Rare earth-transition metal (e.g., iron) scrap (e.g., Nd-Fe-B scrap) is flux (slag) remelted to reduce tramp non-metallic impurities, such as oxygen and nitrogen, and metallic impurities, such as Li, Na, Al, etc., picked up by the scrap from previous fabrication operations. The tramp impurities are reduced to concentrations acceptable for reuse of the treated alloy in the manufacture of end-use articles, such as permanent magnets. The scrap is electroslag or inductoslag melted using a prefused, rare earth fluoride-bearing flux of CaF.sub.2, CaCl.sub.2 or mixtures thereof or the slag resulting from practice of the thermite reduction process to make a rare earth-iron alloy.

Schmidt, Frederick A. (Ames, IA); Peterson, David T. (Ames, IA); Wheelock, John T. (Nevada, IA); Jones, Lawrence L. (Des Moines, IA)

1992-12-29

306

Thermophysical Property Measurements of Silicon-Transition Metal Alloys  

NASA Technical Reports Server (NTRS)

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

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

2014-01-01

307

Transition-metal prion protein attachment: Competition with copper  

NASA Astrophysics Data System (ADS)

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.

Hodak, Miroslav; Bernholc, Jerry

2012-02-01

308

Stability of Multiferroic Transition in FeVO4 against Transition Metal Doping  

NASA Astrophysics Data System (ADS)

FeVO4 is a recently discovered multiferroic material which undergoes successive antiferromagnetic phase transitions at TN1 ˜ 22 K and TN2 ˜ 15 K, with ferroelectricity developing at the TN2 transition. FeVO4 is a type II multiferroic where the ferroelectricity is magnetically driven. We have studied the effect of transition metal doping on these two phase transitions in order to explore how the multiferroic order is affected by introducing perturbations into the lattice. We synthesized polycrystalline MxFe1-xVO4 samples (M = Zn, Mn, Cr) using a standard solid state reaction method, and we used magnetic, dielectric, and heat capacity measurements to track the transition temperatures. Both magnetic and heat capacity measurements show clear peaks at the two transitions, enabling us to map how the transitions are suppressed as the doping fraction is changed. On doping with non magnetic Zn, we find only a minimal suppression of both transition temperatures, indicating the magnetic interactions producing the multiferroic order are surprisingly robust against non-magnetic perturbations. We will also present preliminary results of the effects of magnetic dopants, specifically Mn and Cr.

Kumarasiri, Akila; Dixit, Ambesh; Lawes, Gavin

2012-02-01

309

Transition Metal Speciation in the Cell: Insights from the Chemistry of Metal Ion Receptors  

NSDL National Science Digital Library

The essential transition metal ions are avidly accumulated by cells, yet they have two faces: They are put to use as required cofactors, but they also can catalyze cytotoxic reactions. Several families of proteins are emerging that control the activity of intracellular metal ions and help confine them to vital roles. These include integral transmembrane transporters, metalloregulatory sensors, and diffusible cytoplasmic metallochaperone proteins that protect and guide metal ions to targets. It is becoming clear that many of these proteins use atypical coordination chemistry to accomplish their unique goals. The different coordination numbers, types of coordinating residues, and solvent accessibilities of these sites are providing insight into the inorganic chemistry of the cytoplasm.

Lydia Finney (Northwestern University; Department of Chemistry, Molecular Biology and Cell Biology)

2003-05-09

310

Energy transitions in the early 21st Century  

SciTech Connect

We are in the early stages of a long and complex transition from a global economy based on fossil energy to an economy based on low carbon renewable energy. However, fossil fuel resources are abundant and widely distributed, and they will remain the dominant source of primary energy for at least the next quarter century. In the United States, displacement of coal by natural gas for electric power generation has done more to reduce CO2 emissions than all new renewables combined, and this may occur globally for the next decade or two, even if the European Union does not take advantage of its large unconventional natural gas resources. Greater energy efficiency (not including the efficiencies associated with displacement of coal by gas) will also be more important than new renewables. Cost/benefit ratios are important for sustainability of the transition, and some energy efficiency technologies and displacement of coal by natural gas have lower cost/benefit ratios than wind power, solar power or biofuels. Money spent on the large scale deployment of wind, solar and especially biofuels would be better spent on research, development and demonstration of a broader suite of technologies that would support the energy transition, with a focus on improving the cost benefit ratios of already deployed technologies and developing alternatives. Advanced nuclear reactors, engineered geothermal systems, fossil fuel recovery coupled with CO2 sequestration and pre-combustion or post-combustion decarbonation of fossil fuels with geological CO2 sequestration are among the technologies that might be more cost effective than wind, solar or biofuels, and biofuels have serious adverse societal and environment consequences.

Paul Meakin

2013-01-01

311

Structures and Reactivity of Transition-Metal Compounds Featuring Metal-Ligand Multiple Bonds  

E-print Network

to the formation of transition metal imido compound (M=NR). In the second system a cationic oxorhenium(V) complex reacts with a series of arylazides (N_(3)Ar) to give cationic cis-rhenium(VII) oxo imido complexes. Inductive effect is found in the reaction rates...

Xu, Zhenggang

2014-07-25

312

The nature of transition-metal-oxide surfaces  

NASA Astrophysics Data System (ADS)

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

Henrich, V. E.

313

Enhancing conductivity of metallic carbon nanotube networks by transition metal adsorption  

NASA Astrophysics Data System (ADS)

The conductivity of carbon nanotube thin films is mainly determined by carbon nanotube junctions, the resistance of which can be reduced by several different methods. We investigate electronic transport through carbon nanotube junctions in a four-terminal configuration, where two metallic single-wall carbon nanotubes are linked by a group 6 transition metal atom. The transport calculations are based on the Green's function method combined with the density-functional theory. The transition metal atom is found to enhance the transport through the junction near the Fermi level. However, the size of the nanotube affects the improvement in the conductivity. The enhancement is related to the hybridization of chromium and carbon atom orbitals, which is clearly reflected in the character of eigenstates near the Fermi level. The effects of chromium atoms and precursor molecules remaining adsorbed on the nanotubes outside the junctions are also examined.

Ketolainen, T.; Havu, V.; Puska, M. J.

2015-02-01

314

Alternative Kondo breakdown mechanism: Orbital-selective orthogonal metal transition  

E-print Network

In a recent paper of Nandkishore and Senthil [arxiv:1201.5998 (2012)], a concept of orthogonal metal has been introduced to reinterpret the disordered state of slave-spin representation in the Hubbard model as an exotic gapped metallic state. We extend this concept to study the corresponding quantum phase transition in the extended Anderson lattice model. It is found that the disordered state of slave spins in this model is an orbital-selective orthogonal metal, a generalization of the concept of the orthogonal metal in the Hubbard model. Near the quantum critical point the essential behaviors are dominated by a z = 3 critical mode, which is in contrast to the naive expectation in the Hubbard model. The result provides alternative Kondo breakdown mechanism for heavy fermion compounds underlying the physics of the orbital-selective orthogonal metal in the disordered state, which is different from the conventional Kondo breakdown mechanism with the fractionalized Fermi liquid picture. This work is expected to be useful in understanding the quantum criticality happening in some heavy fermion materials and other related strongly correlated systems.

Yin Zhong; Ke Liu; Yong-Qiang Wang; Hong-Gang Luo

2012-07-06

315

A new class of proteins capable of binding transition metals.  

PubMed

Ion uptake, transport, and sequestration are essential to meet the nutritional requirements for plant growth and development. Furthermore, regulation of these processes is critical for plants to tolerate toxic levels of ions. The examination of isoprenylated proteins encoded by Arabidopsis thaliana and Glycine max cDNAs revealed a unique family of proteins containing putative metal-binding motifs (the core sequence is M/LXCXXC). Here, we describe this new class of proteins, which are capable of being isoprenylated and binding transition metal ions. Members of this family contain consensus isoprenylation (CaaX) sites, which we demonstrate are efficiently isoprenylated in vitro. ATFP3, a representative of the Arabidopsis family, was expressed in Escherichia coli and examined for metal-binding activity in vitro. Analysis of the interaction of ATFP3 with metal-chelating columns (IMAC) suggested that it binds to Cu2+, Ni2+, or Zn2+. To test whether proteins with these characteristics are present in other plant species, tobacco BY2 cells were labeled in vivo with [14C]mevalonate and the resulting mevalonate-labeled proteins were tested for metal-binding activity. Several soluble, isoprenylated proteins which bound copper-IMAC columns were revealed. Consistent with a wide-spread distribution of these proteins in plants, their presence was observed in Arabidopsis, soybean, and tobacco. PMID:10561075

Dykema, P E; Sipes, P R; Marie, A; Biermann, B J; Crowell, D N; Randall, S K

1999-09-01

316

1398 J. Phys. Chem. 1994, 98, 1398-1406 Bond Strengths of Transition Metal Diatomics: Zr2, YCo, YNi, ZrCo, ZrNi, NbCo, and NbNi  

E-print Network

configurationof the atoms isnowcapableof forming a strong su2 bond, and in the early transition metals strong d-orbital1398 J. Phys. Chem. 1994, 98, 1398-1406 Bond Strengths of Transition Metal Diatomics: Zr2, YCo, YNi-late transition metal molecules YCo, YNi, ZrCo, ZrNi, NbCo, and NbNi. In these systems it is argued

Morse, Michael D.

317

Comparative study of the synthesis of layered transition metal molybdates  

SciTech Connect

Mixed metal oxides (MMOs) prepared by the mild thermal decomposition of layered double hydroxides (LDHs) differ in their reactivity on exposure to aqueous molybdate containing solutions. In this study, we investigate the reactivity of some T-Al containing MMOs (T=Co, Ni, Cu or Zn) towards the formation of layered transition metal molybdates (LTMs) possessing the general formula AT{sub 2}(OH)(MoO{sub 4}){sub 2}.H{sub 2}O, where A=NH{sub 4}{sup +}, Na{sup +} or K{sup +}. The phase selectivity of the reaction was studied with respect to the source of molybdate, the ratio of T to Mo and the reaction pH. LTMs were obtained on reaction of Cu-Al and Zn-Al containing MMOs with aqueous solutions of ammonium heptamolybdate. Rehydration of these oxides in the presence of sodium or potassium molybdate yielded a rehydrated LDH phase as the only crystalline product. The LTM products obtained by the rehydration of MMO precursors were compared with LTMs prepared by direct precipitation from the metal salts in order to study the influence of preparative route on their chemical and physical properties. Differences were noted in the composition, morphology and thermal properties of the resulting products. - Graphical abstract: Mixed metal oxides (MMOs) derived from layered double hydroxide precursors differ in their reactivity on exposure to aqueous molybdate containing solutions. We investigate the influence of the molybdate source, the rehydration pH and the ratio of T/Mo on the reactivity of some T-Al containing MMOs (T=Co, Ni, Cu or Zn) towards the formation of layered transition metal molybdates of general formula AT{sub 2}(OH)(MoO{sub 4}){sub 2}.H{sub 2}O (where A{sup +}=NH{sub 4}{sup +}, K{sup +} or Na{sup +}).

Mitchell, S.; Gomez-Aviles, A.; Gardner, C. [Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW (United Kingdom); Jones, W., E-mail: wj10@cam.ac.u [Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW (United Kingdom)

2010-01-15

318

Effect of the d electrons on phase transitions in transition-metal sesquioxides  

Microsoft Academic Search

We present a systematic density-functional study of phase relations in three 4d-transition-metal sesquioxides: Y2O3, Rh2O3, and In2O3. Y2O3 and In2O3 undergo pressure-induced transitions to phases with larger cation coordination number (from 6 to 7) at low pressures. However,\\u000a this does not occur in Rh2O3 at least up to ~300 GPa. This cannot be explained by usual arguments based on ionic-radii ratios

Koichiro UmemotoRenata; Renata M. Wentzcovitch

2011-01-01

319

N-heterocyclic carbene (NHC) complexes of group 4 transition metals.  

PubMed

Since the discovery of a stable N-heterocyclic carbene (NHC), the use of NHCs in chemistry has developed rapidly over the past two decades. These interesting compounds are predominantly employed in organometallic chemistry as ligands for various metal centers, and as organocatalysts for a variety of transformations. In particular, the NHC transition metal complexes have received widespread attention, and significant progress has been made in the development of group 4 NHC-complexes in the last few years. These group 4 NHC-complexes are of interest because of their unique structural properties, and their potential application in organic transformations and catalysis. This review covers the superior design strategies for NHC ligands to stabilize early transition metals and well-defined group 4 metal complexes with mono- and multi-dentate NHC ligands. In this context, four types of NHC-complexes, i.e., carbon-functionalized NHCs, nitrogen-functionalized NHCs, oxygen-functionalized NHCs and nitrogen/oxygen-functionalized unsymmetric NHCs, are described. In addition, the use of group 4 NHC-complexes as catalysts in olefin (co)polymerization, ring-opening polymerization of rac-lactide, copolymerization of epoxides and CO2, as well as hydroamination/cyclization of aminoalkenes, is presented. Furthermore, limitations and challenges are discussed. PMID:25608933

Zhang, Dao; Zi, Guofu

2015-04-01

320

[Assessment of early psychic dysfunctions due to metallic mercury].  

PubMed

The aim of the study was to find the most sensitive psychological test battery, useful for evaluation of the earliest dysfunctions in workers exposed to metallic mercury (Hg). To assess the above mentioned disorders, six tests of interference and four tests of motor reactions were applied. The examinations were performed in 44 male workers exposed to Hg in the process of acetic aldehyde synthesis. The control group was matched for sex, age and educational level. The obtained results showed that in the detection od early dysfunctions of the nervous system, psychological tests of interference are more useful than test of the motor reactions. This toxicological test battery can be recommended for monitoring workers exposed to metallic mercury. PMID:7991051

Sikora, A; Langauer-Lewowicka, H

1994-01-01

321

Mechanically induced metal-insulator transition in carbyne.  

PubMed

First-principles calculations for carbyne under strain predict that the Peierls transition from symmetric cumulene to broken-symmetry polyyne structure is enhanced as the material is stretched. Interpretation within a simple and instructive analytical model suggests that this behavior is valid for arbitrary 1D metals. Further, numerical calculations of the anharmonic quantum vibrational structure of carbyne show that zero-point atomic vibrations eliminate the Peierls distortion in the mechanically free chain, preserving the cumulene symmetry. The emergence and increase of Peierls dimerization under tension then implies a qualitative transition between the two forms, which our computations place around 3% strain. Thus, the competition between the zero-point vibrations and mechanical strain determines a switch in symmetry resulting in the transition from metallic state to a dielectric, with a small effective mass and a high carrier mobility. In any practical realization, it is important that the effect is also chemically modulated by the choice of terminating groups. These findings are promising for applications such as electromechanical switching and band gap tuning via strain, and besides carbyne itself, they directly extend to numerous other systems that show Peierls distortion. PMID:24991984

Artyukhov, Vasilii I; Liu, Mingjie; Yakobson, Boris I

2014-08-13

322

Nature of metal-nonmetal transition in metal-ammonia solutions. II. From uniform metallic state to inhomogeneous electronic microstructure.  

PubMed

Applying semianalytical models of nonideal plasma, we evaluate the behavior of the metallic phase in metal-ammonia solutions (MAS). This behavior is mainly controlled by the degenerate electron gas, which remains stable down to 5 MPM due to high solvent polarizability and strong dielectric screening of solvated ions. Comparing the behavior of the metallic state with those of localized solvated electrons, we have estimated the miscibility gap Delta n for various alkali metals and found Delta n(Na)>Delta n(K). It is rather narrow in Rb-NH3 and does not occur in Cs-NH3 solutions, which is in full agreement with the experiments. The case of Li is discussed separately. The difference calculated in the excess free energies of the metallic and nonmetallic phases is in the order of kBT, yielding a thermally fluctuating mixed state at intermediate metal concentrations. It results in a continuous metal-nonmetal (MNM) transition above the consolute point Tc and a phase separation below Tc. We propose a criterion for the MNM transition which may be attributed to the line of the maximum of compressibility above Tc. This line crosses the spinodal one at the critical temperature. Finally, we assert that a new electronic phase similar to microemulsion should also arise between the spinodal and the binodal lines. PMID:18412455

Chuev, Gennady N; Quémerais, Pascal

2008-04-14

323

Critical Transitions in Early Embryonic Aortic Arch Patterning and Hemodynamics  

PubMed Central

Transformation from the bilaterally symmetric embryonic aortic arches to the mature great vessels is a complex morphogenetic process, requiring both vasculogenic and angiogenic mechanisms. Early aortic arch development occurs simultaneously with rapid changes in pulsatile blood flow, ventricular function, and downstream impedance in both invertebrate and vertebrate species. These dynamic biomechanical environmental landscapes provide critical epigenetic cues for vascular growth and remodeling. In our previous work, we examined hemodynamic loading and aortic arch growth in the chick embryo at Hamburger-Hamilton stages 18 and 24. We provided the first quantitative correlation between wall shear stress (WSS) and aortic arch diameter in the developing embryo, and observed that these two stages contained different aortic arch patterns with no inter-embryo variation. In the present study, we investigate these biomechanical events in the intermediate stage 21 to determine insights into this critical transition. We performed fluorescent dye microinjections to identify aortic arch patterns and measured diameters using both injection recordings and high-resolution optical coherence tomography. Flow and WSS were quantified with 3D computational fluid dynamics (CFD). Dye injections revealed that the transition in aortic arch pattern is not a uniform process and multiple configurations were documented at stage 21. CFD analysis showed that WSS is substantially elevated compared to both the previous (stage 18) and subsequent (stage 24) developmental time-points. These results demonstrate that acute increases in WSS are followed by a period of vascular remodeling to restore normative hemodynamic loading. Fluctuations in blood flow are one possible mechanism that impacts the timing of events such as aortic arch regression and generation, leading to the variable configurations at stage 21. Aortic arch variations noted during normal rapid vascular remodeling at stage 21 identify a temporal window of increased vulnerability to aberrant aortic arch morphogenesis with the potential for profound effects on subsequent cardiovascular morphogenesis. PMID:23555940

Kowalski, William J.; Dur, Onur; Wang, Yajuan; Patrick, Michael J.; Tinney, Joseph P.; Keller, Bradley B.; Pekkan, Kerem

2013-01-01

324

Micro X-Ray Diffraction Study of VO2 Films -- Separation between Metal-Insulator Transition and Structural Phase Transition  

Microsoft Academic Search

It has been well-known that VO2 undergoes both a structural phase transition (SPT) from monoclinic (insulator phase) to tetragonal (metal phase) and a discontinuous first-order metal-insulator transition (MIT) (Jump) near 68^oC. When the MIT and the SPT occurs simultaneously, the MIT can be regarded as the Peierls transition. When both take place separately, the MIT can be interpreted as the

Kim Hyun-Tak; Kim Boung-Jun; Sungyeoul Choi; Jung-Wook Lim; Lim Jung-Wook; Hyun-Tak Kim; Youn Hwa-Sick; Hwa-Sick Yun

2008-01-01

325

Semiconductor-metal and metal-semiconductor transitions in twisting graphene nanoribbons  

NASA Astrophysics Data System (ADS)

The electronic structure and transport properties of twisting graphene nanoribbons (TGNRs) are systematically investigated using the tight-binding model and the non-equilibrium Green's function method. We show that the energy gap and conductance around the Fermi energy can be reversibly modulated. Armchair TGNRs (ATGNRs) can be either metallic or semiconducting depending on the widths and the twist angles of the GNRs. Semiconductor-metal and metal-semiconductor transitions are observed in ATGNRs for N=3i+1 (where i is an integer and N is the number of atoms along the width of the nanoribbon) and N=3i+2, respectively. Narrow ATGNRs are semiconductors for N=3i, whereas zigzag TGNRs (ZTGNRs) are metallic regardless of the width and distortion of the GNRs.

Xu, Ning; Huang, Bolong; Li, Jianfu; Wang, Baolin

2015-01-01

326

Supramolecular control of transition metal complexes in water by a hydrophobic cavity: a bio-inspired strategy.  

PubMed

Supramolecular chemistry in water is a very challenging research area. In biology, water is the universal solvent where transition metal ions play major roles in molecular recognition and catalysis. In enzymes, it participates in substrate binding and/or activation in the heart of a pocket defined by the folded protein. The association of a hydrophobic cavity with a transition metal ion is thus a very appealing strategy for controlling the metal ion properties in the very competitive water solvent. Various systems based on intrinsically water-soluble macrocyclic structures such as cyclodextrins, cucurbituryls, and metallo-cages have been reported. Others use calixarenes and resorcinarenes functionalized with hydrophilic substituents. One approach for connecting a metal complex to these cavities is to graft a ligand for metal ion binding at their edge. Early work with cyclodextrins has shown Michaelis-Menten like catalysis displaying enhanced kinetics and substrate-selectivity. Remarkable examples of regio- and stereo-selective transformation of substrates have been reported as well. Dynamic two-phase systems for transition metal catalysis have also been developed. They rely on either water-transfer of the metal complex through ligand embedment or synergistic coordination of a metal ion and substrate hosting. Another strategy consists in using metallo-cages, which provide a well-defined hydrophobic space, to stabilize metal complexes in water. When the cages can host simultaneously a substrate and a reactive metal complex, size- and regio-selective catalysis was obtained. Finally, construction of a polydentate coordination site closely interlocked with a calixarene or resorcinarene macrocycle has been shown to be a very fruitful strategy for obtaining metal complexes with remarkable hosting properties. For each of these systems, the synergism resulting from the biomimetic association of a hydrophobic cavity and a metal ion is discussed within the objective of developing new tools for either selective molecular recognition (with analytical perspectives) or performant catalysis, in water. PMID:25608497

Bistri, Olivia; Reinaud, Olivia

2015-02-24

327

Effect of the d electrons on phase transitions in transition-metal sesquioxides  

NASA Astrophysics Data System (ADS)

We present a systematic density-functional study of phase relations in three 4 d-transition-metal sesquioxides: Y2O3, Rh2O3, and In2O3. Y2O3 and In2O3 undergo pressure-induced transitions to phases with larger cation coordination number (from 6 to 7) at low pressures. However, this does not occur in Rh2O3 at least up to ~300 GPa. This cannot be explained by usual arguments based on ionic-radii ratios often used successfully to explain phase relations in simple-metal and rare-earth sesquioxides and sesquisulfides. Inspection of their electronic structures shows that, in Rh2O3, the electronic occupancy of 4 d orbitals, 4 d 6, plays a fundamental role in the extraordinary stability of the Rh2O3(II)-type phase with respect to coordination increase. We point out that d-orbital occupancy is a fundamental factor in explaining phase relations in transition-metal sesquioxides and sesquisulfides.

Umemoto, Koichiro; Wentzcovitch, Renata M.

2011-05-01

328

Theoretical study of transition-metal ions bound to benzene  

NASA Technical Reports Server (NTRS)

Theoretical binding energies are reported for all first-row and selected second-row transition metal ions (M+) bound to benzene. The calculations employ basis sets of at least double-zeta plus polarization quality and account for electron correlation using the modified coupled-pair functional method. While the bending is predominantly electrostatic, the binding energies are significantly increased by electron correlation, because the donation from the metal d orbitals to the benzene pi* orbitals is not well described at the self-consistent-field level. The uncertainties in the computed binding energies are estimated to be about 5 kcal/mol. Although the calculated and experimental binding energies generally agree to within their combined uncertainties, it is likely that the true binding energies lie in the lower portion of the experimental range. This is supported by the very good agreement between the theoretical and recent experimental binding energies for AgC6H6(+).

Bauschlicher, Charles W., Jr.; Partridge, Harry; Langhoff, Stephen R.

1992-01-01

329

Theory of the pairbreaking superconductor-metal transition in nanowires  

SciTech Connect

We present a detailed description of a zero temperature phase transition between superconducting and diffusive metallic states in very thin wires due to a Cooper pair breaking mechanism. The dissipative critical theory contains current reducing fluctuations in the guise of both quantum and thermally activated phase slips. A full cross-over phase diagram is computed via an expansion in the inverse number of complex components of the superconducting order parameter (one in the physical case). The fluctuation corrections to the electrical ({sigma}) and thermal ({kappa}) conductivities are determined, and we find that {sigma} has a non-monotonic temperature dependence in the metallic phase which may be consistent with recent experimental results on ultra-narrow wires. In the quantum critical regime, the ratio of the thermal to electrical conductivity displays a linear temperature dependence and thus the Wiedemann-Franz law is obeyed, with a new universal experimentally verifiable Lorenz number.

Del Maestro, Adrian [Department of Physics, Harvard University, 17 Oxford Street, Cambridge, MA 02138 (United States)], E-mail: adrian@delmaestro.org; Rosenow, Bernd; Sachdev, Subir [Department of Physics, Harvard University, 17 Oxford Street, Cambridge, MA 02138 (United States)

2009-03-15

330

Structural and Electronic Transitions in Ytterbium Metal to 202 GPa  

SciTech Connect

Ytterbium (Yb), a member of the rare earth group metals with a filled f shell and a divalent electronic character, has been studied under static high pressures in a diamond anvil cell to 202thinspthinspGPa. We report a new transformation from a face-centered-cubic structure to a hexagonal phase with 3thinspthinspatoms/cell (space group P3{sub 1}21 referred to as hP3 ) at 98{plus_minus}5 GPa . This hP3 phase is similar to that observed in trivalent neodymium and samarium at pressures near 40thinspthinspGPa. Our high pressure study thus clearly demonstrates that Yb is no longer an {open_quotes}irregular{close_quotes} member of the rare earth metals, and divalent to trivalent electronic transition is completed at megabar pressures. {copyright} {ital 1999} {ital The American Physical Society}

Chesnut, G.N.; Vohra, Y.K. [Department of Physics, University of Alabama at Birmingham (UAB), Birmingham, Alabama 35294-1170 (United States)] [Department of Physics, University of Alabama at Birmingham (UAB), Birmingham, Alabama 35294-1170 (United States)

1999-02-01

331

Investigations into Transition Metal Catalyzed Arene Trifluoromethylation Reactions  

PubMed Central

Trifluoromethyl-substituted arenes and heteroarenes are widely prevalent in pharmaceuticals and agrochemicals. As a result, the development of practical methods for the formation of aryl–CF3 bonds has become an active field of research. Over the past five years, transition metal catalyzed cross-coupling between aryl–X (X = halide, organometallic, or H) and various “CF3” reagents has emerged as a particularly exciting approach for generating aryl–CF3 bonds. Despite many recent advances in this area, current methods generally suffer from limitations such as poor generality, harsh reaction conditions, the requirement for stoichiometric quantities of metals, and/or the use of costly CF3 sources. This Account describes our recent efforts to address some of these challenges by: (1) developing aryl trifluoromethylation reactions involving high oxidation state Pd intermediates, (2) exploiting AgCF3 for C–H trifluoromethylation, and (3) achieving Cu-catalyzed trifluoromethylation with photogenerated CF3•.

Ye, Yingda; Sanford, Melanie S.

2015-01-01

332

Spin-Orbit Interaction Rediscovered in Transition Metal Oxides  

NASA Astrophysics Data System (ADS)

The 5d-transition metal oxides are a class of novel materials that exhibit nearly every collective state known for solids. It is commonly expected that iridium oxides should be more metallic and less magnetic than their 3d and 4f counterparts due to the extended nature of the 5d orbitals. In marked contrast, many iridates are magnetic insulators that exhibit a large array of phenomena seldom or never seen in other materials. We review the anomalous physical properties of several iridates and address potential underlying mechanisms, which include strong orbital magnetism, the Jeff = .5ex1 -.1em/ -.15em.25ex2 insulating state, and spin-orbit coupling; the latter strongly competes with other interactions to create an unusual balance between relevant degrees of freedom in this class of materials.

Cao, Gang

2011-03-01

333

Role of transition metals in sclerotization of biological tissue.  

PubMed

Biomimetics seeks to elucidate the biochemical and structural principles governing functionality in biological systems and exploit them in the design of synthetic materials. Although the lure has been great, breakthroughs have been rare. The overwhelming complexity of chemical compositions and structural motifs in biology renders the task of "reverse engineering" a formidable challenge. The challenge is amplified by the inherent limitations in probing the effects of a single test variable, keeping others fixed. Here a novel methodology is presented for probing the effects of various transition metals on the hardness and stiffness of a single biological system, notably the jaws of the marine polychaete annelid Nereis virens. Not only is the exceptionally high efficacy of Zn, Cu, and Mn in hardening demonstrated, but also that metal selection is not restricted to that which occurs naturally in the targeted system. PMID:18653388

Broomell, C C; Zok, F W; Waite, J H

2008-11-01

334

Development of microstrain in aged lithium transition metal oxides.  

PubMed

Cathode materials with high energy density for lithium-ion batteries are highly desired in emerging applications in automobiles and stationary energy storage for the grid. Lithium transition metal oxide with concentration gradient of metal elements inside single particles was investigated as a promising high-energy-density cathode material. Electrochemical characterization demonstrated that a full cell with this cathode can be continuously operated for 2500 cycles with a capacity retention of 83.3%. Electron microscopy and high-resolution X-ray diffraction were employed to investigate the structural change of the cathode material after this extensive electrochemical testing. It was found that microstrain developed during the continuous charge/discharge cycling, resulting in cracking of nanoplates. This finding suggests that the performance of the cathode material can be further improved by optimizing the concentration gradient to minimize the microstrain and to reduce the lattice mismatch during cycling. PMID:24960550

Lee, Eung-Ju; Chen, Zonghai; Noh, Hyung-Ju; Nam, Sang Cheol; Kang, Sung; Kim, Do Hyeong; Amine, Khalil; Sun, Yang-Kook

2014-08-13

335

Metal-insulator transition by holographic charge density waves.  

PubMed

We construct a gravity dual for charge density waves (CDWs) in which the translational symmetry along one spatial direction is spontaneously broken. Our linear perturbation calculation on the gravity side produces the frequency dependence of the optical conductivity, which exhibits the two familiar features of CDWs, namely, the pinned collective mode and gapped single-particle excitation. These two features indicate that our gravity dual also provides a new mechanism to implement the metal to insulator phase transition by CDWs, which is further confirmed by the fact that dc conductivity decreases with the decreased temperature below the critical temperature. PMID:25215974

Ling, Yi; Niu, Chao; Wu, Jian-Pin; Xian, Zhuo-Yu; Zhang, Hongbao

2014-08-29

336

Ionically-mediated electromechanical hysteresis in transition metal oxides  

SciTech Connect

Electromechanical activity, remanent polarization states, and hysteresis loops in paraelectric TiO2 and SrTiO3 are observed. The coupling between the ionic dynamics and incipient ferroelectricity in these materials is analyzed using extended Ginsburg Landau Devonshire (GLD) theory. The possible origins of electromechanical coupling including ionic dynamics, surface-charge induced electrostriction, and ionically-induced ferroelectricity are identified. For the latter, the ionic contribution can change the sign of first order GLD expansion coefficient, rendering material effectively ferroelectric. These studies provide possible explanation for ferroelectric-like behavior in centrosymmetric transition metal oxides.

Kim, Yunseok [ORNL] [ORNL; Kumar, Amit [ORNL] [ORNL; Jesse, Stephen [ORNL] [ORNL; Kalinin, Sergei V [ORNL] [ORNL

2012-01-01

337

Rare earth-transition metal scrap treatment method  

DOEpatents

Rare earth-transition metal (e.g. iron) scrap (e.g. Nd-Fe-B scrap) is melted to reduce the levels of tramp oxygen and nitrogen impurities therein. The tramp impurities are reduced in the melt by virtue of the reaction of the tramp impurities and the rare earth to form dross on the melt. The purified melt is separated from the dross for reuse. The oxygen and nitrogen of the melt are reduced to levels acceptable for reuse of the treated alloy in the manufacture of end-use articles, such as permanent magnets. 3 figs.

Schmidt, F.A.; Peterson, D.T.; Wheelock, J.T.; Jones, L.L.; Lincoln, L.P.

1992-02-11

338

Cross-plane thermal properties of transition metal dichalcogenides  

SciTech Connect

In this work, we explore the thermal properties of hexagonal transition metal dichalcogenide compounds with different average atomic masses but equivalent microstructures. Thermal conductivity values of sputtered thin films were compared to bulk crystals. The comparison revealed a >10 fold reduction in thin film thermal conductivity. Structural analysis of the films revealed a turbostratic structure with domain sizes on the order of 5-10 nm. Estimates of phonon scattering lengths at domain boundaries based on computationally derived group velocities were consistent with the observed film microstructure, and accounted for the reduction in thermal conductivity compared to values for bulk crystals.

Muratore, C. [Department of Chemical and Materials Engineering, University of Dayton, Dayton, Ohio 45469 (United States) [Department of Chemical and Materials Engineering, University of Dayton, Dayton, Ohio 45469 (United States); Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, Ohio 45433 (United States); Varshney, V. [Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, Ohio 45433 (United States) [Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, Ohio 45433 (United States); Universal Technology Corporation, Dayton, Ohio 45432 (United States); Gengler, J. J. [Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, Ohio 45433 (United States) [Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, Ohio 45433 (United States); Spectral Energies LLC, Dayton, Ohio 45431 (United States); Hu, J. J.; Bultman, J. E. [Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, Ohio 45433 (United States) [Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, Ohio 45433 (United States); University of Dayton Research Institute, Dayton, Ohio 45469 (United States); Smith, T. M. [Department of Materials Science and Engineering, Ohio State University, Columbus, Ohio 43210 (United States)] [Department of Materials Science and Engineering, Ohio State University, Columbus, Ohio 43210 (United States); Shamberger, P. J.; Roy, A. K.; Voevodin, A. A. [Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, Ohio 45433 (United States)] [Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, Ohio 45433 (United States); Qiu, B.; Ruan, X. [Department of Mechanical Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907 (United States)] [Department of Mechanical Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907 (United States)

2013-02-25

339

Rare earth-transition metal scrap treatment method  

DOEpatents

Rare earth-transition metal (e.g. iron) scrap (e.g. Nd-Fe-B scrap) is melted to reduce the levels of tramp oxygen and nitrogen impurities therein. The tramp impurities are reduced in the melt by virtue of the reaction of the tramp impurities and the rare earth to form dross on the melt. The purified melt is separated from the dross for reuse. The oxygen and nitrogen of the melt are reduced to levels acceptable for reuse of the treated alloy in the manufacture of end-use articles, such as permanent magnets.

Schmidt, Frederick A. (Ames, IA); Peterson, David T. (Ames, IA); Wheelock, John T. (Nevada, IA); Jones, Lawrence L. (Des Moines, IA); Lincoln, Lanny P. (Woodward, IA)

1992-02-11

340

Correlated Electron Pseudopotentials for 3d-Transition Metals  

E-print Network

A recently published correlated electron pseudopotentials (CEPPs) method has been adapted for application to the 3d-transition metals, and to include relativistic effects. New CEPPs are reported for the atoms Sc$-$Fe, constructed from atomic quantum chemical calculations that include an accurate description of correlated electrons. Dissociation energies, molecular geometries, and zero-point vibrational energies of small molecules are compared with all electron results, with all quantities evaluated using coupled cluster singles doubles and triples (CCSD(T)) calculations. The CEPPs give better results in the correlated-electron calculations than Hartree-Fock-based pseudopotentials available in the literature.

Trail, John

2015-01-01

341

The nature of the bonding in the transition metal trimers  

NASA Technical Reports Server (NTRS)

The electronic structure of the transition metal (TM) trimers was studied by comparing the bonding in the Ca3, Sc3, and Cu3 molecules. The complete active space SCF/externally contracted configuration interaction (CI) ratio for the low-lying states of Sc3 and Sc3(+) and the SCF/CI ratio for Ca3 and Cu3 trimers, all for near equilateral triangle geometries, were calculated. In addition, vertical excitation energies for Cu3 were computed, leading to a new assignment of the upper state in the resonant two-photon ionization spectrum. Based on these studies, bonding in other TM trimers was discussed.

Walch, Stephen P.; Bauschlicher, Charles W., Jr.

1986-01-01

342

Random Local Attraction Driven Metal–Superconductor Transition  

NASA Astrophysics Data System (ADS)

In this paper, we investigate the disordered attractive Hubbard model by combining dynamical mean field theory, coherent potential approximation and iterated perturbation theory for superconductivity as an impurity solver. Disorder is introduced in the local attraction U. We assume that U is distributed according to a bimodal probability distribution, wherein an x fraction of sites are pairing centers (U ? 0) and (1 ? x) fraction of sites are non-interacting (U = 0). It is found that beyond a critical x = xc, a first order metal–superconductor phase transition leads to superconductivity being induced in the interacting as well as non-interacting sites.

Kamar, Naushad Ahmad; Vidhyadhiraja, N. S.

2015-01-01

343

Tetrathiafulvalene-annulated phenanthroline and its complexes with transition metals  

NASA Astrophysics Data System (ADS)

Recent interest in designing multifunctional transition metal complexes that incorporate the redox-active tetrathiafulvalene (TTF) molecule stems from the perspective of embedding specific localized properties of transition metal ions into TTF-containing substructures characterized by extended delocalized conduction pathways. This dissertation reports on the synthesis of tetrathiafulvalene, a ubiquitous component of organic conductors, fused directly to 1,10-phenanthroline, one of the most popular ligands in transition metal chemistry. We have devised and implemented a synthetic pathway to this unique ligand, which then was used to obtain complexes with Ru(II) and Fe(II) ions. Chapter 1 of this dissertation provides an introduction to the chemistry of TTF and its metal complexes. Chapter 2 describes the most important methods of characterization employed in this research project. Chapter 3 is devoted to the preparation and properties of the TTF-annulated phenanthroline ligands. Chapter 4 describes a detailed study of a Ru(II) complex of TTF phenanthroline, including its structural, photophysical, and electrochemical properties. [Ru(bpy) 2(edt-TTF-phen)](PF6)2 exhibits a unique helical packing of molecules in the crystal structure. In contrast to its TTF-free analogues, this complex contains a TTF-centered highest occupied molecular orbital, and the electrochemical data show that the first two oxidations of the complex are TTF-based. Examination of the photophysical properties revealed that this Ru(II) complex experiences excited-state luminescence quenching via reductive electron transfer from the TTF to the Ru3+ center, which opens up a path for non radiative relaxation to the ground state through the low-lying intra-ligand charge transfer state. We also describe an unusual photoreactivity of this complex that leads to the cleavage of the central C=C bond of the TTF unit in solution. Such reactivity was monitored by the evolution of NMR, UV-visible, emission, and transient absorption spectra. Chapter 5 describes spin-crossover behavior of [Fe(NCS)2(L) 2] (L = edt-TTF-phen or hexS2-TTF-phen) and parent Fe(II) complexes. The complex with hexyl substituents is highly soluble and exhibits reversible oxidations centered on the TTF fragments. The observed spin transition was elucidated with variable-temperature Mossbauer and infrared spectroscopies.

Keniley, Lawrence Keith, Jr.

344

Excitonic collapse in semiconducting transition-metal dichalcogenides  

NASA Astrophysics Data System (ADS)

Semiconducting transition metal dichalcogenides (STMDC) are two-dimensional (2D) crystals characterized by electron-volt-size band gaps, spin-orbit coupling (SOC), and d-orbital character of its valence and conduction bands. We show that these materials carry unique exciton quasiparticles (electron-hole bound states) with energy within the gap but which can “collapse” in the strong coupling regime by merging into the band structure continuum. The exciton collapse seems to be a generic effect in these 2D crystals.

Rodin, A. S.; Castro Neto, A. H.

2013-11-01

345

Intrinsic disorder in graphene on transition metal dichalcogenide heterostructures.  

PubMed

Semiconducting transition metal dichalchogenides (TMDs) are a family of van der Waals bonded materials that have recently received interest as alternative substrates to hexagonal boron nitride (hBN) for graphene, as well as for components in novel graphene-based device heterostructures. We elucidate the local structural and electronic properties of graphene on TMD heterostructures through scanning tunneling microscopy and spectroscopy measurements. We find that crystalline defects intrinsic to TMDs induce substantial electronic scattering and charge carrier density fluctuations in the graphene. These signatures of local disorder explain the significant degradation of graphene device mobilities using TMD substrates, particularly compared to similar graphene on hBN devices. PMID:25665012

Yankowitz, Matthew; Larentis, Stefano; Kim, Kyounghwan; Xue, Jiamin; McKenzie, Devin; Huang, Shengqiang; Paggen, Marina; Ali, Mazhar N; Cava, Robert J; Tutuc, Emanuel; LeRoy, Brian J

2015-03-11

346

Metal-insulator Transition by Holographic Charge Density Waves  

E-print Network

We construct a gravity dual for charge density waves (CDW) in which the translational symmetry along one spatial direction is spontaneously broken. Our linear perturbation calculation on the gravity side produces the frequency dependence of the optical conductivity, which exhibits the two familiar features of charge density waves, namely the pinned collective mode and gapped single-particle excitation. These two features indicate that our gravity dual also provides a new mechanism to implement the metal to insulator phase transition by CDW, which is further supported by the fact that d.c. conductivity decreases with the decreased temperature below the critical temperature.

Yi Ling; Chao Niu; Jianpin Wu; Zhuoyu Xian; Hongbao Zhang

2014-08-06

347

Correlated electron pseudopotentials for 3d-transition metals  

NASA Astrophysics Data System (ADS)

A recently published correlated electron pseudopotentials (CEPPs) method has been adapted for application to the 3d-transition metals, and to include relativistic effects. New CEPPs are reported for the atoms Sc - Fe, constructed from atomic quantum chemical calculations that include an accurate description of correlated electrons. Dissociation energies, molecular geometries, and zero-point vibrational energies of small molecules are compared with all electron results, with all quantities evaluated using coupled cluster singles doubles and triples calculations. The CEPPs give better results in the correlated-electron calculations than Hartree-Fock-based pseudopotentials available in the literature.

Trail, J. R.; Needs, R. J.

2015-02-01

348

Novel synthetic routes to nanocomposites of transition metal phosphides  

SciTech Connect

Novel routes to nanocomposites of transition metal phosphides will be presented. Silica xerogels containing covalently attached organometallic or other coordination compounds were prepared using standard sol-gel methods. The doped xerogels were thermally treated in a reducing atmosphere to yield the desired nanocomposite. Using these techniques, Fe{sub 2}P, RuP, Co{sub 2}P, Rh{sub 2}P, Ni{sub 2}P, Pd{sub 5}P{sub 2}, and PtP{sub 2} nanocomposites have been prepared and characterized.

Milne, S.B.; Lukehart, C.M.; Wittig, J.E. [Vanderbilt Univ., Nashville, TN (United States)] [and others

1996-10-01

349

Theoretical study of electron correlation effects in transition metal dimers  

NASA Technical Reports Server (NTRS)

Introduction of partially localized orbitals is shown to reduce the number of terms needed to describe the bonding in transition metal clusters. Using this formalism, it is possible to compute the various intra- and inter-atomic electron correlation contributions to the bond energy. Calculations demonstrate the relative importance of several kinds of electron correlation terms involving the 3p, 3d, and 4s electrons. Improved interaction potentials are obtained for the dimers V(2) and Cr(2) when additional correlation is added to the CAS SCF results of Walch, Bauschlicher, Roos, and Nelin (1983).

Das, G. P.; Jaffe, R. L.

1984-01-01

350

Nonlinear d10-ML2 Transition-Metal Complexes  

PubMed Central

We have investigated the molecular geometries of a series of dicoordinated d10-transition-metal complexes ML2 (M=Co?, Rh?, Ir?, Ni, Pd, Pt, Cu+, Ag+, Au+; L=NH3, PH3, CO) using relativistic density functional theory (DFT) at ZORA-BLYP/TZ2P. Not all complexes have the expected linear ligand–metal–ligand (L–M–L) angle: this angle varies from 180° to 128.6° as a function of the metal as well as the ligands. Our main objective is to present a detailed explanation why ML2 complexes can become bent. To this end, we have analyzed the bonding mechanism in ML2 as a function of the L–M–L angle using quantitative Kohn–Sham molecular orbital (MO) theory in combination with an energy decomposition analysis (EDA) scheme. The origin of bent L–M–L structures is ? backdonation. In situations of strong ? backdonation, smaller angles increase the overlap of the ligand’s acceptor orbital with a higher-energy donor orbital on the metal-ligand fragment, and therefore favor ? backdonation, resulting in additional stabilization. The angle of the complexes thus depends on the balance between this additional stabilization and increased steric repulsion that occurs as the complexes are bent. PMID:24551547

Wolters, Lando P; Bickelhaupt, F Matthias

2013-01-01

351

Glutathione and Transition-Metal Homeostasis in Escherichia coli?  

PubMed Central

Glutathione (GSH) and its derivative phytochelatin are important binding factors in transition-metal homeostasis in many eukaryotes. Here, we demonstrate that GSH is also involved in chromate, Zn(II), Cd(II), and Cu(II) homeostasis and resistance in Escherichia coli. While the loss of the ability to synthesize GSH influenced metal tolerance in wild-type cells only slightly, GSH was important for residual metal resistance in cells without metal efflux systems. In mutant cells without the P-type ATPase ZntA, the additional deletion of the GSH biosynthesis system led to a strong decrease in resistance to Cd(II) and Zn(II). Likewise, in mutant cells without the P-type ATPase CopA, the removal of GSH led to a strong decrease of Cu(II) resistance. The precursor of GSH, ?-glutamylcysteine (?EC), was not able to compensate for a lack of GSH. On the contrary, ?EC-containing cells were less copper and cadmium tolerant than cells that contained neither ?EC nor GSH. Thus, GSH may play an important role in trace-element metabolism not only in higher organisms but also in bacteria. PMID:18539744

Helbig, Kerstin; Bleuel, Corinna; Krauss, Gerd J.; Nies, Dietrich H.

2008-01-01

352

Catalytic Applications of Early\\/Late Heterobimetallic Complexes  

Microsoft Academic Search

Transition metal complexes that combine electronically different metals are most readily designed by combining an early transition metal and a late transition metal, typically via a bridging ligand framework. These so-called “early\\/late” heterobimetallic complexes have recently proven active in a number of catalytic transformations that are not accessible with analogous monometallic complexes. This review discusses recent contributions to catalytic and

Benjamin G. Cooper; J. Wesley Napoline; Christine M. Thomas

2012-01-01

353

The Transition to Kindergarten. A Series from the National Center for Early Development and Learning.  

ERIC Educational Resources Information Center

On the premise that early school transitions affect children's future educational success and that these critical transitions need to be improved, this book explores the research on early schooling and reexamines educational beliefs, policies, and practices relating to the first years of school, including readiness assessment, entrance ages,…

Pianta, Robert C., Ed.; Cox, Martha J., Ed.

354

Strain effects in low-dimensional transition metal oxides Jinbo Cao a,b,  

E-print Network

Strain effects in low-dimensional transition metal oxides Jinbo Cao a,b, *, Junqiao Wu a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 1.1. Spin­lattice­charge coupling in transition metal oxides/nanowires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 3.2. Phase transitions and domain physics under strain

Wu, Junqiao

355

Dense Electron System from Gate-Controlled Surface Metal-Insulator Transition  

E-print Network

mechanism of the phase transition in VO2. It also offers a new material platform for implementing Mott of some phase transition materials, for example, vanadium dioxide (VO2), which possesses a metalDense Electron System from Gate-Controlled Surface Metal- Insulator Transition Kai Liu,,, Deyi Fu

Deshmukh, Mandar M.

356

Charge-transfer metal-insulator transitions in the spin-1 2 Falicov-Kimball model  

E-print Network

ARTICLES Charge-transfer metal-insulator transitions in the spin-1 2 Falicov-Kimball model Woonki-coordination-number Bethe lattice in the thermodynamic limit. This model is a paradigm for a charge-transfer metal-insulator transition, where the occupancy of localized and delocalized electronic orbitals rapidly changes at the metal-insulator

Freericks, Jim

357

Transition metal co-precipitation mechanisms in silicon T. Buonassisi a,*, M. Heuer a,1  

E-print Network

Transition metal co-precipitation mechanisms in silicon T. Buonassisi a,*, M. Heuer a,1 , A accepted as well that interstitially dissolved 3d transition metals in silicon (e.g., iron or cop- per) can Available online 18 September 2007 Abstract Formation mechanisms of precipitates containing multiple-metal

358

Intrinsic spin Hall effect and orbital Hall effect in 4d and 5d transition metals  

Microsoft Academic Search

We study the intrinsic spin Hall conductivity (SHC) in various 5d transition metals (Ta, W, Re, Os, Ir, Pt, and Au) and 4d transition metals (Nb, Mo, Tc, Ru, Rh, Pd, and Ag) based on the Naval Research Laboratory tight-binding model, which enables us to perform quantitatively reliable analysis. In each metal, the obtained intrinsic SHC is independent of resistivity

T. Tanaka; H. Kontani; M. Naito; T. Naito; D. S. Hirashima; K. Yamada; J. Inoue

2008-01-01

359

Flexible metallic nanowires with self-adaptive contacts to semiconducting transition-metal dichalcogenide monolayers  

NASA Astrophysics Data System (ADS)

In the pursuit of ultrasmall electronic components, monolayer electronic devices have recently been fabricated using transition-metal dichalcogenides. Monolayers of these materials are semiconducting, but nanowires with stoichiometry MX (M = Mo or W, X = S or Se) have been predicted to be metallic. Such nanowires have been chemically synthesized. However, the controlled connection of individual nanowires to monolayers, an important step in creating a two-dimensional integrated circuit, has so far remained elusive. In this work, by steering a focused electron beam, we directly fabricate MX nanowires that are less than a nanometre in width and Y junctions that connect designated points within a transition-metal dichalcogenide monolayer. In situ electrical measurements demonstrate that these nanowires are metallic, so they may serve as interconnects in future flexible nanocircuits fabricated entirely from the same monolayer. Sequential atom-resolved Z-contrast images reveal that the nanowires rotate and flex continuously under momentum transfer from the electron beam, while maintaining their structural integrity. They therefore exhibit self-adaptive connections to the monolayer from which they are sculpted. We find that the nanowires remain conductive while undergoing severe mechanical deformations, thus showing promise for mechanically robust flexible electronics. Density functional theory calculations further confirm the metallicity of the nanowires and account for their beam-induced mechanical behaviour. These results show that direct patterning of one-dimensional conducting nanowires in two-dimensional semiconducting materials with nanometre precision is possible using electron-beam-based techniques.

Lin, Junhao; Cretu, Ovidiu; Zhou, Wu; Suenaga, Kazu; Prasai, Dhiraj; Bolotin, Kirill I.; Cuong, Nguyen Thanh; Otani, Minoru; Okada, Susumu; Lupini, Andrew R.; Idrobo, Juan-Carlos; Caudel, Dave; Burger, Arnold; Ghimire, Nirmal J.; Yan, Jiaqiang; Mandrus, David G.; Pennycook, Stephen J.; Pantelides, Sokrates T.

2014-06-01

360

XO-2b: Transiting Hot Jupiter in a Metal-rich Common Proper Motion Binary  

E-print Network

We report on a V=11.2 early K dwarf, XO-2 (GSC 03413-00005), that hosts a Rp=0.98+0.03/-0.01 Rjup, Mp=0.57+/-0.06 Mjup transiting extrasolar planet, XO-2b, with an orbital period of 2.615857+/-0.000005 days. XO-2 has high metallicity, [Fe/H]=0.45+/-0.02, high proper motion, mu_tot=157 mas/yr, and has a common proper motion stellar companion with 31" separation. The two stars are nearly identical twins, with very similar spectra and apparent magnitudes. Due to the high metallicity, these early K dwarf stars have a mass and radius close to solar, Ms=0.98+/-0.02 Msolar and Rs=0.97+0.02/-0.01 Rsolar. The high proper motion of XO-2 results from an eccentric orbit (Galactic pericenter, Rpermetal-rich, inner Thin Disk and subsequent dynamical scattering into the solar neighborhood. We describe an efficient Markov Chain Monte Carlo algorithm for calculating the Bayesian posterior probability of the system parameters from a transit light curve.

Christopher J. Burke; P. R. McCullough; Jeff A. Valenti; Christopher M. Johns-Krull; Kenneth A. Janes; J. N. Heasley; F. J. Summers; J. E. Stys; R. Bissinger; Michael L. Fleenor; Cindy N. Foote; Enrique Garcia-Melendo; Bruce L. Gary; P. J. Howell; F. Mallia; G. Masi; B. Taylor; T. Vanmunster

2007-09-12

361

Parents' Marital Distress, Divorce, and Remarriage: Links with Daughters' Early Family Formation Transitions  

ERIC Educational Resources Information Center

The authors used data from the Add Health study to estimate the effects of parents' marital status and relationship distress on daughters' early family formation transitions. Outcomes included traditional transitions (marriage and marital births) and nontraditional transitions (cohabitation and nonmarital births). Relationship distress among…

Amato, Paul R.; Kane, Jennifer B.

2011-01-01

362

Metal oxide resistive switching: evolution of the density of states across the metal-insulator transition.  

PubMed

We report the study of gold-SrTiO3 (STO)-gold memristors where the doping concentration in STO can be fine-tuned through electric field migration of oxygen vacancies. In this tunnel junction device, the evolution of the density of states (DOS) can be followed continuously across the metal-insulator transition (MIT). At very low dopant concentration, the junction displays characteristic signatures of discrete dopant levels. As the dopant concentration increases, the semiconductor band gap fills in but a soft Coulomb gap remains. At even higher doping, a transition to a metallic state occurs where the DOS at the Fermi level becomes finite and Altshuler-Aronov corrections to the DOS are observed. At the critical point of the MIT, the DOS scales linearly with energy N(?)??, the possible signature of multifractality. PMID:24580702

Mottaghizadeh, A; Yu, Q; Lang, P L; Zimmers, A; Aubin, H

2014-02-14

363

Anderson metal-insulator transitions with classical magnetic impurities  

SciTech Connect

We study the effects of classical magnetic impurities on the Anderson metal-insulator transition (AMIT) numerically. In particular we find that while a finite concentration of Ising impurities lowers the critical value of the site-diagonal disorder amplitude W{sub c}, in the presence of Heisenberg impurities, W{sub c} is first increased with increasing exchange coupling strength J due to time-reversal symmetry breaking. The resulting scaling with J is compared to analytical predictions by Wegner [1]. The results are obtained numerically, based on a finite-size scaling procedure for the typical density of states [2], which is the geometric average of the local density of states. The latter can efficiently be calculated using the kernel polynomial method [3]. Although still suffering from methodical shortcomings, our method proves to deliver results close to established results for the orthogonal symmetry class [4]. We extend previous approaches [5] by combining the KPM with a finite-size scaling analysis. We also discuss the relevance of our findings for systems like phosphor-doped silicon (Si:P), which are known to exhibit a quantum phase transition from metal to insulator driven by the interplay of both interaction and disorder, accompanied by the presence of a finite concentration of magnetic moments [6].

Jung, Daniel [School of Engineering and Science, Jacobs University Bremen gGmbH, Campus Ring 1, 28759 Bremen, Germany and Division of Advanced Materials Science, Pohang University of Science and Technology (POSTECH), San 31, Hyoja-dong, Nam-gu, Pohang 790-784 (Korea, Republic of); Kettemann, Stefan [School of Engineering and Science, Jacobs University Bremen gGmbH,Campus Ring 1, 28759 Bremen, Germany and Division of Advanced Materials Science, Pohang University of Science and Technology (POSTECH), San 31, Hyoja-dong, Nam-gu, Pohang 790-784 (Korea, Republic of)

2014-08-20

364

Nanostructured transition metal oxides for energy storage and conversion  

NASA Astrophysics Data System (ADS)

Lithium-ion batteries, supercapacitors and photovoltaic devices have been widely considered as the three major promising alternatives of fossil fuels facing upcoming depletion to power the 21th century. The conventional film configuration of electrochemical electrodes hardly fulfills the high energy and efficiency requirements because heavy electroactive material deposition restricts ion diffusion path, and lowers power density and fault tolerance. In this thesis, I demonstrate that novel nanoarchitectured transition metal oxides (TMOs), e.g. MnO2, V2O 5, and ZnO, and their relevant nanocomposites were designed, fabricated and assembled into devices to deliver superior electrochemical performances such as high energy and power densities, and rate capacity. These improvements could be attributed to the significant enhancement of surface area, shortened ion diffusion distances and facile penetration of electrolyte solution into open structures of networks as well as to the pseudocapacitance domination. The utilization of ForcespinningRTM, a newly developed nanofiber processing technology, for large-scale energy storage and conversion applications is emphasized. This process simplifies the tedious multi-step hybridization synthesis and facilitates the contradiction between the micro-batch production and the ease of large-scale manufacturing. Key Words: Transition metal oxides, energy storage and conversion, ForcespinningRTM, pseudocapacitance domination, high rate capacity

Li, Qiang

365

Characteristics of thermal decomposition products of rare earth, alkali earth metal and transition metal p -toluenesulfonates  

Microsoft Academic Search

Summary A series of alkali earth (Ca, Ba), lanthanide (La, Ce, Pr, Nd,) and transition metal (Fe, Mn, Co, Ni, Cu, Zn, Cd) p-toluenesulfonates were synthesized. Thermal analysis, infrared spectrophotometry, and XRD powder diffraction patterns were employed to characterize the final thermal decomposition products. By heating in dynamic air atmosphere at 30-850°C, it has been found that the alkali earth

Z.-L. Sun

2005-01-01

366

JOURNAL DE PHYSIQUE Colloque C4, supplkment au no 10, Tome 37, Octobre 1976, page C4-317 CRITICAL CONCENTRATION FOR THE METAL-NON METAL TRANSITION  

E-print Network

CONCENTRATION FOR THE METAL-NON METAL TRANSITION IN n-TYPE GERMANIUM AND SILICON K. F. BERGGREN and B. SERNELIUS in which atomic configurations are disordered in some way or another, metal-non metal (MNM) transitionsC. - La transition mktal-non mktal dans Ge et Si de type n est considkre a l'aide d'un modkle quia

Boyer, Edmond

367

Bond order potentials for bcc transition metals and molybdenum silicides  

NASA Astrophysics Data System (ADS)

One of the most challenging areas in materials science is modeling of the mechanical behavior of materials. Macroscopic properties, such as plastic flow and brittleness, are determined by processes occurring at the atomic level and are mainly influenced by the properties of extended defects. Understanding the energetics and structural properties of dislocations, grain boundaries and other extended defects enables to gain a valuable insight into the deformation mechanisms and allows to design specific ways to overcome intrinsic limitations of materials. In this thesis, we study the properties of extended defects in four bcc transition metals---Nb, Ta, Mo and W, using the bond order potentials (BOP). These potentials are based on the real-space parameterized tight-binding method and are eminently suitable for modeling of extended defects in materials with predominantly metallic and covalent type of bonding. Our results confirm that the unusual plastic behavior of bcc transition metals is governed by the properties of the a/2[111] screw dislocations and reveal quantitatively the overall invalidity of the well-known Schmid law in these materials. The most recent improvement of BOP has been a derivation of analytic environmental dependence of bond integrals. This development extends the transferability of the BOP model and its applicability to multi-component systems. The accuracy of this, so-called, screened bond order potential (SBOP) formalism was studied for the first time for the case of pure Mo as well as the intermetallic compound MOSi2. Molybdenum silicides are prospective high-temperature structural materials and full understanding of the deformation behavior of these compounds is a necessary prerequisite for their extensive use in industrial applications.

Mrovec, Matous

368

Role of Electronic Structure in the Susceptibility of Metastable Transition-Metal Oxide Structures to Transformation  

E-print Network

Role of Electronic Structure in the Susceptibility of Metastable Transition-Metal Oxide Structures Transition Metals 4527 10.1. Ti 4528 10.2. V 4528 10.3. Cr 4529 10.4. Mn 4529 10.5. Fe 4529 10.6. Co 4530 10 transition-metal ions in an oxide and how these factors in turn affect the resistance of metastable 3d

Ceder, Gerbrand

369

Ce 4f orbital coupling to transition-metal band structure: An ion-implantation study  

Microsoft Academic Search

Using ion implantation, we have prepared atomically dispersed alloys of Ce in almost all of the 3d, 4d, and 5d transition metals. We have measured the response of the implanted Ce 4f orbital to its host transition-metal environment via the Ce L3 valence-state determination method. The close correspondence between the Ce 4f orbital occupancy and the host transition-metal d-band electronic

F. Lu; N. Stoffel; R. A. Neifeld; S. Gunapala; M. Croft; M. L. den Boer

1988-01-01

370

A novel synthetic route to transition metal phosphide nanoparticles.  

PubMed

A novel synthetic route was developed to prepare nano-sized and well-dispersed phosphides of transition metals (Mo, Ni, and Co) from their corresponding oxide precursors. The current approach produced metal phosphides in dimethyl ether (DME) using the rapid heating reduction (RHR) method. The synthesis of phosphides in DME was interesting, since the composition of gas-phase products was predominantly H2, CO and CH4 with a minor amount of CO2 but without H2O. Based on XRD and MS results, the formation mechanism of the phosphides was proposed. The overall synthesis process cannot simply be regarded as the reduction of an oxide precursor and the decomposition of DME. The product distribution should be ascribed to a combination of other catalytic reactions. In addition, it is noteworthy that compared with the traditional method, viz. temperature-programmed reduction in H2 (TPR-H2), the present method used a higher heating rate to shorten the reaction time and can yield more finely dispersed metal phosphide nanoparticles. The good dispersion of phosphide nanoparticles is probably achieved due to the fact that no H2O was released in the RHR-DME process, which can avoid strong hydrothermal sintering. PMID:25697219

Yao, Zhiwei; Li, Meng; Wang, Xiang; Qiao, Xue; Zhu, Jiang; Zhao, Yu; Wang, Guanzhang; Yin, Jingzhou; Wang, Haiyan

2015-03-10

371

Theoretical study on the alloying behavior of ?-uranium metal: ?-uranium alloy with 3d transition metals  

NASA Astrophysics Data System (ADS)

We have investigated the alloying behavior of ?-uranium with 3d transition metals (TMs) using the relativistic discrete-variational Dirac-Fock-Slater (DV-DFS) method. The d-orbital energy (Md) as an alloying parameter well reproduces the alloying behavior of ?-uranium metal with TMs: (1) in the case of a large Md value (Ti, V, Cr), the solubility of these TM elements in ?-uranium becomes large; (2) in the case of a middle Md value (Mn, Fe, Co), the tendency to form a uranium intermetallic compound with these elements becomes stronger; (3) in the case of a small Md value (Cu), the alloying element is insoluble in ?-uranium. The alloying behavior of ?-uranium with TMs is also discussed in terms of other parameters such as electronegativity and metallic radius.

Kurihara, Masayoshi; Hirata, Masaru; Sekine, Rika; Onoe, Jun; Nakamatsu, Hirohide

2004-03-01

372

Electrochemical lithiation and delithiation for control of magnetic properties of nanoscale transition metal oxides  

E-print Network

Transition metal oxides comprise a fascinating class of materials displaying a variety of magnetic and electronic properties, ranging from half-metallic ferromagnets like CrO2, ferrimagnetic semiconductors like Fey's, and ...

Sivakumar, Vikram

2008-01-01

373

Quantum Spin Liquids and the Metal-Insulator Transition in Doped Semiconductors  

E-print Network

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 ...

Potter, Andrew Cole

374

The Timing of School Transitions and Early Adolescent Problem Behavior  

PubMed Central

This longitudinal study investigates whether rural adolescents who transition to a new school in sixth grade have higher levels of risky behavior than adolescents who transition in seventh grade. Our findings indicate that later school transitions had little effect on problem behavior between sixth and ninth grades. Cross-sectional analyses found a small number of temporary effects of transition timing on problem behavior: Spending an additional year in elementary school was associated with higher levels of deviant behavior in the Fall of Grade 6 and higher levels of antisocial peer associations in Grade 8. However, transition effects were not consistent across waves and latent growth curve models found no effects of transition timing on the trajectory of problem behavior. We discuss policy implications and compare our findings with other research on transition timing. PMID:24089584

Lippold, Melissa A.; Powers, Christopher J.; Syvertsen, Amy K.; Feinberg, Mark E.; Greenberg, Mark T.

2013-01-01

375

External control of a metal-insulator transition in GaMnAs wires.  

PubMed

Quantum transport in disordered ferromagnetic (III,Mn)V semiconductors is studied theoretically. Mesoscopic wires exhibit an Anderson disorder-induced metal-insulator transition that can be controlled by a weak external magnetic field. This metal-insulator transition should also occur in other materials with large anisotropic magnetoresistance effects. The transition can be useful for studies of zero-temperature quantum critical phase transitions and fundamental material properties. PMID:18764136

Nguyen, Anh Kiet; Brataas, Arne

2008-07-01

376

Electronic Relaxation Processes of Transition Metal Atoms in Helium Nanodroplets  

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

377

Early transitional metal alkyl, alkylidene, and alkylidyne chemistry  

E-print Network

CHAPTER 1. Zirconium and hafnium complexes of several new unsymmetric diamide ligands have been prepared and their proficiency in olefin polymerization reactions evaluated. The first set of supporting ligands examined are ...

Tonzetich, Zachary John

2007-01-01

378

Transition Metal Dichalcogenide Growth via Close Proximity Precursor Supply  

PubMed Central

Reliable chemical vapour deposition (CVD) of transition metal dichalcogenides (TMDs) is currently a highly pressing research field, as numerous potential applications rely on the production of high quality films on a macroscopic scale. Here, we show the use of liquid phase exfoliated nanosheets and patterned sputter deposited layers as solid precursors for chemical vapour deposition. TMD monolayers were realized using a close proximity precursor supply in a CVD microreactor setup. A model describing the growth mechanism, which is capable of producing TMD monolayers on arbitrary substrates, is presented. Raman spectroscopy, photoluminescence, X-ray photoelectron spectroscopy, atomic force microscopy, transmission electron microscopy, scanning electron microscopy and electrical transport measurements reveal the high quality of the TMD samples produced. Furthermore, through patterning of the precursor supply, we achieve patterned growth of monolayer TMDs in defined locations, which could be adapted for the facile production of electronic device components. PMID:25487822

O'Brien, Maria; McEvoy, Niall; Hallam, Toby; Kim, Hye-Young; Berner, Nina C.; Hanlon, Damien; Lee, Kangho; Coleman, Jonathan N.; Duesberg, Georg S.

2014-01-01

379

Continuously tunable electronic structure of transition metal dichalcogenides superlattices  

PubMed Central

Two dimensional transition metal dichalcogenides have very exciting properties for optoelectronic applications. In this work we theoretically investigate and predict that superlattices comprised of MoS2 and WSe2 multilayers possess continuously tunable electronic structure with direct bandgaps. The tunability is controlled by the thickness ratio of MoS2 versus WSe2 of the superlattice. When this ratio goes from 1:2 to 5:1, the dominant K-K direct bandgap is continuously tuned from 0.14?eV to 0.5?eV. The gap stays direct against ?0.6% to 2% in-layer strain and up to ?4.3% normal-layer compressive strain. The valance and conduction bands are spatially separated. These robust properties suggest that MoS2 and WSe2 multilayer superlattice should be a promising material for infrared optoelectronics. PMID:25677917

Zhao, Yong-Hong; Yang, Feng; Wang, Jian; Guo, Hong; Ji, Wei

2015-01-01

380

Post-Growth Manipulation of Transition Metal Dichalcogenides Thin Film  

NASA Astrophysics Data System (ADS)

The intense interest in graphene as the prototype 2D electronic material has recently been complemented by the investigation of layered transition metal dichalcogenides (TMD), notably MoS2 and MoSe2. These materials provide the favorable mechanical properties of graphene, but exhibit a direct bandgap without the need for nanostructuring, chemical functionalization, or the application of a strong electric field to bilayers. As a monolayer, MoS2 becomes a direct-gap semiconductor with a gap of 1.8 eV. In this dissertation, X-ray photoelectron spectroscopy (XPS), photoluminescence, spectroscopy and high-resolution angle resolved photoemission spectroscopy (ARPES) have been used to investigate monolayer and alloy thin films grown on various substrates. My research focuses on the thin film modification and characterization, composition analysis, low-energy argon ion sputtering process and bandgap tuning.

Ma, Quan

381

Continuously tunable electronic structure of transition metal dichalcogenides superlattices  

NASA Astrophysics Data System (ADS)

Two dimensional transition metal dichalcogenides have very exciting properties for optoelectronic applications. In this work we theoretically investigate and predict that superlattices comprised of MoS2 and WSe2 multilayers possess continuously tunable electronic structure with direct bandgaps. The tunability is controlled by the thickness ratio of MoS2 versus WSe2 of the superlattice. When this ratio goes from 1:2 to 5:1, the dominant K-K direct bandgap is continuously tuned from 0.14 eV to 0.5 eV. The gap stays direct against -0.6% to 2% in-layer strain and up to -4.3% normal-layer compressive strain. The valance and conduction bands are spatially separated. These robust properties suggest that MoS2 and WSe2 multilayer superlattice should be a promising material for infrared optoelectronics.

Zhao, Yong-Hong; Yang, Feng; Wang, Jian; Guo, Hong; Ji, Wei

2015-02-01

382

Continuously tunable electronic structure of transition metal dichalcogenides superlattices.  

PubMed

Two dimensional transition metal dichalcogenides have very exciting properties for optoelectronic applications. In this work we theoretically investigate and predict that superlattices comprised of MoS2 and WSe2 multilayers possess continuously tunable electronic structure with direct bandgaps. The tunability is controlled by the thickness ratio of MoS2 versus WSe2 of the superlattice. When this ratio goes from 1:2 to 5:1, the dominant K-K direct bandgap is continuously tuned from 0.14?eV to 0.5?eV. The gap stays direct against -0.6% to 2% in-layer strain and up to -4.3% normal-layer compressive strain. The valance and conduction bands are spatially separated. These robust properties suggest that MoS2 and WSe2 multilayer superlattice should be a promising material for infrared optoelectronics. PMID:25677917

Zhao, Yong-Hong; Yang, Feng; Wang, Jian; Guo, Hong; Ji, Wei

2015-01-01

383

Spin and pseudospins in layered transition metal dichalcogenides  

SciTech Connect

The recent emergence of two-dimensional layered materials in particular the transition metal dichalcogenides provides a new laboratory for exploring the internal quantum degrees of freedom of electrons and their potential for new electronics. These degrees of freedom are the real electron spin, the layer pseudospin, and the valley pseudospin. New methods for the quantum control of the spin and these pseudospins arise from the existence of Berry phase-related physical properties and strong spin orbit coupling. The former leads to the versatile control of the valley pseudospin, whereas the latter gives rise to an interplay between the spin and the pseudospins. Here, we provide a brief review of both theoretical and experimental advances in this field.

Xu, Xiaodong [University of Washington] [University of Washington; Yao, Wang [University of Hong Kong, The] [University of Hong Kong, The; Xiao, Di [Carnegie Mellon University (CMU)] [Carnegie Mellon University (CMU); Heinz, Tony F. [Columbia University, New York] [Columbia University, New York

2014-01-01

384

Moderate temperature sodium cells. I - Transition metal disulfide cathodes  

NASA Technical Reports Server (NTRS)

TiS2, VS2, and Nb(1.1)S2 transition metal disulfides were evaluated as cathode materials for a moderate temperature rechargeable Na cell operating at 130 C. The 1st discharge of TiS2 results in a capacity of 0.85 eq/mole; approximately half of the Na in the 1st phase spanning the Na range from zero to 0.30 and almost all the Na in the 2nd phase spanning the 0.37 to 0.80 range are rechargeable. VS2 intercalates up to one mole of Na/mole of VS2 in the 1st discharge; the resulting Na(x)VS2 ternary consists of 3 phases in the 3 ranges of Na from zero to 1. Niobium disulfide undergoes a phase change in the 1st discharge; the average rechargeable capacity in extended cycling of this cathode is 0.50 eq/mole.

Abraham, K. M.; Pitts, L.; Schiff, R.

1980-01-01

385

Optical limiting of layered transition metal dichalcogenide semiconductors  

E-print Network

Nonlinear optical property of transition metal dichalcogenide (TMDC) nanosheet dispersions, including MoS2, MoSe2, WS2, and WSe2, was performed by using Z-scan technique with ns pulsed laser at 1064 nm and 532 nm. The results demonstrate that the TMDC dispersions exhibit significant optical limiting response at 1064 nm due to nonlinear scattering, in contrast to the combined effect of both saturable absorption and nonlinear scattering at 532 nm. Selenium compounds show better optical limiting performance than that of the sulfides in the near infrared. A liquid dispersion system based theoretical modelling is proposed to estimate the number density of the nanosheet dispersions, the relationship between incident laser fluence and the size of the laser generated micro-bubbles, and hence the Mie scattering-induced broadband optical limiting behavior in the TMDC dispersions.

Dong, Ningning; Feng, Yanyan; Zhang, Saifeng; Zhang, Xiaoyan; Chang, Chunxia; Fan, Jintai; Zhang, Long; Wang, Jun

2015-01-01

386

Electronic, quasiharmonic, and anharmonic entropies of transition metals  

NASA Astrophysics Data System (ADS)

For transition metals at temperatures to melting, the electronic entropy is calculated from linear muffin-tin orbital electronic densities of states (using both the atomic-sphere approximation as well as a full potential), the quasiharmonic entropy is calculated from neutron-scattering data, and the anharmonic entropy is then extracted from the measured entropy. The electronic entropy is large, and is strongly nonlinear in temperature, as a result of both the volume dependence and energy dependence of the electronic density of states. The anharmonic entropy is small and apparently negative for V, Nb, Ta, Pd, and Pt, but is large and positive for Cr, Mo, and W. For Ni, the anharmonic plus magnetic entropy is determined accurately, and the magnetic entropy is estimated. For Ti and Zr, the total lattice-dynamic entropy is accurately given by the quasiharmonic formula with temperature-dependent renormalized phonon frequencies, in both hcp and bcc phases.

Eriksson, Olle; Wills, J. M.; Wallace, Duane

1992-09-01

387

Radiation damage of transition metal carbides. Final technical report  

SciTech Connect

In this grant period we have investigated electrical properties of transition metal carbides and radiation-induced defects produced by low-temperature electron irradiation in them. Special attention has been given to the composition VC{sub 0.88} in which the vacancies on the carbon sublattice of this fcc crystal order to produce a V{sub 8}C{sub 7} superlattice. The existence of this superlattice structure was found to make the crystal somewhat resistant to radiation damage at low doses and/or at ambient temperature. At larger doses significant changes in the resistivity are produced. Annealing effects were observed which we believe to be connected with the reconstitution of the superlattice structure.

Dixon, G.

1991-12-31

388

Moderate temperature sodium cells. I - Transition metal disulfide cathodes  

NASA Astrophysics Data System (ADS)

TiS2, VS2, and Nb(1.1)S2 transition metal disulfides were evaluated as cathode materials for a moderate temperature rechargeable Na cell operating at 130 C. The 1st discharge of TiS2 results in a capacity of 0.85 eq/mole; approximately half of the Na in the 1st phase spanning the Na range from zero to 0.30 and almost all the Na in the 2nd phase spanning the 0.37 to 0.80 range are rechargeable. VS2 intercalates up to one mole of Na/mole of VS2 in the 1st discharge; the resulting Na(x)VS2 ternary consists of 3 phases in the 3 ranges of Na from zero to 1. Niobium disulfide undergoes a phase change in the 1st discharge; the average rechargeable capacity in extended cycling of this cathode is 0.50 eq/mole.

Abraham, K. M.; Pitts, L.; Schiff, R.

1980-12-01

389

Transition Metal Dichalcogenide Growth via Close Proximity Precursor Supply  

NASA Astrophysics Data System (ADS)

Reliable chemical vapour deposition (CVD) of transition metal dichalcogenides (TMDs) is currently a highly pressing research field, as numerous potential applications rely on the production of high quality films on a macroscopic scale. Here, we show the use of liquid phase exfoliated nanosheets and patterned sputter deposited layers as solid precursors for chemical vapour deposition. TMD monolayers were realized using a close proximity precursor supply in a CVD microreactor setup. A model describing the growth mechanism, which is capable of producing TMD monolayers on arbitrary substrates, is presented. Raman spectroscopy, photoluminescence, X-ray photoelectron spectroscopy, atomic force microscopy, transmission electron microscopy, scanning electron microscopy and electrical transport measurements reveal the high quality of the TMD samples produced. Furthermore, through patterning of the precursor supply, we achieve patterned growth of monolayer TMDs in defined locations, which could be adapted for the facile production of electronic device components.

O'Brien, Maria; McEvoy, Niall; Hallam, Toby; Kim, Hye-Young; Berner, Nina C.; Hanlon, Damien; Lee, Kangho; Coleman, Jonathan N.; Duesberg, Georg S.

2014-12-01

390

Thermally induced core-electron binding-energy shifts in transition metals: An experimental investigation of Ta,,100...  

E-print Network

Thermally induced core-electron binding-energy shifts in transition metals: An experimental. The model is further used to estimate thermally induced shifts for the whole 5d transition-metal series. S SCS's .4 In contrast to the simple metals, d-band transition metals have received little attention Lu

Riffe, D. Mark

391

Defect-induced photoluminescence in monolayer semiconducting transition metal dichalcogenides.  

PubMed

It is well established that defects strongly influence properties in two-dimensional materials. For graphene, atomic defects activate the Raman-active centrosymmetric A1g ring-breathing mode known as the D-peak. The relative intensity of this D-peak compared to the G-band peak is the most widely accepted measure of the quality of graphene films. However, no such metric exists for monolayer semiconducting transition metal dichalcogenides such as WS2 or MoS2. Here we intentionally create atomic-scale defects in the hexagonal lattice of pristine WS2 and MoS2 monolayers using plasma treatments and study the evolution of their Raman and photoluminescence spectra. High-resolution transmission electron microscopy confirms plasma-induced creation of atomic-scale point defects in the monolayer sheets. We find that while the Raman spectra of semiconducting transition metal dichalcogenides (at 532 nm excitation) are insensitive to defects, their photoluminescence reveals a distinct defect-related spectral feature located ?0.1 eV below the neutral free A-exciton peak. This peak originates from defect-bound neutral excitons and intensifies as the two-dimensional (2D) sheet is made more defective. This spectral feature is observable in air under ambient conditions (room temperature and atmospheric pressure), which allows for a relatively simple way to determine the defectiveness of 2D semiconducting nanosheets. Controlled defect creation could also enable tailoring of the optical properties of these materials in optoelectronic device applications. PMID:25603228

Chow, Philippe K; Jacobs-Gedrim, Robin B; Gao, Jian; Lu, Toh-Ming; Yu, Bin; Terrones, Humberto; Koratkar, Nikhil

2015-02-24

392

Theoretical study of charge density waves in transition metal materials  

NASA Astrophysics Data System (ADS)

In this thesis we theoretically study new aspects of charge density waves in transition metal materials recently revealed by scanning tunneling microscopy measurements. The two important problems that we have investigated are the effects of orbital degeneracy on the formation of the charge-density waves in cobalt nanowires, and the effects of dilute but strongly pinning impurities on the charge-density wave in niobium diselenide. We first present an overview on charge-density waves, and then introduce a general theoretical model describing charge-density waves. We also explain several known results about disorder effects on charge-density waves. We briefly touch on the principle of scanning tunneling microscopy and its advantages compared to other experimental tools. Second, we discuss the physics of one-dimensional cobalt nanowires along with experimental results. We propose a theoretical model that is relevant to cobalt nanowires, and then analyze the model by two theoretical tools: mean-field theory and bosonization. Our results show that the multi-orbitals allow a spin-triplet interaction among electrons leading to different phase diagrams from the ones considered previously for similar models. Numerical results obtained by first-principles calculations are also briefly explained. Third, we consider the effects of dilute strong impurities on the charge-density wave in niobium diselenide, a transition metal dichalcogenide. We first explain the material and properties of its charge-density wave phase. Then, detailed analysis of a scanning tunneling microscopy measurement is presented. Next, we analytically and numerically study a phenomenological model relevant to the experiment. We show that the dilute strong impurities have little effects at large length scales compared to the average inter-impurity distance, leading to a topologically ordered phase with a (quasi-)long-range autocorrelation; this result is quite different from conventional pictures predicting short-range order with the proliferation of topological defects.

Okamoto, Junichi

393

Elastic properties of C40 transition metal disilicides  

SciTech Connect

Room-temperature and low temperature elastic properties of hexagonal C40 transition metal disilicides, NbSi{sub 2} and TaSi{sub 2}, have been studied using Resonant Ultrasound Spectroscopy (RUS). All five independent elastic stiffness constants c{sub ij} for NbSi{sub 2} and TaSi{sub 2} single crystals have been obtained. The temperature dependence of the c{sub ij} is normal but not large. The orientation dependence of the Young`s and shear moduli was examined in comparison with other transition metal disilicides. The room temperature shear moduli in the {l_brace}0001{r_brace} plane, with values of 145.3 and 143.7 GPa for NbSi{sub 2} and TaSi{sub 2} respectively, are low relative to those in the equivalent pseudo hexagonal {l_brace}220{r_brace} close-packed plane for tetragonal C11{sub b} MoSi{sub 2} and WSi{sub 2}. The isotropic elastic constants for polycrystalline materials were also calculated. The results show that the various moduli are all much higher than those of the constituent elements. The room temperature Poisson`s ratios of NbSi{sub 2} and TaSi{sub 2} are 0.18 and 0.19, respectively, which are smaller than those of the constituent elements and smaller than most materials. The Debye temperatures, {theta}{sub D}, were estimated to be 688 K for NbSi{sub 2} and 552 K for TaSi{sub 2}. The elastic properties of C40 VSi{sub 2}, NbSi{sub 2}, TaSi{sub 2}, and CrSi{sub 2} and C11{sub b} MoSi{sub 2} and WSi{sub 2} are compared and the possible influence on mechanical behavior discussed.

Chu, F.; Maloy, S.A.; Petrovic, J.J.; Mitchell, T.E. [Los Alamos National Lab., NM (United States). Center for Materials Science] [Los Alamos National Lab., NM (United States). Center for Materials Science; Lei, M. [Quatrosonics, Inc., Albuquerque, NM (United States)] [Quatrosonics, Inc., Albuquerque, NM (United States)

1996-08-01

394

Metal-Semiconductor Barrier Modulation for High Photoresponse in Transition Metal Dichalcogenide Field Effect Transistors  

PubMed Central

A gate-controlled metal-semiconductor barrier modulation and its effect on carrier transport were investigated in two-dimensional (2D) transition metal dichalcogenide (TMDC) field effect transistors (FETs). A strong photoresponse was observed in both unipolar MoS2 and ambipolar WSe2 FETs (i) at the high drain voltage due to a high electric field along the channel for separating photo-excited charge carriers and (ii) at the certain gate voltage due to the optimized barriers for the collection of photo-excited charge carriers at metal contacts. The effective barrier height between Ti/Au and TMDCs was estimated by a low temperature measurement. An ohmic contact behavior and drain-induced barrier lowering (DIBL) were clearly observed in MoS2 FET. In contrast, a Schottky-to-ohmic contact transition was observed in WSe2 FET as the gate voltage increases, due to the change of majority carrier transport from holes to electrons. The gate-dependent barrier modulation effectively controls the carrier transport, demonstrating its great potential in 2D TMDCs for electronic and optoelectronic applications. PMID:24509565

Li, Hua-Min; Lee, Dae-Yeong; Choi, Min Sup; Qu, Deshun; Liu, Xiaochi; Ra, Chang-Ho; Yoo, Won Jong

2014-01-01

395

First examples of stable transition metal complexes of an all-metal antiaromatic molecule (Al$_4$Li$_4$)  

Microsoft Academic Search

We propose new methodologies for stabilizing all-metal antiaromatic clusters like: Al$_{4}$Li$_{4}$. We demonstrate that these all-metal species can be stabilized by complexation with 3d-transition metals very similar to its organic counterpart, C$_4$H$_4$. Complexation to transition metal ions reduce the frontier orbital energies and introduces aromaticity. We consider a series of such complexes [$\\\\eta$$^4$(Al$_4$Li$_4$)-Fe(CO)$_3$, $\\\\eta$$^2$$\\\\sigma$$^2$(Al$_4$Li$_4$)-Ni and (Al$_{4}$Li$_{4}$)$_{2}$Ni] and make a comparison

Ayan Datta; Swapan K Pati

2004-01-01

396

Thin film reaction of transition metals with germanium  

SciTech Connect

A systematic study of the thermally induced reaction of 20 transition metals (Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, and Cu) with Ge substrates was carried out in order to identify appropriate contact materials in Ge-based microelectronic circuits. Thin metal films, nominally 30 nm thick, were sputter deposited on both amorphous Ge and crystalline Ge(001). Metal-Ge reactions were monitored in situ during ramp anneals at 3 deg. C s{sup -1} in an atmosphere of purified He using time-resolved x-ray diffraction, diffuse light scattering, and resistance measurements. These analyses allowed the determination of the phase formation sequence for each metal-Ge system and the identification of the most promising candidates--in terms of sheet resistance and surface roughness--for their use as first level interconnections in microelectronic circuits. A first group of metals (Ti, Zr, Hf, V, Nb, and Ta) reacted with Ge only at temperatures well above 450 deg. C and was prone to oxidation. Another set (Cr, Mo, Mn, Re, Rh, Ru, and Ir) did not form low resistivity phases (<130 {mu}{omega} cm) whereas no reaction was observed in the case of W even after annealing at up to 1000 deg. C. We found that Fe, Co, Ni, Pd, Pt, and Cu were the most interesting candidates for microelectronic applications as they reacted at relatively low temperatures (150-360 deg. C) to form low resistivity phases (22-129 {mu}{omega} cm). Among those, two monogermanides, NiGe and PdGe, exhibited the lowest resistivity values (22-30 {mu}{omega} cm) and were stable over the widest temperature window during ramp anneals. In passing, we note that Cu, Ni, and Pd were the most effective in lowering the crystallization temperature of amorphous Ge, by up to 290 deg. C for our typical ramp anneals at 3 deg. C s{sup -1}.

Gaudet, S.; Detavernier, C.; Kellock, A.J.; Desjardins, P.; Lavoie, C. [Regroupement Quebecois sur les Materiaux de Pointe (RQMP), Ecole Polytechnique de Montreal, P.O. Box 6079, Station Centre-Ville, Montreal, Quebec H3C 3A7 (Canada )and Departement de Genie Physique, Ecole Polytechnique de Montreal, P.O. Box 6079, Station Centre-Ville, Montreal, Quebec H3C 3A7 (Canada); Department of Solid State Physics, Ghent University, Ghent 9000 (Belgium); IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120 (United States); Regroupement Quebecois sur les Materiaux de Pointe (RQMP), Ecole Polytechnique de Montreal, P.O. Box 6079, Station Centre-Ville, Montreal, Quebec H3C 3A7 (Canada) and Departement de Genie Physique, Ecole Polytechnique de Montreal, P.O. Box 6079, Station Centre-Ville, Montreal, Quebec H3C 3A7 (Canada); IBM T.J. Watson Research Center, Yorktown Heights, New York 10598 and Departement de Genie Physique, Ecole Polytechnique de Montreal, Montreal, Quebec H3C 3A7 (Canada)

2006-05-15

397

Strong Periodic Lattice Distortion in Transition Metal Dichalcogenides  

NASA Astrophysics Data System (ADS)

The charge density wave (CDW) instability was initially proposed to be the result of the Peierls mechanism in which a divergence in electronic response function results in a periodic charge redistribution; i.e. the electron gas itself is unstable with respect to the formation of a periodically varying electron charge density. However, the mechanism of CDW in many 2D Transition Metal Dichalcogenide (TMD) is still under debate. Fermi surface nesting was originally believed to act as the driving mechanism of CDW transitions in these materials; however, recent reports from both theoretical and experimental studies are not quite within this simple model. We use Spectroscopic Imaging Scanning Tunneling Microscope (SI-STM) to study the surfaces of 2H-TaSe2, 2H-TaS2, and 2H-NbSe2 at various temperatures from 6K to above 100K. Topographic images and differential conductance data were recorded and analyzed in order to help understanding the underlying physics of CDW phases. Our results shows that Periodic Lattice Distortion (PLD) likely plays a more important role than the charge modulation in 2D TMD.

Dai, Jixia; Calleja, Eduardo; Cao, Yue; Dessau, Daniel; McElroy, Kyle; Berger, Helmuth; Zhu, Xiangde; Li, Lijun; Sun, Yuping; Wolf, T.

2012-02-01

398

Nanostructured transition metal oxides for aqueous hybrid electrochemical supercapacitors  

NASA Astrophysics Data System (ADS)

In this paper, we wish to present an overview of the research carried out in our laboratories with low-cost transition metal oxides (manganese dioxide, iron oxide and vanadium oxide) as active electrode materials for aqueous electrochemical supercapacitors. More specifically, the paper focuses on the approaches that have been used to increase the capacitance of the metal oxides and the cell voltage of the supercapacitor. It is shown that the cell voltage of an electrochemical supercapacitor can be increased significantly with the use of hybrid systems. The most relevant associations are Fe3O4 or activated carbon as the negative electrode and MnO2 as the positive. The cell voltage of the Fe3O4/MnO2 device is 1.8 V and this value was increased to 2.2 V by using activated carbon instead of Fe3O4. These two systems have shown superior behavior compared to a symmetric MnO2/MnO2 device which only works within a 1 V potential window in aqueous K2SO4. Furthermore, the activated carbon/MnO2 hybrid device exhibits a real power density of 605 W/kg (maximum power density =19.0 kW/kg) with an energy density of 17.3 Wh/kg. These values compete well with those of standard electrochemical double layer capacitors working in organic electrolytes.

Cottineau, T.; Toupin, M.; Delahaye, T.; Brousse, T.; Bélanger, D.

2006-03-01

399

Transition-metal-oxide coated titanium electrodes for redox batteries  

NASA Astrophysics Data System (ADS)

The production of porous electrodes with reproducible surface activity for experiments to corroborate predictions of porous electrode theory to ascertain if simple one step outer sphere electron transfer mechanism applies to the ferric-ferrous redox reaction at high reactant/product concentrations in a strong acid chloride medium was investigated. Kinetic rate expressions of this couple under these conditions at the metal oxide surfaces were sought. Coatings of the conductive and active rutile structure form of selected transition metal oxides were desired. Both IrO2 and RuO2 coatings having the rutile structure were prepared by thermal decomposition of their respective hydrated chloride salts. Low over potential exchange current densities of the ferric-ferrous couple were measured in concentrated solution at Pt, RuO2 and IrO2 RDF's. Significant corrections were necessary for ohmic effects, mass transfer effects, and nonuniform current distribution. It is shown that the electrocatalytic activity of RuO2 is comparable to that of Pt while the activity of IrO2 is approximately an order of magnitude less than Pt. The measured free energy of activation was similar for all three substrates and a nonbinding interaction between the couple and the surfaces is suggested. The variation in exchange currents among the different substrates can be attributed to some extent on double layer effects but primarily to crystal structure differences.

Savinell, R. F.

1982-12-01

400

Topological superconductivity at the edge of transition-metal dichalcogenides  

NASA Astrophysics Data System (ADS)

Time-reversal breaking topological superconductors are new states of matter which can support Majorana zero modes at the edge. In this Rapid Communication, we propose a different realization of one-dimensional topological superconductivity and Majorana zero modes. The proposed system consists of a monolayer of transition-metal dichalcogenides MX2 (M =Mo,W; X =S,Se) on top of a superconducting substrate. Based on first-principles calculations, we show that a zigzag edge of the monolayer MX2 terminated by a metal atom M has edge states with strong spin-orbit coupling and spontaneous magnetization. By proximity coupling with a superconducting substrate, topological superconductivity can be induced at such an edge. We propose NbS2 as a natural choice of substrate, and estimate the proximity induced superconducting gap based on first-principles calculation and a low energy effective model. As an experimental consequence of our theory, we predict that Majorana zero modes can be detected at the 120° corner of a MX2 flake in proximity to a superconducting substrate.

Xu, Gang; Wang, Jing; Yan, Binghai; Qi, Xiao-Liang

2014-09-01

401

Antiferromagnetic Metal and Mott Transition on Shastry-Sutherland Lattice  

PubMed Central

The Shastry-Sutherland lattice, one of the simplest systems with geometrical frustration, which has an exact eigenstate by putting singlets on diagonal bonds, can be realized in a group of layered compounds and raises both theoretical and experimental interest. Most of the previous studies on the Shastry-Sutherland lattice are focusing on the Heisenberg model. Here we opt for the Hubbard model to calculate phase diagrams over a wide range of interaction parameters, and show the competing effects of interaction, frustration and temperature. At low temperature, frustration is shown to favor a paramagnetic metallic ground state, while interaction drives the system to an antiferromagnetic insulator phase. Between these two phases, there are an antiferromagnetic metal phase and a paramagnetic insulator phase (which should consist of a small plaquette phase and a dimer phase) resulting from the competition of the frustration and the interaction. Our results may shed light on more exhaustive studies about quantum phase transitions in geometrically frustrated systems. PMID:24777282

Liu, Hai-Di; Chen, Yao-Hua; Lin, Heng-Fu; Tao, Hong-Shuai; Liu, Wu-Ming

2014-01-01

402

Electronic properties of transition-metal-decorated silicene.  

PubMed

The electronic properties of 3d transition metal (TM)-decorated silicene were investigated by using density functional calculations in an attempt to replace graphene in electronic applications, owing to its better compatibility with Si-based technology. Among the ten types of TM-doped silicene (TM-silicene) studied, Ti-, Ni-, and Zn-doped silicene became semiconductors, whereas Co and Cu doping changed the substrate to a half-metallic material. Interestingly, in cases of Ti- and Cu-doped silicene, the measured band gaps turned out to be significantly larger than the previously reported band gap in silicene. The observed band-gap openings at the Fermi level were induced by breaking the sublattice symmetry caused by two structural changes, that is, the Jahn-Teller distortion and protrusion of the TM atom. The present calculation of the band gap in TM-silicene suggests useful guidance for future experiments to fabricate various silicene-based applications such as a field-effect transistor, single-spin electron source, and nonvolatile magnetic random-access memory. PMID:25303061

Lee, Youngbin; Yun, Kyung-Han; Cho, Sung Beom; Chung, Yong-Chae

2014-12-15

403

Solubility Behavior and Phase Stability of Transition Metal Oxides in Alkaline Hydrothermal Environments  

SciTech Connect

The solubility behavior of transition metal oxides in high temperature water is interpreted by recognizing three types of chemical reaction equilibria: metal oxide hydration/dehydration, metal oxide dissolution and metal ion hydroxocomplex formation. The equilibria are quantified using thermodynamic concepts and the thermochemical properties of the metal oxides/ions representative of the most common constituents of construction metal alloys, i.e., element shaving atomic numbers between Z = 22 (Ti) and Z = 30 (Zn), are summarized on the basis of metal oxide solubility studies conducted in the laboratory. Particular attention is devoted to the uncharged metal ion hydrocomplex, M{sup Z}(OH){sub Z}(aq), since its thermochemical properties define minimum solubilities of the metal oxide at a given temperature. Experimentally-extracted values of standard partial molal entropy (S{sup 0}) for the transition metal ion neutral hydroxocomplex are shown to be influenced by ligand field stabilization energies and complex symmetry.

S.E. Ziemniak

2000-05-18

404

Kindergarten Transition: Does family involvement make a difference in children's early school adjustment?  

E-print Network

Kindergarten transition is a critical experience for children because of its potential long-term impact on school performance. Recognizing this impact, the field of early childhood education has been making great efforts to facilitate children...

Kang, Jean

2010-07-30

405

Reactivity and Spectroscopic Studies of Selected Transition Metal Clusters.  

NASA Astrophysics Data System (ADS)

Reactions of the group 5 transition-metal clusters (V_{rm n}, Nb _{rm n}, and Ta_ {rm n}) have been investigated in the gas-phase by using a fast-flow chemical reactor. Dissociative chemisorption of D_ 2 and N _ 2 is found to be size selective for these bare metal clusters, as well as for the cluster monoxides V_{rm n}O and Ta _{rm n}O and monocarbides V_{rm n}C. The effect of a single atomic impurity (C or O) decreases for clusters larger than 10 atoms and becomes negligible for clusters larger than 15-20 atoms. This loss of sensitivity to impurities is consistent with the loss of cluster size specificity, which occurs in the same size range. Evidence of structural isomerism is found for Nb_ 9, Nb_{11}, Nb _{12}, and Ta_ {12} which react with N_ 2 with biexponential reaction kinetics. The rate of chemisorption with ethane (C_ 2H _ 6) displays a steady increase with cluster size for V_{rm n} and Nb_{rm n}, but Ta_{rm n} clusters are only slightly reactive. Finally, the rate of addition of a second ligand to a metal cluster is considered, and examples are analyzed for the Nb_{ rm n}N_ 2 + N _ 2 case. Resonant two photon ionization spectroscopy has been used to investigate the optical spectra of jet-cooled MoO. By coupling the technique to a time-of-flight mass spectrometer, spectra of all isotopic species of MoO have been separately recorded. The observed spectra establish the ground state of MoO as ^ 5Pi_ {rm r}, deriving from the 2 delta^{2}12sigma^{1 }6pi^ 1 molecular configuration. Transitions from this ground state to the excited 2delta ^{1}12sigma^{1}6 pi^ 2, A^' ^ 5Delta_{rm r}; 2delta^{2}6 pi^{1}13sigma^ 1; B ^ 5Pi_{rm r} ; and 2delta^{1}12 sigma^{1}6pi^{1 }13sigma^ 1, B^ ' ^ 5Pi_{ rm r} states have been located, rotationally resolved, and anlayzed. Numerous other weak transitions have been observed in the visible, many of which must be due to S = 1 >=ts X^ 5Pi_{rm r} intercombinations. Several strong transitions are observed in the near infrared where the 2delta^{2}12sigma ^{1}13sigma^ 1, ^ 5Sigma^ - >=ts X ^ 5Pi and 2 delta^{2}6pi^ 2, A ^ 5Sigma^ + >=ts X ^ 5Pi band systems are expected. The general electronic structure of MoO is shown to be quite analogous to that of its congener, CrO, and the pattern of molecular orbitial energies is also quite comparable to that found for NbO.

Hamrick, Yoon Mi Lee

1990-01-01

406

X-ray Absorption Spectroscopy of Transition Metal-Magnesium Hydride Thin Films  

E-print Network

X-ray Absorption Spectroscopy of Transition Metal-Magnesium Hydride Thin Films T. J. Richardsona and coordination of the magnesium and transition metal atoms during hydrogen absorption were studied using dynamic in situ transmission mode X-ray absorption spectroscopy. Mg K-edge and Ni, Co, and Ti L-edge spectra

407

Electronic Griffiths Phases and Quantum Criticality at the Metal-Insulator Transition  

E-print Network

Electronic Griffiths Phases and Quantum Criticality at the Metal-Insulator Transition Vladimir and Quantum Criticality at the Metal-Insulator Transition Vladimir Dobrosavljevic Florida State University. Fisher (1992): new scenario for (insulating) QCPs with disorder (Ising) Griffiths phase g T ordered phase

Dobrosavljevic, Vladimir

408

Methane-to-Methanol Conversion by Gas-Phase Transition Metal Oxide Cations: Experiment and Theory  

E-print Network

Methane-to-Methanol Conversion by Gas-Phase Transition Metal Oxide Cations: Experiment and Theory-phase transition metal oxide cations can convert methane to methanol. Methane activation by MO+ is discussed such as methanol has attracted great experimental and theoretical interest due to its importance as an industrial

Metz, Ricardo B.

409

Topological phase transitions in periodically modulated quantized metal films Alexander E. Meyerovich1  

E-print Network

Topological phase transitions in periodically modulated quantized metal films Alexander E August 2002; published 5 December 2002 Electronic topological phase transitions ETT are predicted for any quantized metal films with a periodi- cally modulated boundary commensurate with the bulk lattice. While

Meyerovich, Alex

410

The metal-insulator transition in VO2 studied using terahertz apertureless near-field microscopy  

E-print Network

transmission spec- troscopy, showing a large change in the spatially averaged terahertz dielectric responseThe metal-insulator transition in VO2 studied using terahertz apertureless near-field microscopy studied the metal-insulator transition in a vanadium dioxide VO2 thin film using terahertz apertureless

Mittleman, Daniel

411

A review of modern transition-metal nanoclusters: their synthesis, characterization, and applications in catalysis  

Microsoft Academic Search

A literature review of modern transition-metal nanoclusters, with an emphasis on those nanoclusters which are catalytically active, is presented in two parts. Part One presents background information on transition-metal nanoclusters, including an overview of common synthetic routes, a description of how nanoclusters are stabilized, and a brief summary of the multiple characterization techniques used (and the type of information that

John D. Aiken; Richard G. Finke

1999-01-01

412

XAFS Studies of Transition Metal and Halogen Biomaterials in Invertebrate Tools  

E-print Network

XAFS Studies of Transition Metal and Halogen Biomaterials in Invertebrate Tools Y. Taoad , J, invertebrate tools, biomaterials PACS: 87.64.Fb INTRODUCTION There exists a large amount of transition metals and halide elements in many invertebrate tools [1]. What is the biological role of these elements

Scott, Robert A.

413

Ultrathin nanosheets of half-metallic monoclinic vanadium dioxide with a thermally induced phase transition.  

PubMed

Only the half of it: A modified intercalation-deintercalation strategy that takes advantage of the characteristic thermally induced phase transition of monoclinic VO2 has been developed for the preparation of ultrathin VO2 nanosheets. The resultant nanosheets exhibit half-metallic character and a temperature-dependent phase transition. The half-metallicity could lead to applications in spintronic nanodevices. PMID:23757381

Yao, Tao; Liu, Liang; Xiao, Chong; Zhang, Xiaodong; Liu, Qinghua; Wei, Shiqiang; Xie, Yi

2013-07-15

414

ON THE PRESSURE DEPENDENCE OF SUPERCONDUCTIVITY IN TRANSITION METAL DICHALCOGENIDE LAYER CRYSTALS  

E-print Network

L-279 ON THE PRESSURE DEPENDENCE OF SUPERCONDUCTIVITY IN TRANSITION METAL DICHALCOGENIDE LAYER measurements of the pressure dependence of superconductivity in transition metal dichalco- genide layer, the critical tempe- rature 7c and the critical field Hc2, show very little variation with pressure, at least up

Boyer, Edmond

415

First-order metal-insulator transition not accompanied by the structural phase transition observed in VO2-based devices  

Microsoft Academic Search

An abrupt first-order metal-insulator transition (MIT) is observed during the application of a switching pulse voltage to VO2-based two-terminal devices. When the abrupt MIT occurs, the structural phase transition (SPT) is investigated by a micro- Raman spectroscopy and a micro-XRD. The result shows that the MIT is not accompanied with the structural phase transition (SPT); the abrupt MIT is prior

Hyun-Tak Kim; Byung-Gyu Chae; Bong-Jun Kim; Yong-Wook Lee; Sun-Jin Yun; Kwang-Yong Kang

2006-01-01

416

X-ray absorption to determine the metal oxidation state of transition metal compounds  

NASA Astrophysics Data System (ADS)

We present three examples where x-ray absorption at the transition metal L2,3 edges is used to investigate the valence states of various strongly correlated (SC) and technological relevant materials. Comparison with ligand field multiplet calculations is needed to determine the metal oxidation states. The examples are CrF2, the La1-xSrxCoO3 family and YVO3. For CrF2 the results indicate a disproportionation reaction that generates Cr+, Cr2+ and Cr3+ in different proportions that can be quantified directly from the x-ray spectra. Additionally, it is shown that Co2+ is present in the catalytic La1-xSrxCoO3 perovskite family. Finally, surface effects that change the vanadium valence are also found in YVO3 nanocrystals.

Jiménez-Mier, J.; Olalde-Velasco, P.; Carabalí-Sandoval, G.; Herrera-Pérez, G.; Chavira, E.; Yang, W.-L.; Denlinger, J.

2013-07-01

417

A tight-binding potential for atomistic simulations of carbon interacting with transition metals: Application to the Ni-C system  

E-print Network

A tight-binding potential for atomistic simulations of carbon interacting with transition metals for transition metals, carbon, and transition metal carbides, which has been optimized through a systematic of the transition metal, is used to obtain a transferable tight-binding model of the carbon-carbon, metal-metal

Paris-Sud XI, Université de

418

JOURNAL DE PHYSIQUE Colloque C 1,supple'ment au no 2-3, Tome 32, Fkvrier-Mars 1971,page C 1 -1105 METAL-NON METAL TRANSITION IN HUBBARD MODEL  

E-print Network

METAL-NON METAL TRANSITION IN HUBBARD MODEL M. CYROT Laboratoire de Physique des Solides, FacultC des Sciences, 91, Orsay (France) RBsumB. -Nous etudions la transition metal-isolant due aux corr transition metal-isolant. Abstract. -We study the metal-non metal transition due to correlations between

Paris-Sud XI, Université de

419

Infusing Early Intervention for Substance Use Into Community Mental Health Services for Transitioning Youth  

Microsoft Academic Search

The treatment of transitioning youth (ages 16–25) diagnosed with co-occurring mental health and substance abuse problems has been the focus of numerous research and practice efforts. However, far less attention has been devoted to intervening early to address alcohol and other drug (AOD) use, which has the potential to contribute to the numerous challenges transitioning youth with emotional or behavioral

Sarah A. Taylor; Elizabeth K. Anthony

2011-01-01

420

Nature of the metal-insulator transition in Nb O2  

NASA Astrophysics Data System (ADS)

We report a theoretical study of the structural phase transition and associated metal-to-insulator transition in Nb O2 within density functional theory using the transition state theory as formulated in the generalized solid-state nudged elastic band method. Consistent with prior experimental work, we demonstrate that niobium dimerization is primarily driven by soft modes at the P point of the rutile Brillouin zone. In light of our results, it appears that the metal-to-insulator transition in Nb O2 is driven by a second-order structural transition of the Peierls type.

O'Hara, Andrew; Demkov, Alexander A.

2015-03-01

421

Two-Photon Spectroscopy of Transition-Metal Ions in Cubical Symmetry  

E-print Network

Symmetry adaptation techniques are applied to the determination of intensities of intra-configurational two-photon transitions for transition-metal ions in cubical symmetry. This leads to a simple model giving the polarization dependence of intensities of two-photon (electric dipolar) transitions between Stark levels of the configuration 3dN (N = even or odd).

M. Daoud; M. Kibler

1998-10-26

422

Study of glass transition of metallic glasses by temperature-modulated differential scanning calorimetry (MDSC)  

Microsoft Academic Search

The glass transition behavior of several Zr- and Mg-based metallic glasses has been studied by temperature-modulated differential scanning calorimetry (MDSC). It is clearly demonstrated that the glass transition can be separated from crystallization for these glasses by MDSC. Some glass transitions that could not be observed by a conventional differential scanning calorimetry (DSC) have been detected. Furthermore, the complex change

Z. P Lu; Y Li; S. C Ng; Y. P Feng

2000-01-01

423

JOURNAL DE PHYSIQUE Colloque C4, supplkment au no 10, Tome 37, Octobve 1976, page C4-17 METAL-NON METAL TRANSITION OF Nil -,S AND  

E-print Network

-NON METAL TRANSITION OF Nil -,S AND NiS SUBSTITUTED by Se, As and Fe : TRANSPORT PROPERTIES AND STRUCTURAL temperature phase) of the nickel monosulfide shows a metal-non metal transition as the temperature is loweredJOURNAL DE PHYSIQUE Colloque C4, supplkment au no 10, Tome 37, Octobve 1976, page C4-17 METAL

Paris-Sud XI, Université de

424

Changes in Paratethyan marine molluscs at the Early/Middle Miocene transition: diversity, palaeo-  

E-print Network

Changes in Paratethyan marine molluscs at the Early/Middle Miocene transition: diversity, palaeo: HARZHAUSER, M., MANDIC, O. & ZUSCHIN, M. 2003. Changes in Paratethyan marine molluscs at the Early for the development of mollusc faunas (gastropods and bivalves) in the Central Paratethys. Here, we first discuss

Zuschin, Martin

425

Magnetoconductance of metallic Si:B near the metal-insulator transition  

SciTech Connect

The magnetoconductance of {ital p}-type Si:B samples with dopant concentrations just above the metal-insulator transition is negative (positive magnetoresistance) at all measured temperatures between 0.1 and 4.2 K and for magnetic fields up to 9 T. We attribute this to the effects of strong spin-orbit scattering associated with the valence bands in {ital p}-type materials. The magnetoconductivity varies as {ital H}{sup 2} in small magnetic fields and approximately as {ital H}{sup 1/2} at high fields, with deviations from this simple form which become increasingly significant as the metal-insulator transition is approached. Based on the assumption that the high-field magnetoconductance is attributable mainly to electron-electron interactions, a separation of the low-field magnetoconductance into components associated with interactions and localization yields a hole inelastic scattering rate {h bar}/{tau}{sub in} which varies approximately linearly with temperature.

Dai, P.; Zhang, Y.; Sarachik, M.P. (City College of the City University of New York, New York, New York 10031 (United States))

1992-09-15

426

Explicitly correlated composite thermochemistry of transition metal species  

NASA Astrophysics Data System (ADS)

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)? 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.

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

2013-09-01

427

Fingerprints of spin-orbital entanglement in transition metal oxides  

E-print Network

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 $R$VO$_3$ perovskites, with $R$=La,Pr,...,Yb,Lu, where such finite temperature properties of these compounds can be understood only using entangled states: ($i$) thermal evolution of the optical spectral weights, ($ii$) the dependence of transition temperatures for the onset of orbital and magnetic order on the ionic radius in the phase diagram of the $R$VO$_3$ perovskites, and ($iii$) dimerization observed in the magnon spectra for the $C$-type antiferromagnetic phase of YVO$_3$. Finally, it is shown that joint spin-orbital excitations in an ordered phase with coexisting antiferromagnetic and alternating orbital order introduces topological constraints for the hole propagation and will thus radically modify transport properties in doped Mott insulators where hole motion implies simultaneous spin and orbital excitations.

Andrzej M. Ole?

2012-07-12

428

Photoluminescence properties of Jahn-Teller transition-metal ions  

NASA Astrophysics Data System (ADS)

This work investigates the influence of electron-phonon coupling associated with E ?e and T ?e Jahn-Teller (JT) effect in different transition-metal (TM) ions on de-excitation phenomena through nonradiative multiphonon relaxation, i.e., photoluminescence (PL) quenching. We developed a configurational curve model which is able to predict from the absorption spectrum whether a given JT-TM ion is PL or quenched. The prediction is made on the basis of an adapted Dexter-Klick-Russell parameter for JT systems, defined in terms of spectroscopic parameters through ?JT=??eabs/Eabs, where ?eabs refers to the splitting of the parent octahedral Eg states by the JT distortion in E ?e (? =3/4) or T ?e (? =1/4), and Eabs is the energy of the first absorption band involving electronic transition between Eg and T2g. We show that PL in any JT-TM ion occurs whenever ?JT<0.1 or is quenched if ?JT>0.2. This result is noteworthy since it allows us to establish structural requirements for the JT-TM ion and the host crystal to be PL. Although PL properties of materials containing TM ions depend on a variety of structural factors such as the electronic configuration, the site symmetry, and the crystal field produced by neighboring atoms, the present model achieves this goal through a simple spectroscopic parameter: ?JT. In this work we correlated the PL properties of different sixfold-coordinated JT systems such as Ti3+, Cu2+, Mn3+, Cr2+, Fe2+, Co3+, and Ni3+ in halides and oxides with ?JT obtained from their respective absorption spectra. From this analysis we conclude that depending on the nature of the JT coupling and its strength, PL is either strongly favored or quenched in T ?e while it is mostly quenched in E ?e systems due to the larger JT distortion.

Sanz-Ortiz, Marta N.; Rodríguez, Fernando

2009-09-01

429

Novel quasi-aromatic transition metal cluster compounds  

NASA Astrophysics Data System (ADS)

From the point of view of chemical reactivities, molecular configurations, and bonding characteristics, a series of novel quasi-aromatic transition metal cluster compounds has been studied in this article. Experimental evidences for the cluster compounds [M3(?3-X)(?-y)3]4+ (M = Mo, W; X, Y = O, S, Se, Te) containing a puckered six-membered rings reveal benzene-like structural characteristics and chemical behaviours in a series of ligand substitution, addition, and oxidation reactions. The energy localized CNDO/2 molecular orbital method is applied to elucidate the nature of quasi-aromaticity in this type of cluster compound. The localized molecular orbitals (LMOs) of benzene as an aromatic prototype and a series of planar monocyclic polyene hydrocarbons CnHqn as well as certain typical conjugated six-membered rings are investigated, leading a deep-rooted inherent relationship between their aromaticity and bonding characteristics. The LMO analyses for these cluster compounds with [Mo3(?3-X)(?-y)3]4+ show that in both benzene and such cluster compounds there exists a closed, smoothly continuous conjugated ?-electron system, formed from three synergistically connected three-centred two-electron ? bonds, which is a (p-p-p)? conjugated system in the former, but a (d-p-d)n: one for the latter. The size and electronegativity of the bridging atom (?-Y) affect significantly the degrees of quasi-aromaticity in these cluster compounds with the core [M3(?-X)(?-Y)3]4+ (Y = O, S, Se, Te); on the other hand, the stronger interaction between the metal atom M and the terminal ligands with lone-pair electrons results in a smaller quasi-aromaticity of the puckered [M3Y3] ring. The bonding patterns of the cubane-type [Mo3S4ML2](4+q) and the sandwich-type [Mo3S4MS4Mo3]8+ formed from the quasi-aromatic ligand [Mo3S4]4+ with a metal atom M are discussed in detail. Finally, criteria have been formulated for the formation of a closed, smoothly continuous ?-conjugated system in these [M3Y3] rings.

Lu, Jia-Xi; Chen, Zhi-Da

430

Family Structure and the Transition to Early Parenthood  

Microsoft Academic Search

With the rise in out-of-wedlock childbearing and divorce in the last quarter of the twentieth century, an increasing proportion of children have been exposed to a variety of new family forms. Little research has focused on the consequences of childhood family structure for men's transition to fatherhood or on the family processes that account for the effects of family structure

Sandra L. Hofferth; Frances Goldscheider

2010-01-01

431

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

NASA Astrophysics Data System (ADS)

Comproportionation reactions of rare-earth metal trihalides (RX3) with the respective rare-earth metals (R) and transition metals (T) led to the formation of 22 oligomeric R cluster halides encapsulating T, in 19 cases for the first time. The structures of these compounds were determined by single-crystal X-ray diffraction and are composed of trimers ({T3R11}X15-type, P63/m), tetramers ({T4R16}X28{R4} (P-43m), {T4R16}X20 (P42/nnm), {T4R16}X24(RX3)4 (I41/a) and {T4R16}X23 (C2/m) types of structure) and pentamers ({Ru5La14}2Br39, Cc) of {TRr}n (n=2-5) clusters. These oligomers are further enveloped by inner (Xi) as well as outer (Xa) halido ligands, which possess diverse functionalities and interconnect like oligomers through i-i, i-a and/or a-i bridges. The general features of the crystal structures for these new compounds are discussed and compared to literature entries as well as different structure types with oligomeric T centered R clusters. Dimers and tetramers originating from the aggregation of {TR6} octahedra via common edges are more frequent than trimers and pentamers, in which the {TRr} clusters share common faces.

Steinberg, Simon; Zimmermann, Sina; Brühmann, Matthias; Meyer, Eva; Rustige, Christian; Wolberg, Marike; Daub, Kathrin; Bell, Thomas; Meyer, Gerd

2014-11-01

432

The preparation of transition metal carbides and phosphides from metallic fluxes  

SciTech Connect

Metallic fluxes can be used for the synthesis of binary and ternary carbides, phosphides, and related materials to obtain well crystallized products or when the direct reaction of the elemental components is too slow. Among the requirements for a flux is a moderate affinity (neither too low nor too high) of the flux for all components and the possibility to dissolve the flux without attacking the desired compounds. Lithium is well suited for the growth of carbides, while tin is optimal to synthesize many transition metal phosphides. Recent examples of compounds synthesized via a metallic flux include Yb{sub 2}Cr{sub 2}C{sub 3}, Dy{sub 10.1}Mn{sub 12.9}C{sub 18}, Ln{sub 4}Ni{sub 2}C{sub 5} (Ln = Er, Tm, Yb, Lu), YbCoC, YbAl{sub 3}C{sub 3}, La{sub 2}Fe{sub 25}P{sub 12}, ThFe{sub 4}P{sub 2}, Th{sub 5}Fe{sub 19}P{sub 19}, Ln{sub 6}Co{sub 30}P{sub 19} (Ln = Er-Lu), VFe{sub 2}P{sub 12}, TNi{sub 4}P{sub 12} (T = V, Nb, W), CrMnP{sub 8}, MoNiP{sub 8}, and WNiP{sub 8}. The structural chemistry of these compounds will briefly be discussed.

Jeitschko, W.; Albering, J.H.; Dewalski, M.V.; Jakubowski-Ripke, U.; Kahnert, G.E.; Musanke, U.E.; Poettgen, R.; Wallinda, J.; Zimmer, B.I. [Unversitaet Munster (Germany)

1993-12-31

433

Metal-insulator transitions in IZO, IGZO, and ITZO films  

NASA Astrophysics Data System (ADS)

In this study, we measured the low-temperature resistivity of amorphous two- and three-dimensional (2D and 3D) indium-zinc oxide, indium-gallium-zinc oxide, and indium-tin-zinc oxide films with a wide range of carrier densities. To determine their critical characteristics at the metal-insulator transition (MIT), we used the Ioffe-Regel criterion. We found that the MIT occurs in a narrow range between k F ? = 0.13 and k F ? = 0.25, where k F and ? are the Fermi wave number and electron mean free path, respectively. For films in the insulating region, we analyzed ? ( T ) using a procedure proposed by Zabrodskii and Zinov'eva. This analysis confirmed the occurrence of Mott and Efros-Shklovskii (ES) variable-range hopping. The materials studied show crossover behavior from exp(TMott/T)1/4 or exp(TMott/T)1/3 for Mott hopping conduction to exp(TES/T)1/2 for ES hopping conduction with decreasing temperature. For both 2D and 3D materials, we found that the relationship between TMott and TES satisfies TES ? TMott2/3.

Makise, Kazumasa; Hidaka, Kazuya; Ezaki, Syohei; Asano, Takayuki; Shinozaki, Bunju; Tomai, Shigekazu; Yano, Koki; Nakamura, Hiroaki

2014-10-01

434

Metal-insulator transitions in IZO, IGZO, and ITZO films  

SciTech Connect

In this study, we measured the low-temperature resistivity of amorphous two- and three-dimensional (2D and 3D) indium-zinc oxide, indium-gallium-zinc oxide, and indium-tin-zinc oxide films with a wide range of carrier densities. To determine their critical characteristics at the metal-insulator transition (MIT), we used the Ioffe–Regel criterion. We found that the MIT occurs in a narrow range between k{sub F}??=?0.13 and k{sub F}??=?0.25, where k{sub F} and ? are the Fermi wave number and electron mean free path, respectively. For films in the insulating region, we analyzed ?(T) using a procedure proposed by Zabrodskii and Zinov'eva. This analysis confirmed the occurrence of Mott and Efros–Shklovskii (ES) variable-range hopping. The materials studied show crossover behavior from exp(T{sub Mott}/T){sup 1/4} or exp(T{sub Mott}/T){sup 1/3} for Mott hopping conduction to exp(T{sub ES}/T){sup 1/2} for ES hopping conduction with decreasing temperature. For both 2D and 3D materials, we found that the relationship between T{sub Mott} and T{sub ES} satisfies T{sub ES}???T{sub Mott}{sup 2/3}.

Makise, Kazumasa, E-mail: makise@nict.go.jp [National Institute of Information and Communications Technology, Kobe 651-2492 (Japan); Hidaka, Kazuya; Ezaki, Syohei; Asano, Takayuki; Shinozaki, Bunju [Department of Physics, Kyushu University, Fukuoka 810-8560 (Japan); Tomai, Shigekazu; Yano, Koki; Nakamura, Hiroaki [Central Research Laboratories, Idemitsu Kosan Co. Ltd, Chiba 299-0293 (Japan)

2014-10-21

435

Chemical contrast in STM imaging of transition metal aluminides  

NASA Astrophysics Data System (ADS)

The present manuscript reviews recent scanning tunnelling microscopy (STM) studies of transition metal (TM) aluminide surfaces. It provides a general perspective on the contrast between Al atoms and TM atoms in STM imaging. A general trend is the much stronger bias dependence of TM atoms, or TM-rich regions of the surface. This dependence can be attenuated by the local chemical arrangements and environments. Al atoms can show a stronger bias dependence when their chemical environment, such as their immediate subsurface, is populated with TM. All this is well explained in light of combined results of STM and both theoretical and experimental electronic and crystallographic structure determinations. Since STM probes the Fermi surface, the electronic structure in the vicinity of the Fermi level (EF) is essential for understanding contrast and bias dependence. Hence, partial density of states provides information about the TM d band position and width, s-p-d hybridization or interactions, or charge transfer between constituent elements. In addition, recent developments in STM image simulations are very interesting for elucidating chemical contrast at Al-TM alloy surfaces, and allow direct atomic identification, when the surface does not show too much disorder. Overall, we show that chemically-specific imaging is often possible at these surfaces.

Duguet, T.; Thiel, P. A.

2012-05-01

436

Destabilization effect of transition metal fluorides on sodium borohydride.  

PubMed

The effect of transition metal fluorides on the decomposition of NaBH4 has been investigated for NaBH4 ball milled with TiF3, MnF3 or FeF3. The compounds were examined by thermal programmed desorption with residual gas analysis, thermo gravimetric analysis and volumetric measurements using a Sieverts-type apparatus. The phase formation process during thermal decomposition was studied by in situ synchrotron radiation powder X-ray diffraction on the as-milled powders. NaBF4 was among the products in all mechano-chemical reactions. (11)B-NMR spectra analysis gave NaBF4?:?NaBH4 ratios of 1?:?150 for Na-Ti, 1?:?40 for Na-Mn, and 1?:?10 for Na-Fe. Pure NaBH4 possessed a hydrogen release onset temperature of 430 °C. The hydrogen release in the NaBH4-MnF3 system began as low as 130 °C. FeF3 decreased the onset temperature to 161 °C and TiF3 to 200 °C. TiF3 reacted completely with NaBH4 below 320 °C. All the examined systems have negligible emissions of diborane species. H-sorption studies performed at selected temperatures above 300 °C exhibited relatively fast desorption kinetics. Partial hydrogen re-absorption was observed for the Na-Mn and Na-Fe samples. PMID:25140831

Kalantzopoulos, Georgios N; Guzik, Matylda N; Deledda, Stefano; Heyn, Richard H; Muller, Jiri; Hauback, Bjørn C

2014-10-14

437

Defect-induced semiconductor to metal transition in graphene monoxide.  

PubMed

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. PMID:24886723

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

2014-07-14

438

APCVD Transition Metal Oxides – Functional Layers in "Smart windows"  

NASA Astrophysics Data System (ADS)

Transition metal oxides (TMO) exhibit electrochromic effect. Under a small voltage they change their optical transmittance from transparent to collored (absorbing) state. The individual material can manifest its electrochromic properties only when it is part of electrochromic (EC) multilayer system. Smart window is controlling the energy of solar flux entering the building or car and makes the interiors comfortable and energy utilization more effective. Recently the efforts of material researchers in this field are directed to price decreasing. APCVD technology is considered as promissing as this process permits flowthrough large-scale production process. The paper presents results on device optimization based on WO3-MoO3 working electrode. Extensive research reveals that WO3-MoO3 structure combines positive features of single oxides: excellent electrochromic performance of WO3 and better kinetic properties of MoO3 deposition. The achieved color efficiency of APCVD WO3-MoO3 films is 200cm2/C and optical modulation of 65-70% are practically favorable electrochromic characteristics. To respond to low cost requirement, the expensive hexacarbonyl can be replaced with acetylacetonate. We have started with this precursor to fabricate mixed WxV1-xO3 films. The films possess excellent surface coverage and high growth-rate. CVD deposition of VO2, a promissing thermochromic thin film material is also presented.

Gesheva, K. A.; Ivanova, T. M.; Bodurov, G. K.

2014-11-01

439

Dislocations and Plasticity in bcc Transition Metals at High Pressure  

SciTech Connect

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

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

2009-01-23

440

Valency configuration of transition metal impurities in ZnO  

SciTech Connect

We use the self-interaction corrected local spin-density approximation to investigate the ground state valency configuration of transition metal (TM=Mn, Co) impurities in n- and p-type ZnO. We find that in pure Zn{sub 1-x}TM{sub x}O, the localized TM{sup 2+} configuration is energetically favored over the itinerant d-electron configuration of the local spin density (LSD) picture. Our calculations indicate furthermore that the (+/0) donor level is situated in the ZnO gap. Consequently, for n-type conditions, with the Fermi energy {epsilon}F close to the conduction band minimum, TM remains in the 2+ charge state, while for p-type conditions, with {epsilon}F close to the valence band maximum, the 3+ charge state is energetically preferred. In the latter scenario, modeled here by co-doping with N, the additional delocalized d-electron charge transfers into the entire states at the top of the valence band, and hole carriers will only exist, if the N concentration exceeds the TM impurity concentration.

Petit, Leon [ORNL; Schulthess, Thomas C [ORNL; Svane, Axel [University of Aarhus, Denmark; Temmerman, Walter M [Daresbury Laboratory, UK; Szotek, Zdzislawa [Daresbury Laboratory, UK; Janotti, Anderson [University of California, Santa Barbara

2006-01-01

441

Transition-metal-based perovskite oxides for enhanced thermopower  

NASA Astrophysics Data System (ADS)

Due to the enhancement of thermopower by spin and orbital degrees of freedom, transition-metal-based perovskite oxides are good candidates for stable and nontoxic materials with a large thermoelectric figure of merit ZT. We have investigated the most promising Mn-, Co- and Ti-based perovskite oxides. Electron doping of SrMnO3 materials on either Mn or Sr sites induces a rapid decrease in both electrical resistivity and thermopower with the doping level due to the introduction of itinerant charge carriers. The thermopower of electron-doped SrTiO3 materials satisfy the basic Heikes description, however, no additional enhancement is observed. The hole-doped RCoO3 perovskites exhibit limited solubility of alkaline earth's for small rare earth ion sizes. The dependence of thermopower on charge doping and temperature appears to follow the extended Heikes formulation only at low doping and below 300 K, which indicates that Co^3+ and Co^4+ exist in several spin states beyond that range. Among all investigated compounds the largest ZT˜0.3 values were observed for 3-8% Nb-substituted SrTiO3 materials at about 700 K. Supported by the U.S. DOE-BES DE-AC02-06CH11357.

Kolesnik, Stanislaw; Dabrowski, Bogdan; Wojciechowski, Krzysztof; Swierczek, Konrad

2012-02-01

442

Oxide Wizard: an EELS application to characterize the white lines of transition metal edges.  

PubMed

Physicochemical properties of transition metal oxides are directly determined by the oxidation state of the metallic cations. To address the increasing need to accurately evaluate the oxidation states of transition metal oxide systems at the nanoscale, here we present "Oxide Wizard." This script for Digital Micrograph characterizes the energy-loss near-edge structure and the position of the transition metal edges in the electron energy-loss spectrum. These characteristics of the edges can be linked to the oxidation states of transition metals with high spatial resolution. The power of the script is demonstrated by mapping manganese oxidation states in Fe3O4/Mn3O4 core/shell nanoparticles with sub-nanometer resolution in real space. PMID:24750576

Yedra, Lluís; Xuriguera, Elena; Estrader, Marta; López-Ortega, Alberto; Baró, Maria D; Nogués, Josep; Roldan, Manuel; Varela, Maria; Estradé, Sònia; Peiró, Francesca

2014-06-01

443

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

PubMed Central

Summary In the last few years, transition metal-mediated reactions have joined the toolbox of chemists working in the field of fluorination for Life-Science oriented research. The successful execution of transition metal-catalyzed carbon–fluorine bond formation has become a landmark achievement in fluorine chemistry. This rapidly growing research field has been the subject of some excellent reviews. Our approach focuses exclusively on transition metal-catalyzed reactions that allow the introduction of –CFH2, –CF2H, –CnF2 n +1 and –SCF3 groups onto sp² carbon atoms. Transformations are discussed according to the reaction-type and the metal employed. The review will not extend to conventional non-transition metal methods to these fluorinated groups. PMID:24367416

Landelle, Grégory; Panossian, Armen; Pazenok, Sergiy; Vors, Jean-Pierre

2013-01-01

444

Concomitant Ordering in First Row Transition Metal Fluorides.  

NASA Astrophysics Data System (ADS)

Type of compounds investigated. First row transition metal fluorides with a general formula, A_ {x}M^{2+}_{x}M ^{'3+}_{1-x}F _3, where A = alkali metal ion, M,M ^' = First row transition metal ions, and x = 0-1 are reported to form, ReO_3 , perovskite, GdFeO_3, tetragonal tungsten bronze (TTB), hexagonal tungsten bronze (HTB), and, modified pyrochlore type structures. Compounds of the type LiM^{II}M^{III }F_{6} have been reported to form rutile and trirutile type structures. These compounds display ionic, electronic, and magnetic ordering. Formation of TTB structure and linear trimers. The TTB structure demonstrates ordering between M^ {2+} and M^{3+} ions. Consequently, a variety of TTB fluorides have been tailored that display anitferro-, ferri- or ferro -magnetism. By substituting a diamagnetic ion for either M^{2+} or M^ {3+}, the diluted paramagnetic ions form linear trimers. These linear trimers are useful for the study of 180^circ M-F-M interactions. Structural and magnetic properties of several quaternary TTB fluorides are reported. The Series K_{rm x}CrF _3. The series K_{rm x}CrF_3 (x ~ 0.4-0.6) was reported to form the hexagonal BaTa_2O_6 type structure. It was believed that the TTB structure did not form due to the Jahn-Teller ion Cr^ {2+}. The unit cell did not show any evidence of distortion. Using superior synthesis and characterization techniques, we report formation of three phase in the series K_{rm x}CrF _3 (x ~ 0.42-0.58). In the lower range the structure is a hexagonal BaTa _2O_6 type. In the middle composition range the structure is an orthorhombic distortion of the hexagonal unit cell. At higher values of x, formation of a TTB structure is observed. As expected, the tetragonal unit cell is distorted to orthorhombic due to cooperative Jahn-Teller ordering. Magnetic data support these observations. Derivation of symmetry trees. It is observed that the symmetry of a crystal is lowered as concomitant ordering sets in. This observation in conjunction with the Symmetry Principle has been used to derive Symmetry Trees (or, symmetry lowering diagrams) for the systems mentioned above. These Symmetry Trees experimentally confirm Landau and Lifshitz's contention that ordering reduces symmetry. They also provide experimental evidence for the Special Symmetry Evolution Principle, (the degree of symmetry of the state of an isolated system cannot decrease during evolution but either remains constant or increases). In several cases, where experimental determination of a unique space group is not feasible, the symmetry tree approach is implemented to determine the space group.

Shah, Ajay Vinodbhai

445

Oxidation energies of transition metal oxides within the GGA+U framework Lei Wang, Thomas Maxisch, and Gerbrand Ceder*  

E-print Network

Oxidation energies of transition metal oxides within the GGA+U framework Lei Wang, Thomas Maxisch; published 4 May 2006 The energy of a large number of oxidation reactions of 3d transition metal oxides error makes it possible to address the correlation effects in 3d transition metal oxides with the GGA

Ceder, Gerbrand

446

2180 J. Am. Chem. SOC.1986, 108, 2180-2191 Bonding in Transition-Metal-Methylene Complexes. 2.  

E-print Network

2180 J. Am. Chem. SOC.1986, 108, 2180-2191 Bonding in Transition-Metal-Methylene Complexes. 2. (Ru: The electronicstructure for a representativelate-transition-metal-methylene complex, Ru=H2+, has been studied by ab initio concludethat for highly unsaturated, late-transition-metalsystems, metal-carbene bonding may be competitivewith

Goddard III, William A.

447

Spectroscopic analysis of the open 3d subshell transition metal aluminides: AIV, AICr, and AlCo  

E-print Network

Spectroscopic analysis of the open 3d subshell transition metal aluminides: AIV, AICr, and Al The present study of AlV, AlCr, and AlCo is a continu- ation of the study of the 3d transition metal element, Al, and the atoms of the 3d transition metal series. Specific chemical bonding considerations

Morse, Michael D.

448

Transition-metal interactions in aluminum-rich intermetallics Ibrahim Al-Lehyania;b and Mike Widoma  

E-print Network

Transition-metal interactions in aluminum-rich intermetallics Ibrahim Al-Lehyania;b and Mike Widoma GPT to transition-metal TM aluminides produces pair and many-body interactions that allow e cient limitation is a transition- metal over-binding that creates an unrealistic TM-TM attraction at short

Widom, Michael

449

J. Am. Chem. SOC.1994,116, 8733-8740 8733 Energetics of Third-Row Transition Metal Methylidene Ions  

E-print Network

J. Am. Chem. SOC.1994,116, 8733-8740 8733 Energetics of Third-Row Transition Metal Methylidene Ions both experiment' and theory2that third-row (5d) transition metals form much stronger bonds than do first- row (3d) and second-row (4d) transition metals. Indeed, recent gas-phase studies of the reactions

Goddard III, William A.

450

Strain and electric field induced electronic properties of two-dimensional hybrid bilayers of transition-metal dichalcogenides  

E-print Network

of transition-metal dichalcogenides Munish Sharma, Ashok Kumar, P. K. Ahluwalia, and Ravindra Pandey Citation of semiconducting transition-metal dichalcogenide monolayers: An ab-initio study J. Appl. Phys. 115, 243701 (2014); 10.1063/1.4883995 Electronic and thermoelectric properties of few-layer transition metal

Pandey, Ravi

451

Doping-induced metal-insulator transition in aluminum-doped 4H silicon P. Achatz,1,2,a  

E-print Network

Doping-induced metal-insulator transition in aluminum-doped 4H silicon carbide P. Achatz,1,2,a J an experimental determination of the doping-induced metal-insulator transition in aluminum-doped 4H silicon concentration lying between 6.4 and 8.7 1020 cm-3 for the metal-insulator transition in these epilayers grown

Paris-Sud XI, Université de

452

Comprehensive study of the metal-insulator transition in pulsed laser deposited epitaxial VO2 thin films  

E-print Network

Comprehensive study of the metal-insulator transition in pulsed laser deposited epitaxial VO2 thin properties of high-quality VO2 thin films across its metal-insulator phase transition. Detailed x along three equivalent crystallographic directions. Across the metal-insulator transition

Wu, Junqiao

453

Asymmetric Metal-Insulator Transition in Disordered Ferromagnetic Films R. Misra, A. F. Hebard,* and K. A. Muttalib  

E-print Network

Asymmetric Metal-Insulator Transition in Disordered Ferromagnetic Films R. Misra, A. F. Hebard experimental data and a theoretical interpretation of the conductance near the metal- insulator transition The metal-insulator (M-I) transition in disordered con- ductors [1] has been one of the most extensively

Muttalib, Khandker

454

Variation of the density of states in amorphous GdSi at the metal-insulator transition L. Bokacheva,1  

E-print Network

Variation of the density of states in amorphous GdSi at the metal-insulator transition L. Bokacheva, magnetically doped material -GdxSi1-x, which can be driven through the metal-insulator transition the transition and slightly slower on the metallic side. The tunneling conductance, proportional to the density

Hellman, Frances

455

Theory of elastic phase transitions in metals at high pressures. Application to vanadium  

SciTech Connect

Structural transformations in elementary metals under high pressures are considered using the Landau theory of phase transitions, in which the finite strain tensor components play the role of the order parameter. As an example, the phase transition in vanadium observed at a pressure of 69 GPa is analyzed. It is shown that it is a first-order elastic phase transition, which is close to a second-order transition.

Krasil'nikov, O. M., E-mail: omkras@mail.ru; Vekilov, Yu. Kh.; Isaev, E. I.; Bondarenko, N. G. [National Research Technological University MISiS (Russian Federation)

2011-02-15

456

Dimetallocene Carbonyls of the Third-Row Transition Metals: The Quest for High-Order Metal-Metal Multiple Bonds  

NASA Astrophysics Data System (ADS)

Theoretical studies of the third-row transition-metal derivatives Cp2M2(CO) (Cp = ?5-C5H5; M = Os, Re, W, Ta) indicate that the lowest-energy structures have lower spin states and similar or higher metal-metal bond multiplicities than the corresponding first-row transtion-metal derivatives. Therefore, Cp2Os2(CO) is predicted to be a singlet with an Os-Os formal quadruple bond, whereas Cp2Fe2(CO) is a triplet. Similarly, Cp2Re2(CO) is predicted to be a singlet with a very short rhenium-rhenium distance, which is consistent with the formal quintuple bond required to give both rhenium-rhenium atoms the favored 18-electron configuration. This contrasts with the manganese analogue Cp2Mn2(CO) for which the lowest-energy structure is a septet with a formal Mn-Mn single bond. The tungsten derivative Cp2W2(CO) is predicted to be triplet with a four-electron donor bridging carbonyl group. This contrasts with Cp2Cr2(CO) predicted to be a septet (S = 3) with a two-electron donor carbonyl group. For Cp2Ta2(CO), the lowest-energy structure is predicted to be a triplet with a formal Ta?Ta triple bond and a four-electron donor carbonyl group. However, Cp2V2(CO) is predicted to be a quintet with a formal V?V double bond. In addition to these Cp2M2(CO) structures with one Cp ring bonded to each metal atom, higher-energy Cp2M-MCO structures are found with both Cp rings bonded to the same metal atom. The lowest-energy Cp2M-MCO structures are triplets (M = Os, W) or quintets (M = Re) with agostic hydrogen atoms for M = Os and Re. In these structures, the spin density is concentrated on the metal atom of the MCO group. These results suggest that lower spin states clearly become more viable for highly unsaturated metal complexes upon descending the periodic table.

Xu, Bing; Li, Qian-Shu; Xie, Yaoming; King, R. Bruce; Schaefer, Henry F.

2009-07-01

457

Weakly nonlinear modeling of the early stages of bypass transition  

Microsoft Academic Search

1. Motivation and objectives Under ideal conditions, boundary layer transition occurs in a six-stage process described, for example, by Stuart (1965). The rst stage is that of linear instability, and its onset is predicted accurately by two-dimensional normal mode solutions of the Orr-Sommerfeld equation. In the Blasius case, the critical Reynolds number based on displacement thickness is approximately Re =

S. A. Maslowe

458

Bond-strengthening ? backdonation in a transition-metal ?-diborene complex  

NASA Astrophysics Data System (ADS)

Transition-metal catalysis is founded on the principle that electron donation from a metal to a ligand is accepted by an antibonding orbital of the ligand, thereby weakening one of the bonds in the ligand. Without this, the initial step of bond activation in many catalytic processes would simply not occur. This concept is enshrined in the well-accepted Dewar-Chatt-Duncanson model of transition-metal bonding. We present herein experimental and computational evidence for the first true violation of the Dewar-Chatt-Duncanson bonding model, found in a ?-diborene complex in which an electron-rich group 10 metal donates electrons into an empty bonding ? orbital on the ligand, and thereby strengthens the bond. The complex is also the first transition-metal complex to contain a bound diborene, a species not isolated before, either in its free form or bound to a metal.

Braunschweig, Holger; Damme, Alexander; Dewhurst, Rian D.; Vargas, Alfredo

2013-02-01

459

Adjustable metal-semiconductor transition of FeS thin films by thermal annealing  

SciTech Connect

FeS polycrystalline thin films were prepared on float glass at 500 deg. C by radio-frequency reactive sputtering. The influence of vacuum annealing on the metal-semiconductor transition of FeS films was investigated. It has been found that with the increase of the annealing temperature from 360 to 600 deg. C, the metal-semiconductor transition temperature of FeS films first decreases and then increases, associated with first a reduction and then an enhancement of hysteresis width. The thermal stress is considered to give rise to the abnormal change of the metal-semiconductor transition of the FeS film during annealing.

Fu Ganhua; Polity, Angelika; Volbers, Niklas; Meyer, Bruno K.; Mogwitz, Boris; Janek, Juergen [I. Physikalisches Institut, Justus-Liebig-Universitaet Giessen, Heinrich-Buff-Ring 16, D-35392 Giessen (Germany); Physikalisch-Chemisches Institut, Justus-Liebig-Universitaet Giessen, Heinrich-Buff-Ring 58, D-35392 Giessen (Germany)

2006-12-25

460

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

SciTech Connect

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.

Jones, G

2011-08-18

461

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

DOEpatents

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

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

2003-09-02

462

Phase transition into the metallic state in hypothetical (without molecules) dense atomic hydrogen  

SciTech Connect

A simple physical model of the metal-dielectric (vapor-liquid) phase transition in hypothetical (without molecules) atomic hydrogen is proposed. The reason for such a transition is the quantum collective cohesive energy occurring due to quantum electron-electron exchange similar to the cohesive energy in the liquid-metal phase of alkali metals. It is found that the critical parameters of the transition are P{sub c} ? 41000 atm, ?{sub c} ? 0.1 g/cm{sup 3}, and T{sub c} ? 9750 K.

Khomkin, A. L., E-mail: alhomkin@mail.ru; Shumikhin, A. S. [Russian Academy of Sciences, Joint Institute for High Temperatures (Russian Federation)] [Russian Academy of Sciences, Joint Institute for High Temperatures (Russian Federation)

2013-10-15

463

Quantum phase transition between orbital-selective Mott states in Hund's metals  

NASA Astrophysics Data System (ADS)

We report a quantum phase transition between orbital-selective Mott states, with different localized orbitals, in a Hund's metals model. Using the density matrix renormalization group, the phase diagram is constructed varying the electronic density and Hubbard U , at robust Hund's coupling. We demonstrate that this transition is preempted by charge fluctuations and the emergence of free spinless fermions, as opposed to the magnetically driven Mott transition. The Luttinger correlation exponent is shown to have a universal value in the strong-coupling phase, whereas it is interaction dependent at intermediate couplings. At weak coupling we find a second transition from a normal metal to the intermediate-coupling phase.

Rincón, Julián; Moreo, Adriana; Alvarez, Gonzalo; Dagotto, Elbio

2014-12-01

464

Increasing Choice or Inequality? Pathways through Early Education in Andhra Pradesh, India. Working Papers in Early Childhood Development, No. 58. Studies in Early Childhood Transitions  

ERIC Educational Resources Information Center

This working paper is part of the Studies in Early Transitions series emerging from "Young Lives", a 15-year longitudinal study of childhood poverty in Ethiopia, India, Peru and Vietnam. It explores recent trends for children growing up in Andhra Pradesh, one of India's most populous states, based on Young Lives survey data collected for a sample…

Streuli, Natalia; Vennam, Uma; Woodhead, Martin

2011-01-01

465

Equity and Quality? Challenges for Early Childhood and Primary Education in Ethiopia, India and Peru. Working Papers in Early Childhood Development, No. 55. Studies in Early Childhood Transitions  

ERIC Educational Resources Information Center

Part of the "Studies in Early Transitions" series, this Working Paper draws on interviews and observations carried out as part of "Young Lives", a 15-year longitudinal study of childhood poverty in Ethiopia, India, Peru and Vietnam based at the University of Oxford's Department of International Development. This paper focuses on the challenges of…

Woodhead, Martin; Ames, Patricia; Vennam, Uma; Abebe, Workneh; Streuli, Natalia

2009-01-01

466

Early Learning and Early Identification Follow-Up Study: Transition from the Early to the Later Childhood Grades, 1990-93.  

ERIC Educational Resources Information Center

As follow-up to an in-depth study of the District of Columbia's early learning programs and their impact, this study provided data on the transition of previously studied children from primary education to upper elementary grades. Academic progress of the original group of pre-kindergarten and Head Start children was studied during years 5 and 6…

Marcon, Rebecca A.

467

Normal spectral emittance of crystalline transition metal carbides  

NASA Astrophysics Data System (ADS)

We report on experiments to determine the normal spectral emittance of crystalline forms of five transition metal carbides: hafnium carbide, niobium carbide, tantalum carbide, titanium carbide, and zirconium carbide. These emittance measurements were taken at the commonly used pyrometer wavelength of 0.65 ?m. The specimens were cylindrical with 0.10-cm-diameter blackbody holes drilled axially to a depth of 1.0 cm. The crystalline specimens were prepared from sintered stock by floating zone arc refinement and then centerless ground to the desired diameter. Measurements were made in vacuum in the temperature range 1200

Mackie, William A.; Carleson, Pete; Filion, Janice; Hinrichs, C. H.

1991-05-01

468

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

PubMed

We investigate the physicomechanical properties of polymeric heterogeneous catalysts of transition-metal oxides, specifically, the specific surface area, elongation at break, breaking strength, specific electrical resistance, and volume resistivity. Digital microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and energy-dispersive analysis are used to study the surfaces of the catalysts. The experimental results show that polymeric heterogeneous catalysts of transition-metal oxides exhibit high stability and can maintain their catalytic activity under extreme reaction conditions for long-term use. The oxidation mechanism of sulfur-containing compounds in the presence of polymeric heterogeneous catalysts of transition-metal oxides is confirmed. Microstructural characterization of the catalysts is performed by using X-ray computed tomography. The activity of various catalysts in the oxidation of sulfur-containing compounds is determined. We demonstrate the potential application of polymeric heterogeneous catalysts of transition-metal oxides in industrial wastewater treatment. PMID:24243767

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

2013-12-16

469

Probing the electron states and metal-insulator transition mechanisms in molybdenum disulphide vertical heterostructures  

NASA Astrophysics Data System (ADS)

The metal-insulator transition is one of the remarkable electrical properties of atomically thin molybdenum disulphide. Although the theory of electron–electron interactions has been used in modelling the metal-insulator transition in molybdenum disulphide, the underlying mechanism and detailed transition process still remain largely unexplored. Here we demonstrate that the vertical metal-insulator-semiconductor heterostructures built from atomically thin molybdenum disulphide are ideal capacitor structures for probing the electron states. The vertical configuration offers the added advantage of eliminating the influence of large impedance at the band tails and allows the observation of fully excited electron states near the surface of molybdenum disulphide over a wide excitation frequency and temperature range. By combining capacitance and transport measurements, we have observed a percolation-type metal-insulator transition, driven by density inhomogeneities of electron states, in monolayer and multilayer molybdenum disulphide. In addition, the valence band of thin molybdenum disulphide layers and their intrinsic properties are accessed.

Chen, Xiaolong; Wu, Zefei; Xu, Shuigang; Wang, Lin; Huang, Rui; Han, Yu; Ye, Weiguang; Xiong, Wei; Han, Tianyi; Long, Gen; Wang, Yang; He, Yuheng; Cai, Yuan; Sheng, Ping; Wang, Ning

2015-01-01

470

Theoretical studies of transition metal surfaces as electrocatalysts for oxygen electroreduction  

E-print Network

are actively researched. Platinum alloys with different transition metals (for example: Ni, Co and Fe) have shown improved activity over pure Pt. The design of a Pt-free catalysts is also highly desirable, and different alternatives including metalloporphyrins...

Lamas, Eduardo J.

2007-09-17

471

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

SciTech Connect

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

Carlsson, A.E.

1992-01-01

472

Theoretical research program to study transition metal trimers and embedded clusters  

NASA Technical Reports Server (NTRS)

The results of ab-initio calculations are reported for (1) small transition metal clusters and (2) potential energy surfaces for chemical reactions important in hydrogen combustion and high temperature air chemistry.

Walch, Stephen P.

1987-01-01

473

Selective exchange of divalent transition metal ions in cryptomelane-type manganic acid with tunnel structure  

SciTech Connect

The ion-exchange selectivity of divalent transition metal ions on cryptomelane-type manganic acid (CMA) with tunnel structure has been studied using the distribution coefficients ([ital K][sub [ital d

Tsuji, M. (Department of Chemistry, Faculty of Science, Tokyo Institute of Technology, 2-12-1, O-okayama, Meguro-ku, Tokyo 152 (Japan)); Komarneni, S. (Materials Research Laboratory and Department of Agronomy, The Pennsylvania State University, University Park, Pennsylvania 16802-4801 (United States))

1993-03-01

474

An Evaluation of the Rigid Band Model and the Virtual Crystal Approximation in the Transition Metals  

NASA Astrophysics Data System (ADS)

The Schrodinger equation was solved using the Augmented Plane Wave (APW) Method for transition metals in both the body centered cubic (bcc) and face centered cubic (fcc) structures. This method accurately predicts the equilibrium lattice parameter and the ground state of all transition metals. The Rigid Band Model tests based on the group eight and group nine transition metals was applied to predict the density of states (DOS) at the Fermi level for the rest of the transition metals. This test agreed with direct calculations quite well with only a few exceptions in the hexagonal structures. The APW method was also applied using the virtual crystal approximation to obtain the DOS of binary alloys. The results will be compared with direct calculations of ordered and disordered structures.

Papaconstantopoulos, Dimitrios; Iacoletti, Fred; Koufos, Alex

2008-03-01

475

Zwitterionic late transition metal alkene polymerisation catalysts containing aminofulvene-aldiminate (AFA) ligands   

E-print Network

Over recent years significant progress has been made in the design and development of late transition metal cationic catalysts for olefin polymerisation. Never-the-less, the activation of catalyst precursors and generation ...

Rahman, Mohammed Mahmudur

2010-01-01

476

Synthesis and study of novel zwitterionic transition metal complexes and their application as olefin polymerisation catalysts   

E-print Network

The synthesis, characterization and coordination chemistry of novel zwitterionic late transition metal complexes has been carried out, and an investigation of their ability to act as olefin polymerisation catalysts has ...

Melchionna, Michele

2007-06-25

477

Electron Spin Resonance of Tetrahedral Transition Metal Oxyanions (MO4n-) in Solids.  

ERIC Educational Resources Information Center

Outlines general principles in observing sharp electron spin resonance (ESR) lines in the solid state by incorporating the transition metal ion of interest into an isostructural diamagnetic host material in small concentration. Examples of some recent studies are described. (CS)

Greenblatt, M.

1980-01-01

478

First-principles density functional theory study of sulfur oxide chemistry on transition metal surfaces  

E-print Network

In this thesis, the chemistry of sulfur oxides on transition metals is studied extensively via first-principles density functional theory (DFT) computations, focusing on the chemical reactivity and selectivity in sulfur ...

Lin, Xi, 1973-

2003-01-01

479

Transition metal gettering studies and simulation for the optimization of silicon photovoltaic device processing  

E-print Network

We use what is known about transition metal (TM) defect thermodynamic driving forces and kinetic responses to make predictive simulation of gettering during solar cell fabrication possible. We have developed a simulator ...

Smith, Aimée Louise, 1971-

2002-01-01

480

Role of thermal heating on the voltage induced insulator-metal transition in VO2.  

PubMed

We show that the main mechanism for the dc voltage or dc current induced insulator-metal transition in vanadium dioxide VO(2) is due to local Joule heating and not a purely electronic effect. This "tour de force" experiment was accomplished by using the fluorescence spectra of rare-earth doped micron sized particles as local temperature sensors. As the insulator-metal transition is induced by a dc voltage or dc current, the local temperature reaches the transition temperature indicating that Joule heating plays a predominant role. This has critical implications for the understanding of the dc voltage or dc current induced insulator-metal transition and has a direct impact on applications which use dc voltage or dc current to externally drive the transition. PMID:23414038

Zimmers, A; Aigouy, L; Mortier, M; Sharoni, A; Wang, Siming; West, K G; Ramirez, J G; Schuller, Ivan K

2013-02-01

481

Controlled synthesis of transition metal/conducting polymer nanocomposites.  

PubMed

A novel displacement reaction has been observed to occur between conducting polymers (CP) and metal salts which can be used to fabricate nanostructured CP-metal composites in a one-pot manner. Vanadium pentoxide (V(2)O(5)) nanofiber is used during the synthesis as the reactive seeds to induce the nanofibril CP-metal network formation. The CP-metal nanocomposites exhibit excellent sensory properties for hydrogen peroxide (H(2)O(2)) detection, where both high sensitivity and a low detection limit can be obtained. The sensory performance of the CP-metal composite can be further enhanced by a facile microwave treatment. It is believed that the CP-metal nanofibril network can be converted to a carbon-metal network by a microwave-induced carbonization process and result in the sensory enhancement. PMID:22842608

Liu, Zhen; Liu, Yang; Zhang, Lin; Poyraz, Selcuk; Lu, Ning; Kim, Moon; Smith, James; Wang, Xiaolong; Yu, Yajiao; Zhang, Xinyu

2012-08-24

482

Preparation of transition metal nanoparticles and surfaces modified with (CO)polymers synthesized by RAFT  

SciTech Connect

A new, facile, general one-phase method of generating thio-functionalized transition metal nanoparticles and surfaces modified by (co)polymers synthesized by the RAFT method is described. The method includes the stops of forming a (co)polymer in aqueous solution using the RAFT methodology, forming a colloidal transition metal precursor solution from an appropriate transition metal; adding the metal precursor solution or surface to the (co)polymer solution, adding a reducing agent into the solution to reduce the metal colloid in situ to produce the stabilized nanoparticles or surface, and isolating the stabilized nanoparticles or surface in a manner such that aggregation is minimized. The functionalized surfaces generated using these methods can further undergo planar surface modifications, such as functionalization with a variety of different chemical groups, expanding their utility and application.

McCormick III, Charles L.; Lowe, Andrew B.; Sumerlin, Brent S.

2006-11-21

483

Preparation of transition metal nanoparticles and surfaces modified with (co)polymers synthesized by RAFT  

DOEpatents

A new, facile, general one-phase method of generating thiol-functionalized transition metal nanoparticles and surfaces modified by (co)polymers synthesized by the RAFT method is described. The method includes the steps of forming a (co)polymer in aqueous solution using the RAFT methodology, forming a colloidal transition metal precursor solution from an appropriate transition metal; adding the metal precursor solution or surface to the (co)polymer solution, adding a reducing agent into the solution to reduce the metal colloid in situ to produce the stabilized nanoparticles or surface, and isolating the stabilized nanoparticles or surface in a manner such that aggregation is minimized. The functionalized surfaces generated using these methods can further undergo planar surface modifications, such as functionalization with a variety of different chemical groups, expanding their utility and application.

McCormick, III, Charles L. (Hattiesburg, MS); Lowe, Andrew B. (Hattiesburg, MS); Sumerlin, Brent S. (Pittsburgh, PA)

2011-12-27

484

Preparation of transition metal nanoparticles and surfaces modified with (CO) polymers synthesized by RAFT  

DOEpatents

A new, facile, general one-phase method of generating thiol-functionalized transition metal nanoparticles and surface modified by (co)polymers synthesized by the RAFT method is described. The method includes the steps of forming a (co)polymer in aqueous solution using the RAFT methodology, forming a collidal transition metal precursor solution from an appropriate transition metal; adding the metal precursor solution or surface to the (co)polymer solution, adding a reducing agent into the solution to reduce the metal colloid in situ to produce the stabilized nanoparticles or surface, and isolating the stabilized nanoparticles or surface in a manner such that aggregation is minimized. The functionalized surfaces generated using these methods can further undergo planar surface modifications, such as fuctionalization with a variety of different chemical groups, expanding their utility and application.

McCormick, III, Charles L. (Hattiesburg, MS); Lowe, Andrew B. (Hattiesburg, MS); Sumerlin, Brent S. (Pittsburgh, PA)

2006-10-25

485

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

DOEpatents

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 ancillary 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 producer gas from coal gasification processes. 3 figs.

Lilga, M.A.; Hallen, R.T.

1990-08-28

486

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

DOEpatents

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 ancillary 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 product gas from coal gasification processes. 3 figures.

Lilga, M.A.; Hallen, R.T.

1991-10-15

487

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

DOEpatents

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 th