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Sample records for perovskite transition-metal oxides

  1. First-principles exploration of ferromagnetic and ferroelectric double-perovskite transition-metal oxides

    NASA Astrophysics Data System (ADS)

    Uratani, Y.; Shishidou, T.; Ishii, F.; Oguchi, T.

    2006-08-01

    Possible ferromagnetic and ferroelectric phases are explored for bismuth transition-metal oxides with double-perovskite structure A2BB?O6 on the basis of first-principles calculations within the local spin-density approximation (LSDA) and generalized gradient approximation (GGA). It is found that a lattice instability of the cubic to a non-centrosymmetric phase always happens in the all cases of lead and bismuth perovskite oxides with the 3d transition-metal ions at the B site. Placing bismuth ion at the A site in the double-perovskite structure, several sets of the 3d transition-metal ions are selected according to their total valence sum and the Goodenough-Kanamori rule for the superexchange coupling. Ferromagnetic solutions are actually obtained both within LSDA and GGA for Bi2CrFeO6, Bi2MnNiO6 and Bi2CrCuO6. For non-centrosymmetric monoclinic Bi2MnNiO6, the ferromagnetic and ferroelectric phase has the spin magnetic moment of 5?B and the electric polarization of 28 ?C/cm2.

  2. Correlation effects in (111) bilayers of perovskite transition-metal oxides

    SciTech Connect

    Okamoto, Satoshi; Zhu, Wenguang; Nomura, Yusuke; Arita, R.; Xiao, Di; Nagaosa, Naoto

    2014-01-01

    We investigate the correlation-induced Mott, magnetic, and topological phase transitions in artificial (111) bilayers of perovskite transition-metal oxides LaAuO3 and SrIrO3 for which the previous density-functional theory calculations predicted topological insulating states. Using the dynamical-mean-field theory with realistic band structures and Coulomb interactions, LaAuO3 bilayer is shown to be far away from a Mott insulating regime, and a topological-insulating state is robust. On the other hand, SrIrO3 bilayer is on the verge of an orbital-selective topological Mott transition and turns to a trivial insulator by an antiferromagnetic ordering. Oxide bilayers thus provide a novel class of topological materials for which the interplay between the spin-orbit coupling and electron-electron interactions is a fundamental ingredient.

  3. Doped Mott Insulators in (111) Bilayers of Perovskite Transition-Metal Oxides with a Strong Spin-Orbit Coupling

    SciTech Connect

    Okamoto, Satoshi

    2013-01-01

    The electronic properties of Mott insulators realized in (111) bilayers of perovskite transition-metal oxides are studied. The low-energy effective Hamiltonians for such Mott insulators are derived in the presence of a strong spin-orbit coupling. These models are characterized by the antiferromagnetic Heisenberg interaction and the anisotropic interaction whose form depends on the $d$ orbital occupancy. From exact diagonalization analyses on finite clusters, the ground state phase diagrams are derived, including a Kitaev spin liquid phase in a narrow parameter regime for $t_{2g}$ systems. Slave-boson mean-field analyses indicate the possibility of novel superconducting states induced by carrier doping into the Mott-insulating parent systems, suggesting the present model systems as unique playgrounds for studying correlation-induced novel phenomena. Possible experimental realizations are also discussed.

  4. Transition metal substituted SrTiO3 perovskite oxides as promising functional materials for oxygen sensor

    NASA Astrophysics Data System (ADS)

    Misra, Sunasira

    2012-07-01

    Modern industries employ several gases as process fluids. Leakage of these gases in the operating area could lead to undesirable consequences. Even in chemical industries, which use large quantities of inert gases in confined areas, accidental leakage of these process gases would result in the reduction of oxygen partial pressure in atmospheric air. For instance, large amounts of gaseous nitrogen and argon are used in pharmaceutical industries, gas filling/bottling plants, operating area of Fast Breeder reactors, etc. Fall of concentration of oxygen in air below 17% could lead to life risk (Asphyxiation) of the working personnel that has to be checked well in advance. Further, when the leaking gas is of explosive nature, its damage potential would be very high if its concentration level in air increases beyond its lower explosive limit. Surveillance of the ambient within these industries at the critical areas and also in the environment around them for oxygen therefore becomes highly essential. Sensitive and selective gas sensors made of advanced materials are required to meet this demand of monitoring environmental pollution. The perovskite class of oxides (ABO3) is chemically stable even at high temperatures and can tolerate large levels of dopants without phase transformations. The electronic properties of this parent functional material can be tailored by adding appropriate dopants that exhibit different valence states. Aliovalent transition metal substituted SrTiO3 perovskites are good mixed ionic and electronic conductors and potential candidates for sensing oxygen at percentage level exploiting their oxygen pressure dependent electrical conductivity. This paper presents the preparation, study of electrical conductivity and oxygen-sensing characteristics of iron and cobalt substituted SrTiO3.

  5. Semiconducting transition metal oxides.

    PubMed

    Lany, Stephan

    2015-07-22

    Open shell transition metal oxides are usually described as Mott or charge transfer insulators, which are often viewed as being disparate from semiconductors. Based on the premise that the presence of a correlated gap and semiconductivity are not mutually exclusive, this work reviews electronic structure calculations on the binary 3d oxides, so to distill trends and design principles for semiconducting transition metal oxides. This class of materials possesses the potential for discovery, design, and development of novel functional semiconducting compounds, e.g. for energy applications. In order to place the 3d orbitals and the sp bands into an integrated picture, band structure calculations should treat both contributions on the same footing and, at the same time, account fully for electron correlation in the 3d shell. Fundamentally, this is a rather daunting task for electronic structure calculations, but quasi-particle energy calculations in GW approximation offer a viable approach for band structure predictions in these materials. Compared to conventional semiconductors, the inherent multivalent nature of transition metal cations is more likely to cause undesirable localization of electron or hole carriers. Therefore, a quantitative prediction of the carrier self-trapping energy is essential for the assessing the semiconducting properties and to determine whether the transport mechanism is a band-like large-polaron conduction or a small-polaron hopping conduction. An overview is given for the binary 3d oxides on how the hybridization between the 3d crystal field symmetries with the O-p orbitals of the ligands affects the effective masses and the likelihood of electron and hole self-trapping, identifying those situations where small masses and band-like conduction are more likely to be expected. The review concludes with an illustration of the implications of the increased electronic complexity of transition metal cations on the defect physics and doping, using as an example the diversity of possible atomic and magnetic configurations of the O vacancy in TiO(2), and the high levels of hole doping in Co(2)ZnO(4) due to a self-doping mechanism that originates from the multivalence of Co. PMID:26126022

  6. Semiconducting transition metal oxides

    NASA Astrophysics Data System (ADS)

    Lany, Stephan

    2015-07-01

    Open shell transition metal oxides are usually described as Mott or charge transfer insulators, which are often viewed as being disparate from semiconductors. Based on the premise that the presence of a correlated gap and semiconductivity are not mutually exclusive, this work reviews electronic structure calculations on the binary 3d oxides, so to distill trends and design principles for semiconducting transition metal oxides. This class of materials possesses the potential for discovery, design, and development of novel functional semiconducting compounds, e.g. for energy applications. In order to place the 3d orbitals and the sp bands into an integrated picture, band structure calculations should treat both contributions on the same footing and, at the same time, account fully for electron correlation in the 3d shell. Fundamentally, this is a rather daunting task for electronic structure calculations, but quasi-particle energy calculations in GW approximation offer a viable approach for band structure predictions in these materials. Compared to conventional semiconductors, the inherent multivalent nature of transition metal cations is more likely to cause undesirable localization of electron or hole carriers. Therefore, a quantitative prediction of the carrier self-trapping energy is essential for the assessing the semiconducting properties and to determine whether the transport mechanism is a band-like large-polaron conduction or a small-polaron hopping conduction. An overview is given for the binary 3d oxides on how the hybridization between the 3d crystal field symmetries with the O-p orbitals of the ligands affects the effective masses and the likelihood of electron and hole self-trapping, identifying those situations where small masses and band-like conduction are more likely to be expected. The review concludes with an illustration of the implications of the increased electronic complexity of transition metal cations on the defect physics and doping, using as an example the diversity of possible atomic and magnetic configurations of the O vacancy in TiO2, and the high levels of hole doping in Co2ZnO4 due to a self-doping mechanism that originates from the multivalence of Co.

  7. Magnetochromism in Transition Metal Oxides

    NASA Astrophysics Data System (ADS)

    Musfeldt, Janice; Choi, Jongwoo; Haraldsen, Jason; Woodward, Jonathan; Wei, Xing; He, Jian; Mandrus, David; Landee, Chris; Turnbull, Mark; Suryanarayanan, Ramanathanan; Revcolevschi, Alex

    2004-03-01

    We discuss the discovery and mechanism of magnetic field-induced color changes in three different low-dimensional transition metal oxides: Li purple bronze, (CPA)_2CuBr_4, and Pr-substituted La_1.2Sr_1.8Mn_2O_7. In Li purple bronze, the field manipulates the density of states near E_F, altering O p to Mo d excitations. In the copper halide, the applied field rotates the CuBr4 chromophore units, yielding a strong magnetochromic effect. And in (La_0.4Pr_0.6_1.2Sr_1.8Mn_2O_7, the magnetic field acts on the Jahn-Teller-split Mn^3+ eg orbitals, with consequences of a substantial CMR effect, unusual magnetic relaxation behavior, and a change in orbital occupation.

  8. Nanostructured transition metal oxides useful for water oxidation catalysis

    DOEpatents

    Frei, Heinz M; Jiao, Feng

    2013-12-24

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

  9. Topological crystalline insulators in transition metal oxides.

    PubMed

    Kargarian, Mehdi; Fiete, Gregory A

    2013-04-12

    Topological crystalline insulators possess electronic states protected by crystal symmetries, rather than time-reversal symmetry. We show that the transition metal oxides with heavy transition metals are able to support nontrivial band topology resulting from mirror symmetry of the lattice. As an example, we consider pyrochlore oxides of the form A2M2O7. As a function of spin-orbit coupling strength, we find two Z2 topological insulator phases can be distinguished from each other by their mirror Chern numbers, indicating a different topological crystalline insulators. We also derive an effective k·p Hamiltonian, similar to the model introduced for Pb(1-x)Sn(x)Te, and discuss the effect of an on-site Hubbard interaction on the topological crystalline insulator phase using slave-rotor mean-field theory, which predicts new classes of topological quantum spin liquids. PMID:25167290

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

    SciTech Connect

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

    2013-12-24

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

  11. Orbital physics in transition-metal oxides

    PubMed

    Tokura; Nagaosa

    2000-04-21

    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

  12. On the behavior of Bronsted-Evans-Polanyi Relations for Transition Metal Oxides

    SciTech Connect

    Vojvodic, Aleksandra

    2011-08-22

    Versatile Broensted-Evans-Polanyi (BEP) relations are found from density functional theory for a wide range of transition metal oxides including rutiles and perovskites. For oxides, the relation depends on the type of oxide, the active site and the dissociating molecule. The slope of the BEP relation is strongly coupled to the adsorbate geometry in the transition state. If it is final state-like the dissociative chemisorption energy can be considered as a descriptor for the dissociation. If it is initial state-like, on the other hand, the dissociative chemisorption energy is not suitable as descriptor for the dissociation. Dissociation of molecules with strong intramolecular bonds belong to the former and molecules with weak intramolecular bonds to the latter group. We show, for the prototype system La-perovskites, that there is a 'cyclic' behavior in the transition state characteristics upon change of the active transition metal of the oxide.

  13. (S)TEM analysis of functional transition metal oxides

    NASA Astrophysics Data System (ADS)

    Chi, Miaofang

    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.

  14. Charge, orbital and magnetic ordering in transition metal oxides 

    E-print Network

    Senn, Mark Stephen

    2013-06-29

    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 ...

  15. Topological phases in oxide heterostructures with light and heavy transition metal ions (invited)

    NASA Astrophysics Data System (ADS)

    Fiete, Gregory A.; Rüegg, Andreas

    2015-05-01

    Using a combination of density functional theory, tight-binding models, and Hartree-Fock theory, we predict topological phases with and without time-reversal symmetry breaking in oxide heterostructures. We consider both heterostructures containing light transition metal ions and those containing heavy transition metal ions. We find that the (111) growth direction naturally leads to favorable conditions for topological phases in both perovskite structures and pyrochlore structures. For the case of light transition metal elements, Hartree-Fock theory predicts the spin-orbit coupling is effectively enhanced by on-site multiple-orbital interactions and may drive the system through a topological phase transition, while heavy elements with intrinsically large spin-orbit coupling require much weaker or even vanishing electron interactions to bring about a topological phase.

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

    E-print Network

    Andrzej M. Ole?

    2012-07-12

    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.

  17. Electrocatalytic Activity of Transition Metal Oxide-Carbon Composites for Oxygen Reduction in Alkaline Batteries and Fuel Cells

    SciTech Connect

    Malkhandi, S; Trinh, P; Manohar, AK; Jayachandrababu, KC; Kindler, A; Prakash, GKS; Narayanan, SR

    2013-06-07

    Conductive transition metal oxides (perovskites, spinels and pyrochlores) are attractive as catalysts for the air electrode in alkaline rechargeable metal-air batteries and fuel cells. We have found that conductive carbon materials when added to transition metal oxides such as calcium-doped lanthanum cobalt oxide, nickel cobalt oxide and calcium-doped lanthanum manganese cobalt oxide increase the electrocatalytic activity of the oxide for oxygen reduction by a factor of five to ten. We have studied rotating ring-disk electrodes coated with (a) various mass ratios of carbon and transition metal oxide, (b) different types of carbon additives and (c) different types of transition metal oxides. Our experiments and analysis establish that in such composite catalysts, carbon is the primary electro- catalyst for the two-electron electro-reduction of oxygen to hydroperoxide while the transition metal oxide decomposes the hydroperoxide to generate additional oxygen that enhances the observed current resulting in an apparent four-electron process. These findings are significant in that they change the way we interpret previous reports in the scientific literature on the electrocatalytic activity of various transition metal oxide- carbon composites for oxygen reduction, especially where carbon is assumed to be an additive that just enhances the electronic conductivity of the oxide catalyst. (C) 2013 The Electrochemical Society. All rights reserved.

  18. Monolayered nanodots of transition metal oxides.

    PubMed

    Nakamura, Keisuke; Oaki, Yuya; Imai, Hiroaki

    2013-03-20

    Monolayered nanodots of titanium, tungsten, and manganese oxides were obtained by exfoliation of the nanocrystals through aqueous solution processes at room temperature. The precursor nanocrystals of the layered compounds, such as sodium titanate (Na(0.80)Ti(1.80)?(0.2)O4·xH2O, ?: vacancy (x < 1.17)), cesium tungstate (Cs4W11O35·yH2O (y < 10.5)), and sodium manganate (Na0.44MnO2·zH2O (z < 0.85)), were synthesized in an aqueous solution. These nanocrystals of the layered compounds were delaminated into the monolayered nanodots through introduction of a bulky organic cation in the interlayer space. The resultant monolayered nanodots of the titanate and tungstate 2-5 nm in lateral size showed a remarkable blueshift of the bandgap energies. The calculation studies supported the blueshifts of the bandgap energies. The results suggest that syntheses of monolayered nanodots can expand the tuning range of the properties based on size effect. The present approaches for generation of ultrathin tiny objects can be applied to a variety of nanomaterials. PMID:23441590

  19. Optical properties of transition metal oxide quantum wells

    SciTech Connect

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

    2015-01-21

    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/SrTiO{sub 3}/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.

  20. Templated Assembly of Metal-Anion Arrays within Layered Hosts; Synthesis and Characterization of New Transition-Metal Oxyhalide Perovskites

    E-print Network

    Spinu, Leonard

    ], and Ruddlesden- Popper [4-6] series, [A2An-1B3O3n+1] (A,A= alkali, alkaline earth or rare earth; B = transitionTemplated Assembly of Metal-Anion Arrays within Layered Hosts; Synthesis and Characterization of New Transition-Metal Oxyhalide Perovskites Gabriel Caruntu, Liliana Viciu, Leonard Spinu, Weilie Zhou

  1. Pseudopotentials for quantum Monte Carlo calculations of transition metal oxides

    NASA Astrophysics Data System (ADS)

    Krogel, Jaron; Santana, Juan; Kent, Paul; Reboredo, Fernando

    2015-03-01

    Quantum Monte Carlo calculations of transition metal oxides are partially limited by the availability of high quality pseudopotentials that are both accurate in QMC and compatible with major electronic structure codes, e.g. by not being overly hard in the standard planewave basis. Following insight gained from recent GW calculations, a set of neon core pseudopotentials with small cutoff radii have been created for the early transition metal elements Sc to Zn within the local density approximation of DFT. The pseudopotentials have been tested for energy consistency within QMC by calculating the first through fourth ionization potentials of the isolated transition metal (TM) atoms and the binding curve of each TM-O dimer. The vast majority of the ionization potentials fall within 0.3 eV of the experimental values, with exceptions occurring mainly for atoms with multiple unpaired d electrons where multireference effects are the strongest. The equilibrium bond lengths of the dimers are within 1% of experimental values and the binding energy errors are typically less than 0.3 eV. Given the uniform treatment of the core, the larger deviations occasionally observed may primarily reflect the limitations of a Slater-Jastrow trial wavefunction. This work is supported by the Materials Sciences & Engineering Division of the Office of Basic Energy Sciences, U.S. DOE. Research by PRCK was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility.

  2. Interface engineering of quantum Hall effects in digital transition metal oxide heterostructures

    SciTech Connect

    Xiao, Di; Zhu, Wenguang; Ran, Ying; Nagaosa, Naoto; Okamoto, Satoshi

    2011-01-01

    Topological insulators (TIs) are characterized by a non-trivial band topology driven by the spin-orbit coupling. To fully explore the fundamental science and application of TIs, material realization is indispensable. Here we predict, based on tight-binding modeling and first-principles calculations, that bilayers of perovskite-type transition-metal oxides grown along the [111] crystallographic axis are potential candidates for two-dimensional TIs. The topological band structure of these materials can be fine-tuned by changing dopant ions, substrates and external gate voltages. We predict that LaAuO$_3$ bilayers have a topologically non-trivial energy gap of about 0.15~eV, which is sufficiently large to realize the quantum spin Hall effect at room temperature. Intriguing phenomena, such as fractional quantum Hall effect, associated with the nearly flat topologically non-trivial bands found in $e_g$ systems are also discussed.

  3. Transition Metal Oxide Alloys as Potential Solar Energy Conversion Materials

    SciTech Connect

    Toroker, Maytal; Carter, Emily A.

    2013-02-21

    First-row transition metal oxides (TMOs) are inexpensive potentia alternative materials for solar energy conversion devices. However, some TMOs, such as manganese(II) oxide, have band gaps that are too large for efficiently absorbing solar energy. Other TMOs, such as iron(II) oxide, have conduction and valence band edges with the same orbital character that may lead to unfavorably high electron–hole recombination rates. Another limitation of iron(II) oxide is that the calculated valence band edge is not positioned well for oxidizing water. We predict that key properties, including band gaps, band edge positions, and possibly electron–hole recombination rates, may be improved by alloying TMOs that have different band alignments. A new metric, the band gap center offset, is introduced for simple screening of potential parent materials. The concept is illustrated by calculating the electronic structure of binary oxide alloys that contain manganese, nickel, iron, zinc, and/or magnesium, within density functional theory (DFT)+U and hybrid DFT theories. We conclude that alloys of iron(II) oxide are worth evaluating further as solar energy conversion materials.

  4. Electronic structure of high-k transition metal oxides and their silicate and aluminate alloys

    E-print Network

    Electronic structure of high-k transition metal oxides and their silicate and aluminate alloys G earth dielectrics and ii SiO2 and Si oxynitride alloys by presenting a systematic x-ray absorption alloys of: i group IIIB, IVB, and VB transition metal TM oxides and ii first row RE oxides with SiO2

  5. Resonant Ultrasound Studies of Complex Transition Metal Oxides

    SciTech Connect

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

    2008-08-18

    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.

  6. Development of microstrain in aged lithium transition metal oxides.

    PubMed

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

    2014-08-13

    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

  7. Orbital reconstruction in nonpolar tetravalent transition-metal oxide layers.

    PubMed

    Bogdanov, Nikolay A; Katukuri, Vamshi M; Romhányi, Judit; Yushankhai, Viktor; Kataev, Vladislav; Büchner, Bernd; van den Brink, Jeroen; Hozoi, Liviu

    2015-01-01

    A promising route to tailoring the electronic properties of quantum materials and devices rests on the idea of orbital engineering in multilayered oxide heterostructures. Here we show that the interplay of interlayer charge imbalance and ligand distortions provides a knob for tuning the sequence of electronic levels even in intrinsically stacked oxides. We resolve in this regard the d-level structure of layered Sr2IrO4 by electron spin resonance. While canonical ligand-field theory predicts g||-factors less than 2 for positive tetragonal distortions as present in Sr2IrO4, the experiment indicates g|| is greater than 2. This implies that the iridium d levels are inverted with respect to their normal ordering. State-of-the-art electronic-structure calculations confirm the level switching in Sr2IrO4, whereas we find them in Ba2IrO4 to be instead normally ordered. Given the nonpolar character of the metal-oxygen layers, our findings highlight the tetravalent transition-metal 214 oxides as ideal platforms to explore d-orbital reconstruction in the context of oxide electronics. PMID:26105992

  8. Orbital reconstruction in nonpolar tetravalent transition-metal oxide layers

    NASA Astrophysics Data System (ADS)

    Bogdanov, Nikolay A.; Katukuri, Vamshi M.; Romhányi, Judit; Yushankhai, Viktor; Kataev, Vladislav; Büchner, Bernd; van den Brink, Jeroen; Hozoi, Liviu

    2015-06-01

    A promising route to tailoring the electronic properties of quantum materials and devices rests on the idea of orbital engineering in multilayered oxide heterostructures. Here we show that the interplay of interlayer charge imbalance and ligand distortions provides a knob for tuning the sequence of electronic levels even in intrinsically stacked oxides. We resolve in this regard the d-level structure of layered Sr2IrO4 by electron spin resonance. While canonical ligand-field theory predicts g||-factors less than 2 for positive tetragonal distortions as present in Sr2IrO4, the experiment indicates g|| is greater than 2. This implies that the iridium d levels are inverted with respect to their normal ordering. State-of-the-art electronic-structure calculations confirm the level switching in Sr2IrO4, whereas we find them in Ba2IrO4 to be instead normally ordered. Given the nonpolar character of the metal-oxygen layers, our findings highlight the tetravalent transition-metal 214 oxides as ideal platforms to explore d-orbital reconstruction in the context of oxide electronics.

  9. Orbital reconstruction in nonpolar tetravalent transition-metal oxide layers

    PubMed Central

    Bogdanov, Nikolay A.; Katukuri, Vamshi M.; Romhányi, Judit; Yushankhai, Viktor; Kataev, Vladislav; Büchner, Bernd; van den Brink, Jeroen; Hozoi, Liviu

    2015-01-01

    A promising route to tailoring the electronic properties of quantum materials and devices rests on the idea of orbital engineering in multilayered oxide heterostructures. Here we show that the interplay of interlayer charge imbalance and ligand distortions provides a knob for tuning the sequence of electronic levels even in intrinsically stacked oxides. We resolve in this regard the d-level structure of layered Sr2IrO4 by electron spin resonance. While canonical ligand-field theory predicts g||-factors less than 2 for positive tetragonal distortions as present in Sr2IrO4, the experiment indicates g|| is greater than 2. This implies that the iridium d levels are inverted with respect to their normal ordering. State-of-the-art electronic-structure calculations confirm the level switching in Sr2IrO4, whereas we find them in Ba2IrO4 to be instead normally ordered. Given the nonpolar character of the metal-oxygen layers, our findings highlight the tetravalent transition-metal 214 oxides as ideal platforms to explore d-orbital reconstruction in the context of oxide electronics. PMID:26105992

  10. Chemistry of Sulfur Oxides on Transition Metals. II. Thermodynamics of Sulfur Oxides on Platinum(111)

    E-print Network

    Lin, Xi

    Chemistry of Sulfur Oxides on Transition Metals. II. Thermodynamics of Sulfur Oxides on Platinum at the highest coverages and sulfur oxidation states. Calculated vibrational spectra are used to assign observed the preferred SOx species on Pt(111), consistent with observation. I. Introduction The chemistry of sulfur

  11. Wannier function analysis of charge states in transition metal oxides

    NASA Astrophysics Data System (ADS)

    Quan, Yundi; Pickett, Warren

    2015-03-01

    The charge (or oxidation) state of a cation has been a crucial concept in analyzing the electronic and magnetic properties of oxides as well as interpreting ``charge ordering'' metal-insulator transitions. In recent years a few methods have been proposed for the objective identification of charge states, beyond the conventional (and occasionally subjective) use of projected densities of states, weighted band structures (fatbands), and Born effective charges. In the past two decades Wannier functions (WFs) and particularly maximally localized WFs (MLWFs), have become an indispensable tool for several different purposes in electronic structure studies. These developments have motivated us to explore the charge state picture from the perspective of MLWFs. We will illustrate with a few transition metal oxide examples such as AgO and YNiO3 that the shape, extent, and location of the charge centers of the MLWFs provide insights into how cation-oxygen hybridization determines chemical bonding, charge distribution, and ``charge ordering.'' DOE DE-FG02-04ER46111.

  12. APCVD Transition Metal Oxides - Functional Layers in "Smart windows"

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

    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.

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

    PubMed

    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

    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

  14. Hybrid functional studies of defects in layered transition metal oxides

    NASA Astrophysics Data System (ADS)

    Hoang, Khang; Johannes, Michelle

    2014-03-01

    Layered oxides LiMO2 (M is a transition metal) have been studied extensively for Li-ion battery cathodes. It is known that defects have strong impact on the electrochemical performance. A detailed understanding of native point defects in LiMO2 is however still lacking, thus hindering rational design of more complex materials for battery applications. In fact, first-principles defect calculations in LiMO2 are quite challenging because standard density functional theory (DFT) calculations using the generalized gradient approximation (GGA) of the exchange-correlation functional fail to reproduce the correct physics. The GGA+U extension can produce reasonable results, but the transferability of U across the compounds is limited. In this talk, we present our DFT studies of defects in LiMO2 (M=Co, Ni) using the Heyd-Scuseria-Ernzerhof (HSE) screened hybrid functional. The dominant point defects will be identified and compared with experiment; and their impact on the structural stability and the charge (electronic and ionic) and mass transport will be addressed. We will also discuss possible shortcomings of the HSE functional in the study of these electron-correlated materials.

  15. First-principles density functional theory study of sulfur oxide chemistry on transition metal surfaces

    E-print Network

    Lin, Xi, 1973-

    2003-01-01

    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 ...

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

    PubMed

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

    2001-10-21

    A new type of mesoporous mixed transition metal oxide of Nb and Ta (NbTa-TIT-1) has been prepared through a two-step calcination, which consists of single crystal particles with wormhole mesoporous structure. PMID:12240191

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

    E-print Network

    Sivakumar, Vikram

    2008-01-01

    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 ...

  18. Calibrating transition-metal energy levels and oxygen bands in first-principles calculations: Accurate prediction of redox potentials and charge transfer in lithium transition-metal oxides

    E-print Network

    Seo, Dong-Hwa

    Transition-metal (TM) oxides play an increasingly important role in technology today, including applications such as catalysis, solar energy harvesting, and energy storage. In many of these applications, the details of ...

  19. Porous nanoarchitectures of spinel-type transition metal oxides for electrochemical energy storage systems.

    PubMed

    Park, Min-Sik; Kim, Jeonghun; Kim, Ki Jae; Lee, Jong-Won; Kim, Jung Ho; Yamauchi, Yusuke

    2015-11-18

    Transition metal oxides possessing two kinds of metals (denoted as AxB3-xO4, which is generally defined as a spinel structure; A, B = Co, Ni, Zn, Mn, Fe, etc.), with stoichiometric or even non-stoichiometric compositions, have recently attracted great interest in electrochemical energy storage systems (ESSs). The spinel-type transition metal oxides exhibit outstanding electrochemical activity and stability, and thus, they can play a key role in realising cost-effective and environmentally friendly ESSs. Moreover, porous nanoarchitectures can offer a large number of electrochemically active sites and, at the same time, facilitate transport of charge carriers (electrons and ions) during energy storage reactions. In the design of spinel-type transition metal oxides for energy storage applications, therefore, nanostructural engineering is one of the most essential approaches to achieving high electrochemical performance in ESSs. In this perspective, we introduce spinel-type transition metal oxides with various transition metals and present recent research advances in material design of spinel-type transition metal oxides with tunable architectures (shape, porosity, and size) and compositions on the micro- and nano-scale. Furthermore, their technological applications as electrode materials for next-generation ESSs, including metal-air batteries, lithium-ion batteries, and supercapacitors, are discussed. PMID:26549729

  20. The electronic structure of lithium transition metal oxides

    NASA Astrophysics Data System (ADS)

    Kocher, Michael P.

    Currently, LiCoO2 is the cathode in the majority of the batteries used in cellular phones and laptop computers. Due to the low abundance of cobalt, thermal instability and environmental concerns, there has been a strong effort to find an alternative material. This dissertation focuses on ab initio calculations of the electronic structure of several lithium transition metal oxides used as cathode material in Li-ion batteries, especially layered LiMn1/2Ni1/2O2 and LiMn1/3,Ni 1/3,Co1/3O2, and olivine structure LiFePO 4 and FePO4. These materials offer substantial increases in energy density and cycle life, and could be used in electric vehicles. Density Functional Theory (DFT) was used to calculate the electronic structure of LixMn1/2Ni1/2O2 and LixMn1/3,Ni1/3,Co1/3O2. To understand the fundamental characteristics of these materials, the spherical integrated charge and spin density, and angular momentum projected density of states was calculated to investigate the effect of insertion of Li. The observed changes of the integrated spin density suggest Ni is changing valence state as Li is removed. However, the integrated charge density shows no dependence on the Li concentration, which suggests that Ni remains in the same charge state. The electronic density of states reveals that the hybridized O p near the Fermi level are key component to charge compensation mechanism. This provides evidence that the O has a key role in the charge regulation during delithiation/lithiation and Ni is not changing from Ni2+ to Ni4+. The calculated projected density of states was compared with EELS measurements to further validate these findings. The electronic structure of LiFePO4 and FePO4 was calculated using DFT and DFT+U. The spherically integrated spin and charge densities show a small dependency of the Li concentration, but do not suggest a change from Fealpha to Fealpha+1. The projected density of states shows an increase in the hybridization of the O p and Fe d states as Li is removed, suggesting the covalent bonding within the material is a key component to the charge compensation mechanism.

  1. Synthesis, characterization and formation process of transition metal oxide nanotubes using carbon nanofibers as templates

    SciTech Connect

    Ogihara, Hitoshi; Masahiro, Sadakane; Nodasaka, Yoshinobu; Ueda, Wataru

    2009-06-15

    Mono and binary transition metal oxide nanotubes could be synthesized by the immersion of carbon nanofiber templates into metal nitrate solutions and removal of the templates by heat treatment in air. The transition metal oxide nanotubes were composed of nano-crystallites of metal oxides. The functional groups on the carbon nanofiber templates were essential for the coating of these templates: they acted as adsorption sites for the metal nitrates, ensuring a uniform metal oxide coating. During the removal of the carbon nanofiber templates by calcination in air, the metal oxide coatings promoted the combustion reaction between the carbon nanofibers and oxygen. - Graphical abstract: Mono and binary transition metal-oxide nanotubes could be synthesized by the immersion of carbon nanofiber templates into metal nitrate solutions and removal of the templates by heat treatment in air.

  2. Perovskite oxides: Oxygen electrocatalysis and bulk structure

    NASA Technical Reports Server (NTRS)

    Carbonio, R. E.; Fierro, C.; Tryk, D.; Scherson, D.; Yeager, Ernest

    1987-01-01

    Perovskite type oxides were considered for use as oxygen reduction and generation electrocatalysts in alkaline electrolytes. Perovskite stability and electrocatalytic activity are studied along with possible relationships of the latter with the bulk solid state properties. A series of compounds of the type LaFe(x)Ni1(-x)O3 was used as a model system to gain information on the possible relationships between surface catalytic activity and bulk structure. Hydrogen peroxide decomposition rate constants were measured for these compounds. Ex situ Mossbauer effect spectroscopy (MES), and magnetic susceptibility measurements were used to study the solid state properties. X ray photoelectron spectroscopy (XPS) was used to examine the surface. MES has indicated the presence of a paramagnetic to magnetically ordered phase transition for values of x between 0.4 and 0.5. A correlation was found between the values of the MES isomer shift and the catalytic activity for peroxide decomposition. Thus, the catalytic activity can be correlated to the d-electron density for the transition metal cations.

  3. Transition-Metal-Free Oxidative Aliphatic C-H Azidation.

    PubMed

    Zhang, Xiaofei; Yang, Haodong; Tang, Pingping

    2015-12-01

    The first example of a practical and selective azidation of unactivated aliphatic C-H bonds with easily handled sulfonyl azides as azide source without the use of transition metals has been explored. This method is operationally simple, scalable, and applicable to late-stage azidation of natural products and derivatives, which make it a valuable method for the synthesis of organic azides. PMID:26569439

  4. Hydrothermal synthesis and crystal structures of two novel vanadium oxides containing interlamellar transition metal complexes

    E-print Network

    Hydrothermal synthesis and crystal structures of two novel vanadium oxides containing interlamellar, Syracuse, NY 13244, USA Received 31 October 1997; accepted 5 February 1998 Abstract Two new vanadium oxide compounds, which contain interlamellar transition metal complexes bound to vanadium oxide sheets, were

  5. Compressibility of orthorhombic perovskites. The effect of transition metal ions (TMI)

    NASA Astrophysics Data System (ADS)

    Ardit, Matteo

    2015-12-01

    Interest in perovskites evenly spans Materials Science and Geophysics. Due to their inimitably lattice flexibility enabling small as well as large ions to be accommodated, perovskites have become a base structure for new technological applications. Understanding the mechanisms governing their evolution at non-ambient conditions (such as high-pressure and high-temperature) is fundamentally important both for devising functional materials and in order to provide the most reliable possible deep-Earth model. With particular attention being paid to the chemical nature of the constituent ions, a suite of orthorhombic perovskites has been selected and contrasted using several parameterizations and models. A new perspective on the pressure-induced distortion of orthorhombic perovskite structures has enabled their compressional behaviour to be redefined.

  6. Electronic transitions and multiferroicity in transition metal oxides

    NASA Astrophysics Data System (ADS)

    Zhou, Haidong

    Four systems have been studied for the localized-itinerant electronic transition in transition-metal oxides: (i) In CaV1- xTixO3, substitution of Ti(IV) introduces Anderson-localized states below a mobility edge mu c that increases with x, crossing epsilon F in the range 0.2 < x< 0.4 and also transforms the strong-correlation fluctuations to localized V(IV): t1e0 configurations for x ? 0.1. (ii) The properties of LaTiO3+delta reveal that a hole-poor, strongly correlated electronic phase coexists with a hole-rich, itinerant-electron phase. With delta ? 0.03, the hole-rich phase exists as a minority phase of isolated, mobile itinerant-electron clusters embedded in the hole-poor phase. With delta ? 0.08, isolated hole-poor clusters are embedded in an itinerant-electron matrix. As delta > 0.08 increases, the hole-poor clusters become smaller and more isolated until they are reduced to super-paramagnetic strong-correlation fluctuations by delta = 0.12. (iii) The data of Y1-xLaxTiO 3 appears to distinguish an itinerant-electron antiferromagnetic phase in the La-rich samples from a localized-electron ferromagnetic phase with a cooperative Jahn-Teller distortion in the Y-rich phase. (iv) The transition at Tt in Mg[Ti2]O4 is a semiconductor-semiconductor transition associated with Ti-Ti dimerization instabilities. The dimerization is caused by lattice instabilities resulting from a double-well Ti-Ti bond potential at a crossover from localized to itinerant electronic behavior. RMn1-xGaxO 3 (R = Ho, Y) and Ho1-xY xMnO3 have been studied for the multiferroicity of RMnO3. Ga doping raises the ferrielectric Curie temperature TC and the Mn-spin reorientation temperature TSR while lowering TN of the Mn spins and the Ho magnetic ordering temperature T 2. The data show an important coupling between the Mn3+-ion and HO3+-ion spins as well as a TSR that is driven by a cooperative MnO5 site rotation and R 3+-ion displacements that modify the c lattice parameter. The data also support an enhanced spin-lattice interaction in the geometrically frustrated (GF) Mn-spin system. Y doping enhances the temperature region for the P6'3cm' magnetic phase and thereby increases TSR for Ho1-xY xMnO3. The studies of several oxygen non-stoichiometric Fe4+/Fe 3+ oxoperovskite show that two mechanisms, the formation of Fe 3+-O-Fe4+ pair and the disproportionation reaction 2Fe(IV)O6/2 = Fe3+ + Fe(V)O6, dominate the electronic behavior. The properties of DyBaCo2O5.5 reveal a spin-state transition from the low-spin t 6e0 ground state to higher spin-state at octahedral-site Co3+, which is also accounted for the metamagnetism in the sample.

  7. Route to transition metal carbide nanoparticles through cyanamide and metal oxides

    SciTech Connect

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

    2008-12-01

    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 metal oxides are completely transmitted into the corresponding carbide nanoparticles. A possible mechanism is proposed to explain the results of the reaction between cyanamide and the metal oxides.

  8. Perovskite catalysts for oxidative coupling

    DOEpatents

    Campbell, K.D.

    1991-06-25

    Perovskites of the structure A[sub 2]B[sub 2]C[sub 3]O[sub 10] are useful as catalysts for the oxidative coupling of lower alkane to heavier hydrocarbons. A is alkali metal; B is lanthanide or lanthanum, cerium, neodymium, samarium, praseodymium, gadolinium or dysprosium; and C is titanium.

  9. Perovskite catalysts for oxidative coupling

    DOEpatents

    Campbell, Kenneth D. (Charleston, WV)

    1991-01-01

    Perovskites of the structure A.sub.2 B.sub.2 C.sub.3 O.sub.10 are useful as catalysts for the oxidative coupling of lower alkane to heavier hydrocarbons. A is alkali metal; B is lanthanide or lanthanum, cerium, neodymium, samarium, praseodymium, gadolinium or dysprosium; and C is titanium.

  10. DEVELOPMENT OF TRANSITION METAL OXIDE-ZEOLITE CATALYSTS TO CONTROL CHLORINATED VOC AIR EMISSIONS

    EPA Science Inventory

    The paper discusses the development of transition metal oxide (TMO)-zeolite oxidation catalysts to control chlorinated volatile organic compound (CVOC) air emissions. esearch has been initiated to enhance the utility of these catalysts by the development of a sorption-catalyst sy...

  11. Generalized self-assembly of scalable two-dimensional transition metal oxide nanosheets

    NASA Astrophysics Data System (ADS)

    Sun, Ziqi; Liao, Ting; Dou, Yuhai; Hwang, Soo Min; Park, Min-Sik; Jiang, Lei; Kim, Jung Ho; Dou, Shi Xue

    2014-05-01

    Two-dimensional (2D) transition metal oxide systems present exotic electronic properties and high specific surface areas, and also demonstrate promising applications ranging from electronics to energy storage. Yet, in contrast to other types of nanostructures, the question as to whether we could assemble 2D nanomaterials with an atomic thickness from molecules in a general way, which may give them some interesting properties such as those of graphene, still remains unresolved. Herein, we report a generalized and fundamental approach to molecular self-assembly synthesis of ultrathin 2D nanosheets of transition metal oxides by rationally employing lamellar reverse micelles. It is worth emphasizing that the synthesized crystallized ultrathin transition metal oxide nanosheets possess confined thickness, high specific surface area and chemically reactive facets, so that they could have promising applications in nanostructured electronics, photonics, sensors, and energy conversion and storage devices.

  12. Band Structure and Terahertz Optical Conductivity of Transition Metal Oxides: Theory and Application to CaRuO3

    NASA Astrophysics Data System (ADS)

    Dang, Hung T.; Mravlje, Jernej; Georges, Antoine; Millis, Andrew J.

    2015-09-01

    Density functional plus dynamical mean field calculations are used to show that in transition metal oxides, rotational and tilting (GdFeO3-type) distortions of the ideal cubic perovskite structure produce a multiplicity of low-energy optical transitions which affect the conductivity down to frequencies of the order of 1 or 2 mV (terahertz regime), mimicking non-Fermi-liquid effects even in systems with a strictly Fermi-liquid self-energy. For CaRuO3, a material whose measured electromagnetic response in the terahertz frequency regime has been interpreted as evidence for non-Fermi-liquid physics, the combination of these band structure effects and a renormalized Fermi-liquid self-energy accounts for the low frequency optical response which had previously been regarded as a signature of exotic physics. Signatures of deviations from Fermi-liquid behavior at higher frequencies (˜100 meV ) are discussed.

  13. Highly efficient organic light-emitting diodes with hole injection layer of transition metal oxides

    NASA Astrophysics Data System (ADS)

    Kim, Soo Young; Baik, Jeong Min; Yu, Hak Ki; Lee, Jong-Lam

    2005-11-01

    We report on the advantage of interlayers using transition-metal oxides, such as iridium oxide (IrOx) and ruthenium oxide (RuOx), between indium tin oxide (ITO) anodes and 4'-bis[N-(1-naphtyl)-N-phenyl-amino]biphenyl (?-NPD) hole transport layers on the electrical and optical properties of organic light-emitting diodes (OLEDs). The operation voltage at a current density of 100 mA/cm2 decreased from 17 to 11 V for OLEDs with 3-nm-thick IrOx interlayers and from 17 to 14 V for OLEDs with 2-nm-thick RuOx ones. The maximum luminance value increased about 50% in OLED using IrOx and 108% in OLED using RuOx. Synchrotron radiation photoelectron spectroscopy results revealed that core levels of Ru 3d and Ir 4f shifted to high binding energies and that the valence band was splitting from metallic Fermi level as the surface of the transition metal was treated with O2 plasma. This provides evidence that the transition-metal surface transformed to a transition-metal oxide. The surface of the transition metal became smoother with the O2 plasma treatment. The thickness was calculated to be 0.4 nm for IrOx and 0.6 nm for RuOx using x-ray reflectivity measurements. Secondary electron emission spectra showed that the work function increased by 0.6 eV for IrOx and by 0.4 eV for RuOx. Thus, the transition-metal oxides lowered the potential barrier for hole injection from ITO to ?-NPD, reducing the turn-on voltage of OLEDs and increasing the quantum efficiency.

  14. X-ray Absorption Study of Graphene Oxide and Transition Metal Oxide Nanocomposites

    PubMed Central

    2015-01-01

    The surface properties of the electrode materials play a crucial role in determining the performance and efficiency of energy storage devices. Graphene oxide and nanostructures of 3d transition metal oxides were synthesized for construction of electrodes in supercapacitors, and the electronic structure and oxidation states were probed using near-edge X-ray absorption fine structure. Understanding the chemistry of graphene oxide would provide valuable insight into its reactivity and properties as the graphene oxide transformation to reduced-graphene oxide is a key step in the synthesis of the electrode materials. Polarized behavior of the synchrotron X-rays and the angular dependency of the near-edge X-ray absorption fine structures (NEXAFS) have been utilized to study the orientation of the ? and ? bonds of the graphene oxide and graphene oxide–metal oxide nanocomposites. The core-level transitions of individual metal oxides and that of the graphene oxide nanocomposite showed that the interaction of graphene oxide with the metal oxide nanostructures has not altered the electronic structure of either of them. As the restoration of the ? network is important for good electrical conductivity, the C K edge NEXAFS spectra of reduced graphene oxide nanocomposites confirms the same through increased intensity of the sp2-derived unoccupied states ?* band. A pronounced angular dependency of the reduced sample and the formation of excitonic peaks confirmed the formation of extended conjugated network. PMID:25152800

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

    SciTech Connect

    S.E. Ziemniak

    2000-05-18

    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.

  16. Electronic-band structures and optical properties of transition metal doped Zinc oxide

    NASA Astrophysics Data System (ADS)

    Esakki muthuraju, M.; Mahesh, R.; Sreekanth, T.; Venugopal Reddy, P.

    2014-05-01

    Wide band gap Oxide based diluted magnetic semiconductors (ODMS) exhibit unique magnetic, magneto-optical and magneto-electrical effects and can be exploited as spintronic devices. Theoretical studies of transition metal (TM) doped zinc oxide which belongs to these class of materials has been attracting significant research interest in the recent years. In this paper, the electronic band structures, and band gap energies of ZnO doped with transition metal have been analyzed by ab initio calculations based on the density functional theory using quantum espresso PWscf code. For the band gap calculations, we have used both local density approximation (LDA) and generalized gradient approximation (GGA). The magnetic and optical properties of the materials have been studied using the above method. For all the theoretical calculations, the model structures of transition metal-doped ZnO were constructed by using the 16 atom supercell with one Zn atom replaced by a transition metal atom. The results are useful in understanding the band gap variations with doping and other related properties in oxide based diluted magnetic semiconductors such as ZnO.

  17. A novel method to enhance the conductance of transitional metal oxide electrodes.

    PubMed

    Wang, Ranran; Chen, Zheng; Yu, Hang; Jia, Xilai; Gao, Lian; Sun, Jing; Hicks, Robert F; Lu, Yunfeng

    2014-04-01

    Transitional metal oxides hold great potential for high capacity anodes. However, the low electron conductivity of such materials leads to poor cycling stability and inferior rate capability. We reported herein the use of a novel hydrogen plasma technology to improve the conductance of metal oxides, which leads great success in improving the rate performance of CuO nanotube based anodes. This method has the potential to be widely adopted in the field of lithium ion batteries and supercapacitors. PMID:24577667

  18. Spin and orbital ordering in ternary transition metal oxides 

    E-print Network

    Kimber, Simon A. J.

    Spin and orbital orderings are amongst the most important phenomena in the solid state chemistry of oxides. Physical property and powder neutron and X-ray diffraction measurements are reported for a range of mostly low ...

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

    NASA Astrophysics Data System (ADS)

    Yin, Ming

    2005-12-01

    Chapter 1. A General introduction to the emerging field of nanomaterials is presented highlighting the category of transition metal oxides. The wide variety of structures, properties, and phenomena of transition metal oxides are stressed. Nano-sized transition metal oxides are presented as systems for fundamental and application research. Examples of individual transition metal oxides are provided. Important developments in the synthesis and characterization of nano-sized transition metal oxides that have contributed to this work are reviewed. A novel synthesis (TDMA) is developed and successfully applied to the synthesis of transition metal oxide nanocrystals. Chapter 2. The synthesis of monodisperse cubic wuestite FexO nanocrystals is presented. The influence of reaction temperature and the molar ratio of surfactant to iron precursor was investigated, in order to further understand the ability to control particle size and monodispersity. In contrast to bulk material, it is also found that the nano-sized ligand-capped wuestite FexO particles were stable at room temperature. The procedure enable the collection of highly monodisperse nanocrystals of variable and uniform diameters as a function of time. Sharp Hancock analysis indicates that the reaction proceeds by a diffusion limited mechanism. Routes to control the size of gamma-Fe2O3 nanocrystals are also presented. gamma-Fe2O3 nanocrystals from 6 nm to 12 nm in diameter with uniform size, shape, consistent crystal structure were prepared. Chapter 3. A simple reaction to prepare monodisperse MnO nanocrystals is presented. MnO nanocrystals was prepared by thermal decomposition of manganese acetate in the presence of oleic acid at high temperature and by following annealing. Particles with different sizes and shapes were obtained by controlling annealing time. The morphology of MnO nanocrystals was studied based on their crystal structure and surface energy. SQUID measurement shows ferromagnetic magnetism at low temperature. Chapter 4. Nanosized Copper (I) oxide particles have been prepared by a thereto decomposition of Cu (I) acetate in the presence of oleic acid at high temperature. Nanoparticles from 3.6 net to 10.7 nm could be synthesized by increasing the stoichiometric ratio of surfactant to copper precursor. Chapter 5. Nano-sized ZnO rods are prepared from a simple acetate precursor. The resulting ZnO nanorods are highly crystalline, uniform and with a narrow size distribution, which facilitates the understanding of the optical properties of nanosized ZnO. (Abstract shortened by UMI.)

  20. Real time monitoring oxidation of transition metals with long period fiber gratings

    NASA Astrophysics Data System (ADS)

    Coelho, L.; Viegas, D.; Santos, J. L.; de Almeida, J. M. M.

    2015-09-01

    In this paper real time monitoring of oxidation of transition metals using long period fiber gratings (LPFG) is performed for nickel, copper, titanium, chromium and zinc. A thin layer is deposited over the LPFG with physical process deposition and is annealed up to 700 °C in air with a small oven. The whole oxidation process can be monitored by tracking the LPFG features of the attenuation band which results in an abrupt change when the oxidation occurs depending on the metal sample. A preliminary study to optimize optical fiber sensors sensitivity allowing choosing the correct oxide layer in a specific application is presented.

  1. Coupling between crystal structure and magnetism in transition-metal oxides

    NASA Astrophysics Data System (ADS)

    Barton, Phillip Thomas

    Transition-metal oxides exhibit a fascinating array of phenomena ranging from superconductivity to negative thermal expansion to catalysis. This dissertation focuses on magnetism, which is integral to engineering applications such as data storage, electric motors/generators, and transformers. The investigative approach follows structure-property relationships from materials science and draws on intuition from solid-state chemistry. The interplay between crystal structure and magnetic properties is studied experimentally in order to enhance the understanding of magnetostructural coupling mechanisms and provide insight into avenues for tuning behavior. A combination of diffraction and physical property measurements were used to study structural and magnetic phase transitions as a function of chemical composition, temperature, and magnetic field. The systems examined are of importance in Li-ion battery electrochemistry, condensed-matter physics, solid-state chemistry, and p-type transparent conducting oxides. The materials were prepared by solid-state reaction of powder reagents at high temperatures for periods lasting tens of hours. The first project discussed is of a solid solution between NiO, a correlated insulator, and LiNiO2, a layered battery cathode. Despite the deceptive structural and compositional simplicity of this system, a complete understanding of its complex magnetic properties has remained elusive. This study shows that nanoscale domains of chemical order form at intermediate compositions, creating interfaces between antiferromagnetism and ferrimagnetism that give rise to magnetic exchange bias. A simple model of the magnetism is presented along with a comprehensive phase diagram. The second set of investigations focus on the Ge-Co-O system where the spin-orbit coupling of Co(II) plays a significant role. GeCo2O 4 is reported to exhibit unusual magnetic behavior that arises from Ising spin in its spinel crystal structure. Studies by variable-temperature synchrotron X-ray diffraction reveal a magnetostructural transition and capacitance measurements show evidence for magnetodielectric behavior. The above work uncovered a Co10Ge3O16 phase that had a known structure but whose physical properties were largely uncharacterized. This project examined its metamagnetic properties using detailed magnetometry experiments. Upon the application of a magnetic field, this material goes through a first-order phase transition from a noncollinear antiferromagnet to an unknown ferrimagnetic state. Lastly, this thesis explored the chemical dilution of magnetism in some perovskite and delafossite solid solutions. In the perovskite structure, compositions intermediate to the endmembers SrRuO3, a ferromagnetic metal, and LaRhO3, a diamagnetic semiconductor, were investigated. While the magnetism of this system is poised between localized and itinerant behavior, a compositionally-driven metal to insulator transition, revealed by electrical resistivity measurements, did not strongly impact the magnetic properties. Instead, both octahedral tilting and magnetic dilution had strong effects, and comparison of this characterization to Sr1-- x CaxRuO3 reinforces the important role of structural distortions in determining magnetic ground state. The final materials studied were of composition CuAl1-- xCrxO2 (0 < x < 1) in the delafossite structure. The primary interest was the geometric frustration of antiferromagnetism in CuCrO 2 and significant short-range correlations were observed above TN. The analysis found that reducing the number of degenerate states through Al substitution did not enhance magnetic ordering because of the weakening of magnetic exchange.

  2. Intrinsic Electronically Active Defects in Transition Metal Elemental Oxides

    NASA Astrophysics Data System (ADS)

    Lucovsky, Gerald; Seo, Hyungtak; Lee, Sanghyun; Fleming, Leslie B.; Ulrich, Marc D.; Lüning, Jan; Lysaght, Pat; Bersuker, Gennadi

    2007-04-01

    Densities of interfacial and bulk defects in high-? dielectrics are typically about two orders of magnitude larger than those in Si-SiO2 devices. An asymmetry in electron and hole trapping kinetics, first detected in test capacitor devices with nanocrystalline ZrO2 and HfO2 dielectrics, is a significant potential limitation for Si device operation and reliability in complementary metal oxide semiconductor applications. There are two crucial issues: i) are the electron and hole traps intrinsic defects, or are they associated with processed-introduced impurities?, and ii) what are the local atomic bonding arrangements and electronic state energies of these traps? In this study, thin film nanocrystalline high-? gate dielectrics, TiO2, ZrO2, and HfO2 (group IVB TM oxides), are investigated spectroscopically to identify the intrinsic electronic structures of valence and conduction band states, as well as those of intrinsic bonding defects. A quantitative/qualitative distinction is made between crystal field and Jahn-Teller (J-T) d-state energy differences in nanocrystralline TM elemental oxides, and noncrystalline TM silicates and Si oxynitrides. It is experimentally shown and theoretically supported that a length scale for nanocrystallite size <2-3 nm i) eliminates J-T d-state term splittings in band edge ?-bonded d-states, and ii) represents a transition from the observation of discrete band edge defects to band-tail defects. Additionally, ?-state bonding coherence can also be disrupted with similar effects on band edge and defect states in HfO2 films which have been annealed in NH3 at 700 °C, and display Hf-N bonds in N atom K1 edge X-ray absorption spectra.

  3. Graphene-based transition metal oxide nanocomposites for the oxygen reduction reaction.

    PubMed

    Sun, Meng; Liu, Huijuan; Liu, Yang; Qu, Jiuhui; Li, Jinghong

    2015-01-28

    The development of low cost, durable and efficient nanocatalysts to substitute expensive and rare noble metals (e.g. Pt, Au and Pd) in overcoming the sluggish kinetic process of the oxygen reduction reaction (ORR) is essential to satisfy the demand for sustainable energy conversion and storage in the future. Graphene based transition metal oxide nanocomposites have extensively been proven to be a type of promising highly efficient and economic nanocatalyst for optimizing the ORR to solve the world-wide energy crisis. Synthesized nanocomposites exhibit synergetic advantages and avoid the respective disadvantages. In this feature article, we concentrate on the recent leading works of different categories of introduced transition metal oxides on graphene: from the commonly-used classes (FeOx, MnOx, and CoOx) to some rare and heat-studied issues (TiOx, NiCoOx and Co-MnOx). Moreover, the morphologies of the supported oxides on graphene with various dimensional nanostructures, such as one dimensional nanocrystals, two dimensional nanosheets/nanoplates and some special multidimensional frameworks are further reviewed. The strategies used to synthesize and characterize these well-designed nanocomposites and their superior properties for the ORR compared to the traditional catalysts are carefully summarized. This work aims to highlight the meaning of the multiphase establishment of graphene-based transition metal oxide nanocomposites and its structural-dependent ORR performance and mechanisms. PMID:25502117

  4. Graphene-based transition metal oxide nanocomposites for the oxygen reduction reaction

    NASA Astrophysics Data System (ADS)

    Sun, Meng; Liu, Huijuan; Liu, Yang; Qu, Jiuhui; Li, Jinghong

    2015-01-01

    The development of low cost, durable and efficient nanocatalysts to substitute expensive and rare noble metals (e.g. Pt, Au and Pd) in overcoming the sluggish kinetic process of the oxygen reduction reaction (ORR) is essential to satisfy the demand for sustainable energy conversion and storage in the future. Graphene based transition metal oxide nanocomposites have extensively been proven to be a type of promising highly efficient and economic nanocatalyst for optimizing the ORR to solve the world-wide energy crisis. Synthesized nanocomposites exhibit synergetic advantages and avoid the respective disadvantages. In this feature article, we concentrate on the recent leading works of different categories of introduced transition metal oxides on graphene: from the commonly-used classes (FeOx, MnOx, and CoOx) to some rare and heat-studied issues (TiOx, NiCoOx and Co-MnOx). Moreover, the morphologies of the supported oxides on graphene with various dimensional nanostructures, such as one dimensional nanocrystals, two dimensional nanosheets/nanoplates and some special multidimensional frameworks are further reviewed. The strategies used to synthesize and characterize these well-designed nanocomposites and their superior properties for the ORR compared to the traditional catalysts are carefully summarized. This work aims to highlight the meaning of the multiphase establishment of graphene-based transition metal oxide nanocomposites and its structural-dependent ORR performance and mechanisms.

  5. Intra-shell luminescence of transition-metal-implanted zinc oxide nanowires.

    PubMed

    Müller, Sven; Zhou, Minjie; Li, Quan; Ronning, Carsten

    2009-04-01

    Zinc oxide nanowires were grown by vapor transport using the vapor-liquid-solid growth mechanism. The zinc oxide nanowires were implanted with transition metals (Co, Fe or Ni) and subsequently annealed in air at 700 degrees C for 30 min. Energy-dispersive x-ray spectroscopy and electron energy loss spectroscopy measurements reveal a successful incorporation of the desired transition metals. Transmission electron microscopy analysis of implanted and annealed zinc oxide nanowires shows a strongly damaged zinc oxide lattice but no formation of transition metal-rich secondary phases. The as-grown nanowires show a strong and intensive near-band edge emission and a moderately structured green luminescence band. After ion implantation, the structured green luminescence band increases in intensity and new sharp luminescence lines appear in the red luminescence region. Those sharp transitions are due to intra-shell 3d transitions of iron and cobalt in the corresponding Fe- and Co-doped ZnO samples. PMID:19420513

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

    PubMed Central

    Chen, Hongjun

    2014-01-01

    Summary To better utilize the sunlight for efficient solar energy conversion, the research on visible-light active photocatalysts has recently attracted a lot of interest. The photosensitization of transition metal oxides is a promising approach for achieving effective visible-light photocatalysis. This review article primarily discusses the recent progress in the realm of a variety of nanostructured photosensitizers such as quantum dots, plasmonic metal nanostructures, and carbon nanostructures for coupling with wide-bandgap transition metal oxides to design better visible-light active photocatalysts. The underlying mechanisms of the composite photocatalysts, e.g., the light-induced charge separation and the subsequent visible-light photocatalytic reaction processes in environmental remediation and solar fuel generation fields, are also introduced. A brief outlook on the nanostructure photosensitization is also given. PMID:24991507

  7. Quantum confinement in transition metal oxide quantum wells

    SciTech Connect

    Choi, Miri; Lin, Chungwei; Butcher, Matthew; Posadas, Agham B.; Demkov, Alexander A.; Rodriguez, Cesar; Zollner, Stefan; He, Qian; Borisevich, Albina Y.

    2015-05-11

    We report on the quantum confinement in SrTiO{sub 3} (STO) quantum wells (QWs) grown by molecular beam epitaxy. The QW structure consists of LaAlO{sub 3} (LAO) and STO layers grown on LAO substrate. Structures with different QW thicknesses ranging from two to ten unit cells were grown and characterized. Optical properties (complex dielectric function) were measured by spectroscopic ellipsometry in the range of 1.0 eV–6.0 eV at room temperature. We observed that the absorption edge was blue-shifted by approximately 0.39 eV as the STO quantum well thickness was reduced to two unit cells. This demonstrates that the energy level of the first sub-band can be controlled by the QW thickness in a complex oxide material.

  8. Optical properties of transition metal oxide quantum wells

    NASA Astrophysics Data System (ADS)

    Demkov, Alexander; Choi, Miri; Butcher, Matthew; Rodriguez, Cesar; He, Qian; Posadas, Agham; Borisevich, Albina; Zollner, Stefan; Lin, Chungwei; Ortmann, Elliott

    2015-03-01

    We report on the investigation of SrTiO3/LaAlO3 quantum wells (QWs) grown by molecular beam epitaxy (MBE) on LaAlO3 substrate. Structures with different QW thicknesses ranging from two to ten unit cells were grown and characterized using x-ray photoemission spectroscopy, reflection high-energy electron diffraction (RHEED), scanning transmission electron microscopy (STEM). Optical properties (complex dielectric function) were measured by spectroscopic ellipsometry (SE) in the range of 1.0 eV to 6.0 eV at room temperature. We observed that the absorption edge was blue-shifted by approximately 0.39 eV as the STO quantum well thickness was reduced to two unit cells (uc). Density functional theory and tight-binding are used to model the optical response of these heterostructures. Our results demonstrate that the energy level of the first sub-band can be controlled by the QW thickness in a complex oxide material. We acknowledge support from Air Force Office of Scientific Research (FA9550-12-10494).

  9. Super-exchange in transition-metal oxides

    NASA Astrophysics Data System (ADS)

    Harrison, Walter

    2007-03-01

    Using contemporary tight-binding theory and parameters[1]. Anderson's perturbation approach [2] gives a qualitatively correct energy difference (a factor 2.3 too high) between ferromagnetic and antiferromagnetic configurations for MnO, It corresponds to a Heisenberg model with J2/J1= 11/7. Perturbation theory fails as the energy denominator gets smaller for FeO and CoO, and changes sign for NiO. Use of the special- points method to treat exchange-split bands gives smaller values not well characterized by a J1 and J2. Carrying it out self-consistently reorders the NiO levels and leads to still smaller energy differences near experiment for all four oxides, as estimated from the experimental N'eel temperature TN , The theory predicts a variation with pressure corresponding to (d/ TN)TN/d = -12.2 for MnO , near experiment, dropping to -9.1 for NiO. The theory is applicable also to the paramagnetic susceptibility. [1] Walter A. Harrison, Elementary Electronic Structure, World Scientific (Singapore, 1999), revised edition (2004). [2] P. W. Anderson, Phys. Rev. 115, 2 (1959).

  10. Method of synthesizing a plurality of reactants and producing thin films of electro-optically active transition metal oxides

    DOEpatents

    Tracy, C.E.; Benson, D.K.; Ruth, M.R.

    1985-08-16

    A method of synthesizing a plurality of reactants by inducing a reaction by plasma deposition among the reactants. The plasma reaction is effective for consolidating the reactants and producing thin films of electro-optically active transition metal oxides.

  11. Transition metal oxides deposited on rhodium and platinum: Surface chemistry and catalysis

    SciTech Connect

    Boffa, A B

    1994-07-01

    The surface chemistry and catalytic reactivity of transition metal oxides deposited on Rh and Pt substrates has been examined in order to establish the role of oxide-metal interactions in influencing catalytic activity. The oxides investigated included titanium oxide (TiOx), vanadium oxide (VOx), iron oxide (FeOx), zirconium oxide (ZrOx), niobium oxide (NbOx), tantalum oxide (TaOx), and tungsten oxide (WOx). The techniques used to characterize the sample included AES, XPS, LEED, TPD, ISS, and STM. After characterization of the surface in UHV, the sample was enclosed in an atmospheric reaction cell to measure the influence of the oxide deposits on the catalytic activity of the pure metal for CO and CO{sub 2} hydrogenation. The oxide deposits were found to strongly enhance the reactivity of the Rh foil. The rates of methane formation were promoted by up to 15 fold with the maximum in rate enhancement occurring at oxide coverages of approximately 0.5 ML. TiOx TaOx, and NbOx were the most effective promoters and were stable in the highest oxidation states during both reactions (compared to VOx, WOx, and FeOx). The trend in promoter effectiveness was attributed to the direct relationship between oxidation state and Lewis acidity. Bonding at the metal oxide/metal interface between the oxygen end of adsorbed CO and the Lewis acidic oxide was postulated to facilitate C-O bond dissociation and subsequent hydrogenation. 192 refs.

  12. Strain induced electronic structure changes in magnetic transition metal oxides thin films

    SciTech Connect

    van der Laan, G.; Chopdekar, R.V.; Suzuki, Y.; Arenholz, E.

    2010-07-08

    We show that the angular dependence of x-ray magnetic circular dichroism (XMCD) is strongly sensitive to strain-induced electronic structure changes in magnetic transition metal oxides. We observe a pronounced dependence of the XMCD spectral shape on the experimental geometry as well as nonvanishing XMCD with distinct spectral features in transverse geometry in compressively strained MnCr{sub 2}O{sub 4} films. The angular dependent XMCD can be described as a sum over an isotropic and anisotropic contribution, the latter linearly proportional to the axial distortion due to strain. The XMCD spectra are well reproduced by atomic multiplet calculations.

  13. Pinball liquid phase from Hund's coupling in frustrated transition-metal oxides

    NASA Astrophysics Data System (ADS)

    Ralko, Arnaud; Merino, Jaime; Fratini, Simone

    2015-04-01

    The interplay of nonlocal Coulomb repulsion and Hund's coupling in the d -orbital manifold in frustrated triangular lattices is analyzed by a multiband extended Hubbard model. We find a rich phase diagram with several competing phases, including a robust pinball liquid phase, which is an unconventional metal characterized by threefold charge order, bad metallic behavior, and the emergence of high-spin local moments. Our results naturally explain the anomalous charge-ordered metallic state observed in the triangular layered compound AgNiO2. The potential relevance to other triangular transition-metal oxides is discussed.

  14. Quantum spin Hall effect in a transition metal oxide Na2IrO3

    SciTech Connect

    Shitade, Atsuo

    2010-05-26

    We study theoretically the electronic states in a 5d transition metal oxide Na{sub 2}I{sub r}O{sub 3}, in which both the spin-orbit interaction and the electron correlation play crucial roles. Tight-binding model analysis together with the fisrt-principles band structure calculation predicts that this material is a layered quantum spin Hall system. Due to the electron correlation, an antiferromagnetic order first develops at the edge, and later inside the bulk at low temperatures.

  15. Synthesis of transition metal nitride by nitridation of metastable oxide precursor

    SciTech Connect

    Wang, Huamin; Wu, Zijie; Kong, Jing; Wang, Zhiqiang; Tianjin Key Laboratory of Water Environment and Resources, Tianjin Normal University, No. 393 Binshui Road, Xiqing Dist., Tianjin 300387 ; Zhang, Minghui

    2012-10-15

    Metastable transition metal oxides were used as precursors to synthesize transition metal nitrides at low temperature. Amorphous MoO{sub 2} was prepared by reduction of (NH{sub 4}){sub 6}Mo{sub 7}O{sub 24} solution with hydrazine. As-synthesized amorphous MoO{sub 2} was transformed into fcc {gamma}-Mo{sub 2}N at 400 Degree-Sign C and then into hexagonal {delta}-MoN by further increasing the temperature to 600 Degree-Sign C under a NH{sub 3} flow. The nitridation temperature employed here is much lower than that employed in nitridation of crystalline materials, and the amorphous materials underwent a unique nitridation process. Besides this, the bimetallic nitride Ni{sub 2}Mo{sub 3}N was also synthesized by nitridating amorphous bimetallic precursor. These results suggested that the nitridation of amorphous precursor possessed potential to be a general method for synthesizing many interstitial metallic compounds, such as nitrides and carbides at low temperature. - graphical abstract: Amorphous oxide was used as new precursor to prepare nitride at low temperature. Pure {gamma}-Mo{sub 2}N and {delta}-MoN were obtained at 400 Degree-Sign C and at 600 Degree-Sign C, respectively. Highlights: Black-Right-Pointing-Pointer We bring out a new method to synthesize transition metal nitrides at low temperature. Black-Right-Pointing-Pointer Both mono- and bimetallic molybdenum nitrides were synthesized at a mild condition. Black-Right-Pointing-Pointer The formation of two different molybdenum nitrides {gamma}-Mo{sub 2}N and {delta}-MoN can be controlled from the same metastable precursor. Black-Right-Pointing-Pointer The nitridation temperature was much lower than that reported from crystalline precursors. Black-Right-Pointing-Pointer The metastable precursor had different reaction process in comparison with crystalline precursor.

  16. Electronic structure of transition metal and f-electron oxides by quantum Monte Carlo methods

    NASA Astrophysics Data System (ADS)

    Mitas, L.; Hu, S.; Kolorenc, J.

    2012-12-01

    We report on many-body quantum Monte Carlo (QMC) calculations of electronic structure of systems with strong correlation effects. These methods have been applied to ambient and high pressure transition metal oxides and, very recently, to selected f-electron oxides such as mineral thorianite (ThO2). QMC methods enabled us to calculate equilibrium characteristics such as cohesion, equilibrium lattice constants, bulk moduli, and electronic gaps with an excellent agreement with experiment without any non-variational parameters. In addition, for selected cases, the equations of state were calculated as well. The calculations were carried out using the state-of-the-art twist-averaged sampling of the Brilloiun zone, small-core Dirac-Fock pseudopotentials and one-particle orbitals from hybrid DFT functionals with varying weight of the exact exchange. This enabled us to build high-accuracy Slater-Jastrow explicitly correlated wavefunctions. In particular, we have employed optimization of the weight of the exact exchange in B3LYP and PBE0 functionals to minimize the fixed-node error in the diffusion Monte Carlo calculations. Instead of empirical fitting, we therefore use variational and explicitly many-body QMC method to find the value of the optimal weight, which falls between 15 and 30%. This finding is further supported also by recent calculations of transition metal-organic systems such as transition metal-porphyrins and others, showing thus a very wide range of its applicability. The calculations of ThO_2 appears to follow the same pattern and enabled to reproduce very well the experimental cohesion and very large electronic gap. In addition, we have made an important progress also in explicit treatment of the spin-orbit interaction which has been so far neglected in QMC calculations. Our studies illustrate the remarkable capabilities of QMC methods for strongly correlated solid systems.

  17. Enhanced role of transition metal ion catalysis during in-cloud oxidation of SO2.

    PubMed

    Harris, Eliza; Sinha, Bärbel; van Pinxteren, Dominik; Tilgner, Andreas; Fomba, Khanneh Wadinga; Schneider, Johannes; Roth, Anja; Gnauk, Thomas; Fahlbusch, Benjamin; Mertes, Stephan; Lee, Taehyoung; Collett, Jeffrey; Foley, Stephen; Borrmann, Stephan; Hoppe, Peter; Herrmann, Hartmut

    2013-05-10

    Global sulfate production plays a key role in aerosol radiative forcing; more than half of this production occurs in clouds. We found that sulfur dioxide oxidation catalyzed by natural transition metal ions is the dominant in-cloud oxidation pathway. The pathway was observed to occur primarily on coarse mineral dust, so the sulfate produced will have a short lifetime and little direct or indirect climatic effect. Taking this into account will lead to large changes in estimates of the magnitude and spatial distribution of aerosol forcing. Therefore, this oxidation pathway-which is currently included in only one of the 12 major global climate models-will have a significant impact on assessments of current and future climate. PMID:23661757

  18. Molecular water oxidation mechanisms followed by transition metals: state of the art.

    PubMed

    Sala, Xavier; Maji, Somnath; Bofill, Roger; García-Antón, Jordi; Escriche, Lluís; Llobet, Antoni

    2014-02-18

    One clean alternative to fossil fuels would be to split water using sunlight. However, to achieve this goal, researchers still need to fully understand and control several key chemical reactions. One of them is the catalytic oxidation of water to molecular oxygen, which also occurs at the oxygen evolving center of photosystem II in green plants and algae. Despite its importance for biology and renewable energy, the mechanism of this reaction is not fully understood. Transition metal water oxidation catalysts in homogeneous media offer a superb platform for researchers to investigate and extract the crucial information to describe the different steps involved in this complex reaction accurately. The mechanistic information extracted at a molecular level allows researchers to understand both the factors that govern this reaction and the ones that derail the system to cause decomposition. As a result, rugged and efficient water oxidation catalysts with potential technological applications can be developed. In this Account, we discuss the current mechanistic understanding of the water oxidation reaction catalyzed by transition metals in the homogeneous phase, based on work developed in our laboratories and complemented by research from other groups. Rather than reviewing all of the catalysts described to date, we focus systematically on the several key elements and their rationale from molecules studied in homogeneous media. We organize these catalysts based on how the crucial oxygen-oxygen bond step takes place, whether via a water nucleophilic attack or via the interaction of two M-O units, rather than based on the nuclearity of the water oxidation catalysts. Furthermore we have used DFT methodology to characterize key intermediates and transition states. The combination of both theory and experiments has allowed us to get a complete view of the water oxidation cycle for the different catalysts studied. Finally, we also describe the various deactivation pathways for these catalysts. PMID:24328498

  19. Surface-functionalized monolayered nanodots of a transition metal oxide and their properties.

    PubMed

    Honda, Masashi; Oaki, Yuya; Imai, Hiroaki

    2015-12-28

    Lateral size, surface chemistry, and properties are varied in inorganic monolayers based on a transition metal-oxide. A variety of inorganic monolayers with their emergent properties have been studied in recent decades. However, it is not easy to tune the lateral size, surface chemistry, and dispersibility of monolayers by typical synthetic methods. In the present work, a new approach is developed for the simultaneous surface functionalization and exfoliation of the precursor nanocrystals in a nonpolar organic medium. We obtained monolayered nanodots of a titanium oxide less than 5 nm in lateral size with surface functionalization by an alkylamine (C14H29NH2) and dihydroxynaphthalene (DHN) in toluene. The bandgap energy of the monolayers was changed by the lateral size and surface functionalization. The present study suggests versatile potentials of the monolayers with tuned size, surface chemistry, and properties. PMID:26592924

  20. In-Situ Analysis of Valence Conversion in Transition Metal Oxides Using Electron Energy-Loss Spectroscopy

    E-print Network

    Wang, Zhong L.

    in a solid solution of Fe2O3 and Mn2O3 as well. Transition and rare earth metal oxides are the fundamental and rare-earth compounds usually display sharp peaks at the near edge region, which are known as whiteLETTERS In-Situ Analysis of Valence Conversion in Transition Metal Oxides Using Electron Energy

  1. Fabrication and electrocatalytic application of functionalized nanoporous carbon material with different transition metal oxides

    NASA Astrophysics Data System (ADS)

    Samiee, L.; Shoghi, F.; Vinu, A.

    2013-01-01

    In the work presented here, an attempt is made to study the effect of functionalization with different transition metal oxides on the mesostructural properties as well as electrochemical behavior of Pt/nanoporous carbon supports. In this respect, the functionalized samples have been synthesized by using CMK-3 and metallocene as transition metal sources. The platinum catalysts (5 wt% Pt) obtained through a conventional wet impregnation method. All the materials have been characterized by XRD (low and high), N2 adsorption-desorption isotherms, high-resolution transmission electron microscopy, high-resolution field emission scanning electron, EDX mapping images and cyclic voltammetry (CV) and rotating disk electrode (RDE) techniques. The results showed that the mesostructural order has been destroyed by functionalization of CMK-3 with CoO, whereas it is not that much affected in NiO and CuO functionalized samples. EDX image mapping exhibited the good and uniform dispersion of functionalizing elements (Ni, Cu, Fe and Co), Pt in the carbon supports. Moreover, XRD studies revealed the formation of smaller platinum crystallite sizes in NiO and CuO functionalized samples in relative to other functionalized supports. Electrochemical measurements were performed using CV and RDE method. Kinetic analysis revealed an activity increases in the following order: CMK-3-NiO-Pt > CMK-3-CuO-Pt > CMK-3-CoO-Pt > CMK-3-Fe2O3-Pt which is showing of simultaneous effect of surface area and surface reactivity parameters.

  2. Perovskite-type oxides - Oxygen electrocatalysis and bulk structure

    NASA Technical Reports Server (NTRS)

    Carbonio, R. E.; Fierro, C.; Tryk, D.; Scherson, D.; Yeager, E.

    1988-01-01

    Perovskite type oxides were considered for use as oxygen reduction and generation electrocatalysts in alkaline electrolytes. Perovskite stability and electrocatalytic activity are studied along with possible relationships of the latter with the bulk solid state properties. A series of compounds of the type LaFe(x)Ni1(-x)O3 was used as a model system to gain information on the possible relationships between surface catalytic activity and bulk structure. Hydrogen peroxide decomposition rate constants were measured for these compounds. Ex situ Mossbauer effect spectroscopy (MES), and magnetic susceptibility measurements were used to study the solid state properties. X ray photoelectron spectroscopy (XPS) was used to examine the surface. MES has indicated the presence of a paramagnetic to magnetically ordered phase transition for values of x between 0.4 and 0.5. A correlation was found between the values of the MES isomer shift and the catalytic activity for peroxide decomposition. Thus, the catalytic activity can be correlated to the d-electron density for the transition metal cations.

  3. A comparison of the bonding in the second-row transition-metal oxides and carbenes

    NASA Astrophysics Data System (ADS)

    Siegbahn, Per E. M.

    1993-01-01

    Calculations including electron correlation of all valence electrons have been performed for the sequence of second-row transition-metal oxides and carbenes. For the atoms to the right the bond strengths of the carbenes and the oxides are similar while for the atoms to the left the oxide bond strengths are much larger. The origin of this difference is the interaction between the oxygen lone pairs and empty 4d orbitals on the metal. With the large donation of electrons from the oxygen lone pair to the metal for the atoms to the left, the bonding can almost be described as triple bond formation for YO, ZrO and NbO. For MoO, where a 4d ? orbital is singly occupied on the metal, the bond strength is much smaller than for the oxides to the left. For the metal carbenes two covalent bonds are formed. The ground state spin for the oxides to the right is higher than for the corresponding carbenes, which can be explained by the presence of the ? degeneracy for the oxides. The relevance of the present results for the epoxidation and the olefin metathesis reactions are discussed.

  4. Chemistry of Sulfur Oxides on Transition Metals. III. Oxidation of SO2 and Self-Diffusion of O, SO2, and SO3 on Pt(111)

    E-print Network

    Lin, Xi

    Chemistry of Sulfur Oxides on Transition Metals. III. Oxidation of SO2 and Self-Diffusion of O, SO2 to be an effective SO2 oxidation and reduction catalyst. Interest in the chemistry of sulfur oxides on transition that underlies NOx storage also operate on the sulfur oxides, so that NOx storage activity is readily poisoned

  5. Electronic structure at transition metal phthalocyanine-transition metal oxide interfaces: Cobalt phthalocyanine on epitaxial MnO films

    SciTech Connect

    Glaser, Mathias; Peisert, Heiko Adler, Hilmar; Aygül, Umut; Ivanovic, Milutin; Chassé, Thomas; Nagel, Peter; Merz, Michael; Schuppler, Stefan

    2015-03-14

    The electronic structure of the interface between cobalt phthalocyanine (CoPc) and epitaxially grown manganese oxide (MnO) thin films is studied by means of photoemission (PES) and X-ray absorption spectroscopy (XAS). Our results reveal a flat-lying adsorption geometry of the molecules on the oxide surface which allows a maximal interaction between the ?-system and the substrate. A charge transfer from MnO, in particular, to the central metal atom of CoPc is observed by both PES and XAS. The change of the shape of N-K XAS spectra at the interface points, however, to the involvement of the Pc macrocycle in the charge transfer process. As a consequence of the charge transfer, energetic shifts of MnO related core levels were observed, which are discussed in terms of a Fermi level shift in the semiconducting MnO films due to interface charge redistribution.

  6. Electrical conductivity in oxygen-deficient phases of transition metal oxides from first-principles calculations.

    SciTech Connect

    Bondi, Robert James; Desjarlais, Michael Paul; Thompson, Aidan Patrick; Brennecka, Geoffrey L.; Marinella, Matthew

    2013-09-01

    Density-functional theory calculations, ab-initio molecular dynamics, and the Kubo-Greenwood formula are applied to predict electrical conductivity in Ta2Ox (0x5) as a function of composition, phase, and temperature, where additional focus is given to various oxidation states of the O monovacancy (VOn; n=0,1+,2+). Our calculations of DC conductivity at 300K agree well with experimental measurements taken on Ta2Ox thin films and bulk Ta2O5 powder-sintered pellets, although simulation accuracy can be improved for the most insulating, stoichiometric compositions. Our conductivity calculations and further interrogation of the O-deficient Ta2O5 electronic structure provide further theoretical basis to substantiate VO0 as a donor dopant in Ta2O5 and other metal oxides. Furthermore, this dopant-like behavior appears specific to neutral VO cases in both Ta2O5 and TiO2 and was not observed in other oxidation states. This suggests that reduction and oxidation reactions may effectively act as donor activation and deactivation mechanisms, respectively, for VO0 in transition metal oxides.

  7. On-site screened Coulomb interactions for localized electrons in transition metal oxides and defect systems

    NASA Astrophysics Data System (ADS)

    Shih, Bi-Ching; Zhang, Peihong; Department of Physics Team

    2011-03-01

    Electronic and structural properties of strongly correlated material systems are largely determined by the strength of the on-site Coulomb interaction. Theoretical models devised to capture the physics of strongly correlated materials usually involve screened Coulomb interactions as adjustable parameters. We present first-principles results for the screened on-site Coulomb and exchange energy for transition metal oxides. The dielectric screening is calculated within the random phase approximation and the localized electrons are represented by maximally localized Wannier functions. We further extend our study to calculate on-site Coulomb interactions for localized defect states in semiconductors. We acknowledge the computational support provided by the Center for Computational Research at the University at Buffalo, SUNY. This work is supported by the National Science Foundation under Grant No. DMR-0946404 and by the Department of Energy under Grant No. DE-SC0002623.

  8. Onset conditions for gas phase reaction and nucleation in the CVD of transition metal oxides

    NASA Technical Reports Server (NTRS)

    Collins, J.; Rosner, D. E.; Castillo, J.

    1992-01-01

    A combined experimental/theoretical study is presented of the onset conditions for gas phase reaction and particle nucleation in hot substrate/cold gas CVD of transition metal oxides. Homogeneous reaction onset conditions are predicted using a simple high activation energy reacting gas film theory. Experimental tests of the basic theory are underway using an axisymmetric impinging jet CVD reactor. No vapor phase ignition has yet been observed in the TiCl4/O2 system under accessible operating conditions (below substrate temperature Tw = 1700 K). The goal of this research is to provide CVD reactor design and operation guidelines for achieving acceptable deposit microstructures at the maximum deposition rate while simultaneously avoiding homogeneous reaction/nucleation and diffusional limitations.

  9. Neutron diffraction studies of nickel-containing perovskite oxide catalysts exposed to autothermal reforming environments.

    SciTech Connect

    Mawdsley, J. R.; Vaughey, J. T.; Krause, T. R.; Chemical Sciences and Engineering Division

    2009-10-27

    Six nickel-containing perovskite oxides (La{sub 1-x}Sr{sub x})M{sub 0.9}Ni{sub 0.1}O{sub 3{+-}{delta}}, where x = 0 or 0.2 and M = Cr, Fe, or Mn were used to catalyze the autothermal reforming of isooctane (C{sub 8}H{sub 18}) into a hydrogen-rich gas during short-term tests at 700 C. To determine the phase stability of the samples in the reducing environment of the reforming reactor, characterization studies of the as-prepared and tested perovskite samples were conducted using powder X-ray diffraction, powder neutron diffraction, transmission electron microscopy, and scanning electron microscopy. We determined that the reducing conditions of the microreactor caused metallic nickel to form in all six compositions. However, the extent of the nickel loss from the perovskite lattices varied: the chromium-containing compositions lost the least nickel, compared to the manganese- and iron-containing compositions, and the strontium-free compositions lost more nickel than their strontium-containing analogs. Five of the six perovskite compositions tested showed no breakdown of the perovskite lattice despite the loss of nickel from the B-sites, producing only the third example of a B-cation-deficient, 3d transition-metal-containing perovskite.

  10. Methane Activation by Transition-Metal Oxides, MOx (M ) Cr, Mo, W; x ) 1, 2, 3) Xin Xu,# Francesco Faglioni, and William A. Goddard, III*

    E-print Network

    Goddard III, William A.

    Methane Activation by Transition-Metal Oxides, MOx (M ) Cr, Mo, W; x ) 1, 2, 3) Xin Xu,# Francesco a MoO3/HZSM-5 catalyst stimulated us to examine methane activation by the transition-metal oxide with negligible activation barrier and is predicted to be the most reactive compound of this class toward methane

  11. Calculated Momentum Dependence of Zhang-Rice States in Transition Metal Oxides Alexey Gordienko,1,2

    E-print Network

    Savrasov, Sergej Y.

    Calculated Momentum Dependence of Zhang-Rice States in Transition Metal Oxides Quan Yin,1 Alexey of the lowest occupied electronic states are associated with the Zhang-Rice singlets in cuprates photoemission experiments including the decrease of the spectral weight of the Zhang­Rice band as it approaches

  12. Investigation of coordination changes in substituted transition-metal oxides by K-edge XANES: beyond the pre-edge

    SciTech Connect

    Gaultois, Michael W.; Greedan, John E.; Grosvenor, Andrew P.

    2011-10-25

    Transition-metal oxides are important materials whose properties can be tuned through selective substitution of the constituent elements. For oxygen deficient materials, substitution can lead to variations in coordination number (CN). To understand these changes in CN, the pre-edge peak intensity, resulting primarily from a 1s to n-1d transition, from first-row transition-metal K-edge XANES spectra can be used. However, investigation of these peaks from spectra of second-row transition-metals can be difficult owing to lower spectral resolutions. It is shown here, through examination of Ca{sub 2}Fe{sub 2-x}Ga{sub x}O{sub 5}, SrFe{sub 1-x}Zr{sub x}O{sub 3-{delta}}, and (ZrO{sub 2}){sub x}(SiO{sub 2}){sub 1-x}, that changes in CN also lead to significant variations of the main absorption edge.

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

    SciTech Connect

    Das, Supriyo

    2010-05-16

    Oxide compounds containing the transition metal vanadium (V) have attracted a lot of attention in the field of condensed matter physics owing to their exhibition of interesting properties including metal-insulator transitons, structural transitions, ferromagnetic and antiferromagnetic orderings, and heavy fermion behavior. Binary vanadium oxides V{sub n}O{sub 2n-1} where 2 {le} n {le} 9 have triclinic structures and exhibit metal-insulator and antiferromagnetic transitions. The only exception is V{sub 7}O{sub 13} which remains metallic down to 4 K. The ternary vanadium oxide LiV{sub 2}O{sub 4} has the normal spinel structure, is metallic, does not undergo magnetic ordering and exhibits heavy fermion behavior below 10 K. CaV{sub 2}O{sub 4} has an orthorhombic structure with the vanadium spins forming zigzag chains and has been suggested to be a model system to study the gapless chiral phase. These provide great motivation for further investigation of some known vanadium compounds as well as to explore new vanadium compounds in search of new physics. This thesis consists, in part, of experimental studies involving sample preparation and magnetic, transport, thermal, and x-ray measurements on some strongly correlated eletron systems containing the transition metal vanadium. The compounds studied are LiV{sub 2}O{sub 4}, YV{sub 4}O{sub 8}, and YbV{sub 4}O{sub 8}. The recent discovery of superconductivity in RFeAsO{sub 1-x}F{sub x} (R = La, Ce, Pr, Gd, Tb, Dy, Sm, and Nd), and AFe{sub 2}As{sub 2} (A = Ba, Sr, Ca, and Eu) doped with K, Na, or Cs at the A site with relatively high T{sub c} has sparked tremendous activities in the condensed matter physics community and a renewed interest in the area of superconductivity as occurred following the discovery of the layered cuprate high T{sub c} superconductors in 1986. To discover more superconductors with hopefully higher T{sub c}'s, it is extremely important to investigate compounds having crystal structures related to the compounds showing high T{sub c} superconductivity. Along with the vanadium oxide compounds described before, this thesis describes our investigations of magnetic, structural, thermal and transport properties of EuPd{sub 2}Sb{sub 2} single crystals which have a crystal structure closely related to the AFe{sub 2}As{sub 2} compounds and also a study of the reaction kinetics of the formation of LaFeAsO{sub 1-x}F{sub x}.

  14. Photo-oxidation of Sb(III) in the seawater by marine phytoplankton-transition metals-light system.

    PubMed

    Li, Shun-Xing; Zheng, Feng-Ying; Hong, Hua-Sheng; Deng, Nan-Sheng; Zhou, Xia-Yi

    2006-11-01

    The photo-oxidation of Sb(III) to Sb(V) by marine microalgae (diatom, green and red algae) with or without the presence of transition metals (Fe(III), Cu(II) and Mn(II)). The influence of marine phytoplankton on the photochemistry of antimony was confirmed for the first time. The conversion ratio of Sb(III) to Sb(V) increased with increasing algae concentration and irradiation time. Different species of marine phytoplankton were found to have different photo-oxidizing abilities. The photochemical redox of transition metals could induce the species transformation of antimony. After photo-induced oxidation by marine phytoplankton and transition metals, the ratio of Sb(V) to Sb(III) was in the range of 1.07-5.48 for six algae (Tetraselmis levis, Chlorella autotrophica, Nannochloropsis sp., Tetraselmis subcordiformis, Phaeodactylum tricornutum, and Porphyridium purpureum), and only 0.92 for Dunaliella salina. The distribution of antimony in the sunlit surface seawater was greatly affected by combined effects of marine phytoplankton (main contributor) and transition metals; both synergistic and antagonistic effects were observed. The results provided further insights into the distribution of Sb(III) and Sb(V) and the biogeochemical cycle of antimony, and have significant implications for the risk assessment of antimony in the sunlit surface seawater. PMID:16735057

  15. Unravelling structural ambiguities in lithium- and manganese-rich transition metal oxides

    NASA Astrophysics Data System (ADS)

    Shukla, Alpesh Khushalchand; Ramasse, Quentin M.; Ophus, Colin; Duncan, Hugues; Hage, Fredrik; Chen, Guoying

    2015-10-01

    Although Li- and Mn-rich transition metal oxides have been extensively studied as high-capacity cathode materials for Li-ion batteries, the crystal structure of these materials in their pristine state is not yet fully understood. Here we apply complementary electron microscopy and spectroscopy techniques at multi-length scale on well-formed Li1.2(Ni0.13Mn0.54Co0.13)O2 crystals with two different morphologies as well as two commercially available materials with similar compositions, and unambiguously describe the structural make-up of these samples. Systematically observing the entire primary particles along multiple zone axes reveals that they are consistently made up of a single phase, save for rare localized defects and a thin surface layer on certain crystallographic facets. More specifically, we show the bulk of the oxides can be described as an aperiodic crystal consisting of randomly stacked domains that correspond to three variants of monoclinic structure, while the surface is composed of a Co- and/or Ni-rich spinel with antisite defects.

  16. Hydrazine reduction of transition metal oxides - In situ characterization using X-ray photoelectron spectroscopy

    NASA Technical Reports Server (NTRS)

    Littrell, D. M.; Tatarchuk, B. J.

    1986-01-01

    The transition metal oxides (TMOs) V2O5, FeO3, Co3O4, NiO, CuO, and ZnO were exposed to hydrazine at various pressures. The metallic surfaces were surveyed by in situ X-ray photoelectron spectroscopy to determine the irrelative rate of reduction by hydrazine. The most easily reducible oxide, CuO, could be reduced to the metallic state at room temperature and 10 to the -6th torr. The reaction is first order with respect to CuO, with an activation energy of about 35 kJ/mol. Two types of adsorption were seen to occur at 295 K: (1) a reversible component in which the measured N:Cu ratio increased to 0.60 at hydrazine pressures up to 0.5 torr, and (2) an irreversible component, with a N:Cu ratio of 0.28, which could not be removed by extended vacuum pumping. The results of this study are useful for the identification of TMO's that can be used as solid neatallizers of hydrazine spills, and for the preparation of metal surfaces for electroplating and evaporative thin-film coating.

  17. Unravelling structural ambiguities in lithium- and manganese-rich transition metal oxides.

    PubMed

    Shukla, Alpesh Khushalchand; Ramasse, Quentin M; Ophus, Colin; Duncan, Hugues; Hage, Fredrik; Chen, Guoying

    2015-01-01

    Although Li- and Mn-rich transition metal oxides have been extensively studied as high-capacity cathode materials for Li-ion batteries, the crystal structure of these materials in their pristine state is not yet fully understood. Here we apply complementary electron microscopy and spectroscopy techniques at multi-length scale on well-formed Li1.2(Ni0.13Mn0.54Co0.13)O2 crystals with two different morphologies as well as two commercially available materials with similar compositions, and unambiguously describe the structural make-up of these samples. Systematically observing the entire primary particles along multiple zone axes reveals that they are consistently made up of a single phase, save for rare localized defects and a thin surface layer on certain crystallographic facets. More specifically, we show the bulk of the oxides can be described as an aperiodic crystal consisting of randomly stacked domains that correspond to three variants of monoclinic structure, while the surface is composed of a Co- and/or Ni-rich spinel with antisite defects. PMID:26510508

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

    SciTech Connect

    Lai-Sheng Wang

    2009-07-07

    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).

  19. Influence of perovskite termination on oxide heteroepitaxy D. A. Schmidta

    E-print Network

    Olmstead, Marjorie

    Influence of perovskite termination on oxide heteroepitaxy D. A. Schmidta Department of Physics, regardless of termination, indicating that the substrate cations and perovskite surface polarity play little- monly used substrate for growth of high Tc super- conductors1­4 and other perovskite-based materials,5

  20. Thermodynamic stability and activity volcano for perovskite-based oxide as OER catalyst

    E-print Network

    Rong, Xi, S.M. Massachusetts Institute of Technology

    2014-01-01

    Design of efficient and cost-effective catalysts for the oxygen evolution reaction (OER) is crucial for the development of electrochemical conversion technologies. Recent experiments show that perovskite transition-metal ...

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

    SciTech Connect

    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

    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.

  2. Rovibronically Selected and Resolved Laser Photoionization and Photoelectron Studies of Transition Metal Carbides, Nitrides, and Oxides.

    NASA Astrophysics Data System (ADS)

    Luo, Zhihong; Chang, Yih-Chung; Huang, Huang; Ng, Cheuk-Yiu

    2014-06-01

    Transition metal (M) carbides, nitrides, and oxides (MX, X = C, N, and O) are important molecules in astrophysics, catalysis, and organometallic chemistry. The measurements of the ionization energies (IEs), bond energies, and spectroscopic constants for MX/MX+ in the gas phase by high-resolution photoelectron methods represent challenging but profitable approaches to gain fundamental understandings of the electronic structures and bonding properties of these compounds and their cations. We have developed a two-color laser excitation scheme for high-resolution pulse field ionization photoelectron (PFI-PE) measurements of MX species. By exciting the neutral MX species to a single rovibronic state using a visible laser prior to photoionization by a UV laser, we have obtained fully rotational resolved PFI-PE spectra for TiC+, TiO+, VCH+, VN+, CoC+, ZrO+, and NbC+. The unambiguous rotational assignments of these spectra have provided highly accurate IE values for TiC, TiO, VCH, VN, CoC, ZrO, and NbC, and spectroscopic constants for their cations.

  3. Transition Metal Dopants Essential for Producing Ferromagnetism in Metal Oxide Nanoparticles

    SciTech Connect

    Johnson, Lydia; Thurber, Aaron P.; Anghel, Josh; Sabetian, Maryam; Engelhard, Mark H.; Tenne, D.; Hanna, Charles; Punnoose, Alex

    2010-08-13

    Recent claims that ferromagnetism can be produced in nanoparticles of metal oxides without the presence of transition metal dopants has been refuted in this work by investigating 62 high quality well-characterized nanoparticle samples of both undoped and Fe doped (0-10% Fe) ZnO. The undoped ZnO nanoparticles showed zero or negligible magnetization, without any dependence on the nanoparticle size. However, chemically synthesized Zn??xFexO nanoparticles showed clear ferromagnetism, varying systematically with Fe concentration. Furthermore, the magnetic properties of Zn??xFexO nanoparticles showed strong dependence on the reaction media used to prepare the samples. The zeta potentials of the Zn??xFexO nanoparticles prepared using different reaction media were significantly different, indicating strong differences in the surface structure. Electron paramagnetic resonance studies clearly showed that the difference in the ferromagnetic properties of Zn??xFexO nanoparticles with different surface structures originate from differences in the fraction of the doped Fe³? ions that are coupled ferromagnetically.

  4. A comparative study of layered transition metal oxide cathodes for application in sodium-ion battery.

    PubMed

    Hasa, Ivana; Buchholz, Daniel; Passerini, Stefano; Hassoun, Jusef

    2015-03-11

    Herein, we report a study on P-type layered sodium transition metal-based oxides with a general formula of NaxMO2 (M = Ni, Fe, Mn). We synthesize the materials via coprecipitation followed by annealing in air and rinsing with water, and we examine the electrodes as cathodes for sodium-ion batteries using a propylene carbonate-based electrolyte. We fully investigate the effect of the Ni-to-Fe ratio, annealing temperature, and sodium content on the electrochemical performances of the electrodes. The impact of these parameters on the structural and electrochemical properties of the materials is revealed by X-ray diffraction, scanning electron microscopy, and cyclic voltammetry, respectively. The suitability of this class of P-type materials for sodium battery application is finally demonstrated by cycling tests revealing an excellent electrochemical performance in terms of delivered capacity (i.e., about 200 mAh g(-1)) and charge-discharge efficiency (approaching 100%). PMID:25692933

  5. Improved layered mixed transition metal oxides for Li-ion batteries

    SciTech Connect

    Doeff, Marca M.; Conry, Thomas; Wilcox, James

    2010-03-05

    Recent work in our laboratory has been directed towards development of mixed layered transition metal oxides with general composition Li[Ni, Co, M, Mn]O2 (M=Al, Ti) for Li ion battery cathodes. Compounds such as Li[Ni1/3Co1/3Mn1/3]O2 (often called NMCs) are currently being commercialized for use in consumer electronic batteries, but the high cobalt content makes them too expensive for vehicular applications such as electric vehicles (EV), plug-in hybrid electric vehicles (PHEVs), or hybrid electric vehicles (HEVs). To reduce materials costs, we have explored partial or full substitution of Co with Al, Ti, and Fe. Fe substitution generally decreases capacity and results in poorer rate and cycling behavior. Interestingly, low levels of substitution with Al or Ti improve aspects of performance with minimal impact on energy densities, for some formulations. High levels of Al substitution compromise specific capacity, however, so further improvements require that the Ni and Mn content be increased and Co correspondingly decreased. Low levels of Al or Ti substitution can then be used offset negative effects induced by the higher Ni content. The structural and electrochemical characterization of substituted NMCs is presented in this paper.

  6. Carrier behavior in special multilayer device composed of different transition metal oxide-based intermediate connectors

    SciTech Connect

    Deng, Yan-Hong; Chen, Xiang-Yu E-mail: xychen@suda.edu.cn; Ou, Qing-Dong; Wang, Qian-Kun; Jiang, Xiao-Cheng; Zhang, Dan-Dan; Li, Yan-Qing E-mail: xychen@suda.edu.cn

    2014-06-02

    The impact of illumination on the connection part of the tandem organic light-emitting diodes was studied by using a special organic multilayer sample consisted of two organic active layers coupled with different transition metal oxide (TMO)-based intermediate connectors (ICs). Through measuring the current density-voltage characteristic, interfacial electronic structures, and capacitance-voltage characteristic, we observe an unsymmetrical phenomenon in current density-voltage and capacitance-voltage curves of Mg:Alq{sub 3}/MoO{sub 3} and MoO{sub 3} composed devices, which was induced by the charge spouting zone near the ICs region and the recombination state in the MoO{sub 3} layer. Moreover, Mg:Alq{sub 3}/MoO{sub 3} composed device displays a photovoltaic effect and the V{sub oc} shifts to forward bias under illumination. Our results demonstrate that the TMO-based IC structure coupled with photovoltaic effect can be a good approach for the study of photodetector, light sensor, and so on.

  7. High-resolution structural studies of ultra-thin magnetic, transition metal overlayers and two-dimensional transition metal oxides using synchrotron radiation

    SciTech Connect

    Kellar, S.A.

    1997-05-01

    This thesis report the surface-structure determination of three, ultra-thin magnetic transition-metal films, Fe/Au(100), Mn/Ni(100), and Mn/Cu(100) using Angle-Resolved Photoemission Extended Fine Structure (ARPEFS) and photoelectron holography. These structural studies are the first to use non-s initial states in the ARPEFS procedure. This thesis also reports an ARPEFS surface-structure determination of a two-dimensional transition-metal oxide, [(1 x 1)O/W(110)] x 12. The authors have analyzed the ARPFES signal from the Au 4f{sub 7/5} core level of the Au(1 ML)/Fe(15 ML)/Au(100) system. The analysis shows that the Fe grows layer by layer with one monolayer of gold, acting as a surfactant, remaining on top of the growing Fe layers. These surface gold atoms sit in the four-fold hollow site, 1.67 {+-} 0.02 A above the iron surface. The grown Fe layer is very much like the bulk, bcc iron, with an interlayer spacing of 1.43 {+-} 0.03 A. Analysis of the Mn 3p ARPEFS signals from c(2 x 2)Mn/Ni(100) and c(2 x 2)Mn/Cu(100) shows that the Mn forms highly corrugated surface alloys. The corrugation of the Mn/Ni(100) and Mn/Cu(100) systems are 0.24 {+-} 0.02 A and 0.30 {+-} 0.04 A respectively. In both cases the Mn is sticking above the plane of the surface substrate atoms. For the Mn/Ni(100) system the first layer Ni is contracted 4% from the bulk value. The Mn/Cu(100) system shows bulk spacing for the substrate Cu. Photoelectron holography shows that the Mn/Ni interface is very abrupt with very little Mn leaking into the second layer, while the Mn/Cu(100) case has a significant amount of Mn leaking into the second layer. A new, five-element electrostatic electron lens was developed for hemispherical electron-energy analyzers. This lens system can be operated at constant transverse or constants angular magnification, and has been optimized for use with the very small photon-spot sizes. Improvements to the hemispherical electron-energy analyzer are also discussed.

  8. Calibrating transition-metal energy levels and oxygen bands in first-principles calculations: Accurate prediction of redox potentials and charge transfer in lithium transition-metal oxides

    NASA Astrophysics Data System (ADS)

    Seo, Dong-Hwa; Urban, Alexander; Ceder, Gerbrand

    2015-09-01

    Transition-metal (TM) oxides play an increasingly important role in technology today, including applications such as catalysis, solar energy harvesting, and energy storage. In many of these applications, the details of their electronic structure near the Fermi level are critically important for their properties. We propose a first-principles-based computational methodology for the accurate prediction of oxygen charge transfer in TM oxides and lithium TM (Li-TM) oxides. To obtain accurate electronic structures, the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional is adopted, and the amount of exact Hartree-Fock exchange (mixing parameter) is adjusted to reproduce reference band gaps. We show that the HSE06 functional with optimal mixing parameter yields not only improved electronic densities of states, but also better energetics (Li-intercalation voltages) for LiCo O2 and LiNi O2 as compared to the generalized gradient approximation (GGA), Hubbard U corrected GGA (GGA +U ), and standard HSE06. We find that the optimal mixing parameters for TM oxides are system specific and correlate with the covalency (ionicity) of the TM species. The strong covalent (ionic) nature of TM-O bonding leads to lower (higher) optimal mixing parameters. We find that optimized HSE06 functionals predict stronger hybridization of the Co 3 d and O 2 p orbitals as compared to GGA, resulting in a greater contribution from oxygen states to charge compensation upon delithiation in LiCo O2 . We also find that the band gaps of Li-TM oxides increase linearly with the mixing parameter, enabling the straightforward determination of optimal mixing parameters based on GGA (? =0.0 ) and HSE06 (? =0.25 ) calculations. Our results also show that G0W0@GGA +U band gaps of TM oxides (M O ,M =Mn ,Co ,Ni ) and LiCo O2 agree well with experimental references, suggesting that G0W0 calculations can be used as a reference for the calibration of the mixing parameter in cases when no experimental band gap has been reported.

  9. Experimental bandstructure of the 5 d transition metal oxide IrO2

    NASA Astrophysics Data System (ADS)

    Kawasaki, Jason; Nie, Yuefeng; Uchida, Masaki; Schlom, Darrell; Shen, Kyle

    2015-03-01

    In the 5 d iridium oxides the close energy scales of spin-orbit coupling and electron-electron correlations lead to emergent quantum phenomena. Much research has focused on the ternary iridium oxides, e.g. the Ruddlesden-Poppers An + 1BnO3 n + 1 , which exhibit behavior from metal to antiferromagnetic insulator ground states, share common features with the cuprates, and may host a number of topological phases. The binary rutile IrO2 is another important 5 d oxide, which has technological importance for spintronics due to its large spin Hall effect and also applications in catalysis. IrO2 is expected to share similar physics as its perovskite-based cousins; however, due to bond-length distortions of the IrO6 octahedra in the rutile structure, the extent of similarities remains an open question. Here we use angle-resolved photoemission spectroscopy to perform momentum-resolved measurements of the electronic structure of IrO2 . IrO2 thin films were grown by molecular beam epitaxy on TiO2 (110) substrates using an Ir e-beam source and distilled ozone. Films were subsequently transferred through ultrahigh vacuum to a connected ARPES system. Combined with first-principles calculations we explore the interplay of spin-orbit coupling and correlations in IrO2 .

  10. First-principles study of nitric oxide oxidation on Pt(111) versus Pt overlayer on 3d transition metals

    SciTech Connect

    Arevalo, Ryan Lacdao; Escaño, Mary Clare Sison; Kasai, Hideaki

    2015-03-15

    Catalytic oxidation of NO to NO{sub 2} is a significant research interest for improving the quality of air through exhaust gas purification systems. In this paper, the authors studied this reaction on pure Pt and Pt overlayer on 3d transition metals using kinetic Monte Carlo simulations coupled with density functional theory based first principles calculations. The authors found that on the Pt(111) surface, NO oxidation proceeds via the Eley–Rideal mechanism, with O{sub 2} dissociative adsorption as the rate-determining step. The oxidation path via the Langmuir–Hinshelwood mechanism is very slow and does not significantly contribute to the overall reaction. However, in the Pt overlayer systems, the oxidation of NO on the surface is more thermodynamically and kinetically favorable compared to pure Pt. These findings are attributed to the weaker binding of O and NO on the Pt overlayer systems and the binding configuration of NO{sub 2} that promotes easier N-O bond formation. These results present insights for designing affordable and efficient catalysts for NO oxidation.

  11. High Content Screening in Zebrafish Speeds up Hazard Ranking of Transition Metal Oxide Nanoparticles

    PubMed Central

    Lin, Sijie; Zhao, Yan; Xia, Tian; Meng, Huan; Zhaoxia, Ji; Liu, Rong; George, Saji; Xiong, Sijing; Wang, Xiang; Zhang, Haiyuan; Pokhrel, Suman; Mädler, Lutz; Damoiseaux, Robert; Lin, Shuo; Nel, Andre E.

    2014-01-01

    Zebrafish is an aquatic organism that can be used for high content safety screening of engineered nanomaterials (ENMs). We demonstrate, for the first time, the use of high content bright-field and fluorescence-based imaging to compare the toxicological effect of transition metal oxide (CuO, ZnO, NiO and Co3O4) nanoparticles in zebrafish embryos and larvae. High content bright-field imaging demonstrated potent and dose-dependant hatching interference in the embryos, with the exception of Co3O4 which was relatively inert. We propose that the hatching interference was due to the shedding of Cu and Ni ions, compromising the activity of the hatching enzyme, ZHE1, similar to what we previously proposed for Zn2+. This hypothesis is based on the presence of metal–sensitive histidines in the catalytic center of this enzyme. Co-introduction of a metal ion chelator, diethylene triamine pentaacetic acid (DTPA), reversed the hatching interference of Cu, Zn and Ni. While neither the embryos nor larvae demonstrated morphological abnormalities, high content fluorescence-based imaging demonstrated that CuO, ZnO and NiO could induce increased expression of the heat shock protein 70:enhanced green fluorescence protein (hsp70:eGFP) in transgenic zebrafish larvae. Induction of this response by CuO required a higher nanoparticle dose than the amount leading to hatching interference. This response was also DTPA sensitive. In conclusion, we demonstrate that high content imaging of embryo development, morphological abnormalities and HSP70 expression can be used for hazard ranking and determining the dose-response relationships leading to ENM effects on the development of the zebrafish embryo. PMID:21851096

  12. Electrochemical study of lithiated transition metal oxide composite for single layer fuel cell

    NASA Astrophysics Data System (ADS)

    Hu, Huiqing; Lin, Qizhao; Muhammad, Afzal; Zhu, Bin

    2015-07-01

    This study analyzed the effect of various semiconductors of transition metal oxides in modified lithiated NiO on the electrochemical performance of a single layer fuel cell (SLFC). A typical ionic conductor Ce0.8Sm0.2O2-? (SDC) and three types of semiconductors Li0.3Ni0.6Cu0.07Sr0.03O2-? (LNCuS), Li0.3Ni0.6Mn0.07Sr0.03O2-? (LNMnS) and Li0.3Ni0.6Co0.07Sr0.03O2-? (LNCoS), were the fundamental components of the SLFCs. The components were characterized by using X-ray diffraction (XRD), a scanning electron microscope (SEM), and an energy-dispersive X-ray spectrometer (EDS). The stability of the synthesized materials was evaluated using thermal gravity analysis (TGA). The ohmic resistances at 500 °C were 0.36, 0.48 and 0.58 ? cm2 for 6SDC-4LNMnS, 6SDC-4LNCoS and 6SDC-4LNCuS, respectively. Among the three SLFCs, the single cell with 6SDC-4LNMnS achieves the highest power density (422 mW cm-2) but the lowest temperature stability, while the single cell with 6SDC-4LNCuS achieved the lowest power density (331 mW cm-2) but the highest temperature stability during the operation temperature.

  13. Structure-composition-activity relationships in transition-metal oxide and oxyhydroxide oxygen-evolution electrocatalysts

    NASA Astrophysics Data System (ADS)

    Trotochaud, Lena

    Solar water-splitting is a potentially transformative renewable energy technology. Slow kinetics of the oxygen evolution reaction (OER) limit the efficiency of solar-watersplitting devices, thus constituting a hurdle to widespread implementation of this technology. Catalysts must be stable under highly oxidizing conditions in aqueous electrolyte and minimally absorb light. A grand goal of OER catalysis research is the design of new materials with higher efficiencies enabled by comprehensive understanding of the fundamental chemistry behind catalyst activity. However, little progress has been made towards this goal to date. This dissertation details work addressing major challenges in the field of OER catalysis. Chapter I introduces the current state-of-the-art and challenges in the field. Chapter II highlights work using ultra-thin films as a platform for fundamental study and comparison of catalyst activity. Key results of this work are (1) the identification of a Ni0.9Fe0.1OOH catalyst displaying the highest OER activity in base to date and (2) that in base, many transition-metal oxides transform to layered oxyhydroxide materials which are the active catalysts. The latter result is critical in the context of understanding structure-activity relationships in OER catalysts. Chapter III explores the optical properties of these catalysts, using in situ spectroelectrochemistry to quantify their optical absorption. A new figure-of-merit for catalyst performance is developed which considers both optical and kinetic losses due to the catalyst and describes how these factors together affect the efficiency of composite semiconductor/catalyst photoanodes. In Chapter IV, the fundamental structure-composition-activity relationships in Ni1--xFexOOH catalysts are systematically investigated. This work shows that nearly all previous studies of Ni-based catalysts were likely affected by the presence of Fe impurities, a realization which holds significant weight for future study of Ni-based catalyst materials. Chapter V discusses the synthesis of tin-titanium oxide nanoparticles with tunable lattice constants. These materials could be used to make high-surface-area supports for thin layers of OER catalysts, which is important for maximizing catalyst surface area, minimizing the use of precious-metal catalysts, and optimizing 3D structure for enhanced mass/bubble transport. Finally, Chapter VI summarizes this work and outlines directions for future research.

  14. Electronic and Magnetic Properties of Double Perovskites and Oxide Interfaces

    NASA Astrophysics Data System (ADS)

    Erten, Onur

    Transition metal oxides exhibit a wide range of fascinating phenomena ranging from high Tc superconductivity to colossal magnetoresistance. In this thesis, we examine the novel electronic and magnetic properties of double perovskites and oxide interfaces. First we focus on Sr2FeMoO6 which has a half-metallic ground state and a ferrimagnetic Tc=420 K, well above the room temperature. There are very few half-metals in nature and along with its high Tc, Sr2FeMoO6 has enormous potential in spintronics applications. We develop a minimal model that couples the conduction electrons on Mo (4d1) to the core spins of Fe (3d5). Delocalization of conduction electrons and maximizing the kinetic energy drives the long-range magnetic order. "Integrating out" the conduction electrons, we derive a new effective Hamiltonian, H eff, only for the localized spins. Heff is unique to double perovskites, and with its peculiar double square root form, it is different from standard Heisenberg or Anderson-Hasegawa Hamiltonians. Using Heff, we perform the first 3D, finite temperature calculations of double perovskites, going well beyond previous mean field or small cluster calculations. Next we consider Sr2CrOsO6 which has the highest Tc among all perovskites with a net moment. Its insulating behavior is puzzling given that Cr and Os are in the 3d3 and 5d3 configurations, half filled in t2g orbitals. The net moment at low temperature is M(0)=0.75 muB and non-monotonic magnetization as a function of temperature are quite unusual. To address these questions, we organize the problem through the hierarchy of its energy scales. To deal with the highest energy scale, the charge sector, we develop a multi-band Hubbard model that has different on-site Coulomb correlations on the Cr and Os sites. We solve this model using slave-rotor mean field theory which captures the essentials of the metal-Mott insulator transition and goes well beyond Hartree-Fock. We find a new criterion for the Mott transition where the effective Coulomb correlation is determined by the geometric mean of the Coulomb correlations on Cr and Os. We show that the peculiar magnetic properties of SCOO can be explained through a weakly frustrated magnetic model. In the last chapter we focus on oxide interfaces, particularly LaAlO 3/SrTiO3 interface. Due to polar nature of LaAlO3, two dimensional electron gas is formed at the interface of these two band insulators. An exciting new development is the observation of robust magnetism which persists up to high temperatures ˜100 K. We present a microscopic theory where local moments are stabilized by crystal field splitting at the interface and strong Coulomb correlations. We find that conduction electrons with a gate-tunable Rashba spin-orbit coupling mediate ferromagnetic exchange with a twist. We predict that the zero- field ground state is a long-wavelength spiral. Its evolution in an external field accounts semi-quantitatively for torque magnetometry data and describes qualitative aspects of the scanning SQUID measurements.

  15. A study of bond-length fluctuations in transition metal oxides

    NASA Astrophysics Data System (ADS)

    Yan, Jiaqiang

    Bond-length fluctuations with different origins have been investigated by thermal conductivity measurement performed on La1.60-xNd 0.40SrxCuO4, RCoO3, and RVO3 single crystals grown by floating zone method. Thermal conductivity has been proved to be a sensitive probe to bond-length fluctuations in strongly-correlated transition-metal oxides. Superconductivity in cuprates occurs at a crossover from localized to itinerant electronic behavior. The segregation of localized spins and delocalized holes into hole-poor and hole-rich regions in La2-xSr xCuO4 induces bond-length fluctuations via a strong electron-lattice coupling. This bond-length fluctuation suppresses in-plane thermal conductivity due to charge fluctuations in this quasi-2D system. In the La1.60-x Nd0.40SrxCuO4 system, the low-temperature orthorhombic (LTO) phase transforms into a low-temperature-tetragonal (LTT) phase with decreasing temperature. The hole-rich regions order into static stripes in the LTT phase of La2-x-yNdySr xCuO4; this charge order revives the phonon contribution to the thermal conductivity. The phonon thermal conductivity in the normal state of LTT phase and the LTO phase of some underdoped compositions of LSCO calls for reconsideration of the role of bond-length fluctuations on superconducting pairing in different structures. Suppression of the phonon thermal conductivity in the Mott-Hubbard insulator RCoO3 is interpreted to be caused by the spin-state transition from the low-spin t6e0 ground state to a higher spin-state, either intermediate-spin t 5e1 or high-spin t4e2, with increasing temperature. RVO3 offers us a unique chance to study the bond-length fluctuations caused by strong spin-orbital-lattice coupling. An unusually strong orbital-lattice and spin-lattice coupling has been clearly demonstrated.

  16. Lifetime of combustion-generated environmentally persistent free radicals on Zn(II)O and other transition metal oxides

    PubMed Central

    Vejerano, Eric; Dellinger, Barry

    2014-01-01

    Previous studies indicated that Environmentally Persistent Free Radicals (EPFRs) are formed in the post-flame, cool zone of combustion. They result from the chemisorption of gas-phase products of incomplete combustion (particularly hydroxyl- and chlorine-substituted aromatics) on Cu(II)O, Fe(III)2O3, and Ni(II)O domains of particulate matter (fly ash or soot particles). This study reports our detailed laboratory investigation on the lifetime of EPFRs on Zn(II)O/silica surface. Similarly, as in the case of other transition metals, chemisorption of the adsorbate on the Zn(II)O surface and subsequent transfer of electron from the adsorbate to the metal forms a surface-bound EPFR and a reduced metal ion center. The EPFRs are stabilized by their interaction with the metal oxide domain surface. The half-lives of EPFRs formed on Zn(II)O domains were the longest observed among the transition metal oxides studied and ranged from 3 to 73 days. These half-lives were an order of magnitude longer than those formed on nickel and iron oxides, and were 2 orders of magnitude longer compared to the EPFRs on copper oxide which have half-lives only on the order of hours. The longest-lived radicals on Zn(II)O correspond to the persistency in ambient air particles of almost a year. The half-life of EPFRs was found to correlate with the standard reduction potential of the associated metal. PMID:22990982

  17. First-principles exploration of multiferroic oxides with double-perovskite structure

    NASA Astrophysics Data System (ADS)

    Oguchi, Tamio; Shishidou, Tatsuya; Uratani, Yoshitaka

    2006-03-01

    Multiferroics have attracted much attention recently because of their novel properties. There are a few known as ferromagnetic and ferroelectric materials, particularly with perovskite-type crystal structure. Ferroelectrics should be insulating and likely ionic. Furthermore, it is widely recognized that covalent bonds between the cation and anion orbitals are crucial to realize atomic displacements to a noncentrosymmetric structure. As for magnetism, most of magnetic perovskite oxides usually have an antiferromagnetic order (mostly frustrating) due to a superexchange coupling. According to the Kanamori-Goodenough rule for the superexchange coupling, certain combinations of the transition-metals ions (d^3-d^5 and d^3-d^8 configurations) may possibly give a ferromagnetic coupling by the 180^o superexchange mechanism. In this study, we explore possible co-existence of spontaneous electric polarization and ferromagnetic ordering from first principles, by focusing bismuth double-perovskite oxides Bi2BB'O6 (B, B' = 3d ions) as target materials. Ferromagnetic and ferrimagnetic solutions are obtained for cubic Bi2MnNiO6, Bi2CrFeO6 and Bi2CrCuO6 with nearly gapped electronic structure. Quite recently, Bi2MnNiO6 has been successfully synthesized by a high-pressure technique and revealed multiferroic properties. Possible multiferroic properties of Bi2MnNiO6 with the observed monoclinic structure are investigated in detail.

  18. Oxidation does not (always) kill reactivity of transition metals: solution-phase conversion of nanoscale transition metal oxides to phosphides and sulfides.

    PubMed

    Muthuswamy, Elayaraja; Brock, Stephanie L

    2010-11-17

    Unexpected reactivity on the part of oxide nanoparticles that enables their transformation into phosphides or sulfides by solution-phase reaction with trioctylphosphine (TOP) or sulfur, respectively, at temperatures of ?370 °C is reported. Impressively, single-phase phosphide products are produced, in some cases with controlled anisotropy and narrow polydispersity. The generality of the approach is demonstrated for Ni, Fe, and Co, and while manganese oxides are not sufficiently reactive toward TOP to form phosphides, they do yield MnS upon reaction with sulfur. The reactivity can be attributed to the small size of the precursor particles, since attempts to convert bulk oxides or even particles with sizes approaching 50 nm were unsuccessful. Overall, the use of oxide nanoparticles, which are easily accessed via reaction of inexpensive salts with air, in lieu of organometallic reagents (e.g., metal carbonyls), which may or may not be transformed into metal nanoparticles, greatly simplifies the production of nanoscale phosphides and sulfides. The precursor nanoparticles can easily be produced in large quantities and stored in the solid state without concern that "oxidation" will limit their reactivity. PMID:20964294

  19. Recent advances of lanthanum-based perovskite oxides for catalysis

    DOE PAGESBeta

    Zhu, Huiyuan; Zhang, Pengfei; Dai, Sheng

    2015-09-21

    There is a need to reduce the use of noble metal elements especially in the field of catalysis, where noble metals are ubiquitously applied. To this end, perovskite oxides, an important class of mixed oxide, have been attracting increasing attention for decades as potential replacements. Benefiting from the extraordinary tunability of their compositions and structures, perovskite oxides can be rationally tailored and equipped with targeted physical and chemical properties e.g. redox behavior, oxygen mobility, and ion conductivity for enhanced catalysis. Recently, the development of highly efficient perovskite oxide catalysts has been extensively studied. This review article summarizes the recent developmentmore »of lanthanum-based perovskite oxides as advanced catalysts for both energy conversion applications and traditional heterogeneous reactions.« less

  20. Epitaxial integration of perovskite-based multifunctional oxides on silicon q

    E-print Network

    Eom, Chang Beom

    Epitaxial integration of perovskite-based multifunctional oxides on silicon q Seung-Hyub Baek Epitaxial heterostructures of perovskite-type oxides have attracted much attention due to their enormous and multiferroics have been demonstrated in perovskite oxides. The combination of cations within perovskite unit

  1. Interaction at the silicon/transition metal oxide heterojunction interface and its effect on the photovoltaic performance.

    PubMed

    Liang, Zhimin; Su, Mingze; Zhou, Yangyang; Gong, Li; Zhao, Chuanxi; Chen, Keqiu; Xie, Fangyan; Zhang, Weihong; Chen, Jian; Liu, Pengyi; Xie, Weiguang

    2015-10-14

    The interfacial reaction and energy level alignment at the Si/transition metal oxide (TMO, including MoO3-x, V2O5-x, WO3-x) heterojunction are systematically investigated. We confirm that the interfacial reaction appears during the thermal deposition of TMO, with the reaction extent increasing from MoO3-x, to V2O5-x, and to WO3-x. The reaction causes the surface oxidation of silicon for faster electron/hole recombination, and the reduction of TMO for effective hole collection. The photovoltaic performance of the Si/TMO heterojunction devices is affected by the interface reaction. MoO3-x are the best hole selecting materials that induce least surface oxidation but strongest reduction. Compared with H-passivation, methyl group passivation is an effective way to reduce the interface reaction and improve the interfacial energy level alignment for better electron and hole collection. PMID:26422643

  2. Control of Octahedral Tilts and Magnetic Properties of Perovskite Oxide Heterostructures by Substrate Symmetry

    E-print Network

    Pennycook, Steve

    Control of Octahedral Tilts and Magnetic Properties of Perovskite Oxide Heterostructures, Nashville, Tennessee 37235, USA (Received 29 June 2010; published 23 November 2010) Perovskite transition functionalities of perovskites are also influenced by the deformations and distortions of the octahedral network

  3. High-pressure Synthesis and Magnetic Properties of 4d and 5d Transition-metal Oxides

    NASA Astrophysics Data System (ADS)

    Cheng, J.-G.

    2011-03-01

    The pressure effect on synthesis of oxides with perovskite A BO3 and perovskite-related structures has become more clear in recent years. The geometric tolerance factor t ? (A-O)/ ? 2 (B-O) measures the structural stability. High-pressure synthesis enlarges the range of the t factor where the perovskite structure can be stabilized. For the A BO3 compounds with t 1, high pressure reduces the t factor since the A-O bond is more compressible than the B-O bond. Therefore, perovskite would be the high-pressure phase for ambient-pressure polytype structures. However, the bonding compressibility argument is no longer valid for the ABO3 with t < 1 . Adt / dP 0 isnormallyobtainedfortlessthanbutverycloseto 1 , i . e . theorthorhombicdistortionbecomessmallerunderpressure . Forthosehighlydistortedperovskiteswithtfactorfarlessthanone , pressureenlargesfurthertheorthorhombicdistortionandeventuallyleadstoaphasetransitiontothepost - perovskitephase . Asfor < formula > < ? TeX , high pressure prefers the small-volume perovskite phase relative to a competitive pyrochlore phase . Understanding the pressure effect and the new capacity provided by a Walker-type multianvil press enabled us to expand the perovskite family and to obtain new phases of 4d and 5d oxides. Studies of these new 4d and 5d oxides allow us not only to address long-standing problems, but also to explore exotic physical properties. (1) In the perovskite (A= alkaline earth), we have completed the phase diagram from A= Ca to Sr and to Ba and also accounted for the A-cation size-variance effect. A systematic study of the Curie temperature and the critical behavior as a function of the average A-site size and the size variance as well as external high pressures reveals explicitly the crucial role of the lattice strain on the ferromagnetism. The mean-field critical behaviour near found previously in is not typical of these perovskite ruthenates. is completely suppressed by Pb doping in not due to the steric effect, but to the orbital hybridization between 6 s and . As the end member, metallic undergoes a first-order phase transition to a metallic Imma phase at . (2) A new polytype phase 5H has been synthesized under a narrow pressure range, which fits the structural sequence along with other polytypes 9R, 6H and 3C of t ~ . The ground states of these polytypes evolve from a ferromagnetic insulator with 3 in the 9R phase to a ferromagnetic metal with BaIrO in the 5H phase, and finally to an exchange-enhanced paramagnetic metal in the 6H phase, which may be close to a quantum critical point. (3) In the system, high pressure stabilizes the post-perovskite structure on the Ca side (x < 0.3), but favors the perovskite structure on the Sr side (x > 0.6). Refs. J.-G. Cheng, et al. PRB 80, 104430(2009); 80, 174426 (2009);81, 134412(2010); JACS 131, 7461(2009). Supported by NSF-DMR-0904282. Work under the supervision of Profs. J.-S. Zhou and J. B. Goodenough.

  4. Atomic-Resolution Visualization of Distinctive Chemical Mixing Behavior of Ni, Co and Mn with Li in Layered Lithium Transition-Metal Oxide Cathode Materials

    SciTech Connect

    Yan, Pengfei; Zheng, Jianming; Lv, Dongping; Wei, Yi; Zheng, Jiaxin; Wang, Zhiguo; Kuppan, Saravanan; Yu, Jianguo; Luo, Langli; Edwards, Danny J.; Olszta, Matthew J.; Amine, Khalil; Liu, Jun; Xiao, Jie; Pan, Feng; Chen, Guoying; Zhang, Jiguang; Wang, Chong M.

    2015-07-06

    Capacity and voltage fading of layer structured cathode based on lithium transition metal oxide is closely related to the lattice position and migration behavior of the transition metal ions. However, it is scarcely clear about the behavior of each of these transition metal ions. We report direct atomic resolution visualization of interatomic layer mixing of transition metal (Ni, Co, Mn) and lithium ions in layer structured oxide cathodes for lithium ion batteries. Using chemical imaging with aberration corrected scanning transmission electron microscope (STEM) and DFT calculations, we discovered that in the layered cathodes, Mn and Co tend to reside almost exclusively at the lattice site of transition metal (TM) layer in the structure or little interlayer mixing with Li. In contrast, Ni shows high degree of interlayer mixing with Li. The fraction of Ni ions reside in the Li layer followed a near linear dependence on total Ni concentration before reaching saturation. The observed distinctively different behavior of Ni with respect to Co and Mn provides new insights on both capacity and voltage fade in this class of cathode materials based on lithium and TM oxides, therefore providing scientific basis for selective tailoring of oxide cathode materials for enhanced performance.

  5. Semiconducting Transition-Metal Oxides Based on D5 Cations: Theory for MnO and Fe2O3

    SciTech Connect

    Peng, H.; Lany, S.

    2012-05-15

    Transition-metal oxides with partially filled d shells are typically Mott or charge-transfer insulators with notoriously poor transport properties due to large effective electron/hole masses or due to carrier self-trapping. Employing band-structure calculations and ab initio small-polaron theory for MnO and Fe{sub 2}O{sub 3}, we explore the potential of d{sup 5} oxides for achieving desirable semiconducting properties, e.g., in solar energy applications. The quantification of self-trapping energies and the trends with the coordination symmetry suggest strategies to overcome the main bottlenecks, i.e., the tendency for self-trapping of holes due to Mn(II) and of electrons due to Fe(III).

  6. Oxidation of Methanol on 2nd and 3rd Row Group VIII Transition Metals (Pt, Ir, Os, Pd, Rh, and Ru): Application to Direct Methanol

    E-print Network

    Goddard III, William A.

    Oxidation of Methanol on 2nd and 3rd Row Group VIII Transition Metals (Pt, Ir, Os, Pd, Rh, and Ru): Application to Direct Methanol Fuel Cells Jeremy Kua and William A. Goddard III* Contribution from functional theory (B3LYP)], we calculated the 13 most likely intermediate species for methanol oxidation

  7. High Performance Full Sodium-Ion Cell Based on a Nanostructured Transition Metal Oxide as Negative Electrode.

    PubMed

    López, María C; Aragón, María J; Ortiz, Gregorio F; Lavela, Pedro; Alcántara, Ricardo; Tirado, José L

    2015-10-12

    A novel design of a sodium-ion cell is proposed based on the use of nanocrystalline thin films composed of transition metal oxides. X-ray diffraction, Raman spectroscopy and electron microscopy were helpful techniques to unveil the microstructural properties of the pristine nanostructured electrodes. Thus, Raman spectroscopy revealed the presence of amorphous NiO, ?-Fe2 O3 (hematite) and ?-Fe2 O3 (maghemite). Also, this technique allowed the calculation of an average particle size of 23.4?Å in the amorphous carbon phase in situ generated on the positive electrode. The full sodium-ion cell performed with a reversible capacity of 100?mA?h?g(-1) at C/2 with an output voltage of about 1.8?V, corresponding to a specific energy density of about 180?W?h?kg(-1) . These promising electrochemical performances allow these transition metal thin films obtained by electrochemical deposition to be envisaged as serious competitors for future negative electrodes in sodium-ion batteries. PMID:26305272

  8. Self-interaction correction in multiple scattering theory: application to transition metal oxides

    SciTech Connect

    Daene, Markus W; Lueders, Martin; Ernst, Arthur; Diemo, Koedderitzsch; Temmerman, Walter M; Szotek, Zdzislawa; Wolfam, Hergert

    2009-01-01

    We apply to transition metal monoxides the self-interaction corrected (SIC) local spin density (LSD) approximation, implemented locally in the multiple scattering theory within the Korringa-Kohn-Rostoker (KKR) band structure method. The calculated electronic structure and in particular magnetic moments and energy gaps are discussed in reference to the earlier SIC results obtained within the LMTO-ASA band structure method, involving transformations between Bloch and Wannier representations to solve the eigenvalue problem and calculate the SIC charge and potential. Since the KKR can be easily extended to treat disordered alloys, by invoking the coherent potential approximation (CPA), in this paper we compare the CPA approach and supercell calculations to study the electronic structure of NiO with cation vacancies.

  9. Spectral observations of hole injection with transition metal oxides for an efficient organic light-emitting diode

    NASA Astrophysics Data System (ADS)

    Chiu, Tien-Lung; Chuang, Ya-Ting

    2015-02-01

    Transition metal oxides, such as molybdenum trioxide (MoO3), tungsten trioxide (WO3) and vanadium pent-oxide (V2O5), are well-known hole injection materials used for organic electronic devices. These materials promote work functions of anodes, reduce energy barriers, and facilitate hole transport at the interface between the inorganic anode and organic hole-transporting layer (HTL). In this study, we characterized the transmittance spectra and work function of these materials. Furthermore, we employed a hole-injection layer (HIL) in a blue phosphorescent organic light-emitting diode (OLED) to evaluate their hole-injection capacity by detecting the variation in the emission spectra. Thus, we utilized an OLED structure that has fast electron transporting dynamics to establish the recombination zone located at emitting layer and a partial HTL close to the anode. We used these three transition metal oxides individually as HILs sandwiched between the ITO anode and HTL and concluded that the strength of emissive light from the HTL was determined by their hole-injection capacity, depending on work function. The small amount of HTL emission light of the V2O5 OLED was explained by the high work function of 5.8?eV for the V2O5 film. However, the V2O5 OLED demonstrated the least favorable optoelectrical performance because of its low transmittance and high resistance of the V2O5 film. Ultimately, the 5?nm-MoO3 OLED exhibited the highest device performance because of its high material conductivity and transparency in the visible band.

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

    E-print Network

    Metz, Ricardo B.

    such as methanol has attracted great experimental and theoretical interest due to its importance as an industrial direct oxidation by nitrous oxide in a plasma,(6) oxidation of methane to a methyl ester with a platinum

  11. Fluorescence-based detection methodologies for nitric oxide using transition metal scaffolds

    E-print Network

    Hilderbrand, Scott A. (Scott Alan), 1976-

    2004-01-01

    Chapter 1. Fluorescence-Based Detection Methodologies for Nitric Oxide: A Review. Chapter 2. Cobalt Chemistry with Mixed Aminotroponimine Salicylaldimine Ligands: Synthesis, Characterization, and Nitric Oxide Reactivity. ...

  12. Single-step preparation and consolidation of reduced early-transition-metal oxide/metal n-type thermoelectric composites

    NASA Astrophysics Data System (ADS)

    Gaultois, Michael W.; Douglas, Jason E.; Sparks, Taylor D.; Seshadri, Ram

    2015-09-01

    Reduced early transition metal oxides/metal composites have been identified here as interesting thermoelectric materials. Numerous compositions in the Nb-rich portion of the WO3-Nb2O5 system have been studied, in composite formulations with elemental W. Spark plasma sintering (SPS) has been employed to achieve rapid preparation and consolidation of composite materials containing W metal precipitates with characteristic length scales that range from under 20 nm to a few microns, that exhibit thermal conductivities that are constant from 300 K to 1000 K, approximately 2.5 W m-1 K-1. Thermoelectric properties of these n-type materials were measured, and the highest-performing compositions were found to reach figure of merit zT values close to 0.1 at 950 K. The measurements point to higher zT values at yet-higher temperatures.

  13. Density Functional Theory and Beyond for Band-Gap Screening: Performance for Transition-Metal Oxides and Dichalcogenides.

    PubMed

    Li, Wenqing; Walther, Christian F J; Kuc, Agnieszka; Heine, Thomas

    2013-07-01

    The performance of a wide variety of commonly used density functionals, as well as two screened hybrid functionals (HSE06 and TB-mBJ), on predicting electronic structures of a large class of en vogue materials, such as metal oxides, chalcogenides, and nitrides, is discussed in terms of band gaps, band structures, and projected electronic densities of states. Contrary to GGA, hybrid functionals and GGA+U, both HSE06 and TB-mBJ are able to predict band gaps with an appreciable accuracy of 25% and thus allow the screening of various classes of transition-metal-based compounds, i.e., mixed or doped materials, at modest computational cost. The calculated electronic structures are largely unaffected by the choice of basis functions and software implementation, however, might be subject to the treatment of the core electrons. PMID:26583978

  14. Laser Desorption/Ionization of Transition Metal Atoms and Oxides from Solid Argon Lester Andrews,*, Andreas Rohrbacher, Christopher M. Laperle, and Robert E. Continetti

    E-print Network

    Continetti, Robert E.

    Laser Desorption/Ionization of Transition Metal Atoms and Oxides from Solid Argon Lester Andrews of the laser-ablated metal atoms and O2 in excess argon during condensation at 10 K, have been laser desorbed of organic acid typically used as a matrix in matrix- assisted laser desorption/ionization (MALDI) mass

  15. Chemistry of Sulfur Oxides on Transition Metals I: Configurations, Energetics, Orbital Analyses, and Surface Coverage Effects of SO2 on Pt(111)

    E-print Network

    Lin, Xi

    Chemistry of Sulfur Oxides on Transition Metals I: Configurations, Energetics, Orbital Analyses, respectively, are consistent with experimental observations. It is found that strong sulfur-metal bonds, sulfur-containing molecules, such as SO2, have highly poisonous effects on the automotive emission

  16. Development of biomimetic catalytic oxidation methods and non-salt methods using transition metal-based acid and base ambiphilic catalysts

    PubMed Central

    MURAHASHI, Shun-Ichi

    2011-01-01

    This review focuses on the development of ruthenium and flavin catalysts for environmentally benign oxidation reactions based on mimicking the functions of cytochrome P-450 and flavoenzymes, and low valent transition-metal catalysts that replace conventional acids and bases. Several new concepts and new types of catalytic reactions based on these concepts are described. PMID:21558760

  17. Enhanced catalytic complete oxidation of 1,2-dichloroethane over mesoporous transition metal-doped ?-Al2O3.

    PubMed

    Khaleel, Abbas; Nawaz, Muhammad

    2015-03-01

    High-surface-area mesoprous powders of ?-Al2O3 doped with Cu2+, Cr3+, and V3+ ions were prepared via a modified sol-gel method and were investigated as catalysts for the oxidation of chlorinated organic compounds. The composites retained high surface areas and pore volumes comparable with those of undoped ?-Al2O3 and the presence of the transition metal ions enhanced their surface acidic properties. The catalytic activity of the prepared catalysts in the oxidation of 1,2-dichloroethane (DCE) was studied in the temperature range of 250-400°C. The catalytic activity and product selectivity were strongly dependent on the presence and the type of dopant ion. While Cu2+- and Cr3+-containing catalysts showed 100% conversion at 300°C and 350°C, V3+-containing catalyst showed considerably lower conversion. Furthermore, while the major products of the reactions over ?-alumina were vinyl chloride (C2H3Cl) and hydrogen chloride (HCl) at all temperatures, Cu- and Cr-doped catalysts showed significantly stronger capability for deep oxidation to CO2. PMID:25766029

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

    NASA Astrophysics Data System (ADS)

    Kwon, Jang Yeon; Kyeong Jeong, Jae

    2015-02-01

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

  19. n-Type transition metal oxide as a hole extraction layer in PbS quantum dot solar cells.

    PubMed

    Gao, Jianbo; Perkins, Craig L; Luther, Joseph M; Hanna, Mark C; Chen, Hsiang-Yu; Semonin, Octavi E; Nozik, Arthur J; Ellingson, Randy J; Beard, Matthew C

    2011-08-10

    The n-type transition metal oxides (TMO) consisting of molybdenum oxide (MoO(x)) and vanadium oxide (V(2)O(x)) are used as an efficient hole extraction layer (HEL) in heterojunction ZnO/PbS quantum dot solar cells (QDSC). A 4.4% NREL-certified device based on the MoO(x) HEL is reported with Al as the back contact material, representing a more than 65% efficiency improvement compared with the case of Au contacting the PbS quantum dot (QD) layer directly. We find the acting mechanism of the hole extraction layer to be a dipole formed at the MoO(x) and PbS interface enhancing band bending to allow efficient hole extraction from the valence band of the PbS layer by MoO(x). The carrier transport to the metal anode is likely enhanced through shallow gap states in the MoO(x) layer. PMID:21688813

  20. Transition Metal-Free Visible Light-Driven Photoredox Oxidative Annulation of Arylamidines.

    PubMed

    Shen, Zi-Chao; Yang, Pan; Tang, Yu

    2016-01-01

    A fast catalytic synthesis of multisubstituted quinazolines from readily available amidines via visible light-mediated oxidative C(sp(3))-C(sp(2)) bond formation has been established. This reaction is a metal-free oxidative coupling catalyzed by a photoredox organocatalyst. The protocol features low catalyst loading (1 mol %). PMID:26641939

  1. Superconductors and Complex Transition Metal Oxides for Tunable THz Plasmonic Metamaterials

    SciTech Connect

    Singh, Ranjan; Xiong, Jie; Azad, Md A.; Yang, Hao; Trugman, Stuart A.; Jia, Quanxi; Taylor, Antoinette; Chen, Houtong

    2012-07-13

    The outline of this presentation are: (1) Motivation - Non-tunability of metal metamaterials; (2) Superconductors for temperature tunable metamaterials; (3) Ultrafast optical switching in superconductor metamaterials; (4) Controlling the conductivity with infrared pump beam; (5) Complex metal oxides as active substrates - Strontium Titanate; and (6) Conclusion. Conclusions are: (1) High Tc superconductors good for tunable and ultrafast metamaterials; (2) Large frequency and amplitude tunability in ultrathin superconductor films; (3) Such tunable properties cannot be accessed using metals; (4) Complex metal oxides can be used as active substrates - large tunability; (5) Complex oxides fail to address the issue of radiation losses in THz metamaterials.

  2. The detection of nitric oxide and its reactivity with transition metal thiolate complexes

    E-print Network

    Tennyson, Andrew Gregory

    2008-01-01

    Nitric oxide (NO) is a molecule that is essential for life and regulates both beneficial and harmful processes. Because this gaseous radical influences many aspects of health and disease, we wish to explore the relationship ...

  3. Mechanism of oxygen reduction reaction on transition metal oxide catalysts for high temperature fuel cells

    E-print Network

    La O', Gerardo Jose Cordova

    2008-01-01

    The solid oxide fuel cell (SOFC) with its high energy conversion efficiency, low emissions, silent operation and its ability to utilize commercial fuels has the potential to create a large impact on the energy landscape. ...

  4. Universal method for the fabrication of detachable ultrathin films of several transition metal oxides.

    PubMed

    Singh, Sherdeep; Festin, Miguel; Barden, Warren R T; Xi, Luan; Francis, James T; Kruse, Peter

    2008-11-25

    Ultrathin films are important nanoscale structures that are used extensively in a variety of technological contexts. However, it has traditionally been difficult and costly to fabricate detachable and purely inorganic high aspect ratio films with controlled thickness and good uniformity. Here we report a versatile method to make separable purely inorganic membranes of various metal oxides such as Nb(2)O(5), TiO(2), WO(3), and Ta(2)O(5) with thicknesses ranging from 30 to 150 nm. Fluoride ions are migrated through the oxide film and upon arrival at the oxide-metal interface form a sacrificial soluble oxyfluoride layer. Fluorine also plays a role in controlling the porosity of the films. The study exposes the mechanism behind the detachment process that is largely due to the fast migration of fluoride anions relative to oxygen anions. The resulting films have a wide range of potential applications as catalysts or catalyst supports, filtration membranes, sensors, and more. PMID:19206404

  5. Decomposition of Organometal Halide Perovskite Films on Zinc Oxide Nanoparticles.

    PubMed

    Cheng, Yuanhang; Yang, Qing-Dan; Xiao, Jingyang; Xue, Qifan; Li, Ho-Wa; Guan, Zhiqiang; Yip, Hin-Lap; Tsang, Sai-Wing

    2015-09-16

    Solution processed zinc oxide (ZnO) nanoparticles (NPs) with excellent electron transport properties and a low-temperature process is a viable candidate to replace titanium dioxide (TiO2) as electron transport layer to develop high-efficiency perovskite solar cells on flexible substrates. However, the number of reported high-performance perovskite solar cells using ZnO-NPs is still limited. Here we report a detailed investigation on the chemistry and crystal growth of CH3NH3PbI3 perovskite on ZnO-NP thin films. We find that the perovskite films would severely decompose into PbI2 upon thermal annealing on the bare ZnO-NP surface. X-ray photoelectron spectroscopy (XPS) results show that the hydroxide groups on the ZnO-NP surface accelerate the decomposition of the perovskite films. To reduce the decomposition, we introduce a buffer layer in between the ZnO-NPs and perovskite layers. We find that a commonly used buffer layer with small molecule [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) can slow down but cannot completely avoid the decomposition. On the other hand, a polymeric buffer layer using poly(ethylenimine) (PEI) can effectively separate the ZnO-NPs and perovskite, which allows larger crystal formation with thermal annealing. The power conversion efficiencies of perovskite photovoltaic cells are significantly increased from 6.4% to 10.2% by replacing PC61BM with PEI as the buffer layer. PMID:26280249

  6. Tunable Ultraviolet Photoresponse in Solution-Processed p-n Junction Photodiodes Based on Transition-Metal Oxides.

    PubMed

    Xie, Ting; Liu, Guannan; Wen, Baomei; Ha, Jong Y; Nguyen, Nhan V; Motayed, Abhishek; Debnath, Ratan

    2015-05-13

    Solution-processed p-n heterojunction photodiodes have been fabricated based on transition-metal oxides in which NiO and ternary Zn(1-x)Mg(x)O (x = 0-0.1) have been employed as p-type and n-type semiconductors, respectively. Composition-related structural, electrical, and optical properties are also investigated for all the films. It has been observed that the bandgap of Zn(1-x)Mg(x)O films can be tuned between 3.24 and 3.49 eV by increasing Mg content. The fabricated highly visible-blind p-n junction photodiodes show an excellent rectification ratio along with good photoresponse and quantum efficiency under ultraviolet (UV) illumination. With an applied reverse bias of 1 V and depending on the value of x, the maximum responsivity of the devices varies between 0.22 and 0.4 A/W and the detectivity varies between 0.17 × 10(12) and 2.2 × 10(12) cm?(Hz)(1/2)/W. The photodetectors show an excellent UV-to-visible rejection ratio. Compositional nonuniformity has been observed locally in the alloyed films with x = 0.1, which is manifested in photoresponse and X-ray analysis data. This paper demonstrates simple solution-processed, low cost, band tunable photodiodes with excellent figures of merit operated under low bias. PMID:25898025

  7. The Influence of Doping with Transition Metal Ions on the Structure and Magnetic Properties of Zinc Oxide Thin Films

    PubMed Central

    2014-01-01

    Zn1?xNixO (x = 0.03 ÷ 0.10) and Zn1?xFexO (x = 0.03 ÷ 0.15) thin films were synthesized by sol-gel method. The structure and the surface morphology of zinc oxide thin films doped with transition metal (TM) ions have been investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM). The magnetic studies were done using vibrating sample magnetometer (VSM) at room temperature. Experimental results revealed that the substitution of Ni ions in ZnO wurtzite lattice for the contents x = 0.03 ÷ 0.10 (Ni2+) leads to weak ferromagnetism of thin films. For Zn1?xFexO with x = 0.03 ÷ 0.05, the Fe3+ ions are magnetic coupling by superexchange interaction via oxygen ions in wurtzite structure. For x = 0.10 ÷ 0.15 (Fe3+) one can observe the increasing of secondary phase of ZnFe2O4 spinel. The Zn0.9Fe0.1O film shows a superparamagnetic behavior due to small crystallite sizes and the net spin magnetic moments arisen from the interaction between the iron ions through an oxygen ion in the spinel structure. PMID:24683324

  8. The influence of doping with transition metal ions on the structure and magnetic properties of zinc oxide thin films.

    PubMed

    Neamtu, Jenica; Volmer, Marius

    2014-01-01

    Zn1-x Ni x O (x = 0.03 ÷ 0.10) and Zn1-x Fe x O (x = 0.03 ÷ 0.15) thin films were synthesized by sol-gel method. The structure and the surface morphology of zinc oxide thin films doped with transition metal (TM) ions have been investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM). The magnetic studies were done using vibrating sample magnetometer (VSM) at room temperature. Experimental results revealed that the substitution of Ni ions in ZnO wurtzite lattice for the contents x = 0.03 ÷ 0.10 (Ni(2+)) leads to weak ferromagnetism of thin films. For Zn1-x Fe x O with x = 0.03 ÷ 0.05, the Fe(3+) ions are magnetic coupling by superexchange interaction via oxygen ions in wurtzite structure. For x = 0.10 ÷ 0.15 (Fe(3+)) one can observe the increasing of secondary phase of ZnFe2O4 spinel. The Zn0.9Fe0.1O film shows a superparamagnetic behavior due to small crystallite sizes and the net spin magnetic moments arisen from the interaction between the iron ions through an oxygen ion in the spinel structure. PMID:24683324

  9. Oxidative photoreactivity of mono-transition-metal functionalized lacunary Keggin anions.

    PubMed

    Dave, M; Streb, C

    2015-10-27

    A comparative study investigating the effects of metal substitution on the photocatalytic activity of metal oxide cluster anions is presented. The study shows that metal functionalization can be used to alter the photochemical properties of monolacunary tungstate - based Keggin clusters (?-[TM(H2O)SiW11O39](n-) (M = Co(2+), Cu(2+), Ni(2+), Mn(2+))). It is demonstrated that the photoactivity for the photooxidation of the model pollutant basic blue 41 is dependent of the type of metal employed and increases in the order Co < Cu < Ni < Mn under aerobic conditions and 390 nm monochromatic irradiation. A significant increase of the reaction rate is observed under aerated conditions compared with de-aerated conditions, suggesting that oxygen serves as a re-oxidant for the reduced clusters. Radical scavenging experiments suggest that the photocatalysis proceeds via formation of hydroxyl radicals. PMID:26467271

  10. Factors that Influence Cation Segregation at the Surfaces of Perovskite Oxides Wonyoung Lee and Bilge Yildiz

    E-print Network

    Yildiz, Bilge

    Factors that Influence Cation Segregation at the Surfaces of Perovskite Oxides Wonyoung Lee segregation, a detrimental process on the surface of perovskite cathodes (1). Motivated by those results, here separation. Introduction Cation segregation on the perovskite oxide surface imposes the significant impacts

  11. LETTER doi:10.1038/nature12622 Perovskite oxides for visible-light-absorbing

    E-print Network

    Rappe, Andrew M.

    LETTER doi:10.1038/nature12622 Perovskite oxides for visible-light-absorbing ferroelectric perovskites (with ABO3 composition) is due to the fundamental characteristics of the metal­ oxygen A­O and B cations enable the perovskite oxide to exhibitferroelectricity12 . Owing to a large difference

  12. High Performance Ceramic Interconnect Material for Solid Oxide Fuel Cells (SOFCs): Ca- and Transition Metal-doped Yttrium Chromite

    SciTech Connect

    Yoon, Kyung J.; Stevenson, Jeffry W.; Marina, Olga A.

    2011-10-15

    The effect of transition metal substitution on thermal and electrical properties of Ca-doped yttrium chromite was investigated in relation to use as a ceramic interconnect in high temperature solid oxide fuel cells (SOFCs). 10 at% Co, 4 at% Ni, and 1 at% Cu substitution on B-site of 20 at% Ca-doped yttrium chromite led to a close match of thermal expansion coefficient (TEC) with that of 8 mol% yttria-stabilized zirconia (YSZ), and a single phase Y0.8Ca0.2Cr0.85Co0.1Ni0.04Cu0.01O3 remained stable between 25 and 1100 degree C over a wide oxygen partial pressure range. Doping with Cu significantly facilitated densification of yttrium chromite. Ni dopant improved both electrical conductivity and dimensional stability in reducing environments, likely through diminishing the oxygen vacancy formation. Substitution with Co substantially enhanced electrical conductivity in oxidizing atmosphere, which was attributed to an increase in charge carrier density and hopping mobility. Electrical conductivity of Y0.8Ca0.2Cr0.85Co0.1Ni0.04Cu0.01O3 at 900 degree C is 57 S/cm in air and 11 S/cm in fuel (pO2=5×10^-17 atm) environments. Chemical compatibility of doped yttrium chromite with other cell components was verified at the processing temperatures. Based on the chemical and dimensional stability, sinterability, and thermal and electrical properties, Y0.8Ca0.2Cr0.85Co0.1Ni0.04Cu0.01O3 is suggested as a promising SOFC ceramic interconnect to potentially overcome technical limitations of conventional acceptor-doped lanthanum chromites.

  13. Synthesis, Characterization, and Catalytic Applications of Transition Metal Oxide/Carbonate Nanomaterials

    NASA Astrophysics Data System (ADS)

    Jin, Lei

    2011-12-01

    This thesis contains two parts: 1) Studies of novel synthesis methods and characterization of advanced functional manganese oxide octahedral molecular sieves (OMS) and their applications in Li/Air batteries, solvent free toluene oxidations, and ethane oxydehydrogenation (ODH) in the presence of CO2, recycling the green house gas. 2) Development of unique Ln2O2CO3 (Ln = rare earth) layered materials and ZnO/La2O2CO3 composites as clean energy biofuel catalysts. These parts are separated into five different focused topics included in this thesis. The first topic presents studies of catalytic activities of a single step synthesized gamma-MnO2 octahedral molecular sieve nano fiber in solvent free atmospheric oxidation of toluene with molecular oxygen. Solvent free atmospheric oxidation of toluene is a notoriously difficult liquid phase oxidation process due to the challenge of oxidizing sp³ hybridized carbon in inactive hydrocarbons. The synthesized gamma-MnO2 showed excellent catalytic activity and good selectivity under the mild atmospheric reflux system. Under optimized conditions, a 47.8% conversion of toluene, along with 57% selectivity of benzoic acid and 15% of benzaldehyde were obtained. The effects of reaction time, amount of catalyst and initiator, and the reusability of the catalyst were investigated. The second topic involves developing titanium containing gamma-MnO 2 (TM) hollow spheres as electrocatalysts in Li/Air Batteries. Li/air batteries have recently attracted interest because they have the largest theoretical specific energy (11,972 Wh.kg-1) among all practical electrochemical couples. In this study, unique hollow aspheric materials were prepared for the first time using a one-step synthesis method and fully characterized by various techniques. These prepared materials were found to have excellent electrocatalytic activation as cathode materials in lithium-air batteries with a very high specific capacity (up to 2.3 A.h/g of carbon). The third topic in this thesis presents studies of ethane oxydehydrogenation (ODH) in the presence of CO2 over the octahedral molecular sieve (OMS-2) catalyst. Conversion of CO2 into organic compounds has been studied intensively. Ethane catalytic oxydehydrogenation in the presence of CO2 offers an attractive route for converting CO2. In this study, using OMS-2 as the catalyst in C2H6 dehydrogenation in the presence of CO2 is an example where extreme conditions are used to drive high conversions of ethane (> 70%) and CO2 (up to 56%) with high selectivity towards ethylene (87%) with a short contact time (0.6 s). This inexpensive material also showed high stability during the process, and the presence of CO2 removed coke depositions throughout the catalyst. The results obtained from this study open up new possibilities for olefin dehydrogenations in the presence of CO2, a perfect feedstock for any process involving ethylene carbonylation with the recycling of the greenhouse gas. The fourth part of this thesis presents a ZnO/La2O2CO 3 composite prepared by a new and easy method and discusses the use of these materials as heterogeneous catalysts for ultra-fast microwave biodiesel production at low temperatures. The search for solid state materials with high catalytic activities is one of the key steps toward reducing the cost of producing biodiesel. We present a high biodiesel yield (> 95%) in less than 5 minutes under mild reaction conditions (< 100°C) on a ZnO/La 2O2CO3 heterogeneous catalyst, showing no Zn and La leaching into the reaction medium. The catalyst has a higher reaction rate than the homogeneous KOH catalyst with the assistance of microwave irradiation. All of these results promote the industrial application of the synthesized ZnO/La2O2CO3 as a potential heterogeneous catalyst for fast biodiesel production, avoiding many of the issues found in both commercial and independently published catalysts. Following the fourth part of this thesis, the fifth part presents the synthesis and characterization of a series of rare earth Ln2O 2CO3 (Ln = La, Eu, Nd, a

  14. Transparent conducting oxide free backside illuminated perovskite solar cells

    NASA Astrophysics Data System (ADS)

    Li, Jia; Yao, Jiexiong; Xia, Huarong; Sun, Wentao; Liu, Jian; Peng, Lianmao

    2015-07-01

    Recently, hybrid perovskites have attracted great attention because of their promising applications in solar cells. However, perovskite solar devices reported till now are mostly based on transparent conducting oxide (TCO) substrates which account for a large proportion in the total cost. Herein, TCO-free perovskite solar cells are fabricated. A photo-electricity conversion efficiency of 5.27% is obtained with short circuit current density (Jsc) of 10.7 mA/cm2, open circuit voltage (Voc) of 0.837 V, and fill factor of 0.588. This study points a feasible way of replacing TCO substrate by low cost substrates, indicating promising potentials in solar energy conversion applications.

  15. Approach to multifunctional device platform with epitaxial graphene on transition metal oxide.

    PubMed

    Park, Jeongho; Back, Tyson; Mitchel, William C; Kim, Steve S; Elhamri, Said; Boeckl, John; Fairchild, Steven B; Naik, Rajesh; Voevodin, Andrey A

    2015-01-01

    Heterostructures consisting of two-dimensional materials have shown new physical phenomena, novel electronic and optical properties, and new device concepts not observed in bulk material systems or purely three dimensional heterostructures. These new effects originated mostly from the van der Waals interaction between the different layers. Here we report that a new optical and electronic device platform can be provided by heterostructures of 2D graphene with a metal oxide (TiO2). Our novel direct synthesis of graphene/TiO2 heterostructure is achieved by C60 deposition on transition Ti metal surface using a molecular beam epitaxy approach and O2 intercalation method, which is compatible with wafer scale growth of heterostructures. As-grown heterostructures exhibit inherent photosensitivity in the visible light spectrum with high photo responsivity. The photo sensitivity is 25 times higher than that of reported graphene photo detectors. The improved responsivity is attributed to optical transitions between O 2p orbitals in the valence band of TiO2 and C 2p orbitals in the conduction band of graphene enabled by Coulomb interactions at the interface. In addition, this heterostructure provides a platform for realization of bottom gated graphene field effect devices with graphene and TiO2 playing the roles of channel and gate dielectric layers, respectively. PMID:26395160

  16. Designed Synthesis of Transition Metal/Oxide Hierarchical Peapods Array with the Superior Lithium Storage Performance

    PubMed Central

    Zhang, Huijuan; Bai, Yuanjuan; Zhang, Yan; Li, Xiao; Feng, Yangyang; Liu, Qing; Wu, Kai; Wang, Yu

    2013-01-01

    In this report, a novel hierarchical peapoded array with Co3O4 nanoparticles encapsulated in graphitized carbon fiber is introduced for the first time. The unique peapoded structure is suitable for the excellent anode in LIBs and demonstrates enhanced rate capability, cyclability and prolonged lifespan, e.g. the specific capacity can reach up to 1150?mAh/g. All the enhanced electrochemical performance is reasonably derived from the peapod-like and aligned conformation. Furthermore, due to the specialty of the structure and the versatility of Co3O4, the composite will find more applications in specific catalysis, biomedicine, electronics, optoelectronic engineering and gas sensing. The fabrication strategy developed here is also a rational and universal approach towards peapod-like architecture and has significantly widened the specific functional material domain we created before. In our design, more peapod-like aligned samples with various nanoparticles, e.g. oxides, phosphides, even nitrides, encapsulated in graphitized carbon fibers, have been lifted on the research agenda and the results will be presented soon. PMID:24056414

  17. Approach to multifunctional device platform with epitaxial graphene on transition metal oxide

    PubMed Central

    Park, Jeongho; Back, Tyson; Mitchel, William C.; Kim, Steve S.; Elhamri, Said; Boeckl, John; Fairchild, Steven B.; Naik, Rajesh; Voevodin, Andrey A.

    2015-01-01

    Heterostructures consisting of two-dimensional materials have shown new physical phenomena, novel electronic and optical properties, and new device concepts not observed in bulk material systems or purely three dimensional heterostructures. These new effects originated mostly from the van der Waals interaction between the different layers. Here we report that a new optical and electronic device platform can be provided by heterostructures of 2D graphene with a metal oxide (TiO2). Our novel direct synthesis of graphene/TiO2 heterostructure is achieved by C60 deposition on transition Ti metal surface using a molecular beam epitaxy approach and O2 intercalation method, which is compatible with wafer scale growth of heterostructures. As-grown heterostructures exhibit inherent photosensitivity in the visible light spectrum with high photo responsivity. The photo sensitivity is 25 times higher than that of reported graphene photo detectors. The improved responsivity is attributed to optical transitions between O 2p orbitals in the valence band of TiO2 and C 2p orbitals in the conduction band of graphene enabled by Coulomb interactions at the interface. In addition, this heterostructure provides a platform for realization of bottom gated graphene field effect devices with graphene and TiO2 playing the roles of channel and gate dielectric layers, respectively. PMID:26395160

  18. Approach to multifunctional device platform with epitaxial graphene on transition metal oxide

    NASA Astrophysics Data System (ADS)

    Park, Jeongho; Back, Tyson; Mitchel, William C.; Kim, Steve S.; Elhamri, Said; Boeckl, John; Fairchild, Steven B.; Naik, Rajesh; Voevodin, Andrey A.

    2015-09-01

    Heterostructures consisting of two-dimensional materials have shown new physical phenomena, novel electronic and optical properties, and new device concepts not observed in bulk material systems or purely three dimensional heterostructures. These new effects originated mostly from the van der Waals interaction between the different layers. Here we report that a new optical and electronic device platform can be provided by heterostructures of 2D graphene with a metal oxide (TiO2). Our novel direct synthesis of graphene/TiO2 heterostructure is achieved by C60 deposition on transition Ti metal surface using a molecular beam epitaxy approach and O2 intercalation method, which is compatible with wafer scale growth of heterostructures. As-grown heterostructures exhibit inherent photosensitivity in the visible light spectrum with high photo responsivity. The photo sensitivity is 25 times higher than that of reported graphene photo detectors. The improved responsivity is attributed to optical transitions between O 2p orbitals in the valence band of TiO2 and C 2p orbitals in the conduction band of graphene enabled by Coulomb interactions at the interface. In addition, this heterostructure provides a platform for realization of bottom gated graphene field effect devices with graphene and TiO2 playing the roles of channel and gate dielectric layers, respectively.

  19. An Oxofluoride Catalyst Comprised of Transition Metals and a Metalloid for Application in Water Oxidation.

    PubMed

    Svengren, Henrik; Hu, Shichao; Athanassiadis, Ioannis; Laine, Tanja M; Johnsson, Mats

    2015-09-01

    The application of the recently discovered oxofluoride solid solution (Cox Ni1-x )3 Sb4 O6 F6 as a catalyst for water oxidation is demonstrated. The phase exhibits a cubic arrangement of the active metal that forms oxo bridges to the metalloid with possible catalytic participation. The Co3 Sb4 O6 F6 compound proved to be capable of catalyzing 2H2 O?O2 +4H(+) +4e(-) at 0.33?V electrochemical and ?0.39?V chemical overpotential with a TOF of 4.4?10(-3) , whereas Ni3 Sb4 O6 F6 needs a higher overpotential. Relatively large crystal cubes (0.3-0.5?mm) are easily synthesized and readily handled as they demonstrate both chemical resistance to wear after repeated in?situ tests under experimental conditions, and have a mechanical hardness of 270?V0.1 using Vickers indentation. The combined properties of this compound offer a potential technical advantage for incorporation to a catalytic interface in future sustainable fuel production. PMID:26219925

  20. Hydrolysis on transition metal oxide clusters and the stabilities of M-O-M bridges.

    PubMed

    Johnson, J R; Panas, I

    2000-07-24

    Water addition to molecular single, double and triple M-O-M bridges (M = Sc, Ti, V, Cr, and Mn) were considered, and the stabilities toward stepwise hydrolysis of the oxygen bridges were studied by means of quantum chemistry. The M-O bond distances for the studied systems were compared to experiment for demonstration of the applicability of the B3LYP functional to the investigated systems. While substantial exothermicities were found for the hydrolysis of double and triple M-O-M bridges, addition of water to a single bridge was generally found to be slightly endothermic. The lack of enthalpy drive for the (OH)yOxM-O-MOx(OH)y + H2O-->2MOx-1(OH)y+2 reaction was taken to suggest that entropy increase and the formation of mononuclear water complexe, would be decisive factors for the dissociation. A mechanism was proposed for the observed erosion of the protective chromium oxide scale on high-temperature alloys at elevated temperatures and high humidities, based on the formation of CrO2(OH)2(g). PMID:11196854

  1. STUDY MAGNETIC EXCITATIONS IN DOPED TRANSITION METAL OXIDES USING INELASTIC NEUTRON SCATTERING

    SciTech Connect

    Dai, Pengcheng

    2014-02-18

    Understanding the interplay between magnetism and superconductivity continues to be a “hot” topic in modern condensed matter physics. The discovery of high-temperature superconductivity in iron-based materials in 2008 provided an unique opportunity to compare and contrast these materials with traditional high-Tc copper oxide superconductors. Neutron scattering plays an important role in determining the dynamical spin properties in these materials. This proposal is a continuation of previous DOE supported proposal. This report summarizes the final progress we have made over from May 2005 till Aug. 2013. Overall, we continue to carry out extensive neutron scattering experiments on Fe-based materials, focusing on understanding their magnetic properties. In addition, we have established a materials laboratory at UT that has allowed us to grow these superconductors. Because neutron scattering typically demands a large amount of samples, by growing these materials in our own laboratory, we can now pursuit neutron scattering experiments over the entire electronic phase diagram, focusing on regions of interests. The material synthesis laboratory at UT was established entirely with the support of DOE funding. This not only allowed us to carry out neutron scattering experiments, but also permit us to provide samples to other US/International collaborators for studying these materials.

  2. Electrochemical tuning of layered lithium transition metal oxides for improvement of oxygen evolution reaction

    NASA Astrophysics Data System (ADS)

    Lu, Zhiyi; Wang, Haotian; Kong, Desheng; Yan, Kai; Hsu, Po-Chun; Zheng, Guangyuan; Yao, Hongbin; Liang, Zheng; Sun, Xiaoming; Cui, Yi

    2014-07-01

    Searching for low-cost and efficient catalysts for the oxygen evolution reaction has been actively pursued owing to its importance in clean energy generation and storage. While developing new catalysts is important, tuning the electronic structure of existing catalysts over a wide electrochemical potential range can also offer a new direction. Here we demonstrate a method for electrochemical lithium tuning of catalytic materials in organic electrolyte for subsequent enhancement of the catalytic activity in aqueous solution. By continuously extracting lithium ions out of LiCoO2, a popular cathode material in lithium ion batteries, to Li0.5CoO2 in organic electrolyte, the catalytic activity is significantly improved. This enhancement is ascribed to the unique electronic structure after the delithiation process. The general efficacy of this methodology is demonstrated in several mixed metal oxides with similar improvements. The electrochemically delithiated LiCo0.33Ni0.33Fe0.33O2 exhibits a notable performance, better than the benchmark iridium/carbon catalyst.

  3. Elementary reaction schemes for physical and chemical vapor deposition of transition metal oxides on silicon for high-k gate dielectric applications

    NASA Astrophysics Data System (ADS)

    Niu, D.; Ashcraft, R. W.; Kelly, M. J.; Chambers, J. J.; Klein, T. M.; Parsons, G. N.

    2002-05-01

    This article describes the kinetics of reactions that result in substrate consumption during formation of ultrathin transition metal oxides on silicon. Yttrium silicate films (˜40 Å) with an equivalent silicon dioxide thickness of ˜11 Å are demonstrated by physical vapor deposition (PVD) routes. Interface reactions that occur during deposition and during postdeposition treatment are observed and compared for PVD and chemical vapor deposition (CVD) yttrium oxides and CVD aluminum-oxide systems. Silicon diffusion, metal-silicon bond formation, and reactions involving hydroxides are proposed as critical processes in interface layer formation. For PVD of yttrium silicate, oxidation is thermally activated with an effective barrier of 0.3 eV, consistent with the oxidation of silicide being the rate-limited step. For CVD aluminum oxide, interface oxidation is consistent with a process limited by silicon diffusion into the deposited oxide layer.

  4. Synthesis and characterization of three-dimensional transition metal ions doped zinc oxide based dilute magnetic semiconductor thin films

    NASA Astrophysics Data System (ADS)

    Samanta, Kousik

    Dilute magnetic semiconductors (DMS), especially 3d-transition metal (TM) doped ZnO based DMS materials are the most promising candidates for optoelectronics and spintronics applications; e.g. in spin light emitting diode (SLED), spin transistors, and spin field effect transistors (SFET), etc. In the present dissertation, thin films of Zn1-xTMxO (TM = Co2+, Cu2+, and Mn2+) were grown on (0001) oriented Al2O3 substrates by pulsed laser deposition (PLD) technique. The films were highly c-axis oriented, nearly single crystalline, and defects free for a limited concentration of the dilution of transition metal ions. In particular, we have obtained single crystalline phases of Zn1-xTMxO thin films for up to 10, 3, and 5 stoichiometric percentages of Co2+, Cu2+, and Mn2+ respectively. Raman micro-probe system was used to understand the structural and lattice dynamical properties at different physical conditions. The confinement of optical phonons in the disorder lattice was explained by alloy potential fluctuation (APF) using a spatial correlation (SC) model. The detailed analysis of the optical phonon behavior in disorder lattice confirmed the substitution of the transition metal ions in Zn 2+ site of the ZnO host lattice. The secondary phases of ZnCo 2O4, CuO, and ZnMn2O4 were detected in higher Co, Cu, and Mn doped ZnO thin films respectively; where as, XRD did not detect these secondary phases in the same samples. Room temperature ferromagnetism was observed in Co2+ and Cu2+ ions doped ZnO thin films with maximum saturation magnetization (Ms) of 1.0 and 0.76 muB respectively. The origin of the observed ferromagnetism in Zn1-xCoxO thin films was tested by the controlled introduction of shallow donors (Al) in Zn0.9-x Co0.1O:Alx (x = 0.005 and 0.01) thin films. The saturation magnetization for the 10% Co-doped ZnO (1.0 muB /Co) at 300K reduced (˜0.25 muB/Co) due to Al doping. The observed ferromagnetism and the reduction due to Al doping can be explained by the Bound Magnetic Polaron (BMP) model. The Resistivity of ZCO sample (˜ 103 O-cm) dropped by 5 orders of magnitude (0.02 O-cm) in Co, Al co-doped samples and the carrier concentrations increases 4 orders of magnitude (˜ 1019/cm3). The Cu2+ doped ZnO thin films showed the ferromagnetic property at 300K. The p-d orbital mixing of high spin Cu2+ (d9) state with the nearest neighbor oxygen p-orbital can explain the origin of RTFM in Zn 1-xCuxO thin films. The optical transmission spectroscopy and the photoluminescence spectroscopy analysis were used to understand the electronic band structure, near band edge (NBE) transition, and the excitonic behavior in ZnO and Zn1-xTMxO thin films. We have found the reduction of NBE transition at 300K due to the substitution of Co and Cu in ZnO host lattice. This narrowing of the optical band gap (NBE) is due to the sp-d exchange interaction between the d electrons of transition metal ions and the band electrons of ZnO; the strength of this interaction strongly depends on the number of d electrons. The s-d and p-d exchanges give rise to negative and positive corrections to the conduction and valance band edges respectively, leading to the NBE narrowing. We have observed the characteristic inter atomic d-d transitions in Co doped samples; thus confirming the substitution of Co2+ in the tetrahedral site in ZnO. The low temperature (77K) PL spectrum showed the basic excitonic characteristics of pure ZnO in Zn1-xTMxO thin films. The X-ray photoelectron spectroscopy (XPS) showed that the Co and Cu are normally in 2+ oxidation state, but in the case of higher Cu concentrations (>3%), the mixed state of Cu2+ and Cu1+ were detected.

  5. Transition metal sulfide loaded catalyst

    DOEpatents

    Maroni, V.A.; Iton, L.E.; Pasterczyk, J.W.; Winterer, M.; Krause, T.R.

    1994-04-26

    A zeolite-based catalyst is described for activation and conversion of methane. A zeolite support includes a transition metal (Mo, Cr or W) sulfide disposed within the micropores of the zeolite. The catalyst allows activation and conversion of methane to C[sub 2]+ hydrocarbons in a reducing atmosphere, thereby avoiding formation of oxides of carbon.

  6. Transition metal sulfide loaded catalyst

    DOEpatents

    Maroni, Victor A. (Naperville, IL); Iton, Lennox E. (Downers Grove, IL); Pasterczyk, James W. (Westmont, IL); Winterer, Markus (Westmont, IL); Krause, Theodore R. (Lisle, IL)

    1994-01-01

    A zeolite based catalyst for activation and conversion of methane. A zeolite support includes a transition metal (Mo, Cr or W) sulfide disposed within the micropores of the zeolite. The catalyst allows activation and conversion of methane to C.sub.2 + hydrocarbons in a reducing atmosphere, thereby avoiding formation of oxides of carbon.

  7. Electronic structure of perovskite oxide surfaces at elevated temperatures and its correlation with oxygen reduction reactivity

    E-print Network

    Chen, Yan, Ph. D. Massachusetts Institute of Technology

    2014-01-01

    The objective is to understand the origin of the local oxygen reduction reaction (ORR) activity on the basis of the local electronic structure at the surface of transition metal oxides at elevated temperatures and in oxygen ...

  8. Varied roles of Pb in transition-metal PbMO3 perovskites (M = Ti, V, Cr, Mn, Fe, Ni, Ru)

    NASA Astrophysics Data System (ADS)

    Goodenough, John B.; Zhou, Jianshi

    2015-06-01

    Different structural chemistries resulting from the Pb2+ lone-pair electrons in the PbMO3 perovskites are reviewed. The Pb2+ lone-pair electrons enhance the ferroelectric transition temperature in PbTiO3, stabilize vanadyl formation in PbVO3, and induce a disproportionation reaction of CrIV in PbCrO3. A Pb2+ + NiIV = Pb4+ + NiII reaction in PbNiO3 stabilizes the LiNbO3 structure at ambient pressure, but an A-site Pb4+ in an orthorhombic perovskite PbNiO3 is stabilized at modest pressures at room temperature. In PbMnO3, a ferroelectric displacement due to the lone pair electron effect is minimized by the spin-spin exchange interaction and the strong octahedral site preference of the MnIV/III cation. PbRuO3 is converted under pressure from the defective pyrochlore to the orthorhombic (Pbnm) perovskite structure where Pb-Ru interactions via a common O -2p orbital stabilize at low temperature a metallic Imma phase at ambient pressure. Above Pc ? ~32 GPa, a covalent Pb-Ru bond is formed by Pb2+ + RuIV = Pb4+ + RuII electron sharing.

  9. Rapid Microwave Synthesis of Perovskite Oxide Nanostructures with Enhanced Functionality

    NASA Astrophysics Data System (ADS)

    Salazar, Gregory; Datta, Anuja; Mukherjee, Pritish

    2015-03-01

    Perovskite oxides are an important class of materials having high dielectric and piezoelectric coefficients, switchable ferroelectric (FE) polarization and interesting optical and electrical properties. Realization of functional devices based on classic perovskite oxides such as Pb(Zr0.52Ti0.48) O3 (PZT), and emerging Pb-free noncentrosymmetric (NCS) oxides, such as, ZnSnO3, ZnTiO3 and CaTiO3 have reinforced the investigation of these materials in multiple dimensions and length scales. However, large-scale synthesis and integration of ordered low-dimensional structures is a challenge, due to their complicated methodologies, high-cost and difficulties with phase stability. We discuss a generalized, cost-effective, rapid microwave synthesis route for size and shape selective nanostructure growth of these functional perovskite oxides on industrially viable flexible and hard substrates, stabilized by an enhanced ionic covalence. The rational synthesis approach allowed improved tunability of the size, shape, and orientation of the structures with improved electrical and FE properties. The facile fabrication route of these nanostructures may expand the outreach of probes for understanding the structure-property relationships in these hitherto unexplored and technologically important materials.

  10. Temperature-independent sensors based on perovskite-type oxides

    NASA Astrophysics Data System (ADS)

    Zaza, F.; Frangini, S.; Leoncini, J.; Luisetto, I.; Masci, A.; Pasquali, M.; Tuti, S.

    2014-06-01

    The need of energy security and environment sustainability drives toward the development of energy technology in order to enhance the performance of internal combustion engines. Gas sensors play a key role for controlling the fuel oxygen ratio and monitoring the pollution emissions. The perovskite-type oxides can be synthesized for an extremely wide variety of combinations of chemical elements, allowing to design materials with suitable properties for sensing application. Lanthanum strontium ferrites, such as La0.7Sr0.3FeO3, are suitable oxygen sensing materials with temperature-independence conductivity, but they have low chemical stability under reducing conditions. The addition of aluminum into the perovskite structure improves the material properties in order to develop suitable oxygen sensing probes for lean burn engine control systems. Perovskite-type oxides with formula (La0.7Sr0.3)(AlxFe1-x)O3 was synthesized by the citrate-nitrate combustion synthesis method. XRD analyses, show that it was synthesized a phase-pure powder belonging to the perovskite structure. Aluminum affects both the unit cell parameters, by shrinking the unit cell, and the powder morphology, by promoting the synthesis of particles with small crystallite size and large specific surface area. The partial substitution of iron with aluminum improves the chemical stability under reducing gas conditions and modulates the oxygen sensitivity by affecting the relative amount of Fe4+ and Fe3+, as confirmed from TPR profiles. In the same time, the addition of aluminum does not affects the temperature-independent properties of lanthanum strontium ferrites. Indeed, the electrical measurements show that (La0.7Sr0.3)(AlxFe1-x)O3 perovskites have temperature-independence conductivity from 900 K.

  11. Temperature-independent sensors based on perovskite-type oxides

    SciTech Connect

    Zaza, F.; Frangini, S.; Masci, A.; Leoncini, J.; Pasquali, M.; Luisetto, I.; Tuti, S.

    2014-06-19

    The need of energy security and environment sustainability drives toward the development of energy technology in order to enhance the performance of internal combustion engines. Gas sensors play a key role for controlling the fuel oxygen ratio and monitoring the pollution emissions. The perovskite-type oxides can be synthesized for an extremely wide variety of combinations of chemical elements, allowing to design materials with suitable properties for sensing application. Lanthanum strontium ferrites, such as La{sub 0.7}Sr{sub 0.3}FeO{sub 3}, are suitable oxygen sensing materials with temperature-independence conductivity, but they have low chemical stability under reducing conditions. The addition of aluminum into the perovskite structure improves the material properties in order to develop suitable oxygen sensing probes for lean burn engine control systems. Perovskite-type oxides with formula (La{sub 0.7}Sr{sub 0.3})(Al{sub x}Fe{sub 1?x})O{sub 3} was synthesized by the citrate-nitrate combustion synthesis method. XRD analyses, show that it was synthesized a phase-pure powder belonging to the perovskite structure. Aluminum affects both the unit cell parameters, by shrinking the unit cell, and the powder morphology, by promoting the synthesis of particles with small crystallite size and large specific surface area. The partial substitution of iron with aluminum improves the chemical stability under reducing gas conditions and modulates the oxygen sensitivity by affecting the relative amount of Fe{sup 4+} and Fe{sup 3+}, as confirmed from TPR profiles. In the same time, the addition of aluminum does not affects the temperature-independent properties of lanthanum strontium ferrites. Indeed, the electrical measurements show that (La{sub 0.7}Sr{sub 0.3})(Al{sub x}Fe{sub 1?x})O{sub 3} perovskites have temperature-independence conductivity from 900 K.

  12. Oxide perovskite crystals for HTSC film substrates microwave applications

    NASA Technical Reports Server (NTRS)

    Bhalla, A. S.; Guo, Ruyan

    1995-01-01

    The research focused upon generating new substrate materials for the deposition of superconducting yttrium barium cuprate (YBCO) has yielded several new hosts in complex perovskites, modified perovskites, and other structure families. New substrate candidates such as Sr(Al(1/2)Ta(1/2))O3 and Sr(Al(1/2)Nb(1/2))O3, Ba(Mg(1/3)Ta(2/3))O3 in complex oxide perovskite structure family and their solid solutions with ternary perovskite LaAlO3 and NdGaO3 are reported. Conventional ceramic processing techniques were used to fabricate dense ceramic samples. A laser heated molten zone growth system was utilized for the test-growth of these candidate materials in single crystal fiber form to determine crystallographic structure, melting point, thermal, and dielectric properties as well as to make positive identification of twin free systems. Some of those candidate materials present an excellent combination of properties suitable for microwave HTSC substrate applications.

  13. Transition metals activate TFEB in overexpressing cells

    PubMed Central

    Peña, Karina A.; Kiselyov, Kirill

    2015-01-01

    Transition metal toxicity is an important factor in the pathogenesis of numerous human disorders, including neurodegenerative diseases. Lysosomes have emerged as important factors in transition metal toxicity because they handle transition metals via endocytosis, autophagy, absorption from the cytoplasm and exocytosis. Transcription factor EB (TFEB) regulates lysosomal biogenesis and the expression of lysosomal proteins in response to lysosomal and/or metabolic stresses. Since transition metals cause lysosomal dysfunction, we proposed that TFEB may be activated to drive gene expression in response to transition metal exposure and that such activation may influence transition metal toxicity. We found that transition metals copper (Cu) and iron (Fe) activate recombinant TFEB and stimulate the expression of TFEB-dependent genes in TFEB-overexpressing cells. In cells that show robust lysosomal exocytosis, TFEB was cytoprotective at moderate levels of Cu exposure, decreasing oxidative stress as reported by the expression of heme oxygenase-1 (HMOX1) gene. However, at high levels of Cu exposure, particularly in cells with low levels of lysosomal exocytosis, activation of overexpressed TFEB was toxic, increasing oxidative stress and mitochondrial damage. Based on these data, we conclude that TFEB-driven gene network is a component of the cellular response to transition metals. These data suggest limitations and disadvantages of TFEB overexpression as a therapeutic approach. PMID:26251447

  14. Electronic transport and mixed conductivity in perovskite type oxides

    SciTech Connect

    Anderson, H.U.; Nasrallah, M.M.; Sparlin, D.M.; Parris, P.E.

    1992-03-03

    The goal of the investigation presented in this report is to study the inter-relationship between electrical conductivity, oxidation-reduction kinetics, defect structure, and composition of n- and p-type binary and ternary transition metal oxides. The experimental part of the investigation included specimen preparation, thermogravimetric measurements, X-ray diffraction, thermally stimulated current, DTA/TGA, optical absorption, transmission electron microscopy, electrical conductivity, and Seebeck measurements. The systems studied or being studied are LaMnO{sub 3}-LaCrO{sub 3}-LaCrO{sub 3}, (La,Ca)(Mn,Al)O{sub 3}, Y{sub 1-x}Ca{sub x}CrO{sub 3}, YMnO{sub 3}-CaMnO{sub 3}, and LaMnO{sub 3}-CaMnO{sub 3}.

  15. Solvothermal synthesis of perovskites and pyrochlores: crystallisation of functional oxides under mild conditions.

    PubMed

    Modeshia, Deena R; Walton, Richard I

    2010-11-01

    In this critical review we consider the large literature that has accumulated in the past 5-10 years concerning solution-mediated crystallisation of complex oxide materials using hydrothermal, or more generally solvothermal, reaction conditions. The aim is to show how the synthesis of dense, mixed-metal oxide materials, usually prepared using the high temperatures associated with solid-chemistry, is perfectly feasible from solution in one step reactions, typically at temperatures as low as 200 °C, and that important families of oxide materials have now been reported to crystallise using such synthetic approaches. We will focus on two common structures seen in oxide chemistry, ABO(3) perovskites and A(2)B(2)O(6)O' pyrochlores, and include a systematic survey of the variety of chemical elements now included in these two prototypical structure types, from transition metals, in families of materials that include titanates, niobates, manganites and ferrites, to main-group elements in stannates, plumbates and bismuthates. The significant advantages of solution-mediated crystallisation are well illustrated by the recent literature: examples are provided of elegant control of crystal form from the nanometre to the micron length scale to give thin films, anisotropic crystal morphologies, or hierarchical structures of materials with properties desirable for many important contemporary applications. In addition, new metastable materials have been reported, not stable once high temperatures and pressures are applied and hence not amenable using conventional synthesis. We critically discuss the possible control offered by solvothermal synthesis from crystal chemistry to crystal form and how the discovery of new materials may be achieved. Computer simulation, combinatorial synthesis approaches and in situ methods to follow crystallisation will be vital in providing the predictability in synthesis that is needed for rational design of new materials (232 references). PMID:20532260

  16. Method for dry etching of transition metals

    DOEpatents

    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

    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.

  17. Method for dry etching of transition metals

    DOEpatents

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

    1998-09-29

    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.

  18. Site and Oxidation-State Specificity Yielding Dimensional Control in Perovskite Ruthenates

    E-print Network

    Poeppelmeier, Kenneth R.

    Site and Oxidation-State Specificity Yielding Dimensional Control in Perovskite Ruthenates Job T perovskite, Sr3CaRu2O9. Ruthenium's unusual ability to readily adopt both IV(d4) and V(d3) oxidation states-sites of the perovskite lattice (Figure 1). Similarly ordered materials based on Nb5+ or Ta5+ are known and serve as good

  19. Oxidation Potential, Not Crystal Structure, Controls the Oxidation State of Iron in Perovskite

    NASA Astrophysics Data System (ADS)

    Panero, W. R.; Pigott, J. S.; Watson, H. C.; Scharenberg, M.; Green, H. W.; McComb, D. W.; Williams, R. E.

    2013-12-01

    The mantle's oxidation state has broad implications on the state and evolution of the earth's interior. The relatively high oxidation potential of the upper mantle is such that iron is predominantly Fe2+ with small amounts of Fe3+ . Fe3+ is more stable than Fe2+ in the dominant lower mantle mineral, perovskite, despite the fact that the effect of pressure is to reduce the oxidizing potential of a system. It is therefore suggested that iron undergoes a disproportionation reaction of 3Fe2+ =2Fe3+ +Fe0 , controlled by the crystallography instead of oxidation potential. We crystallized synthetic enstatite glass with 5% Al2O3, 14% FeO, and 3% Fe2O3 in the laser-heated diamond anvil cell at 25-63 GPa and 1700-2800 K. We find that for temperatures <2200 K, the sample crystallizes to only perovskite, while at higher temperatures, the sample crystallizes to perovskite and stishovite as evident in x-ray diffraction, with 5-50 nm iron precipitates on grain boundaries. The precipitates have small amounts of dissolved oxygen, but are Mg- and Al- free. We interpret that the stishovite is forming due to the oxidation of the ferric iron to ferrous iron according to (Mg2+,Al3+)(Fe3+,Si4+)O3 +SiO2 + Fe0 while the lower-temperature samples crystallizing as approximately (Mg2+ Fe2+ Al3+ )(Fe3+ Al3+ Si4+ )O3. We observe 2.8(2) Å3 volume expansion of the perovskite and a 28(2) GPa decrease in compressibility of the perovskite relative to the perovskite forming at lower temperature, consistent with the proposed compositions of the perovskites. As the increased temperature increases the oxidation potential of the system, we suggest that the oxidation state of iron in perovskite is dependent on oxidation potential as opposed to perovskite's crystal structure. Transmission Electron Microscopy (TEM) coupled with Electron Energy Loss Spectroscopy (EELS) show iron precipitation on grain boundaries supporting the conclusion. We present a discussion of the results and implications for core formation and lower mantle dynamics.

  20. Autothermal reforming catalyst having perovskite structure

    DOEpatents

    Krumpel, Michael (Naperville, IL); Liu, Di-Jia (Naperville, IL)

    2009-03-24

    The invention addressed two critical issues in fuel processing for fuel cell application, i.e. catalyst cost and operating stability. The existing state-of-the-art fuel reforming catalyst uses Rh and platinum supported over refractory oxide which add significant cost to the fuel cell system. Supported metals agglomerate under elevated temperature during reforming and decrease the catalyst activity. The catalyst is a perovskite oxide or a Ruddlesden-Popper type oxide containing rare-earth elements, catalytically active firs row transition metal elements, and stabilizing elements, such that the catalyst is a single phase in high temperature oxidizing conditions and maintains a primarily perovskite or Ruddlesden-Popper structure under high temperature reducing conditions. The catalyst can also contain alkaline earth dopants, which enhance the catalytic activity of the catalyst, but do not compromise the stability of the perovskite structure.

  1. General facile approach to transition-metal oxides with highly uniform mesoporosity and their application as adsorbents for heavy-metal-ion sequestration.

    PubMed

    Seisenbaeva, Gulaim A; Daniel, Geoffrey; Kessler, Vadim G; Nedelec, Jean-Marie

    2014-08-18

    Mesoporous powders of transition-metal oxides, TiO2, ZrO2, HfO2, Nb2O5, and Ta2O5, pure from organic impurities were produced by a rapid single-step thermohydrolytic approach. The obtained materials display an impressively large active surface area and sharp pore-size distribution, being composed of partially coalesced uniform nanoparticles with crystalline cores and amorphous shells. They reveal extremely high adsorption capacity in removal of Cr(VI) anions from solutions (25.8 for TiO2, 73.0 for ZrO2, and 74.7?mg?g(-1) for Nb2O5 in relation to the Cr2O7(2-) anion), making them very attractive as adsorbents in water remediation applications. The difference in adsorption capacities for the studied oxides may be explained by variation in surface hydration and surface-charge distribution. PMID:25042144

  2. Oligocyclopentadienyl transition metal complexes

    SciTech Connect

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

    2002-01-18

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

  3. Oxygen transport in perovskite-type solid oxide fuel cell materials: insights from quantum mechanics.

    PubMed

    Muñoz-García, Ana B; Ritzmann, Andrew M; Pavone, Michele; Keith, John A; Carter, Emily A

    2014-11-18

    CONSPECTUS: Global advances in industrialization are precipitating increasingly rapid consumption of fossil fuel resources and heightened levels of atmospheric CO2. World sustainability requires viable sources of renewable energy and its efficient use. First-principles quantum mechanics (QM) studies can help guide developments in energy technologies by characterizing complex material properties and predicting reaction mechanisms at the atomic scale. QM can provide unbiased, qualitative guidelines for experimentally tailoring materials for energy applications. This Account primarily reviews our recent QM studies of electrode materials for solid oxide fuel cells (SOFCs), a promising technology for clean, efficient power generation. SOFCs presently must operate at very high temperatures to allow transport of oxygen ions and electrons through solid-state electrolytes and electrodes. High temperatures, however, engender slow startup times and accelerate material degradation. SOFC technologies need cathode and anode materials that function well at lower temperatures, which have been realized with mixed ion-electron conductor (MIEC) materials. Unfortunately, the complexity of MIECs has inhibited the rational tailoring of improved SOFC materials. Here, we gather theoretically obtained insights into oxygen ion conductivity in two classes of perovskite-type materials for SOFC applications: the conventional La1-xSrxMO3 family (M = Cr, Mn, Fe, Co) and the new, promising class of Sr2Fe2-xMoxO6 materials. Using density functional theory + U (DFT+U) with U-J values obtained from ab initio theory, we have characterized the accompanying electronic structures for the two processes that govern ionic diffusion in these materials: (i) oxygen vacancy formation and (ii) vacancy-mediated oxygen migration. We show how the corresponding macroscopic oxygen diffusion coefficient can be accurately obtained in terms of microscopic quantities calculated with first-principles QM. We find that the oxygen vacancy formation energy is a robust descriptor for evaluating oxide ion transport properties. We also find it has a direct relationship with (i) the transition metal-oxygen bond strength and (ii) the extent to which electrons left behind by the departing oxygen delocalize onto the oxygen sublattice. Design principles from our QM results may guide further development of perovskite-based MIEC materials for SOFC applications. PMID:24972154

  4. Elastic moduli of orthorhombic perovskites

    NASA Astrophysics Data System (ADS)

    Verma, A. S.

    2013-03-01

    In this paper, semiempirical formulae for both bulk modulus (B in GPa) and shear modulus (G in GPa) of orthorhombic perovskite structured solids are elaborated in terms of volume (Vm) and product of ionic charges (ZaZbZc) of the bonding. Values of elastic moduli, of the group A+1B+2X3, (X=F. Cl, Br), A+2B+4O3 and A+3B+3O3 orthorhombic perovskites exhibit a linear relationship when plotted against the volume (Vm) normalization, but fall on different straight lines according to the product of ionic charges of the compounds. The resulting expressions can be applied to a broad selection of perovskite (ABX3=A: large cation with different valence, B: transition metal and X: oxides and halides) materials and their modulus predictions are in good agreement with the experimental data and those from ab initio calculations.

  5. High-pressure phase behaviors of ZnTiO3: ilmenite-perovskite transition, decomposition of perovskite into constituent oxides, and perovskite-lithium niobate transition

    NASA Astrophysics Data System (ADS)

    Akaogi, M.; Abe, K.; Yusa, H.; Kojitani, H.; Mori, D.; Inaguma, Y.

    2015-06-01

    High-pressure high-temperature phase transitions of ZnTiO3 ilmenite were examined using multianvil apparatus up to 25.5 GPa and 1,500 °C and diamond anvil cell to 26.5 GPa and about 2,000 °C. Combined results of the multianvil quench experiments and in situ diamond anvil cell experiments indicated that at about 10 GPa and 1,200 °C ZnTiO3 ilmenite transforms to orthorhombic perovskite which is converted to lithium niobate phase on release of pressure. The boundary of the ilmenite-provskite transition is expressed by P(GPa) = 15.9 - 0.005 T (°C). The high-pressure experiments also indicated that at 20-24 GPa and 1,000-1,400 °C ZnTiO3 orthorhombic perovskite dissociates into rocksalt-type ZnO + baddeleyite-type TiO2 which are recovered, respectively, as wurtzite-type ZnO and ?-PbO2-type TiO2 at 1 atm. The boundary of the perovskite dissociation is expressed by P(GPa) = 8.7 + 0.011 T (°C). Molar volume changes of ZnTiO3 at ambient conditions were estimated as -4.7 % for the ilmenite-perovskite transition and -3.5 % for the perovskite decomposition into the oxides. The absence of CaIrO3-type postperovskite in ZnTiO3 is consistent with that dissociation of ZnTiO3 perovskite into the oxides has the larger molar volume change than -1 to -2 % of the perovskite-postperovskite transition in various ABO3 compounds and with previous data that ABO3 perovskites with relatively ionic B-O bonds do not transform to the postperovskite. The transition behaviors of ZnTiO3 are similar to those of MnTiO3 and FeTiO3, but ZnTiO3 perovskite dissociates into the constituent oxides.

  6. Spin-Orbital Order Modified by Orbital Dilution in Transition-Metal Oxides: From Spin Defects to Frustrated Spins Polarizing Host Orbitals

    NASA Astrophysics Data System (ADS)

    Brzezicki, Wojciech; Ole?, Andrzej M.; Cuoco, Mario

    2015-01-01

    We investigate the changes in spin and orbital patterns induced by magnetic transition-metal ions without an orbital degree of freedom doped in a strongly correlated insulator with spin-orbital order. In this context, we study the 3 d ion substitution in 4 d transition-metal oxides in the case of 3 d3 doping at either 3 d2 or 4 d4 sites, which realizes orbital dilution in a Mott insulator. Although we concentrate on this doping case as it is known experimentally and more challenging than other oxides due to finite spin-orbit coupling, the conclusions are more general. We derive the effective 3 d -4 d (or 3 d -3 d ) superexchange in a Mott insulator with different ionic valencies, underlining the emerging structure of the spin-orbital coupling between the impurity and the host sites, and demonstrate that it is qualitatively different from that encountered in the host itself. This derivation shows that the interaction between the host and the impurity depends in a crucial way on the type of doubly occupied t2 g orbital. One finds that in some cases, due to the quench of the orbital degree of freedom at the 3 d impurity, the spin and orbital order within the host is drastically modified by doping. The impurity either acts as a spin defect accompanied by an orbital vacancy in the spin-orbital structure when the host-impurity coupling is weak or favors doubly occupied active orbitals (orbital polarons) along the 3 d -4 d bond leading to antiferromagnetic or ferromagnetic spin coupling. This competition between different magnetic couplings leads to quite different ground states. In particular, for the case of a finite and periodic 3 d atom substitution, it leads to striped patterns either with alternating ferromagnetic or antiferromagnetic domains or with islands of saturated ferromagnetic order. We find that magnetic frustration and spin degeneracy can be lifted by the quantum orbital flips of the host, but they are robust in special regions of the incommensurate phase diagram. Orbital quantum fluctuations modify quantitatively spin-orbital order imposed by superexchange. In contrast, the spin-orbit coupling can lead to anisotropic spin and orbital patterns along the symmetry directions and cause a radical modification of the order imposed by the spin-orbital superexchange. Our findings are expected to be of importance for future theoretical understanding of experimental results for 4 d transition-metal oxides doped with 3 d3 ions. We suggest how the local or global changes of the spin-orbital order induced by such impurities could be detected experimentally.

  7. CHIN.PHYS.LETT. Vol. 25, No. 2 (2008) 663 Growth Model for Pulsed-Laser Deposited Perovskite Oxide Films

    E-print Network

    Zhu, Xiangdong

    2008-01-01

    CHIN.PHYS.LETT. Vol. 25, No. 2 (2008) 663 Growth Model for Pulsed-Laser Deposited Perovskite Oxide features of perovskite oxide film growth as observed in the reflection high energy electron diffraction the Ostwald ripening dur- ing and after deposition as the effect is prevalent in the growth of perovskite

  8. The oxidation state and microstructural environment of transition metals (V, Co, and Ni) in magnetite: an XAFS study

    NASA Astrophysics Data System (ADS)

    Liang, Xiaoliang; He, Zisen; Tan, Wei; Liu, Peng; Zhu, Jianxi; Zhang, Jing; He, Hongping

    2015-05-01

    Transition metal-substituted magnetite minerals have attracted increasing attention for their wide application in industry and environmental protection. In this study, the valence and atomic environment of some substituting metals in magnetites (Fe3- x M x O4, M = V, Co, and Ni) were investigated using X-ray absorption fine structure spectroscopy. The results deduced from X-ray absorption near-edge structure spectroscopy indicated that the valences of V, Co, and Ni in Fe3- x M x O4 were +3, +2, and +2, respectively. The valences did not change as the substitution extent increased. Extended X-ray absorption fine structure spectroscopy suggested that the substituting cations occupied octahedral sites in the magnetite structure. The M-O and M-M/Fe distances were consistent with the Feoct-O and Feoct-Fe distances, respectively, in the magnetite (Fe3O4) structure. The occupancy of the substituting cations was assessed by crystal-field theory. We also considered the relationship between the chemical environment of substituting cations and their effects on the physicochemical properties of magnetite, including thermal stability, surface properties, and catalytic reactivity.

  9. Catalytic oxidation of CO, hydrocarbons, and ethyl acetate over perovskite-type complex oxides

    SciTech Connect

    Pirogova, G.N.; Korosteleva, R.I.; Panich, N.M.

    1994-10-01

    The catalytic activity of M{sup I}M{sup II}O{sub 3} perovskite-type complex oxides (M{sup I}=La, Y, Nd, Yb;M{sup II}=Co, Mn, Ni) in the oxidation of CO, propylene, benzene, ethylbenzene, o-xylene, and ethyl acetate was investigated. The Co-containing catalysts were shown to be more active in the oxidation than the Mn-containing catalysts. A relationship between the catalytic and adsorption properties was established.

  10. Transition metals in superheat melts

    NASA Technical Reports Server (NTRS)

    Jakes, Petr; Wolfbauer, Michael-Patrick

    1993-01-01

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

  11. Calixarene supported transition metal clusters 

    E-print Network

    Taylor, Stephanie Merac

    2013-06-29

    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 ...

  12. Oxidations of Organic and Inorganic Substrates by Superoxo-, hydroperoxo-, and oxo-compounds of the transition metals.

    SciTech Connect

    Michael John Vasbinder

    2006-12-12

    Chapters 1 and 2 dealt with the chemistry of superoxo-, hydroperoxo-, and oxo- complexes of chromium, rhodium and cobalt. Chapter 3 dealt with the mechanism of oxygen-atom transfer catalyzed by an oxo-complex of rhenium. In Chapter 1, it was shown that hydroperoxometal complexes of cobalt and rhodium react with superoxochromium and chromyl ions, generating reduced chromium species while oxidizing the hydroperoxometal ions to their corresponding superoxometal ions. It was shown that the chromyl and superoxochromium ions are the more powerful oxidants. Evidence supports hydrogen atom transfer from the hydroperoxometal ion to the oxidizing superoxochromium or chromyl ion as the reaction mechanism. There is a significant H/D kinetic isotope effect. Comparisons to the rate constants of other known hydrogen atom transfer reactions show the expected correlation with bond dissociation energies. In Chapter 2, it was found that the superoxometal complexes Cr{sub aq}OO{sup 2+} and Rh(NH{sub 3}){sub 4}(H{sub 2}O)OO{sup 2+} oxidize stable nitroxyl radicals of the TEMPO series with rate constants that correlate with the redox potentials of both the oxidant and reductant. These reactions fit the Marcus equation for electron transfer near the theoretical value. Acid catalysis is important to the reaction, especially the thermodynamically limited cases involving Rh(NH{sub 3}){sub 4}(H{sub 2}O)OO{sup 2+} as the oxidant. The rate constants are notably less than those measured in the reaction between the same nitroxyl radicals and other strong free-radical oxidants, an illustration of the delocalized and stabilized nature of the superoxometal ions. Chapter 3 showed that oxo-rhenium catalysts needed a nucleophile to complete the catalytic oxygen-atom transfer from substituted pyridine-N-oxides to triphenylphosphine. The reaction was studied by introducing various pyridine-derived nucleophiles and monitoring their effect on the rate, then fitting the observed rate constants to the Hammett correlation. It was found that the values of the Hammett reaction constant PN were -1.0(1) for 4-nitro-2-methylpyridine-N-oxide and -2.6(4) for 4-methylpyridine-N-oxide as substrates. The negative value confirms pyridine is acting as a nucleophile. Nucleophiles other than pyridine derivatives were also tested. In the end, it was found that the most effective nucleophiles were the pyridine-N-oxides themselves, meaning that a second equivalent of substrate serves as the most efficient promoter of this oxygen-atom transfer reaction. This relative nucleophilicity of pyridines and pyridine-N-oxides is similar to what is observed in other OAT reactions generating high-valent metal-oxo species.

  13. Hybrid functionals applied to perovskites.

    PubMed

    Franchini, Cesare

    2014-06-25

    After being used for years in the chemistry community to describe molecular properties, hybrid functionals have been increasingly and successfully employed for a wide range of solid state problems which are not accurately accessible by standard density functional theory. In particular, the upsurge of interest in transition metal perovskite-based compounds, motivated by their technological relevance and functional ductility, has incentivized the use of hybrid functionals for realistic applications, as hybrid functionals appear to be capable of capturing the complex correlated physics of this class of oxide material, characterized by a subtle coupling between several competing interactions (lattice, orbital, spin). Here we present a map of recent applications of hybrid functionals to perovskites, aiming to cover an ample spectra of cases, including the 'classical' 3d compounds (manganites, titanates, nickelates, ferrites, etc.), less conventional examples from the the 4d (technetiates) and 5d (iridates) series, and the (non-transition metal) sp perovskite BaBiO3. We focus our attention on the technical aspects of the hybrid functional formalism, such as the role of the mixing and (for range-separated hybrids) screening parameters, and on an extended array of physical phenomena: pressure- and doping-induced insulator-to-metal and structural phase transitions, multiferroism, surface and interface effects, charge ordering and localization effects, and spin-orbit coupling. PMID:24871431

  14. Hydrocracking and hydroisomerization of long-chain alkanes and polyolefins over metal-promoted anion-modified transition metal oxides

    SciTech Connect

    Venkatesh, Koppampatti R.; Hu, Jianli; Tierney, John W.; Wender, Irving

    1996-12-01

    A method is described for cracking a feedstock by contacting the feedstock with a metal-promoted anion-modified metal oxide catalyst in the presence of hydrogen gas. The metal oxide of the catalyst is one or more of ZrO{sub 2}, HfO{sub 2}, TiO{sub 2} and SnO{sub 2}, and the feedstock is principally chains of at least 20 carbon atoms. The metal-promoted anion-modified metal oxide catalyst contains one or more of Pt, Ni, Pd, Rh, Ir, Ru, (Mn and Fe) or mixtures of them present between about 0.2% to about 15% by weight of the catalyst. The metal-promoted anion-modified metal oxide catalyst contains one or more of SO{sub 4}, WO{sub 3}, or mixtures of them present between about 0.5% to about 20% by weight of the catalyst.

  15. Hydrocracking and hydroisomerization of long-chain alkanes and polyolefins over metal-promoted anion-modified transition metal oxides

    DOEpatents

    Venkatesh, Koppampatti R. (Pittsburgh, PA); Hu, Jianli (Cranbury, NJ); Tierney, John W. (Pittsburgh, PA); Wender, Irving (Pittsburgh, PA)

    2001-01-01

    A method of cracking a feedstock by contacting the feedstock with a metal-promoted anion-modified metal oxide catalyst in the presence of hydrogen gas. The metal oxide of the catalyst is one or more of ZrO.sub.2, HfO.sub.2, TiO.sub.2 and SnO.sub.2, and the feedstock is principally chains of at least 20 carbon atoms. The metal-promoted anion-modified metal oxide catalyst contains one or more of Pt, Ni, Pd, Rh, Ir, Ru, (Mn & Fe) or mixtures of them present between about 0.2% to about 15% by weight of the catalyst. The metal-promoted anion-modified metal oxide catalyst contains one or more of SO.sub.4, WO.sub.3, or mixtures of them present between about 0.5% to about 20% by weight of the catalyst.

  16. A new simple method for point contact Andreev reflection (PCAR) using a self-aligned atomic filament in transition-metal oxides

    NASA Astrophysics Data System (ADS)

    Hwang, Inrok; Lee, Keundong; Jin, Hyunwoo; Choi, Sunhwa; Jung, Eunok; Park, Bae Ho; Lee, Suyoun

    2015-04-01

    Point contact Andreev reflection (PCAR) has become a standard method for measuring the spin polarization (P) of spintronic materials due to its unique simplicity and the firm physical ground, but it is still challenging to achieve a clean point contact between a superconductor (SC) and a metal (N) for implementing PCAR. In this work, we suggest a much simpler method for PCAR measurement, where a point contact between SC and N is provided by a metallic filament in a transition-metal oxide generated by electrical bias. This method has been successfully demonstrated using a structure composed of Nb/NiO/Pt, where P of the Ni filament was estimated to be about 40%, consistent with the known value of the bulk Ni. In addition, we investigated the dependence of the conductance spectrum on the measurement temperature and the magnetic field. We found that the superconductivity is not fully suppressed until 9 T far above the critical field of Nb, which is associated with the nm-sized constriction of our SC/N junction, much smaller than the coherence length of the SC.Point contact Andreev reflection (PCAR) has become a standard method for measuring the spin polarization (P) of spintronic materials due to its unique simplicity and the firm physical ground, but it is still challenging to achieve a clean point contact between a superconductor (SC) and a metal (N) for implementing PCAR. In this work, we suggest a much simpler method for PCAR measurement, where a point contact between SC and N is provided by a metallic filament in a transition-metal oxide generated by electrical bias. This method has been successfully demonstrated using a structure composed of Nb/NiO/Pt, where P of the Ni filament was estimated to be about 40%, consistent with the known value of the bulk Ni. In addition, we investigated the dependence of the conductance spectrum on the measurement temperature and the magnetic field. We found that the superconductivity is not fully suppressed until 9 T far above the critical field of Nb, which is associated with the nm-sized constriction of our SC/N junction, much smaller than the coherence length of the SC. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr07262f

  17. Superconductivity in transition metals.

    PubMed

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

    2015-03-13

    A qualitative account of the occurrence and magnitude of superconductivity in the transition metals is presented, with a primary emphasis on elements of the first row. Correlations of the important parameters of the Bardeen-Cooper-Schrieffer theory of superconductivity are highlighted with respect to the number of d-shell electrons per atom of the transition elements. The relation between the systematics of superconductivity in the transition metals and the periodic table high-lights the importance of short-range or chemical bonding on the remarkable natural phenomenon of superconductivity in the chemical elements. A relationship between superconductivity and lattice instability appears naturally as a balance and competition between localized covalent bonding and so-called broken covalency, which favours d-electron delocalization and superconductivity. In this manner, the systematics of superconductivity and various other physical properties of the transition elements are related and unified. PMID:25666075

  18. Final-state effect on x-ray photoelectron spectrum of nominally d1 and n -doped d0 transition-metal oxides

    NASA Astrophysics Data System (ADS)

    Lin, Chungwei; Posadas, Agham; Hadamek, Tobias; Demkov, Alexander A.

    2015-07-01

    We investigate the x-ray photoelectron spectroscopy (XPS) of nominally d1 and n -doped d0 transition-metal oxides including NbO2,SrVO3, and LaTiO3 (nominally d1), as well as n -doped SrTiO3 (nominally d0). In the case of single phase d1 oxides, we find that the XPS spectra (specifically photoelectrons from Nb 3 d , V 2 p , Ti 2 p core levels) all display at least two, and sometimes three distinct components, which can be consistently identified as d0,d1, and d2 oxidation states (with decreasing order in binding energy). Electron doping increases the d2 component but decreases the d0 component, whereas hole doping reverses this trend; a single d1 peak is never observed, and the d0 peak is always present even in phase-pure samples. In the case of n -doped SrTiO3, the d1 component appears as a weak shoulder with respect to the main d0 peak. We argue that these multiple peaks should be understood as being due to the final-state effect and are intrinsic to the materials. Their presence does not necessarily imply the existence of spatially localized ions of different oxidation states nor of separate phases. A simple model is provided to illustrate this interpretation, and several experiments are discussed accordingly. The key parameter to determine the relative importance between the initial-state and final-state effects is also pointed out.

  19. Design Insights for Tuning the Electrocatalytic Activity of Perovskite Oxides for the Oxygen Evolution Reaction

    SciTech Connect

    Malkhandi, S; Trinh, P; Manohar, AK; Manivannan, A; Balasubramanian, M; Prakash, GKS; Narayanan, SR

    2015-04-16

    Rechargeable metal-air batteries and water electrolyzers based on aqueous alkaline electrolytes hold the potential to be sustainable solutions to address the challenge of storing large amounts of electrical energy generated from solar and wind resources. For these batteries and electrolyzers to be economically viable, it is essential to have efficient, durable, and inexpensive electrocatalysts for the oxygen evolution reaction. In this article, we describe new insights for predicting and tuning the activity of inexpensive transition metal oxides for designing efficient and inexpensive electrocatalysts. We have focused on understanding the factors determining the electrocatalytic activity for oxygen evolution in a strong alkaline medium. To this end, we have conducted a systematic investigation of nanophase calcium-doped lanthanum cobalt manganese oxide, an example of a mixed metal oxide that can be tuned for its electrocatalytic activity by varying the transition metal composition. Using X-ray absorption spectroscopy (XANES), X-ray photoelectron spectroscopy (XPS), electrochemical polarization experiments, and analysis of mechanisms, we have identified the key determinants of electrocatalytic activity. We have found that the Tafel slopes are determined by the oxidation states and the bond energy of the surface intermediates of Mn-OH and Co-OH bonds while the catalytic activity increased with the average d-electron occupancy of the sigma* orbital of the M-OH bond. We anticipate that such understanding will be very useful in predicting the behavior of other transition metal oxide catalysts.

  20. Mass fractionation processes of transition metal isotopes

    NASA Astrophysics Data System (ADS)

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

    2002-06-01

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

  1. BUFFER ADDITIVES FOR LIME/LIMESTONE SLURRY SCRUBBING: SULFITE OXIDATION WITH ENHANCED OXYGEN ABSORPTION CATALYZED BY TRANSITION METALS

    EPA Science Inventory

    The report gives results of a study of sulfite oxidation, involving the measurement of the rate of enhanced oxygen absorption across an unbroken interface into solution containing sulfite (2-100 mM) and catalyst (0.01-100 mM) at pH 4-6 and 50 C. Fe, Mn, Co, Cu and Cr ions were po...

  2. Modeling of thermal expansion coefficient of perovskite oxide for solid oxide fuel cell cathode

    NASA Astrophysics Data System (ADS)

    Heydari, F.; Maghsoudipour, A.; Alizadeh, M.; Khakpour, Z.; Javaheri, M.

    2015-09-01

    Artificial intelligence models have the capacity to eliminate the need for expensive experimental investigation in various areas of manufacturing processes, including the material science. This study investigates the applicability of adaptive neuro-fuzzy inference system (ANFIS) approach for modeling the performance parameters of thermal expansion coefficient (TEC) of perovskite oxide for solid oxide fuel cell cathode. Oxides (Ln = La, Nd, Sm and M = Fe, Ni, Mn) have been prepared and characterized to study the influence of the different cations on TEC. Experimental results have shown TEC decreases favorably with substitution of Nd3+ and Mn3+ ions in the lattice. Structural parameters of compounds have been determined by X-ray diffraction, and field emission scanning electron microscopy has been used for the morphological study. Comparison results indicated that the ANFIS technique could be employed successfully in modeling thermal expansion coefficient of perovskite oxide for solid oxide fuel cell cathode, and considerable savings in terms of cost and time could be obtained by using ANFIS technique.

  3. Significant enhancement of photovoltage in artificially designed perovskite oxide structures

    NASA Astrophysics Data System (ADS)

    Zhou, Wen-jia; Jin, Kui-juan; Guo, Hai-zhong; He, Xu; He, Meng; Xu, Xiu-lai; Lu, Hui-bin; Yang, Guo-zhen

    2015-03-01

    La0.9Sr0.1MnO3/insulator/SrNb0.007Ti0.993O3 multilayer and La0.9Sr0.1MnO3/SrNb0.007Ti0.993O3/In2O3:SnO2(ITO)/La0.9Sr0.1MnO3/SrNb0.007Ti0.993O3 multilayer structures were designed to enhance the photovoltage. The photovoltages of these two structures under an illumination of 308 nm laser are 410 and 600 mV, respectively. The latter is 20 times larger than that (30 mV) observed in La0.9Sr0.1MnO3/SrNb0.007Ti0.993O3 single junction. The origin of such significant enhancement of photovoltage is discussed in this letter. These results suggest that the photoelectric property of perovskite oxides could be much improved by artificial structure designing. The enhanced photovoltaic effects have potential applications in the ultraviolet photodetection and solar cells.

  4. The electronic structure of metal oxide/organo metal halide perovskite junctions in perovskite based solar cells

    PubMed Central

    Dymshits, Alex; Henning, Alex; Segev, Gideon; Rosenwaks, Yossi; Etgar, Lioz

    2015-01-01

    Cross-sections of a hole-conductor-free CH3NH3PbI3 perovskite solar cell were characterized with Kelvin probe force microscopy. A depletion region width of about 45?nm was determined from the measured potential profiles at the interface between CH3NH3PbI3 and nanocrystalline TiO2, whereas a negligible depletion was measured at the CH3NH3PbI3/Al2O3 interface. A complete solar cell can be realized with the CH3NH3PbI3 that functions both as light harvester and hole conductor in combination with a metal oxide. The band diagrams were estimated from the measured potential profile at the interfaces, and are critical findings for a better understanding and further improvement of perovskite based solar cells. PMID:25731963

  5. Atomic layer deposition of perovskite oxides and their epitaxial integration with Si, Ge, and other semiconductors

    NASA Astrophysics Data System (ADS)

    McDaniel, Martin D.; Ngo, Thong Q.; Hu, Shen; Posadas, Agham; Demkov, Alexander A.; Ekerdt, John G.

    2015-12-01

    Atomic layer deposition (ALD) is a proven technique for the conformal deposition of oxide thin films with nanoscale thickness control. Most successful industrial applications have been with binary oxides, such as Al2O3 and HfO2. However, there has been much effort to deposit ternary oxides, such as perovskites (ABO3), with desirable properties for advanced thin film applications. Distinct challenges are presented by the deposition of multi-component oxides using ALD. This review is intended to highlight the research of the many groups that have deposited perovskite oxides by ALD methods. Several commonalities between the studies are discussed. Special emphasis is put on precursor selection, deposition temperatures, and specific property performance (high-k, ferroelectric, ferromagnetic, etc.). Finally, the monolithic integration of perovskite oxides with semiconductors by ALD is reviewed. High-quality epitaxial growth of oxide thin films has traditionally been limited to physical vapor deposition techniques (e.g., molecular beam epitaxy). However, recent studies have demonstrated that epitaxial oxide thin films may be deposited on semiconductor substrates using ALD. This presents an exciting opportunity to integrate functional perovskite oxides for advanced semiconductor applications in a process that is economical and scalable.

  6. Ligand field splittings in core level transitions for transition metal (TM) oxides: Tanabe-Sugano diagrams and (TM) dangling bonds in vacated O-atom defects

    NASA Astrophysics Data System (ADS)

    Lucovsky, Gerry; Wu, Kun; Pappas, Brian; Whitten, Jerry

    2013-04-01

    Defect states in the forbidden band-gap below the conduction band edge are active as electron traps in nano-grain high-) transition metal (TM) oxides with thickness >0.3 nm, e.g., ZrO2 and HfO2. These oxides have received considerable attention as gate-dielectrics in complementary metal oxide semiconductor (CMOS) devices, and more recently are emerging as candidates for charge storage and memory devices. To provide a theoretical basis for device functionality, ab-initio many-electron theory is combined with X-ray absorption spectroscopy (XAS) to study O K edge and TM core level transitions. These studies identify ligand field splittings (?LF) for defect state features,. When compared with those obtained from O-atom and TM-atom core spectroscopic transitions, this provides direct information about defect state sun-nm bonding arrangements. comparisons are made for (i) elemental TiO2 and Ti2O3 with different formal ionic charges, Ti4+ and Ti3+ and for (ii) Magneli Phase alloys, TinO2n-1, n is an integer 9>=n>3, and (TiO2)x(HfO2)1-x alloys. The alloys display multi-valent behavior from (i) different ionic-charge states, (ii} local bond-strain, and (iii) metallic hopping transport. The intrinsic bonding defects in TM oxides are identified as pairs of singly occupied dangling bonds. For 6-fold coordinated Ti-oxides defect excited states in 2nd derivative O K pre-edge spectra are essentially the same as single Ti-atom d2 transitions in Tanabe-Sugano (T-S) diagrams. O-vacated site defects in 8-fold coordinated ZrO2 and HfO2 are described by d8 T-S diagrams. T-S defect state ordering and splittings are functions of the coordination and symmetry of vacated site bordering TM atoms. ?LF values from the analysis of T-S diagrams indicate medium range order (MRO) extending to 3rd and 4th nearest-neighbor (NN) TM-atoms. Values are different for 6-fold Ti, and 8-fold ZrO2 and HfO2, and scale inversely with differences in respective formal ionic radii. O-vacated site bonding defects in TM nano-grain oxides are qualitatively similar to vacant-site defects in non-crystalline SiO2 and GeO2 for ulta-thin films, < 0.2 nm thick, and yield similar performance in MOSCAPs on Ge substrates heralding applications in aggressively-scale CMOS devices.

  7. Transition metal (Fe, Co and Ni) oxide nanoparticles grafted graphitic carbon nitrides as efficient optical limiters and recyclable photocatalysts

    NASA Astrophysics Data System (ADS)

    Sridharan, Kishore; Kuriakose, Tintu; Philip, Reji; Park, Tae Joo

    2014-07-01

    A single-step pyrolysis assisted route towards the large scale fabrication of metal oxide nanoparticles (Fe2O3, Co3O4 and NiO) ingrained in graphitic carbon nitride (GCN) is demonstrated. Urea, an abundantly available precursor, plays a dual role during the synthesis: while it acts as a reducing agent, it also gets converted to GCN. The formation of GCN and the in-situ growth and embedment of oxide nanoparticles are discussed on the basis of the experimental results. The wide absorption of the samples in the visible light region makes them suitable for nonlinear transmission and photocatalytic activity studies. Visible light photocatalytic activities of the samples are studied by monitoring the degradation of Rhodamine B dye. Optical limiting properties of the prepared samples are studied through the open aperture z-scan technique using 5 ns laser pulses at a wavelength of 532 nm. The cost-efficient and time saving synthetic approach is complemented by the magnetic behaviour of the samples, which enables their use as recyclable photocatalyst and magnetically controllable optical limiters.

  8. Transition Metal Switchable Mirror

    SciTech Connect

    2009-08-21

    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.

  9. Transition Metal Switchable Mirror

    ScienceCinema

    None

    2010-01-08

    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.

  10. Transition Metal Switchable Mirror

    ScienceCinema

    None

    2013-05-29

    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

  11. Tribochemical properties of metastable states of transition metals 

    E-print Network

    Kar, Prasenjit

    2009-05-15

    challenges in directing the reaction kinetics. This dissertation studied the dynamics and kinetics of oxidation of transitional metals, particularly on tantalum through mechanical forces. This is a new area of research in surface science. Experimentally using...

  12. Kinetic and mechanistic studies of reactive intermediates in photochemical and transition metal-assisted oxidation, decarboxylation and alkyl transfer reactions

    NASA Astrophysics Data System (ADS)

    Carraher, Jack McCaslin

    Reactive species like high-valent metal-oxo complexes and carbon and oxygen centered radicals are important intermediates in enzymatic systems, atmospheric chemistry, and industrial processes. Understanding the pathways by which these intermediates form, their relative reactivity, and their fate after reactions is of the utmost importance. Herein are described the mechanistic detail for the generation of several reactive intermediates, synthesis of precursors, characterization of precursors, and methods to direct the chemistry to more desirable outcomes yielding 'greener' sources of commodity chemicals and fuels. High-valent Chromium from Hydroperoxido-Chromium(III). The decomposition of pentaaquahydroperoxido chromium(III) ion (hereafter Cr aqOOH2+) in acidic aqueous solutions is kinetically complex and generates mixtures of products (Craq3+, HCrO 4-, H2O2, and O2). The yield of high-valent chromium products (known carcinogens) increased from a few percent at pH 1 to 70 % at pH 5.5 (near biological pH). Yields of H 2O2 increased with acid concentration. The reproducibility of the kinetic data was poor, but became simplified in the presence of H2O2 or 2,2?-azinobis(3-ethylbenzothiazoline-6-sulfonate) dianion (ABTS2-). Both are capable of scavenging strongly oxidizing intermediates). The observed rate constants (pH 1, [O2] ? 0.03 mM) in the presence of these scavengers are independent of [scavenger] and within the error are the same (k,ABTS2- = (4.9 +/- 0.2) x 10-4 s-1 and kH2O2 = (5.3 +/- 0.7) x 10-4 s-1); indicating involvement of the scavengers in post-rate determining steps. In the presence of either scavenger, decomposition of CrOOH2+ obeyed a two-term rate law, k obs / s-1 = (6.7 +/- 0.7) x 10-4 + (7.6 +/- 1.1) x 10-4 [H+]. Effect of [H+] on the kinetics and the product distribution, cleaner kinetics in the presence of scavengers, and independence of kobs on [scavenger] suggest a dual-pathway mechanism for the decay of Craq OOH2+. The H+-catalyzed path leads to the dissociation of H2O2 from Cr(III), while in the H+-independent reaction, CraqOOH2+ is transformed to Cr(V). Both scavengers rapidly remove Cr(V) and simplify both the kinetics and products by impeding formation of Cr(IV, V, VI). Syntheses, Reactivity, and Thermodynamic Considerations LRhR2+. Macrocyclic rhodium(II) complexes LRh(H 2O)2+ (L = L1= cyclam and L2 = meso-Me6-cyclam) react with alkyl hydroperoxides R(CH3)2COOH to generate the corresponding rhodium(III) alkyls LRh(H2O)R2+ (R = CH3, C2 H5, PhCH2). Methyl and benzyl complexes can also be prepared by bimolecular group transfer from alkyl cobaloximes (dmgX) 2(H2O)CoR (where R = CH3, CH2Ph and dmgX is either dimethylglyoxime or a BF2-capped derivative of dmg) to LRh(H2O)2+. When R = C2H5, C3H7 or C4H9, the mechanism changes from group transfer to hydrogen atom abstraction from the coordinated alkyl and produces LRh(H2O)H2+ and an a-olefin. The new LRh(H2O)R2+ complexes were characterized by solution NMR and by crystal structure analysis. They exhibit great stability in aqueous solution at room temperature, but undergo efficient Rh-C bond cleavage upon photolysis. 'Green' Model for Decarboxylation of Biomass Derived Acids via Photolysis of in situ formed Metal-Carboxylate Complexes. Photolysis of aqueous solutions containing propionic acid and Fe 3+ aq in the absence of oxygen generates a mixture of hydrocarbons (ethane, ethylene and butane), carbon dioxide, and Fe2+. Photolysis in the presence of O2 yields catalytic amounts of hydrocarbon products. When halide ions are present during photolysis; nearly quantitative yields of ethyl halides are produced via extraction of a halide atom from FeX2+ by ethyl radical. The rate constants for ethyl radical reactions with FeCl2+ (k = 4.0 (+/- 0.5) x 106 M-1s-1) and with FeBr 2+ (k = 3.0 (+/- 0.5) x 107 M-1s -1) were determined via competition reactions. Irradiation of solutions containing aqueous Cu2+ salts and linear carboxylic acids yield alpha-olefins selectively. This process is made catalytic by the introduction of O2. Photochemical decarboxylation of

  13. Electronically conductive perovskite-based oxide nanoparticles and films for optical sensing applications

    DOEpatents

    Ohodnicki, Jr., Paul R; Schultz, Andrew M

    2015-04-28

    The disclosure relates to a method of detecting a change in a chemical composition by contacting a electronically conducting perovskite-based metal oxide material with a monitored stream, illuminating the electronically conducting perovskite-based metal oxide with incident light, collecting exiting light, monitoring an optical signal based on a comparison of the incident light and the exiting light, and detecting a shift in the optical signal. The electronically conducting perovskite-based metal oxide has a perovskite-based crystal structure and an electronic conductivity of at least 10.sup.-1 S/cm, where parameters are specified at the gas stream temperature. The electronically conducting perovskite-based metal oxide has an empirical formula A.sub.xB.sub.yO.sub.3-.delta., where A is at least a first element at the A-site, B is at least a second element at the B-site, and where 0.8perovskite-based oxides include but are not limited to La.sub.1-xSr.sub.xCoO.sub.3, La.sub.1-xSr.sub.xMnO.sub.3, LaCrO.sub.3, LaNiO.sub.3, La.sub.1-xSr.sub.xMn.sub.1-yCr.sub.yO.sub.3, SrFeO.sub.3, SrVO.sub.3, La-doped SrTiO.sub.3, Nb-doped SrTiO.sub.3, and SrTiO.sub.3-.delta..

  14. Melting of Transition Metals

    SciTech Connect

    Ross, M; Japel, S; Boehler, R

    2005-04-11

    We review the transition melting studies carried out at Mainz, and describe a recently developed model used to explain that the relatively low melting slopes are due to the partially filled d-bands, and the persistence of the pressure induced s-d transition. The basic tenets of the model have now been reconfirmed by new measurements for Cu and Ni. The measurements show that Cu which has a filled 3d-band, has a melt slope that is about 2.5 greater than its neighbor Ni. In the case of Mo, the apparent discrepancy of DAC melting measurements with shock melting can be explained by accounting for the change in melt slope due to the bcc-cp transition observed in the shock studies. The Fe melt curve is revisited. The possible relevance of the Jahn-Teller effect and recently observed transition metal melts with Icosahedral Short-Range Order (ISRO) is discussed.

  15. Structure Determination of Ba8CoRh6O21, a New Member of the 2H-Perovskite Related Oxides

    E-print Network

    zur Loye, Hans-Conrad

    Structure Determination of Ba8CoRh6O21, a New Member of the 2H-Perovskite Related Oxides H.-C. zur of an m = 5, n = 3 member of the A3n+3mA'nB3m+nO9m+6n family of 2H hexagonal perovskite related oxides. For this reason, perovskite and perovskite-related oxides in particular have long provided excellent candidates

  16. Design principles for oxygen-reduction activity on perovskite oxide catalysts for fuel cells and metal-air batteries.

    PubMed

    Suntivich, Jin; Gasteiger, Hubert A; Yabuuchi, Naoaki; Nakanishi, Haruyuki; Goodenough, John B; Shao-Horn, Yang

    2011-07-01

    The prohibitive cost and scarcity of the noble-metal catalysts needed for catalysing the oxygen reduction reaction (ORR) in fuel cells and metal-air batteries limit the commercialization of these clean-energy technologies. Identifying a catalyst design principle that links material properties to the catalytic activity can accelerate the search for highly active and abundant transition-metal-oxide catalysts to replace platinum. Here, we demonstrate that the ORR activity for oxide catalysts primarily correlates to ?-orbital (e(g)) occupation and the extent of B-site transition-metal-oxygen covalency, which serves as a secondary activity descriptor. Our findings reflect the critical influences of the ? orbital and metal-oxygen covalency on the competition between O(2)(2-)/OH(-) displacement and OH(-) regeneration on surface transition-metal ions as the rate-limiting steps of the ORR, and thus highlight the importance of electronic structure in controlling oxide catalytic activity. PMID:21697876

  17. Towards printed perovskite solar cells with cuprous oxide hole transporting layers: a theoretical design

    NASA Astrophysics Data System (ADS)

    Wang, Yan; Xia, Zhonggao; Liang, Jun; Wang, Xinwei; Liu, Yiming; Liu, Chuan; Zhang, Shengdong; Zhou, Hang

    2015-05-01

    Solution-processed p-type metal oxide materials have shown great promise in improving the stability of perovskite-based solar cells and offering the feasibility for a low cost printing fabrication process. Herein, we performed a device modeling study on planar perovskite solar cells with cuprous oxide (Cu2O) hole transporting layers (HTLs) by using a solar cell simulation program, wxAMPS. The performance of a Cu2O/perovskite solar cell was correlated to the material properties of the Cu2O HTL, such as thickness, carrier mobility, mid-gap defect, and doping concentrations. The effect of interfacial defect densities on the solar cell performance was also investigated. Our simulation indicates that, with an optimized Cu2O HTL, high performance perovskite solar cells with efficiencies above 13% could be achieved, which shows the potential of using Cu2O as an alternative HTL over other inorganic materials, such as NiOx and MoOx. This study provides theoretical guidance for developing perovskite solar cells with inorganic hole transporting materials via a printing process.

  18. Surface structural changes of perovskite oxides during oxygen evolution in alkaline electrolyte

    E-print Network

    May, Kevin J. (Kevin Joseph)

    2013-01-01

    Perovskite oxides such Ba0.5Sr0.5Co0.8Fe0.8O3-6 (BSCF82) are among the most active catalysts for the oxygen evolution reaction (OER) in alkaline solution reported to date. In this work it is shown via high resolution ...

  19. Relationship between Local Structure and Relaxor Behavior in Perovskite Oxides Ilya Grinberg,1

    E-print Network

    Rappe, Andrew M.

    Relationship between Local Structure and Relaxor Behavior in Perovskite Oxides Ilya Grinberg,1 intensive investigations over the past five decades, the microscopic origins of the fascinating dielectric of relaxors is their tempera- ture- and frequency-dependent dielectric response. While normal ferroelectrics

  20. Perovskite-type oxide membranes for the oxidative coupling of methane

    SciTech Connect

    Xu, S.J.; Thomson, W.J.

    1997-12-31

    A series of ion-conducting perovskites of the form [La{sub 1{minus}x}A{sub x}][Co{sub 0.2}Fe{sub 0.8}]O{sub 3{minus}{delta}} (x = 0.4, 0.6 for A = Sr; x = 0.8 for A = Ba) were investigated for their use as a catalytic membrane for the oxidative coupling of methane (OCM). A-site cations consisting of La{sub 0.4}Sr{sub 0.6} and La{sub 0.2}Ba{sub 0.8} produce materials with the highest oxygen fluxes and result in C{sub 2+} selectivities of 50% at 1,098 K, which are significantly higher than those achieved with a powdered catalyst in a packed-bed reactor configuration. Selectivities in these materials appear to be limited by high oxygen ion recombination rates that compete for oxygen with the desired coupling reaction(s). The results also indicate that oxygen fluxes are not limited by diffusion, but by surface exchange rates at the oxygen-lean side of the membrane. The study on stability of these materials showed that all three perovskites could be reduced in a pure methane or ethane stream at 1,023 K, but they were totally stable under reaction conditions where oxygen is present.

  1. Novel 2D electron gases at the surface of transition-metal oxides: role of topology and spin-orbit coupling

    NASA Astrophysics Data System (ADS)

    Santander-Syro, Andrés F.

    2014-03-01

    Transition-metal oxides (TMOs) are correlated-electron systems with remarkable properties, such as high-temperature superconductivity or large magnetoresistance. The realization of two-dimensional electron gases (2DEGs) at surfaces or interfaces of TMOs, a field of current active research, is crucial for harnessing the functionalities of these materials for future applications. Additionally, these 2DEGs offer the possibility to explore new physics emerging from the combined effects of electron correlations and low-dimensional confinement. Recently, we discovered that a 2DEG can be simply realized at the vacuum-cleaved surface of SrTiO3, a transparent, insulating TMO with a gap of 3.5 eV. We directly imaged its multiple heavy and light subbands using angle-resolved photoemission spectroscopy [A. F. Santander-Syro et al., Nature 469, 189 (2011)]. In this talk, I will show that one can also create and tailor 2DEGs in other TMO surfaces, opening vast possibilities for the study of correlations in low dimensions in materials showing diverse functionalities. I will first discuss the specific case of KTaO3, a wide-gap insulator with a spin-orbit coupling 30 times larger than in SrTiO3. I will show that quasi-2D confinement in this system results in comparable scales for the Fermi energy, the subband splitting, and the spin-orbit coupling, leading to a complete reconstruction of the orbital symmetries and band masses [A. F. Santander-Syro et al., Phys. Rev. B 86, 121107(R) (2012)]. Then, I will show that by choosing various surface terminations of different symmetries one can modify the electronic structure of the 2DEGs at the surface of TMOs [C. Bareille et al., submitted (2013); T. Rödel et al., submitted (2013)]. All these results demonstrate that, in TMOs, the strong correlations, together with the electron confinement and the surface-lattice symmetry, can lead to novel states at the surface that are not simple extensions of the bulk bands. Acknowledgements: support from ANR (project LACUNES), LabEx PALM (project ELECTROX), RTRA Triangle de la Physique (project PEGASOS), and Institut Universitaire de France.

  2. p-type Mesoscopic Nickel Oxide/Organometallic Perovskite Heterojunction Solar Cells

    PubMed Central

    Wang, Kuo-Chin; Jeng, Jun-Yuan; Shen, Po-Shen; Chang, Yu-Cheng; Diau, Eric Wei-Guang; Tsai, Cheng-Hung; Chao, Tzu-Yang; Hsu, Hsu-Cheng; Lin, Pei-Ying; Chen, Peter; Guo, Tzung-Fang; Wen, Ten-Chin

    2014-01-01

    In this article, we present a new paradigm for organometallic hybrid perovskite solar cell using NiO inorganic metal oxide nanocrystalline as p-type electrode material and realized the first mesoscopic NiO/perovskite/[6,6]-phenyl C61-butyric acid methyl ester (PC61BM) heterojunction photovoltaic device. The photo-induced transient absorption spectroscopy results verified that the architecture is an effective p-type sensitized junction, which is the first inorganic p-type, metal oxide contact material for perovskite-based solar cell. Power conversion efficiency of 9.51% was achieved under AM 1.5 G illumination, which significantly surpassed the reported conventional p-type dye-sensitized solar cells. The replacement of the organic hole transport materials by a p-type metal oxide has the advantages to provide robust device architecture for further development of all-inorganic perovskite-based thin-film solar cells and tandem photovoltaics. PMID:24755642

  3. Iron-based perovskite cathodes for solid oxide fuel cells

    DOEpatents

    Ralph, James M.; Rossignol, Cecile C.R.; Vaughey, John T.

    2007-01-02

    An A and/or A' site deficient perovskite of general formula of (A.sub.1-xA'.sub.x).sub.1-yFeO.sub.3-.delta. or of general formula A.sub.1-x-yA'.sub.xFeO.sub.3-67, wherein A is La alone or with one or more of the rare earth metals or a rare earth metal other than Ce alone or a combination of rare earth metals and X is in the range of from 0 to about 1; A' is Sr or Ca or mixtures thereof and Y is in the range of from about 0.01 to about 0.3; .delta. represents the amount of compensating oxygen loss. If either A or A' is zero the remaining A or A' is deficient. A fuel cell incorporating the inventive perovskite as a cathode is disclosed as well as an oxygen separation membrane. The inventive perovskite is preferably single phase.

  4. Selenophene transition metal complexes

    SciTech Connect

    White, C.J.

    1994-07-27

    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.

  5. Late transition metal anions acting as p-metal elements

    NASA Astrophysics Data System (ADS)

    Köhler, Jürgen; Whangbo, Myung-Hwan

    2008-04-01

    A brief review is given for those extended solids of transition metal compounds in which their transition metal atoms are best described as existing as anions. Analyses of the electronic structures of metal-rich fluorides and oxides containing octahedral metallo-complexes [MIn 6- xSn x] (M = Fe, Ni, Ru, Os, Ir and Pt) indicate that their transition metal atoms M are present as anions with the valence electron configuration ( n + 1)s 2nd 10. In compounds RE 2M 2In (RE = rare earth element, M = Pt, Cu and Au), Ca 5Au 4, Ca 3Hg 2 and Ca 5M 3 (M = Cu, Au, Zn, Cd and Hg), the transition metal atoms exist as dimeric Zintl anions with the valence electron configuration ( n + 1)s 2nd 10( n + 1)p 1. Consequently, the frontier orbitals of these compounds are not described by the transition metal nd orbitals, but by the transition metal ( n + 1)p orbitals. A similar situation is found for most 18-electron half-Heusler compounds (e.g., ScAuSn), for which the valence electron configuration of the transition metal is given by ( n + 1)s 2nd 10( n + 1)p 2.

  6. NdBaCo2/3Fe2/3Cu2/3O5+? double perovskite as a novel cathode material for CeO2- and LaGaO3-based solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Jin, Fangjun; Li, Lei; He, Tianmin

    2015-01-01

    Double perovskites LnBaCo2O5+? (Ln = rare earth) are explored as cathode materials for intermediate-temperature solid oxide fuel cell. Barriers to the applicability of double perovskite cathodes include high thermal expansion coefficient (TEC) and poor chemical compatibility with common electrolytes. In this paper, we report the characteristics and applicability of a double perovskite NdBaCo2/3Fe2/3Cu2/3O5+? (NBCFC) cathode on CeO2- and LaGaO3-based electrolytes. NBCFC is found to crystallize in a tetragonal structure. Partial substitution of Fe and Cu for cobalt in NBCFC demonstrates significantly decreased TEC and good chemical compatibility with both Gd0.1Ce0.9O1.95 (GDC) and La0.9Sr0.1Ga0.8Mg0.2O3-? (LSGM) electrolytes, while maintaining its good electrochemical performance. The oxidation states of transition metal cations are Co3+/Co4+, Fe3+/Fe4+, and Cu+/Cu2+, respectively. The average TEC of NBCFC is 15.7 × 10-6 K-1 between 30 and 850 °C, and the polarization resistance values are 0.056 and 0.023 ? cm2 at 800 °C with GDC and LSGM electrolytes, respectively. The absence of spin-state transition in copper contributes to the TEC reduction. Addition of appropriate amounts of GDC into NBCFC to form NBCFC-GDC composite cathodes further reduce the TEC and improve cathode performance. These results can be used to improve and develop novel double perovskite cathode materials.

  7. Perovskite-type catalytic materials for environmental applications

    NASA Astrophysics Data System (ADS)

    Labhasetwar, Nitin; Saravanan, Govindachetty; Megarajan, Suresh Kumar; Manwar, Nilesh; Khobragade, Rohini; Doggali, Pradeep; Grasset, Fabien

    2015-06-01

    Perovskites are mixed-metal oxides that are attracting much scientific and application interest owing to their low price, adaptability, and thermal stability, which often depend on bulk and surface characteristics. These materials have been extensively explored for their catalytic, electrical, magnetic, and optical properties. They are promising candidates for the photocatalytic splitting of water and have also been extensively studied for environmental catalysis applications. Oxygen and cation non-stoichiometry can be tailored in a large number of perovskite compositions to achieve the desired catalytic activity, including multifunctional catalytic properties. Despite the extensive uses, the commercial success for this class of perovskite-based catalytic materials has not been achieved for vehicle exhaust emission control or for many other environmental applications. With recent advances in synthesis techniques, including the preparation of supported perovskites, and increasing understanding of promoted substitute perovskite-type materials, there is a growing interest in applied studies of perovskite-type catalytic materials. We have studied a number of perovskites based on Co, Mn, Ru, and Fe and their substituted compositions for their catalytic activity in terms of diesel soot oxidation, three-way catalysis, N2O decomposition, low-temperature CO oxidation, oxidation of volatile organic compounds, etc. The enhanced catalytic activity of these materials is attributed mainly to their altered redox properties, the promotional effect of co-ions, and the increased exposure of catalytically active transition metals in certain preparations. The recent lowering of sulfur content in fuel and concerns over the cost and availability of precious metals are responsible for renewed interest in perovskite-type catalysts for environmental applications.

  8. Protonic and electronic conductivity of the layered perovskite oxides HCa2Nb3O10 and Ca4Nb6O19

    E-print Network

    Protonic and electronic conductivity of the layered perovskite oxides HCa2Nb3O10 and Ca4Nb6O19 February 2014 Keywords: Layer perovskite Solid electrolyte Mixed valence Electronic conductivityJacobson series layer perovskite HCa2Nb3O10 were investigated. Within the intermediate temperature range (200e475

  9. Development and Application of a Multielectron-Accepting Organic Oxidant for the Catalytic Transition-Metal-Free Oxidative Homocoupling of Grignard Reagents in Air.

    PubMed

    Korenaga, Toshinobu; Nitatori, Kaoru; Muraoka, Hiroki; Ogawa, Satoshi; Shimada, Kazuaki

    2015-11-01

    Heptafluorotolyl-substituted perfluorocyclopentene acts as a four-electron oxidant for the homocoupling of Grignard reagents. It can also be used for catalytic homocoupling with a low catalyst loading (up to 2 mol %) in the presence of atmospheric oxygen. The organocatalytic cycle involves the generation of an organic radical and a perfluorocyclopentadienyl anion. PMID:26503294

  10. Nonaqueous synthesis of metal oxide nanoparticles: Short review and doped titanium dioxide as case study for the preparation of transition metal-doped oxide nanoparticles

    NASA Astrophysics Data System (ADS)

    Djerdj, Igor; Ar?on, Denis; Jagli?i?, Zvonko; Niederberger, Markus

    2008-07-01

    The liquid-phase synthesis of metal oxide nanoparticles in organic solvents under exclusion of water is nowadays a well-established alternative to aqueous sol-gel chemistry. In this article, we highlight some of the advantages of these routes based on selected examples. The first part reviews some recent developments in the synthesis of ternary metal oxide nanoparticles by surfactant-free nonaqueous sol-gel routes, followed by the discussion of the morphology-controlled synthesis of lanthanum hydroxide nanoparticles, and the presentation of structural peculiarities of manganese oxide nanoparticles with an ordered Mn vacancy superstructure. These examples show that nonaqueous systems, on the one hand, allow the preparation of compositionally complex oxides, and, on the other hand, make use of the organic components (initially present or formed in situ) in the reaction mixture to tailor the morphology. Furthermore, obviously even the crystal structure can differ from the corresponding bulk material like in the case of MnO nanoparticles. In the second part of the paper we present original results regarding the synthesis of dilute magnetic semiconductor TiO 2 nanoparticles doped with cobalt and iron. The structural characterization as well as the magnetic properties with special attention to the doping efficiency is discussed.

  11. Nonaqueous synthesis of metal oxide nanoparticles: Short review and doped titanium dioxide as case study for the preparation of transition metal-doped oxide nanoparticles

    SciTech Connect

    Djerdj, Igor Arcon, Denis; Jaglicic, Zvonko; Niederberger, Markus

    2008-07-15

    The liquid-phase synthesis of metal oxide nanoparticles in organic solvents under exclusion of water is nowadays a well-established alternative to aqueous sol-gel chemistry. In this article, we highlight some of the advantages of these routes based on selected examples. The first part reviews some recent developments in the synthesis of ternary metal oxide nanoparticles by surfactant-free nonaqueous sol-gel routes, followed by the discussion of the morphology-controlled synthesis of lanthanum hydroxide nanoparticles, and the presentation of structural peculiarities of manganese oxide nanoparticles with an ordered Mn vacancy superstructure. These examples show that nonaqueous systems, on the one hand, allow the preparation of compositionally complex oxides, and, on the other hand, make use of the organic components (initially present or formed in situ) in the reaction mixture to tailor the morphology. Furthermore, obviously even the crystal structure can differ from the corresponding bulk material like in the case of MnO nanoparticles. In the second part of the paper we present original results regarding the synthesis of dilute magnetic semiconductor TiO{sub 2} nanoparticles doped with cobalt and iron. The structural characterization as well as the magnetic properties with special attention to the doping efficiency is discussed. - Graphical abstract: In the first part of this article, nonaqueous sol-gel routes to ternary metal oxide nanoparticles are briefly reviewed, followed by the discussion of the morphology-controlled synthesis of lanthanum hydroxide nanoparticles, and the appearance of an unprecedented superstructure in MnO nanoparticles. In the second part, doping experiments of TiO{sub 2} with Fe and Co are presented, along with their characterization including magnetic measurements.

  12. Photocatalytic oxidation of VOC, nitrogen oxide and atrazine using titanium dioxide modified with perovskite materials

    NASA Astrophysics Data System (ADS)

    Vajifdar, Kayzad Jimmy

    Photocatalysis utilizes near-UV or visible light to break down organic pollutants into innocuous compounds at room temperatures and has gained much attention in air and water pollution control. Chapter 1 introduces the use of semiconducting optical crystals as an additive to a photocatalyst. The perovskite optical material BaTiO3 (band gap of 3.7-3.8 eV) is found to increase VOC destruction when black light is used. The best composition found is 0.1 wt% BaTiO3 with the balance being TiO2. This photocatalyst increases perchloroethylene (PCE) conversion by 12% to 32% for space times between 1.4 and 17.2 seconds and inlet concentrations of 40 to 130 ppm with a 4 W black light. The average enhancement is approximately 25%. For butyraldehyde conversion the maximum enhancement is 20% at 130 ppm in 3.6 seconds. The UV/Vis spectroscopy data indicate a lower absorbance with the additive. The reaction parameters studied are space velocity, inlet concentration and light source. Oxidation by-products are identified using a GCMS. Chapter 2 introduces photocatalysis as an emerging green technology for environmental protection to oxidize NOx. The experimental results indicate that the coating of photocatalytic materials on concrete pavements can harvest the light energy for NOx pollution control. The photocatalytic coating has the potential to reduce NOx concentration in the atmosphere economically, nearly maintenance-free. NOx will be oxidized to nitric acid, neutralized by the alkaline base materials in concrete, and washed away by rain. The reduction in the number of high ozone days can be significant to allow sustainable economic developments in the many ozone-non-attainment areas worldwide. One of the foci will be pavement coated with photocatalysts enhanced with perovskites/ferroelectric optical crystals such as BaTiO3 via increased transmission/scattering and electron-hole pair stabilization. The developed technology can be transferred to the cement and coating industries to meet the EPA's ever tightening emission standards and will give architects and town planners a new weapon in the fight against pollution in the foreseeable future. This chapter also shows the visible-light excited photocatalytic oxidation of NOx at different inlet NO concentration, space time, and relative humidity. The reaction products are studied with a NOx analyzer and ion chromatography from gas phase, catalyst and scrubber liquor. A possible mechanism is proposed. The oxidation products are NO 2, HNO2, and HNO3. The former can be captured in an adsorbent bed and recovered as nitric acid. Chapter 3 investigates the photocatalytic oxidation (PCO) of atrazine in aqueous solution under 9 W fluorescent light irradiation using four different types of photocatalysts: Degussa P-25 standard TiO2, Ecodevice BA-PW25, Nd-doped TiO2 prepared by sol-gel technique and TiO 2 modified with BaTiO3. With an initial atrazine concentration of 60 ppb, after PCO only two products remain in detectable levels. Up to 77% of decomposed atrazine becomes hydroxyatrazine, the major byproduct; the second product peak remains undefined. Both atrazine and hydroxyatrazine photodecompose following the first order rate equation, but the hydroxyatrazine photodecomposition rate is significantly slower than that of atrazine. Doping TiO2 with Nd+3/Ba+2 reduces the photodegradation time. The difference in the ionic radii of Ba+2 and Nd +3 as compared to Ti+4, and the oxygen affinities of Ba and Nd as compared to Ti are responsible for this effect. These differences help to promote electron trapping, thereby increasing the lifetime of the holes that are responsible for the oxidation of atrazine.

  13. Selective Deposition of Insulating Metal Oxide in Perovskite Solar Cells with Enhanced Device Performance.

    PubMed

    Yue, Youfeng; Yang, Xudong; Wu, Yongzhen; Salim, Noviana Tjitra; Islam, Ashraful; Noda, Takeshi; Han, Liyuan

    2015-08-24

    We report a simple methodology for the selective deposition of an insulating layer on the nanoparticulate TiO2 (np-TiO2) mesoporous layer of perovskite solar cells. The deposited MgO insulating layer mainly covered the bottom part of the np-TiO2 layer with less coverage at the top. The so-called quasi-top-open structure is introduced to act as an efficient hole-blocking layer to prevent charge recombination at the physical contact of the transparent conducting oxide with the perovskite. This leads to an open-circuit voltage higher than that of the reference cell with a compact TiO2 hole-blocking layer. Moreover, such a quasi-top-open structure can facilitate the electron injection from perovskite into the np-TiO2 mesoporous layer and improve the spectral response at longer wavelength because of the less covered insulating layer at the top. This work provides an alternative way to fabricate perovskite solar cells without the need to use a conventional compact TiO2 layer. PMID:26230988

  14. Atomic level observation of octahedral distortions at the perovskite oxide heterointerface

    PubMed Central

    Aso, Ryotaro; Kan, Daisuke; Shimakawa, Yuichi; Kurata, Hiroki

    2013-01-01

    For perovskite oxides, ABO3, slight octahedral distortions have close links to functional properties. While perovskite oxide heterostructures offer a good platform for controlling functionalities, atomistic understanding of octahedral distortion at the interface has been a challenge as it requires precise measurements of the oxygen atomic positions. Here we demonstrate an approach to clarify distortions at an atomic level using annular bright-field imaging in aberration-corrected scanning transmission electron microscopy, which provides precise mappings of cation and oxygen atomic positions from distortion-minimized images. This technique revealed significant distortions of RuO6 and ScO6 octahedra at the heterointerface between a SrRuO3 film and a GdScO3 substrate. We also found that structural mismatch was relieved within only four unit cells near the interface by shifting the oxygen atomic positions to accommodate octahedral tilt angle mismatch. The present results underscore the critical role of the oxygen atom in the octahedral connectivity at the perovskite oxide heterointerface. PMID:23856752

  15. PREFACE: INERA Workshop: Transition Metal Oxide Thin Films-functional Layers in "Smart windows" and Water Splitting Devices. Parallel session of the 18th International School on Condensed Matter Physics

    NASA Astrophysics Data System (ADS)

    2014-11-01

    The Special issue presents the papers for the INERA Workshop entitled "Transition Metal Oxides as Functional Layers in Smart windows and Water Splitting Devices", which was held in Varna, St. Konstantin and Elena, Bulgaria, from the 4th-6th September 2014. The Workshop is organized within the context of the INERA "Research and Innovation Capacity Strengthening of ISSP-BAS in Multifunctional Nanostructures", FP7 Project REGPOT 316309 program, European project of the Institute of Solid State Physics at the Bulgarian Academy of Sciences. There were 42 participants at the workshop, 16 from Sweden, Germany, Romania and Hungary, 11 invited lecturers, and 28 young participants. There were researchers present from prestigious European laboratories which are leaders in the field of transition metal oxide thin film technologies. The event contributed to training young researchers in innovative thin film technologies, as well as thin films characterization techniques. The topics of the Workshop cover the field of technology and investigation of thin oxide films as functional layers in "Smart windows" and "Water splitting" devices. The topics are related to the application of novel technologies for the preparation of transition metal oxide films and the modification of chromogenic properties towards the improvement of electrochromic and termochromic device parameters for possible industrial deployment. The Workshop addressed the following topics: Metal oxide films-functional layers in energy efficient devices; Photocatalysts and chemical sensing; Novel thin film technologies and applications; Methods of thin films characterizations; From the 37 abstracts sent, 21 manuscripts were written and later refereed. We appreciate the comments from all the referees, and we are grateful for their valuable contributions. Guest Editors: Assoc. Prof. Dr.Tatyana Ivanova Prof. DSc Kostadinka Gesheva Prof. DSc Hassan Chamatti Assoc. Prof. Dr. Georgi Popkirov Workshop Organizing Committee Prof.DSc Kostadinka Gesheva, Central Laboratory of Solar Energy and New Energy Sources, Bulgarian Academy of Sciences (CL SENES-BAS) - Chairperson Assoc. Prof. Dr Anna Szekeres - Institute of Solid State Physics- BAS Assoc. Prof Dr. Tatyana Ivanova - CL SENES -BAS Assist. Prof. Radostina Kamburova - ISSP-BAS

  16. Topotactic synthesis of strontium cobalt oxyhydride thin film with perovskite structure

    NASA Astrophysics Data System (ADS)

    Katayama, Tsukasa; Chikamatsu, Akira; Kamisaka, Hideyuki; Yokoyama, Yuichi; Hirata, Yasuyuki; Wadati, Hiroki; Fukumura, Tomoteru; Hasegawa, Tetsuya

    2015-10-01

    The substitution of hydride anions (H-) into transition metal oxides has recently become possible through topotactic reactions or high-pressure synthesis methods. However, the fabrication of oxyhydrides is still difficult because of their inherently less-stable frameworks. In this study, we successfully fabricated perovskite SrCoOxHy thin films via the topotactic hydride doping of brownmillerite SrCoO2.5 epitaxial thin films with CaH2. The perovskite-type cation framework was maintained during the topotactic treatment owing to epitaxial stabilization. Structural and chemical analyses accompanied by X-ray absorption spectroscopy measurements revealed that the doped hydride ions form a two-dimensional network of Co-H--Co bonds, in contrast to other reported perovskite oxyhydrides, SrMO3-xHx (M = Cr, Ti, V). The SrCoOxHy thin film exhibited insulating behavior and had a direct band gap of 2.1 eV. Thus, topotactic hydride doping of transition-metal-oxide thin films on suitable substrates is a promising method for the synthesis of new transition metal oxyhydrides.

  17. Surface chemistry on transition metal carbides

    NASA Astrophysics Data System (ADS)

    Hwu, Henry Hanyuan

    The carbides of Groups IVB-VIB early transition metals have been shown to exhibit catalytic properties similar to those observed for Pt-Group metals in reactions with hydrocarbon molecules. Various electrochemical studies revealed tungsten carbides (WC and W2C) to be remarkably resistant to acidic corrosion at anodic potentials, though their effectiveness as electrocatalysts remained inconclusive. The first part of this research therefore focused on the fundamental mechanistic studies of the reactivity of the clean and carbide-modified W(111), W(110), and Mo(110) surfaces toward the direct methanol fuel cell (DMFC) molecules, methanol, water, and carbon monoxide. Temperature-programmed desorption and electron energy loss spectroscopy results showed that the carbide-modified surfaces were highly active toward the decomposition of methanol and water. Furthermore, the desorption of CO from both carbide surfaces occurred at near room temperature. To better characterize the carbide surfaces, the second part of this research concentrated on identifying the various parameters influencing the surface chemistry of carbides. Studies comparing the reaction of ethylene on carbide-modified W(111) and W(110) showed that, though both surfaces readily decomposed ethylene, only the C/W(110) surface was able to form the ethylidyne intermediate commonly observed on Pt-group metals. Additionally, the Pt-like reactivity of C/Mo(110) was modified after exposure to oxygen. Similar to many carbide-modified early transition metal surfaces, C/Ti(0001) also demonstrated Pt-like reactivity toward cyclohexene and ethylene. Lastly, the effects of carbon-modification was examined on Ni(111), a late transition metal surface. Although the carbide-modified Ni(111) surface was similar to other early transition metal carbide surfaces in the selective dehydrogenation of cyclohexene to benzene, the carbide layer converted to graphitic carbon at higher temperatures. This dissertation showed that tungsten carbide materials may be considered as a potential electrocatalyst for the direct methanol fuel cell on the basis that, when compared to Pt-group metal surfaces, they exhibited higher oxidation activity toward methanol and water, and that they were able to desorb carbon monoxide at lower temperatures. In addition, this study also demonstrated that substrate structure, surface modifications, and the position of the transition metal in the periodic table could influence the reactivity of the carbide surfaces.

  18. Thermal diffusivity of oxide perovskite compounds at elevated temperature

    NASA Astrophysics Data System (ADS)

    Hofmeister, Anne M.

    2010-05-01

    The phonon component of thermal diffusivity (D) for eleven compounds (synthetic SrTiO3, SrTiO3:Fe3+, BaTiO3, KTaO3, KNbO3, NdGaO3, YAlO3, YAlO3:Tm, LaAlO3, La0.29Sr0.66Al0.65Ta0.35O3, and natural Ca1.01Mn0.001Fe0.007Ti0.99O3) with various perovskite structures was measured from ambient temperature (T) up to ˜2000 K using contact-free, laser-flash analysis, from which effects of ballistic radiative transfer were removed. Structural transitions (e.g., orthorhombic to tetragonal) below 800 K were manifest as sharp steps in 1/D. Above 800 K, structural transitions occur over intervals of ˜150 K. Similarly broad peaks accompany changes from colorless to black, attributable to partial reduction in Ti, Nb, or Ta from contact with graphite coatings. Otherwise, D decreases with increasing T and, if substitutional disorder exists, approaches a constant (Dsat) near 1600 K. Our data are best described as D-1 following a low order polynomial in T. Ordered, cubic perovskites occupy a single trend for D(T )-1, defining the contribution of the ideal lattice. Distortion, disorder, and polymorphism affect D-1 in a manner that is consistent with the damped harmonic oscillator-phonon gas model which relates phonon lifetimes to infrared peak widths. Calculated D-values at ambient and high T agree with measurements. The behavior of D is simple compared to that of thermal conductivity, k =?CPD, where ? is density and CP is heat capacity. Combining our data with cryogenic measurements of YAlO3 and LaAlO3 shows that D-1 depends on T similarly to CP, consistent with phonon lifetime depending on the density of states but, the best description for D-1(T) is a proportionality to ?T from ˜0 K up to the limit of measurements, where ? is thermal expansivity, a strongly anharmonic property. At low T, D-1 due to phonon scattering follows that of CP, generally?T3, so klat=k0+k1T. Defects being present preclude scattering at sample walls, adding a small constant D0-1 ˜0.0001 mm-2 s as T ?0, and an additional contribution of kdfctT3. Forms previously inferred for thermal insulators include systematic errors stemming from ballistic radiative transfer and/or interface resistance. Our results show that optical phonons largely govern heat transport of complex insulators.

  19. Towards enhancing two-dimensional electron gas quantum confinement effects in perovskite oxide heterostructures

    NASA Astrophysics Data System (ADS)

    Yang, Kesong; Nazir, Safdar; Behtash, Maziar

    2015-03-01

    The two-dimensional electron gas (2DEG) in LaAlO3/SrTiO3 perovskite-oxide heterostructure has attracted much attention because of its potential applications in nanoelectronic devices. A 2DEG has two landmark characters: strong charge confinement in the third dimension and high electron conductivity in two dimensions. In an ideal 2DEG system, electrons can move freely along the interface but are tightly confined in the c-axis that is perpendicular to the interface. Nevertheless, the actual electron gas in the SrTiO3-based perovskite heterostructures is extended a few nanometers along the c-axis into the SrTiO3 substrate, and thus they are also called as quasi-2DEG. Actually, it is a problem of both fundamental and practical interest to achieve an ideal 2DEG via enhancing the lateral quantum confinement effects. By using first-principles electronic structure calculations, herein we proposed two possible approaches to enhance the quantum charge confinement effects by confining the electron gas within one single atomic layer in the perovskite oxide heterostructure. This work is supported by start-up funds at the University of California, San Diego.

  20. Syntheses, structures, and ionic conductivities of perovskite-structured lithium-strontium-aluminum/gallium-tantalum-oxides

    NASA Astrophysics Data System (ADS)

    Phraewphiphat, Thanya; Iqbal, Muhammad; Suzuki, Kota; Matsuda, Yasuaki; Yonemura, Masao; Hirayama, Masaaki; Kanno, Ryoji

    2015-05-01

    The ionic conductivities of new perovskite-structured lithium-strontium-aluminum/gallium-tantalum oxides were investigated. Solid solutions of the new perovskite oxides, (LixSr1-x)(Al(1-x)/2Ta(1+x)/2)O3 and (LixSr1-x)(Ga(1-x)/2Ta(1+x)/2)O3, were synthesized using a ball-milled-assisted solid-state method. The partial substitution of the smaller Ga+3 for Ta+5 resulted in new compositions, the structures of which were determined by neutron diffraction measurements using a cubic perovskite structural model with the Pm-3m space group. Vacancies were introduced into the Sr(Li) sites by the formation of solid solutions with compositions (LixSr1-x-y?y)(Ga[(1-x)/2]-yTa[(1+x)/2]+y)O3, where the composition range of 0?y?0.20 was examined for x=0.2 and 0.25. The highest conductivity, 1.85×10-3 S cm-1 at 250 °C, was obtained for (Li0.25Sr0.625?0.125)(Ga0.25Ta0.75)O3 (x=0.25, y=0.125). Enhanced ionic conductivities were achieved by the introduction of vacancies at the A-sites.

  1. Electrical Conductivity in Transition Metals

    ERIC Educational Resources Information Center

    Talbot, Christopher; Vickneson, Kishanda

    2013-01-01

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

  2. Reduced Graphene Oxide/Mesoporous TiO2 Nanocomposite Based Perovskite Solar Cells.

    PubMed

    Han, Gill Sang; Song, Young Hyun; Jin, Young Un; Lee, Jin-Wook; Park, Nam-Gyu; Kang, Bong Kyun; Lee, Jung-Kun; Cho, In Sun; Yoon, Dae Ho; Jung, Hyun Suk

    2015-10-28

    We report on reduced graphene oxide (rGO)/mesoporous (mp)-TiO2 nanocomposite based mesostructured perovskite solar cells that show an improved electron transport property owing to the reduced interfacial resistance. The amount of rGO added to the TiO2 nanoparticles electron transport layer was optimized, and their impacts on film resistivity, electron diffusion, recombination time, and photovoltaic performance were investigated. The rGO/mp-TiO2 nanocomposite film reduces interfacial resistance when compared to the mp-TiO2 film, and hence, it improves charge collection efficiency. This effect significantly increases the short circuit current density and open circuit voltage. The rGO/mp-TiO2 nanocomposite film with an optimal rGO content of 0.4 vol % shows 18% higher photon conversion efficiency compared with the TiO2 nanoparticles based perovskite solar cells. PMID:26445167

  3. Lanthanum cobaltite perovskite supported onto mesoporous zirconium dioxide: nature of active sites of VOC oxidation.

    PubMed

    Kustov, Alexander L; Tkachenko, Olga P; Kustov, Leonid M; Romanovsky, Boris V

    2011-08-01

    Novel catalytic nano-sized materials based on LaCoO(x) perovskite nanoparticles incapsulated in the mesoporous matrix of zirconia were prepared, characterized by physicochemical methods and tested in complete methanol oxidation. LaCoO(x) nanoparticles were prepared inside the mesopores of ZrO(2) by decomposition of bimetallic La-Co glycine precursor complexes. The catalysts have been studied by diffuse-reflectance FTIR-spectroscopy using such probe molecules as CO, CD(3)CN and CDCl(3) to test low-coordinated metal ions. At low temperatures of decomposition of complexes (up to 400°C), low-coordinated Co(3+) ions predominate in the LaCoO(x) nanoparticles, whereas basically Co(2+) ions are found upon increasing the decomposition temperature to 600°C. The novel nano-sized perovskite catalysts exhibit a very high catalytic activity in the abatement of volatile organic compounds present in air, like methanol and light hydrocarbons. PMID:21665054

  4. Water-Gas Shift and Methane Reactivity on Reducible Perovskite-Type Oxides

    PubMed Central

    2015-01-01

    Comparative (electro)catalytic, structural, and spectroscopic studies in hydrogen electro-oxidation, the (inverse) water-gas shift reaction, and methane conversion on two representative mixed ionic–electronic conducting perovskite-type materials La0.6Sr0.4FeO3?? (LSF) and SrTi0.7Fe0.3O3?? (STF) were performed with the aim of eventually correlating (electro)catalytic activity and associated structural changes and to highlight intrinsic reactivity characteristics as a function of the reduction state. Starting from a strongly prereduced (vacancy-rich) initial state, only (inverse) water-gas shift activity has been observed on both materials beyond ca. 450 °C but no catalytic methane reforming or methane decomposition reactivity up to 600 °C. In contrast, when starting from the fully oxidized state, total methane oxidation to CO2 was observed on both materials. The catalytic performance of both perovskite-type oxides is thus strongly dependent on the degree/depth of reduction, on the associated reactivity of the remaining lattice oxygen, and on the reduction-induced oxygen vacancies. The latter are clearly more reactive toward water on LSF, and this higher reactivity is linked to the superior electrocatalytic performance of LSF in hydrogen oxidation. Combined electron microscopy, X-ray diffraction, and Raman measurements in turn also revealed altered surface and bulk structures and reactivities. PMID:26045733

  5. Research Update: Interface-engineered oxygen octahedral tilts in perovskite oxide heterostructures

    SciTech Connect

    Kan, Daisuke Aso, Ryotaro; Kurata, Hiroki; Shimakawa, Yuichi

    2015-06-01

    Interface engineering of structural distortions is a key for exploring the functional properties of oxide heterostructures and superlattices. In this paper, we report on our comprehensive investigations of oxygen octahedral distortions at the heterointerface between perovskite oxides SrRuO{sub 3} and BaTiO{sub 3} on GdScO{sub 3} substrates and of the influences of the interfacially engineered distortions on the magneto-transport properties of the SrRuO{sub 3} layer. Our state-of-the-art annular bright-field imaging in aberration-corrected scanning transmission electron microscopy revealed that the RuO{sub 6} octahedral distortions in the SrRuO{sub 3} layer have strong dependence on the stacking order of the SrRuO{sub 3} and BaTiO{sub 3} layers on the substrate. This can be attributed to the difference in the interfacial octahedral connections. We also found that the stacking order of the oxide layers has a strong impact on the magneto-transport properties, allowing for control of the magnetic anisotropy of the SrRuO{sub 3} layer through interface engineering. Our results demonstrate the significance of the interface engineering of the octahedral distortions on the structural and physical properties of perovskite oxides.

  6. Design Principles for Oxygen-Reduction Activity on Perovskite Oxide Catalysts for Fuel Cells and Metal-air Batteries

    SciTech Connect

    J Suntivich; H Gasteiger; N Yabuuchi; H Nakanishi; J Goodenough; Y Shao-Horn

    2011-12-31

    The prohibitive cost and scarcity of the noble-metal catalysts needed for catalysing the oxygen reduction reaction (ORR) in fuel cells and metal-air batteries limit the commercialization of these clean-energy technologies. Identifying a catalyst design principle that links material properties to the catalytic activity can accelerate the search for highly active and abundant transition-metal-oxide catalysts to replace platinum. Here, we demonstrate that the ORR activity for oxide catalysts primarily correlates to {sigma}*-orbital (e{sub g}) occupation and the extent of B-site transition-metal-oxygen covalency, which serves as a secondary activity descriptor. Our findings reflect the critical influences of the {sigma}* orbital and metal-oxygen covalency on the competition between O{sub 2}{sup 2-}/OH{sup -} displacement and OH{sup -} regeneration on surface transition-metal ions as the rate-limiting steps of the ORR, and thus highlight the importance of electronic structure in controlling oxide catalytic activity.

  7. Structure-property relationships of BaCeO perovskites for the oxidative dehydrogenation of alkanes

    SciTech Connect

    Nenoff, T.M.; Jackson, N.B.; Miller, J.E.; Sault, A.G.; Trudell, D.

    1997-12-01

    The oxidative dehydrogenation (ODH) reactions for the formation of two important organic feedstocks ethylene and propylene are of great interest because of the potential in capital and energy savings associated with these reactions. Theoretically, ODH can achieve high conversions of the starting materials (ethane and propane) at lower temperatures than conventional dehydrogenation reactions. The important focus in this study of ODH catalysts is the development of a structure-property relationship for catalyst with respect to selectivity, so as to avoid the more thermodynamically favorable combustion reaction. Catalysts for the ODH reaction generally consist of mixed metal oxides. Since for the most selective catalyst lattice oxygen is known to participate in the reaction, catalysts are sought with surface oxygen atoms that are labile enough to perform dehydrogenation, but not so plentiful or weakly bound as to promote complete combustion. Also, catalysts must be able to replenish surface oxygen by transport from the bulk. Perovskite materials are candidates to fulfill these requirements. The authors are studying BaCeO{sub 3} perovskites doped with elements such as Ca, Mg, and Sr. During the ODH of the alkanes at high temperatures, the perovskite structure is not retained and a mixture of carbonates and oxides is formed, as revealed by XRD. While the Ca doped materials showed enhanced total combustion activity below 600 C, they only showed enhanced alkene production at 700 C. Bulk structural and surface changes, as monitored by powder X-ray diffraction, and X-ray photoelectron spectroscopy are being correlated with activity in order to understand the factors affecting catalyst performance, and to modify catalyst formulations to improve conversion and selectivity.

  8. [Non-empirical interatomic potentials for transition metals

    SciTech Connect

    Not Available

    1993-01-01

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

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

    SciTech Connect

    Not Available

    1993-05-01

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

  10. “Structural Transformations in Ceramics: Perovskite-like Oxides and Group III, IV, and V Nitrides”

    SciTech Connect

    James P. Lewis , Dorian M. Hatch , and Harold T. Stokes

    2006-12-31

    1 Overview of Results and their Significance Ceramic perovskite-like oxides with the general formula (A. A0. ...)(B. B0. ...)O3and titanium-based oxides are of great technological interest because of their large piezoelectric and dielectric response characteristics.[1] In doped and nanoengineered forms, titantium dioxide finds increasing application as an organic and hydrolytic photocatalyst. The binary main-group-metal nitride compounds have undergone recent advancements of in-situ heating technology in diamond anvil cells leading to a burst of experimental and theoretical interest. In our DOE proposal, we discussed our unique theoretical approach which applies ab initio electronic calculations in conjunction with systematic group-theoretical analysis of lattice distortions to study two representative phase transitions in ceramic materials: (1) displacive phase transitions in primarily titanium-based perovskite-like oxide ceramics, and (2) reconstructive phase transitions in main-group nitride ceramics. A sub area which we have explored in depth is doped titanium dioxide electrical/optical properties.

  11. Lanthanoid-free perovskite oxide catalyst for dehydrogenation of ethylbenzene working with redox mechanism

    PubMed Central

    Watanabe, Ryo; Ikushima, Maiko; Mukawa, Kei; Sumomozawa, Fumitaka; Ogo, Shuhei; Sekine, Yasushi

    2013-01-01

    For the development of highly active and robust catalysts for dehydrogenation of ethylbenzene (EBDH) to produce styrene; an important monomer for polystyrene production, perovskite-type oxides were applied to the reaction. Controlling the mobility of lattice oxygen by changing the structure of Ba1 ? xSrxFeyMn1 ? yO3 ? ? (0 ? x ? 1, 0.2 ? y ? 0.8), perovskite catalyst showed higher activity and stability on EBDH. The optimized Ba/Sr and Fe/Mn molar ratios were 0.4/0.6 and 0.6/0.4, respectively. Comparison of the dehydrogenation activity of Ba0.4Sr0.6Fe0.6Mn0.4O3 ? ? catalyst with that of an industrial potassium promoted iron (Fe–K) catalyst revealed that the Ba0.4Sr0.6Fe0.6Mn0.4O3 ? ? catalyst showed higher initial activity than the industrial Fe–K oxide catalyst. Additionally, the Ba0.4Sr0.6Fe0.6Mn0.4O3 ? ? catalyst showed high activity and stability under severe conditions, even at temperatures as low as 783 K, or at the low steam/EB ratio of 2, while, the Fe–K catalyst showed low activity in such conditions. Comparing reduction profiles of the Ba0.4Sr0.6Fe0.6Mn0.4O3 ? ? and the Fe–K catalysts in a H2O/H2 atmosphere, reduction was suppressed by the presence of H2O over the Ba0.4Sr0.6Fe0.6Mn0.4O3 ? ? catalyst while the Fe–K catalyst was reduced. In other words, Ba0.4Sr0.6Fe0.6Mn0.4O3 ? ? catalyst had higher potential for activating the steam than the Fe–K catalyst. The lattice oxygen in perovskite-structure was consumed by H2, subsequently the consumed lattice oxygen was regenerated by H2O. So the catalytic performance of Ba0.4Sr0.6Fe0.6Mn0.4O3 ? ? was superior to that of Fe–K catalyst thanks to the high redox property of the Ba0.4Sr0.6Fe0.6Mn0.4O3 ? ? perovskite oxide. PMID:24790949

  12. Observation of a Large Magnetic Anisotropy in the New 2H-Perovskite Related Oxide Ba8CoRh6O21: Magnetic Measurements on Aligned Single Crystals

    E-print Network

    zur Loye, Hans-Conrad

    Observation of a Large Magnetic Anisotropy in the New 2H-Perovskite Related Oxide Ba8CoRh6O21 of the A3n+3mAnB3m+nO9m+6n family of 2H hexagonal perovskite related oxides and contains chains consisting, perovskite and perovskite-related oxides in particular have long provided excellent candidates for structural

  13. Thermochemistry of perovskites in the lanthanum-strontium-manganese-iron oxide system

    NASA Astrophysics Data System (ADS)

    Marinescu, Cornelia; Vradman, Leonid; Tanasescu, Speranta; Navrotsky, Alexandra

    2015-10-01

    The enthalpies of formation from binary oxides of perovskites (ABO3) based on lanthanum strontium manganite La(Sr)MnO3 (LSM) and lanthanum strontium ferrite La(Sr)FeO3 (LSF) and mixed lanthanum strontium manganite ferrite La(Sr)Mn(Fe)O3 (LSMF) were measured by high temperature oxide melt solution calorimetry. Using iodometric titration, the oxygen content was derived. The perovskites with A-site cation deficiency have greater oxygen deficiency than the corresponding A-site stoichiometric series. Stability of LSMF decreases with increasing iron content. Increasing oxygen deficiency clearly destabilizes the perovskites. The results suggest an enthalpy of oxygen incorporation that is approximately independent of composition. 0.35La2O3 (xl, 25 °C)+Mn2O3 (xl, 25 °C)+0.3SrO (xl, 25 °C)+Fe2O3 (xl, 25 °C)+O2 (g, 25 °C)?La0.7Sr0.3Mn1-yFeyO3-? (xl, 25 °C). (b) ?ubscriptshift="90%"superscriptshift="90%">Hf, ox * (La0.7Sr0.3Mn1-yFeyO3-?) .0.35 La2O3 (xl, 25 ººC) + (0.7-y+ 2?)/2 Mn2O3 (xl, 25 ºC) + 0.3 SrO (xl, 25 ºC) + y/2Fe2O3 (xl, 25 ºC) + (0.3-2?) MnO2 (xl, 25 ºC)?La0.7Sr0.3Mn1-yFeyO3-? (xl, 25 ºC).

  14. Copper-substituted perovskite compositions for solid oxide fuel cell cathodes and oxygen reduction electrodes in other electrochemical devices

    DOEpatents

    Rieke, Peter C. (Pasco, WA); Coffey, Gregory W. (Richland, WA); Pederson, Larry R. (Kennewick, WA); Marina, Olga A. (Richland, WA); Hardy, John S. (Richland, WA); Singh, Prabhaker (Richland, WA); Thomsen, Edwin C. (Richland, WA)

    2010-07-20

    The present invention provides novel compositions that find advantageous use in making electrodes for electrochemical cells. Also provided are electrochemical devices that include active oxygen reduction electrodes, such as solid oxide fuel cells, sensors, pumps and the like. The compositions comprises a copper-substituted ferrite perovskite material. The invention also provides novel methods for making and using the electrode compositions and solid oxide fuel cells and solid oxide fuel cell assemblies having cathodes comprising the compositions.

  15. Synthesis, structural and property studies of bismuth containing perovskites 

    E-print Network

    Chen, Wei-tin

    2009-01-01

    Several bismuth-containing transition metal perovskites that are of interest as potential multiferroic materials have been synthesised and studied. These materials have been structurally characterised and their physical ...

  16. Fine-tuning optical and electronic properties of graphene oxide for highly efficient perovskite solar cells

    NASA Astrophysics Data System (ADS)

    Liu, Tongfa; Kim, Dongcheon; Han, Hongwei; Mohd Yusoff, Abd. Rashid Bin; Jang, Jin

    2015-06-01

    Simplifying the process of fine-tuning the electronic and optical properties of graphene oxide (GO) is of importance in order to fully utilize it as the hole interfacial layer (HIL). We introduced silver trifluoromethanesulfonate (AgOTf), an inorganic chemical dopant, that tunes and controls the properties of single-layered GO films synthesized by chemical vapor deposition. The morphology, work function, mobility, sheet resistance, and transmittance of the GO film were systematically tuned by various doping concentrations. We further developed a solution-processable low-temperature hole interfacial layer (HIL) poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS):AgOTf-doped GO HIL in highly efficient perovskite solar cells. The PEDOT:PSS:AgOTf-doped GO HIL grants the desirable charge-collection in the HIL allowing the entire device to be prepared at temperatures less than 120 °C. The fabricated perovskite solar cells utilize a rigid substrate and demonstrate compelling photovoltaic performance with a power conversion efficiency (PCE) of 11.90%. Moreover, flexible devices prepared using a polyethylene terephthalate (PET)/ITO demonstrate a PCE of 9.67%, while ITO-free flexible devices adopting PET/aluminum doped zinc oxide (AZO)/silver (Ag)/AZO demonstrate a PCE of 7.97%. This study shows that the PEDOT:PSS:AgOTf-doped GO HIL has significant potential to contribute to the development of low-cost solar cells.

  17. Time-Resolved XAFS Spectroscopic Studies of B-H and N-H Oxidative Addition to Transition Metal Catalysts Relevant to Hydrogen Storage

    SciTech Connect

    Bitterwolf, Thomas E.

    2014-12-09

    Successful catalytic dehydrogenation of aminoborane, H3NBH3, prompted questions as to the potential role of N-H oxidative addition in the mechanisms of these processes. N-H oxidative addition reactions are rare, and in all cases appear to involve initial dative bonding to the metal by the amine lone pairs followed by transfer of a proton to the basic metal. Aminoborane and its trimethylborane derivative block this mechanism and, in principle, should permit authentic N-H oxidative attrition to occur. Extensive experimental work failed to confirm this hypothesis. In all cases either B-H complexation or oxidative addition of solvent C-H bonds dominate the chemistry.

  18. Ferroelectricity in d0 double perovskite fluoroscandates

    NASA Astrophysics Data System (ADS)

    Charles, Nenian; Rondinelli, James M.

    2015-08-01

    Ferroelectricity in strain-free and strained double perovskite fluorides, Na3ScF6 and K2NaScF6 , is investigated using first-principles density functional theory. Although the experimental room temperature crystal structures of these fluoroscandates are centrosymmetric, i.e., Na3ScF6 (P 21/n ) and K2NaScF6 (F m 3 ¯m ), lattice dynamical calculations reveal that soft polar instabilities exist in each prototypical cubic phase and that the modes harden as the tolerance factor approaches unity. Thus the double fluoroperovskites bear some similarities to A B O3 perovskite oxides; however, in contrast, these fluorides exhibit large acentric displacements of alkali metal cations (Na, K) rather than polar displacements of the transition metal cations. Biaxial strain investigations of the centrosymmetric and polar Na3ScF6 and K2NaScF6 phases reveal that the paraelectric structures are favored under compressive strain, whereas polar structures with in-plane electric polarizations (˜5 -18 ? C cm-2 ) are realized at sufficiently large tensile strains. The electric polarization and stability of the polar structures for both chemistries are found to be further enhanced and stabilized by a coexisting single octahedral tilt system. Our results suggest that polar double perovskite fluorides may be realized by suppression of octahedral rotations about more than one Cartesian axis; structures exhibiting in- or out-of-phase octahedral rotations about the c axis are more susceptible to polar symmetries.

  19. Crystal structure and magnetic properties of 5d double perovskite oxide Sr2EuOsO6

    NASA Astrophysics Data System (ADS)

    He, Jianfeng; Feng, Hai L.; Yuan, Yahua; Tsujimoto, Yoshihiro; Yamaura, Kazunari; Superconducting Properties Unit, National InstituteMaterials Science Team; Graduate School of Chemical Sciences; Engineering, Hokkaido University Team; Materials Processing Unit, National InstituteMaterials Science Team

    2015-03-01

    Polycrystalline Sr2EuOsO6 has been synthesized with high-pressures and temperatures. It crystallizes in a monoclinic double perovskite structure and shows an antiferromagnetic-like transition at 51 K in a magnetic susceptibility measurement. The transition has been further characterized by specific measurements and electrical resistivity measurements. The results are compared with the magnetic properties of Ba2EuOsO6 and other double perovskite oxides containing Os(V) atom. We will discuss role of spin-orbit coupling and spin polarization on the gapped electronic structure of Sr2EuOsO6 and other related compounds.

  20. Synthesis, structural studies, and oxidation catalysis of the late-first-row-transition-metal complexes of a 2-pyridylmethyl pendant-armed ethylene cross-bridged cyclam.

    PubMed

    Jones, Donald G; Wilson, Kevin R; Cannon-Smith, Desiray J; Shircliff, Anthony D; Zhang, Zhan; Chen, Zhuqi; Prior, Timothy J; Yin, Guochuan; Hubin, Timothy J

    2015-03-01

    The first 2-pyridylmethyl pendant-armed ethylene cross-bridged cyclam ligand has been synthesized and successfully complexed to Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), and Zn(2+) cations. X-ray crystal structures were obtained for all six complexes and demonstrate pentadentate binding of the ligand with the requisite cis-V configuration of the cross-bridged cyclam ring in all cases, leaving a potential labile binding site cis to the pyridine donor for interaction of the complex with oxidants and/or substrates. The electronic properties of the complexes were evaluated using solid-state magnetic moment determination and acetonitrile solution electronic spectroscopy, which both agree with the crystal structure determination of high-spin divalent metal complexes in all cases. Cyclic voltammetry in acetonitrile revealed reversible redox processes in all but the Ni(2+) complex, suggesting that catalytic reactivity involving electron-transfer processes is possible for complexes of this ligand. Kinetic studies of the dissociation of the ligand from the copper(II) complex under strongly acidic conditions and elevated temperatures revealed that the pyridine pendant arm actually destabilizes the complex compared to the parent cross-bridged cyclam complex. Screening for oxidation catalysis using hydrogen peroxide as the terminal oxidant for the most biologically relevant Mn(2+), Fe(2+), and Cu(2+) complexes identified the Mn(2+) complex as a potential mild oxidation catalyst worthy of continued development. PMID:25671291

  1. An experimental study of perovskite-structured mixed ionic- electronic conducting oxides and membranes

    NASA Astrophysics Data System (ADS)

    Zeng, Pingying

    In recent decades, ceramic membranes based on mixed ionic and electronic conducting (MIEC) perovskite-structured oxides have received many attentions for their applications for air separation, or as a membrane reactor for methane oxidation. While numerous perovskite oxide materials have been explored over the past two decades; there are hardly any materials with sufficient practical economic value and performance for large scale applications, which justifies continuing the search for new materials. The main purposes of this thesis study are: (1) develop several novel SrCoO3-delta based MIEC oxides, SrCoCo1-xMxO3-delta, based on which membranes exhibit excellent oxygen permeability; (2) investigate the significant effects of the species and concentration of the dopants M (metal ions with fixed valences) on the various properties of these membranes; (3) investigate the significant effects of sintering temperature on the microstructures and performance of oxygen permeation membranes; and (4) study the performance of oxygen permeation membranes as a membrane reactor for methane combustion. To stabilize the cubic phase structure of the SrCoO3-delta oxide, various amounts of scandium was doped into the B-site of SrCoO 3-delta to form a series of new perovskite oxides, SrScxCoCo 1-xO3-delta (SSCx, x = 0-0.7). The significant effects of scandium-doping concentration on the phase structure, electrical conductivity, sintering performance, thermal and structural stability, cathode performance, and oxygen permeation performance of the SSCx membranes, were systematically studied. Also for a more in-depth understanding, the rate determination steps for the oxygen transport process through the membranes were clarified by theoretical and experimental investigation. It was found that only a minor amount of scandium (5 mol%) doping into the B-site of SrCoO3-delta can effectively stabilize the cubic phase structure, and thus significantly improve the electrical conductivity and oxygen permeability of the SrCoO3-delta membrane. Among all the disk-shaped SSCx (x = 0-0.7) membranes with a thickness of 0.91 mm, both SSC0.05 and SSC0.1 exhibit the highest oxygen permeation rate of about 3.2 mL.cm-2.min-1 (STP) at 900 °C, SSC0.1 also shows excellent cathode performance for a solid oxide fuel cell. Therefore SSC0.1 is of special interest, and thus investigated regarding the performance as a membrane reactor for methane combustion. The performance was evaluated based on the results of methane conversion rates and CO 2 selectivity. Inspired by the above findings, a series of mixed-conducting perovskite oxides SrCo0.95M0.05O3-delta (SCM, M = Bi5+, Zr4+, Ce4+, Sc3+ , La3+, Y3+, Al3+, Zn 2+) were prepared to study the effects of different dopants M on the performance of SrCo0.95M0.05O3-delta. It was found that the M cations significantly affect the crystal phase structure, grain growth, membrane porosity, electrical conductivity, and the oxygen permeability of the SCM membranes. Specifically, it is postulated in this study that the formation of the cubic perovskite structure is dependent on the electron configuration in the outer orbits of M cations, which may provide theoretical guidance for future development of high oxygen permeation ceramic membranes based on the perovskite materials. To study the significant effects of grain sizes on the oxygen permeation behaviors of La0.6Sr0.4Co0.2Fe0.8O3-delta (LSCF) and SrSc0.1Co0.9O 3-delta (SSC0.1) membranes, the LSCF and SSC0.1 membranes were sintered at various temperatures to form different microstructures. Properties of these membranes with varied grain sizes were compared. Results showed that the oxygen permeation rate of the LSCF membrane increases with increasing the grain size, however, it is interesting that the oxygen permeation rate of the SSC0.1 membrane decreases with increasing the grain size. This implies that oxygen transport occurs more, however, less rapidly along grain boundaries than through the bulks in the LSCF and SSC0.1 membranes, respectively. A LSCF hollow fiber membrane and a SSC

  2. Synthesis of transition metal carbonitrides

    DOEpatents

    Munir, Zuhair A. R. (Davis, CA); Eslamloo-Grami, Maryam (Davis, CA)

    1994-01-01

    Transition metal carbonitrides (in particular, titanium carbonitride, TiC.sub.0.5 N.sub.0.5) are synthesized by a self-propagating reaction between the metal (e.g., titanium) and carbon in a nitrogen atmosphere. Complete conversion to the carbonitride phase is achieved with the addition of TiN as diluent and with a nitrogen pressure .gtoreq.0.6 MPa. Thermodynamic phase-stability calculations and experimental characterizations of quenched samples provided revealed that the mechanism of formation of the carbonitride is a two-step process. The first step involves the formation of the nonstoichiometric carbide, TiC.sub.0.5, and is followed by the formation of the product by the incorporation of nitrogen in the defect-structure carbide.

  3. O3-type layered transition metal oxide Na(NiCoFeTi)1/4O2 as a high rate and long cycle life cathode material for sodium ion batteries

    DOE PAGESBeta

    Yue, Ji -Li; Yang, Xiao -Qing; Zhou, Yong -Ning; Yu, Xiqian; Bak, Seong -Min; Fu, Zheng -Wen

    2015-10-09

    High rate capability and long cycle life are challenging goals for the development of room temperature sodium-ion batteries. Here we report a new single phase quaternary O3-type layer-structured transition metal oxide Na(NiCoFeTi)1/4O2 synthesized by a simple solid-state reaction as a new cathode material for sodium-ion batteries. It can deliver a reversible capacity of 90.6 mA h g–1 at a rate as high as 20C. At 5C, 75.0% of the initial specific capacity can be retained after 400 cycles with a capacity-decay rate of 0.07% per cycle, demonstrating a superior long-term cyclability at high current density. X-ray diffraction and absorption characterizationmore »revealed reversible phase transformations and electronic structural changes during the Na+ deintercalation/intercalation process. Ni, Co and Fe ions contribute to charge compensation during charge and discharge. Although Ti ions do not contribute to the charge transfer, they play a very important role in stabilizing the structure during charge and discharge by suppressing the Fe migration. Additionally, Ti substitution can also smooth the charge–discharge plateaus effectively, which provides a potential advantage for the commercialization of this material for room temperature sodium-ion batteries.« less

  4. O3-type layered transition metal oxide Na(NiCoFeTi)1/4O2 as a high rate and long cycle life cathode material for sodium ion batteries

    SciTech Connect

    Yue, Ji -Li; Yang, Xiao -Qing; Zhou, Yong -Ning; Yu, Xiqian; Bak, Seong -Min; Fu, Zheng -Wen

    2015-10-09

    High rate capability and long cycle life are challenging goals for the development of room temperature sodium-ion batteries. Here we report a new single phase quaternary O3-type layer-structured transition metal oxide Na(NiCoFeTi)1/4O2 synthesized by a simple solid-state reaction as a new cathode material for sodium-ion batteries. It can deliver a reversible capacity of 90.6 mA h g–1 at a rate as high as 20C. At 5C, 75.0% of the initial specific capacity can be retained after 400 cycles with a capacity-decay rate of 0.07% per cycle, demonstrating a superior long-term cyclability at high current density. X-ray diffraction and absorption characterization revealed reversible phase transformations and electronic structural changes during the Na+ deintercalation/intercalation process. Ni, Co and Fe ions contribute to charge compensation during charge and discharge. Although Ti ions do not contribute to the charge transfer, they play a very important role in stabilizing the structure during charge and discharge by suppressing the Fe migration. Additionally, Ti substitution can also smooth the charge–discharge plateaus effectively, which provides a potential advantage for the commercialization of this material for room temperature sodium-ion batteries.

  5. [Photoreduction of Se (VI) by marine algae-transitional metals-light system].

    PubMed

    Li, Shun-Xing; Zheng, Feng-Ying; Deng, Nan-Sheng; Hong, Hua-Sheng; Zhu, Guo-Hui

    2005-07-01

    Seven marine phytoplankton, including five green algae (Tetraselmis levis, Chlorella autotrophica, Dunaliella salina, Nannochloropsis sp. and Tetraselmis subcordiformis), one diatom (Phaeodactylum tricornutum), one red alga (Porphyridium purpureum), and three usual transitional metals (Fe(III), Cu(II), Mn(II)) were used to make up marine phytoplankton-light or transitional metals-light or marine phytoplankton-transitional metals-light system. In such system, Se(VI) could be transformed into Se(IV) by photoreduction. The species transformation of selenium could be photo-induced by redox reaction of transitional metals. The photochemical activity of marine phytoplankton was confirmed for the first time, because marine phytoplankton could adsorb and concentrated of selenium, transitional metals and organic substances (including the exudation of algae, as reducing agent) which redox potentials were changed. The ratios of Se(VI) to Se(IV) were dominated by the species, the concentration of marine phytoplankton and transitional metals, and it could be enhanced through increasing the concentration of marine algae or the combined effect from marine algae and transitional metals. After photoreduction by ternary system, the ratio of Se(VI) to Se(IV) ranges from 1.17 to 2.85, which is close to the actual value in euphotic layer of seawater. The photochemical process that is induced by marine algae and transitional metals dominative the leading effects on the distribution of oxidation states of selenium. PMID:16212166

  6. Theoretical Investigation of H? Oxidation on the Sr2Fe1.5Mo0.5O6 (001) Perovskite Surface Under Anodic Solid Oxide Fuel Cell Conditions

    SciTech Connect

    Suthirakun, Suwit; Ammal, Salai Cheettu; Munoz-Garcia, Ana B.; Xiao, Guoliang; Chen, Fanglin; zur Loye, Hans-Conrad; Carter, Emily A.; Heyden, Andreas

    2014-06-11

    Periodic density functional theory (DFT) calculations and microkinetic modeling are used to investigate the electrochemical oxidation of H? fuel on the (001) surface of Sr2Fe1.5Mo0.5O6 (SFMO) perovskite under anodic solid oxide fuel cell conditions. Three surface models with different Fe/Mo ratios in the topmost layer-identified by ab initio thermodynamic analysis-are used to investigate the H? oxidation mechanism. A microkinetic analysis that considers the effects of anode bias potential suggests that a higher Mo concentration in the surface increases the activity of the surface toward H? oxidation. At operating voltage and anodic SOFC conditions, the model predicts that water desorption is rate-controlling and that stabilizing the oxygen vacancy structure increases the overall rate for H? oxidation. Although we find that Mo plays a crucial role in improving catalytic activity of SFMO, under fuel cell operating conditions, the Mo content in the surface layer tends to be very low. On the basis of these results and in agreement with previous experimental observations, a strategy for improving the overall electrochemical performance of SFMO is increasing the Mo content or adding small amounts of an active transition metal, such as Ni, to the surface to lower the oxygen vacancy formation energy of the SFMO surface.

  7. Dense perovskite membrane reactors for partial oxidation of methane to syngas

    SciTech Connect

    Tsai, C.Y.; Dixon, A.G.; Moser, W.R.; Ma, Y.H.

    1997-12-31

    The partial oxidation of methane to synthesis gas (syngas, CO + H{sub 2}) was performed in a mixed-conducting perovskite dense membrane reactor at 850 C, in which oxygen was separated from air and simultaneously fed into the methane stream. Steady-state oxygen permeation rates for La{sub 1{minus}x}A{sub x}{prime}Fe{sub 0.8} CO{sub 0.2}O{sub 3{minus}{delta}} perovskite membranes in nonreacting air/helium experiments were in the order of A{sub x}{prime} = Ba{sub 0.8} > Ba{sub 0.6}>Ca{sub 0.6} > Sr{sub 0.6}. Deep oxidation products were obtained from a La{sub 0.2} Ba{sub 0.8} Fe{sub 0.8} Co{sub 0.2} O{sub 3{minus}{delta}} disk-shaped membrane reactor without catalyst, with a 4.6% CH{sub 4} inlet stream. These products were further reformed to syngas when a downstream catalytic bed was added. Packaging the 5% Ni/Al{sub 2}O{sub 3} catalyst directly on the membrane reaction-side surface resulted in a slow fivefold increase in O{sub 2} permeation, and a fourfold increase in CH{sub 4} conversion, XRD, EDS, and SEM analyses revealed structure and composition changes on the membrane surfaces. Oxygen continuously transported from the air side appeared to stabilize the membrane interior, and the reactor was operated for up to 850 h.

  8. Density functional study on redox energetics of LaMO3-? (M=Sc-Cu) perovskite-type oxides

    NASA Astrophysics Data System (ADS)

    Pishahang, Mehdi; Erik Mohn, Chris; Stølen, Svein

    2016-01-01

    This study evaluates the redox energetics of LaMO3-? (M=Sc-Cu) perovskite-type oxides via generalized gradient approximation (GGA) to DFT. Two different approaches to redox energetics of oxygen deficient perovskites of strongly non-stoichiometric (?=0.5) and dilute defect limits (??0) are studied. In the first approach the enthalpies of oxidation are calculated using the stoichiometric end-compounds of LaMO3 and LaMO2.5. The most common structures for the reduced lanthanides and strontides similar to the ones experimentally reported for SrMnO2.5, SrFeO2.5, and LaNiO2.5 are considered. The second approach to the oxidation enthalpies termed (??0) follow the trend observed experimentally. This approach represents the experimental conditions of the measured oxygen enthalpies, and is hampered less by the artificial features due to spurious self-interaction errors in GGA.

  9. Epitaxial growth and stabilization of transition metal nitride-based superlattices and buffer layers

    NASA Astrophysics Data System (ADS)

    Kim, Ilwon

    The epitaxial stabilization of cubic, non-equilibrium AlN in epitaxial, AlN/TiN, AlN/VN, and AlN/W superlattices was investigated. While the bulk stable structure of AlN is hexagonal wurtzite, cubic rocksalt structure AlN was epitaxially stabilized in AlN/TiN superlattice and AlN/VN superlattices. The films were characterized using X-ray diffraction (XRD), simulations of XRD patterns, cross-sectional transmission electron microscopy (XTEM) and Low Energy Electron Diffraction (LEED). The effect of superlattice period ?, total film thickness, AlN layer thickness fraction (lAlN/?) and coherency strain on epitaxial stabilization were studied. The mechanical properties of the AlN/TiN superlattices were investigated by nanoindentation. It was found that zinc-blende AlN was stabilized in AlN/W superlattices, whereas rock-salt AlN was stabilized in AlN/NbN superlattices suggesting that the symmetry of the underlying template affected stabilized phase. The second area of focus of this research was the growth and characterization of epitaxial transition metal nitride buffer layers. The study was geared towards the development of a commercially viable buffer layer between the superconducting perovskite oxides such as Yttrium barium Copper Oxide (YBCO) and reactive Ni substrates. High quality TiN and VN buffer layers were grown on MgO and Ni RABiTS (Rolling Assisted Biaxially Textured Substrate) and structurally characterized by XRD, High Resolution SEM and TEM. High quality YBCO layers were subsequently grown on TiN with thin (<100nm) MgO and ceria layers as a intermediate oxide layers in order to prevent oxidation of nitride layers. Relatively high Jc (6 x 105 A/cm2) and Tc (˜89K) were demonstrated for YBCO layers. Epitaxial YSZ on TiN was studied for a potential alternative intermediate oxide.

  10. A combinatorial chemistry method for fast screening of perovskite-based NO oxidation catalyst.

    PubMed

    Yoon, Dal Young; Lim, Eunho; Kim, Young Jin; Cho, Byong K; Nam, In-Sik; Choung, Jin Woo; Yoo, Seungbeom

    2014-11-10

    A fast parallel screening method based on combinatorial chemistry (combichem) has been developed and applied in the screening tests of perovskite-based oxide (PBO) catalysts for NO oxidation to hit a promising PBO formulation for the oxidation of NO to NO2. This new method involves three consecutive steps: oxidation of NO to NO2 over a PBO catalyst, adsorption of NOx onto the PBO and K2O/Al2O3, and colorimetric assay of the NOx adsorbed thereon. The combichem experimental data have been used for determining the oxidation activity of NO over PBO catalysts as well as three critical parameters, such as the adsorption efficiency of K2O/Al2O3 for NO2 (?) and NO (?), and the time-average fraction of NO included in the NOx feed stream (?). The results demonstrated that the amounts of NO2 produced over PBO catalysts by the combichem method under transient conditions correlate well with those from a conventional packed-bed reactor under steady-state conditions. Among the PBO formulations examined, La0.5Ag0.5MnO3 has been identified as the best chemical formulation for oxidation of NO to NO2 by the present combichem method and also confirmed by the conventional packed-bed reactor tests. The superior efficiency of the combichem method for high-throughput catalyst screening test validated in this study is particularly suitable for saving the time and resources required in developing a new formulation of PBO catalyst whose chemical composition may have an enormous number of possible variations. PMID:25321326

  11. Preparation and use of high surface area transition metal catalysts

    SciTech Connect

    Atkinson, G.B.

    1981-03-17

    Highly active catalysts, suitable for use in hydrogenation and other reactions, are prepared from an alloy of one or more of the group VIII transition metals with yttrium or a rare earth metal. The alloy is ground to the desired particle size and is thereafter reacted with a gas containing carbon monoxide and hydrogen to form an intimate physical admixture of the group viii metal or its corresponding carbide with the oxide of yttrium or the rare earth metal.

  12. Spintronic oxides grown by laser-MBE

    NASA Astrophysics Data System (ADS)

    Opel, Matthias

    2012-01-01

    The recent study of oxides led to the discovery of several new fascinating physical phenomena. High-temperature superconductivity, colossal magnetoresistance, dilute magnetic doping, or multiferroicity were discovered and investigated in transition-metal oxides, representing a prototype class of strongly correlated electronic systems. This development was accompanied by enormous progress regarding thin film fabrication. Within the past two decades, epitaxial thin films with crystalline quality approaching semiconductor standards became available using laser-molecular beam epitaxy. This evolution is reviewed, particularly with emphasis on transition-metal oxide thin films, their versatile physical properties, and their impact on the field of spintronics. First, the physics of ferromagnetic half-metallic oxides, such as the doped manganites, the double perovskites and magnetite is presented together with possible applications based on magnetic tunnel junctions. Second, the wide bandgap semiconductor zinc oxide is discussed particularly with regard to the controversy of dilute magnetic doping with transition-metal ions and the possibility of realizing p-type conductivity. Third, the field of oxide multiferroics is presented with the recent developments in single-phase multiferroic thin film perovskites as well as in composite multiferroic hybrids.

  13. Photoinduced charge, ion & energy transfer processes at transition-metal coordination compounds anchored to mesoporous, nanocrystalline metal-oxide thin films

    NASA Astrophysics Data System (ADS)

    Ardo, Shane

    Photovoltaics provide a direct means of converting photons into useful, electric power; however traditional silicon-based technologies are too expensive for global commercialization. Dye-sensitized mesoporous semiconducting thin films, when utilized in regenerative photoelectrochemical cells, are one category of next generation photovoltaics that could eventually circumvent this issue. In fact, their architecture also affords a clear platform for implementation of a direct, solar fuel-forming system. The mechanisms involved in the myriad of molecular processes that occur in these molecular--solid-state hybrid materials are poorly understood. Thus, the overriding goal of this dissertation was to evaluate sensitized mesoporous, nanocrystalline metal-oxide thin films critically so as to elucidate mechanistic phenomena. Using transient and steady-state absorption and emission spectroscopies as well as (photo)electrochemistry, various previously unobserved processes have been identified. Chapter 2 demonstrates for the first time that the electric fields emanating from these charged thin films affect surface-anchored molecular sensitizers via a Stark effect. In most cases, further, but incomplete, ionic screening of the charged nanoparticles from the sensitizers, as non-Faradaic electrolyte redistribution, was spectroscopically inferred after rapid semiconductor charging. Chapter 3 highlights the reactivity of Co(I) coordination-compound catalysts anchored to anatase TiO2 thin-film electrodes. Visible-light excitation resulted in prompt excited-state electron injection into TiO2 while introduction of benzylbromide into the fluid solution surrounding the thin film led to a 2e--transfer, oxidative-addition reaction to Co1 forming a stable Co--benzyl product. Subsequent visible-light excitation initiated a photocatalytic cycle for C--C bond formation. Unique to the nanocrystalline thin films employed here, Chapter 4 demonstrates that traditional time-resolved polarization spectroscopy can be employed to monitor lateral self-exchange energy- and hole-transfer reactions across the sensitized TiO2 surface. Under conditions of poor excited-state injection, support for Ru*/II self exchange was obtained, while subsequent to electron injection, the resulting RuIII state of the sensitizer was often capable of RuIII/II self-exchange reactions. The kinetics for many processes associated with mesoporous, nanocrystalline TiO2 thin films can be modeled by a stretched-exponential function, which possesses an underlying distribution of rate constants. In Chapter 5, we provide the first implementation of an Arrhenius analysis for the temperature dependence of these distributions.

  14. Correlation between resistance-change effect in transition-metal oxides and secondary-electron contrast of scanning electron microscope images

    SciTech Connect

    Kinoshita, K.; Kishida, S.; Yoda, T.

    2011-09-15

    Conductive atomic-force microscopy (C-AFM) writing is attracting attention as a technique for clarifying the switching mechanism of resistive random-access memory by providing a wide area filled with filaments, which can be regarded as one filament with large radius. The writing area on a nickel-oxide (NiO) film formed by conductive atomic-force microscopy was observed by scanning electron microscope, and a correlation between the contrast in a secondary-electron image (SEI) and the resistance written by C-AFM was revealed. In addition, the dependence of the SEI contrast on the beam accelerating voltage (V{sub accel}) suggests that the resistance-change effect occurs near the surface of the NiO film. As for the effects of electron irradiation and vacuum annealing on the C-AFM writing area, it was shown that the resistance-change effect is caused by exchange of oxygen with the atmosphere at the surface of the NiO film. This result suggests that the low-resistance and high-resistance areas are, respectively, p-type Ni{sub 1+{delta}}O ({delta} < 0) and insulating (stoichiometric) or n-type Ni{sub 1+{delta}}O ({delta}{>=} 0).

  15. Synthesis of ferromagnetic nanoparticles, formic acid oxidation catalyst nanocomposites, and late-transition metal-boride intermetallics by unique synthetic methods and single-source precursors

    NASA Astrophysics Data System (ADS)

    Wellons, Matthew S.

    The design, synthesis, and characterization of magnetic alloy nanoparticles, supported formic acid oxidation catalysts, and superhard intermetallic composites are presented. Ferromagnetic equatomic alloy nanoparticles of FePt, FePd, and CoPt were synthesized utilizing single-source heteronuclear organometallic precursors supported on an inert water-soluble matrix. Direct conversion of the precursor-support composite to supported ferromagnetic nanoparticles occurs under elevated temperatures and reducing conditions with metal-ion reduction and minimal nanoparticle coalescence. Nanoparticles were easily extracted from the support by addition of water and characterized in structure and magnetic properties. Palladium and platinum based nanoparticles were synthesized with microwave-based and chemical metal-ion reduction strategies, respectively, and tested for catalytic performance in a direct formic acid fuel cell (DFAFC). A study of palladium carbide nanocomposites with various carbonaceous supports was conducted and demonstrated strong activity comparable to commercially available palladium black, but poor catalytic longevity. Platinum-lead alloy nanocomposites synthesized with chemical reduction and supported on Vulcan carbon demonstrated strong activity, excellent catalytic longevity, and were subsequently incorporated into a prototype DFAFC. A new method for the synthesis of superhard ceramics on polymer substrates called Confined Plasma Chemical Deposition (CPCD) was developed. The CPCD method utilizes a tuned Free Electron Laser to selectively decompose the single-source precursor, Re(CO)4(B3H8), in a plasma-like state resulting in the superhard intermetallic ReB2 deposited on polymer substrates. Extension of this method to the synthesis of other hard of superhard ceramics; WB4, RuB2, and B4C was demonstrated. These three areas of research show new synthetic methods and novel materials of technological importance, resulting in a substantial advance in their respective fields.

  16. Synthesis, crystal chemistry, and physical properties of new mixed-metal perovskite-related oxides

    SciTech Connect

    Anderson, M.T.

    1992-01-01

    The goal of this work is to synthesize and characterize multiple-B-cation perovskite-related compounds (A[prime] [sub 1[minus]x]A[double prime][sub x]) (B[prime] [sub 1[minus]y]B[double prime] [sub y])O[sub 3[minus]z], that are structurally and chemically related to high-temperature cuprate superconductors. High-temperature superconductors have two common features (1) copper-oxygen CuO[sub 4/2] nets (layers) separated by inorganic metal-oxide spacer layers and (2) formal mixed valency of copper or a mechanism of charge transfer between the copper-oxygen and space layers. To achieve structural similarity, that is, to provide distinct CuO[sub 4/2] and B[double prime] O[sub 4/2] layers, two synthetic strategies were developed, one for stoichiometric and the other for nonstoichiometric mixed-metal oxides. To develop and refine the strategies, La[sub 2]CuSnO[sub 6], La[sub 2[minus]x]M[sub x]CuSnO[sub 6[minus]x/2+[sigma

  17. Conductive Perovskite-type Metal Oxide Thin Films Prepared by Chemical Solution Deposition Technique

    NASA Astrophysics Data System (ADS)

    Sasajima, K.; Uchida, H.

    2011-10-01

    Metal oxide electrode have been widely developed for high-performance electric device because they possess some attractive characteristic such as thermal/chemical stabilities and change compensation for oxygen vacancies in interconnected dielectric layers, etc., which is often hardly achieved by convention metal electrodes. As almost all metal oxide electrodes were usually fabricated by some vapour deposition techniques which require large-scale equipments, power, resources and costs, film deposition via solution technique would be worthy for familiarizing the metal oxide electrodes. In this research, thin films of conductive perovskite-type oxides, (La,Sr)CoO3 [LSCO], were fabricated by chemical solution deposition technique. The precursor solution for LSCO was prepared using metal nitrate, acetates, and iso-propoxide and 2-methoxyethanol. The solution was spin-coated on substrates, followed by drying, pyrolysis and RTA-treatment for crystallization at 500-750°C, for 5 min in air. These processes were repeated to obtain desired film thickness. (100)Si and (100)SrTiO3 were used as substrate. XRD analysis indicated that both of LSCO films fabricated on (100)SrTiO3 and (100)Si substrates were crystallized at and above 600°C. The films on (100)SrTiO3 had preferential crystal orientation of (100)LSCO normal to the substrate surface, while random crystal orientation was confirmed for the films on (100)Si. Electrical resistivity of the both films fabricated at 700°C were 6.09 × 10-5 ? cm and 1.12 × 10-4 ? cm, respectively, which is almost same as the LSCO films fabricated by conventional vapour deposition technique.

  18. Atomic-Scale Chemical Imaging of Composition and Bonding at Perovskite Oxide Interfaces

    NASA Astrophysics Data System (ADS)

    Fitting Kourkoutis, L.

    2010-03-01

    Scanning transmission electron microscopy (STEM) in combination with electron energy loss spectroscopy (EELS) has proven to be a powerful technique to study buried perovskite oxide heterointerfaces. With the recent addition of 3^rd order and now 5^th order aberration correction, which provides a factor of 100x increase in signal over an uncorrected system, we are now able to record 2D maps of composition and bonding of oxide interfaces at atomic resolution [1]. Here, we present studies of the microscopic structure of oxide/oxide multilayers and heterostructures by STEM in combination with EELS and its effect on the properties of the film. Using atomic-resolution spectroscopic imaging we show that the degradation of the magnetic and transport properties of La0.7Sr0.3MnO3/SrTiO3 multilayers correlates with atomic intermixing at the interfaces and the presence of extended defects in the La0.7Sr0.3MnO3 layers. When these defects are eliminated, metallic ferromagnetism at room temperature can be stabilized in 5 unit cell thick manganite layers, almost 40% thinner than the previously reported critical thickness of 3-5 nm for sustaining metallic ferromagnetism below Tc in La0.7Sr0.3MnO3 thin films grown on SrTiO3.[4pt] [1] D.A. Muller, L. Fitting Kourkoutis, M. Murfitt, J.H. Song, H.Y. Hwang, J. Silcox, N. Dellby, O.L. Krivanek, Science 319, 1073-1076 (2008).

  19. Flexible high power-per-weight perovskite solar cells with chromium oxide-metal contacts for improved stability in air.

    PubMed

    Kaltenbrunner, Martin; Adam, Getachew; G?owacki, Eric Daniel; Drack, Michael; Schwödiauer, Reinhard; Leonat, Lucia; Apaydin, Dogukan Hazar; Groiss, Heiko; Scharber, Markus Clark; White, Matthew Schuette; Sariciftci, Niyazi Serdar; Bauer, Siegfried

    2015-10-01

    Photovoltaic technology requires light-absorbing materials that are highly efficient, lightweight, low cost and stable during operation. Organolead halide perovskites constitute a highly promising class of materials, but suffer limited stability under ambient conditions without heavy and costly encapsulation. Here, we report ultrathin (3??m), highly flexible perovskite solar cells with stabilized 12% efficiency and a power-per-weight as high as 23?W?g(-1). To facilitate air-stable operation, we introduce a chromium oxide-chromium interlayer that effectively protects the metal top contacts from reactions with the perovskite. The use of a transparent polymer electrode treated with dimethylsulphoxide as the bottom layer allows the deposition-from solution at low temperature-of pinhole-free perovskite films at high yield on arbitrary substrates, including thin plastic foils. These ultra-lightweight solar cells are successfully used to power aviation models. Potential future applications include unmanned aerial vehicles-from airplanes to quadcopters and weather balloons-for environmental and industrial monitoring, rescue and emergency response, and tactical security applications. PMID:26301766

  20. Flexible high power-per-weight perovskite solar cells with chromium oxide-metal contacts for improved stability in air

    NASA Astrophysics Data System (ADS)

    Kaltenbrunner, Martin; Adam, Getachew; G?owacki, Eric Daniel; Drack, Michael; Schwödiauer, Reinhard; Leonat, Lucia; Apaydin, Dogukan Hazar; Groiss, Heiko; Scharber, Markus Clark; White, Matthew Schuette; Sariciftci, Niyazi Serdar; Bauer, Siegfried

    2015-10-01

    Photovoltaic technology requires light-absorbing materials that are highly efficient, lightweight, low cost and stable during operation. Organolead halide perovskites constitute a highly promising class of materials, but suffer limited stability under ambient conditions without heavy and costly encapsulation. Here, we report ultrathin (3 ?m), highly flexible perovskite solar cells with stabilized 12% efficiency and a power-per-weight as high as 23 W g-1. To facilitate air-stable operation, we introduce a chromium oxide-chromium interlayer that effectively protects the metal top contacts from reactions with the perovskite. The use of a transparent polymer electrode treated with dimethylsulphoxide as the bottom layer allows the deposition--from solution at low temperature--of pinhole-free perovskite films at high yield on arbitrary substrates, including thin plastic foils. These ultra-lightweight solar cells are successfully used to power aviation models. Potential future applications include unmanned aerial vehicles--from airplanes to quadcopters and weather balloons--for environmental and industrial monitoring, rescue and emergency response, and tactical security applications.

  1. Epitaxial heterojunctions of oxide semiconductors and metals on high temperature superconductors

    NASA Technical Reports Server (NTRS)

    Vasquez, Richard P. (inventor); Hunt, Brian D. (inventor); Foote, Marc C. (inventor)

    1994-01-01

    Epitaxial heterojunctions formed between high temperature superconductors and metallic or semiconducting oxide barrier layers are provided. Metallic perovskites such as LaTiO3, CaVO3, and SrVO3 are grown on electron-type high temperature superconductors such as Nd(1.85)Ce(0.15)CuO(4-x). Alternatively, transition metal bronzes of the form A(x)MO(3) are epitaxially grown on electron-type high temperature superconductors. Also, semiconducting oxides of perovskite-related crystal structures such as WO3 are grown on either hole-type or electron-type high temperature superconductors.

  2. Layered oxygen-deficient double perovskite as an efficient and stable anode for direct hydrocarbon solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Sengodan, Sivaprakash; Choi, Sihyuk; Jun, Areum; Shin, Tae Ho; Ju, Young-Wan; Jeong, Hu Young; Shin, Jeeyoung; Irvine, John T. S.; Kim, Guntae

    2015-02-01

    Different layered perovskite-related oxides are known to exhibit important electronic, magnetic and electrochemical properties. Owing to their excellent mixed-ionic and electronic conductivity and fast oxygen kinetics, cation layered double perovskite oxides such as PrBaCo2O5 in particular have exhibited excellent properties as solid oxide fuel cell oxygen electrodes. Here, we show for the first time that related layered materials can be used as high-performance fuel electrodes. Good redox stability with tolerance to coking and sulphur contamination from hydrocarbon fuels is demonstrated for the layered perovskite anode PrBaMn2O5+? (PBMO). The PBMO anode is fabricated by in situ annealing of Pr0.5Ba0.5MnO3-? in fuel conditions and actual fuel cell operation is demonstrated. At 800 °C, layered PBMO shows high electrical conductivity of 8.16 S cm-1 in 5% H2 and demonstrates peak power densities of 1.7 and 1.3 W cm-2 at 850 °C using humidified hydrogen and propane fuels, respectively.

  3. Layered oxygen-deficient double perovskite as an efficient and stable anode for direct hydrocarbon solid oxide fuel cells.

    PubMed

    Sengodan, Sivaprakash; Choi, Sihyuk; Jun, Areum; Shin, Tae Ho; Ju, Young-Wan; Jeong, Hu Young; Shin, Jeeyoung; Irvine, John T S; Kim, Guntae

    2015-02-01

    Different layered perovskite-related oxides are known to exhibit important electronic, magnetic and electrochemical properties. Owing to their excellent mixed-ionic and electronic conductivity and fast oxygen kinetics, cation layered double perovskite oxides such as PrBaCo2O5 in particular have exhibited excellent properties as solid oxide fuel cell oxygen electrodes. Here, we show for the first time that related layered materials can be used as high-performance fuel electrodes. Good redox stability with tolerance to coking and sulphur contamination from hydrocarbon fuels is demonstrated for the layered perovskite anode PrBaMn2O5+? (PBMO). The PBMO anode is fabricated by in situ annealing of Pr0.5Ba0.5MnO3-? in fuel conditions and actual fuel cell operation is demonstrated. At 800 °C, layered PBMO shows high electrical conductivity of 8.16 S cm(-1) in 5% H2 and demonstrates peak power densities of 1.7 and 1.3 W cm(-2) at 850 °C using humidified hydrogen and propane fuels, respectively. PMID:25532072

  4. Chemical Trends for Transition Metal Compound Bonding to Graphene

    NASA Astrophysics Data System (ADS)

    Lange, Bjoern; Blum, Volker

    2015-03-01

    Transition metal compounds are of interest as catalysts for the hydrogen evolution reaction (HER). However, a perfect candidate to replace expensive platinum has not yet been identified. To tailor a specific compound, several properties come into play. One is the bonding to the underlying substrate, for which ?-bonded carbon nanostructures are promising candidates. Here we analyze the bonding of small transition metal compound nanoclusters to a graphene layer for a range of chemical compositions: MxAy (M = Mo, Ti; A = S, O, B, N, C). The clusters are generated by an unbiased random search algorithm. We perform total energy calculations based on density functional theory to identify lowest energy clusters. We calculate binding energies using the PBE and HSE functionals with explicit van der Waals treatment and benchmark those against RPA cluster calculations. Our results indicate that molybdenum-carbides and -nitrides tend to bond tightly to graphene. Mo-oxides and -sulfides show small binding energies, indicating van der Waals bonding.

  5. Electronic transport and mixed conductivity in perovskite type oxides. Progress report, October 1, 1990--June 30, 1992

    SciTech Connect

    Anderson, H.U.; Nasrallah, M.M.; Sparlin, D.M.; Parris, P.E.

    1992-03-03

    The goal of the investigation presented in this report is to study the inter-relationship between electrical conductivity, oxidation-reduction kinetics, defect structure, and composition of n- and p-type binary and ternary transition metal oxides. The experimental part of the investigation included specimen preparation, thermogravimetric measurements, X-ray diffraction, thermally stimulated current, DTA/TGA, optical absorption, transmission electron microscopy, electrical conductivity, and Seebeck measurements. The systems studied or being studied are LaMnO{sub 3}-LaCrO{sub 3}-LaCrO{sub 3}, (La,Ca)(Mn,Al)O{sub 3}, Y{sub 1-x}Ca{sub x}CrO{sub 3}, YMnO{sub 3}-CaMnO{sub 3}, and LaMnO{sub 3}-CaMnO{sub 3}.

  6. Transition metal fluorides: from superconductors to multiferroics. 

    E-print Network

    Drathen, Christina

    2013-06-29

    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 ...

  7. Nanosized perovskite oxide NdFeO3 as material for a carbon-monoxide catalytic gas sensor

    NASA Astrophysics Data System (ADS)

    Giang Ho, Truong; Duy Ha, Thai; Ngan Pham, Quang; Giang, Hong Thai; Thu Do, Thi Anh; Nguyen, Ngoc Toan

    2011-03-01

    In this paper, research on a CO catalytic gas sensor based on nano-crystalline perovskite oxide NdFeO3 designed for exhaust gas measurement is presented. Nano-crystalline oxide NdFeO3 was synthesized by a sol-gel citrate technique. The gas sensing characteristics of this sensor were investigated in the concentration range of CO between 0 and 5?vol.% in air. The influences of C3H8, C4H16 gases, relative humidity and air-flow rate on the cross-sensitivity of the CO sensor were also studied.

  8. Partial oxidation of methane to synthesis gas using LnCoO{sub 3} perovskites as catalyst precursors

    SciTech Connect

    Lago, R.; Pena, M.A.; Fierro, J.L.G.

    1997-04-01

    In this work, a series of cobalt-containing perovskites LnCoO{sub 3} (Ln = La, Pr, Nd, Sm, and Gd) has been studied as catalyst precursors for the partial oxidation of methane to synthesis gas. All the perovskite precursors were prereduced in situ, producing cobalt metal finely dispersed over the rare earth sesquioxide support described here as Ln-Co-O. Of the catalyst tested, the system Gd-Co-O showed exceptionally better performance for CO and H{sub 2} production (with methane conversion of 73% and selectivities of 79 and 81% for CO and H{sub 2}, respectively, at 1009 K). The production of synthesis gas over the other catalysts decreased in the following order: Sm-Co-O {much_gt} Nd-Co-O > Pr-Co-O. The catalyst La-Co-O was active for methane combustion and only traces of CO and H{sub 2} were observed under the reaction conditions. Based on results obtained here, it is proposed that the deactivation of the catalysts Ln-Co-O by reoxidation of cobalt metal is related to the thermodynamic stability of the parent perovskite structure. The authors also present evidence that hydroxyl groups on the rare earth oxide, specially in the La-Co-O system, might make some contribution to the reoxidation of cobalt metal during the reaction via a reverse spillover process. 48 refs., 12 figs., 2 tabs.

  9. Electrode effect on high-detectivity ultraviolet photodetectors based on perovskite oxides

    NASA Astrophysics Data System (ADS)

    Zhou, Wen-jia; Jin, Kui-juan; Guo, Hai-zhong; Ge, Chen; He, Meng; Lu, Hui-bin

    2013-12-01

    High-detectivity metal-semiconductor-metal ultraviolet photodetectors have been fabricated based on SrTiO3 with different types of metal electrodes (Ag, Ni, and Pt), and the effects of the different types of the electrodes on the photoelectric properties were investigated. Comparing with three types of the metal electrodes, the largest responsivity of 0.517 A/W and the smallest dark current of 2.215 × 10-11 A were obtained by using Ag electrode due to the largest Schottky barrier between Ag electrode and SrTiO3. The detectivities of all the photodetectors are achieved about 1012 cm.HZ1/2/W, which can be comparable to Si-based photodetectors. Furthermore, a transient photovoltaic signal with a rise time of ˜360 ps and a full width at half-maximum of ˜576 ps are obtained in the Ag/SrTiO3/Ag photodetectors under the illumination of a 355 nm laser with 15 ps duration. These results provide a useful guide for designing high-performance photodetectors based on perovskite oxides and the appropriate metal electrode selected.

  10. Nanostructured Double Perovskite Cathode With Low Sintering Temperature For Intermediate Temperature Solid Oxide Fuel Cells.

    PubMed

    Kim, Seona; Jun, Areum; Kwon, Ohhun; Kim, Junyoung; Yoo, Seonyoung; Jeong, Hu Young; Shin, Jeeyoung; Kim, Guntae

    2015-09-21

    This study focuses on reducing the cathode polarization resistance through the use of mixed ionic electronic conductors and the optimization of cathode microstructure to increase the number of electrochemically active sites. Among the available mixed ionic electronic conductors (MIECs), the layered perovskite GdBa0.5 Sr0.5 CoFeO5+? (GBSCF) was chosen as a cathode material for intermediate temperature solid oxide fuel cells owing to its excellent electrochemical performance and structural stability. The optimized microstructure of a GBSCF-yttria-stabilized zirconia (YSZ) composite cathode was prepared through an infiltration method with careful control of the sintering temperature to achieve high surface area, adequate porosity, and well-organized connection between nanosized particles to transfer electrons. A symmetric cell shows outstanding results, with the cathode exhibiting an area-specific resistance of 0.006???cm(2) at 700?°C. The maximum power density of a single cell using Ce-Pd anode with a thickness of ?80??m electrolyte was ?0.6?W?cm(-2) at 700?°C. PMID:26227300

  11. Microwave-assisted synthesis of transition metal phosphide

    SciTech Connect

    Viswanathan, Tito

    2014-12-30

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

  12. Activation of methane by transition metal-substituted aluminophosphate molecular sieves

    DOEpatents

    Iton, Lennox E. (Downers Grove, IL); Maroni, Victor A. (Naperville, IL)

    1991-01-01

    Aluminophosphate molecular sieves substituted with cobalt, manganese or iron and having the AlPO.sub.4 -34 or AlPO.sub.4 -5, or related AlPO.sub.4 structure activate methane starting at approximately 350.degree. C. Between 400.degree. and 500.degree. C. and at methane pressures .ltoreq.1 atmosphere the rate of methane conversion increases steadily with typical conversion efficiencies at 500.degree. C. approaching 50% and selectivity to the production of C.sub.2+ hydrocarbons approaching 100%. The activation mechanism is based on reduction of the transition metal(III) form of the molecular sieve to the transition metal(II) form with accompanying oxidative dehydrogenation of the methane. Reoxidation of the - transition metal(II) form to the transition metal(III) form can be done either chemically (e.g., using O.sub.2) or electrochemically.

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

    SciTech Connect

    Yoshitake, Michiko

    2014-11-15

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

  14. Complex perovskite oxide nanocrystals: low-temperature synthesis and crystal structure.

    PubMed

    Rabuffetti, Federico A; Brutchey, Richard L

    2014-10-21

    This Perspective reviews our recent efforts towards the low-temperature synthesis of complex perovskite oxide ABO3 (A = Sr, Ba; B = Ti, Zr) nanocrystals using the vapor diffusion sol-gel method and the determination of their room-temperature crystal structure. From a synthetic standpoint, emphasis is placed on demonstrating the ability of the vapor diffusion sol-gel approach to yield compositionally complex nanocrystals at low temperatures and atmospheric pressure without the need for postsynthetic heat treatment to achieve a crystalline and phase-pure oxide product. The ability to successfully achieve this is illustrated using Ba1-xSrxTi1-yZryO3 (0 ? x ? 1, 0 ? y ? 1) and Eu(3+)-doped Ba(Ti,Zr)O3 nanocrystals as examples. From the standpoint of the structural analysis, emphasis is placed on highlighting how multiple and complementary spectroscopic techniques that probe atomic correlations in short (?1 nm), intermediate (?1-3 nm), and long (?3 nm) length scales can be employed to gain insight into the atomic structure of the resulting nanocrystals. Examples that clearly illustrate this strategy of structural characterization are the investigation of the size- and composition-dependence of the structure of polar nanoregions in sub-10 nm BaTiO3 and sub-20 nm Ba1-xSrxTiO3 and BaTi1-yZryO3 nanocrystals, and the investigation of the distribution of rare earth dopants in sub-15 nm Eu(3+):BaTiO3 nanocrystals. PMID:25154461

  15. Insertion of a Two-Dimensional Iron-Chloride Network between Perovskite Blocks. Synthesis and

    E-print Network

    Spinu, Leonard

    ) alkali metal; A ) alkaline earth metal or rare earth metal; B ) transition metal; n g 2) layered and anions can be co-inserted into layered perovskites. In the case of metal halides, we have found in the synthesis of metal-chloride arrays with iron as well as other first-row transition metals.7,8 Herein we

  16. Cross-plane electronic and thermal transport properties of p-type La0.67Sr0.33MnO3/LaMnO3 perovskite oxide metal/semiconductor

    E-print Network

    Xu, Xianfan

    perovskite oxide metal/semiconductor superlattices Pankaj Jha,1,2 Timothy D. Sands,1,2,3,a) Laura Cassels,4)/lanthanum manganate (LaMnO3, i.e., LMO) perovskite oxide metal/semiconductor superlattices were investigated

  17. Method of boronizing transition metal surfaces

    DOEpatents

    Koyama, Koichiro; Shimotake, Hiroshi.

    1983-08-16

    A method is presented for preparing a boride layer on a transition metal substrate for use in corrosive environments or as a harden surface in machine applications. This method is particularly useful in treating current collectors for use within a high temperature and corrosive electrochemical cell environment. A melt of a alkali metal boride tetrafluoride salt including such as KF to lower its melting point is prepared including a dissolved boron containing material, for instance NiB, MnB[sub 2], or CrB[sub 2]. A transition metal to be coated is immersed in the melt at a temperature of no more than 700 C and a surface boride layer of that transition metal is formed within a period of about 24 hours on the substrate surface. 4 figs.

  18. Neutron structural characterization and transport properties of the oxidized and reduced LaCo0.5Ti0.5O3 perovskite oxide

    NASA Astrophysics Data System (ADS)

    Martinez-Coronado, R.; Aguadero, A.; Alonso, J. A.; Perez-Coll, D.; Fernandez-Díaz, M. T.

    2014-11-01

    Polycrystalline oxygen-stoichiometric LaCo0.5Ti0.5O3 perovskite oxide has been prepared by soft-chemistry procedures followed by annealing in air at 800°C. A new reduced LaCo0.5Ti0.5O3-? specimen has been obtained by topotactical oxygen removal in an H2/N2 (5%/95%) flow at 600°C. The structural characterization has been conducted from neutron powder diffraction (NPD) data, very sensitive to the contrast between Co and Ti and the oxygen stoichiometry. Both perovskites (oxidized and reduced) crystallize in the orthorhombic Pbnm, space group. The partial reduction of Ti4+ to Ti3+ in the reduced phase is accompanied with the occurrence of oxygen vacancies, located at the axial octahedral sites, and it is expected to support the ionic conductivity, as usually observed in oxygen-defective perovskites. Thermogravimetric analysis (TGA) substantiates the oxygen stoichiometry and the stability range of the reduced sample. All the samples in study display a semiconductor-like behavior with values that not reach below to 0.5 Scm-1 for all the phases. Moreover, the measured thermal expansion coefficients perfectly match with the values usually displayed by SOFC electrolytes.

  19. La-doped BaSnO3—Degenerate perovskite transparent conducting oxide: Evidence from synchrotron x-ray spectroscopy

    NASA Astrophysics Data System (ADS)

    Sallis, S.; Scanlon, D. O.; Chae, S. C.; Quackenbush, N. F.; Fischer, D. A.; Woicik, J. C.; Guo, J.-H.; Cheong, S. W.; Piper, L. F. J.

    2013-07-01

    We report direct evidence of conduction band filling in 3% La-doped BaSnO3 using hard x-ray photoelectron spectroscopy. Direct comparisons with hybrid density functional theory calculations support a 3.2 eV indirect band gap. The use of hybrid DFT is verified by excellent agreement between our photoelectron spectra and O K-edge x-ray emission and absorption spectra. Our experimental and computational results demonstrate that the conduction band is primarily of Sn 5s orbital character with little O 2p contribution, which is a prerequisite for designing a perovskite-based transparent conducting oxide.

  20. Mössbauer study of iron-based perovskite-type materials as potential catalysts for ethyl acetate oxidation

    NASA Astrophysics Data System (ADS)

    Paneva, D.; Dimitrov, M.; Velinov, N.; Kolev, H.; Kozhukharov, V.; Tsoncheva, T.; Mitov, I.

    2010-03-01

    La-Sr-Fe perovskite-type oxides were prepared by the nitrate-citrate method. The basic object of this study is layered Ruddlesden-Popper phase LaSr3Fe3O10. The phase composition and structural properties of the obtained materials are investigated by Mössbauer spectroscopy, X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS) and temperature programmed reduction (TPR). The preliminary catalytic tests show a high potential of these materials for volatile organic compounds (VOCs) elimination as they possess high conversion ability and selectivity to total oxidation of ethyl acetate. Catalytic performance of LaSr3Fe3O10 is depended on the stability of structure and Fe4+-oxidation state.

  1. 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...

  2. High Pressure Synthesis of Transition Metal Carbonyls.

    ERIC Educational Resources Information Center

    Hagen, A. P.; And Others

    1979-01-01

    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)

  3. 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 ...

  4. Study of planar heterojunction perovskite photovoltaic cells using compact titanium oxide by chemical bath deposition

    NASA Astrophysics Data System (ADS)

    Yamamoto, Kouhei; Kuwabara, Takayuki; Takahashi, Kohshin; Taima, Tetsuya

    2015-08-01

    Spin-coated perovskite solar cells from sol-gels result in high processing costs because of the need for high temperatures. Here, we report a low-temperature spin-coating route to fabricate planar heterojunction perovskite solar cells using chemical bath deposition of compact-TiOx layers. Comparison of the solar cell properties of compact-TiOx and compact-TiO2 layers show that the power conversion efficiency of the planar heterojunction perovskite solar cell fabricated by the low-temperature, compact-TiOx route is comparable to that of conventional TiO2. The chemical bath deposition method requires heating to 150 °C only to form amorphous compact-TiOx films compared with the 450 °C required for crystalline anatase compact-TiO2 films.

  5. Exclusion of metal oxide by an RF sputtered Ti layer in flexible perovskite solar cells: energetic interface between a Ti layer and an organic charge transporting layer.

    PubMed

    Ameen, Sadia; Akhtar, M Shaheer; Seo, Hyung-Kee; Nazeeruddin, Mohammad Khaja; Shin, Hyung-Shik

    2015-04-14

    In this work, the effects of a titanium (Ti) layer on the charge transport and recombination rates of flexible perovskite solar cells were studied. Ti as an efficient barrier layer was deposited directly on PET-ITO flexible substrates through RF magnetic sputtering using a Ti-source and a pressure of ?5 mTorr. A Ti coated PET-ITO was used for the fabrication of a flexible perovskite solar cell without using any metal oxide layer. The fabricated flexible perovskite solar cell was composed of a PET-ITO/Ti/perovskite (CH3NH3PbI3)/organic hole transport layer of 2,2',7,7'-tetrakis [N,N'-di-p-methoxyphenylamine]-9,9'-spirobifluorene (spiro-OMeTAD)-Li-TFSI/Ag. A high conversion efficiency of ?8.39% along with a high short circuit current (JSC) of ?15.24 mA cm(-2), an open circuit voltage (VOC) of ?0.830 V and a high fill factor (FF) of ?0.66 was accomplished by the fabricated flexible perovskite solar cell under a light illumination of ?100 mW cm(-2) (1.5 AM). Intensity-modulated photocurrent (IMPS)/photovoltage spectroscopy (IMVS) studies demonstrated that the fabricated flexible perovskite solar cell considerably reduced the recombination rate. PMID:25747794

  6. Ab initio defect energetics of perovskite (001) surfaces for solid oxide fuel cells: A comparative study of LaMn O3 versus SrTi O3 and LaAl O3

    NASA Astrophysics Data System (ADS)

    Lee, Yueh-Lin; Morgan, Dane

    2015-05-01

    In this paper, we perform a comparative study based on ab initio modeling for perovskite A B O3 (001) surfaces and surface defect energetics in order to understand the influence of polarity and redox active Mn in the LaMn O3 system. We consider LaMn O3 ,LaAl O3 ,SrTi O3 , and briefly LaFe O3 systems for comparison, which illustrate the interplay between properties of polar surfaces and the varying d -electron shell of transition metals. We are motivated by the need to understand the surfaces of mixed electronic and ionic conductors typically used in solid oxide fuel cell cathodes and other ion conducting technologies, which are represented here by the LaMn O3 system. We focus on the influence of the metal character and surface polarity on the surface and surface defect chemistry in these selected systems. We demonstrate that the facile redox of the TM (3 d4 ) in LaMn O3 with partial eg orbital occupation (or specifically eg occupancy close to 1) allows the polar surfaces to be compensated by changes in charge density over relatively short length scales (3 to 4 unit cells or ˜1.5 nm) near the surface as compared to LaAl O3 . In contrast to LaAl O3 , this low-energy and short-range screening mechanism leads to low surface energies without any additional reconstruction, rapidly converging surface properties with film thickness (by ˜8 unit cells), bulklike defect chemistry more than ˜1.5 nm from the surface, and surface defect energetics that are primarily governed by the local charge doping or the created electric field near the polar surfaces. We show that LaMn O3 exhibits very different surface properties from LaAl O3 and SrTi O3 , thereby demonstrating that these properties are due to the presence of the redox active transition metal with partial eg orbital occupation and a polar surface, respectively. These understandings can help guide qualitative analysis, computational study, and design of surfaces of mixed electronic and ionic conductors.

  7. XANES study of 3d oxides: Dependence on crystal structure

    NASA Astrophysics Data System (ADS)

    Knapp, G. S.; Veal, B. W.; Pan, H. K.; Klippert, T.

    1982-12-01

    XANES measurements are reported for a number of transition metal oxides. Oxide phases, in which the transition element could be widely varied (within the 3d series) while preserving the crystal structure, were systematically examined. The materials examined include monoxides, perovskites, zircons and spinels. For those samples of a given oxide phase, the near edge spectra are nearly identical but spectra for different phases are dissimilar. These observations are consistent with the simplest view of the x-ray absorption process, namely that dipole selection rules are obeyed and spectral features predominately result from transitions between the K shell and empty states with p-character.

  8. Single Sublattice Endotaxial Phase Separation Driven by Charge Frustration in a Complex Oxide

    PubMed Central

    2013-01-01

    Complex transition-metal oxides are important functional materials in areas such as energy and information storage. The cubic ABO3 perovskite is an archetypal example of this class, formed by the occupation of small octahedral B-sites within an AO3 network defined by larger A cations. We show that introduction of chemically mismatched octahedral cations into a cubic perovskite oxide parent phase modifies structure and composition beyond the unit cell length scale on the B sublattice alone. This affords an endotaxial nanocomposite of two cubic perovskite phases with distinct properties. These locally B-site cation-ordered and -disordered phases share a single AO3 network and have enhanced stability against the formation of a competing hexagonal structure over the single-phase parent. Synergic integration of the distinct properties of these phases by the coherent interfaces of the composite produces solid oxide fuel cell cathode performance superior to that expected from the component phases in isolation. PMID:23750709

  9. Chemical vapour deposition: Transition metal carbides go 2D

    NASA Astrophysics Data System (ADS)

    Gogotsi, Yury

    2015-11-01

    The unique properties of 2D materials, such as graphene or transition metal dichalcogenides, have been attracting much attention in the past decade. Now, metallically conductive and even superconducting transition metal carbides are entering the game.

  10. Interface physics of perovskite manganese oxides: A polarized x-ray spectroscopy and scattering study

    NASA Astrophysics Data System (ADS)

    Kavich, Jerald J., Jr.

    Interface physics of strongly correlated electron materials is at the forefront of experimental and theoretical investigation. From a fundamental perspective, the ultimate goal is a complete understanding of the electronic and magnetic properties of these materials. In the case of perovskite oxides, this will lead to the precise control and optimization of material properties for a variety of new spintronic device applications. This work focuses on x = 1/3 hole-doped La1-xSrMnO3, where the interface behaves much differently from the bulk. A suppressed magnetization at the interface was postulated very early due to the surprisingly poor performance of novel spintronic devices. Attempts were made to atomically modify the interface to improve the magnetization even before the precise nature and functional dependence was known. Using the technique of soft x-ray resonant magnetic scattering, we probe interfaces of complicated layered structures and quantitatively model depth-dependent magnetic profiles as a function of distance from the interface on atomically flat, molecular beam expitaxy grown single interfaces and digital superlattices. Comparisons of the average electronic and magnetic properties at interfaces were made independently using x-ray absorption spectroscopy and x-ray magnetic circular dichroism. The first scientific contribution of this work is a direct measurement of the magnetization profile at La 2/3Sr1/3MnO3/SrTiO3 single interfaces. Measurements indicate that the properties of the modified interfaces are equivalent to the unmodified La2/3Sr1/3MnO3 film. Temperature dependent measurements show that below 300K, the surface exhibits a highly suppressed ferromagnetic moment that evolves to the bulk value over a length scale of ˜1.6--2.4 nm. Secondly, by using superlattices to investigate the behavior of electrons in these materials to study the origin of the magnetization, it was discovered that the mechanism of the loss of magnetization is different from the mechanism which leads to long range magnetic order. In the superlattice structures, the delocalization of charge in these materials creates a ferromagnetic state near the interface but is limited to just one unit cell. This is in contrast to the longer length scale of the suppressed surface magnetization in the random alloy.

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

    SciTech Connect

    Not Available

    1992-01-01

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

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

    PubMed

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

    2015-06-01

    Roles of antisite transition metals interchanging with Li atoms in electrode materials of Li transition-metal complex oxides were clarified using a newly developed direct labeling method, termed powder diffraction anomalous fine structure (P-DAFS) near the Ni K-edge. We site-selectively investigated the valence states and local structures of Ni in Li0.89Ni1.11O2, where Ni atoms occupy mainly the NiO2 host-layer sites and partially the interlayer Li sites in-between the host layers, during electrochemical Li insertion/extraction in a lithium-ion battery (LIB). The site-selective X-ray near edge structure evaluated via the P-DAFS method revealed that the interlayer Ni atoms exhibited much lower electrochemical activity as compared to those at the host-layer site. Furthermore, the present analyses of site-selective extended X-ray absorption fine structure performed using the P-DAFS method indicates local structural changes around the residual Ni atoms at the interlayer space during the initial charge; it tends to gather to form rock-salt NiO-like domains around the interlayer Ni. The presence of the NiO-like domains in the interlayer space locally diminishes the interlayer distance and would yield strain energy because of the lattice mismatch, which retards the subsequent Li insertion both thermodynamically and kinetically. Such restrictions on the Li insertion inevitably make the NiO-like domains electrochemically inactive, resulting in an appreciable irreversible capacity after the initial charge but an achievement of robust linkage of neighboring NiO2 layers that tend to be dissociated without the Li occupation. The P-DAFS characterization of antisite transition metals interchanging with Li atoms complements the understanding of the detailed charge-compensation and degradation mechanisms in the electrode materials. PMID:25959625

  13. Recognition- and Reactivity-Based Fluorescent Probes for Studying Transition Metal Signaling in Living Systems

    PubMed Central

    2015-01-01

    Conspectus Metals are essential for life, playing critical roles in all aspects of the central dogma of biology (e.g., the transcription and translation of nucleic acids and synthesis of proteins). Redox-inactive alkali, alkaline earth, and transition metals such as sodium, potassium, calcium, and zinc are widely recognized as dynamic signals, whereas redox-active transition metals such as copper and iron are traditionally thought of as sequestered by protein ligands, including as static enzyme cofactors, in part because of their potential to trigger oxidative stress and damage via Fenton chemistry. Metals in biology can be broadly categorized into two pools: static and labile. In the former, proteins and other macromolecules tightly bind metals; in the latter, metals are bound relatively weakly to cellular ligands, including proteins and low molecular weight ligands. Fluorescent probes can be useful tools for studying the roles of transition metals in their labile forms. Probes for imaging transition metal dynamics in living systems must meet several stringent criteria. In addition to exhibiting desirable photophysical properties and biocompatibility, they must be selective and show a fluorescence turn-on response to the metal of interest. To meet this challenge, we have pursued two general strategies for metal detection, termed “recognition” and “reactivity”. Our design of transition metal probes makes use of a recognition-based approach for copper and nickel and a reactivity-based approach for cobalt and iron. This Account summarizes progress in our laboratory on both the development and application of fluorescent probes to identify and study the signaling roles of transition metals in biology. In conjunction with complementary methods for direct metal detection and genetic and/or pharmacological manipulations, fluorescent probes for transition metals have helped reveal a number of principles underlying transition metal dynamics. In this Account, we give three recent examples from our laboratory and collaborations in which applications of chemical probes reveal that labile copper contributes to various physiologies. The first example shows that copper is an endogenous regulator of neuronal activity, the second illustrates cellular prioritization of mitochondrial copper homeostasis, and the third identifies the “cuprosome” as a new copper storage compartment in Chlamydomonas reinhardtii green algae. Indeed, recognition- and reactivity-based fluorescent probes have helped to uncover new biological roles for labile transition metals, and the further development of fluorescent probes, including ones with varied Kd values and new reaction triggers and recognition receptors, will continue to reveal exciting and new biological roles for labile transition metals. PMID:26215055

  14. Recognition- and reactivity-based fluorescent probes for studying transition metal signaling in living systems.

    PubMed

    Aron, Allegra T; Ramos-Torres, Karla M; Cotruvo, Joseph A; Chang, Christopher J

    2015-08-18

    Metals are essential for life, playing critical roles in all aspects of the central dogma of biology (e.g., the transcription and translation of nucleic acids and synthesis of proteins). Redox-inactive alkali, alkaline earth, and transition metals such as sodium, potassium, calcium, and zinc are widely recognized as dynamic signals, whereas redox-active transition metals such as copper and iron are traditionally thought of as sequestered by protein ligands, including as static enzyme cofactors, in part because of their potential to trigger oxidative stress and damage via Fenton chemistry. Metals in biology can be broadly categorized into two pools: static and labile. In the former, proteins and other macromolecules tightly bind metals; in the latter, metals are bound relatively weakly to cellular ligands, including proteins and low molecular weight ligands. Fluorescent probes can be useful tools for studying the roles of transition metals in their labile forms. Probes for imaging transition metal dynamics in living systems must meet several stringent criteria. In addition to exhibiting desirable photophysical properties and biocompatibility, they must be selective and show a fluorescence turn-on response to the metal of interest. To meet this challenge, we have pursued two general strategies for metal detection, termed "recognition" and "reactivity". Our design of transition metal probes makes use of a recognition-based approach for copper and nickel and a reactivity-based approach for cobalt and iron. This Account summarizes progress in our laboratory on both the development and application of fluorescent probes to identify and study the signaling roles of transition metals in biology. In conjunction with complementary methods for direct metal detection and genetic and/or pharmacological manipulations, fluorescent probes for transition metals have helped reveal a number of principles underlying transition metal dynamics. In this Account, we give three recent examples from our laboratory and collaborations in which applications of chemical probes reveal that labile copper contributes to various physiologies. The first example shows that copper is an endogenous regulator of neuronal activity, the second illustrates cellular prioritization of mitochondrial copper homeostasis, and the third identifies the "cuprosome" as a new copper storage compartment in Chlamydomonas reinhardtii green algae. Indeed, recognition- and reactivity-based fluorescent probes have helped to uncover new biological roles for labile transition metals, and the further development of fluorescent probes, including ones with varied Kd values and new reaction triggers and recognition receptors, will continue to reveal exciting and new biological roles for labile transition metals. PMID:26215055

  15. Transition-Metal Solid-State Lasers Kenneth L. Schepler

    E-print Network

    Van Stryland, Eric

    but not as solid state lasers Important Transition Metal Lasers #12;Transition Metals vs. Rare Earths d orbitals f · Rare Earth Lasers ­ Specific wavelengths dependent on ion and host ­ High energy storage ­ EfficiencyTransition-Metal Solid-State Lasers Kenneth L. Schepler CREOL, The College of Optics & Photonics

  16. Incorporation effect of nanosized perovskite LaFe?.?Co?.?O? on the electrochemical activity of Pt nanoparticles-multi walled carbon nanotube composite toward methanol oxidation

    SciTech Connect

    Noroozifar, Meissam; Khorasani-Motlagh, Mozhgan; Khaleghian-Moghadam, Roghayeh; Ekrami-Kakhki, Mehri-Saddat; Shahraki, Mohammad

    2013-05-01

    Nanosized perovskite LaFe?.?Co?.?O? (LFCO) is synthesized through conventional co-precipitation method and characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) techniques. The incorporation effect of the mentioned perovskite to catalytic activity of the PtNPs-MWCNTs-nafion (or -chitosan) catalyst toward methanol oxidation has been studied by cyclic voltammetry. Based on the electrochemical studies, all MWCNTs-PtNPs-nafion (or chitosan) and MWCNTs-PtNPs-LFCO-nafion (or chitosan) catalysts show a considerable activity for methanol oxidation. However, a synergistic effect is observed when LFCO is added to the catalyst by decreasing the poisoning rate of the Pt catalyst. - Graphical abstract: Nanosized perovskite LaFe?.?Co?.?O? is synthesized and characterized. The incorporation effect of the mentioned perovskite to catalytic activity of the PtNPS-MWCNTs-nafion (or -chitosan) catalyst toward methanol oxidation is studied. Highlights: • Nanocrystalline LaFe?.?Co?.?O? (LFCO) is prepared by a new simple co-precipitation method. • Effect of LFCO to catalytic activity of PtNPS for methanol oxidation is studied. • A synergistic effect is observed when LFCO is added to the Pt catalyst. • Oxygen of LFCO could be considered as active oxygen to remove CO intermediates.

  17. Lattice Location of Transition Metals in Semiconductors

    E-print Network

    2002-01-01

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

  18. Single-layer transition metal sulfide catalysts

    DOEpatents

    Thoma, Steven G. (Albuquerque, NM)

    2011-05-31

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

  19. Lanthanoid-transition-metal bonding in bismetallocenes.

    PubMed

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

    2014-03-01

    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

  20. Corrosion behavior of mesoporous transition metal nitrides

    SciTech Connect

    Yang, Minghui; Allen, Amy J.; Nguyen, Minh T.; Ralston, Walter T.; MacLeod, Michelle J.; DiSalvo, Francis J.

    2013-09-15

    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.

  1. Interplay between spin-orbit coupling and Hubbard interaction in SrIrO3 and related Pbnm perovskite oxides

    NASA Astrophysics Data System (ADS)

    Zeb, M. Ahsan; Kee, Hae-Young

    2012-08-01

    There has been a rapidly growing interest in the interplay between spin-orbit coupling (SOC) and the Hubbard interaction U in correlated materials. A current consensus is that the stronger the SOC, the smaller is the critical interaction Uc required for a spin-orbit Mott insulator, because the atomic SOC splits a band into different total angular momentum bands, narrowing the effective bandwidth. It was further claimed that at large enough SOC, the stronger the SOC, the weaker the Uc, because in general the effective SOC is enhanced with increasing electron-electron interaction strength. Contrary to this expectation, we find that, in orthorhombic perovskite oxides (Pbnm), the stronger the SOC, the bigger the Uc. This originates from a line of Dirac nodes in Jeff=1/2 bands near the Fermi level, inherited from a combination of the lattice structure and a large SOC. Due to this protected line of nodes, there are small hole and electron pockets in SrIrO3, and such a small density of states makes the Hubbard interaction less efficient in building a magnetic insulator. The full phase diagram in U vs SOC is obtained, where nonmagnetic semimetal, magnetic metal, and magnetic insulator are found. Magnetic ordering patterns beyond Uc are also presented. We further discuss implications of our finding in relation to other perovskites such as SrRhO3 and SrRuO3.

  2. Transition-Metal-Free Synthesis of Carbonyl-Containing Oxindoles from N-Arylacrylamides and ?-Diketones via TBHP- or Oxone-Mediated Oxidative Cleavage of C(sp(2))-C(sp(2)) Bonds.

    PubMed

    Zhang, Ming-Zhong; Ji, Peng-Yi; Liu, Yu-Feng; Guo, Can-Cheng

    2015-11-01

    Carbonyl-containing oxindoles can be prepared from N-arylacrylamides and ?-diketones by TBHP- or oxone (KHSO5)-mediated C(sp(2))-C(sp(2)) bond cleavage and new C(sp(2))-C(sp(3)) bond formation. This methodology is characterized by its simple and transition-metal-free conditions and good functional group compatibility utilizing inexpensive and readily available reagents, thus providing a practical and efficient approach to an important class of 3-(2-oxoethyl)indolin-2-ones which are highly valued synthetic intermediates of biologically active molecules. In this transformation, alkylcarbonyl-containing oxindoles were obtained in majority when N-arylacrylamides reacted with asymmetric aliphatic/aromatic ?-diketones. On the basis of the preliminary experiments, a plausible mechanism of this transformation is disclosed. PMID:26488108

  3. Comparative study of the synthesis of layered transition metal molybdates

    SciTech Connect

    Mitchell, S.; Gomez-Aviles, A.; Gardner, C.; Jones, W.

    2010-01-15

    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 +}).

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

    PubMed Central

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

    2015-01-01

    Cadmium is a transition metal ion that is highly toxic in biological systems. Although relatively rare in the Earth’s crust, anthropogenic release of cadmium since industrialization has increased biogeochemical cycling and the abundance of the ion in the biosphere. Despite this, the molecular basis of its toxicity remains unclear. Here we combine metal-accumulation assays, high-resolution structural data and biochemical analyses to show that cadmium toxicity, in Streptococcus pneumoniae, occurs via perturbation of first row transition metal ion homeostasis. We show that cadmium uptake reduces the millimolar cellular accumulation of manganese and zinc, and thereby increases sensitivity to oxidative stress. Despite this, high cellular concentrations of cadmium (~17?mM) are tolerated, with negligible impact on growth or sensitivity to oxidative stress, when manganese and glutathione are abundant. Collectively, this work provides insight into the molecular basis of cadmium toxicity in prokaryotes, and the connection between cadmium accumulation and oxidative stress. PMID:25731976

  5. Monitoring non-pseudomorphic epitaxial growth of spinel/perovskite oxide heterostructures by reflection high-energy electron diffraction

    SciTech Connect

    Schütz, P.; Pfaff, F.; Scheiderer, P.; Sing, M.; Claessen, R.

    2015-02-09

    Pulsed laser deposition of spinel ?-Al{sub 2}O{sub 3} thin films on bulk perovskite SrTiO{sub 3} is monitored by high-pressure reflection high-energy electron diffraction (RHEED). The heteroepitaxial combination of two materials with different crystal structures is found to be inherently accompanied by a strong intensity modulation of bulk diffraction patterns from inelastically scattered electrons, which impedes the observation of RHEED intensity oscillations. Avoiding such electron surface-wave resonance enhancement by de-tuning the RHEED geometry allows for the separate observation of the surface-diffracted specular RHEED signal and thus the real-time monitoring of sub-unit cell two-dimensional layer-by-layer growth. Since these challenges are essentially rooted in the difference between film and substrate crystal structure, our findings are of relevance for the growth of any heterostructure combining oxides with different crystal symmetry and may thus facilitate the search for novel oxide heterointerfaces.

  6. Effect of the filtration of PbI2 solution for zinc oxide nanowire based perovskite solar cells

    NASA Astrophysics Data System (ADS)

    Mijanur Rahman, Md.; Uekawa, Naofumi; Shiba, Fumiyuki; Okawa, Yusuke; Sakai, Masatoshi; Yamamoto, Kazunuki; Kudo, Kazuhiro; Konishi, Takehisa

    2016-01-01

    Zinc oxide (ZnO) nanowires (NWs) are grown on fluorine-doped tin oxide (FTO) glass substrates via a simple reactive evaporation method without the presence of any catalysts or additives. The ZnO NWs show high crystallinity and preferential elongation along the c-axis of the hexagonal wurtzite crystal structure. The highly crystalline NWs as electron transporting layer have been used to fabricate the CH3NH3PbI3 perovskite solar cells and their photovoltaic performance were investigated. In this report, we studied the effect of filtration of PbI2-solution on surface morphology of CH3NH3PbI3 layer. Spin-coating of the filtered PbI2-solution leads to a better crystallization and relatively homogenous coverage of the CH3NH3PbI3 film, resulting in an enhancement of the solar cell efficiency compared to the cell fabricated using non-filtrated PbI2-solution. By synthesizing the CH3NH3PbI3 film using filtrated PbI2-solution, we achieved the best power conversion efficiency of 4.8% with a current density of 7.6 mA cm?2, the open circuit voltage of 0.79 V and fill factor of 0.63.

  7. Immobilization of nanofibrous A- or B-site substituted LaMnO{sub 3} perovskite-type oxides on macroscopic fiber with carbon nanofibers templates

    SciTech Connect

    Wu, Qiang; Sadakane, Masahiro; Ogihara, Hitoshi; Ueda, Wataru

    2010-09-15

    The immobilization of nanofibrous A- or B-site substituted LaMnO{sub 3} perovskite-type oxides on macroscopic silica fiber via a unique and facile carbon nanofibers (CNFs) template-based method was reported. Field emission scanning electron microscopy (FE-SEM), coupled with X-ray diffraction (XRD) analysis confirmed the template effect and the existence of nanofibrous materials immobilized on silica fiber.

  8. Electronic reorganization in the photoelectron spectra of transition metal compounds

    NASA Astrophysics Data System (ADS)

    Böhm, Michael C.

    1983-06-01

    The validity of Koopmans' theorem in a series of 16 transition metal compounds with a large variety of 3d centers (Ti, Cr, Mn, Fe, Co, Ni, and Zn) is investigated. The reorganization energies are determined by means of the Green's function method employed in a semiempirical INDO Hamiltonian. A self-energy approximation is used that allows a fragmentation of the calculated Koopmans' defects into relaxation increments as well as into correlation parameters that take into account the loss of pair correlation in the electronic ground state and the modification of the pair correlation in the cationic hole state. The magnitude and the importance of these parameters are studied as a function of the 3d occupation pattern, the oxidation state of the transition metal center, the nature of the orbital wave functions and the one-particle energies. It is demonstrated that pair relaxation energies in the various hole states are by no means negligible in comparison to the relaxational corrections that lead to the most pronounced deviations from IKv,j (IKv,j=- ?j). The limitations of purely relaxational models (e.g., ?SCF approach) are analyzed in detail. The gradual modifications of the calculated Koopman's defects within the 3d series are rationalized. The most pronounced reorganization energies are encountered in d6-d8 complexes. The magnitude of relaxation and correlation is reduced with a decreasing and an increasing number of 3d electrons. The physical background leading to the breakdown of Koopman's theorem in 3d derivatives is compared with the results of recent studies in various molecular species (e.g., small molecules, organic lone-pair systems).

  9. Structure Sensitivity of Methanol Electrooxidation on Transition Metals

    SciTech Connect

    Ferrin, Peter A.; Mavrikakis, Manos

    2009-10-14

    We have investigated the structure sensitivity of methanol electrooxidation on eight transition metals (Au, Ag, Cu, Pt, Pd, Ir, Rh, and Ni) using periodic, self-consistent density functional theory (DFTGGA). Using the adsorption energies of 16 intermediates on two different facets of these eight face-centeredcubic transition metals, combined with a simple electrochemical model, we address the differences in the reaction mechanism between the (111) and (100) facets of these metals. We investigate two separate mechanisms for methanol electrooxidation: one going through a CO* intermediate (the indirect pathway) and another that oxidizes methanol directly to CO2 without CO* as an intermediate (the direct pathway). A comparison of our results for the (111) and (100) surfaces explains the origin of methanol electrooxidation’s experimentally-established structure sensitivity on Pt surfaces. For most metals studied, on both the (111) and (100) facets, we predict that the indirect mechanism has a higher onset potential than the direct mechanism. Ni(111), Au(100), and Au(111) are the cases where the direct and indirect mechanisms have the same onset potential. For the direct mechanism, Rh, Ir, and Ni show a lower onset potential on the (111) facet, whereas Pt, Cu, Ag, and Au possess lower onset potential on the (100) facet. Pd(100) and Pd(111) have the same onset potential for the direct mechanism. These results can be rationalized by the stronger binding energy of adsorbates on the (100) facet versus the (111) facet. Using linear scaling relations, we establish reactivity descriptors for the (100) surface similar to those recently developed for the (111) surface; the free energies of adsorbed CO* and OH* can describe methanol electrooxidation trends on various metal surfaces reasonably well.

  10. Solvation Effects on Transition Metal Hydricity.

    PubMed

    Tsay, Charlene; Livesay, Brooke N; Ruelas, Samantha; Yang, Jenny Y

    2015-11-11

    The free energy of hydride donation (hydricity) for [HNi(DHMPE)2][BF4] (DHMPE = 1,2-bis(dihydroxymethylphosphino)ethane was experimentally determined versus the heterolytic cleavage energy of hydrogen in acetonitrile, dimethyl sulfoxide, and water to be 57.4, 55.5, and 30.0 kcal/mol, respectively. This work represents the first reported hydricity values for a transition metal hydride donor in three different solvents. A comparison between our values and the hydricity of hydrogen and formate reveals a narrowing in the range of values with increasing solvent polarity. The thermochemical values also reveal solvation effects that impact the overall thermodynamic favorability of hydride generation from hydrogen and transfer to carbon dioxide. The quantitative solvation effects described herein have important consequences to the design and reactivity of catalysts for transformations that have hydride transfer steps throughout synthetic chemistry. PMID:26466014

  11. Oxide Thermoelectric Materials: A Structure-Property Relationship

    NASA Astrophysics Data System (ADS)

    Nag, Abanti; Shubha, V.

    2014-04-01

    Recent demand for thermoelectric materials for power harvesting from automobile and industrial waste heat requires oxide materials because of their potential advantages over intermetallic alloys in terms of chemical and thermal stability at high temperatures. Achievement of thermoelectric figure of merit equivalent to unity ( ZT ? 1) for transition-metal oxides necessitates a second look at the fundamental theory on the basis of the structure-property relationship giving rise to electron correlation accompanied by spin fluctuation. Promising transition-metal oxides based on wide-bandgap semiconductors, perovskite and layered oxides have been studied as potential candidate n- and p-type materials. This paper reviews the correlation between the crystal structure and thermoelectric properties of transition-metal oxides. The crystal-site-dependent electronic configuration and spin degeneracy to control the thermopower and electron-phonon interaction leading to polaron hopping to control electrical conductivity is discussed. Crystal structure tailoring leading to phonon scattering at interfaces and nanograin domains to achieve low thermal conductivity is also highlighted.

  12. Sr(2-X)VMoO(6-Y) double perovskites: A new generation of Solid Oxide Fuel Cell anodes

    NASA Astrophysics Data System (ADS)

    Childs, Nicholas Brule

    Fuel cells are an attractive power source due to their ability to efficiently convert chemical energy stored in fuel directly into electricity. The ability of Solid Oxide Fuel Cells (SOFCs) to reform hydrocarbons at the anode provides for fuel flexibility, an advantage over other types of fuel cell technologies. The primary goals of this dissertation were to investigate the limitations of the currently used anode cermet material, synthesize a double perovskite material (Sr2-xVMoO6-y) without these limitations and investigate the electrical conduction properties of this mixed ionic and electronic conductor (MEIC) in a SOFC anode environment. The electronic current density limitation of a Ni-YSZ anode was determined through the development of a computer simulation and use of experimental data. The electronic current density distribution for nickel particles in a Ni-YSZ anode was calculated via a Monte-Carlo percolation model. Experiments were performed to determine the failure current densities of thin nickel wires in a SOFC anode environment. The results show a current density limitation of Ni-YSZ anodes that is not expected with MEIC anodes. A MEIC anode material, Sr2-xVMoO6-y, was synthesized and characterized using a variety of techniques. The expected MEIC nature of this perovskite material eliminates a potential anode limitation, while adding other benefits over Ni-YSZ. X-ray diffraction (XRD) was used to verify crystal structure. In contrast to the trace amounts of secondary insulating phases found through XRD, XPS shows a high percentage (85-90%) of these secondary phases at the surface. The electrical conductivity of Sr2-xVMoO6-y was found to exceed that reported for Ni-YSZ anodes in a typical SOFC anode environment. Polycrystalline Sr2-xVMoO6-y'' samples exhibited higher electrical conductivity than that reported for SrMoO3 polycrystalline samples, making it a candidate for being the highest electrical conducting oxide known. These conduction values were only measured after specific thermal treatments in a reducing atmosphere. These treatments reduced secondary surface phases, Sr3V2O8 and SrMoO4, into their more conducting counterparts, SrVO3 and SrMoO3. Vanadium and molybdenum valence state XPS fitting parameters for primary and secondary phases are reported.

  13. Design of a dual-layer ceramic interconnect based on perovskite oxides for segmented-in-series solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Park, Beom-Kyeong; Kim, Dae-Wi; Song, Rak-Hyun; Lee, Seung-Bok; Lim, Tak-Hyoung; Park, Seok-Joo; Park, Chong-Ook; Lee, Jong-Won

    2015-12-01

    A segmented-in series (SIS) SOFC consists of segmented unit cells connected in electrical series and shows improved stack efficiency over conventional SOFCs. In this design, a thin interconnect film provides both electrical contact and sealing between the anode of one cell and the cathode of the next; thus, it should have high conductivity and chemical/structural stability in both reducing and oxidizing atmospheres as well as impermeability to gases. Here, we report a dual-layer interconnect film for SIS-SOFCs comprising perovskite-type oxides, Sr0.7La0.2TiO3 (exposed to a reducing atmosphere) and La0.8Sr0.2FeO3 (exposed to an oxidizing atmosphere). The interconnect film is not only very dense but also highly conductive and stable under SOFC operating conditions; in particular, it shows an area-specific resistance of 19.6 m? cm2 at 800 °C, which is much lower than the generally accepted limit for SOFCs. A flat-tubular SIS-SOFC fabricated using these interconnect films exhibits a power density as high as 340 mW cm-2, which proves the feasibility of the dual-layer interconnect design.

  14. Quantum-Mechanical Force Laws for Transition Metals in Biomolecules.

    NASA Astrophysics Data System (ADS)

    Carlsson, Anders E.

    1998-03-01

    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 form of angular forces surrounding transition metals in biomolecules. The method begins with a quantum-mechanical ligand-field Hamiltonian for the transition-metal d-shell, that contains couplings resulting from interaction with the ligand orbitals. It is shown that the moments of the d-complex electron density of states are given rigorously as sums of two-body and higher-order interactions between the ligands. For most transition metals, two-ligand (angular) potential has minima at 90 and 180 degrees, corresponding to the commonly formed octahedral structure. The three-ligand interaction changes sign as a function of band filling, and for late transition metals such as copper and nickel favors square-planar coordination over tetrahedral coordination. The functional forms developed here are a suitable starting point for developing semi-empirical force fields that can treat transition metals in biomolecules.

  15. Trends in Ionization Energy of Transition-Metal Elements

    ERIC Educational Resources Information Center

    Matsumoto, Paul S.

    2005-01-01

    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…

  16. Polarity compensation in ultra-thin films of complex oxides: The case of a perovskite nickelate

    DOE PAGESBeta

    Middey, S.; Rivero, P.; Meyers, D.; Kareev, M.; Liu, X.; Cao, Y.; Freeland, J. W.; Barraza-Lopez, S.; Chakhalian, J.

    2014-10-29

    We address the fundamental issue of growth of perovskite ultra-thin films under the condition of a strong polar mismatch at the heterointerface exemplified by the growth of a correlated metal LaNiO3 on the band insulator SrTiO3 along the pseudo cubic [111] direction. While in general the metallic LaNiO3 film can effectively screen this polarity mismatch, we establish that in the ultra-thin limit, films are insulating in nature and require additional chemical and structural reconstruction to compensate for such mismatch. A combination of in-situ reflection high-energy electron diffraction recorded during the growth, X-ray diffraction, and synchrotron based resonant X-ray spectroscopy revealmore »the formation of a chemical phase La2Ni2O5 (Ni2+) for a few unit-cell thick films. First-principles layer-resolved calculations of the potential energy across the nominal LaNiO3/SrTiO3 interface confirm that the oxygen vacancies can efficiently reduce the electric field at the interface.« less

  17. Polarity compensation in ultra-thin films of complex oxides: The case of a perovskite nickelate

    SciTech Connect

    Middey, S.; Rivero, P.; Meyers, D.; Kareev, M.; Liu, X.; Cao, Y.; Freeland, J. W.; Barraza-Lopez, S.; Chakhalian, J.

    2014-10-29

    We address the fundamental issue of growth of perovskite ultra-thin films under the condition of a strong polar mismatch at the heterointerface exemplified by the growth of a correlated metal LaNiO3 on the band insulator SrTiO3 along the pseudo cubic [111] direction. While in general the metallic LaNiO3 film can effectively screen this polarity mismatch, we establish that in the ultra-thin limit, films are insulating in nature and require additional chemical and structural reconstruction to compensate for such mismatch. A combination of in-situ reflection high-energy electron diffraction recorded during the growth, X-ray diffraction, and synchrotron based resonant X-ray spectroscopy reveal the formation of a chemical phase La2Ni2O5 (Ni2+) for a few unit-cell thick films. First-principles layer-resolved calculations of the potential energy across the nominal LaNiO3/SrTiO3 interface confirm that the oxygen vacancies can efficiently reduce the electric field at the interface.

  18. Polarity compensation in ultra-thin films of complex oxides: The case of a perovskite nickelate

    PubMed Central

    Middey, S.; Rivero, P.; Meyers, D.; Kareev, M.; Liu, X.; Cao, Y.; Freeland, J. W.; Barraza-Lopez, S.; Chakhalian, J.

    2014-01-01

    We address the fundamental issue of growth of perovskite ultra-thin films under the condition of a strong polar mismatch at the heterointerface exemplified by the growth of a correlated metal LaNiO3 on the band insulator SrTiO3 along the pseudo cubic [111] direction. While in general the metallic LaNiO3 film can effectively screen this polarity mismatch, we establish that in the ultra-thin limit, films are insulating in nature and require additional chemical and structural reconstruction to compensate for such mismatch. A combination of in-situ reflection high-energy electron diffraction recorded during the growth, X-ray diffraction, and synchrotron based resonant X-ray spectroscopy reveal the formation of a chemical phase La2Ni2O5 (Ni2+) for a few unit-cell thick films. First-principles layer-resolved calculations of the potential energy across the nominal LaNiO3/SrTiO3 interface confirm that the oxygen vacancies can efficiently reduce the electric field at the interface. PMID:25352069

  19. Towards enhancing two-dimensional electron gas quantum confinement effects in perovskite oxide heterostructures

    SciTech Connect

    Nazir, Safdar; Behtash, Maziar; Yang, Kesong

    2015-03-21

    We explore the possibility of achieving highly confined two-dimensional electron gas (2DEG) within one single atomic layer through a comprehensive comparison study on three prototypical perovskite heterostructures, LaAlO{sub 3}/ATiO{sub 3} (A = Ca, Sr, and Ba), using first-principles electronic structure calculations. We predict that the heterostructure LaAlO{sub 3}/BaTiO{sub 3} has a highly confined 2DEG within a single atomic layer of the substrate BaTiO{sub 3}, and exhibits relatively higher interfacial charge carrier density and larger magnetic moments than the well-known LaAlO{sub 3}/SrTiO{sub 3} system. The long Ti-O bond length in the ab-plane of the LaAlO{sub 3}/BaTiO{sub 3} heterostructure is responsible for the superior charge confinement. We propose BaTiO{sub 3} as an exceptional substrate material for 2DEG systems with potentially superior properties.

  20. Reductive lithium insertion into B-cation deficient niobium perovskite oxides.

    PubMed

    Perejon, Antonio; Hayward, Michael A

    2015-06-21

    Reaction between LiH and the A(n)B(n-1)O(3n) cation deficient perovskite phases Ba(5)Nb(4)O(15), Ba(6)TiNb(4)O(18) and Ba(3)LaNb(3)O(12) proceeds by reductive lithium insertion, leading to the formation of Ba(5)LiNb(4)O(15), Ba(6)LiTiNb(4)O(18) and Ba(3)LaLiNb(3)O(12) respectively. During lithium insertion into Ba(5)Nb(4)O(15) and Ba(6)TiNb(4)O(18) the respective ccchh and cccchh stacking sequences are converted into entirely cubic stacking sequences, while the B-cation vacancy order of the two phases is faithfully converted into Li-Nb or Li-Nb/Ti cation order in the lithiated products. In contrast lithium insertion into Ba(3)LaNb(3)O(12) leads to no gross change in structure, with the inserted lithium cations displacing some of the niobium cations leading to a cation disordered material. Transport measurements indicate semiconducting behaviour consistent with variable range hopping for Ba(5)LiNb(4)O(15) and insulating behaviour for Ba(6)LiTiNb(4)O(18) and Ba(3)LaLiNb(3)O(12). Detailed analysis of the crystal structure of Ba(6)LiTiNb(4)O(18) suggests crystallographic charge ordering in this phase. PMID:25557159

  1. Neutron diffraction and /sup 170/Yb Moessbauer investigation of the perovskite ytterbium titanium oxide

    SciTech Connect

    Greedan, J.E.; Soderholm, L.; Friedt, J.M.

    1985-09-02

    A phase with the perovskite structure (Pbnm) and a composition YbTiO/sub 2.95/ has been prepared by a high-temperature carbothermic method. Neutron diffraction shows a colinear ferrimagnetic structure at 7 K with Yb and Ti moments antiparallel along the c-axis of the orthorhombic cell and a Yb moment of 1.8(3) ..mu../sub B/. /sup 170/Yb Moessbauer measurements find a more precise and accurate value of 2.0(1)..mu../sub B/ from the maximum hyperfine field. From the temperature dependence of the hyperfine field a T/sub c/ = 42(1) K is found. The Yb sublattice magnetization below T/sub c/ follows a Brillouin function. At low temperature a distribution of hyperfine fields is observed which is attributed to a random distribution of defects surrounding the Yb sites. The magnetic structure is discussed in relation to possible values of the crystal field parameters, especially B/sub 0//sup 2/. 24 references, 4 figures, 3 tables.

  2. Conductivity and redox stability of perovskite oxide SrFe1-xTixO3-? (x ? 0.3)

    NASA Astrophysics Data System (ADS)

    Cowin, Peter I.; Lan, Rong; Petit, Christophe T. G.; Tao, Shanwen

    2015-08-01

    A solid solution with the cubic perovskite structure was observed for SrFe1-xTixO3-? (x = 0-0.3), with an increase in the lattice parameters noted upon increasing dopant concentration. Material stability in air was observed for all compounds, with a decrease in conductivity noted upon increasing dopant concentration attributed to a reduction in charge carrier concentration. A reduction in weight proportional to the titanium content was observed upon exposure to 5% H2/Ar, although reduction at 700 °C was observed to elicit a structural transitions and the formation of a secondary phase for samples SrFeO3-? and SrFe0.9Ti0.1O3-? respectively. Conductivity measurements at 600 °C demonstrated a larger decrease in the conductivity with increasing dopant concentration, while all investigated oxides are stable after reducing in 5%H2/Ar at 600 °C. It was found that the conductivity of SrFe0.8Ti0.2O3-? and SrFe0.7Ti0.3O3-? in 5%H2/Ar is insufficient to be used as anode for SOFCs. In the investigated compositions, SrFe0.9Ti0.1O3-? exhibits desired conductivity and redox stability, reduced thermal expansion coefficient compared to SrFeO3-?, which is a promising redox stable anode for IT-SOFCs.

  3. Electronic Structure, Oxidation State of Sn, and Chemical Stability of Photovoltaic Perovskite Variant Cs2SnI6

    E-print Network

    Xiao, Zewen; Zhang, Xiao; Zhou, Yuanyuan; Hosono, Hideo; Kamiya, Toshio

    2015-01-01

    Cs2SnI6, a variant of perovskite CsSnI3, is expected for a photovoltaic material. Based on a simple ionic model, it is expected that Cs2SnI6 is composed of Cs+, I-, and Sn4+ ions and that the band gap is primarily made of occupied I- 5p6 valence band maximum (VBM) and unoccupied Sn4+ 5s conduction band minimum (CBM) similar to SnO2. In this work, we performed density functional theory (DFT) calculations and revealed that the real charge state of the Sn ion in this compound is +2 similar to CsSnI3. This is due to strong covalent nature between the I ion and the Sn ion, the VBM consists of I 5p - I 5p antibonding states, and the CBM of I 5p - Sn 5s antibonding states. The +2 oxidation state of Sn is realized by the apparent charge state of I-2/3, because the I 5p - Sn 5s antibonding states form the unoccupied CBM and apparently 1/18 of the I 5p orbitals are unoccupied. These results are further supported by comparing chemical bonding analyses with those of related compounds. The chemical stability of the Cs2SnI...

  4. Epitaxial growth of highly-crystalline spinel ferrite thin films on perovskite substrates for all-oxide devices.

    PubMed

    Moyer, Jarrett A; Gao, Ran; Schiffer, Peter; Martin, Lane W

    2015-01-01

    The potential growth modes for epitaxial growth of Fe3O4 on SrTiO3 (001) are investigated through control of the energetics of the pulsed-laser deposition growth process (via substrate temperature and laser fluence). We find that Fe3O4 grows epitaxially in three distinct growth modes: 2D-like, island, and 3D-to-2D, the last of which is characterized by films that begin growth in an island growth mode before progressing to a 2D growth mode. Films grown in the 2D-like and 3D-to-2D growth modes are atomically flat and partially strained, while films grown in the island growth mode are terminated in islands and fully relaxed. We find that the optimal structural, transport, and magnetic properties are obtained for films grown on the 2D-like/3D-to-2D growth regime boundary. The viability for including such thin films in perovskite-based all-oxide devices is demonstrated by growing a Fe3O4/La0.7Sr0.3MnO3 spin valve epitaxially on SrTiO3. PMID:26030835

  5. Epitaxial growth of highly-crystalline spinel ferrite thin films on perovskite substrates for all-oxide devices

    PubMed Central

    Moyer, Jarrett A.; Gao, Ran; Schiffer, Peter; Martin, Lane W.

    2015-01-01

    The potential growth modes for epitaxial growth of Fe3O4 on SrTiO3 (001) are investigated through control of the energetics of the pulsed-laser deposition growth process (via substrate temperature and laser fluence). We find that Fe3O4 grows epitaxially in three distinct growth modes: 2D-like, island, and 3D-to-2D, the last of which is characterized by films that begin growth in an island growth mode before progressing to a 2D growth mode. Films grown in the 2D-like and 3D-to-2D growth modes are atomically flat and partially strained, while films grown in the island growth mode are terminated in islands and fully relaxed. We find that the optimal structural, transport, and magnetic properties are obtained for films grown on the 2D-like/3D-to-2D growth regime boundary. The viability for including such thin films in perovskite-based all-oxide devices is demonstrated by growing a Fe3O4/La0.7Sr0.3MnO3 spin valve epitaxially on SrTiO3. PMID:26030835

  6. Electrical properties of double perovskite oxide Sr2LaSbO6: An impedance spectroscopic study

    NASA Astrophysics Data System (ADS)

    Dutta, Alo; Kumari, Premlata; Sinha, T. P.

    2015-09-01

    The Rietveld refinement of the room temperature x-ray diffraction pattern of double perovskite oxide, Sr2LaSbO6 (SLS) synthesized by the solid-state reaction technique shows monoclinic phase with P21/ n symmetry, which is substantiated by the Raman spectrum of the sample. The dielectric relaxation of SLS is investigated in the temperature range from 30°C to 300°C and in the frequency range from 50 Hz to 1 MHz. The Cole-Cole model is used to explain the dielectric relaxation of SLS. The most probable relaxation frequencies at various temperatures are found to obey the Arrhenius law with an activation energy of 0.36 eV, which indicates that the polaron hopping plays the main role in the dielectric relaxation of SLS. The complex impedance plane plots are analyzed by an electrical equivalent circuit consisting of a resistance and a constant phase element. The frequency dependent conductivity spectra obey the power law. [Figure not available: see fulltext.

  7. An A-site-deficient perovskite offers high activity and stability for low-temperature solid-oxide fuel cells.

    PubMed

    Zhu, Yinlong; Chen, Zhi-Gang; Zhou, Wei; Jiang, Shanshan; Zou, Jin; Shao, Zongping

    2013-12-01

    Solid oxide fuel cells (SOFCs) directly convert fossil and/or renewable fuels into electricity and/or high-quality heat in an environmentally friendly way. However, high operating temperatures result in high cost and material issues, which have limited the commercialization of SOFCs. To lower their operating temperatures, highly active and stable cathodes are required to maintain a reasonable power output. Here, we report a layer-structured A-site deficient perovskite Sr0.95 Nb0.1 Co0.9 O3-? (SNC0.95) prepared by solid-state reactions that shows not only high activity towards the oxygen reduction reaction (ORR) at operating temperatures below 600?°C, but also offers excellent structural stability and compatibility, and improved CO2 resistivity. An anode-supported fuel cell with SNC0.95 cathode delivers a peak power density as high as 1016?mW?cm(-2) with an electrode-area-specific resistance of 0.052???cm(2) at 500?°C. PMID:24155098

  8. Comparative study of the synthesis of layered transition metal molybdates

    NASA Astrophysics Data System (ADS)

    Mitchell, S.; Gómez-Avilés, A.; Gardner, C.; Jones, W.

    2010-01-01

    Mixed metal oxides (MMOs) prepared by the mild thermal decomposition of layered double hydroxides (LDHs) differ in their reactivity on exposure to aqueous molybdate containing solutions. In this study, we investigate the reactivity of some T-Al containing MMOs ( T=Co, Ni, Cu or Zn) towards the formation of layered transition metal molybdates (LTMs) possessing the general formula AT2(OH)(MoO 4) 2·H 2O, where A=NH 4+, Na + or K +. The phase selectivity of the reaction was studied with respect to the source of molybdate, the ratio of T to Mo and the reaction pH. LTMs were obtained on reaction of Cu-Al and Zn-Al containing MMOs with aqueous solutions of ammonium heptamolybdate. Rehydration of these oxides in the presence of sodium or potassium molybdate yielded a rehydrated LDH phase as the only crystalline product. The LTM products obtained by the rehydration of MMO precursors were compared with LTMs prepared by direct precipitation from the metal salts in order to study the influence of preparative route on their chemical and physical properties. Differences were noted in the composition, morphology and thermal properties of the resulting products.

  9. Factors that Influence Cation Segregation at the Surfaces of Perovskite Oxides

    E-print Network

    Lee, Wonyoung

    As the oxygen reduction reaction (ORR) becomes more critical for development of solid oxide fuel cells (SOFCs) that operate at 500-700 °C, the correlation between the surface chemistry and electrochemical performance is ...

  10. Perovskite Solar Cells: Beyond Methylammonium Lead Iodide.

    PubMed

    Boix, Pablo P; Agarwala, Shweta; Koh, Teck Ming; Mathews, Nripan; Mhaisalkar, Subodh G

    2015-03-01

    Organic-inorganic lead halide based perovskites solar cells are by far the highest efficiency solution-processed solar cells, threatening to challenge thin film and polycrystalline silicon ones. Despite the intense research in this area, concerns surrounding the long-term stability as well as the toxicity of lead in the archetypal perovskite, CH3NH3PbI3, have the potential to derail commercialization. Although the search for Pb-free perovskites have naturally shifted to other transition metal cations and formulations that replace the organic moiety, efficiencies with these substitutions are still substantially lower than those of the Pb-perovskite. The perovskite family offers rich multitudes of crystal structures and substituents with the potential to uncover new and exciting photophysical phenomena that hold the promise of higher solar cell efficiencies. In addressing materials beyond CH3NH3PbI3, this Perspective will discuss a broad palette of elemental substitutions, solid solutions, and multidimensional families that will provide the next fillip toward market viability of the perovskite solar cells. PMID:26262670

  11. Polytypism in superhard transition-metal triborides

    PubMed Central

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

    2014-01-01

    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

  12. Transition Metal Phosphide Hydroprocessing Catalysts: A review

    SciTech Connect

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

    2009-01-01

    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.

  13. Transition metal-free olefin polymerization catalyst

    DOEpatents

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

    2001-01-01

    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).

  14. Tunable magnetocaloric effect in transition metal alloys

    PubMed Central

    Belyea, Dustin D.; Lucas, M. S.; Michel, E.; Horwath, J.; Miller, Casey W.

    2015-01-01

    The unpredictability of geopolitical tensions and resulting supply chain and pricing instabilities make it imperative to explore rare earth free magnetic materials. As such, we have investigated fully transition metal based “high entropy alloys” in the context of the magnetocaloric effect. We find the NiFeCoCrPdx family exhibits a second order magnetic phase transition whose critical temperature is tunable from 100?K to well above room temperature. The system notably displays changes in the functionality of the magnetic entropy change depending on x, which leads to nearly 40% enhancement of the refrigerant capacity. A detailed statistical analysis of the universal scaling behavior provides direct evidence that heat treatment and Pd additions reduce the distribution of exchange energies in the system, leading to a more magnetically homogeneous alloy. The general implications of this work are that the parent NiFeCoCr compound can be tuned dramatically with FCC metal additives. Together with their relatively lower cost, their superior mechanical properties that aid manufacturability and their relative chemical inertness that aids product longevity, NiFeCoCr-based materials could ultimately lead to commercially viable magnetic refrigerants. PMID:26507636

  15. Tunable magnetocaloric effect in transition metal alloys.

    PubMed

    Belyea, Dustin D; Lucas, M S; Michel, E; Horwath, J; Miller, Casey W

    2015-01-01

    The unpredictability of geopolitical tensions and resulting supply chain and pricing instabilities make it imperative to explore rare earth free magnetic materials. As such, we have investigated fully transition metal based "high entropy alloys" in the context of the magnetocaloric effect. We find the NiFeCoCrPdx family exhibits a second order magnetic phase transition whose critical temperature is tunable from 100?K to well above room temperature. The system notably displays changes in the functionality of the magnetic entropy change depending on x, which leads to nearly 40% enhancement of the refrigerant capacity. A detailed statistical analysis of the universal scaling behavior provides direct evidence that heat treatment and Pd additions reduce the distribution of exchange energies in the system, leading to a more magnetically homogeneous alloy. The general implications of this work are that the parent NiFeCoCr compound can be tuned dramatically with FCC metal additives. Together with their relatively lower cost, their superior mechanical properties that aid manufacturability and their relative chemical inertness that aids product longevity, NiFeCoCr-based materials could ultimately lead to commercially viable magnetic refrigerants. PMID:26507636

  16. Tunable magnetocaloric effect in transition metal alloys

    NASA Astrophysics Data System (ADS)

    Belyea, Dustin D.; Lucas, M. S.; Michel, E.; Horwath, J.; Miller, Casey W.

    2015-10-01

    The unpredictability of geopolitical tensions and resulting supply chain and pricing instabilities make it imperative to explore rare earth free magnetic materials. As such, we have investigated fully transition metal based “high entropy alloys” in the context of the magnetocaloric effect. We find the NiFeCoCrPdx family exhibits a second order magnetic phase transition whose critical temperature is tunable from 100?K to well above room temperature. The system notably displays changes in the functionality of the magnetic entropy change depending on x, which leads to nearly 40% enhancement of the refrigerant capacity. A detailed statistical analysis of the universal scaling behavior provides direct evidence that heat treatment and Pd additions reduce the distribution of exchange energies in the system, leading to a more magnetically homogeneous alloy. The general implications of this work are that the parent NiFeCoCr compound can be tuned dramatically with FCC metal additives. Together with their relatively lower cost, their superior mechanical properties that aid manufacturability and their relative chemical inertness that aids product longevity, NiFeCoCr-based materials could ultimately lead to commercially viable magnetic refrigerants.

  17. Resonant tunnelling in a quantum oxide superlattice

    NASA Astrophysics Data System (ADS)

    Choi, Woo Seok; Lee, Sang A.; You, Jeong Ho; Lee, Suyoun; Lee, Ho Nyung

    2015-06-01

    Resonant tunnelling is a quantum mechanical process that has long been attracting both scientific and technological attention owing to its intriguing underlying physics and unique applications for high-speed electronics. The materials system exhibiting resonant tunnelling, however, has been largely limited to the conventional semiconductors, partially due to their excellent crystalline quality. Here we show that a deliberately designed transition metal oxide superlattice exhibits a resonant tunnelling behaviour with a clear negative differential resistance. The tunnelling occurred through an atomically thin, lanthanum ?-doped SrTiO3 layer, and the negative differential resistance was realized on top of the bipolar resistance switching typically observed for perovskite oxide junctions. This combined process resulted in an extremely large resistance ratio (~105) between the high and low-resistance states. The unprecedentedly large control found in atomically thin ?-doped oxide superlattices can open a door to novel oxide-based high-frequency logic devices.

  18. Thermochemistry of Multiferroic Organic-Inorganic Hybrid Perovskites [(CH3)2NH2][M(HCOO)3] (M = Mn, Co, Ni, and Zn).

    PubMed

    Nagabhushana, G P; Shivaramaiah, Radha; Navrotsky, Alexandra

    2015-08-19

    Organic-inorganic hybrid materials have enormous potential for applications in catalysis, gas storage, sensors, drug delivery, and energy generation, among others. A class of hybrid materials adopts the ABX3 perovskite topology. We report here the synthesis and characterization of an isostructural series of dense hybrid perovskites, [(CH3)2NH2][M(HCOO)3], with M = Mn, Co, Ni, and Zn. These compounds have shown promising multiferroic behavior. Understanding their stability is crucial for their practical application. We report their formation enthalpies based on direct measurement by room-temperature acid solution calorimetry. The enthalpy of formation of this dimethylammonium metal formate series becomes less exothermic in the order Mn, Zn, Co, Ni. The stability of the hybrid perovskite decreases as the tolerance factor increases, unlike trends seen in inorganic perovskites. However, the trends are similar to those seen in a number of ternary transition metal oxides, suggesting that specific bonding interactions rather than geometric factors dominate the energetics. PMID:26214549

  19. Nutritional immunity: transition metals at the pathogen-host interface

    PubMed Central

    Hood, M. Indriati; Skaar, Eric P.

    2013-01-01

    Transition metals occupy an essential niche in biological systems. Their electrostatic properties stabilize substrates or reaction intermediates in the active sites of enzymes, while their heightened reactivity is harnessed for catalysis. However, the latter property renders transition metals toxic at high concentrations. Bacteria, like all living organisms, must regulate the levels of these elements to satisfy their physiological needs while avoiding harm. It is therefore not surprising that the host capitalizes on both the essentiality and toxicity of transition metals to defend against bacterial invaders. This review will discuss established and emerging paradigms in nutrient metal homeostasis at the pathogen-host interface. PMID:22796883

  20. Process for making transition metal nitride whiskers

    DOEpatents

    Bamberger, Carlos E. (Oak Ridge, TN)

    1989-01-01

    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. Process for making transition metal nitride whiskers

    DOEpatents

    Bamberger, C.E.

    1988-04-12

    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.

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

    DOEpatents

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

    2015-04-21

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

  3. Organic carbonates as stabilizing solvents for transition-metal nanoparticles.

    PubMed

    Vollmer, Christian; Thomann, Ralf; Janiak, Christoph

    2012-08-28

    Biodegradable, non-toxic, "green" and inexpensive propylene carbonate (PC) solvent is shown to function as a stabilizing medium for the synthesis of weakly-coordinated transition-metal nanoparticles. Kinetically stable nanoparticles (M-NPs) with a small and uniform particle size (typically <5 ± 1 nm) have been reproducibly obtained by easy, rapid (3 min) and energy-saving 50 W microwave irradiation under an argon atmosphere from their metal-carbonyl precursors in PC. The M-NP/PC dispersions are stable for up to three weeks according to repeated TEM studies over this time period. The rhodium nanoparticle/PC dispersion is a highly active catalyst for the biphasic liquid-liquid hydrogenation of cyclohexene to cyclohexane with activities of up to and 1875 (mol product) (mol Rh)(-1) h(-1) and near quantitative conversion at 4 to 10 bar H(2) and 90 °C. From the PC dispersion the M-NPs can be coated with organic capping ligands such as 3-mercaptopropionic acid or trioctylphosphine oxide for further stabilization. PMID:22786622

  4. New catalysts for hydroprocessing: Transition metal carbides and nitrides

    SciTech Connect

    Ramanathan, S.; Oyama, S.T. |

    1995-11-02

    A series of moderate surface area transition metal carbides and nitrides of molybdenum, tungsten, vanadium, niobium, and titanium were prepared by temperature-programmed reaction of the oxide precursor with a reactant gas (20% CH{sub 4}/H{sub 2} for the carbides and 100% NH{sub 3} for the nitrides). The phase purity and composition of the samples were established by X-ray diffraction photoelectron spectroscopy (XPS), while surface properties were determined by N{sub 2} BET and CO chemisorption measurements. The catalysts were tested in three-phase trickle-bed reactor for their activity in hydrodenitrogenation (HDN), hydrodesulfurization, and hydrodeoxygenation, with particular emphasis on HDN. The catalytic tests were carried out using a model liquid feed mixture containing 3000 ppm sulfur (dibenzothiophene), 2000 ppm nitrogen (quinoline), 500 ppm oxygen (benzofuran), 20 wt% aromatics (tetralin), and balance aliphatics (tetradecane). The carbides and nitrides were found to be active for HDN of quinoline with activity following the order group 6 > group 5 > group 4. Notably, Mo{sub 2}C showed superior areal HDN activity than a commercial sulfided Ni-Mo/Al{sub 2} O{sub 3} catalyst (shell 324). The XRD analysis of the spent catalysts indicated no change in the bulk structure, while XPS results showed little incorporation of sulfur in the surface region of the catalysts, suggesting that these materials are tolerant of sulfur. 42 refs., 11 figs., 7 tabs.

  5. Atomic Natural Orbital Basis Sets for Transition Metals

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

    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.

  6. Mechanisms of transition-metal catalyzed additions to olefins 

    E-print Network

    Nowlan, Daniel Thomas

    2005-08-29

    Transition metal catalyzed reactions have an important place in synthetic chemistry, but the mechanistic details for many of these reactions remain undetermined. Through a combination of experimentally determined 13C kinetic ...

  7. The local structure of transition metal doped semiconducting boron carbides

    NASA Astrophysics Data System (ADS)

    Liu, Jing; Dowben, P. A.; Luo, Guangfu; Mei, Wai-Ning; Kizilkaya, Orhan; Shepherd, Eric D.; Brand, J. I.

    2010-03-01

    Transition metal doped boron carbides produced by plasma-enhanced chemical vapor deposition of orthocarborane (closo-1,2-C2B10H12) and metallocenes were investigated by performing K-edge extended X-ray absorption fine structure and X-ray absorption near edge structure measurements. The Mn, Fe and Co transition metal atoms dope boron carbide pairwise. The transition metal atom occupies one of icosahedral boron or carbon apical site atomic site within the icosahedral cage on adjacent icosahedral cages. There is good agreement between the experiment and theoretical modeling of the local structure two adjoined carborane cages each with a Mn, Fe and Co metal atom (forming the pair wise doping). The local spin configurations of transition metal doped boron carbides, from Ti to Cu, are compared.

  8. The local structure of transition metal doped semiconducting boron carbides

    NASA Astrophysics Data System (ADS)

    Liu, Jing; Luo, Guangfu; Mei, Wai-Ning; Kizilkaya, Orhan; Shepherd, Eric D.; Brand, J. I.; Dowben, P. A.

    2010-03-01

    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 experiment and models for Mn, Fe and Co doping, based on the model structures of two adjoined vertex sharing carborane cages, each containing a transition metal. The local spin configurations of all the 3d transition metal doped boron carbides, Ti through Cu, are compared using cluster and/or icosahedral chain calculations, where the latter have periodic boundary conditions.

  9. Nitrene transfer reactions by late transition metal complexes

    E-print Network

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

    2007-01-01

    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 ...

  10. Photochemical reductive elimination of halogen from transition metal complexes

    E-print Network

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

    2010-01-01

    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 ...

  11. Optical properties of two-dimensional transition metal dichalcogenides

    E-print Network

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

    2014-01-01

    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 ...

  12. Room temperature oxidative intercalation with chalcogen hydrides: Two-step method for the formation of alkali-metal chalcogenide arrays within layered perovskites

    SciTech Connect

    Ranmohotti, K.G. Sanjaya; Montasserasadi, M. Dariush; Choi, Jonglak; Yao, Yuan; Mohanty, Debasish; Josepha, Elisha A.; Adireddy, Shiva; Caruntu, Gabriel; Wiley, John B.

    2012-06-15

    Highlights: ? Topochemical reactions involving intercalation allow construction of metal chalcogenide arrays within perovskite hosts. ? Gaseous chalcogen hydrides serve as effect reactants for intercalation of sulfur and selenium. ? New compounds prepared by a two-step intercalation strategy are presented. -- Abstract: A two-step topochemical reaction strategy utilizing oxidative intercalation with gaseous chalcogen hydrides is presented. Initially, the Dion-Jacobson-type layered perovskite, RbLaNb{sub 2}O{sub 7}, is intercalated reductively with rubidium metal to make the Ruddlesden-Popper-type layered perovskite, Rb{sub 2}LaNb{sub 2}O{sub 7}. This compound is then reacted at room-temperature with in situ generated H{sub 2}S gas to create Rb-S layers within the perovskite host. Rietveld refinement of X-ray powder diffraction data (tetragonal, a = 3.8998(2) ?, c = 15.256(1) ?; space group P4/mmm) shows the compound to be isostructural with (Rb{sub 2}Cl)LaNb{sub 2}O{sub 7} where the sulfide resides on a cubic interlayer site surrounded by rubidium ions. The mass increase seen on sulfur intercalation and the refined S site occupation factor (?0.8) of the product indicate a higher sulfur content than expected for S{sup 2?} alone. This combined with the Raman studies, which show evidence for an H-S stretch, indicate that a significant fraction of the intercalated sulfide exists as hydrogen sulfide ion. Intercalation reactions with H{sub 2}Se{sub (g)} were also carried out and appear to produce an isostructural selenide compound. The utilization of such gaseous hydride reagents could significantly expand multistep topochemistry to a larger number of intercalants.

  13. Synergistic bifunctional catalyst design based on perovskite oxide nanoparticles and intertwined carbon nanotubes for rechargeable zinc-air battery applications.

    PubMed

    Lee, Dong Un; Park, Hey Woong; Park, Moon Gyu; Ismayilov, Vugar; Chen, Zhongwei

    2015-01-14

    Advanced morphology of intertwined core-corona structured bifunctional catalyst (IT-CCBC) is introduced where perovskite lanthanum nickel oxide nanoparticles (LaNiO3 NP) are encapsulated by high surface area network of nitrogen-doped carbon nanotubes (NCNT) to produce highly active and durable bifunctional catalyst for rechargeable metal-air battery applications. The unique composite morphology of IT-CCBC not only enhances the charge transport property by providing rapid electron-conduction pathway but also facilitates in diffusion of hydroxyl and oxygen reactants through the highly porous framework. Confirmed by electrochemical half-cell testing, IT-CCBC in fact exhibits very strong synergy between LaNiO3 NP and NCNT demonstrating bifunctionality with significantly improved catalytic activities of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Furthermore, when compared to the state-of-art catalysts, IT-CCBC outperforms Pt/C and Ir/C in terms of ORR and OER, respectively, and shows improved electrochemical stability compared to them after cycle degradation testing. The practicality of the catalyst is corroborated by testing in a realistic rechargeable zinc-air battery utilizing atmospheric air in ambient conditions, where IT-CCBC demonstrates superior charge and discharge voltages and long-term cycle stability with virtually no battery voltage fading. These improved electrochemical properties of the catalyst are attributed to the nanosized dimensions of LaNiO3 NP controlled by simple hydrothermal technique, which enables prolific growth of and encapsulation by highly porous NCNT network. The excellent electrochemical results presented in this study highlight IT-CCBC as highly efficient and commercially viable bifunctional catalyst for rechargeable metal-air battery applications. PMID:25494945

  14. Quantum Monte Carlo study of porphyrin transition metal complexes

    NASA Astrophysics Data System (ADS)

    Koseki, Jun; Maezono, Ryo; Tachikawa, Masanori; Towler, M. D.; Needs, R. J.

    2008-08-01

    Diffusion quantum Monte Carlo (DMC) calculations for transition metal (M) porphyrin complexes (MPo, M=Ni,Cu,Zn) are reported. We calculate the binding energies of the transition metal atoms to the porphin molecule. Our DMC results are in reasonable agreement with those obtained from density functional theory calculations using the B3LYP hybrid exchange-correlation functional. Our study shows that such calculations are feasible with the DMC method.

  15. Synthesis, structural studies, kinetic stability, and oxidation catalysis of the late first row transition metal complexes of 4,10-dimethyl-1,4,7,10-tetraazabicyclo[6.5.2]pentadecane.

    PubMed

    Matz, Dallas L; Jones, Donald G; Roewe, Kimberly D; Gorbet, Michael-Joseph; Zhang, Zhan; Chen, Zhuqi; Prior, Timothy J; Archibald, Stephen J; Yin, Guochuan; Hubin, Timothy J

    2015-07-21

    Synthetic details for 4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.5.2]pentadecane, the dimethyl ethylene cross-bridged homocyclen ligand are presented for the first time. Its novel Mn(2+), Fe(2+), Mn(3+), and Fe(3+) complexes have been synthesized and characterized. X-ray crystal structures were obtained for both manganese complexes, along with five additional Co(3+), Cu(2+), and Zn(2+) structures, the first structural characterization of complexes of this ligand. Each complex has the cis-V configuration of the cross-bridged macrocycle ring, leaving cis labile binding sites for interaction of the complex with oxidants and/or substrates. The copper(II) complex kinetic stability in 5 M HCl and at elevated temperatures was determined and compared to related complexes in the literature. The electronic properties of the manganese and iron complexes were evaluated using solid state magnetic moment determination and acetonitrile solution electronic spectroscopy, revealing high spin metal complexes in all cases. Cyclic voltammetry in acetonitrile of the divalent iron and manganese complexes revealed reversible redox processes, suggesting catalytic reactivity involving electron transfer processes are possible for both complexes. Screening of the Mn(2+) and Fe(2+) complexes for oxidation catalysis using hydrogen peroxide as the terminal oxidant showed both complexes are worthy of continued development. PMID:25876140

  16. A High-Performing Sulfur-Tolerant and Redox-Stable Layered Perovskite Anode for Direct Hydrocarbon Solid Oxide Fuel Cells

    PubMed Central

    Ding, Hanping; Tao, Zetian; Liu, Shun; Zhang, Jiujun

    2015-01-01

    Development of alternative ceramic oxide anode materials is a key step for direct hydrocarbon solid oxide fuel cells (SOFCs). Several lanthanide based layered perovskite-structured oxides demonstrate outstanding oxygen diffusion rate, favorable electronic conductivity, and good oxygen surface exchange kinetics, owing to A-site ordered structure in which lanthanide and alkali-earth ions occupy alternate (001) layers and oxygen vacancies are mainly located in [LnOx] planes. Here we report a nickel-free cation deficient layered perovskite, (PrBa)0.95(Fe0.9Mo0.1)2O5?+?? (PBFM), for SOFC anode, and this anode shows an outstanding performance with high resistance against both carbon build-up and sulfur poisoning in hydrocarbon fuels. At 800?°C, the layered PBFM showed high electrical conductivity of 59.2?S cm?1 in 5% H2 and peak power densities of 1.72 and 0.54?W?cm?2 using H2 and CH4 as fuel, respectively. The cell exhibits a very stable performance under a constant current load of 1.0?A?cm?2. To our best knowledge, this is the highest performance of ceramic anodes operated in methane. In addition, the anode is structurally stable at various fuel and temperature conditions, suggesting that it is a feasible material candidate for high-performing SOFC anode. PMID:26648509

  17. A High-Performing Sulfur-Tolerant and Redox-Stable Layered Perovskite Anode for Direct Hydrocarbon Solid Oxide Fuel Cells.

    PubMed

    Ding, Hanping; Tao, Zetian; Liu, Shun; Zhang, Jiujun

    2015-01-01

    Development of alternative ceramic oxide anode materials is a key step for direct hydrocarbon solid oxide fuel cells (SOFCs). Several lanthanide based layered perovskite-structured oxides demonstrate outstanding oxygen diffusion rate, favorable electronic conductivity, and good oxygen surface exchange kinetics, owing to A-site ordered structure in which lanthanide and alkali-earth ions occupy alternate (001) layers and oxygen vacancies are mainly located in [LnOx] planes. Here we report a nickel-free cation deficient layered perovskite, (PrBa)0.95(Fe0.9Mo0.1)2O5?+?? (PBFM), for SOFC anode, and this anode shows an outstanding performance with high resistance against both carbon build-up and sulfur poisoning in hydrocarbon fuels. At 800?°C, the layered PBFM showed high electrical conductivity of 59.2?S cm(-1) in 5% H2 and peak power densities of 1.72 and 0.54?W?cm(-2) using H2 and CH4 as fuel, respectively. The cell exhibits a very stable performance under a constant current load of 1.0?A?cm(-2). To our best knowledge, this is the highest performance of ceramic anodes operated in methane. In addition, the anode is structurally stable at various fuel and temperature conditions, suggesting that it is a feasible material candidate for high-performing SOFC anode. PMID:26648509

  18. Hollow spherical La0.8Sr0.2MnO3 perovskite oxide with enhanced catalytic activities for the oxygen reduction reaction

    NASA Astrophysics Data System (ADS)

    Lu, Fanliang; Sui, Jing; Su, Jianmin; Jin, Chao; Shen, Ming; Yang, Ruizhi

    2014-12-01

    A hollow spherical La0.8Sr0.2MnO3 (HS-LSM) perovskite oxide has been prepared using a new carbonate-template route, and characterized by XRD, SEM and TEM. SEM and TEM results show that the pre-prepared oxides consist of porous microspheres composed of submicrometer-sized subunits with a secondary particle diameter of ˜20-50 nm. The catalytic activity of the oxide for the oxygen reduction reaction (ORR) in 0.1 M KOH solution has been studied using a rotating ring-disk electrode (RRDE). In the ORR tests, a maximum cathodic current density of 6.4 mA cm-2 at -0.9 V (vs. Ag/AgCl) with 2500 rpm has been obtained, and the ORR mainly favors a direct four-electron pathway. The chronoamperometric test shows that the HS-LSM exhibits excellent stability for the ORR.

  19. Reaction kinetics of methane oxidation over LaCr{sub 1-x}Ni{sub x}O{sub 3} perovskite catalysts

    SciTech Connect

    Stojanovic, M.; Mims, C.A.; Moudallal, H.

    1997-03-01

    Ternary perovskite oxides LaCr{sub 1-x}Ni{sub x}O{sub 3}, (x = 0 to 1.0) were evaluated as methane oxidation catalysts over the temperature range 300-500{degrees}C and as a function of the partial pressures of oxygen and methane (12-90 kPa). All catalysts are stable in oxygen containing atmospheres, while oxygen starvation causes destructive reduction to Ni metal for x > 0.5. The catalytic activity increases monotonically with the value of x. The nonseparable (composition, temperature) kinetics behavior is well correlated by an oxidation-reduction mechanism for all catalysts. Based on the observed nonlinear increase in catalytic activity with nickel content, Ni-O-Ni ensembles are proposed as the key surface reagent. 52 refs., 6 figs., 2 tabs.

  20. Ultrafast photophysics of transition metal complexes.

    PubMed

    Chergui, Majed

    2015-03-17

    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

  1. Pristine and intercalated transition metal dichalcogenide superconductors

    NASA Astrophysics Data System (ADS)

    Klemm, Richard A.

    2015-07-01

    Transition metal dichalcogenides (TMDs) are quasi-two-dimensional layered compounds that exhibit strongly competing effects of charge-density wave (CDW) formation and superconductivity (SC). The weak van der Waals interlayer bonding between hexagonal layers of octahedral or trigonal prismatic TMD building blocks allows many polytypes to form. In the single layer 1 T polytype materials, one or more CDW states can form, but the pristine TMDs are not superconducting. The 2 H polytypes have two or more Fermi surfaces and saddle bands, allowing for dual orderings, which can be coexisting CDW and SC orderings, two SC gaps as in MgB2, two CDW gaps, and possibly even pseudogaps above the onset TCDW s of CDW orderings. Higher order polytypes allow for multiple CDW gaps and at least one superconducting gap. The CDW transitions TCDW s usually greatly exceed the superconducting transitions at their low Tc values, their orbital order parameters (OPs) are generally highly anisotropic and can even contain nodes, and the SC OPs can be greatly affected by their simultaneous presence. The properties of the CDWs ubiquitously seen in TMDs are remarkably similar to those of the pseudogaps seen in the high-Tc cuprates. In 2H-NbSe2, for example, the CDW renders its general s-wave SC OP orbital symmetry to be highly anisotropic and strongly reduces its Josephson coupling strength (IcRn) with the conventional SC, Pb. Hence, the pristine TMDs are highly "unconventional" in comparison with Pb, but are much more "conventional" than are the ferromagnetic superconductors such as URhGe. Applied pressure and intercalation generally suppress the TMD CDWs, allowing for enhanced SC formation, even in the 1 T polytype materials. The misfit intercalation compound (LaSe)1.14(NbSe2) and many 2 H -TMDs intercalated with organic Lewis base molecules, such as TaS2(pyridine)1/2, have completely incoherent c-axis transport, dimensional-crossover effects, and behave as stacks of intrinsic Josephson junctions. Except for the anomalously large apparent violation of the Pauli limit of the upper critical field of (LaSe)1.14(NbSe2), these normal state and superconducting properties of these intercalation compounds are very similar to those seen in the high-Tc superconductor, Bi2Sr2CaCu2O8+? and in the organic layered superconductor, ?-(ET)2Cu[N(CN)2]Br, where ET is bis(ethylenedithio) tetrathiafulvalene. Electrolytic intercalation of TMDs with water and metallic ions leads to compounds with very similar properties to cobaltates such as NaxCoO2 · y H2O.

  2. Triple-conducting layered perovskites as cathode materials for proton-conducting solid oxide fuel cells.

    PubMed

    Kim, Junyoung; Sengodan, Sivaprakash; Kwon, Goeun; Ding, Dong; Shin, Jeeyoung; Liu, Meilin; Kim, Guntae

    2014-10-01

    We report on an excellent anode-supported H(+) -SOFC material system using a triple conducting (H(+) /O(2-) /e(-) ) oxide (TCO) as a cathode material for H(+) -SOFCs. Generally, mixed ionic (O(2-) ) and electronic conductors (MIECs) have been selected as the cathode material of H(+) -SOFCs. In an H(+) -SOFC system, however, MIEC cathodes limit the electrochemically active sites to the interface between the proton conducting electrolyte and the cathode. New approaches to the tailoring of cathode materials for H(+) -SOFCs should therefore be considered. TCOs can effectively extend the electrochemically active sites from the interface between the cathode and the electrolyte to the entire surface of the cathode. The electrochemical performance of NBSCF/BZCYYb/BZCYYb-NiO shows excellent long term stability for 500 h at 1023 K with high power density of 1.61 W?cm(-2) . PMID:25146887

  3. Chem. Rev. 1988, 86, 1049-1109 1049 Clusters of Transition-Metal Atoms

    E-print Network

    Morse, Michael D.

    Chem. Rev. 1988, 86, 1049-1109 1049 Clusters of Transition-Metal Atoms MICHAEL D. MORSE Department 1050 Transition-Metal Clusters A. Homonuclear Transition-Metal Diatomics 1. Scandium, Sc, 2. Titanium. Osmium, Os, 27. Iridium, Ir, 28. Platinum, Pt, 30. Mercury, Hg, 29. Gold, Au, B. Heteronuclear Transition-Metal

  4. Low-temperature solution-processed tin oxide as an alternative electron transporting layer for efficient perovskite solar cells.

    PubMed

    Ke, Weijun; Fang, Guojia; Liu, Qin; Xiong, Liangbin; Qin, Pingli; Tao, Hong; Wang, Jing; Lei, Hongwei; Li, Borui; Wan, Jiawei; Yang, Guang; Yan, Yanfa

    2015-06-01

    Lead halide perovskite solar cells with the high efficiencies typically use high-temperature processed TiO2 as the electron transporting layers (ETLs). Here, we demonstrate that low-temperature solution-processed nanocrystalline SnO2 can be an excellent alternative ETL material for efficient perovskite solar cells. Our best-performing planar cell using such a SnO2 ETL has achieved an average efficiency of 16.02%, obtained from efficiencies measured from both reverse and forward voltage scans. The outstanding performance of SnO2 ETLs is attributed to the excellent properties of nanocrystalline SnO2 films, such as good antireflection, suitable band edge positions, and high electron mobility. The simple low-temperature process is compatible with the roll-to-roll manufacturing of low-cost perovskite solar cells on flexible substrates. PMID:25987132

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

    SciTech Connect

    Kwong, Philip; Seidel, Scott; Gupta, Malancha

    2015-05-15

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

  6. Transition-metal doped sulfide, selenide, and telluride laser crystal and lasers

    DOEpatents

    Krupke, William F. (Pleasanton, CA); Page, Ralph H. (San Ramon, CA); DeLoach, Laura D. (Manteca, CA); Payne, Stephen A. (Castro Valley, CA)

    1996-01-01

    A new class of solid state laser crystals and lasers are formed of transition metal doped sulfide, selenide, and telluride host crystals which have four fold coordinated substitutional sites. The host crystals include II-VI compounds. The host crystal is doped with a transition metal laser ion, e.g., chromium, cobalt or iron. In particular, Cr.sup.2+ -doped ZnS and ZnSe generate laser action near 2.3 .mu.m. Oxide, chloride, fluoride, bromide and iodide crystals with similar structures can also be used. Important aspects of these laser materials are the tetrahedral site symmetry of the host crystal, low excited state absorption losses and high luminescence efficiency, and the d.sup.4 and d.sup.6 electronic configurations of the transition metal ions. The same materials are also useful as saturable absorbers for passive Q-switching applications. The laser materials can be used as gain media in amplifiers and oscillators; these gain media can be incorporated into waveguides and semiconductor lasers.

  7. Transition-metal doped sulfide, selenide, and telluride laser crystal and lasers

    DOEpatents

    Krupke, W.F.; Page, R.H.; DeLoach, L.D.; Payne, S.A.

    1996-07-30

    A new class of solid state laser crystals and lasers are formed of transition metal doped sulfide, selenide, and telluride host crystals which have four fold coordinated substitutional sites. The host crystals include II-VI compounds. The host crystal is doped with a transition metal laser ion, e.g., chromium, cobalt or iron. In particular, Cr{sup 2+}-doped ZnS and ZnSe generate laser action near 2.3 {micro}m. Oxide, chloride, fluoride, bromide and iodide crystals with similar structures can also be used. Important aspects of these laser materials are the tetrahedral site symmetry of the host crystal, low excited state absorption losses and high luminescence efficiency, and the d{sup 4} and d{sup 6} electronic configurations of the transition metal ions. The same materials are also useful as saturable absorbers for passive Q-switching applications. The laser materials can be used as gain media in amplifiers and oscillators; these gain media can be incorporated into waveguides and semiconductor lasers. 18 figs.

  8. FERROELECTRICS Electrothermal properties of perovskite ferroelectric films

    E-print Network

    Alpay, S. Pamir

    FERROELECTRICS Electrothermal properties of perovskite ferroelectric films J. Zhang Æ A. A of the perovskite oxides barium titanate (BTO), lead titanate (PTO), and strontium titanate (STO) are computed near of a dielectric solid wherein an adiabatic change in temperature (DT) is produced in response to a change

  9. Synthesis, structure and properties of high pressure and ambient pressure ternary vanadium oxides 

    E-print Network

    Markkula, Mikael

    2013-11-28

    Transition metal oxides have been extensively studied during past decades. The purpose of this research was to synthesize new or little characterised transition metal oxides using high-pressure/high-temperature (HPHT) ...

  10. Flexible transition metal dichalcogenide nanosheets for band-selective photodetection

    PubMed Central

    Velusamy, Dhinesh Babu; Kim, Richard Hahnkee; Cha, Soonyoung; Huh, June; Khazaeinezhad, Reza; Kassani, Sahar Hosseinzadeh; Song, Giyoung; Cho, Suk Man; Cho, Sung Hwan; Hwang, Ihn; Lee, Jinseong; Oh, Kyunghwan; Choi, Hyunyoug; Park, Cheolmin

    2015-01-01

    The photocurrent conversions of transition metal dichalcogenide nanosheets are unprecedentedly impressive, making them great candidates for visible range photodetectors. Here we demonstrate a method for fabricating micron-thick, flexible films consisting of a variety of highly separated transition metal dichalcogenide nanosheets for excellent band-selective photodetection. Our method is based on the non-destructive modification of transition metal dichalcogenide sheets with amine-terminated polymers. The universal interaction between amine and transition metal resulted in scalable, stable and high concentration dispersions of a single to a few layers of numerous transition metal dichalcogenides. Our MoSe2 and MoS2 composites are highly photoconductive even at bending radii as low as 200??m on illumination of near infrared and visible light, respectively. More interestingly, simple solution mixing of MoSe2 and MoS2 gives rise to blended composite films in which the photodetection properties were controllable. The MoS2/MoSe2 (5:5) film showed broad range photodetection suitable for both visible and near infrared spectra. PMID:26333531

  11. Accordion-like swelling of layered perovskite crystals via massive permeation of aqueous solutions into 2D oxide galleries.

    PubMed

    Song, Yeji; Iyi, Nobuo; Hoshide, Tatsumasa; Ozawa, Tadashi C; Ebina, Yasuo; Ma, Renzhi; Miyamoto, Nobuyoshi; Sasaki, Takayoshi

    2015-12-14

    Platelet crystals of a layered perovskite showed massive accordion-like swelling in a tetrabutylammonium hydroxide solution. The permeation of the solution induced the huge expansion of the interlayer spacing as well as the crystal thickness up to 50-fold, leading to a very high water content of >90 wt%. PMID:26439314

  12. A family of oxide ion conductors based on the ferroelectric perovskite Na0.5Bi0.5TiO3.

    PubMed

    Li, Ming; Pietrowski, Martha J; De Souza, Roger A; Zhang, Huairuo; Reaney, Ian M; Cook, Stuart N; Kilner, John A; Sinclair, Derek C

    2014-01-01

    Oxide ion conductors find important technical applications in electrochemical devices such as solid-oxide fuel cells (SOFCs), oxygen separation membranes and sensors. Na0.5Bi0.5TiO3 (NBT) is a well-known lead-free piezoelectric material; however, it is often reported to possess high leakage conductivity that is problematic for its piezo- and ferroelectric applications. Here we report this high leakage to be oxide ion conduction due to Bi-deficiency and oxygen vacancies induced during materials processing. Mg-doping on the Ti-site increases the ionic conductivity to ~0.01 S cm(-1) at 600 °C, improves the electrolyte stability in reducing atmospheres and lowers the sintering temperature. This study not only demonstrates how to adjust the nominal NBT composition for dielectric-based applications, but also, more importantly, gives NBT-based materials an unexpected role as a completely new family of oxide ion conductors with potential applications in intermediate-temperature SOFCs and opens up a new direction to design oxide ion conductors in perovskite oxides. PMID:24193663

  13. Room-temperature, solution-processable organic electron extraction layer for high-performance planar heterojunction perovskite solar cells

    NASA Astrophysics Data System (ADS)

    Kim, Jong H.; Chueh, Chu-Chen; Williams, Spencer T.; Jen, Alex K.-Y.

    2015-10-01

    In this work, we describe a room-temperature, solution-processable organic electron extraction layer (EEL) for high-performance planar heterojunction perovskite solar cells (PHJ PVSCs). This EEL is composed of a bilayered fulleropyrrolidinium iodide (FPI)-polyethyleneimine (PEIE) and PC61BM, which yields a promising power conversion efficiency (PCE) of 15.7% with insignificant hysteresis. We reveal that PC61BM can serve as a surface modifier of FPI-PEIE to simultaneously facilitate the crystallization of perovskite and the charge extraction at FPI-PEIE/CH3NH3PbI3 interface. Furthermore, the FPI-PEIE can also tune the work function of ITO and dope PC61BM to promote the efficient electron transport between ITO and PC61BM. Based on the advantages of room-temperature processability and decent electrical property of FPI-PEIE/PC61BM EEL, a high-performance flexible PVSC with a PCE ~10% is eventually demonstrated. This study shows the potential of low-temperature processed organic EEL to replace transition metal oxide-based interlayers for highly printing compatible PVSCs with high-performance.In this work, we describe a room-temperature, solution-processable organic electron extraction layer (EEL) for high-performance planar heterojunction perovskite solar cells (PHJ PVSCs). This EEL is composed of a bilayered fulleropyrrolidinium iodide (FPI)-polyethyleneimine (PEIE) and PC61BM, which yields a promising power conversion efficiency (PCE) of 15.7% with insignificant hysteresis. We reveal that PC61BM can serve as a surface modifier of FPI-PEIE to simultaneously facilitate the crystallization of perovskite and the charge extraction at FPI-PEIE/CH3NH3PbI3 interface. Furthermore, the FPI-PEIE can also tune the work function of ITO and dope PC61BM to promote the efficient electron transport between ITO and PC61BM. Based on the advantages of room-temperature processability and decent electrical property of FPI-PEIE/PC61BM EEL, a high-performance flexible PVSC with a PCE ~10% is eventually demonstrated. This study shows the potential of low-temperature processed organic EEL to replace transition metal oxide-based interlayers for highly printing compatible PVSCs with high-performance. Electronic supplementary information (ESI) available: AFM images, transfer characteristics of field-effect transistors and J-V curve for hysteresis measurement. See DOI: 10.1039/c5nr04250j

  14. Electronic properties of intercalation complexes of the transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Friend, R. H.; Yoffe, A. D.

    1987-11-01

    Intercalation of the layer type transition metal dichalcogenides by a variety of organic molecules, alkali metals, or ‘3d’ transition metals, provides a powerful way to finely tune the electron occupation of the relatively narrow ‘d’ bands met in these solids. These transition metal dichalcogenides are highly anisotropic solids, sometimes referred to as ‘two-dimensional’ solids, and the intercalant molecules which are electron donors enter between the layers. This can result in profound changes in the electronic properties of the host lattice, and these changes can be understood in terms of charge transfer and increased interlayer separation. The phenomena discussed include optical properties, transport properties, super-conductivity, order-disorder phenomena and phase changes, staging, magnetic properties, metal-insulator transitions, Anderson localization, and fast-ion conduction. Some possible practical applications are also considered.

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

    SciTech Connect

    Striebel, Kathryn A.; Wen, Shi-Jie

    1998-12-01

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

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

    DOEpatents

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

    2000-01-01

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

  17. NCORRECTEDPROOF ELSPEC 45066 16

    E-print Network

    discuss the use of resonant photoemission in the study of rare earth/transition metal perovskites; 3p threshold; 4d threshold; transition metal/rare earth perovskite21 22 1. Introduction1 to families of complex transition metal/rare earth oxides 28 with perovskite or perovskite-derived structures

  18. Ellipsometric method for the measurement of temperature and optical constants of incandescent transition metals

    NASA Technical Reports Server (NTRS)

    Hansen, George P.; Krishnan, Shankar; Hauge, Robert H.; Margrave, John L.

    1989-01-01

    The development of a unique noncontact temperature measurement device utilizing rotating analyzer ellipsometry is described. The technique circumvents the necessity of spectral emissivity estimation by direct measurement concomitant with radiance brightness. Simultaneous determinations of dielectric constants and refractive indices allow changes in the physical and chemical state of a heated surface to be monitored. The results of optical property measurements at 633 nm as functions of temperature between 1000 and 2500 K for eight transition metals including Hf, Ir, Mo, Nb, Pd, Pt, Ta, and V are presented together with preliminary results of oxidation studies on iridium.

  19. Magnetization Reversal in Transition Metal Doped ZnO Nanoparticles

    NASA Astrophysics Data System (ADS)

    Mondal, Trisha; Tripathi, Ajay; Tiwari, Archana

    We report magnetic properties of transition metal (TM) doped ZnO nanoparticles and compare the doping effects of different transition metal ions into the ZnO matrix. Stoner-Wohlfarth model has been used to study the switching behavior of magnetic moments by observing energy diagram and hysteresis. Low magnetic anisotropy in Zn1-xMxO nanoparticles is observed where M=Fe, Co, Ni and x is the dopant amount. We have considered chemical precipitation technique for the preparation of Zn1-xMxO samples and have compared the reversal processes of magnetic moments with respect to time in the nanoparticles.

  20. Melting of bcc Transition Metals and Icosahedral Clustering

    SciTech Connect

    Ross, M; Boehler, R; Japel, S

    2006-05-26

    In contrast to polyvalent metals, transition metals have low melting slopes(dT/dP) that are due to partially filled d-bands that allow for a lowering of liquid phase energy through s-d electron transfer and the formation of local structures. In the case of bcc transition metals we show the apparent discrepancy of DAC melting measurements with shock melting of Mo can be understood by reexamining the shock data for V and Ta and introducing the presence of an icosahedral short range order (ISRO) melt phase.

  1. Surface properties and performance for VOCs combustion of LaFe{sub 1-y}Ni{sub y}O{sub 3} perovskite oxides

    SciTech Connect

    Pecchi, G. Reyes, P.; Zamora, R.; Cadus, L.E.; Fierro, J.L.G.

    2008-04-15

    LaFeO{sub 3}, LaNiO{sub 3} and substituted LaFe{sub 1-y}Ni{sub y}O{sub 3} (y=0.1, 0.2 and 0.3) perovskites were synthesized by the citrate method and used in the catalytic combustion of ethanol and acetyl acetate. Chemical composition was determined by atomic absorption spectrometry (AAS) and specific areas from nitrogen adsorption isotherms. Structural details and surface properties were evaluated by temperature-programmed reduction (TPR), infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), temperature-programmed desorption of oxygen (O{sub 2}-TPD) and photoelectron spectroscopy (XPS). Characterization data revealed that total insertion of nickel in the LaFeO{sub 3} takes place for substitution y=0.1. However, NiO segregation occurs to some extent, specifically at higher substitutions (y>0.1). The catalytic performance of these perovskites was evaluated in the combustion of acetyl acetate and ethanol. Among these molecules, ethanol exhibited the lowest ignition temperature, and the catalytic activity expressed as intrinsic activity (mol m{sup -2} h{sup -1}) was found to increase substantially with the nickel substitution. These results can be explained in terms of the cooperative effect of a LaFe{sub 1-y}Ni{sub y}O{sub 3} and NiO phases, whose relative concentration determines the oxygen activation capability and hence their reactivity. - Graphical abstract: LaFeO{sub 3}, LaNiO{sub 3} and substituted LaFe{sub 1-y}Ni{sub y}O{sub 3} (y=0.1, 0.2 and 0.3) perovskite-type oxides have been investigated as catalysts in the total combustion of ethanol and acetylacetate. The characterization indicate variation in specific surface area, crystal structure, reducibility and surface composition. The catalytic activity expressed as intrinsic activity (mol m{sup -2} h{sup -1}) increases with nickel substitution. A synergy between Ni{sup 3+} and Fe{sup 3+} cations at the B position of the LaFe{sub 1-y}Ni{sub y}O{sub 3} perovskite for VOCs combustion was observed.

  2. Synthesis and magnetic properties of double-perovskite oxide La2MnFeO6 thin films

    NASA Astrophysics Data System (ADS)

    Yoshimatsu, K.; Nogami, K.; Watarai, K.; Horiba, K.; Kumigashira, H.; Sakata, O.; Oshima, T.; Ohtomo, A.

    2015-02-01

    We have investigated epitaxial structures and physical properties of double-perovskite La2MnFeO6 films grown by pulsed-laser deposition. The films showed magnetic hysteresis at low temperatures regardless of the degree of Mn/Fe order and the saturation magnetization became smaller for the higher Mn/Fe-order films. The x-ray absorption and x-ray magnetic circular dichroism measurements revealed antiferromagnetic coupling between Mn3 + and Fe3 + ions, resulting in ferrimagnetism of double-perovskite La2MnFeO6 . A band structure was established based on the synchrotron radiation photoemission and optical spectra. The optical gap ranged 1.1 eV above the valence state dominated by the Mn 3 d eg orbitals, which is similar to the charge-transfer insulating state in the end member compound of LaMnO3.

  3. Processing of transition metal silicides for high-temperature applications

    SciTech Connect

    Deevi, S.C.; Sikka, V.K.

    1995-12-31

    The authors review and discuss recent developments in the processing and mechanical properties of MoSi{sub 2} and its composites. High-temperature creep rates of MoSi{sub 2} and its composites are compared to those of several intermetallics and discussed in relation to grain-size effects. Thermophysical properties of MoSi{sub 2} and Si{sub 3}N{sub 4} are compared, and the need for functionally graded composites of MoSi{sub 2}-Si{sub 3}N{sub 4} is discussed. This is followed by a discussion of combustion synthesis, reaction synthesis and densification, in-situ composite development, and reactive hot extrusion of metal-silicon mixtures. In combustion synthesis, a heterogeneous reaction occurs between liquid Si and Mo powder to form MoSi{sub 2}. This technique can be applied to obtain composites and alloys of MoSi{sub 2} and various other transition-metal silicides. In-situ synthesis of a composite of MoSi{sub 2}-Al{sub 2}O{sub 3} was carried out by reacting a thermite mixture consisting of MoO{sub 3}, Al, and Si powders. X-ray characterization of the products obtained at various temperatures reveals that the mechanism consists of a reduction of MoO{sub 3} by Al to MoO{sub 2}, followed by a simultaneous oxidation of Al to Al{sub 2}O{sub 3} and a synthesis reaction between reduced Mo and Si to form MoSi{sub 2}. The rate-determining step is found to be reduction of MoO{sub 2} by Al and oxidation of Al to Al{sub 2}O{sub 3}. The thermite reaction was moderated by adding Mo and Si to the mixture of MoO{sub 3}, Al, and Si, such that the ratio of MoSi{sub 2} to the thermite was in the range of 60:40 to 90:10. Reactive extrusion of metal-silicon mixtures of 3Ni-Si and Co-2Si results in a dense product with at least two phases.

  4. Solid-state chemistry on a surface and in a beaker: Unconventional routes to transition metal chalcogenide nanomaterials

    SciTech Connect

    Stender, Christopher L.; Sekar, Perumal; Odom, Teri W.

    2008-07-15

    This article focuses on two different approaches to create nanoscale transition metal chalcogenide materials. First, we used chemical nanofabrication, a combination of top-down patterning and bottom-up solid-state synthesis, to achieve control over the shape, size, and ordering of the patterned nanomaterials. We demonstrated orientational control over nanocrystals within sub-300 nm patterns of MoS{sub 2} and formed free-standing nanostructures of crystalline NiS{sub 2}. In addition, crossed line arrays of mixed metal chalcogenide nanostructures were achieved, and TaS{sub 2} nanopatterns were made by the chemical transformation of tantalum oxide templates. Second, we developed a one-pot procedure using molecular precursors to synthesize two-dimensional NbSe{sub 2}, TaS{sub 2} and TaSe{sub 2} nanoplates and one-dimensional NbSe{sub 2} wires depending on the relative amount of surfactants in the reaction mixture. Prospects for these transition metal chalcogenide nanomaterials with controlled shapes and morphologies will be discussed. - Graphical abstract: This paper describes how transition metal chalcogenide nanomaterials can be produced by two approaches. First, chemical nanofabrication-a combination of top-down patterning and bottom-up solid-state synthesis-was used to achieve control over the shape, size, and ordering of patterned nanomaterials. Second, a one-pot procedure using molecular precursors was developed to synthesize two-dimensional nanoplates and one-dimensional nanowires of conducting transition metal dichalcogenides.

  5. Symmetry analysis of complex oxides of transition metals

    NASA Astrophysics Data System (ADS)

    Men'shenin, V. V.

    2014-11-01

    Some specific properties of antiferromagnetically ordered crystals, such as the antiferromagnetic photovoltaic effect, interaction of spin waves with polar optical phonons, and the effect of this interaction on the structural phase transitions and magnetic transitions into incommensurate structures, have been considered based on the group-theoretical approach.

  6. Models for transition metal oxides and for protein design

    E-print Network

    Zhou, Fei, Ph. D. Massachusetts Institute of Technology

    2006-01-01

    A large number of properties of solid state materials can now be predicted with standard first-principles methods such as the Local Density (LDA) or Generalized Gradient Approximation (GGA). However, known problems exist ...

  7. Electronic structure of noncrystalline transition metal silicate and aluminate alloys

    E-print Network

    Electronic structure of noncrystalline transition metal silicate and aluminate alloys G. Lucovsky metal TM noncrystalline silicate and aluminate alloys establishes that the lowest conduction band states approach, and have been measured by x-ray absorption spectroscopy for ZrO2 ­SiO2 alloys, and deduced from

  8. Epoxy nanocomposites with two-dimensional transition metal dichalcogenide additives.

    PubMed

    Eksik, Osman; Gao, Jian; Shojaee, S Ali; Thomas, Abhay; Chow, Philippe; Bartolucci, Stephen F; Lucca, Don A; Koratkar, Nikhil

    2014-05-27

    Emerging two-dimensional (2D) materials such as transition metal dichalcogenides offer unique and hitherto unavailable opportunities to tailor the mechanical, thermal, electronic, and optical properties of polymer nanocomposites. In this study, we exfoliated bulk molybdenum disulfide (MoS2) into nanoplatelets, which were then dispersed in epoxy polymers at loading fractions of up to 1% by weight. We characterized the tensile and fracture properties of the composite and show that MoS2 nanoplatelets are highly effective at enhancing the mechanical properties of the epoxy at very low nanofiller loading fractions (below 0.2% by weight). Our results show the potential of 2D sheets of transition metal dichalcogenides as reinforcing additives in polymeric composites. Unlike graphene, transition metal dichalcogenides such as MoS2 are high band gap semiconductors and do not impart significant electrical conductivity to the epoxy matrix. For many applications, it is essential to enhance mechanical properties while also maintaining the electrical insulation properties and the high dielectric constant of the polymer material. In such applications, conductive carbon based fillers such as graphene cannot be utilized. This study demonstrates that 2D transition metal dichalcogenide additives offer an elegant solution to such class of problems. PMID:24754702

  9. TRANSITION METAL ACTIVATION AND FUNCTIONALIZATION OF CARBON-HYDROGEN BONDS

    E-print Network

    Jones, William D.

    TRANSITION METAL ACTIVATION AND FUNCTIONALIZATION OF CARBON-HYDROGEN BONDS William D. Jones-H and C-C bond functionalization, and (4) carbon-fluorine bond activation. We have made progress in each in our proposal where we have had success. These include: (1) carbon-carbon bond cleavage reactions, (2

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

    PubMed

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

    2005-01-01

    A number of transition-metal complexes have been reported to exhibit rich luminescence, usually originating from phosphorescence. Such luminescence properties of the triplet excited state with a large Stoke's shift, long lifetime, high luminescence quantum yield as well as lower excitation energy, are envisaged to serve as an ideal candidate in the area of potential applications for chemosensors, dye-sensitized solar cells, flat panel displays, optics, new materials and biological sciences. Organic alkynes (poly-ynes), with extended or conjugated?-systems and rigid structure with linear geometry, have become a significant research area due to their novel electronic and physical properties and their potential applications in nanotechnology. Owing to the presence of unsaturated sp-hybridized carbon atoms, the alkynyl unit can serve as a versatile building block in the construction of alkynyl transition-metal complexes, not only through?-bonding but also via?-bonding interactions. By incorporation of linear alkynyl groups into luminescent transition-metal complexes, the alkynyl moiety with good?-donor,?-donor and?-acceptor abilities is envisaged to tune or perturb the emission behaviors, including emission energy (color), intensity and lifetime by its role as an auxiliary ligand as well as to govern the emission origin from its direct involvement. This review summarizes recent efforts on the synthesis of luminescent rod-like alkynyl complexes with different classes of transition metals and details the effects of the introduction of alkynyl groups on the luminescence properties of the complexes. PMID:22179333

  11. Transition Metal Nutrition: A Balance Between Deficiency and Toxicity

    E-print Network

    Hamel, Patrice

    333 Transition Metal Nutrition: A Balance Between Deficiency and Toxicity CHAPTER 10 CHAPTER CONTENTS I. Introduction 334 II. Components of the metal homeostasis network 335 A. Metal transporters 335 B. Metal chelation 349 C. Differences with other photosynthetic organisms 352 III. Metal tolerance

  12. Synthesis, characterization and reactivity of transition-metal-containing zeolites

    SciTech Connect

    Rossin, J.A.

    1986-01-01

    Transition metal containing zeolites (zeolite A and ZSM-5) were prepared by addition of various transition metal containing substrates to zeolite synthesis gels. Crystal growth data were recorded in order to determine the influence of the transition metal species on the rate of crystal growth. X-ray diffraction, oxygen adsorption, FTIR and SEM were utilized to evaluate crystal purity. X-ray photoelectron spectroscopy (XPS), chemical analysis and electron microprobe analysis were performed in order to ascertain the position (intrazeolitic versus surface) and homogeneity of the transition metal. It was concluded that intrazeolitic transition metals are produced by the novel procedure presented in this work. 1-Hexane hydroformylation by rhodium zeolite A showed intrazeolitic rhodium to migrate to the external surface of the zeolite. However, in the presence of a solution and surface rhodium poison, intrazeolitic rhodium was found to hydroformylate 1-hexene exclusively to heptanal. Ruthenium containing zeolite A was evaluated under CO-hydrogenation conditions. No migration of intrazeolitic ruthenium to the external surface of the zeolite was observed over the course of the reaction. The product distribution obtained for this catalyst did not follow a log normal behavior. Also, loss of zeolite crystallinity was observed following the reaction. Cobalt ZSM-5 was evaluated under CO-hydrogenation conditions. No migration of cobalt to the external surface of the zeolite occurred. XPS analysis of the catalyst following various stages of the reaction indicated that intrazeolitic cobalt was not reduced to the zero valent state. Consequently, the non-zero valent cobalt was not capable of hydrogenating carbon monoxide.

  13. Cantilever stress measurements for pulsed laser deposition of perovskite oxides at 1000 K in an oxygen partial pressure of 10-4 millibars

    NASA Astrophysics Data System (ADS)

    Premper, J.; Sander, D.; Kirschner, J.

    2015-03-01

    An in situ stress measurement setup using an optical 2-beam curvature technique is described which is compatible with the stringent growth conditions of pulsed laser deposition (PLD) of perovskite oxides, which involves high substrate temperatures of 1000 K and oxygen partial pressures of up to 1 × 10-4 millibars. The stress measurements are complemented by medium energy electron diffraction (MEED), Auger electron spectroscopy, and additional growth rate monitoring by a quartz microbalance. A shielded filament is used to allow for simultaneous stress and MEED measurements at high substrate temperatures. A computer-controlled mirror scans an excimer laser beam over a stationary PLD target. This avoids mechanical noise originating from rotating PLD targets, and the setup does not suffer from limited lifetime issues of ultra high vacuum (UHV) rotary feedthroughs.

  14. Cantilever stress measurements for pulsed laser deposition of perovskite oxides at 1000 K in an oxygen partial pressure of 10(-4) millibars.

    PubMed

    Premper, J; Sander, D; Kirschner, J

    2015-03-01

    An in situ stress measurement setup using an optical 2-beam curvature technique is described which is compatible with the stringent growth conditions of pulsed laser deposition (PLD) of perovskite oxides, which involves high substrate temperatures of 1000 K and oxygen partial pressures of up to 1 × 10(-4) millibars. The stress measurements are complemented by medium energy electron diffraction (MEED), Auger electron spectroscopy, and additional growth rate monitoring by a quartz microbalance. A shielded filament is used to allow for simultaneous stress and MEED measurements at high substrate temperatures. A computer-controlled mirror scans an excimer laser beam over a stationary PLD target. This avoids mechanical noise originating from rotating PLD targets, and the setup does not suffer from limited lifetime issues of ultra high vacuum (UHV) rotary feedthroughs. PMID:25832240

  15. Phase transitions in heated Sr2MgTeO6 double perovskite oxide probed by X-ray diffraction and Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Manoun, Bouchaib; Tamraoui, Y.; Lazor, P.; Yang, Wenge

    2013-12-01

    Double-perovskite oxide Sr2MgTeO6 has been synthetized, and its crystal structure was probed by the technique of X-ray diffraction at room temperature. The structure is monoclinic, space group I2/m. Temperature-induced phase transitions in this compound were investigated by Raman spectroscopy up to 550 °C. Two low-wavenumber modes corresponding to external lattice vibrations merge at temperature of around 100 °C, indicating a phase transition from the monoclinic (I2/m) to the tetragonal (I4/m) structure. At 300 °C, changes in the slopes of temperature dependencies of external and O-Te-O bending modes are detected and interpreted as a second phase transition from the tetragonal (I4/m) to the cubic (Fm-3m) structure.

  16. Phase transitions in heated Sr{sub 2}MgTeO{sub 6} double perovskite oxide probed by X-ray diffraction and Raman spectroscopy

    SciTech Connect

    Manoun, Bouchaib Tamraoui, Y.; Lazor, P.; Yang, Wenge

    2013-12-23

    Double-perovskite oxide Sr{sub 2}MgTeO{sub 6} has been synthetized, and its crystal structure was probed by the technique of X-ray diffraction at room temperature. The structure is monoclinic, space group I2/m. Temperature-induced phase transitions in this compound were investigated by Raman spectroscopy up to 550?°C. Two low-wavenumber modes corresponding to external lattice vibrations merge at temperature of around 100?°C, indicating a phase transition from the monoclinic (I2/m) to the tetragonal (I4/m) structure. At 300?°C, changes in the slopes of temperature dependencies of external and O–Te–O bending modes are detected and interpreted as a second phase transition from the tetragonal (I4/m) to the cubic (Fm-3m) structure.

  17. Studies on polymorphic sequence during the formation of the 1:1 ordered perovskite-type BaCa(0.335)M(0.165)Nb(0.5)O(3-?) (M = Mn, Fe, Co) using in situ and ex situ powder X-ray diffraction.

    PubMed

    Kan, Wang Hay; Lussier, Joey; Bieringer, Mario; Thangadurai, Venkataraman

    2014-10-01

    Here, we report a synthetic strategy to control the B-site ordering of the transition metal-doped perovskite-type oxides with the nominal formula of BaCa(0.335)M(0.165)Nb(0.5)O(3-?) (M = Mn, Fe, Co). Variable temperature (in situ) and ex situ powder X-ray diffraction (PXRD), selected area electron diffraction (SAED), energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), scanning/transmission electron microscopy (SEM/TEM), and thermogravimetic analysis (TGA) were used to understand the B-site ordering as a function of temperature. The present study shows that BaCa(0.335)M(0.165)Nb(0.5)O(3-?) crystallizes in the B-site disordered primitive perovskite (space group s.g. Pm3?m) at 900 °C in air, which can be converted into the B-site 1:2 ordered perovskite (s.g. P3?m1) at 1200 °C and the B-site 1:1 ordered perovskite phase (s.g. Fm3?m) at 1300 °C. However, the reverse reaction is not feasible when the temperature is reduced. FTIR revealed that no carbonate species were present in all three polymorphs. The chemical stability of the investigated perovskites in CO2 and H2 highly depends on the B-site cation ordering. For example, TGA confirmed that the B-site disordered primitive perovskite phase is more readily reduced in dry and wet 10% H2/90% N2 and is less stable in pure CO2 at elevated temperature, compared to the B-site 1:1 ordered perovskite-type phase of the same nominal composition. PMID:25211299

  18. Double perovskite oxides Sr{sub 2}MMoO{sub 6} (M = Fe and Co) as cathode materials for oxygen reduction in alkaline medium

    SciTech Connect

    Cheriti, Mabrouk; Kahoul, Abdelkrim

    2012-01-15

    Graphical abstract: The oxygen reduction over the surface of the electrocatalysts exhibiting high currents shows that SCMO/C electrocatalyst is slightly more active than the SFMO/C one. The relatively high electrochemical activity of the first may be ascribed to its high specific surface area providing a higher electrode current. Highlights: Black-Right-Pointing-Pointer SCMO/C and SFMO/C as catalysts for oxygen reduction were studied. Black-Right-Pointing-Pointer SCMO/C catalyst showed a relatively high activity. Black-Right-Pointing-Pointer A change in the reaction mechanism from a direct 'four-electron pathway' to a 'peroxide pathway' was observed. -- Abstract: The oxygen reduction reaction (ORR) was studied on Sr{sub 2}MMoO{sub 6} (M = Fe and Co) double perovskites, prepared by a solid-state reaction, in 0.5 M NaOH at 25 Degree-Sign C with a rotating disk electrode (RDE). The two oxide powders were characterized by X-ray diffraction, scanning electron microscopy and BET analysis. The electrochemical techniques considered are linear voltammetry, steady state polarization and ac impedance spectroscopy. The electrocatalysts (SFMO/C, SCMO/C) consisting of the double perovskite oxides and carbon (Vulcan XC-72) were mixed and spread out into a thin layer on a glassy carbon substrate. At room temperature, a significantly electrocatalytic activity is observed for both electrocatalysts. Compared to SFMO/C, the SCMO/C electrocatalyst was found to show a relatively high electrocatalytic activity for O{sub 2} reduction, which agrees well with the results obtained using the ac impedance spectroscopy.

  19. Perovskite-type halo-oxide La{sub 1{minus}x}Sr{sub x}FeO{sub 3{minus}{delta}}X{sub {sigma}} (X=F, Cl) catalysts selective for the oxidation of ethane to ethene

    SciTech Connect

    Dai, H.X.; Ng, C.F.; Au, C.T.

    2000-01-01

    The catalytic performance and characterization of perovskite-type halo-oxide La{sub 1{minus}x}Sr{sub x}FeO{sub 3{minus}{delta}}X{sub {sigma}} (X = F, Cl) as well as La{sub 1{minus}x}Sr{sub x}FeO{sub 3{minus}{delta}} (x = 0--0.8) for the oxidative dehydrogenation of ethane (ODE) to ethene have been investigated. XRD results indicate that the catalysts had oxygen-deficient perovskite structures and TGA results demonstrated that the F- and Cl-doped perovskites were thermally stable. Under the reaction conditions of C{sub 2}H{sub 6}/O{sub 2}/N{sub 2} = 2/1/3.7, temperature = 660 C, and space velocity = 6000 mL/h g, C{sub 2}H{sub 6} conversion, C{sub 2}H{sub 4} selectivity, and C{sub 2}H{sub 4} yield were, respectively, 55.3, 45.1, and 24.9% over La{sub 0.6}Sr{sub 0.4}FeO{sub 3--0.048}; 76.8, 62.1, and 47.7% over La{sub 0.8}Sr{sub 0.2}FeO{sub 3--0.103}F{sub 0.216}; and 84.4, 68.4, and 57.6% over La{sub 0.6}Sr{sub 0.4}FeO{sub 3--0.103}Cl{sub 0.164}. Over the two halo-oxide catalysts, with an increase in space velocity, C{sub 2}H{sub 6} conversion decreased, whereas C{sub 2}H{sub 4} selectivity increased. Both La{sub 0.8}Sr{sub 0.2}FeO{sub 3--0.103}F{sub 0216} and La{sub 0.6}Sr{sub 0.4}FeO{sub 3--0.103}Cl{sub 0.164} were durable within 40 h of onstream ODE reaction. XPS results suggested that the presence of halide ions in the perovskite lattices promotes lattice oxygen mobility. It is apparent that the inclusion of F{sup {minus}} or Cl{sup {minus}} ions in La{sub 1{minus}x}Sr{sub x}FeO{sub 3{minus}{delta}} can reduce the deep oxidation of C{sub 2}H{sub 4} and thus enhance C{sub 2}H{sub 4} selectivity. Based on the results of O{sub 2}-TPD and TPR studies, the authors suggest that the oxygen species that desorbed at temperatures ranging from 590 to 700 C over the La{sub 0.8}Sr{sub 0.2}FeO{sub 3--0.103}F{sub 0.216} and La{sub 0.6}Sr{sub 0.4}FeO{sub 3--0.103}Cl{sub 0.164} catalysts are active for the selective oxidation of ethane to ethene. By regulating the oxygen vacancy density and the oxidation states of B-site cations by implanting halide ions into oxygen vacancies in perovskite-type oxides (ABO{sub 3}), one may obtain catalysts that are durable and selective for the ODE reaction.

  20. Redox potential trend with transition metal elements in lithium-ion battery cathode materials

    NASA Astrophysics Data System (ADS)

    Chen, Zhenlian; Li, Jun

    2013-03-01

    First-principles calculations are performed to investigate the relationship between the intrinsic voltage and element-lattice for the popular transition metal oxides and polyoxyanionic compounds as cathode materials for lithium-ion batteries. A V-shape redox potential in olivine phosphates LiMPO4 and orthogonal silicates Li2MSiO4 (M =Mn, Fe, Co, Ni), and an N-shape one in layered oxides LiMO2 (M =Mn, Fe, Co, Ni, Cu) relative to transition metal M elements are found to be inversely characteristic of electronic energy contribution, which costs energy in the lithiation process and is defined as electron affinity. The maxima of electron affinity, locating at different elements for different types of crystal lattices are determined by delectronic configurations that cross the turning point of a full occupancy of electronic bands, which is determined by the cooperative effect of crystal field splitting and intraionic exchange interactions. The Ningbo Key Innovation Team, National Natural Science Foundation of China, Postdoctoral Foundation of China

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

    ERIC Educational Resources Information Center

    Hathaway, Brian

    1979-01-01

    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)

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

    DOEpatents

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

    1991-03-05

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

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

    DOEpatents

    Kostic, N.M.; Chen, J.

    1991-03-05

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

  4. Intercalation of Transition Metals into Stacked Benzene Rings: A Model Study of the Intercalation of Transition Metals into Bilayered Graphene.

    PubMed

    Youn, Il Seung; Kim, Dong Young; Singh, N Jiten; Park, Sung Woo; Youn, Jihee; Kim, Kwang S

    2012-01-10

    Structures of neutral metal-dibenzene complexes, M(C6H6)2 (M = Sc-Zn), are investigated by using Møller-Plesset second order perturbation theory (MP2). The benzene molecules change their conformation and shape upon complexation with the transition metals. We find two types of structures: (i) stacked forms for early transition metal complexes and (ii) distorted forms for late transition metal ones. The benzene molecules and the metal atom are bound together by ? bonds which originate from the interaction of ?-MOs and d orbitals. The binding energy shows a maximum for Cr(C6H6)2, which obeys the 18-electron rule. It is noticeable that Mn(C6H6)2, a 19-electron complex, manages to have a stacked structure with an excess electron delocalized. For other late transition metal complexes having more than 19 electrons, the benzene molecules are bent or stray away from each other to reduce the electron density around a metal atom. For the early transition metals, the M(C6H6) complexes are found to be more weakly bound than M(C6H6)2. This is because the M(C6H6) complexes do not have enough electrons to satisfy the 18-electron rule, and so the M(C6H6)2 complexes generally tend to have tighter binding with a shorter benzene-metal length than the M(C6H6) complexes, which is quite unusual. The present results could provide a possible explanation of why on the Ni surface graphene tends to grow in a few layers, while on the Cu surface the weak interaction between the copper surface and graphene allows for the formation of a single layer of graphene, in agreement with chemical vapor deposition experiments. PMID:26592872

  5. Molybdenum doped Pr0.5Ba0.5MnO3-? (Mo-PBMO) double perovskite as a potential solid oxide fuel cell anode material

    NASA Astrophysics Data System (ADS)

    Sun, Yi-Fei; Zhang, Ya-Qian; Hua, Bin; Behnamian, Yashar; Li, Jian; Cui, Shao-Hua; Li, Jian-Hui; Luo, Jing-Li

    2016-01-01

    A layered Mo doped Pr0.5Ba0.5MnO3-? (Mo-PBMO) double perovskite oxide was prepared by a modified sol-gel method and the properties of the fabricated material are characterized by various technologies. The results of X-ray diffraction (XRD), H2-temperature programmed reduction (H2-TPR), NH3-temperature programmed desorption (NH3-TPD), and thermogravimetric analysis (TGA) demonstrate that the treatment in reducing atmosphere at high temperature lead to a significant phase transformation of the material to a single cubic phase as well as with the Mo in multiple oxidized states. Such character leads to the production of large amount of oxygen deficiency with facilitated oxygen diffusion. The electrochemical performance tests of half-cell and single cell SOFCs exhibit the promoted effect of Mo on catalytic activity for the oxidation of H2 and CH4, indicating that Mo-PBMO could serve as an anode material candidate for SOFCs.

  6. The performance of La0.6Sr1.4MnO4 layered perovskite electrode material for intermediate temperature symmetrical solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Zhou, Jun; Chen, Gang; Wu, Kai; Cheng, Yonghong

    2014-12-01

    A layered perovskite electrode material, La0.6Sr1.4MnO4+? (LSMO4), has been studied for intermediate temperature symmetrical solid oxide fuel cells (IT-SSOFCs) on La0.9Sr0.1Ga0.8Mg0.2O3-? (LSGM) electrolyte. The chemical compatibility tests indicate that no reaction occurred between LSMO4 oxide and LSGM electrolyte at temperature up to 1000 °C both in air and 5% H2. The lower conductivity in 5% H2 and higher conduction activation energy than those in air would be caused by poorer overlap of both ? and ? bonds. DFT + U calculations also show that oxygen vacancies which formed in reducing atmosphere may block the 3D hopping path for electrons or holes through Mn-O-Mn chains. For LSMO4 electrode, SEM results indicate that the electrode formed good contact with the electrolyte after being sintered at 900 °C for 2 h. At 800 °C, the polarization resistance of the LSMO4 cathode is about 0.87 ? cm2 in air, while the polarization resistance of the LSMO4 anode is about 2.07 ? cm2 in 5% H2. LSMO4 exhibits better electrochemical activity for oxygen reduction than that for hydrogen oxidation. A cell with LSGM electrolyte, LSMO4-LSGM mixture as anode and cathode simultaneously displays a maximum power density of 59 mW cm-2 at 800 °C.

  7. Continuous solid solution of {kappa}-phase in the third period transition metals-aluminum-carbon pseudo-ternary systems

    SciTech Connect

    Hosoda, Hideki; Suzuki, Kensyo; Hanada, Shuji

    1999-07-01

    Phase stability of {kappa}-phases (perovskite-type phases) was studied in the third-period transition-metals (M: Mn to Cu) - aluminum (Al) - carbon (C) systems. The concentrations of transition metals (C{sub M}) were systematically changed from 60mol%Mn to 20mol%Ni+40mol%Cu along the periodic table under the constant nominal alloy compositions of C{sub M1}+C{sub M2} = 60mol%, C{sub Al} = 20mol% and C{sub C} = 20mol%. Alloys were prepared using mechanical alloying and hot pressing. Constituent phases were investigated by X-ray diffraction analysis, scanning electron microscopy and electron probe microanalysis. It is confirmed that Mn{sub 3}Al(C,O){sub 0.95}, Fe{sub 3}Al(C,O){sub 0.87}, Co{sub 3}Al(C,O){sub 0.6} and Ni{sub 3}Al(C,O){sub 0.26} exist in their ternary systems where oxygen is introduced during the process. Also, only one {kappa}-phase is recognized in an alloy having an intermediate composition in every system. This suggests that continuous solid solutions between these {kappa}-phases are formed in the pseudo-ternary systems. Composition dependence of lattice parameter is discussed.

  8. Recent Advances in Transition Metal-Catalyzed Glycosylation

    PubMed Central

    McKay, Matthew J.; Nguyen, Hien M.

    2012-01-01

    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

  9. Kinetic studies of reduction of some transition metal tungstates

    SciTech Connect

    Bustnes, J.A.; Du Sichen; Seetharaman, S.

    1996-10-01

    The present study deals with the kinetic studies of reduction of some selected transition metal tungstates with hydrogen. The measurements were carried out by the isothermal thermogravimetric method. Shallow powder beds were employed in order to avoid the effects due to transport phenomena affecting the reaction rate. In this way, the chemical reaction rates could be selectively studied. The experiments were carried out in the temperature range 873--1,173 K. From the experimental data, the activation energies were evaluated and were found to be around 88 kJ/mol in the case of both iron as well as cobalt tungstates indicating the similarities in W-O bonds in both cases. The activation energies obtained are discussed in the light of the position of the transition metal in the periodic table as well as the thermodynamic stabilities of the various tungstates.

  10. Tailoring magnetic skyrmions in ultra-thin transition metal films.

    PubMed

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

    2014-01-01

    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

  11. Exciton complexes in low dimensional transition metal dichalcogenides

    SciTech Connect

    Thilagam, A.

    2014-08-07

    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.

  12. Transition metal catalysis in the generation of natural gas

    SciTech Connect

    Mango, F.D.

    1995-12-31

    The view that natural gas is thermolytic, coming from decomposing organic debris, has remained almost unchallenged for nearly half a century. Disturbing contradictions exist, however: Oil is found at great depth, at temperatures where only gas should exist and oil and gas deposits show no evidence of the thermolytic debris indicative of oil decomposing to gas. Moreover, laboratory attempts to duplicate the composition of natural gas, which is typically between 60 and 95+ wt% methane in C{sub 1}-C{sub 4}, have produced insufficient amounts of methane (10 to 60%). It has been suggested that natural gas may be generated catalytically, promoted by the transition metals in carbonaceous sedimentary rocks. This talk will discuss experimental results that support this hypothesis. Various transition metals, as pure compounds and in source rocks, will be shown to generate a catalytic gas that is identical to natural gas. Kinetic results suggest robust catalytic activity under moderate catagenetic conditions.

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

    PubMed

    Meng, Yu-Fei; Peng, Ming-Sheng

    2004-07-01

    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

  14. Multireference Character for 4d Transition Metal-Containing Molecules.

    PubMed

    Wang, Jiaqi; Manivasagam, Sivabalan; Wilson, Angela K

    2015-12-01

    Four diagnostic criteria have been examined to identify the suitability of single-reference wave function-based quantum chemistry methods for a set of 118 4d transition metal species. These diagnostics include the weight of the leading configuration of the CASSCF wave function, C0(2); the Frobenius norm of the coupled cluster amplitude vector related to single excitations, T1; the matrix 2-norm of the coupled cluster T1 amplitude vector arising from coupled cluster calculations, D1; and the percent total atomization energy, %TAE, corresponding to a relationship between energies determined with CCSD and CCSD(T) calculations. New criteria, namely, T1 ? 0.045, D1 ? 0.120, and %TAE ? 10%, are herein proposed as a gauge for 4d transition metal-containing molecules to predict the possible need to employ multireference (MR) wave function-based methods to describe energetic and spectroscopic properties. PMID:26642991

  15. High-pressure synthesis, crystal structures, and magnetic properties of 5d double-perovskite oxides Ca2MgOsO6 and Sr2MgOsO6.

    PubMed

    Yuan, Yahua; Feng, Hai L; Ghimire, Madhav Prasad; Matsushita, Yoshitaka; Tsujimoto, Yoshihiro; He, Jianfeng; Tanaka, Masahiko; Katsuya, Yoshio; Yamaura, Kazunari

    2015-04-01

    Double-perovskite oxides Ca2MgOsO6 and Sr2MgOsO6 have been synthesized under high-pressure and high-temperature conditions (6 GPa and 1500 °C). Their crystal structures and magnetic properties were studied by a synchrotron X-ray diffraction experiment and by magnetic susceptibility, specific heat, isothermal magnetization, and electrical resistivity measurements. Ca2MgOsO6 and Sr2MgOsO6 crystallized in monoclinic (P21/n) and tetragonal (I4/m) double-perovskite structures, respectively; the degree of order of the Os and Mg arrangement was 96% or higher. Although Ca2MgOsO6 and Sr2MgOsO6 are isoelectric, a magnetic-glass transition was observed for Ca2MgOsO6 at 19 K, while Sr2MgOsO6 showed an antiferromagnetic transition at 110 K. The antiferromagnetic-transition temperature is the highest in the family. A first-principles density functional approach revealed that Ca2MgOsO6 and Sr2MgOsO6 are likely to be antiferromagnetic Mott insulators in which the band gaps open, with Coulomb correlations of ?1.8-3.0 eV. These compounds offer a better opportunity for the clarification of the basis of 5d magnetic sublattices, with regard to the possible use of perovskite-related oxides in multifunctional devices. The double-perovskite oxides Ca2MgOsO6 and Sr2MgOsO6 are likely to be Mott insulators with a magnetic-glass (MG) transition at ?19 K and an antiferromagnetic (AFM) transition at ?110 K, respectively. This AFM transition temperature is the highest among double-perovskite oxides containing single magnetic sublattices. Thus, these compounds offer valuable opportunities for studying the magnetic nature of 5d perovskite-related oxides, with regard to their possible use in multifunctional devices. PMID:25751088

  16. Zwitterionic Group VIII transition metal initiators supported by olefin ligands

    DOEpatents

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

    2011-10-25

    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.

  17. Vibrational energy transfer dynamics in ruthenium polypyridine transition metal complexes.

    PubMed

    Fedoseeva, Marina; Delor, Milan; Parker, Simon C; Sazanovich, Igor V; Towrie, Michael; Parker, Anthony W; Weinstein, Julia A

    2015-01-21

    Understanding the dynamics of the initial stages of vibrational energy transfer in transition metal complexes is a challenging fundamental question which is also of crucial importance for many applications, such as improving the performance of solar devices or photocatalysis. The present study investigates vibrational energy transport in the ground and the electronic excited state of Ru(4,4'-(COOEt)2-2,2-bpy)2(NCS)2, a close relative of the efficient "N3" dye used in dye-sensitized solar cells. Using the emerging technique of ultrafast two-dimensional infrared spectroscopy, we show that, similarly to other transition-metal complexes, the central Ru heavy atom acts as a "bottleneck" making the energy transfer from small ligands with high energy vibrational stretching frequencies less favorable and thereby affecting the efficiency of vibrational energy flow in the complex. Comparison of the vibrational relaxation times in the electronic ground and excited state of Ru(4,4'-(COOEt)2-2,2-bpy)2(NCS)2 shows that it is dramatically faster in the latter. We propose to explain this observation by the intramolecular electrostatic interactions between the thiocyanate group and partially oxidised Ru metal center, which increase the degree of vibrational coupling between CN and Ru-N modes in the excited state thus reducing structural and thermodynamic barriers that slow down vibrational relaxation and energy transport in the electronic ground state. As a very similar behavior was earlier observed in another transition-metal complex, Re(4,4'-(COOEt)2-2,2'-bpy)(CO)3Cl, we suggest that this effect in vibrational energy dynamics might be common for transition-metal complexes with heavy central atoms. PMID:25463745

  18. The chemistry and physics of transition metal clusters

    SciTech Connect

    Parks, E.K.; Jellinek, J.; Knickelbein, M.B.; Riley, S.J.

    1994-06-01

    In this program the authors study the fundamental properties of isolated clusters of transition metal atoms. Experimental studies of cluster chemistry include determination of cluster structure, reactivity, and the nature of cluster-adsorbate interactions. Studies of physical properties include measurements of cluster ionization potentials and photoabsorption cross sections. Theoretical studies focus on the structure and dynamics of clusters, including isomers, phases and phase changes, interactions with molecules, and fragmentation process.

  19. Room-temperature, solution-processable organic electron extraction layer for high-performance planar heterojunction perovskite solar cells.

    PubMed

    Kim, Jong H; Chueh, Chu-Chen; Williams, Spencer T; Jen, Alex K-Y

    2015-10-15

    In this work, we describe a room-temperature, solution-processable organic electron extraction layer (EEL) for high-performance planar heterojunction perovskite solar cells (PHJ PVSCs). This EEL is composed of a bilayered fulleropyrrolidinium iodide (FPI)-polyethyleneimine (PEIE) and PC61BM, which yields a promising power conversion efficiency (PCE) of 15.7% with insignificant hysteresis. We reveal that PC61BM can serve as a surface modifier of FPI-PEIE to simultaneously facilitate the crystallization of perovskite and the charge extraction at FPI-PEIE/CH3NH3PbI3 interface. Furthermore, the FPI-PEIE can also tune the work function of ITO and dope PC61BM to promote the efficient electron transport between ITO and PC61BM. Based on the advantages of room-temperature processability and decent electrical property of FPI-PEIE/PC61BM EEL, a high-performance flexible PVSC with a PCE ?10% is eventually demonstrated. This study shows the potential of low-temperature processed organic EEL to replace transition metal oxide-based interlayers for highly printing compatible PVSCs with high-performance. PMID:26426581

  20. Rietveld refinement and dielectric relaxation of a new rare earth based double perovskite oxide: BaPrCoNbO6

    NASA Astrophysics Data System (ADS)

    Bharti, Chandrahas; Das, Mrinmoy K.; Sen, A.; Chanda, Sadhan; Sinha, T. P.

    2014-02-01

    A new rare earth based double perovskite oxide barium praseodymium cobalt niobate, BaPrCoNbO6 (BPCN) is synthesized by solid-state reaction technique. Rietveld analysis of X-ray diffraction (XRD) data shows that the compound crystallizes in a perovskite like tetragonal structure which belongs to the I4/mmm space group with lattice parameters a=b=5.6828(9) Å, c=8.063(2) Å. Structural analysis reveals 1:1 ordered arrangement for the Co2+ and Nb5+ cations over the six-coordinate B-sites of BPCN. The superlattice line (1 0 1) at 2?=19.10° arising from the alternate ordering of Co2+ and Nb5+ sites is observed in the XRD pattern which confirms the presence of cation ordering in BPCN. Fourier transform infrared spectrum shows two phonon modes of the sample due to the antisymmetric NbO6 stretching vibration. The relaxation dynamics of the conductive process in BPCN is investigated in the temperature range 303 to 503 K and in the frequency range 100 Hz to 1 MHz using impedance spectroscopy. The relaxation mechanism of the sample in the framework of electric modulus formalism is modeled by Davidson-Cole model (DCM). The values of ? (distribution of relaxation time) for the DCM varies from 0.1 to 0.3 which suggests the asymmetric distribution of relaxation time for BPCN. The activation energy of the sample, calculated from both conductivity and modulus spectra, are found to be almost the same ~0.4 eV, which indicates that the conduction mechanism for BPCN is polaron hopping. The scaling behaviour of the imaginary part of electric modulus suggests that the relaxation follows the same mechanism at various temperatures.

  1. Transition metal complexes of phyllobilins – a new realm of bioinorganic chemistry

    PubMed Central

    Li, Chengjie

    2015-01-01

    Natural cyclic tetrapyrroles feature outstanding capacity for binding transition metal ions, furnishing Nature with the important metallo-porphyrinoid ‘Pigments of Life’, such as heme, chlorophyll (Chl) and vitamin B12. In contrast, linear tetrapyrroles are not generally ascribed a biologically relevant ability for metal-binding. Indeed, when heme or Chl are degraded to natural linear tetrapyrroles, their central Fe- or Mg-ions are set free. Some linear tetrapyrroles are, however, effective multi-dentate ligands and their transition metal complexes have remarkable chemical properties. The focus of this short review is centred on such complexes of the linear tetrapyrroles derived from natural Chl-breakdown, called phyllobilins. These natural bilin-type compounds are massively produced in Nature and in highly visible processes. Colourless non-fluorescing Chl-catabolites (NCCs) and the related dioxobilin-type NCCs, which typically accumulate in leaves as ‘final’ products of Chl-breakdown, show low affinity for transition metal-ions. However, NCCs are oxidized in leaves to give less saturated coloured phyllobilins, such as yellow or pink Chl-catabolites (YCCs or PiCCs). YCCs and PiCCs are ligands for various biologically relevant transition metal-ions, such as Zn(ii)-, Ni(ii)- and Cu(ii)-ions. Complexation of Zn(ii)- and Cd(ii)-ions by the effectively tridentate PiCC produces blue metal-complexes that exhibit an intense red fluorescence, thus providing a tool for the sensitive detection of these metal ions. Outlined here are fundamental aspects of structure and metal coordination of phyllobilins, including a comparison with the corresponding properties of bilins. This knowledge may be valuable in the quest of finding possible biological roles of the phyllobilins. Thanks to their capacity for metal-ion coordination, phyllobilins could, e.g., be involved in heavy-metal transport and detoxification, and some of their metal-complexes could act as sensitizers for singlet oxygen or as plant toxins against pathogens. PMID:25923782

  2. Crystal engineering of lanthanide transition-metal coordination polymers

    NASA Astrophysics Data System (ADS)

    Gu, Xiaojun; Xue, Dongfeng; Ratajczak, Henryk

    2008-09-01

    Crystal engineering allows us to predict and control the packing of molecular building units in solid state, which has been attracting much attention due to its exploitation for the synthesis of crystalline materials with novel structures and promising properties. The crystal engineering strategies toward the synthesis of high-nuclearity lanthanide clusters and three-dimensional (3D) lanthanide-transition-metal (Ln-M) coordination polymers were well discussed in the present work. It has shown that the high-nuclearity lanthanide clusters can be rationally synthesized by surface modification strategy. On the basis of the different coordination nature of lanthanide and transition-metal ions, the multifunctional organic ligands with mixed coordination sites such as isonicotinate have been elaborately selected to rationally construct a series of homochrial and achiral 3D Ln-M coordination frameworks built from inorganic heterometallic chains with improved thermal stability. Furthermore, novel 3D Ln-M coordination frameworks have been built from discrete lanthanide clusters (or cluster polymers) and transition-metal clusters (or cluster polymers) by faultlessly harmonizing the subtle relationship between these two different types of metal cluster or cluster polymer units. The current work offers us great potential toward the pursuit of rational synthesis of Ln-M coordination assemblies on the basis of crystal engineering principles.

  3. Journal of Magnetism and Magnetic Materials 272276 (2004) 122123 LSD-SIC studies of localization in the 4d-transition metal

    E-print Network

    Svane, Axel Torstein

    2004-01-01

    Journal of Magnetism and Magnetic Materials 272­276 (2004) 122­123 LSD-SIC studies of localization Published by Elsevier B.V. PACS: 75.50.Gg; 75.47.Pq Keywords: LSD-SIC; Localization Although many density (LSD) [3] calculations to study how close these 4d-transition metal oxides are to a localization

  4. Electrical and magnetic effect of transition metals in SnSb nanoalloy

    NASA Astrophysics Data System (ADS)

    Nithyadharseni, P.; Nalini, B.; Saravanan, P.

    2014-08-01

    Influence of incorporating transition metal impurities such as Fe, Co and Ni on the magnetic and electrical properties of SnSb alloy nanopowders synthesized by reductive co-precipitation is reported. Structural elucidation of all the samples by X-ray diffraction (XRD) confirms hexagonal structure and the morphological observations through scanning electron microscope (SEM) show a minimal particle size of 20 nm for the Co substituted SnSb sample, among all the other impurity incorporated samples. Compositional confirmation of Sn, Sb, Fe, Co, and Ni was made using EDAX. The X-ray photoelectron spectroscopy (XPS) is used to investigate the surface of SnSb and the change in surface activity due to the addition of transition metal impurities. The magnetic hysteresis studies indicate that SnSb and SnSb:Ni exhibit diamagnetic behaviour; while the Fe and Co incorporation resulted in ferromagnetic nature. The conductivity of SnSb:Fe, SnSb:Ni shows a semiconducting nature with negative temperature coefficient of resistance; whereas pure and Co substitution exhibit metallic behaviour with positive temperature coefficient of resistance. The switching of metallic to semiconducting regime is explained in this paper. Also an attempt has been made to correlate electrical and magnetic properties with the surface oxidation effect through XPS data.

  5. Molecular jeff states in ternery transition metal chalcogenides AM4X8

    NASA Astrophysics Data System (ADS)

    Kim, Heung-Sik; Im, Jino; Han, Myung Joon; Jin, Hosub

    2014-03-01

    Spin-orbit-coupling(SOC)-induced jeff states, reported in several iridium oxide compounds, is the key ingredient in understanding the interesting cooperation between SOC and the electron correlations. From our density functional theory calculations we suggest that, a series of ternery transition metal chalcogenides AM4X8 (A = Ga, M = 4 d and 5 d transition metal atoms, X = chalcogen atoms) host the jeff states in a molecular form. Wide range of the bandwidth covered with the external or chemical pressure enable one to access a broad range of electron correlation strength in a single compound. Implications of our results in both the weak and strong coupling regime are discussed. Our finding provides an ideal playground in exploring the jeff physics and the resulting emergent phenomena. This work was supported by the Institute for Basic Science in Korea. Computational resources were provided by the National Institute of Supercomputing and Networking with supercomputing resources including technical support (Grant No. KSC-2013-C2-005).

  6. Understanding the Enhanced Catalytic Performance of Ultrafine Transition Metal Nanoparticles-Graphene Composites

    NASA Astrophysics Data System (ADS)

    Liu, Xin; Meng, Changgong; Han, Yu

    2015-09-01

    Catalysis, as the key to minimize the energy requirement and environmental impact of today's chemical industry, plays a vital role in many fields directly related to our daily life and economy, including energy generation, environment control, manufacture of chemicals, medicine synthesis, etc. Rational design and fabrication of highly efficient catalysts have become the ultimate goal of today's catalysis research. For the purpose of handling and product separation, heterogeneous catalysts are highly preferred for industrial applications and a large part of which are the composites of transition metal nanoparticles (TMNPs). With the fast development of nanoscience and nanotechnology and assisted with theoretical investigations, basic understanding on tailoring the electronic structure of these nanocomposites has been gained, mainly by precise control of the composition, morphology, interfacial structure and electronic states. With the rise of graphene, chemical routes to prepare graphene were developed and various graphene-based composites were fabricated. Transition metal nanoparticles-reduced graphene oxide (TMNPs-rGO) composites have attracted considerable attention, because of their intriguing catalytic performance which have been extensively explored for energy- and environment-related applications to date. This review summarizes our recent experimental and theoretical efforts on understanding the superior catalytic performance of subnanosized TMNPs-rGO composites.

  7. Enhanced visible-light absorption of mesoporous TiO2 by co-doping with transition-metal/nitrogen ions

    SciTech Connect

    Mathis, John; Bi, Zhonghe; Bridges, Craig A; Kidder, Michelle; Paranthaman, Mariappan Parans

    2013-01-01

    Titanium (IV) oxide, TiO2, has been the object of intense scrutiny for energy applications. TiO2 is inexpensive, non-toxic, and has excellent corrosion resistance when exposed to electrolytes. A major drawback preventing the widespread use TiO2 for photolysis is its relatively large band gap of ~3eV. Only light with wavelengths shorter than 400 nm, which is in the ultraviolet portion of the spectrum, has sufficient energy to be absorbed. Less than 14 percent of the solar irradiation reaching the earth s surface has energy exceeding this band gap. Adding dopants such as transition metals has long been used to reduce the gap and increase photocatalytic activity by accessing the visible part of the solar spectrum. The degree to which the band gap is reduced using transition metals depends in part on the overlap of the d-orbitals of the transition metals with the oxygen p-orbitals. Therefore, doping with anions such as nitrogen to modify the cation-anion orbital overlap is another approach to reduce the gap. Recent studies suggest that using a combination of transition metals and nitrogen as dopants is more effective at introducing intermediate states within the band gap, effectively narrowing it. Here we report the synthesis of mesoporous TiO2 spheres, co-doped with transition metals and nitrogen that exhibit a nearly flat absorbance response across the visible spectrum extending into the near infrared.

  8. Co-operative and frustration effects in novel perovskite-related phases

    NASA Astrophysics Data System (ADS)

    Ebbinghaus, S. G.; Riegg, S.; Götzfried, T.; Reller, A.

    2009-12-01

    We report on magnetic and electronic properties of various perovskite-type oxides containing 4d- and 5d-transition metals. The compounds under investigation crystallize in (distorted) cubic, layered, and hexagonal perovskite-related structures. These changes in structural dimensionality are reflected by different ordering phenomena. (Pseudo-) cubic perovskites ACu3B4O12 (with A = alkali, alkaline earth or rare earth; B = Ru, Ti) possess an A-site ordered structure with copper on modified A-positions. Structural investigations as well as XANES (X-ray absorption near edge structure) measurements indicate a valence degeneracy, which is keeping the oxidation state of Ru close to +4. Upon replacing Ru by Ti, the itinerant magnetism and metallic conductivity of the pure ruthenates successively change to a localized magnetic moment and a semiconducting behavior. The pure titanates like Ln2/3Cu3Ti4O12 or CaCu3Ti4O12are insulators with colossal dielectric constants. The cation-deficient Cu2+xTa4O12+? shows a large compositional flexibility with 0.125 ? x ? 0.500. Both copper content and cooling speed have a strong impact on the crystal structure and the observed magnetic ordering. This behavior can be explained by uncompensated Cu2+-moments resulting from different site occupations. Quasi-2D La2RuO5 undergoes a structural and magnetic phase transition at roughly 160 K, leading to a diminishing magnetic moment and a semiconductor-semiconductor transition. LDA calculations reveal an antiferromagnetic coupling within pairs of neighboring Ru4+-ions, leading to a spin-Peierls like transition. New hexagonal perovskites containing Ru, Ir, and Pt crystallize in the [AO1+?][A2BO6] structure type and contain peroxide ions (O) in the [AO1+?] layers. La1.2Sr2.7IrO7.33 exhibits a small temperature-independent paramagnetism, which can be explained on basis of the crystal-field splitting and the strong spin-orbit coupling. The isostructural La1.2Sr2.7RuO7.33 shows a frustrated magnetic ordering at roughly 6 K. The frustration results from the alignment of Ru5+-ions, which form elongated, edge-sharing Ru4-tetrahedra. Substituting La3+ by the smaller Nd3+ results in shorter Ru-Ru distances and leads to an increase of the frustrated magnetic interaction.

  9. Synthesis and X-ray characterization of 3D transition metal intercalates of transition metal dichalcogenides and their superlattices

    NASA Astrophysics Data System (ADS)

    Hughes, Thomas Abbott

    1998-12-01

    New superlattices of 3d transition metal intercalates of transition metal dichalcogenides have been synthesized by deposition and annealing of layered reactants. Sheets of atoms are the building blocks of transition metal dichalcogenides. Since the inter-sheet bonding is weak, guest atoms may be introduced between the sheets (intercalation) and sheets of differing atomic species may be stacked one atop the other (forming a superlattice), and, by intermingling such modifications, many different bulk materials may potentially be synthesized. FexNbSe 2/FexTiSe2 and CrxNbSe2/Cr xTiSe2 superlattices and NixMoSe2 intercalates have been grown and characterized with X-ray diffraction. These materials display anticipated atomic structures and are stable in a Nitrogen atmosphere at temperatures up to 500°C, testifying to the synthetic feasibility of this novel family of superlattices. The 3d transition metal intercalates order magnetically and exhibit other electron correlation effects which could potentially be tailored by rational superlattice design. However, preliminary investigations have not found evidence of such effects in the new superlattices; presumably, structural defects in the samples are inhibiting these phenomena. We demonstrate that standard X-ray diffraction structure analysis techniques are generally inapplicable to superlattices; these new materials are no exception. An original procedure for structural refinement, utilizing both conjugate gradient and simulated annealing optimization methods, is used to generate a model superlattice having a calculated X-ray diffraction profile which matches experimental measurements. This procedure satisfactorily fits X-ray diffraction peak shapes over a large range of scattering angles, and is demonstrated in determining the distribution of crystal sizes, the distribution of defects, and the average superlattice unit cell parameters for an (Fe0.3NbSe2)8/(Fe0.3TiSe 2)8 sample.

  10. Surface plasmon resonances behavior in visible light of non-metal perovskite oxides AgNbO{sub 3}

    SciTech Connect

    Zhou, Fei; Zhu, Jingchuan Liu, Yong; Zhao, Xiaoliang; Lai, Zhonghong

    2014-12-08

    We investigate the surface plasmon resonances (SPRs) behavior of silver niobate (AgNbO{sub 3}) experimentally and theoretically. Result shows that the localized SPRs (LSPRs) of AgNbO{sub 3} combining with its interband transitions enlarge the absorption band across the whole ultraviolet-visible range. The LSPRs behavior in visible-light is mainly ascribed to the metal-like state of silver ion and self-assembled microstructures of AgNbO{sub 3} microcrystal. The ab initio density functional theory calculations are carried out to obtain the further insight of the SPRs behaviors. Theoretical study indicates that the Ag atoms are weakly bound in the perovskite structure, leading to a metal-like state, which was the key factor to SPRs behavior of AgNbO{sub 3}.

  11. A Single-Atom-Thick TiO2 Nanomesh on an Insulating Oxide.

    PubMed

    Ohsawa, Takeo; Saito, Mitsuhiro; Hamada, Ikutaro; Shimizu, Ryota; Iwaya, Katsuya; Shiraki, Susumu; Wang, Zhongchang; Ikuhara, Yuichi; Hitosugi, Taro

    2015-09-22

    The electronic structures and macroscopic functionalities of two-dimensional (2D) materials are often controlled according to their size, atomic structures, and associated defects. This controllability is particularly important in ultrathin 2D nanosheets of transition-metal oxides because these materials exhibit extraordinary multifunctionalities that cannot be realized in their bulk constituents. To expand the variety of materials with exotic properties that can be used in 2D transition-metal-oxide nanosheets, it is essential to investigate fabrication processes for 2D materials. However, it remains challenging to fabricate such 2D nanosheets, as they are often forbidden because of the crystal structure and nature of their host oxides. In this study, we demonstrate the synthesis of a single-atom-thick TiO2 2D nanosheet with a periodic array of holes, that is, a TiO2 nanomesh, by depositing a LaAlO3 thin film on a SrTiO3(001)-(?13×?13)-R33.7° reconstructed substrate. In-depth investigations of the detailed structures, local density of states, and Ti valency of the TiO2 nanomesh using scanning tunneling microscopy/spectroscopy, scanning transmission electron microscopy, and density functional theory calculations reveal an unexpected upward migration of the Ti atoms of the substrate surface onto the LaAlO3 surface. These results indicate that the truncated TiO5 octahedra on the surface of perovskite oxides are very stable, leading to semiconducting TiO2 nanomesh formation. This nanomesh material can be potentially used to control the physical and chemical properties of the surfaces of perovskite oxides. Furthermore, this study provides an avenue for building functional atomic-scale oxide 2D structures and reveals the thin-film growth processes of complex oxides. PMID:26291512

  12. Persistent semi-metal-like nature of epitaxial perovskite CaIrO3 thin films

    NASA Astrophysics Data System (ADS)

    Biswas, Abhijit; Jeong, Yoon Hee

    2015-05-01

    Strong spin-orbit coupled 5d transition metal based ABO3 oxides, especially iridates, allow tuning parameters in the phase diagram and may demonstrate important functionalities, for example, by means of strain effects and symmetry-breaking, because of the interplay between the Coulomb interactions and strong spin-orbit coupling. Here, we have epitaxially stabilized high quality thin films of perovskite (Pv) CaIrO3. Film on the best lattice-matched substrate shows semi-metal-like characteristics. Intriguingly, imposing tensile or compressive strain on the film by altering the underlying lattice-mismatched substrates still maintains semi-metallicity with minute modification of the effective correlation as tensile (compressive) strain results in tiny increases (decreases) of the electronic bandwidth. In addition, magnetoresistance remains positive with a quadratic field dependence. This persistent semi-metal-like nature of Pv-CaIrO3 thin films with minute changes in the effective correlation by strain may provide new wisdom into strong spin-orbit coupled 5d based oxide physics.

  13. Topological phases in Iridium oxide superlattices: quantized anomalous charge or valley Hall insulators

    NASA Astrophysics Data System (ADS)

    Kee, Hae-Young; Chen, Yige

    2015-03-01

    Designing materials is one of intense topics in modern condensed matter physics. Recently, how to achieve a topological insulator in transition metal oxides with strong spin-orbit coupling became an interesting subject. We have investigated possible topological phases in orthorhombic perovskite Iridium (Ir) oxide superlattices grown along the [001] crystallographic axis. We found that bilayer Ir oxide superlattices exhibit quantized anomalous Hall effects in magnetic topological insulating phases. We also found, depending on the stacking of two layers, a valley Hall insulator with nontrivial valley dependent surface modes and a topological crystalline insulator with the crystal symmetry protected edge states can be realized. Experimental tools to detect such topological phases are also discussed.

  14. A Heteroepitaxial Perovskite Metal-Base Transistor

    SciTech Connect

    Yajima, T.; Hikita, Y.; Hwang, H.Y.; ,

    2011-08-11

    'More than Moore' captures a concept for overcoming limitations in silicon electronics by incorporating new functionalities in the constituent materials. Perovskite oxides are candidates because of their vast array of physical properties in a common structure. They also enable new electronic devices based on strongly-correlated electrons. The field effect transistor and its derivatives have been the principal oxide devices investigated thus far, but another option is available in a different geometry: if the current is perpendicular to the interface, the strong internal electric fields generated at back-to-back heterojunctions can be used for oxide electronics, analogous to bipolar transistors. Here we demonstrate a perovskite heteroepitaxial metal-base transistor operating at room temperature, enabled by interface dipole engineering. Analysis of many devices quantifies the evolution from hot-electron to permeable-base behaviour. This device provides a platform for incorporating the exotic ground states of perovskite oxides, as well as novel electronic phases at their interfaces.

  15. The development of a biological interface for transition metal implants

    NASA Astrophysics Data System (ADS)

    Melton, Kim R.

    The specific goal of this research was to develop an in vitro model for a root-form endosseous dental implant that contains a periodontal ligament and that is biologically integratable into alveolar bone. This objective was based on the following two hypotheses. (1) The chemical attachment of extracellular matrix proteins to the surface of transition metals increases the number of fibroblast cells attached to the surface of the metal. (2) The chemical attachment of extracellular matrix proteins to the surface of transition metals increases the strength of the fibroblast cell attachment to the surface of the metal. The model needed to have a well-controlled surface that was reproducible. Thus, a layer of Au was deposited over a Ti base, and dithiobis(succinimidylpropionate) (DSP) a chemical containing disulfide groups was adsorbed to the Au. Next, extracellular matrix proteins which are periodontal ligament components were attached to the free end group of the chemical that was adsorbed to the Au. This surface served as an attachment substrate on which additional periodontal ligament components such as fibroblast cells could grow. From this model a new implant interface may be developed. This model was tested using the following polypeptides; collagen type I, collagen type IV, fibronectin, and poly-D-lysine. L929 cells were grown on Ti, Ti + Au, Ti + Au + polypeptide, and Ti + Au + DSP + polypeptide. After 72 hours, the live cells were stained with neutral red. The substrates were then subjected to increasing centrifugal forces. The viable stained cells were fixed onto the substrates and cells were counted. The hypotheses were proven for three polypeptides: fibronectin, collagen type I, and poly-D-lysine. The strongest attachment was found with collagen type I. Collagen type IV did not provide any advantage for attachment over uncoated transition metals.

  16. Correlated electron pseudopotentials for 3d-transition metals.

    PubMed

    Trail, J R; Needs, R J

    2015-02-14

    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. PMID:25681890

  17. Vacancy hardening and softening in transition metal carbides and nitrides

    SciTech Connect

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

    2000-10-31

    The effects of vacancies on mechanical properties of the transition metal carbides and nitrides are studied using the ab initio pseudopotential approach. Calculated shear elastic stiffness and electronic structures show that the vacancy produces entirely different effects on the mechanical strength of groups IVb nitrides and Vb carbides. It is found that the occupation of shear-unstable metallic dd bonding states changes essentially in an opposite way for the carbides and nitrides in the presence of vacancies, resulting in different responses to shear stress. Our study provides an atomistic understanding of the anomaly in hardness for these substoichiometric materials.

  18. Vacancy Hardening and Softening in Transition Metal Carbides and Nitrides

    SciTech Connect

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

    2001-04-09

    The effects of vacancies on mechanical properties of the transition metal carbides and nitrides are studied using the ab initio pseudopotential approach. Calculated shear elastic stiffness and electronic structures show that the vacancy produces entirely different effects on the mechanical strength of groups IVb nitrides and Vb carbides. It is found that the occupation of shear-unstable metallic dd bonding states changes essentially in an opposite way for the carbides and nitrides in the presence of vacancies, resulting in different responses to shear stress. Our study provides an atomistic understanding of the anomaly in hardness for these substoichiometric materials.

  19. The nature of the bonding in the transition metal trimers

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

    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.

  20. Rare earth-transition metal scrap treatment method

    DOEpatents

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

    1992-02-11

    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.

  1. Rare earth-transition metal scrap treatment method

    DOEpatents

    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

    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.

  2. Solution processed transition metal sulfides: application as counter electrodes in dye sensitized solar cells (DSCs).

    PubMed

    Mulmudi, Hemant Kumar; Batabyal, Sudip Kumar; Rao, Manohar; Prabhakar, Rajiv Ramanujam; Mathews, Nripan; Lam, Yeng Ming; Mhaisalkar, Subodh Gautam

    2011-11-21

    A solution processed method for fabricating transition metal sulfides on fluorine doped tin oxide (FTO) as efficient counter electrodes in iodine/iodide based solar cells has been demonstrated. Conversion efficiencies of 7.01% and 6.50% were obtained for nickel and cobalt sulfides, respectively, comparable to the conventional thermally platinised FTO electrodes (7.32%). A comparable charge transfer resistance of Ni(3)S(2) and Co(8.4)S(8) to conventional Pt was found to be a key factor for such high efficiencies. Cyclic voltammetry, Kelvin probe microscopy, Electrochemical Impedance Spectroscopy, and Tafel polarization were performed to study the underlying reasons behind such efficient counter electrode performance. PMID:21964615

  3. Enhancement of dielectric constant in transition metal doped ZnO nanocrystals

    NASA Astrophysics Data System (ADS)

    Singh, Swati; Dey, P.; Roy, J. N.; Mandal, S. K.

    2014-09-01

    We have presented dielectric studies on Zn1-xCoxO, Zn1-xFexO, and Zn1-xFex/2Cox/2O (x = doping level) semiconducting nanoparticles (˜2-40 nm). For all those samples, dielectric constant (?) is found to exhibit a maximum with x. Enhancement of ? is found to be ˜250 times for Zn0.85Co0.15O and ˜400 times for Zn0.8Fe0.1Co0.1O from that of ZnO. Presence of effective higher oxidation state of transition metals ions in ZnO due to Fe/Co doping resulting in space charge polarization possibly yields this effect. The simultaneous existence of high ?, semiconducting, and ferromagnetic like behaviour at 300 K seems to propose Zn0.8Fe0.1Co0.1O, promising for technological application.

  4. Secondary phase segregation in heavily transition metal implanted ZnO

    SciTech Connect

    Schumm, Marcel; Koerdel, Martin; Geurts, Jean; Mueller, Sven; Ronning, Carsten; Dynowska, Elzbieta; Golacki, Zbigniew; Szuszkiewicz, Wojciech

    2009-04-15

    With micro-Raman spectroscopy and x-ray diffraction (XRD), we studied ZnO crystals implanted with Mn, Fe, Co, and Ni, respectively, with implantation concentrations from 4 up to 16 at. %. Using thermal treatments in air up to 700 deg. C, we analyzed the annealing effect on the ZnO crystal lattice as well as the onset of secondary phases and their microstructure on the sample surface. While the 500 deg. C treatment induces a considerable annealing, secondary phases are observed for transition metal (TM) concentrations >=8 at. % after the treatment at 700 deg. C. Their microstructure strongly depends on the TM species. Various stoichiometric and nonstoichiometric TM oxide precipitates as well as elemental TM clusters are identified by their Raman and XRD signatures and their possible magnetic impact is discussed.

  5. Transition metal solute interactions with point defects in fcc iron from first principles

    NASA Astrophysics Data System (ADS)

    Hepburn, D. J.; MacLeod, E.; Ackland, G. J.

    2015-07-01

    We present a comprehensive set of first-principles electronic structure calculations of the properties of substitutional transition metal solutes and point defects in austenite (face-centered cubic, paramagnetic Fe). Clear trends were observed in these quantities across the transition metal series, with solute-defect interactions strongly related to atomic size, and only weakly related to more subtle details of magnetic or electronic structure. Oversized solutes act as strong traps for both vacancy and self-interstitial defects and as nucleation sites for the development of protovoids and small self-interstitial loops. The consequent reduction in defect mobility and net defect concentrations in the matrix explains the observation of reduced swelling and radiation-induced segregation. Our analysis of vacancy-mediated solute diffusion demonstrates that below about 400 K Ni and Co will be dragged by vacancies and their concentrations should be enhanced at defect sinks. Cr and Cu show opposite behavior and are depleted at defect sinks. The stable configuration of some oversized solutes is neither interstitial nor substitutional; rather they occupy two adjacent lattice sites. The diffusion of these solutes proceeds by a novel mechanism, which has important implications for the nucleation and growth of complex oxide nanoparticles contained in oxide dispersion strengthened steels. Interstitial-mediated solute diffusion is negligible for all except the magnetic solutes (Cr, Mn, Co, and Ni). Our results are consistent across several antiferromagnetic states and surprising qualitative similarities with ferromagnetic (body-centered cubic) Fe were observed; this implies that our conclusions will be valid for paramagnetic iron.

  6. Pyrochemical extraction of transition metals from Pacific Ocean deep sea nodules

    SciTech Connect

    von Winbush, S.; Maroni, V.A.

    1987-01-01

    Considerable success has been achieved in lixiviation transition metals from Pacific Ocean deep sea nodules. These nodules typically contain approx.30 wt% Mn, approx.7 wt% Fe, approx.1 wt% Ni, approx.1 wt% Cu, and approx.0.3 wt% Co. Samples of the nodules have been subjected to extraction tests at 450C using LiCl-KCl eutectic and MgCl2-NaCl-KCl eutectic. The most impressive results came from studies using the Mg, Na, K/Cl eutectic. With this salt, nearly 100% of the Co, Cu, Fe, Mn, and Ni are brought into solution. The dissolution reaction is quite vigorous, with nearly complete extraction occurring in a very short time (minutes) following melting of the eutectic. Quantitative recovery of cobalt is achieved with nodule-to-salt weight ratios as high as 1:3. Electronic absorption spectroscopy (carried out on the molten extract solution at the test temperature) showed that the oxidation state of the dissolved transition metals are CoS , CuS , FeT , MnS , and NiS . At temperatures greater than or equal to450C, the FeT and CuS distill out of the extract solution at a rapid rate and condense as binary halides or halide complexes. Using a combination of distillation followed by electrochemical reduction of the CoS and NiS in the extract salt, it appears possible to recover a fairly high grade of cobalt metal and nickel metal as well as high grade CuS , FeT , and MnS in the form of a halide salt (CuCl2, FeCl3) or an oxide precipitate (Mn2O3).

  7. “True” negative thermal expansion in Mn-doped LaCu{sub 3}Fe{sub 4}O{sub 12} perovskite oxides

    SciTech Connect

    Yamada, Ikuya; Marukawa, Shohei; Murakami, Makoto; Mori, Shigeo

    2014-12-08

    Negative and zero thermal expansion near room temperature have been achieved in a cubic A-site ordered perovskite oxide LaCu{sub 3}Fe{sub 4?x}Mn{sub x}O{sub 12}. A discontinuous volume change in the parent material LaCu{sub 3}Fe{sub 4}O{sub 12}, owing to a first-order intermetallic charge transfer transition (3Cu{sup 2+?}+?4Fe{sup 3.75+} ? 3Cu{sup 3+?}+?4Fe{sup 3+}), is efficiently relaxed to a second-order-type negative thermal expansion with a linear thermal expansion coefficient (?{sub L}) of ?2.2(1)?×?10{sup ?5?}K{sup ?1} between 300 and 340?K at x?=?0.75, followed by an almost zero thermal expansion [?{sub L} of ?1.1(2)?×?10{sup ?6?}K{sup ?1}] at x?=?1 in a wide temperature range (240–360?K) including room temperature. Magnetic susceptibility measurements display substantial broadenings of the antiferromagnetic transition when x increases, supporting the relaxation of first-order electronic phase transition of the parent material. These findings indicate that the significant adjustability of thermal expansion properties can be achieved in first-order intermetallic charge-transfer transition.

  8. Layed Perovskite PRBA0.5SR0.5CO205 as High Performance Cathode for Solid Oxide Fuels Using Photon Conducting Electrolyte

    SciTech Connect

    Brinkman, K.

    2010-05-05

    The layered perovskite PrBa{sub 0.5}Sr{sub 0.5}Co{sub 2}O{sub 5+{delta}} (PBSC) was investigated as a cathode material for a solid oxide fuel cell using a proton-conducting electrolyte based on BaCe{sub 0.7}Y{sub 0.2}Zr{sub 0.1}O{sub 3-{delta}} (BCYZ). The sintering conditions for the PBSC-BCYZ composite cathode were optimized resulting in the lowest area-specific resistance and apparent activation energy obtained with the cathode sintered at 1200 C for 2h. The maximum power densities of the PBSC-BCYZ/BZCY/NiO-BCYZ cell were 0.179, 0.274, 0.395, and 0.522 Wcm{sup -2} at 550, 600, 650, and 700 C, respectively with a 15{micro}m thick electrolyte. A relatively low cell interfacial polarization resistance of 0.132 {Omega}cm{sup 2} at 700 C indicated that the PBSC-BCYZ could be a good cathode candidate for intermediate temperature SOFCs with proton-conducting electrolyte.

  9. Electrical Conductivity of SrxVMoO6-y (x=0.0, 0.1, 0.2) Double Perovskite Solid Oxide Fuel Cell Anode

    NASA Astrophysics Data System (ADS)

    Childs, Nicholas; Weisenstein, Adam; Key, Camas; Sofie, Stephen; Smith, Richard

    2012-10-01

    Solid Oxide Fuel Cells (SOFCs) are suited for high efficiency power generation, fuel flexibility, high temperature electrolysis, closed loop regenerative systems, oxygen generation, and carbon dioxide reduction. These capabilities make the SOFC highly versatile for: primary/secondary power systems, advanced life support, and in-situ resource utilization which may all be desired for a forthcoming lunar return and Mars Exploration. A promising anode material for a SOFCs is the double perovskite Sr2-xVMoO6-y(x=0.0-0.2), due to its stability, electronic, and ionic conduction. Anodes of this material were prepared via a tape casting technique. Electrical conductivity was studied in reducing atmospheres at temperatures up to 800 ^oC. V and Mo valence states were indentified before and after annealing in a hydrogen environment. Samples exhibited metallic conduction with electrical conductivity of ˜10^4S/cm in a reducing atmosphere at 25 ^oC. A highly insulating SrMoO4 phase forms upon room temperature exposure to air. The SrMoO4 phase can be reduced above 400 ^oC resulting in an increase in conductivity.

  10. Studies of Perovskite Materials for High-Performance Storage Media, Piezoelectric, and Solar Energy Conversion Devices

    E-print Network

    Rappe, Andrew M.

    Studies of Perovskite Materials for High-Performance Storage Media, Piezoelectric, and Solar Energy, Massachusetts Institute of Technology, Cambridge, MA {kaloyeh, kanelson}@mit.edu Abstract Perovskite materials-oxide perovskite BaZrS3 are investigated in detail. We also microscopically model relaxor behavior demonstrated

  11. ORIGINAL PAPER Thermal equation of state of CaIrO3 post-perovskite

    E-print Network

    Duffy, Thomas S.

    ORIGINAL PAPER Thermal equation of state of CaIrO3 post-perovskite Wei Liu · Matthew L. Whitaker-Verlag 2011 Abstract The pressure­volume­temperature (P­V­T) relation of CaIrO3 post-perovskite (ppv for several oxide post-perovskites can be described approximately by the relationship KT0 = 5406.0/ V

  12. Synthesis and characterization of perovskite PbTiO3 nanoparticles with solution processability

    E-print Network

    Lin, Zhiqun

    Synthesis and characterization of perovskite PbTiO3 nanoparticles with solution processability Jun with perovskite structure (ABO3), for example, lead titanate (PbTiO3), are the most studied ferroelectric oxides polarization direction. Ferroelectrics with perovskite structure (ABO3), such as barium titanate (BaTiO3

  13. Negative ions of transition metal-halogen clusters

    NASA Astrophysics Data System (ADS)

    Pradhan, Kalpataru; Gutsev, Gennady L.; Jena, Purusottam

    2010-10-01

    A systematic density functional theory based study of the structure and spectroscopic properties of neutral and negatively charged MXn clusters formed by a transition metal atom M (M =Sc,Ti,V) and up to seven halogen atoms X (X =F,Cl,Br) has revealed a number of interesting features: (1) Halogen atoms are bound chemically to Sc, Ti, and V for n ?nmax, where the maximal valence nmax equals to 3, 4, and 5 for Sc, Ti, and V, respectively. For n >nmax, two halogen atoms became dimerized in the neutral species, while dimerization begins at n =5, 6, and 7 for negatively charged clusters containing Sc, Ti, and V. (2) Magnetic moments of the transition metal atoms depend strongly on the number of halogen atoms in a cluster and the cluster charge. (3) The number of halogen atoms that can be attached to a metal atom exceeds the maximal formal valence of the metal atom. (4) The electron affinities of the neutral clusters abruptly rise at n =nmax, reaching values as high as 7 eV. The corresponding anions could be used in the synthesis of new salts, once appropriate counterions are identified.

  14. Stabilization of Small Boron Cage by Transition Metal Encapsulation

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  15. Soldering of Carbon Materials Using Transition Metal Rich Alloys.

    PubMed

    Burda, Marek; Lekawa-Raus, Agnieszka; Gruszczyk, Andrzej; Koziol, Krzysztof K K

    2015-08-25

    Joining of carbon materials via soldering has not been possible up to now due to lack of wetting of carbons by metals at standard soldering temperatures. This issue has been a severely restricting factor for many potential electrical/electronic and mechanical applications of nanostructured and conventional carbon materials. Here we demonstrate the formation of alloys that enable soldering of these structures. By addition of several percent (2.5-5%) of transition metal such as chromium or nickel to a standard lead-free soldering tin based alloy we obtained a solder that can be applied using a commercial soldering iron at typical soldering temperatures of approximately 350 °C and at ambient conditions. The use of this solder enables the formation of mechanically strong and electrically conductive joints between carbon materials and, when supported by a simple two-step technique, can successfully bond carbon structures to any metal terminal. It has been shown using optical and scanning electron microscope images as well as X-ray diffraction patterns and energy dispersive X-ray mapping that the successful formation of carbon-solder bonds is possible, first, thanks to the uniform nonreactive dispersion of transition metals in the tin-based matrix. Further, during the soldering process, these free elements diffuse into the carbon-alloy border with no formation of brazing-like carbides, which would damage the surface of the carbon materials. PMID:26256042

  16. Synthesis of arsenic transition metal sulfides and metal arsenides

    SciTech Connect

    Singhal, G.H.; Brown, L.D.; Ryan, D.F.

    1993-12-31

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

  17. Exfoliation of large-area transition metal chalcogenide single layers

    NASA Astrophysics Data System (ADS)

    Magda, Gábor Zsolt; Pet?, János; Dobrik, Gergely; Hwang, Chanyong; Biró, László P.; Tapasztó, Levente

    2015-10-01

    Isolating large-areas of atomically thin transition metal chalcogenide crystals is an important but challenging task. The mechanical exfoliation technique can provide single layers of the highest structural quality, enabling to study their pristine properties and ultimate device performance. However, a major drawback of the technique is the low yield and small (typically transition metal chalcogenides.

  18. Exfoliation of large-area transition metal chalcogenide single layers.

    PubMed

    Magda, Gábor Zsolt; Pet?, János; Dobrik, Gergely; Hwang, Chanyong; Biró, László P; Tapasztó, Levente

    2015-01-01

    Isolating large-areas of atomically thin transition metal chalcogenide crystals is an important but challenging task. The mechanical exfoliation technique can provide single layers of the highest structural quality, enabling to study their pristine properties and ultimate device performance. However, a major drawback of the technique is the low yield and small (typically transition metal chalcogenides. PMID:26443185

  19. Exfoliation of large-area transition metal chalcogenide single layers

    PubMed Central

    Magda, Gábor Zsolt; Pet?, János; Dobrik, Gergely; Hwang, Chanyong; Biró, László P.; Tapasztó, Levente

    2015-01-01

    Isolating large-areas of atomically thin transition metal chalcogenide crystals is an important but challenging task. The mechanical exfoliation technique can provide single layers of the highest structural quality, enabling to study their pristine properties and ultimate device performance. However, a major drawback of the technique is the low yield and small (typically transition metal chalcogenides. PMID:26443185

  20. Rietveld refinement and dielectric relaxation of a new rare earth based double perovskite oxide: BaPrCoNbO{sub 6}

    SciTech Connect

    Bharti, Chandrahas; Das, Mrinmoy K.; Sen, A.; Chanda, Sadhan; Sinha, T.P.

    2014-02-15

    A new rare earth based double perovskite oxide barium praseodymium cobalt niobate, BaPrCoNbO{sub 6} (BPCN) is synthesized by solid-state reaction technique. Rietveld analysis of X-ray diffraction (XRD) data shows that the compound crystallizes in a perovskite like tetragonal structure which belongs to the I4/mmm space group with lattice parameters a=b=5.6828(9) Å, c=8.063(2) Å. Structural analysis reveals 1:1 ordered arrangement for the Co{sup 2+} and Nb{sup 5+} cations over the six-coordinate B-sites of BPCN. The superlattice line (1 0 1) at 2?=19.10° arising from the alternate ordering of Co{sup 2+} and Nb{sup 5+} sites is observed in the XRD pattern which confirms the presence of cation ordering in BPCN. Fourier transform infrared spectrum shows two phonon modes of the sample due to the antisymmetric NbO{sub 6} stretching vibration. The relaxation dynamics of the conductive process in BPCN is investigated in the temperature range 303 to 503 K and in the frequency range 100 Hz to 1 MHz using impedance spectroscopy. The relaxation mechanism of the sample in the framework of electric modulus formalism is modeled by Davidson–Cole model (DCM). The values of ? (distribution of relaxation time) for the DCM varies from 0.1 to 0.3 which suggests the asymmetric distribution of relaxation time for BPCN. The activation energy of the sample, calculated from both conductivity and modulus spectra, are found to be almost the same ?0.4 eV, which indicates that the conduction mechanism for BPCN is polaron hopping. The scaling behaviour of the imaginary part of electric modulus suggests that the relaxation follows the same mechanism at various temperatures. - Graphical abstract: Rietveld refinement plot for BPCN. Inset shows the schematic presentation of the BPCN tetragonal unit cell. The Co{sup 2+} atoms are located at the centers of the CoO{sub 6} (blue) octahedra. The Nb{sup 5+} atoms are located at the centers of the NbO{sub 6} (green) octahedra. Display Omitted - Highlights: • BaPrCoNbO{sub 6} is synthesized for the first time. • Rietveld refinement of XRD data confirms tetragonal phase. • XRD confirms the presence of cation ordering in BaPrCoNbO{sub 6}. • The activation energy is ?0.4 eV. • The conduction mechanism for BPCN is due to polaron hopping.

  1. Configuring Bonds between First-Row Transition Metals.

    PubMed

    Eisenhart, Reed J; Clouston, Laura J; Lu, Connie C

    2015-11-17

    Alfred Werner, who pioneered the field of coordination chemistry, envisioned coordination complexes as a single, transition metal atom at the epicenter of a vast ligand space. The idea that the locus of a coordination complex could be shared by multiple metals held together with covalent bonds would eventually lead to the discovery of the quadruple and quintuple bond, which have no analogues outside of the transition metal block. Metal-metal bonding can be classified into homometallic and heterometallic groups. Although the former is dominant, the latter is arguably more intriguing because of the inherently larger chemical space in which metal-metal bonding can be explored. In 2013, Lu and Thomas independently reported the isolation of heterometallic multiple bonds with exclusively first-row transition metals. Structural and theoretical data supported triply bonded Fe-Cr and Fe-V cores. This Account describes our continued efforts to configure bonds between first-row transition metals from titanium to copper. Double-decker ligands, or binucleating platforms that brace two transition metals in proximity, have enabled the modular synthesis of diverse metal-metal complexes. The resulting complexes are also ideal for investigating the effects of an "ancillary" metal on the properties and reactivities of an "active" metal center. A total of 38 bimetallic complexes have been compiled comprising 18 unique metal-metal pairings. Twenty-one of these bimetallics are strictly isostructural, allowing for a systematic comparison of metal-metal bonding. The nature of the chemical bond between first-row metals is remarkably variable and depends on two primary factors: the total d-electron count, and the metals' relative d-orbital energies. Showcasing the range of covalent bonding are a quintuply bonded (d-d)(10) Mn-Cr heterobimetallic and the singly bonded late-late pairings, e.g., Fe-Co, which adopt unusually high spin states. A long-term goal is to rationally tailor the properties and reactivities of the bimetallic complexes. In some cases, synergistic redox and magnetic properties were found that are different from the expected sum of the individual metals. Intermetal charge transfer was shown in a Co-M series, for M = Mn to Cu, where the transition energy decreases as M is varied across the first-row period. The potential of using metal-metal complexes for multielectron reduction of small-molecules is addressed by N2 binding studies and a mechanistic study of a dicobalt catalyst in reductive silylation of N2 to N(SiMe3)3. Finally, metal-ion exchange reactions with metal-metal complexes can be selective under appropriate reaction conditions, providing an alternative synthetic route to metal-metal species. PMID:26492331

  2. Synthesis and characterization of volatile, thermally stable, reactive transition metal amidinates.

    PubMed

    Lim, Booyong S; Rahtu, Antti; Park, Jin-Seong; Gordon, Roy G

    2003-12-01

    A series of homoleptic metal amidinates of the general type [M(R-R'AMD)(n)](x) (R = (i)Pr, (t)Bu, R' = Me, (t)Bu) has been prepared and structurally characterized for the transition metals Ti, V, Mn, Fe, Co, Ni, Cu, Ag, and La. In oxidation state 3, monomeric structures were found for the metals Ti(III), V(III), and La(III). Bridging structures were observed for the metals in oxidation state 1. Cu(I) and Ag(I) are held in bridged dimers, and Ag(I) also formed a trimer that cocrystallized with the dimer. Metals in oxidation state 2 occurred in either monomeric or dimeric form. Metals with smaller ionic radii (Co, Ni) were monomeric. Larger metals (Fe, Mn) gave monomeric structures only with the bulkier tert-butyl-substituted amidinates, while the less bulky isopropyl-substituted amidinates formed dimers. The new compounds were found to have properties well-suited for use as precursors for atomic layer deposition (ALD) of thin films. They have high volatility, high thermal stability, and high and properly self-limited reactivity with molecular hydrogen, depositing pure metals, or water vapor, depositing metal oxides. PMID:14632513

  3. Neutron Diffraction Study of Silicate Perovskites

    NASA Astrophysics Data System (ADS)

    Mao, H. K.; van Orman, J.; Fei, Y.; Hemley, R. J.; Loveday, J.; Nelmes, R.; Smith, R. I.

    2002-12-01

    The oxygen deficiency and cation-site distribution of silicate perovskite control its physical and chemical properties, including density, bulk modulus, defect mobility, ionic transport, flow behavior, oxidation states, hydration, and minor-element solubility. These properties of perovskite, in turn control the geophysical and geochemical processes of the Earth. The possibility of oxygen deficiency was first recognized in perovskite with minor amounts of Al replacing Mg and Si [1, 2], and its significance is compared to the analogous defect perovskite in ceramics [3]. Basic crystallographic characteristics of the silicate perovskite, including the lattice parameters of the orthorhombic unit cell, the Pbmn space group, and atomic positions, were previously determined by x-ray diffraction [4]. The defect crystallography of silicate perovskite, however, cannot be measured by x-rays because the relevant ions (Mg2+, Al3+, Si4+ and O2-) are isoelectronic. These ions have very different neutron cross-section and can be readily resolved by neutron diffraction. Using multianvil apparatus, we synthesized perovskite samples at 1700°C and 25-28 GPa. We perform multiple runs to accumulate 3 mm3 sample each for the MgSiO3 end member and MgSiO3 plus 5 weight %\\ Al2O3 in perovskite structure. Excellent powder diffraction data were collected at the POLARIS Beamline of ISIS, Rutherford Appleton Lab, and were subjected to Rietveld analysis. Neutron derived information sheds light on the unusual effects found for Al3+ substitution on the compressibility of the silicate perovskite [1]. 1. J. Zhang and D. J. Weidner, Science 284, 782 (1999). 2. J. P. Brodholt, Nature 407, 620 (2000). 3. A. Navrotsky, Science 284, 1788 (1999). 4. N. L. Ross and R. M. Hazen, Phys. Chem. Minerals 17, 228 (1990).

  4. Structures of Late Transition Metal Monoxides from Jahn-Teller Instabilities in the Rock Salt Lattice

    NASA Astrophysics Data System (ADS)

    Derzsi, Mariana; Piekarz, Przemys?aw; Grochala, Wojciech

    2014-07-01

    Most late transition metal (LTM) monoxides crystallize in other than a rock salt structure, which is so common in the earlier transition metal monoxides. Here we present theoretical evidence based on density functional theory that an electron-phonon coupling involving a single soft mode in the cubic cell is responsible for the onset of the experimentally observed structures of the late transition metal monoxides.

  5. Band gap engineering strategy via polarization rotation in perovskite ferroelectrics

    SciTech Connect

    Wang, Fenggong Grinberg, Ilya; Rappe, Andrew M.

    2014-04-14

    We propose a strategy to engineer the band gaps of perovskite oxide ferroelectrics, supported by first principles calculations. We find that the band gaps of perovskites can be substantially reduced by as much as 1.2?eV through local rhombohedral-to-tetragonal structural transition. Furthermore, the strong polarization of the rhombohedral perovskite is largely preserved by its tetragonal counterpart. The B-cation off-center displacements and the resulting enhancement of the antibonding character in the conduction band give rise to the wider band gaps of the rhombohedral perovskites. The correlation between the structure, polarization orientation, and electronic structure lays a good foundation for understanding the physics of more complex perovskite solid solutions and provides a route for the design of photovoltaic perovskite ferroelectrics.

  6. Relationships between the surface electronic and chemical properties of doped 4d and 5d late transition metal dioxides

    SciTech Connect

    Xu, Zhongnan; Kitchin, John R.

    2015-03-14

    Density functional theory calculations were performed to elucidate the underlying physics describing the adsorption energies on doped late transition metal dioxide rutiles. Adsorption energies of atomic oxygen on doped rutiles M{sup D}-M{sup H}O{sub 2}, where transition metal M{sup D} is doped into M{sup H}O{sub 2}, were expressed in terms of a contribution from adsorption on the pure oxide of the dopant M{sup D} and perturbations to this adsorption energy caused by changing its neighboring metal cations and lattice parameters to that of the host oxide M{sup H}O{sub 2}, which we call the ligand and strain effects, respectively. Our analysis of atom projected density of states revealed that the t{sub 2g}-band center had the strongest correlation with adsorption energies. We show that charge transfer mediated shifts to the t{sub 2g}-band center describe the ligand effect, and the radii of the atomic orbitals of metal cations can predict the magnitude and direction of this charge transfer. Strain produces systematic shifts to all features of the atom projected density of states, but correlations between the strain effect and the electronic structure were dependent on the chemical identity of the metal cation. The slope of these correlations can be related to the idealized d-band filling. This work elucidates the underlying physics describing adsorption on doped late transition metal oxides and establishes a foundation for models that use known chemical properties for the prediction of reactivity.

  7. Transition-Metal-Free Synthesis of Carbazoles and Indoles by an SN Ar-Based "Aromatic Metamorphosis" of Thiaarenes.

    PubMed

    Bhanuchandra, M; Murakami, Kei; Vasu, Dhananjayan; Yorimitsu, Hideki; Osuka, Atsuhiro

    2015-08-24

    Dibenzothiophene dioxides, which are readily prepared through oxidation of the parent dibenzothiophenes, undergo nucleophilic aromatic substitution with anilines intermolecularly and then intramolecularly to yield the corresponding carbazoles in a single operation. The "aromatic metamorphosis" of dibenzothiophenes into carbazoles does not require any heavy metals. This strategy is also applicable to the synthesis of indoles. Since electron-deficient thiaarene dioxides exhibit interesting reactivity, which is not observed for that the corresponding electron-rich azaarenes, a combination of a thiaarene-dioxide-specific reaction with the SN Ar-based aromatic metamorphosis allows transition-metal-free construction of difficult-to-prepare carbazoles. PMID:26183910

  8. Molten salt extraction process for the recovery of valued transition metals from land-based and deep-sea minerals

    DOEpatents

    Maroni, V.A.; von Winbush, S.

    1987-05-01

    A process for extracting transition metals and particularly cobalt and manganese together with iron, copper and nickel from low grade ores (including ocean-floor nodules) by converting the metal oxides or other compositions to chlorides in a molten salt, and subsequently using a combination of selective distillation at temperatures below about 500/degree/C, electrolysis at a voltage not more negative that about /minus/1.5 volt versus Ag/AgCl, and precipitation to separate the desired manganese and cobalt salts from other metals and provide cobalt and manganese in metallic forms or compositions from which these metals may be more easily recovered.

  9. Molten salt extraction process for the recovery of valued transition metals from land-based and deep-sea minerals

    DOEpatents

    Maroni, Victor A. (Naperville, IL); von Winbush, Samuel (Huntington, NY)

    1988-01-01

    A process for extracting transition metals and particularly cobalt and manganese together with iron, copper and nickel from low grade ores (including ocean-floor nodules) by converting the metal oxides or other compositions to chlorides in a molten salt, and subsequently using a combination of selective distillation at temperatures below about 500.degree. C., electrolysis at a voltage not more negative than about -1.5 volt versus Ag/AgCl, and precipitation to separate the desired manganese and cobalt salts from other metals and provide cobalt and manganese in metallic forms or compositions from which these metals may be more easily recovered.

  10. Enhanced Performance in Fluorene-Free Organometal Halide Perovskite Light Emitting Diodes using Tunable, Low Electron-Affinity Oxide Electron-Injectors

    E-print Network

    Hoye, Robert L. Z.; Chua, Matthew R.; Musselman, Kevin P.; Li, Guangru; Lai, May-Ling; Tan, Zhi-Kuang; Greenham, Neil C.; MacManus-Driscoll, Judith L.; Friend, Richard H.; Credgington, Dan

    2015-01-09

    bright future for perovs- kite LED (PeLED) technology. [ 4 ] The appealing properties of organometal halide perovskites enabling these advances are their sharp band edges, [ 11 ] low non-radiative recombination rates, and suppressed defect formation... , directly onto perovskite emitters to produce PeLEDs that do not rely on fl uorene-based organic transport layers. In conclusion, we produced fl uorene-free PeLEDs by adopting a very careful synthesis approach that enabled the deposition of SAALD Zn...

  11. Discovering the electronic circuit diagram of life: structural relationships among transition metal binding sites in oxidoreductases

    PubMed Central

    Kim, J. Dongun; Senn, Stefan; Harel, Arye; Jelen, Benjamin I.; Falkowski, Paul G.

    2013-01-01

    Oxidoreductases play a central role in catalysing enzymatic electron-transfer reactions across the tree of life. To first order, the equilibrium thermodynamic properties of these proteins are governed by protein folds associated with specific transition metals and ligands at the active site. A global analysis of holoenzyme structures and functions suggests that there are fewer than approximately 500 fundamental oxidoreductases, which can be further clustered into 35 unique groups. These catalysts evolved in prokaryotes early in the Earth's history and are largely responsible for the emergence of non-equilibrium biogeochemical cycles on the planet's surface. Although the evolutionary history of the amino acid sequences in the oxidoreductases is very difficult to reconstruct due to gene duplication and horizontal gene transfer, the evolution of the folds in the catalytic sites can potentially be used to infer the history of these enzymes. Using a novel, yet simple analysis of the secondary structures associated with the ligands in oxidoreductases, we developed a structural phylogeny of these enzymes. The results of this ‘composome’ analysis suggest an early split from a basal set of a small group of proteins dominated by loop structures into two families of oxidoreductases, one dominated by ?-helices and the second by ?-sheets. The structural evolutionary patterns in both clades trace redox gradients and increased hydrogen bond energy in the active sites. The overall pattern suggests that the evolution of the oxidoreductases led to decreased entropy in the transition metal folds over approximately 2.5 billion years, allowing the enzymes to use increasingly oxidized substrates with high specificity. PMID:23754810

  12. Discovering the electronic circuit diagram of life: structural relationships among transition metal binding sites in oxidoreductases.

    PubMed

    Kim, J Dongun; Senn, Stefan; Harel, Arye; Jelen, Benjamin I; Falkowski, Paul G

    2013-07-19

    Oxidoreductases play a central role in catalysing enzymatic electron-transfer reactions across the tree of life. To first order, the equilibrium thermodynamic properties of these proteins are governed by protein folds associated with specific transition metals and ligands at the active site. A global analysis of holoenzyme structures and functions suggests that there are fewer than approximately 500 fundamental oxidoreductases, which can be further clustered into 35 unique groups. These catalysts evolved in prokaryotes early in the Earth's history and are largely responsible for the emergence of non-equilibrium biogeochemical cycles on the planet's surface. Although the evolutionary history of the amino acid sequences in the oxidoreductases is very difficult to reconstruct due to gene duplication and horizontal gene transfer, the evolution of the folds in the catalytic sites can potentially be used to infer the history of these enzymes. Using a novel, yet simple analysis of the secondary structures associated with the ligands in oxidoreductases, we developed a structural phylogeny of these enzymes. The results of this 'composome' analysis suggest an early split from a basal set of a small group of proteins dominated by loop structures into two families of oxidoreductases, one dominated by ?-helices and the second by ?-sheets. The structural evolutionary patterns in both clades trace redox gradients and increased hydrogen bond energy in the active sites. The overall pattern suggests that the evolution of the oxidoreductases led to decreased entropy in the transition metal folds over approximately 2.5 billion years, allowing the enzymes to use increasingly oxidized substrates with high specificity. PMID:23754810

  13. Resistance switching in oxides with inhomogeneous conductivity

    NASA Astrophysics Data System (ADS)

    Shang, Da-Shan; Sun, Ji-Rong; Shen, Bao-Gen; Wuttig, Matthias

    2013-06-01

    Electric-field-induced resistance switching (RS) phenomena have been studied for over 60 years in metal/dielectrics/metal structures. In these experiments a wide range of dielectrics have been studied including binary transition metal oxides, perovskite oxides, chalcogenides, carbon- and silicon-based materials, as well as organic materials. RS phenomena can be used to store information and offer an attractive performance, which encompasses fast switching speeds, high scalability, and the desirable compatibility with Si-based complementary metal—oxide—semiconductor fabrication. This is promising for nonvolatile memory technology, i.e., resistance random access memory (RRAM). However, a comprehensive understanding of the underlying mechanism is still lacking. This impedes faster product development as well as accurate assessment of the device performance potential. Generally speaking, RS occurs not in the entire dielectric but only in a small, confined region, which results from the local variation of conductivity in dielectrics. In this review, we focus on the RS in oxides with such an inhomogeneous conductivity. According to the origin of the conductivity inhomogeneity, the RS phenomena and their working mechanism are reviewed by dividing them into two aspects: interface RS, based on the change of contact resistance at metal/oxide interface due to the change of Schottky barrier and interface chemical layer, and bulk RS, realized by the formation, connection, and disconnection of conductive channels in the oxides. Finally the current challenges of RS investigation and the potential improvement of the RS performance for the nonvolatile memories are discussed.

  14. Competition between heavy fermion and Kondo interaction in isoelectronic A-site-ordered perovskites.

    PubMed

    Meyers, D; Middey, S; Cheng, J-G; Mukherjee, Swarnakamal; Gray, B A; Cao, Yanwei; Zhou, J-S; Goodenough, J B; Choi, Yongseong; Haskel, D; Freeland, J W; Saha-Dasgupta, T; Chakhalian, J

    2014-01-01

    With current research efforts shifting towards the 4d and 5d transition metal oxides, understanding the evolution of the electronic and magnetic structure as one moves away from 3d materials is of critical importance. Here we perform X-ray spectroscopy and electronic structure calculations on A-site-ordered perovskites with Cu in the A-site and the B-sites descending along the ninth group of the periodic table to elucidate the emerging properties as d-orbitals change from partially filled 3d to 4d to 5d. The results show that when descending from Co to Ir, the charge transfers from the cuprate-like Zhang-Rice state on Cu to the t(2g) orbital of the B site. As the Cu d-orbital occupation approaches the Cu(2+) limit, a mixed valence state in CaCu(3)Rh(4)O(12) and heavy fermion state in CaCu(3)Ir(4)O(12) are obtained. The investigated d-electron compounds are mapped onto the Doniach phase diagram of the competing RKKY and Kondo interactions developed for the f-electron systems. PMID:25517129

  15. Intrinsic Exciton Linewidth in Monolayer Transition Metal Dichalcogenides

    NASA Astrophysics Data System (ADS)

    Hao, Kai; Moody, Galan; Dass, Chandriker; Chen, Chang-Hsiao; Li, Lain-Jong; Singh, Akshay; Tran, Kha; Clark, Genevieve; Xu, Xiaodong; Bergäuser, Gunnar; Malic, Ermin; Knorr, Andreas; Li, Xiaoqin

    2015-03-01

    Excitons in monolayer transition metal dichalcogenides (TMDCs) exhibit exceptionally large binding energy, strong optical absorption, and spin valley coupling. These characteristics make TMDCs a promising system for optoelectronics and valleytronics. An important yet unknown property of excitons in TMDCs is the intrinsic homogeneous linewidth, which reflect radiative recombination and irreversible dissipative decay. Here, we use optical coherent two-dimensional spectroscopy to reveal the exciton homogeneous linewidth in monolayer CVD grown Tungsten Diselenide (WSe2). With excitation density and temperature dependent measurements, exciton-exciton interaction and exciton-phonon interactions are quantitatively evaluated. Extrapolating to zero density and temperature, we obtain a residual homogeneous linewidth of ~ 1.5 meV, which places a lower bound of 0.2 ps on the exciton radiative lifetime. This result is consistent with microscopic calculations, which suggest that fast radiative decay of delocalized excitons arises from their large oscillator strength. We acknowledge AFOSR and NSF for funding.

  16. Transition Metals Catalyzed Element-Cyano Bonds Activations

    PubMed Central

    Wang, Rui; Falck, John R.

    2014-01-01

    Cyano group as a versatile functionalized intermediate has been explored for several decades, as it readily transfers to many useful functionalization groups such as amine, amide, acid, etc., which make it possess high popularization and use value in organic synthesis. Reactions involved with element-cyano bond cleavage can provide not only a new cyano group but also a freshly functionalized skeleton in one-pot, consequently making it of high importance. The highlights reviewed herein include H-CN, Si-CN, C-CN, B-CN, Sn-CN, Ge-CN, S-CN, Halo-CN, N-CN, and O-CN bonds cleavages and will summarize progress in such an important research area. This review article will focus on transition metal catalyzed reactions involving element-cyano bond activation. PMID:25558119

  17. Dirac cones in transition metal doped boron nitride

    SciTech Connect

    Feng, Min; Cao, Xuewei; Shao, Bin; Zuo, Xu

    2015-05-07

    The transition metal (TM) doped zinc blende boron nitride (c-BN) is studied by using the first principle calculation. TM atoms fill in the interstitials in c-BN and form two-dimensional honeycomb lattice. The generalized gradient approximation and projector augmented wave method are used. The calculated density of states and band structures show that d electrons of TM atoms form impurity bands in the gap of c-BN. When the TM-BN system is in ferromagnetic or non-magnetic state, Dirac cones emerge at the K point in Brillouin zone. When TM is Ti and Co, the Dirac cones are spin polarized and very close to the Fermi level, which makes them promising candidates of Dirac half-metal [H. Ishizuka and Y. Motome, Phys. Rev. Lett. 109, 237207 (2012)]. While TM is Ni and Cu, the system is non-magnetic and Dirac cones located above the Fermi level.

  18. Kondo Effects in Single Layer Transition Metal Dichalcogenides

    NASA Astrophysics Data System (ADS)

    Phillips, Michael; Aji, Vivek

    2015-03-01

    Inversion symmetry breaking and strong spin orbit coupling in two dimensional transition metal dichalcogenides leads to interesting new phenomena such as the valley hall and spin hall effects. They display optical circular dichroism and the ability to generate excitation with valley specificity. In this talk we report on the consequences of these properties on correlated states in hole doped systems focussing on the physics of the screening of magnetic impurities. Unlike typical metals, the breaking of inversion symmetry leads to the mixing of a triplet component to the Kondo cloud. Using a variational wave function approach we determine the nature of the many body state. With the ground state in hand we analyze the excitations generated by valley discriminating perturbations. Graduate Student.

  19. Theory of strain in single-layer transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Rostami, Habib; Roldán, Rafael; Cappelluti, Emmanuele; Asgari, Reza; Guinea, Francisco

    2015-11-01

    Strain engineering has emerged as a powerful tool to modify the optical and electronic properties of two-dimensional crystals. Here we perform a systematic study of strained semiconducting transition metal dichalcogenides. The effect of strain is considered within a full Slater-Koster tight-binding model, which provides us with the band structure in the whole Brillouin zone (BZ). From this, we derive an effective low-energy model valid around the K point of the BZ, which includes terms up to second order in momentum and strain. For a generic profile of strain, we show that the solutions for this model can be expressed in terms of the harmonic oscillator and double quantum well models, for the valence and conduction bands respectively. We further study the shift of the position of the electron and hole band edges due to uniform strain. Finally, we discuss the importance of spin-strain coupling in these 2D semiconducting materials.

  20. Work Functions of the transition Metals and Metal Silicides

    SciTech Connect

    Drummond, T.J.

    1999-02-15

    The work functions of polycrystalline metals are often used to systematize Schottky barrier height data for rectifying contacts to semiconductors. Rectifying contacts to silicon devices are predominantly formed using conductive metal silicides with work functions which are not as well characterized as metal work functions. The present work has two objectives. First, it classifies the transition metals using correlations between the metal work function and the atomic chemical potential. Second, the available data for metal silicides is collected and interpreted using an average charge transfer (ACT) model. The ACT model accounts for the electronic hardness of the component elements in addition to their chemical potentials. New trends in the behavior of silicide work functions are identified.