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1

Transition-metal-based perovskite oxides for enhanced thermopower  

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

2

Ionic liquid-mediated synthesis of meso-scale porous lanthanum-transition-metal perovskites with high CO oxidation performance.  

PubMed

Lanthanum-transition-metal perovskites with robust meso-scale porous frameworks (meso-LaMO3) are synthesized through the use of ionic liquids. The resultant samples demonstrate a rather high activity for CO oxidation, by taking advantage of unique nanostructure-derived benefits. This synthesis strategy opens up a new opportunity for preparing functional mesoporous complex oxides of various compositions. PMID:25727232

Lu, Hanfeng; Zhang, Pengfei; Qiao, Zhen-An; Zhang, Jinshui; Zhu, Huiyuan; Chen, Jihua; Chen, Yinfei; Dai, Sheng

2015-04-01

3

Structure-property relationships: Synthesis and characterization of Perovskite-related transition metal oxides  

Microsoft Academic Search

The fundamental structural component of perovskite-related phases is the octahedrally coordinated transition metal ion, symbolized as BO6 . Corner-sharing networks of BO6 octahedra are present in perovskites and related Ruddlesden-Popper Phases, ABO3 and AO(ABO 3)n, respectively. Face-sharing octahedra arranged into columns are characteristic of hexagonal, perovskite-related phases, and the relationship will be described in detail in Chapter 1. Edge sharing

Louis Whaley

2007-01-01

4

Transition metal oxides with the perovskite structure show a wide variety of physical properties. This is correlated with the strong coupling between the electrons and the  

E-print Network

Summary Transition metal oxides with the perovskite structure show a wide variety of physical channel and gate-oxide materials, such as transition metal oxides. This thesis describes the influence of unit-cell high steps on the substrate surface. This chapter also describes the several

Hille, Sander

5

Doped Mott insulators in (111) bilayers of perovskite transition-metal oxides with a strong spin-orbit coupling.  

PubMed

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. PMID:23432283

Okamoto, Satoshi

2013-02-01

6

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

SciTech Connect

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.

Okamoto, Satoshi [ORNL

2013-01-01

7

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

NASA Astrophysics Data System (ADS)

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.

Misra, Sunasira

2012-07-01

8

Orbital magnetization of insulating perovskite transition-metal oxides with a net ferromagnetic moment in the ground state  

NASA Astrophysics Data System (ADS)

Modern theory of the orbital magnetization is applied to the series of prototype insulating perovskite transition metal oxides (orthorhombic YTiO3,LaMnO3, and YVO3, as well as monoclinic YVO3), carrying a net ferromagnetic (FM) moment in the ground state. For these purposes, we use an effective Hubbard-type model, derived from the first-principles electronic structure calculations and describing the behavior of magnetically active states near the Fermi level. The solution of this model in the mean-field Hartree-Fock approximation with the relativistic spin-orbit coupling typically gives us a distribution of the local orbital magnetic moments, which are related to the site-diagonal part of the density matrix D? by the "classical" expression ?0=-?BTr{L?D?}. These moments are usually well quenched by the crystal field. In this work, we evaluate "itinerant" corrections ?M to the net FM moment, suggested by the modern theory. We show that these corrections are small and in most cases can be neglected. Nevertheless, the most interesting aspect of our analysis is that, even for these compounds, which are frequently regarded as prototype Mott insulators, the "itinerant" corrections reveal a strong k dependence in the reciprocal space, following the behavior of Chern invariants. Therefore, the small value of ?M is the result of strong cancellation of relatively large contributions, coming from different parts of the Brillouin zone. We discuss details as well as possible implications of this cancellation, which depends on the crystal structure as well as the type of the magnetic ground state.

Nikolaev, S. A.; Solovyev, I. V.

2014-02-01

9

Mechanism for bipolar resistive switching in transition metal oxides  

Microsoft Academic Search

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

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

2010-01-01

10

Nanostructured transition metal oxides useful for water oxidation catalysis  

DOEpatents

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

Frei, Heinz M; Jiao, Feng

2013-12-24

11

Orbital Physics in Transition-Metal Oxides  

Microsoft Academic Search

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

Y. Tokura; N. Nagaosa

2000-01-01

12

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

DOEpatents

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.

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

2013-12-24

13

Electric-field-induced resistance switching universally observed in transition-metal-oxide thin films  

Microsoft Academic Search

We show that polarity-dependent, nonvolatile resistance switching by electric field occurs in the thin film of various transition-metal oxides in almost the same manner. This result indicates that, contrary to the general acceptance, perovskite manganite is by no means a special compound for this phenomenon. It is also suggested that the resistance switching is not dominated by a detailed electronic

M. Hamaguchi; K. Aoyama; S. Asanuma; Y. Uesu; T. Katsufuji

2006-01-01

14

MATERIALS THEORY From transition metal oxides to cosmic strings  

E-print Network

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

15

PEROVSKITE-TYPE THERMOELECTRIC OXIDES AND OXYNITRIDES  

Microsoft Academic Search

Direct and efficient thermoelectric conversion of solar or geothermal waste heat into electricity requires the development of p- and n-type thermoelectrics with similar materials properties. Perovskite-type transition metal- oxides and oxynitrides are investigated as potential candidates for thermoelectric devices operating at high temperatures as they can possess large positive as well as large negative thermopower depending on their composition. Cobaltates,

A. Weidenkaff; R. Robert; L. Bocher; P. Tomes; M. Trottmann; M. H. Aguirre

16

Orbital physics in transition-metal oxides  

PubMed

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

Tokura; Nagaosa

2000-04-21

17

Orbital Physics in Transition-Metal Oxides  

NASA Astrophysics Data System (ADS)

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

Tokura, Y.; Nagaosa, N.

2000-04-01

18

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

SciTech Connect

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.

Vojvodic, Aleksandra

2011-08-22

19

Oxidation of dodecane on transition metal oxides  

NASA Astrophysics Data System (ADS)

The catalytic oxidation of dodecane on individual and mixed vanadium and molybdenum oxides is studied. Products of the oxidation of alkane are studied qualitatively and quantitatively. The activities of the samples of the catalysts with various ratios of vanadium and molybdenum oxides are compared. One possible scheme for the activation of reagents on a catalyst is given.

Vishnetskaya, M. V.; Vakhrushin, P. A.

2012-11-01

20

(S)TEM analysis of functional transition metal oxides  

NASA Astrophysics Data System (ADS)

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

Chi, Miaofang

21

Dielectric response of sputtered transition metal oxides  

NASA Astrophysics Data System (ADS)

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

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

2004-06-01

22

Methane and propane combustion over lanthanum transition-metal perovskites: role of oxygen mobility  

Microsoft Academic Search

Catalytic hydrocarbon combustion is a technologically important, but still relatively poorly understood reaction. To shed more light on the role of various physical and chemical characteristics of the catalyst on its activity for hydrocarbon combustion, La1?xSrxM1?yMy?O3?? perovskites (M and M? represent transition metals) were used as a model system. Four representative compositions were prepared and fully characterized by different methods

M Alifanti; J Kirchnerova; B Delmon; D Klvana

2004-01-01

23

Charge transfer across transition-metal oxide interfaces: Emergent conductance and electronic structure  

NASA Astrophysics Data System (ADS)

We perform density functional theory plus dynamical mean-field theory calculations to investigate internal charge transfer in a superlattice composed of alternating layers of vanadate and manganite perovskite and Ruddlesden-Popper structure materials. We show that the electronegativity difference between vanadium and manganese causes moderate charge transfer from VO2 to MnO2 layers in both perovskite and Ruddlesden-Popper-based superlattices, leading to hole doping of the VO2 layer and electron doping of the MnO2 layer. Comparison of the perovskite and Ruddlesden-Popper-based heterostructures shows that apical oxygen motion in the perovskite superlattice enhances charge transfer. Our first principles simulations demonstrate that the combination of internal charge transfer and quantum confinement provided by heterostructuring is a powerful approach to engineering electronic structure and tailoring correlation effects in transition metal oxides.

Chen, Hanghui; Park, Hyowon; Millis, Andrew J.; Marianetti, Chris A.

2014-12-01

24

Charge, orbital and magnetic ordering in transition metal oxides   

E-print Network

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

Senn, Mark Stephen

2013-06-29

25

Electrolytic separation of crystals of transition-metal oxides  

NASA Technical Reports Server (NTRS)

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

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

1969-01-01

26

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

NASA Astrophysics Data System (ADS)

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.

Fiete, Gregory A.; Rüegg, Andreas

2015-05-01

27

Fingerprints of spin-orbital entanglement in transition metal oxides  

E-print Network

The concept of spin-orbital entanglement on superexchange bonds in transition metal oxides is introduced and explained on several examples. It is shown that spin-orbital entanglement in superexchange models destabilizes the long-range (spin and orbital) order and may lead either to a disordered spin-liquid state or to novel phases at low temperature which arise from strongly frustrated interactions. Such novel ground states cannot be described within the conventionally used mean field theory which separates spin and orbital degrees of freedom. Even in cases where the ground states are disentangled, spin-orbital entanglement occurs in excited states and may become crucial for a correct description of physical properties at finite temperature. As an important example of this behaviour we present spin-orbital entanglement in the $R$VO$_3$ perovskites, with $R$=La,Pr,...,Yb,Lu, where such finite temperature properties of these compounds can be understood only using entangled states: ($i$) thermal evolution of the optical spectral weights, ($ii$) the dependence of transition temperatures for the onset of orbital and magnetic order on the ionic radius in the phase diagram of the $R$VO$_3$ perovskites, and ($iii$) dimerization observed in the magnon spectra for the $C$-type antiferromagnetic phase of YVO$_3$. Finally, it is shown that joint spin-orbital excitations in an ordered phase with coexisting antiferromagnetic and alternating orbital order introduces topological constraints for the hole propagation and will thus radically modify transport properties in doped Mott insulators where hole motion implies simultaneous spin and orbital excitations.

Andrzej M. Ole?

2012-07-12

28

Electronic entanglement in late transition metal oxides  

E-print Network

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

Patrik Thunström; Igor Di Marco; Olle Eriksson

2013-01-28

29

THEORY OF MOTTTRANSITION : APPLICATION S TO TRANSITION METAL OXIDES  

E-print Network

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

Paris-Sud XI, Université de

30

Disorder driven quantum phase transitions in transition metal oxides  

Microsoft Academic Search

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

Kohjiro Kobayashi; Nandini Trivedi

2007-01-01

31

Interaction between the d-Shells in the Transition Metals. II. Ferromagnetic Compounds of Manganese with Perovskite Structure  

Microsoft Academic Search

Recently, Jonker and Van Santen have found an empirical correlation between electrical conduction and ferromagnetism in certain compounds of manganese with perovskite structure. This observed correlation is herein interpreted in terms of those principles governing the interaction of the d-shells of the transition metals which were enunciated in the first paper of this series. Both electrical conduction and ferromagnetic coupling

Clarence Zener

1951-01-01

32

Optical properties of transition metal oxide quantum wells  

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

33

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

E-print Network

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

Ceder, Gerbrand

34

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

E-print Network

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

Ceder, Gerbrand

35

The nature of transition-metal-oxide surfaces  

NASA Astrophysics Data System (ADS)

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

Henrich, V. E.

36

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

E-print Network

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

Ceder, Gerbrand

37

Ionically-mediated electromechanical hysteresis in transition metal oxides  

SciTech Connect

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

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

2012-01-01

38

Nanostructured transition metal oxides for energy storage and conversion  

NASA Astrophysics Data System (ADS)

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

Li, Qiang

39

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

40

Spin-Orbit Interaction Rediscovered in Transition Metal Oxides  

NASA Astrophysics Data System (ADS)

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

Cao, Gang

2011-03-01

41

Resonant Ultrasound Studies of Complex Transition Metal Oxides  

SciTech Connect

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

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

2008-08-18

42

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

E-print Network

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

Ceder, Gerbrand

43

Development of microstrain in aged lithium transition metal oxides.  

PubMed

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

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

2014-08-13

44

Nanostructured transition metal oxides for aqueous hybrid electrochemical supercapacitors  

NASA Astrophysics Data System (ADS)

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

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

2006-03-01

45

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

E-print Network

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

Metz, Ricardo B.

46

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

E-print Network

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

Islam, M. Saif

47

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

E-print Network

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

Wu, Junqiao

48

Transition-metal-oxide coated titanium electrodes for redox batteries  

NASA Astrophysics Data System (ADS)

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

Savinell, R. F.

1982-12-01

49

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

50

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

PubMed

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

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

2014-06-01

51

Route to transition metal carbide nanoparticles through cyanamide and metal oxides  

Microsoft Academic Search

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

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

2008-01-01

52

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

PubMed

We investigate the physicomechanical properties of polymeric heterogeneous catalysts of transition-metal oxides, specifically, the specific surface area, elongation at break, breaking strength, specific electrical resistance, and volume resistivity. Digital microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and energy-dispersive analysis are used to study the surfaces of the catalysts. The experimental results show that polymeric heterogeneous catalysts of transition-metal oxides exhibit high stability and can maintain their catalytic activity under extreme reaction conditions for long-term use. The oxidation mechanism of sulfur-containing compounds in the presence of polymeric heterogeneous catalysts of transition-metal oxides is confirmed. Microstructural characterization of the catalysts is performed by using X-ray computed tomography. The activity of various catalysts in the oxidation of sulfur-containing compounds is determined. We demonstrate the potential application of polymeric heterogeneous catalysts of transition-metal oxides in industrial wastewater treatment. PMID:24243767

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

2013-12-16

53

Perovskite oxides: Oxygen electrocatalysis and bulk structure  

NASA Technical Reports Server (NTRS)

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.

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

1987-01-01

54

Hybrid uranium-transition-metal oxide cage clusters.  

PubMed

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

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

2014-12-15

55

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

E-print Network

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

Sivakumar, Vikram

2008-01-01

56

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

E-print Network

In this thesis, the chemistry of sulfur oxides on transition metals is studied extensively via first-principles density functional theory (DFT) computations, focusing on the chemical reactivity and selectivity in sulfur ...

Lin, Xi, 1973-

2003-01-01

57

Transition metals  

PubMed Central

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

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

2013-01-01

58

Transition-metal oxides with triangular lattices: generation of new magnetic and electronic properties.  

PubMed

The search for multifunctional materials as multiferroics to be applied in microelectronic or for new, chemically stable and nontoxic, thermoelectric materials to recover waste heat is showing a common interest in the oxides whose structures contain a triangular network of transition-metal cations. To illustrate this point, two ternary systems, Ba-Co-O and Ca-Co-O, have been chosen. It is shown that new phases with a complex triangular structure can be discovered, for instance, by introduction of Ga (3+) into the Ba-Co-O system to stabilize Ba 6Ga 2Co 11O 26 and Ba 2GaCo 8O 14, which both belong to a large family of compounds with formula [Ba(Co,Ga)O 3-delta] n [BaCo 8O 11]. In the latter, both sublattices contain triangular networks derived from the hexagonal perovskite and the spinel structure. Among the hexagonal perovskite, the Ca 3Co 2O 6 crystals give clear evidence where the coupling of charges and spins is at the origin of a magnetocapacitance effect. In particular, the ferrimagnetic to ferromagnetic transition, with a one-third plateau on the M( H) curve characteristic of triangular magnetism, is accompanied by a peak in the dielectric constant. A second class of cobaltites is the focus of much interest. Their 2D structure, containing CoO 2 planes isostructural to a CdI 2 slice that are stacked in an incommensurate way with rock salt type layers, is referred to misfit cobaltite. The 2D triangular network of edge-shared CoO 6 octahedra is believed to be responsible for large values of the Seebeck coefficient and low electrical resistivity. A clear relationship between the structuresincommensurability ratiosand the electronic properties is evidenced, showing that the charge carrier concentration can be tuned via the control of the ionic radius of the cations in the separating layers. PMID:18821821

Maignan, A; Kobayashi, W; Hébert, S; Martinet, G; Pelloquin, D; Bellido, N; Simon, Ch

2008-10-01

59

Perovskite catalysts for oxidative coupling  

DOEpatents

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.

Campbell, Kenneth D. (Charleston, WV)

1991-01-01

60

Properties of transition metal oxides with layered perovskite structure  

Microsoft Academic Search

The manganates of Lan?nxSr1+nxMnnO3n+1(x=0.4; n=1, 2, ?) were prepared to study the relationship between their electronic properties and their crystal structure; two-dimensional structure with n=1, pseudo-two-dimensional with n=2 and three-dimensional with n=?. The n=1 manganate exhibits semiconducting behavior below room temperature. When the manganate has a higher dimensional structure with an increase in the value of n, the electric conduction

Minoru Takemoto; Tatsuya Miyajima; Kazuyoshi Takayanagi; Takeshi Ogawa; Hiroyuki Ikawa; Takahisa Omata

1998-01-01

61

Inter-network magnetic interactions in GdMe xMn 1-xO 3 perovskites (Me=transition metal)  

NASA Astrophysics Data System (ADS)

The gadolinium-based manganite GdMnO 3 of perovskite structure has been partially substituted at the manganese site by transition metal elements Me like Cu, Ni and Co, leading to a general formula GdMe xMn 1-xO 3, in which different magnetic entities (e.g., Gd 3+, Cu 2+, Ni 2+, Co 2+, Co 3+, Mn 3+, Mn 4+) can coexist, depending on charge equilibrium conditions. For divalent cations such as Cu 2+ and Ni 2+, the solid solution extends from x(Me)=0-0.5, with O-type orthorhombic symmetry (a0.5. In this latter case, the synthesis is performed under oxygen flow, which allows the cobalt ion to take a 3+ oxidation state. Magnetic properties were studied through susceptibility and magnetization measurements. A paramagnetic-ferromagnetic transition occurs at Tc, due to double-exchange interactions between transition metal ions (Mn 3+-Mn 4+, Ni 2+-Mn 4+, Co 2+-Mn 4+), leading to an optimum value at x(Me)=0.50 ( Tc=145 and 120 K, for GdNi 0.5Mn 0.5O 3 and GdCo 0.5Mn 0.5O 3, respectively). Different situations were identified, among them, a spin reversal in GdNi 0.3Mn 0.7O 3, strong ferromagnetic interactions in GdNi 0.5Mn 0.5O 3, large coercive fields in GdCo 0.5Mn 0.5O 3 or Co 3+-Mn 4+ antiferromagnetic interactions in GdCo 0.9Mn 0.1O 3. Most of these situations are explained by a phenomenological model of two magnetic sublattices: a transition-metal |Me+Mn| network which orders ferromagnetically at Tc and a gadolinium sublattice, composed of independent Gd 3+ ions. These networks are antiferromagnetically coupled through a negative exchange interaction. The local field created by the ferromagnetic |Me+Mn| lattice at the gadolinium site polarizes the Gd moment in a direction opposite to the applied field. When the magnetization of paramagnetic gadolinium, which varies as T-1, gets larger than the ferromagnetic magnetization of the transition metal, which is "frozen" at T< Tc, then the total magnetic moment changes its sign, leading to an overall ferrimagnetic state.

Peña, O.; Antunes, A. B.; Martínez, G.; Gil, V.; Moure, C.

2007-03-01

62

Optical study of orbital excitations in transition-metal oxides  

Microsoft Academic Search

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

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

2005-01-01

63

The role of metal/transition metal oxide/organic interface  

NASA Astrophysics Data System (ADS)

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

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

2008-03-01

64

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

Microsoft Academic Search

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

Lai-Sheng Wang

2009-01-01

65

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...

66

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

PubMed

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. PMID:24814859

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

2014-01-01

67

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

Microsoft Academic Search

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

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

2005-01-01

68

d-Band Surface States on Transition-Metal Perovskite Crystals: I. Qualitative Features and Application to SrTiO3  

Microsoft Academic Search

The qualitative features of the bulk and surface energy bands of ionic transition-metal perovskite crystals such as SrTiO3, BaTiO3, KTaO3, and BaZrO3 are discussed. The linear-combination-of-atom orbitals (LCAO) method is used in combination with a generalized-Seitzionic model to derive parameters for calculating the bulk and surface energy bands. The model for the bulk bands differs in detail from that used

T. Wolfram; E. A. Kraut; F. J. Morin

1973-01-01

69

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

PubMed

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 sp(2)-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

Gandhiraman, Ram P; Nordlund, Dennis; Javier, Cristina; Koehne, Jessica E; Chen, Bin; Meyyappan, M

2014-08-14

70

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

SciTech Connect

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

S.E. Ziemniak

2000-05-18

71

A review of catalytic partial oxidation of methane to synthesis gas with emphasis on reaction mechanisms over transition metal catalysts  

Microsoft Academic Search

Catalytic partial oxidation of methane has been reviewed with an emphasis on the reaction mechanisms over transition metal catalysts. The thermodynamics and aspects related to heat and mass transport is also evaluated, and an extensive table on research contributions to methane partial oxidation over transition metal catalysts in the literature is provided.Presented are both theoretical and experimental evidence pointing to

Bjørn Christian Enger; Rune Lødeng; Anders Holmen

2008-01-01

72

A new nonhydrolytic single-precursor approach to surfactant-capped nanocrystals of transition metal oxides  

Microsoft Academic Search

The advent of new methods to prepare semiconductor and metal nanocrystals, specifically the injection of molecular precursors into hot organic surfactants, has yielded markedly improved samples with good size control, narrow size distribution, and good crystallinity of individual and dispersable nanocrystals. It is of considerable interest to apply these methods to the synthesis of transition metal oxide nanoparticles, which typically

Jörg Rockenberger; Erik C. Scher; A. Paul Alivisatos

1999-01-01

73

Direct access to thermally stable and highly crystalline mesoporous transition-metal oxides with uniform pores  

Microsoft Academic Search

Even after a decade or so of research, the direct synthesis of highly crystalline mesoporous transition-metal oxides that are thermally stable and well ordered still constitutes a major challenge. Although various soft- and hard-templating approaches have been developed in the past, they usually suffer from multiple, tedious steps and often result in poor structure control. For many applications including power

Jinwoo Lee; M. Christopher Orilall; Scott C. Warren; Marleen Kamperman; Francis J. Disalvo; Ulrich Wiesner

2008-01-01

74

MAGNETIC COLLAPSE AND THE BEHAVIOR OF TRANSITION METAL OXIDES: FeO AT HIGH PRESSURES  

E-print Network

MAGNETIC COLLAPSE AND THE BEHAVIOR OF TRANSITION METAL OXIDES: FeO AT HIGH PRESSURES ** *** ****R augmented plane wave (LAPW) results are presented for FeO at high pressures using the Generalized Gradient that the high pressure hexagonal phase of FeO is likely a polytype between the B8 NiAs and anti-B8 As

Downs, Robert T.

75

Role of oxide surface in coordination chemistry of transition metal ions in catalytic systems  

Microsoft Academic Search

On going from the solution into the bulk of an oxide through the fluid-solid interface, it is possible to encounter four types of coordina- tion chemistry (CC) for a transition metal ion (TMI) : solution coordina- tion chemistry, extraframework ion CC, surface framework ion CC and solid state CC. In each case, the reactivity of the TMI is discussed on

L. Bonneviot; M. Curie

1988-01-01

76

X-ray Scattering Studies of Charge and Orbital Order in Transition Metal Oxides  

Microsoft Academic Search

Disentangling the origins of high temperature superconductivity and collossal magnetoresistance in the transition metal oxides remains at the center of current activity in condensed matter physics. An important aspect of these strongly correlated systems is that no single degree of freedom dominates their response. Rather, the ground state properties reflect a balance among several correlated processes, including orbital and charge

Doon Gibbs

2001-01-01

77

Emerging catalytic applications of transition metal oxide nanomaterials under microwave and conventional heating  

NASA Astrophysics Data System (ADS)

Heterogeneous transition metal oxide catalysts have advantages over homogeneous catalysts, such as easy separations and efficient recycling and minimization of metal traces in the products. Transition metal oxide nanomaterials with different properties such as shapes and particle size were synthesized by hydrothermal, solvothermal, solvent-free and by energy efficient microwave heating methods and characterized using X-Ray and microscopic techniques. The synthesized catalysts were tested for tandem reactions to form quinoxalines, oxidations of hydrocarbons to form alcohols, aldehydes and ketones, epoxidation, epoxide ring opening, and N-aryl coupling reactions. The kinetics and energy consumption associated with these reactions were compared for both microwave and conventionally heated reactions. Further, Synchrotron radiation-based time-resolved XRD experiments under a wide variety of temperature and pressure conditions were conducted to study the reactions under working conditions. EXAFS and XANES data collections were performed to determine inter-atomic distances and oxidation states of the catalysts.

Sithambaram, Shanthakumar

78

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

PubMed

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

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

2014-04-01

79

Spin and orbital ordering in ternary transition metal oxides   

E-print Network

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 ...

Kimber, Simon A. J.

80

Magnetopolaron-induced optical response in transition metal oxides  

NASA Astrophysics Data System (ADS)

We report on the optical response of different magnetic oxides (manganites, ruthenates, and magnetite) and show that for photons with energies ?1.5-3.5 eV the intensity of light reflected by these epitaxial oxide thin films is strongly modulated by magnetic fields. We argue that this behavior is related to the magnetopolaron physics, and the magnitude of the magnetoreflectance is a fingerprint and a measure of the electron-lattice coupling strength. Our research provides the basis for a fresh experimental approach to the physics of strongly correlated electronic systems.

Caicedo, J. M.; Fontcuberta, J.; Herranz, G.

2014-01-01

81

Transition metal oxides as charge injecting layer for admittance spectroscopy  

NASA Astrophysics Data System (ADS)

Admittance spectroscopy is a simple yet powerful tool to determine the carrier mobility of organic compounds. One requirement is to have an Ohmic contact for charge injection. By employing a thin interfacial layer of tungsten oxide, or molybdenum oxide we have found a possibility to efficiently inject holes into organic materials with a deep highest occupied molecular orbital level down to 6.3eV. These results considerably enhance the application range of the admittance spectroscopy method. The measured data are in excellent agreement with data obtained by the time-of-flight technique.

Hoping, M.; Schildknecht, C.; Gargouri, H.; Riedl, T.; Tilgner, M.; Johannes, H.-H.; Kowalsky, W.

2008-05-01

82

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

Microsoft Academic Search

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 (alpha-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

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

2005-01-01

83

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

PubMed

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

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

2015-01-28

84

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

NASA Astrophysics Data System (ADS)

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.

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

2015-01-01

85

Comparison Between Crystalline and Amorphous Surfaces of Transition Metal Oxide Water Oxidation Catalysts: a Theoretical Perspective  

NASA Astrophysics Data System (ADS)

Amorphous films of transition-metal oxide water oxidation catalysts (WOCs) often show an enhanced catalytic activity compared to their crystalline counterparts [1-4]. In particular, in the case of cobalt-oxide based WOCs the observed similarity in their electrochemical properties and catalytic activity, under oxidative conditions, has been correlated with the formation of similar amorphous surface morphologies, suggesting the presence of a common, catalytically active amorphous structural motif [3,4]. We present ab initio calculations of cobalt oxide based material surfaces and we compare the electronic properties of crystalline and amorphous surfaces, with the aim of identifying differences related to their different catalytic activity.[4pt] [1] Blakemore, J. D., Schley, N. D., Kushner-Lenhoff, M. N., Winter, A. M., D'Souza, F., Crabtree, R. H., and Brudvig, G. W. Inorg. Chem. 51, 7749 (2012); [2] Tsuji, E., Imanishi, A., Fukui, K.-I. and Nakato, Y. Electrochimica Acta 56, 2009 (2011); [3] Jia, H., Stark, J., Zhou, L. Q., Ling, C., Takeshi, S., and Markin, Z. RSC Advances 2, 10874 (2012); [4] Lee, S. W., Carlton, C., Risch, M., Surendranath, Y., Chen, S., Furutsuki, S., Yamada, A., Nocera, D. G., and Shao-Horn, Y. J. Am. Chem. Soc. 134, 16959 (2012).

Skone, Jonathan H.; Galli, Giulia

2013-03-01

86

Nanostructure sensitization of transition metal oxides for visible-light photocatalysis  

PubMed Central

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

Chen, Hongjun

2014-01-01

87

Chemistry of sulfur oxides on transition metal surfaces: BOC-MP analysis  

Microsoft Academic Search

The bond order conservation-Morse potential (BOC-MP) method proved to be versatile and useful in analyzing chemisorption and reactivity on transition metal surfaces [1–3]. Most recently, we have applied the BOC-MP method to analyze surface chemistry of sulfur oxides on the Cu and Ni group metals [4,5]. We have calculated the reaction energetics (heats of adsorption, reaction enthalpies and intrinsic activation

Harrell Sellers; Evgeny Shustorovich

1997-01-01

88

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

Microsoft Academic Search

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

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

2007-01-01

89

Transition metal\\/UV-based advanced oxidation technologies for water decontamination  

Microsoft Academic Search

This study explores the effect of ultraviolet (UV) light radiation and\\/or transition metals (M) for the activation of common oxidants (Ox) with the objective of treating recalcitrant organic contaminants in water. Hydrogen peroxide, potassium peroxymonosulfate and potassium persulfate were combined with iron, cobalt and silver, respectively, and\\/or with UV light (254nm) and were tested for the treatment of 2,4-dichlorophenol (2,4-DCP).

George P. Anipsitakis; Dionysios D. Dionysiou

2004-01-01

90

Optical absorption of gamma-irradiated lithium-borate glasses doped with different transition metal oxides  

Microsoft Academic Search

We have investigated the effect of gamma irradiation on the optical properties of Li2O B2O3 containing two concentrations (0.2 or 0.5 g) of each one of the following transition metals, V, Mn, Fe or Ni oxide glass samples. We studied the impacts of gamma irradiation in terms of the mechanism by which radiation-induced defects are generated. A resolution of the

S. Y. Marzouk; N. A. Elalaily; F. M. Ezz-Eldin; W. M. Abd-Allah

2006-01-01

91

Influence of d orbitals on the nonlinear optical response of transparent transition-metal oxides  

Microsoft Academic Search

The bond-orbital theory of linear and nonlinear electronic response in optically transparent materials, developed earlier for pretransition-metal halides and chalcogenides, is expanded to embrace the transition-metal (TM) oxides. The extension requires an explicit recognition of the influence of cationic empty d orbitals on electronic polarizability. Two competing mechanisms, involving, respectively, virtual electronic excitations to the d orbitals and to the

M. E. Lines

1991-01-01

92

Super-exchange in transition-metal oxides  

NASA Astrophysics Data System (ADS)

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).

Harrison, Walter

2007-03-01

93

The Influence of Oxygen in Transition Metal Oxides  

NASA Astrophysics Data System (ADS)

The existence of a 2D metallic state at the interface between LaAlO3 and SrTiO3 (LAO/STO) has generated much excitement. Its origin has been attributed to charge redistribution to avoid a dielectric catastrophe; however, oxygen vacancies in TiO2-terminated STO can play a significant role in the electronic properties of the interface. In order to determine the nature and origin of the metallic phase, we have induced vacancies in TiO2-terminated STO single crystal substrates by annealing under controlled vacuum conditions. We report resistivity, Hall effect, and thermopower measurements on these materials and discuss their implications for the nature of the 2D electron gas at the STO surface. We have explored the possibility of gate-tuning these systems in order to fabricate single-oxide based devices. This work was supported by the Ministerio de Ciencia e Innovaci'on (Spain), grant MAT2010-16157, and the European Research Council, grant ERC-2010-StG 259082 2D THERMS.

Bach, P. L.; Leboran, V.; Rivadulla, F.

2012-02-01

94

The low-temperature reduction of Pd-doped transition metal oxide surfaces with hydrogen  

Microsoft Academic Search

The reaction of hydrogen with a series of polyvalent metal oxides (Fe2O3, WO3, MoO3, V2O5, Sb2O3, PbO2, Cr2O3, NiO, CuO, Co3O4, MnO2, PdO, Ag2O) was investigated at low temperatures (77–320K) and pressures (0.001–0.7kPa). Pd-doped (0.1–0.5wt.%) transition metal oxides can be reduced by hydrogen at 77–320K whereas the onset of the reduction of the pure oxides occurs at temperatures higher than

V. M. Belousov; M. A. Vasylyev; L. V. Lyashenko; N. Yu. Vilkova; B. E. Nieuwenhuys

2003-01-01

95

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

DOEpatents

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.

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

1985-08-16

96

Transition metal oxides: CrO, MoO, NiO, PdO, AgO  

Microsoft Academic Search

The transition metal oxides are quite ionic, Mulliken population analyses for several oxides give a negative charge of ?0.7 electrons for oxygen. When the transition metal d shell is only partially filled, the d orbitals are involved in covalent bonds with O; both two electron (bonding2–antibonding0) and one electron (bonding2–antibonding1) bonds are formed. These covalent bonds occur in addition to

Charles W. Bauschlicher; Constance J. Nelina; Paul S. Bagus

1985-01-01

97

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

SciTech Connect

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.

Boffa, A.B. [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry]|[Lawrence Berkeley Lab., CA (United States). Materials Sciences Div.

1994-07-01

98

A study on the grindability of portland cement clinker containing transition metal oxides  

Microsoft Academic Search

The subject of this paper is to investigate the effect of transition metal oxides on the grindability of clinker. As it is concluded clinker containing ZnO has the lower grindability while clinker containing MnO or Cr2O3 has the higher grindability. The classification of the added oxides, concerning the clinker grindability (descending sort), is: MnO, Cr2O3, Ni2O3, ZrO2, CuO, Co2O3, V2O5,

S. Tsivilis; G. Kakali

1997-01-01

99

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

PubMed

This tutorial review highlights the methods for the preparation of metal modified precursor derived ceramics (PDCs) and concentrates on the rare non-oxide systems enhanced with late transition metals. In addition to the main synthetic strategies for modified SiC and SiCN ceramics, an overview of the morphologies, structures and compositions of both, ceramic materials and metal (nano) particles, is presented. Potential magnetic and catalytic applications have been discussed for the so manufactured metal containing non-oxide ceramics. PMID:22337594

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

2012-08-01

100

Effect of transition metal oxides on mullite whisker formation from mechanochemically activated powders  

Microsoft Academic Search

The effect of transition metal oxides, including FeO1.5, CoO and NiO, on the phase formation and morphology development of mullite (3Al2O3·2SiO2) whiskers from oxide mixtures activated by the high-energy ball milling process, were investigated. With the addition of FeO1.5, the mullite formation temperature was almost the same as that required for the system of Al2O3 and SiO2 without doping, while

L. B. Kong; H. Huang; T. S. Zhang; Y. B. Gan; J. Ma; F. Boey; R. F. Zhang

2003-01-01

101

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

PubMed

A green, rapid microwave-assisted solvothermal process using tetraethylene glycol (TEG) as a reducing agent has been explored as a soft-chemistry route for the preparation of various lower-valent transition metal oxides. To demonstrate the feasibility of the approach, lower-valent binary oxides such as V4O9, Mn3O4 or MnO, CoO, and Cu2O have been obtained within a short reaction time of 30 min by reducing, respectively, V2O5, MnO2, Co3O4, and CuO with TEG at <300 °C. Moreover, the approach has been used to extract oxygen from ternary oxides such as LaFeO3, SrMnO3, LaCoO3, LaNiO3, and La4Ni3O10. The oxidation state of the transition metal ions and the oxygen content in these ternary oxides could be tuned by precisely controlling the reaction temperatures from 160 to 300 °C. The products have been characterized by X-ray powder diffraction and iodometric titration. The versatility of this novel technique is demonstrated by the facile synthesis of V4O9, which has only been produced recently in single-phase form. PMID:24191765

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

2013-11-18

102

Reduction of aqueous transition metal species on the surfaces of Fe(II)-containing oxides  

USGS Publications Warehouse

Experimental studies demonstrate that structural Fe(II) in magnetite and ilmenite heterogeneously reduce aqueous ferric, cupric, vanadate, and chromate ions at the oxide surfaces over a pH range of 1-7 at 25??C. For an aqueous transition metal m, such reactions are 3[Fe2+Fe3+2]O4(magnetite) + 2/nmz ??? 4[Fe3+2]O3(maghemite) + Fe2+ + 2/nmz-n and 3[Fe2+Ti]O3(ilmenite) + 2/nmz ??? Fe3+2Ti3O9(pseudorutile) + Fe2+ + 2/nmz-n, where z is the valance state and n is the charge transfer number. The half cell potential range for solid state oxidation [Fe(II)] ??? [Fe(III)] is -0.34 to -0.65 V, making structural Fe(II) a stronger reducing agent than aqueous Fe2+ (-0.77 V). Reduction rates for aqueous metal species are linear with time (up to 36 h), decrease with pH, and have rate constants between 0.1 and 3.3 ?? 10-10 mol m-2 s-1. Iron is released to solution both from the above reactions and from dissolution of the oxide surface. In the presence of chromate, Fe2+ is oxidized homogeneously in solution to Fe3+. X-ray photoelectron spectroscopy (XPS) denotes a Fe(III) oxide surface containing reduced Cr(III) and V(IV) species. Magnetite and ilmenite electrode potentials are insensitive to increases in divalent transition metals including Zn(II), Co(II), Mn(II), and Ni(II) and reduced V(IV) and Cr(III) but exhibit a log-linear concentration-potential response to Fe(III) and Cu(II). Complex positive electrode responses occur with increasing Cr(VI) and V(V) concentrations. Potential dynamic scans indicate that the high oxidation potential of dichromate is capable of suppressing the cathodic reductive dissolution of magnetite. Oxide electrode potentials are determined by the Fe(II)/Fe(III) composition of the oxide surface and respond to aqueous ion potentials which accelerate this oxidation process. Natural magnetite sands weathered under anoxic conditions are electrochemically reactive as demonstrated by rapid chromate reduction and the release of aqueous Fe(III) to experimental solution. In contrast, magnetite weathered under oxidizing vadose conditions show minimum reactivity toward chromate ions. The ability of Fe(II) oxides to reduce transition metals in soils and groundwaters will be strongly dependent on the redox environment.

White, A.F.; Peterson, M.L.

1996-01-01

103

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

Microsoft Academic Search

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

Hua-Jin Zhai; Lai-Sheng Wang

2010-01-01

104

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

NASA Astrophysics Data System (ADS)

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.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. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr05880h

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

2014-03-01

105

Oxygen vacancies in transition metal and rare earth oxides: Current state of understanding and remaining challenges  

NASA Astrophysics Data System (ADS)

Defects at transition metal (TM) and rare earth (RE) oxide surfaces, neutral oxygen vacancies in particular, play a major role in a variety of technological applications. This is the motivation of numerous studies of partially reduced oxide surfaces. We review, discuss, and compare theoretical data for structural and electronic properties and energetic quantities related to the formation of oxygen defects at TM and RE oxide surfaces using TiO 2, ZrO 2, V 2O 5, and CeO 2 as examples. Bulk defects, as far as relevant for comparison with the properties of reduced surfaces, are briefly reviewed. Special attention is given to the fate of the electrons left in the system upon vacancy formation and the ability of state-of-the-art quantum-mechanical methods to provide reliable energies and an accurate description of the electronic structure of the partially reduced oxide systems.

Ganduglia-Pirovano, M. Verónica; Hofmann, Alexander; Sauer, Joachim

2007-06-01

106

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

SciTech Connect

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.

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

2010-07-08

107

One- and two-photon absorption in transition metal oxide glasses  

SciTech Connect

Scaling of nonlinear two-photon absorption to optical bandgap (which describes the electronic structure of material) in transition metal glasses is given through a proposed empirical equation. A wide applicability of the relation is proven through the 21 studied glasses. The relationship between the calculated nonlinear absorption coefficient and the measured bandgap energy using Tauc's parabolic band model is discussed in terms of electronic structure of constituent oxides, ionic polarizability, hyperpolarizability of cations, nonbridging oxygen bonds, and the cationic bond-length approach.

El-Diasty, Fouad [Department of Physics, Faculty of Science, Ain Shams University, 11566 Cairo (Egypt); Abdel-Baki, Manal [Department of Glass, National Research Center, 12311 Cairo (Egypt)

2009-09-01

108

Variation of Some Physical Properties of Brownmillerite Doped with a Transition Metal Oxide  

Microsoft Academic Search

Cement clinker is the main component of Portland cement. It is composed of four main phases. One of them is the brownmillerite\\u000a or the ferrite phase of cement clinker. It is prepared according to the formula (4CaO)(Al2O3)(Fe2O3)1?x\\u000a (M)\\u000a x\\u000a , where M represents transition metal oxides (TMO): TiO2, Cr2O3, Mn2O3 and WO3, where x=1, 2, 3, 4 and 5 mol%.

M. Y. Hassaan; F. M. Ebrahim; S. H. Salah

2004-01-01

109

Variation of Some Physical Properties of Brownmillerite Doped with a Transition Metal Oxide  

Microsoft Academic Search

Cement clinker is the main component of Portland cement. It is composed of four main phases. One of them is the brownmillerite or the ferrite phase of cement clinker. It is prepared according to the formula (4CaO)(Al2O3)(Fe2O3)1-x (M) x , where M represents transition metal oxides (TMO): TiO2, Cr2O3, Mn2O3 and WO3, where x=1, 2, 3, 4 and 5 mol%.

M. Y. Hassaan; F. M. Ebrahim; S. H. Salah

2004-01-01

110

Spectroscopic Studies of Electronically Active Defects in Transition Metal Oxides for Advanced Si Devices  

SciTech Connect

Based on spectroscopic studies, and guided by ab initio theory, the electron and hole traps in HfO2 and other transition metal elemental oxides e.g., TiO2, are assigned to O-atom divacancies, clustered at internal grain boundaries. Engineering solutions for defect reduction are identified: (i) deposition of ultra-thin, < 2 nm HfO2 and phase separated Hf silicate dielectrics, in which grain boundary formation is suppressed by effectively eliminating inter-primitive unit cell {pi}-bonding interactions, and (ii) non-crystalline Zr/Hf Si oxynitrides without nanocrystalline grain boundaries.

Lucovsky, G.; Luning, J.

2009-06-04

111

Quantum spin Hall effect in a transition metal oxide Na2IrO3  

SciTech Connect

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.

Shitade, Atsuo

2010-05-26

112

Perovskite-type oxides - Oxygen electrocatalysis and bulk structure  

NASA Technical Reports Server (NTRS)

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.

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

1988-01-01

113

Redox activity of surface oxygen anions in oxygen-deficient perovskite oxides during electrochemical reactions.  

PubMed

Surface redox-active centres in transition-metal oxides play a key role in determining the efficacy of electrocatalysts. The extreme sensitivity of surface redox states to temperatures, to gas pressures and to electrochemical reaction conditions renders them difficult to investigate by conventional surface-science techniques. Here we report the direct observation of surface redox processes by surface-sensitive, operando X-ray absorption spectroscopy using thin-film iron and cobalt perovskite oxides as model electrodes for elevated-temperature oxygen incorporation and evolution reactions. In contrast to the conventional view that the transition metal cations are the dominant redox-active centres, we find that the oxygen anions near the surface are a significant redox partner to molecular oxygen due to the strong hybridization between oxygen 2p and transition metal 3d electronic states. We propose that a narrow electronic state of significant oxygen 2p character near the Fermi level exchanges electrons with the oxygen adsorbates. This result highlights the importance of surface anion-redox chemistry in oxygen-deficient transition-metal oxides. PMID:25598003

Mueller, David N; Machala, Michael L; Bluhm, Hendrik; Chueh, William C

2015-01-01

114

Out-of-Center Distortions in d0 Transition Metal Oxide Fluoride Anions Margaret E. Welk, Alexander J. Norquist,  

E-print Network

)x,pyridine (pyridinium poly(hydrogen fluoride), 70 wt % HF, Aldrich) were used as received. Reagent amounts of deionizedOut-of-Center Distortions in d0 Transition Metal Oxide Fluoride Anions Margaret E. Welk, Alexander oxide fluoride anions. Overlap between filled oxide p orbitals and vacant cation d orbitals results

Poeppelmeier, Kenneth R.

115

Electronic structure of mixed valence transition metal oxides Institute of Physics, Academy of Sciences of the Czech Republic,  

E-print Network

metals. Traditionally oxides were considered to be ionic compounds, in which the oxygen ions have fullyElectronic structure of mixed valence transition metal oxides P. Nov´ak1 1 Institute of Physics on a particular, yet broad and important class of these compounds - mixed valence oxides of the 3d transition

Tebbens, Jurjen Duintjer

116

Formation of transition layers at metal/perovskite oxide interfaces showing resistive switching behaviors  

NASA Astrophysics Data System (ADS)

The authors have investigated the chemical states at the interface of metal/perovskite oxides both with and without bipolar resistive switching (RS) behavior using photoemission spectroscopy and x-ray absorption spectroscopy. Al/Pr0.7Ca0.3MnO3 (PCMO), Al/La0.7Ca0.3MnO3 (LCMO), and Al/La0.33Sr0.67FeO3 interfaces were chosen as typical examples of interfaces for the perovskite-based resistance random access memory (ReRAM), while Pt/PCMO and Ag/LCMO were chosen as references for the metal/perovskite interface without RS behavior. Detailed analyses of spectroscopic data revealed that transition layers were formed at the interfaces showing RS behavior as a result of interfacial redox reactions between the Al electrodes and the transition metal ions in the oxides. On the other hand, for the interfaces that did not exhibit RS behavior, no chemical reaction occurred at the interface. The formation of the interfacial transition layer is naturally explained by considering the redox potential between the electrode materials and transition metal ions. These results suggest that a suitable combination of electrodes and oxides could be designed based on their redox potentials.

Yamamoto, T.; Yasuhara, R.; Ohkubo, I.; Kumigashira, H.; Oshima, M.

2011-09-01

117

Stoichiometry determined exchange interactions in amorphous ternary transition metal oxides: Theory and experiment  

SciTech Connect

Amorphous transition metal oxides exhibit exotic transport and magnetic properties, while the absence of periodic structure has long been a major obstacle for the understanding of their electronic structure and exchange interaction. In this paper, we have formulated a theoretical approach, which combines the melt-quench approach and the spin dynamic Monte-Carlo simulations, and based on it, we explored amorphous Co{sub 0.5}Zn{sub 0.5}O{sub 1?y} ternary transition metal oxides. Our theoretical results reveal that the microstructure, the magnetic properties, and the exchange interactions of Co{sub 0.5}Zn{sub 0.5}O{sub 1?y} are strongly determined by the oxygen stoichiometry. In the oxygen-deficient sample (y?>?0), we have observed the long-range ferromagnetic spin ordering which is associated with the non-stoichiometric cobalt-rich region rather than metallic clusters. On the other hand, the microstructure of stoichiometric sample takes the form of continuous random networks, and no long-range ferromagnetism has been observed in it. Magnetization characterization of experimental synthesized Co{sub 0.61}Zn{sub 0.39}O{sub 1?y} films verifies the relation between the spin ordering and the oxygen stoichiometry. Furthermore, the temperature dependence of electrical transport shows a typical feature of semiconductors, in agreement with our theoretical results.

Hu, Shu-jun; Yan, Shi-shen, E-mail: shishenyan@sdu.edu.cn; Zhang, Yun-peng; Zhao, Ming-wen; Kang, Shi-shou; Mei, Liang-mo [School of Physics, National Key Laboratory of Crystal Materials, Shandong University, Jinan, Shandong 250100 (China)

2014-07-28

118

Variation of Some Physical Properties of Brownmillerite Doped with a Transition Metal Oxide  

NASA Astrophysics Data System (ADS)

Cement clinker is the main component of Portland cement. It is composed of four main phases. One of them is the brownmillerite or the ferrite phase of cement clinker. It is prepared according to the formula (4CaO)(Al2O3)(Fe2O3)1-x (M) x , where M represents transition metal oxides (TMO): TiO2, Cr2O3, Mn2O3 and WO3, where x=1, 2, 3, 4 and 5 mol%. Each mixture was fired at 1300°C for 30 minutes in a platinum crucible. The samples were pulverized for Mössbauer spectroscopy, X-ray diffraction and a.c. conductivity measurements. A shift in the position of the characterized peaks of pure brownmillerite appears in the X-ray diffraction patterns of brownmillerite doped with a transition metal oxide. The a.c. conductivity showed a maximum value for the samples containing 3 mol% TiO2, Cr2O3 and Mn2O3, and 2 mol% WO3. The Mössbauer parameters for the sample containing 5 mol% M showed a gradual increase in the isomer shift values. The number of electrons in d-orbital for the doped transition atoms, as the nearest neighbor atoms increased from 2 to 5 electrons. The hyperfine magnetic field at Fe3+ (Oh) iron nucleus decreases with increasing M content. This may be due to the decrease of the particle size of brownmillerite.

Hassaan, M. Y.; Ebrahim, F. M.; Salah, S. H.

2004-12-01

119

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

120

Influence of d orbitals on the nonlinear optical response of transparent transition-metal oxides  

NASA Astrophysics Data System (ADS)

The bond-orbital theory of linear and nonlinear electronic response in optically transparent materials, developed earlier for pretransition-metal halides and chalcogenides, is expanded to embrace the transition-metal (TM) oxides. The extension requires an explicit recognition of the influence of cationic empty d orbitals on electronic polarizability. Two competing mechanisms, involving, respectively, virtual electronic excitations to the d orbitals and to the conduction-band ``sp orbitals,'' are shown to be essentially additive for linear polarizability ?(1) and lowest-order nonlinear polarizability ?(2), but not for ?(3). The d-orbital contributions to linear and nonlinear response are found to be negligible for bond lengths d>~2.3 Å, but to increase rapidly as a function of decreasing bond length within each TM series to become dominant when d<~2.0 Å. Numerical evaluations of nonlinear refractive index n2 are presented for each series of TM oxides.

Lines, M. E.

1991-05-01

121

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

E-print Network

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

Napp, Nils

122

Band-structure calculations for the 3d transition metal oxides in GW  

NASA Astrophysics Data System (ADS)

Many-body GW calculations have emerged as a standard for the prediction of band gaps, band structures, and optical properties for main-group semiconductors and insulators, but it is not well established how predictive the GW method is in general for transition metal (TM) compounds. Surveying the series of 3d oxides within a typical GW approach using the random-phase approximation reveals mixed results, including cases where the calculated band gap is either too small or too large, depending on the oxidation states of the TM (e.g., FeO/Fe2O3, Cu2O/CuO). The problem appears to originate mostly from a too high average d-orbital energy, whereas the splitting between occupied and unoccupied d symmetries seems to be reasonably accurate. It is shown that augmenting the GW self-energy by an attractive (negative) and occupation-independent on-site potential for the TM d orbitals with a single parameter per TM cation can reconcile the band gaps for different oxide stoichiometries and TM oxidation states. In Cu2O, which is considered here in more detail, standard GW based on wave functions from initial density or hybrid functional calculations yields an unphysical prediction with an incorrect ordering of the conduction bands, even when the magnitude of the band gap is in apparent agreement with experiment. The correct band ordering is restored either by applying the d-state potential or by iterating the wave functions to self-consistency, which both have the effect of lowering the Cu-d orbital energy. While it remains to be determined which improvements over standard GW implementations are needed to achieve an accurate ab initio description for a wide range of transition metal compounds, the application of the empirical on-site potential serves to mitigate the problems specifically related to d states in GW calculations.

Lany, Stephan

2013-02-01

123

Synthesis of new transition metal nitrides using solid state oxide precursors: Structures and properties  

SciTech Connect

Solid state nitrides are of interest because they exhibit technologically useful properties. For example, some transition metal nitrides are extremely hard and strong, yet are good conductors of heat and electricity. Others show interesting catalytic properties and the similarity between nitrides and Group VIII metals has been pointed out. Despite the potential technological importance of these materials, only a relatively small number are known. This talk will present some recent developments in ternary nitride synthesis and discuss the preparation and characterization of series of new ternary transition metal nitrides (FeWN{sub 2}, Ta{sub 5}N{sub 6}, Nb{sub 5}N{sub 6}, MnMoN{sub 2}, {alpha}- and {beta}-MnWN{sub 2}) from oxide precursors. The electronic properties and the structures of these nitrides, which were determined by powder X-ray and powder neutron Rietveld refinement, will be discussed. These structures, although distinct, share common motifs, such as layers of MN{sub 6} trigonal prisms and layers of MN{sub 6} octahedra.

Loye, H.C. zur; Bem, D.S.; Houmes, J.D. [Massachusetts Institute of Technology, Cambridge, MA (United States)

1995-12-31

124

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

NASA Astrophysics Data System (ADS)

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.

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

2013-01-01

125

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

SciTech Connect

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

Scalettar, Richard T.; Pickett, Warren E.

2004-07-01

126

Energetics of perovskite-type materials applied in solid oxide fuel cells (SOFCs): Electrolytes, cathodes and interconnects  

NASA Astrophysics Data System (ADS)

Perovskite-type oxides (ABO3) find a great variety of applications in solid oxide fuel cells (SOFCs), including solid electrolytes, cathodes and interconnects, which are closely related to the defect chemistry involved. Thermodynamic studies are needed to systematically understand the nature of the structure-property relations and provide guidance to predict and/or select proper materials. High temperature solution calorimetry in molten oxide solvents is a powerful tool and has been applied for several perovskite systems that have simple (undoped) and complex (doped) compositions. LaBO3 perovskites (B = Al, Ga, Sc, In, Cr, Fe, Co, Ni) represent a group of excellent parent materials for electrolytes, cathodes, and interconnects in SOFCs. Their enthalpies of formation from oxides generally exhibit a relationship between stability and the major structural parameter for perovskites, the tolerance factor. As the tolerance factor deviates more from unity, the enthalpy of formation from oxides becomes less exothermic. This work verifies this general trend for A3+B3+O3 type perovskites, joining other two types, i.e., A1+B5+O 3 and A2+B4+O3. In alkaline earth doped perovskites, though structural parameters are likely to continue affecting stability, defects, which are introduced upon doping, actually play a more profound role in defining energetic trends. In the newly developed electrolyte materials, Mg, Sr, and Ba-doped LaGaO 3 perovskites, oxygen vacancies are created to compensate the charge imbalance between dopant and host ions. Oxygen vacancies have a destabilization effect on the structure due to the partial disconnection of the corner-shared BO6 octahedral framework. On the other hand, they tend to order at the short-range scale, forming vacancy-dopant clusters, as evidenced by neutron diffraction. In alkaline earth doped perovskites that contain transition metals, two charge compensation scenarios are possible: oxidation of the transition metal or creation of oxygen vacancies, which strongly depend on the oxygen partial pressure and temperature. Major defects are dopants, oxygen vacancies and electron holes. La1-xSrxFeO3-delta (cathode materials) and La1-x-AxCrO 3-delta (A = Ca or Sr) (interconnect materials) were chosen for study. The overall energetic trends in these complex perovskites are modeled by several competing factors: (1) the chemical nature of dopant ions (acidity/basicity), (2) coupled substitution involving oxygen vacancy formation, (3) redox of the transition metal in each sample series with a given dopant composition, and (4) short-range oxygen vacancy ordering in oxygen-deficient samples.

Cheng, Jihong

127

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

NASA Astrophysics Data System (ADS)

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.

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

2015-03-01

128

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

PubMed

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. PMID:25770507

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

2015-03-14

129

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

SciTech Connect

Perovskite transition-metal oxides are networks of corner-sharing octahedra whose tilts and distortions are known to affect their electronic and magnetic properties. We report calculations on a model interfacial structure which avoids chemical influences and show that the symmetry mismatch imposes an interfacial layer with distortion modes that do not exist in either bulk material, creating new interface properties driven by symmetry alone. Depending on the resistance of the octahedra to deformation, the interface layer can be as small as one unit cell or extend deep into the thin film.

He, Jun [ORNL; Borisevich, Albina Y [ORNL; Kalinin, Sergei V [ORNL; Pennycook, Stephen J [ORNL; Pantelides, Sokrates T [ORNL

2010-01-01

130

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

NASA Astrophysics Data System (ADS)

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.

Shih, Bi-Ching; Zhang, Peihong

2011-03-01

131

Quantum Monte Carlo study of ground state properties of transition metal oxides  

NASA Astrophysics Data System (ADS)

We apply a recently developed quantum Monte Carlo method ( S. Zhang and H. Krakauer, Phys. Rev. Lett. 90, 126401 (2003).) to study the transition metal oxides TiO and MnO. Starting from a trial wavefunction, this method uses much of the same machinery of density functional methods (single particle basis, non-local pseudopotentials) to project the system ground state by random walks in the space of Slater determinants, using auxiliary Hubbard-Stratonovich complex fields. The trial wave function, which is used to control the phase/sign problem, is a single Slater determinant generated using a density functional or Hartree-Fock type calculation. Our preliminary results as well as previous results show the robustness of this method for studying atoms, molecules, and solids. (Supported by ONR and NSF)

Al-Saidi, Wissam; Krakauer, Henry; Zhang, Shiwei

2004-03-01

132

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

NASA Technical Reports Server (NTRS)

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.

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

1992-01-01

133

Spectroscopic Studies of O-Vacancy Defects in Transition Metal Oxides  

SciTech Connect

Dielectrics comprised of nano-crystalline HfO{sub 2} in gate stacks with thin SiO{sub 2}/SiON interfacial transition regions display significant asymmetries with respect to trapping of Si substrate injected holes and electrons. Based on spectroscopic studies, and guided by ab initio theory, electron and hole traps in HfO{sub 2} and other transition metal elemental oxides are assigned to O-atom divacancies clustered at internal grain boundaries of nano-crystalline films. Engineering solutions in which grain boundary defects are suppressed include: (i) ultra-thin, <2 nm, HfO{sub 2} fims, (ii) chemically phase separated high HfO2 content silicate films, and (iii) non-crystalline Zr/Hf Si oxynitride films.

Lucovsky, G.; Luning, J.; Fleming, L.B.; Ulrich, M.D.; Rowe, J.E.; Seo, H.; Lee, S.; Lysaght, P.; Bersuker, G.

2009-06-03

134

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

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

Lin, Xi

135

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

SciTech Connect

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.

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

2013-09-01

136

Photocatalytic overall water splitting on the perovskite-type transition metal oxynitride CaTaO2N under visible light irradiation.  

PubMed

Overall water splitting was achieved on a simple perovskite oxynitride photocatalyst, CaTaO2N, with an absorption edge at 510 nm. This photocatalyst, modified with a Rh-Cr bimetallic oxide cocatalyst, produced stoichiometric H2 and O2 steadily under UV and visible light irradiation after coating of the photocatalyst particles with amorphous Ti oxyhydroxide. PMID:25812174

Xu, Jiasheng; Pan, Chengsi; Takata, Tsuyoshi; Domen, Kazunari

2015-04-01

137

Transition metal-catalyzed oxidation of atmospheric sulfur: Global implications for the sulfur budget  

NASA Astrophysics Data System (ADS)

We use observations of the oxygen-17 excess (?17O) of sulfate in the Arctic to quantify the sulfate source from aqueous SO2 (S(IV)) oxidation by O2 catalyzed by transition metals. Due to the lack of photochemically produced OH and H2O2 in high latitudes during winter, combined with high anthropogenic SO2 emissions in the Northern Hemisphere, oxidation by O3 is predicted to dominate sulfate formation during winter in this region. However, ?17O measurements of sulfate aerosol collected in Alert, Canada, are not consistent with O3 as the dominant oxidant and indicate that a S(IV) oxidant with near-zero ?17O values (O2) is important during winter. We use a global chemical transport model to interpret quantitatively the Alert observations and assess the global importance of sulfate production by Fe(III)- and Mn(II)-catalyzed oxidation of S(IV) by O2. We scale anthropogenic and natural atmospheric metal concentrations to primary anthropogenic sulfate and dust concentrations, respectively. The solubility and oxidation state of these metals is determined by cloud liquid water content, source, and sunlight. By including metal-catalyzed S(IV) oxidation, the model is consistent with the ?17O magnitudes in the Alert data during winter. Globally, we find that this mechanism contributes 9-17% to sulfate production. The inclusion of metal-catalyzed oxidation does not resolve model discrepancies with surface SO2 and sulfate observations in Europe. Oxygen isotope measurements of sulfate aerosols collected near anthropogenic and dust sources of metals would help to verify the importance of this sulfur oxidation pathway.

Alexander, Becky; Park, Rokjin J.; Jacob, Daniel J.; Gong, Sunling

2009-01-01

138

Transition metal oxides for organic electronics: energetics, device physics and applications.  

PubMed

During the last few years, transition metal oxides (TMO) such as molybdenum tri-oxide (MoO(3) ), vanadium pent-oxide (V(2) O(5) ) or tungsten tri-oxide (WO(3) ) have been extensively studied because of their exceptional electronic properties for charge injection and extraction in organic electronic devices. These unique properties have led to the performance enhancement of several types of devices and to a variety of novel applications. TMOs have been used to realize efficient and long-term stable p-type doping of wide band gap organic materials, charge-generation junctions for stacked organic light emitting diodes (OLED), sputtering buffer layers for semi-transparent devices, and organic photovoltaic (OPV) cells with improved charge extraction, enhanced power conversion efficiency and substantially improved long term stability. Energetics in general play a key role in advancing device structure and performance in organic electronics; however, the literature provides a very inconsistent picture of the electronic structure of TMOs and the resulting interpretation of their role as functional constituents in organic electronics. With this review we intend to clarify some of the existing misconceptions. An overview of TMO-based device architectures ranging from transparent OLEDs to tandem OPV cells is also given. Various TMO film deposition methods are reviewed, addressing vacuum evaporation and recent approaches for solution-based processing. The specific properties of the resulting materials and their role as functional layers in organic devices are discussed. PMID:22945550

Meyer, Jens; Hamwi, Sami; Kröger, Michael; Kowalsky, Wolfgang; Riedl, Thomas; Kahn, Antoine

2012-10-23

139

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

E-print Network

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 ...

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

2014-01-01

140

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

SciTech Connect

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.

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

2011-10-25

141

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

SciTech Connect

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}.

Das, Supriyo

2010-05-16

142

Realizing a family of transition-metal-oxide memristors based on volatile resistive switching at a rectifying metal/oxide interface  

NASA Astrophysics Data System (ADS)

There is strong interest in creating new memristors due to their significant impact in many fields including digital information systems, analogue circuits and artificial neural networks as a new class of fundamental electronic elements. Here we report a volatile resistive switching effect at a prototypical Schottky metal/oxide interface and realize a family of transition-metal-oxide memristors showing distinct hysteresis characteristics based on the interface. The results not only provide further understanding on the electrical behaviour of metal/oxide interfaces but also indicate the key role of metal/oxide interfaces as basic building blocks in transition-metal-oxide memristors.

Yang, M.; Qin, N.; Ren, L. Z.; Wang, Y. J.; Yang, K. G.; Yu, F. M.; Zhou, W. Q.; Meng, M.; Wu, S. X.; Bao, D. H.; Li, S. W.

2014-01-01

143

Influence of the negative oxygen ions on the structure evolution of transition metal oxide thin films  

NASA Astrophysics Data System (ADS)

The energy distributions of O- ions of magnetron sputtered Nb, Ta, Zr, and Hf in an Ar /O2 atmosphere were measured as a function of the oxygen partial pressure. Three ion populations were detected in the plasma: high, medium, and low energy ions, with energies corresponding to the target potential, half of the target potential, and <150eV, respectively. The ion energy distribution functions were compared to distributions obtained based on Sigmund's linear collision cascade sputtering theory. If the surface binding energy is assumed to be equal to the heat of formation, good agreement between the experiment and theory was achieved. From correlating the measured ion energy distributions with previously published phase stability data [Ngaruiya et al., Appl. Phys. Lett. 85, 748 (2004)], it can be deduced that large fluxes of medium and high energy O- ions comparable to the fluxes of the low energy O- ions enable formation of crystalline transition metal oxide thin films during low temperature growth. The presented data here may be of general relevance for understanding the structure evolution of thin oxide films.

Mráz, Stanislav; Schneider, Jochen M.

2006-07-01

144

Multi-orbital subband structure of transition-metal oxide 2DEGs  

NASA Astrophysics Data System (ADS)

We demonstrate the creation and control of two-dimensional electron gases (2DEGs) in the 3d and 5d transition metal oxides SrTiO3 and KTaO3. These 2DEGs, of the form usually generated by interface engineering, are created here at the bare oxide surfaces. This permits their detailed spectroscopic investigation using angle-resolved photoemission (ARPES), and we employ this to directly image the d-orbital subband structure of the 2DEGs. We find that quantum confinement lifts the degeneracy of the bulk band structure, driving orbital ordering of the 2DEG. We measure the resulting ladder of light dxy subbands, which co-exist at lower binding energies with heavy dxz/yz-derived states. The electronic structure revealed by ARPES is in quantitative agreement with our model tight-binding calculations. While the strong spin-orbit coupling of KTaO3 promotes substantial orbital mixing, our calculations predict only a small Rashba splitting of the 2DEG states, consistent with our experimental measurements where any spin splitting is too small to be resolved. The polar nature of the KTaO3(100) surface plays a striking role in mediating formation of the 2DEG as compared to non-polar SrTiO3(100), reminiscent of the polar catastrophe at LaAlO3/SrTiO3 interfaces.

King, Phil D. C.; Meevasana, W.; Hwang, H. Y.; Shen, Z.-X.; Baumberger, F.

2012-02-01

145

Control method for transition metal oxides as a hole-injection layer for organic light-emitting devices  

NASA Astrophysics Data System (ADS)

The mechanism of transition metal oxide, molybdenum oxide (MoOx), used as interlayers in organic light-emitting devices (OLEDs) are investigated. The electronic structures and interfacial chemical reactions are investigated with ultraviolet and x-ray photoelectron spectroscopy. The influence of evaporation temperatures on the electronic structures of MoOx films and the electrical properties of organic light emitting diodes are investigated.

Zhang, Wejiang; Zhang, Jie

2013-12-01

146

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

Microsoft Academic Search

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

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

2008-01-01

147

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

SciTech Connect

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

Lai-Sheng Wang

2009-07-07

148

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

SciTech Connect

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.

Kellar, S.A. [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry; [Lawrence Berkeley National Lab., CA (United States). Advanced Light Source Div.

1997-05-01

149

Density functional theory study of CO2 capture with transition metal oxides and hydroxides  

NASA Astrophysics Data System (ADS)

We have used density functional theory (DFT) employing several different exchange-correlation functionals (PW91, PBE, PBEsol, TPSS, and revTPSS) coupled with lattice dynamics calculations to compute the thermodynamics of CO2 absorption/desorption reactions for selected transition metal oxides, (TMO), and hydroxides, TM(OH)2, where TM = Mn, Ni, Zn, and Cd. The van't Hoff plots, which describe the reaction equilibrium as a function of the partial pressures of CO2 and H2O as well as temperature, were computed from DFT total energies, complemented by the free energy contribution of solids and gases from lattice dynamics and statistical mechanics, respectively. We find that the PBEsol functional calculations are generally in better agreement with experimental phase equilibrium data compared with the other functionals we tested. In contrast, the formation enthalpies of the compounds are better computed with the TPSS and revTPSS functionals. The PBEsol functional gives better equilibrium properties due to a partial cancellation of errors in the enthalpies of formation. We have identified all CO2 capture reactions that lie on the Gibbs free energy convex hull as a function of temperature and the partial pressures of CO2 and H2O for all TMO and TM(OH)2 systems studied here.

Zhang, Bo; Duan, Yuhua; Johnson, Karl

2012-02-01

150

Microscopic magnetic nature of K2NiF4-type 3d transition metal oxides  

NASA Astrophysics Data System (ADS)

In order to elucidate the magnetic nature of K2NiF4-type 3d transition metal oxides, we have measured ?+SR spectra for Sr2VO4, LaSrVO4, and Sr2CrO4 using powder samples. ZF- and wTF-?+SR measurements propose that Sr2VO4 enters into the static antiferromagnetic (AF) order phase below 8 K. In addition, TF-?+SR measurements evidence that the transition at 105 K is not magnetic but structural and/or electronic in origin. For LaSrVO4, static long-range order has not been observed down to 20 K, while, as T decreases from 145 K, wTF asymmetry starts to decrease below 60 K, suggesting the appearance and evolution of localized magnetic moments below 60 K. For Sr2CrO4, by contrast, both ZF- and wTF-?+SR have confirmed the presence of antiferromagnetic order below 117 K, as predicted in the ?(T) curve.

Sugiyama, J.; Nozaki, H.; Umegaki, I.; Higemoto, W.; Ansaldo, E. J.; Brewer, J. H.; Sakurai, H.; Kao, T.-H.; Yang, H.-D.; Månsson, M.

2014-12-01

151

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

SciTech Connect

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

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

2007-05-20

152

Improved layered mixed transition metal oxides for Li-ion batteries  

SciTech Connect

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.

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

2010-03-05

153

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

PubMed

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

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

2015-03-11

154

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

NASA Astrophysics Data System (ADS)

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:Alq3/MoO3 and MoO3 composed devices, which was induced by the charge spouting zone near the ICs region and the recombination state in the MoO3 layer. Moreover, Mg:Alq3/MoO3 composed device displays a photovoltaic effect and the Voc 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.

Deng, Yan-Hong; Chen, Xiang-Yu; Ou, Qing-Dong; Wang, Qian-Kun; Jiang, Xiao-Cheng; Zhang, Dan-Dan; Li, Yan-Qing

2014-06-01

155

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

SciTech Connect

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.

Deng, Yan-Hong; Chen, Xiang-Yu, E-mail: yqli@suda.edu.cn, E-mail: xychen@suda.edu.cn; Ou, Qing-Dong; Wang, Qian-Kun; Jiang, Xiao-Cheng; Zhang, Dan-Dan; Li, Yan-Qing, E-mail: yqli@suda.edu.cn, E-mail: xychen@suda.edu.cn [Jiangsu Key Laboratory for Carbon-Based Functional Materials and Devices, Institute of Functional Nano and Soft Materials (FUNSOM), Soochow University, Suzhou 215123 (China)

2014-06-02

156

The growth and analysis of transition metal oxide superlattices using advanced magnetometry techniques  

NASA Astrophysics Data System (ADS)

Magnetic superlattices are the subject of increasing interest in the condensed matter community due to the consequences that arise from their reduced dimensionality. Such aspects make these superlattices useful in various electronic applications. High quality films of transition metal oxides SrRuO3 and SrMnO3, were grown by pulsed laser deposition (PLD) method in order to gain a further understanding of the parameters that determine the magnetic properties of such films. X-ray reflectivity was used to verify film thickness and quality, while the magnetic properties of the film and of the individual layers were probed using a superconducting quantum interference device (SQUID) and x-ray magnetic circular dichroism (XMCD). Some of the effects observed were expected, including enhanced coercivity, but others were more unexpected, such as anti-ferromagnetic coupling between thin layers of SrMnO3 and SrRuO3. This coupling was conspicuously absent in samples with thicker SrMnO3 layers. These results serve to further illuminate the basic properties of ferromagnetic/anti-ferromagnetic multilayers and have brought us closer to being able to individually manipulate the magnetic properties of such systems.

Danaher, David J.

157

Spin-phonon coupling effects in transition-metal perovskites: A DFT + U and hybrid-functional study  

NASA Astrophysics Data System (ADS)

Spin-phonon coupling effects, as reflected in phonon frequency shifts between ferromagnetic (FM) and G-type antiferromagnetic (AFM) configurations in cubic CaMnO3, SrMnO3, BaMnO3, LaCrO3, LaFeO3, and La2(CrFe)O6, are investigated using density-functional methods. The calculations are carried out both with a hybrid-functional Heyd-Scuseria-Ernzerhof (HSE) approach and with a DFT + U approach using a U that has been fitted to HSE calculations. The phonon frequency shifts obtained in going from the FM to the AFM spin configuration agree well with those computed directly from the more accurate HSE approach, but are obtained with much less computational effort. We find that in the AMnO3 materials class with A= Ca, Sr, and Ba, this frequency shift decreases as the A cation radius increases for the ? phonons, while it increases for R-point phonons. In LaMO3 with M= Cr, Fe, and Cr/Fe, the phonon frequencies at ? decrease as the spin order changes from AFM to FM for LaCrO3 and LaFeO3, but they increase for the double perovskite La2(CrFe)O6. We discuss these results and the prospects for bulk and superlattice forms of these materials to be useful as multiferroics.

Hong, Jiawang; Stroppa, Alessandro; Íñiguez, Jorge; Picozzi, Silvia; Vanderbilt, David

2012-02-01

158

Transition metal oxides - CrO, MoO, NiO, PdO, AgO  

NASA Technical Reports Server (NTRS)

The transition-metal oxides are quite ionic; Mulliken population analyses for several oxides give a negative charge of about 0.7 electrons for oxygen. When the transition-metal d shell is only partially filled, the orbitals are involved in covalent bonds with O; both two-electron bonding (2)-antibonding (0) and one-electron bonding (2)-antibonding (1) bonds are formed. These covalent bonds occur in addition to the ionic bonding. There is d-sigma-O2 p sigma repulsion, and this repulsion is reduced when the d-sigma electron is promoted into an orbital which has dominantly 4sp-sigma character and is polarized away from O.

Bauschlicher, C. W., Jr.; Nelin, C. J.; Bagus, P. S.

1985-01-01

159

Perovskite LaRhO3 as a p-type active layer in oxide photovoltaics  

NASA Astrophysics Data System (ADS)

Perovskite-type transition-metal oxides have a wide variety of physical properties and triggered intensive research on functional devices in the form of heteroepitaxial junctions. However, there is a missing component that is a p-type conventional band semiconductor. LaRhO3 (LRO) is one of very few promising candidates having its bandgap between filled t2g and empty eg of Rh in low-spin state, but there has been no report on the synthesis of large-size single crystals or thin films. Here, we report on the junction properties of single-crystalline thin films of LRO grown on (110) oriented Nb-doped SrTiO3 substrates. The external quantum efficiency of the photo-electron conversion exceeds 1% in the visible-light region due to the wide depletion layer and long diffusion length of minority carriers in LRO. Clear indication of p-type band semiconducting character in a perovskite oxide of LRO will pave a way to explore oxide electronics of perovskite heterostructures.

Nakamura, Masao; Krockenberger, Yoshiharu; Fujioka, Jun; Kawasaki, Masashi; Tokura, Yoshinori

2015-02-01

160

The Kinetic Studies of Elimination of HCl During Thermal Decomposition of PVC in the Presence of Transition Metal Oxides  

Microsoft Academic Search

The effects of nine kinds of transition metal oxides on the elimination kinetics of hydrogen chloride (HCl) during thermal decomposition of polyvinyl chloride (PVC) at 210°C were investigated using online measurement of conductivity. It was found that the presence of TiO2, V2O5, Cr2O3, and MoO3 obviously decreases the elimination rate of HCl and the amount of HCl released by a

Hong Pi; Ying Xiong; Shaoyun Guo

2005-01-01

161

Synthesis of the New Ternary Transition Metal Nitride FeWN 2 via Ammonolysis of a Solid State Oxide Precursor  

NASA Astrophysics Data System (ADS)

A new ternary nitride, FeWN 2, was prepared via ammonolysis of the solid state oxide precursor FeWO 4 at 800°C. The powder diffraction data were indexed as a hexagonal structure with lattice parameters a = 2.867(2) Å and c = 16.458(9) Å. The successful preparation of FeWN 2 demonstrates that the inductive effect is not necessary for preparing some ternary transition metal nitrides.

Bem, David S.; Loye, Hans-Conrad Zur

1993-06-01

162

Negative ion photoelectron spectroscopy of alkyl peroxides, alkoxides, and group VIII transition metal oxides  

NASA Astrophysics Data System (ADS)

I employed negative ion photoelectron spectroscopy to investigate the structure and energetics of three groups of anions and their corresponding neutrals: alkyl peroxides ROO-, (R = H, D, CH3, CD3, and CH3CH2); alkoxides RO- (R=CH3, CD3, CH3CH2, CD3CD2, (CH3)2CH, and (CH 3)3C); and Group VIII transition metal oxides XO- and OXO- (X = Ni, Pd, Pt). The peroxides and the alkoxides are of great interest to those who study atmospheric or combustion chemistry, while the metal oxides play an important role in catalysis reactions. However, each of these groups of molecules displays interesting behavior that is itself a motivation for their investigation. The spectra of HOO- and DOO- are relatively straightforward to analyze and understand and provide a good basis from which to compare the larger alkyl peroxides. The ROO- spectra exhibit the normal Franck-Condon behavior leading to clear assignments of the expected vibrational progressions in both the ground and first excited state of the neutral species. Although the molecules increase in size from HOO to CH3CH2OO, many of the spectral characteristics such as electron affinity (EA) and prominence of the O-O stretch vibration do not appreciably change. The EA of HOO is revised, which becomes important as part of a newly revised thermochemistry of HOO and HOOH. The RO- species exhibit an additional layer of complexity. Both the CH3O- and (CH3)3 CO- molecules possess relatively high C3v , symmetry about the CO axis as well as a doubly degenerate ground electronic state of the neutral RO molecule. Both of these elements are expected to produce a Jahn-Teller effect, where in order to break the molecular symmetry and electronic state degeneracy, the Born-Oppenheimer approximation breaks down and nuclear and electronic wavefunctions become coupled. The extent to which Jahn-Teller effects affect the RO molecule photoelectron spectra is discussed. Although the transition metal monoxides are diatomics and thus perhaps presumed to be uncomplicated molecules, they are the most difficult to understand in this thesis and the most difficult to obtain in the laboratory. The d orbitals of the metals are closely spaced together, leading to congested spectra and mixing of the properties of orbitals that complicates analysis and ab initio calculations. Furthermore, the high nuclear charge of the atoms involved leads to non-negligible spin-orbit and other relativistic effects. Perhaps for these reasons there is relatively little information in the literature on these molecules. However, despite the complexities involved, comparison of all three metal molecules has allowed for a consistent interpretation of the spectra. Assignments are made including electron affinities, spin-orbit excited states of both anion and neutral XO molecules, other excited electronic states of anion and neutral, and vibrational frequencies and bond length changes. Analysis of the OXO molecules yields electron affinities, vibrational frequencies, and anion to neutral geometry changes.

Ramond, Tanya Michelle

163

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

NASA Astrophysics Data System (ADS)

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

Wang, Xin

2012-02-01

164

Scanning Tunneling Spectroscopy Studies of Transition Metal Oxides and Spin Light Emitting Diode Studies  

NASA Astrophysics Data System (ADS)

Studies of three transition metal oxide (TMO) materials and two types of spin light emitting diodes (LEDs) are contained in this dissertation. The studies of the samples processed into spin LEDs contained herein were all grown with molecular beam epitaxy (MBE), and utilize the same spin injector material, manganese arsenide (MnAs). We have demonstrated that MnAs is an efficient spin injector of spin polarized electrons into gallium arsenide (GaAs) and indium arsenide (InAs). It has also been shown that annealing MnAs grown on GaAs does not cause Mn ions to diffuse into GaAs; such diffusion would be detrimental to spin injection. A scanning tunneling spectroscopy (STS) modulation bias technique was used to examine and spatially map the local density of states (LDOS) of the surfaces of these TMOs with sub-nanometer resolution. Two of the TMO materials have possible photovoltaic/photocatalytic applications, while the other undergoes a metal-insulator transition (MIT) and is a promising material for high-speed field effect transistors. The distributions of energy gaps measured across the surface of the two solar materials were found to be consistent with their respective absorption measurements. This confirms that the utilization of the successful co-doping scheme/alteration of the growth parameters effectively reduced the energy gaps thereby increasing the solar efficiency of these materials. Also, the electronic structure of an intermediate metallic phase was measured with STS for the first time to our knowledge in the MIT TMO material examined herein.

Hatch, John B.

165

VOLUME 78, NUMBER 3 P H Y S I C A L R E V I E W L E T T E R S 20 JANURY 1997 Dramatic Switching of Magnetic Exchange in a Classic Transition Metal Oxide  

E-print Network

of Magnetic Exchange in a Classic Transition Metal Oxide: Evidence for Orbital Ordering Wei Bao,1,2 C. Broholm ingredi- ents for explanations of many curious phenomena in solids, most notably the transition metal insulating phases of the classic transition metal oxide V2O3. The switching is most naturally explained

Broholm, Collin Leslie

166

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

NASA Astrophysics Data System (ADS)

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.

Trotochaud, Lena

167

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

NASA Astrophysics Data System (ADS)

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

Zhai, Hua-Jin; Wang, Lai-Sheng

2010-11-01

168

Generalized trends in the formation energies of perovskite oxides.  

PubMed

Generalized trends in the formation energies of several families of perovskite oxides (ABO3) and plausible explanations to their existence are provided in this study through a combination of DFT calculations, solid-state physics analyses and simple physical/chemical descriptors. The studied elements at the A site of perovskites comprise rare-earth, alkaline-earth and alkaline metals, whereas 3d and 5d metals were studied at the B site. We also include ReO3-type compounds, which have the same crystal structure of cubic ABO3 perovskites except without A-site elements. From the observations we extract the following four conclusions for the perovskites studied in the present paper: for a given cation at the B site, (I) perovskites with cations of identical oxidation state at the A site possess close formation energies; and (II) perovskites with cations of different oxidation states at the A site usually have quite different but ordered formation energies. On the other hand, for a given A-site cation, (III) the formation energies of perovskites vary linearly with respect to the atomic number of the elements at the B site within the same period of the periodic table, and the slopes depend systematically on the oxidation state of the A-site cation; and (IV) the trends in formation energies of perovskites with elements from different periods at the B site depend on the oxidation state of A-site cations. Since the energetics of perovskites is shown to be the superposition of the individual contributions of their constituent oxides, the trends can be rationalized in terms of A-O and B-O interactions in the ionic crystal. These findings reveal the existence of general systematic trends in the formation energies of perovskites and provide further insight into the role of ion-ion interactions in the properties of ternary compounds. PMID:23579382

Zeng, ZhenHua; Calle-Vallejo, Federico; Mogensen, Mogens B; Rossmeisl, Jan

2013-05-28

169

Solventless oxidative coupling of amines to imines by using transition-metal-free metal-organic frameworks.  

PubMed

A highly efficient, simple, and versatile transition-metal-free metal-organic framework catalytic system is proposed for the oxidative coupling of amines to imines. The catalytic protocol features high activities and selectivities to target products; compatibility with a variety of substrates, including aliphatic amines and secondary amines; and the possibility to efficiently and selectively promote amine cross-coupling reactions. A high stability and recyclability of the catalyst is also observed under the investigated conditions. Insights into the reaction mechanism indicate the formation of a superoxide species able to efficiently promote oxidative couplings. PMID:24801486

Qiu, Xuan; Len, Christophe; Luque, Rafael; Li, Yingwei

2014-06-01

170

A study of bond-length fluctuations in transition metal oxides  

NASA Astrophysics Data System (ADS)

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.

Yan, Jiaqiang

171

Artificial layered perovskite oxides A(B0.5B'0.5)O3 as potential solar energy conversion materials  

NASA Astrophysics Data System (ADS)

Perovskite oxides with a d0 electronic configuration are promising photocatalysts and exhibit high electron mobilities. However, their band gaps are too large for efficient solar energy conversion. On the other hand, transition metal cations with partially filled dn electronic configurations give rise to visible light absorption. In this study, by using hybrid density functional theory calculations, it is demonstrated that the virtues of the two categories of materials can be combined in perovskite oxide A(B0.5B'0.5)O3 with a layered B-site ordering along the [001] direction. The electronic structures of the four selected perovskite oxide compounds, La(Ti0.5Ni0.5)O3, La(Ti0.5Zn0.5)O3, Sr(Nb0.5Cr0.5)O3, and Sr(Nb0.5Fe0.5)O3 are calculated and discussed.

Chen, Hungru; Umezawa, Naoto

2015-02-01

172

Topological Oxide Insulator in Cubic Perovskite Structure  

PubMed Central

The emergence of topologically protected conducting states with the chiral spin texture is the most prominent feature at the surface of topological insulators. On the application side, large band gap and high resistivity to distinguish surface from bulk degrees of freedom should be guaranteed for the full usage of the surface states. Here, we suggest that the oxide cubic perovskite YBiO3, more than just an oxide, defines itself as a new three-dimensional topological insulator exhibiting both a large bulk band gap and a high resistivity. Based on first-principles calculations varying the spin-orbit coupling strength, the non-trivial band topology of YBiO3 is investigated, where the spin-orbit coupling of the Bi 6p orbital plays a crucial role. Taking the exquisite synthesis techniques in oxide electronics into account, YBiO3 can also be used to provide various interface configurations hosting exotic topological phenomena combined with other quantum phases. PMID:23575973

Jin, Hosub; Rhim, Sonny H.; Im, Jino; Freeman, Arthur J.

2013-01-01

173

Experimental Studies of Modulated Crystal Phases in the Transition Metal Tetrachalcogenides and Oxide Superconductors  

Microsoft Academic Search

The structures and properties of several modulated crystal phases have been studied using electron diffraction and electron microscopy as the primary investigative techniques. Incommensurate and commensurate modulated structures in the transition metal tetrachalcogenides NbTe_4 and TaTe_4, associated with the presence of a charge-density wave (CDW) at room temperature, are examined in depth. These compounds possess a quasi -one-dimensional crystal structure

J. Craig Bennett

1992-01-01

174

Angular overlap model applied to transition metal complexes and d N -ions in oxide host lattices  

Microsoft Academic Search

The ability of the angular overlap model (AOM) to rationalize the dN energy level scheme of an arbitrarily coordinated transition metal complex is shown. The underlying theory is summarized,\\u000a including recent extensions such as s-d mixing, misdirected valency, and non-additive ?-contributions (Orgel effect), which may be important when chelate ligands\\u000a with conjugated ?-electrons are present. Experimental data obtained from optical

Thomas Schönherr; Theoretische Chemie

175

Exchange interactions and magnetic phases of transition metal oxides: Benchmarking advanced ab initio methods  

Microsoft Academic Search

The magnetic properties of the transition metal monoxides MnO and NiO are investigated at equilibrium and under pressure via several advanced first-principles methods coupled with Heisenberg Hamiltonian Monte Carlo. The comparative first-principles analysis involves two promising beyond-local density functionals approaches, namely the hybrid density functional theory and the recently developed variational pseudo-self-interaction correction method, implemented with both plane-wave and atomic-orbital

T. Archer; C. D. Pemmaraju; S. Sanvito; C. Franchini; J. He; A. Filippetti; P. Delugas; D. Puggioni; V. Fiorentini; R. Tiwari; P. Majumdar

2011-01-01

176

On dithiothreitol (DTT) as a measure of oxidative potential for ambient particles: evidence for the importance of soluble transition metals  

PubMed Central

The rate of consumption of dithiothreitol (DTT) is increasingly used to measure the oxidative potential of particulate matter (PM), which has been linked to the adverse health effects of PM. While several quinones are known to be very reactive in the DTT assay, it is unclear what other chemical species might contribute to the loss of DTT in PM extracts. To address this question, we quantify the rate of DTT loss from individual redox-active species that are common in ambient particulate matter. While most past research has indicated that the DTT assay is not sensitive to metals, our results show that seven out of the ten transition metals tested do oxidize DTT, as do three out of the five quinones tested. While metals are less efficient at oxidizing DTT compared to the most reactive quinones, concentrations of soluble transition metals in fine particulate matter are generally much higher than those of quinones. The net result is that metals appear to dominate the DTT response for typical ambient PM2.5 samples. Based on particulate concentrations of quinones and soluble metals from the literature, and our measured DTT responses for these species, we estimate that for typical PM2.5 samples approximately 80 % of DTT loss is from transition metals (especially copper and manganese), while quinones account for approximately 20 %. We find a similar result for DTT loss measured in a small set of PM2.5 samples from the San Joaquin Valley of California. Because of the important contribution from metals, we also tested how the DTT assay is affected by EDTA, a chelator that is sometimes used in the assay. EDTA significantly suppresses the response from both metals and quinones; we therefore recommend that EDTA should not be included in the DTT assay. PMID:23393494

Charrier, J. G.; Anastasio, C.

2013-01-01

177

Chemical control of orbital polarization in artificially structured transition-metal oxides: La2NiXO6 (X=B,Al,Ga,In) from first principles  

Microsoft Academic Search

The application of modern layer-by-layer growth techniques to transition-metal oxide materials raises the possibility of creating new classes of materials with rationally designed correlated electron properties. An important step toward this goal is the demonstration that electronic structure can be controlled by atomic composition. In compounds with partially occupied transition-metal d shells, one important aspect of the electronic structure is

M. J. Han; C. A. Marianetti; A. J. Millis

2010-01-01

178

High-fat diet induced an oxidative stress in white adipose tissue and disturbed plasma transition metals in rat: prevention by grape seed and skin extract.  

PubMed

Obesity is a public health problem characterized by increased accumulation of fat into adipose tissues leading to oxidative stress, dyslipidemia, and chronic inflammatory status. We used an experimental model of high-fat diet-induced obesity to analyze the link between dyslipidemia, oxidative stress, and fat accumulation into adipose tissue of rats, as well as the involvement of intracellular mediators such as transition metals on signal transduction. We also looked at the ability of a grape seed and skin extract (GSSE) from a Tunisian cultivar to prevent fat-induced disturbances. Data showed that a high-fat diet (HFD) provoked dyslipidemia into plasma which is linked to an oxidative stress, an accumulation of transition metals such as manganese, copper, and zinc and a depletion of iron. GSSE prevented dyslipidemia by modulating lipase activity, together with increased antioxidant capacity and depletion of transition metals as well as of free radicals such as O2 (-) and OH. These data indicated that GSSE has important preventive effects on HFD-induced obesity and oxidative stress whose transduction seems to involve transition metals. GSSE should be used as a safe anti-obesity agent that could find potential applications in metabolic disorders involving transition metals dyshomeostasis. PMID:24158847

Charradi, Kamel; Elkahoui, Salem; Limam, Ferid; Aouani, Ezzedine

2013-11-01

179

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

SciTech Connect

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).

Peng, H.; Lany, S.

2012-05-15

180

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

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

Goddard III, William A.

181

A generalized method toward high dispersion of transition metals in large pore mesoporous metal oxide/silica hybrids.  

PubMed

A series of transition metal acetylacetonates and acetates were used as precursors to generate high loadings of metal sites finely dispersed on SBA-15 silica. To achieve this, grafting of chelated transition metal precursors was performed directly to the surface of the as-synthesized SBA-15/P123 composite material. The thus-obtained metal/SBA-15 materials were studied by a variety of methods, e.g., elemental analysis, Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance UV-visible spectroscopy (DR-UV-vis), X-ray photoelectron spectroscopy (XPS) and N2 physisorption measurements at -196°C. From the results, the proposed functionalization method was found to be a highly tunable and reproducible strategy to disperse transition metal oxides in mesoporous silica materials. The results from elemental analysis of the modified materials confirmed that the amount of grafted species is a function of the initial concentration of precursor in the solution used for grafting. The chelated complexes were found to strongly interact with the silanol groups of the silica material, resulting in a ligand-exchange process, as corroborated by FTIR. However, different metal precursors showed distinct reactivity towards the surface of mesoporous silica, owing to differences in the stability of the complexes under the conditions used for grafting. DR-UV-vis and XPS analyses suggest that when the stability of a given precursor decreases, the grafting procedure can lead to the formation of small clusters of the metal oxide on the silica surface. XRD and SEM also show that grafting of lower stability complexes, such as Mn(acac)3, Cu(acetate)2 and VO(acac)2, on the silica surface can result in the formation of large crystals on the external surface of the SBA-15 particles. Nevertheless, it was established by XPS analysis that only a small percentage of the grafted species leads to the formation of bulk crystals while the remaining species are substituted into the silica framework. Obviously, a well-controlled and increased dispersion of the metal cations/oxides on the surface of highly porous silica materials is of great interest since these MxOy-SiO2 mixed oxides could demonstrate high catalytic activity in a large variety of reactions. PMID:25591825

Bérubé, François; Khadraoui, Abdelkarim; Florek, Justyna; Kaliaguine, Serge; Kleitz, Freddy

2015-07-01

182

Synthesis and structural, magnetic, thermal, and transport properties of several transition metal oxides and arsenides  

NASA Astrophysics Data System (ADS)

Several transition metal oxides and arsenides have been synthesized and their magnetic, thermal, structural, and transport properties have been studied in this thesis. Magnetically pure spinel compound LiV2O4 is a rare d-electron heavy fermion. The presence of small concentrations of magnetic defects, which are produced by the crystal defects in the spinel structure, strongly affect the physical properties of LiV2O 4. The phase relations in the Li2O-V2O3-V 2O5 ternary system at 700°C for compositions in equilibrium with LiV2O4 are reported. This study clarified the synthesis conditions under which low and high magnetic defect concentrations can be obtained within the spinel structure of LiV2O4. We confirmed that the LiV2O4 phase can be obtained containing low (0.006 mol%) to high (0.83 mol%) magnetic defect concentrations ndefect and with consistently high magnetic defect spin S values between 3 and 6.5. The high ndefect values were obtained in the LiV 2O4 phase in equilibrium with V2O3, Li3VO4, or LiVO2 and the low values in the LiV2O4 phase in equilibrium with V3O 5. A model is suggested to explain this correlation. We grew single crystals of LiV2O4 using Li3VO4 as a self-flux. The magnetic susceptibility of some as-grown crystals show a Curie-like upturn at low temperatures, showing the presence of magnetic defects within the spinel structure. The magnetic defects could be removed in some of the crystals by annealing them at 700°C. A very high specific heat coefficient gamma = 450 mJ/(mol K2) was obtained at a temperature of 1.8 K for a crystal containing a magnetic defect concentration ndefect = 0.5 mol%. A crystal with ndefect = 0.01 mol% showed a residual resistivity ratio of 50. To search for superstructure peaks or other evidence of spatial correlations in the arrangement of the crystal defects with in the crystal structure which give rise to magnetic defects, we carried out high-energy x-ray diffraction studies on LiV2O4 single crystals. Entire reciprocal lattice planes were mapped out with the help of synchrotron radiation. No noticeable differences in the x-ray diffraction data between a crystal with high magnetic defect concentration and a crystal with low magnetic defect concentration were found. This indicates the absence of any long-range periodicity or short-range correlations in the arrangements of the crystal/magnetic defects. In addition to LiV2O4, we synthesized and studied the properties of LV4O8 (L = Yb, Y, Lu) compounds which crystallize in a structure similar to that of the orthorhombic CaFe2 O4 structure-type, and contain four inequivalent V sites arranged in zigzag chains. We confirm the structure and report the magnetic, thermal, and transport properties of polycrystalline YV4O 8 and LuV4O8. A first-order like phase transition is observed at 50 K in both YV4O8 and LuV4O 8. The symmetry remains the same with the lattice parameters changing discontinuously. The structural transition in YV4O8 leads to partial dimerization of the V atoms resulting in a sudden sharp drop in the magnetic susceptibility. The V spins that do not form dimers order in a canted antiferromagnetic state. The magnetic susceptibility of LuV 4O8 shows a sharp peak at ˜ 50 K. The magnetic entropies calculated from heat capacity versus temperature measurements indicate bulk magnetic transitions below 90 K for both YV4O8 and LuV 4O8. We also grew single crystals of EuPd2Sb2 from PdSb self-flux. Single crystal x-ray diffraction studies confirmed that EuPd 2Sb2 crystallizes in the CaBe2Ge2-type structure which is closely related to the structure of the recently discovered iron-arsenide based superconductors. Antiferromagnetic ordering in the crystallographic ab-plane at ˜ 6 K with a spin-reorientation transition at 4.5 K is suggested from the magnetic susceptibility versus temperature chi (T) and heat capacity versus temperature Cp(T) data. The electrical resistivity versus temperature rho (T) data show metallic behavior down to 1.8 K along with an anomaly at 5.5 K in zero field. The anomaly is suppressed to 2.7 K in an 8 T fie

Das, Supriyo

183

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

SciTech Connect

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.

Daene, Markus W [ORNL; Lueders, Martin [Daresbury Laboratory, UK; Ernst, Arthur [Max Planck Institute of Microstructure Physics; Diemo, Koedderitzsch [Ludwig-Maximilian University; Temmerman, Walter M [Daresbury Laboratory, UK; Szotek, Zdzislawa [Daresbury Laboratory, UK; Wolfam, Hergert [Martin-Luther University Halle-Wittenberg

2009-01-01

184

Structural and vibrational properties of transition-metal oxides from first-principles calculations  

NASA Astrophysics Data System (ADS)

The calculation of the vibrational spectrum of minerals is of fundamental importance to assess their behavior (e.g. their elastic properties, or possible structural phase transitions) under the high-temperature, high-pressure conditions of the Earth’s interior. The ubiquitous presence of transition metals and the consequent importance of electronic correlations make the study of these materials quite difficult to approach with approximate DFT functionals (as LDA or GGA). The DFT+U, consisting in a Hubbard-modeled correction to the DFT energy functionals, has been successfully used to study the electronic, structural, and magnetic properties of several Fe-bearing minerals. However, the vibrational spectrum of these systems has never been determined entirely (frozen- phonon techniques are overly expensive except for zone-center phonons). In this work we introduce the extension of Density-Functional-Perturbation-Theory to DFT+U, that allows to efficiently compute the phonon spectrum of transition-metal compounds from their correlated ground states. A comparative analysis between the vibrational properties of MnO, FeO, CoO, and NiO (in the undistorted cubic cell) highlights a marked dependence of several features of their phonon spectrum on the occupancy of localized d orbitals and thus, on elec- tronic correlation. The new computational tool is also employed to evaluate the rhombohedral distortion of FeO (particularly abundant in the Earth’s lower mantle) and to assess the stability of its B1 phase in different conditions of pressure and temperature.

Cococcioni, M.; Floris, A.; Himmetoglu, B.

2010-12-01

185

Electrical and magnetic properties of manganates with perovskite-related structure  

Microsoft Academic Search

Multi-metal transition metal oxides with perovskite and related structures are known to exhibit a variety of interesting electrical and magnetic properties. In the work presented in this dissertation two systems were chosen to highlight the influence of lattice distortion and structure on those properties. The first system investigated was a series of charge ordered Ruddlesden-Popper (layered perovskite) manganates with a

Antonio Francisco Moreira Dos Santos

2002-01-01

186

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

NASA Astrophysics Data System (ADS)

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.

Chiu, Tien-Lung; Chuang, Ya-Ting

2015-02-01

187

Understanding chemical expansion in perovskite-structured oxides.  

PubMed

In this work, chemical expansion in perovskite oxides was characterized in detail, motivated, inter alia, by a desire to understand the lower chemical expansion coefficients observed for perovskites in comparison to fluorite-structured oxides. Changes in lattice parameter and in local atomic arrangements taking place during compositional changes of perovskites, i.e., stoichiometric expansion, were investigated by developing an empirical model and through molecular dynamics and density functional theory atomistic simulations. An accurate empirical expression for predicting lattice constants of perovskites was developed, using a similar approach to previous reports. From this equation, analytical expressions relating chemical expansion coefficients to separate contributions from the cation and anion sublattices, assuming Shannon ionic radii, were developed and used to isolate the effective radius of an oxygen vacancy, rV. Using both experimental and simulated chemical expansion coefficient data, rV for a variety of perovskite compositions was estimated, and trends in rV were studied. In most cases, rV was slightly smaller than or similar to the radius of an oxide ion, but larger than in the fluorite structured materials. This result was in good agreement with the atomistic simulations, showing contractive relaxations of the closest oxide ions towards the oxygen vacancy. The results indicate that the smaller chemical expansion coefficients of perovskites vs. fluorites are largely due to the smaller change in cation radii in perovskites, given that the contraction around the oxygen vacancy appears to be less in this structure. Limitations of applicability for the model are discussed. PMID:25785684

Marrocchelli, Dario; Perry, Nicola H; Bishop, Sean R

2015-04-01

188

The compatibility of transition metal oxide\\/carbon composite anode and ionic liquid electrolyte for the lithium-ion battery  

Microsoft Academic Search

Three types of transition metal oxide\\/carbon composites including Fe2O3\\/C, NiO\\/C and CuO\\/Cu2O\\/C synthesized via spray pyrolysis were used as anode for lithium ion battery application in conjunction with two types of\\u000a ionic liquid: 1 M LiN(SO2CF3)2 (LiTFSI) in 1-ethyl-3-methyl-imidazolium bis(fluorosulfonlyl)imide (EMI-FSI) or 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide\\u000a (Py13-FSI). From the electrochemical measurements, the composite electrodes using Py13-FSI as electrolyte show much better\\u000a electrochemical performance

Shu-Lei ChouLin; Lin Lu; Jia-Zhao Wang; M. M. Rahman; Chao Zhong; Hua-Kun Liu

189

Nickel-rich layered lithium transition-metal oxide for high-energy lithium-ion batteries.  

PubMed

High energy-density lithium-ion batteries are in demand for portable electronic devices and electrical vehicles. Since the energy density of the batteries relies heavily on the cathode material used, major research efforts have been made to develop alternative cathode materials with a higher degree of lithium utilization and specific energy density. In particular, layered, Ni-rich, lithium transition-metal oxides can deliver higher capacity at lower cost than the conventional LiCoO2 . However, for these Ni-rich compounds there are still several problems associated with their cycle life, thermal stability, and safety. Herein the performance enhancement of Ni-rich cathode materials through structure tuning or interface engineering is summarized. The underlying mechanisms and remaining challenges will also be discussed. PMID:25801735

Liu, Wen; Oh, Pilgun; Liu, Xien; Lee, Min-Joon; Cho, Woongrae; Chae, Sujong; Kim, Youngsik; Cho, Jaephil

2015-04-01

190

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

E-print Network

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. ...

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

2004-01-01

191

Energy loss by channeled electrons: a quantitative study on transition metal oxides.  

PubMed

Electron energy-loss spectroscopy (EELS) attached to current transmission electron microscopes can probe not only element-selective chemical information, but also site-selective information that depends on the position that a specific element occupies in a crystal lattice. The latter information is exploited by utilizing the Bloch waves symmetry in the crystal, which changes with its orientation with respect to the incident electron wave (electron channeling). We demonstrate the orientation dependence of the cross-section of the electron energy-loss near-edge structure for particular crystalline sites of spinel ferrites, by quantitatively taking into account the dynamical diffraction effects with a large number of the diffracted beams. The theoretical results are consistent with a set of experiments in which the transition metal sites in spinel crystal structures are selectively excited. A new measurement scheme for site-selective EELS using a two-dimensional position-sensitive detector is proposed and validated by theoretical predictions and trial experiments. PMID:23985156

Tatsumi, Kazuyoshi; Muto, Shunsuke; Rusz, Ján

2013-12-01

192

Microwave-assisted carbohydrohalogenation of first-row transition-metal oxides (M = V, Cr, Mn, Fe, Co, Ni, Cu) with the formation of element halides.  

PubMed

The anhydrous forms of first-row transition-metal chlorides and bromides ranging from vanadium to copper were synthesized in a one-step reaction using the relatively inexpensive element oxides, carbon sources, and halogen halides as starting materials. The reactions were carried out in a microwave oven to give quantitative yields within short reaction times. PMID:24099620

Berger, Matthias; Neumeyer, Felix; Auner, Norbert

2013-10-21

193

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

E-print Network

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

Lin, Xi

194

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

PubMed Central

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

MURAHASHI, Shun-Ichi

2011-01-01

195

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

PubMed

High-surface-area mesoprous powders of ?-Al2O3 doped with Cu(2+), Cr(3+), and V(3+) 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 Cu(2+)- and Cr(3+)-containing catalysts showed 100% conversion at 300°C and 350°C, V(3+)-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

Khaleel, Abbas; Nawaz, Muhammad

2015-03-01

196

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

NASA Astrophysics Data System (ADS)

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.

Kwon, Jang Yeon; Kyeong Jeong, Jae

2015-02-01

197

Soluble transition metal oxide/polymeric acid composites for efficient hole-transport layers in polymer solar cells.  

PubMed

We report a new method for developing a low-temperature solution processed vanadium oxide (s-VOx) and poly(4-styrene sulfonic acid) (PSS) composite to act as an efficient hole-transport layer (HTL) in polymer solar cells (PSCs). By compositing the s-VOx and PSS (s-VOx:PSS), the work function values of the s-VOx:PSS changed from 5.0 to 5.3 eV. Therefore, the energy level barrier between the HTL and organic active layer decreased, facilitating charge injection/extraction at the interfaces. In addition, the s-VOx:PSS films were denser and had more pin-hole-free surfaces than pristine s-VOx films, resulting in enhanced PSC performance due to significantly decreased leakage currents and excellent device stability in ambient condition. Because our approach of combining soluble transition metal oxide (TMO) and polymeric acid shows dramatically better performance than pristine TMO, we expect that it can provide useful guidelines for the synthesis and application of TMOs for organic electronics in the future. PMID:24369710

Kim, Junghwan; Kim, Heejoo; Kim, Geunjin; Back, Hyungcheol; Lee, Kwanghee

2014-01-22

198

Superconductors and Complex Transition Metal Oxides for Tunable THz Plasmonic Metamaterials  

SciTech Connect

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.

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

2012-07-13

199

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

E-print Network

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 ...

Tennyson, Andrew Gregory

2008-01-01

200

Microwave Absorption Behavior of Mesoporous Transition Metal Oxide Templated from SBA-15 and KIT-6  

NASA Astrophysics Data System (ADS)

In this paper, we have synthesized meso-oxides (i.e., Co3O4 and NiO) by using mesoporous silica as hard template. The microstructures and chemical compositions of the corresponding meso-oxides were characterized by the Transmission electron microscope-selected area electron diffusion (TEM-SAED), X-ray diffraction (XRD), scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS), respectively. And, their electromagnetic and microwave absorption properties were investigated in the frequency range of 2-18 GHz. The results indicate that meso-oxide templated from KIT-6 (i.e., meso-K-Co/Ni) exhibit a dual absorption characteristic compared with those using SBA-15 as hard template. This phenomenon suggests that meso-oxides templated from SBA-15 and KIT-6 can exhibit different microwave absorption behaviors due to their respective microstructures.

Wu, Hongjing; Wang, Liuding; Wang, Yiming

2014-12-01

201

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

E-print Network

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. ...

La O', Gerardo Jose Cordova

2008-01-01

202

Synthesis of Polysubstituted Quinolines via Transition-Metal-Free Oxidative Cycloisomerization of o-Cinnamylanilines.  

PubMed

An efficient synthesis of 2-aryl 4-substituted quinolines from stable and readily available o-cinnamylanilines, prepared from anilines and cinnamylalcohols, has been developed. The reaction occurred via a regioselective 6-endo-trig intramolecular oxidative cyclization using KO(t)Bu as a mediator and DMSO as an oxidant at rt. The reaction showed a broad substrate scope with good to excellent yields. PMID:25768127

Rehan, Mohammad; Hazra, Gurupada; Ghorai, Prasanta

2015-04-01

203

Synthesis and Characterization of Nanostructure Transition Metal Oxides Extracted from Industrial Waste (EOFD) by Hydrothermal Method  

NASA Astrophysics Data System (ADS)

Electric oil furnace dust (EOFD) is a solid waste generated in the collection of particulate material during steelmaking process in electric and oil furnaces. Over 7 million metric tons dust produced per annum in worldwide creates deep impacts like soil, ground water and ecology pollutions. This article reports the simple one step process for the extraction of nanostructured metal oxides from the industrial waste (EOFD) for the realization of low cost solar applications. By hydrothermal technique valuable metals were obtained in the form of metal oxides. Initially the presence of metals was identified by ICP analysis. XRD analysis confirms the formation of nano structured titanium oxide (TiO) along with traces of iron oxide (Fe2O3). The surface morphology and the particle size were analyzed by SEM analysis. Thus the metal oxides derived could be helpful to reduce the burden on the environment, increase the development of the source nano material and reduce the cost of raw materials for solar cell applications.

Girisun, T. C. Sabari; Babeela, C.; Vidhya, V.

2011-10-01

204

P-type conductive amorphous oxides of transition metals from solution processing  

NASA Astrophysics Data System (ADS)

We report a series of solution-processed p-type conductive amorphous Ln-M-O (a-Ln-M-O, where M = Ru, Ir, and Ln is a lanthanide element except Ce) having low resistivities (10-3 to 10-2 ? cm). These oxides are thermally stable to a high degree, being amorphous up to 800 °C, and processable below 400 °C. Their film surfaces are smooth on the atomic scale, and the process allows patterning simply by direct imprinting without distortion of the pattern after annealing. These properties have high potential for use in printed electronics. The electron configurations of these oxides are apparently different from existing p-type oxides.

Li, Jinwang; Kaneda, Toshihiko; Tokumitsu, Eisuke; Koyano, Mikio; Mitani, Tadaoki; Shimoda, Tatsuya

2012-07-01

205

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

E-print Network

is composed of vanadium(V) oxide layers with nickel atoms coordinated within a single layer via four Ni­O­V linkages. Bidentate bipyridine (bpy) ligands complete the coordination sphere of the nickel atoms as black plates in the space group P21/n (#14) with unit cell parameters a = 8X934(2) °A, b = 6X558(1) °A

206

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

PubMed

Systems of iron tellurite glasses were prepared by melt quenching with compositions of [85%TeO2+5%Fe2O3+10%TMO], where transition metal oxides (TMO) are TiO2, V2O5, MnO, CoO, NiO and CuO. Furthermore, the main structural units of these samples have been characterized by means of Raman spectra (150-1200 cm(-1)) as well as wavenumber predictions by means of Gaussian 98 ab initio calculations for the proposed site symmetries of TeO4(4-) triagonal bipyramid (C2v) and Te2O7(6-) bridged tetrahedra (Cs and C1). Aided by normal coordinate analysis, calculated vibrational frequencies, Raman scattering activities, force constants in internal coordinates and potential energy distributions (PEDs), revised vibrational assignments for the fundamental modes have been proposed. The main structural features are correlated to the dominant units of triagonal bipyramid (tbp) or bridged tetrahedral (TeO3+1 binds to TeO3 through TeOTe bridge; corner sharing). Moreover, the Raman spectra of the investigated tellurites reflect a structural change from tbp (coordination number is four) to triagonal pyramidal (coordination number is three). PMID:16098796

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

2006-05-01

207

Importance of tetrahedral coordination for high-valent transition-metal oxides: YCrO4 as a model system  

NASA Astrophysics Data System (ADS)

We have investigated the electronic structure of the high oxidation state material YCrO4 within the framework of the Zaanen-Sawatzky-Allen phase diagram. While Cr4+-based compounds such as SrCrO3/CaCrO3 and CrO2 can be classified as small-gap or metallic negative-charge-transfer systems, we find using photoelectron spectroscopy that YCrO4 is a robust insulator despite the fact that its Cr ions have an even higher formal valence state of 5+. We reveal using band-structure calculations that the tetrahedral coordination of the Cr5+ ions in YCrO4 plays a decisive role, namely to diminish the bonding of the Cr 3d states with the top of the O 2p valence band. This finding not only explains why the charge-transfer energy remains effectively positive and the material stable, but also opens up a new route to create doped carriers with symmetries different from those of other transition-metal ions.

Tsirlin, A. A.; Rabie, M. G.; Efimenko, A.; Hu, Z.; Saez-Puche, R.; Tjeng, L. H.

2014-08-01

208

Stable, Single-Layer MX2 Transition-Metal Oxides and Dichalcogenides in a Honeycomb-Like Structure  

NASA Astrophysics Data System (ADS)

Recent studies have revealed that single-layer transition-metal oxides and dichalcogenides (MX2) might offer properties superior to those of graphene. So far, only very few MX2 compounds have been synthesized as suspended single layers, and some of them have been exfoliated as thin sheets. Using first-principles structure optimization and phonon calculations based on density functional theory, we predict that, out of 88 different combinations of MX2 compounds, several of them can be stable in free-standing, single-layer honeycomb-like structures. Our analysis of stability was extended to include in-plane stiffness, as well as ab initio, finite-temperature molecular dynamics calculations. Some of these single-layer structures are direct- or indirect-band-gap semiconductors, only one compound is half-metal, and the rest are either ferromagnetic or nonmagnetic metals. Because of their surface polarity, band gap, high in-plane stiffness, and suitability for functionalization by adatoms or vacancies, these single-layer structures can be utilized in a wide range of technological applications, especially as nanoscale coatings for surfaces contributing crucial functionalities. In particular, the manifold WX2 heralds exceptional properties promising future nanoscale applications.

Ataca, Can; Sahin, Hasan; Ciraci, Salim

2013-03-01

209

Numerical model of tandem organic light-emitting diodes based on a transition metal oxide interconnector layer  

NASA Astrophysics Data System (ADS)

By utilizing a two-step process to express the charge generation and separation mechanism of the transition metal oxides (TMOs) interconnector layer, a numerical model was proposed for tandem organic light emitting diodes (OLEDs) with a TMOs thin film as the interconnector layer. This model is valid not only for an n-type TMOs interconnector layer, but also for a p-type TMOs interconnector layer. Based on this model, the influences of different carrier injection barriers at the interface of the electrode/organic layer on the charge generation ability of interconnector layers were studied. In addition, the distribution characteristics of carrier concentration, electric field intensity and potential in the device under different carrier injection barriers were studied. The results show that when keeping one carrier injection barrier as a constant while increasing another carrier injection barrier, carriers injected into the device were gradually decreased, the carrier generation ability of the interconnector layer was gradually reduced, the electric field intensity at the interface of the organic/electrode was gradually enhanced, and the electric field distribution became nearly linear: the voltage drops in two light units gradually became the same. Meanwhile, the carrier injection ability decreased as another carrier injection barrier increased. The simulation results agree with the experimental data. The obtained results can provide us with a deep understanding of the work mechanism of TMOs-based tandem OLEDs.

Feiping, Lu; Yingquan, Peng; Yongzhong, Xing

2014-04-01

210

Synthesis, characterization, and magnetic susceptibility of the heavy-fermion transition-metal oxide LiV2O4  

NASA Astrophysics Data System (ADS)

The preparative method, characterization, and magnetic susceptibility ? measurements versus temperature T of the heavy-fermion transition-metal oxide LiV2O4 are reported in detail. The intrinsic ?(T) shows a nearly T-independent behavior below ~30 K with a shallow broad maximum at ~16 K, whereas Curie-Weiss-like behavior is observed above ~50-100 K. Field-cooled and zero-field-cooled magnetization Mobs measurements in applied magnetic fields H=10-100 G from 1.8 to 50 K showed no evidence for spin-glass ordering. Crystalline electric field theory for an assumed cubic V point group symmetry is found insufficient to describe the observed temperature variation of the effective magnetic moment. The Kondo and Coqblin-Schrieffer models do not describe the magnitude and T dependence of ? with realistic parameters. In the high-T range, fits of ?(T) by the predictions of high-temperature series expansion calculations provide estimates of the V-V antiferromagnetic exchange coupling constant J/kB~20 K, g factor g~2, and the T-independent susceptibility. Other possible models to describe the ?(T) are discussed. The paramagnetic impurities in the samples were characterized using isothermal Mobs(H) measurements with 0

Kondo, S.; Johnston, D. C.; Miller, L. L.

1999-01-01

211

High-pressure synthesis and electrochemical properties of lithium transition metal oxides with layered rock-salt structure  

NASA Astrophysics Data System (ADS)

Li-rich layered transition metal oxides with the nominal composition of Li1+x[Li0.2Mn?Co?Ni?]O2 with 0.0 ? x ? 0.7 are synthesized using a high-pressure technique. The chemical compositions are determined using inductively coupled plasma (ICP) spectroscopy and the structure is identified from X-ray diffraction measurements as a mixture of rhombohedral R-3m and cubic Fm-3m phases. Rietveld refinement analysis reveals that the layered to cubic phase ratio increases as x tends towards 0.7, with an almost complete cubic phase present for x ? 0.6. Electrochemical charge-discharge experiments performed using coin cells and show capacities of around 200 mAh g-1 for 0.0 ? x ? 0.4 samples, although the capacity quickly decreases for x ? 0.5, which is consistent with the trend towards a predominantly cubic phase. The plateau for oxygen generation, which appears at the 4.4 V threshold, is reduced as x increases.

Chang, Hansen; Kubota, Kei; Kobayashi, Genki; Hirayama, Masaaki; Kanno, Ryoji

2014-04-01

212

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

PubMed Central

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

2014-01-01

213

Surface redox induced bipolar switching of transition metal oxide films examined by scanning probe microscopy  

NASA Astrophysics Data System (ADS)

The bipolar resistive switching mechanisms of a p-type NiO film and n-type TiO2 film were examined using local probe-based measurements. Scanning probe-based current-voltage ( I- V) sweeps and surface potential/current maps obtained after the application of dc bias suggested that resistive switching is caused mainly by the surface redox reactions involving oxygen ions at the tip/oxide interface. This explanation can be applied generally to both p-type and n-type conducting resistive switching films. The contribution of oxygen migration to resistive switching was also observed indirectly, but only in the cases where the tip was in (quasi-) Ohmic contact with the oxide.

Lee, Min Hwan; Kim, Kyung Min; Song, Seul Ji; Rha, Sang Ho; Seok, Jun Yeong; Jung, Ji Sim; Kim, Gun Hwan; Yoon, Jung Ho; Hwang, Cheol Seong

2011-03-01

214

Hot electron transport in a strongly correlated transition-metal oxide  

PubMed Central

Oxide heterointerfaces are ideal for investigating strong correlation effects to electron transport, relevant for oxide-electronics. Using hot-electrons, we probe electron transport perpendicular to the La0.7Sr0.3MnO3 (LSMO)- Nb-doped SrTiO3 (Nb:STO) interface and find the characteristic hot-electron attenuation length in LSMO to be 1.48 ± 0.10 unit cells (u.c.) at ?1.9?V, increasing to 2.02 ± 0.16?u.c. at ?1.3?V at room temperature. Theoretical analysis of this energy dispersion reveals the dominance of electron-electron and polaron scattering. Direct visualization of the local electron transport shows different transmission at the terraces and at the step-edges. PMID:23429420

Rana, Kumari Gaurav; Yajima, Takeaki; Parui, Subir; Kemper, Alexander F.; Devereaux, Thomas P.; Hikita, Yasuyuki; Hwang, Harold Y.; Banerjee, Tamalika

2013-01-01

215

Electron magnetic resonance study of transition-metal magnetic nanoclusters embedded in metal oxides  

Microsoft Academic Search

Here, we report on the results of an electron magnetic resonance (EMR) study of a series of Ni\\/ZnO and Ni\\/gamma-Fe2O3 nanocomposites (NCs) to probe the resonance features of ferromagnetic (FM) Ni nanoclusters embedded in metal oxides. Interest in these NCs stems from the fact that they are promising for implementing the nonreciprocal functionality employed in many microwave devices, e.g., circulators.

Vincent Castel; Christian Brosseau

2008-01-01

216

Stabilization of mixed valence states in partly oxidized one-dimensional transition metal systems  

Microsoft Academic Search

The spatial hole-state properties of partly oxidized one-dimensional (1 D) organometallic solids with weak metal-metal interactions (either due to large separations between the corresponding building blocks or due to bridging organic ligand functions) have been studied in the crystal orbital (CO) formalism based on the tight-binding technique. The numerical analysis is restricted to insulating band states. The employed computational model

Michael C. Böhm

1984-01-01

217

First principles study of transition metal (TM=Pb, Cu) oxides/sulfides  

NASA Astrophysics Data System (ADS)

Earth-abundant transition meal oxides/sulfides have inspired special research attention recently due to their potential applications in solar cells. A clear understanding of the fundamental properties of these materials, especially the electronic properties and their tunability via chemical doping, are critically important towards the applications. In this presentation, we report first principles density-functional theory (DFT) study on the electronic structures of Pb and Cu oxides/sulfides and their oxysulfides compositions. The band structure and bandgap can be systematically tuned by increasing S component in the metal oxides. For example, the DFT predicted bandgap for PbO is 1.72 eV. While the bandgaps for PbO0.937 S0.063, PbO0.875S0.125, and PbO0.75S0.25 are 1.64 eV, 1.43 eV, and 0.79 eV, respectively. For Cu2O, the standard DFT seriously underestimates the bandgap to be 0.49 eV, compared to the experimental value of 2.17 eV. Two methods, DFT+U and hybrid functional (HSE06), were implemented to overcome this problem. Our results showed that DFT+U method fails and the bandgap doesn't further open up by providing a U potential. The hybrid functional predicts the bandgap to be 2.00 eV, which is in a good agreement with the experimental value.

Caudle, Sean; Tao, Meng; Peng, Xihong

2012-10-01

218

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

E-print Network

for efficient and durable operation of SOFCs at intermediate temperatures. Cation segregation on the perovskiteFactors that Influence Cation Segregation at the Surfaces of Perovskite Oxides Wonyoung Lee transforms to different chemical phases, including the perovskite-termination structure with the Sr replacing

Yildiz, Bilge

219

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

E-print Network

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 ...

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

2014-01-01

220

Temperature-independent sensors based on perovskite-type oxides  

NASA Astrophysics Data System (ADS)

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.

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

2014-06-01

221

Temperature-independent sensors based on perovskite-type oxides  

SciTech Connect

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.

Zaza, F.; Frangini, S.; Masci, A. [ENEA-Casaccia R.C., Via Anguillarese 301, 00123 S.Maria di Galeria, Rome (Italy); Leoncini, J.; Pasquali, M. [University La Sapienza, Piazza Via del Castro Laurenziano 7, 00161 Rome (Italy); Luisetto, I.; Tuti, S. [University RomaTre, Rome 00146 (Italy)

2014-06-19

222

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

SciTech Connect

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.

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

2011-10-15

223

Fabrication of functional transition metal oxide and hydroxide used as catalysts and battery materials  

NASA Astrophysics Data System (ADS)

My research is focused on developing metal oxide and hydroxide nanomaterials which can be used as battery materials, organic transformation catalysts, and photocatalysts. This research involves studying ZnO with different morphologies as photocatalysts for phenol degradation, producing CuO as olefin epoxidation catalysts, developing V and Cu incorporated manganese oxides as cathode materials for Li-ion batteries, and fabricating alpha-nickel hydroxide for Li-air battery materials. The first part includes producing ZnO as a photocatalyst for phenol degradation. The goal of this study is the synthesis of ZnO with different morphologies using the solvothermal method. The influence of solvents has been studied in detail. Their properties and photocatalytic performances have been explored as well. The second part of the research is concerned with developing novel urchin-like CuO as an olefin epoxidation catalyst. The purpose of this study is to develop a new catalyst, CuO, for olefin epoxidation. The copper source and precipitators were optimized, and the possible self-assembly mechanism of the urchin-like morphology was proposed. The catalytic activity of CuO for olefin epoxidation was studied. The third part of this work includes developing V, Cu incorporated manganese oxide (V-Cu-OMS-2) as cathode materials for Li-ion batteries. The purpose of this project is to develop a new material with enhanced battery performance. V and Cu incorporated manganese oxide were developed using hydrothermal methods. Octahedral molecular sieve (OMS) materials show mixed valences of Mn 3+ and Mn4+, which produces novel properties in battery applications. Inexpensive starting materials make OMS materials more promising for commercial applications. How the incorporation of V and Cu affected OMS-2 materials was investigated in terms of their crystal structure, morphologies, and surface areas. The battery performance of the incorporated OMS-2 materials with different loading amounts of V and Cu was also studied. In the fourth part of this research, 3D flower-like alpha-nickel hydroxide with enhanced electrochemical activity was fabricated using a microwave-assisted hydrothermal method. The focus of this study is the synthesis of alpha-nickel hydroxide and its application for O2 reduction. The synthetic work focused on the preparation of flower-like alpha-nickel hydroxide using the microwave-assisted hydrothermal method. The alpha-nickel hydroxide shows superior electrochemical properties compared to those of the beta-form. However, it is difficult to make the alpha-form, since the structure of alpha-nickel hydroxide is unstable, and it prefers to transfer to the beta-form under basic conditions. In this study, flower-like alpha-nickel hydroxide was prepared using urea as the precipitating agent. The factors, which affected the formation of flower-like morphologies, have been investigated. The electrochemical activity of as-synthesized alpha-nickel hydroxide for oxygen reduction in an alkaline media was studied.

Xu, Linping

224

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

NASA Astrophysics Data System (ADS)

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

Jin, Lei

2011-12-01

225

Oxide perovskite crystals for HTSC film substrates microwave applications  

SciTech Connect

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.

Bhalla, A.S.; Guo, R.

1995-04-01

226

Oxide perovskite crystals for HTSC film substrates microwave applications  

NASA Technical Reports Server (NTRS)

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.

Bhalla, A. S.; Guo, Ruyan

1995-01-01

227

Giant magnetoresistance of manganese oxides with a layered perovskite structure  

Microsoft Academic Search

MANGANESE oxides with the cubic perovskite structure (typified by LaMnO3) have stimulated considerable interest because of their magnetoresistive properties1-9 they exhibit extremely large changes in electrical resistance in response to applied magnetic fields, a property that is of technological relevance for the development of magnetic memory and switching devices. But for such applications to be viable, great improvements will be

Y. Moritomo; A. Asamitsu; H. Kuwahara; Y. Tokura

1996-01-01

228

Second-sphere ligand field effects on oxygen ligator atoms and experimental evidence—the transition metal–oxygen bond in oxidic solids  

Microsoft Academic Search

The properties of the M–O bond in oxidic solids, where M is a low-valent 3d transition metal ion such as NiII, CuII, CoII or CrIII, are very variable depending on the structure and constitution of the respective compound, and are studied by optical and EPR spectroscopy. Specifically, high-valent cations in the cationic coordination of the oxygen ligator atoms beside M

Dirk Reinen; Michail Atanasov; Show-Ling Lee

1998-01-01

229

Ground and low-lying excited state properties of the first-row transition-metal oxide diatomics calculated by an improved ASED-MO model  

Microsoft Academic Search

The ground and selected low-lying electronic states of the entire series of the first-row transition-metal neutral oxides are investigated by the use of an improved atom superposition and electron delocalization molecular orbital (ASED-MO) approach. Two quantities are found to be very important in achieving agreement with experiment: these are the ??, ?? parameter set-involved in the Wolfsberg-Helmholz constant, K —

Evangelos G Bakalbassis; Maria-Aglaia D Stiakaki; Athanasios C Tsipis; Constantinos A Tsipis

1996-01-01

230

Ground and excited state properties of the cationic and anionic first-row transition-metal oxide diatomics calculated by an improved ASED-MO model  

Microsoft Academic Search

The performance of an improved atom superposition and electron delocalization molecular orbital (ASED-MO) model has been investigated for the ground and selected low-lying excited states of the entire sequence of the highly-polar cationic and anionic first-row transition-metal oxide diatomics. In particular, in both series of compounds deep potential energy curves of an almost Morse-type shape were derived allowing for an

Evangelos G. Bakalbassis; Maria-Aglaia D. Stiakaki; Athanasios C. Tsipis; Constantinos A. Tsipis

1997-01-01

231

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

SciTech Connect

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.

Dai, Pengcheng

2014-02-18

232

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

NASA Astrophysics Data System (ADS)

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.

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

2014-07-01

233

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

PubMed

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. PMID:24993836

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

2014-01-01

234

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

NASA Astrophysics Data System (ADS)

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.

Samanta, Kousik

235

Electronic transport and mixed conductivity in perovskite type oxides  

SciTech Connect

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}.

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

1992-03-03

236

Transition-metal-free C-H oxidative activation: persulfate-promoted selective benzylic mono- and difluorination.  

PubMed

An operationally simple and selective method for the direct conversion of benzylic C-H to C-F to obtain mono- and difluoromethylated arenes using Selectfluor™ as a fluorine source is developed. Persulfate can be used to selectively activate benzylic hydrogen atoms toward C-F bond formation without the aid of transition metal catalysts. PMID:25645405

Ma, Jing-Jing; Yi, Wen-Bin; Lu, Guo-Ping; Cai, Chun

2015-02-24

237

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

NASA Astrophysics Data System (ADS)

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.

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

2013-12-01

238

Synthesis, Dioxygen Affinities and Biomimetic Catalytic Oxidation Performance of Crown Ether-tethered Schiff Base Transition-Metal Complexes  

Microsoft Academic Search

Mono-Schiff bases containing crown ether ring (HL1, HL2, HL3 and HL4) and their transition-metal complexes were synthesized and characterized by 1H NMR, IR, MS spectra and elemental analysis. The crystal structures of HL1, HL3 and CoL21 were determined from X-ray diffraction data. The oxygenation constants (Ko2) of Schiff-base Co (II) complexes were measured over a range of ?5°C to 25°C,

Wei Zeng; Zhihua Mao; Xingyao Wei; Jianzhang Li; Zhou Hong; Shengying Qin

2002-01-01

239

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

Microsoft Academic Search

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

Kousik Samanta

2009-01-01

240

Method for dry etching of transition metals  

DOEpatents

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

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

1998-09-29

241

Method for dry etching of transition metals  

DOEpatents

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

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

1998-01-01

242

Autothermal reforming catalyst having perovskite structure  

DOEpatents

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.

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

2009-03-24

243

Fabrication of ultralong hybrid microfibers from nanosheets of reduced graphene oxide and transition-metal dichalcogenides and their application as supercapacitors.  

PubMed

Two-dimensional materials have attracted increasing research interest owing to their unique electronic, physical, optical, and mechanical properties. We thus developed a general strategy for the fabrication of ultralong hybrid microfibers from a mixture of reduced graphene oxide and transition-metal dichalcogenides (TMDs), including MoS2 , TiS2 , TaS2 , and NbSe2 . Furthermore, we prepared fiber-based solid-state supercapacitors as a proof-of-concept application. The performance of thus-prepared supercapacitors was greatly improved by the introduction of the TMDs. PMID:25130600

Sun, Gengzhi; Liu, Juqing; Zhang, Xiao; Wang, Xuewan; Li, Hai; Yu, Yang; Huang, Wei; Zhang, Hua; Chen, Peng

2014-11-10

244

Synthesis of the new ternary transition metal nitride FeWN[sub 2] via ammonolysis of a solid state oxide precursor  

SciTech Connect

A new ternary nitride, FeWN[sub 2], was prepared via ammonolysis of the solid state oxide precursor FeWO[sub 4] at 800[degrees]C. The powder diffraction data were indexed as a hexagonal structure with lattice parameters a = 2.867(2) [angstrom] and c = 16.458(9) [angstrom]. The successful preparation of FeWN[sub 2] demonstrates that the inductive effect is not necessary for preparing some ternary transition metal nitrides. 13 refs., 1 fig., 1 tab.

Bem, D.S.; zur Loye, H.C. (Massachusetts Inst. of Technology, Cambridge, MA (United States))

1993-06-01

245

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)

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 - 0.005T (°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 + 0.011T (°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.

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

2015-01-01

246

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

PubMed

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

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

2014-11-18

247

Tuning ferromagnetism at interfaces between insulating perovskite oxides.  

PubMed

We use density functional theory calculations to show that the LaAlO3|SrTiO3 interface between insulating perovskite oxides is borderline in satisfying the Stoner criterion for itinerant ferromagnetism and explore other oxide combinations with a view to satisfying it more amply. The larger lattice parameter of a LaScO3|BaTiO3 interface is found to be less favorable than the greater interface distortion of LaAlO3|CaTiO3. Compared to LaAlO3|SrTiO3, the latter is predicted to exhibit robust magnetism with a larger saturation moment and a higher Curie temperature. Our results provide support for a "two phase" picture of coexistent superconductivity and ferromagnetism. PMID:25279639

Ganguli, Nirmal; Kelly, Paul J

2014-09-19

248

Tuning Ferromagnetism at Interfaces between Insulating Perovskite Oxides  

NASA Astrophysics Data System (ADS)

We use density functional theory calculations to show that the LaAlO3|SrTiO3 interface between insulating perovskite oxides is borderline in satisfying the Stoner criterion for itinerant ferromagnetism and explore other oxide combinations with a view to satisfying it more amply. The larger lattice parameter of a LaScO3|BaTiO3 interface is found to be less favorable than the greater interface distortion of LaAlO3|CaTiO3. Compared to LaAlO3|SrTiO3, the latter is predicted to exhibit robust magnetism with a larger saturation moment and a higher Curie temperature. Our results provide support for a "two phase" picture of coexistent superconductivity and ferromagnetism.

Ganguli, Nirmal; Kelly, Paul J.

2014-09-01

249

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

Microsoft Academic Search

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

Edward Siegel

1978-01-01

250

Transition Metal Compounds  

NASA Astrophysics Data System (ADS)

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

Khomskii, Daniel I.

2014-10-01

251

Modification of MCM-48-, SBA-15-, MCF-, and MSU-type mesoporous silicas with transition metal oxides using the molecular designed dispersion method.  

PubMed

Four various mesoporous silicas (MCM-48, SBA-15, MCF, and MSU) were modified by the molecular designed dispersion method using Fe(acac)3, Cr(acac)3, and Cu(acac)2 complexes. The deposition was performed at the same concentration of the metal acetylacetonate (acac) complex in a toluene solution. All as-synthesized samples were investigated by diffuse reflectance infrared Fourier transform spectroscopy, Fourier transform infrared photoacoustic spectroscopy, and thermogravimetric analysis. The calcined materials were studied with respect to their textural properties (Brunauer-Emmett-Teller adsorption isotherm) and chemical composition (electron microprobe analysis). It allowed elucidation of the mechanism of interaction between the acac complex and the silanol groups. For the MCM-48, SBA-15, and MCF materials, the formation of hydrogen bonding was found for the chromium- and copper-modified samples, whereas the Fe-containing materials showed the ligand exchange mechanism. The strong interaction of the MSU support and the different acetylacetonate complexes, resulting in a loss of at least one acac ligand, was observed. The mesoporous silicas modified with transition metal oxides were studied by UV-vis-DR spectroscopy. The different metal dispersions were found for the samples containing various transition metal oxides. PMID:16852417

Ku?trowski, Piotr; Chmielarz, Lucjan; Dziembaj, Roman; Cool, Pegie; Vansant, Etienne F

2005-06-16

252

Synthesis-microstructure-performance relationship of layered transition metal oxides as cathode for rechargeable sodium batteries prepared by high-temperature calcination.  

PubMed

Research on sodium batteries has made a comeback because of concern regarding the limited resources and cost of lithium for Li-ion batteries. From the standpoint of electrochemistry and economics, Mn- or Fe-based layered transition metal oxides should be the most suitable cathode candidates for affordable sodium batteries. Herein, this paper reports a novel cathode material, layered Na1+x(Fey/2Niy/2Mn1-y)1-xO2 (x = 0.1-0.5), synthesized through a facile coprecipitation process combined with subsequent calcination. For such cathode material calcined at 800 °C for 20 h, the Na/Na1+x(Fey/2Niy/2Mn1-y)1-xO2 (x = 0.4) electrode exhibited a good capacity of 99.1 mAh g(-1) (cycled at 1.5-4.0 V) and capacity retention over 87% after 50 cycles. Optimization of this material would make layered transition metal oxides a strong candidate for the Na-ion battery cathode. PMID:25192293

Xie, Man; Luo, Rui; Lu, Jun; Chen, Renjie; Wu, Feng; Wang, Xiaoming; Zhan, Chun; Wu, Huiming; Albishri, Hassan M; Al-Bogami, Abdullah S; El-Hady, Deia Abd; Amine, Khalil

2014-10-01

253

Spin and orbital degrees of freedom in transition metal oxides and oxide thin films studied by soft x-ray absorption spectroscopy  

Microsoft Academic Search

The class of transition metal compounds shows an enormous richness of physical properties, such as metal-insulator transitions, colossal magneto-resistance, super-conductivity, magneto-optics and spin-depend transport. It now becomes more and more clear that in order to describe transition metal compounds the charge, orbital, spin and lattice degrees of freedom should all be taken into account. With the recognition that the local

M. W. Haverkort

2005-01-01

254

Oligocyclopentadienyl transition metal complexes  

SciTech Connect

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

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

2002-01-18

255

Tuning complex transition metal hydroxide nanostructures as active catalysts for water oxidation by a laser-chemical route.  

PubMed

Diverse transition metal hydroxide nanostructures were synthesized by laser-induced hydrolysis in a liquid precursor solution for alkaline oxygen evolution reaction (OER). Several active OER catalysts with fine control of composition, structure, and valence state were obtained including (Lix)[Ni0.66Mn0.34(OH)2](NO3)(CO3) · mH2O, Lix[Ni0.67Co0.33(OH)2](NO3)0.25(ORO)0.35 · mH2O, etc. An operate overpotential less than 0.34 V at current density of 10 mA cm(-2) was achieved. Such a controllable laser-chemical route for assessing complex nanostructures in liquids opens many opportunities to design novel functional materials for advanced applications. PMID:25723892

Niu, Kai-Yang; Lin, Feng; Jung, Suho; Fang, Liang; Nordlund, Dennis; McCrory, Charles C L; Weng, Tsu-Chien; Ercius, Peter; Doeff, Marca M; Zheng, Haimei

2015-04-01

256

Consistent LDA' + DMFT approach to the electronic structure of transition metal oxides: Charge transfer insulators and correlated metals  

SciTech Connect

We discuss the recently proposed LDA' + DMFT approach providing a consistent parameter-free treatment of the so-called double counting problem arising within the LDA + DMFT hybrid computational method for realistic strongly correlated materials. In this approach, the local exchange-correlation portion of the electron-electron interaction is excluded from self-consistent LDA calculations for strongly correlated electronic shells, e.g., d-states of transition metal compounds. Then, the corresponding double-counting term in the LDA' + DMFT Hamiltonian is consistently set in the local Hartree (fully localized limit, FLL) form of the Hubbard model interaction term. We present the results of extensive LDA' + DMFT calculations of densities of states, spectral densities, and optical conductivity for most typical representatives of two wide classes of strongly correlated systems in the paramagnetic phase: charge transfer insulators (MnO, CoO, and NiO) and strongly correlated metals (SrVO{sub 3} and Sr{sub 2}RuO{sub 4}). It is shown that for NiO and CoO systems, the LDA' + DMFT approach qualitatively improves the conventional LDA + DMFT results with the FLL type of double counting, where CoO and NiO were obtained to be metals. Our calculations also include transition-metal 4s-states located near the Fermi level, missed in previous LDA + DMFT studies of these monoxides. General agreement with optical and the X-ray experiments is obtained. For strongly correlated metals, the LDA' + DMFT results agree well with the earlier LDA + DMFT calculations and existing experiments. However, in general, LDA' + DMFT results give better quantitative agreement with experimental data for band gap sizes and oxygen-state positions compared to the conventional LDA + DMFT method.

Nekrasov, I. A., E-mail: nekrasov@iep.uran.ru; Pavlov, N. S.; Sadovskii, M. V. [Russian Academy of Sciences, Institute for Electrophysics, Ural Branch (Russian Federation)

2013-04-15

257

Copper catalysts for soot oxidation: alumina versus perovskite supports.  

PubMed

Copper catalysts prepared using four supports (Mg- and Sr-modified Al2O3 and MgTiO3 and SrTiO3 perovskites) have been tested for soot oxidation by 02 and NOx/O2. Among the catalysts studied, Cu/SrTiO3 is the most active for soot oxidation by NOx/O2 and the support affects positively copper activity. With this catalyst, and under the experimental conditions used, the soot combustion by NOx/O2 presents a considerable rate from 500 degrees C (100 degrees C below the uncatalysed reaction). The Cu/ SrTiO3 catalyst is also the most effective for NOx chemisorption around 425 degrees C. The best activity of Cu/SrTiO3 can be attributed to the improved redox properties of copper originated by Cu-support interactions. This seems to be related to the presence of weakly bound oxygen on this sample. The copper species present in the catalyst Cu/SrTiO3 can be reduced more easily than those in other supports, and for this reason, this catalyst seems to be the most effective to convert NO into NO2, which explains its highest activity for soot oxidation. PMID:18983091

López-Suárez, F E; Bueno-López, A; Illán-Gómez, M J; Adamski, A; Ura, B; Trawczynski, J

2008-10-15

258

OH radical-initiated oxidation of organic compounds in atmospheric water phases: part 2. Reactions of peroxyl radicals with transition metals  

NASA Astrophysics Data System (ADS)

The aim of this series of two publications is to characterise radical reactions of organic molecules, occurring in atmospheric water phases. In this second study, the reactions occurring in a mixed peroxyl radical system generated from the OH radical attack on a model compound, 2-butoxyethanol, in oxygenated aqueous solution are investigated in the presence of O 2-/HO 2 radicals, H 2O 2, and of copper (I and II)- and iron (II and III) species. A general mechanism of the reactions occurring in such systems is discussed and compared to the formation of organic hydroperoxides and hydrogen peroxide from this oxidation reactions. The main features of the mechanism are as follows: (i) production of peroxyl radicals following OH-attack on the model compound; (ii) cycling of the transition metals between the oxidation states given above, arising from a reduction reaction with superoxide, O 2-, and oxidation reactions by organic peroxyl radicals, organic hydroperoxides, superoxide, and oxygen; (iii) reactions of organic peroxyl radicals, in contrast to superoxide radicals, occur only with the reduced forms of the transition metals and lead to the formation of organic hydroperoxides; (iv) the reaction of organic peroxyl radicals with Cu (I) is fast ( k>10 8 M -1 s -1); (v) the reaction of organic hydroperoxides with Cu (I) can be much faster (2 orders of magnitude) than the analogous reaction of hydrogen peroxide and leads to the production of oxyl radicals; and (vi) oxalate, a strong ligand for Cu (II), reduces the activity of copper, owing to its stabilisation of the copper (II) complex. The mechanism is discussed in relation to atmospheric conditions.

Stemmler, Konrad; von Gunten, Urs

259

The performance of perovskites and spinels as catalysts for oxygen reduction in solid oxide fuel cell cathodes  

NASA Astrophysics Data System (ADS)

The lack of understanding of the catalytic process at the state-of-the-art cathode material surface in solid oxide fuel cells, (La0.8Sr 0.2)0.98MnO3+delta (LSM), has hindered the design of better catalysts. The objectives of this study were to design a system enabling the comparison of catalytic activities of different cathode materials independently of morphological factors, as well as to resolve catalytic processes at the LSM surface. The selection and optimization of potential cathode materials were performed on the basis of thermal expansion, four-probe dc-conductivity and thermoelectric power measurements in air. The materials studied as potential cathodes were tungsten, niobium and molybdenum doped barium cobaltite perovskites, copper manganese, cobalt manganese and cobalt ferrite spinels as well as strontium doped lanthanum cobalt ferrites and lanthanum manganite perovskites. The doped barium cobaltites were found lo offer superior electrical conductivity when octahedral site transition metal average valence was mixed 3+ /4+ compared to mixed 2+/3+. On the other hand, the loss of conductivity associated with octahedral site doping rendered these materials inadequate for solid oxide fuel cells (SOFC) cathode applications. Copper manganese spMd was found to exhibit electrical conductivity as high as ˜200 S.cm-1 at 1073 K and thermal expansion ˜ 11 ppm/K between 298 K and 1200 K. Thermal and chrono-potentiometric studies were used to determine the oxygen diffusivity, in cobalt and strontium doped lanthanum iron perovskites (LSCF), and revealed that the activation of strontium doped lanthanum manganese perovskites (LSM) under cathodic bias is kinetically limited by its rate of oxygen surface exchange, suggesting that the cathodic activation of LSM is due to its change in oxygen content under bias. The electronic defect structure of the cubic spinels was resolved in a defect reaction model involving the thermally activated redox of Cu + and Mn4+ to Cu2+ and Mn3+, as well as the disproportionation of Jahn-Teller ion Mn3+ into Mn2+ and Mn4+ and demonstrated that copper doping enhanced the amount of Mn4+ on octahedral sites. Cyclic voltammetry and potential-dependent electrochemical impedance spectroscopy studies of dense (La0.8Sr0.2)0.98MnO3+delta polycrystalline films revealed that the rate determining step in the oxygen reduction reaction, in the conditions of our study was the first charge transfer between oxygen ad-atoms and octahedral manganese III, as described by (S)Oad + MnxMn?O -adS +Mn•Mn. The catalytic activity of CuzMn3-- zO4 cubic spinets was found superior to that of LSM and of stoichiometrie CoFe2O4 and Co2MnO 4 spinal at intermediate temperature, suggesting that the Mn 3+/Mn4+ redox couple on octahedral sites plays a major role in the catalysis of the oxygen reduction reaction on those transition metal oxide surfaces.

Martin, Boris E.

260

The Local Electronic and Crystal Structure of Transition Metal and Group III A-Vii a Oxides Probed by X-Ray Absorption Spectroscopy.  

NASA Astrophysics Data System (ADS)

The d-orbitals of transition metals and the p -orbitals of the Group III A-VII A elements dominate the local electronic and structural properties in compounds of these materials. These important orbitals being, partially -filled and close to the Fermi level (E_ {F}) in energy, can be probed by X-ray absorption spectroscopy (XAS) which involves electronic transitions from atomic core-levels to empty states above the Fermi level. Specifically, the orbital electron/hole count, and the distribution in energy of these states can be addressed with XAS. In this work we develop XAS methods to probe local electronic and crystal structure and apply them to materials of current fundamental interest. In one part of this work we present XAS studies (L_1- and L_{2,3 }-edges) of a wide range of oxides involving all of the 4d-row transition metals (T). In view of the d-character of the final states at the L_ {2,3}-edges, XAS can provide a direct probe of the number and energy distribution of the T-d -states above E_{F}. We correlate the d-orbital occupancies with area of the intense 2p to 4d related "White Line" features at the L_{2,3}-edges of the transition metals in these compounds. Here the L _1-edge spectra are used to estimate the background continuum onset underlying the L_ {2,3}-edges and thereby to extract the d-orbital features. In addition we study the energy distribution of the d-states in a range of Mo-based oxides via L_{2,3}-edge XAS. The distinctive crystalline electric field splittings in the octahedral and tetrahedral ligand fields are observed in the L _{2,3}-edge WL-features. In an another part of this work, using K-edges of Cu and Ni in rm La_{2-x}Sr _{x}TO_4 (T = Cu, Ni) systems we investigate the changes in the local electronic and crystal structure and the nature of doped holes into the system upon Sr substitution. Our polarization dependent XAS results from single crystals of rm La _{2-x}Sr_{x}NiO_4 clarify the previous ambiguities in the spectral feature identification of Ni-K edge spectra. The splittings of the Ni 4p-levels (4p_pi - 4p_sigma) are shown to correlate with the anisotropies in the Ni-O distances in the crystal. The collapse of the pi-sigma ^littings, mainly moving of the 4p_ pi states to higher energies, causes an overestimation in the absorption edge shift and consequently the Ni-valence upon Sr substitution. Finally, we utilize the p-final state of the L_1- and K-edge transitions to investigate, for the first time, the p-level occupancies of Group III A-VII A elements in a wide range of compounds and make use of the systematics we obtain from these relatively simple structured oxides in more complex materials of interest. rm IBi_2Sr_2CaCu_2O_ {y}, for example, is a high-T _{c} material showing interesting anisotropic normal state resistivity. In investigating the anisotropies in the local electronic structure we benefit from the previously described transition metal oxide studies (Cu, Ni K-edges) and the Group III A-VII A element studies (I L_1-edge). The results show that the intercalated I layers extract electronic charge from the adjacent Bi-O layers.

Sahiner, Mehmet Alper

261

Mössbauer study of perovskite oxides for oxidative coupling of Ch4 and absorption of Co2  

NASA Astrophysics Data System (ADS)

Perovskite oxides, (Ba0.95 Ca0.05) (Co1- x Fe x ) O3-?, are prominent materials for oxidative coupling of methane and for CO2 absorption at high temperature, and these oxides before and after treatment in CH4 and CO2 atmosphere were analysed by Mössbauer spectroscopy. The perturbation of microstructure by substitution of Ba sites with Ca, and the electron transfer of mixed valences in Fe and Co ions with the formation of oxygen vacancies at high temperatures, are considered to contribute strongly to the selectivity of CH4 coupling and the rapid absorption of CO2 at high temperatures.

Nomura, K.; Homonnay, Z.; Vertes, A.; Chechersky, V.; Nath, A.; Ujihira, Y.; Hayakawa, T.; Takehira, K.

1997-05-01

262

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

NASA Astrophysics Data System (ADS)

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.

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

2014-04-01

263

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

NASA Astrophysics Data System (ADS)

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.

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

2014-12-01

264

A general polymer-assisted solution approach to grow transition metal oxide nanostructures directly on nickel foam as anodes for Li-ion batteries  

NASA Astrophysics Data System (ADS)

Cobalt oxide nanostructures have been successfully grown on nickel foam by a facile polymer-assisted chemical solution method for lithium-ion battery anodes. The carbon left from the decomposition of polymers is an effective binder between the metal oxides and nickel foam. As compared to the metal oxide powder prepared in a conventional way by using polymer binder and carbon black, these one-step direct growth electrodes showed much better Li storage properties with high capacities, stable cyclability, and rate capability: Co3O4 on nickel foam gave a capacity of 900 mAh g-1 at a current density of 1 A g-1 and 600 mAh g-1 at 4 A g-1. The good performances of these electrodes could be attributed to intimate contact between the active material and nickel foam, the porosity of the current collector, and the network structure of the active materials. This general method could also be applied to other transition metal oxides.

Xu, Yun; Fei, Ling; Fu, Engang; Yuan, Bin; Hill, Joshua; Chen, Yingxi; Deng, Shuguang; Andersen, Paul; Wang, Yongqiang; Luo, Hongmei

2013-11-01

265

Epitaxial integration of perovskite-based multifunctional oxides on silicon q  

E-print Network

- tifunctional oxide devices, these multifunctional films should be integrated directly on Si, maintaining high of oxides into a Si-based platform to realize multifunctional devices. In this sense, it is highly desirableEpitaxial integration of perovskite-based multifunctional oxides on silicon q Seung-Hyub Baek

Eom, Chang Beom

266

Efficient planar heterojunction perovskite solar cells employing graphene oxide as hole conductor  

NASA Astrophysics Data System (ADS)

Graphene oxide (GO) is employed as a hole conductor in inverted planar heterojunction perovskite solar cells, and the devices with CH3NH3PbI3-xClx as absorber achieve an efficiency of over 12%. The perovskite film grown on GO exhibits enhanced crystallization, high surface coverage ratio as well as preferred in-plane orientation of the (110) plane. Efficient hole extraction from the perovskite to GO is demonstrated.Graphene oxide (GO) is employed as a hole conductor in inverted planar heterojunction perovskite solar cells, and the devices with CH3NH3PbI3-xClx as absorber achieve an efficiency of over 12%. The perovskite film grown on GO exhibits enhanced crystallization, high surface coverage ratio as well as preferred in-plane orientation of the (110) plane. Efficient hole extraction from the perovskite to GO is demonstrated. Electronic supplementary information (ESI) available: Additional device cross-section, GO morphologies on ITO, transmittance of different substrates, morphologies and absorbances of perovskite films on different substrates and electrical characterization of devices with different hole conductors. See DOI: 10.1039/c4nr03181d

Wu, Zhongwei; Bai, Sai; Xiang, Jian; Yuan, Zhongcheng; Yang, Yingguo; Cui, Wei; Gao, Xingyu; Liu, Zhuang; Jin, Yizheng; Sun, Baoquan

2014-08-01

267

Electronic conduction in La-based perovskite-type oxides  

NASA Astrophysics Data System (ADS)

A systematic study of La-based perovskite-type oxides from the viewpoint of their electronic conduction properties was performed. LaCo0.5Ni0.5O3±? was found to be a promising candidate as a replacement for standard metals used in oxide electrodes and wiring that are operated at temperatures up to 1173 K in air because of its high electrical conductivity and stability at high temperatures. LaCo0.5Ni0.5O3±? exhibits a high conductivity of 1.9 × 103 S cm?1 at room temperature (R.T.) because of a high carrier concentration n of 2.2 × 1022 cm?3 and a small effective mass m* of 0.10 me. Notably, LaCo0.5Ni0.5O3±? exhibits this high electrical conductivity from R.T. to 1173 K, and little change in the oxygen content occurs under these conditions. LaCo0.5Ni0.5O3±? is the most suitable for the fabrication of oxide electrodes and wiring, though La1?xSrxCoO3±? and La1?xSrxMnO3±? also exhibit high electronic conductivity at R.T., with maximum electrical conductivities of 4.4 × 103 S cm?1 for La0.5Sr0.5CoO3±? and 1.5 × 103 S cm?1 for La0.6Sr0.4MnO3±? because oxygen release occurs in La1?xSrxCoO3±? as elevating temperature and the electrical conductivity of La0.6Sr0.4MnO3±? slightly decreases at temperatures above 400 K.

Kozuka, Hisashi; Ohbayashi, Kazushige; Koumoto, Kunihito

2015-04-01

268

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

PubMed

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

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

2015-01-01

269

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

PubMed Central

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

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

2015-01-01

270

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

NASA Astrophysics Data System (ADS)

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.

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

2015-03-01

271

Transition metals in superheat melts  

NASA Technical Reports Server (NTRS)

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

Jakes, Petr; Wolfbauer, Michael-Patrick

1993-01-01

272

Facile and novel electrochemical preparation of a graphene-transition metal oxide nanocomposite for ultrasensitive electrochemical sensing of acetaminophen and phenacetin  

NASA Astrophysics Data System (ADS)

A facile and novel preparation strategy based on electrochemical techniques for the fabrication of electrodeposited graphene (EGR) and zinc oxide (ZnO) nanocomposite was developed. The morphology and structure of the EGR-based nanocomposite were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (XPS) and Raman spectroscopy. Meanwhile, the electrochemical performance of the nanocomposite was demonstrated with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Due to the synergistic effect of EGR and ZnO nanoparticles, an ultrasensitive electrochemical sensor for acetaminophen (AC) and phenacetin (PCT) was successfully fabricated. The linearity ranged from 0.02 to 10 ?M for AC and 0.06 to 10 ?M for PCT with high sensitivities of 54 295.82 ?A mM-1 cm2 for AC and 21 344.66 ?A mM-1 cm2 for PCT, respectively. Moreover, the practical applicability was validated to be reliable and desirable in pharmaceutical detections. The excellent results showed the promise of the proposed preparation strategy of EGR-transition metal oxide nanocomposite in the field of electroanalytical chemistry.A facile and novel preparation strategy based on electrochemical techniques for the fabrication of electrodeposited graphene (EGR) and zinc oxide (ZnO) nanocomposite was developed. The morphology and structure of the EGR-based nanocomposite were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (XPS) and Raman spectroscopy. Meanwhile, the electrochemical performance of the nanocomposite was demonstrated with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Due to the synergistic effect of EGR and ZnO nanoparticles, an ultrasensitive electrochemical sensor for acetaminophen (AC) and phenacetin (PCT) was successfully fabricated. The linearity ranged from 0.02 to 10 ?M for AC and 0.06 to 10 ?M for PCT with high sensitivities of 54 295.82 ?A mM-1 cm2 for AC and 21 344.66 ?A mM-1 cm2 for PCT, respectively. Moreover, the practical applicability was validated to be reliable and desirable in pharmaceutical detections. The excellent results showed the promise of the proposed preparation strategy of EGR-transition metal oxide nanocomposite in the field of electroanalytical chemistry. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr03620k

Jiang, Lin; Gu, Shuqing; Ding, Yaping; Jiang, Feng; Zhang, Zhen

2013-12-01

273

Calixarene supported transition metal clusters   

E-print Network

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

Taylor, Stephanie Merac

2013-06-29

274

Chemistry of sulfur oxides on transition metal surfaces: a bond order conservation-Morse potential modeling perspective  

Microsoft Academic Search

We have employed the bond order conservation-Morse potential (BOC-MP) method to analyze the chemistry of sulfur oxides on the copper and nickel group metals. Specifically, we have calculated the reaction energetics (heats of adsorption, reaction enthalpies and intrinsic activation barriers) of the decomposition and oxidation of sulfur dioxide at low coverages on fcc (111) surfaces of Cu, Ag, Au, Ni,

Harrell Sellers; Evgeny Shustorovich

1996-01-01

275

Aqueous transition-metal cations as impurities in a wide gap oxide: the Cu(2+)/Cu(+) and Ag(2+)/Ag(+) redox couples revisited.  

PubMed

The interactions of the d electrons of transition-metal aqua ions with the solvent are usually divided in short-range electronic interactions with ligand water molecules and long-range electrostatic interactions with molecules beyond the first coordination shell. This is the rationale behind the cluster continuum and QM/MM methods developed for the computation of the redox potentials. In the density functional theory based molecular dynamics (DFTMD) method, the electronic states of the complex are also allowed to mix with the extended band states of the solvent. Returning to the Cu(+) and Ag(+) oxidation reaction, which has been the subject of DFTMD simulation before, we show that coupling to the valence band states of water is greatly enhanced by the band gap error in the density functional approximation commonly used in DFTMD (the generalized gradient approximation). This effect is analyzed by viewing the solvent as a wide gap oxide and the redox active ions as electronic defects. The errors can be reduced significantly by application of hybrid functionals containing a fraction of Hartree-Fock exchange. These calculations make use of recent progress in DFTMD technology, enabling us to include sp core polarization and Hartree-Fock exchange in condensed-phase model systems. PMID:25386900

Liu, Xiandong; Cheng, Jun; Sprik, Michiel

2015-01-22

276

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

SciTech Connect

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.

Michael John Vasbinder

2006-12-12

277

Transition metals in silicon  

Microsoft Academic Search

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

Eicke R. Weber

1983-01-01

278

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

SciTech Connect

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.

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

1996-12-01

279

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

DOEpatents

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.

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

2001-01-01

280

Analysis of charge-injection characteristics at electrode-organic interfaces: Case study of transition-metal oxides  

Microsoft Academic Search

The formation of resistance-free or Ohmic contacts at metal\\/organic interfaces remains a significant challenge for achieving high-performance organic electronic devices such as organic light-emitting diodes. Several oxides have recently been reported to yield extremely low-voltage devices and thus have excited a renewed interest in developing the next generation of contacting electrodes. In this paper, major metal oxides, CuO, Cu2O ,

Z. B. Wang; M. G. Helander; M. T. Greiner; J. Qiu; Z. H. Lu

2009-01-01

281

Study of the temperature-programmed reaction synthesis of early transition metal carbide and nitride catalyst materials from oxide precursors  

Microsoft Academic Search

The synthesis of high surface area carbide and nitride materials from binary and ternary oxides of vanadium, niobium, tantalum, molybdenum, and tungsten, suitable for use as catalysts for a wide range of reactions, has been investigated via the temperature-programmed reaction (TPRe) method, in various gas mixtures. TPRe of oxides in CHâ\\/Hâ, CâHâ\\/Hâ, or NHâ yield materials with surface areas >

John B. Claridge; Andrew P. E. York; Attila J. Brungs; Malcolm L. H. Green

2000-01-01

282

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...

283

Development of novel low-temperature selective hydrogen gas sensors made of palladium/oxide or nitride capped Magnesium-transition metal hydride films  

NASA Astrophysics Data System (ADS)

Palladium capped Mg-based transition metal alloy film (Pd/Mg-TM) is a potentially useful hydrogen gas (H2) sensing material, which can operate at low temperature for detection of H2 leakage in an environment to ensure safe use and storage of the gas. The Pd layer catalytically dissociates hydrogen molecules, and the hydrogen atoms produced can enter (hydridation) or be detached (dehydridation) from the alloy layer. These processes are reversible, such that the film is switchable between a metal state and a hydride state, giving rise to substantial changes in its optical transmittance/reflectance and electrical resistivity. Unlike a conventional metal-oxide (MOx) H2 sensor, hydridation of an Mg-TM film is associated with relatively low enthalpy, and hence can perform at temperature much lower than the operation temperature of an MOx sensor (typically around 500°C or above). As such, an Mg-TM based sensor does not experience undesired annealing effect during operation, and hence is much more stable and durable. Furthermore, the detection selectivity of a Pd/Mg-TM film versus other reducing gases is superior to most conventional MOx-type hydrogen sensors. In this project, we systematically investigated the H2 sensing properties of Pd/Mg-TM films.

Tang, Yu Ming

284

The formation of carbon surface oxygen complexes by oxygen and ozone. The effect of transition metal oxides  

Microsoft Academic Search

Various surface oxygen complexes (SOCs) have been identified by DRIFT spectroscopy on the surface of carbon black (Printex-U) after partial non-catalytic conversion in 10% O2 in Ar and ozone. An in situ DRIFT analysis of the oxidation of fullerene C60 showed the formation of similar functionalities and validated the use of C60 as a carbon black model compound for DRIFT

G. Mul; J. P. A. Neeft; F. Kapteijn; J. A. Moulijn

1998-01-01

285

Structures, Energetics, and Vibrations of Small Transition Metal Oxide Clusters by High-Resolution Anion Photoelectron Spectroscopy  

NASA Astrophysics Data System (ADS)

Anion photoelectron spectroscopy has been a major tool in understanding the vibronic structure of metal oxide clusters, due to its universality and sensitivity. However, high ion temperatures and modest photoelectron energy resolutions have hampered the observation of vibrational structure. We have recently coupled our high-resolution slow photoelectron velocity-map imaging (SEVI) spectrometer to a cryogenic ion trap and a laser ablation ion source, allowing for the acquisition of photoelectron spectra of vibrationally cold metal oxide anions with a resolution down to ˜4 cm-1, limited by unresolved rotational structure. A test study of the simple d^0 group 4 MO_2 triatomic metal oxides yielded fully vibrationally-resolved spectra, allowing for reassignments of electron affinities, new measurements of vibrational fundamentals, and estimates of the anion geometries based on the observed FC structure. Studies of the corresponding Ti_2O_4 and Zr_2O_4 systems revealed vibrational progressions that allows for an unambiguous assignment of the anion isomers; previous photoelectron spectra could not distinguish the isomers based on detachment energies alone. Spectra of the VO_2^- anion identified the first three electronic states of the d^1 neutral as well as ?_1 and ?_2 vibrations in each state.

Kim, Jongjin B.; Weichman, Marissa L.; Neumark, Daniel

2014-06-01

286

Spin and orbital degrees of freedom in transition metal oxides and oxide thin films studied by soft x-ray absorption spectroscopy  

Microsoft Academic Search

The class of transition metal compounds shows an enormous richness of\\u000aphysical properties, such as metal-insulator transitions, colossal\\u000amagneto-resistance, super-conductivity, magneto-optics and spin-depend\\u000atransport. It now becomes more and more clear that in order to describe\\u000atransition metal compounds the charge, orbital, spin and lattice degrees of\\u000afreedom should all be taken into account. With the recognition that the local

M. W. Haverkort

2005-01-01

287

Coulomb interaction in oxygen \\\\textit{p}-shell in LDA+U method and its influence on calculated spectral and magnetic properties of transition metal oxides  

Microsoft Academic Search

Coulomb interaction between electrons on p-orbitals of oxygen atom in strongly correlated compounds is not negligible, since its value (U_p) has comparable order of magnitude with the value of Coulomb interaction on d-orbitals of transition metal atom (U_d). We investigate the effect of taking into account Coulomb correlations in oxygen p-shell in addition to the correlations in the transition metal

I. A. Nekrasov; M. A. Korotin; V. I. Anisimov

2000-01-01

288

Ab initio study of perovskite type oxide materials for solid oxide fuel cells  

NASA Astrophysics Data System (ADS)

Perovskite type oxides form a family of materials of significant interest for cathodes and electrolytes of solid oxide fuel cells (SOFCs). These perovskites not only are active catalysts for surface oxygen reduction (OR) reactions but also allow incorporating the spilt oxygen monomers into their bulk, an unusual and poorly understood catalytic mechanism that couples surface and bulk properties. The OR mechanisms can be influenced strongly by defects in perovskite oxides, composition, and surface defect structures. This thesis work initiates a first step in developing a general strategy based on first-principles calculations for detailed control of oxygen vacancy content, transport rates of surface and bulk oxygen species, and surface/interfacial reaction kinetics. Ab initio density functional theory methods are used to model properties relevant for the OR reactions on SOFC cathodes. Three main research thrusts, which focus on bulk defect chemistry, surface defect structures and surface energetics, and surface catalytic properties, are carried to investigate different level of material chemistry for improved understanding of key physics/factors that govern SOFC cathode OR activity. In the study of bulk defect chemistry, an ab initio based defect model is developed for modeling defect chemistry of LaMnO 3 under SOFC conditions. The model suggests an important role for defect interactions, which are typically excluded in previous defect models. In the study of surface defect structures and surface energetics, it is shown that defect energies change dramatically (1˜2 eV lower) from bulk values near surfaces. Based on the existing bulk defect model with the calculated ab initio surface defect energetics, we predict the (001) MnO 2 surface oxygen vacancy concentration of (La0.9Sr0.1 )MnO3 is about 5˜6 order magnitude higher than that of the bulk under typical SOFC conditions. Finally, for surface catalytic properties, we show that area specific resistance, oxygen exchange rates, and key OR energetics of the SOFC cathode perovskites, can be described by a single descriptor, either the bulk O p-band or the bulk oxygen vacancy formation energy. These simple descriptors will further enable first-principles optimization/design of new SOFC cathodes.

Lee, Yueh-Lin

2011-12-01

289

Transition Metal Switchable Mirror  

SciTech Connect

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

None

2009-01-01

290

Transition Metal Switchable Mirror  

SciTech Connect

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

2009-08-21

291

Transition Metal Switchable Mirror  

ScienceCinema

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

None

2013-05-29

292

Transition Metal Switchable Mirror  

ScienceCinema

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

None

2010-01-08

293

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

NASA Astrophysics Data System (ADS)

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.

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

2014-07-01

294

Structural and Electronic Properties of Reduced Transition Metal Oxide Clusters, M3O8 and M3O8- (M = Cr, W), from Photoelectron Spectroscopy and Quantum Chemical Calculations  

Microsoft Academic Search

We report a comparative study of reduced transition metal oxide clusters, M3O8- (M = Cr, W) anions and their neutrals, via anion photoelectron spectroscopy (PES) and density functional theory (DFT) and molecular orbital theory (CCSD(T)) calculations. Well-resolved PES spectra are obtained for M3O8- (M = Cr, W) at 193 and 157 nm photon energies. Different PES spectra are observed for

Shenggang Li; Hua-Jin Zhai; Lai-Sheng Wang; David A. Dixon

2009-01-01

295

Electronic structures of transition metal to hydrogen bonds: oxidative addition of dihydrogen to a square planar rhodium complex and quantum mechanical prediction of the geometry of a metal hydride  

E-print Network

ELECTRONIC STRUCTURES OF TRANSITION METAL TO HYDROGEN BONDS: OXIDATIVE ADDITION OF DIHYDROGEN TO A SQUARE PLANAR RHODIUM COMPLEX AND QUANTUM MECHANICAL PREDICTION OF THE GEOMETRY OF A METAL HYDRIDE A Thesis CAROLYN F. HALPIN Submitted... OF DIHYDROGEN TO A SQUARE PLANAR RHODIUM COMPLEX AND QUANTUM MECHAMCAL PREDICTION OF THE GEOMETRY OF A METAL HYDRlDE A Thesis by CAROLYN F. HALPIN Approved as to style and content by: ~c ae (Chairman) ona . areas o (Member) aan aane (Member) en...

Halpin, Carolyn F.

1986-01-01

296

Exploring the color of transition metal ions in irregular coordination geometries: new colored inorganic oxides based on the spiroffite structure, Zn(2-x)M(x)Te3O8 (M = Co, Ni, Cu).  

PubMed

We describe the synthesis, crystal structures, and optical absorption spectra of transition metal-substituted spiroffite derivatives, Zn(2-x)M(x)Te3O8 (M(II) = Co, Ni, Cu; 0 < x ? 1.0). The oxides are readily synthesized by solid state reaction of stoichiometric mixtures of the constituent binaries at 620 °C. Reitveld refinement of the crystal structures from powder X-ray diffraction (XRD) data shows that the Zn/MO6 octahedra are strongly distorted, as in the parent Zn2Te3O8 structure, consisting of five relatively short Zn/M(II)-O bonds (1.898-2.236 Å) and one longer Zn/M(II)-O bond (2.356-2.519 Å). We have interpreted the unique colors and the optical absorption/diffuse reflectance spectra of Zn(2-x)M(x)Te3O8 in the visible, in terms of the observed/irregular coordination geometry of the Zn/M(II)-O chromophores. We could not however prepare the fully substituted M2Te3O8 (M(II) = Co, Ni, Cu) by the direct solid state reaction method. Density Functional Theory (DFT) modeling of the electronic structure of both the parent and the transition metal substituted derivatives provides new insights into the bonding and the role of transition metals toward the origin of color in these materials. We believe that transition metal substituted spiroffites Zn(2-x)M(x)Te3O8 reported here suggest new directions for the development of colored inorganic materials/pigments featuring irregular/distorted oxygen coordination polyhedra around transition metal ions. PMID:23659639

Tamilarasan, S; Sarma, Debajit; Bhattacharjee, S; Waghmare, U V; Natarajan, S; Gopalakrishnan, J

2013-05-20

297

Computational screening of perovskite metal oxides for optimal solar light Ivano E. Castelli,a  

E-print Network

Computational screening of perovskite metal oxides for optimal solar light capture Ivano E have appropriate bandgaps to absorb a large part of the solar spectrum at the same time as being stable is to a large extent due to easy access to cheap fossil fuels. These resources are limited, and the ever

Thygesen, Kristian

298

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

E-print Network

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 ...

May, Kevin J. (Kevin Joseph)

2013-01-01

299

A First Principles Investigation of Proton Chemistry in Perovskite-Type Oxides  

NASA Astrophysics Data System (ADS)

Certain acceptor-doped perovskite-type oxides show significant promise for deployment into a number of electrochemical device applications, including fuel cells, batteries, and electrolyzers, owing to their rapid proton conductivities at high temperatures. However, limitations in bulk material hydration and slow grain boundary conductivities have reduced the viability of these materials in intermediate temperatures applications. This thesis work uses density functional theory to gain a fundamental understanding of proton and defect chemistry within various perovskite environments in order to identify strategies to increase proton concentration and improve overall proton conductivity. First, material hydration was probed within yttrium-doped barium cerate (BCY) to examine how the thermodynamics of material hydration are influenced by dopant concentration. A model was derived from solely first principle techniques to describe hydration within BCY as a function of dopant concentration, temperature, and partial pressure of water. The resulting model can be used to screen for favorable perovskite-dopant combinations with enhanced hydration capabilities. Next, defect segregation was investigated in the more complex interfacial environment to probe the origin of low proton conductivity across perovskite grain boundaries (GB). The results of this study suggest that screening for perovskite-dopant combinations with strong dopant-oxygen bond strengths may reduce the segregation of dopant ions and oxygen vacancies to the GB interface, mitigating the development of a positive GB core and enhancing proton conduction across the GB. Finally, proton stability was assessed at various interfacial regions within the perovskite material. An examination of proton adsorption at the BaZrO3-vacuum interface reveals a destabilization of protons in the first subsurface layer of the perovskite, yielding a potential barrier for proton diffusion into and out of the perovskite membrane. An electronic analysis of oxygen ions indicates that the oxygen p-band center influences proton adsorption strength. This p-band center model was shown to accurately describe adsorption trends within bulk BCY as well. An analysis of proton adsorption at BaZrO3-metal heterointerfaces displayed a stabilization of protons in the near heterointerfacial environment compared to the BaZrO 3-vacuum surface. This stabilization reduces the barrier for proton diffusion near the perovskite interface and likely leads to increased proton concentrations at the perovskite-metal heterointerface.

Tauer, Tania Allison

300

Simultaneous no x reduction and soot elimination from diesel exhaust on perovskite-type oxide catalysts  

Microsoft Academic Search

Series of partially substituted manganates belonging to perovskite structure family is prepared and characterized with a view to use them as catalyst for reduction of nitric oxides with carbon black. Catalytic tests show that the series La0.8Sr0.2Mn1?xCuxO3±1 have the best activity among the perovskite samples. La2CuO4, which belongs to K2NiF4 structure family, is more active than the others, but unfortunately

V. Duriez; L. Monceaux; P. Courtine

1995-01-01

301

Iron-based perovskite cathodes for solid oxide fuel cells  

DOEpatents

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.

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

2007-01-02

302

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

PubMed Central

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

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

303

Coulomb interaction in oxygen \\\\textit{p}-shell in LDA+U method and its influence on calculated spectral and magnetic properties of transition metal oxides  

Microsoft Academic Search

Coulomb interaction between electrons on p-orbitals of oxygen atom in\\u000astrongly correlated compounds is not negligible, since its value (U_p) has\\u000acomparable order of magnitude with the value of Coulomb interaction on\\u000ad-orbitals of transition metal atom (U_d). We investigate the effect of taking\\u000ainto account Coulomb correlations in oxygen p-shell in addition to the\\u000acorrelations in the transition metal

I. A. Nekrasov; M. A. Korotin; V. I. Anisimov

2000-01-01

304

Tailored surfaces of perovskite oxide substrates for conducted growth of thin films.  

PubMed

Oxide electronics relies on the availability of epitaxial oxide thin films. The extreme flexibility of the chemical composition of ABO3 perovskites and the broad spectrum of properties they cover, inspire the creativity of scientists and place perovskites in the lead of functional materials for advanced technologies. Moreover, emerging properties are being discovered at interfaces between distinct perovskites that could not be anticipated on the basis of those of the adjacent epitaxial layers. All dreamed new prospects require the use of suitable substrates for epitaxial growth. Perovskite single crystals are the workhorses of this activity and understanding and controlling their surface properties have become critical. In this tutorial review we will chiefly focus on the impact of the morphology and composition of the surface of ABO3 perovskite substrates on the growth mechanisms and properties of thin films epitaxially grown on them. As SrTiO3 is the most popular substrate, we will mostly concentrate on describing the current understanding and achievements for it. Illustrative examples of other perovskite substrates (LaAlO3, LSAT and DyScO3) will be also included. We will show that distinct chemical terminations can exist on the surfaces used for growth and we will review methods employed either to select the most appropriate one for specific growth to allow, for instance, tailoring the ultimate outmost epilayer, or to induce self-ordering to engineer long-range nanoscale patterns of chemical terminations. We will demonstrate the capacity of this knowledge by the growth of low-dimensional organic and inorganic structures. PMID:24553667

Sánchez, Florencio; Ocal, Carmen; Fontcuberta, Josep

2014-04-01

305

Selective hydrogen oxidation in the presence of C3 hydrocarbons using perovskite oxygen reservoirs.  

PubMed

Perovskite-type oxides, ABO(3), can be successfully applied as solid "oxygen reservoirs" in redox reactions such as selective hydrogen combustion. This reaction is part of a novel process for propane oxidative dehydrogenation, wherein the lattice oxygen of the perovskite is used to combust hydrogen selectively from the dehydrogenation mixture at 550 degrees C. This gives three key advantages: it shifts the dehydrogenation equilibrium to the side of the desired products, heat is generated, thus aiding the endothermic dehydrogenation, and it simplifies product separation (H(2)O vs H(2)). Furthermore, the process is safer since it uses the catalysts' lattice oxygen instead of gaseous O(2). We screened fourteen perovskites for activity, selectivity and stability in selective hydrogen combustion. The catalytic properties depend strongly on the composition. Changing the B atom in a series of LaBO(3) perovskites shows that Mn and Co give a higher selectivity than Fe and Cr. Replacing some of the La atoms with Sr or Ca also affects the catalytic properties. Doping with Sr increases the selectivity of the LaFeO(3) perovskite, but yields a catalyst with low selectivity in the case of LaCrO(3). Conversely, doping LaCrO(3) with Ca increases the selectivity. The best results are achieved with Sr-doped LaMnO(3), with selectivities of up to 93 % and activities of around 150 mumol O m(-2). This catalyst, La(0.9)Sr(0.1)MnO(3), shows excellent stability, even after 125 redox cycles at 550 degrees C (70 h on stream). Notably, the activity per unit surface area of the perovskite catalysts is higher than that of doped cerias, the current benchmark of solid oxygen reservoirs. PMID:18418824

Beckers, Jurriaan; Drost, Ruben; van Zandvoort, Ilona; Collignon, Paul F; Rothenberg, Gadi

2008-05-16

306

Electrocatalysis of hydrogen peroxide reactions on perovskite oxides: experiment versus kinetic modeling.  

PubMed

Hydrogen peroxide has been identified as a stable intermediate of the electrochemical oxygen reduction reaction on various electrodes including metal, metal oxide and carbon materials. In this article we study the hydrogen peroxide oxidation and reduction reactions in alkaline medium using a rotating disc electrode (RDE) method on oxides of the perovskite family (LaCoO3, LaMnO3 and La0.8Sr0.2MnO3) which are considered as promising electrocatalytic materials for the cathode of liquid and solid alkaline fuel cells. The experimental findings, such as the higher activity of Mn-compared to that of Co-perovskites, the shape of RDE curves, and the influence of the H2O2 concentration, are rationalized with the help of a microkinetic model. PMID:24643772

Poux, T; Bonnefont, A; Ryabova, A; Kéranguéven, G; Tsirlina, G A; Savinova, E R

2014-07-21

307

Selenophene transition metal complexes  

SciTech Connect

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

White, C.J.

1994-07-27

308

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)

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.

Jin, Fangjun; Li, Lei; He, Tianmin

2015-01-01

309

Transition metals as catalysts of "autoxidation" reactions.  

PubMed

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

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

1990-01-01

310

Homogeneous catalysis by transition metal oxygen anion clusters  

Microsoft Academic Search

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

Craig L. Hill; Christina M. Prosser-McCartha

1995-01-01

311

Epitaxial perovskite magnetic oxide thin films and bilayers  

NASA Astrophysics Data System (ADS)

Exchange bias is a phenomenon observed at interfaces between ferromagnetic (F) and antiferromagnetic (AF) materials. Exchange coupling between spins in the two materials results in a unidirectional anisotropy which manifests itself in experiments as a shift of the magnetization hysteresis loop of the ferromagnet. Despite substantial research efforts, the mechanism of this interfacial phenomenon has yet to be fully understood. The amount of shift serves as a measure of the effect called the exchange bias field, or briefly, exchange bias. We have studied the exchange bias in a series of thin F/AF bilayers grown by ozone-assisted molecular beam epitaxy. Calcium doped lanthanum manganite perovskites La(1-x)Ca xMnO3 of appropriate doping levels x were used to realize the bilayers. The films were grown on (100)-oriented closely lattice-matched perovskite SrTiO3 substrates. Through detailed structural characterization, we show that our bilayers resemble very much a model system, on which the simple theoretical approach of Meiklejohn and Bean can be tested. In our series of bilayers, the thickness of the AF layer has been varied, while that of the F layer has been kept constant. We have studied the exchange bias as a function of the AF layer thickness The observed dependence is similar to that exhibited by exchange-biased systems based on other materials. The exchange bias effect has been successfully utilized in the magnetic recording industry. From the applications standpoint, it is interesting to know the critical AF thickness of an exchange-biased system---a value, below which the effect vanishes. From the results of our investigation, we determine the critical AF thickness. Within the framework of the simple model of Meiklejohn and Bean for the exchange bias, we have used the AF thickness dependence and the critical value to estimate the magnetocrystalline anisotropy of the antiferromagnetic material, a quantity not previously reported for AF manganites.

Kobrinskii, Alexey Leonidovich

312

A half-metallic A- and B-site-ordered quadruple perovskite oxide CaCu3Fe2Re2O12 with large magnetization and a high transition temperature  

NASA Astrophysics Data System (ADS)

Strong correlation between spins and conduction electrons is key in spintronic materials and devices. A few ferro- or ferrimagnetic transition metal oxides such as La1-xSrxMnO3, Fe3O4, CrO2 and Sr2FeMoO6 have spin-polarized conduction electrons at room temperature, but it is difficult to find other spin-polarized oxides with high Curie temperatures (well above room temperature) and large magnetizations for spintronics applications. Here we show that an A- and B-site-ordered quadruple perovskite oxide, CaCu3Fe2Re2O12, has spin-polarized conduction electrons and is ferrimagnetic up to 560?K. The couplings between the three magnetic cations lead to the high Curie temperature, a large saturation magnetization of 8.7??B and a half-metallic electronic structure, in which only minority-spin bands cross the Fermi level, producing highly spin-polarized conduction electrons. Spin polarization is confirmed by an observed low-field magnetoresistance effect in a polycrystalline sample. Optimization of CaCu3Fe2Re2O12 and related quadruple perovskite phases is expected to produce a new family of useful spintronic materials.

Chen, Wei-Tin; Mizumaki, Masaichiro; Seki, Hayato; Senn, Mark S.; Saito, Takashi; Kan, Daisuke; Attfield, J. Paul; Shimakawa, Yuichi

2014-05-01

313

P-type perovskite oxide metal\\/semiconductor superlattices for thermoelectric generators  

Microsoft Academic Search

Metal\\/semiconductor superlattices with cross-plane transport offer a novel approach towards improving the thermoelectric figure of merit (ZT) over conventional thermoelectric materials operating at high temperatures 800–1000K. The perovskite oxides are a promising materials system for these metal\\/semiconductor superlattices due to their diverse range of properties, which allows tuning of the intertwined thermoelectric properties. ^ Lanthanum Strontium Manganate (LSMO)\\/Lanthanum Manganate (LMO)

Pankaj Jha

2010-01-01

314

Solid Electrolyte NOx Gas Sensor Using Perovskite-Type Oxide Electrodes  

Microsoft Academic Search

Electrochemical devices based on coupling an oxygen ionic conductor (Y2O3-stabilized ZrO2 : YSZ) with a perovskite-type oxide (LaFeO3) were found to exhibit promising performance for the sensing of NO2 at 400 and 450°C. EMF values of the (Pt)LaFeO3\\/YSZ\\/Pt sensor increased in NO2 atmosphere with a quick response time. The increase in EMF value has been attributed to an increase in

Jong-Won Yoon; Maria Luisa Grilli; Elisabetta di Bartolomeo; Enrico Traversa

2000-01-01

315

Electrical properties of the double perovskite oxide Ho2CuZrO6  

Microsoft Academic Search

The double perovskite oxide holmium copper zirconate, Ho2CuZrO6 (HCZ), was synthesized by a solid-state reaction technique. The crystal structure of HCZ shows a monoclinic phase. The dielectric relaxation of HCZ was investigated in the frequency range 44 Hz-1 MHz and in the temperature range 40-360 °C by using impedance spectroscopy. The complex impedance data were analysed by the Cole-Cole model.

D. K. Mahato; Alo Dutta; Nishant Kumar; T. P. Sinha

2011-01-01

316

Lattice distortion and magnetism of 3d-t2g perovskite oxides  

Microsoft Academic Search

Several puzzling aspects of interplay of the experimental lattice distortion and the magnetic behavior of four narrow t2g -band perovskite oxides ( YTiO3 , LaTiO3 , YVO3 , and LaVO3 ) are clarified using results of first-principles electronic structure calculations. First, we derive parameters of the effective Hubbard-type Hamiltonian for the isolated t2g bands using newly developed downfolding method for

I. V. Solovyev

2006-01-01

317

Electrostatic Spray Deposition of Perovskite-Type Oxides Thin Films with Porous Microstructure  

Microsoft Academic Search

The deposition of perovskite-type oxides thin films [La0.8Sr0.2MnO3 and La1-xSrxCo1-yFeyO3 (0 ? x ? 0.4 and 0 ? y ? 1)] was investigated using the electrostatic spray deposition (ESD) technique. Lanthanum nitrate, strontium chloride and manganese nitrate, or cobalt nitrate and iron nitrate were dissolved into a mixture of 33 vol% ethanol and 67 vol% butyl carbitol, which was used

I. Taniguchi; J. Schoonman

2002-01-01

318

High throughput fabrication of transition-metal-doped epitaxial ZnO thin films: A series of oxide-diluted magnetic semiconductors and their properties  

Microsoft Academic Search

Combinatorial laser molecular-beam epitaxy method was employed to fabricate epitaxial ZnO thin films doped with all the 3d transition metal (TM) ions in a high throughput fashion. The solubility behavior of TM ions was discussed from the viewpoints of the ionic radius and valence state. The magneto-optical responses coincident with absorption spectra were observed for Mn- and Co-doped samples. Cathodoluminescence

Zhengwu Jin; T. Fukumura; M. Kawasaki; K. Ando; H. Saito; T. Sekiguchi; Y. Z. Yoo; M. Murakami; Y. Matsumoto; T. Hasegawa; H. Koinuma

2001-01-01

319

The Local Electronic and Crystal Structure of Transition Metal and Group III A-Vii a Oxides Probed by X-Ray Absorption Spectroscopy  

Microsoft Academic Search

The d-orbitals of transition metals and the p -orbitals of the Group III A-VII A elements dominate the local electronic and structural properties in compounds of these materials. These important orbitals being, partially -filled and close to the Fermi level (E_ {F}) in energy, can be probed by X-ray absorption spectroscopy (XAS) which involves electronic transitions from atomic core-levels to

Mehmet Alper Sahiner

1995-01-01

320

Tensile strain effect in ferroelectric perovskite oxide thin films on spinel magnesium aluminum oxide substrate  

NASA Astrophysics Data System (ADS)

Ferroelectrics are used in FeRAM (Ferroelectric random-access memory). Currently (Pb,Zr)TiO3 is the most common ferroelectric material. To get lead-free and high performance ferroelectric material, we investigated perovskite ferroelectric oxides (Ba,Sr)TiO3 and BiFeO3 films with strain. Compressive strain has been investigated intensively, but the effects of tensile strain on the perovskite films have yet to be explored. We have deposited (Ba,Sr)TiO3, BiFeO3 and related films by pulsed laser deposition (PLD) and analyzed the films by X-ray diffractometry (XRD), atomic force microscopy (AFM), etc. To obtain inherently fully strained films, the selection of the appropriate substrates is crucial. MgAl2O4 matches best with good quality and size, yet the spinel structure has an intrinsic incompatibility to that of perovskite. We introduced a rock-salt structure material (Ni 1-xAlxO1+delta) as a buffer layer to mediate the structural mismatch for (Ba,Sr)TiO3 films. With buffer layer Ni1-xAlxO1+delta, we show that the BST films have high quality crystallization and are coherently epitaxial. AFM images show that the films have smoother surfaces when including the buffer layer, indicating an inherent compatibility between BST-NAO and NAO-MAO. In-plane Ferroelectricity measurement shows double hysteresis loops, indicating an antiferroelectric-like behavior: pinned ferroelectric domains with antiparallel alignments of polarization. The Curie temperatures of the coherent fully strained BST films are also measured. It is higher than 900°C, at least 800°C higher than that of bulk. The improved Curie temperature makes the use of BST as FeRAM feasible. We found that the special behaviors of ferroelectricity including hysteresis loop and Curie temperature are due to inherent fully tensile strain. This might be a clue of physics inside ferroelectric stain engineering. An out-of-plane ferroelectricity measurement would provide a full whole story of the tensile strain. However, a well suited electrode material that is both conducting, and full strained on the MgAl2O4 substrate is quite rare. We will supply some answers to this unique problem. XRD results show that Ni1-xAlxO1+delta (x=0.3, 0.4 & 0.5) film, although highly mixed with Al2O3, still takes rock-salt structure and is grown very well on the spinel MgAl 2O4 substrate, with perfect crystallization and a smooth surface. Ni0.7Al0.3O1+ delta and Ni 0.6Al0.4O1+ delta are good buffer layers for perovskite film on spinel MgAl2O4 substrate. Ni 0.5Al0.5O1+ delta could also be a good buffer layer. The structural transition from rock-salt to spinel was found at x=0.67. Tensile strain effects from thermal expansion difference of BiFeO3 films were found. Thermal expansion difference caused strain does not change the ferroelectric property greatly, due to film relaxation. BiFeO3 film with NAO buffer exhibit much larger strain.

Zhou, Xiaolan

321

Atomic level observation of octahedral distortions at the perovskite oxide heterointerface  

PubMed Central

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

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

2013-01-01

322

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

NASA Astrophysics Data System (ADS)

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.

Vajifdar, Kayzad Jimmy

323

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

Microsoft Academic Search

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

Igor Djerdj; Denis Arcon; Zvonko Jaglicic; Markus Niederberger

2008-01-01

324

Bismuth doped lanthanum ferrite perovskites as novel cathodes for intermediate-temperature solid oxide fuel cells.  

PubMed

Bismuth is doped to lanthanum strontium ferrite to produce ferrite-based perovskites with a composition of La(0.8-x)Bi(x)Sr0.2FeO(3-?) (0 ? x ? 0.8) as novel cathode material for intermediate-temperature solid oxide fuel cells. The perovskite properties including oxygen nonstoichiometry coefficient (?), average valence of Fe, sinterability, thermal expansion coefficient, electrical conductivity (?), oxygen chemical surface exchange coefficient (K(chem)), and chemical diffusion coefficient (D(chem)) are explored as a function of bismuth content. While ? decreases with x due to the reduced Fe(4+) content, D(chem) and K(chem) increase since the oxygen vacancy concentration is increased by Bi doping. Consequently, the electrochemical performance is substantially improved and the interfacial polarization resistance is reduced from 1.0 to 0.10 ? cm(2) at 700 °C with Bi doping. The perovskite with x = 0.4 is suggested as the most promising composition as solid oxide fuel cell cathode material since it has demonstrated high electrical conductivity and low interfacial polarization resistance. PMID:24971668

Li, Mei; Wang, Yao; Wang, Yunlong; Chen, Fanglin; Xia, Changrong

2014-07-23

325

The structures of transition metal-transition metal alloys  

Microsoft Academic Search

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

Jeremy K. Burdett; Timothy J. McLarnan

1984-01-01

326

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)

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

2014-11-01

327

In situ XPS studies of perovskite oxide surfaces under electrochemical polarization.  

PubMed

An in situ XPS study of oxidation-reduction processes on three perovskite oxide electrode surfaces was carried out by incorporating the materials in an electrochemical cell mounted on a heated sample stage in an ultrahigh vacuum (UHV) chamber. Electrodes made of powdered LaCr(1-x)Ni(x)O(3-delta) (x = 0.4, 1) showed changes in the XPS features of all elements upon redox cycling between formal Ni3+ and Ni2+ oxidation stoichiometries, indicating the delocalized nature of the electronic states involved and strong mixing of O 2p to Ni 3d levels to form band states. The surface also showed changes in adsorption capacity for CO2 upon reduction as a result of increased nucleophilicity of surface oxygen. Another perovskite oxide, La(0.5)Sr(0.5)CoO(3-delta), laser deposited as highly oriented thin films on (100) oriented yttria-stabilized zirconia (YSZ), also showed evidence of both local and nonlocal effects in the XPS features upon redox cycling. In contrast to LaCr(1-x)Ni(x)O(3-delta), redox cycling mainly affected the XPS features of cobalt with little effect on oxygen. This signifies reduced participation of O 2p states in the conduction band of this material. Small changes in surface cation stoichiometry in this film were observed and attributed to mobility of the A-site Sr dopant under polarization. PMID:16851240

Vovk, Greg; Chen, Xiaohua; Mims, Charles A

2005-02-17

328

Electrical Conductivity in Transition Metals  

ERIC Educational Resources Information Center

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

Talbot, Christopher; Vickneson, Kishanda

2013-01-01

329

Modeling of complex oxide materials from the first principles: systematic applications to vanadates R VO 3 with distorted perovskite structure  

Microsoft Academic Search

“Realistic modeling” is a new direction of electronic structure calculations, where the main emphasis is made on the construction\\u000a of some effective low-energy model entirely within a first-principle framework. Ideally, it is a model in form, but with all\\u000a the parameters derived rigorously, on the basis of first-principles electronic structure calculations. The method is especially\\u000a suit for transition-metal oxides and

Igor Solovyev

2011-01-01

330

Reactivity of hydrated monovalent first row transition metal ions M(+)(H2O)n, M = V, Cr, Mn, Fe, Co, Ni, Cu, Zn, toward molecular oxygen, nitrous oxide, and carbon dioxide.  

PubMed

The reactions of hydrated monovalent transition metal ions M(+)(H(2)O)(n), M = V, Cr, Mn, Fe, Co, Ni, Cu, Zn, toward molecular oxygen, nitrous oxide, and carbon dioxide were studied by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Clusters containing monovalent chromium, cobalt, nickel, or zinc were reactive toward O(2), while only hydrated cobalt was reactive toward N(2)O. A strongly size dependent reactivity was observed. Chromium and cobalt react very slowly with carbon dioxide. Nanocalorimetric analysis, (18)O(2) exchange, and collision induced dissociation (CID) experiments were done to learn more about the structure of the O(2) products. The thermochemistry for cobalt, nickel, and zinc is comparable to the formation of O(2)(-) from hydrated electrons. These results suggest that cobalt, nickel, and zinc are forming M(2+)/O(2)(-) ion pairs in the cluster, while chromium rather forms a covalently bound dioxygen complex in large clusters, followed by an exothermic dioxide formation in clusters with n ? 5. The results show that hydrated singly charged transition metal ions exhibit highly specific reactivities toward O(2), N(2)O, and CO(2). PMID:22506540

van der Linde, Christian; Hemmann, Sonja; Höckendorf, Robert F; Balaj, O Petru; Beyer, Martin K

2013-02-14

331

Oxygen stoichiometry, unit cell volume, and thermodynamic quantities of perovskite-type oxides  

Microsoft Academic Search

Perovskite-type oxides $${\\\\text{A}}_{{{\\\\text{1 - }}a}} {\\\\text{A}}^{\\\\prime }_{{\\\\text{a}}} {\\\\text{B}}_{{{\\\\text{1 - }}b}} {\\\\text{B}}^{\\\\prime }_{{\\\\text{b}}} {\\\\text{O}}_{{{\\\\text{3 - }}x}}$$ with A, A?=La, Ba, Sr; B, B?=Mn, Fe, Co were investigated by means of thermal analysis, solid electrolyte cells, and X-ray\\u000a diffraction. Partial molar thermodynamic quantities are determined and their relations with O\\/M stoichiometry, unit cell volume,\\u000a and phase stability were studied. The absolute values

Egle Girdauskaite; Helmut Ullmann; Mahmoud Al Daroukh; Vladimir Vashook; Martin Bülow; Ulrich Guth

2007-01-01

332

Solid-state perovskite-sensitized p-type mesoporous nickel oxide solar cells.  

PubMed

Perovskite has been adopted as photosensitizer to develop solid state p-type mesoporous nickel oxide (NiO) dye-sensitized solar cells (DSCs) employing PCBM as electron conductor. The optimal device achieved an efficiency of 1.5% with an impressive open circuit voltage of more than 800 mV, which is the record of solar cell based on p-type mesoporous NiO electrode. This result shows the potential for building highly efficient p-type NiO solar cells as stand-alone device. PMID:24764196

Tian, Haining; Xu, Bo; Chen, Hong; Johansson, Erik M J; Boschloo, Gerrit

2014-08-01

333

Effect of Mn valence on crystal structure of La-Mn-O perovskite oxides  

NASA Astrophysics Data System (ADS)

La:Mn = 1:1 mixtures of lanthanum oxide and manganese carbonate were heat-treated under various oxygen partial pressures at 1400 C or 1300 C. The Mn valence of the samples was measured by a chemical analysis, and the crystal structures were refined by the powder x-ray diffraction and the Rietveld analysis. A novel orthorhombic perovskite phase, belonging to the space group Pbnm and containing Mn(2+) ions, was formed by heat-treatment under low oxygen partial pressures. The structure was very close to a cubic symmetry. It is supposed that the micro Jahn-Teller effects of Mn(2+) ions were nearly canceled by one another.

Yao, Takeshi; Ito, Toyoji; Kokubo, Tadashi

1995-05-01

334

Application of Two Dimensional Flourescence Spectroscopy to Transition Metal Clusters.  

NASA Astrophysics Data System (ADS)

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

Kokkin, Damian L.; Steimle, Timothy

2014-06-01

335

Oxidative coupling of methane by water as the oxidant on perovskite oxide catalysts  

Microsoft Academic Search

We found that methane was selectively oxidized by water to give C2 hydrocarbons and hydrogen on ATi1-xBxO3-d (A=Sr, Ba, B=Mg, Ca). The coupling activity and selectivity on SrTi0.4Mg0.6O3-d in the presence of steam was ~95%, which was much higher than that on pure SrTiO3. This suggests that the selective oxidative coupling of methane by water was catalyzed by the oxide

Xiaohong Li; Keiichi Tomishige; Kaoru Fujimoto

1996-01-01

336

Dense ceramic membranes for partial oxidation of methane to syngas  

Microsoft Academic Search

Several perovskite-type oxides (ABO3) containing transition metals on the B-site show mixed (electronic\\/ionic) conductivity. These mixed-conductivity oxides are promising materials for oxygen-permeating membranes that can operate without electrodes or external electrical circuitry. Oxides in the system La?Sr?Fe?Co?O permeate large amounts of oxygen, and extruded tubes of these materials have been evaluated in a reactor operating at ca. 850°C for direct

U. Balachandran; J. T. Dusek; R. L. Mieville; R. B. Poeppel; M. S. Kleefisch; S. Pei; T. P. Kobylinski; C. A. Udovich; A. C. Bose

1995-01-01

337

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

PubMed Central

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

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

2013-01-01

338

Surface electronic structure transitions at high temperature on perovskite oxides: the case of strained La0.8Sr0.2CoO3 thin films.  

PubMed

In-depth probing of the surface electronic structure on solid oxide fuel cell (SOFC) cathodes, considering the effects of high temperature, oxygen pressure, and material strain state, is essential toward advancing our understanding of the oxygen reduction activity on them. Here, we report the surface structure, chemical state, and electronic structure of a model transition metal perovskite oxide system, strained La(0.8)Sr(0.2)CoO(3) (LSC) thin films, as a function of temperature up to 450 °C in oxygen partial pressure of 10(-3) mbar. Both the tensile and the compressively strained LSC film surfaces transition from a semiconducting state with an energy gap of 0.8-1.5 eV at room temperature to a metallic-like state with no energy gap at 200-300 °C, as identified by in situ scanning tunneling spectroscopy. The tensile strained LSC surface exhibits a more enhanced electronic density of states (DOS) near the Fermi level following this transition, indicating a more highly active surface for electron transfer in oxygen reduction. The transition to the metallic-like state and the relatively more enhanced DOS on the tensile strained LSC at elevated temperatures result from the formation of oxygen vacancy defects, as supported by both our X-ray photoelectron spectroscopy measurements and density functional theory calculations. The reversibility of the semiconducting-to-metallic transitions of the electronic structure discovered here, coupled to the strain state and temperature, underscores the necessity of in situ investigations on SOFC cathode material surfaces. PMID:21913726

Cai, Zhuhua; Kuru, Yener; Han, Jeong Woo; Chen, Yan; Yildiz, Bilge

2011-11-01

339

Remarkable effect of Pt nanoparticles on visible light-induced oxygen generation from water catalysed by perovskite oxides.  

PubMed

Oxidation of water is a challenging process with a positive free energy change and it is purposeful to find good catalysts to facilitate the process. While the perovskite oxides, LaCoO3 and LaMnO3, are good electron transfer catalysts in artificial photosynthesis to produce oxygen by the oxidation of water, the electron transfer is further favoured by the presence of platinum nanoparticles, causing a substantial increase in oxygen evolution. PMID:25407344

Gupta, Uttam; Naidu, B S; Rao, C N R

2015-01-14

340

Synthesis, structural and property studies of bismuth containing perovskites   

E-print Network

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 ...

Chen, Wei-tin

2009-01-01

341

Valence Tautomeric Transition Metal Complexes  

Microsoft Academic Search

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

David N. Hendrickson; Cortlandt G. Pierpont

342

Multiple magnetic interactions in A-site-ordered perovskite-structure oxides  

NASA Astrophysics Data System (ADS)

Multiple magnetic interactions in A-site-ordered perovskite-structure oxides AA?3B2B?2O12 with A?-site Cu and B-site Fe ions are highlighted here. Several new compounds with this structure type were obtained by high-pressure synthesis and have been given unusual magnetic properties due to multiple interactions of Cu and Fe ions (A?–A?, A?–B, A?–B?, B–B, B–B?, and B?–B? interactions). The magnetic interaction is discussed here in light of the results of magnetic structure analysis with neutron powder diffraction data and x-ray magnetic circular dichroism spectra obtained in x-ray absorption experiments. The characteristic structural framework with ordered cation arrangements and the variation in the oxidation state of the ions at the A? and B sites are shown to play roles crucial for the diverse and intriguing physical properties of these new compounds.

Shimakawa, Yuichi; Mizumaki, Masaichiro

2014-11-01

343

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

E-print Network

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

Goddard III, William A.

344

Stable singlet carbenes as mimics for transition metal centers  

PubMed Central

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

Martin, David; Soleilhavoup, Michele

2011-01-01

345

[Non-empirical interatomic potentials for transition metals  

SciTech Connect

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

Not Available

1993-01-01

346

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

SciTech Connect

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

Not Available

1993-05-01

347

Transition metal-substituted cobalt ferrite nanoparticles for biomedical applications.  

PubMed

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

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

2013-03-01

348

Alumina supported, perovskite oxide based catalytic materials and their auto-exhaust application  

Microsoft Academic Search

Substituted lanthanum manganate type perovskites have been synthesized following co-precipitation and a modified in situ method. These perovskites have been supported on cordierite honeycomb with and without alumina washcoat. Alumina washcoated supports with lanthana pre-coat, have been found suitable for the in situ synthesis of perovskites to avoid reactivity of perovskite precursors with alumina (in absence of lanthana pre-coat). This

Nitin K Labhsetwar; A Watanabe; R. B Biniwale; R Kumar; T Mitsuhashi

2001-01-01

349

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

Microsoft Academic Search

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

Kayzad Jimmy Vajifdar

2007-01-01

350

Magnetron sputtered zinc oxide nanorods as thickness-insensitive cathode interlayer for perovskite planar-heterojunction solar cells.  

PubMed

Suitable electrode interfacial layers are essential to the high performance of perovskite planar heterojunction solar cells. In this letter, we report magnetron sputtered zinc oxide (ZnO) film as the cathode interlayer for methylammonium lead iodide (CH3NH3PbI3) perovskite solar cell. Scanning electron microscopy and X-ray diffraction analysis demonstrate that the sputtered ZnO films consist of c-axis aligned nanorods. The solar cells based on this ZnO cathode interlayer showed high short circuit current and power conversion efficiency. Besides, the performance of the device is insensitive to the thickness of ZnO cathode interlayer. Considering the high reliability and maturity of sputtering technique both in lab and industry, we believe that the sputtered ZnO films are promising cathode interlayers for perovskite solar cells, especially in large-scale production. PMID:25405518

Liang, Lusheng; Huang, Zhifeng; Cai, Longhua; Chen, Weizhong; Wang, Baozeng; Chen, Kaiwu; Bai, Hua; Tian, Qingyong; Fan, Bin

2014-12-10

351

Transition metal atomic multiplets in the ligand K-edge x-ray absorption spectra and multiple oxidation states in the L2,3 emission of strongly correlated compounds  

NASA Astrophysics Data System (ADS)

We present results that show that atomic multiplet ligand field calculations are in very good agreement with experimental x-ray absorption spectra at the L2,3 edge of transition metal (TM) di-fluorides (MF2, MCrCu). For chromium more than one TM oxidation state is needed to achieve such an agreement. We also show that signature of the TM atomic multiplet can be found at the pre-edge of the fluorine K-edge x-ray absorption spectra. TM atomic multiplet ligand field calculations with a structureless core hole show good agreement with the observed pre-edges in the experimental fluorine absorption spectra. Preliminary results for the comparison between calculated and experimental resonant x-ray emission spectra for nominal CrF2 with more than one oxidation state indicate the presence of three chromium oxidation states in the bulk.

Jiménez-Mier, J.; Olalde-Velasco, P.; Yang, W.-L.; Denlinger, J.

2014-07-01

352

Thermal-expansion behaviors and mechanisms for Ca- or Sr-doped lanthanum manganite perovskites under oxidizing atmospheres  

SciTech Connect

The thermal expansion behavior and mechanism of A-site-deficient lanthanum manganite perovskites, La{sub 1{minus}x}MnO{sub 3} (0 < x {le} 0.1), and alkaline earth metal (AE)-doped lanthanum manganite perovskites, La{sub 1{minus}x}AE{sub x}MnO{sub 3} (AE = Ca and Sr, 0 {le} x {le} 0.4), under oxidizing atmospheres have been investigated. The average linear thermal expansion coefficients of the AE-doped lanthanum manganites decreased with increasing Ca content up to 20 mol % and with increasing Sr content up to 10 mol %, and then increased. During the thermal cycle measurement, the La{sub 1{minus}x}MnO{sub 3} (0 {le} x {le} 0.1) perovskite samples and the La{sub 1{minus}x}AE{sub x}MnO{sub 3} perovskites (0 {le} x {le} 0.3) shrank, while no anomalous shrinkage behavior was observed for the La{sub 0.6}AE{sub 0.4}MnO{sub 3} samples. From the results of high-temperature X-ray diffraction analysis, no dependency of cell volume of the perovskites on aging time at selected temperatures and on thermal cycles was observed.

Mori, Masashi; Hiei, Yoshiko; Sammes, N.M.; Tompsett, G.A.

2000-04-01

353

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

NASA Astrophysics Data System (ADS)

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

Zeng, Pingying

354

Electronic Structure and Bonding in Transition Metal Inorganic and Organometallic Complexes: New Basis Sets, Linear Semibridging Carbonyls and Thiocarbonyls, and Oxidative Addition of Molecular Hydrogen to Square - Iridium Complexes  

Microsoft Academic Search

Approximate molecular orbital and ab initio quantum chemical techniques are used to investigate the electronic structure, bonding and reactivity of several transition metal inorganic and organometallic complexes. Modest-sized basis sets are developed for the second-row transition metal atoms and are designed for use in geometry optimizations of inorganic and organometallic complexes incorporating these atoms. The basis sets produce optimized equilibrium

Andrew Landman Sargent

1991-01-01

355

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

SciTech Connect

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.

Bitterwolf, Thomas E. [University of Idaho

2014-12-09

356

Electrical properties of the double perovskite oxide Ho2CuZrO6  

NASA Astrophysics Data System (ADS)

The double perovskite oxide holmium copper zirconate, Ho2CuZrO6 (HCZ), was synthesized by a solid-state reaction technique. The crystal structure of HCZ shows a monoclinic phase. The dielectric relaxation of HCZ was investigated in the frequency range 44 Hz-1 MHz and in the temperature range 40-360 °C by using impedance spectroscopy. The complex impedance data were analysed by the Cole-Cole model. The ac conductivity follows the power law. The value of activation energy obtained from the temperature dependence of the dc conductivity plot indicates a hopping-type conduction mechanism. The scaling behaviour of the imaginary part of impedance indicates that relaxation in HCZ describes the same mechanism at various temperatures.

Mahato, D. K.; Dutta, Alo; Kumar, Nishant; Sinha, T. P.

2011-07-01

357

Mechanistic differences between electrochemical and gas-phase thermal oxidation of platinum-group transition metals as discerned by surface-enhanced Raman spectroscopy  

SciTech Connect

The oxidation of five Pt-group metals--platinum, palladium, iridium, rhodium, and ruthenium--is examined by means of surface-enhanced Raman spectroscopy (SERS) in aqueous electrochemical and gaseous dioxygen environments as a function of electrode potential and temperature, respectively, with the objective of intercomparing systematically the conditions required for surface oxide formation and discerning the reaction mechanisms involved. The SERS strategy, utilizing ultrathin Pt-group metal films electrodeposited on a gold substrate, enables monolayer-level metal oxide vibrational spectra to readily be obtained in both the electrochemical and gaseous environments. The SER spectra obtained during positive- and then negative-going potential excursions in aqueous 0.1 M HCLO{sub 4} display metal-oxygen vibrational bands signaling anodic oxide formation and subsequent removal at potentials consistent with corresponding voltammetric data. The nature of the amorphous oxides (or hydroxides) formed is deduced by comparison with bulk-phase metal oxide Raman spectra. The onset potentials for surface oxide formation are comparable to the thermodynamic potentials for the bulk-phase metal oxides. In contrast, the onset of surface oxidation even in ambient-pressure dioxygen uniformly requires elevated temperatures, {gt}200 C for each metal except for iridium, where oxide formation occurs at ca. 100 C. While spectral differences are evident, especially on palladium and ruthenium, the nature of the oxides formed in the electrochemical and gaseous systems is largely similar. The highly activated nature of the gaseous O{sub 2} oxidations is consistent with literature reports for Pt-group surfaces in ultrahigh vacuum as well as higher-pressure conditions. Likely reasons for the markedly more efficacious metal electrooxidations are discussed. Thermodynamic factors are not responsible, since the free-energy driving forces for the gaseous O{sub 2} oxidations are larger than for the electrochemical reactions at the applied potentials where surface oxidation for the latter processes proceeds at room temperature. The electrostatic driving forces for oxygen incorporation into the metal lattice (via high-field ion transport) are also typically more favorable for the gaseous systems, as evidenced by a comparison of the metal-solution and metal-gas surface potentials. The intrinsically more facile electrochemical processes thereby deduced are attributed to the occurrence of direct oxide production via a metal-oxygen place-exchange mechanism, expedited by interfacial solvation and therefore being energetically unfavorable in the anhydrous gas-phase environment. Other factors, such as the formation of precursor chemisorbed oxygen, are also considered.

Chan, H.Y.H.; Zou, S.; Weaver, M.J.

1999-12-16

358

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

PubMed

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

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

2014-11-10

359

Direct Synthesis of 2-Aryl-4-quinolones via Transition-Metal-Free Intramolecular Oxidative C(sp(3))-H/C(sp(3))-H Coupling.  

PubMed

A novel, metal-free oxidative intramolecular Mannich reaction was developed between secondary amines and unmodified ketones, affording a simple and direct access to a broad range of 2-arylquinolin-4(1H)-ones through C(sp(3))-H activation/C(sp(3))-C(sp(3)) bond formation from readily available N-arylmethyl-2-aminophenylketones, using TEMPO as the oxidant and KO(t)Bu as the base. PMID:25700137

Hu, Wei; Lin, Jian-Ping; Song, Li-Rui; Long, Ya-Qiu

2015-03-01

360

Mechanistic differences between electrochemical and gas-phase thermal oxidation of platinum-group transition metals as discerned by surface-enhanced Raman spectroscopy  

Microsoft Academic Search

The oxidation of five Pt-group metals--platinum, palladium, iridium, rhodium, and ruthenium--is examined by means of surface-enhanced Raman spectroscopy (SERS) in aqueous electrochemical and gaseous dioxygen environments as a function of electrode potential and temperature, respectively, with the objective of intercomparing systematically the conditions required for surface oxide formation and discerning the reaction mechanisms involved. The SERS strategy, utilizing ultrathin Pt-group

Ho Yeung H. Chan; Shouzhong Zou; Michael J. Weaver

1999-01-01

361

Ti-doped molybdenum-based perovskites as anodes for solid oxide fuel cells  

NASA Astrophysics Data System (ADS)

Ti doping is found to increase the stability of Sr2NiMoO6 perovskite oxides in reducing atmosphere. The composition Sr2TiNi0.5Mo0.5O6 (STNM) is further evaluated as a potential oxide anode for solid oxide fuel cells (SOFCs). Electrical conductivity, thermal expansion coefficient, surface exchange coefficient, chemical diffusion coefficient, and its electrochemical performance in single cells with La0.8Sr0.2Ga0.8Mg0.2O3-? (LSGM) electrolytes are investigated. STNM exhibits a high conductivity of 17.5 S cm-1 at 800 °C at anodic atmosphere. The material shows good chemical and thermal expansion compatibilities with LSGM. To investigate the effect of Ti doping on the conduction properties, first-principle calculations are performed using the Vienna Ab initio Simulation. The strong Ti-O bond is held responsible for the enhanced structural stability of STNM under humidified H2 atmospheres, relative to that of the undoped system. The remarkable cell performance with both H2 and dry CH4 as the fuel indicates the potential ability of STNM to be used as SOFC anodes. These results obtained indicate that Sr2TiNi0.5Mo0.5O6 is a promising material for use as anode for intermediate temperature SOFCs.

He, Beibei; Wang, Zhenbin; Zhao, Ling; Pan, Xin; Wu, Xiaojun; Xia, Changrong

2013-11-01

362

XAFS Study of Platinum Group Metals Occluded in LaScO3-BASED Perovskite Oxide by Solid-Phase Reaction at High Temperatuers  

NASA Astrophysics Data System (ADS)

We have recently found a new preparation route for platinum group metal containing LaScO3-based perovskite oxides. Sr and Ba containing perovskite powder, (La0.7Sr0.2Ba0.1)ScO3-? (LSBS) reacted with the solid-state platinum group metals at temperatures from 1623 to 1898K in air, and formed platinum group metal containing perovskite oxides without changing the perovskite structure. In this study we made X-ray absorption fine structure (XAFS) analysis of platinum group metals (M = Ir, Pd, Pt, Rh and Ru) occluded in the LSBS perovskite oxide by the solid-phase reaction at high temperatures. The results of the analysis for XANES regions and the radial structure functions showed that the platinum group metals exist not in the metallic but rather in an ionic state in the LSBS perovskite oxide and that the platinum group metals are mainly introduced into the ScO6 octahedral sites in LSBS perovskite structure, respectively.

Kageyama, Hiroyuki; Nomura, Katsuhiro; Ohmi, Kentaro; Fujita, Mitsuharu; Ueda, Tetsuya

2013-07-01

363

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

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

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

364

Radiationless processes in transition-metal complexes  

Microsoft Academic Search

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

D. J. Robbins; A. J. Thomson

1973-01-01

365

Electronic Structures of Transition-Metal Complexes  

Microsoft Academic Search

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

L. E. Orgel

1955-01-01

366

Methane oxidation over perovskite-related ferrites: Effects of oxygen nonstoichiometry  

NASA Astrophysics Data System (ADS)

The oxidation of CH 4 pulses supplied in helium flow over perovskite-related La 0.3Sr 0.7Fe 0.8MO 3- ? ( M=Ga, Al) and SrFe 0.7Al 0.3O 3- ? leads to significant yields of CO and H 2 after achieving a critical level of oxygen deficiency in the ferrite-based mixed conductors. This effect, reproducible under steady-state conditions in the membrane reactors for methane conversion, may be of interest for the development of monolithic ceramic reactors where the dense membrane and porous catalyst at the permeate-side surface are made of similar compositions. The Mössbauer spectroscopy and coulometric titration studies show that the presence of metallic Fe under typical operation conditions can be neglected, whilst most oxygen vacancies in the ferrite lattices are ordered. Increasing selectivity towards the partial oxidation of methane is observed in the vicinity of the state where the iron cations are predominantly trivalent and massive ordering processes in the oxygen sublattice start. The catalytic activity of ferrite-based materials may hence result from the lattice instability characteristic of morphotropic phase transformations. The correlations between catalytic behavior and oxygen ionic transport are briefly discussed.

Kharton, V. V.; Patrakeev, M. V.; Waerenborgh, J. C.; Sobyanin, V. A.; Veniaminov, S. A.; Yaremchenko, A. A.; Gaczy?ski, P.; Belyaev, V. D.; Semin, G. L.; Frade, J. R.

2005-11-01

367

Chemical control of orbital polarization in artificially structured transition-metal oxides: La2NiXO6 (X=B, Al, Ga, In) from first principles  

Microsoft Academic Search

The application of modern layer-by-layer growth techniques to\\u000atransition-metal oxide materials raises the possibility of creating new classes\\u000aof materials with rationally designed correlated electron properties. An\\u000aimportant step toward this goal is the demonstration that electronic structure\\u000acan be controlled by atomic composition. In compounds with partially occupied\\u000atransition-metal d shells, one important aspect of the electronic structure is

Myung Joon Han; Chris A. Marianetti; Andrew J. Millis

2010-01-01

368

Magnetism of perovskite oxides: The effect of strain and phase separation  

NASA Astrophysics Data System (ADS)

The magnetic properties of perovskite oxides can be affected by various conditions such as doping concentration, finite size limitation, and mechanical strain, which are associated with a range of intriguing physical phenomena in highly correlated electron systems such as colossal magnetoresistance, high temperature superconductivity, and phase inhomogeneities. In this thesis, we studied several topics concerning the cobaltates and nickelates which are associated with magnetism in perovskite oxides. La0.5Sr0.5CoO3 is a ferromagnetic material with Curie temperature TC of 250 K. In a form of thin films, we studied strain effect on its ferromagnetism. However, ferromagnetism in thin films is affected by both finite size effect and strain effect. We have used a series of films of different thicknesses and on different substrates to quantitatively determine the change in TC contributed by each effect. The phase diagram of TC versus in-plane strain suggests that TC is suppressed by tensile strain and enhanced by compressive strain. The general method of separating strain and finite thickness effects should be applicable to any ordering phase transition in thin films. The local structure of LSCO thin films was investigated by Extended X-ray Absorption Fine Structure technique. Our results suggest that the tensile strain elongates the Co-O bond length, while compressive strain shortens the bond length. The change of bond length is mainly responsible for the modulation of TC upon strain. This is contrary to assumptions generally used in literature on strained manganite films. Current double exchange model is not adequate to describe the ferromagnetic mechanism for cobaltate. In a case of no La, we studied the magnetic properties of SrCoO 2.5+x. SrCoO2.5 is an antiferromaget with Neel temperature of 570 K. With a starting material of SrCoO 2.88, we have carried out oxidization and reduction experiments through an electrochemical method. The hole doping introduced into SrCoO2.5 by oxygen has shown to play a crucial role in determining the materials' ferromagnetic characters such as Curie temperature, spin state, magnetic saturation moment, etc. A magnetic phase diagram of SrCoO2.5+x is thus proposed for the first time. The striking feature of the diagram is the existence of several line phases which contain antiferromagnetic and ferromagnetic phases. In high contrast with La1-ySryCoO 3, SrCoO2.5+x can be phase separated into a number of magnetic regions for which each one has a unique oxygen/hole concentration such as x = 0, 0.25, 0.375, and 0.5, respectively. Our results suggest that the mobile holes are playing a key role in ferromagnetism and phase separation in the system. For perovskite nickelate, we have successfully grown high-quality epitaxial La1.67Sr0.33NiO4 films using pulsed laser deposition. For the first time, the x-ray diffraction superlattice peaks associated with charge stripe phase have been successfully observed in films. By studying the evolution of the stripe phase as the film thicknesses are decreased, we provide direct evidence for suppression of the stripe phase in thinner samples with thicknesses of less than 2600 A. A scenario of short-range ordered stripes due to a lattice clamping effect is proposed to account for the suppression in light of a model of electronic stripe-glass.

Xie, Changkun

369

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

NASA Astrophysics Data System (ADS)

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.

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

370

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

PubMed

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

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

371

Ballistic performance comparison of monolayer transition metal dichalcogenide MX2 (M = Mo, W; X = S, Se, Te) metal-oxide-semiconductor field effect transistors  

NASA Astrophysics Data System (ADS)

We study the transport properties of monolayer MX2 (M = Mo, W; X = S, Se, Te) n- and p-channel metal-oxide-semiconductor field effect transistors (MOSFETs) using full-band ballistic non-equilibrium Green's function simulations with an atomistic tight-binding Hamiltonian with hopping potentials obtained from density functional theory. We discuss the subthreshold slope, drain-induced barrier lowering (DIBL), as well as gate-induced drain leakage (GIDL) for different monolayer MX2 MOSFETs. We also report the possibility of negative differential resistance behavior in the output characteristics of nanoscale monolayer MX2 MOSFETs.

Chang, Jiwon; Register, Leonard F.; Banerjee, Sanjay K.

2014-02-01

372

Ballistic performance comparison of monolayer transition metal dichalcogenide MX{sub 2} (M = Mo, W; X = S, Se, Te) metal-oxide-semiconductor field effect transistors  

SciTech Connect

We study the transport properties of monolayer MX{sub 2} (M?=?Mo, W; X?=?S, Se, Te) n- and p-channel metal-oxide-semiconductor field effect transistors (MOSFETs) using full-band ballistic non-equilibrium Green's function simulations with an atomistic tight-binding Hamiltonian with hopping potentials obtained from density functional theory. We discuss the subthreshold slope, drain-induced barrier lowering (DIBL), as well as gate-induced drain leakage (GIDL) for different monolayer MX{sub 2} MOSFETs. We also report the possibility of negative differential resistance behavior in the output characteristics of nanoscale monolayer MX{sub 2} MOSFETs.

Chang, Jiwon; Register, Leonard F.; Banerjee, Sanjay K. [Microelectronics Research Center, The University of Texas at Austin, Austin, Texas 78758 (United States)

2014-02-28

373

Preparation of nanocomposites containing nanoclusters of transition metals  

SciTech Connect

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

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

1996-10-01

374

Atomic layer deposition of transition metals.  

PubMed

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

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

2003-11-01

375

Spintronic oxides grown by laser-MBE  

NASA Astrophysics Data System (ADS)

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.

Opel, Matthias

2012-01-01

376

Covalent functionalization of monolayered transition metal dichalcogenides by  

E-print Network

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

Muzzio, Fernando J.

377

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

SciTech Connect

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}.

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

1992-03-03

378

Piperazine pivoted transition metal dithiocarbamates  

NASA Astrophysics Data System (ADS)

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

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

2008-03-01

379

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

NASA Astrophysics Data System (ADS)

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.

Ardo, Shane

380

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

SciTech Connect

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).

Kinoshita, K.; Kishida, S. [Department of Information and Electronics, Graduate School of Engineering, Tottori University, 4-101 Koyama-Minami, Tottori 680-8552 (Japan); Tottori University Electronic Display Research Center, 522-2 Koyama-Kita, Tottori 680-0941 (Japan); Yoda, T. [Department of Information and Electronics, Graduate School of Engineering, Tottori University, 4-101 Koyama-Minami, Tottori 680-8552 (Japan)

2011-09-15

381

Investigation of hyperfine interactions in GdCrO3 perovskite oxide using PAC spectroscopy  

NASA Astrophysics Data System (ADS)

Perturbed angular correlation (PAC) measurements have been carried out in the antiferromagnetic GdCrO3 perovskite oxide using 111In (111Cd) and 181Hf(181Ta) nuclear probes. The radioactive parent nuclei 111In and 181Hf were introduced in the compound through a chemical process during sample preparation. The PAC measurements were carried out in the temperature range 20-300 K. Measurements with the 181Ta indicated a unique quadrupole interaction above 170 K and a combined electric quadrupole and magnetic dipole interactions below this temperature. The observed interaction was assigned to the probe nuclei substituting Cr sites. Measurements with 111Cd showed two quadrupole interactions. Only one of the fractions however, showed a combined electric and magnetic interaction in the temperature rage 20-170 K which was assigned to 111Cd probe substituting Cr site. The other fraction was attributed to the Gd site. The present results are compared with those of LaCrO3 and NdCrO3.

Silva, Renilson A. Da; Saxena, R. N.; Carbonari, A. W.; Cabrera-Pasca, G. A.

2010-04-01

382

Bandgap engineering in perovskite oxides: Al-doped SrTiO3  

NASA Astrophysics Data System (ADS)

The ability to modulate the bandgap of a material without altering its functional properties is crucial for fabricating heterojunctions for device applications. Here, we explore experimentally and theoretically the effect of the substitution of Ti with Al on the bandgap of perovskite oxide SrTiO3. We grow Al-doped SrTiO3 films directly on Si(100) and show from electron energy loss spectra that the bandgap is increased by approximately 0.3 eV over undoped SrTiO3. This bandgap increase is confirmed by spectroscopic ellipsometry measurements on identical films grown on LaAlO3 substrates, which show a 0.3 eV blue shift in the steep increase of the absorption edge. Current vs. voltage measurements show a reduction in leakage current by six orders of magnitude at a field of 1 MV/cm. We use density functional theory to explain how Al replacing Ti modifies the conduction band edge density of states resulting in the experimentally observed increase in the bandgap.

Posadas, Agham B.; Lin, Chungwei; Demkov, Alexander A.; Zollner, Stefan

2013-09-01

383

Epitaxial heterojunctions of oxide semiconductors and metals on high temperature superconductors  

NASA Technical Reports Server (NTRS)

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.

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

1994-01-01

384

Physical, mechanical and electrochemical characterization of all-perovskite intermediate temperature solid oxide fuel cells  

NASA Astrophysics Data System (ADS)

Strontium- and magnesium-doped lanthanum gallate (LSGM) has been considered as a promising electrolyte for solid oxide fuel cell (SOFC) systems in recent years due to its high ionic conductivity and chemical stability over a wide range of oxygen partial pressures and temperatures. This research describes synthesis, physical and mechanical behavior, electrochemical properties, phase evolution, and microstructure of components of an all-perovskite anode-supported intermediate temperature solid oxide fuel cell (ITSOFC), based on porous La 0.75Sr0.25Cr0.5Mn0.5O3 (LSCM) anode, La0.8Sr0.2Ga0.8Mg0.2O 2.8 (LSGM) electrolyte, and porous La0.6Sr0.4Fe 0.8Co0.2O3 (LSCF) cathode. The phase evolution of synthesized LSGM and LSCM powders has been investigated, and it has been confirmed that there is no reaction between LSGM and LSCM at sintering temperature. Using different amounts of poreformers and binders as well as controlling firing temperature, porosity of the anode was optimized while still retaining good mechanical integrity. The effect of cell operation conditions under dry hydrogen fuel on the SOFC open circuit voltage (OCV) and cell performance were also investigated. Characterization study of the synthesized LSGM indicates that sintering at 1500°C obtains higher electrical conductivity compared to the currently published results, while conductivity of pellets sintered at 1400°C and 1450°C would be slightly lower. The effect of sintering temperature on bulk and grain boundary resistivities was also discussed. The mechanical properties, such as hardness, Young's modulus, fracture toughness and modulus of rupture of the electrolyte were determined and correlated with scanning electron microscopy (SEM) morphological characterization. Linear thermal expansion and thermal expansion coefficient of LSGM were also measured.

Mohammadi, Alidad

385

Multiferroic materials based on organic transition-metal molecular nanowires.  

PubMed

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

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

2012-09-01

386

Resistive switching mechanisms in random access memory devices incorporating transition metal oxides: TiO2, NiO and Pr0.7Ca0.3MnO3  

NASA Astrophysics Data System (ADS)

Resistance change random access memory (RRAM) cells, typically built as MIM capacitor structures, consist of insulating layers I sandwiched between metal layers M, where the insulator performs the resistance switching operation. These devices can be electrically switched between two or more stable resistance states at a speed of nanoseconds, with long retention times, high switching endurance, low read voltage, and large switching windows. They are attractive candidates for next-generation non-volatile memory, particularly as a flash successor, as the material properties can be scaled to the nanometer regime. Several resistance switching models have been suggested so far for transition metal oxide based devices, such as charge trapping, conductive filament formation, Schottky barrier modulation, and electrochemical migration of point defects. The underlying fundamental principles of the switching mechanism still lack a detailed understanding, i.e. how to control and modulate the electrical characteristics of devices incorporating defects and impurities, such as oxygen vacancies, metal interstitials, hydrogen, and other metallic atoms acting as dopants. In this paper, state of the art ab initio theoretical methods are employed to understand the effects that filamentary types of stable oxygen vacancy configurations in TiO2 and NiO have on the electronic conduction. It is shown that strong electronic interactions between metal ions adjacent to oxygen vacancy sites results in the formation of a conductive path and thus can explain the 'ON' site conduction in these materials. Implication of hydrogen doping on electroforming is discussed for Pr0.7Ca0.3MnO3 devices based on electrical characterization and FTIR measurements.

Magyari-Köpe, Blanka; Tendulkar, Mihir; Park, Seong-Geon; Lee, Hyung Dong; Nishi, Yoshio

2011-06-01

387

Transition metal fluorides: from superconductors to multiferroics.   

E-print Network

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

Drathen, Christina

2013-06-29

388

Density functionals and transition-metal atoms  

Microsoft Academic Search

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

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

2007-01-01

389

Semiconducting Al transition-metal quasicrystals  

Microsoft Academic Search

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

M. Krajcí; J. Hafner

2003-01-01

390

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

E-print Network

, and condensation re- actions, which provide synthetic routes to unique ceramic materials and thin films activity, and fewer engineering is- sues stemming from the high temperature of operation of SOFCs. Perovskite oxides are often used as oxide ion conductors in SOFCs and have been the focus of much research

391

Spectroscopic investigations of complex transition metal oxides  

NASA Astrophysics Data System (ADS)

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

Cao, Jinbo

392

Theory of metal-insulator transition in the family of perovskite iridium oxides  

NASA Astrophysics Data System (ADS)

Perovskite iridium oxides Srn+1IrnO3n+1 exhibit fascinating phenomena due to the combined effects of spin-orbit coupling (SOC) and electronic interactions. It was suggested that electronic correlation amplified via the strong SOC leads to a spin-orbit Mott insulator for n=1 and 2, while three-dimensional (3D) SrIrO3 remains metallic because of the large bandwidth from the 3D structure. However, this bandwidth-controlled metal-insulator transition (MIT) is only valid when SOC is large enough to split Jeff=1/2 and 3/2 bands, while the mixing of 1/2 and 3/2 bands is conspicuous among the occupied bands. Here, we investigate the MIT as a function of n using weak-coupling theory. In this approach, the magnetic instability is determined by the states near the Fermi level rather than the entire band structure. Starting from t2g tight-binding models for n=1, 2, and ?, the states near the Fermi level are found to be predominantly Jeff=1/2 allowing an effective single-band model. Supplementing this effective Jeff=1/2 model with Hubbard-type interactions, transitions from a metal to magnetically ordered states are obtained. Strong-coupling spin models are derived to compare the magnetic ordering patterns obtained in the weak- and strong-coupling limits. We find that they are identical, indicating that these iridates are likely in an intermediate-coupling regime.

Carter, Jean-Michel; Shankar V., Vijay; Kee, Hae-Young

2013-07-01

393

High-pressure transitions in NaZnF3 and NaMnF3 perovskites, and crystal-chemical characteristics of perovskite-postperovskite transitions in ABX3 fluorides and oxides  

NASA Astrophysics Data System (ADS)

Phase transitions in NaZnF3 and NaMnF3 were examined up to 24 GPa and 1100 °C using a multianvil apparatus. NaZnF3 perovskite transforms to postperovskite above 11-16 GPa at 600-1000 °C, and the postperovskite is quenchable at ambient conditions. The NaZnF3 perovskite-postperovskite transition boundary is expressed as P (GPa) = 4.9 + 0.011T (°C). At 8-11 GPa and 900-1100 °C, NaMnF3 perovskite dissociates into two phases of Na3Mn2F7 and MnF2. The latter phase is suggested to have the structure of orthorhombic-I type ZrO2 or cotunnite. Using available experimental data on the perovskite-postperovskite transitions in thirteen compounds of A2+B4+O3 and A+B2+F3, several crystal-chemical characteristics of the transition are elucidated as follows. In the transition, the volume change is between -1% and -2%, and the Clapeyron slope of the boundary is 10-17 MPa/°C. These support reliability of recently determined Clapeyron slope of 13 MPa/°C in MgSiO3 which suggests that the perovskite-postperovskite boundary intersects the temperature profile twice in the D? layer. Postperovskites of ABX3 whose enthalpies are higher by more than 70 kJ/mol relative to the phase stable at 1 atm are unquenchable, while those by less than 15 kJ/mol are quenchable to ambient conditions. Structure refinements indicate that A+B2+F3 postperovskites quenched at 1 atm are more similar to that of MgSiO3 postperovskite at high pressure, than those of quenched A2+B4+O3 postperovskites. With increasing pressure, octahedral tilt angles of both A2+B4+O3 and A+B2+F3 perovskites increase, resulting in transition to postperovskite at the angle of about 26°, and fluoride perovskites are more rapidly distorted with pressure than oxide perovskites. Covalent character of B-X bonds of ABX3 postperovskite is suggested to be favorable for stabilization of the postperovskite structure. All these features suggest that NaNiF3 is a good quenchable, low-pressure analogue compound to MgSiO3 to investigate the perovskite-postperovskite transition.

Akaogi, Masaki; Shirako, Yuichi; Kojitani, Hiroshi; Nagakari, Takayuki; Yusa, Hitoshi; Yamaura, Kazunari

2014-03-01

394

Microwave-assisted synthesis of transition metal phosphide  

DOEpatents

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

Viswanathan, Tito

2014-12-30

395

Transition Metal Nutrition: A Balance Between Deficiency and Toxicity  

E-print Network

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

Hamel, Patrice

396

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

NASA Astrophysics Data System (ADS)

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.

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

2014-11-01

397

Mössbauer spectrometric study of nonstoichiometric perovskite, A (Co0.8Fe0.2) O3-° (A=Ba, Sr, Ca), for oxidative coupling of methane  

NASA Astrophysics Data System (ADS)

Nonstoichiometric perovskites. A(Co0.8Fe0.2)O3-6, were prepared by a pyrolysis of mixed metal citrates, and the catalytic property and structure of these perovskites were investigated. The efficiency of an oxidative coupling of methane increases with the order of Ba. Sr, and Ca substituted in A site and decreases with the amounts of deficient oxygens. The mixed valence of B site ions in the disordering of deficient oxygen is considered to contribute mainly to the oxidative coupling of methane.

Nomura, Kiyoshi; Goda, Takeshi; Ujihira, Yusuke; Hayakawa, Takashi; Takehira, Katsuomi

1992-04-01

398

A neutron diffraction study of the magnetic structure for the perovskite-type mixed oxides La(Mn, Cr)03 and (La, Sr)Fe03  

E-print Network

A NEUTRON DIFFRACTION STUDY OF THE MAGNETIC STRUCTURE FOR THE PEROVSKITE-TYPE MIXED OXIDES La(Mn,Cr)03 AND (La,Sr)Fe03 A Dissertation By ULRICH H. BENTS Submitted to the Graduate School of the Agricultural and Mechanical College of Texas... in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY May 1956 Major Subjectj Physics l i b r a r y l A i braayb?y r? ???l? A NEUTRON DIFFRACTION STUDY OF THE MAGNETIC STRUCTURE FOR THE PEROVSKITE-TYPE MIXED OXIDES La...

Bents, Ulrich H.

1956-01-01

399

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

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

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

2015-03-24

400

JOURNAL DE PHYSIQUE Colloque C1, supplPment au no 4, Tome 38, Avril 1977, page Cl-147 ANISOTROPY AND MAGNETOSTRICTION OF 4d AND 5d TRANSITION-METAL  

E-print Network

of the 3d transition-metal ions and rare earth ions except for some studies in the recent past concerning that ferrimagnetism of magnetic oxides essentially is based on 3d transition-metal ions and rare earth ions. However AND MAGNETOSTRICTION OF 4d AND 5d TRANSITION-METAL IONS IN GARNETS AND SPINEL FERRITES P. HANSEN Philips Gmb

Paris-Sud XI, Université de

401

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

NASA Astrophysics Data System (ADS)

Pulsed laser deposition of spinel ?-Al2O3 thin films on bulk perovskite SrTiO3 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.

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

2015-02-01

402

Chemical vapor deposition and electric characterization of perovskite oxides LaMO{sub 3} (M=Co, Fe, Cr and Mn) thin films  

SciTech Connect

Oxides with a perovskite structure are important functional materials often used for the development of modern devices. In view of extending their applicability, it is necessary to efficiently control their growth as thin films using technologically relevant synthesis methods. Pulsed spray evaporation CVD was used to grow several perovskite-type oxides on planar silicon substrates at temperatures ranging from 500 to 700 deg. C. The optimization of the process control parameters allows the attainment of the perovskite structure as a single phase. The electrical characterization using the temperature-dependent conductivity and thermopower indicates the p-type conduction of the grown films and shows a decreasing concentration of the charge carrier, mobility and band gap energy in the sequence LaCoO{sub 3}>LaMnO{sub 3}>LaCrO{sub 3}>LaFeO{sub 3}. The investigation of the electric properties of the obtained perovskite thin films shows the versatility of CVD as a method for the development of innovative devices. - Graphical abstract: We report a single step deposition of perovskite thin films LaMO{sub 3} (M: Co, Mn, Cr, Fe) using pulsed spray evaporation chemical vapor deposition. Electrical and thermopower properties, similar to these of bulk materials, could promote the development of modern thermoelectric devices based on thin films technology.

Ngamou, Patrick Herve Tchoua [Department of Chemistry, Bielefeld University, Universitaetsstr. 25, 33615 Bielefeld (Germany); Bahlawane, Naoufal, E-mail: naoufal@pc1.uni-bielefeld.d [Department of Chemistry, Bielefeld University, Universitaetsstr. 25, 33615 Bielefeld (Germany)

2009-04-15

403

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 ...

404

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...

405

Mass fractionation processes of transition metal isotopes  

Microsoft Academic Search

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

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

2002-01-01

406

High Pressure Synthesis of Transition Metal Carbonyls.  

ERIC Educational Resources Information Center

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

Hagen, A. P.; And Others

1979-01-01

407

Correlated hybridization in transition metal complexes  

Microsoft Academic Search

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

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

2006-01-01

408

Correlated Hybridization in Transition-Metal Complexes  

Microsoft Academic Search

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

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

2006-01-01

409

Weak covalency in transition metal salts  

Microsoft Academic Search

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

J Hubbard; D E Rimmer; F R A Hopgood

1966-01-01

410

Molecular orbital calculations on transition metal clusters  

Microsoft Academic Search

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

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

1989-01-01

411

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

PubMed Central

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

2013-01-01

412

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

NASA Astrophysics Data System (ADS)

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.

Zeb, M. Ahsan; Kee, Hae-Young

2012-08-01

413

Changes in electronic structure upon lithium insertion reaction into the A-site-deficient perovskite-type oxides, Gd 1\\/3TaO 3  

Microsoft Academic Search

Electrochemical behavior and the variation of electronic structure upon lithium insertion into the A-site-deficient perovskite oxide, Gd1\\/3TaO3, have been studied by X-ray absorption spectroscopy (XAS). During electrochemical lithium insertion, Gd LIII-edge and Ta LI-edge XAS revealed that Gd ion did not contribute the charge compensation, while Ta ion reduced its oxidation state. Furthermore, the changes in O K-edge spectra with

Kazuomi Imaki; Masanobu Nakayama; Yoshiharu Uchimoto; Masataka Wakihara

2004-01-01

414

(Electronic structure and reactivities of transition metal clusters)  

SciTech Connect

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

Not Available

1992-01-01

415

Perovskite ferroelectric nanomaterials  

NASA Astrophysics Data System (ADS)

In this review, the main concept of ferroelectricity of perovskite oxides and related materials at nanometer scale and existing difficulties in the synthesis of those nanocrystals are discussed. Important effects, such as depolarization field and size effect, on the existence of ferroelectricity in perovskite nanocrystals are deliberated. In the discussion of modeling works, different theoretical calculations are pinpointed focusing on their studies of lattice dynamics, phase transitions, new origin of ferroelectricity in nanostructures, etc. As the major part of this review, recent research progress in the facile synthesis, characterization and various applications of perovskite ferroelectric nanomaterials, such as BaTiO3, PbTiO3, PbZrO3, and BiFeO3, are also scrutinized. Perspectives concerning the future direction of ferroelectric nanomaterials research and its potential applications in renewable energy, etc., are presented. This review provides an overview in this area and guidance for further studies in perovskite ferroelectric nanomaterials and their applications.In this review, the main concept of ferroelectricity of perovskite oxides and related materials at nanometer scale and existing difficulties in the synthesis of those nanocrystals are discussed. Important effects, such as depolarization field and size effect, on the existence of ferroelectricity in perovskite nanocrystals are deliberated. In the discussion of modeling works, different theoretical calculations are pinpointed focusing on their studies of lattice dynamics, phase transitions, new origin of ferroelectricity in nanostructures, etc. As the major part of this review, recent research progress in the facile synthesis, characterization and various applications of perovskite ferroelectric nanomaterials, such as BaTiO3, PbTiO3, PbZrO3, and BiFeO3, are also scrutinized. Perspectives concerning the future direction of ferroelectric nanomaterials research and its potential applications in renewable energy, etc., are presented. This review provides an overview in this area and guidance for further studies in perovskite ferroelectric nanomaterials and their applications. The authors declare no competing financial interests.

Nuraje, Nurxat; Su, Kai

2013-09-01

416

Monolayer semiconducting transition metal dichalcogenide alloys: Stability and band bowing  

E-print Network

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

Wu, Junqiao

417

Quantum-Mechanical Force Laws for Transition Metals in Biomolecules  

Microsoft Academic Search

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

Anders E. Carlsson

1998-01-01

418

Mechanism of stearic acid oxidation over nanocrystalline L a 1 ? x A ? x B O 3 (A? = Sr, Ce; B = Co, Mn): The role of oxygen mobility  

Microsoft Academic Search

Catalytic wet air oxidation reaction (CWAO) of stearic acid is carried out in a batch reactor over a series of transition metal-based perovskite samples synthesized by reactive grinding. It is observed that the LaCoO3 sample presents the highest initial activity for this reaction. For comparison, pure and substituted LaMnO3 samples show largely smaller activity in spite of similar specific surface

S. Royer; B. Levasseur; H. Alamdari; J. Barbier; D. Duprez; S. Kaliaguine

2008-01-01

419

Investigation of hyperfine interactions in RMO 3 (R = La, Nd; M = Cr, Fe) antiferromagnetic perovskite oxides using PAC spectroscopy  

NASA Astrophysics Data System (ADS)

The local magnetic interaction at the transition metal sites in RMO3 (R = La, Nd; M = Cr, Fe) compounds has been investigated by perturbed angular correlation (PAC) technique using 181Hf?181Ta probe nuclei. The present measurements cover a temperature range from 10 K to 1000 K. Above the respective Néel temperature, each compound shows a unique quadrupolar frequency that decreases linearly with temperature. These interactions were assigned to the radioactive probe substituting Cr or Fe sites. Below T N , a combined electric plus magnetic hyperfine interaction was observed. The magnetic interaction revealed that the super transferred hyperfine fields on 181Ta at the Cr sites in (La,Nd)CrO3 extrapolated to 0 K, are much smaller than the corresponding values at Fe sites in (La,Nd)FeO3. This difference was attributed to different distribution of d electrons in Cr3 + (3d3) and Fe3 + (3d5) ions in each compound. As the fields for Nd compounds are smaller than those for La compounds, the role of rare-earth ions in the magnetism of these oxides is also discussed.

Carbonari, A. W.; Cavalcante, F. H. M.; Junqueira, A. C.; Leite, D. M. T.; Saxena, R. N.; Mestnik-Filho, J.

2007-07-01

420

Investigation of hyperfine interactions in RMO3 (R =La, Nd; M =Cr, Fe) antiferromagnetic perovskite oxides using PAC spectroscopy  

NASA Astrophysics Data System (ADS)

The local magnetic interaction at the transition metal sites in RMO3 (R=La, Nd; M=Cr, Fe) compounds has been investigated by perturbed angular correlation (PAC) technique using 181Hf?181Ta probe nuclei. The present measurements cover a temperature range from 10 K to 1000 K. Above the respective Neel temperature, each compound shows a unique quadrupolar frequency that decreases linearly with temperature. These interactions were assigned to the radioactive probe substituting Cr or Fe sites. Below TN, a combined electric plus magnetic hyperfine interaction was observed. The magnetic interaction revealed that the super transferred hyperfine fields on 181Ta at the Cr sites in (La,Nd)CrO3 extrapolated to 0 K, are much smaller than the corresponding values at Fe sites in (La,Nd)FeO3. This difference was attributed to different distribution of d electrons in Cr3+ (3d3) and Fe3+ (3d5) ions in each compound. As the fields for Nd compounds are smaller than those for La compounds, the role of rare-earth ions in the magnetism of these oxides is also discussed.

Carbonari, A. W.; Cavalcante, F. H. M.; Junqueira, A. C.; Leite, D. M. T.; Saxena, R. N.; Mestnik-Filho, J.

421

Impurity effects in transition metal silicides  

NASA Technical Reports Server (NTRS)

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

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

1984-01-01

422

Structures of large transition metal clusters  

Microsoft Academic Search

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

O. A. Belyakova; Yu. L. Slovokhotov

2003-01-01

423

Correlated Hybridization in Transition-Metal Complexes  

Microsoft Academic Search

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

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

2006-01-01

424

The Electronic Structure of Transition Metal Carbides  

Microsoft Academic Search

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

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

1998-01-01

425

Transition metal-silicate analogs of zeolites  

Microsoft Academic Search

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

Paul Ratnasamy; Rajiv Kumar

1993-01-01

426

Single-layer transition metal sulfide catalysts  

DOEpatents

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

Thoma, Steven G. (Albuquerque, NM)

2011-05-31

427

Lattice oxygen of La 1? x Sr x MO 3 (M = Mn, Ni) and LaMnO 3? ? F ? perovskite oxides for the partial oxidation of methane to synthesis gas  

Microsoft Academic Search

The partial oxidation of methane to synthesis gas by using the lattice oxygen of La1?xSrxMO3 (M=Mn, Ni; x=0–0.4) and LaMnO3??F? (?\\/(3??)=0.1) perovskite oxides was explored. Approximately 75% CO selectivity at 16% CH4 conversion with H2\\/CO molar ratio of ca. 2.5 can be achieved at 800°C. The stability of the perovskite structure and the reactivity\\/selectivity of lattice oxygen are found to

H. J. Wei; Y. Cao; W. J. Ji; C. T. Au

2008-01-01

428

Electronic properties of double perovskite compounds  

Microsoft Academic Search

The double perovskites family A2MMO6 (A being an alkaline-earth and M, M two different transition-metal elements) is considered as a serious candidate for magnetoelectronic applications. It appears to be fundamental to understand the role of electronic parameters controlling the half-metallic ground state and high Curie temperature Tc. In this respect it is very interesting that different members of the family

E. Carvajal; O. Navarro; R. Allub; M. Avignon; B. Alascio

2005-01-01

429

Lanthanoid-transition-metal bonding in bismetallocenes.  

PubMed

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

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

2014-03-01

430

Corrosion behavior of mesoporous transition metal nitrides  

SciTech Connect

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

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

2013-09-15

431

XRD and FTIR studies the effect of heat treatment and doping the transition metal oxide on LiNbO3 and LiNb3O8 nano-crystallite phases in lithium borate glass system  

NASA Astrophysics Data System (ADS)

Glasses of various compositions in the system 90 Li2B4O7sbnd 10 Nb2O5 mixed with T.M ions (where T.M is the transition metal) were prepared by quenching technique. Heat-treatment of the parent glasses was performed at 540, 570 and 620 °C, for 5 and 16 h. The glass structure evolution during the controlled crystallization was examined by XRD and FT-IR spectroscopy analysis. The crystalline phases present in the glass ceramics were identified via X-ray diffraction as a function of heat treatment. The FT-IR data propose for these glasses and heat-treated glass network structures mainly built by: di-, tri-, tetra-, penta-and ortho-borate groups. It was found that the quantitative evolution of these various borate species in the glass structures is influenced by the transition metal. A detailed discussion relating to the N4 evolution with the T.M content was made.

Kashif, Ismail; Soliman, Ashia A.; Sakr, Elham M.; Ratep, Asmaa

2013-09-01

432

The pure rotational spectrum of TiF,,X4 r...: 3d transition metal  

E-print Network

fluorides and oxides. © 2003 American Institute of Physics. DOI: 10.1063/1.1615753 I. INTRODUCTION TitaniumThe pure rotational spectrum of TiF,,X4 r...: 3d transition metal fluorides revisited P. M in this radical lie in orbitals primarily located on the titanium atom and support the molecular orbital picture

Ziurys, Lucy M.

433

Quenching of Lanthanide Emission by Intervalence Charge Transfer in Crystals Containing Closed Shell Transition Metal Ions  

Microsoft Academic Search

The quenching of the luminescence originating from the excited states P0 and D2 of Pr and D3 and D4 of Tb has been studied in oxide crystals containing closed shell transition metal ions, such as titanates, vanadates, niobates, and tantalates. It has been shown that the emission from these excited states can be quenched by an intervalence charge transfer mechanism.

Philippe Boutinaud; Piotr Putaj; Rachid Mahiou; Enrico Cavalli; Adolfo Speghini; Marco Bettinelli

2007-01-01

434

Electrochemical behavior of transition metals and refractory compounds of titanium in synthetic sea water  

Microsoft Academic Search

Investigations were conducted into the corrosion-electrochemical behavior of the compounds of titanium with boron, carbon, and nitrogen produced by powder metallurgy and also of the transition metals in synthetic sea water. The results show that the start of pitting coincides with the process of intensive oxidation on the surface of the refractory compound. On the basis of the increasing corrosion

A. D. Verkhoturov; M. A. Kuzenkova; N. V. Lebukhova; I. A. Podchernyaeva

1988-01-01

435

Room-Temperature Ferromagnetism in Transparent Transition Metal-Doped Titanium Dioxide  

Microsoft Academic Search

Dilute magnetic semiconductors and wide gap oxide semiconductors are appealing materials for magnetooptical devices. From a combinatorial screening approach looking at the solid solubility of transition metals in titanium dioxides and of their magnetic properties, we report on the observation of transparent ferromagnetism in cobalt-doped anatase thin films with the concentration of cobalt between 0 and 8%. Magnetic microscopy images

Yuji Matsumoto; Makoto Murakami; Tomoji Shono; Tetsuya Hasegawa; Tomoteru Fukumura; Masashi Kawasaki; Parhat Ahmet; Toyohiro Chikyow; Shin-ya Koshihara; Hideomi Koinuma

2001-01-01

436

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

E-print Network

)/lanthanum manganate (LaMnO3, i.e., LMO) perovskite oxide metal/semiconductor superlattices were investigated perovskite oxide metal/semiconductor superlattices Pankaj Jha,1,2 Timothy D. Sands,1,2,3,a) Laura Cassels,4 2012; published online 26 September 2012) Lanthanum strontium manganate (La0.67Sr0.33MnO3, i.e., LSMO

Xu, Xianfan

437

Comparative study of the synthesis of layered transition metal molybdates  

SciTech Connect

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

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

2010-01-15

438

An investigation of the Fe and Mo oxidation states in Sr[subscript 2]Fe[subscript 2]Mo[subscript x]O[subscript 6] (0.25 [less than] x [less than] 1.0) double perovskites by X-ray absorption spectroscopy  

SciTech Connect

Sr{sub 2}FeMoO{sub 6} double perovskite systems are widely studied because of their interesting and technologically relevant physical properties. Sr{sub 2}FeMoO{sub 6} is just a single composition in the Sr{sub 2}Fe{sub 2-x}Mo{sub x}O{sub 6} solid-solution, and it is important to understand how the composition impacts the transition-metal valence states. Variations in the lattice parameters of these materials were studied using powder X-ray diffraction and it was found that a large change in the lattice constant occurs between Sr{sub 2}Fe{sub 1.50}Mo{sub 0.50}O{sub 6} and Sr{sub 2}Fe{sub 1.35}Mo{sub 0.65}O{sub 6} that likely coincides with a transition from a cubic to a tetragonal unit cell, in agreement with previous studies. Fe K- and Mo K-edge X-ray absorption near-edge spectra were also collected to investigate how the oxidation state and coordination environment change with composition. When the Mo content is low, Fe adopts a 3+ oxidation state and Mo adopts a 6+ oxidation state. As the Mo content is increased, the Fe and Mo cations are both partially reduced, resulting in a mixture of Fe{sup 3+} and Fe{sup 2+} and Mo{sup 5+} and Mo{sup 6+}. The reduction of the metal centers apparently drives the change in unit cell. The influence of preparation method on the oxidation states of Fe and Mo was also investigated by annealing the materials under vacuum. The results reported here show that the oxidation states of Fe and Mo are strongly impacted by both composition and preparation method, which may account for the wide variety of oxidation state and magnetic properties that have been reported previously.

Hayes, John R.; Grosvenor, Andrew P. (Saskatchewan)

2012-10-25

439

Voltage-induced Metal-Insulator Transitions in Perovskite Oxide Thin Films Doped with Strongly Correlelated Electrons  

NASA Astrophysics Data System (ADS)

We have observed a reversible metal-insulator transition in perovskite oxide thin films that can be controlled by charge trapping pumped by a bipolar voltage bias. In the as-fabricated state, the thin film is metallic with a very low resistance comparable to that of the metallic bottom electrode, showing decreasing resistance with decreasing temperature. This metallic state switches to a high-resistance state after applying a voltage bias: such state is non-ohmic showing a negative temperature dependence of resistance. Switching at essentially the same voltage bias was observed down to 2K. The metal-insulator transition is attributed to charge trapping that disorders the energy of correlated electron states in the conduction band. By increasing the amount of charge trapped, which increases the disorder relative to the band width, increasingly more insulating states with a stronger temperature dependence of resistivity are accessed. This metal-insulator transition provides a platform to engineer new nonvolatile memory that does not require heat (as in phase transition) or dielectric breakdown (as in most other oxide resistance devices).

Wang, Yudi; Gil Kim, Soo; Chen, I.-Wei

2007-03-01

440

Tetrathiafulvalene-annulated phenanthroline and its complexes with transition metals  

NASA Astrophysics Data System (ADS)

Recent interest in designing multifunctional transition metal complexes that incorporate the redox-active tetrathiafulvalene (TTF) molecule stems from the perspective of embedding specific localized properties of transition metal ions into TTF-containing substructures characterized by extended delocalized conduction pathways. This dissertation reports on the synthesis of tetrathiafulvalene, a ubiquitous component of organic conductors, fused directly to 1,10-phenanthroline, one of the most popular ligands in transition metal chemistry. We have devised and implemented a synthetic pathway to this unique ligand, which then was used to obtain complexes with Ru(II) and Fe(II) ions. Chapter 1 of this dissertation provides an introduction to the chemistry of TTF and its metal complexes. Chapter 2 describes the most important methods of characterization employed in this research project. Chapter 3 is devoted to the preparation and properties of the TTF-annulated phenanthroline ligands. Chapter 4 describes a detailed study of a Ru(II) complex of TTF phenanthroline, including its structural, photophysical, and electrochemical properties. [Ru(bpy) 2(edt-TTF-phen)](PF6)2 exhibits a unique helical packing of molecules