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1

Catalytic oxidation over lanthanum-transition metal perovskite materials  

Microsoft Academic Search

The thrust of this work is to follow the defect chemistry of the simple LaCoO3 system in an attempt to probe if there is a relationship between the defect chemistry and the activity of this perovskite-type material to catalytic methane combustion. A simple flow-through reactor has been used to study the combustion of methane between room temperature and 1100°C. Using

M O'Connell; A. K Norman; C. F Hüttermann; M. A Morris

1999-01-01

2

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

SciTech Connect

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

Okamoto, Satoshi [ORNL] [ORNL; Zhu, Wenguang [University of Science and Technology of China] [University of Science and Technology of China; Nomura, Yusuke [University of Tokyo, Japan] [University of Tokyo, Japan; Arita, R. [University of Tokyo, Japan] [University of Tokyo, Japan; Xiao, Di [Carnegie Mellon University (CMU)] [Carnegie Mellon University (CMU); Nagaosa, Naoto [University of Tokyo, Japan] [University of Tokyo, Japan

2014-01-01

3

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 to consider applications. The doping-induced metal-insulator transition in (La,Ca)MnO3 can for instance lead

Hille, Sander

4

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

5

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

6

Electronic structure of perovskite-type transition metal oxides LaMO3 (M=T?Cu) by U+GW approximation  

NASA Astrophysics Data System (ADS)

We investigate electronic structures of LaMO3 (M=T?Cu) systematically by means of U+GW approximation. In these strongly correlated systems, it is important to treat large on-site Coulomb interactions and their dynamical screening effects. Transition-metal ions in perovskite-type lanthanum oxides are trivalent and their physics is qualitatively different from that of divalent transition-metal ions in transition-metal mono-oxides. The localization of wave functions of La4f and 3d orbitals of Ti, V, and Co is crucial. On the other hand, the screening effect for other transition-metal 3d orbitals is strong enough so as to reduce the on-site static-screened Coulomb interaction in trivalent oxides. The band gaps, the magnetic moments, and energy spectra are discussed in comparison with the experimentally observed results. Calculated energy spectra of LaMO3 (M=?Cu) are in good agreement with experimental results.

Nohara, Yoshiro; Yamamoto, Susumu; Fujiwara, Takeo

2009-05-01

7

(S)TEM analysis of functional transition metal oxides  

Microsoft Academic Search

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

Miaofang Chi

2008-01-01

8

Wettability of transition metal oxide surfaces  

Microsoft Academic Search

The wettability of transition metal oxide surfaces (TiO2, ZrO2 and HfO2) by water was investigated by measuring the contact angles using the sessile drop method. The oxide surfaces were prepared by thermal oxidation of polished metal foils of Ti, Zr and Hf, which had been polished to different levels of surface roughness. The surfaces were also characterized by optical microscopy,

Aiguo Feng; Benjamin J McCoy; Zuhair A Munir; Domenick Cagliostro

1998-01-01

9

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

10

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 discuss the relevance of the theory to transition metal oxides. The main qualitative features in transition metal oxides. These oxides form a very interesting class of materials [1]. Their electrical

Paris-Sud XI, Université de

11

MATERIALS THEORY From transition metal oxides to cosmic strings  

E-print Network

MATERIALS THEORY From transition metal oxides to cosmic strings (and how electronic structure Transition metal oxides Thursday, September 20, 2012 6D-MATL / Materials Theory Compounds containing and competing interactions! Energy scale ~ 1eV #12;MATERIALS THEORY Where do transition metal oxides fit

12

Topological crystalline insulators in transition metal oxides.  

PubMed

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

Kargarian, Mehdi; Fiete, Gregory A

2013-04-12

13

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

14

Quantum Criticality in Transition-Metal Oxides  

Microsoft Academic Search

We report on experiments of the bulk susceptibility ?(T), heat capacity C(T)\\/T, resistivity ?(T) and nuclear resonances (NMR and NQR) in order to review evidence of quantum critical behaviour in some metallic transition-metal\\u000a oxides. In analogy to the conventional 4f- and 5f-electron based heavy-fermion compounds, the prerequisites of quantum criticality, i.e. a magnetic phase transition at T=0 accompanied by non-Fermi

N. Büttgen; H.-A. Krug von Nidda; W. Kraetschmer; A. Günther; S. Widmann; S. Riegg; A. Krimmel; A. Loidl

2010-01-01

15

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

16

Magnetic correlations in doped transition metal oxides  

SciTech Connect

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

Aeppli, G. [AT and T Bell Labs., Murray Hill, NJ (United States); Bao, W.; Broholm, C. [Johns Hopkins Univ., Baltimore, MD (United States)] [and others

1995-02-15

17

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

18

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

19

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

20

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

21

Fingerprints of spin-orbital entanglement in transition metal oxides.  

PubMed

The concept of spin-orbital entanglement on superexchange bonds in transition metal oxides is introduced and explained on several examples. It is shown that spin-orbital entanglement in superexchange models destabilizes the long-range (spin and orbital) order and may lead either to a disordered spin-liquid state or to novel phases at low temperature which arise from strongly frustrated interactions. Such novel ground states cannot be described within the conventionally used mean field theory which separates spin and orbital degrees of freedom. Even in cases where the ground states are disentangled, spin-orbital entanglement occurs in excited states and may become crucial for a correct description of physical properties at finite temperature. As an important example of this behaviour we present spin-orbital entanglement in the RV O(3) perovskites, with R = La,Pr,…,Y b,Lu, where the finite temperature properties of these compounds can be understood only using entangled states: (i) the thermal evolution of the optical spectral weights, (ii) the dependence of the transition temperatures for the onset of orbital and magnetic order on the ionic radius in the phase diagram of the RV O(3) perovskites, and (iii) the dimerization observed in the magnon spectra for the C-type antiferromagnetic phase of Y V O(3). Finally, it is shown that joint spin-orbital excitations in an ordered phase with coexisting antiferromagnetic and alternating orbital order introduce topological constraints for the hole propagation and will thus radically modify the transport properties in doped Mott insulators where hole motion implies simultaneous spin and orbital excitations. PMID:22776856

Ole?, Andrzej M

2012-08-01

22

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

23

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

24

Chromite\\/titanate based perovskites for application as anodes in solid oxide fuel cells  

Microsoft Academic Search

Perovskites containing lanthanides, partially substituted by alkaline-earth elements and transition metals like Cr, Ti, Fe or Co show a very broad range of physical properties. Therefore several perovskite materials, based on lanthanum chromite and strontium titanate were synthesised and investigated with regard to their application as anodes in solid oxide fuel cells. The perovskite powders were studied by thermogravimetric and

G. Pudmich; B. A. Boukamp; M. Gonzalez-Cuenca; W. Jungen; W. Zipprich; F. Tietz

2000-01-01

25

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

Wu, Junqiao

26

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-metal ions in an oxide and how these factors in turn affect the resistance of metastable 3d transition-metal oxides against transformation. This is a relevant topic to the Li rechargeable battery field

Ceder, Gerbrand

27

Transition metal-catalyzed oxidation of sulfur(IV) oxides. Atmospheric-relevant processes and mechanisms  

Microsoft Academic Search

The transition metal-catalyzed oxidation of sulfur(IV) oxides has been known for more than 100 years. There is a significant lack of information on the actual role of the transition metal-catalyzed reactions, and much of the earlier work was performed without a detailed knowledge of the chemical system. For this reason attention is focused on the role of transition metal ions

Christian. Brandt; Rudi. van Eldik

1995-01-01

28

PHYSICAL REVIEW B 85, 054417 (2012) Spin-phonon coupling effects in transition-metal perovskites: A DFT + U and  

E-print Network

,7 alternative routes are needed in order to optimize materials for functional device application. This could­10 or by modifying already-known materials to engineer specific properties. In the latter direction, an intriguingPHYSICAL REVIEW B 85, 054417 (2012) Spin-phonon coupling effects in transition-metal perovskites

Vanderbilt, David

29

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

30

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

31

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 functional­14 however, no such studies, to our knowledge, have been performed in transition metal oxides or other of the lithium local environment and electronic configuration of the transition metal ions. We focus

Ceder, Gerbrand

32

Transition metal dioxygen complexes as intermediates in homogeneous catalytic oxidations  

NASA Astrophysics Data System (ADS)

The formation and main structural properties of superoxo and peroxo complexes are briefly described. These complexes are involved in catalytic oxidations (oxygenations) by dioxygen occurring under mild conditions in the presence of iron, cobalt, manganese, rhodium and other transition metal complexes. Examples of catalytic systems are taken from cytochrome P-450 models with specific reference to the mechanisms involved. Metalloporphyrin-catalysed oxidations of hydrocarbons involve free-radical chain processes in most cases. Added reducing agents modify the mechanism of oxidation by pumping electrons into key intermediates. They help the formation of oxometal species, which may transfer oxygen atoms to substrates, thereby improving the selectivity. Olefin oxidation is a difficult task for the homogeneous catalysts described: only a few working systems are available, based mainly on rhodium phosphine complexes. Peroxometalacycles are presumably formed, whose decomposition involves co-oxidation of a phosphine molecule. The oxidation of hindered phenols catalysed by cobalt (II) Schiff-base complexes points to the involvement of superoxocobalt species abstracting a H-atom from the phenol. Complex reaction patterns emerge from the oxidation of o-disubstituted phenols. The synthetic potential of homogeneous catalytic oxidation is illustrated on examples including various types of organic compounds.

Simándi, Lászlò I.

33

Hubbard Thomas Fermi theory of transition metal oxide heterostructures  

NASA Astrophysics Data System (ADS)

We demonstrate that the charge distributions in Hubbard-model representations of transition metal oxide heterojunctions can be described by a Thomas-Fermi theory in which the energy is approximated as the sum of the electrostatic energy and the uniform three-dimensional Hubbard model energy per site at the local density equals to a constant. When charged atomic layers in the oxides are approximated as two-dimensional sheets with uniform charge density, the electrostatic energy is simply evaluated. We find that this Thomas-Fermi theory can reproduce results obtained from full Hartree-Fock theory for various different heterostructures. We also show explicitly how Thomas-Fermi theory can be used to estimate some key properties qualitatively.

Lee, Wei-Cheng; MacDonald, A. H.

2008-04-01

34

Effects of transition metals on nitric oxide synthase catalysis  

PubMed Central

The biosynthesis of nitric oxide (NO) by the enzyme NO synthase (NOS) proceeds by the hydroxylation of l-arginine to form NG-hydroxy-l-arginine followed by the conversion of NG-hydroxy-l-arginine to l-citrulline and NO. The previously identified requirements of this relatively complicated reaction include several protein-bound cofactors: cytochrome P450-type heme, flavin mononucleotide (FMN), flavin adenine dinucleotide (FAD), and tetrahydrobiopterin (H4B). In addition to l-arginine, NOS also requires the substrates NADPH and molecular oxygen. The role of H4B in NOS catalysis has long been a subject of debate and uncertainty fueled, in part, by the failure to detect any dependence of the NOS reaction on nonheme iron, a cofactor integral to catalysis in every other H4B-dependent enzyme. Here we report the ability of NOS to bind transition metals stoichiometrically, and demonstrate that the rate of catalysis is enhanced by nonheme iron. We also show that other divalent transition metals, including Cu, Zn, Co, and Ni, inhibit NOS catalysis. Also, the addition of Cu2+ to NOS inhibits heme reduction, whereas the addition of Fe2+ does not. Overall, the results appear to connect NOS to the known H4B/nonheme iron-dependent hydroxylases, and suggest a similar, if not identical, step in the NOS reaction mechanism. PMID:9736696

Perry, Jason M.; Marletta, Michael A.

1998-01-01

35

Luminescence in some lithiated transition metal oxide cathodes  

NASA Astrophysics Data System (ADS)

Lithiated transition metal oxides such as LiNiVO 4, Li 2MnO 3 and Li 0.4WO 3 used as cathode materials in high density lithium-ion batteries, show intense optical absorption followed by fluorescence in the region of 2-4 eV. These optical transitions can tentatively be assigned to either transition metal to oxygen charge transfer type or Jahn-Teller type local distortion. For fluorescing samples (LiNiVO 4, Li 2MnO 3 and Li 0.4WO 4), photo-induced impedance (Bode plot) data show significant enhancement in impedance under low frequency range (˜10 Hz). However, more important cathode materials such as LiCoO 2 and LiMn 2O 4 do not show either fluorescence or photo-induced impedance enhancement. The presence or absence of an optical transition in the cathode system may give some clues on the tendency for electrochemical fading.

Kalyani, P.; Jagannathan, R.; Gopukumar, S.; Lu, Chung-Hsin

36

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

37

Transition metal oxide nanowires synthesized by heating metal substrates  

SciTech Connect

Highlights: {center_dot} This paper describes a simple and general method to synthesize 3d metal oxide nanowires. {center_dot} Self-catalysis growth mechanism was proposed to explain the growth of the nanowires. {center_dot} The temperature range for the growth of nanowires was estimated by taking into account the Gibbs free energy of reaction. {center_dot} This synthesis approach could be applied to synthesize other one-dimensional structures, such as FeSe and Bi{sub 2}Te{sub 3} nanowires. -- Abstract: Here we reported a simple method to synthesize transition metal oxide nanowires. Copper oxide (CuO), zinc oxide (ZnO), and cobalt oxide (Co{sub 3}O{sub 4}) nanowires were synthesized by heating the copper, zinc, and cobalt substrates under atmosphere condition. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to analyze the morphology and microstructure of the nanowires. According to our experimental results, self-catalysis growth mechanism was proposed to explain the growth of the nanowires. The temperature window for the growth of nanowires was estimated by taking into account the Gibbs free energy of reaction. The synthesis approach observed in our experiment could be applied to synthesize other one-dimensional structures, such as FeSe and Bi{sub 2}Te{sub 3} nanowires.

Yan, Hui; Sun, Yi [Department of Physics, Beijing Normal University, 100875 Beijing (China)] [Department of Physics, Beijing Normal University, 100875 Beijing (China); He, Lin, E-mail: helin@bnu.edu.cn [Department of Physics, Beijing Normal University, 100875 Beijing (China)] [Department of Physics, Beijing Normal University, 100875 Beijing (China); Nie, Jia-Cai [Department of Physics, Beijing Normal University, 100875 Beijing (China)] [Department of Physics, Beijing Normal University, 100875 Beijing (China)

2011-11-15

38

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

39

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 be corrected by fitting the formation enthalpy of simple nontransition metal oxides. Removal of the O2 binding

Ceder, Gerbrand

40

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

41

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

42

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

43

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

44

Transition-metal acceptor complexes in zinc oxide  

NASA Astrophysics Data System (ADS)

The incorporation of hydrogen shallow donors gives rise to Mn2+ fine and hyperfine lines in the electron paramagnetic resonance of ZnO. This cannot be explained by recharging of isolated Mn atoms. First-principles density functional calculations reveal that transition metals readily form complexes with acceptors by a charge-transfer process or by bond formation. This mechanism has implications on both complex partners. Acceptors are neutralized and uncommon charge states of the transition metals are stabilized. Implications for dilute magnetic ZnO are discussed.

Gluba, M. A.; Nickel, N. H.

2013-02-01

45

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

46

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

47

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

SciTech Connect

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

Ogihara, Hitoshi, E-mail: ogihara@cms.titech.ac.j [Catalysis Research Center, Hokkaido University, N21-W10 Kita-ku, Sapporo 001-002 (Japan); Japan Society for the Promotion of Science, Chiyoda-ku, Tokyo 102-8472 (Japan); Masahiro, Sadakane [Catalysis Research Center, Hokkaido University, N21-W10 Kita-ku, Sapporo 001-002 (Japan); Nodasaka, Yoshinobu [Oral Functional Science, Graduate School of Dental Medicine, Hokkaido University, N13-W7 Kita-ku, Sapporo 060-8586 (Japan); Ueda, Wataru, E-mail: ueda@cat.hokudai.ac.j [Catalysis Research Center, Hokkaido University, N21-W10 Kita-ku, Sapporo 001-002 (Japan)

2009-06-15

48

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

49

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, K.D.

1991-06-25

50

Route to transition metal carbide nanoparticles through cyanamide and metal oxides  

SciTech Connect

We have designed an efficient route to the synthesis of transition metal carbide nanoparticles starting from an organic reagent cyanamide and transition metal oxides. Four technologically important metal carbide nanoparticles such as tungsten carbide, niobium carbide, tantalum carbide and vanadium carbide were synthesized successfully at moderate temperatures. It is found that cyanamide is an efficient carburization reagent and that the metal oxides are completely transmitted into the corresponding carbide nanoparticles. A possible mechanism is proposed to explain the results of the reaction between cyanamide and the metal oxides.

Li, P.G. [Department of Physics, Center for Optoelectronics Materials and Devices, Zhejiang Sci-Tech University, Xiasha College Park, Hangzhou 310018 (China)], E-mail: peigangiphy@yahoo.com.cn; Lei, M.; Tang, W.H. [Department of Physics, Center for Optoelectronics Materials and Devices, Zhejiang Sci-Tech University, Xiasha College Park, Hangzhou 310018 (China)

2008-12-01

51

Effect of dipolar fields, surface termination, and surface orientation on photochemical reactions on transition metal oxides  

NASA Astrophysics Data System (ADS)

Experiments have been conducted to determine the effects of dipolar fields, surface termination, and surface orientation on the photochemical reactivity of several transition metal oxides. These compounds include BaTiO3, SrTiO3, BaTi4O9, Sr2Nb2O 7, and Sr2Ta2O7 which were studied as polycrystalline ceramics, single crystals, micron-sized faceted particles, or some combination of these forms. The reduction of Ag+ from an aqueous AgNO3 solution (Ag0 product) and the oxidation of Pb2+ from an aqueous lead acetate solution (PbO 2 product) were selected as probe reactions because they leave insoluble products on the oxide surfaces. The reactivity of ferroelectric BaTiO3 was dominated by the effect of dipolar fields on the transport of photogenerated charge carriers. Silver was reduced on domains with a positive surface charge while lead was oxidized on domains with a negative surface charge. This reactivity implies that the dipolar field in individual domains drives photogenerated charge carriers to oppositely charged surfaces. This reaction mechanism results in a physical separation of the photogenerated charge carriers and the locations of the oxidation and reduction half reactions on the catalyst surface. Experiments performed on polycrystalline ceramics, single crystals, and micron-sized particles all showed this domain specific reactivity. SrTiO3 has the ideal cubic perovskite structure from which the tetragonally distorted ferroelectric BaTiO3 phase is derived. Polished and annealed surfaces of randomly oriented grain surfaces were bound by some combination of the following three planes: {110}, {111}, and a complex facet inclined approximately 24° from {100}. Surfaces with the complex {100} facet were found to be the most active for Ag reduction. Single crystal studies also showed that the nonpolar (100) surface is the most reactive and that the composition of the termination layer does not influence this reaction. However, the polar (111) and (110) surfaces had a non-uniform distribution of reaction products. For these orientations, the location of the reduction and oxidation reactions is determined by the chemical and charge terminations of the different terraces or facets. The reactivity for silver reduction on the faceted particles is ranked as (100) > (111) > (110) while the (100) surface was least reactive for lead oxidation. Overall, these results show that the photochemical reactivity of SrTiO3 is anisotropic and that on polar surfaces, dipolar fields arising from charged surface domains influence the transport of photogenerated charge carriers and promote spatially selective oxidation and reduction reactions. (Abstract shortened by UMI.)

Giocondi, Jennifer Lynn

52

Instabilities in the ferro- and antiferroelectric lead perovskites driven by transition metal ion mass: from PbTiO3 via PbZrO3 to PbHfO3  

NASA Astrophysics Data System (ADS)

The lattice dynamics of Pb-containing perovskite oxides are investigated theoretically for the transition metal series Ti, Zr, Hf, in order to elucidate their commonalities and their distinctions. For all three compounds, pronounced precursor effects are found to their phase transition temperatures, which get more pronounced the heavier the central transition metal ion is. In addition, a competition between a polar and an antiferrodistortive instability is predicted to take place, which is strongly mass dependent. While in PbTiO3 the polar instability wins, both instabilities are active in PbZrO3, whereas in PbHfO3 the antiferrodistortive phase transition dominates the dynamics. For all three compounds, marked anomalies in the elastic constants are predicted, which are most pronounced in PbHfO3. Experimental results for elastic anomalies preceding the phase transition, which agree qualitatively with the model calculations are presented for PbHfO3.

Bussmann-Holder, Annette; Roleder, Krystian; Ko, Jae-Hyeon

2014-07-01

53

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...

54

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

NASA Astrophysics Data System (ADS)

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.

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

2014-05-01

55

Density functional plus dynamical mean-field theory of the metal-insulator transition in early transition-metal oxides  

NASA Astrophysics Data System (ADS)

The combination of density functional theory and single-site dynamical mean-field theory, using both Hartree and full continuous-time quantum Monte Carlo impurity solvers, is used to study the metal-insulator phase diagram of perovskite transition-metal oxides of the form ABO3 with a rare-earth ion A =Sr, La, Y and transition metal B =Ti, V, Cr. The correlated subspace is constructed from atomiclike d orbitals defined using maximally localized Wannier functions derived from the full p-d manifold; for comparison, results obtained using a projector method are also given. Paramagnetic DFT + DMFT computations using full charge self-consistency along with the standard "fully localized limit" (FLL) double counting are shown to incorrectly predict that LaTiO3, YTiO3, LaVO3, and SrMnO3 are metals. A more general examination of the dependence of physical properties on the mean p-d energy splitting, the occupancy of the correlated d states, the double-counting correction, and the lattice structure demonstrates the importance of charge-transfer physics even in the early transition-metal oxides and elucidates the factors underlying the failure of the standard approximations. If the double counting is chosen to produce a p-d splitting consistent with experimental spectra, single-site dynamical mean-field theory provides a reasonable account of the materials properties. The relation of the results to those obtained from "d-only" models in which the correlation problem is based on the frontier orbital p-d antibonding bands is determined. It is found that if an effective interaction U is properly chosen the d-only model provides a good account of the physics of the d1 and d2 materials.

Dang, Hung T.; Ai, Xinyuan; Millis, Andrew J.; Marianetti, Chris A.

2014-09-01

56

Compositional dependence of elastic moduli for transition-metal oxide spinels  

NASA Astrophysics Data System (ADS)

Spinel phases (AB2O4) are common non-silicate oxides in the Earth's crust and upper mantle. A characteristic of this mineral group is the ability to host a wide range of transition metals. Here we summarize the influence of transition metals (Fe, Zn, and Mn) on the pressure dependence of elastic moduli of related spinels (magnetite, gahnite, and franklinite) using GHz-ultrasonic interferometry. Measurements were carried out up to 10 GPa in diamond-anvil cells using hydrostatic pressure media. Transition metals with unfilled 3d orbitals strongly influence the elastic properties of spinels. Franklinite (Zn,Mn)Fe2O4 and magnetite Fe3O4 with transition metals on both A and B cation sites exhibit pressure-induced mode softening of C44, whereas C44 of gahnite(ZnAl2O4) and spinel (MgAl2O4) exhibit positive pressure derivatives of the shear moduli. Spinels with two transition elements tend to undergo phase changes at a lower pressure than those with none or only one transition metal. Along the Mn-Zn solid solution, the variation of moduli with composition is non-linear, and a mid-range franklinite composition studied here shows a minimum in C44 compared with either end-member: MnFe2O 4 or ZnFe2O4. In general, the linear variation of sound velocity with density (Birch's Law) is followed by spinels, however spinels containing only one or no transition metals follow a distinct slope from those containing transition metals on both A and B sites. The Cauchy relation, 0.5(C12 - C44) = P is fulfilled by spinels with only one or no transition metals, suggesting that that Coulomb interactions dominate. Spinels with two transition metals fail to meet the Cauchy relation, indicating strong directional dependence and covalent character of bonding. The bonding character of transition metals is crucial to understanding the elastic behavior of natural and synthetic spinel solid solutions containing transition metals.

Reichmann, H. J.; Jacobsen, S. D.; Boffa Ballaran, T.

2012-12-01

57

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

E-print Network

Electronic structure of mixed valence transition metal oxides P. Nov´ak1 1 Institute of Physics: 1 #12;I. INTRODUCTION The character of the charge carriers in oxides of transition metals belongs metals. Traditionally oxides were considered to be ionic compounds, in which the oxygen ions have fully

Tebbens, Jurjen Duintjer

58

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

59

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

60

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

61

Photochromism in composite and hybrid materials based on transition-metal oxides and polyoxometalates  

Microsoft Academic Search

Photochromic materials are attractive and promising for applications in many fields. One subject in this area is to prepare and study the photochromism in composite or hybrid materials based on transition-metal oxides or polyoxometalates. Their properties not depend only on the chemical nature of each component, but also on the interface and synergy between them. Since the charge transfer plays

Tao He; Jiannian Yao

2006-01-01

62

Oxygen Auger spectra of some transition-metal oxides: relaxation energies and d-band screening  

Microsoft Academic Search

A number of transition-metal oxides have been investigated by ESCA and special attention has been paid both to the valence band and to the oxygen Auger spectra. Lang and Williams' Auger parameters (1979) have been calculated and the results show that large screening effects, attributable to the metal d band, take place provided the d band is not separated from

P. Humbert; J. P. Deville

1987-01-01

63

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

64

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.

65

Characterization of nanometer scale wear and oxidation of transition metal dichalcogenide lubricants by atomic force microscopy  

Microsoft Academic Search

Atomic force microscopy has been used to characterize wear and oxidation of transition metal dichalcogenide surfaces. Sequential images recorded on molybdenum disulfide (MoS2) and niobium diselenide (NbSe2) surfaces show that wear proceeds at defects, and that MoS2 wears at least five times more slowly than NbSe2. Images of thermally treated MoS2 and NbSe2 further demonstrate that oxidation creates surface defects

Yun Kim; Jin-Lin Huang; Charles M. Lieber

1991-01-01

66

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

67

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

68

Characterization of nanometer scale wear and oxidation of transition metal dichalcogenide lubricants by atomic force microscopy  

SciTech Connect

Atomic force microscopy has been used to characterize wear and oxidation of transition metal dichalcogenide surfaces. Sequential images recorded on molybdenum disulfide (MoS{sub 2}) and niobium diselenide (NbSe{sub 2}) surfaces show that wear proceeds at defects, and that MoS{sub 2} wears at least five times more slowly than NbSe{sub 2}. Images of thermally treated MoS{sub 2} and NbSe{sub 2} further demonstrate that oxidation creates surface defects on both materials. However, for similar oxidation conditions, NbSe{sub 2} surfaces show extensive degradation, while MoS{sub 2} surfaces only exhibit isolated defects. The implications of these results to understanding the tribological properties of the transition metal dichalcogenides are discussed.

Kim, Y.; Huang, J.; Lieber, C.M. (Division of Applied Sciences, Harvard University, Cambridge, Massachusetts (United States). Department of Chemistry)

1991-12-23

69

Probing nanoscale inhomogeneities in transition metal oxides with ultrafast mid-infrared spectroscopy  

NASA Astrophysics Data System (ADS)

Transition metal oxides are a rich area of investigation for experimentalists and theorists alike due to their coupling of multiple degrees of freedom with similar interaction strengths. This complexity leads to intrinsic phase inhomogeneities that are believed to play a significant role in the fascinating phenomena observed in these systems. We use ultrafast mid-infrared spectroscopy to probe quasiparticle dynamics in the colossal magnetoresistive oxides, Nd 0.5Sr 0.5MnO 3 and Tl 2Mn 2O 7. Our results demonstrate for the first time that ultrafast spectroscopy is sensitive to the presence of nanoscale phase inhomogeneities, strongly indicating the universality of phase coexistence in complex transition metal oxides.

Prasankumar, R. P.; Lee, H. J.; Okamura, H.; Imai, H.; Shimakawa, Y.; Kubo, Y.; Zvyagin, S.; Kamenev, K.; Balakrishnan, G.; Paul, D. McK.; Trugman, S. A.; Taylor, A. J.; Averitt, R. D.

2008-04-01

70

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

71

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

2015-01-01

72

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

73

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

74

Optical and Electrical Properties of Rare Earth and Transition Metal Oxide Thin Films and Crystals  

Microsoft Academic Search

Optical and electrical properties of rare earth and transition metal oxide thin films and crystals have been studied in this work. We report the first explanation of the novel switching mechanism in two terminal devices based on the layered material rm V_2O_5cdot 1.6H_2O. The switching is shown to be associated with the existence of a current-induced channel between the contacts.

Ji-Guang Zhang

1990-01-01

75

Hydrogen-atom abstraction from methane by stoichiometric early transition metal oxide cluster cations.  

PubMed

Stoichiometric early transition metal oxide cations (TiO(2))(1-5)(+), (ZrO(2))(1-4)(+), (HfO(2))(1-2)(+), (V(2)O(5))(1-5)(+), (Nb(2)O(5))(1-3)(+), (Ta(2)O(5))(1-2)(+), (MoO(3))(1-2)(+), (WO(3))(1-3)(+), and Re(2)O(7)(+) are able to activate the C-H bond of methane under near room temperature conditions. PMID:20177633

Zhao, Yan-Xia; Wu, Xiao-Nan; Wang, Zhe-Chen; He, Sheng-Gui; Ding, Xun-Lei

2010-03-14

76

Insertion\\/extraction of lithium and sodium in transition metal oxides and chalcogenides  

Microsoft Academic Search

Lithium and sodium can be reversibly inserted into a variety of transition metal oxide and chalcogenide hosts at low temperatures.\\u000a The reaction is essentially topochemical involving electron-transfer and accompanying diffusionless transformation of the\\u000a anion array in many cases. Alkali metal insertion\\/extraction reactions provide new routes for the synthesis of novel solids\\u000a exhibiting unusual structure and properties. It appears that while

J Gopalakrishnan

1985-01-01

77

Surface Electronic Structure and Chemisorption on Corundum Transition-Metal Oxides  

Microsoft Academic Search

The surface electronic structures of all of the conducting corundum oxides of the fourth-period transition -metals have been studied using an ultra-high vacuum (UHV), multiple-technique surface analysis system. This system, which permits comprehensive determination of surface properties, includes ultra-violet and x-ray photoemission, low energy electron diffraction (LEED), Auger electron spectroscopy, and electron energy-loss spectroscopy. The complementary nature of the information

Richard Leigh Kurtz

1983-01-01

78

Wide bandgap tunability in complex transition metal oxides by site-specific substitution  

SciTech Connect

Fabricating complex transition metal oxides with a tunable bandgap without compromising their intriguing physical properties is a longstanding challenge. Here we examine the layered ferroelectric bismuth titanate and demonstrate that, by site-specific substitution with the Mott insulator lanthanum cobaltite, its bandgap can be narrowed by as much as 1 eV, while remaining strongly ferroelectric. We find that when a specific site in the host material is preferentially substituted, a split-off state responsible for the bandgap reduction is created just below the conduction band of bismuth titanate. This provides a route for controlling the bandgap in complex oxides for use in emerging oxide optoelectronic and energy applications.

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

2012-01-01

79

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

80

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

81

Transition-metal-catalyzed oxidation of metallic Sn in NiO/SnO2 nanocomposite.  

PubMed

It is well accepted that metallic tin as a discharge (reduction) product of SnO(x) cannot be electrochemically oxidized below 3.00?V versus Li(+)/Li(0) due to the high stability of Li2O, though a similar oxidation can usually occur for a transition metal formed from the corresponding oxide. In this work, nanosized Ni2 SnO4 and NiO/SnO2 nanocomposite were synthesized by coprecipitation reactions and subsequent heat treatment. Owing to the catalytic effect of nanosized metallic nickel, metallic tin can be electrochemically oxidized to SnO2 below 3.00?V. As a result, the reversible lithium-storage capacities of the nanocomposite reach 970?mAh?g(-1) or above, much higher than the theoretical capacity (ca. 750?mAh?g(-1)) of SnO2, NiO, or their composites. These findings extend the well-known electrochemical conversion reaction to non-transition-metal compounds and may have important applications, for example, in constructing high-capacity electrode materials and efficient catalysts. PMID:24648283

Hua, Chunxiu; Fang, Xiangpeng; Wang, Zhaoxiang; Chen, Liquan

2014-04-25

82

Mesoscale Charge-Ordering in Transition Metal Oxides: Formation and Signatures  

SciTech Connect

The authors briefly outline the value of an inhomogeneous (unrestricted) Hartree-Fock plus Random Phase approach for understanding the types and properties of mesoscopic patterns of localized small polarons in transition metal oxides. Using a multiband Peierls-Hubbard model for a hole-doped CuO{sub 2} layer as an illustrative example, they demonstrate the appearance of correlated high-energy (electronic) and low-energy (localized phonon and spin-wave) signatures of various vertical, diagonal, metal-centered, and oxygen-centered mesoscopic stripe patterns of localized holes (small polarons).

Bishop, A.R.; Yu, Z.G.

1998-06-01

83

Probing the local coordination environment for transition metal dopants in zinc oxide nanowires.  

PubMed

It is hypothesized that a highly ordered, relatively defect-free dilute magnetic semiconductor system should act as a weak ferromagnet. Transition-metal-doped ZnO nanowires, being single crystalline, single domain, and single phase, are used here as a model system for probing the local dopant coordination environments using X-ray absorption spectroscopy and diffraction. Our X-ray spectroscopic data clearly show that the dopant resides in a uniform environment, and that the doping does not induce a large degree of disorder in the nanowires. This homogeneous nature of the doping inside the oxide matrix correlates well with observed weakly ferromagnetic behavior of the nanowires. PMID:17335268

Yuhas, Benjamin D; Fakra, Sirine; Marcus, Matthew A; Yang, Peidong

2007-04-01

84

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

85

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

86

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

PubMed

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

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

2014-02-18

87

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

NASA Astrophysics Data System (ADS)

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 Co0.5Zn0.5O1-y ternary transition metal oxides. Our theoretical results reveal that the microstructure, the magnetic properties, and the exchange interactions of Co0.5Zn0.5O1-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 Co0.61Zn0.39O1-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; Zhang, Yun-peng; Zhao, Ming-wen; Kang, Shi-shou; Mei, Liang-mo

2014-07-01

88

Total oxidation of carbon monoxide and methane over transition metal-fluorite oxide composite catalysts. I. Catalyst composition and activity  

SciTech Connect

A novel metal oxide composite catalyst for the total oxidation of carbon monoxide and methane was prepared by combining fluorite oxides with active transition metals. The fluorite oxides, such as ceria and zirconia, are oxygen-ion-conducting materials having catalytic properties usually at high temperatures. Active base metal catalysts, such as copper, were used as additives to promote the catalytic properties of these oxides. The contact of the two types of materials gave rise to a high active oxidation catalyst. At a space velocity of about 42,000 h{sup {minus}1}, complete carbon monoxide oxidation in air occurred at room temperature on the Au{sub 0.05}[Ce(La)]{sub 0.95}L{sub x} catalyst and at ca. 100{degrees}C on Cu-Ce-O composite catalysts. At the same space velocity, total oxidation of methane on the Cu-Ce-O catalyst doped with La{sub 2}O{sub 3} or SrO took place at ca. 550{degrees}C. The specific carbon monoxide oxidation activity of the Cu-Ce-O catalyst was several orders of magnitude higher than that of conventional copper-based catalysts and comparable or superior to platinum catalysts. This type of composite catalyst also showed excellent resistance to water vapor poisoning. The enhanced catalyst activity and stability resulted from strong interaction of the transition metal and fluorite oxide materials. 44 refs., 14 figs., 5 tabs.

Liu, W.; Flytzani-Stephanopoulos, F. [Tufts Univ., Medford, MA (United States)] [Tufts Univ., Medford, MA (United States)

1995-05-01

89

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

90

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

NASA Astrophysics Data System (ADS)

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.

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

2015-01-01

91

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

92

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

E-print Network

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

Napp, Nils

93

First principles scheme to evaluate band edge positions in potential transition metal oxide photocatalysts and photoelectrodes.  

PubMed

The positions of electronic band edges are one important metric for determining a material's capability to function in a solar energy conversion device that produces fuels from sunlight. In particular, the position of the valence band maximum (conduction band minimum) must lie lower (higher) in energy than the oxidation (reduction) reaction free energy in order for these reactions to be thermodynamically favorable. We present first principles quantum mechanics calculations of the band edge positions in five transition metal oxides and discuss the feasibility of using these materials in photoelectrochemical cells that produce fuels, including hydrogen, methane, methanol, and formic acid. The band gap center is determined within the framework of DFT+U theory. The valence band maximum (conduction band minimum) is found by subtracting (adding) half of the quasiparticle gap obtained from a non-self-consistent GW calculation. The calculations are validated against experimental data where possible; results for several materials including manganese(ii) oxide, iron(ii) oxide, iron(iii) oxide, copper(i) oxide and nickel(ii) oxide are presented. PMID:21853210

Toroker, Maytal Caspary; Kanan, Dalal K; Alidoust, Nima; Isseroff, Leah Y; Liao, Peilin; Carter, Emily A

2011-10-01

94

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

SciTech Connect

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

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

2009-10-27

95

Mixed transition-metal oxides: design, synthesis, and energy-related applications.  

PubMed

A promising family of mixed transition-metal oxides (MTMOs) (designated as Ax B3-x O4 ; A, B=Co, Ni, Zn, Mn, Fe, etc.) with stoichiometric or even non-stoichiometric compositions, typically in a spinel structure, has recently attracted increasing research interest worldwide. Benefiting from their remarkable electrochemical properties, these MTMOs will play significant roles for low-cost and environmentally friendly energy storage/conversion technologies. In this Review, we summarize recent research advances in the rational design and efficient synthesis of MTMOs with controlled shapes, sizes, compositions, and micro-/nanostructures, along with their applications as electrode materials for lithium-ion batteries and electrochemical capacitors, and efficient electrocatalysts for the oxygen reduction reaction in metal-air batteries and fuel cells. Some future trends and prospects to further develop advanced MTMOs for next-generation electrochemical energy storage/conversion systems are also presented. PMID:24382683

Yuan, Changzhou; Wu, Hao Bin; Xie, Yi; Lou, Xiong Wen David

2014-02-01

96

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

97

Perovskite oxide nanowires: synthesis, property and structural characterization.  

PubMed

Perovskite oxide materials display a wide spectrum of functional properties, including switchable polarization, piezoelectricity, pyroelectricity, and non-linear dielectric behavior. These properties are indispensable for application in electronic devices such as non-volatile memories, sensors, microactuators, infrared detectors, microwave phase filters, and so on. Recent advances in science and technology of perovskite oxide materials have resulted in the feature sizes of perovskite oxides-based electronic devices entering into nanoscale dimensions. At nanoscale perovskite oxide materials exhibit a pronounced size effect manifesting itself in a significant deviation of the properties of low-dimensional structures from the bulk and film counterparts. In the last decade low-dimensional perovskite nanosized oxides have been received much attention because of their superior physical and chemical properties. Among them, perovskite oxide nanowires are especially attractive for nanoscience studies and nanotechnology applications. Compared to other low-dimensional perovskite oxide systems, perovskite oxide nanowires are not only used as the building blocks of future nanodevices, but also they offer fundamental scientific opportunities for investigating the intrinsic size effects of physical properties. In the recent years, much progress has been made both in synthesis and physical property testing of perovskite oxide nanowires, which have a profound impact on the nanoelectronics. In this work, an overview of the state of art in perovskite oxide nanowires is presented, which covers their synthesis, property, and structural characterization. In the first part, the recent literatures for fabricating perovskite oxide nanowires with promising features, are critically reviewed. The second part deals with the recent advances on the physical property testing of perovskite oxide nanowires. The third part summarizes the recent progress on microstructural characterizations of perovskite oxide nanowires, to improve their crystalline quality, morphology and uniformity. Finally, this review concludes with some perspectives and outlook on the future developments of perovskite oxide nanowires. PMID:21128390

Zhu, Xinhua; Liu, Zhiguo; Ming, Naiben

2010-07-01

98

A molecular placeholder strategy to access a family of transition-metal-functionalized vanadium oxide clusters.  

PubMed

Systematic access to metal-functionalized polyoxometalates has thus far been limited to lacunary tungsten oxide and molybdenum oxide clusters. The first controlled, stepwise bottom-up assembly route to metal-functionalized molecular vanadium oxides is now presented. A di-vacant vanadate cluster with two metal binding sites, (DMA)2[V12O32Cl](3-) (DMA = dimethylammonium) is formed spontaneously in solution and characterized by single-crystal X-ray diffraction, ESI mass spectrometry, (51)V?NMR spectroscopy, and elemental analyses. In the cluster, the metal binding sites are selectively blocked by hydrogen-bonded DMA placeholder cations. Reaction of the cluster with transition metals TM (Fe(3+), Co(2+), Cu(2+), Zn(2+)) gives access to mono-functionalized vanadate clusters (DMA)[{TM(L)}V12O32Cl](n-) (L = ligand). Metal binding is accomplished by significant distortions of the vanadium oxide framework reminiscent of a pincer movement. Cluster stability under technologically relevant conditions in the solid-state and solution is demonstrated. PMID:25082170

Kastner, Katharina; Margraf, Johannes T; Clark, Timothy; Streb, Carsten

2014-09-15

99

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

100

Synthesis of Single-Crystalline Perovskite Nanorods Composed of Barium Titanate and Strontium Titanate  

E-print Network

Synthesis of Single-Crystalline Perovskite Nanorods Composed of Barium Titanate and Strontium report the first solution-based synthesis of nanorods composed of ternary perovskite oxides. Transition metal oxides with a cubic-perovskite structure rep- resent a particularly interesting class of materials

Heller, Eric

101

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

DOEpatents

A method of synthesizing electro-optically active reaction products from 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. Edwin (Golden, CO); Benson, David K. (Golden, CO); Ruth, Marta R. (Golden, CO)

1987-01-01

102

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

103

Spin-assisted covalent bond mechanism in ``charge-ordering'' perovskite oxides  

NASA Astrophysics Data System (ADS)

First-principles density functional calculations on the metal-insulator transition (MIT) in perovskite CaFeO3 point to local ferromagnetic coupling as the microscopic origin for the electronic “charge order” transition. Our atomic, electronic, and magnetic structure analyses reveal that the MIT results from a spin-assisted covalent bonding mechanism between the O 2p and Fe 3d states with anisotropic Fe-O bonds and negligible intersite Fe-Fe charge transfer. We suggest that control of the lattice distortions, which mediate the covalent bond formation, in oxides containing late transition-metal row cations in high valence states provides a platform to tailor electronic transitions.

Cammarata, Antonio; Rondinelli, James M.

2012-11-01

104

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

105

Simulation of no oxidation catalysis over oxygen-covered transition metal surfaces  

NASA Astrophysics Data System (ADS)

Lean burn (excess O2) automobile engines are more energy efficient than their stoichiometric or rich (O2 starved) burn counterparts, but technologies do not exist to effectively remediate harmful NO x (x = 1,2) compounds from lean exhaust. Current removal strategies rely in part on the catalytic oxidation of NO to NO 2 NO+1/2O2 \\rarrr NO2 Pt is the most active metal, but there is a strong drive to use less expensive materials. Understanding how Pt functions is a key step in catalyst design. Prior experiments and theory indicate the catalysis is promoted at high O coverage (thetaO = NO/ NPt), but too much O is inhibitive: Pt is prone to oxidative deactivation. The rate is promoted by high O2 pressures and inhibited by product NO2. The latter is true even after correcting for approach to equilibrium, suggesting NO2 hinders the reaction kinetics. In this work, we attempt to understand these phenomena with molecular simulation. We use density functional theory, first principles thermodynamics, and mean field microkinetic modeling to elucidate the catalysis under actual reaction conditions. We find the reaction occurs at 0.25--0.50 monolayer O. At these thetaO, the kinetics of O2 dissociation (O2 + 2* ? 2O*) are strongly inhibited due to repulsive interactions on the surface, but the O--NO bond formation (NO* + O* ? NO2 + 2*) kinetics are facile. In contrast to prior reports, we show O2 dissociation is rate limiting, and O--NO bond formation is equilibrated. The rate is strongly dependent on pO2 , and the O coverage is governed by pNO2 /pNO, leading to the observed rate inhibition by NO2. These observations are in excellent agreement with experiment. We apply our models to other transition metals and transition metal alloys to facilitate new catalyst design. Analysis indicates such materials should exhibit nearly identical behavior to Pt, offering no improvements in rate or propensity to oxidize. Screening the catalytic properties of Au nanoparticles and the O buffering properties of Co3O4/metal oxide supports is recommended for future work.

Getman, Rachel B.

106

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

107

Perovskite oxide superlattices: Magnetotransport and magnetic properties  

Microsoft Academic Search

We have fabricated perovskite superlattices consisting of two ferromagnetic metallic oxides: La0.67Ca0.33MnO3 (LCMO) and SrRuO3 (SRO). We have investigated the magnetotransport and magnetic properties of a series of samples, in which the layer thickness of LCMO is fixed and that of SRO varied from 0 to 20 unit cells. The magnetoresistance ratio in a superlattice can be increased by a

G. Q. Gong; A. Gupta; Gang Xiao; P. Lecoeur; T. R. McGuire

1996-01-01

108

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

for formation and release of odorous H2S.6-8 The addition of basic oxides, like baria, into three-way catalystChemistry of Sulfur Oxides on Transition Metals. III. Oxidation of SO2 and Self-Diffusion of O, SO2 Pt SO3(g) are studied using first-principles density functional theory (DFT). The diffusion processes

Lin, Xi

109

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

110

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

111

Probing the reactivity and radical nature of oxidized transition metal-thiolate complexes by mass spectrometry.  

PubMed

Transition metal thiolate complexes such as [PPN](+)[RuL3](-) (PPN = bis(triphenylphosphoranylidene) ammonium and L = diphenylphosphinobenzenethiolate) are known to undergo addition reactions with unsaturated hydrocarbons via the formation of new C-S bonds in solution upon oxidation. The reaction mechanism is proposed to involve metal-stabilized thiyl radical intermediates, a new type of distonic ions such as [RuL3](+) ion in the case of [PPN](+)[RuL3](-). This study presents the reactivity and structure investigation of [RuL3](+) by mass spectrometry (MS) in conjunction with ion/molecule reactions. The addition reactions of [RuL3](+) with alkenes or methyl ketones in the gas phase are indeed observed, in agreement with the proposed mechanism. Such reactivity is also maintained by several fragment ions of [RuL3](+), indicating the preserved thiyl diradical core structure is responsible for the addition reaction. The thiyl radical nature of [RuL3](+) was further verified by the ion/molecule reaction of [RuL3](+) with dimethyl disulfide, in which the characteristic CH3S• transfer occurs, both at atmospheric pressure and also at low pressure (~mTorr). These results provide, for the first time, clear mass spectrometric evidence of the radical nature of [RuL3](+) (i.e., the distonic ion structure of [RuL3](+)), arising from the oxidation of non-innocent thiolate ligands of the complex [PPN](+)[RuL3](-). Similar thiolate complexes, including ReL3 and NiL2, were also examined. Although reactions of oxidized ReL3 or NiL2 with CH3SSCH3 take place at atmospheric pressure, the corresponding reaction did not occur in vacuum. Consistent with these data, the addition of ethylene was not observed either, indicating lower reactivities of [ReL3](+) and [NiL2](+) in comparison to [RuL3](+). PMID:23315345

Lu, Mei; Campbell, J Larry; Chauhan, Rajat; Grapperhaus, Craig A; Chen, Hao

2013-04-01

112

Probing the Reactivity and Radical Nature of Oxidized Transition Metal-Thiolate Complexes by Mass Spectrometry  

NASA Astrophysics Data System (ADS)

Transition metal thiolate complexes such as [PPN]+[RuL3]- (PPN = bis(triphenylphosphoranylidene) ammonium and L = diphenylphosphinobenzenethiolate) are known to undergo addition reactions with unsaturated hydrocarbons via the formation of new C-S bonds in solution upon oxidation. The reaction mechanism is proposed to involve metal-stabilized thiyl radical intermediates, a new type of distonic ions such as [RuL3]+ ion in the case of [PPN]+[RuL3]-. This study presents the reactivity and structure investigation of [RuL3]+ by mass spectrometry (MS) in conjunction with ion/molecule reactions. The addition reactions of [RuL3]+ with alkenes or methyl ketones in the gas phase are indeed observed, in agreement with the proposed mechanism. Such reactivity is also maintained by several fragment ions of [RuL3]+, indicating the preserved thiyl diradical core structure is responsible for the addition reaction. The thiyl radical nature of [RuL3]+ was further verified by the ion/molecule reaction of [RuL3]+ with dimethyl disulfide, in which the characteristic CH3S• transfer occurs, both at atmospheric pressure and also at low pressure (~mTorr). These results provide, for the first time, clear mass spectrometric evidence of the radical nature of [RuL3]+ (i.e., the distonic ion structure of [RuL3]+), arising from the oxidation of non-innocent thiolate ligands of the complex [PPN]+[RuL3]-. Similar thiolate complexes, including ReL3 and NiL2, were also examined. Although reactions of oxidized ReL3 or NiL2 with CH3SSCH3 take place at atmospheric pressure, the corresponding reaction did not occur in vacuum. Consistent with these data, the addition of ethylene was not observed either, indicating lower reactivities of [ReL3]+ and [NiL2]+ in comparison to [RuL3]+.

Lu, Mei; Campbell, J. Larry; Chauhan, Rajat; Grapperhaus, Craig A.; Chen, Hao

2013-04-01

113

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

114

SIC-LSD study of transition metal valencies in oxide materials  

NASA Astrophysics Data System (ADS)

The electronic and magnetic properties of transition metal (TM) oxide materials are largely determined by the degree of localization of the TM d-electrons. With the self-interaction corrected (SIC) local spin density (LSD) approximation, we are able to differentiate between various localization/delocalization scenarios based on total energy considerations, and thus to determine the ground state valency onfiguration from the global energy minimum. Using the SIC-LSD, we studied the valencies of TM (Co, Mn) impurities in ZnO. We find the position of the TM(0/+) donor level to be such that the TM^2+ configuration is energetically most favourable both in n-type ZnO, and in ZnO without additional codopants, whilst in p-type ZnO one additional d-electron prefers to delocalize with the resulting TM^3+ groundstate configuration. We furthermore investigated the possibility of ferromagnetic order in the corresponding groundstate scenarios. Work supported in part by the Defense Advanced Research Agency and by the Division of Materials Science and Engineering, US Department of Energy. The Oak Ridge National Laboratory is managed by UT-Battelle LLC for the Department of Energy under Contract No. DE-AC05-00OR22725.

Petit, Leon; Schulthess, Thomas; Svane, Axel; Janotti, Anderson; Szotek, Zdzislawa; Temmerman, Walter

2005-03-01

115

Oxygen 1s x-ray-absorption edges of transition-metal oxides  

NASA Astrophysics Data System (ADS)

The oxygen 1s x-ray-absorption edges of a series of 3d-transition-metal oxides have been measured. The structures at the edge arise from covalent mixing of the metal and oxygen states, which introduces oxygen p character in unoccupied states of mainly metal character. The spectra can be divided into two regions: The first is a double-peaked sharp structure near threshold, which can be related to the metal 3d states; the second is a broader structure 5-10 eV above the edge and is related to the metal 4s and 4p bands. We attribute the oxygen p character up to 15 eV above threshold to mainly oxygen 2p character. The data are analyzed in terms of ligand-field and exchange splittings. It is shown that the splitting between the two sharp peaks near threshold is related closely to the ligand-field splitting, but the relative intensities of the peaks are not fully explained at the present time.

de Groot, F. M. F.; Grioni, M.; Fuggle, J. C.; Ghijsen, J.; Sawatzky, G. A.; Petersen, H.

1989-09-01

116

Charge transfer satellites in x-ray spectra of transition metal oxides  

NASA Astrophysics Data System (ADS)

Strongly correlated materials such as transition metal oxides (TMOs) often exhibit large satellites in their x-ray photoemission (XPS) and x-ray absorption spectra (XAS). These satellites arise largely from localized charge transfer excitations that accompany the sudden creation of a core hole. Here we use a two-step approach to treat such excitations in a localized system embedded in a condensed-matter environment and coupled to a photoelectron. The total XAS is then given by a convolution of an energy-dependent spectral function representing the localized excitations coupled to the photoelectron and the XAS of the extended system. The local system is modeled roughly in terms of a simplified three-level model, leading to a double-pole approximation for the spectral function that represents dynamically weighted contributions from the dominant neutral and charge transfer excitations. This method is implemented using a resolvent approach, with potentials, radial wave functions, and matrix elements from the real-space Green's function code feff9, and parameters fitted to XPS experiments. Representative calculations for several TMOs are found to be in reasonable agreement with experiment and with other calculations.

Klevak, E.; Kas, J. J.; Rehr, J. J.

2014-02-01

117

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

118

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

119

Unexpected change in the electron affinity of diamond caused by the ultra-thin transition metal oxide films  

NASA Astrophysics Data System (ADS)

The energetics and electronic properties of oxides of selected transition metals (Cu, Ni, Ti and Zn) adsorbed onto a diamond (001) surface are examined using density functional simulations. We find that the stoichiometric oxides of Ti and Zn exhibit large negative electronic affinities of around 3 eV, whereas the oxides Cu and Ni have a relatively small impact on the affinity. Although reactions of most metal oxides with the diamond surface are exothermic in nature, we propose that titanium, which exhibit large binding energies per metal atom in addition to a large negative electron affinity, is of particular interest for the surface coating of diamond-based electron emitters.

Tiwari, Amit K.; Goss, J. P.; Briddon, P. R.; Horsfall, A. B.; Wright, N. G.; Jones, R.; Rayson, M. J.

2014-11-01

120

Understanding interface effects in perovskite thin films Marie-Bernadette Lepetit, Bernard Mercey, and Charles Simon  

E-print Network

Understanding interface effects in perovskite thin films Marie-Bernadette Lepetit, Bernard Mercey transition metal oxide in perovskite structure (as for instance SrTiO3). The model is checked against, the existence of a so-called "dead layer" at the interface between the manganite film and most perovskite

Paris-Sud XI, Université de

121

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

122

Mechanistic investigation of oxidative Mannich reaction with tert-butyl hydroperoxide. The role of transition metal salt.  

PubMed

A general mechanism is proposed for transition metal-catalyzed oxidative Mannich reactions of N,N-dialkylanilines with tert-butyl hydroperoxide (TBHP) as the oxidant. The mechanism consists of a rate-determining single electron transfer (SET) that is uniform from 4-methoxy- to 4-cyano-N,N-dimethylanilines. The tert-butylperoxy radical is the major oxidant in the rate-determining SET step that is followed by competing backward SET and irreversible heterolytic cleavage of the carbon-hydrogen bond at the ?-position to nitrogen. A second SET completes the conversion of N,N-dimethylaniline to an iminium ion that is subsequently trapped by the nucleophilic solvent or the oxidant prior to formation of the Mannich adduct. The general role of Rh(2)(cap)(4), RuCl(2)(PPh(3))(3), CuBr, FeCl(3), and Co(OAc)(2) in N,N-dialkylaniline oxidations by T-HYDRO is to initiate the conversion of TBHP to tert-butylperoxy radicals. A second pathway, involving O(2) as the oxidant, exists for copper, iron, and cobalt salts. Results from linear free-energy relationship (LFER) analyses, kinetic and product isotope effects (KIE and PIE), and radical trap experiments of N,N-dimethylaniline oxidation by T-HYDRO in the presence of transition metal catalysts are discussed. Kinetic studies of the oxidative Mannich reaction in methanol and toluene are also reported. PMID:23298175

Ratnikov, Maxim O; Doyle, Michael P

2013-01-30

123

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

124

Comparison of Transition Metal-Mediated Oxidation Reactions of Guanine in Nucleoside and Single-Stranded Oligodeoxynucleotide Contexts  

PubMed Central

As the most readily oxidized of DNA’s four natural bases, guanine is a prime target for attack by reactive oxygen species (ROS) and transition metal-mediated oxidants. The oxidation products of a modified guanosine nucleoside and of a single-stranded oligodeoxynucleotide, 5?-d(TTTTTTTGTTTTTTT)-3? have been studied using oxidants that include CoII, NiII, and IrIV compounds as well as photochemically generated oxidants such as sulphate radical, electron-transfer agents (riboflavin) and singlet oxygen. The oxidized lesions formed include spiroiminodihydantoin (Sp), guanidinohydantoin (Gh), imidazolone (Iz), oxazolone (Z) and 5-carboxamido-5-formamido-2-iminohydantion (2-Ih) nucleosides with a high degree of dependence on the exact oxidation system employed. Interestingly, a nickel(II) macrocyclic complex in conjunction with KHSO5 leads to the recently reported 2-Ih heterocycle as the major product in both the nucleoside and oligonucleotide contexts. PMID:21516189

Ghude, Pranjali; Schallenberger, Mark A.; Fleming, Aaron M.; Muller, James G.; Burrows, Cynthia J.

2011-01-01

125

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

E-print Network

) MO+ + CH4 M+ + CH3OH (3) Reaction 2 is exothermic if Do(M+ -O) > 249 kJ/mol, and reaction 3 that reaction with methane is endothermic, while some of the late transition metals bind oxygen so weakly that #12;reaction 2 is endothermic, although MO+ may react efficiently with methane. The electronic

Metz, Ricardo B.

126

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

PubMed Central

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

Vejerano, Eric; Dellinger, Barry

2014-01-01

127

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

E-print Network

- monly used substrate for growth of high Tc super- conductors1­4 and other perovskite-based materials,5­11 for spintronic applications raises the question of whether the interface properties may be op- timizedInfluence of perovskite termination on oxide heteroepitaxy D. A. Schmidta Department of Physics

Olmstead, Marjorie

128

LiV2O4: A Heavy Fermion Transition Metal Oxide  

Microsoft Academic Search

A crossover with decreasing temperature T from localized moment magnetism to heavy Fermi liquid behavior is reported for the metallic compound LiV2O4 with the fcc normal-spinel structure. At T = 1 K, the electronic heat capacity coefficient gamma~0.42 J\\/mol K2 is exceptionally large for a transition metal compound, the Wilson ratio ~1.7, and the Korringa ratio ~0.7. Our sample with

S. Kondo; D. C. Johnston; C. A. Swenson; F. Borsa; A. V. Mahajan; L. L. Miller; T. Gu; A. I. Goldman; M. B. Maple; D. A. Gajewski; E. J. Freeman; N. R. Dilley; R. P. Dickey; J. Merrin; K. Kojima; G. M. Luke; Y. J. Uemura; O. Chmaissem; J. D. Jorgensen

1997-01-01

129

CVD - technology of transition metal oxides and their impact on solar energy utilization  

Microsoft Academic Search

The paper presents results concerning CVD thin films of transition metals (W and Mo) and their composite structures W02:W and MoOZ:Mo, as well as WO films. The composite structure materials 3 consisting of a suspension of metallic molybdenum or tungsten grains in a host matrix of metal dioxide demonstrate significant solar absorptance coupled with a high infrared reflectance, which is

K. A. GESHEVA; D. S. GOGOVA

1993-01-01

130

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

131

Strain-Relief at Internal Dielectric Interfaces in High k Gate Stacks with Transition Metal and Rare Earth Atom Oxide Dielectrics  

Microsoft Academic Search

This Chapter addresses the effects of bonding discontinuities at the internal dielectric interfaces in gate stacks that include\\u000a transition metal and rare earth atom elemental and complex oxides, as well as transition metal silicate alloys. The focus\\u000a is on the strain-induced defects, and the reduction of defect densities through strain-driven self-organizations that take\\u000a place during high-temperature post-deposition annealing.

Gerald Lucovsky; James C. Phillips

132

N-Bromosuccinimide as an oxidant for the transition-metal-free synthesis of 2-aminobenzoxazoles from benzoxazoles and secondary amines.  

PubMed

A facile and transition-metal-free method was developed through merging the ring opening of benzoxazoles with secondary amines and N-bromosuccinimide (NBS) mediated oxidative cyclization toward the synthesis of 2-aminobenzoxazoles. NBS was selected as a powerful oxidant in the oxidative cyclization of ring-opening amidines to provide the desirable 2-aminobenzoxazoles in excellent yields (up to 94%). PMID:24705619

Wang, Xiaoe; Xu, Daqian; Miao, Chengxia; Zhang, Qiaohong; Sun, Wei

2014-05-21

133

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

PubMed

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

Muthuswamy, Elayaraja; Brock, Stephanie L

2010-11-17

134

Composition Valence Diagrams: A New Representation of Topotactic Reactions in Ternary Transition Metal Oxide Systems. Application to Lithium Intercalation  

NASA Astrophysics Data System (ADS)

Topotactic reactions in Li- M-O systems with M= Mn, Ti, V, Fe are described in the framework of composition-valence diagrams, using the Li/ Mand the transition metal valence ?( M) as coordinates. We show that this representation is very convenient to depict and compare the various parameters associated with insertion/extraction reactions, i.e., the evolution of ?( M), the extent of intercalation xin Li xMO y, the electrochemical potentials, and the cell parameter changes. New directions are suggested for topotactic reaction in oxides, especially in titanium ones. The composition-valence diagram helped in the detection of inconsistencies in the intercalation potentials in LiFe 5O 8, which are corrected using new voltammetric data. We conclude that lithium intercalation in octahedral sites of iron spinel oxides occurs at constant voltage around 1.6 V, whichever the Li-Fe-O host may be.

Strobel, P.; Le Cras, F.; Anne, M.

1996-06-01

135

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

136

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, Cubic Perovskite Oxides and Cubic Perovskite Oxinitrides sections; Table 1, 2, 3; Fig. 1, 2. See DOI: 10/oxynitride compounds in the cubic perovskite structure covering 52 metals. The screening is based on criteria

Thygesen, Kristian

137

The influence of transition metal oxides on the kinetics of Li2O2 oxidation in Li-O2 batteries: high activity of chromium oxides.  

PubMed

Reducing the energy loss associated with Li2O2 electrochemical oxidation is paramount to the development of efficient rechargeable lithium-oxygen (Li-O2) batteries for practical use. The influence of a series of perovskites with different eg filling on the kinetics of Li2O2 oxidation was examined using Li2O2-prefilled electrodes. While LaCrO3 is inactive for oxygen evolution upon water oxidation in alkaline solution, it was found to provide the highest specific current towards Li2O2 oxidation among all the perovskites examined. Further exploration of Cr-based catalysts showed that Cr nanoparticles (Cr NP) with an average particle size of 40 nm, having oxidized surfaces, had comparable surface area activities to LaCrO3 but much greater mass activities. Unlike Pt/C and Ru/C that promote electrolyte oxidation in addition to Li2O2 oxidation, no evidence of enhanced electrolyte oxidation was found for Cr NP relative to Vulcan carbon. X-ray absorption spectroscopy at the O K and Cr L edge revealed a redox process of Cr(3+) ? Cr(6+) on the surface of Cr NP upon Li2O2 oxidation, which might be responsible for the enhanced oxidation kinetics of Li2O2 and the reduced charging voltages of Li-O2 batteries. PMID:24352578

Yao, Koffi P C; Lu, Yi-Chun; Amanchukwu, Chibueze V; Kwabi, David G; Risch, Marcel; Zhou, Jigang; Grimaud, Alexis; Hammond, Paula T; Bardé, Fanny; Shao-Horn, Yang

2014-02-14

138

Calculated formation and reaction energies of 3d transition metal oxides using a hierachy of exchange-correlation functionals  

NASA Astrophysics Data System (ADS)

The formation and oxidation reaction energies of 16 transition metal oxides (TMOs) are benchmarked against experiments with an increasing complexity of the exchange-correlation (xc) functionals: PBE, PBE + U with a single U for each transition metal element, PBE0 (25% exact exchange included), EXX (100% exact exchange), and EXX + RPA (random phase approximation for the correlation energy). Although rather challenging on standard CPU computing facilities, the RPA calculations were performed efficiently on graphic processing units (GPUs). For the formation energies, the PBE + U, PBE0, EXX + RPA improves significantly over PBE with mean absolute errors (MAE) of 0.83 (PBE), 0.39 (PBE + U), 0.34 (PBE0), and 0.39 (EXX + RPA) eV per oxygen. In addition, EXX + RPA improves over the other xc functionals on the oxidation reaction energies, with MAE of 0.27 (PBE), 0.28 (PBE + U), 0.30 (PBE0), to 0.13 (EXX + RPA) eV per oxygen. The distinct trend observed for the calculated oxidation reaction energies compared to the formation energies is due to that the errors in formation energies for PBE and EXX + RPA are systematic; while for PBE + U and PBE0 the deviations have both signs, so that the error cancellations between different valence states work better for PBE and EXX + RPA. Finally, we compared the performance of the EXX + RPA for total energies and G0W0, which uses the random phase approximation in constructing the W kernel, for band gaps, and discuss a few challenges for the EXX + RPA method on TMOs.

Yan, Jun; Nørskov, Jens K.

2013-12-01

139

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

140

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

141

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

142

Synthesis, structure and magnetic properties of low dimensional spin systems in the 3d transition metal oxides and superconductivity in magnesium borate  

Microsoft Academic Search

The major part of this thesis deals with the synthesis and magnetic characterization of low dimensional spin systems in the 3d transition metal oxides. Such systems are of interest due to the simplicity of their structures, allowing theoretical modeling of their electronic and magnetic behavior. Exotic properties are also often encountered. Studies involving layered magnetic materials based on triangle lattices,

Nyrissa S. Rogado

2003-01-01

143

Transition metal free intramolecular selective oxidative C(sp(3))-N coupling: synthesis of N-aryl-isoindolinones from 2-alkylbenzamides.  

PubMed

A synthetic method has been developed for the preparation of biologically important isoindolinones including indoprofen and DWP205190 drugs from 2-alkylbenzamide substrates by transition metal-free intramolecular selective oxidative coupling of C(sp(3))-H and N-H bonds utilizing iodine, potassium carbonate and di-tert-butyl peroxide in acetonitrile at 110-140 °C. PMID:25487732

Verma, Ajay; Patel, Saket; Meenakshi; Kumar, Amit; Yadav, Abhimanyu; Kumar, Shailesh; Jana, Sadhan; Sharma, Shubham; Prasad, Ch Durga; Kumar, Sangit

2014-12-23

144

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

145

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

E-print Network

the atmosphere by oxidation of SO2, which is itself directly emitted (fossil fuel combustion, industrial measurements of sulfate aerosol collected in Alert, Canada, are not consistent with O3 as the dominant oxidant importance of sulfate production by Fe(III)- and Mn(II)-catalyzed oxidation of S(IV) by O2. We scale

Alexander, Becky

146

Cytotoxicity in the age of nano: the role of fourth period transition metal oxide nanoparticle physicochemical properties.  

PubMed

A clear understanding of physicochemical factors governing nanoparticle toxicity is still in its infancy. We used a systematic approach to delineate physicochemical properties of nanoparticles that govern cytotoxicity. The cytotoxicity of fourth period metal oxide nanoparticles (NPs): TiO2, Cr2O3, Mn2O3, Fe2O3, NiO, CuO, and ZnO increases with the atomic number of the transition metal oxide. This trend was not cell-type specific, as observed in non-transformed human lung cells (BEAS-2B) and human bronchoalveolar carcinoma-derived cells (A549). Addition of NPs to the cell culture medium did not significantly alter pH. Physiochemical properties were assessed to discover the determinants of cytotoxicity: (1) point-of-zero charge (PZC) (i.e., isoelectric point) described the surface charge of NPs in cytosolic and lysosomal compartments; (2) relative number of available binding sites on the NP surface quantified by X-ray photoelectron spectroscopy was used to estimate the probability of biomolecular interactions on the particle surface; (3) band-gap energy measurements to predict electron abstraction from NPs which might lead to oxidative stress and subsequent cell death; and (4) ion dissolution. Our results indicate that cytotoxicity is a function of particle surface charge, the relative number of available surface binding sites, and metal ion dissolution from NPs. These findings provide a physicochemical basis for both risk assessment and the design of safer nanomaterials. PMID:24120544

Chusuei, Charles C; Wu, Chi-Heng; Mallavarapu, Shravan; Hou, Fang Yao Stephen; Hsu, Chen-Ming; Winiarz, Jeffrey G; Aronstam, Robert S; Huang, Yue-Wern

2013-11-25

147

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

148

Magnetoelectric and multiferroic properties in layered 3D transition metal oxides  

NASA Astrophysics Data System (ADS)

Functional ferroelectric and magnetic materials have played an important role of modern technology in the sensor or storage device industries. Ferroelectricity and ferromagnetism emerge from different origins. However, it is discovered that these two seemingly unrelated phenomena can actually coexist in materials called multiferroics. Since current trends toward device miniaturization have increased interests in combining electronic and magnetic properies into multifunctional materials, multiferroics have attracted great attention. Ferromagnetic ferroelectric multiferroics are especially fascinating not only because they have both ferroic properties, but also because of the magnetoelectric coupling which leads the interaction between the magnetic and electric polarization. Recent theoretical breakthroughs in understanding the coexistence of magnetic and electrical ordering have regenerated a great interests in research of such magnetoelectric multiferroics. The long-sought control of electric polarization by magnetic fields was recently discovered in 'frustrated magnets', for example the perovskites RMnO3, RMn 2O5 (R: rare earth elements), Ni3V 2O8, delafossite CuFeO2, spinel CoCr2O 4, MnWO4, etc. In this dissertation, I have explored several magnetoelectric materials and multiferroics, which show significant magnetoelectric interactions between electric and magnetic orderings. The objects of my projects are focused on understanding the origins of such magnetoelectric couplings and establishing the magnetic/electric phase diagrams and the spin structures. I believe that my works would help to understand the mechanisms of magnetoelectric effects and multiferroics.

Hwang, Jungmin

149

Electronic structure and photoemission studies of late transition-metal oxides — Mott insulators and high-temperature superconductors  

NASA Astrophysics Data System (ADS)

Stimulated by the discovery of high-temperature superconductivity, the electronic structure of late 3d transition-metal oxides is presently one of the most extensively studied subjects in condensed matter physics. In this review, we hope to summarize the progress we have made and the problems we are facing. The emphasis of the review is on the latest angle-resolved photoemission studies that have provided much insight towards the understanding of these materials. This includes the recent experiments from transition-metal mono-oxides, normal state electronic structure and Fermi surface mapping of Bi 2Sr 2CaCu 2O 8+?, Bi 2Sr 2CuO 6+?, YBa 2Cu 3O 7- x, YBa 2Cu 4O 8, Nd 2- xCe xCuO 4, and the superconducting gap of Bi 2Sr 2CaCu 2O 8+?. For the transition-metal mono-oxides, we discuss the experimental manifestation of the four aspects of the electronic structure that make these Mott Hubbard insulators so interesting. This includes the large Coulomb interaction U (on the cation sites), the charge transfer as a result of strong hybridization, the energy dispersion in the crystal lattice, and the multiplet and magnetic splittings. For the high-temperature superconductors, we concentrate on the low energy excitations, the topology of the Fermi surface in the normal state, and the superconducting gap. Angle-resolved photoemission data show that the oxide superconductors have well defined Fermi surfaces. The volume of the Fermi surface in the high doping regime appears to be consistent with the results of band calculations. A striking feature of the low energy excitations is the presence of some very flat bands (due to a saddle point singularity in the band structure) which lie near the Fermi energy in p-type compounds near their optimal doping levels for superconductivity. The corresponding flat bands are well below the Fermi energy in n-type cuprates. The energy position of these flat bands is expected to have wide ranging effects on the physical properties of these materials, including the temperature dependence of the resistivity and the superconducting transition temperature. High-resolution photoemission has also been successfully applied to the study of the superconducting gap in Bi 2Sr 2CaCu 2O 8+?. While the presently attainable energy resolution is poorer than that of many other spectroscopies, photoemission has the advantage that it is k-resolved as well as being very direct. This unique capability has enabled recent photoemission experiments to reveal the highly anisotropic nature of the superconducting gap in the a-b plane. This suggests the possibility of a detailed experimental determination of the superconducting order parameter.

Shen, Z.-X.; Dessau, D. S.

1995-03-01

150

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

151

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

152

Fabrication of transition metal oxide-carbon nanofibers with novel hierarchical architectures.  

PubMed

We report a facile two-step methodology; electrospinning followed by high temperature treatment, to produce manganese oxide-based nanofibers with well-controlled nanoscale architectures. Electrospinning of manganese acetate-based solution (MnOx precursor) has been utilized to fabricate meso-porous manganese oxide nanofibers. These fibers have diameters of about 200-300 nm and fiber mats have been shown to have specific surface area of over 12 m2/g. Scanning and transmission electron microscopy results show that electrospinning has been successfully utilized to create nanofibers with deep inter-connected internal meso-pores for high surface area. In addition, fibers have been spun in a co-axial arrangement to fabricate hollow meso-porous nanofibers, or to develop core-shell nanofibers with nanoparticles of manganese oxides decorated over current conducting carbon core. X-ray diffraction analysis of the oxide fibers confirms the presence of manganese oxides (MnO2, Mn3O4) after calcination at 700 degrees C. These architectures, we believe, are potentially favorable for use in Li-ion batteries, Li-air batteries and supercapacitors. PMID:24758057

Hu, Alice; Curran, Chris; Tran, Chau; Kapllani, Alda; Kalra, Vibha

2014-07-01

153

Synthesis and characterization of transition metal oxide nanotubes for photoelectrochemical hydrogen generation  

NASA Astrophysics Data System (ADS)

Two different configurations of photo anodes based on anodic iron oxide were investigated for photo electrochemical water oxidation. Self ordered and vertically oriented array of iron oxide nanotubes was obtained by anodization of pure iron substrate in ethylene glycol based electrolyte containing 0.1 M NH4F + 3 vol% water (EGWF solution) at 50 V for 15 minutes. Annealing of the oxide nanotubes in hydrogen environment at 500 °C for 1 h resulted in predominantly hematite phase. The second type of photo anode was obtained by a two-step anodization procedure. This process resulted in a two- layered oxide structure, a top layer of nano-dendrite morphology and a bottom layer of nanoporous morphology. This electrode configuration combined the better photo catalytic properties of the nano-dendritic iron oxide and better electron transportation behavior of vertically oriented nano-channels. Annealing of these double anodized samples in acetylene environment at 550 °C for 10 minutes resulted in a mixture of maghemite and hematite phases. Photo current densities of 0.74 mA/cm2 at 0.2 VAg/AgCl and 1.8 mA/cm 2 at 0.5 VAg/AgCl were obtained under AM 1.5 illumination in 1 M KOH solution. The double anodized samples showed high photo conductivity and more negative flat band potential (-0.8 VAg/AgCl), which are the properties required for promising photo anode materials. Apart from the above work, mild steel which is 10 times less the cost of Ti is also being tested for its photoelectrochemical properties. TiO2 nanotubes synthesized and annealed in different conditions are compared for their quantum efficiency is also carried out in this work. Quantum efficiency measurements gives more reliable and photocurrent data towards photoelectrochemical applications.

Rangaraju, Raghu Raj

154

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

E-print Network

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

Rappe, Andrew M.

155

The ferroelectricity of perovskite-type oxides with alkylamine interlayer Zhaohui Zhong, Weiping Ding,a)  

E-print Network

The ferroelectricity of perovskite-type oxides with alkylamine interlayer Zhaohui Zhong, Weiping The ferroelectricity of layer perovskite-type oxides intermittent with alkylamine, synthesized by hydrothermal method. The results show that perovskite layer contributes to the ferroelectric property. So-synthesized samples may

Zhong, Zhaohui

156

Epitaxial Growth and Properties of Doped Transition Metal and Complex Oxide Films  

Microsoft Academic Search

The detailed science and technology of crystalline oxide film growth using vacuum methods is reviewed and discussed with an eye toward gaining fundamental insights into the relationships between growth process and parameters, film and interface structure and composition, and electronic, magnetic and photochemical properties. The topic is approached first from a comparative point of view based on the most widely

Scott A. Chambers; Scott A

2010-01-01

157

Crystal structure of double oxides of the perovskite type  

Microsoft Academic Search

The cell dimensions of a number of double oxides belonging to the perovskite type have been accurately determined from examination of high-angle lines on x-ray powder photographs. The structures found fall into groups, as follows:Cubic (ideal perovskite type). This includes SrTiO3, SrSnO3, SrZrO3, BaSnO3, BaZrO3, BaThO3; also BaTiO3 above 120°C.Tetragonal. This includes the usual form of BaTiO3 at room temperature,

Helen D Megaw

1946-01-01

158

Hot electron transport in a strongly correlated transition-metal oxide.  

PubMed

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 La?.?Sr?.?MnO? (LSMO)- Nb-doped SrTiO? (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

159

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

160

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

161

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

162

Resolving surface chemical states in XPS analysis of first row transition metals, oxides and hydroxides: Sc, Ti, V, Cu and Zn  

Microsoft Academic Search

Chemical state X-ray photoelectron spectroscopic analysis of first row transition metals and their oxides and hydroxides is challenging due to the complexity of the 2p spectra resulting from peak asymmetries, complex multiplet splitting, shake-up and plasmon loss structure, and uncertain, overlapping binding energies. A review of current literature shows that all values necessary for reproducible, quantitative chemical state analysis are

Mark C. Biesinger; Leo W. M. Lau; Andrea R. Gerson; Roger St. C. Smart

2010-01-01

163

Transition-metal-free oxidative carboazidation of acrylamides via cascade C-N and C-C bond-forming reactions.  

PubMed

A novel transition-metal-free oxidative carboazidation of acrylamides using inexpensive NaN3 and K2S2O8 was achieved, which not only provided an efficient method to prepare various N3-substituted oxindoles, but also represented a novel strategy for C-N and C-C bond formation via a free-radical cascade process. This transformation exhibits excellent functional group tolerance, affording the desired oxindoles in good to excellent yields. PMID:24854242

Qiu, Jun; Zhang, Ronghua

2014-07-01

164

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

PubMed Central

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

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

2013-01-01

165

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

166

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

167

Investigation of factors affecting adsorption of transition metals on oxidized carbon nanotubes.  

PubMed

Adsorption of nickel, copper, zinc and cadmium from aqueous solutions on carbon nanotubes oxidized with concentrated nitric acid was carried out in single, binary, ternary and quaternary systems. TEM and adsorption of nitrogen were used to determine texture and structural parameters, respectively. The surface chemistry was evaluated using the pH at the point of zero charge, FTIR spectroscopy and XPS analysis. The experimental results showed that all isotherms for Cu(2+)(aq) fit to Langmuir model in each system. On the other hand, the isotherms for Ni(2+)(aq), Cd(2+)(aq) and Zn(2+)(aq) in multi-component systems reveal the effect of competition for adsorption sites seen as a decrease in the amount adsorbed. The uptakes at the equilibrium concentration of 0-0.04 mmol L(-1) in single system and 0-0.15 mmol L(-1) in binary system are in the order Cu(2+)(aq)>Ni(2+)(aq)>Cd(2+)(aq)>Zn(2+)(aq) while for the ternary and quaternary, the order is Cu(2+)(aq)>Cd(2+)(aq)>Zn(2+)(aq)>Ni(2+)(aq). The results indicate that the mechanism of adsorption is governed by the surface features, ion exchange process and electrochemical potential. The latter plays a significant role in multi-component adsorption where redox reactions, not only on the adsorbent surface but also between the adsorbates, are likely to occur. PMID:19264402

Gao, Zhanming; Bandosz, Teresa J; Zhao, Zongbin; Han, Mei; Qiu, Jieshan

2009-08-15

168

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

169

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

170

Transition metal sulfide loaded catalyst  

DOEpatents

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

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

1994-01-01

171

Transition metal sulfide loaded catalyst  

DOEpatents

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

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

1994-04-26

172

Screening of transition and post-transition metals to incorporate into copper oxide and copper bismuth oxide for photoelectrochemical hydrogen evolution.  

PubMed

A new dispenser and scanner system is used to create and screen Bi-M-Cu oxide arrays for cathodic photoactivity, where M represents 1 of 22 different transition and post-transition metals. Over 3000 unique Bi?:?M?:?Cu atomic ratios are screened. Of the 22 metals tested, 10 show a M-Cu oxide with higher photoactivity than CuO and 10 show a Bi-M-Cu oxide with higher photoactivity than CuBi2O4. Cd, Zn, Sn, and Co produce the most photoactive M-Cu oxides, all showing a 200-300% improvement in photocurrent over CuO. Ag, Cd, and Zn produce the highest photoactivity Bi-M-Cu oxides with a 200-400% improvement over CuBi2O4. Most notable is a Bi-Ag-Cu oxide (Bi?:?Ag?:?Cu atomic ratio of 22?:?3?:?11) which shows 4 times higher photocurrent than CuBi2O4. This material is capable of evolving hydrogen under illumination in neutral electrolyte solutions at 0.6 V vs. RHE when Pt is added to the surface as an electrocatalyst. PMID:23420023

Berglund, Sean P; Lee, Heung Chan; Núñez, Paul D; Bard, Allen J; Mullins, C Buddie

2013-04-01

173

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

174

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

175

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

176

Theoretical study of the reaction mechanism of nitrogen hydrogenation on transition metal oxides (TiO, VO, and CuO)  

Microsoft Academic Search

Density functional calculations of potential energy surfaces for the N2\\/H2\\/MO systems (M=Ti, V, and Cu) have been carried out at the B3LYP\\/6-311+G(3df,2p)\\/\\/B3LYP\\/6-31G** level in order to investigate the mechanism of nitrogen hydrogenation in the presence of transition metal oxides. The reaction mechanism has been shown to involve the addition of H2 to the metal oxide to form the HMOH species

Der-Yan Hwang; Alexander M. Mebel

2004-01-01

177

Atomic-Scale Studies Of Structure And Bonding At Perovskite Oxide Heterointerfaces .  

E-print Network

??Perovskite oxides exhibit an almost universal range of ground states including insulator, semiconductor, metal, superconductor, ferromagnet, antiferromagnet, spin glass, ferroelectric, and piezoelectric. Many of these… (more)

Kourkoutis, Lena

2009-01-01

178

Bacterial Transition Metal Homeostasis  

Microsoft Academic Search

Since details on metal cation transport proteins and on the allocation mechanisms for transition metals\\u000a are provided elsewhere in this book, I will present aspects of transition metal homeostasis in a hopefully\\u000a novel overview. We will start with a microbial look at the transition metal Periodic Table, cation speciation,\\u000a and availability in the environment. This information provides rules that might

Dietrich H. Nies

179

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

PubMed

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

Modeshia, Deena R; Walton, Richard I

2010-11-01

180

Thermal activation of N-H bonds by transition-metal oxide cations: does a hierarchy exist in the first row?  

PubMed

The thermal reactions of first-row transition-metal oxide cations [MO](+) (M=Sc-Ni, Zn) with ammonia have been studied by gas-phase experiments and computational methods. The activation of N-H bonds is brought about by the monoxides of the middle and late 3d metals Mn-Ni and Zn. The two primary reaction channels correspond to dehydration, which leads to [M(NH)](+), and hydrogen-atom abstraction to form [M(OH)](+). Oxygen-atom transfer from [MO](+) to NH(3) to produce neutral or ionized hydroxylamine was observed as a minor channel for some of the late transition-metal oxides. The computational analysis of these reactions, which was aimed at elucidating the reaction mechanisms and to uncover possible periodic trends across the first row, have been performed for the couples [MO](+) /NH(3) (M=Sc-Zn). Dehydration is found to be endothermic for the oxides of scandium to vanadium and exothermic for the other systems. Hydrogen-atom abstraction becomes exothermic starting with [MnO](+) and, finally, oxygen-atom transfer is feasible for the cationic oxides of nickel to zinc. PMID:21370291

Kretschmer, Robert; Zhang, Xinhao; Schlangen, Maria; Schwarz, Helmut

2011-03-28

181

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

E-print Network

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

Poeppelmeier, Kenneth R.

182

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

183

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

184

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

185

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

186

Role of transition metal impurities on the functional properties of dilute magnetic nitride semiconductors and high-performance microwave oxide dielectrics  

NASA Astrophysics Data System (ADS)

The thesis investigates transition metal doping in two types of materials: wide bandgap semiconductors for spintronic applications and oxide dielectrics for microwave applications. MBE grown Cr-doped GaN has been found to exhibit ferromagnetism at over 900 K. The measured magnetic moment per Cr atom in Cr-doped GaN varied significantly as a function of Cr concentration, with a maximum magnetic moment occurring at 3% Cr. Transport measurements of Cr-doped GaN revealed properties characteristic of hopping conduction. These measurements also inferred that the carrier concentration is similar in magnitude to the measured concentration of magnetically active Cr. This fits well into the scenario that electrons at the partially filled Cr t2 level contribute to the hopping conduction. These results, along with extensive structural characterization, suggest that ferromagnetism in Cr-doped GaN best fits the double exchange like mechanism as a result of hopping between near-midgap substitutional Cr impurity band. Exchange biasing effects were observed in sample structures of Cr-doped GaN thin films with an antiferromagnetic MnO overlayer. The center of the magnetic hysteresis loop shifts to negative magnetic field by ˜70 Oe when measured after field cooling. Enhancement of the coercive field of the Cr-doped GaN film is also found. The mechanism responsible for the exchange bias is attributed to the exchange coupling at the ferromagnetic Cr-doped GaN/antiferromagnetic MnO interface. The observed exchange biasing indicates that Cr-doped GaN has properties of a conventional ferromagnet and has potential use in practical magnetoelectronic devices. The effect of Ni-doping on the structural, dielectric and optical properties of Ba(Cd1/3Ta2/3)O3 (BCT) dielectrics has been explored. Rietveld analysis of the X-ray diffraction (XRD) data indicates that the BCT structure is similar to other Ba(B'1/3B" 2/3)O3 perovskites, although the Ta-O-Cd is distorted to an angle of ˜173°; very close to the earlier theoretical prediction of 172°. The XRD analysis also indicates that Ni doping significantly enhances the extent of Cd-Ta ordering in BCT. The temperature coefficient of resonant frequency decreases with Ni concentration up to 2 wt%. While the loss tangent of BCT is reduced at small levels of Ni doping (up to 0.5 wt%), it increases abruptly at higher concentrations. A correlation exists between the loss tangent of Ni-doped BCT samples and the intensity of a continuous absorption background in the optical spectra. This optical activity results from the presence of optically active point defects and is suggestive that these defects play an important role in the microwave loss in BCT dielectrics.

Liu, Hongxue

187

Oxidative dehydrogenation (ODH) of ethane with O[subscript 2] as oxidant on selected transition metal-loaded zeolites  

SciTech Connect

Ni-, Cu-, and Fe-loaded acidic and basic Y zeolites were synthesized, and their catalytic properties for oxidative dehydrogenation of ethane (ODHE) to ethylene were characterized. Acidic Ni-loaded Y zeolite exhibits an ethylene productivity of up to 108 g{sub C{sub 2}H{sub 4}}g{sub cat}{sup -1} h{sup -1} with a selectivity of {approx}75%. Acidic Cu- and Fe-loaded Y zeolites have an ethylene productivity of up to 0.37 g{sub C{sub 2}H{sub 4}}g{sub cat}{sup -1} h{sup -1} and a selectivity of {approx}50%. For the same metal, the acidity of the zeolite favors both ODHE productivity and ethylene selectivity. Extended X-ray absorption fine structure (EXAFS) studies show that Ni, present in particles on Ni/HY during the ODHE catalytic process, contains both Ni-Ni and Ni-O bonds, and that the ratio of oxidized Ni versus metallic Ni increases with the temperature. The insights these studies provide into the ODHE reaction mechanism are discussed.

Lin, Xufeng; Hoel, Cathleen A.; Sachtler, Wolfgang M.H.; Poeppelmeier, Kenneth R.; Weitz, Eric; (NWU)

2009-09-14

188

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

189

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

190

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

191

Resonant 3d, 3p and 3s Photoemission in Transition Metal Oxides Predicted at 2p Threshold  

NASA Astrophysics Data System (ADS)

We present calculated 3d, 3p and 3s resonant photoemission (RPE) spectra in the transition metal (TM) compounds CuO, NiO, CoO, FeO, MnO and TiO2 at TM 2p core threshold on the basis of a cluster model. Our model includes the intraatomic multipole electron-electron interactions and the hybridization between transition metal ions and ligand. The imaginary part of the self-energy matrix of the intermediate state is calculated by taking into account the 2p3d3d, 2p3d3p, 2p3d3s and 2p3p3p Coster-Kronig decay, which guarantees a sum rule between the integrated RPE spectra and absorption spectra. The dependence of RPE on the incident photon energy tuned to various multiplet structures of TM 2p absorption spectra is shown to be useful to identify the second order optical process, which is argued to include much Auger decay component. It is also shown, by a comparison with experiment, that the present 3d RPE contributes to a removal of discrepancies of estimated parameter values among analyses of other spectra.

Tanaka, Arata; Jo, Takeo

1994-07-01

192

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

193

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

194

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

PubMed

Graphene oxide (GO) is employed as a hole conductor in inverted planar heterojunction perovskite solar cells, and the devices with CH?NH?PbI?-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. PMID:25081348

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

2014-09-21

195

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

196

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

197

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

E-print Network

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

Zhu, Xiangdong

198

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

199

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

E-print Network

Factors that Influence Cation Segregation at the Surfaces of Perovskite Oxides Wonyoung Lee is important to understand and enable design of cathode materials with optimal surface chemistry. Recently we segregation, a detrimental process on the surface of perovskite cathodes (1). Motivated by those results, here

Yildiz, Bilge

200

Thermodynamic properties of some perovskite type oxides used as SOFC cathode materials  

Microsoft Academic Search

The solid-oxide electrolyte galvanic cells method has been employed in order to obtain the thermodynamic properties of some perovskite-type materials based on lanthanum strontium manganite and lanthanum strontium ferrite manganite. The relative partial molar free energies, enthalpies and entropies of oxygen dissolution in the perovskite phase, as well as the partial pressures of oxygen have been obtained in the temperature

S. Tanasescu; N. D. Totir; D. I. Marchidan

1999-01-01

201

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

202

Modification of MWCNT@TiO2 core-shell nanocomposites with transition metal oxide dopants for photoreduction of carbon dioxide into methane  

NASA Astrophysics Data System (ADS)

Titanium dioxide (TiO2) doped with visible-light-responsive metal oxides has been widely reported for improving the visible light absorption performance of TiO2 and its photocatalytic activity. The metal oxides could function as 'charge-carrier traps' that transport electrons from TiO2 through the heterojunction of the TiO2-metal oxides. In this work, the common transition metal oxides, i.e. FeOx, CuOx, NiO, CoOx and ZnO, were doped onto MWCNT@TiO2 core-shell nanocomposites. The effects of the metal oxide dopants on the photoactivity of the core-shell nanocomposites on CO2 reduction were studied. Characterization with diffuse-reflectance UV-vis showed significant improvement on visible light absorption after doping MWCNT@TiO2 with CuOx, FeOx and CoOx with the adsorption band-edge position red-shifted into the wavelength range of 480-630 nm. CuO-MWCNT@TiO2 appeared to be the most active one among all the studied photocatalysts, achieving a total methane formation of 0.93 ?mol/g-catalyst.

Gui, Meei Mei; Chai, Siang-Piao; Mohamed, Abdul Rahman

2014-11-01

203

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

204

Microstructure of Perovskite Oxides Thin Films Grown on Miscut/Small Lattice-Mismatched Substrates.  

E-print Network

??Perovskite oxides exhibit a wide range of physical properties, such as high dielectric, piezoelectric, pyroelectric, ferroelectric/multiferroic, non-linear optical and high temperature superconducting properties. The unique… (more)

Chen, Yanbin

2008-01-01

205

Oxide Spintronics  

Microsoft Academic Search

Concomitant with the development of metal-based spintronics in the late 1980s and 1990s, important advances were made on the growth of high-quality oxide thin films and heterostructures. While this was at first motivated by the discovery of high-temperature superconductivity in perovskite Cu oxides, this technological breakthrough was soon applied to other transition-metal oxides and, notably, mixed-valence manganites. The discovery of

Manuel Bibes; Agns Barthelemy

2007-01-01

206

Synthesis of inside-out core–shell perovskite-type oxide nanopowder  

Microsoft Academic Search

Core–shell perovskite-type oxides, with a relatively pure core and highly donor-doped shell, are widely investigated for, e.g., multilayer ceramic capacitors. Acceptor doped perovskite oxides are also widely investigated due to their applications as proton conductors. In the quest for new materials with novel properties we try to reverse both traits and form an inside-out core–shell structure with a highly donor-doped

Omri Mazar; Michael Schroeder; Yoed Tsur

2011-01-01

207

Activity and structure of perovskites as diesel reforming catalysts for solid oxide fuel cells  

Microsoft Academic Search

Recent progress in developing perovskite materials as more cost-effective catalysts in autothermal reforming (ATR) of diesel fuel to hydrogen-rich reformate for solid oxide fuel cell (SOFC) application is reported. Perovskite-type metal oxides with B sites partially exchanged by ruthenium were prepared and evaluated under ATR reaction conditions. The hydrogen yield, reforming efficiency, and CO selectivity of these catalysts were investigated

Di-Jia Liu; Michael Krumpelt

2005-01-01

208

Specific enrichment and direct detection of phosphopeptides on insoluble transition metal oxide particles in matrix-assisted laser desorption/ionization mass spectrometry applications.  

PubMed

Several transition metal oxides, such as iron (III), nickel (II) and zirconium (IV) oxides, were examined in detail for the specific enrichment and the purification of phosphopeptides from a digested peptide mixture solution. Phosphopeptide enrichment was performed on the metal oxide particles using a peptide mixture obtained bytryptic digestion of beta-casein. The mixture of protein digests containing bovine serum albumin (BSA): beta-casein digests (100:1 mole ratio) was also used for the phosphopeptide enrichment. Furthermore, non-fat milk digest was examined as a complex biological sample. In each phosphopeptide enrichment process, phosphopeptides were specifically enriched and separated from the non-phosphopeptides. The phosphopeptides were adsorbed onto the metal oxide surface at acidic pH values between 1.0 and 2.0 and, for desorption of phosphopeptides from metal oxide particles, pH values were examined and optimized in the enrichment studies. The analysis of phosphopeptides were carried out by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) using 2,5-dihydroxybenzoic acid matrix containing 1.0% phosphoric acid to obtain intense protonated signals and to overcome degradation of the phosphopeptides by phosphate group loss in mass spectrometric conditions. Moreover, it was demonstrated that the direct detection of phosphopeptides from the surface of the metal oxide particles was possible using MALDI-MS by mixing the phosphopeptide-adsorbed metal oxide particles with MALDI matrix solution in slurry form before the analysis. Thus, the effects of interferences arising from chemical species used in the desorption process was successfully eliminated for the fast and sensitive detection of phosphopeptides in MALDI-MS applications. PMID:24308196

Celikbiçak, Omür; Kaynar, Gizem; Atakay, Mehmet; Güler, Ulkü; Kayili, H Mehmet; Salih, Bekir

2013-01-01

209

hal-00087421,version2-21Dec2006 The interface between a polar perovskite oxide and silicon from  

E-print Network

hal-00087421,version2-21Dec2006 The interface between a polar perovskite oxide and silicon from). Many of them belong to the class of perovskites (cubic crystals whose chemical formula is ABO3) which structure. In the search of the best candidate, the LaAlO3 crystal raised out of the perovskite family

Paris-Sud XI, Université de

210

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

211

Double perovskites as a family of highly active catalysts for oxygen evolution in alkaline solution.  

PubMed

The electronic structure of transition metal oxides governs the catalysis of many central reactions for energy storage applications such as oxygen electrocatalysis. Here we exploit the versatility of the perovskite structure to search for oxide catalysts that are both active and stable. We report double perovskites (Ln?.?Ba?.?)CoO(?-?) (Ln=Pr, Sm, Gd and Ho) as a family of highly active catalysts for the oxygen evolution reaction upon water oxidation in alkaline solution. These double perovskites are stable unlike pseudocubic perovskites with comparable activities such as Ba?.?Sr?.?Co?.?Fe?.?O(?-?) which readily amorphize during the oxygen evolution reaction. The high activity and stability of these double perovskites can be explained by having the O p-band centre neither too close nor too far from the Fermi level, which is computed from ab initio studies. PMID:24042731

Grimaud, Alexis; May, Kevin J; Carlton, Christopher E; Lee, Yueh-Lin; Risch, Marcel; Hong, Wesley T; Zhou, Jigang; Shao-Horn, Yang

2013-01-01

212

Hybrid functionals applied to perovskites.  

PubMed

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

Franchini, Cesare

2014-06-25

213

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

214

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

215

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

216

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

217

Dense perovskite membrane reactors for partial oxidation of methane to syngas  

Microsoft Academic Search

The partial oxidation of methane to synthesis gas (syngas, CO + Hâ) was performed in a mixed-conducting perovskite dense membrane reactor at 850 C, in which oxygen was separated from air and simultaneously fed into the methane stream. Steady-state oxygen permeation rates for La{sub 1-x}Aââ²Fe{sub 0.8} CO{sub 0.2}O{sub 3-δ} perovskite membranes in nonreacting air\\/helium experiments were in the order of

Chung-Yi Tsai; Anthony G. Dixon; William R. Moser; Yi Hua Ma

1997-01-01

218

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...

219

Local Octahedral Distortions and Magnetic Properties Controlled by Substrate Symmetry at Perovskite Oxide Interfaces  

NASA Astrophysics Data System (ADS)

We have investigated the oxygen octahedral distortions and local magnetism at the interfaces of magnetic perovskite oxide heterostructures using first principles calculations. The studied prototype oxide heterostructures include La0.7Sr0.3MnO3, SrRuO3, and BiFeO3. The results show that the symmetry mismatch at interfaces between two perovskite oxides imposes an interfacial layer with distortion modes that do not exist in either bulk material, creating new interface properties by symmetry alone. The thickness of such interface layer depends on the resistance of the octahedra to deformation.

He, Jun; Borisevich, Albina; Kalinin, Sergei; Pennycook, Stephen; Pantelides, Sokrates

2011-03-01

220

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

221

Change in the optical properties of amorphous films of transition metal oxides upon formation of the nanocrystalline phase  

Microsoft Academic Search

Weakly absorbing films of tantalum oxide Ta2O5 with the crystallization kinetics typical of amorphous films have been investigated. The films have been prepared by reactive\\u000a magnetron sputtering on substrates of different natures (titanium and optical silica glass). The crystallization heat treatment\\u000a of the films has been performed at temperatures ranging from 500 to 700 °C. Changes in the optical properties

V. I. Shapovalov; L. P. Efimenko; A. E. Komlev; K. E. Pugachev; V. G. Baryshnikov; I. G. Polyakova

2009-01-01

222

Strong metal-support interaction between mononuclear and polynuclear transition metal complexes and oxide supports which dramatically affects catalytic activity  

Microsoft Academic Search

The interaction of carbonyl complexes with catalyst supports, primarily ..gamma..-alumina, has been studied by temperature-programmed decomposition. In all cases, including cluster complexes and complexes of noble metals, after heating to 600°C in flowing He the catalysts are significantly oxidized due to a redox reaction between surface hydroxyl groups and the initially zero-valent metal. Contrary reports are probably incorrect and likely

Dennis A. Hucul; Alan Brenner

1981-01-01

223

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

224

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

225

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

226

Oxygen exchange measurements on perovskites as cathode materials for solid oxide fuel cells  

Microsoft Academic Search

Oxygen exchange measurements have been applied to determine simultaneously the chemical diffusion coefficient and the surface exchange coefficient of oxide perovskites. The oxygen partial pressure is changed in a step-wise manner and the relaxation of the oxide ceramics is followed as a function of time. Instead of recording the amount of exchanged oxygen, the rate of oxygen incorporation reactions is

W. Preis; E. Bucher; W. Sitte

2002-01-01

227

Characterization of single transition metal oxide nanorods by combining atomic force microscopy and polarized micro-Raman spectroscopy  

NASA Astrophysics Data System (ADS)

Accurate chemical and structural characterization of free-standing zinc oxide (ZnO) and hematite (?-Fe2O3) nanorods has been carried out using an AFM/Raman correlative technique under polarized light. ZnO nanorods are found to be wurtzite-type single crystalline objects homogeneous in composition and grown along their principal axis of symmetry. Hematite specimens are rhombohedral corundum-type single crystals grown along a direction orthogonal to their principal axis of symmetry and exhibiting structural disorder. Certain hematite nanorods turn out to be very sensitive to laser heating. These studies reveal the high potential of the coupled AFM/Raman technique to examine the properties of these promising nanomaterials.

Najjar, Samar; Talaga, David; Coffinier, Yannick; Szunerits, Sabine; Boukherroub, Rabah; Servant, Laurent; Couzi, Michel; Bonhommeau, Sébastien

2011-09-01

228

Resolving surface chemical states in XPS analysis of first row transition metals, oxides and hydroxides: Sc, Ti, V, Cu and Zn  

NASA Astrophysics Data System (ADS)

Chemical state X-ray photoelectron spectroscopic analysis of first row transition metals and their oxides and hydroxides is challenging due to the complexity of the 2p spectra resulting from peak asymmetries, complex multiplet splitting, shake-up and plasmon loss structure, and uncertain, overlapping binding energies. A review of current literature shows that all values necessary for reproducible, quantitative chemical state analysis are usually not provided. This paper reports a more consistent, practical and effective approach to curve-fitting the various chemical states in a variety of Sc, Ti, V, Cu and Zn metals, oxides and hydroxides. The curve-fitting procedures proposed are based on a combination of (1) standard spectra from quality reference samples, (2) a survey of appropriate literature databases and/or a compilation of the literature references, and (3) specific literature references where fitting procedures are available. Binding energies, full-width at half maximum (FWHM) values, spin-orbit splitting values, asymmetric peak-shape fitting parameters, and, for Cu and Zn, Auger parameters values are presented. The quantification procedure for Cu species details the use of the shake-up satellites for Cu(II)-containing compounds and the exact binding energies of the Cu(0) and Cu(I) peaks. The use of the modified Auger parameter for Cu and Zn species allows for corroborating evidence when there is uncertainty in the binding energy assignment. These procedures can remove uncertainties in analysis of surface states in nano-particles, corrosion, catalysis and surface-engineered materials.

Biesinger, Mark C.; Lau, Leo W. M.; Gerson, Andrea R.; Smart, Roger St. C.

2010-11-01

229

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

NASA Astrophysics Data System (ADS)

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

Carraher, Jack McCaslin

230

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

E-print Network

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

zur Loye, Hans-Conrad

231

Complexity in Transition Metal Oxides.  

NASA Astrophysics Data System (ADS)

The properties of manganites, exhibiting colossal magnetoresistance, and high critical temperature cuprates are studied numerically using a variety of microscopic and phenomenological models. Inhomogeneous ground states are discovered in many regions of parameter space.[1] It is shown how colossal magnetoresistance arises in manganites due to the high susceptibility of complex inhomogeneous states to small disturbances. Comparison with experimental data lends support to our theoretical results. Based on similar inhomogeneous characteristics observed in simulations of models for high Tc cuprates, we predict the possibility of ``colossal'' effects in the cuprates as well [2]. Here the states of relevance contain clusters where the amplitude of the superconducting (SC) order parameter is developed, but the SC phase is random. The results are compatible with the recently reported giant proximity effect in cuprates. [1] J. Burgy, et al., Phys. Rev. Lett.87, 277202 (2001); E. Dagotto, T. Hotta and A. Moreo. Physics Reports 344, 1 (2001); J. Burgy,et al., cond-mat/0308456. [2] G. Alvarez, M. Mayr, A. Moreo and E. Dagotto, preprint.

Moreo, Adriana

2004-03-01

232

Complexity in Transition Metal Oxides  

NASA Astrophysics Data System (ADS)

Recent computational results in the context of models for manganites and cuprates will be briefly discussed. It is argued that correlations in quenched disorder -- needed to mimic cooperative Jahn-Teller effects -- are important to have colossal magnetoresistance in 3D. A related recently discussed metal-insulator transition induced by disorder in a one-orbital model with cooperative phonons is intuitively explained [1]. In addition, it is argued that colossal effects should be far more common than currently known, and they may appear in cuprate superconductors as well [2]. [1] J. Burgy et al., cond-mat/0308456; C. Sen, G. Alvarez, and E. Dagotto, preprint. [2] See also Adriana Moreo, invited talk, March APS 04; G. Alvarez, M. Mayr et al., preprint.

Dagotto, Elbio; Alvarez, Gonzalo; Moreo, Adriana

2004-03-01

233

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

E-print Network

Control of Octahedral Tilts and Magnetic Properties of Perovskite Oxide Heterostructures T. Pantelides3,1 1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA 2 The Center for Nanophase Materials Science, Oak Ridge National Laboratory

Pennycook, Steve

234

Epitaxial integration of perovskite-based multifunctional oxides on silicon q  

E-print Network

) at the LaAlO3 (LAO)/SrTiO3 (STO) interface have led researchers to explore the novel physics arising by MBE, moti- vated by the search for new gate dielectrics replacing SiO2. Since then, many researchers to grow perovskite-type multifunc- tional oxides on Si. STO has been commonly used as a sin- gle

Eom, Chang Beom

235

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

236

Covalent dependence of octahedral rotations in orthorhombic perovskite oxides  

NASA Astrophysics Data System (ADS)

The compositional dependence of metal-oxygen BO6 octahedral distortions, including bond elongations and rotations, is frequently discussed in the ABO3 perovskite literature; structural distortions alleviate internal stresses driven by under- or over-coordinated bond environments. Here we identify the dependence of octahedral rotations from changes in metal-oxygen bond covalency in orthorhombic perovskites. Using density functional theory we formulate a covalency metric, which captures both the real and k-space interactions between the magnitude and sense, i.e., in-phase or out-of-phase, octahedral rotations, to explore the link between the ionic-covalent Fe-O bond and the interoctahedral Fe-O-Fe bond angles in Pbnm ferrates. Our survey finds that the covalency of the metal-oxygen bond is correlated with the rotation amplitude: We find the more covalent the Fe-O bond, the less distorted is the structure and the more important the long-range inter-octahedral (Fe-O-Fe bond angle) interactions. Finally, we show how to indirectly tune the B-O bond covalency by A-cation induced BO6 rotations independent of ionic size, facilitating design of targeted bonding interactions in complex perovskites.

Cammarata, Antonio; Rondinelli, James M.

2014-09-01

237

Covalent dependence of octahedral rotations in orthorhombic perovskite oxides.  

PubMed

The compositional dependence of metal-oxygen BO6 octahedral distortions, including bond elongations and rotations, is frequently discussed in the ABO3 perovskite literature; structural distortions alleviate internal stresses driven by under- or over-coordinated bond environments. Here we identify the dependence of octahedral rotations from changes in metal-oxygen bond covalency in orthorhombic perovskites. Using density functional theory we formulate a covalency metric, which captures both the real and k-space interactions between the magnitude and sense, i.e., in-phase or out-of-phase, octahedral rotations, to explore the link between the ionic-covalent Fe-O bond and the interoctahedral Fe-O-Fe bond angles in Pbnm ferrates. Our survey finds that the covalency of the metal-oxygen bond is correlated with the rotation amplitude: We find the more covalent the Fe-O bond, the less distorted is the structure and the more important the long-range inter-octahedral (Fe-O-Fe bond angle) interactions. Finally, we show how to indirectly tune the B-O bond covalency by A-cation induced BO6 rotations independent of ionic size, facilitating design of targeted bonding interactions in complex perovskites. PMID:25240365

Cammarata, Antonio; Rondinelli, James M

2014-09-21

238

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

239

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

240

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… (more)

Taylor, Stephanie Merac

2013-01-01

241

Cation disorder and size effects in magnetoresistive manganese oxide perovskites  

Microsoft Academic Search

Large disorder effects due to size differences between {ital A}-site {ital R}{sup 3+} ({ital R}=La,Pr,Nd,Sm) and {ital M}{sup 2+} ({ital M}=Ca,Sr,Ba) cations have been found in magnetoresistive ({ital R}{sub 0.7}{ital M}{sub 0.3})MnOâ perovskites. The ferromagnetic-metalâparamagnetic-insulator transition temperature {ital T}{sub {ital m}} varies as {ital T}{sub {ital m}}={ital T}{sub {ital m}}(0)-{ital pQ}² due to strain fields resulting from ordered or disordered

Lide Rodriguez-Martinez; J. P. Attfield

1996-01-01

242

Self-propagating high-temperature synthesis of Sr-doped LaMnO 3 perovskite as oxidation catalyst  

Microsoft Academic Search

Sr-doped LaMnO3 perovskite oxide has been focused on as one of the alternative catalysts to precious metals such as platinum that are used for cleaning automotive emission gas. The conventional Solid-state reaction method is a popular productive process for perovskite oxide, however, it is time and energy consuming process because it requires repeated prolonged heat treatment at high temperatures. Therefore,

T. Hirano; H. Purwanto; T. Watanabe; T. Akiyama

2007-01-01

243

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

PubMed

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-(x)Sr(x)MnO3, 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. PMID:24849185

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

2014-01-01

244

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

245

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

E-print Network

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

246

Crystal chemistry of non-perovskite manganese oxides - implications for magnetic properties  

Microsoft Academic Search

This paper reviews crystal structures of ternary manganese oxides and their implications for magnetic properties. We point out the critical role of the counter-cation (A) size in driving given stoichiometries to different structure types, in particular AMnO3 compositions to ilmenite or perovskite structure, or A2MnO4 ones to spinel or K2NiF4 type. Mn2+ lies near the size borderline. It occupies the

P. Strobel; A. Ibarra-Palos; M. Pernet; S. Zouari; W. Cheikh-Rouhou; A. Cheikh-Rouhou

2004-01-01

247

Optical Response of High-Dielectric-Constant Perovskite-Related Oxide  

Microsoft Academic Search

Optical conductivity measurements on the perovskite-related oxide CaCu3Ti4O12 provide a hint of the physics underlying the observed giant dielectric effect in this material. A low-frequency vibration displays anomalous behavior, implying that there is a redistribution of charge within the unit cell at low temperature. At infrared frequencies (terahertz), the value for the dielectric constant is ~80 at room temperature, which

C. C. Homes; T. Vogt; S. M. Shapiro; S. Wakimoto; A. P. Ramirez

2001-01-01

248

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

249

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

250

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

SciTech Connect

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

Djerdj, Igor [ETH Zuerich, Department of Materials, Wolfgang-Pauli-Strasse 10, 8093 Zuerich (Switzerland)], E-mail: igor.djerdj@mat.ethz.ch; Arcon, Denis [Institute Jozef Stefan, Jamova 39, 1000 Ljubljana (Slovenia); Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana (Slovenia); Jaglicic, Zvonko [Institute of Mathematics, Physics and Mechanics, Jadranska 19, 1000 Ljubljana (Slovenia); Faculty of Civil and Geodetic Engineering, University of Ljubljana, Jamova 2, 1000 Ljubljana (Slovenia); Niederberger, Markus [ETH Zuerich, Department of Materials, Wolfgang-Pauli-Strasse 10, 8093 Zuerich (Switzerland)], E-mail: markus.niederberger@mat.ethz.ch

2008-07-15

251

Topotactical growth of thick perovskite oxynitride layers by nitridation of single crystalline oxides  

NASA Astrophysics Data System (ADS)

Thick films of the perovskite-related oxynitrides LaTiO 2N, NdTiO 2N, SrNbO 2N and SrTaO 2N were synthesised by nitridation of single crystals of the corresponding oxides with general composition ABO 3.5. The oxide crystals were obtained by optical floating zone growth. They correspond to n = 4 member of the A nB nO 3 n+2 family of layered perovskites and were reacted at temperatures between 900 °C and 1050 °C to form the oxynitrides. Electron probe microanalysis proved the presence of nitrogen in a surface layer of a few micrometer thickness. Cross-section SEM revealed additional thin stripes of oxynitride within the bulk of the crystals, indicating that nitrogen is incorporated preferably parallel to the perovskite-type layers, which in turn are connected in a zipper-type mechanism. The formation of the desired perovskite-type oxynitrides was confirmed by X-ray diffraction. Pole figure measurements proved an epitaxial orientation ABO 2N (110)[001] ? ABO 3.5 (001)[100]. The mosaicity of the oxynitrides both in polar and azimuthal direction was very small (<2°) indicating a nearly single crystalline quality of the surface layer. The nitridation of the crystals results in a dramatic change in colour. Optical spectroscopy revealed shifts of the absorption edge by more than 200 nm to longer wavelengths with respect to the parent oxides, corresponding to a reduction of the band gap energies by 1.4-1.8 eV.

Ebbinghaus, Stefan G.; Aguiar, Rosiana; Weidenkaff, Anke; Gsell, Stefan; Reller, Armin

2008-06-01

252

Perovskite oxides for semiconductor-based gas sensors  

Microsoft Academic Search

The oxygen partial pressure dependence of the point defect concentration, and thus conductivity, in oxide semiconductors allows for their use in high-temperature gas sensors. In addition to responding to oxygen partial pressure, the resistance of oxide semiconductors can be affected by other gases, such as carbon monoxide, hydrocarbons and ethanol, which creates opportunities for developing new sensors, but also leads

Jeffrey W. Fergus

2007-01-01

253

Correlation between thermal expansion and oxide ion transport in mixed conducting perovskite-type oxides for SOFC cathodes  

Microsoft Academic Search

Oxygen deficiency, electrical conductivity, ionic transport and thermal expansion of alternative cathode materials of the A1?aA?aBO3 perovskite-type oxides (A=La, Pr, Ce; A?=Sr; B=Mn, Fe, Co, Ni, Ga, Mg) were measured as a function of temperature and oxygen partial pressure. Additionally, lanthanum strontium gallates were investigated as electrolyte materials. On the basis of the results a general picture of the A-

H. Ullmann; N. Trofimenko; F. Tietz; D. Stöver; A. Ahmad-Khanlou

2000-01-01

254

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

255

Ferrite-based perovskites as cathode materials for anode-supported solid oxide fuel cells  

Microsoft Academic Search

The properties and the applicability of iron- and cobalt-containing perovskites were evaluated as cathodes for solid oxide fuel cells (SOFCs) in comparison to state-of-the-art manganite-based perovskites. The materials examined were La1?x?ySrxCo0.2Fe0.8O3?? (x=0.2 and 0.4; y=0?0.05), La0.8Sr0.2FeO3??, La0.7Ba0.3Co0.2Fe0.8O3?? and Ce0.05Sr0.95Co0.2Fe0.8O3??. The main emphasis was placed on the electrochemical properties of the materials, which were investigated on planar anode-supported SOFCs with 8

Andreas Mai; Vincent A. C. Haanappel; Sven Uhlenbruck; Frank Tietz; Detlev Stöver

2005-01-01

256

Oxygen permeation properties of perovskite-related intergrowth oxides exhibiting mixed ionic-electronic conduction  

NASA Astrophysics Data System (ADS)

Mixed ionic-electronic conductors that exhibit high oxygen permeability and good structural stability at elevated temperatures and in reducing atmospheres are of interest for many applications. For example, they can be used as electrodes for solid oxide fuel cells, as oxygen gas separation membranes, and in methane conversion reactors. The ABO3-delta perovskites are the most extensively investigated oxides for use as oxygen permeation membranes due to their high oxygen permeability. Unfortunately, many of the ABO 3-delta perovskites experience oxygen loss at high temperatures and in reducing atmospheres, which can lead to phase transformations and structural instability. A possible solution and alternative to ABO3-delta perovskites are the development of mixed conductors having a perovskite-related intergrowth structure. This dissertation explores the oxygen permeation properties of various intergrowth oxides. The composition SrFeCo0.5Oy has been reported in the literature to exhibit high electronic and oxide-ion conductivities, high oxygen permeability, and good stability in reducing atmospheres at high temperatures. However, the SrFeCo0.5Oy composition is a three phase mixture consisting of an intergrowth phase Sr4Fe6-x CoxO13+delta (x ? 1.5), the perovskite phase SrFe0.75Co0.25O3-delta, and a cubic spinel phase Fe3-xCoxO4. From a systematic study, it is shown that the oxygen permeation properties of SrFeCo0.5 Oy (x = 2 composition in Sr4Fe6-xCO xO13+delta) are dominated by the perovskite phase SrFe 1-xCoxO3-delta, and not the intergrowth phase Sr4Fe6-xCoxO13+delta. The oxygen permeation flux values for the composition Sr4Fe 4Co2O3-delta are two orders of magnitude lower than that for the perovskite phase SrFe0.2Co0.8O 3-delta. The layered compounds La1-xSr1-xFeO 4, La1-xSr1-xCoO4, Sr 3Fe2-xCoO7-delta, and LaSr 3Fe3-xCoxO10, belonging to the Ruddlesden-Popper series, were synthesized and investigated for use as oxygen permeation membranes. The oxygen permeation properties of the La1-x Sr1-xFeO4 and La1-xSr 1-xCoO4 phases were poor, with flux values on the order of 10-9 to 10-8 mol cm-2 s-1 at 900°C. On the other hand, the oxygen flux values for Sr3Fe2-xCoxO7-delta and LaSr3Fe3-xCoxO10, ranged between 10-8 and 10-7 mol cm-2 s-1 at 900°C, which is about one order of magnitude lower than that exhibited by the perovskite phase SrFe0.2Co0.8O3-delta. Despite the lower oxygen permeation flux values, the layered compounds experienced no phase transitions aid showed no signs of structural instability under permeating conditions, which may make them attractive for use in high temperature electrochemical applications.

Armstrong, Tad John

257

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

258

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

259

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

Microsoft Academic Search

The prohibitive cost and scarcity of the noble-metal catalysts needed for catalysing the oxygen reduction reaction (ORR) in fuel cells and metal-air batteries limit the commercialization of these clean-energy technologies. Identifying a catalyst design principle that links material properties to the catalytic activity can accelerate the search for highly active and abundant transition-metal-oxide catalysts to replace platinum. Here, we demonstrate

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

2011-01-01

260

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

SciTech Connect

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

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

2011-12-31

261

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

262

Oxidative coupling of methane in a mixed-conducting perovskite membrane reactor  

Microsoft Academic Search

Ionic-electronic mixed-conducting perovskite-type oxide La0.6Sr0.4Co0.8Fe0.2O3 was applied as a dense membrane for oxygen supply in a reactor for methane coupling. The oxygen permeation properties were studied in the pO2-range of 10?3?1 bar at 1073–1273 K, using helium as a sweeping gas at the permeate side of the membrane. The oxygen semi-permeability has a value close to 1 mmol m?2 s?1

J. E. ten Elshof; H. J. M. Bouwmeester; H. Verweij

1995-01-01

263

Influence of order-disorder transitions on oxygen permeability through selected nonstoichiometric perovskite-type oxides  

Microsoft Academic Search

New results on the oxygen permeability of perovskite-type oxides SrCo0.8B'0.2O3¿¿ (with B'=Cr, Fe, Co and Cu) and La0.6Sr0.4CoO3¿¿ are presented. The occurrence of order-disorder transitions at elevated temperatures (790¿940°C) in these phases has been confirmed by DSC measurements and, in some cases, by X-ray powder diffraction of samples either slowly cooled or quenched from high temperature after annealing in different

H. Kruidhof; H. J. M. Bouwmeester; Doorn van R. H. E; A. J. Burggraaf

1993-01-01

264

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

265

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

SciTech Connect

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

James P. Lewis (PI, former Co-PI), Dorian M. Hatch (Co-PI, former PI), and Harold T. Stokes (Co-PI)

2006-12-31

266

Atomic layer deposition of transition metals  

NASA Astrophysics Data System (ADS)

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.

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

2003-11-01

267

[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

268

[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

269

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

270

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

271

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

PubMed

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 - x SrxFe y Mn1 - y O3 - ? (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

272

Pyroelectric response of perovskite heterostructures incorporating conductive oxide electrodes  

NASA Astrophysics Data System (ADS)

The use of imaging technologies has become pervasive in many applications as the demand for situational awareness information has increased over the last decade. No better example of the integration of these technologies can be found than that of infrared or thermal imaging. This dissertation, in the field of thermal imaging, has been motivated by the desire to advance the technology of uncooled, thin-film pyroelectric sensors and focuses on the materials and structures from which the detector elements will be built. This work provides a detailed study of the pyroelectric response of the La-Sr-Co-O/Pb-La-Zr-Ti-O/La-Sr-Co-O (LPL) structure. The LPL structure was chosen based on the needs of thin film detectors, the unique properties of the conductive oxide La-Sr-Co-O (LSCO), and the broad applicability of the Pb-La-Zr-Ti-O (PLZT) material system. Epitaxial heterostructures were grown by pulsed laser deposition on single-crystal oxide substrates. Using the oxygen pressure during cooling and heating of the LSCO layer as a key variable, we have been able to produce structures that have a pronounced internal field in the as-grown state. In these capacitors, where the bottom electrode has a large concentration of oxygen vacancies, we have discovered very large pyroelectric responses that are 10 to 30 times larger than expected of PLZT-based pyroelectric materials (typical values are 20 to 40 nCcm-2K -1). The enhanced pyroelectric responses are very repeatable, stable over time, and distinctly different from responses attributed to thermally stimulated currents. Detailed positron annihilation spectroscopy measurements reveal that there is indeed an oxygen concentration gradient across the capacitor. Based on the results of this study, I will present an analysis of the enhanced pyroelectric response. Although the enhanced response has been correlated with high concentrations of oxygen vacancies in the PLZT film and LSCO electrodes, the mechanism by which the large pyroelectric currents are generated is not yet known. It is likely, however, that a sub-lattice of oxygen and lead vacancies forms the enhanced dipoles and that due to the highly defective nature of the lattice, has a large effective pyroelectric coefficient.

Tipton, Charles Wesley, IV

2000-10-01

273

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

274

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

Microsoft Academic Search

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

Jihong Cheng

2004-01-01

275

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

E-print Network

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

zur Loye, Hans-Conrad

276

Competing magnetic phases in mixed-valent manganese oxide perovskites  

NASA Astrophysics Data System (ADS)

Measurement of specific heat Cp(T) below 300K of melt-grown samples of La1-xCaxMnO3 (0?x?0.3) and R0.7A0.3MnO3 (R=rare-earth,A=alkaline-earth) with room-temperature tolerance factor 0.950?t?0.996 have been supplemented by transport and magnetic measurements. Comparison of the phase diagram of La1-xCaxMnO3 with that of La1-xSrxMnO3 and the evolution with t of the R0.7A0.3MnO3 family illustrate the sensitivity to t of the crossover from localized to itinerant behavior of the ? -bonding electrons and support the model of two magnetic phases in the crossover compositional range that has been used to account for the colossal magnetoresistance (CMR) phenomenon found in these oxides. A vanishing of the specific-heat anomaly at the Curie temperature Tc and the magnetic data at crossover are typical of a spin glass, and a broad hump in Cp(T) below a Th>Tc , where there is no anomaly at the Tc signal ferromagnetic ordering within isolated pockets of a hole-rich, conductive O* minority phase at Th . On cooling through TN of the antiferromagnetic matrix, the spins freeze at a spin-glass temperature Tg in zero magnetic field H if the ferromagnetic phase does not percolate; the ferromagnetic phase grows in an applied H , and a modest H converts the spin glass to a bulk ferromagnet with a Curie temperature Tc?Tg , where the ferromagnetic phase grows to beyond percolation. As x increases in La1-xCaxMnO3 , a ferromagnetic-insulator O? phase having a charge ordering and a different orbital ordering than the parent O' phase percolates below a Tg?Tc , and the minority O' phase remains paramagnetic until it becomes antiferromagnetic below a TM

Liu, G.-L.; Zhou, J.-S.; Goodenough, J. B.

2004-12-01

277

Effects of spin-orbit interaction on the electronic structures of 5d double perovskite A2FeReO6 (A=Ba and Ca)  

Microsoft Academic Search

Recently, the role of spin-orbit coupling (SOC) in 5d transition metal oxides (TMOs) attracted a lot of attention. In 5d TMOs, the energy scale of the SOC is larger than that of 4d or 3d TMOs and it can induce novel Mott insulating state through the cooperation with the electron correlation.[1] We investigated the electronic structures of 5d double perovskite

B. C. Jeon; C. H. Kim; S. J. Moon; W. S. Choi; Y. S. Lee; J. Yu; C. J. Won; J. H. Jung; N. Hur; T. W. Noh

2010-01-01

278

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

PubMed

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. PMID:25352258

Shimakawa, Yuichi; Mizumaki, Masaichiro

2014-11-26

279

Catabolism of hyaluronan: involvement of transition metals.  

PubMed

One of the very complex structures in the vertebrates is the joint. The main component of the joint is the synovial fluid with its high-molar-mass glycosaminoglycan hyaluronan, which turnover is approximately twelve hours. Since the synovial fluid does not contain any hyaluronidases, the fast hyaluronan catabolism is caused primarily by reductive-oxidative processes.Eight transition metals - V(23), Mn(25), Fe(26), Co(27), Ni(28), Cu(29), Zn(30), and Mo(42) - naturally occurring in living organism are essential for the control of various metabolic and signaling pathways. They are also the key elements in catabolism of hyaluronan in the joint.In this overview, the role of these metals in physiological and pathophysiological catabolism of hyaluronan is described. The participation of these metals in the initiation and propagation of the radical degradation hyaluronan is critically reviewed. PMID:21217859

Soltés, Ladislav; Kogan, Grigorij

2009-12-01

280

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

281

Colossal Magnetoresistance in Perovskite Oxides II Gang Xiao, Chairman Giant magnetoresistance induced by spin-correlation scattering  

E-print Network

Colossal Magnetoresistance in Perovskite Oxides II Gang Xiao, Chairman Giant magnetoresistance magnetoresistance effect in ferromagnetically ordered thin film and bulk based on the Hund's rule coupling between value, which is in agreement with the experiments. The giant magnetoresistance effect in thin film

Gong, Xingao

282

On the Structural and Electronic Factors Governing the Magnetic Properties of the Hexagonal Perovskite-Type Oxides AxBO 3 ( A=Ca, Sr, Ba; B=Co, Ni)  

NASA Astrophysics Data System (ADS)

The hexagonal perovskite-type oxides AxBO 3 ( A=Ca, Sr, Ba; B=Co, Ni) consist of ( BO 3) ? chains made up of face-sharing BO 6 octahedra and BO 6 trigonal prisms. On the basis of molecular orbital calculations for their structural building blocks we examined why the transition metal atoms in the trigonal prisms of Sr 9/7NiO 3 and Sr 14/11CoO 3 occupy the positions away from their trigonal prism centers and why Ba 6/5NiO 3 and Ca 3/2CoO 3 exhibit apparently puzzling magnetic properties. Our analysis indicates that the structural building units of the ( BO 3) ? chains in these oxides adopt high-spin states to reduce the metal-metal ?-antibonding interactions between adjacent metal atoms as well as the on-site repulsion. This finding led us to predict the number of unpaired spins that the oxides Sr 9/7NiO 3, Sr 6/5CoO 3, and Sr 14/11CoO 3 are expected to have.

Whangbo, M.-H.; Koo, H.-J.; Lee, K.-S.; Gourdon, O.; Evain, M.; Jobic, S.; Brec, R.

2001-08-01

283

Electronic and ionic transport properties and other physical aspects of perovskites  

NASA Astrophysics Data System (ADS)

The perovskites and perovskite-related structures exhibit several features of technical as well as fundamental interest. Technically useful properties include oxide-ion conduction with/without electronic conduction, oxidation catalysis, ferroic displacements in classic and relaxor ferroelectrics, half-metallic ferromagnetism and high-temperature superconductivity. Of more fundamental interest is the ability to tune, by chemical substitution on the large-cation subarray, transition-metal oxides through the crossover on the transition-metal array from localized dn configurations to itinerant d-electron behaviour without/with changing the valence state of that array. The localized-electron configurations may exhibit cooperative Jahn-Teller distortions that introduce anisotropic exchange interactions. At crossover, bond-length fluctuations may segregate into an ordered array of alternating covalent and ionic bonding in a single-valent perovskite; multicentre polarons or correlation bags may replace small polarons in a mixed-valent system. Bond-length fluctuations at crossover give vibronic conduction and suppression of the phonon contribution to the thermal conductivity; the fluctuations may order, to give high-temperature superconductivity, or transform to quantum-critical-point behaviour at lowest temperatures. Crossover of sgr-bonding electrons in the presence of localized spins associated with pgr-bonding electrons gives rise to the colossal magnetoresistance phenomenon above a ferromagnetic Curie temperature.

Goodenough, J. B.

2004-11-01

284

Improper ferroelectricity and piezoelectric responses in rhombohedral (A,A')B2O6 perovskite oxides  

NASA Astrophysics Data System (ADS)

High-temperature electronic materials are in constant demand as the required operational range for various industries increases. Here we design (A,A')B2O6 perovskite oxides with [111] "rock salt" A-site cation order and predict them to be potential high-temperature piezoelectric materials. By selecting bulk perovskites which have a tendency towards only out-of-phase BO6 rotations, we avoid possible staggered ferroelectric to paraelectric phase transitions while also retaining noncentrosymmetric crystal structures necessary for ferro- and piezoelectricity. Using density functional theory calculations, we show that (La,Pr)Al2O6 and (Ce,Pr)Al2O6 display spontaneous polarizations in their polar ground state structures; we also compute the dielectric and piezoelectric constants for each phase. Additionally, we predict the critical phase transition temperatures for each material from first-principles to demonstrate that the piezoelectric responses, which are comparable to traditional lead-free piezoelectrics, should persist to high temperature. These features make the rock salt A-site-ordered aluminates candidates for high-temperature sensors, actuators, or other electronic devices.

Young, Joshua; Rondinelli, James M.

2014-05-01

285

Thermophysical properties of perovskite type alkaline-earth metals and plutonium complex oxides  

NASA Astrophysics Data System (ADS)

Polycrystalline specimens of strontium plutonate, SrPuO3, have been prepared by mixing the appropriate amounts of PuO2 and SrCO3 powders followed by reacting and sintering at 1600 K under the flowing gas atmosphere of dry-air. The sintered specimens had a single phase of orthorhombic perovskite structure and were crack-free. The elastic moduli of SrPuO3 were determined from the longitudinal and shear sound velocities. The Debye temperature was also determined from the sound velocities and lattice parameter measurements. The thermal conductivity of SrPuO3 was calculated from the measured density at room temperature, literature values of heat capacity, and thermal diffusivity measured by laser flash method in vacuum. Although the thermal conductivity of SrPuO3 slightly decreased with increasing temperature to 800 K, the range of change was extremely narrow and the temperature dependence did not completely follow the 1/T law. The thermal conductivity of SrPuO3 was lower than those of other perovskite type oxides.

Tanaka, Kosuke; Sato, Isamu; Hirosawa, Takashi; Kurosaki, Ken; Muta, Hiroaki; Yamanaka, Shinsuke

2012-03-01

286

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

287

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

288

Synthesis of transition metal carbonitrides  

DOEpatents

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

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

1994-01-01

289

Transition Metal Dichalcogenides and Their Intercalates  

Microsoft Academic Search

The transition metal dichalcogenides form a group of layered, highly anisotropic compounds which exhibit interesting and unusual physical properties. Compounds formed from the Group Iv, Group V and Group VI transition metals and from sulphur or selenium have been the subject of a great deal of interest in the past few years because of the possibility of introducing foreign species

E. A. Marseglia

1983-01-01

290

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

291

Band offsets in heterojunctions formed by oxides with cubic perovskite structure  

NASA Astrophysics Data System (ADS)

A number of recent discoveries on heterostructures formed by oxides suggest the emergence of a new direction in microelectronics, the oxide electronics. In the present work, band offsets in nine heterojunctions formed by titanates, zirconates, and niobates with the cubic perovskite structure are calculated from first principles. The effect of strain in contacting oxides on their energy structure; the GW corrections to the band edge positions resulting from many-body effects; and the conduction band edge splitting resulting from spinorbit coupling are consistently taken into account. It is shown that the neglect of the many-body effects can cause errors in the determination of the band offsets, reaching 0.36 eV. The fundamental inapplicability of the transitivity rule often used to determine the band offsets in heterojunctions by comparing the band offsets in a pair of heterojunctions formed by the components of the heterojunction under study with a third common component is demonstrated. The cause of the inapplicability is explained.

Lebedev, A. I.

2014-05-01

292

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

293

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

294

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

295

Chemistry of (and on) transition metal clusters: a Fourier transform ion cyclotron resonance study of the reaction of niobium cluster cations with nitric oxide.  

PubMed

The reactions of niobium cluster cations, Nb(+)(n) (n = 2-19), with nitric oxide have been investigated using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR). The overall reaction rate constants are found to be in reasonable agreement with collision rates calculated using the surface charge capture model. The dominant reaction for small clusters (n <9) involves reaction-induced fragmentation resulting in the loss of either NbO or NbN. By contrast, the main reaction observed for the larger clusters (n> 11) is sequential NO chemisorption. Clusters n = 9, 10 exhibit both extremes of behaviour and are the only clusters upon which there is evidence of NO decomposition with N(2) loss observed whenever multiple NO molecules are co-adsorbed. The rate constants for each process have been determined as a function of cluster size. PMID:19423895

Harding, Daniel J; Oliver, Thomas A A; Walsh, Tiffany R; Drewello, Thomas; Woodruff, D Phil; Derrick, Peter J; Mackenzie, Stuart R

2009-01-01

296

Studies on the structural dielectric electrical and thermoelectric properties of some complex perovskite oxides; -.  

E-print Network

??The thesis presents an investigation of dielectric electric and newlinethermoelectric properties of some rare earth substituted barium and strontium newlinebased complex perovskites The synthesis of… (more)

Vimala, R

2014-01-01

297

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

298

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

Microsoft Academic Search

La-Sr-Fe perovskite-type oxides were prepared by the nitrate-citrate method. The basic object of this study is layered Ruddlesden-Popper phase LaSr3Fe3O10. The phase composition and structural properties of the obtained materials are investigated by Mössbauer spectroscopy, X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS) and temperature programmed reduction (TPR). The preliminary catalytic tests show a high potential of these materials for volatile

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

2010-01-01

299

Interfacial properties of semiconducting transition metal chalcogenides  

NASA Astrophysics Data System (ADS)

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

Jaegermann, W.; Tributsch, H.

300

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

301

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

302

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

303

Oxidation state analysis of a four-component redox series [Os(pap)2(Q)]n involving two different non-innocent ligands on a redox-active transition metal.  

PubMed

Complexes [Os(pap)(2)(Q)] (1-4) have been obtained and structurally characterized for pap = 2-phenylazopyridine and Q = 4,6-di-tert-butyl-N-aryl-o-iminobenzoquinone (aryl = phenyl (1), 3,5-dichlorophenyl (2), 3,5-dimethoxyphenyl (3), or 3,5-di-tert-butylphenyl (4)). The oxidized form (3)(ClO(4))(2) was also crystallographically characterized while the odd-electron intermediates [Os(pap)(2)(Q)](+) (1(+)-4(+)) and [Os(pap)(2)(Q)](-) (2(-)) were investigated by electron paramagnetic resonance (EPR) and UV-vis-NIR spectroelectrochemistry in conjunction with density functional theory (DFT) spin density and time-dependent DFT (TD-DFT) calculations. The results from the structural, spectroscopic, and electrochemical experiments and from the computational studies allow for the assignments [Os(II)(pap(0))(2)(Q(0))](2+), [Os(II)(pap(0))(2)(Q(•-))](+), [Os(IV)(pap(•-))(2)(Q(2-))], and [Os(II)(pap(•-))(pap(0))(Q(2-))](-), with comproportionation constants K(c) ? 10(3.5), 10(10), 10(18), and 10(5), respectively. The redox potentials and the comproportionation constants exhibit similarities and differences between Ru and Os analogues. While the Q-based redox reactions show identical potentials, the more metal-involving processes exhibit cathodic shifts for the osmium systems, leading to distinctly different comproportionation constants for some intermediates, especially to a stabilization of the neutral osmium compounds described in this article. The example [Os(pap)(2)(Q)](n) illustrates especially the power of combined structural and EPR analysis with support from DFT towards the valence state description of transition metal complexes incorporating redox non-innocent ligands. PMID:21699145

Das, Dipanwita; Sarkar, Biprajit; Mondal, Tapan Kumar; Mobin, Shaikh M; Fiedler, Jan; Kaim, Wolfgang; Lahiri, Goutam Kumar

2011-08-01

304

Thermomechanical properties of 3d transition metals  

SciTech Connect

The authors have investigated the density variation of the Einstein temperatures and elastic constants of the 3d transition metals. In this respect they have employed the transition metal (TM) pair potentials involving the sp contribution with an appropriate exchange and correlation function, the d-band broadening contribution and the d-band hybridization term. These calculations are aimed at testing the TM pair potentials in generating the quasilocal and local thermomechanical properties.

Karaoglu, B.; Rahman, S.M.M. (Sultan Qaboos Univ., Muscat (Oman). Dept. of Physics)

1994-05-15

305

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

306

Piezoelectric properties of high Curie temperature barium titanate-bismuth perovskite-type oxide system ceramics  

NASA Astrophysics Data System (ADS)

Barium titanate (BaTiO3, BT)—bismuth magnesium titanium oxide [Bi(Mg0.5Ti0.5)O3, BMT] system ceramics were prepared in an ambient atmosphere in order to increase the Curie temperature (Tc) of BT above 132 °C. A single perovskite phase was observed for BT-BMT ceramics with BMT compositions less than 50 mol %, and their relative densities were greater than 94%. Synchrotron measured x-ray diffraction patterns revealed that all the cations in the ceramics were homogeneously distributed. The temperature dependence of the dielectric properties revealed that the BT-BMT system ceramics exhibited relaxorlike characteristics with a dielectric maximum temperature as high as 360 °C for the 0.5BT-0.5BMT ceramic. The apparent piezoelectric constant (d?) was 60 pC/N for the 0.4BT-0.6BMT ceramic. Based upon these results, the BT-BMT system shows potential as a new type of lead-free material for high Tc piezoelectric applications.

Wada, Satoshi; Yamato, Keisuke; Pulpan, Petr; Kumada, Nobuhiro; Lee, Bong-Yeon; Iijima, Takashi; Moriyoshi, Chikako; Kuroiwa, Yoshihiro

2010-11-01

307

High-pressure synthesis, crystal structure and magnetic properties of double perovskite oxide Ba2CuOsO6  

NASA Astrophysics Data System (ADS)

A new compositional double perovskite oxide Ba2CuOsO6 was synthesized under high-pressure (6 GPa) and high-temperature (1500 °C) conditions. The polycrystalline Ba2CuOsO6 was characterized by synchrotron X-ray diffraction, thermogravimetric analysis, and magnetic susceptibility, isothermal magnetization, and specific heat measurements. The oxide crystallizes in a double-perovskite structure with an I4/m space group, in which Os(VI) and Cu(II) are ordered in the perovskite B-site. Ba2CuOsO6 is electrically insulating with an activation energy of 0.813(2) eV and shows antiferromagnetic-like characteristics at temperatures of ~55 K and ~70 K. The results of the first-principle calculation suggested that the spin-orbit interaction of Os(VI) plays a substantial role in the insulating state. The Jahn-Teller distortion of CuO6 octahedra influences the magnetic characteristics with regard to possible two-dimensional magnetic correlations.

Feng, Hai L.; Arai, Masao; Matsushita, Yoshitaka; Tsujimoto, Yoshihiro; Yuan, Yahua; Sathish, Clastin I.; He, Jianfeng; Tanaka, Masahiko; Yamaura, Kazunari

2014-09-01

308

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

309

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

310

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

311

Activation of methane by transition metal-substituted aluminophosphate molecular sieves  

DOEpatents

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

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

1991-01-01

312

Study of Ba3M(II)M(IV)WO9 (M(II) = Ca, Zn; M(IV) = Ti, Zr) perovskite oxides: competition between 3C and 6H perovskite structures.  

PubMed

We describe an investigation of Ba3MIIMIVWO9 oxides for MII = Ca, Zn, and other divalent metals and MIV = Ti, Zr. In general, a 1:2-ordered 6H (hexagonal, P63/mmc) perovskite structure is stabilized at high temperatures (1300 degrees C) for all of the Ba3MIITiWO9 oxides investigated. An intermediate phase possessing a partially ordered 1:1 double perovskite (3C) structure with the cation distribution, Ba2(Zn2/3Ti1/3)(W2/3Ti1/3)O6, is obtained at 1200 degrees C for Ba3ZnTiWO9. Sr substitution for Ba in the latter stabilizes the cubic 3C structure instead of the 6H structure. A metastable Ba3CaZrWO9 that adopts the 3C (cubic, Fmm) structure has also been synthesized by a low-temperature metathesis route. Besides yielding several new perovskite oxides that may be useful as dielectric ceramics, the present investigation provides new insights into the complex interplay of crystal chemistry (tolerance factor) and chemical bonding (anion polarization and d0-induced distortion of metal-oxygen octahedra) in the stabilization of 6H versus 3C perovskite structures for the Ba3MIIMIVWO9 series. PMID:17630730

Mani, Rohini; Selvamani, P; Joy, Joby E; Gopalakrishnan, J; Mandal, Tapas Kumar

2007-08-01

313

Efficacy of the DFT + U formalism for modeling hole polarons in perovskite oxides  

NASA Astrophysics Data System (ADS)

We investigate the formation of self-trapped holes (STH) in three prototypical perovskites (SrTiO3, BaTiO3, PbTiO3) using a combination of density functional theory (DFT) calculations with local potentials and hybrid functionals. First we construct a local correction potential for polaronic configurations in SrTiO3 that is applied via the DFT + U method and matches the forces from hybrid calculations. We then use the DFT + U potential to search the configuration space and locate the lowest energy STH configuration. It is demonstrated that both the DFT + U potential and the hybrid functional yield a piecewise linear dependence of the total energy on the occupation of the STH level, suggesting that self-interaction effects have been properly removed. The DFT + U model is found to be transferable to BaTiO3 and PbTiO3, and STH formation energies from DFT + U and hybrid calculations are in close agreement for all three materials. STH formation is found to be energetically favorable in SrTiO3 and BaTiO3 but not in PbTiO3, which can be rationalized by considering the alignment of the valence band edges on an absolute energy scale. In the case of PbTiO3 the strong coupling between Pb 6s and O 2p states lifts the valence band minimum (VBM) compared to SrTiO3 and BaTiO3. This reduces the separation between VBM and STH level and renders the STH configuration metastable with respect to delocalization (band hole state). We expect that the present approach can be adapted to study STH formation also in oxides with different crystal structures and chemical compositions.

Erhart, Paul; Klein, Andreas; Åberg, Daniel; Sadigh, Babak

2014-07-01

314

Method of boronizing transition metal surfaces  

DOEpatents

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

Koyama, Koichiro; Shimotake, Hiroshi.

1983-08-16

315

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

E-print Network

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

Xu, Xianfan

316

Antiferromagnetism in 4 d transition metals  

SciTech Connect

Total-energy band calculations employing a fixed-spin-moment procedure and the augmented-spherical-wave method are used to study the volume dependences and existence ranges of antiferromagnetic behavior in the 4{ital d} transition metals constrained to cubic lattices. At expanded volumes we find stable antiferromagnetic solutions of the Kohn-Sham equations for bcc niobium, molybdenum, and technetium, and for fcc technetium, and metastable antiferromagnetic solutions for fcc ruthenium. We find no stable antiferromagnetic solutions for fcc rhodium or palladium. Comparisons are made with the occurrence of antiferromagnetism in the 3{ital d} transition metals.

Moruzzi, V.L.; Marcus, P.M. (IBM Research Division, Thomas J. Watson Research Center, Yorktown Heights, NY (USA))

1990-12-01

317

Synthesis, characterization, sintering and dielectric properties of nanostructured perovskite-type oxide, Ba 2 GdSbO 6  

Microsoft Academic Search

Nanoparticles of barium gadolinium antimonate (Ba2GdSbO6), a complex perovskite-type oxide, has been synthesized using an auto ignition combustion process for the first time. The\\u000a nanoparticles thus obtained have been characterized by powder X-ray diffraction, thermogravimetric analysis, differential\\u000a thermal analysis, Fourier transform infrared spectroscopy and transmission electron microscopy. The XRD studies have shown\\u000a that the as-prepared powder is phase pure Ba2GdSbO6

C. Vijayakumar; H. Padma Kumar; Sam Solomon; J. K. Thomas; P. R. S. Warriar; J. Koshy

2008-01-01

318

Double Perovskite Anode Materials Sr2MMoO6 (M = Co, Ni) for Solid-Oxide Fuel Cells  

Microsoft Academic Search

Double-perovskites Sr2MMoO6 (M = Co, Ni) have been investigated as anode materials for a solid oxide fuel cell. At room temperature, both Sr2CoMoO6 and Sr2NiMoO6 are tetragonal (I4\\/m). X-ray absorption spectroscopy confirmed the presence of Co2+\\/Mo6+ and Ni2+\\/Mo6+ pairs in the oxygen-stoichiometric compounds. The samples contain a limited concentration of oxygen vacancies in the reducing atmospheres at an anode. Reoxidation

Yun-Hui Huang; Gan Liang; Mark Croft; M Lehtimaki; Maarit Karppinen; John B. Goodenough

2009-01-01

319

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

320

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

321

TOPICAL REVIEW: The physics of the non-oxide perovskite superconductor MgCNi3  

NASA Astrophysics Data System (ADS)

The present review article discusses the physics of the non-oxide perovskite superconductor MgCNi3 on the basis of theoretical and experimental results available on the material up to July 2004. It was discovered following on from the breakthrough of the finding of the MgB2 superconductor at the beginning of 2001, which has subsequently been intensively studied; however, less attention has been paid to it due to its much lower superconducting transition temperature, Tc ({\\sim }8 K), as compared to that of MgB2 (T_{\\mathrm {c}}\\sim 39 K). But it has many interesting properties which need to be focused on to obtain an understanding of its complicated physics. Energy band calculations show that the density of states (DOS) at the Fermi level, N(EF), is dominated by Ni d states and there is a von Hove singularity in the DOS just below EF (<50-120 meV). It is surprising that the conduction electrons in it are derived from partially filled Ni d states, which typically lead to ferromagnetism in metallic Ni and many Ni-based binary alloys. MgCxNi3 has a simple cubic perovskite structure with space group Pm\\bar {3}m and the lattice parameter a is {\\sim }3.812~{\\AA } for x \\sim 0.97 at ambient temperature and pressure. However, the Ni6(O6) octahedron is locally distorted from those expected in the perfect cubic Pm\\bar {3}m form. The carbon atom of MgCNi3 at the body centre is surrounded by six Ni atoms at the face centred positions and eight Mg atoms at the cube corners. The carriers in it are of electron type in the normal state, although theoretically they were predicted to be of hole type. Tc increases with increase of x in MgCxNi3, but generally decreases with Ni site doping with Co, Fe, Mn, Cu etc. Theoretically, the DOS peak should be greatly reduced by doping at the Mg or Ni site, which accounts for the reduced Tc. The Tc is found to increase with increase of the external pressure (P) at a rate of \\rmd T_{\\mathrm {c}}/\\rmd P\\sim 0.0155~{\\mathrm {K~kbar^{-1}}} , which is the same as that for the intermetallic RNi2B2C (R = rare earth) superconductors but about one order lower than that for MgB2. The Tc(P) result focuses our attention on the feature that N(EF) should increase with pressure due to the broadening of the energy level. Also, a controversial magnetoresistance is reported. It has been observed that the electronic contribution is slightly higher than the lattice one in the normal state thermal conductivity. Specific heat and tunnelling spectroscopic studies indicate that this is an s-wave BCS-type weak/moderate coupling type-II superconductor, but this needs further confirmation as the penetration depth distinctly exhibits a non-s-wave BCS low temperature behaviour which theoretically suggests a d-wave superconductor.

Mollah, S.

2004-11-01

322

Transition metal surfaces under oxygen-rich conditions (abstract only)  

NASA Astrophysics Data System (ADS)

The catalytic oxidation activity of transition metal particles in automobile catalysts is influenced by the superficial oxide phases which form under oxygen-rich reaction conditions. Here we study the thermodynamic stability of ultrathin oxide films on low-index surfaces of transition metals by means of first-principles atomistic thermodynamics calculations based on density functional theory. On Pd(111) a surface oxide with Pd5O4 stoichiometry is stable, which does not correspond to any bulk structure. At the same time, a variety of metastable structures form. On Pd(100) a PdO(101) trilayer is the stable surface oxide. All structures display two-oxygen-coordinated and four-oxygen-coordinated Pd atoms, the difference lying in the spatial arrangement of these basic structural elements. On rhodium surfaces a Rh oxide trilayer forms that corresponds to a bulk oxide structure. On the Pt(111) surface the most stable superficial oxide phase is found to be a thin layer of ?-PtO2, which appears not to be reactive to either methane dissociation or carbon monoxide adsorption. On Pt(100) an ?-PtO2 layer is thermodynamically the most stable, even if Pt3O4 films could grow in a coherent and stress-free manner. Bulk Pt3O4 is found to be thermodynamically stable in a region around 900 K at atmospheric pressure. The enthalpy barrier for the adsorption of CO molecules on oxygen atoms of this surface is as low as 0.34 eV, and desorption of CO2 is observed in molecular dynamics simulations to occur without any appreciable energy barrier.

Seriani, Nicola

2008-02-01

323

New intercalation compounds of transition metal dichalcogenides  

Microsoft Academic Search

In this paper we describe the preparation and characterization of ethylenediamine-intercalated 6R-TaS2 and octylamine-intercalated 2H-TaS2. We also describe attempts to intercalate various electron acceptor species into transition metal dichalcogenides.

E. Figueroa; J. W. Brill; J. P. Selegue

1996-01-01

324

Structure, Bonding, and Catalytic Activity of Monodisperse, Transition-Metal-Substituted CeO2 Nanoparticles.  

PubMed

We present a simple and generalizable synthetic route toward phase-pure, monodisperse transition-metal-substituted ceria nanoparticles (M0.1Ce0.9O2-x, M = Mn, Fe, Co, Ni, Cu). The solution-based pyrolysis of a series of heterobimetallic Schiff base complexes ensures a rigorous control of the size, morphology and composition of 3 nm M0.1Ce0.9O2-x crystallites for CO oxidation catalysis and other applications. X-ray absorption spectroscopy confirms the dispersion of aliovalent (M(3+) and M(2+)) transition metal ions into the ceria matrix without the formation of any bulk transition metal oxide phases, while steady-state CO oxidation catalysis reveals an order of magnitude increase in catalytic activity with copper substitution. Density functional calculations of model slabs of these compounds confirm the stabilization of M(3+) and M(2+) in the lattice of CeO2. These results highlight the role of the host CeO2 lattice in stabilizing high oxidation states of aliovalent transition metal dopants that ordinarily would be intractable, such as Cu(3+), as well as demonstrating a rational approach to catalyst design. The current work demonstrates, for the first time, a generalizable approach for the preparation of transition-metal-substituted CeO2 for a broad range of transition metals with unparalleled synthetic control and illustrates that Cu(3+) is implicated in the mechanism for CO oxidation on CuO-CeO2 catalysts. PMID:25406101

Elias, Joseph S; Risch, Marcel; Giordano, Livia; Mansour, Azzam N; Shao-Horn, Yang

2014-12-10

325

PARTICLE SIZE AND MORPHOLOGY CONTROL OF PEROVSKITE OXIDE NANOPOWDERS FOR NANOSTRUCTURED MATERIALS  

Microsoft Academic Search

Due to the high permittivity and low losses, ferroelectric ceramics with perovskite structure are largely used in the electronics industry for many applications. Presently, miniaturization of the components is one of the main goal in the field of microelectronics and communication. Accordingly, the current trend in high-tech ceramics is to realize sintered bodies with grain size below a few hundred

A. BASSANO; M. T. BUSCAGLIA; V. BUSCAGLIA; P. NANNI

2009-01-01

326

Polymer nanocomposites based on transition metal ion modified organoclays  

E-print Network

Polymer nanocomposites based on transition metal ion modified organoclays Pranav Nawani a , Priya: Transition metal ion; Organoclay; Nanocomposite 1. Introduction Thermoplastic nanocomposites with improved; accepted 4 December 2006 Available online 3 January 2007 Abstract A unique class of nanocomposites

Frenkel, Anatoly

327

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

328

(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

329

Studies of the oxygen and oxide redox chemistry at lanthanum-strontium-M oxide (M = chromium to cobalt) perovskite-like electrode materials for solid oxide fuel cells  

NASA Astrophysics Data System (ADS)

The O2 reduction reaction (ORR) is commonly the greatest source of internal resistance in solid oxide fuel cells (SOFC). SOFC operate at 600 to 1000°C, depending on the choice of cathode and solid electrolyte materials. Standard cathode materials are Sr doped LaMnO3+/-delta perovskite-like oxides (La1-xSrxMnO3+/-delta), the solid electrolyte is Y2O3 stabilized ZrO2, and the anode material is Ni. In this work, the ORR, the O2 evolution reaction (OER) and the equilibrium O2 redox reactions were examined using Sr doped La1-xSrxMO3+/-delta (M = Cr, Mn, Fe, Co) perovskite-like cathode materials. The role of the solid electrolyte was studied using both YSZ and Gd2O3 doped Ceria (GDC). Three electrode half cell techniques were conducted at 500 to 900°C in both air and N2, to quantify the area specific polarization resistance (ASRp) of the O2 redox reaction, as well as the electrochemical capacitance (C). The study of the La1-xSrxMnO3+/-delta oxides (xSr = 0, 0.2 and 0.5) on both YSZ and GDC revealed that the O2 redox ASRp decreased with increasing x Sr, and that the ORR and OER rates at a given xSr, were higher on GDC versus YSZ. The study of the La1-xSrxMO 3-delta (M = Fe, Co) oxides (xSr = 0, 0.2, 0.4, and 0.6) on GDC showed that the O2 redox ASRp decreased by ˜100x and that the electrochemical capacitance increased by ˜10,000x as x Sr was varied from 0 to 0.6. Thermogravimetric analysis (TGA) in air revealed that the propensity of these oxides to lose mass (i.e., reduce) at higher temperatures, also increased with xSr. The study of the La1-xSrxCoO3-delta (xSr = 0.6, 0.8 and 1) and the xSr = 1 SrCo1-yFeyO 3-delta oxides on GDC, revealed non-ideal electrochemical behaviour that was attributed to solid state defect ordering processes. The applicability of non-ideal transition state theory was demonstrated through (i) the nonstationary O2 redox rates at the La1-x SrxMnO3+/-delta oxides, (ii) transfer coefficient analysis of the OER and ORR, and (iii) the non-ideal Arrhenius behaviour of the O2 redox rates and oxide capacitance at the La1-xSr xCoO3-delta (xSr = 0.6, 0.8, 1) and xSr = 1 SrCo1-yFeyO3-delta oxides.

Fournier, Joseph Lawrence

330

Electronic properties of intercalation complexes of the transition metal dichalcogenides  

Microsoft Academic Search

Intercalation of the layer type transition metal dichalcogenides by a variety of organic molecules, alkali metals, or `3d' transition metals, provides a powerful way to finely tune the electron occupation of the relatively narrow `d' bands met in these solids. These transition metal dichalcogenides are highly anisotropic solids, sometimes referred to as `two-dimensional' solids, and the intercalant molecules which are

R. H. Friend; A. D. Yoffe

1987-01-01

331

Electronic properties of intercalation complexes of the transition metal dichalcogenides  

Microsoft Academic Search

Intercalation of the layer type transition metal dichalcogenides by a variety of organic molecules, alkali metals, or ‘3d’ transition metals, provides a powerful way to finely tune the electron occupation of the relatively narrow ‘d’ bands met in these solids. These transition metal dichalcogenides are highly anisotropic solids, sometimes referred to as ‘two-dimensional’ solids, and the intercalant molecules which are

R. H. Friend; A. D. Yoffe

1987-01-01

332

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

333

Transition metal dichalcogenide\\/polymer nanocomposites  

Microsoft Academic Search

Single molecular layers of transition metal dichalcogenides (TMDs) such as MoS2, MoSe2 and WS2, have been formed in suspension in water by lithium intercalation of crystalline powders and then exfoliation in water. The two-dimensionality of such systems is readily identified using powder X-ray diffraction, where the strong asymmetric shape of the (hk0) peaks and the absence of (00?) peaks and

D. Yang; P. Westreich; R. F. Frindt

1999-01-01

334

Surface resonances at transition metal dichalcogenide heterostructures  

Microsoft Academic Search

Layered transition metal dichalcogenides do generally not exhibit characteristic electronic surface states localized perpendicular to the layers. Employing van der Waals epitaxy together with angle-resolved photoemission spectroscopy we show how surface-layer-derived electronic states can be generated on these materials. For a heterojunction consisting of one HfS2 epilayer adsorbed on bulk WSe2, purely two-dimensional behavior as well as three-dimensional coupling of

C. Kreis; S. Werth; R. Adelung; L. Kipp; M. Skibowski; D. Voß; P. Krüger; A. Mazur; J. Pollmann

2002-01-01

335

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

336

Effect of Transition Metal Impurities on Superconductivity  

Microsoft Academic Search

The existing experimental results on the effect of transition metal impurities on superconductivity in several alloy systems were compared with theories based on two different models, the Anderson model and the s-d model. It was found that the theory of Müller-Hartmann and Zittartz (s-d model) reproduces the experimental results in Kondo alloys with TK\\/Tco≲1 fairly well if TK of the

Shigeru Takayanagi; Tadashi Sugawara

1975-01-01

337

Perovskite-type oxides for high-temperature oxygen separation membranes  

Microsoft Academic Search

Oxygen permeation through dense ceramic membranes of perovskite-like SrCo0.9?xFe0.1CrxO3?? (x=0.01–0.05), Sr1?x?yLnxCoO3??(Ln=La, Nd, Sm, Gd; x=0.30–0.35; y=0–0.10), SrCo1?xTixO3?? (x=0.05–0.20) and LaM1?xNixO3?? (M=Ga, Co, Fe; x=0–0.6) was studied. The SrCoO3??-based solid solutions with cubic perovskite structure were found to exhibit highest permeation fluxes compared to other membranes. However, high thermal expansion coefficients and interaction with gas species such as carbon dioxide may

V. V Kharton; A. A Yaremchenko; A. V Kovalevsky; A. P Viskup; E. N Naumovich; P. F Kerko

1999-01-01

338

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

339

Synthesis and X-ray characterization of 3D transition metal intercalates of transition metal dichalcogenides and their superlattices  

Microsoft Academic Search

New superlattices of 3d transition metal intercalates of transition metal dichalcogenides have been synthesized by deposition and annealing of layered reactants. Sheets of atoms are the building blocks of transition metal dichalcogenides. Since the inter-sheet bonding is weak, guest atoms may be introduced between the sheets (intercalation) and sheets of differing atomic species may be stacked one atop the other

Thomas Abbott Hughes

1998-01-01

340

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

341

Highly stereoselective epoxidation of (?)-?-pinene over chiral transition metal (salen) complexes occluded in zeolitic hosts  

Microsoft Academic Search

Various transition metal complexes of seven different salen ligands have been incorporated in specially modified zeolitic host materials. The thus immobilized sterically demanding complexes have been tested in the diastereoselective epoxidation of (-)-a-pinene in the liquid phase in an autoclave at room temperature and elevated pressure using O2 as oxidant. In most cases conversions of 100% could be achieved. Best

Carmen Schuster; Eugen Möllmann; Andras Tompos; Wolfgang F. Hölderich

2001-01-01

342

First-principles calculations of the dielectric properties of perovskite-type materials  

Microsoft Academic Search

We compare first-principles (FP) calculations of the ionic effective charges, phonon frequencies, and static dielectric permittivities ?s of several perovskite-type materials. Transition metal ions have anomalously large effective charges, though in the double perovskite CaAl1\\/2Nb1\\/2O3 (CAN), the effective charge of Nb is significantly lower than in the simple perovskite KNbO3, showing different Nb–O bonding chemistry. Tolerance factors, cation chemistry, and

2003-01-01

343

Rational design of mixed ionic and electronic conducting perovskite oxides for solid oxide fuel cell anode materials: A case study for doped SrTiO3  

NASA Astrophysics Data System (ADS)

The effect of p- and n-type dopants on ionic and electronic conductivity of SrTiO3 based perovskites were investigated both computationally and experimentally. Specifically, we performed density functional theory (DFT) calculations of Na- and La-doped SrTiO3 and Na- and Nb-doped SrTiO3 systems. Constrained ab initio thermodynamic calculations were used to evaluate the phase stability and reducibility of doped SrTiO3 under both oxidizing and reducing synthesis conditions, as well as under anodic solid oxide fuel cell (SOFC) conditions. The density of states (DOS) of these materials was analyzed to study the effects of p- and n-doping on the electronic conductivity. Furthermore, Na- and La-doped SrTiO3 and Na- and Nb-doped SrTiO3 samples were experimentally prepared and the conductivity was measured to confirm our computational predictions. The experimental observations are in very good agreement with the theoretical predictions that doping n-doped SrTiO3 with small amounts of p-type dopants promotes both the ionic and electronic conductivity of the material. This doping strategy is valid independent of p- and n-doping site and permits the synthesis of perovskite based mixed ionic/electronic conductors.

Suthirakun, Suwit; Xiao, Guoliang; Ammal, Salai Cheettu; Chen, Fanglin; zur Loye, Hans-Conrad; Heyden, Andreas

2014-01-01

344

Perovskite oxide nanosheets with tunable band-edge potentials and high photocatalytic hydrogen-evolution activity.  

PubMed

Perovskite nanosheets of HCa2-x Srx Nb3 O10 and HCa2 Nb3-y Tay O10 with controlled band-edge potentials were prepared. They worked as highly efficient heterogeneous photocatalysts for H2 evolution from a water/methanol mixture under band-gap irradiation. The activity was found to depend on the composition. The highest activity was obtained with HCa2 Nb2 TaO10 nanosheets, recording an apparent quantum yield of approximately 80?% at 300?nm, which is the highest value for a nanosheet-based photocatalyst reported to date. PMID:25258214

Maeda, Kazuhiko; Eguchi, Miharu; Oshima, Takayoshi

2014-11-24

345

Protons in perovskite nitrides and oxide nitrides: A first principles study of ThTaN3 and SrTaO2N  

NASA Astrophysics Data System (ADS)

Nitrides and oxide nitrides are evaluated as a new class of proton conducting ceramics by first principles defect calculations on SrTaO2N and ThTaN3 perovskites. The level of proton incorporation is obtained from the thermodynamics of dissociative absorption of water and ammonia into anion vacancies in the acceptor doped materials. Protons are found to be significantly more stable associated with the nitride ions than the oxide ions in SrTaO2N and the proton position and bond length to the anions in both materials are mostly very similar to those in corresponding perovskite oxides such as SrZrO3. In comparison to SrZrO3, the concentration of protons is significantly lower in ThTaN3 and SrTaO2N.

Polfus, Jonathan M.; Haugsrud, Reidar

2012-10-01

346

Structure-property relationships of new bismuth and lead oxide based perovskite ternary solid solutions  

NASA Astrophysics Data System (ADS)

Two new bismuth and lead oxide based perovskite ternary solid solutions, namely xBi(Zn1/2Ti1/2)O3-yPbZrO3-zPbTiO3 [xBZT-yPZ-zPT] and xBi(Mg1/2Ti1/2)O3-yBi(Zn 1/2Ti1/2)O3-zPbTiO3 [xBMT-yBZT-zPT] have been developed and their structural and electrical properties have been determined. Various characterization techniques such as X-ray diffraction, calorimetery, electron microscopy, dielectric and piezoelectric measurements have been performed to determine the details of the phase diagram, crystal structure, and domain structure. The selection of these materials is based on the hypothesis that the presence of BZT-PT (Case I ferroelectric (FE)) will increase the transition temperature of MPB systems BMT-PT (Case II FE), and PZ-PT (Case III FE), and subsequently a MPB will be observed in the ternary phase diagrams. The Case I, II, and III classification has been outlined by Stringer et al., is on the basis of the transition temperatures (TC) behavior with composition in the Bi and Pb oxide based binary systems. Several pseudobinary lines have been investigated across the xBZT-yPZ-zPT ternary phase diagram which exhibit varied TC behavior with composition, showing both Case I- and Case III-like TC trends in different regions. A MPB between rhombohedral to tetragonal phases has been located on a pseudobinary line 0.1BZT-0.9[xPT-(1-x)PZ]. Compositions near MPB exhibit mainly soft PZT-like properties with the TC around 60°C lower than the unmodified PZT near its MPB. Electrical properties are reported for the MPB composition, TC = 325°C, Pr = 35 microC/cm2, d33 = 300 pC/N and kP =0.45. Rhombohedral compositions show diffuse phase transition with small frequency dispersion, similar to relaxors. Two transition peaks in the permittivity as well as in the latent heat has been observed in some compositions near the BZT-PT binary. This leads to the speculation for the existence of miscibility gap in the solid solutions in these regions. Transmission electron microscopy (TEM) performed on these compositions show subdomain modulation contrast suggesting the presence of localized and correlated spatial fluctuations in the spontaneous strain. In the xBMT-yBZT-zPT system, very small rhombohedral region in the room temperature phase diagram has been observed. Owing to the limited solid solubility, only a part of the phase diagram could be explored. Compositions on pseudobinary xPT-(1-x)[0.9BMT-0.1BZT] has been successfully fabricated and characterized. High c/a ratio of 1.04 has been observed for a surprisingly low tolerance factor of 0.9732. Transition temperature trends have been established from DSC and dielectric data along this pseudobinary line. The following trend in the TC has been observed with the increase in non PT end member that has been divided into three zones: in Zone I TC increases, in Zone II it decreases, and in the Zone III, two transition temperatures are observed. From the TEM investigation, it has been noted that these compositions exhibit subdomain modulations which reflects the presence of spontaneous strain. These modulations increase with the increase in non PT end member, and at certain composition along pseudobinary, both macro and micro domains structure can be observed. Compositions in the rhombohedral phase of xBMT-yBZT-zPT show dramatic changes in dielectric and piezoelectric properties when quenched from high temperature. Samples quenched from temperature range 650°C-900°C show classical ferroelectric switching behavior, which is not observed on either side of this temperature range. These quenched states are however, unstable in nature and lose their ferroelectric properties when heated to a temperature as low as 400°C. Structural analysis by TEM shows varied domain structures for samples quenched from different temperatures. Evidences of tilt transitions and intermediate phases have also been observed in the TEM study. New insights into solid solution development and defect metastability are gained and discussed in relation to relaxor based ferroelectric phenomena. Complex domains and intermediate displ

Dwivedi, Akansha

347

A novel perovskite based catalyst with high selectivity and activity for partial oxidation of methane for fuel cell applications.  

PubMed

Solid oxide fuel cells (SOFCs) have the potential to revolutionise the present fuel economy due to their higher fuel conversion efficiency compared with standard heat engines and the possibility of utilizing the heat produced in a combined heat and power system. One of the reasons they have yet to fulfil this potential is that the conventional anode material of choice, a nickel/yttria-stabilised zirconia cermet, requires a high temperature production process and under operating conditions is susceptible to carbon and sulphur poisoning. Perovskite-based materials have been proposed as potential anode materials for SOFCs due to their potentially high electronic conductivity and catalytic properties. One of the problems in realizing this potential has been their low catalytic activity towards methane reforming compared to conventional nickel based cermet materials. A nickel doped strontium zirconate material produced by low temperature hydrothermal synthesis is described which has high activity for methane reforming and high selectivity towards partial oxidation of methane as opposed to total oxidation products. Initial studies show a very low level of carbon formation which does not increase over time. PMID:25069597

Staniforth, J; Evans, S E; Good, O J; Darton, R J; Ormerod, R M

2014-10-28

348

Multivariate data analysis approach to understand magnetic properties of perovskite manganese oxides  

SciTech Connect

Here we apply statistical multivariate data analysis techniques to obtain some insights into the complex structure-property relations in antiferromagnetic (AFM) and ferromagnetic (FM) manganese perovskite systems, AMnO{sub 3}. The 131 samples included in the present analyses are described by 21 crystal-structure or crystal-chemical (CS/CC) parameters. Principal component analysis (PCA), carried out separately for the AFM and FM compounds, is used to model and evaluate the various relationships among the magnetic properties and the various CS/CC parameters. Moreover, for the AFM compounds, PLS (partial least squares projections to latent structures) analysis is performed so as to predict the magnitude of the Neel temperature on the bases of the CS/CC parameters. Finally, so-called PLS-DA (PLS discriminant analysis) method is employed to find out the most influential/characteristic CS/CC parameters that differentiate the two classes of compounds from each other. - Graphical abstract: Statistical multivariate data analysis techniques are applied to detect structure-property relations in antiferromagnetic (AFM) and ferromagnetic (FM) manganese perovskites. For AFM compounds, partial least squares projections to latent structures analysis predict the magnitude of the Neel temperature on the bases of structural parameters only. Moreover, AFM and FM compounds are well separated by means of so-called partial least squares discriminant analysis method.

Imamura, N. [Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503 (Japan); Laboratory of Inorganic Chemistry, Department of Chemistry, Helsinki University of Technology, FI-02015 TKK (Finland); Mizoguchi, T. [Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503 (Japan); Yamauchi, H. [Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503 (Japan); Laboratory of Inorganic Chemistry, Department of Chemistry, Helsinki University of Technology, FI-02015 TKK (Finland); Karppinen, M. [Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503 (Japan); Laboratory of Inorganic Chemistry, Department of Chemistry, Helsinki University of Technology, FI-02015 TKK (Finland)], E-mail: maarit.karppinen@tkk.fi

2008-05-15

349

Magnetic Properties and Electronic Structure in Transition Metal Doped La0.5Ca0.5MnO3  

Microsoft Academic Search

The magnetic properties of La0.5Ca0.5Mn0.98TM0.02O3 (TM = Cr, Ti) perovskites were studied by using the temperature dependences of magnetization and coercive field. The transition-metal doping like La0.5Ca0.5Mn1-yTMyO3 (TM = transition metal) can alter the Mn^3+ \\/Mn^4+ratio, and lead to significant modifications in the magnetic properties. The observed reductions of Curie temperature and magnetization are interpreted with the calculated ratio of

K. K. Yu; S. J. Jun; J. S. Park; J. Y. Kim; Y. P. Lee; K. H. Han; Y. S. Lee; J.-H. Kang

2006-01-01

350

Tetrathiafulvalene-annulated phenanthroline and its complexes with transition metals  

NASA Astrophysics Data System (ADS)

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

Keniley, Lawrence Keith, Jr.

351

Two-dimensional transition metal carbides.  

PubMed

Herein we report on the synthesis of two-dimensional transition metal carbides and carbonitrides by immersing select MAX phase powders in hydrofluoric acid, HF. The MAX phases represent a large (>60 members) family of ternary, layered, machinable transition metal carbides, nitrides, and carbonitrides. Herein we present evidence for the exfoliation of the following MAX phases: Ti(2)AlC, Ta(4)AlC(3), (Ti(0.5),Nb(0.5))(2)AlC, (V(0.5),Cr(0.5))(3)AlC(2), and Ti(3)AlCN by the simple immersion of their powders, at room temperature, in HF of varying concentrations for times varying between 10 and 72 h followed by sonication. The removal of the "A" group layer from the MAX phases results in 2-D layers that we are labeling MXenes to denote the loss of the A element and emphasize their structural similarities with graphene. The sheet resistances of the MXenes were found to be comparable to multilayer graphene. Contact angle measurements with water on pressed MXene surfaces showed hydrophilic behavior. PMID:22279971

Naguib, Michael; Mashtalir, Olha; Carle, Joshua; Presser, Volker; Lu, Jun; Hultman, Lars; Gogotsi, Yury; Barsoum, Michel W

2012-02-28

352

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

353

Bonding and phase transitions in transition metal dichalcogenide layer compounds  

Microsoft Academic Search

The electronic structure of the transition metal dichalcogenide layer compounds is studied using hybridised orbitals appropriate to the transition metal atom coordination. Non-bonding orbitals on the transition metal atoms give the conduction electron bands which are responsible for the charge-density-wave phase transitions in the VB compounds, and the band structure of 1T- and 2H-TaS2 is found using tight binding. The

J. E. Inglesfield

1980-01-01

354

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

355

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

SciTech Connect

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

Wu, Qiang; Sadakane, Masahiro; Ogihara, Hitoshi [Catalysis Research Center, Hokkaido University, N21-W10 Kita-ku, Sapporo 001-0021 (Japan)] [Catalysis Research Center, Hokkaido University, N21-W10 Kita-ku, Sapporo 001-0021 (Japan); Ueda, Wataru, E-mail: Ueda@cat.hokudai.ac.jp [Catalysis Research Center, Hokkaido University, N21-W10 Kita-ku, Sapporo 001-0021 (Japan)] [Catalysis Research Center, Hokkaido University, N21-W10 Kita-ku, Sapporo 001-0021 (Japan)

2010-09-15

356

Nickel oxide electrode interlayer in CH3 NH3 PbI3 perovskite/PCBM planar-heterojunction hybrid solar cells.  

PubMed

This study successfully demonstrates the application of inorganic p-type nickel oxide (NiOx ) as electrode interlayer for the fabrication of NiOx /CH3 NH3 PbI3 perovskite/PCBM PHJ hybrid solar cells with a respectable solar-to-electrical PCE of 7.8%. The better energy level alignment and improved wetting of the NiOx electrode interlayer significantly enhance the overall photovoltaic performance. PMID:24687334

Jeng, Jun-Yuan; Chen, Kuo-Cheng; Chiang, Tsung-Yu; Lin, Pei-Ying; Tsai, Tzung-Da; Chang, Yun-Chorng; Guo, Tzung-Fang; Chen, Peter; Wen, Ten-Chin; Hsu, Yao-Jane

2014-06-25

357

Oxygen-deficient perovskites: linking structure, energetics and ion transport.  

PubMed

The present review focuses on links between structure, energetics and ion transport in oxygen-deficient perovskite oxides, ABO(3-delta). The perfect long-range order, convenient for interpretations of the structure and properties of ordered materials, is evidently not present in disordered materials and highly defective perovskite oxides are spatially inhomogeneous on an intermediate length scale. Although this makes a fundamental description of these and other disordered materials very difficult, it is becoming increasingly clear that this complexity is often essential for the functional properties. In the present review we advocate a potential energy barrier description of the disordered state in which the possible local (or inherent) structures are seen to correspond to separate local minima on the potential energy surface. We interpret the average structure observed experimentally at any temperature as a time and spatial average of the different local structures which are energetically accessible. The local structure is largely affected by preferences for certain polyhedron coordinations and the oxidation state stability of the transition metals, and the strong long-range electrostatic interactions present in non-stoichiometric oxides imply that only a small fraction of the local energy minima on the potential energy surface are accessible at most temperatures. We will show that models neglecting the spatial inhomogeneity and thus the local structure serve as useful empirical tools for particular purposes, e.g. for understanding the main features of the complex redox properties that are so crucial for many applications of these oxides. The short-range order is on the other hand central for understanding ionic transport. Oxide ion transport involves the transformation of one energetically accessible local structure into another. Thus, strongly correlated transport mechanisms are expected; in addition to the movement of the oxygen ions giving rise to the transport, other ions are involved and even the A and B atoms move appreciably in a cooperative fashion along the transition path. Such strongly correlated or collective ionic migration mechanisms should be considered for fast oxide ion conductors in general and in particular for systems forming superstructures at low temperatures. Structural criteria for fast ion conduction are discussed. A high density of low-lying local energy minima is certainly a prerequisite and for perovskite-related A(2)B(2)O(5) oxides, those containing B atoms that have energetic preference for tetrahedral coordination geometry are especially promising. PMID:16482285

Stølen, Svein; Bakken, Egil; Mohn, Chris E

2006-01-28

358

Transition-metal-ion-mediated polymerization of dopamine: mussel-inspired approach for the facile synthesis of robust transition-metal nanoparticle-graphene hybrids.  

PubMed

Inspired by the high transition-metal-ion content in mussel glues, and the cross-linking and mechanical reinforcement effects of some transition-metal ions in mussel threads, high concentrations of nickel(II), cobalt(II), and manganese(II) ions have been purposely introduced into the reaction system for dopamine polymerization. Kinetics studies were conducted for the Ni(2+)-dopamine system to investigate the polymerization mechanism. The results show that the Ni(2+) ions could accelerate the assembly of dopamine oligomers in the polymerization process. Spectroscopic and electron microscopic studies reveal that the Ni(2+) ions are chelated with polydopamine (PDA) units, forming homogeneous Ni(2+)-PDA complexes. This facile one-pot approach is utilized to construct transition-metal-ion-PDA complex thin coatings on graphene oxide, which can be carbonized to produce robust hybrid nanosheets with well-dispersed metallic nickel/metallic cobalt/manganese(II) oxide nanoparticles embedded in PDA-derived thin graphitic carbon layers. The nickel-graphene hybrid prepared by using this approach shows good catalytic properties and recyclability for the reduction of p-nitrophenol. PMID:24862644

Yang, Liping; Kong, Junhua; Zhou, Dan; Ang, Jia Ming; Phua, Si Lei; Yee, Wu Aik; Liu, Hai; Huang, Yizhong; Lu, Xuehong

2014-06-16

359

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

NASA Astrophysics Data System (ADS)

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

Childs, Nicholas Brule

360

Aspects of the formation and mobility of protonic charge carriers and the stability of perovskite-type oxides  

Microsoft Academic Search

Proton conducting acceptor-doped perovskite-type alkaline earth cerates, zirconates, niobates and titanates have been investigated experimentally and by numerical simulations. For all cubic perovskites the concentration of protonic defects almost reaches the acceptor dopant concentration under appropriate conditions, and the mobility of protonic defects fall into a narrow range. Any symmetry reduction, however, leads to a reduction of the concentration and

K. D Kreuer

1999-01-01

361

Electrochemical studies of perovskite mixed conductors  

Microsoft Academic Search

Research into the growth of high-quality single crystal thin films of high transition temperature {Tc} superconductors have stimulated interest in other perovskite metal oxides with a variety of physical properties. Thin films of perovskite materials are among the major focal research areas for optical, sensor, electronic, and superconducting applications. Two lanthanum-based oxygen\\/electronic conducting perovskite oxides of particular interest for high

E. L. Brosha; B. W. Chung; F. H. Garzon

1994-01-01

362

p-i-n Heterojunctions with BiFeO3 Perovskite Nanoparticles and p- and n-Type Oxides: Photovoltaic Properties.  

PubMed

We formed p-i-n heterojunctions based on a thin film of BiFeO3 nanoparticles. The perovskite acting as an intrinsic semiconductor was sandwiched between a p-type and an n-type oxide semiconductor as hole- and electron-collecting layer, respectively, making the heterojunction act as an all-inorganic oxide p-i-n device. We have characterized the perovskite and carrier collecting materials, such as NiO and MoO3 nanoparticles as p-type materials and ZnO nanoparticles as the n-type material, with scanning tunneling spectroscopy; from the spectrum of the density of states, we could locate the band edges to infer the nature of the active semiconductor materials. The energy level diagram of p-i-n heterojunctions showed that type-II band alignment formed at the p-i and i-n interfaces, favoring carrier separation at both of them. We have compared the photovoltaic properties of the perovskite in p-i-n heterojunctions and also in p-i and i-n junctions. From current-voltage characteristics and impedance spectroscopy, we have observed that two depletion regions were formed at the p-i and i-n interfaces of a p-i-n heterojunction. The two depletion regions operative at p-i-n heterojunctions have yielded better photovoltaic properties as compared to devices having one depletion region in the p-i or the i-n junction. The results evidenced photovoltaic devices based on all-inorganic oxide, nontoxic, and perovskite materials. PMID:25350523

Chatterjee, Soumyo; Bera, Abhijit; Pal, Amlan J

2014-11-26

363

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

364

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

PubMed Central

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

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

2014-01-01

365

Characterization of electrically conductive transition metal dichalcogenide lubricant films  

Microsoft Academic Search

Groups VB and VIB transition metal dichalcogenides with layered structures, are intrinsic solid lubricants, and constitute a class of materials with unique and unusual properties based on their extreme anisotropy. The primary objective of this investigation was to conduct a comprehensive study on the tribological and electrical properties of burnished and sputtered transition metal dichalcogenide films, and characterize the performance

Harish C. Waghray

1997-01-01

366

Trends in Ionization Energy of Transition-Metal Elements  

ERIC Educational Resources Information Center

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

Matsumoto, Paul S.

2005-01-01

367

SmBaCo 2O 5+ x double-perovskite structure cathode material for intermediate-temperature solid-oxide fuel cells  

Microsoft Academic Search

SmBaCo2O5+x (SBCO), an oxide with double-perovskite structure, has been developed as a novel cathode material for intermediate-temperature solid-oxide fuel cells (IT-SOFCs). The electrical conductivity of an SBCO sample reaches 815–434Scm?1 in the temperature range 500–800°C. XRD results show that an SBCO cathode is chemically compatible with the intermediate-temperature electrolyte materials Sm0.2Ce0.8O1.9 (SDC) and La0.9Sr0.1Ga0.8Mg0.2O3?? (LSGM). The polarization resistances of an

Qingjun Zhou; Tianmin He; Yuan Ji

2008-01-01

368

"True" negative thermal expansion in Mn-doped LaCu3Fe4O12 perovskite oxides  

NASA Astrophysics Data System (ADS)

Negative and zero thermal expansion near room temperature have been achieved in a cubic A-site ordered perovskite oxide LaCu3Fe4-xMnxO12. A discontinuous volume change in the parent material LaCu3Fe4O12, owing to a first-order intermetallic charge transfer transition (3Cu2+ + 4Fe3.75+ ? 3Cu3+ + 4Fe3+), is efficiently relaxed to a second-order-type negative thermal expansion with a linear thermal expansion coefficient (?L) of -2.2(1) × 10-5 K-1 between 300 and 340 K at x = 0.75, followed by an almost zero thermal expansion [?L of -1.1(2) × 10-6 K-1] at x = 1 in a wide temperature range (240-360 K) including room temperature. Magnetic susceptibility measurements display substantial broadenings of the antiferromagnetic transition when x increases, supporting the relaxation of first-order electronic phase transition of the parent material. These findings indicate that the significant adjustability of thermal expansion properties can be achieved in first-order intermetallic charge-transfer transition.

Yamada, Ikuya; Marukawa, Shohei; Murakami, Makoto; Mori, Shigeo

2014-12-01

369

Redox potential trend with transition metal elements in lithium-ion battery cathode materials  

NASA Astrophysics Data System (ADS)

First-principles calculations are performed to investigate the relationship between the intrinsic voltage and element-lattice for the popular transition metal oxides and polyoxyanionic compounds as cathode materials for lithium-ion batteries. A V-shape redox potential in olivine phosphates LiMPO4 and orthogonal silicates Li2MSiO4 (M=Mn, Fe, Co, Ni), and an N-shape one in layered oxides LiMO2 (M=Mn, Fe, Co, Ni, Cu) relative to transition metal M elements are found to be inversely characteristic of electronic energy contribution, which costs energy in the lithiation process and is defined as electron affinity. The maxima of electron affinity, locating at different elements for different types of crystal lattices are determined by delectronic configurations that cross the turning point of a full occupancy of electronic bands, which is determined by the cooperative effect of crystal field splitting and intraionic exchange interactions.

Chen, Zhenlian; Li, Jun

2013-03-01

370

Mixed Metal Oxides with the Structure of Perovskite for Anticorrosion Organic Coatings  

NASA Astrophysics Data System (ADS)

Mixed metal oxides pigments of TiO2.ZnO, 2TiO2.ZnO, Zn2TiO4, MgTiO3, CaTiO3, TiO2.ZnO.MgO, and TiO2.ZnO.SrO were synthesized from corresponding oxides or carbonates at high temperature. The obtained metal mixed oxides were characterized by means of X-fray diffraction analysis, measurement of particle sizes and scanning electron microscopy. The synthesized metal mixed oxides were used to produce epoxy-ester coatings with PVC = 10% for a synthesized pigment. The coatings were tested for physical-mechanical properties and in corrosion atmospheres. The results of corrosion tests were compared with standard alumino zinc phosphomolybdate.

Kantorová, M.; Veselý, D.

371

Ferromagnetism and possible application in spintronics of transition-metal-doped ZnO films  

Microsoft Academic Search

This review article first presents a summary of current understanding of the magnetic properties and intrinsic ferromagnetism of transition-metal (TM)-doped ZnO films, which are typical diluted magnetic oxides used in spintronics. The local structure and magnetic behavior of TM-doped ZnO are strongly sensitive to the preparation parameters. In the second part, we discuss in detail the effects of doping elements

F. Pan; C. Song; X. J. Liu; Y. C. Yang; F. Zeng

2008-01-01

372

Transition Metal Phosphide Hydroprocessing Catalysts: A review  

SciTech Connect

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

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

2009-01-01

373

Tunable dielectric properties of transition metal dichalcogenides.  

PubMed

Since discovery of graphene, layered materials have drawn considerable attention because of their possible exfoliation into single and multilayer 2D sheets. Because of strong surface effects, the properties of these materials vary drastically with the number of layers in a sheet. We have performed first-principles density functional based calculations to evaluate the electron energy loss spectrum (EELS) of bulk, monolayer, and bilayer configurations of several transition metal dichalcogenides, which include semiconducting as well as metallic compounds. Our investigation shows that the peaks in the EELS spectra move toward larger wavelengths (red shift) with the decrease in number of layers. The ? plasmon peak shifts slightly by 0.5-1.0 eV, while a significant shift of around 5.5-13.0 eV is obtained for ? + ? plasmon, when exfoliated from bulk to single-layer. This underscores the importance of the interlayer coupling on the loss spectra and the dielectric properties. Our results are found to be in very good agreement with the recent measurements performed by Coleman et al. (Science2011, 331, 568). PMID:21707067

Johari, Priya; Shenoy, Vivek B

2011-07-26

374

Transition metal-free olefin polymerization catalyst  

DOEpatents

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

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

2001-01-01

375

Nanocrystalline transition metal ferrites: Synthesis, characterization and surface functionalization  

NASA Astrophysics Data System (ADS)

In this thesis, a new synthetic methodology for the high yield synthesis of spinel-type transition metal ferrite nanoparticles has been developed. This approach is based on the complexation of the first-row transition metal cations with diethylene glycol (DEG) followed by the hydrolysis of the resulting chelate iron alkoxide complexes in the presence of an alkaline hydroxide. Due to the passivation of their surfaces with DEG molecules, the as-prepared nanoparticles are stable against agglomeration and can be easily dispersed in polar protic solvents (water, alcohols, etc.). Alternatively, a postsynthesis passivation with carboxylate ions can render the iron oxide nanocrystals highly dispersible in non-polar solvents. Optimization of the reaction conditions suggested that the size of the nanocrystals could be controlled by changing the complexing strength of the reaction medium. This hypothesis was verified in the case of the Fe3O4 nanoparticles: their sizes vary from 5.7 nm when the reaction is performed in neat diethylene glycol to 16.8 nm in N-methyl diethanolamine (NMDEA), whereas a 1:1 (%wt) mixture of these solvents yields nanocrystals with an average size of and 12.7 nm. A detailed characterization by using a wide variety of techniques, including powder X-Ray diffraction, IR spectroscopy, thermogravimetric analysis (TGA), transmission electron microscopy (TEM) and 1H-NMR spectrometry was performed in order to elucidate the composition and the morphology of the variable-sized iron oxide nanoparticles. Both finite size and interparticle interaction effects were identified to influence the magnetic behavior of the oleate-capped nanosized particles. At low temperatures the Fe3O 4 nanocrystals exhibit a ferromagnetic behavior with blocking temperatures which increase with the average particle size, whereas at room temperature, except for the largest nanoparticles, they undergo a superparamagnetic relaxation. We exploited the high surface reactivity of the 10 nm Fe3O 4 nanoparticles to attach 2-3 nm gold grains to their surfaces through a simple, two-step chemically controlled procedure. By chemically bonding bioactive molecules to the attached Au nanoparticles these novel nanoarchitectures open up new opportunities for the implementation of the magnetic nanoparticles as a platform for various applications in the biomedical field.

Caruntu, Daniela

376

Double Perovskites as Anode Materials for Solid-Oxide Fuel Cells  

Microsoft Academic Search

Extensive efforts to develop a solid-oxide fuel cell for transportation, the bottoming cycle of a power plant, and distributed generation of electric energy are motivated by a need for greater fuel efficiency and reduced air pollution. Barriers to the introduction of hydrogen as the fuel have stimulated interest in developing an anode material that can be used with natural gas

Yun-Hui Huang; Ronald I. Dass; Zheng-Liang Xing; John B. Goodenough

2006-01-01

377

Nutritional immunity: transition metals at the pathogen-host interface  

PubMed Central

Transition metals occupy an essential niche in biological systems. Their electrostatic properties stabilize substrates or reaction intermediates in the active sites of enzymes, while their heightened reactivity is harnessed for catalysis. However, the latter property renders transition metals toxic at high concentrations. Bacteria, like all living organisms, must regulate the levels of these elements to satisfy their physiological needs while avoiding harm. It is therefore not surprising that the host capitalizes on both the essentiality and toxicity of transition metals to defend against bacterial invaders. This review will discuss established and emerging paradigms in nutrient metal homeostasis at the pathogen-host interface. PMID:22796883

Hood, M. Indriati; Skaar, Eric P.

2013-01-01

378

Superconductivity in carbon nanotubes coupled to transition metal atoms  

NASA Astrophysics Data System (ADS)

The electronic structures of zigzag and armchair single-walled carbon nanotubes interacting with a transitional-metal atomic nanowire of Ni have been determined. The Ni nanowire creates a large electron density of states (DOS) at the Fermi energy. The dependence of the enhanced DOS on the spin state and positioning of the transition metal wire (inside or outside the nanotube) is studied. Preliminary estimates of the electron-phonon interaction suggest that such systems may have a superconducting transition temperature of ~ 10 50 K. The signs of superconductivity seen in "ropes" of nanotubes may also be related to the effect of intrinsic transition metal impurities.

Tit, N.; Dharma-wardana, M. W. C.

2003-05-01

379

Investigation of methods for the selective removal and characterization of transition metals associated with solids in the marine environment  

SciTech Connect

The operation of an OTEC plant will result in the mixing of large volumes of seawater from different depths within the ocean. Because suspended particulate material is intimately involved in marine food webs and transition metals, such as copper, can have toxic effects, it is important to develop a sound methodology for characterizing and quantifying transition metal behavior associated with the solid material. The characterization of solid-phase-associated transition metals in the marine environment has largely been directed at marine sediments. These studies have generally indicated that it is not possible to uniquely identify the solid phases or chemical speciation of a given metal. There are many reasons for this difficulty, but the probable major analytical problems arise from the fact that many of the transition metals of interest are present only in trace concentrations as adsorbed species on amorphous oxides or as coprecipitates. In one approach transition metals are classified according to how easily they are solubilized when exposed to different types of chemical attack, as defined in chemical extraction schemes. In this study, several of the most widely accepted extraction techniques were compared for many of the most commonly measured transition metals to a variety of marine sediments. Based on the results of this study, the sequential extraction scheme of Tessler et al. (1979) is the recommended method for the characterization of solid-phase associated transition metals. An increase of the reducing agent concentration in the intermediate step and temperature decrease with an additional HCl digestion in the residual step are recommended as improvements, based on the results of the individual extraction method studies.

Van Valin, R.; Morse, J.W.

1981-02-01

380

Development of lanthanum strontium manganite perovskite cathode materials of solid oxide fuel cells: a review  

Microsoft Academic Search

The high-temperature solid oxide fuel cell (SOFC) is the most efficient and environmentally friendly energy conversion technology\\u000a to generate electricity from fuels such as hydrogen and natural gas as compared to the traditional thermal power generation\\u000a plants. In the last 20–30 years, there has been significant progress in the materials development and stack technologies in\\u000a SOFC. Among the electrode materials, lanthanum

San Ping Jiang

2008-01-01

381

Synthesis of oxide perovskite solid solutions using the molten salt method  

Microsoft Academic Search

The molten salt method has in the past been employed to synthesize a large number of compounds at low temperatures. In this work we report the formation of solid solutions of BaTiO3 - SrTiO3 and BaZrO3 - SrZrO3 using a molten salt eutectic of NaOH- KOH as a solvent. Alkaline earth carbonates and titanium oxide were used as precursors for

Srikanth Gopalan; Karun Mehta; Anil V. Virkar

1996-01-01

382

Magnetoelectric Effects in Bilayers and Multilayers of Magnetostrictive and Piezoelectric Perovskite Oxides  

Microsoft Academic Search

We report strong ME effects and its unique magnetic field dependence in composites of La0.7Sr0.3MnO3 (LSMO) PZT and La0.7Ca0.3MnO3 (LCMO)- PZT. The oxide films were made by the tape casting technique and were laminated and sintered to obtain the required hetrostructures. The ME voltage coefficient (MEVC) measurements involved the response of a poled composite to an applied ac magnetic field

E. T. Rasmussen; B. Levin; R. Hayes; G. Srinivasan

2002-01-01

383

Structural studies on transition metal compounds  

NASA Astrophysics Data System (ADS)

Accurate determination of the electron-density distribution in transition metal complexes provides important information on the electronic ground state of the d electrons placed in a ligand field. The high-spin and low-spin states can be distinguished unequivocally. The degree of hybridization of the component orbitals can also be determined. If the intensity data are good enough, the wavefunction analysis can be carried out and the orbital coefficients can be obtained by a least squares method. In spite of a very small valence/total electron ratio the asphericity of 4d and 5d electrons in a ligand field can be detected. This is owing to sharp deformation density located outside of the high-density inner core region. The crystal structures of a series of dimeric copper(II) carboxylate adducts of the general formula [Cu(RCOO)2L]2 have been accurately determined or redetermined. The temperature-dependent magnetic susceptibility of these crystals indicates that the isolated pairs of Cu(II) ions interact strongly through exchange forces. The present structure investigation has established that there exist no magneto-structural correlations. Instead, it was found that the values of singlet-triplet separation increase roughly linearly with the number of electrons in the bridging OCO group calculated by the molecular orbital method. The chiral cyanoethyl group in a series of cobaloxime complexes was found to racemize on exposure to X-rays without degradation of crystallinity. The rate of racemization was so slow that several structures of intermediate stages could be determined by X-ray analysis. In this way various reaction pathways were recognized and the reaction rate could be correlated quantitatively with the atomic arrangement in the crystal. The related complexes were found to undergo reversible phase transition and/or photoisomerization without degradation of crystallinity.

Saito, Yoshihiko

384

Process for making transition metal nitride whiskers  

DOEpatents

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

Bamberger, Carlos E. (Oak Ridge, TN)

1989-01-01

385

Synergistic Bifunctional Catalyst Design based on Perovskite Oxide Nanoparticles and Intertwined Carbon Nanotubes for Rechargeable Zinc-Air Battery Applications.  

PubMed

Advanced morphology of intertwined core-corona structured bifunctional catalyst (IT-CCBC) is introduced where perovskite lanthanum nickel oxide nanoparticles (LaNiO3 NP) are encapsulated by high surface area network of nitrogen-doped carbon nanotubes (NCNT) to produce highly active and durable bifunctional catalyst for rechargeable metal-air battery applications. The unique composite morphology of IT-CCBC not only enhances the charge transport property by providing rapid electron-conduction pathway but also facilitates in diffusion of hydroxyl and oxygen reactants through the highly porous framework. Confirmed by electrochemical half-cell testing, IT-CCBC in fact exhibits very strong synergy between LaNiO3 NP and NCNT demonstrating bifunctionality with significantly improved catalytic activities of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Furthermore, when compared to the state-of-art catalysts, IT-CCBC outperforms Pt/C and Ir/C in terms of ORR and OER, respectively, and shows improved electrochemical stability compared to them after cycle degradation testing. The practicality of the catalyst is corroborated by testing in a realistic rechargeable zinc-air battery utilizing atmospheric air in ambient conditions, where IT-CCBC demonstrates superior charge and discharge voltages and long-term cycle stability with virtually no battery voltage fading. These improved electrochemical properties of the catalyst are attributed to the nanosized dimensions of LaNiO3 NP controlled by simple hydrothermal technique, which enables prolific growth of and encapsulation by highly porous NCNT network. The excellent electrochemical results presented in this study highlight IT-CCBC as highly efficient and commercially viable bifunctional catalyst for rechargeable metal-air battery applications. PMID:25494945

Lee, Dong Un; Park, Hey Woong; Park, Moon Gyu; Ismayilov, Vugar; Chen, Zhongwei

2015-01-14

386

Room temperature oxidative intercalation with chalcogen hydrides: Two-step method for the formation of alkali-metal chalcogenide arrays within layered perovskites  

SciTech Connect

Highlights: ? Topochemical reactions involving intercalation allow construction of metal chalcogenide arrays within perovskite hosts. ? Gaseous chalcogen hydrides serve as effect reactants for intercalation of sulfur and selenium. ? New compounds prepared by a two-step intercalation strategy are presented. -- Abstract: A two-step topochemical reaction strategy utilizing oxidative intercalation with gaseous chalcogen hydrides is presented. Initially, the Dion-Jacobson-type layered perovskite, RbLaNb{sub 2}O{sub 7}, is intercalated reductively with rubidium metal to make the Ruddlesden-Popper-type layered perovskite, Rb{sub 2}LaNb{sub 2}O{sub 7}. This compound is then reacted at room-temperature with in situ generated H{sub 2}S gas to create Rb-S layers within the perovskite host. Rietveld refinement of X-ray powder diffraction data (tetragonal, a = 3.8998(2) ?, c = 15.256(1) ?; space group P4/mmm) shows the compound to be isostructural with (Rb{sub 2}Cl)LaNb{sub 2}O{sub 7} where the sulfide resides on a cubic interlayer site surrounded by rubidium ions. The mass increase seen on sulfur intercalation and the refined S site occupation factor (?0.8) of the product indicate a higher sulfur content than expected for S{sup 2?} alone. This combined with the Raman studies, which show evidence for an H-S stretch, indicate that a significant fraction of the intercalated sulfide exists as hydrogen sulfide ion. Intercalation reactions with H{sub 2}Se{sub (g)} were also carried out and appear to produce an isostructural selenide compound. The utilization of such gaseous hydride reagents could significantly expand multistep topochemistry to a larger number of intercalants.

Ranmohotti, K.G. Sanjaya; Montasserasadi, M. Dariush; Choi, Jonglak; Yao, Yuan; Mohanty, Debasish; Josepha, Elisha A.; Adireddy, Shiva; Caruntu, Gabriel [Department of Chemistry and the Advanced Materials Research Institute, University of New Orleans, New Orleans, LA 70148-2820 (United States)] [Department of Chemistry and the Advanced Materials Research Institute, University of New Orleans, New Orleans, LA 70148-2820 (United States); Wiley, John B., E-mail: jwiley@uno.edu [Department of Chemistry and the Advanced Materials Research Institute, University of New Orleans, New Orleans, LA 70148-2820 (United States)

2012-06-15

387

Obtaining Mixed Ionic/Electronic Conductivity in Perovskite Oxides in a Reducing Environment: A Computational Prediction for Doped SrTiO3  

SciTech Connect

The electronic conductivity and thermodynamic stability of mixed p- and n-doped SrTiO3 perovskites have been investigated under anodic solid oxide fuel cell conditions using density functional theory (DFT). In particular, constrained ab initio thermodynamic calculations have been performed to evaluate the phase stability of various Ga- and La-doped SrTiO3 at synthesized and anodic SOFC conditions. The density of states (DOS) of these materials was analyzed to determine the number of charge carriers and the degree of electronic conductivity. We find that a mixed ionic/electronic conductor can be obtained when doping SrTiO3 perovskite oxide with both p-type and n-type dopants. Calculations show that 10% Ga- and 20% La-doped SrTiO3 exhibit mixed ionic/electronic conductivity at high temperature and low oxygen partial pressure whereas doping with higher concentrations of Ga, e.g., 20%, diminishes the electronic conductivity of the material. Furthermore, changing the n-dopant from La (A-site) to Nb (B-site) does not significantly affect the reducibility and number of charge carriers in p- and n-doped SrTiO3. However, a higher degree of oxygen vacancy clustering is observed for the La-doped material which reduces the oxygen ion diffusion rate and traps electrons. Nevertheless, our findings suggest that independent of doping site, mixed ionic/ electronic conductivity can be obtained in SrTiO3 perovskite oxides under reducing conditions and high temperatures when using a mixed p- and n-type doping strategy that uses a p-dopant concentration smaller than the n-dopant concentration.

Suthirakun, Suwit; Ammal, Salai Cheettu; Xiao, Guoliang; Chen, Fanglin; Huang, Kevin; zur Loye, Hans-Conrad; Heyden, Andreas

2012-11-30

388

Radiative properties of molybdenum sulfide and other transition metal dichalcogenides .  

E-print Network

??Low temperature radiative properties of the layered transition metal dichalcogenides 2H-MoS2, 2H-WS2 and 2H-WSe 2 are investigated. Synthetically grown crystals of all three materials, natural… (more)

Charron, Luc G

2013-01-01

389

Photochemical reductive elimination of halogen from transition metal complexes  

E-print Network

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

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

2010-01-01

390

Optical properties of two-dimensional transition metal dichalcogenides  

E-print Network

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

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

2014-01-01

391

Nitrene transfer reactions by late transition metal complexes  

E-print Network

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

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

2007-01-01

392

Photoresponse study on transition metal (Co, Ni, Mn) doped ZnO thin films  

NASA Astrophysics Data System (ADS)

The photoresponse characteristics of chemical solution deposited, undoped and transition metal doped zinc oxide thin films have been studied. The x-ray diffraction studies confirm the formation of the crystalline ZnO phase. The FESEM analysis of the deposited films indicates a granular surface with grains of hexagonal facet morphology. The photoluminescence spectra of the deposited films show a strong violet-blue-green emission band. The devices for photoresponse study were made by in-plane Ag contacts on the films, to form metal-semiconductor-metal configuration. The current-voltage characteristics of our transition metal doped ZnO films under illumination reveals the suitability of our thin films in visible-infra red light sensing applications.

Rajalakshmi, R.; Angappane, S.

2013-02-01

393

Universality in surface mixing rule of adsorption strength for small adsorbates on binary transition metal alloys.  

PubMed

Understanding the adsorption phenomena of small adsorbates involved in surface reactions on transition metals is important because their adsorption strength can be a descriptor for predicting the catalytic activity. To explore adsorption energies on a wide range of binary transition metal alloys, however, tremendous computational efforts are required. Using density functional theory (DFT) calculations, here we suggest a "surface mixing rule" to predict the adsorption energies of H, O, S, CO and OH on bimetallic alloys, based on the linear interpolation of adsorption energies on each pure surface. As an application, the activity of CO oxidation on various bimetallic alloys is predicted from the adsorption energies of CO and O easily obtained by the surface mixing rule. Our results provide a useful tool for rapidly estimating adsorption energies, and furthermore, catalytic activities on multi-component metal alloy surfaces. PMID:25515855

Ko, Jeonghyun; Kwon, Hyunguk; Kang, Hyejin; Kim, Byung-Kook; Han, Jeong Woo

2015-02-01

394

Perovskite oxides for visible-light-absorbing ferroelectric and photovoltaic materials  

NASA Astrophysics Data System (ADS)

Ferroelectrics have recently attracted attention as a candidate class of materials for use in photovoltaic devices, and for the coupling of light absorption with other functional properties. In these materials, the strong inversion symmetry breaking that is due to spontaneous electric polarization promotes the desirable separation of photo-excited carriers and allows voltages higher than the bandgap, which may enable efficiencies beyond the maximum possible in a conventional p-n junction solar cell. Ferroelectric oxides are also stable in a wide range of mechanical, chemical and thermal conditions and can be fabricated using low-cost methods such as sol-gel thin-film deposition and sputtering. Recent work has shown how a decrease in ferroelectric layer thickness and judicious engineering of domain structures and ferroelectric-electrode interfaces can greatly increase the current harvested from ferroelectric absorber materials, increasing the power conversion efficiency from about 10-4 to about 0.5 per cent. Further improvements in photovoltaic efficiency have been inhibited by the wide bandgaps (2.7-4electronvolts) of ferroelectric oxides, which allow the use of only 8-20 per cent of the solar spectrum. Here we describe a family of single-phase solid oxide solutions made from low-cost and non-toxic elements using conventional solid-state methods: [KNbO3]1-x[BaNi1/2Nb1/2O3-?]x (KBNNO). These oxides exhibit both ferroelectricity and a wide variation of direct bandgaps in the range 1.1-3.8electronvolts. In particular, the x = 0.1 composition is polar at room temperature, has a direct bandgap of 1.39electronvolts and has a photocurrent density approximately 50 times larger than that of the classic ferroelectric (Pb,La)(Zr,Ti)O3 material. The ability of KBNNO to absorb three to six times more solar energy than the current ferroelectric materials suggests a route to viable ferroelectric semiconductor-based cells for solar energy conversion and other applications.

Grinberg, Ilya; West, D. Vincent; Torres, Maria; Gou, Gaoyang; Stein, David M.; Wu, Liyan; Chen, Guannan; Gallo, Eric M.; Akbashev, Andrew R.; Davies, Peter K.; Spanier, Jonathan E.; Rappe, Andrew M.

2013-11-01

395

Catalytic Properties of Oxygen Semipermeable Perovskite-Type Ceramic Membrane Materials for Oxidative Coupling of Methane  

Microsoft Academic Search

The catalytic properties for the oxidative coupling of methane (OCM) of La0.8Sr0.2CoO3(LSC) and SrCo0.8Fe0.2O3(SCF) in solid solution were studied and compared with those of 5 wt% Li\\/MgO, using a steady\\/unsteady state packed-bed reactor and a transient microbalance. The results of the steady-state cofeed experiments show that LSC possesses OCM catalytic properties similar to those of Li\\/MgO in terms of C2yield

Y. S. Lin; Y. Zeng

1996-01-01

396

Electrical conduction behavior of La, Co co-doped SrTiO 3 perovskite as anode material for solid oxide fuel cells  

Microsoft Academic Search

The effects of La- and Co-doping into SrTiO3 perovskite oxides on their phase structure, electrical conductivity, ionic conductivity and oxygen vacancy concentration have been investigated. The solid solution limits of La in LaxSr1?xTiO3?? and Co in La0.3Sr0.7CoyTi1?yO3?? are about 40mol% and 7mol%, respectively, at 1500°C. The incorporation of La decreases the band gap and thus increases the electrical conductivity of

Xue Li; Hailei Zhao; Nansheng Xu; Xiong Zhou; Cuijuan Zhang; Ning Chen

2009-01-01

397

Ambipolar Field Effect Transistors Based on Transition-Metal Dichalcogenides  

Microsoft Academic Search

A novel class of the field-effect transistors (FETs) based on transition-metal dichalcogenides has been fabricated. In the single crystals of these layered semiconductors, a weak Van der Waals inter-layer bonding is combined with a strong covalent\\/ionic intra-layer bonding. These materials represent a class of layered inorganic semiconductors with a chemical formula MX_2, where M stands for a transition metal and

Vitaly Podzorov; Michael E. Gershenson; Christian Kloc; Roswitha Zeis; Ernst Bucher

2004-01-01

398

Microwave absorption of mixed-layer transition metal dichalcogenides  

Microsoft Academic Search

‘Mixed-layer mechanism’, a new concept in microwave absorption, was observed in mixed-layer transition-metal dichalcogenides. Two things were observed: first, the strong microwave absorption in the mixed-layer transition metal dichalcogenides, MXM?1 ? Xch2 (M = Re, Ru and Os; M? = Nb and Ta; ch = S and Se); second, the low microwave absorption in the nominally-perfect stacking 3R-MoS2 and MXM?1

K. Hayashi; D. Serikawa; Y. Chijimatsu; M. Shimakawa; S. Kume; K. Manabe; T. Takahashi

1997-01-01

399

The Electronic Structure of Transition Metal Coated Fullerenes  

Microsoft Academic Search

Clusters composed of fullerene molecules with an outer shell of transition metal atoms in the composition C_60M_62 (M being a transition metal) have been produced with laser vaporisation techniques(F. Tast, N. Malinowski, S. Frank, M. Heinebrodt, I.M.L. Billas, and T. P. Martin, Z. Phys D 40), 351 (1997).. We have studied several of these very large systems with a parallel

David C. Patton; Mark R. Pederson; Efthimios Kaxiras

1998-01-01

400

Hollow spherical La0.8Sr0.2MnO3 perovskite oxide with enhanced catalytic activities for the oxygen reduction reaction  

NASA Astrophysics Data System (ADS)

A hollow spherical La0.8Sr0.2MnO3 (HS-LSM) perovskite oxide has been prepared using a new carbonate-template route, and characterized by XRD, SEM and TEM. SEM and TEM results show that the pre-prepared oxides consist of porous microspheres composed of submicrometer-sized subunits with a secondary particle diameter of ?20-50 nm. The catalytic activity of the oxide for the oxygen reduction reaction (ORR) in 0.1 M KOH solution has been studied using a rotating ring-disk electrode (RRDE). In the ORR tests, a maximum cathodic current density of 6.4 mA cm-2 at -0.9 V (vs. Ag/AgCl) with 2500 rpm has been obtained, and the ORR mainly favors a direct four-electron pathway. The chronoamperometric test shows that the HS-LSM exhibits excellent stability for the ORR.

Lu, Fanliang; Sui, Jing; Su, Jianmin; Jin, Chao; Shen, Ming; Yang, Ruizhi

2014-12-01

401

Temperature-induced A-B intersite charge transfer in an A-site-ordered LaCu(3)Fe(4)O(12) perovskite.  

PubMed

Changes of valence states in transition-metal oxides often cause significant changes in their structural and physical properties. Chemical doping is the conventional way of modulating these valence states. In ABO(3) perovskite and/or perovskite-like oxides, chemical doping at the A site can introduce holes or electrons at the B site, giving rise to exotic physical properties like high-transition-temperature superconductivity and colossal magnetoresistance. When valence-variable transition metals at two different atomic sites are involved simultaneously, we expect to be able to induce charge transfer-and, hence, valence changes-by using a small external stimulus rather than by introducing a doping element. Materials showing this type of charge transfer are very rare, however, and such externally induced valence changes have been observed only under extreme conditions like high pressure. Here we report unusual temperature-induced valence changes at the A and B sites in the A-site-ordered double perovskite LaCu(3)Fe(4)O(12); the underlying intersite charge transfer is accompanied by considerable changes in the material's structural, magnetic and transport properties. When cooled, the compound shows a first-order, reversible transition at 393 K from LaCu(2+)(3)Fe(3.75+)(4)O(12) with Fe(3.75+) ions at the B site to LaCu(3+)(3)Fe(3+)(4)O(12) with rare Cu(3+) ions at the A site. Intersite charge transfer between the A-site Cu and B-site Fe ions leads to paramagnetism-to-antiferromagnetism and metal-to-insulator isostructural phase transitions. What is more interesting in relation to technological applications is that this above-room-temperature transition is associated with a large negative thermal expansion. PMID:19262669

Long, Y W; Hayashi, N; Saito, T; Azuma, M; Muranaka, S; Shimakawa, Y

2009-03-01

402

Binding and Activation of N2O at Transition Metal Centers: Recent Mechanistic Insights  

PubMed Central

No laughing matter, nitrous oxide’s role in stratospheric ozone depletion and as a greenhouse gas has stimulated great interest in developing and understanding its decomposition, particularly through the use of transition metal promoters. Recent advances in our understanding of the reaction pathways for N2O reduction by metal ions in the gas phase and in heterogeneous, homogeneous, and biological catalytic systems have provided provocative ideas about the structure and properties of metal-N2O adducts and derived intermediates. These ideas are likely to inform efforts to design more effective catalysts for N2O remediation. PMID:20058284

Tolman, William B.

2010-01-01

403

Self-templated synthesis and thermal conductivity investigation for ultrathin perovskite oxide nanowires  

NASA Astrophysics Data System (ADS)

The large thermal conductivity of bulk complex metal oxides such as SrTiO3, NaCo2O4, and Ca3Co4O9 has set a barrier for the improvement of thermoelectric figure of merit and the applications of these materials in high temperature (>=1000 K) thermoelectric energy harvesting and solid-state cooling. Here, we present a self-templated synthesis approach to grow ultrathin SrTiO3 nanowires with an average diameter of 6 nm in large quantity. The thermal conductivity of the bulk pellet made by compressing nanowire powder using spark plasma sintering shows a 64% reduction in thermal conductivity at 1000 K, which agrees well with theoretical modeling.The large thermal conductivity of bulk complex metal oxides such as SrTiO3, NaCo2O4, and Ca3Co4O9 has set a barrier for the improvement of thermoelectric figure of merit and the applications of these materials in high temperature (>=1000 K) thermoelectric energy harvesting and solid-state cooling. Here, we present a self-templated synthesis approach to grow ultrathin SrTiO3 nanowires with an average diameter of 6 nm in large quantity. The thermal conductivity of the bulk pellet made by compressing nanowire powder using spark plasma sintering shows a 64% reduction in thermal conductivity at 1000 K, which agrees well with theoretical modeling. Y. Wu thanks the support from the Purdue University new faculty startup grant, Kick Grant from Birck Nanotechnology Center, DuPont Young Faculty Award, Midwest Institute for Nanoelectronics Discovery (MIND), and NSF/DOE Thermoelectric Partnership (Award Number 1048616). Y. Wu acknowledges the help from Dr Douglas Dudis and Charles Cooke at Wright-Patterson Air Force Research Lab on the spark plasma sintering of nanowire powder. X.L. Ruan and B. Qiu acknowledge the partial support of Air Force Office of Scientific Research (Grant Number FA9550-11-1-0057).

Yadav, Gautam G.; Zhang, Genqiang; Qiu, Bo; Susoreny, Joseph A.; Ruan, Xiulin; Wu, Yue

2011-10-01

404

PrBa0.5Sr0.5Co2O5+? layered perovskite cathode for intermediate temperature solid oxide fuel cells  

SciTech Connect

Layered perovskite oxides have ordered A-cations localizing oxygen vacancies, and may potentially improve oxygen ion diffusivity and surface exchange coefficient. The A-site-ordered layered perovskite PrBa{sub 0.5}Sr{sub 0.5}Co{sub 2}O{sub 5+?} (PBSC) was evaluated as new cathode material for intermediate temperature solid oxide fuel cells (IT-SOFCs). The material was characterized using electrochemical impedance spectroscopy in a symmetrical cell system (PBSC/Ce{sub 0.9}Sm{sub 0.1}O{sub 1.9} (SDC)/PBSC), exhibiting excellent performance in the intermediate temperature range of 500–700 °C. An area-specific-resistance (ASR) of 0.23 ? cm{sup 2} was achieved at 650 °C for cathode polarization. The low activation energy (Ea) 124 kJ mol{sup ?1} is comparable to that of La{sub 0.8}Sr{sub 0.2}CoO{sub 3??}. A laboratory-scaled SDC-based tri-layer cell of Ni-SDC/SDC/PBSC was tested in intermediate temperature conditions of 550 to 700 °C. A maximum power density of 1045 mW cm{sup ?2} was achieved at 700 °C. The interfacial polarization resistance is as low as 0.285, 0.145, 0.09 and 0.05 ? cm{sup 2} at 550, 600, 650 and 700 °C, respectively. Layered perovskite PBSC shows promising performance as cathode material for IT-SOFCs.

Ding, Hanping; Xue, Xingjian

2010-01-01

405

Strain-induced significant increase in metal-insulator transition temperature in oxygen-deficient Fe oxide epitaxial thin films.  

PubMed

Oxygen coordination of transition metals is a key for functional properties of transition-metal oxides, because hybridization of transition-metal d and oxygen p orbitals determines correlations between charges, spins and lattices. Strain often modifies the oxygen coordination environment and affects such correlations in the oxides, resulting in the emergence of unusual properties and, in some cases, fascinating behaviors. While these strain effects have been studied in many of the fully-oxygenated oxides, such as ABO3 perovskites, those in oxygen-deficient oxides consisting of various oxygen coordination environments like tetrahedra and pyramids as well as octahedra remain unexplored. Here we report on the discovery of a strain-induced significant increase, by 550?K, in the metal-insulator transition temperature of an oxygen-deficient Fe oxide epitaxial thin film. The observed transition at 620?K is ascribed to charge disproportionation of Fe(3.66+) into Fe(4+) and Fe(3+), associated with oxygen-vacancy ordering. The significant increase in the metal-insulator transition temperature, from 70?K in the bulk material, demonstrates that epitaxial growth of oxygen-deficient oxides under substrate-induced strain is a promising route for exploring novel functionality. PMID:25600001

Hirai, Kei; Kan, Daisuke; Ichikawa, Noriya; Mibu, Ko; Yoda, Yoshitaka; Andreeva, Marina; Shimakawa, Yuichi

2015-01-01

406

Strain-induced significant increase in metal-insulator transition temperature in oxygen-deficient Fe oxide epitaxial thin films  

NASA Astrophysics Data System (ADS)

Oxygen coordination of transition metals is a key for functional properties of transition-metal oxides, because hybridization of transition-metal d and oxygen p orbitals determines correlations between charges, spins and lattices. Strain often modifies the oxygen coordination environment and affects such correlations in the oxides, resulting in the emergence of unusual properties and, in some cases, fascinating behaviors. While these strain effects have been studied in many of the fully-oxygenated oxides, such as ABO3 perovskites, those in oxygen-deficient oxides consisting of various oxygen coordination environments like tetrahedra and pyramids as well as octahedra remain unexplored. Here we report on the discovery of a strain-induced significant increase, by 550 K, in the metal-insulator transition temperature of an oxygen-deficient Fe oxide epitaxial thin film. The observed transition at 620 K is ascribed to charge disproportionation of Fe3.66+ into Fe4+ and Fe3+, associated with oxygen-vacancy ordering. The significant increase in the metal-insulator transition temperature, from 70 K in the bulk material, demonstrates that epitaxial growth of oxygen-deficient oxides under substrate-induced strain is a promising route for exploring novel functionality.

Hirai, Kei; Kan, Daisuke; Ichikawa, Noriya; Mibu, Ko; Yoda, Yoshitaka; Andreeva, Marina; Shimakawa, Yuichi

2015-01-01

407

Strain-induced significant increase in metal-insulator transition temperature in oxygen-deficient Fe oxide epitaxial thin films  

PubMed Central

Oxygen coordination of transition metals is a key for functional properties of transition-metal oxides, because hybridization of transition-metal d and oxygen p orbitals determines correlations between charges, spins and lattices. Strain often modifies the oxygen coordination environment and affects such correlations in the oxides, resulting in the emergence of unusual properties and, in some cases, fascinating behaviors. While these strain effects have been studied in many of the fully-oxygenated oxides, such as ABO3 perovskites, those in oxygen-deficient oxides consisting of various oxygen coordination environments like tetrahedra and pyramids as well as octahedra remain unexplored. Here we report on the discovery of a strain-induced significant increase, by 550?K, in the metal-insulator transition temperature of an oxygen-deficient Fe oxide epitaxial thin film. The observed transition at 620?K is ascribed to charge disproportionation of Fe3.66+ into Fe4+ and Fe3+, associated with oxygen-vacancy ordering. The significant increase in the metal-insulator transition temperature, from 70?K in the bulk material, demonstrates that epitaxial growth of oxygen-deficient oxides under substrate-induced strain is a promising route for exploring novel functionality. PMID:25600001

Hirai, Kei; Kan, Daisuke; Ichikawa, Noriya; Mibu, Ko; Yoda, Yoshitaka; Andreeva, Marina; Shimakawa, Yuichi

2015-01-01

408

Characterization and evaluation of double perovskites LnBaCoFeO5+? (Ln = Pr and Nd) as intermediate-temperature solid oxide fuel cell cathodes  

NASA Astrophysics Data System (ADS)

Double perovskites LnBaCoFeO5+? (Ln = Pr and Nd, PBCF and NBCF) are comparatively investigated as potential cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). LnBaCoFeO5+? materials are chemically compatible with La0.9Sr0.1Ga0.8Mg0.2O3-? (LSGM) electrolyte at temperatures below 1000 °C. Fe and Co ions in LnBaCoFeO5+? exist in two oxidation states, 3+ and 4+. Pr ions are found in PBCF mostly as Pr3+. Thermal expansion coefficients (TECs) of PBCF and NBCF are 21.0 × 10-6 and 19.5 × 10-6 K-1, respectively, between 30 and 1000 °C; these are lower than the TECs of undoped LnBaCo2O5+?. The best electrical conductivity for both materials is observed near 350 °C: 321 and 172 S cm-1 for PBCF and NBCF, respectively. Polarization resistances of PBCF and NBCF cathodes on LSGM electrolyte are 0.049 and 0.062 ? cm2 at 800 °C, respectively. Maximum power densities of the single-cell with Ni/SDC as anode on a 0.3 mm-thick LSGM electrolyte reach 749 and 669 mW cm-2 for PBCF and NBCF cathodes at 800 °C, respectively. As cathodes for application in IT-SOFCs, the performance of PBCF and NBCF double perovskites is promising.

Jin, Fangjun; Xu, Huawei; Long, Wen; Shen, Yu; He, Tianmin

2013-12-01

409

Preparation and electrochemical properties of urchin-like La0.8Sr0.2MnO3 perovskite oxide as a bifunctional catalyst for oxygen reduction and oxygen evolution reaction  

NASA Astrophysics Data System (ADS)

An urchin-like La0.8Sr0.2MnO3 (LSM) perovskite oxide has been synthesized through a co-precipitation method with urea as a precipitator, and characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and BET analysis. SEM results show that a micro/nanocomposite with an urchin-like morphology has been obtained. The as-synthesized LSM perovskite oxide has a high specific surface area of 48 m2 g-1. The catalytic activity of the oxide for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) in 0.1 M KOH solution has been studied by using a rotating-ring-disk electrode (RRDE). In the ORR test, a maximum cathodic current density of 5.2 mA cm-2 at -1.0 V (vs. Ag/AgCl) with 2500 rpm was obtained, and the ORR mainly favors a direct four-electron pathway. The results of anodic linear scanning voltammograms indicate that the urchin-like LSM perovskite oxide exhibits an encouraging catalytic activity for the OER. All electrochemical measurements suggest that the urchin-like LSM perovskite oxide could be used as a bifunctional catalyst for the ORR and the OER.

Jin, Chao; Cao, Xuecheng; Zhang, Liya; Zhang, Cong; Yang, Ruizhi

2013-11-01

410

Effects of strain, d-band filling, and oxidation state on the surface electronic structure and reactivity of 3d perovskite surfaces.  

PubMed

Trends in the dissociative oxygen adsorption energy and oxygen vacancy formation energy on cubic LaBO(3) and SrBO(3) perovskite (001) surfaces (where B = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) and their dependence on strain, d-band filling, and oxidation state were examined using density functional theory in the generalized gradient approximation. The effects of strain were found to be small compared to the effects of d-band filling and oxidations state. Electronic structure descriptors such as the d-band center of the B-atom were identified for trends in the dissociative oxygen adsorption energy and for the oxygen vacancy formation energy. A chemical correlation between these two reaction energies was also identified showing the trends in these reaction energies are not independent of each other. PMID:22938255

Akhade, Sneha A; Kitchin, John R

2012-08-28

411

[Transition metal mediated transformations of small molecules  

SciTech Connect

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

Sen, A.

1992-01-01

412

A family of oxide ion conductors based on the ferroelectric perovskite Na0.5Bi0.5TiO3  

NASA Astrophysics Data System (ADS)

Oxide ion conductors find important technical applications in electrochemical devices such as solid-oxide fuel cells (SOFCs), oxygen separation membranes and sensors. Na0.5Bi0.5TiO3 (NBT) is a well-known lead-free piezoelectric material; however, it is often reported to possess high leakage conductivity that is problematic for its piezo- and ferroelectric applications. Here we report this high leakage to be oxide ion conduction due to Bi-deficiency and oxygen vacancies induced during materials processing. Mg-doping on the Ti-site increases the ionic conductivity to ~0.01?S?cm-1 at 600?°C, improves the electrolyte stability in reducing atmospheres and lowers the sintering temperature. This study not only demonstrates how to adjust the nominal NBT composition for dielectric-based applications, but also, more importantly, gives NBT-based materials an unexpected role as a completely new family of oxide ion conductors with potential applications in intermediate-temperature SOFCs and opens up a new direction to design oxide ion conductors in perovskite oxides.

Li, Ming; Pietrowski, Martha J.; de Souza, Roger A.; Zhang, Huairuo; Reaney, Ian M.; Cook, Stuart N.; Kilner, John A.; Sinclair, Derek C.

2014-01-01

413

Nanodisperse transition metal electrodes (NTME) for electrochemical cells  

DOEpatents

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

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

2000-01-01

414

Nanodisperse transition metal electrodes (NTME) for electrochemical cells  

SciTech Connect

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

Striebel, Kathryn A.; Wen, Shi-Jie

1998-12-01

415

Laser ablation mass spectrometry of inorganic transition metal compounds. Additional knowledge for the understanding of ion formation.  

PubMed

Laser ablation of transition-metal oxides have been investigated to better understand the formation processes of inorganic cluster ions. The study of binary oxide mixtures and the relative distribution of the ions produced suggest three salient mechanisms that occur after laser/matter interaction, that function to produce the observed ensemble of ionic species. Molecular recombination reactions, unimolecular dissociation processes, emission of small neutrals, including molecular oxygen from transition-metal oxide samples, or from species expelled in gas phase appear to be a significant mechanism, especially under high laser irradiance conditions. These processes are used to propose a set of pathways to rationalize the envelope of ionic clusters formed under photon bombardment. PMID:18258451

Aubriet, Frédéric; Muller, Jean-François

2008-04-01

416

On superconductivity of high-spin transition metal compounds  

SciTech Connect

The possibility of Cooper instability in transition metal compounds is established based of the concept of the strong interaction in the same unit cell. The multicomponent scattering amplitude of excitations is calculated. The superconductivity equations are derived for compounds of 3d transition metals. It is shown that in the pole approximation, the superconductivity equations can be reduced to the multicomponent superconductivity equations with preset BCS constants. A method is developed for calculating one-orbital constants and constants with different orbitals as functions of the total spin. The concentration ranges of superconducting ordering are obtained for one-orbital equations.

Zaitsev, R. O., E-mail: Zaitsev_rogdai@mail.ru [Moscow Institute of Physics and Technology (State University) (Russian Federation)

2011-11-15

417

Synthesis, characterization and photocatalytic performance of transition metal tungstates  

NASA Astrophysics Data System (ADS)

Tungstates of divalent transition metals (M IIWO 4, M = Co II, Ni II, Cu II, Zn II) were synthesized by reaction of transition metal nitrates with sodium tungstate. The precipitates were then calcined at 500 °C. The materials were characterized by means of ICP-AES elemental analysis, UV-Visible spectroscopy, X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and surface area analysis. The higher activity for the decolourization of Methylene Blue (MB) and Methyl Orange (MO) of ZnWO 4 compared to that of the other investigated tungstates was correlated with its strong tendency of excitons self-trapping.

Montini, Tiziano; Gombac, Valentina; Hameed, Abdul; Felisari, Laura; Adami, Gianpiero; Fornasiero, Paolo

2010-09-01

418

Magnetization Reversal in Transition Metal Doped ZnO Nanoparticles  

NASA Astrophysics Data System (ADS)

We report magnetic properties of transition metal (TM) doped ZnO nanoparticles and compare the doping effects of different transition metal ions into the ZnO matrix. Stoner-Wohlfarth model has been used to study the switching behavior of magnetic moments by observing energy diagram and hysteresis. Low magnetic anisotropy in Zn1-xMxO nanoparticles is observed where M=Fe, Co, Ni and x is the dopant amount. We have considered chemical precipitation technique for the preparation of Zn1-xMxO samples and have compared the reversal processes of magnetic moments with respect to time in the nanoparticles.

Mondal, Trisha; Tripathi, Ajay; Tiwari, Archana

419

Distinctive Charge Density Distributions of Perovskite-Type Antiferroelectric Oxides PbZrO3 and PbHfO3 in Cubic Phase  

NASA Astrophysics Data System (ADS)

The electron charge density distributions of simple perovskite oxides, PbBO3 (B = Ti, Zr and Hf), in their cubic phase are investigated by analyzing high-energy synchrotron powder diffraction data by the maximum entropy method (MEM)/Rietveld method. Clear structural differences between the antiferroelectric and ferroelectric perovskites are revealed. In the cubic phase of PbZrO3 and PbHfO3 that undergo antiferroelectric phase transitions, the Pb atom is disordered around the special Wyckoff position. The thermal motion of the O atom is anisotropic, and the charge density distributions around the O atom are extended in the directions perpendicular to the Zr(Hf)-O covalent bond. None of these structural characteristics are observed in the cubic phase of PbTiO3 that undergoes ferroelectric phase transition. The distinctive structural features observed in PbZrO3 and PbHfO3 should provide a clue to the mechanism of antiferroelectric phase transition.

Kuroiwa, Yoshihiro; Fujiwara, Hiroshi; Sawada, Akikatsu; Aoyagi, Shinobu; Nishibori, Eiji; Sakata, Makoto; Takata, Masaki; Kawaji, Hitoshi; Atake, Tooru

2004-09-01

420

Electron sampling depth and saturation effects in perovskite films investigated by soft x-ray absorption spectroscopy  

NASA Astrophysics Data System (ADS)

Knowledge of the electron sampling depth is important for quantitative analysis of x-ray absorption spectroscopy data, yet for oxides with the perovskite structure no quantitative values are so far available. Here, we study absorption saturation in films of two of the most-studied perovskites, La0.7Ca0.3MnO3 (LCMO) and YBa2Cu3O7 (YBCO), at the L2,3 edges of Mn and Cu, respectively. By measuring the electron-yield intensity as a function of photon incidence angle and film thickness, the sampling depth d, photon attenuation length ?, and ratio ?/d have been independently determined between 50 and 300 K. The extracted sampling depth dLCMO?3 nm for LCMO films at high temperatures in the polaronic insulator state (150-300 K) is near the values reported for some transition metals (dX=1.7-2.5 nm, where X = Fe, Co, Ni) at room temperature, and it is much smaller than dYBCO?5 nm measured for YBCO films and the value previously reported for Fe3O4 (dFe3O4=4.5nm). The measured dLCMO increases to 4.5 nm when LCMO is in the metallic state at low temperatures. These results indicate that the sampling depth in oxides is strongly material dependent and can be measurably influenced by electronic phase transitions deriving from strong correlations.

Ruosi, A.; Raisch, C.; Verna, A.; Werner, R.; Davidson, B. A.; Fujii, J.; Kleiner, R.; Koelle, D.

2014-09-01

421

Studies on catalytic and structural properties of BaRuO3 type perovskite1 material for diesel soot oxidation2  

E-print Network

1 Studies on catalytic and structural properties of BaRuO3 type perovskite1 material for diesel.1016/j.jece.2014.01.002 #12;2 Abstract23 BaRuO3 based perovskite type catalytic material was synthesized perovskite type material, which can be a potential candidate for control of soot emissions from32 combustion

Paris-Sud XI, Université de

422

Density functional studies of functionalized graphitic materials with late transition metals for Oxygen Reduction Reactions.  

PubMed

Low-temperature fuel cells are appealing alternatives to the conventional internal combustion engines for transportation applications. However, in order for them to be commercially viable, effective, stable and low-cost electrocatalysts are needed for the Oxygen Reduction Reaction (ORR) at the cathode. In this contribution, on the basis of Density Functional Theory (DFT) calculations, we show that graphitic materials with active sites composed of 4 nitrogen atoms and transition metal atoms belonging to groups 7 to 9 in the periodic table are active towards ORR, and also towards Oxygen Evolution Reaction (OER). Spin analyses suggest that the oxidation state of those elements in the active sites should in general be +2. Moreover, our results verify that the adsorption behavior of transition metals is not intrinsic, since it can be severely altered by changes in the local geometry of the active site, the chemical nature of the nearest neighbors, and the oxidation states. Nonetheless, we find that these catalysts trend-wise behave as oxides and that their catalytic activity is limited by exactly the same universal scaling relations. PMID:21796295

Calle-Vallejo, Federico; Martínez, José Ignacio; Rossmeisl, Jan

2011-09-14

423

Dense organic-inorganic framework materials containing transition metal ions  

NASA Astrophysics Data System (ADS)

Hybrid inorganic-organic framework materials built upon metal cations and polyfunctional anionic ligands have arrived at the forefront of chemical research, boasting unique properties that derive from their diverse structures. The majority of these compounds are prepared through mild hydrothermal or solvothermal synthesis, at temperatures below 225°C. There has been a great deal of emphasis on porous coordination polymers, or "metal-organic frameworks" (MOFs), which exhibit a wide range of useful sorption and catalytic properties, but there is growing interest in a second class of hybrid frameworks which are denser and often have extended inorganic connectivity, which may be thought of as hybrid metal oxides. These denser compounds provide access to more oxide-like properties such as magnetism, along with improved thermal stability. The flourishing diversity of structures and dimensionalities seen in these materials has led to their growth into a major field of research. Here, the hydrothermal syntheses and crystal structures of fourteen new hybrid framework materials are reported, and additional properties are measured for several of them. The terminology used to describe this class of materials is laid out, and a classification scheme is introduced based on the dimensionalities of their structures. While a combinatorial approach for new compound discovery is often used, strategies for rational synthesis are also discussed. A family of isostructural 3,4,5-trihydroxybenzoate (gallate) hybrid frameworks of the first-row transition metals is produced, with chiral structures imparted by helical packing arrangements. Complex magnetic behavior is characterized in a pillared layered cobalt ethanedisulfonate, the structure of which features intricate metal-oxygen-metal connectivity. Frameworks of new, sometimes unreported, ligand molecules are created through the reactivities of aspartic acid and 5-hydroxyisophthalic acid under hydrothermal conditions. A family of two-ligand frameworks are created using 5-hydroxyisophthalic acid and 4,4'-bipyridyl, which form very different structures when reacted with Mn, Ni, Cu and Zn. Finally, reactions of Cu and Zn together with these two ligands lead to a family of four- and five-component hybrid frameworks showing even greater degrees of structural complexity.

Feller, Russell Kenneth

2008-10-01

424

Solid-state chemistry on a surface and in a beaker: Unconventional routes to transition metal chalcogenide nanomaterials  

SciTech Connect

This article focuses on two different approaches to create nanoscale transition metal chalcogenide materials. First, we used chemical nanofabrication, a combination of top-down patterning and bottom-up solid-state synthesis, to achieve control over the shape, size, and ordering of the patterned nanomaterials. We demonstrated orientational control over nanocrystals within sub-300 nm patterns of MoS{sub 2} and formed free-standing nanostructures of crystalline NiS{sub 2}. In addition, crossed line arrays of mixed metal chalcogenide nanostructures were achieved, and TaS{sub 2} nanopatterns were made by the chemical transformation of tantalum oxide templates. Second, we developed a one-pot procedure using molecular precursors to synthesize two-dimensional NbSe{sub 2}, TaS{sub 2} and TaSe{sub 2} nanoplates and one-dimensional NbSe{sub 2} wires depending on the relative amount of surfactants in the reaction mixture. Prospects for these transition metal chalcogenide nanomaterials with controlled shapes and morphologies will be discussed. - Graphical abstract: This paper describes how transition metal chalcogenide nanomaterials can be produced by two approaches. First, chemical nanofabrication-a combination of top-down patterning and bottom-up solid-state synthesis-was used to achieve control over the shape, size, and ordering of patterned nanomaterials. Second, a one-pot procedure using molecular precursors was developed to synthesize two-dimensional nanoplates and one-dimensional nanowires of conducting transition metal dichalcogenides.

Stender, Christopher L.; Sekar, Perumal [Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208 (United States); Odom, Teri W. [Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208 (United States); Department of Materials Science and Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208 (United States)], E-mail: todom@northwestern.edu

2008-07-15

425

Synthesis, Superstructure, Vacancy-Ordering of Intercalated Transition Metal Dichalcogenides.  

E-print Network

??In this thesis, the synthesis and crystal structures are discussed of intercalated transition metal dichalcogenides (TMDCs) 6R-CuxTa1+yS2 and 2H-CuxTa1+ySe2, as well as the compound Cu3TaSe4.… (more)

Ali, Sk Imran

2014-01-01

426

Band mapping of in situ Cs intercalated transition metal dichalcogenides  

Microsoft Academic Search

The valence band structure of in situ Cs intercalated layered transition metal dichalcogenides has been studied with photoemission spectroscopy. The intercalation was achieved by room temperature deposition of Cs onto clean sample surfaces in UHV. The changes in the valence band structure upon intercalation were more extensive than predicted by the rigid band model, with the most profound change being

H. E. Brauer; H. I. Starnberg; H. P. Hughes; L. J. Holleboom

1996-01-01

427

Electron energy loss studies of the transition metal dichalcogenides  

Microsoft Academic Search

AbstractAn analysis of electron energy loss spectra of some 12 transition metal dichalcogenides has given useful information towards the understanding of the band structures of these layer-type solids. Using the experience gained from studying graphite in which the valence band consists of two groups, namely ? and ? bands, a similar band scheme has also been established for the transition

W. Y. Liang; S. L. Cundy

1969-01-01

428

Magnetic susceptibility of metallic transition-metal dichalcogenides  

Microsoft Academic Search

A tight-binding model has been used to estimate the anisotropy of the magnetic susceptibility of the metallic transition-metal dichalcogenides. The calculated anisotropies obtained are in qualitative agreement with experiment and can be interpreted in terms of the electronic structure of these compounds. It is expected that these results will make possible a more detailed interpretation of the changes in magnetic

A. H. MacDonald; D. J. W. Geldart

1981-01-01

429

Electromagnetic Generation of Ultrasonic Waves in 3-d Transition Metals  

Microsoft Academic Search

Ultrasonic waves at megahertz frequencies can be generated in a metal by rf excitation of a coil placed next to the surface of the metal in the presence of a static magnetic field. We applied this technique to 3-d transition metals. The observed results differ from those obtained previously from nonmagnetic metals. When the static field was normal to the

M. Hanabusa; T. Kushida; J. C. Murphy

1974-01-01

430

Electromagnetic generation of ultrasonic waves in 3-d transition metals  

Microsoft Academic Search

We investigated experimentally acoustic waves generated by electromagnetic means in the surface of 3-d transition metals. The signal amplitude was greatest when the static magnetic field was normal to the generating surface. The amplitude increased in proportion to the external field only up to 3 kOe in both polycrystalline and single crystals of Ni, while there was a tendency for

M. Hanabusa; T. Kushida; J. C. Murphy

1973-01-01

431

Probing the Local Coordination Environment for Transition Metal  

E-print Network

ABSTRACT It is hypothesized that a highly ordered, relatively defect-free dilute magnetic semiconductor correlates well with observed weakly ferromagnetic behavior of the nanowires. Dilute magnetic semiconductors with the magnetic properties of the nanowires. These transition-metal- doped ZnO nanowires, being single crystalline

Yang, Peidong

432

Rare earth transition metal magnesium compounds—An overview  

NASA Astrophysics Data System (ADS)

Intermetallic rare earth-transition metal-magnesium compounds play an important role as precipitations in modern light weight alloys and as host materials for hydrogen storage applications. Recent results on the crystal chemistry, the chemical bonding peculiarities, physical properties, and hydrogenation behavior of these materials are reviewed.

Rodewald, Ute Ch.; Chevalier, Bernard; Pöttgen, Rainer

2007-05-01

433

Induced transition metal moments in rare-earth (yttrium) compounds  

NASA Astrophysics Data System (ADS)

The exchange interactions were analysed in rare-earth (yttrium) transition metal compounds. A transition from nonmagnetic to magnetic state was shown for Co and Ni at ? 70 T and ? 35 T, respectively. The temperature dependences of the magnetic susceptibilities, for the exchange enhanced paramagnets, which change from a T2 dependence to a Curie-Weiss behaviour, as temperature increases, is also analysed.

Burzo, E.

2007-04-01

434

Building a FET with 2D Transition Metal Dichalcogenides  

E-print Network

transfer method ­ New method using polycarbonate (PC) spun on PDMS, then pick up flakes · Once device ­ Spinning ­ Exfoliating ­ Searching ­ Transferring · Future goals · Conclusion #12;Transition Metal to valleytronics Pelant. Nanocrystalline Silicon for Nanophotonics. file=4

Washington at Seattle, University of - Department of Physics, Electroweak Interaction Research Group

435

Band Structure of Transition Metals Studied by ESCA  

Microsoft Academic Search

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

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

1970-01-01

436

Epoxy nanocomposites with two-dimensional transition metal dichalcogenide additives.  

PubMed

Emerging two-dimensional (2D) materials such as transition metal dichalcogenides offer unique and hitherto unavailable opportunities to tailor the mechanical, thermal, electronic, and optical properties of polymer nanocomposites. In this study, we exfoliated bulk molybdenum disulfide (MoS2) into nanoplatelets, which were then dispersed in epoxy polymers at loading fractions of up to 1% by weight. We characterized the tensile and fracture properties of the composite and show that MoS2 nanoplatelets are highly effective at enhancing the mechanical properties of the epoxy at very low nanofiller loading fractions (below 0.2% by weight). Our results show the potential of 2D sheets of transition metal dichalcogenides as reinforcing additives in polymeric composites. Unlike graphene, transition metal dichalcogenides such as MoS2 are high band gap semiconductors and do not impart significant electrical conductivity to the epoxy matrix. For many applications, it is essential to enhance mechanical properties while also maintaining the electrical insulation properties and the high dielectric constant of the polymer material. In such applications, conductive carbon based fillers such as graphene cannot be utilized. This study demonstrates that 2D transition metal dichalcogenide additives offer an elegant solution to such class of problems. PMID:24754702

Eksik, Osman; Gao, Jian; Shojaee, S Ali; Thomas, Abhay; Chow, Philippe; Bartolucci, Stephen F; Lucca, Don A; Koratkar, Nikhil

2014-05-27

437

Catalytic effect of transition metals on microwave-induced degradation of atrazine in mineral micropores.  

PubMed

With their high catalytic activity for redox reactions, transition metal ions (Cu(2+) and Fe(3+)) were exchanged into the micropores of dealuminated Y zeolites to prepare effective microporous mineral sorbents for sorption and microwave-induced degradation of atrazine. Due to its ability to complex with atrazine, loading of copper greatly increased the sorption of atrazine. Atrazine sorption on iron-exchanged zeolites was also significantly enhanced, which was attributed to the hydrolysis of Fe(3+) polycations in mineral micropores and electrostatic interactions of protonated atrazine molecules with the negatively charged pore wall surface. Copper and iron species in the micropores also significantly accelerated degradation of the sorbed atrazine (and its degradation intermediates) under microwave irradiation. The catalytic effect was attributed to the easy reducibility and high oxidation activity of Cu(2+) and Fe(3+) species stabilized in the micropores of the zeolites. It was postulated that the surface species of transition metals (monomeric Cu(2+), Cu(2+)-O-Cu(2+) complexes, FeO(+), and dinuclear Fe-O-Fe-like species) in the mineral micropores were thermally activated under microwave irradiation, and subsequently formed highly reactive sites catalyzing oxidative degradation of atrazine. The transition metal-exchanged zeolites, particularly the iron-exchanged ones, were relatively stable when leached under acidic conditions, which suggests that they are reusable in sorption and microwave-induced degradation. These findings offer valuable insights on designing of effective mineral sorbents that can selectively uptake atrazine from aqueous solutions and catalyze its degradation under microwave irradiation. PMID:24698722

Hu, Erdan; Cheng, Hefa

2014-06-15