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1

Electronic structure of double-perovskite transition-metal oxides  

Microsoft Academic Search

Electronic structure has been investigated by reflectivity measurement for ordered-perovskite transition-metal oxides, Sr2MMoO6 (M=Cr, Mn, Fe, and Co). The ground states of the Co and Mn compounds are paramagnetic insulators, making a sharp contrast with the ferrimagnetic metallic Sr2FeMoO6. For all the compounds, we have observed intense optical transition at ~2 eV, which has been ascribed to the charge-transfer excitation

Y. Moritomo; Sh. Xu; A. Machida; T. Akimoto; E. Nishibori; M. Takata; M. Sakata

2000-01-01

2

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

Microsoft Academic Search

Possible ferromagnetic and ferroelectric phases are explored for bismuth transition-metal oxides with double-perovskite structure A2BB?O6 on the basis of first-principles calculations within the local spin-density approximation (LSDA) and generalized gradient approximation (GGA). It is found that a lattice instability of the cubic to a non-centrosymmetric phase always happens in the all cases of lead and bismuth perovskite oxides with the

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

2006-01-01

3

Non-volatile memory based on transition metal perovskite oxide resistance switching  

NASA Astrophysics Data System (ADS)

Driven by the non-volatile memory market looking for new advanced materials, this dissertation focuses on the study of non-volatile resistive random access memory (RRAM) based on transition metal perovskite oxides. Pr0.7Ca0.3MnO3 (PCMO), one of the representative materials in this family, has demonstrated a large range of resistance change when short electrical pulses with different polarity are applied. Such electrical-pulse-induced resistance (EPIR), with attractive features such as fast response, low power, high-density and non-volatility, makes PCMO and related materials promising candidates for non-volatile RRAM application. The objective of this work is to investigate, optimize and understand the properties of this universal EPIR behavior in transition metal perovskite oxide, represented by PCMO thin film devices. The research work includes fabrication of PCMO thin film devices, characterization of these EPIR devices as non-volatile memories, and investigation of their resistive switching mechanisms. The functionality of this perovskite oxide RRAM, including pulse magnitude/width dependence, power consumption, retention, endurance and radiation-hardness has been investigated. By studying the "shuttle tail" in hysteresis switching loops of oxygen deficient devices, a diffusion model with oxygen ions/vacancies as active agents at the metal/oxide interface is proposed for the non-volatile resistance switching effect in transition metal perovskite oxide thin films. The change of EPIR switching behavior after oxygen/argon ion implantation also shows experiment support for the proposed model. Furthermore, the universality, scalability and comparison with other non-volatile memories are discussed for future application.

Nian, Yibo

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

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 properties. This is correlated with the strong coupling between the electrons and the crystal lattice physical limit. Therefore, further increase of the circuit density requires the consideration of other

Hille, Sander

6

Magnetochromism in Transition Metal Oxides  

NASA Astrophysics Data System (ADS)

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

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

2004-03-01

7

Photoredox laser chemistry of transition metal oxides  

NASA Astrophysics Data System (ADS)

We describe two-color laser excitation of tungsten oxide in ambient air to effect a fully reversible photoredox cycle. One color is infrared, apparently functioning as heat, and the other is visible or shorter wavelength, but not necessarily super bandgap, apparently supplying electronic excitation. In the case of either tungsten oxide or molybdenum oxide, the process can be monitored using a very strong set of Raman spectroscopic features. This process could find application in optical data storage and may be a generally useful strategy for manipulating transition metal oxides.

Osman, J. M.; Bussjager, R. J.; Nash, F.; Chaiken, J.; Villarica, R. M.

8

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

9

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

10

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

E-print Network

of New Transition-Metal Oxyhalide Perovskites Gabriel Caruntu, Liliana Viciu, Leonard Spinu, Weilie Zhou Orleans, New Orleans, LA 70148-2820 ABSTRACT Ion exchange of Dion-Jacobson-type double- and triple-layered perovskites with divalent transition-metal halides leads to the templated assembly of metal-anion layers

Spinu, Leonard

11

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

12

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

13

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

Microsoft Academic Search

Chapter 1. A General introduction to the emerging field of nanomaterials is presented highlighting the category of transition metal oxides. The wide variety of structures, properties, and phenomena of transition metal oxides are stressed. Nano-sized transition metal oxides are presented as systems for fundamental and application research. Examples of individual transition metal oxides are provided. Important developments in the synthesis

Ming Yin

2005-01-01

14

Nano Fabrication of Functional Transition Metal Oxide Thin Films  

Microsoft Academic Search

Transition metal oxide films show a rich variety of peculiar properties, such as ferroelectricity, ferromagnetism, high Tc superconductivity, colossal magnetoresistance, and so on. The method to process the oxide films down to nano scale is still under development. In this paper we introduce several techniques to process oxide films on the basis of AFM lithography and nanoimprint lithography. Using AFM

Naoki Suzuki; Hidekazu Tanaka; Yoshihiko Yanagisawa; Satoru Yamanaka; Luca Pellegrino; Bong Kuk Lee; Hea Yeon Lee; Tomoji Kawai

2008-01-01

15

Photoelectron spectroscopic studies on the electronic structures of transition metal clusters and transition metal oxide clusters  

NASA Astrophysics Data System (ADS)

Photoelectron spectroscopic (PES) studies have been conducted on the bare transition metal clusters: Tin/ (n = 1~65),/ Vn/ (n = 1~70),/ Crn/ (n = 1~70),/ Fen/ (n = 1~33), Con/ (n = 1~51) and Nin/ (n = 1~50). The PES spectra of these clusters are taken at several detachment photon energies ranging from the second harmonic (532 nm) to fourth harmonic (266 nm) of the YAG laser and the 193 nm from an ArF excimer laser. Transition metals are very important catalysis elements; the photoelectron spectroscopic studies on the clusters provide a powerful tool for us to understand the metal- metal bonding and their electronic structures atom by atom. The electronic structure of titanium clusters is found to become bulk-like at relative small cluster sizes. It is observed that the 3d band emerges at the eight-atom cluster beyond which the d-band broadens and evolves toward that of the bulk. The vanadium clusters show three regions of spectral evolution: molecular behavior for n = 3-12; transition from molecular to bulk- like for n = 13-17; gradual convergence to bulk for n > 17, for which a surface-like feature is observed to slowly merge into the bulk feature near n = 60. Even-odd alternations are observed in the photoelectron spectra of small Crn clusters. Density functional calculations reveal a unique dimer growth route for chromium clusters up to Cr11, at which a structural transition occurs from the dimer growth to a bulklike body-centered-cubic structure. The PES spectra of the ferromagnetic metal clusters (Fen,/ Con, and Nin) reveal interesting relationships among the electronic structures and reactivity, geometric and magnetic properties, respectively. Photoelectron spectroscopic studies on the transition metal oxide clusters are also conducted. The study on the novel molecules Mx,/ Oy, (M = Ti, V, Cr, Fe, Cu, and Ni) shows the sequential oxidation behavior of the transition metals. Information about the structures and chemical bonding of these oxide molecules is also obtained.

Wu, Hongbin

16

Strain effects in low-dimensional transition metal oxides  

Microsoft Academic Search

Transition metal oxides offer a wide spectrum of properties which provide the foundation for a broad range of potential applications. Many of these properties originate from intrinsic coupling between lattice deformation and nanoscale electronic and magnetic ordering. Lattice strain thus has a profound influence on the electrical, optical, and magnetic properties of these materials. Recent advances in materials processing have

Jinbo Cao; Junqiao Wu

2011-01-01

17

Transition metal oxides for hot gas desulphurisation  

Microsoft Academic Search

Thermodynamic equilibrium simulations were made to determine suitable materials for intensive desulphurisation of fuel gases from an IGCC. Zinc-based materials are the most promising for high temperature intensive desulphurisation, but cause evaporation and regenerability problems. To overcome these problems, a new material was synthesised, containing zinc oxide supported on a titanium dioxide support. The material is able to reduce H2S

W. F. Elseviers; H. Verelst

1999-01-01

18

Dynamics and Control in Complex Transition Metal Oxides  

NASA Astrophysics Data System (ADS)

Advances in the synthesis, growth, and characterization of complex transition metal oxides coupled with new experimental techniques in ultrafast optical spectroscopy have ushered in an exciting era of dynamics and control in these materials. Experiments utilizing femtosecond optical pulses can initiate and probe dynamics of the spin, lattice, orbital, and charge degrees of freedom. Major goals include (a) determining how interaction and competition between the relevant degrees of freedom determine macroscopic functionality in transition metal oxides (TMOs) and (b) searching for hidden phases in TMOs by controlling dynamic trajectories in a complex and pliable energy landscape. Advances in creating intense pulses from the far-IR spectrum through the visible spectrum enable mode-selective excitation to facilitate exploration of these possibilities. This review covers recent developments in this emerging field and presents examples that include the cuprates, manganites, and vanadates.

Zhang, J.; Averitt, R. D.

2014-07-01

19

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

20

Ionically-mediated electromechanical hysteresis in transition metal oxides  

SciTech Connect

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

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

2012-01-01

21

EPR monitoring of redox processes in transition metal oxide catalysts.  

PubMed

Transition metal oxides (TMO) are widely used as catalysts of a number of catalytic reactions, mainly of redox nature. This is due to the unique ability of transition metal ions to change easily their oxidation state, coordination, and/or arrangement of the coordination polyhedra. At present, the only abundant, direct information available about paramagnetic centers formed during interaction of the reagents with the TMO surface stems from EPR studies. This technique is very sensitive and allows detection of very small concentration of paramagnetic sites. Moreover, analysis of the EPR spectrum offers a direct approach to the determination of symmetry and electronic structure of the centers concerned. Such information is of particular value for understanding the operating reduction/reoxidation mechanisms, with immediate implications for solid-state structural studies, catalysis and so forth. The present work shows two aspects of the use of EPR for monitoring of redox processes with the participation of TMO: a) investigation of the reaction kinetics and b) description of the individual active sites involved in the catalytically important redox processes. The presented examples include: a) kinetic descriptions (including mathematical models) of reduction and oxidation processes in the vanadia-molybdena catalysts occurring upon interaction with propene and oxygen, b) identification of paramagnetic centers formed in the reduced molybdena, c) analysis of the butene interaction with a nickel catalyst, and d) description of the radical oxygen species on the surface of manganese-containing catalysts. PMID:23686922

Labanowska, M

2001-12-17

22

Nanostructured transition metal oxides for energy storage and conversion  

NASA Astrophysics Data System (ADS)

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

Li, Qiang

23

Resonant Ultrasound Studies of Complex Transition Metal Oxides  

SciTech Connect

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

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

2008-08-18

24

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

SciTech Connect

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

Xiao, Di [ORNL; Zhu, Wenguang [University of Tennessee, Knoxville (UTK); Ran, Ying [Boston College, Chestnut Hill; Nagaosa, Naoto [University of Tokyo, Tokyo, Japan; Okamoto, Satoshi [ORNL

2011-01-01

25

Transition metal oxide improves overall efficiency and maintains performance with inexpensive metals.  

E-print Network

Transition metal oxide improves overall efficiency and maintains performance with inexpensive that inserting a transition metal oxide (TMO) between the lead sulfide (PbS) quantum dot (QD) layer and the metal Oxide as a Hole Extraction Layer in PbS Quantum Dot Solar Cells."Nano Letters 11, 3263 (2011). Key

26

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

Microsoft Academic Search

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

Hitoshi Ogihara; Sadakane Masahiro; Yoshinobu Nodasaka; Wataru Ueda

2009-01-01

27

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

E-print Network

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

Lin, Xi

28

Structural, electrical and magnetic properties of transition metal nickel oxides  

NASA Astrophysics Data System (ADS)

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

Wu, Guoqing

29

Observations of Electron Irradiation Effects at Transition Metal Oxide Surfaces.  

NASA Astrophysics Data System (ADS)

In this dissertation the effects of electron irradiation on several maximally-valent transition-metal oxides have been investigated using a combination of surface profile imaging, selected-area-electron diffraction, optical diffractograms, and electron-energy-loss spectroscopy. It was found that the surfaces of TiO_2, Nb _2O_5, V_2 O_5 and Ti_2 Nb_{10}O _{29} were reduced to the corresponding binary oxide phase inside a 400keV high-resolution electron microscope during observation at high magnification and high current density (5-50A/cm^2). These reduced surface phases, which are all based on cubic rock -salt structures, grow with a well-defined three-dimensional epitaxial relationship with the bulk oxide. Certain structural features of the epitaxy were found to be common to the oxides studied and computer-drawn models of the crystalline structures were used to gain insight into the atomic rearrangements which took place during the monoxide growth. In the case of WO_3, for which no stable monoxide phase has been reported, the striking similarity in the epitaxial growth of a surface phase led to the proposal of a novel monoxide phase. The metallic conductivity of each of these monoxide phases was considered to be significant in terms of the mechanism which is proposed to initiate the electron-stimulated-desorption of oxygen from the original oxides. Evidence for a current density threshold for the accumulation of the monoxide phase and observation of recrystallization below this threshold are reported. In contrast, in response to extremely high-current density irradiation (10 ^3-10^4A/cm ^2), the surfaces of these oxides developed sputter pits and were reduced beyond the monoxide phase. These observations were repeated for TiO_2 in a ultra-high-vacuum microscope. Secondary electron images, high-angle annular dark-field images and EELS confirmed that the improved vacuum did not affect substantially the beam-induced reactions.

McCartney, Martha Rogers

30

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

31

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

PubMed

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

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

2001-10-21

32

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

33

Identifying the isolated transition metal ions\\/oxides in molecular sieves and on oxide supports by UV resonance Raman spectroscopy  

Microsoft Academic Search

Isolated transition metal ions\\/oxides in molecular sieves and on surfaces are a class of active sites for selective oxidation of hydrocarbons. Identifying the active sites and their coordination structure is vital to understanding their essential role played in catalysis and designing and synthesizing more active and selective catalysts. The isolated transition metal ions in the framework of molecular sieves (e.g.,

2003-01-01

34

Evidence for an oxygen diffusion model for the electric pulse induced resistance change effect in transition-metal oxides.  

PubMed

Electric-pulse induced resistance hysteresis switching loops for Pr0.7Ca0.3MnO3 perovskite oxide films were found to exhibit an additional sharp "shuttle tail" peak around the negative pulse maximum for films deposited in an oxygen-deficient ambient. The resistance relaxation in time of this "shuttle tail" peak as well as resistance relaxation in the transition regions of the resistance hysteresis loop show evidence of oxygen diffusion under electric pulsing, and support a proposed oxygen diffusion model with oxygen vacancy pileup at the metal electrode interface region as the active process for the nonvolatile resistance switching effect in transition-metal oxides. PMID:17501295

Nian, Y B; Strozier, J; Wu, N J; Chen, X; Ignatiev, A

2007-04-01

35

Three-particle approximation for transition-metal oxides  

NASA Astrophysics Data System (ADS)

Quasiparticle spectra are calculated for NiO and CuO on the basis of band structures obtained within the ab initio self-interaction-corrected local-spin density (SIC-LSD) and LSD+U approximations. On-site Coulomb correlations are described by a multiband Hubbard model, which is treated within Igarashi's three-particle approximation. The transition-metal d-state spectral weight is split into a main dnL peak and a dn-1 satellite. We show that mean-field band structures in this way can lead to a good description of the experimental photoemission spectra of these compounds. The validity of the three-particle approach is investigated, and it is concluded that the method is best suited for a system which is well orbitally polarized on the mean-field level.

Lægsgaard, J.; Svane, A.

1997-02-01

36

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

Microsoft Academic Search

Defects at transition metal (TM) and rare earth (RE) oxide surfaces, neutral oxygen vacancies in particular, play a major role in a variety of technological applications. This is the motivation of numerous studies of partially reduced oxide surfaces. We review, discuss, and compare theoretical data for structural and electronic properties and energetic quantities related to the formation of oxygen defects

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

2007-01-01

37

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 change us, but we start and end with family" -Anthony Brandt ii #12;Acknowledgements I would like Metal Oxides and Rare Earth Metals by Brian Ross Maddox Electron correlation can affect profound changes

Islam, M. Saif

38

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

39

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

40

Transition Metal Oxide Core-Shell Nanowires: Generic Synthesis and Transport Studies  

Microsoft Academic Search

A generic non-equilibrium synthesis technique has been developed to produce novel transition metal oxide nanowires, including YBa2Cu3O6.66, La0.67Ca0.33MnO3, PbZr0.58Ti0.42O3, and Fe3O4. Key to our success is the growth of vertically aligned single-crystalline MgO nanowires, which worked as excellent templates for epitaxial deposition of the desired transition metal oxides and led to high-quality core-shell nanowires. Transport studies on La0.67Ca0.33MnO3 nanowires have

Song Han; Chao Li; Zuqin Liu; Bo Lei; Daihua Zhang; Wu Jin; Xiaolei Liu; Tao Tang; Chongwu Zhou

2004-01-01

41

Nanophase transition metal oxides show large thermodynamically driven shifts in oxidation-reduction equilibria.  

PubMed

Knowing the thermodynamic stability of transition metal oxide nanoparticles is important for understanding and controlling their role in a variety of industrial and environmental systems. Using calorimetric data on surface energies for cobalt, iron, manganese, and nickel oxide systems, we show that surface energy strongly influences their redox equilibria and phase stability. Spinels (M(3)O(4)) commonly have lower surface energies than metals (M), rocksalt oxides (MO), and trivalent oxides (M(2)O(3)) of the same metal; thus, the contraction of the stability field of the divalent oxide and expansion of the spinel field appear to be general phenomena. Using tabulated thermodynamic data for bulk phases to calculate redox phase equilibria at the nanoscale can lead to errors of several orders of magnitude in oxygen fugacity and of 100 to 200 kelvin in temperature. PMID:20929770

Navrotsky, Alexandra; Ma, Chengcheng; Lilova, Kristina; Birkner, Nancy

2010-10-01

42

Restructuring transition metal oxide nanorods for 100% selectivity in reduction of nitric oxide with carbon monoxide.  

PubMed

Transition metal oxide is one of the main categories of heterogeneous catalysts. They exhibit multiple phases and oxidation states. Typically, they are prepared and/or synthesized in solution or by vapor deposition. Here we report that a controlled reaction, in a gaseous environment, after synthesis can restructure the as-synthesized transition metal oxide nanorods into a new catalytic phase. Co3O4 nanorods with a preferentially exposed (110) surface can be restructured into nonstoichiometric CoO1-x nanorods. Structure and surface chemistry during the process were tracked with ambient pressure X-ray photoelectron spectroscopy (AP-XPS) and environmental transmission electron microscopy (E-TEM). The restructured nanorods are highly active in reducing NO with CO, with 100% selectivity for the formation of N2 in temperatures of 250-520 °C. AP-XPS and E-TEM studies revealed the nonstoichiometric CoO1-x nanorods with a rock-salt structure as the active phase responsible for the 100% selectivity. This study suggests a route to generate new oxide catalysts. PMID:23731229

Zhang, Shiran; Shan, Junjun; Zhu, Yuan; Nguyen, Luan; Huang, Weixin; Yoshida, Hideto; Takeda, Seiji; Tao, Franklin Feng

2013-07-10

43

Status in calculating electronic excited States in transition metal oxides from first principles.  

PubMed

Characterization of excitations in transition metal oxides is a crucial step in the development of these materials for photonic and optoelectronic applications. However, many transition metal oxides are considered to be strongly correlated materials, and their complex electronic structure is challenging to model with many established quantum mechanical techniques. We review state-of-the-art first-principles methods to calculate charged and neutral excited states in extended materials, and discuss their application to transition metal oxides. We briefly discuss developments in density functional theory (DFT) to calculate fundamental band gaps, and introduce time-dependent DFT, which can model neutral excitations. Charged excitations can be described within the framework of many-body perturbation theory based on Green's functions techniques, which predominantly employs the GW approximation to the self-energy to facilitate a feasible solution to the quasiparticle equations. We review the various implementations of the GW approximation and evaluate each approach in its calculation of fundamental band gaps of many transition metal oxides. We also briefly review the related Bethe-Salpeter equation (BSE), which introduces an electron-hole interaction between GW-derived quasiparticles to describe accurately neutral excitations. Embedded correlated wavefunction theory is another framework used to model localized neutral or charged excitations in extended materials. Here, the electronic structure of a small cluster is modeled within correlated wavefunction theory, while its coupling to its environment is represented by an embedding potential. We review a number of techniques to represent this background potential, including electrostatic representations and electron density-based methods, and evaluate their application to transition metal oxides. PMID:24488486

Bendavid, Leah Isseroff; Carter, Emily Ann

2014-01-01

44

Spectroscopic Studies of Diatomic Transition Metal Oxides and Fluorides.  

NASA Astrophysics Data System (ADS)

Wavelength selected fluorescence excitation spectroscopy (WSFES) techniques and ligand field theory (LFT) calculations have been applied to the following transition metal diatomics: CeO, UO, LaF, YF, ScF, HfO, TiO, and ZrO. All of the rotational spectra recorded for these molecules were at a resolution of 0.03 cm^{-1}, and, with few exceptions, Omega assignments for electronic states were unambiguously determined from observations of the first lines in at least two rotational branches. Accurate term energies and rotational constants are reported. Thirty one electronic transitions of CeO were recorded, and all of the sixteen states that correlate with rm Ce^{2+}(4f6s)O^ {2-} were characterized. The results are in good accord with a ligand field theory model of the low-lying states. New assignments were established for four previously observed transitions, and spectra for three new excited states were analyzed. LFT calculations have been used in an attempt to provide configurational assignments for the excited states (including those from previous studies). Twenty two states are tentatively assigned to the rm Ce^{2+}(4f6p)O ^{2-} configuration. Twelve others are tentatively assigned to rm Ce^ {2+}(4f5d)O^{2-}.. Rotation-electronic interactions between states of the 4f6s configuration of CeO, mediated by the operator {-}B(R)( J^+ cdot J_sp{a}{-}+ J^-cdot J_sp{a} {+}), have been calculated. Second-order perturbation theory was used to account for the effect of heterogeneous interactions on the rotation constants within a single configuration. Thirty-three electronic transitions of UO were analyzed, and nine low-lying electronic states that correlated with either rm U^{2+}(5f ^37s)O^{2-} or rm U^{2+}(5f^27s^2)O ^{2-} were characterized. Ligand field theory calculations were also used in an attempt to provide configurational assignments for the excited states of UO and ThO. Experimentally derived values for Delta B_sp{0} {0}(nl/n^' l^') parameters were used to predict the electronic structures of UO and UO^+.. Eight electronic transitions of LaF and nine transitions of YF were studied. LFT calculations (and in the case of LaF, hyperfine constants) were used to suggest electronic configurational assignments for the excited states of these molecules. WSFE spectra of the 0-0 and 1-1 bands of the ScF F^1Phi-A^1 Delta transition were observed, and perturbations in the F^1Phi state, caused by interactions with the h^3Pi_2 state, were analyzed. Using a method based on Franck-Condon factors, the vibrational numbering in the perturbing h^3Pi_2 state was estimated. The 5698 A band of HfO has been re examined. The wavelength-resolved fluorescence excitation technique was used to record the (2,0) band of the C ^3Delta_3-a^1 Delta transition, and the (2,3) and (2,4) bands of the C^3Delta_3 -X^3Delta_3 electronic transition of TiO. The (0,0) bands of the satellite e^3 Pi_1-a^3Delta _1 and e^3Pi_2 -a^3Delta_2 transitions of ZrO were investigated, and these data were combined with previous high resolution analyses of the ZrO beta-system and with the analysis of the intercombination e^3Pi_1 -X^1Sigma ^+ transition to obtain accurate term energies for the triplet states of ^{90 }Zr^{16}O. (Abstract shortened by UMI.).

McCord, John Edward

45

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

46

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

NASA Astrophysics Data System (ADS)

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

Yin, Ming

2005-12-01

47

Effects of Transition Metals on Nitric Oxide Synthase Catalysis  

Microsoft Academic Search

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

Jason M. Perry; Michael A. Marletta

1998-01-01

48

Novel photoinduced phase transitions in transition metal oxides and diluted magnetic semiconductors  

NASA Astrophysics Data System (ADS)

Some transition metal oxides have frustrated electronic states under multiphase competition due to strongly correlated d electrons with spin, charge, and orbital degrees of freedom and exhibit drastic responses to external stimuli such as optical excitation. Here, we present photoemission studies on Pr0.55(Ca1 - y Sr y )0.45MnO3 ( y = 0.25), SrTiO3, and Ti1 - x Co x O2 ( x = 0.05, 0.10) under laser illumination and discuss electronic structural changes induced by optical excitation in these strongly correlated oxides. We discuss the novel photoinduced phase transitions in these transition metal oxides and diluted magnetic semiconductors on the basis of polaronic pictures such as orbital, ferromagnetic, and ferroelectric polarons.

Mizokawa, Takashi

2012-10-01

49

Enhancement of spin polarization in a transition metal oxide ferromagnetic nanodot diode.  

PubMed

Enhancement of spin polarization was observed in a transition metal oxide (Fe,Zn)(3)O(4)/Nb-SrTiO(3) ferromagnetic nanodot Schottky diode. The highly integrated oxide nanodot diodes were constructed using nanoimprint lithography based on a Mo lift-off method in combination with a pulsed laser deposition technique. The junction magnetoresistance of diodes increased as diode size increased. The spin polarization estimated from the thermionic emission model is enhanced from P = 0.74 in a conventional film to P = 0.89 in a nanodot diode whose size is 300 × 300 nm(2). The nanofabrication technique used here will enable us to construct superior transition metal oxide spintronic nanomaterial and nanodevices. PMID:21171625

Yamanaka, Satoru; Kanki, Teruo; Kawai, Tomoji; Tanaka, Hidekazu

2011-02-01

50

Transition metal-catalyzed selective oxidation in carbon dioxide  

SciTech Connect

Carbon dioxide represents an enviromentally benign replacement for conventional solvents in homogeneous catalysis. Above its critical temperature (T{sub c} = 31.1{degrees}C) its density can be varied via the pressure, potentially allowing selectivity to be {open_quotes}pressure-tuned.{close_quotes} Rates and selectivity for epoxidation of allylic alcohols by vanadium catalysts, including V{sub 2}O{sub 5}, VO(acac){sub 2}, and VO(OiPr){sub 3} were measured in supercritical and subcritical CO{sub 2} (25{degrees}C) and compared to results in conventional solvents; oxidation of the alcohol is competitive with epoxidation above T{sub c}. VO(OiPr){sub 3} proved to be the most active catalyst due to its superior solubility. Dihydroxylation of olefins with stoichiometric OsO{sub 4} proved facile in supercritical CO{sub 2}, but two-phase CO{sub 2}/H{sub 2}O catalytic oxidation was unsuccessful due to the acidity of the medium. Rate and enantioselectivity data for the Ti catalyzed enantioselective epoxidation will also be presented.

Morita, D.K.; Tumas, W. [Los Alamos National Laboratory, NM (United States); Pesiri, D.R. [Univ. of North Carolina, Chapel Hill, NC (United States)

1996-10-01

51

Natural media with negative index of refraction: Perspectives of complex transition metal oxides (Review Article)  

NASA Astrophysics Data System (ADS)

The capabilities of perovskite-like compounds with the effect of colossal magnetoresistance (CMR) and some other complex oxides to have a negative index of refraction (NIR) are considered. Physical properties of these compounds are also analyzed from the standpoint of designing tunable metamaterials on their base. Of particular interest are temperature and magnetic field driven first-order transformations in oxides with perovskite structure and in spinels. These transformations give rise to nanophase separated states, using which the properties of negative refraction can be affected. The magnetic-field controlled metamaterials with CMR oxides as a boundary NIR media for a photonic crystal are discussed.

Fertman, E. L.; Beznosov, A. B.

2011-07-01

52

Structure of transition-metal-oxygen-vacancy pair centers  

Microsoft Academic Search

The microscopic structure of the Fe3+-VO and Mn2+-VO pair centers has been considered using the Newman superposition model. This model yields the EPR parameter b02 as a function of transition-metal-ion-oxygen distance d and position. It is found, for the oxide perovskites, that the transition-metal ion moves by a distance Delta=0.1 d=0.2 Å towards the vacancy VO. The four lateral oxygens

E. Siegel; K. A. Müller

1979-01-01

53

Synthesis of transition-metal phosphides from oxidic precursors by reduction in hydrogen plasma  

SciTech Connect

A series of transition metal phosphides, including MoP, WP, CoP, Co{sub 2}P, and Ni{sub 2}P, were synthesized from their oxidic precursors by means of hydrogen plasma reduction under mild conditions. The effects of reduction conditions, such as metal to phosphorus molar ratio, power input, and reduction time, on the synthesis of metal phosphides were investigated. The products were identified by means of XRD characterization. It is indicated that metal phosphides were readily synthesized stoichiometrically from their oxides in hydrogen plasma under mild conditions. - Graphical abstract: Metal phosphides were obtained stoichiometrically from their oxidic precursors by hydrogen plasma reaction under mild conditions.

Guan Jie [Department of Catalytic Chemistry and Engineering, State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116012 (China); Wang Yao [Liaoning Key Laboratory of Petrochemical Technology and Equipments, Dalian University of Technology, Dalian 116012 (China); Qin Minglei; Yang Ying [Department of Catalytic Chemistry and Engineering, State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116012 (China); Li Xiang [Department of Catalytic Chemistry and Engineering, State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116012 (China); Liaoning Key Laboratory of Petrochemical Technology and Equipments, Dalian University of Technology, Dalian 116012 (China); Wang Anjie, E-mail: ajwang@dlut.edu.c [Department of Catalytic Chemistry and Engineering, State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116012 (China); Liaoning Key Laboratory of Petrochemical Technology and Equipments, Dalian University of Technology, Dalian 116012 (China)

2009-06-15

54

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

DOEpatents

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

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

1985-08-16

55

Evolution of charge and spin state of transition metals in the LaMn1-xCoxO3 perovskite series  

NASA Astrophysics Data System (ADS)

Charge and spin state evolution of the transition metals in the LaMn1-xCoxO3 perovskite series was studied by means of high resolution x-ray absorption and emission spectroscopy. The gradual charge transfer from Mn to Co sites was observed upon increasing Co doping. The high spin of the Mn3+/4+ and Co2+ ions is preserved in the entire solid solution. Co3+ ions reveal low spin state at low doping, while the gradual increase of the average Co3+ spin state is observed at higher cobalt concentrations. The results plausibly explain the observed magnetization anomalies.

Sikora, M.; Knizek, K.; Kapusta, Cz.; Glatzel, P.

2008-04-01

56

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

NASA Astrophysics Data System (ADS)

The 6,7Li MAS NMR spectra of lithium ions in paramagnetic host materials are extremely sensitive to number and nature of the paramagnetic cations in the Li local environments and large shifts (Fermi contact shifts) are often observed. The work presented in this paper aims to provide a rational basis for the interpretation of the 6,7Li NMR shifts, as a function of the lithium local environment and electronic configuration of the transition metal ions. We focus on the layered rocksalts often found for LiMO2 compounds and on materials that are isostructural with the K2NiF4 structure. In order to understand the spin-density transfer mechanism from the transition metal ion to the lithium nucleus, which gives rise to the hyperfine shifts observed by NMR, we have performed density functional theory (DFT) calculations in the generalized gradient approximation. For each compound, we calculate the spin densities values on the transition metal, oxygen and lithium ions and map the spin density in the M-O-Li plane. Predictions of the calculations are in good agreement with several experimental results. We show that DFT calculations are a useful tool with which to interpret the observed paramagnetic shifts in layered oxides and to understand the major spin-density transfer processes. This information should help us to predict the magnitudes and signs of the Li hyperfine shifts for different Li local environments and t2g vs eg electrons in other compounds.

Carlier, D.; Ménétrier, M.; Grey, C. P.; Delmas, C.; Ceder, G.

2003-05-01

57

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

PubMed

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

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

2013-11-18

58

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

NASA Astrophysics Data System (ADS)

Transitional metal oxides hold great potential for high capacity anodes. However, the low electron conductivity of such materials leads to poor cycling stability and inferior rate capability. We reported herein the use of a novel hydrogen plasma technology to improve the conductance of metal oxides, which leads great success in improving the rate performance of CuO nanotube based anodes. This method has the potential to be widely adopted in the field of lithium ion batteries and supercapacitors.Transitional metal oxides hold great potential for high capacity anodes. However, the low electron conductivity of such materials leads to poor cycling stability and inferior rate capability. We reported herein the use of a novel hydrogen plasma technology to improve the conductance of metal oxides, which leads great success in improving the rate performance of CuO nanotube based anodes. This method has the potential to be widely adopted in the field of lithium ion batteries and supercapacitors. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr05880h

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

2014-03-01

59

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

60

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

61

Insights and challenges of applying the GW method to transition metal oxides  

NASA Astrophysics Data System (ADS)

The ab initio GW method is considered as the most accurate approach for calculating the band gaps of semiconductors and insulators. Yet its application to transition metal oxides (TMOs) has been hindered by the failure of traditional approximations developed for conventional semiconductors. In this work, we examine the effects of these approximations on the values of band gaps for ZnO, Cu2O, and TiO2. In particular, we explore the origin of the differences between the two widely used plasmon-pole models. Based on the comparison of our results with the experimental data and previously published calculations, we discuss which approximations are suitable for TMOs and why.

Samsonidze, Georgy; Park, Cheol-Hwan; Kozinsky, Boris

2014-11-01

62

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

SciTech Connect

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

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

2010-07-08

63

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

64

Elucidation of Proton-Assisted Fluxionality in Transition-Metal Oxide Clusters  

NASA Astrophysics Data System (ADS)

The phenomenon of fluxionality in the reactions of transition-metal oxide clusters provides many opportunities in various industrial and catalytic processes. We present an electronic structure investigation of the fluxionality pathways when anionic W3O6- and Mo3O6- clusters react with three small molecules - water, ammonia and hydrogen sulfide. The presentation features a detailed understanding of (a) how the fluxionality pathway occurs and (b) the various factors that affect the fluxionality pathway - such as the metal, different spin-states and the nature of the non-metal in the reacting small molecule.

Ramabhadran, Raghunath O.; Mayhall, Nicholas J.; Becher, Edwin L. Becher, Iii; Chowdhury, Arefin; Raghavachari(s), Krishnan

2012-06-01

65

Electron enrichment in 3d transition metal oxide hetero-nanostructures.  

PubMed

Direct experimental observation of spontaneous electron enrichment of metal d orbitals in a new transition metal oxide heterostructure with nanoscale dimensionality is reported. Aqueous chemical synthesis and vapor phase deposition are combined to fabricate oriented arrays of high-interfacial-area hetero-nanostructures comprised of titanium oxide and iron oxide nanomaterials. Synchrotron-based soft X-ray spectroscopy techniques with high spectral resolution are utilized to directly probe the titanium and oxygen orbital character of the interfacial region's occupied and unoccupied densities of states. These data demonstrate the interface to possess electrons in Ti 3d bands and an emergent degree of orbital hybridization that is absent in parent oxide reference crystals. The carrier dynamics of the hetero-nanostructures are studied by ultrafast transient absorption spectroscopy, which reveals the presence of a dense manifold of states, the relaxations from which exhibit multiple exponential decays whose magnitudes depend on their energetic positions within the electronic structure. PMID:21834542

Kronawitter, Coleman X; Bakke, Jonathan R; Wheeler, Damon A; Wang, Wei-Cheng; Chang, Chinglin; Antoun, Bonnie R; Zhang, Jin Z; Guo, Jinghua; Bent, Stacey F; Mao, Samuel S; Vayssieres, Lionel

2011-09-14

66

Low temperature synthesis of lamellar transition metal oxides containing surfactant ions  

SciTech Connect

Recently there has been much interest in reacting vanadium oxides hydrothermally with cationic surfactants to form novel layered compounds. A series of new transition metal oxides, however, has also been formed at or near room temperature in open containers. Synthesis, characterization, and proposed mechanisms of formation are the focus of this work. Low temperature reactions of vanadium pentoxide and ammonium (DTA) transition metal oxides with long chain amine surfactants, such as dodecyltrimethylammonium bromide yielded interesting new products many of which are layered phases. DTA{sub 4}H{sub 2}V{sub 10}O{sub 28}{center_dot}8H{sub 2}O, a layered highly crystalline phase, is the first such phase for which a single crystal X-ray structure has been determined. The unit cell for this material was found to be triclinic with space group P {bar 1} and dimensions a = 9.895(1){angstrom}, b = 11.596(1){angstrom}, c = 21.924(1){angstrom}, {alpha} = 95.153(2){degree}, {beta} = 93.778(1){degree}, and {gamma} = 101.360(1){degree}. Additionally, the authors synthesized a dichromate phase and a manganese chloride layered phase, with interlayer spacings of 26.8{angstrom}, and 28.7{angstrom} respectively. The structure, composition, and synthesis of the vanadium compound are described, as well as the synthesis and preliminary characterization of the new chromium and manganese materials.

Janauer, G.G.; Chen, R.; Dobley, A.D.; Zavalij, P.Y.; Whittingham, M.S. [State Univ. of New York, Binghamton, NY (United States)

1997-09-01

67

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

68

Synthesis of transition metal nitride by nitridation of metastable oxide precursor  

SciTech Connect

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

Wang, Huamin; Wu, Zijie; Kong, Jing [Key Laboratory of Advanced Energy Materials Chemistry (MOE), College of Chemistry, Nankai University, Tianjin 300071 (China)] [Key Laboratory of Advanced Energy Materials Chemistry (MOE), College of Chemistry, Nankai University, Tianjin 300071 (China); Wang, Zhiqiang, E-mail: zqwang@mail.nankai.edu.cn [Key Laboratory of Advanced Energy Materials Chemistry (MOE), College of Chemistry, Nankai University, Tianjin 300071 (China) [Key Laboratory of Advanced Energy Materials Chemistry (MOE), College of Chemistry, Nankai University, Tianjin 300071 (China); Tianjin Key Laboratory of Water Environment and Resources, Tianjin Normal University, No. 393 Binshui Road, Xiqing Dist., Tianjin 300387 (China); Zhang, Minghui, E-mail: zhangmh@nankai.edu.cn [Key Laboratory of Advanced Energy Materials Chemistry (MOE), College of Chemistry, Nankai University, Tianjin 300071 (China)] [Key Laboratory of Advanced Energy Materials Chemistry (MOE), College of Chemistry, Nankai University, Tianjin 300071 (China)

2012-10-15

69

Multistep soft chemistry method for valence reduction in transition metal oxides with triangular (CdI2-type) layers.  

PubMed

Transition metal (M) oxides with MO2 triangular layers demonstrate a variety of physical properties depending on the metal oxidation states. In the known compounds, metal oxidation states are limited to either 3+ or mixed-valent 3+/4+. A multistep soft chemistry synthetic route for novel phases with M(2+/3+)O2 triangular layers is reported. PMID:24487411

Blakely, Colin K; Bruno, Shaun R; Poltavets, Viktor V

2014-03-14

70

TOPICAL REVIEW: Surface oxides on close-packed surfaces of late transition metals  

NASA Astrophysics Data System (ADS)

In recent years, the formation of thin, well-ordered but complex surface oxides on late transition metals has been discovered. The driving force for this line of research has been the strong incentive to increase the partial pressure of oxygen from ultra-high vacuum to conditions more relevant for heterogeneous catalysis. Here we review the present status of the research field. Compared to oxygen adatom superstructures, the structure of the surface oxides has proven to be extremely complex, and the investigations have therefore relied on a combination of several experimental and theoretical techniques. The approach to solving the structures formed on close-packed surfaces of Pd and Rh is presented in some detail. Focusing on the structures found, we show that the surface oxides share some general properties with the corresponding bulk oxides. Nevertheless, of all surface oxide structures known today, only the two-dimensional surface oxides on Pd(100) and Pt(110) have the same lattice as the bulk oxides (PdO and PtO, respectively). In addition to two-dimensional oxides, including the O-Rh-O trilayers found on Rh, one-dimensional oxides were observed at ridges or steps of open surfaces such as (110) or vicinal surfaces. Finally, we briefly report on a few studies of the reactivity of surface oxides with well-known structure.

Lundgren, Edvin; Mikkelsen, Anders; Andersen, Jesper N.; Kresse, Georg; Schmid, Michael; Varga, Peter

2006-08-01

71

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

72

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

73

Factors that affect Li mobility in layered lithium transition metal oxides  

NASA Astrophysics Data System (ADS)

The diffusion constant of Li in electrode materials is a key aspect of the rate capability of rechargeable Li batteries. The factors that affect Li mobility in layered lithium transition metal oxides are systematically studied in this paper by means of first-principles calculations. In close packed oxides octahedral ions diffuse by migrating through intermediate tetrahedral sites. Our results indicate that the activation barrier for Li hopping is strongly affected by the size of the tetrahedral site and the electrostatic interaction between Li+ in that site and the cation in the octahedron that shares a face with it. The size of the tetrahedral site is determined by the c -lattice parameter which has a remarkably strong effect on the activation barrier for Li migration. The effect of other factors such as cation mixing and doping with nontransition metal ions can be interpreted quantitatively in terms of the size and electrostatic effect. A general strategy to design high rate electrode materials is discussed.

Kang, Kisuk; Ceder, Gerbrand

2006-09-01

74

Charge generation layers comprising transition metal-oxide/organic interfaces: Electronic structure and charge generation mechanism  

NASA Astrophysics Data System (ADS)

The energetics of an archetype charge generation layer (CGL) architecture comprising of 4,4',4?-tris(N-carbazolyl)triphenylamine (TCTA), tungsten oxide (WO3), and bathophenanthroline (BPhen) n-doped with cesium carbonate (Cs2CO3) are determined by ultraviolet and inverse photoemission spectroscopy. We show that the charge generation process occurs at the interface between the hole-transport material (TCTA) and WO3 and not, as commonly assumed, at the interface between WO3 and the n-doped electron-transport material (BPhen:Cs2CO3). However, the n-doped layer is also essential to the realization of an efficient CGL structure. The charge generation mechanism occurs via electron transfer from the TCTA highest occupied molecular orbital level to the transition metal-oxide conduction band.

Meyer, J.; Kröger, M.; Hamwi, S.; Gnam, F.; Riedl, T.; Kowalsky, W.; Kahn, A.

2010-05-01

75

Influence of spin configuration on the transport properties of transition metal oxide nanostructures  

NASA Astrophysics Data System (ADS)

We investigate the influence of spin configuration on the transport properties of transition metal oxide nanostructures (TMOns). As a first step, to describe the system, we adopted the Kondo lattice-like Hamiltonian with Coulomb repulsion, U. To calculate the corresponding conductance/current through the TMOns, upon application of a small external voltage/field, we use the Keldysh Green function technique. We found that the conductance of the TMOns strongly depends on the localized spins configuration of the transition metal (TM) ions. In particular, the conductance increases when the angle between the configurations of the nearest neighbour spins changes, corresponding to a change from an anti-ferromagnetic state to a spin-spiral state. Previously, we found that the spin configuration of the TMOns strongly depends on the number of itinerant electrons. From these results, we can infer that it would be possible to alter the conductance of TMOns by changing the spin configuration. The TMOns spin configuration can, in turn, be controlled/altered by applying an external voltage/field, which would change the number of itinerant electrons.

Minamitani, Emi; David, Melanie; Nakanishi, Hiroshi; Diño, Wilson Agerico; Kasai, Hideaki

2007-04-01

76

Synthesis, characterization, and applications of nano-functional transition metal oxides materials and graphite anode modified by CVD carbon coating  

Microsoft Academic Search

This research consists of two major sections. The first section of this research is focused on developing novel synthesis methods, characterization, and catalytic applications of multi-functional transition metal oxides including manganese oxide nano-materials (2x2 tunel structured manganese oxide octahedral molecular sieve), 3D hierarchical nano-architecture epsilon-MnO2 and cobalt oxides, and cobalt based materials. Manganese oxide octahedral molecula sieves (OMS) have ID

Yunshuang Ding

2008-01-01

77

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

78

Investigation of possible half-metal material on double perovskites Sr2BBO6 (B, B=3d transition metal) using first-principle calculations  

NASA Astrophysics Data System (ADS)

We investigated the possible candidates of half-metal (HM) material in double perovskites structure Sr2BB'O6 (B, B'=3d transition metal). The electronic structure calculations were based on density functional theory (DFT) with both generalized gradient approximation (GGA) and GGA+U approaches, where +U is on-site Coulomb interaction correction. With the consideration of 4 types of magnetic states, i.e. ferromagnetic (FM), ferromagnetic (FiM), antimagnetic (AF) and nonmagnetic (NM), we found 5 promising candidates for half-metallic (HM) materials: Sr2ScCrO6, Sr2TiCrO6, Sr2MnCrO6, Sr2ZnMnO6 and Sr2ZnFeO6.

Liu, Y. P.; Chen, S. H.; Tung, J. C.; Wang, Y. K.

2012-06-01

79

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

SciTech Connect

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

Scalettar, Richard T.; Pickett, Warren E.

2004-07-01

80

Insights and challenges of applying the GW method to transition metal oxides.  

PubMed

The ab initio GW method is considered as the most accurate approach for calculating the band gaps of semiconductors and insulators. Yet its application to transition metal oxides (TMOs) has been hindered by the failure of traditional approximations developed for conventional semiconductors. In this work, we examine the effects of these approximations on the values of band gaps for ZnO, Cu2O, and TiO2. In particular, we explore the origin of the differences between the two widely used plasmon-pole models. Based on the comparison of our results with the experimental data and previously published calculations, we discuss which approximations are suitable for TMOs and why. PMID:25351575

Samsonidze, Georgy; Park, Cheol-Hwan; Kozinsky, Boris

2014-11-26

81

Spectroscopic Studies of O-Vacancy Defects in Transition Metal Oxides  

SciTech Connect

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

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

2009-06-03

82

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

83

Ferromagnetism in cluster free, transition metal doped high ? dilute magnetic oxides: Films and nanocrystals  

NASA Astrophysics Data System (ADS)

The structural and magnetic properties of high ? dilute magnetic oxides (DMOs) have been studied in two types of samples: thin films and nanocrystals, including Co doped HfO2 films, Co doped Y2O3 films, Co doped Y2O3 nanocrystals, and Mn doped Y2O3 nanocrystals. The characterizations were conducted by extended x-ray absorption fine structure, x-ray absorption near edge structure, and superconducting quantum interference device vibrating sample magnetometer. Oxygen vacancies are shown to play a crucial role in ferromagnetic ordering, as defect centers in the bound magnetic polaron model to account for DMOs with medium band gap and low carrier concentration. The observation of room temperature ferromagnetism in tri-valence oxide of Y2O3 as well as in tetra-valence oxide of HfO2 suggests a generic feature of transition metal doped high ? oxides as good candidates for DMO. The ability to modulate the magnetic behavior of DMO via oxygen vacancy concentration by means of post anneals can be exploited for potential applications in spintronics.

Wu, C. N.; Wu, T. S.; Huang, S. Y.; Lee, W. C.; Chang, Y. H.; Soo, Y. L.; Hong, M.; Kwo, J.

2013-05-01

84

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

E-print Network

) and G- type antiferromagnetic (AFM) configurations in cubic CaMnO3, SrMnO3, BaMnO3, LaCrO3, LaFeO3 as the spin order changes from AFM to FM for LaCrO3 and LaFeO3, but they increase for the double perovskite La

Vanderbilt, David

85

Nitrogen and transition-metal codoped titania nanotube arrays for visible-light-sensitive photoelectrochemical water oxidation.  

PubMed

Vertically aligned titanium dioxide nanotube (TNT) arrays codoped with nitrogen and 3d transition metals were successfully fabricated using anodization and nitridation processes. The codoping of N and Fe yielded the highest visible-light-induced photoelectrochemical water oxidation due to bandgap narrowing of impurity levels by N and Fe. PMID:24888413

Suzuki, Tomiko M; Kitahara, Gaku; Arai, Takeo; Matsuoka, Yoriko; Morikawa, Takeshi

2014-07-21

86

Oxidative stress and DNA damage in relation to transition metals overload in Abu-Qir Bay, Egypt  

Microsoft Academic Search

The aim of the present study is to evaluate the transition metals overload in Abu-Qir Bay in Egypt, as compared to a less polluted area (reference area) through some biomarkers of oxidative stress. Catalase enzyme activity, malondialdehyde (MDA) concentration and DNA damage (number of apurinic\\/apyrimidinic sites) were the tested biomarkers. The levels of iron and copper in Mugil cephalus liver

Haiam M. Aboul-Ela; Abir A. Saad; Amany M. A. El-Sikaily; Taha I. Zaghloul

2011-01-01

87

Non--Cubic Symmetry of the Electronic Response in AFM Late Transition--Metal Oxides.  

NASA Astrophysics Data System (ADS)

The late transition--metal monoxides (MnO, FeO, CoO, NiO) have the rocksalt structure in their paramagnetic phase, while below the Neel temperature a weak structural distortion accompanies an AFM ordering of type II. Therefore, it is generally assumed that most nonmagnetic (i.e. spin--integrated) crystalline properties are essentially cubic: we give here convincing evidence of the contrary. We focus on the half--filled d shell oxide MnO as the most suitable case study, on which we perform accurate ab--initio, all--electron calculations, within different one--particle schemes. In order to study the symmetry lowering due to AFM ordering, we assume an ideal cubic geometry throughout. The calculated TO frequencies and Born effective charge tensor do not have cubic symmetry. The standard LSD severely exaggerates the deviations from cubic symmetry, confirming its unreliability for calculating properties of insulating AFM oxides, while a model self--energy correction scheme(S. Massidda et al.), Phys. Rev. B 55, 13494 (1997). reduces considerably the anisotropy. We also explain the origin and the magnitude of this effect in terms of the mixed charge--transfer/Mott--Hubbard character of MnO.

Posternak, M.; Baldereschi, A.; Massidda, S.; Resta, R.

1998-03-01

88

Band edge electronic structure of transition metal/rare earth oxide dielectrics  

NASA Astrophysics Data System (ADS)

This article addresses band edge electronic structure of transition metal/rare earth (TM/RE) non-crystalline and nano-crystalline elemental and complex oxide high- k dielectrics for advanced semiconductor devices. Experimental approaches include X-ray absorption spectroscopy (XAS) from TM, RE and oxygen core states, photoconductivity (PC), and visible/vacuum ultra-violet (UV) spectroscopic ellipsometry (SE) combined with ab initio theory is applied to small clusters. These measurements are complemented by Fourier transform infra-red absorption (FTIR), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). Two issues are highlighted: Jahn-Teller term splittings that remove d-state degeneracies of states at the bottom of the conduction band, and chemical phase separation and crystallinity in Zr and Hf silicates and ternary (Zr(Hf)O 2) x(Si 3N 4) y(SiO 2) 1- x- y alloys. Engineering solutions for optimization of both classes of high- k dielectric films, including limits imposed on the continued and ultimate scaling of the equivalent oxide thickness (EOT) are addressed.

Lucovsky, Gerald

2006-10-01

89

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

90

Investigation of thermal and electrical conductivity of phosphate glasses containing two transition metal oxides, lithium oxide and calcium oxide  

NASA Astrophysics Data System (ADS)

The purpose of this investigation is to study dc conductivity in glass systems with a combination of 40P2O5_xV2O5_(35-x)MoO3_5CaO_20Li2O. The specimens were prepared by the conventional melt-quenching technique. The dependence of the dc conductivity on temperature and the initial concentration of samples was evaluated, and it was observed that it increases with an increase in temperature for all samples. As the vanadium oxide percentage increased, the dc conductivity also increased, and the activation energy decreased almost uniformly. Variations of activation energy and conductivity are compatible with theoretical concepts. The conductivity of these samples is mixed electronic-ionic conduction, but because of variation in the transition metal oxide concentration, electronic conductivity is more effective as a result of small polaron hopping. Also, the differential scanning calorimetry measurements of these glasses (a heating rate of 10 °C Min-1) were investigated, and glass transition temperatures (Tg) were determined for each chemical composition. It was shown that the enhancement of MoO3 concentration leads to a decrease in Tg values.

Soheyli, Ehsan; Hekmat Shoar, Mohammad Hossein

2014-07-01

91

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

92

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

93

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

NASA Astrophysics Data System (ADS)

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

Danaher, David J.

94

Polar alignment of ?-shaped basic building units within transition metal oxide fluoride materials.  

PubMed

A series of pseudosymmetrical structures of formula K10(M2OnF11-n)3X (M = V and Nb, n = 2, X = (F2Cl)1/3, Br, Br4/2,I4/2; M = Mo, n = 4, X = Cl, Br4/2, I4/2) illustrates generation of polar structures with the use of ?-shaped basic building units (BBUs). For a compound to belong to a polar space group, dipole moments of individual species must be partially aligned. Incorporation of d(0) early transition metal polyhedral BBUs into structures is a common method to create polar structures, owing to the second-order Jahn-Teller distortion these polyhedra contain. Less attention has been spent examining how to align the polar moments of BBUs. To address alignment, we present a study on previously reported bimetallic BBUs and synthesized compounds K10(M2OnF11-n)3X. These materials differ in their (non)centrosymmetry despite chemical and structural similarities. The vanadium compounds are centrosymmetric (space groups P3m1 or C2/m) while the niobium and molybdenum heterotypes are noncentrosymmetric (Pmn21). The difference in symmetry occurs owing to the presence of linear, bimetallic BBUs or ?-shaped bimetallic BBUs and related packing effects. These ?-shaped BBUs form as a consequence of the coordination environment around the bridging anion of the metal oxide fluoride BBUs. PMID:24328163

Holland, Michael; Donakowski, Martin D; Pozzi, Eric A; Rasmussen, Andrew M; Tran, Thanh Thao; Pease-Dodson, Shannon E; Halasyamani, P Shiv; Seideman, Tamar; Van Duyne, Richard P; Poeppelmeier, Kenneth R

2014-01-01

95

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

NASA Astrophysics Data System (ADS)

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

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

1993-06-01

96

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

97

Total Oxidation of Carbon-Monoxide and Methane over Transition Metal Fluorite Oxide Composite Catalysts  

Microsoft Academic Search

Cu-Ce-O and Au-Ce-O catalysts were characterized by XRD, XPS, and STEM. Copper in small amounts showed a strong tendency to associate with cerium oxide, When the cerium oxide surface was saturated with copper, excess copper formed bulk copper oxide particles. The cuprous(+1) oxidation state was identified by XPS for the copper clusters distributed in cerium oxide, while gold in the

W. Liu; M. Flytzani-Stephanopoulos

1995-01-01

98

Optical, vibrational, and structural properties of high-?0 transition metal oxides  

NASA Astrophysics Data System (ADS)

According to the International Technology Roadmap for Semiconductors (ITRS), the present structure of CMOS devices using SiO2 gate oxides (maybe lightly nitrided) will change around 2005, when the SiO2 thickness reaches 15-20 Åand the gate length 0.1 ?m. Beyond this technology node, the physical thickness of the gate oxide can no longer shrink, since the leakage currents due to quantum-mechanical tunneling would render the devices useless. Instead of reducing the physical thickness, scaling the gate length is accompanied by increasing the low-frequency dielectric constant ?0 of the gate material, thus increasing the areal capacitance. Therefore, the industry is searching for novel high-?0 (or high-k) materials. These materials need to fulfill a number of requirements: (1) A large band gap with reasonable band offsets compared to the valence and conduction bands of Si. (2) They should be amorphous to prevent diffusion of dopants (from the poly-Si gate to the channel in the Si substrate) along grain boundaries. (3) They need to be thermodynamically stable (particularly towards reaction with Si or O) to allow subsequent CMOS processing. (A simple phase diagram would help.) (4) A large lattice polarizability (?_0-?_?-1), which is usually associated with a soft phonon driving a transition between two crystalline phases. No simple requirements! Optical spectroscopies (spectroscopic ellipsometry from 300 ?m to 9 eV, FTIR transmission and reflection, UV Raman scattering) and x-ray structural analysis are ideally suited for a rapid screening of a large class of materials for potential high-k applications, since they do not require processing for electrical measurements. Ab initio band structure calculations can assist in the interpretation of experimental results. This talk will describe recent work on SrTiO_3, various transition metal oxides (TiO_2, ZrO_2, and HfO_2), as well as other classes of emerging materials, both in bulk and thin-film form. Of particular importance is the detection of an amorphous interfacial layer that may form during deposition on Si.

Zollner, Stefan

2001-03-01

99

Transition-metal-oxide coated titanium electrodes for redox batteries. Final report  

SciTech Connect

A primary motivation for this work was to produce porous electrodes (of titanium) with reproducible surface activity for experiments to corroborate predictions of porous electrode theory. An additional goal of this research program was to ascertain if simple one-step outer-sphere electron transfer mechanism applies to the ferric-ferrous redox reaction at high reactant/product concentrations in a strong acid chloride medium. Kinetic rate expressions of this couple under these conditions at the metal oxide surfaces were sought. Coatings of the conductive and active rutile structure form of selected transition metal oxides (namely RuO/sub 2/, IrO/sub 2/, OsO/sub 2/) were desired. Both IrO/sub 2/ and RuO/sub 2/ coatings having the rutile structure (as confirmed by x-ray diffraction) were prepared by thermal decomposition of their respective hydrated chloride salts. In the case of OsO/sub 2/ only amorphous coatings have been achieved. Low over potential exchange current densities of the ferric-ferrous couple were measured in concentrated solution (0.5 M Fe/sup 2 +/, 0.5 M Fe/sup 3 +/, 1 M HCl) at Pt, RuO/sub 2/ and IrO/sub 2/ RDE's. Significant corrections were necessary for ohmic effects, mass transfer effects, and nonuniform current distribution. The data show that the electrocatalytic activity of RuO/sub 2/ (ks = 1.92 x 10/sup -3/ cm/s) is comparable to that of Pt (ks = 1.42 x 10/sup -3/ cm/s) while the activity of IrO/sub 2/ (ks = 1.21 x 10/sup -4/ cm/s) is approximately an order of magnitude less than Pt. Since the measured free energy of activation was similar for all three substrates (5.4 to 5.8 Kcal/mole), a nonbinding interaction between the couple and the surfaces is suggested. The variation in exchange currents among the different substrates can be attributed to some extent on double layer effects but primarily to crystal structure differences.

Savinell, R.F.

1982-12-01

100

Synthesis and physical property characterization of layered transition metal pnictide-oxide compounds  

NASA Astrophysics Data System (ADS)

Several layered pnictide-oxide compounds of the Sr2Mn 3As2O2 and K2NiF4 structure type have been synthesized, and their structure as well as electronic and magnetic properties have been characterized. Chapter 1 reports the synthesis and characterization of A 2(MnO2)(Zn2As2) where A = Ba or Sr. These compounds contain two kinds of transition metals, Mn and Zn. The main interest in characterization of these compounds is to determine if Mn and Zn localize in different crystallographic sites in an ordered manner. Also, the physical properties of these compounds are compared with those of previously published isostructural compounds in order to establish the structure-property relationship. Chapter 2 reports several approaches to synthesize a conceptually designed novel pnictide-oxide containing infinity2[CuO 4/2]2- layers. Solid state and flux reactions were explored. Various synthetic conditions and the product characterization by powder and single crystal X-ray diffraction, powder neutron diffraction and electron microprobe experiments are discussed. Chapter 3 reports a temperature dependent structure investigation of Na2Ti2Sb2O by powder neutron diffraction. Powder neutron diffraction studies of Na2Ti2Sb 2O indicate that this compound has a structural distortion in the [Ti 2Sb2O]2- layer at T ˜ 120 K. This transition temperature corresponds well to the previously reported anomalous transition temperature in the magnetic susceptibility and electrical resistivity measurements. Several models to explain the data are discussed. Chapter 4 reports the synthesis and temperature dependent physical property anomaly of Na2Ti2Pn2O ( Pn = As, Sb). These compounds exhibit anomalous transitions in temperature dependent magnetic susceptibility and electrical resistivity measurements. The structure-property relationship of these compounds is discussed in terms of a charge-density-wave and spin-density-wave mechanism. Chapter 5 reports the Na2Ti2Sb2O single crystal growth via a NaSb flux method and the synthesis parameter optimization. The optimized reaction yields plate shaped crystals of Na2Ti 2Sb2O, and the largest crystal obtained has dimensions of 5 mm x 5 mm x 0.2 mm. These single crystals are indispensable in order to confirm the existence of a charge-density-wave/spin-density-wave in the Na 2Ti2Sb2O system.

Ozawa, Tadashi C.

101

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 Form: June 14, 2004 The chemical kinetics of the Pt catalyzed oxidation reaction SO2(g) + 1/2O2(g) 798

Lin, Xi

102

Facile synthesis of transition-metal oxide nanocrystals embedded in hollow carbon microspheres for high-rate lithium-ion-battery anodes.  

PubMed

Charged up: A general soft-template route for the synthesis of uniform hollow carbon microspheres embedded with transition-metal oxide nanocrystals (OHCMs) has been developed (see figure). The obtained OHCMs possess a microsized spherical shape, embedded transition-metal oxide nanocrystals, and fully encapsulating conductive carbon shells, which endow the resulting anode materials with high specific capacities, rate capabilities, electrode densities, and cycle stabilities. PMID:23788047

Liu, Jun; Liu, Wei; Chen, Kunfeng; Ji, Shaomin; Zhou, Yichun; Wan, Yanling; Xue, Dongfeng; Hodgson, Peter; Li, Yuncang

2013-07-22

103

Physica B 403 (2008) 14011403 Probing nanoscale inhomogeneities in transition metal oxides with  

E-print Network

example being the perovskite manganites. However, CMR has also been observed in other systems, such as the pyrochlore Tl2Mn2O7, in which the double exchange and Jahn­Teller effects that are believed to contribute

104

Magnetic and electrical properties of transition-metal-doped oxide thin films  

Microsoft Academic Search

In this research programme, the electrical and magnetic properties of PLD and room temperature grown TM-doped TiO2 and TM-doped Cu xO thin films have been investigated. We used Co and Fe as the TM dopants for the TiO2 based films. Mn was however used to dope the Cu xO materials systems. Among the various electrical properties, resistive switching of transition-metal

Ching Yee Lam

2009-01-01

105

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

NASA Astrophysics Data System (ADS)

The pressure effect on synthesis of oxides with perovskite ABO3 and perovskite-related structures has become more clear in recent years. The geometric tolerance factor t ? (A-O)/2(B-O) measures the structural stability. High-pressure synthesis enlarges the range of the t factor where the perovskite structure can be stabilized. For the ABO3 compounds with t > 1, high pressure reduces the t factor since the A-O bond is more compressible than the B-O bond. Therefore, perovskite would be the high-pressure phase for ambient-pressure polytype structures. However, the bonding compressibility argument is no longer valid for the ABO3 with t < 1. A dt/dP > 0 is normally obtained for t less than but very close to 1, i.e. the orthorhombic distortion becomes smaller under pressure. For those highly distorted perovskites with t factor far less than one, pressure enlarges further the orthorhombic distortion and eventually leads to a phase transition to the post-perovskite phase. As for PbRuO3, high pressure prefers the small-volume perovskite phase relative to a competitive pyrochlore phase Pb2Ru2O7. Understanding the pressure effect and the new capacity provided by a Walker-type multianvil press enabled us to expand the perovskite family and to obtain new phases of 4d and 5d oxides. Studies of these new 4d and 5d oxides allow us not only to address long-standing problems, but also to explore exotic physical properties. (1) In the perovskite ARuO3 (A= alkaline earth), we have completed the phase diagram from A= Ca to Sr and to Ba and also accounted for the A-cation size-variance effect. A systematic study of the Curie temperature Tc and the critical behavior as a function of the average A-site size and the size variance as well as external high pressures reveals explicitly the crucial role of the lattice strain on the ferromagnetism. The mean-field critical behaviour near Tc found previously in SrRuO3 is not typical of these perovskite ruthenates. Tc is completely suppressed by Pb doping in Sr1-xPbxRuO3 not due to the steric effect, but to the orbital hybridization between Pb^2+ 6s and Ru^4+ 4d. As the end member, metallic PbRuO3 undergoes a first-order phase transition to a metallic Imma phase at Tt 90 K. (2) A new polytype phase 5H has been synthesized under a narrow pressure range, which fits the structural sequence along with other polytypes 9R, 6H and 3C of BaIrO3. The ground states of these BaIrO3 polytypes evolve from a ferromagnetic insulator with Tc 180 K in the 9R phase to a ferromagnetic metal with Tc 50 K in the 5H phase, and finally to an exchange-enhanced paramagnetic metal in the 6H phase, which may be close to a quantum critical point. (3) In the Ca1-xSrxIrO3 system, high pressure stabilizes the post-perovskite structure on the Ca side (x < 0.3), but favors the perovskite structure on the Sr side (x > 0.6). Refs. J.-G. Cheng, et al. PRB 80, 104430(2009); 80, 174426 (2009); 81, 134412(2010); JACS 131, 7461(2009).

Cheng, J.-G.

2011-03-01

106

Charge transfer in some lanthanum transition metallates with the perovskite and K2NiF4 structures: an infrared spectroscopic study  

NASA Astrophysics Data System (ADS)

The electronic properties of transition metal-containing systems sometimes indirectly manifest themselves through their infrared spectra. The infrared spectra of some lanthanum and dilanthanum transition metallates have been probed either as a function of composition or applied pressure. It is suggested that there is charge transfer to and from neighboring transition metal ions. In some cases, La2CuO4 for instance, charge separation (valence localization) is manifest at ambient temperature and pressure. In others, such as LaV0.5Ni0.5O3, it is necessary to apply an external pressure in order to induce charge separation.

Mortimer, Richard

1998-06-01

107

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

108

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

109

Review of magnetocaloric effect in perovskite-type oxides  

NASA Astrophysics Data System (ADS)

We survey the magnetocaloric effect in perovskite-type oxides (including doped ABO3-type manganese oxides, A3B2O7-type two-layered perovskite oxides, and A2B'B?O6-type ordered double-perovskite oxides). Magnetic entropy changes larger than those of gadolinium can be observed in polycrystalline La1-xCaxMnO3 and alkali-metal (Na or K) doped La0.8Ca0.2MnO3 perovskite-type manganese oxides. The large magnetic entropy change produced by an abrupt reduction of magnetization is attributed to the anomalous thermal expansion at the Curie temperature. Considerable magnetic entropy changes can also be observed in two-layered perovskites La1.6Ca1.4Mn2O7 and La2.5-xK0.5+xMn2O7+? (0 < x < 0.5), and double-perovskite Ba2Fe1+XMo1-xO6 (0 <= x <= 0.3) near their respective Curie temperatures. Compared with rare earth metals and their alloys, the perovskite-type oxides are lower in cost, and they exhibit higher chemical stability and higher electrical resistivity, which together favor lower eddy-current heating. They are potential magnetic refrigerants at high temperatures, especially near room temperature.

Zhong, Wei; Au, Chak-Tong; Du, You-Wei

2013-05-01

110

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

111

perovskites  

Microsoft Academic Search

Ba2La(1-x)EuxBiO6, with x = 2%, 4% and 8wt% cubic perovskites was obtained by combustion synthesis using urea as fuel. The precursors (oxidizing and reductors) are mixed in aqueous solution to form powders after ignition and burn. The samples were characterized by scanning electron microscopy (SEM), X-ray diffraction, photoluminescence and IR fluorescence. The x-ray analyses of the sinterized powders at the

P. L. Cunha Filho; J. Albino Aguiar; Luiz Freire; Química Fundamental

112

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

113

Topological Oxide Insulator in Cubic Perovskite Structure  

PubMed Central

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

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

2013-01-01

114

Tetravalent dysprosium in a perovskite-type oxide.  

PubMed

The existence of tetravalent dysprosium in perovskite-type oxide barium zirconate is confirmed in this work. This discovery will stimulate many researchers in diverse fields such as catalysts, solid state ionics, sensors, and fluorescent materials. PMID:22430942

Han, Donglin; Uda, Tetsuya; Nose, Yoshitaro; Okajima, Toshihiro; Murata, Hidenobu; Tanaka, Isao; Shinoda, Kozo

2012-04-17

115

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

PubMed

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

Berger, Matthias; Neumeyer, Felix; Auner, Norbert

2013-10-21

116

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

117

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

E-print Network

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

Lin, Xi

118

Synthesis, characterization, and applications of nano-functional transition metal oxides materials and graphite anode modified by CVD carbon coating  

NASA Astrophysics Data System (ADS)

This research consists of two major sections. The first section of this research is focused on developing novel synthesis methods, characterization, and catalytic applications of multi-functional transition metal oxides including manganese oxide nano-materials (2x2 tunel structured manganese oxide octahedral molecular sieve), 3D hierarchical nano-architecture epsilon-MnO2 and cobalt oxides, and cobalt based materials. Manganese oxide octahedral molecula sieves (OMS) have ID open framework structures with various theoretical nano-scale tunnel size materials have been investigated extensively as low cost and environmentally benign ionic and molecular sieves and efficient redox catalysts. A novel and efficient solvent-free method has been developed to synthesize manganese oxides with 2 x 2 tunnel structures. The properties of the synthesized OMS-2 materilas have been compared with that synthesized by conventional reflux and hydrothermal methods. Epsilon manganese dioxides with controlled novel 3D architectures have been fabricated via a hydrothermal chemical reaction. The effects of reaction time and reaction temperature on the morphology of the final epsilon-MnO2 are investigated, and the formation mechanisms of the hierarchical nano-architectures are proposed. The magnetic properties of epsilon-MnO2 are also studied. Resides manganese oxides, a microwave-heating reflux route has been used to synthesize 3D flower like cobalt hydrotalcite-like compounds with layered structure and these compounds can be transferred into spinel structure of Co3O 4. Both materials show the electrocatalytic activity and stability for the electrochemical reduction of oxygen. Therefore these materials have the potential to be electrocatyltic catalysts. The second section of the research is to study the microstructure of carbon films coated on the iron and graphite particles by a Chemical Vapor Deposition (CVD) method and the relationship between the microstructure of the carbon coatings and their effects on electrochemical properties.

Ding, Yunshuang

119

Molten lithium sulfate-sodium sulfate-potassium sulfate eutectic: oxidation-reduction reactions of transition-metal compounds  

SciTech Connect

Sulfur dioxide was found to reduce a number of first-row transition-metal compounds in molten ternary sulfate eutectic, the ease of reduction being Cr(VI) > Mn(IV) > Fe(III) > Cu(II). A number of other, probably polymeric, cations (Ti(IV), Nb(V), Mo(VI), Ta(V), W(VI)) were not reduced. Potassium dichromate was unstable, slowly decomposing to chromium(III) oxide, chromate, and oxygen, and was converted to chromate by solutions of sodium carbonate. Chromium metal was little attacked by the ternary eutectic, but copper metal reduced copper(II) to copper(I) cations. Solutions of potassium pyrosulfate decomposed thermally but also oxidized chromium metal (to Cr(III)) and iron(II) (to Fe(III)) and reduced manganese(IV) oxide (to Mn(II)) and chromium(VI) (completely to chromium(III)). Though simple cations (Fe(II), Mn(II)) accelerated the thermal decomposition of pyrosulfate, the more polymeric cations (Ti(IV), Nb(V), Mo(VI), Ta(V), W(VI)) caused considerably less evolution of sulfur trioxide. 25 references, 4 figures, 3 tables.

Dearnaley, R.I.; Kerridge, D.H.; Rogers, D.J.

1986-05-07

120

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

121

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

E-print Network

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

Tennyson, Andrew Gregory

2008-01-01

122

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

123

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

Microsoft Academic Search

My research is focused on developing metal oxide and hydroxide nanomaterials which can be used as battery materials, organic transformation catalysts, and photocatalysts. This research involves studying ZnO with different morphologies as photocatalysts for phenol degradation, producing CuO as olefin epoxidation catalysts, developing V and Cu incorporated manganese oxides as cathode materials for Li-ion batteries, and fabricating alpha-nickel hydroxide for

Linping Xu

2010-01-01

124

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

PubMed

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

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

2014-01-22

125

Electron microscopy study of gold nanoparticles deposited on transition metal oxides.  

PubMed

Many researchers have investigated the catalytic performance of gold nanoparticles (GNPs) supported on metal oxides for various catalytic reactions of industrial importance. These studies have consistently shown that the catalytic activity and selectivity depend on the size of GNPs, the kind of metal oxide supports, and the gold/metal oxide interface structure. Although researchers have proposed several structural models for the catalytically active sites and have identified the specific electronic structures of GNPs induced by the quantum effect, recent experimental and theoretical studies indicate that the perimeter around GNPs in contact with the metal oxide supports acts as an active site in many reactions. Thus, it is of immense importance to investigate the detailed structures of the perimeters and the contact interfaces of gold/metal oxide systems by using electron microscopy at an atomic scale. This Account describes our investigation, at the atomic scale using electron microscopy, of GNPs deposited on metal oxides. In particular, high-resolution transmission electron microscopy (HRTEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) are valuable tools to observe local atomic structures, as has been successfully demonstrated for various nanoparticles, surfaces, and material interfaces. TEM can be applied to real powder catalysts as received without making special specimens, in contrast to what is typically necessary to observe bulk materials. For precise structure analyses at an atomic scale, model catalysts prepared by using well-defined single-crystalline substrates are also adopted for TEM observations. Moreover, aberration-corrected TEM, which has high spatial resolution under 0.1 nm, is a promising tool to observe the interface structure between GNPs and metal oxide supports including oxygen atoms at the interfaces. The oxygen atoms in particular play an important role in the behavior of gold/metal oxide interfaces, because they may participate in catalytic reaction steps. Detailed information about the interfacial structures between GNPs and metal oxides provides valuable structure models for theoretical calculations which can elucidate the local electronic structure effective for activating a reactant molecule. Based on our observations with HRTEM and HAADF-STEM, we report the detailed structure of gold/metal oxide interfaces. PMID:23777292

Akita, Tomoki; Kohyama, Masanori; Haruta, Masatake

2013-08-20

126

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

127

Silica supported transition metal substituted polyoxotungstates: Novel heterogeneous catalysts in oxidative transformations with hydrogen peroxide  

Microsoft Academic Search

The preparation and characterization (FT-IR, FT-Raman, diffuse reflectance, elemental analysis) of novel catalysts with iron or manganese substituted polyoxotungstates [XMIII(H2O)W11O39]n? (X=P, M=Fe or Mn; X=Si or B, M=Fe) immobilized on a functionalized silica matrix are reported. The new materials were tested as heterogeneous catalysts in the oxidation of cis-cyclooctene and cyclooctane at 80°C, using environmentally safe hydrogen peroxide as oxidant

Ana C. Estrada; Isabel C. M. S. Santos; Mário M. Q. Simões; M. Graça P. M. S. Neves; José A. S. Cavaleiro; Ana M. V. Cavaleiro

2011-01-01

128

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

Microsoft Academic Search

Electric oil furnace dust (EOFD) is a solid waste generated in the collection of particulate material during steelmaking process in electric and oil furnaces. Over 7 million metric tons dust produced per annum in worldwide creates deep impacts like soil, ground water and ecology pollutions. This article reports the simple one step process for the extraction of nanostructured metal oxides

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

2011-01-01

129

Oxidative addition of C--H bonds in organic molecules to transition metal centers  

SciTech Connect

Alkanes are among the most chemically inert organic molecules. They are reactive toward a limited range of reagents, such as highly energetic free radicals and strongly electrophilic and oxidizing species. This low reactivity is a consequence of the C--H bond energies in most saturated hydrocarbons. These values range from 90 to 98 kcal/mole for primary and secondary C--H bonds; in methane, the main constituent of natural gas, the C--H bond energy is 104 kcal/mole. This makes methane one of the most common but least reactive organic molecules in nature. This report briefly discusses the search for metal complexes capable of undergoing the C--H oxidative addition process allowing alkane chemistry to be more selective than that available using free radical reagents. 14 refs.

Bergman, R.G.

1989-04-01

130

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

SciTech Connect

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 used growth methods, and then on the basis of specific material systems that have generated very high levels of interest. Emphasis is placed on the wide diversity of structural, electronic, optical and magnetic properties exhibited by oxides, and the fascinating results that this diversity of properties can produce when combined with the degrees of freedom afforded by heteroepitaxy.

Chambers, Scott A.

2010-01-12

131

Transition metal-free oxidative esterification of benzylic alcohols in aqueous medium.  

PubMed

Oxidative esterification of benzylic alcohols with a catalytic amount of HBr-H2O2 in aqueous medium under mild conditions is reported with a wide range of substrate scope for both benzylic and aliphatic alcohols. The conditions are also suitable for selective mono-esterification of ethylene glycol and glycerol. With catalytic amounts of HBr (20 mol%) and H2O2, the generation of reactive intermediate species BrOH has been ascertained by UV-visible spectra. PMID:25325738

Samanta, Supravat; Pappula, Venkatanarayana; Dinda, Milan; Adimurthy, Subbarayappa

2014-12-14

132

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

133

Local and remote charge-transfer-enhanced Raman scattering on one-dimensional transition-metal oxides.  

PubMed

The one-dimensional (1D) transition-metal oxide MoO(3) belt is synthesized and characterized with X-ray diffraction, scanning electron microscopy, and Raman spectroscopy. Charge-transfer-(CT) enhanced Raman scattering of 4-mercaptobenzoic acid (4-MBA) on a 1D MoO(3) belt was investigated experimentally and theoretically. The chemical enhancement of surface-enhanced Raman scattering (SERS) of 4-MBA on the MoO(3) belt by CT is in the order of 10(3). The SERS of 4-MBA was investigated theoretically by using a quantum chemical method. The remote SERS of 4-MBA along the 1D MoO(3) belt (the light excitation to one side of the MoO(3) belt, and the SERS spectrum is collected on the other side of the MoO(3) belt) is also shown experimentally, which provides potential applications of SERS. The incident polarization dependence of remote SERS spectra has also been investigated experimentally. PMID:20540066

Dong, Bin; Huang, Yingzhou; Yu, Naisen; Fang, Yurui; Cao, Baosheng; Li, Yuanzuo; Xu, Hongxing; Sun, Mengtao

2010-08-01

134

On the origins of the deficiencies of density functional theory exchange-correlation functionals for transition metal oxides  

NASA Astrophysics Data System (ADS)

The transition metal oxides (TMO) are a class of compounds that are difficult to treat in density functional theory (DFT) with simple local and semi-local functionals. Especially for CuO, they failed to give the correct equilibrium monoclinic structure. The major source of the deficiency is attributed to the imperfect cancellation of the electronic self-interaction (SI) in the approximated exchange energy. Previous studies [1] show that a large part of the SI error is connected to the confinement error that can be modeled by harmonic-oscillator (HO) systems. We discuss recent advances towards a simple methodology to quantify the confinement errors in real TMO systems. Our results show that these confinement errors may account for the deficiencies of DFT functionals in obtaining the correct equilibrium structure of the TMO. Sandia is a multiprogram laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. Department of Energy's National Nuclear Security Administration under Contract No. DE-AC04-94AL85000.[4pt] [1] Hao et al, PRB 82, 115103 (2010).

Mattsson, Ann E.; Armiento, Rickard; Hao, Feng

2011-03-01

135

Unusual magnetic phases in the strong interaction limit of two-dimensional topological band insulators in transition metal oxides  

NASA Astrophysics Data System (ADS)

The expected phenomenology of non-interacting topological band insulators (TBI) is now largely theoretically understood. However, the fate of TBIs in the presence of interactions remains an active area of research with novel, interaction-driven topological states possible, as well as new exotic magnetic states. In this work we study the magnetic phases of an exchange Hamiltonian arising in the strong interaction limit of a Hubbard model on the honeycomb lattice whose non-interacting limit is a two-dimensional TBI recently proposed for the layered heavy transition metal oxide compound, (Li,Na)2IrO3. By a combination of analytical methods and exact diagonalization studies on finite size clusters, we map out the magnetic phase diagram of the model. We find that strong spin-orbit coupling can lead to a phase transition from an antiferromagnetic Neél state to a spiral or stripy ordered state. We also discuss the conditions under which a quantum spin liquid may appear in our model, and we compare our results with the different but related Kitaev-Heisenberg-J2-J3 model which has recently been studied in a similar context.

Kargarian, Mehdi; Langari, Abdollah; Fiete, Gregory A.

2013-03-01

136

Unusual magnetic phases in the strong interaction limit of two-dimensional topological band insulators in transition metal oxides  

NASA Astrophysics Data System (ADS)

The expected phenomenology of noninteracting topological band insulators (TBIs) is now largely theoretically understood. However, the fate of TBIs in the presence of interactions remains an active area of research with novel, interaction-driven topological states possible, as well as new exotic magnetic states. In this work we study the magnetic phases of an exchange Hamiltonian arising in the strong interaction limit of a Hubbard model on the honeycomb lattice whose noninteracting limit is a two-dimensional TBI recently proposed for the layered heavy transition metal oxide compound (Li,Na)2IrO3. By a combination of analytical methods and exact diagonalization studies on finite-size clusters, we map out the magnetic phase diagram of the model. We find that strong spin-orbit coupling can lead to a phase transition from an antiferromagnetic Neél state to a spiral or stripy ordered state. We also discuss the conditions under which a quantum spin liquid may appear in our model, and we compare our results with the different but related Kitaev-Heisenberg-J2-J3 model which has recently been studied in a similar context.

Kargarian, Mehdi; Langari, Abdollah; Fiete, Gregory A.

2012-11-01

137

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

PubMed

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

Neamtu, Jenica; Volmer, Marius

2014-01-01

138

Supported transition-metal oxide catalysts for reduction of sulfur dioxide with hydrogen to elemental sulfur.  

PubMed

This work is for the purpose to find a high performance catalyst for the catalytic reduction of SO2 with H2 as a reducing agent. NiO/gamma-Al2O3 catalyst was found to be the most active catalyst among the seven gamma-Al2O3-supported metal-oxide catalysts tested. With NiO as the active species, of the supports tested, gamma-Al2O3 was the most suitable one and the optimal Ni content was 16 wt%. Using this NiO/gamma-Al2O3 catalyst, we found that the optimal feed ratio of H2/SO2 is 2:1 and the catalyst presulfided with H2 + H2S exhibits a higher performance than that pretreated with H2 or He. XRD patterns reveal that the nickel oxide experienced a transformation to Ni3S2 and NiS, and then to NiS2, the most active nickel sulfide, during the reaction process. The reason for the highest catalyst activity of 16 wt% Ni was attributed to the largest amount of NiS2. Water vapor in the feed gas reactant caused inhibition of catalyst activity, whereas H2S promoted the reduction of SO2. These phenomena were rationalized with the aid of Claus reaction. PMID:15212907

Chen, Chun-Liang; Wang, Ching-Huei; Weng, Hung-Shan

2004-08-01

139

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

NASA Astrophysics Data System (ADS)

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

Xu, Linping

140

Kinetics and Mechanisms of Oxidative Cleavage of HIV RRE RNA by Rev-Coupled Transition Metal Chelates.  

PubMed

Catalytic metallodrugs were used to oxidatively cleave HIV-1 Rev Response Element RNA (RRE RNA), and the mechanisms of RNA cleavage were studied using a combination of matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS), fluorescence spectroscopy, and gel electrophoresis. The metallodrugs, which contained combinations of the transition metals Fe(2+), Co(2+), Ni(2+), and Cu(2+) and the Rev-coupled chelators DOTA, DTPA, EDTA, NTA, tripeptide GGH, and tetrapeptide KGHK, bind to and cleave HIV RRE RNA through heretofore unknown oxidative mechanisms. The broad spectrum of metal catalysts and co-reagents provided a means for systematic variation of oxidative reactivity without significant perturbation of binding between catalyst and RNA. Detailed MS analyses were used to monitor formation of RNA fragments containing terminal 2',3'-cyclic phosphate (2',3'-cPO4), 3'-phosphate (3'-PO4), 3'-phosphoglycolate (3'-PG), 5'- hydroxyl (5'-OH), 5'- phosphate (5'-PO4) and other nascent overhangs at sites of cleavage. The distinct overhangs corresponded to distinct mechanisms of oxidative hydrogen-abstraction (H abstraction), hydrolysis, and/or endonucleolysis, allowing a dissection of the contributions of various mechanisms of oxidative cleavage. Rapid co-reactant- and catalyst-dependent formation of fragments containing terminal 3'-PG, 3'-PO4 and 5'-PO4 overhangs appeared to be initiated primarily by H abstraction events. The standard thiobarbituric acid (TBA) assay was employed herein in a novel usage to monitor the formation of base 2-hydroxypropenal products produced by 4'-H abstraction in RNA. Formation of an adduct with TBA was monitored by fluorescence, and its quantification correlated with the formation of 3'-PG monitored by MALDI-TOF MS, confirming oxidative 4'-H abstraction as a major mechanism of rapid catalyst-mediated cleavage of RRE RNA. Rapid formation of 3'-PO4 overhangs was most likely a result of 5'-H abstraction. Apparent rates of formation of 3'-PG (a unique product of 4'-H abstraction) at differing nucleotide positions within the RNA were used to triangulate probable 3D positions of metal centers and establish the distance-dependence of 4'-H abstraction for certain catalytic metallodrugs. PMID:23626900

Joyner, Jeff C; Keuper, Kevin D; Cowan, J A

2013-04-01

141

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

SciTech Connect

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

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

2011-10-15

142

High performance ceramic interconnect material for solid oxide fuel cells (SOFCs): Ca- and transition metal-doped yttrium chromite  

NASA Astrophysics Data System (ADS)

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

Yoon, Kyung Joong; Stevenson, Jeffrey W.; Marina, Olga A.

2011-10-01

143

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

144

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

145

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

PubMed

Searching for low-cost and efficient catalysts for the oxygen evolution reaction has been actively pursued owing to its importance in clean energy generation and storage. While developing new catalysts is important, tuning the electronic structure of existing catalysts over a wide electrochemical potential range can also offer a new direction. Here we demonstrate a method for electrochemical lithium tuning of catalytic materials in organic electrolyte for subsequent enhancement of the catalytic activity in aqueous solution. By continuously extracting lithium ions out of LiCoO2, a popular cathode material in lithium ion batteries, to Li0.5CoO2 in organic electrolyte, the catalytic activity is significantly improved. This enhancement is ascribed to the unique electronic structure after the delithiation process. The general efficacy of this methodology is demonstrated in several mixed metal oxides with similar improvements. The electrochemically delithiated LiCo0.33Ni0.33Fe0.33O2 exhibits a notable performance, better than the benchmark iridium/carbon catalyst. PMID:24993836

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

2014-01-01

146

Oxygen vacancy motion in perovskite oxides  

Microsoft Academic Search

Using electron paramagnetic resonance, the motion of oxygen vacancies within the oxygen octahedron in perovskite BaTiOâ is observed via the alignment of oxygen vacancy-related defect dipoles induced by bias\\/heat combinations. The vacancy motion is found to have an activation energy of 0.91 eV, in excellent agreement with the predicted. It is found that the onset of resistance degradation is also

William L. Warren; Karel Vanheusden; Duane Dimos; Gordon E. Pike; Bruce A. Tuttle

1996-01-01

147

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

148

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

149

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

150

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

151

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

152

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

153

First principles study of magnetostructural instabilities in magnetic perovskite oxides  

Microsoft Academic Search

First principles phonon dispersion relations are reported for a range of magnetic perovskite oxides in cubic high-symmetry reference structures. Materials considered include EuTiO3 and BiFeO3. For each system, the dominant lattice instabilities are identified. These are frozen-in, singly and in combination, and the structures are optimized in the resulting space groups. From this, we identify distinct low-energy alternatives to the

Jun Hee Lee; Lucia Palova; Karin M. Rabe

2009-01-01

154

Relation between structure and catalytic properties of transition metal complexes with heteropolyanion PW 11O 7? 39 in oxidative reactions  

Microsoft Academic Search

The content and structural features of transition metals Fe(III), Cr(III), Ru(IV), Ti(IV) and V(IV) complexes with the heteropolyanion PW11O7?39 depending on the starting M-compound, molar ratio of reagents, temperature and pH of the solution were studied. Heteropolycomplexes (HPC) of three types were identified using NMR 31P, 17O, 183W, IR, UV-VIS spectroscopy, magnetic measurements and elemental analysis: I — M-substituted HPC,

L. I. Kuznetsova; L. G. Detusheva; N. I. Kuznetsova; M. A. Fedotov; V. A. Likholobov

1997-01-01

155

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

156

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

157

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

158

VOLUME 85, NUMBER 24 P H Y S I C A L R E V I E W L E T T E R S 11 DECEMBER 2000 Observation of Charge Stripes in Cupric Oxide  

E-print Network

distortion brought about by the Jahn-Teller effect [15,16]. The structure can be viewed as ribbons running for their versatile properties. By doping antiferromagnetic insulators of transition metal oxides of a perovskite

159

The polarizability model for ferroelectricity in perovskite oxides.  

PubMed

This article reviews the polarizability model and its applications to ferroelectric perovskite oxides. The motivation for the introduction of the model is discussed and nonlinear oxygen ion polarizability effects and their lattice dynamical implementation outlined. While a large part of this work is dedicated to results obtained within the self-consistent-phonon approximation, nonlinear solutions of the model are also handled, which are of interest to the physics of relaxor ferroelectrics, domain wall motions, and incommensurate phase transitions. The main emphasis is to compare the results of the model with experimental data and to predict novel phenomena. PMID:22718683

Bussmann-Holder, Annette

2012-07-11

160

Methane combustion on some perovskite-like mixed oxides  

Microsoft Academic Search

Some perovskite-like mixed oxides of general formula La1?xA?xBO3 were prepared by the amorphous citrate method and tested for methane combustion within the 300–600°C temperature range. Substitution at A-site with a bivalent (Eu, Sr) or tetravalent (Ce) metal cation led to a decrease or increase of catalytic activity, respectively. La0.9Ce0.1CoO3 proved to be the most active catalyst, showing complete conversion at

Davide Ferri; Lucio Forni

1998-01-01

161

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

162

Effect of Jahn-Teller distortions on the structural and magnetic ordering in perovskite-type transition-metal oxides  

Microsoft Academic Search

The effect of local and cooperative distortions of oxygen octahedra containing Jahn-Teller ions on the elastic, electric,\\u000a magnetic, and optical properties of lightly doped lanthanum strontium manganites and irondoped lithium niobate ferroelectric\\u000a has been experimentally investigated. The formation of nano-and microscale clusters and domains around, respectively, Mn3+ and Fe2+ Jahn-Teller ions at phase transitions and in magnetic or electric fields

Kh. G. Bogdanova; A. R. Bulatov; V. A. Golenishchev-Kutuzov; R. I. Kalimullin; A. A. Potapov

2008-01-01

163

Resolving surface chemical states in XPS analysis of first row transition metals, oxides and hydroxides: Cr, Mn, Fe, Co and Ni  

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 their 2p spectra resulting from peak asymmetries, complex multiplet splitting, shake-up and plasmon loss structure, and uncertain, overlapping binding energies. Our previous paper [M.C. Biesinger et al., Appl. Surf. Sci. 257 (2010) 887-898.] in which we examined Sc, Ti, V, Cu and Zn species, has shown that all the values of the spectral fitting parameters for each specific species, i.e. binding energy (eV), full wide at half maximum (FWHM) value (eV) for each pass energy, spin-orbit splitting values and asymmetric peak shape fitting parameters, are not all normally provided in the literature and data bases, and are necessary for reproducible, quantitative chemical state analysis. A more consistent, practical and effective approach to curve fitting was developed based on a combination of (1) standard spectra from quality reference samples, (2) a survey of appropriate literature databases and/or a compilation of literature references and (3) specific literature references where fitting procedures are available. This paper extends this approach to the chemical states of Cr, Mn, Fe, Co and Ni metals, and various oxides and hydroxides where intense, complex multiplet splitting in many of the chemical states of these elements poses unique difficulties for chemical state analysis. The curve fitting procedures proposed use the same criteria as proposed previously but with the additional complexity of fitting of multiplet split spectra which has been done based on spectra of numerous reference materials and theoretical XPS modeling of these transition metal species. Binding energies, FWHM values, asymmetric peak shape fitting parameters, multiplet peak separation and peak area percentages are presented. The procedures developed can be utilized to remove uncertainties in the analysis of surface states in nano-particles, corrosion, catalysis and surface-engineered materials.

Biesinger, Mark C.; Payne, Brad P.; Grosvenor, Andrew P.; Lau, Leo W. M.; Gerson, Andrea R.; Smart, Roger St. C.

2011-01-01

164

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

165

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

166

Tuning Ferromagnetism at Interfaces between Insulating Perovskite Oxides.  

PubMed

We use density functional theory calculations to show that the LaAlO_{3}|SrTiO_{3} 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 LaScO_{3}|BaTiO_{3} interface is found to be less favorable than the greater interface distortion of LaAlO_{3}|CaTiO_{3}. Compared to LaAlO_{3}|SrTiO_{3}, 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

167

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

168

Paramagnetic point and pair defects in oxide perovskites (*) K. A. Mller  

E-print Network

+ in a cubic crystal field [1], or into the Jahn- Teller effect [2], and they permitted an investigation551 Paramagnetic point and pair defects in oxide perovskites (*) K. A. Müller IBM Zurich Research de structure perovskite. Les sites du réseau et les valences des ions substituants sont considérés

Paris-Sud XI, Université de

169

A team of researchers is focusing on the mechanistic aspects of selective oxidation by transition metal-mediated catalysis.  

E-print Network

,3-dimethyl-2-butene with styrene oxide is possible using MTO as a catalyst. Although not all side products intermediates for a variety of applications ­ often involve the use of expensive oxidants or processes-step process: oxygen transfer from an epoxide to the catalyst (bottom) and its subsequent incorporation

Ottino, Julio M.

170

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

171

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

PubMed

A facile and novel preparation strategy based on electrochemical techniques for the fabrication of electrodeposited graphene (EGR) and zinc oxide (ZnO) nanocomposite was developed. The morphology and structure of the EGR-based nanocomposite were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (XPS) and Raman spectroscopy. Meanwhile, the electrochemical performance of the nanocomposite was demonstrated with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Due to the synergistic effect of EGR and ZnO nanoparticles, an ultrasensitive electrochemical sensor for acetaminophen (AC) and phenacetin (PCT) was successfully fabricated. The linearity ranged from 0.02 to 10 ?M for AC and 0.06 to 10 ?M for PCT with high sensitivities of 54,295.82 ?A mM(-1) cm(2) for AC and 21,344.66 ?A mM(-1) cm(2) for PCT, respectively. Moreover, the practical applicability was validated to be reliable and desirable in pharmaceutical detections. The excellent results showed the promise of the proposed preparation strategy of EGR-transition metal oxide nanocomposite in the field of electroanalytical chemistry. PMID:24201458

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

2014-01-01

172

Synthesis under pressure and characterizations through optical spectroscopy of jahn-teller cations (LS Ni3+, is Co3+) as probes diluted in a perovskite matrix  

Microsoft Academic Search

The objective is to explore through optical spectroscopy and magnetic measurements the coordination and electronic structures of transition-metal ions introduced as impurities with unusual valence states in the oxide perovskite LaAlO3. The selected transition-metal ions Ni3+(3d7) and Co3+(3d6) are characterized by an electronic configuration likely leading to an orbital degenerate E state in Oh symmetry, and thus electron-lattice coupling due

M. N. Sanz-Ortiz; F. Rodríguez; A. Baranov; G. Demazeau

2008-01-01

173

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

174

X-ray study of two complex oxides, each having octahedral oxygen co-ordination of transition metals  

NASA Astrophysics Data System (ADS)

We have studied the system [Ba0.6 Sr0.4] [(Y Ta) 0.03 Ti0.94]O3, as produced using two different sintering temperatures. It was shown by others that for a sample sintered at 1550 °C the material is a relaxor, whereas for the same composition produced with sintering temperature of 1600 °C the sample is a normal ferroelectric. We have employed analysis of x-ray diffraction peak broadening, Ti K edge x-ray near edge spectroscopy, and extended x-ray absorption edge fine structure spectroscopy of Ta and Y sites in our study. We find that the 1550 °C sinter sample has over double the lattice strain as does the 1600 °C sample. For the lower temperature sinter material, both Ta and Y go to sites substitutional for Ti in the lattice, with a significant expansion (contraction) of the local perovskite structure about Y/Ta dopants. Thus, with only three percent B site addition of Y and Ta dopants, there is a strain associated relaxor behavior produced in a bulk sample. For the higher temperature sinter specimen, there is a marked change in the average Y environment relative to the lower temperature sinter sample. We also have studied the structural transformations around both V and Cr atoms in (V1-xCrx) 2O3 across its metal-insulator transition (MIT) have been studied by extended x-ray absorption fine-structure technique. Our new results for Cr made possible by the use of a novel x-ray analyzer that we developed reveal the substitutional mechanism of Cr doping. We find that this system has a buckled structure with short Cr-V and long V-V bonds. This system of bonds is disordered around the average trigonal lattice ascertained by x-ray diffraction. Such local distortions can result in a long range strain field that sets in around dilute Cr atoms in microscopic regions. We suggest that such locally strained regions should be insulating even at small x. The possibility of local insulating regions within a metallic phase, first suggested by Rice and Brinkman in 1972, remains unaccounted for in modern MIT theories. Also for the bulk single crystals, the glancing emergent angle method was used to minimize fluorescence distortion in V K-edge fluorescence XAFS. These data were compared to transmission results on finely ground powders. The powder XAFS is expected to be closely reproduced by weighting the c perpendicular to E data twice, the c parallel to E once, and dividing by three. For V-O and V-V distances, excellent agreement was obtained between the averaged single crystal and transmission powder data. Surprisingly, the amplitude of the weighed average glancing emergent angle data was in all cases greater, not less, than the amplitude of the corresponding powder data.

Shanthakumar, Poorani

175

Effect of Li ion in transition metal sites on electrochemical behavior of layered lithium manganese oxides solid solutions  

Microsoft Academic Search

Two solid solutions of Li[Li1\\/5Ni1\\/10Co1\\/5Mn1\\/2]O2 and Li[Ni1\\/4Co1\\/2Mn1\\/4]O2 compositions were synthesized using a sol–gel method. The solid solutions with layered manganese oxides were both formed with typical hexagonal structure with maintaining the manganese oxidation state of 4+. The electrochemical characterization of the synthesized materials showed a monotonous discharge curve shape without structural transformation to spinel during charge–discharge processes. The Li[Li1\\/5Ni1\\/10Co1\\/5Mn1\\/2]O2 and

K. S Park; M. H Cho; S. J Jin; K. S Nahm; Y. S Hong

2004-01-01

176

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

177

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

178

Anisotropic oxygen diffusion at low temperature in perovskite-structure iron oxides  

Microsoft Academic Search

Oxygen-ion conduction in transition-metal oxides is exploited in, for example, electrolytes in solid-oxide fuel cells and oxygen-separation membranes, which currently work at high temperatures. Conduction at low temperature is a key to developing further utilization, and an understanding of the structures that enable conduction is also important to gain insight into oxygen-diffusion pathways. Here we report the structural changes observed

Satoru Inoue; Masanori Kawai; Noriya Ichikawa; Hiroshi Kageyama; Werner Paulus; Yuichi Shimakawa

2010-01-01

179

Oxidative addition of the C?-C? bond in ?-O-4 linkage of lignin to transition metals using a relativistic pseudopotential-based ccCA-ONIOM method.  

PubMed

A multi-level multi-layer QM/QM method, the relativistic pseudopotential correlation-consistent composite approach within an ONIOM framework (rp-ccCA-ONIOM), was applied to study the oxidative addition of the C(?)-C(?) bond in an archetypal arylglycerol ?-aryl ether (?-O-4 linkage) substructure of lignin to Ni, Cu, Pd and Pt transition metal atoms. The chemically active high-level layer is treated using the relativistic pseudopotential correlation-consistent composite approach (rp-ccCA), an efficient methodology designed to reproduce an accuracy that would be obtained using the more computationally demanding CCSD(T)/aug-cc-pCV?Z-PP, albeit at a significantly reduced computational cost, while the low-level layer is computed using B3LYP/cc-pVTZ. The thermodynamic and kinetic feasibilities of the model reactions are reported in terms of enthalpies of reactions at 298 K (?H°(298)) and activation energies (?H-act). The results obtained from the rp-ccCA:B3LYP hybrid method are compared to the corresponding values using CCSD(T) and several density functionals including B3LYP, M06, M06 L, B2PLYP, mPWPLYP and B2GP-PLYP. The energetics of the oxidative addition of C?C bond in ethane to Ni, Cu, Pd and Pt atoms are also reported to demonstrate that the rp-ccCA method effectively reproduces the accuracy of the CCSD(T)/aug-cc-pCV?Z method. Our results show that in the catalytic activation of the C(?)-C(?) bond of ?-O-4, the use of platinum metal catalysts will lead to the most thermodynamically favored reaction with the lowest activation barrier. PMID:22144374

Oyedepo, Gbenga A; Wilson, Angela K

2011-12-01

180

Structural and dynamic properties of oxygen vacancies in perovskite oxides--analysis of defect chemistry by modern multi-frequency and pulsed EPR techniques.  

PubMed

Multi-frequency and pulsed electron paramagnetic resonance (EPR) provides a sensitive spectroscopic tool to elucidate the defect structure of transition-metal doped perovskite oxides, as well as to monitor dynamic processes of oxygen vacancies in these materials. In this regard, high-frequency EPR spectrometers and pulsed EPR techniques such as the hyperfine sublevel correlation experiment (HYSCORE) may now routinely be used for dedicated investigations, providing considerably more insight than the application of standard continuous-wave EPR. Recent results include the formation of defect complexes between acceptor-type transition-metal centers with either one or two oxygen vacancies for the reason of charge compensation. Furthermore, such defect complexes follow the domain switching upon poling ferroelectric compounds with correspondingly high electric fields. On the other hand, multi-valent manganese functional centers provide trapping centers for electronic and ionic charge carriers (e', ) such that valency altered acceptor states or defect complexes are formed. Additionally, the trapping of charge carriers at the intrinsic 'reduced' B-site ions, and , can be observed by means of EPR spectroscopy. PMID:21082136

Eichel, Rüdiger-A

2011-01-14

181

Electronic structure of lanthanum perovskites with 3d transition elements  

Microsoft Academic Search

The systematics of the electronic structure of LaBOâ perovskite oxides, where the B element scans the 3d transition-metal series from Ti to Co, are examined. X-ray photoelectron spectra of valence bands and shallow core states are presented and compared with theoretical molecular cluster and free-ion multiplet models. Self-consistent ionic configurations are obtained from the embedded cluster calculations, which differ from

D. J. Lam; B. W. Veal; D. E. Ellis

1980-01-01

182

Electronic structure of lanthanum perovskites with 3d transition elements  

Microsoft Academic Search

The systematics of the electronic structure of LaBO3 perovskite oxides, where the B element scans the 3d transition-metal series from Ti to Co, are examined. X-ray photoelectron spectra of valence bands and shallow core states are presented and compared with theoretical molecular cluster and free-ion multiplet models. Self-consistent ionic configurations are obtained from the embedded cluster calculations, which differ from

D. J. Lam; B. W. Veal; D. E. Ellis

1980-01-01

183

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

184

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 that these proposed mechanisms do not provide a satisfactory answer. The double exchange and magnetic polaron transfer

Gong, Xingao

185

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

E-print Network

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

Halpin, Carolyn F.

2012-06-07

186

First principles study of magnetostructural instabilities in magnetic perovskite oxides  

NASA Astrophysics Data System (ADS)

First principles phonon dispersion relations are reported for a range of magnetic perovskite oxides in cubic high-symmetry reference structures. Materials considered include EuTiO3 and BiFeO3. For each system, the dominant lattice instabilities are identified. These are frozen-in, singly and in combination, and the structures are optimized in the resulting space groups. From this, we identify distinct low-energy alternatives to the ground-state structure. We focus particularly on the dependence of the lattice instabilities and structural energetics of low-lying phases on the magnetic order, and extract key magnetostructural coupling parameters. The analysis is applied to predict possible structural and magnetic phase transitions as a function of epitaxial strain and/or of composition in low-concentration solid solutions (A1-xA'xBO3, AB1-xB'xO3, A1-xA'xB1-yB'yO3 for small x,y).

Lee, Jun Hee; Palova, Lucia; Rabe, Karin M.

2009-03-01

187

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

SciTech Connect

We report a comparative study of reduced transition metal oxide clusters, M?O?? (M = Cr, W) anions and their neutrals, via anion photoelectron spectroscopy (PES) and density functional theory (DFT) and molecular orbital theory (CCSD(T)) calculations. Well-resolved PES spectra are obtained for M?O?? (M = Cr, W) at 193 and 157 nm photon energies. Different PES spectra are observed for M = Cr versus M = W. ExtensiveDFT and CCSD(T) calculations are performed to locate the ground and low-lying excited states for the neutrals and anions. The ground states of Cr?O? and Cr?O?? are predicted to be the ³B? and ?B? states of a C?v structure, respectively, revealing ferromagnetic spin coupling for Cr 3d electrons. In contrast, the ground states of W?O? and W?O?? are predicted to be the ¹A? state (Cs symmetry) and the ²A? state (C?v symmetry), respectively, showing metal-metal d-d bonding in the anion. The current cluster geometries are in qualitative agreement with prior DFT studies at the PBE level for M = Cr and the B3LYP level for M = W. The BP86 and PW91 functionals significantly outperform the B3LYP functional for the Cr species, in terms of relative energies, electron detachment energies, and electronic excitation energies, whereas the B3LYP functional is better for the W species. Accurate heats of formation for the ground states of M?O? are calculated from the clustering energies and the heats of formation of MO? and MO?. The energetics have been used to predict redox reaction thermochemistry.

Li, Shenggang; Zhai, Hua Jin; Wang, Lai S.; Dixon, David A.

2009-09-28

188

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

189

Transition metal nitride functional coatings  

NASA Astrophysics Data System (ADS)

During the past decade, interest in transition metal nitrides has grown considerably. Nitrides of various elements play an important role in industry, science, and technology for their interesting and useful resilient properties. For example, many transition metal nitrides based on titanium, boron, and nitrogen have stimulated commercial interest because of their extreme hardness, wear and corrosion resistance, and thermal and electrical properties. All of these features are enhanced by the resulting structures and the large degree of covalency exhibited by the transition metal-nitride bonds. Coatings of select nitrides may particularly influence physico-chemical properties in critical surface and interface regions. This article attempts to present a brief overview on transition metal-nitride research for advancement in reliable machine part manufacturing.

Navinsek, B.; Seal, Sudipta

2001-09-01

190

Solid electrolyte CO 2 sensor using NASICON and perovskite-type oxide electrode  

Microsoft Academic Search

Solid-state electrochemical sensor devices combined with sodium super ionic conductor (NASICON: Na1+xZr2SixP3?xO12) discs and perovskite-type oxide electrodes have been developed for the detection of CO2 in the range of 100–2000 ppm. Among the various sensor devices tested, Co-based perovskite-type oxide electrodes were found to show excellent sensing properties to CO2 at 200–300°C. Especially, NdCoO3- and La0.8Ba0.2CoO3-based elements showed the best

Youichi Shimizu; Nami Yamashita

2000-01-01

191

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

NASA Astrophysics Data System (ADS)

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

Lee, Yueh-Lin

192

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

NASA Astrophysics Data System (ADS)

The prohibitive cost and scarcity of the noble-metal catalysts needed for catalysing the oxygen reduction reaction (ORR) in fuel cells and metal-air batteries limit the commercialization of these clean-energy technologies. Identifying a catalyst design principle that links material properties to the catalytic activity can accelerate the search for highly active and abundant transition-metal-oxide catalysts to replace platinum. Here, we demonstrate that the ORR activity for oxide catalysts primarily correlates to ?*-orbital (eg) occupation and the extent of B-site transition-metal-oxygen covalency, which serves as a secondary activity descriptor. Our findings reflect the critical influences of the ?* orbital and metal-oxygen covalency on the competition between O22-/OH- displacement and OH- regeneration on surface transition-metal ions as the rate-limiting steps of the ORR, and thus highlight the importance of electronic structure in controlling oxide catalytic activity.

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

2011-07-01

193

Oxygen Ion Migration in Perovskite-Type Oxides  

Microsoft Academic Search

Computer simulation techniques have been applied to perovskite-structured LaBO3 (where B = Cr, Mn, Fe, Co) in order to elucidate the mechanistic features and energetics of oxygen ion migration. For the four compounds considered, a common set of interatomic potentials was derived that correctly reproduces their observed cubic structures. The results support models in which diffusion is mediated by oxygen

M. Cherry; M. S. Islam; C. R. A. Catlow

1995-01-01

194

Single-source materials for metal-doped titanium oxide: syntheses, structures, and properties of a series of heterometallic transition-metal titanium oxo cages.  

PubMed

Titanium dioxide (TiO(2)) doped with transition-metal ions (M) has potentially broad applications in photocatalysis, photovoltaics, and photosensors. One approach to these materials is through controlled hydrolysis of well-defined transition-metal titanium oxo cage compounds. However, to date very few such cages have been unequivocally characterized, a situation which we have sought to address here with the development of a simple synthetic approach which allows the incorporation of a range of metal ions into titanium oxo cage arrangements. The solvothermal reactions of Ti(OEt)(4) with transition-metal dichlorides (M(II)Cl(2), M = Co, Zn, Fe, Cu) give the heterometallic transition-metal titanium oxo cages [Ti(4)O(OEt)(15)(MCl)] [M = Co (2), Zn (3), Fe (4), Cu (5)], having similar MTi(4)(?(4)-O) structural arrangements involving ion pairing of [Ti(4)O(OEt)(15)](-) anion units with MCl(+) fragments. In the case of the reaction of MnCl(2), however, two Mn(II) ions are incorporated into this framework, giving the hexanuclear Mn(2)Ti(4)(?(4)-O) cage [Ti(4)O(OEt)(15)(Mn(2)Cl(3))] (6) in which the MCl(+) fragments in 2-5 are replaced by a [ClMn(?-Cl)MnCl](+) unit. Emphasizing that the nature of the heterometallic cage is dependent on the metal ion (M) present, the reaction of Ti(OEt)(4) with NiCl(2) gives [Ti(2)(OEt)(9)(NiCl)](2) (7), which has a dimeric Ni(?-Cl)(2)Ni bridged arrangement arising from the association of [Ti(2)(OEt)(9)](-) ions with NiCl(+) units. The syntheses, solid-state structures, spectroscopic and magnetic properties of 2-7 are presented, a first step toward their applications as precursor materials. PMID:21086988

Eslava, Salvador; McPartlin, Mary; Thomson, Richard I; Rawson, Jeremy M; Wright, Dominic S

2010-12-20

195

A facile and general approach for the direct fabrication of 3D, vertically aligned carbon nanotube array/transition metal oxide composites as non-Pt catalysts for oxygen reduction reactions.  

PubMed

A simple and effective strategy involving nebulized ethanol assisted infiltration for the general synthesis of 3D structure-based vertically aligned carbon nanotube arrays (VACNTs) uniformly and deeply decorated with various transition-metal oxide (MOs) has been developed. Furthermore, it is demonstrated that the 3D structure-based VACNTs with decorated MnO2 can exhibit superior electrocatalytic oxygen reduction reaction activity, long-term stability, and an excellent resistance to crossover effects compared to the commercial Pt/C catalyst. PMID:24616041

Yang, Zhi; Zhou, Xuemei; Jin, Zhiping; Liu, Zheng; Nie, Huagui; Chen, Xi'an; Huang, Shaoming

2014-05-21

196

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

E-print Network

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

May, Kevin J. (Kevin Joseph)

2013-01-01

197

Room-temperature magnetoresistance in an oxide material with an ordered double-perovskite structure  

Microsoft Academic Search

Colossal magnetoresistance-a huge decrease in resistance in response to a magnetic field-has recently been observed in manganese oxides with perovskite structure. This effect is attracting considerable interest from both fundamental and practical points of view. In the context of using this effect in practical devices, a noteworthy feature of these materials is the high degree of spin polarization of the

K.-I. Kobayashi; T. Kimura; H. Sawada; K. Terakura; Y. Tokura

1998-01-01

198

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

199

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

200

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

Microsoft Academic Search

The liquid-phase synthesis of metal oxide nanoparticles in organic solvents under exclusion of water is nowadays a well-established alternative to aqueous sol–gel chemistry. In this article, we highlight some of the advantages of these routes based on selected examples. The first part reviews some recent developments in the synthesis of ternary metal oxide nanoparticles by surfactant-free nonaqueous sol–gel routes, followed

Igor Djerdj; Denis Arcon; Zvonko Jaglicic; Markus Niederberger

2008-01-01

201

p-type Mesoscopic nickel oxide/organometallic perovskite heterojunction solar cells.  

PubMed

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

202

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

203

Theoretical investigation of H2 oxidation on the Sr2Fe(1.5)Mo(0.5)O6 (001) perovskite surface under anodic solid oxide fuel cell conditions.  

PubMed

Periodic density functional theory (DFT) calculations and microkinetic modeling are used to investigate the electrochemical oxidation of H2 fuel on the (001) surface of Sr2Fe1.5Mo0.5O6 (SFMO) perovskite under anodic solid oxide fuel cell conditions. Three surface models with different Fe/Mo ratios in the topmost layer-identified by ab initio thermodynamic analysis-are used to investigate the H2 oxidation mechanism. A microkinetic analysis that considers the effects of anode bias potential suggests that a higher Mo concentration in the surface increases the activity of the surface toward H2 oxidation. At operating voltage and anodic SOFC conditions, the model predicts that water desorption is rate-controlling and that stabilizing the oxygen vacancy structure increases the overall rate for H2 oxidation. Although we find that Mo plays a crucial role in improving catalytic activity of SFMO, under fuel cell operating conditions, the Mo content in the surface layer tends to be very low. On the basis of these results and in agreement with previous experimental observations, a strategy for improving the overall electrochemical performance of SFMO is increasing the Mo content or adding small amounts of an active transition metal, such as Ni, to the surface to lower the oxygen vacancy formation energy of the SFMO surface. PMID:24826843

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

2014-06-11

204

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

PubMed

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

Sánchez, Florencio; Ocal, Carmen; Fontcuberta, Josep

2014-04-01

205

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

206

Crystal and Magnetic Structure of Conducting Double Perovskite Sr 2FeMoO 6  

Microsoft Academic Search

We have investigated, crystal and magnetic structure of conducting double perovskite transition metal oxide, Sr2FeMoO6, which has been grown by the floating-zone method.The resisitvity shows T2-dependence in a wide temperature range (50 350 K), perhaps due to magnon scattering.We further have determined the crystal and magnetic structure in the ferrimagnetic state by means of synchrotron radiation X-ray powder measurements as

Yutaka Moritomo; Sheng Xu; Akihiko Machida; Takumi Akimoto; Eiji Nishibori; Masaki Takata; Makoto Sakata; Kenji Ohoyama

2000-01-01

207

Intergranular giant magnetoresistance in a spontaneously phase separated perovskite oxide.  

PubMed

We present small-angle neutron scattering data proving that, on the insulating side of the metal-insulator transition, the doped perovskite cobaltite La(1-x)Sr(x)CoO(3) phase separates into ferromagnetic metallic clusters embedded in a nonferromagnetic matrix. This induces a hysteretic magnetoresistance, with temperature and field dependence characteristic of intergranular giant magnetoresistance (GMR). We argue that this system is a natural analog to the artificial structures fabricated by depositing nanoscale ferromagnetic particles in a metallic or insulating matrix; i.e., this material displays a GMR effect without the deliberate introduction of chemical interfaces. PMID:15698314

Wu, J; Lynn, J W; Glinka, C J; Burley, J; Zheng, H; Mitchell, J F; Leighton, C

2005-01-28

208

Transition metals in plant photosynthesis.  

PubMed

Transition metals are involved in essential biological processes in plants since they are cofactors of metalloproteins and also act as regulator elements. Particularly, plant chloroplasts are organelles with high transition metal ion demand because metalloproteins are involved in the photosynthetic electron transport chain. The transition metal requirement of photosynthetic organisms greatly exceeds that of non-photosynthetic organisms, and either metal deficiency or metal excess strongly impacts photosynthetic functions. In chloroplasts, the transition metal ion requirement needs a homeostasis network that strictly regulates metal uptake, chelation, trafficking and storage since under some conditions metals cause toxicity. This review gives an overview of the current understanding of main features concerning the role of copper (Cu), iron (Fe), manganese (Mn) and zinc (Zn) in plant photosynthesis as well as the mechanisms involved in their homeostasis within chloroplasts. The metalloproteins functioning in photosynthetic proteins of plants as well as those proteins participating in the metal transport and metal binding assembly are reviewed. Furthermore, the role of nickel (Ni) in artificial photosynthesis will be discussed. PMID:23739807

Yruela, Inmaculada

2013-09-01

209

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

PubMed

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

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

2014-07-21

210

Helicoidal ordering in iron perovskites.  

PubMed

We study the double exchange in transition metal oxides with itinerant and localized electrons. We show that the charge transfer energy Delta and the oxygen-oxygen hopping amplitude t(pp) have a strong effect on magnetic ordering: while for Delta>0 the ground state is ferromagnetic, for negative Delta and large t(pp) the double exchange gives rise to an incommensurate helicoidal ordering of local spins, observed, e.g., in the iron perovskites SrFeO3 and CaFeO3. For negative Delta, the metal-insulator transition into a charge-ordered state has little effect on magnetic ordering. This explains the difference in magnetic and transport properties of ferrates and manganites. PMID:15904026

Mostovoy, Maxim

2005-04-01

211

Luminescence of rare-earth ions in perovskite-type oxides: from basic research to applications  

Microsoft Academic Search

Luminescence of a rare-earth ion in SrTiO3 or other perovskite-type oxides was used as a probe of physical properties of a host crystal, but not as a phosphor because observed luminescence efficiency was low. Recent investigations have shown that the luminescence efficiency of SrTiO3:Pr3+ is intensified up to 200 times by addition of Al ions. This paper reviews experimental results

Haijme Yamamoto; Shinji Okamoto; Hiroshi Kobayashi

2002-01-01

212

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

213

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

Microsoft Academic Search

La:Mn = 1:1 mixtures of lanthanum oxide and manganese carbonate were heat-treated under various oxygen partial pressures at 1400 C or 1300 C. The Mn valence of the samples was measured by a chemical analysis, and the crystal structures were refined by the powder x-ray diffraction and the Rietveld analysis. A novel orthorhombic perovskite phase, belonging to the space group

Takeshi Yao; Toyoji Ito; Tadashi Kokubo

1995-01-01

214

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

NASA Astrophysics Data System (ADS)

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 large site in A2Mn2O7 pyrochlores, contrary to Mn4+, and occupies separate crystallographic sites in known mixed-valent Mn2+-Mn3+ or 4+ oxides. The bond distances, Mn-O-Mn bonding angles and Mn sublattice topology are given for the main A-Mn-O structures. Only the perovskite and K2NiF4 structures give Mn-O-Mn angles near 180°, while these are close to 90° in spinels, to 135° in pyrochlores and marokites. The magnetic properties of non-perovskite manganese oxides are briefly discussed in view of these structural features.

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

2004-05-01

215

Screened hybrid functional applied to 3d0?3d8 transition-metal perovskites LaMO3 (M = Sc-Cu): Influence of the exchange mixing parameter on the structural, electronic, and magnetic properties  

NASA Astrophysics Data System (ADS)

We assess the performance of the Heyd-Scuseria-Ernzerhof (HSE) screened hybrid density functional scheme applied to the perovskite family LaMO3 (M = Sc-Cu) and discuss the role of the mixing parameter ? [which determines the fraction of exact Hartree-Fock exchange included in the density functional theory (DFT) exchange-correlation functional] on the structural, electronic, and magnetic properties. The physical complexity of this class of compounds, manifested by the largely varying electronic characters (band/Mott-Hubbard/charge-transfer insulators and metals), magnetic orderings, structural distortions (cooperative Jahn-Teller-type instabilities), as well as by the strong competition between localization/delocalization effects associated with the gradual filling of the t2g and eg orbitals, symbolize a critical and challenging case for theory. Our results indicate that HSE is able to provide a consistent picture of the complex physical scenario encountered across the LaMO3 series and significantly improve the standard DFT description. The only exceptions are the correlated paramagnetic metals LaNiO3 and LaCuO3, which are found to be treated better within DFT. By fitting the ground-state properties with respect to ?, we have constructed a set of “optimum” values of ? from LaScO3 to LaCuO3: it is found that the optimum mixing parameter decreases with increasing filling of the d manifold (LaScO3: 0.25; LaTiO3 and LaVO3: 0.10-0.15; LaCrO3, LaMnO3, and LaFeO3: 0.15; LaCoO3: 0.05; LaNiO3 and LaCuO3: 0). This trend can be nicely correlated with the modulation of the screening and dielectric properties across the LaMO3 series, thus providing a physical justification to the empirical fitting procedure. Finally, we show that by using this set of optimum mixing parameter, HSE predict dielectric constants in very good agreement with the experimental ones.

He, Jiangang; Franchini, Cesare

2012-12-01

216

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

217

[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

218

[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

219

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

220

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

221

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

Microsoft Academic Search

The thermal expansion behavior and mechanism of A-site-deficient lanthanum manganite perovskites, La{sub 1-x}MnOâ (0 < x ⤠0.1), and alkaline earth metal (AE)-doped lanthanum manganite perovskites, La{sub 1-x}AEâMnOâ (AE = Ca and Sr, 0 ⤠x ⤠0.4), under oxidizing atmospheres have been investigated. The average linear thermal expansion coefficients of the AE-doped lanthanum manganites decreased with increasing Ca content

Masashi Mori; Yoshiko Hiei; Nigel M. Sammes; Geoff A. Tompsett

2000-01-01

222

Catalytic combustion of methane on nano-structured perovskite-type oxides fabricated by ultrasonic spray combustion  

Microsoft Academic Search

The synthesis of perovskite-type oxides using ultrasonic spray combustion (USC) was investigated by adjusting the composition of the precursor solution and the temperature of synthesis and calcination. LaMnO3 was chosen as model perovskite to systematically analyze the effect of USC operating parameters. XRD, IR spectroscopy, TG-TPD, SEM, TEM and BET were used to characterize the samples with respect to phase

Xun Wei; Paul Hug; Renato Figi; Matthias Trottmann; Anke Weidenkaff; Davide Ferri

2010-01-01

223

Electronic structure of lanthanum perovskites with 3d transition elements  

NASA Astrophysics Data System (ADS)

The systematics of the electronic structure of LaBO3 perovskite oxides, where the B element scans the 3d transition-metal series from Ti to Co, are examined. X-ray photoelectron spectra of valence bands and shallow core states are presented and compared with theoretical molecular cluster and free-ion multiplet models. Self-consistent ionic configurations are obtained from the embedded cluster calculations, which differ from the assumptions of crystal-field theory due to metal-oxygen covalency. The prospect for more rigorous many-electron models is discussed.

Lam, D. J.; Veal, B. W.; Ellis, D. E.

1980-12-01

224

Influence of magnetic ordering on structural instabilities in insulating perovskites  

NASA Astrophysics Data System (ADS)

We propose a general model, based on Anderson superexchange and the pseudo Jahn-Teller effect, to explain why ferroelectric and octahedral tilting distortions are favored by ferromagnetic ordering when compared to antiferromagnetic tilting distortions in ABX3 (A = alkali, alkaline-earth ion, f-filling rare earth; B = magnetic transition-metal ion; X = O2-, F-) perovskite crystals. Ab initio calculations are used to check the model under a wide range of pressures for oxides and fluorides, with the latter displaying an enhancement of the ferroelectric distortion when pressure is increased.

Garcia-Fernandez, Pablo; Aramburu, Jose Antonio; Moreno, Miguel

2011-05-01

225

Enantioselective, transition metal catalyzed cycloisomerizations.  

PubMed

This review illustrates enantioselective transition-metal promoted skeletal rearrangements of polyunsaturated substrates possessing olefin, alkyne or allene functions. These processes are classified according to the number of carbon atoms involved in the cyclization, from (1C+1C) to (2C+2C+2C) or (2C+5C) cyclizations. Thus, for instance, (1C+1C) processes are typified notably by Alder-ene type reactions taking place mainly under palladium and rhodium catalysis, in the presence of chiral phosphorus ligands. Also, rhodium, platinum, and gold promoted insertions of unsaturated carbon-carbon bonds into C-H bonds belong to this class. For each class of reactions or substrate type the best ligand-metal pairs are highlighted. Unfortunately, unlike other transition metal promoted reactions, the mechanisms of chiral induction and stereochemical pathways have not been established so far in any of these reactions. In only a few instances, qualitative heuristic models have been tentatively proposed. Although the available stereochemical information is systematically given here, the paper focuses mainly on synthetic aspects of enantioselective cycloisomerizations. PMID:22674143

Marinetti, Angela; Jullien, Hélène; Voituriez, Arnaud

2012-07-21

226

Photoluminescence of Perovskite Nanosheets Prepared by Exfoliation of Layered Oxides, K2Ln2Ti3O10, KLnNb2O7, and  

E-print Network

_ida@chem.chem.kumamoto-u.ac.jp Abstract: Luminescent perovskite nanosheets were prepared by exfoliation of single- or double- layeredPhotoluminescence of Perovskite Nanosheets Prepared by Exfoliation of Layered Oxides, K2Ln2Ti3O10 perovskite oxides, K2Ln2Ti3O10, KLnNb2O7, and RbLnTa2O7 (Ln: lanthanide ion). The thickness of the individual

227

Transition-metal-mediated thiosulfinate ester synthesis  

SciTech Connect

Unlike sulfur dioxide (SO{sub 2}), the coordination and organic reaction chemistry of disulfur monoxide (S{sub 2}O) has received little attention. A few Diels-Alder reactions of simple dienes with S{sub 2}O have been reported. However, there were no reports of direct S{sub 2}O complex synthesis prior to our initial work. The authors recently published a synthesis of 4,5-diphenyl-3,6-dihydro-1,2-dithiin 1-oxide (2) which liberates S{sub 2}O via a transition-metal-assisted retro-Diels-Alder reaction. Here we report further on the unusual reactivity of 2 and its utilization in the synthesis of cyclic thiosulfinate esters.

Raseta, M.E.; Cawood, S.A.; Welker, M.E. (Wake Forest Univ., Winston-Salem, NC (USA)); Rheingold, A.L. (Univ. of Delaware, Newark (USA))

1989-10-11

228

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

Microsoft Academic Search

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

Igor Solovyev

2011-01-01

229

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

E-print Network

charge: La3+ O2- = La­O + and Al3+ O2- 2= Al­O2 - . In growth of SrTiO3 STO on LaAlO3 LAO Ref. 5 and vice direct role in controlling the morphology of this single-metal oxide heteroepitaxy. TiO2 films of 1.5 nm

Olmstead, Marjorie

230

Interplay of octahedral rotations and breathing distortions in charge-ordering perovskite oxides  

NASA Astrophysics Data System (ADS)

We investigate the structure-property relationships in ABO3 perovskites exhibiting octahedral rotations and cooperative octahedral breathing distortions (CBD) using group theoretical methods. Rotations of octahedra are ubiquitous in the perovskite family, while the appearance of breathing distortions—oxygen displacement patterns that lead to approximately uniform dilation and contraction of the BO6 octahedra—are rarer in compositions with a single, chemically unique B site. The presence of a CBD relies on electronic instabilities of the B-site cations, either orbital degeneracies or valence-state fluctuations, and often appear concomitant with charge order metal-insulator transitions or B-site cation ordering. We enumerate the structural variants obtained from rotational and breathing lattice modes and formulate a general Landau functional describing their interaction. We use this information and combine it with statistical correlation techniques to evaluate the role of atomic scale distortions on the critical temperatures in representative charge ordering nickelate and bismuthate perovskites. Our results provide microscopic insights into the underlying structure-property interactions across electronic and magnetic phase boundaries, suggesting plausible routes to tailor the behavior of functional oxides by design.

Balachandran, Prasanna V.; Rondinelli, James M.

2013-08-01

231

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 by co-precipitation24 method and its catalytic activity has been tested for diesel soot oxidation processes and vehicle exhaust.33 Key words: BaRuO3, perovskite, diesel soot oxidation, vehicular exhaust

Paris-Sud XI, Université de

232

Nanostructured magnetoelectric thin films of ferroelectric perovskite and magnetic oxides  

Microsoft Academic Search

Nanostructured thin films of ferroelectric (e.g., BaTiO3, PZT, and BiFeO3) and magnetic oxides (e.g., cobalt-ferrites and nickel-ferrites) prepared by physical deposition techniques (e.g., pulsed laser deposition) and chemical solution processing (e.g., sol-gel spin-coating method) have recently become new routes to multiferroic magnetoelectric (ME) composites. In comparison to bulk ME ceramic composites, the nanostructured thin films provide more degrees of freedom,

Ce-Wen Nan

2008-01-01

233

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

NASA Astrophysics Data System (ADS)

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

Yao, Takeshi; Ito, Toyoji; Kokubo, Tadashi

1995-05-01

234

Transformation of crystalline heteronuclear cyano complex to crystalline perovskite-type oxide by thermal decomposition  

Microsoft Academic Search

The thermal decomposition reaction of crystalline heteronuclear cyano complex precursor to crystalline perovskite-type oxide catalyst was investigated. From X-ray single crystal analysis and XRD, FT-IR, TG-DTA, SEM, and BET measurements, the thermal decomposition process of Sm[Fe(CN)6]·4H2O precursor was elucidated. It was found that the specific surface area of SmFeO3 decreased monotonously with increasing calcination temperature of Sm[Fe(CN)6]·4H2O, while the highest

Makiko Asamoto; Masataka Hino; Syuhei Yamaguchi; Hidenori Yahiro

2011-01-01

235

Electrical conductivity and thermal stability measurements of a mixed perovskite oxide system  

SciTech Connect

For the mixed perovskite oxide system (Sr/sub 0.8125/La/sub 0.1875/ ) (Zr/sub 0.75/Fe/sub x/Ru/sub 0.25-x/)O/sub 3-delta/ , electrical conductivities were measured in air as a function of temperature and Ru/Fe ratio. Liquidus and solidus temperatures were determined in air by the laser melting point measurement technique. The substitution of Ru for Fe was found to increase the electrical conductivity by over an order of magnitude while decreasing the solidus temperature of the Fe-rich solid solution by less than 10%.

Sukkar, M.H.; Sadoway, D.R.

1982-05-01

236

Synthesis under pressure and characterizations through optical spectroscopy of jahn-teller cations (LS Ni3+, is Co3+) as probes diluted in a perovskite matrix  

NASA Astrophysics Data System (ADS)

The objective is to explore through optical spectroscopy and magnetic measurements the coordination and electronic structures of transition-metal ions introduced as impurities with unusual valence states in the oxide perovskite LaAlO3. The selected transition-metal ions Ni3+(3d7) and Co3+(3d6) are characterized by an electronic configuration likely leading to an orbital degenerate E state in Oh symmetry, and thus electron-lattice coupling due to the Jahn-Teller effect may induce low symmetry distortion around the impurity oxygen octahedron. We show that a sol-gel process followed by high oxygen pressure treatments yields stabilization of trivalent state in oxide perovskite. Information about the coordination, electronic structure and aggregation around the magnetic impurity was obtained from X-ray diffraction, FTIR and optical spectroscopy. Finally, evidence on the possible existence of intermediate spin state in Co3+ is under consideration.

Sanz-Ortiz, M. N.; Rodríguez, F.; Baranov, A.; Demazeau, G.

2008-07-01

237

Direct fabrication of integrated 3D epitaxial functional transition metal oxide nanostructures using extremely small hollow nanopillar nano-imprint metal masks  

Microsoft Academic Search

A novel nanofabrication technique is developed for functional oxides. Combining nano-imprint lithography, sidewall-etching and sidewall-deposition processes enables us to prepare Mo hollow nanopillar masks with 100 and 60 nm window sizes, which is smaller than the original nano-imprint mold size of 250 nm. Using this Mo nanomask, extremely small epitaxial ferromagnetic oxide (Fe2.5Mn0.5O4) nanostructures can be directly grown on sapphire

Nam-Goo Cha; Teruo Kanki; Hidekazu Tanaka

2011-01-01

238

On the feasibility of synthesizing complex perovskite ferroelectric ceramics via a B-site oxide mixing route  

Microsoft Academic Search

Several relaxor-based complex perovskite ferroelectric ceramics were synthesized by conventional solid-state reaction method\\u000a via different routes, i.e., the B-site oxide mixing route, the straight calcination method and the columbite\\/wolframite precursor\\u000a method. Structure analysis and physical properties measurements prove that the B-site oxide mixing route is efficient and\\u000a feasible in the synthesizing of complex perovskite ferroelectrics since such a technique is

Bijun Fang; Renbing Sun; Yuejin Shan; Keitaro Tezuka; Hideo Imoto

2007-01-01

239

Surface lattice dynamics of layered transition metal oxides: Sr2RuO4 and La0.5Sr1.5MnO4  

NASA Astrophysics Data System (ADS)

Momentum resolved inelastic electron scattering has been used to study the surface lattice dynamics of two layered isostructural perovskite crystals (Sr2RuO4 and La0.5Sr1.5MnO4), two materials with different physical properties. There were three surface optical phonons observed with the energies at 30.0, 50.0, and 75.0 meV with a shoulder appearing at 67.5 meV for Sr2RuO4 and at 26.0, 56.5, and 78.5 meV for La0.5Sr1.5MnO4. In the K2NiF4-type structure, these phonons are associated with the La/Sr vibrational (external), Mn-O-Mn (Ru-O-Ru) bending, and MnO6 (RuO6) stretching modes, respectively. The observed surface phonons, especially for breathing and stretching modes, are at significantly higher energies than the corresponding modes in the bulk, which are directly associated with the relative reduction of out-of-plane Mn-O/Ru-O bond lengths at the surfaces. The line shapes of the quasielastic scattering peaks reflects the surface conductivity of Sr2RuO4 and the insulating behavior of La0.5Sr1.5MnO4. For Sr2RuO4, the large line width of the external mode is attributed to nonequivalent Sr vibrational sites due to the surface reconstruction. For La0.5Sr1.5MnO4, the broad character of both the bending and the stretching modes results from surface electronic inhomogeneities. In contrast to the bulk, the absence of phonon restructuring in the observed temperature range suggests that the long-range charge/orbital ordering transition occurring in the bulk may not take place on the surface, probably correlated with stiffening of observed optical phonons at the surface.

Ismail; Zhang, Jiandi; Matzdorf, R.; Kimura, T.; Tokura, Y.; Plummer, E. W.

2003-01-01

240

Comparative study of the formation of oxidative damage marker 8-hydroxy-2'-deoxyguanosine (8-OHdG) adduct from the nucleoside 2'-deoxyguanosine by transition metals and suspensions of particulate matter in relation to metal content and redox reactivity.  

PubMed

An association between exposure to ambient particulate matter (PM) and increased incidence of mortality and morbidity due to lung cancer and cardiovascular diseases has been demonstrated by recent epidemiological studies. Reactive oxygen species (ROS), especially hydroxyl radicals, generated by PM, have been suggested by many studies as an important factor in the oxidative damage of DNA by PM. The purpose of this study was to characterize quantitatively hydroxyl radical generation by various transition metals in the presence of H2O2 in aqueous buffer solution (pH 7.4) and hydroxylation of 2'-deoxyguanosine (dG) to 8-hydroxy-2'-deoxyguanosine (8-OHdG) under similar conditions. The order of metals' redox reactivity and hydroxyl radical production was Fe(II), V(IV), Cu(I), Cr(III), Ni(II), Co(II), Pb(II), Cd(II). Then, we investigated the generation of hydroxyl radicals in the presence of H2O2 by various airborne PM samples, such as total suspended particulate (TSP), PM10, PM2.5 (PM with aerodynamic diameter 10 and 2.5 microm), diesel exhaust particles (DEP), gasoline exhaust particles (GEP) and woodsmoke soot under the same conditions. When suspensions of PMs were incubated with H2O2 and dG at pH 7.4, all particles induced hydroxylation of dG and formation of 8-OHdG in a dose-dependent increase. Our findings demonstrated that PM's hydroxyl radical (HO radical) generating ability and subsequent dG hydroxylation is associated with the concentration of water-soluble metals, especially Fe and V and other redox or ionizable transition metals and not their total metal content, or insoluble metal oxides, via a Fenton-driven reaction of H2O2 with metals. Additionally, we observed, by Electron paramagnetic resonance (EPR), that PM suspensions in the presence of H2O2 generated radical species with dG, which were spin-trapped by 2-methyl-2-nitroso-propane (MNP). PMID:16298732

Valavanidis, Athanasios; Vlahoyianni, Thomais; Fiotakis, Konstantinos

2005-10-01

241

The Optical Properties of R Titanium Oxides Perovskites  

NASA Astrophysics Data System (ADS)

Reflectance spectroscopy (50-40000 cm ^{-1}) has been used to study the rare earth titanium (III) oxides (RTiO_3 , R = La, Ce, Pr, Nd, Sm, Gd). A mid-infrared absorption has been observed in all members of the series. With decreasing rare earth radius (and decreasing Ti-O-Ti bond angle) the band shifts to higher frequencies. A tight-binding calculation of the effect of the Ti-O-Ti bond angle on the conduction band width supports the picture in which the mid-infrared band is due to transition from the lower Hubbard to the upper Hubbard band. Because this intrinsic absorption is at lower energy than transitions corresponding to O(2p) -Ti(3d) charge transfer (~4 eV) the rare earth titanites are classified as Mott-Hubbard insulators. Systematic variations in the infrared active phonon spectra were observed and related to a tetragonal distortion of the TiO_6 octahedron in NdTiO_3, SmTiO_3 and GdTiO_3. In a second study, the reflectance of four well characterized (x-ray, neutron activation, thermogravimetric, dc resistivity, magnetization) doped LaTiO_3 samples was measured. Although the starting materials contained equimolar amounts of La and Ti, the neutron activation results and structural considerations indicate the presence of La vacancies. There is a transfer of oscillator strength from the mid-infrared band to lower frequencies in highly doped samples but transitions placing two electrons on one site (from the lower to the upper Hubbard band) retain considerable oscillator strength even in a sample where approximately one-fifth of the sites are empty.

Crandles, David Anthony

242

Electrochemistry of transition metal complex catalysts. Part 9. One and two-electron oxidation of iridium complexes with cyclohexane-derived tripod phosphine ligands  

Microsoft Academic Search

The redox chemistry of Ir tripod-type tri-phosphine complexes in dichloromethane is investigated by cyclic voltammetry, hold-ramp experiments, and preparative electrolysis at Pt electrodes. Products are identified by spectroscopic data, as well as EDX and EXAFS results. Complexes with the Ir central atom in the oxidation states +I, +II and +III are detected and several follow-up reactions are possible from those.

Silke Buchmann; Hermann A Mayer; Bernd Speiser; Michael Seiler; Martin P Feth; Helmut Bertagnolli; Stefan Steinbrecher; Erich Plies

2003-01-01

243

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

244

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

NASA Astrophysics Data System (ADS)

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

Shimakawa, Yuichi; Mizumaki, Masaichiro

2014-11-01

245

Comparative perspective and synthetic applications of transition metal mediated oxidative cyclisation of 1,5-dienes towards cis-2,5-disubstituted tetrahydrofurans.  

PubMed

cis-2,5-Disubstituted tetrahydrofurans constitute the core of several natural products and synthetic analogues which exhibit a broad and interesting range of biological activities. This review highlights a personal perspective and provides a comparative note on the synthesis of cis-2,5-disubstituted tetrahydrofuran rings from 1,5-diene precursors using metal-oxo species. Also, mechanistic insights for these synthetically significant protocols are given and striking examples from the literature are reported, which draw attention towards the scope and synthetic utility of metal oxidants in the domain of cis-2,5-tetrahydrofuran containing bioactive natural product synthesis. PMID:25350842

Sheikh, Nadeem S

2014-12-21

246

Monocrystalline mesoporous metal oxide with perovskite structure: a facile solid-state transformation of a coordination polymer.  

PubMed

Monocrystalline mesoporous BiFeO3 crystals were obtained via a multi-step single-crystal to single-crystal transformation of a coordination polymer, Bi[Fe(CN)6]·4H2O. This unique transformation process significantly decreased the crystallization temperature of perovskite oxide without losing high crystallinity. PMID:25259374

Xu, Li; Bu, Fan-Xing; Hu, Ming; Jin, Chuan-Yin; Jiang, Dong-Mei; Zhao, Zhen-Jie; Zhang, Qing-Hong; Jiang, Ji-Sen

2014-10-14

247

Oxidative nonstoichiometry in perovskites, an experimental survey; the defect structure of an oxidized lanthanum manganite by powder neutron diffraction  

Microsoft Academic Search

Oxide perovskites showing oxidative nonstoichiometry (ABO3+x) have been investigated. The structure of LaMn3+0.76Mn4+0.24O3.12 has been investigated by powder neutron diffraction and a composition (La0.94+\\/-0.02□0.06+\\/-0.02)(Mn3+0.745Mn4+0.235□0.02)O3 with partial elimination of La2O3 and vacancies on both the A and B metal sites determined. A much smaller degree of nonstoichiometry has been found for LaVO3+x(x <= 0.05), and LaCrO3, and EuTiO3 did not show

B. C. Tofield; W. R. Scott

1974-01-01

248

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

NASA Astrophysics Data System (ADS)

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 (Vaccel) 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 Ni1+?O (? < 0) and insulating (stoichiometric) or n-type Ni1+?O (? ? 0).

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

2011-09-01

249

Thermogravimetric Study on Oxygen Adsorption\\/Desorption Properties of Double Perovskite Structure Oxides REBaCo 2 O 5+? (RE = Pr, Gd, Y)  

Microsoft Academic Search

The oxygen adsorption\\/desorption properties of double perovskite structure oxides PrBaCo2O5+?, GdBa-Co2O5+? and YBaCo2O5+? were investigated by the thermogravimetry (TG) method in the temperature range of 400 ? 900 °C. The calculated oxygen adsorption\\/desorption surface reaction rate constants ka and kd of these double perovskite structure oxides were larger than the commonly used cubic perovskite oxides, such as Ba0.95Ca0.05Co0.8Fe0.2O3-? and Ba0.5

Hao Haoshan; Zheng Lu; Wang Yingfang; Liu Shijiang; Hu Xing

2007-01-01

250

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

251

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

252

Double perovskites as anode materials for solid-oxide fuel cells.  

PubMed

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 under operating temperatures 650 degrees C < T < 1000 degrees C. Here we report identification of the double perovskites Sr2Mg(1-x)MnxMoO(6-delta) that meet the requirements for long-term stability with tolerance to sulfur and show a superior single-cell performance in hydrogen and methane. PMID:16614219

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

2006-04-14

253

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

PubMed

Resistance change random access memory (RRAM) cells, typically built as MIM capacitor structures, consist of insulating layers I sandwiched between metal layers M, where the insulator performs the resistance switching operation. These devices can be electrically switched between two or more stable resistance states at a speed of nanoseconds, with long retention times, high switching endurance, low read voltage, and large switching windows. They are attractive candidates for next-generation non-volatile memory, particularly as a flash successor, as the material properties can be scaled to the nanometer regime. Several resistance switching models have been suggested so far for transition metal oxide based devices, such as charge trapping, conductive filament formation, Schottky barrier modulation, and electrochemical migration of point defects. The underlying fundamental principles of the switching mechanism still lack a detailed understanding, i.e. how to control and modulate the electrical characteristics of devices incorporating defects and impurities, such as oxygen vacancies, metal interstitials, hydrogen, and other metallic atoms acting as dopants. In this paper, state of the art ab initio theoretical methods are employed to understand the effects that filamentary types of stable oxygen vacancy configurations in TiO(2) and NiO have on the electronic conduction. It is shown that strong electronic interactions between metal ions adjacent to oxygen vacancy sites results in the formation of a conductive path and thus can explain the 'ON' site conduction in these materials. Implication of hydrogen doping on electroforming is discussed for Pr(0.7)Ca(0.3)MnO(3) devices based on electrical characterization and FTIR measurements. PMID:21572196

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

2011-06-24

254

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

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

255

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

256

Structural and surface analysis of unsupported and alumina-supported La(Mn,Fe,Mo)O3 perovskite oxides.  

PubMed

A series of bulk and Al(2)O(3)-supported perovskite oxides of the type LaMn(1-x-y)Fe(x)Mo(y)O(3) (x = 0.00-0.90 and y = 0.00-0.09) were synthesized by the citric acid complexation-gelation method followed by annealing in air at 800 degrees C. For all samples, the local environment and the chemical state and concentration of surface species were determined. Mössbauer spectra revealed the only presence of octahedral Fe(3+) ions dispersed in the perovskite structure, however well-crystallized together with a poorly crystalline LaFeO(3) phases were detected for larger substitutions (x = 0.90). A similar picture was obtained for Mo-loaded (y = 0.02 and 0.05) samples but a new phase most likely related to Fe(3+) ions dispersed aside from the perovskite structure was found for larger substitutions (y = 0.09). Together with these structures, supported samples showed the presence of LaFeO(3) nanoparticles. Finally, photoelectron spectroscopy indicated that the chemical state and composition of the samples in the surface region (2-3 nm) approaches that of the bulk. For the unsupported substituted samples, iron (and molybdenum) enters into the perovskite structure while manganese tends to be slightly segregated. Moreover, in supported perovskites, a fraction of Mo and La atoms interact with the alumina surface. All these oxides were active in methane combustion and best performance was recorded for the Fe-rich composition (x = 0.9) in which both Mn(3+) and Mo(3+) ions were in the same proportion (y = 0.05). PMID:19956932

Rosmaninho, M G; Tristão, J C; Moura, F C C; Lago, R M; Araújo, M H; Fierro, J L G

2010-04-01

257

Hydrothermal synthesis and characterization of perovskite-type Ba 2SbMO 6 (M=In, Y, Nd) oxides  

Microsoft Academic Search

Perovskite-type Ba2SbMO6 (M=In, Y, Nd) oxides have been synthesized in Ba2O–Sb2O5–M2O3–K2O–H2O hydrothermal system. The synthesized Ba2SbMO6 oxide powders were characterized by the techniques such as XRD, IR, SEM, XPS and ICP methods. The results indicated that the Ba\\/Sb\\/M ratio is very similar and closing to 2:1:1 in all the products, and the particle sizes of Ba2SbMO6 oxides, where M=In, Y

Wenjun Zheng; Wenqin Pang; Guangyao Meng

1998-01-01

258

Electrochemical hydrogen property improved in nano-structured perovskite oxide LaFeO3 for Ni/MH battery  

NASA Astrophysics Data System (ADS)

Perovskite oxide LaFeO3, as a novel candidate for the electrode of Ni/MH battery, holds high specific capacity and good cyclical durability at elevated temperatures. However, the poor electrochemical kinetics is a bottleneck for the application of this type of material. By use of nano-structured materials, there are greatly enhanced values of exchange current density I0 and hydrogen diffusion coefficient D, which resulted in an improvement of electrochemical kinetics, a much higher specific capacity and excellent stability during cycling for nano-structured LaFeO3. In theory, there is a significant possibility of further advancing the hydrogen reaction kinetics of perovskite type oxides for Ni/MH battery.

Wang, Qiang; Deng, Gang; Chen, Zhiqian; Chen, Yungui; Cheng, Nanpu

2013-02-01

259

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

260

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

NASA Astrophysics Data System (ADS)

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

Sasajima, K.; Uchida, H.

2011-10-01

261

Transition metal-catalyzed functionalization of pyrazines.  

PubMed

Transition metal-catalyzed reactions are generally used for carbon-carbon bond formation on pyrazines and include, but are not limited to, classical palladium-catalyzed reactions like Sonogashira, Heck, Suzuki, and Stille reactions. Also a few examples of carbon-heteroatom bond formation in pyrazines are known. This perspective reviews recent progress in the field of transition metal-catalyzed cross-coupling reactions on pyrazine systems. It deals with the most important C-C- and C-X-bond formation methodologies. PMID:23632914

Nikishkin, Nicolai I; Huskens, Jurriaan; Verboom, Willem

2013-06-14

262

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

SciTech Connect

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

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

1992-03-03

263

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

264

LABORATORY EXPERIMENT 6 TRANSITION METAL DETERMINATION USING  

E-print Network

, and titrate through purple to green color. Zn: Add ammonia buffer with pH 9-10 to convert all Zn(II) ions or an Erlenmeyer flask), pH is adjusted by addition of an appropriate buffer, necessary amount of suitable to be analyzed are all water soluble inorganic salts of various transition metals: Zinc, Cobalt, Nickel

Nazarenko, Alexander

265

High Pressure Synthesis of Transition Metal Carbonyls.  

ERIC Educational Resources Information Center

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

Hagen, A. P.; And Others

1979-01-01

266

Mass fractionation processes of transition metal isotopes  

Microsoft Academic Search

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

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

2002-01-01

267

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

268

Synthesis of LaMeO{sub 3} (Me = Cr, Mn, Fe, Co) perovskite oxides from aqueous solutions  

SciTech Connect

LaMeO{sub 3} (Me = Cr, Mn, Fe, Co) perovskite oxides have many functional uses, and methods for forming films from aqueous solutions are advantageous compared with CVD, sputtering, sol-gel methods, etc., because of lower cost, no requirement for a vacuum or high temperature, and applicability to films with wide areas and/or complicated shapes. A novel method for synthesizing LaMeO{sub 3} from aqueous solutions at ordinary temperature and pressure has been discovered. LaMeO{sub 3} powder produced by solid-state reaction was dissolved in hydrofluoric acid. Boric acid was added to shift the chemical equilibrium, then LaMeO{sub 3} was synthesized. This method promises to lead to applications for preparing perovskite films for various uses.

Yao, Takeshi; Ariyoshi, Akira; Inui, Takashi [Kyoto Univ. (Japan)

1997-09-01

269

Superconducting double perovskite bismuth oxide prepared by a low-temperature hydrothermal reaction.  

PubMed

Perovskite-type structures (ABO3) have received significant attention because of their crystallographic aspects and physical properties, but there has been no clear evidence of a superconductor with a double-perovskite-type structure, whose different elements occupy A and/or B sites in ordered ways. In this report, hydrothermal synthesis at 220?°C produced a new superconductor with an A-site-ordered double perovskite structure, (Na(0.25)K(0.45))(Ba(1.00))3(Bi(1.00))4O12, with a maximum T(c) of about 27?K. PMID:24573781

Rubel, Mirza H K; Miura, Akira; Takei, Takahiro; Kumada, Nobuhiro; Mozahar Ali, M; Nagao, Masanori; Watauchi, Satoshi; Tanaka, Isao; Oka, Kengo; Azuma, Masaki; Magome, Eisuke; Moriyoshi, Chikako; Kuroiwa, Yoshihiro; Azharul Islam, A K M

2014-04-01

270

(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

271

Transition metal sulfur dioxide hexafluoroarsenates and hexafluoroantimonates  

Microsoft Academic Search

The preparation and characterization by X-ray crystallography of transition metal sulfur dioxide hexafluoroarsenates of the general formula [M(SO2)x](AsF6)21 (1a: M=Mn, x=2; 1c: M=Co, x=4; 1e: M=Cu, x=4) and the hexafluoroantimonate [Co(SO2)2](SbF6)23 is reported. The structural features of the compounds mentioned are compared with those of [Fe(SO2)4](AsF6)2 (1b) and [Ni(SO2)6](AsF6)2 (1d), reported previously. The structural diversity of transition metal sulfur dioxide

E Lork; R Mews; J Petersen; M Schröter; B Žemva

2001-01-01

272

Phonon self energy in transition metals  

NASA Astrophysics Data System (ADS)

We present ab initio calculations of the phonon self energy of transition metals obtained using second order many body perturbation theory.ootnotetextS. Narasimhan and D. Vanderbilt, Phys. Rev. B, 43, 4541 (1991) The code we have implementedootnotetextL. Chaput, A. Togo, I. Tanaka and G. Hug, submitted to Phys. Rev. B use the symmetry properties of the phonon-phonon interactions to express the self energy as a sum over irreducible triplets. It is analogous to the reduction of integration to the irreducible part of the Brillouin zone for one particle properties. The self energy of transition metals is then calculated. We show that the Peierls approximationootnotetextR. E. Peierls, Quantum Theory of Solids, Oxford University Press,1964 is in fact reasonable for bcc and fcc metals, but fails for the hcp. The decays paths of phonons producing the self energy is finally analyzed using surfaces of reciprocal space defined by conservation law.

Chaput, Laurent; Togo, Atsushi; Tanaka, Isao; Hug, Gilles

2011-03-01

273

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

274

Semiconducting Al transition-metal quasicrystals  

NASA Astrophysics Data System (ADS)

We report on a class of icosahedral aluminum transition-metal (Al-TM) alloys with true semiconducting behavior. Our description of the structure of these icosahedral quasicrystals is based on the six-dimensional Katz-Gratias-Boudard (KGB) model of the face-centered-icosahedral (fci) quasicrystal and its rational approximants. The shell structure of the atomic surfaces in perpendicular space defines the chemical order of aluminum and transition-metal (TM) atoms leading to semiconducting transport properties. In transition-metal aluminides the hybridization between the Al(s,p) and transition-metal d orbitals is responsible for the formation of a semiconducting gap in the electronic spectrum. We have analyzed the electronic charge distribution and observed an enhanced charge density along the Al-TM bonds that is characteristic of covalent bonding. The existence of an energy gap in the electronic spectrum at or in the vicinity of the Fermi level is explicitly demonstrated for several low-order approximants in the hierarchy of Fibonacci approximants which converges to the icosahedral quasicrystals of the fci class, to which also the i-AlPdRe belongs. We predict existence of truly semiconducting quasicrystalline 1/1-approximants. Our results also lead to the prediction of the existence of new semiconducting quasicrystals with specified Al-TM compositions. The possibility of the existence of a semiconducting band gap suggests an explanation for the anomalously high resistivity of the icosahedral AlPdRe quasicrystals. We demonstrate that substitutional defects violating the ideal Al-TM ordering predicted by the KGB model lead to the formation of localized states in the band gap. A real sample of i-AlPdRe thus seems to be a semiconductor with a band gap filled by the localized states.

Kraj?í, M.; Hafner, J.

2003-10-01

275

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

276

Lanthanoid-transition-metal bonding in bismetallocenes.  

PubMed

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

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

2014-03-01

277

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

278

Comparative study of Nickel-based perovskite-like mixed oxide catalysts for direct decomposition of NO  

Microsoft Academic Search

The mixed oxides LaNiO3, La0.1Sr0.9NiO3, La2NiO4 and LaSrNiO4 were prepared and used as catalysts for the direct decomposition of NO. The catalysts were characterized by means of XRD, XPS, O2-TPD, NO-TPD and chemical analysis. By comparing the physico-chemical properties and catalytic activity for NO decomposition, a conclusion could be drawn as follows. The direct decomposition of NO over perovskite and

Zhen Zhao; Xiangguang Yang; Yue Wu

1996-01-01

279

Evaluation of La–Sr–Co–Fe–O perovskites for solid oxide fuel cells and gas separation membranes  

Microsoft Academic Search

Perovskites based on alkaline-earth containing lanthanum cobaltites exhibit high electronic and ionic conductivities but their application as cathodes for solid oxide fuel cells (SOFC) or gas separation membranes may be limited by thermal expansion and low stability of certain compositions. To identify the optimum composition regime, the following three series in the system La1?xSrxCo1?yFeyO3?? were studied: (a) La1?xSrxCoO3??, (b) La0.3Sr0.7Co1?yFeyO3??

Anthony Petric; Peng Huang; Frank Tietz

2000-01-01

280

The double perovskite oxide Sr2CrMoO6-? as an efficient electrocatalyst for rechargeable lithium air batteries.  

PubMed

A double perovskite oxide Sr2CrMoO6-? (SCM), synthesized using the sol-gel and annealing method with the assistance of citric acid and ethylene diamine tetraacetic acid, was investigated for the first time as an efficient catalyst for rechargeable lithium air batteries. The SCM cathode enables higher specific capacity, lower overpotential and a much better cyclability compared to the pure Super P electrode owing to its excellent electrocatalytic activity towards the formation/decomposition of Li2O2. PMID:25325080

Ma, Zhong; Yuan, Xianxia; Li, Lin; Ma, Zi-Feng

2014-10-30

281

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

NASA Astrophysics Data System (ADS)

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

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

2010-03-01

282

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

E-print Network

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

Bents, Ulrich H.

2013-10-04

283

Simultaneous removal of NO x and diesel soot over nanometer Ln-Na-Cu-O perovskite-like complex oxide catalysts  

Microsoft Academic Search

The nanometric Ln-Na-Cu-O (Ln=La, Pr, Nd, Sm, Gd) perovskite-like complex oxide catalysts were prepared by sol–gel auto-combustion method using citric acid as a ligand and an adjusting agent of particle-size and morphology. Their structures and physico-chemical properties were examined by chemical analysis, XRD, SEM, FT-IR, H2-TPR and MS-NO-TPD. The catalytic performances of these perovskite-like oxides for the simultaneous removal of

Jian Liu; Zhen Zhao; Chun-ming Xu; Ai-jun Duan

2008-01-01

284

Transition metal complexes as molecular machine prototypes.  

PubMed

The field of molecular machines, i.e. multicomponent systems able to undergo large amplitude motions under the action of an external signal, has experienced a spectacular development since the beginning of the 1990s. Transition metal complexes have played an important role in this context, often as components of catenanes and rotaxanes. The present tutorial review will discuss a few systems of this type, taken from the contributions of our group or from others. The stimulus responsible for the controlled motion of the machine can be chemical, electrochemical, or photochemical. Examples of these three categories will be considered. PMID:17264936

Champin, Benoît; Mobian, Pierre; Sauvage, Jean-Pierre

2007-02-01

285

Thin Film Perovskites  

Microsoft Academic Search

A multilayer perovskite thin film resistive memory device has been developed comprised of: a Pr0.7Ca0.3MnO3 (PCMO) perovskite oxide epitaxial layer on a YBCO bottom thin film electrode; a thin yttria stabilized zirconia (YSZ) buffer layer grown on the PCMO layer, and a gold thin film top electrode. The multi-layer thin film lattice structure has been characterized by XRD and TEM

Xin CHEN; Naijuan WU; Alex IGNATIEV

286

LaFeO3 perovskite-type oxide prepared by oxide-mixing, co-precipitation and complex synthesis methods  

Microsoft Academic Search

The perovskite oxide, LaFeO3, was synthesized by three different preparation methods i.e., the calcination of a mixture of La2O3 and Fe2O3 (La-Fe-O), a co-precipitated precursor (La-Fe-OH), La(OH)3 and Fe(OH)3, and a heteronuclear complex (La-Fe-CN), La[Fe(CN)6] · 5H2O. The obtained powders were characterized by thermogravimetric analysis, powder X-ray diffraction, electron microprobe analysis, specific surface area measurement and scanning electron microscopy. The

S. Nakayama

2001-01-01

287

Magnetoresistance in ordered and disordered double perovskite oxide, Sr 2FeMoO 6  

Microsoft Academic Search

We have prepared crystallographically ordered and disordered specimens of the double perovskite, Sr2FeMoO6, and investigated their magnetoresistance (MR) behaviour. The extent of ordering between the Fe and Mo sites in the two samples is determined by Rietveld analysis of powder X-ray diffraction patterns and reconfirmed by Mössbauer studies. While the ordered sample exhibits the sharp low-field response, followed by moderate

D. D. Sarma; E. V. Sampathkumaran; Sugata Ray; R. Nagarajan; Subham Majumdar; Ashwani Kumar; G. Nalini; T. N. Guru Row

2000-01-01

288

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

NASA Astrophysics Data System (ADS)

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

Zeb, M. Ahsan; Kee, Hae-Young

2012-08-01

289

Structural study of supercooled liquid transition metals  

NASA Astrophysics Data System (ADS)

Local structural models for supercooled liquid transition metals (Ti, Ni, and Zr) are proposed based on a reverse Monte Carlo analysis of high-energy x-ray diffraction data taken from the electrostatically levitated liquids. The resulting structures are characterized by their bond angle distributions, Honeycutt and Andersen indices [J. Phys. Chem. 91, 4950 (1987)], and bond orientational order parameters. All analyses suggest that an icosahedral short-range order is present in these supercooled liquids, but it is distorted in liquid Ti. These results are in agreement with the observed evolution of the high-q shoulder on the second peak in the structure factor S(q ) and with an earlier analysis based on a local cluster model.

Kim, T. H.; Kelton, K. F.

2007-02-01

290

Radiation damage of transition metal carbides  

SciTech Connect

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

Dixon, G.

1991-01-01

291

Spin-orbit damping in transition metals  

NASA Astrophysics Data System (ADS)

Magnetization dynamics are routinely described with the Landau-Lifshitz-Gilbert (LLG) equation. However, it is expected that the LLG equation fails to properly describe the large amplitude dynamics that occur during magnetization reversal. Improving switching speeds in nanoscale devices by tailoring materials requires both a qualitative understanding of the relaxation processes that contribute to damping and the ability to quantitatively calculate the resulting damping rates. We consider small amplitude LLG damping in transition metals as a prelude to approaching the more complicated mechanisms expected in complete reversal events. LLG damping rates in pure transition metal systems have non-monotonic temperature dependencies that have been empirically shown by Heinrich et al. [1] to have one part proportional to the conductivity and one part proportional to the resistivity. Kambersky [2] postulated that both contributions result from a torque between the spin and orbital moments. We have conducted first-principles calculations that validate this claim for single element systems [3]. Our calculations for Fe, Co, and Ni both qualitatively match the two trends observed in measurements and quantitatively agree with the observed damping rates. We will discuss how the spin-orbit interaction produces two contributions to damping with nearly opposite temperature dependencies and compare calculations of the damping rate versus resistivity with experimental results. [1] B. Heinrich, D.J. Meredith, and J.F. Cochran, J. Appl. Phys., 50(11), 7726 (1979). [2] V. Kambersky, Czech. J. Phys. B, 26, 1366 (1976). [3] K. Gilmore, Y.U. Idzerda, and M.D. Stiles, Phys. Rev. Lett., 99, 027204 (2007).

Gilmore, Keith

2008-03-01

292

Preparation and characterization of CaTiO 3 -based perovskitic oxides as catalysts for partial oxidation of light hydrocarbons  

Microsoft Academic Search

A series of perovskites of the formula Ca1-xSrxTi1-yMyO3-d, M=Fe, Co, Cr or Ni,x = 0-1,y = 0-0.6, has been synthesized by a modified sol-gel method using citrate. Several of these materials were proved to be stable under operating conditions in reducing atmospheres of air and hydrocarbons. An outline of the synthesis procedure is given, together with the results of XRD,

Arnfinn G. Andersen; Takashi Hayakawa; Tatsuo Tsunoda; Hideo Orita; Masao Shimizu; Katsuomi Takehira

1993-01-01

293

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

294

Preparation and Mixed Conductivity of Mn-DOPED Bi-Sr-Fe-BASED Perovskite Type Oxides  

NASA Astrophysics Data System (ADS)

Bi0.7Sr0.3FeO3-? (BSF) with perovskite structure and Mn-doped BSFs were prepared by solid-state reaction and their mixed conductivities were discussed based on results of electrical conductivity and oxygen permeation measurement through membranes of those compounds. BSF showed only 2 S/cm at 800 °C suggesting that its charge unbalance is likely to be compensated by generation of oxygen vacancies. However, Mn-doping caused the increase of electrical conductivity and the decrease of oxygen permeation rate, that is, the extent of charge compensation by electron holes increased through Mn-doping.

Baek, Doohyun; Takamura, Hitoshi

2013-07-01

295

Transition Metal Nutrition: A Balance Between Deficiency and Toxicity  

E-print Network

359 A. Iron 359 B. Copper 369 C. Manganese and selenium 375 V. Conclusions and perspectives 376 of transition metal ions for biochemical functions is essen- tial as evidenced by the fact that metalloproteins and Clemens, 2005; 1 Commonly, "transition metal" refers to the 40 elements which belong to groups 3

Hamel, Patrice

296

Structures of ordered tungsten- or molybdenum-containing quaternary perovskite oxides  

SciTech Connect

The room temperature crystal structures of six A{sub 2}MMoO{sub 6} and A{sub 2}MWO{sub 6} ordered double perovskites were determined from X-ray and neutron powder diffraction data. Ba{sub 2}MgWO{sub 6} and Ba{sub 2}CaMoO{sub 6} both adopt cubic symmetry (space group Fm3-bar m, tilt system a{sup 0}a{sup 0}a{sup 0}). Ba{sub 2}CaWO{sub 6} has nearly the same tolerance factor (t=0.972) as Ba{sub 2}CaMoO{sub 6} (t=0.974), yet it surprisingly crystallizes with I4/m symmetry indicative of out-of-phase rotations of the MO{sub 6} octahedra about the c-axis (a{sup 0}a{sup 0}c{sup -}). Sr{sub 2}ZnMoO{sub 6} (t=0.979) also adopts I4/m symmetry; whereas, Sr{sub 2}ZnWO{sub 6} (t=0.976) crystallizes with monoclinic symmetry (P2{sub 1}/n) with out-of-phase octahedral tilting distortions about the a- and b-axes, and in-phase tilting about the c-axis (a{sup -}a{sup -}c{sup +}). Ca{sub 2}CaWO{sub 6} (t=0.867) also has P2{sub 1}/n symmetry with large tilting distortions about all three crystallographic axes and distorted CaO{sub 6} octahedra. Analysis of 93 double perovskites and their crystal structures showed that while the type and magnitude of the octahedral tilting distortions are controlled primarily by the tolerance factor, the identity of the A-cation acts as the secondary structure directing factor. When A=Ba{sup 2+} the boundary between cubic and tetragonal symmetries falls near t=0.97, whereas when A=Sr{sup 2+} this boundary falls somewhere between t=1.018 and t=0.992. - Graphical abstract: A survey of the tolerance factor of 41 Mo/W- and 52 Nb/Ta-containing quaternary perovskites plotted as a function of the difference between the two six-coordinate M-cation ionic radii. Compounds with cubic symmetry are represented by diamonds, those with tetragonal symmetry are represented by squares, those with I2/m monoclinic symmetry are represented by Multiplication-Sign , and those with P2{sub 1}/n monoclinic symmetry are represented by triangles. White symbols represent compositions where A=Ba{sup 2+}, gray symbols represent compositions where A=Sr{sup 2+}, and black symbols represent where A=Ca{sup 2+}. The filled circle represents rhombohedral Ba{sub 2}BiTaO{sub 6} (t=0.961; space group-R3-bar ; tilt system-a{sup -}a{sup -}a{sup -}). References for the compounds included in this figure are listed in the Supporting Information File. Black-Small-Square Highlights: Black-Right-Pointing-Pointer Reports the structures of six double perovskites containing either Mo{sup 6+} or W{sup 6+}. Black-Right-Pointing-Pointer Compounds with similar tolerance factors (t) exhibited different symmetries. Black-Right-Pointing-Pointer This effect was observed in Sr{sub 2}ZnMO{sub 6} and Ba{sub 2}CaMO{sub 6} (M=Mo or W). Black-Right-Pointing-Pointer Contains a structural survey of 93 double perovskites. Black-Right-Pointing-Pointer Octahedral tilting distortions are controlled by t and the nature of the A-cation.

Day, Bradley E.; Bley, Nicholas D.; Jones, Heather R.; McCullough, Ryan M. [Department of Chemistry, Millikin University, 1184 W. Main Street, Decatur, IL 62522 (United States); Eng, Hank W. [Department of Natural Sciences, San Antonio College, 1300 San Pedro Avenue, San Antonio, TX 78212 (United States); Department of Natural Sciences, St. Philip's College, 1801 Martin Luther King Drive, San Antonio, TX 78203 (United States); Porter, Spencer H.; Woodward, Patrick M. [Department of Chemistry, The Ohio State University, 100 W. 18th Avenue, Columbus, OH 43210 (United States); Barnes, Paris W., E-mail: pbarnes@millikin.edu [Department of Chemistry, Millikin University, 1184 W. Main Street, Decatur, IL 62522 (United States)

2012-01-15

297

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

298

X-ray photoelectron spectroscopy of Sm-doped layered perovskite for intermediate temperature-operating solid oxide fuel cell  

NASA Astrophysics Data System (ADS)

Chemical states of Sm doped layered perovksite, SmBa1-xSrxCo2O5+d (x = 0 and 0.5), have been investigated by X-ray Photoelectron Spectroscopy (XPS). Substitution of Sr in SmBa1-xSrxCo2O5+d oxide system shifts the binding energy of Sm 3d5/2 to the more positive side and the charge state of Sm remained Sm3+. Therefore, the substitution of Sr into the SmBa1-xSrxCo2O5+d oxide system does not change the charge state of Sm. Three types of oxygen species were observed in SmBa0.5Sr0.5Co2O5+d (SBSCO) and SBCO from the O 1s spectra comprised of lattice oxygen, carbonated species and adsorbed oxygen species with respect to the measured binding energy ranges. The more Sr was substituted into the Sm doped layered perovskite, the larger the binding energy values became. In case of the Co spectra of SBSCO, two satellite peaks were observed at the range of 786.0-789.0 eV and at 804.93 eV. The evidence of Co3+ and Co4+ indicated that Co is existing in the chemical form of mixed valence state including Co3+ and Co4+ in SBCO and SBSCO oxide systems.

Kim, Yongmin; Schlegl, Harald; Kim, Keunsoo; Irvine, John T. S.; Kim, Jung Hyun

2014-01-01

299

Transition metal abnormalities in progressive dementias.  

PubMed

Abnormal distributions of transition metals inside the brain are potential diagnostic markers for several central nervous system diseases, including Alzheimer's disease (AD), Parkinson's disease, dementia with Lewy bodies (DLB), bipolar disorders and depression. To further explore this possibility, the total concentrations of iron, zinc, copper, manganese, aluminum, chromium and cadmium were measured in post-mortem hippocampus and amygdala tissues taken from AD, DLB and Control patients. A statistically significant near fifty percent reduction in the total copper levels of AD patients was observed in both the hippocampus and amygdala. The statistical power of the hippocampus and amygdala copper analysis was found to be 86 and 74% respectively. No statistically significant deviations in the total metal concentrations were found for zinc, manganese, chromium or aluminum. Iron was found to be increased by 38% in AD amygdala tissues, but was unchanged in AD hippocampus tissues. Accounting for differences in tissue water content, as a function of both tissue type and disease state, revealed more consistencies with previous literature. To aid in the design of future experiments, the effect sizes for all tissue types and metals studied are also presented. PMID:22080191

Akatsu, Hiroyasu; Hori, Akira; Yamamoto, Takayuki; Yoshida, Mari; Mimuro, Maya; Hashizume, Yoshio; Tooyama, Ikuo; Yezdimer, Eric M

2012-04-01

300

Density Functional Theory of Transition Metal Phthalocyanines  

NASA Astrophysics Data System (ADS)

Metal phthalocyanines (MPc's) are a family of highly stable molecules that, as a molecular solid, form organic semiconductors. They have been used in a broad range of applications, e.g., light emitting diodes, solar cells, gas sensors, thin film transistors, and even as single molecule devices. Here, we present a systematic density functional theory (DFT) study of the electronic structure of selected transition metal Pc's: CuPc, NiPc, CoPc, MnPc, and FePc. We critically assess the performance of several semi-local and hybrid exchange-correlation functionals for these systems, and compare the results to experimental photoemission data. For the low-spin systems CuPc, NiPc, and CoPc, we show that semi-local functionals fail qualitatively, primarily because of under- binding of localized orbitals due to self-interaction errors. For the intermediate-spin systems, MnPc and FePc, we show that DFT calculations are extremely sensitive to the choice of functional and basis set with respect to the obtained electronic configuration and to symmetry breaking. However, interestingly, all simulated spectra are in good agreement with experiment despite the differences in the underlying electronic configurations.

Marom, Noa; Kronik, Leeor

2009-03-01

301

Polytypism in superhard transition-metal triborides  

PubMed Central

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

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

2014-01-01

302

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

303

Probing the Electronic Structure of Early Transition Metal Oxide Clusters: Polyhedral Cages of (V2O5)n- (n=2-4) and (M2O5)2- (M=Nb, Ta)  

Microsoft Academic Search

Vanadium oxide clusters, (V2O5)n, have been predicted to possess interesting polyhedral cage structures, which may serve as ideal molecular models for oxide surfaces and catalysts. Here we examine the electronic properties of these oxide clusters via anion photoelectron spectroscopy for (V2O5)n (n = 2-4), as well as for the 4d\\/5d species, Nb4O10 and Ta4O10 . Wellresolved photoelectron spectra have been

Hua-Jin Zhai; Jens Dobler; Joachim Sauer; Lai-Sheng Wang

2007-01-01

304

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

305

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

306

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

307

Process for making transition metal nitride whiskers  

DOEpatents

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

Bamberger, C.E.

1988-04-12

308

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

309

Jahn-teller co-operative effect and ferroelectric phase transitions of complex metal oxides with perovskite-type structure  

Microsoft Academic Search

The experimental data about crystal structures, phase transitions and dielectric properties of Cu(II) and Mn(III)-containing complex perovskites are analysed. The principal result is that the presence of Jahn-Teller cations in oxygen octahedra of perovskites is favourable for the origination of spontaneously polarized state (SPS).

Yu. N. Venevtsev; D. F. Dzmuhadze; N. V. Fadeeva; S. A. Ivanov

1988-01-01

310

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

311

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

312

Electrical properties of transition metal hydrogen complexes in silicon  

SciTech Connect

A summary is given on the electrical properties of transition-metal hydrogen complexes in silicon. Contrary to the general understanding, hydrogen leads not only to passivation of deep defect levels but also creates several new levels in the band gap due to electrically active transition-metal complexes. The author presents detailed data for Pt-H complexes and summarize briefly the results on the transition metals Ti, Co, Ni, Pd, and Ag. The introduction of hydrogen at room temperature by wet chemical etching, followed by specific annealing steps allows us to study the formation of the different complexes. In particular, depth profiles of the defect concentrations give an estimate of the number of hydrogen atoms involved in the complexes. Transition-metals binding up to four hydrogen atoms are identified.

Weber, J. [Max-Planck-Inst. fuer Festkoerperforschung, Stuttgart (Germany)

1998-12-31

313

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

314

Mechanisms of transition-metal gettering in silicon  

SciTech Connect

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

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

2000-03-23

315

Group 7 transition metal complexes with N-heterocyclic carbenes.  

PubMed

This tutorial review summarizes all works and highlights recent advances published in the growing field of group 7 N-heterocyclic carbene (NHC) complexes. It provides a valuable source for all scientists that are interested in conducting research with new compounds bearing these metals. The article provides an overview of all manganese NHC complexes that are known to date. There are a lot of examples where manganese NHC complexes show unpredicted behaviour during synthesis, very different from other transition metal NHC complexes and their higher homologues rhenium and technetium. These differences are depicted and discussed. Furthermore, the chemistry of technetium NHC compounds and their chemical behaviour are discussed. To date published work on technetium NHC chemistry has been restricted to the oxidation state +v. It was found that such compounds are very reactive but show great stability in dry air. Their radioactivity makes such compounds interesting candidates for radiochemical applications. Since most group 7 NHC chemistry was conducted on rhenium NHC complexes, this tutorial review highlights the chemical behaviour of such compounds. Rhenium(i) complexes reveal luminescent properties, making them interesting candidates for applications ranging from biological markers to organic light-emitting diodes (OLEDs). Another interesting feature is the radioactivity of some compounds, which makes them excellent candidates for radiopharmaceutical research; hence their synthesis and reactivity are discussed. PMID:23475206

Hock, Sebastian J; Schaper, Lars-Arne; Herrmann, Wolfgang A; Kühn, Fritz E

2013-06-21

316

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

PubMed

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 (Ni(2+)) 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

317

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

318

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

319

Improving Levine model for dielectric constants of transition metal compounds  

NASA Astrophysics Data System (ADS)

The density of states and optical properties of several transition metal compounds have been simulated using local density approximations+U. Results show that s electrons of nontransition elements in the compounds cannot be considered to have the same contribution on the number of valence electrons. In light of this observation, the parameter ? in the Levine model is improved, which leads to better prediction for dielectric constants of transition metal compounds.

Li, C.; Li, J. C.; Lian, J. S.; Jiang, Q.

2009-11-01

320

Combined experimental and theoretical investigation of the CO 2 adsorption on LaMnO 3+y perovskite oxide  

NASA Astrophysics Data System (ADS)

The surface interaction of CO 2 with the perovskite-type oxide LaMnO 3+y has been investigated by means of density functional theory calculations and experimental measurements of adsorption isotherms in the temperature range 298-473 K. A (1 0 0) oriented slab of the cubic structure was used for modeling CO 2 adsorption. The reference unit cell contains alternating LaO + layers and MnO2- layers; one slab is LaO +-terminated and the opposite surface is MnO2- terminated. A Freundlich isotherm fitted the experimental data satisfactorily. Analysis of the isosteric heat revealed an energetically heterogeneous character for the lanthanum manganite oxide surface, mainly due to the degree of heterogeneity of the adsorption center and due to the adsorbate-adsorbate lateral interactions. Considering theoretical calculations and thermodynamical approaches, two types of active sites were found to be responsible for irreversible and reversible adsorption of CO 2 as a function of surface coverage and O 2 treatment. Strong adsorption takes place on the surface containing La cations. The strongest adsorption is associated with surface oxygen vacancies, Fs° center. The next strongest adsorption, a flat adaptation of CO 2 molecules with respect to the surface sites, with a strong binding to a surface oxygen, leads to chemisorbed carbonate species. These adsorption modes are chiefly indicative of a high basic character of the lanthanum manganite oxide surface. Several cationic sites formed by lanthanum and manganese cations are able to weakly adsorb CO 2 molecules in perpendicular or bridged forms. The latter adsorption modes suggest a weak acidic character of the manganite adsorbent.

Hammami, Ramzi; Batis, Habib; Minot, Christian

2009-10-01

321

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

322

A comprehensive comparison of transition-metal and actinyl polyoxometalates.  

PubMed

While the d(0) transition-metal POMs of Group V (V(5+), Nb(5+), Ta(5+)) and Group VI (Mo(6+), W(6+)) have been known for more than a century, the actinyl peroxide POMs, specifically those built of uranyl triperoxide or uranyl dihydroxidediperoxide polyhedra, were only realized within the last decade. While virtually every metal on the Periodic Table can form discrete clusters of some type, the actinyls are the only-in addition to the transition-metal POMs- whose chemistry is dictated by the prevalence of the 'yl' oxygen ligand. Thus this emerging structural, solution, and computational chemistry of actinide POMs warrants comparison to the mature chemistry of transition-metal POMs. This assessment between the transition-metal POMs and actinyl POMs (uranyl peroxide POMs, specifically) has provided much insight to the similarities and differences between these two chemistries. We further break down the comparison between the alkaline POMs of Nb and Ta; and the acidic POMs of V, Mo and W. This more indepth literature review and discussion reveals that while an initial evaluation suggests the actinyl POMs are more akin to the alkaline transition-metal POMs, they actually share characteristics unique to the acidic POMs as well. This tutorial review is meant to provide fodder for deriving new POM chemistries of both the familiar transition-metals and the emerging actinides, as well as fostering communication and collaboration between the two scientific communities. PMID:22695929

Nyman, May; Burns, Peter C

2012-11-21

323

Transition metal (Mn, Fe, Co, Ni)-doped graphene hybrids for electrocatalysis.  

PubMed

The development of electrocatalysts is crucial for renewable energy applications. Metal-doped graphene hybrid materials have been explored for this purpose, however, with much focus on noble metals, which are limited by their low availability and high costs. Transition metals may serve as promising alternatives. Here, transition metal-doped graphene hybrids were synthesized by a simple and scalable method. Metal-doped graphite oxide precursors were thermally exfoliated in either hydrogen or nitrogen atmosphere; by changing exfoliation atmospheres from inert to reductive, we produced materials with different degrees of oxidation. Effects of the presence of metal nanoparticles and exfoliation atmosphere on the morphology and electrocatalytic activity of the hybrid materials were investigated using electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and cyclic voltammetry. Doping of graphene with transition metal nanoparticles of the 4th?period significantly influenced the electrocatalysis of compounds important in energy production and storage applications, with hybrid materials exfoliated in nitrogen atmosphere displaying superior performance over those exfoliated in hydrogen atmosphere. Moreover, nickel-doped graphene hybrids displayed outstanding electrocatalytic activities towards reduction of O2 when compared to bare graphenes. These findings may be exploited in the research field of renewable energy. PMID:23495248

Toh, Rou Jun; Poh, Hwee Ling; Sofer, Zden?k; Pumera, Martin

2013-06-01

324

Removal of salicylic acid on perovskite-type oxide LaFeO3 catalyst in catalytic wet air oxidation process.  

PubMed

It has been found that salicylic acid can be removal effectively at the lower temperature of 140 degrees C on perovskite-type oxide LaFeO3 catalyst in the catalytic wet air oxidation (CWAO) process. Under the same condition, the activities for the CWAO of phenol, benzoic acid and sulfonic salicylic acid have been also investigated. The results indicated that, with compared to the very poor activities for phenol and benzoic acid, the activities for salicylic acid and sulfonic salicylic acid were very high, which are attributed to their same intramolecular H-bonding structures. With the role of hard acidity of intramolecular H-bonding, salicylic acid and sulfonic salicylic acid can be adsorbed effectively on the basic center of LaFeO3 catalyst and are easy to take place the total oxidation reaction. However, at temperatures higher than 140 degrees C, the intramolecular H-bonding structure of salicylic acid was destroyed and the activities at 160 and 180 degrees C decreased greatly, which confirms further the key role of intramolecular H-bonding in the CWAO. Moreover, the LaFeO3 catalyst also indicated a superior stability of activity and structure in CWAO of salicylic acid. PMID:16870333

Yang, Min; Xu, Aihua; Du, Hongzhang; Sun, Chenglin; Li, Can

2007-01-01

325

Transition-metal-doped chalcogenide glasses for broadband near-infrared sources  

NASA Astrophysics Data System (ADS)

In this paper we report the spectroscopic data for samples of 0.031% iron, 0.017% nickel, 0.01% chromium and 0.017% cobalt (molar) doped gallium lanthanum sulphide (GLS) glass. Photoluminescence (PL) with a full width half maximum (FWHM) of around 500 nm and peaking between 1120 nm and 1460 nm is observed when excited using wavelengths of 850 nm and 1064 nm. The emission lifetime for nickel-doped GLS at 300 K was measured to be 40 ?s. Photoluminescence excitation (PLE) peaks for chromium-doped GLS at 700 nm and 1020 nm have been observed. By comparisons of our spectroscopic data to that of transition metals doped into other hosts we determine the oxidation states of the transition metal ions and propose transitions for the observed spectroscopic peaks.

Hughes, Mark A.; Aronson, Jonathan E.; Brocklesby, William S.; Shepherd, David P.; Hewak, Daniel W.; Curry, Richard J.

2004-12-01

326

Crystal Structure and Magnetic Properties of B-Site Ordered Perovskite-type Oxides A 2Cu B?O 6 ( A=Ba, Sr; B?=W, Te)  

Microsoft Academic Search

Four cuprate perovskites with the general formula A2CuB?O6 (A=Ba, Sr; B?=W, Te) were synthesized and the structural and the magnetic properties were investigated. Among four samples, perovskite Ba2CuTeO6 was formed only under high pressure. All the samples were tetragonally distorted B-site ordered perovskite-type oxides with I4\\/m symmetry. The CuO6 octahedra is elongated by the Jahn–Teller effect of Cu2+ ion and

Daisuke Iwanaga; Yoshiyuki Inaguma; Mitsuru Itoh

1999-01-01

327

Oxide Thermoelectric Materials: A Structure-Property Relationship  

NASA Astrophysics Data System (ADS)

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

Nag, Abanti; Shubha, V.

2014-04-01

328

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

PubMed

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

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

2013-12-01

329

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

330

Early Transition Metal Alkyl and Tetrahydroborate Complexes.  

NASA Astrophysics Data System (ADS)

An investigation of early transition metal alkyl and tetrahydroborate complexes as catalytic models and ceramic precursors has been initiated. The compounds MX _2 (dmpe)_2, dmpe = 1,2-bis(dimethylphosphino)ethane, for M = Ti, V, Cr, and X = Br, I, BH_4, have been prepared. These complexes are paramagnetic and have been shown by X-ray crystallography to have trans-octahedral structures. The BH_4^{-} groups in Ti(BH_4)_2(dmpe) _2 bond to the metal in a bidentate manner. This structure is in marked contrast to the structure of the vanadium analogue, V(BH_4)_2 (dmpe)_2, which displays two unidentate BH_4^{-} groups. Alkylation of Ti(BH_4)_2 (dmpe)_2 with LiMe results in the complex TiMe_2(dmpe) _2 which is diamagnetic in both solution and solid state. Single crystal X-ray and neutron diffraction studies show that there may be strong Ti-C pi -bonding. A tetragonal compression along the C -Ti-C bond vector accounts for the observed diamegnetism. A series of complexes of the formula Ti(BH _4)_3(PR_3)_2 has been prepared where PR_3 = PMe_3, PEt_3, PMe_3Ph, and P(OMe)_3 . The X-ray crystal structure of Ti(BH _4)_3(PMe_3)_2 reveals a pseudo trigonal bipyramidal geometry in which two BH_4^{-} groups display an unusual "side-on" bonding mode. The "side-on" ligation mode has been attributed to a Jahn-Teller distortion of the orbitally degenerate d^1 ground state. In contrast, the non-Jahn-Teller susceptible vanadium analogue, V(BH_4)_3 (PMe_3)_2, possesses a nearly ideal D_{rm 3h} >=ometry with three bidentate tetrahydroborate groups. Addition of excess PMe_3 to V(BH_4)_3(PMe _3)_2<=ads to the vanadium(II) hydride -bridged dimer (V(H)(BH_4)(PMe _3)_2]_2, while addition of PMe_3 and water forms the vanadium(III) oxo dimer (V(BH_4)_2 (PMe_3)_2]_2 [mu-O) which has been structurally characterized. The compound Ti(CH_2CMe _3)_4 can be prepared by addition of Ti(OEt)_4 to LiCH_2 CMe_3. Sublimation of Ti(CH _2CMe_3)_4 over a substrate heated to 250^ circC results in the chemical vapor deposition of amorphous TiC thin films. This CVD approach has been extended to the Group 4 borides: Ti(BH_4) _3(MeOCH_2CH _2OMe) yields TiB_2 at 200^circC, while Zr(BH _4)_4 and Hf(BH_4) _4 yield ZrB_2 and HfB_2 at 250^circ C using the CVD process. The X-ray crystal structure of Ti(BH_4)_3(MeOCH _2CH_2OMe) is reported.

Jensen, James Allen

1988-06-01

331

The Synthesis and Properties of the Chemically Oxidized Perovskite, La 1- xSr xCoO 3- ?(0.5? x?0.9)  

NASA Astrophysics Data System (ADS)

The series of La 1- xSr xCoO 3- ?(0.5? x?0.9) perovskites have been prepared using the Pechini gel technique. The products were chemically oxidized by stirring in a sodium hypobromite solution. The samples have been characterized by powder X-ray diffraction, thermal analysis, iodometric titration, Co K edge X-ray absorption spectroscopy, temperature-dependent SQUID magnetic susceptibility, and temperature-dependent electrical resistivity. The Sr-rich samples ( x>0.7) have the brownmillerite-type structure prior to oxidation and the cubic perovskite structure after treatment with sodium hypobromite. Iodometric titration shows as much as a ˜14% increase in Co(IV) concentration in the Sr-rich samples after chemical oxidation. The Co K edge spectra show that there is very little change in the formal cobalt valence with increasing Sr content. The effective magnetic moments of the oxidized compounds level off with increasing Sr concentration. All of the chemically oxidized samples exhibit small-bandgap semiconducting behavior. The data lead to the postulation of an equilibrium between Co(IV) and O -in the series.

Sunstrom, Joseph E.; Ramanujachary, K. V.; Greenblatt, Martha; Croft, Mark

1998-09-01

332

Electrochemistry of transition metal complex catalysts  

Microsoft Academic Search

The electrochemical properties of a promising catalyst for C?H bond activation are investigated. This P–C–P-pincer complex of iridium exhibits an intramolecular C?H oxidative addition at room temperature, which becomes enhanced upon oxidation. The reaction product is detected by cyclic voltammetry. Mechanistic, kinetic, and thermodynamic information is extracted from experiments in combination with digital simulation. Multicycle voltammograms and voltammograms of mixtures

Filip Novak; Bernd Speiser; Hani A. Y Mohammad; Hermann A Mayer

2004-01-01

333

Perovskite fever  

NASA Astrophysics Data System (ADS)

Staggering increases in the performance of organic-inorganic perovskite solar cells have renewed the interest in these materials. However, further developments and the support from academic and industrial partners will hinge on the reporting of accurate efficiency values.

2014-09-01

334

perovskite system  

NASA Astrophysics Data System (ADS)

Experiments using laser-heated diamond anvil cells combined with synchrotron X-ray diffraction and SEM-EDS chemical analyses have confirmed the existence of a complete solid solution in the MgSiO3-MnSiO3 perovskite system at high pressure and high temperature. The (Mg, Mn)SiO3 perovskite produced is orthorhombic, and a linear relationship between the unit cell parameters of this perovskite and the proportion of MnSiO3 components incorporated seems to obey Vegard's rule at about 50 GPa. The orthorhombic distortion, judged from the axial ratios of a/ b and monotonically decreases from MgSiO3 to MnSiO3 perovskite at about 50 GPa. The orthorhombic distortion in (Mg0.5, Mn0.5)SiO3 perovskite is almost unchanged with increasing pressure from 30 to 50 GPa. On the other hand, that distortion in (Mg0.9, Mn0.1)SiO3 perovskite increases with pressure. (Mg, Mn)SiO3 perovskite incorporating less than 10 mol% of MnSiO3 component is quenchable. A value of the bulk modulus of 256(2) GPa with a fixed first pressure derivative of four is obtained for (Mg0.9, Mn0.1)SiO3. MnSiO3 is the first chemical component confirmed to form a complete solid solution with MgSiO3 perovskite at the P- T conditions present in the lower mantle.

Li, Lin; Nagai, Takaya; Ishido, Tomoki; Motai, Satoko; Fujino, Kiyoshi; Itoh, Shoichi

2014-06-01

335

[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

336

Transition-metal doped sulfide, selenide, and telluride laser crystal and lasers  

DOEpatents

A new class of solid state laser crystals and lasers are formed of transition metal doped sulfide, selenide, and telluride host crystals which have four fold coordinated substitutional sites. The host crystals include II-VI compounds. The host crystal is doped with a transition metal laser ion, e.g., chromium, cobalt or iron. In particular, Cr{sup 2+}-doped ZnS and ZnSe generate laser action near 2.3 {micro}m. Oxide, chloride, fluoride, bromide and iodide crystals with similar structures can also be used. Important aspects of these laser materials are the tetrahedral site symmetry of the host crystal, low excited state absorption losses and high luminescence efficiency, and the d{sup 4} and d{sup 6} electronic configurations of the transition metal ions. The same materials are also useful as saturable absorbers for passive Q-switching applications. The laser materials can be used as gain media in amplifiers and oscillators; these gain media can be incorporated into waveguides and semiconductor lasers. 18 figs.

Krupke, W.F.; Page, R.H.; DeLoach, L.D.; Payne, S.A.

1996-07-30

337

Temperature-programmed reduction and HDS activity of sulfided transition metal catalyst: Formation of nonstoichiometric sulfur  

SciTech Connect

Sulfided alumina-supported transition metal catalysts have been studied using temperature-programmed reduction (TPR). The H{sup 2} and H{sub 2}S concentrations were determined simultaneously and the major processes occurring were discriminated, namely reduction of oxidic and sulfidic species and desorption of H{sub 2}S. Because of the high maximum reduction temperature and the high hydrogen partial pressure applied, a complete description of all species was acquired, except for the Cr and Mn catalysts which could not be reduced below 1270 K. After sulfiding at 673 K, TPR of alumina-supported transition metals showed that several types of sulfur were present, viz. (i) sulfur species with a stoichiometry in agreement with bulk thermodynamics, indicated as stoichiometric sulfur, (ii) a nonstochiometric sulfur species (S{sub x}) which was present in excess of the S/Me ratio based on bulk thermodynamics (not identical to elemental sulfur since it is present after purging at 673 K), (iii) S-H groups, and (iv) adsorbed H{sub 2}S. The mechanism of S{sub x} formation is discussed. The amounts of nonstoichiometric sulfur mainly depended on the type of transition metal and the pretreatment procedure. The influence of the reducibility of the stoichiometric and nonstoichiometric sulfur species on the hydrodesulfurization activity is discussed. The results presented indicate that chemisorption measurements may depend on the pretreatment of sulfided catalysts. 26 refs., 13 figs., 4 tabs.

Mangnus, P.J.; Riezebos, A.; Langeveld, A.D. van; Moulijn, J.A. [Univ. of Asterdam (Netherlands)] [Univ. of Asterdam (Netherlands)

1995-01-01

338

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

339

Covalency and the metal-insulator transition in titanate and vanadate perovskites  

NASA Astrophysics Data System (ADS)

A combination of density functional and dynamical mean-field theory is applied to the perovskites SrVO3, LaTiO3, and LaVO3. We show that DFT + DMFT in conjunction with the standard fully localized-limit (FLL) double-counting predicts that LaTiO3 and LaVO3 are metals even though experimentally they are correlation-driven ("Mott") insulators. In addition, the FLL double counting implies a splitting between oxygen p and transition metal d levels, which differs from experiment. Introducing into the theory an ad hoc double counting correction, which reproduces the experimentally measured insulating gap leads also to a p-d splitting consistent with experiment if the on-site interaction U is chosen in a relatively narrow range (˜6±1 eV). The results indicate that these early transition metal oxides will serve as critical test for the formulation of a general ab initio theory of correlated electron metals.

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

2014-04-01

340

Electrochemistry of transition metal complex catalysts  

Microsoft Academic Search

The electrochemical oxidation of Ir(tdppcyme)(CO)Cl, tdppcyme=cis,cis-1,3,5-tris(di-phenylphosphine)-cis,cis-1,3,5-tris(methoxycarbonyl)cyclohexane, is investigated in dichloromethane–0.1 M tetrabutylammonium hexafluorophosphate at Pt electrodes with cyclic voltammetry, chronoamperometry and chronocoulometry, as well as preparative electrolysis. While the primary one-electron oxidation to Ir+II appears quasi-reversible in the electroanalytical experiments, the longer time scale of electrolysis allows the formation of an insoluble product by a follow-up reaction. By means of

Silke Buchmann; Hermann A Mayer; Bernd Speiser; Michael Seiler; Helmut Bertagnolli; Stefan Steinbrecher; Erich Plies

2001-01-01

341

Photoluminescence properties of Jahn-Teller transition-metal ions  

NASA Astrophysics Data System (ADS)

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

Sanz-Ortiz, Marta N.; Rodríguez, Fernando

2009-09-01

342

Reactive Ion Etching of Transition-Metal Alloys  

NASA Astrophysics Data System (ADS)

For production of advanced spin-electronic devices, such as a magnetic random access memory with the higher-density memory cell, a reactive ion etching (RIE) process of transition metal alloys is the indispensable component of development, while no transition-metal compounds with the relatively high vapor pressure have been founded so far. Here, we show the RIE process of a NiFe thin film by using CH4:O2:NH3 discharge. The RIE process was designed by ab initio calculations, and the present result is the first successful demonstration of the chemical effect in the RIE process for transition-metal alloys. The relative etching ratio of NiFe against Ti as the metal mask was decreased by substituting CH4 with CHF3.

Akinaga, Hiro; Takano, Fumiyoshi; Matsumoto, Shigeno; Diño, Wilson A. T.

343

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

344

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

345

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

SciTech Connect

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 is facile below 600 C; they become antiferromagnetic at low temperatures TN = 37 and 80 K for M = Co and Ni, respectively. As an anode with a 300 em thick La0.8Sr0.2Ga0.83Mg0.17O2.815 electrolyte and SrFe0.2Co0.8O3-d as a cathode, Sr2CoMoO6 exhibited maximum power densities of 735 mW/cm2 in H2 and 527 mW/cm2 in wet CH4 at 800 C; Sr2NiMoO6 shows a notable power output only in dry CH4. The high performance of Sr2CoMoO6 in wet CH4 may be due to its catalytic effect on steam reforming of methane, but some degradation of the structure that occurred in CH4 obscures identification of the catalytic reaction processes at the surface. However, the stronger octahedral-site preference of Ni2+ versus Co2+ can account for the lower performance of the M = Ni anode.

Huang, Y.; Liang, G; Croft, M; Lehtimaki, M; Karppinen, M; Goodenough, J

2009-01-01

346

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

347

Highly Active La 1? x K x CoO 3 Perovskite-type Complex Oxide Catalysts for the Simultaneous Removal of Diesel Soot and Nitrogen Oxides Under Loose Contact Conditions  

Microsoft Academic Search

The nanometric La1?x\\u000a K\\u000a x\\u000a CoO3 (x = 0–0.30) perovskite-type oxides were prepared by a citric acid-ligated method. The catalysts were characterized by means\\u000a of XRD, IR, BET, XPS and SEM. The catalytic activity for the simultaneous removal of soot and nitrogen oxides was evaluated\\u000a by a technique of the temperature-programmed oxidation reaction. In the LaCoO3 catalyst, the partial substitution of La3+

Hong Wang; Zhen Zhao; Peng Liang; Chunming Xu; Aijun Duan; Guiyuan Jiang; Jie Xu; Jian Liu

2008-01-01

348

New antiferromagnetic perovskite CaCo3V4O12 prepared at high-pressure and high-temperature conditions.  

PubMed

A new perovskite, CaCo(2+)3V(4+)4O12, has been synthesized at high-pressure and high-temperature (HP-HT) conditions. The properties of this perovskite were examined by a range of techniques. CaCo3V4O12 was found to adopt a double-perovskite cubic lattice [a = 7.3428(6) Å] with Im3 symmetry. We have established that this new perovskite is stable at ambient conditions, and its oxidation and/or decomposition at ambient pressure begins above 500 °C. It undergoes an abrupt antiferromagnetic transition around 98 K. Electrical resistivity data suggest semimetallic conductivity in the temperature range of 1.6-370 K. We have established that the Co(2+) ions in CaCo3V4O12 are in the high-spin state with a sizable orbital moment, even though their square-planar oxygen coordination could be more suitable for the low-spin state, which is prone to Jahn-Teller distortion. Electrical resistivity curves also exhibit a distinct steplike feature around 100 K. CaCo3V4O12 is a first example of perovskite in which the sites A' are fully occupied by Co(2+) ions, and hence its synthesis opens the door to a new class of double perovskites, ACo3B4O12, that may be derived by chemical substitution of the A sublattice by lanthanides, sodium, strontium, and bismuth and by other elements and/or of the B sublattice by some other transition metals. PMID:24083336

Ovsyannikov, Sergey V; Zainulin, Yury G; Kadyrova, Nadezda I; Tyutyunnik, Alexander P; Semenova, Anna S; Kasinathan, Deepa; Tsirlin, Alexander A; Miyajima, Nobuyoshi; Karkin, Alexander E

2013-10-21

349

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

350

Synergy of polydimethylsiloxanes and late transition metal complexes  

Microsoft Academic Search

The fluxional behaviors of organosilicon groups on cyclopentadienyl derivatives were assessed in the presence and absence of late transition metal centers and, in separate work, the catalytic activity of transition metal complexes were examined in a siloxane environment. ^ Dichloro-methyl-(2,3,4,5-tetramethyl-cyclopentadienyl)-silane CpMe 4H(SiMeCl2) showed reversible variable-temperature 1H, 13C and 29Si NMR spectra without producing either Diels-Alder adducts or decomposition products. The

Masaaki Amako

2005-01-01

351

Melting of bcc Transition Metals and Icosahedral Clustering  

SciTech Connect

In contrast to polyvalent metals, transition metals have low melting slopes(dT/dP) that are due to partially filled d-bands that allow for a lowering of liquid phase energy through s-d electron transfer and the formation of local structures. In the case of bcc transition metals we show the apparent discrepancy of DAC melting measurements with shock melting of Mo can be understood by reexamining the shock data for V and Ta and introducing the presence of an icosahedral short range order (ISRO) melt phase.

Ross, M; Boehler, R; Japel, S

2006-05-26

352

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

353

Effect of the rare earth in the perovskite-type mixed oxides AMnO{sub 3} (A=Y, La, Pr, Sm, Dy) as catalysts in methanol oxidation  

SciTech Connect

The effect of the rare earth in the perovskite-type mixed oxides AMnO{sub 3} (A=Y, La, Pr, Sm, Dy) on catalytic properties in methanol oxidation was investigated in this work. The perovskites were prepared by reactive grinding in order to enhance the specific surface area in comparison with other classical synthesis procedures. These catalysts were characterized by N{sub 2} adsorption, X-ray diffraction, H{sub 2} temperature-programmed reduction (TPR-H{sub 2}), O{sub 2}-, CH{sub 3}OH- and CO{sub 2}-temperature-programmed desorption (TPD). The activity of the five catalysts under study in the methanol oxidation reaction was evaluated. The behaviour of the {alpha}-O{sub 2} from the surface of the perovskite was strongly related to the nature of the A-site cation and particularly to its electronegativity but also to its density. Concerning the {beta}-O{sub 2} from the bulk, the rare earth only induces an indirect effect notably due to structural modifications. As suggested in a previous study, the activity in methanol oxidation was directly linked with the surface oxygen density. Under an excess of {alpha}-oxygen, the reaction intermediate was found to be a monodentate carbonate that decomposes into CO{sub 2}. The stability of monodentate carbonates was also found to be related to the electronegativity of the rare earth during both CH{sub 3}OH- and CO{sub 2}-temperature-programmed desorption. However, as soon as a lack of {alpha}-oxygen was observed in the structure, the dominant reaction intermediate was a bidentate carbonate that induces a consumption of anion vacancies in spite of the production of CO{sub 2}. Nevertheless, the accumulation of these carbonates leads to a decrease in the oxidation rate since their desorption requires high temperatures. - Graphical abstract: Perovskite-type mixed oxides AMnO{sub 3} (with A=Y, La, Pr, Sm, Dy) with high specific surface area were prepared by reactive grinding. The influence of the rare earth on the two kinds of oxygen in the perovskite structure ({alpha}-O{sub 2} and {beta}-O{sub 2}) was correlated with a variety of intrinsic properties of the A-site cation. Moreover, the catalytic performance of the samples for methanol oxidation was evaluated.

Levasseur, B. [Department of Chemical Engineering, Laval University, Sainte-Foy, Que., G1K 7P4 (Canada); Kaliaguine, S. [Department of Chemical Engineering, Laval University, Sainte-Foy, Que., G1K 7P4 (Canada)], E-mail: serge.kaliaguine@gch.ulaval.ca

2008-11-15

354

The Synthesis and Properties of the Chemically Oxidized Perovskite, La 1– x Sr x CoO 3? ? (0.5? x?0.9)  

Microsoft Academic Search

The series of La1?xSrxCoO3??(0.5?x?0.9) perovskites have been prepared using the Pechini gel technique. The products were chemically oxidized by stirring in a sodium hypobromite solution. The samples have been characterized by powder X-ray diffraction, thermal analysis, iodometric titration, Co K edge X-ray absorption spectroscopy, temperature-dependent SQUID magnetic susceptibility, and temperature-dependent electrical resistivity. The Sr-rich samples (x>0.7) have the brownmillerite-type structure

Joseph E. Sunstrom; K. V. Ramanujachary; Martha Greenblatt; Mark Croft

1998-01-01

355

The catalytic behavior of La-Mn-O nanoparticle perovskite-type oxide catalysts for the combustion of the soot particle from the diesel engine  

Microsoft Academic Search

The La1?xMx MnO3(M=Li, Na, K, Rb, x=0, 0.10, 0.25) perovskite-type oxides whose sizes are nanoparticle have been prepared by the citric acid-ligated\\u000a method. The characters of the catalysts were characterized by means of XRD, IR, SEM and BET surface area measurement. The\\u000a catalytic activity for the combustion of soot particulate was evaluated by a technique of the temperature-programmed reaction.\\u000a In

Hong Wang; Zhen Zhao; Chunming Xu; Jian Liu; Zhixiao Lu

2005-01-01

356

Structural and Electrochemical Characterization of Lithium Transition Metal Phosphates  

NASA Astrophysics Data System (ADS)

The lithium ion battery has emerged as one of the most promising hybrid vehicle energy storage systems of the future. Of the potential cathode chemistries explored, lithium transition metal phosphates have generated a significant amount of interest due to their low-cost precursors, potential ease of synthesis, stability, and their environmentally friendly nature. This is in contrast to layered oxide systems such as LiCoO2, which have long been considered state of the art, but are now being reevaluated due to their structural instability at elevated temperatures, and higher cost. In particular, LiFePO4 has an operating potential comparable to those batteries available on the market (˜3.5V vs. Li/Li+), and higher theoretical specific capacity (170mAh/g vs. that of LiCoO2 which is 140mAh/g). The manganese analog to LiFePO4, LiMnPO4, exhibits a higher operating potential (˜4.1V v Li/Li+), and the same theoretical capacity, however Li-ion diffusion through this structure is much more rate limited and its theoretical capacity cannot be realized at rates suitable for commercial applications. The purpose of this work was threefold: 1) To explore the impact of Fe substitution on Mn sites in LiMnPO 4. 2) To examine the effects of alterations to the particle/electrolyte interface on rate capability. 3) To explore a novel fabrication route for LiMnPO4 using microwaves, and determine an optimal power and time combination for best performance. The coexistence of Fe and Mn on the transition metal site M, of LiMPO 4 resulted in an improved apparent Li-ion diffusivity in both Fe and Mn regimes as compared to that observed for LiFePO4 and LiMnPO 4 respectively. Calculations made from two different analysis methods, cyclic voltammetry (CV) and galvanostatic intermittent titration (GITT) drew this same conclusion. The signature characteristics observed from the CVs pertaining to single and dual phase reactions led to a delithiation model of LiFe0.5Mn0.5PO4 proposing the localization of half the Li atoms with Fe and half with Mn. Following this work, pure LiMnPO 4 was explored. LiMnPO4 was successfully fabricated using rapid, solid state microwave irradiation. Three classes of materials were prepared to study the effects of particle size, carbon coating, and electrolytic environment on rate capability. Reduction in particle size, carbon coating, and the aqueous electrolyte environment provided the most favorable conditions for performance enhancement. Based on the initial promising results of solid state microwave synthesis, further studies were conducted to optimize irradiation parameters. C-LiMnPO 4 fabricated at 200W for 5.0 minutes demonstrated the most superior rate capability. This material attained its full theoretical specific capacity, showing promise for the advancement of materials fabricated via this method.

Hashambhoy, Ayesha Maria

357

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

358

Reaction kinetics of methane oxidation over LaCr{sub 1-x}Ni{sub x}O{sub 3} perovskite catalysts  

SciTech Connect

Ternary perovskite oxides LaCr{sub 1-x}Ni{sub x}O{sub 3}, (x = 0 to 1.0) were evaluated as methane oxidation catalysts over the temperature range 300-500{degrees}C and as a function of the partial pressures of oxygen and methane (12-90 kPa). All catalysts are stable in oxygen containing atmospheres, while oxygen starvation causes destructive reduction to Ni metal for x > 0.5. The catalytic activity increases monotonically with the value of x. The nonseparable (composition, temperature) kinetics behavior is well correlated by an oxidation-reduction mechanism for all catalysts. Based on the observed nonlinear increase in catalytic activity with nickel content, Ni-O-Ni ensembles are proposed as the key surface reagent. 52 refs., 6 figs., 2 tabs.

Stojanovic, M.; Mims, C.A. [Univ. of Toronto, Ontario (Canada)] [Univ. of Toronto, Ontario (Canada); Moudallal, H. [Univ. of Houston, TX (United States)] [and others] [Univ. of Houston, TX (United States); and others

1997-03-01

359

Triple-conducting layered perovskites as cathode materials for proton-conducting solid oxide fuel cells.  

PubMed

We report on an excellent anode-supported H(+) -SOFC material system using a triple conducting (H(+) /O(2-) /e(-) ) oxide (TCO) as a cathode material for H(+) -SOFCs. Generally, mixed ionic (O(2-) ) and electronic conductors (MIECs) have been selected as the cathode material of H(+) -SOFCs. In an H(+) -SOFC system, however, MIEC cathodes limit the electrochemically active sites to the interface between the proton conducting electrolyte and the cathode. New approaches to the tailoring of cathode materials for H(+) -SOFCs should therefore be considered. TCOs can effectively extend the electrochemically active sites from the interface between the cathode and the electrolyte to the entire surface of the cathode. The electrochemical performance of NBSCF/BZCYYb/BZCYYb-NiO shows excellent long term stability for 500 h at 1023 K with high power density of 1.61 W?cm(-2) . PMID:25146887

Kim, Junyoung; Sengodan, Sivaprakash; Kwon, Goeun; Ding, Dong; Shin, Jeeyoung; Liu, Meilin; Kim, Guntae

2014-10-01

360

Spin polarization in ordered and disordered double-perovskites  

Microsoft Academic Search

Recently, the double perovskites family A2MM?O6 (A being a divalent or trivalent cation and M, M? two transition metals) has attracted considerable interest with the view of using these materials in spin electronics. This has been triggered but the fact that some members, in particular SrFe2MoO6, present a Curie temperature TC above room temperature and complete spin polarization. In view

B. Aguilar; O. Navarro; M. Avignon

2008-01-01

361

Phase Transitions in Transition Metal Monooxides: Interplay Between Structural, Magnetic, and Electronic Properties  

Microsoft Academic Search

The iron monoxide Fe1-xO (wustite) is an important member of the highly correlated transition metal monoxide group which includes NiO, CoO, and MnO, and is also an end-member component of the (Mg,Fe)O solid solution, the most abundant non-silicate oxide in the Earth. At ambient conditions wustite exists in a cubic fcc-based rock-salt structure with a nonstoichiometric formula Fe1-xO. At low

L. S. Dubrovinsky; I. Y. Kantor; A. P. Kantor; C. McCammon; W. Crichton; I. N. Goncharenko

2005-01-01

362

Binding and activation of N2O at transition-metal centers: recent mechanistic insights.  

PubMed

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 N(2)O 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 N(2)O adducts and derived intermediates. These ideas are likely to inform efforts to design more effective catalysts for N(2)O remediation. PMID:20058284

Tolman, William B

2010-02-01

363

Investigation of LaFeO 3 perovskite growth mechanism through mechanical ball milling of lanthanum and iron oxides  

Microsoft Academic Search

LaFeO3 perovskite was synthesized mechanochemically through ball milling of La2O3 and Fe2O3 in stoichiometric ratio. X-ray powder diffraction (XRPD), simultaneous differential scanning calorimetry and thermogravimetry\\u000a analysis (DSC–TGA), Mössbauer spectroscopy, scanning electron microscopy (SEM), and optical diffuse reflectance spectroscopy\\u000a were combined for a detailed study of the growth mechanism of LaFeO3 perovskite during the ball milling process. The XRPD results showed

Monica Sorescu; Tianhong Xu; Johanna D. Burnett; Jennifer A. Aitken

364

Magnetic susceptibility and specific heat of uranium double perovskite oxides Ba 2 MUO 6 ( M=Co, Ni)  

Microsoft Academic Search

Double perovskites Ba2MUO6 (M=Co, Ni) were prepared by the solid-state reaction. X-ray diffraction measurements show that both cobalt (nickel) and uranium ions are ordered in the NaCl type over the six-coordinate B sites of the perovskite ABO3. Detailed magnetic susceptibility and specific heat measurements show that Ba2CoUO6 and Ba2NiUO6 order ferromagnetically at 9.1 and 25K, respectively. From the analysis of

Yukio. Hinatsu; Yoshihiro Doi

2006-01-01

365

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

366

The Electrochemical Synthesis of Transition-Metal Acetylacetonates  

ERIC Educational Resources Information Center

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

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

2008-01-01

367

Magnetic states of transition metal impurities in silicon carbide.  

PubMed

Electronic properties of 3C silicon carbide with substitutional transition metal impurities are calculated using an ab initio full-potential linearized augmented plane wave technique. It is shown that transition metal atoms in an SiC host may exist in both magnetic and nonmagnetic states. For different impurity species, the transition from the nonmagnetic to the magnetic state and the corresponding change of the atomic magnetic moments may take place either gradually as the volume of the unit cell changes or when the energy gap between the two states is overcome. The magnetic and nonmagnetic solutions are characterized by significantly different unit cell geometries, which are analysed in detail. Magnetic ordering is studied for a number of transition metal impurities in SiC and mean-field estimates of the Curie temperature are given. Calculated densities of states are used to analyse the nature of the exchange interaction between the impurities. Some properties of transition metal impurities are compared for 3C and 4H silicon carbide substitution. PMID:21825541

Los, Andrei; Los, Victor

2009-05-20

368

Volume variation of Gruneisen parameters of fcc transition metals  

Microsoft Academic Search

The volume variation of the Gruneisen parameters of tenfcc transition metals, up to 40% compression, has been studied on the basis of a model approach proposed by Antonovet al. The results are reasonably good for six metals except for Rh, Ag, Au and Ni when compared with available experimental and\\u000a other theoretical values. The model requires an appropriate modification for

C. V. Pandya; P. R. Vyas; T. C. Pandya; V. B. Gohel

2002-01-01

369

The Existence of Pure?Phase Transition Metal Hydroxy Apatites  

Microsoft Academic Search

The existence of pure?phase transition metal hydroxy apatites of zinc, copper, manganese, and cobalt could not be verified by repeated attempts to duplicate the few literature procedures reported for their preparation in aqueous solution. Variations of temperature, time of reactions, pH, and use of decomplexation also did not produce apatitic compounds. In the case of zinc, the product resulting from

Claude H. Yoder; Nathan Fedors; Natalie J. Flora; Heather Brown; Keith Hamilton; Charles D. Schaeffer Jr

2004-01-01

370

Luminescent molecular rods - transition-metal alkynyl complexes.  

PubMed

A number of transition-metal complexes have been reported to exhibit rich luminescence, usually originating from phosphorescence. Such luminescence properties of the triplet excited state with a large Stoke's shift, long lifetime, high luminescence quantum yield as well as lower excitation energy, are envisaged to serve as an ideal candidate in the area of potential applications for chemosensors, dye-sensitized solar cells, flat panel displays, optics, new materials and biological sciences. Organic alkynes (poly-ynes), with extended or conjugated?-systems and rigid structure with linear geometry, have become a significant research area due to their novel electronic and physical properties and their potential applications in nanotechnology. Owing to the presence of unsaturated sp-hybridized carbon atoms, the alkynyl unit can serve as a versatile building block in the construction of alkynyl transition-metal complexes, not only through?-bonding but also via?-bonding interactions. By incorporation of linear alkynyl groups into luminescent transition-metal complexes, the alkynyl moiety with good?-donor,?-donor and?-acceptor abilities is envisaged to tune or perturb the emission behaviors, including emission energy (color), intensity and lifetime by its role as an auxiliary ligand as well as to govern the emission origin from its direct involvement. This review summarizes recent efforts on the synthesis of luminescent rod-like alkynyl complexes with different classes of transition metals and details the effects of the introduction of alkynyl groups on the luminescence properties of the complexes. PMID:22179333

Yam, Vivian Wing-Wah; Wong, Keith Man-Chung

2005-01-01

371

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

372

Polyaniline–transition metal salt complexes: insight into formation mechanisms  

Microsoft Academic Search

Two basic morphologies of emeraldine base of polyaniline–transition metal salt complex films cast from N-methylpyrrolidinone solutions are described. The first morphology consists of grains and the other consists of loose aggregates, respectively. The correlation of the film morphology with formation of precipitate in the complex solution, kinetics of solvent evaporation from the cast film, amount of solvent entrapped in the

O. P. Dimitriev; P. S. Smertenko; B. Stiller; L. Brehmer

2005-01-01

373

Binding and catalytic reduction of NO by transition metal aluminosilicates  

SciTech Connect

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

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

1991-09-01

374

Transition Metal Photoredox Catalysis of Radical Thiol-Ene Reactions  

PubMed Central

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

Tyson, Elizabeth L.; Ament, Michael S.

2012-01-01

375

Unambiguously identifying spin states of transition-metal ions in the Earth (Invited)  

NASA Astrophysics Data System (ADS)

The spin state of a transition-metal ion in crystalline solids, defined by the number of unpaired electrons in the ion’s incomplete 3d shell, may vary with many factors, such as temperature, pressure, strain, and the local atomic configuration, to name a few. Such a phenomenon, known as spin-state crossover, plays a crucial role in spintronic materials. Recently, the pressure-induced spin-state crossover in iron-bearing minerals has been recognized to affect the minerals’ structural and elastic properties. However, the detailed mechanism of such crossover in iron-bearing magnesium silicate perovskite, the most abundant mineral in the Earth, remains unclear. A significant part of this confusion arises from the difficulty in reliably extracting the spin state from experiments. For the same reason, the thermally-induced spin-state crossover in lanthanum cobaltite (LaCoO3) has been controversial for more than four decades. In this talk, I will discuss how first-principle calculations can help clarifying these long-standing controversies. In addition to the total energy, equation of state, and elastic properties of each spin state, first-principle calculations also predict the electric field gradient (EFG) at the nucleus of each transition-metal ion. Our calculations showed that the nuclear EFG, a quantity that can be measured via Mössbauer or nuclear magnetic resonance (NMR) spectroscopy, depends primarily on the spin state, irrespective of the concentration or configuration of transition-metal ions. Such robustness makes EFG a unique fingerprint to identify the spin state. The combination of first-principle calculations and Mössbauer/NMR spectroscopy can therefore be a reliable and efficient approach in tackling spin-state crossover problems in the Earth. This work was primarily supported by the MRSEC Program of NSF under Awards Number DMR-0212302 and DMR-0819885, and partially supported by NSF under ATM-0428774 (V-Lab), EAR-1019853, and EAR-0810272. The computations were performed mainly at the Minnesota Supercomputing Institute (MSI).

Hsu, H.

2010-12-01

376

Magnetic field effect on quantum corrections to the low-temperature conductivity in metallic perovskite oxides  

NASA Astrophysics Data System (ADS)

The transport and magnetotransport properties of the metallic and ferromagnetic SrRu O3 (SRO) and the metallic and paramagnetic LaNi O3 (LNO) epitaxial thin films have been investigated in fields up to 55 T at temperatures down to 1.8 K . At low temperatures both samples display a well-defined resistivity minimum. We argue that this behavior is due to the increasing relevance of quantum corrections to the conductivity (QCC) as temperature is lowered; this effect being particularly relevant in these oxides due to their short mean free path. However, it is not straightforward to discriminate between contributions of weak localization and renormalization of electron-electron interactions to the QCC through temperature dependence alone. We have taken advantage of the distinct effect of a magnetic field on both mechanisms to demonstrate that in ferromagnetic SRO the weak-localization contribution is suppressed by the large internal field leaving only renormalized electron-electron interactions, whereas in the nonmagnetic LNO thin films the weak-localization term is relevant.

Herranz, G.; Sánchez, F.; Fontcuberta, J.; Laukhin, V.; Galibert, J.; García-Cuenca, M. V.; Ferrater, C.; Varela, M.

2005-07-01

377

Depth profiling the potential in perovskite oxide heterojunctions using photoemission spectroscopy  

NASA Astrophysics Data System (ADS)

The authors report on the potential profiling in depth for promising oxide heterojunctions: La0.6Sr0.4MnO3 (LSMO)/Nb-doped SrTiO3 (Nb:STO) having different interfacial terminating layer and SrRuO3/Nb:STO heterojunctions. The precise depth-profiling analysis of LSMO/TiO2-Nb:STO interfaces with -La0.6Sr0.4O/TiO2/SrO- structure reveals the existence of a certain thin depletion layer of 1-2 nm with an abrupt potential drop near the interface. In contrast, the ideal depletion layer is formed for other interfaces with a -SrO/TiO2/SrO- terminating layer. These results suggest that the adjacency of TiO2 layer with La0.6Sr0.4O donor layers at the interface is responsible for the formation of the thin depletion layer near the interface.

Minohara, M.; Horiba, K.; Kumigashira, H.; Ikenaga, E.; Oshima, M.

2012-04-01

378

Catalytic conversion of syn gas with perovskites  

SciTech Connect

Perovskites, mixed metal oxides of the general formula ABO/sub 3/, have been examined as catalysts for conversion of syn gas to oxygenated organic chemicals. Several of these perovskites have been found to provide moderate to high selectivities to oxygenated organics, particularly methanol and C2OX (acetic acid, acetaldehyde, and ethanol).

Broussard, J.A.; Wade, L.E.

1986-01-01

379

Catalytic conversion of syn gas with perovskites  

Microsoft Academic Search

Perovskites, mixed metal oxides of the general formula ABOâ, have been examined as catalysts for conversion of syn gas to oxygenated organic chemicals. Several of these perovskites have been found to provide moderate to high selectivities to oxygenated organics, particularly methanol and C2OX (acetic acid, acetaldehyde, and ethanol).

J. A. Broussard; L. E. Wade

1986-01-01

380

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

381

Models for transition metal oxides and for protein design  

E-print Network

A large number of properties of solid state materials can now be predicted with standard first-principles methods such as the Local Density (LDA) or Generalized Gradient Approximation (GGA). However, known problems exist ...

Zhou, Fei, Ph. D. Massachusetts Institute of Technology

2006-01-01

382

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

383

Transition metal activation and functionalization of carbon-hydrogen bonds  

SciTech Connect

We are investigating the fundamental thermodynamic and kinetic factors that influence carbon-hydrogen bond activation at homogeneous transition metal centers and the conversion of hydrocarbons into functionalized products of potential use to the chemical industry. Advances have been made in both understanding the interactions of hydrocarbons with metals and in the functionalization of hydrocarbons. We have found that RhCl(PR{sub 3}){sub 2}(CNR) complexes can catalyze the insertion of isonitriles into the C-H bonds or arenes upon photolysis. The mechanism of these reactions was found to proceed by way of initial phosphine dissociation, followed by C-H activation and isonitrile insertion. We have also examined reactions of a series of arenes with (C{sub 5}Me{sub 5})Rh(PMe{sub 3})PhH and begun to map out the kinetic and thermodynamic preferences for arene coordination. The effects of resonance, specifically the differences in the Hueckel energies of the bound vs free ligand, are now believed to fully control the C-H activation/{eta}{sup 2}-coordination equilibria. We have begun to examine the reactions of rhodium isonitrile pyrazolylborates for alkane and arene C-H bond activation. A new, labile, carbodiimide precursor has been developed for these studies. We have completed studies of the reactions of (C{sub 5}Me{sub 5})Rh(PMe{sub 3})H{sub 2} with D{sub 2} and PMe{sub 3} that indicate that both {eta}{sup 5} {yields} {eta}{sup 3} ring slippage and metal to ring hydride migration occur more facilely than thermal reductive elimination of H{sub 2}. We have examined the reactions of heterocycles with (C{sub 5}Me{sub 5})Rh(PMe{sub 3})PhH and found that pyrrole and furan undergo C-H or N-H activation. Thiophene, however, undergoes C-S bond oxidative addition, and the mechanism of activation has been shown to proceed through sulfur coordination prior to C-S insertion.

Jones, W.D.

1992-06-01

384

Effect of perovskite oxide cap layer on superconducting properties of YBa 2Cu 3O x films grown on mechanically polished SOE substrates  

NASA Astrophysics Data System (ADS)

A new oxide cap layer, BaZrO 3 (BZO) with the perovskite structure, on the NiO buffer produced by surface-oxidation epitaxy is reported. BZO is the product as yttrium stabilized ZrO 2 buffer reacted with YBa 2Cu 3O x (YBCO), and it is chemically stable. BZO cap layer deposited on the polished NiO surface by pulsed laser deposition (PLD) was strongly (1 0 0) oriented, and in-plane texture, ? ? for BZO was 10°. ? ? for YBCO film, subsequently deposited on BZO/NiO/Ni substrate at 690 °C by PLD, is 9°. As the result, critical current density, Jc, of YBCO/BZO/NiO/Ni reached 0.89 MA/cm 2 at 77 K and self-field.

Matsumoto, K.; Takechi, A.; Ono, T.; Hirabayashi, I.; Osamura, K.

385

Cross-linking proteins with bimetallic tetracarboxylate compounds of transition metals  

DOEpatents

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

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

1991-03-05

386

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

ERIC Educational Resources Information Center

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

Hathaway, Brian

1979-01-01

387

Cross-linking proteins with bimetallic tetracarboxylate compounds of transition metals  

DOEpatents

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

Kostic, N.M.; Chen, J.

1991-03-05

388

Catalytic Combustion Over Transition Metal Oxides and Platinum-Transition Metal Oxides Supported on Knitted Silica Fibre  

Microsoft Academic Search

A textile made up of an organic-inorganic hybrid fibre containing 70% cellulose and 30% silicic acid was used as a raw material for the preparation of the thermostable support for combustion catalysts. The hybrid textile was burnt to obtain a pure knitted silica fibre. The surface area and crystallinity of this fibre was measured as a function of burning temperature.

A. K. Neyestanaki; L.-E. Lindfors

1994-01-01

389

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

PubMed

Oxide ion conductors find important technical applications in electrochemical devices such as solid-oxide fuel cells (SOFCs), oxygen separation membranes and sensors. Na0.5Bi0.5TiO3 (NBT) is a well-known lead-free piezoelectric material; however, it is often reported to possess high leakage conductivity that is problematic for its piezo- and ferroelectric applications. Here we report this high leakage to be oxide ion conduction due to Bi-deficiency and oxygen vacancies induced during materials processing. Mg-doping on the Ti-site increases the ionic conductivity to ~0.01 S cm(-1) at 600 °C, improves the electrolyte stability in reducing atmospheres and lowers the sintering temperature. This study not only demonstrates how to adjust the nominal NBT composition for dielectric-based applications, but also, more importantly, gives NBT-based materials an unexpected role as a completely new family of oxide ion conductors with potential applications in intermediate-temperature SOFCs and opens up a new direction to design oxide ion conductors in perovskite oxides. PMID:24193663

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

390

Transition metal-depleted graphenes for electrochemical applications via reduction of CO? by lithium.  

PubMed

Graphene has immense potential for future applications in the electrochemical field, such as in supercapacitors, fuel cells, batteries, or sensors. Graphene materials for such applications are typically fabricated through a top-down approach towards oxidation of graphite to graphite oxide, with consequent exfoliation/reduction to yield reduced graphenes. Such a method allows the manufacture of graphenes in gram/kilogram quantities. However, graphenes prepared by this method can contain residual metallic impurities from graphite which dominate the electrochemical properties of the graphene formed. This dominance hampers their electrochemical application. The fabrication of transition metal-depleted graphene is described, using ultrapure CO? (with benefits of low cost and easy availability) and elemental lithium by means of reduction of CO? to graphene. This preparation method produces graphene of high purity with electrochemical behavior that is not dominated by any residual transition metal impurities which would dramatically alter its electrochemical properties. Wide application of such methodology in industry and research laboratories is foreseen, especially where graphene is used for electrochemical devices. PMID:24344051

Poh, Hwee Ling; Sofer, Zdenek; Luxa, Jan; Pumera, Martin

2014-04-24

391

Promoting Li2O2 oxidation by an La(1.7)Ca(0.3)Ni(0.75)Cu(0.25)O4 layered perovskite in lithium-oxygen batteries.  

PubMed

We demonstrate for the first time that La(1.7)Ca(0.3)Ni(0.75)Cu(0.25)O(4) with a layered perovskite structure promotes electrochemical oxidation of Li(2)O(2) in lithium-oxygen batteries with a non-aqueous aprotic electrolyte. PMID:22890004

Jung, Kyu-Nam; Lee, Ji-In; Im, Won Bin; Yoon, Sukeun; Shin, Kyung-Hee; Lee, Jong-Won

2012-09-28

392

Polybutadiene and Hydroxyl-Terminated Polybutadiene Epoxidation Using In Situ-Generated Dimethyl Dioxirane (DMD)\\/Transition Metal Salts Complex  

Microsoft Academic Search

Epoxidation of polybutadiene (PB) and hydroxyl terminated polybutadiene (HTPB) was performed using in situ-generated dimethyl dioxirane (DMD) as an oxidant and some transition metal salts as catalysts. Differences in the degree of epoxidation of various C=C bonds was evaluated in detail at various reaction times. That is, cis C=C bonds had a relatively high reactivity which is known to be

Mir Mohammad Alavi Nikje; Zahra Mozaffari

2008-01-01

393

DFT modeling of Spectral and Redox Properties of Di-and Tetranuclear Ruthenium Transition Metal Complexes with Bridging Ligands  

NASA Astrophysics Data System (ADS)

The electronic structures of di-and tetranuclear transition metal complexes with bridging ligands (tetracyanoethene, tetracyano-p-quinodimethane, divinylphenylene and tetrakis(4-styryl)ethene) were calculated by density functional (DFT) method. DFT method was used for calculations of IR frequencies in different oxidation states and EPR parameters of radical ions. The observed electronic transitions of closed shell systems were assigned by TD DFT. The different aspects of bridge mediated metal-metal interaction are discussed.

Záliš, S.; Winter, R. S.; Linseis, M.; Kaim, A.; Sarkar, B.; Kratochvílová, I.

2009-08-01

394

Recent Advances in Transition Metal-Catalyzed Glycosylation  

PubMed Central

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

McKay, Matthew J.; Nguyen, Hien M.

2012-01-01

395

Multiphase reaction diffusion in transition metal-boron systems  

Microsoft Academic Search

The formation of various diffusion layers in selected transition metal-boron systems was investigated by means of pack-boriding. Samples of commercially pure titanium, molybdenum and tantalum were packed in pre-calcined amorphous boron powder and annealed for 1–4 h at temperatures between 1200 and 1500°C. Experiments were carried out in a high-frequency furnace in inert gas atmosphere (? 500 mbar Ar) or

J. Brandstötter; W. Lengauer

1997-01-01

396

Zwitterionic Group VIII transition metal initiators supported by olefin ligands  

DOEpatents

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

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

2011-10-25

397

Electrical conductivity of transition metal containing crystalline zirconium phosphate materials  

Microsoft Academic Search

?-Zirconium phosphate (?-ZrP) has been prepared in various transition metal containing forms, and their structure (identified by XRD), thermal behaviour and specific surface area were determined and their electrical resistivity was measured. On the basis of experimental data, the monoclinic cell parameters for Co(II), Ni(II), Cu(II), and Zn(II) containing crystalline zirconium phosphates were calculated. They showed characteristic thermal decomposition and

L Szirtes; J Megyeri; E Kuzmann; Z Klencsár

2001-01-01

398

Upconversion Processes in Transition Metal and Rare Earth Metal Systems  

Microsoft Academic Search

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

Daniel R. Gamelin; Hans U. Güdel

399

ZnO Doped With Transition Metal Ions  

Microsoft Academic Search

Spin-dependent phenomena in ZnO may lead to devices with new or enhanced functionality, such as polarized solid-state light sources and sensitive biological and chemical sensors. In this paper, we review the experimental results on transition metal doping of ZnO and show that the material can be made with a single phase at high levels of Co incorporation (~15 at.%) and

Stephen J. Pearton; David P. Norton; M. P. Mil; Art F. Hebard; John M. Zavada; Weimin M. Chen; Irina A. Buyanova

2007-01-01

400

Charge dependence of chemisorption patterns for transition metal clusters  

Microsoft Academic Search

A method is presented for the measurement of the chemisorptive reactivity of transition metal cluster ions at near room temperature. Similar to a technique introduced previously for neutral clusters [Rev. Sci. Instrum. 56, 2123 (1985)], this cluster ion method utilizes a fast-flow reactor attached to a supersonic, laser vaporization metal cluster source, followed by time-of-flight mass spectral analysis of the

P. J. Brucat; C. L. Pettiette; S. Yang; L.-S. Zheng; M. J. Craycraft; R. E. Smalley

1986-01-01

401

Superparamagnetism of transition metal nanoparticles in conducting polymer film  

NASA Astrophysics Data System (ADS)

Magnetic properties of transition metal (cobalt, iron, nickel, manganese, chromium) nanoparticles prepared by ion-exchange method in the perfluorinated sulfo-cation polymeric membrane (MF-4SK) have been investigated. While manganese and chromium in MF-4SK exhibited paramagnetic properties, cobalt, iron and nickel particles showed superparamagnetic behaviors. Our experimental evidence suggests that cobalt, iron and nickel nanoparticles in the polymer film obey a single-domain theory.

Yoon, M.; Kim, Y.; Kim, Y. M.; Yoon, H.; Volkov, V.; Avilov, A.; Park, Y. J.; Park, I.-W.

2004-05-01

402

Superparamagnetism of transition metal nanoparticles in conducting polymer film  

NASA Astrophysics Data System (ADS)

Magnetic properties of transition metal (cobalt, iron, nickel, manganese, chromium) nanoparticles prepared by ion-exchange method in the perfluorinated sulfo-cation polymeric membrane (MF-4SK) have been investigated. While manganese and chromium in MF-4SK exhibited paramagnetic properties, cobalt, iron and nickel particles showed superparamagnetic behaviors. Our experimental evidence suggests that cobalt, iron and nickel nanoparticles in the polymer film obey a single-domain theory.

Yoon, M.; Kim, Y.; Kim, Y. M.; Yoon, H.; Volkov, V.; Avilov, A.; Park, Y. J.; Park, I.-W.

403

Reductive dechlorination catalyzed by bacterial transition-metal coenzymes  

Microsoft Academic Search

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

Charles J. Gantzer; Lawrence P. Wackett

1991-01-01

404

The electronic Gruneisen parameter for the transition metals  

Microsoft Academic Search

A generalisation of the Lang-Ehrenreich-Heine model for the transition metals is applied to give specific formulae for their electronic Gruneisen parameters within normal band theory. Numerical values are calculated both with and without consideration of electron-phonon interaction with the aid of data from band calculations. Agreement with the experimental values available is variable but a simple framework for discussing the

G. C. Fletcher; M. Yahaya

1979-01-01

405

A systems view of haloarchaeal strategies to withstand stress from transition metals  

PubMed Central

Given that transition metals are essential cofactors in central biological processes, misallocation of the wrong metal ion to a metalloprotein can have resounding and often detrimental effects on diverse aspects of cellular physiology. Therefore, in an attempt to characterize unique and shared responses to chemically similar metals, we have reconstructed physiological behaviors of Halobacterium NRC-1, an archaeal halophile, in sublethal levels of Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and Zn(II). Over 20% of all genes responded transiently within minutes of exposure to Fe(II), perhaps reflecting immediate large-scale physiological adjustments to maintain homeostasis. At steady state, each transition metal induced growth arrest, attempts to minimize oxidative stress, toxic ion scavenging, increased protein turnover and DNA repair, and modulation of active ion transport. While several of these constitute generalized stress responses, up-regulation of active efflux of Co(II), Ni(II), Cu(II), and Zn(II), down-regulation of Mn(II) uptake and up-regulation of Fe(II) chelation, confer resistance to the respective metals. We have synthesized all of these discoveries into a unified systems-level model to provide an integrated perspective of responses to six transition metals with emphasis on experimentally verified regulatory mechanisms. Finally, through comparisons across global transcriptional responses to different metals, we provide insights into putative in vivo metal selectivity of metalloregulatory proteins and demonstrate that a systems approach can help rapidly unravel novel metabolic potential and regulatory programs of poorly studied organisms. PMID:16751342

Kaur, Amardeep; Pan, Min; Meislin, Megan; Facciotti, Marc T.; El-Gewely, Raafat; Baliga, Nitin S.

2006-01-01

406

Crystal structure of a layered perovskite, barium europium manganese oxide [BaEu 2Mn 2O 7  

Microsoft Academic Search

The crystal structure of BaEu2Mn2O7 with a layered perovskite was determined for the powder X-ray diffraction data by Rietveld analysis. The unit cell is orthorhombic with a a0 = 0.5503(1), b0 = 0.5481(3), c0 = 2.030(9) nm amd Z = 4 with the space group Fmmm. The oxygen octahedron in this structure was elongated along c axis and distorted along

S. Ueno; J. Meng; N. Kamegashira; H. Saito-Nakano; K. Enami

1996-01-01

407

Continuous solid solution of {kappa}-phase in the third period transition metals-aluminum-carbon pseudo-ternary systems  

SciTech Connect

Phase stability of {kappa}-phases (perovskite-type phases) was studied in the third-period transition-metals (M: Mn to Cu) - aluminum (Al) - carbon (C) systems. The concentrations of transition metals (C{sub M}) were systematically changed from 60mol%Mn to 20mol%Ni+40mol%Cu along the periodic table under the constant nominal alloy compositions of C{sub M1}+C{sub M2} = 60mol%, C{sub Al} = 20mol% and C{sub C} = 20mol%. Alloys were prepared using mechanical alloying and hot pressing. Constituent phases were investigated by X-ray diffraction analysis, scanning electron microscopy and electron probe microanalysis. It is confirmed that Mn{sub 3}Al(C,O){sub 0.95}, Fe{sub 3}Al(C,O){sub 0.87}, Co{sub 3}Al(C,O){sub 0.6} and Ni{sub 3}Al(C,O){sub 0.26} exist in their ternary systems where oxygen is introduced during the process. Also, only one {kappa}-phase is recognized in an alloy having an intermediate composition in every system. This suggests that continuous solid solutions between these {kappa}-phases are formed in the pseudo-ternary systems. Composition dependence of lattice parameter is discussed.

Hosoda, Hideki; Suzuki, Kensyo; Hanada, Shuji

1999-07-01

408

The influence of transition metal ions on collagen mineralization.  

PubMed

The ions in body fluid play an important role in bone formation besides being a synthesizing material. Transition metal ions Co(2+), Ni(2+), Zn(2+), Fe(3+), Mn(2+), Cu(2+), Cd(2+) and Hg(2+) doped hydroxyapatite (HAP)/collagen composites were synthesized successfully in the presence of collagen traces at mild acidic pH for the first time. However, the amount of doped Hg(2+) and Cd(2+) was relatively low. Meanwhile, through soaking the collagen sponge as a template in simulated body fluid (SBF) which contains different transition metal ions (Mn(2+), Cu(2+), Ni(2+), Co(2+), Cd(2+), Hg(2+)), bone-like HAP/collagen composites were synthesized. Hg(2+) had a certain inhibitory effect on the formation of HAP crystals on the surface of the collagen sponge while Co(2+) can promote the formation of HAP on the collagen sponge. For both HAP/collagen composites and HAP/collagen sponge, it was found that transition metal ions Mn(2+) had a significant effect on the morphology of HAP particles and could induce to form floc-like HAP particle aggregates. PMID:23498275

Jia, Mingfen; Hong, Yuanping; Duan, Shuyuan; Liu, Yongjun; Yuan, Bo; Jiang, Fengzhi

2013-05-01

409

Low temperature complete combustion of methane over Ag-doped LaFeO 3 and LaFe 0.5Co 0.5O 3 perovskite oxide catalysts  

Microsoft Academic Search

Partial substitution of La by Ag, instead of Sr, in LaFeO3 and LaFe0.5Co0.5O3 perovskite oxides causes large increase in the catalytic activity of the perovskite in the complete combustion of dilute methane for its emission control, at low temperature (below 700°C) and high space velocity (51?000cm3g?1h?1). Ag-doped LaFe0.5 Co0.5O3 shows the highest methane combustion activity.

V. R. Choudhary; B. S. Uphade; S. G. Pataskar

1999-01-01

410

Studies on Polymorphic Sequence during the Formation of the 1:1 Ordered Perovskite-Type BaCa0.335M0.165Nb0.5O3-? (M = Mn, Fe, Co) Using in Situ and ex Situ Powder X-ray Diffraction.  

PubMed

Here, we report a synthetic strategy to control the B-site ordering of the transition metal-doped perovskite-type oxides with the nominal formula of BaCa0.335M0.165Nb0.5O3-? (M = Mn, Fe, Co). Variable temperature (in situ) and ex situ powder X-ray diffraction (PXRD), selected area electron diffraction (SAED), energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), scanning/transmission electron microscopy (SEM/TEM), and thermogravimetic analysis (TGA) were used to understand the B-site ordering as a function of temperature. The present study shows that BaCa0.335M0.165Nb0.5O3-? crystallizes in the B-site disordered primitive perovskite (space group s.g. Pm3?m) at 900 °C in air, which can be converted into the B-site 1:2 ordered perovskite (s.g. P3?m1) at 1200 °C and the B-site 1:1 ordered perovskite phase (s.g. Fm3?m) at 1300 °C. However, the reverse reaction is not feasible when the temperature is reduced. FTIR revealed that no carbonate species were present in all three polymorphs. The chemical stability of the investigated perovskites in CO2 and H2 highly depends on the B-site cation ordering. For example, TGA confirmed that the B-site disordered primitive perovskite phase is more readily reduced in dry and wet 10% H2/90% N2 and is less stable in pure CO2 at elevated temperature, compared to the B-site 1:1 ordered perovskite-type phase of the same nominal composition. PMID:25211299

Kan, Wang Hay; Lussier, Joey; Bieringer, Mario; Thangadurai, Venkataraman

2014-10-01

411

Oxygen rocking aqueous batteries utilizing reversible topotactic oxygen insertion/extraction in iron-based perovskite oxides Ca1–xLaxFeO3??  

PubMed Central

Developments of large-scale energy storages with not only low cost and high safety but also abundant metals are significantly demanded. While lithium ion batteries are the most successful method, they cannot satisfy all conditions. Here we show the principle of novel lithium-free secondary oxygen rocking aqueous batteries, in which oxygen shuttles between the cathode and anode composed of iron-based perovskite-related oxides Ca0.5La0.5FeOz (2.5 ? z ? 2.75 and 2.75 ? z ? 3.0). Compound Ca0.5La0.5FeOz can undergo two kinds of reduction and reoxidation of Fe4+/Fe3+ and Fe3+/Fe2+, that are accompanied by reversible and repeatable topotactic oxygen extraction and reinsertion during discharge and charge processes. PMID:22924108

Hibino, Mitsuhiro; Kimura, Takeshi; Suga, Yosuke; Kudo, Tetsuichi; Mizuno, Noritaka

2012-01-01

412

Phase transitions in heated Sr{sub 2}MgTeO{sub 6} double perovskite oxide probed by X-ray diffraction and Raman spectroscopy  

SciTech Connect

Double-perovskite oxide Sr{sub 2}MgTeO{sub 6} has been synthetized, and its crystal structure was probed by the technique of X-ray diffraction at room temperature. The structure is monoclinic, space group I2/m. Temperature-induced phase transitions in this compound were investigated by Raman spectroscopy up to 550?°C. Two low-wavenumber modes corresponding to external lattice vibrations merge at temperature of around 100?°C, indicating a phase transition from the monoclinic (I2/m) to the tetragonal (I4/m) structure. At 300?°C, changes in the slopes of temperature dependencies of external and O–Te–O bending modes are detected and interpreted as a second phase transition from the tetragonal (I4/m) to the cubic (Fm-3m) structure.

Manoun, Bouchaib, E-mail: manounb@gmail.com; Tamraoui, Y. [Equipe Ingénierie et environnement, Laboratoire de Chimie Appliquée et Environnement, Université Hassan 1er, Settat 26000 (Morocco)] [Equipe Ingénierie et environnement, Laboratoire de Chimie Appliquée et Environnement, Université Hassan 1er, Settat 26000 (Morocco); Lazor, P. [Department of Earth Sciences, Uppsala University, SE-752 36 Uppsala (Sweden)] [Department of Earth Sciences, Uppsala University, SE-752 36 Uppsala (Sweden); Yang, Wenge [High Pressure Synergetic Consortium, Geophysical Laboratory, Carnegie Institution of Washington, Argonne, Illinois 60439, USA and Center for High Pressure Science and Technology Advanced Research (HPSTAR), Shanghai 201203 (China)] [High Pressure Synergetic Consortium, Geophysical Laboratory, Carnegie Institution of Washington, Argonne, Illinois 60439, USA and Center for High Pressure Science and Technology Advanced Research (HPSTAR), Shanghai 201203 (China)

2013-12-23

413

Oxygen rocking aqueous batteries utilizing reversible topotactic oxygen insertion/extraction in iron-based perovskite oxides Ca(1-x)La(x)FeO(3-?).  

PubMed

Developments of large-scale energy storages with not only low cost and high safety but also abundant metals are significantly demanded. While lithium ion batteries are the most successful method, they cannot satisfy all conditions. Here we show the principle of novel lithium-free secondary oxygen rocking aqueous batteries, in which oxygen shuttles between the cathode and anode composed of iron-based perovskite-related oxides Ca(0.5)La(0.5)FeO(z) (2.5 ? z ? 2.75 and 2.75 ? z ? 3.0). Compound Ca(0.5)La(0.5)FeO(z) can undergo two kinds of reduction and reoxidation of Fe(4+)/Fe(3+) and Fe(3+)/Fe(2+), that are accompanied by reversible and repeatable topotactic oxygen extraction and reinsertion during discharge and charge processes. PMID:22924108

Hibino, Mitsuhiro; Kimura, Takeshi; Suga, Yosuke; Kudo, Tetsuichi; Mizuno, Noritaka

2012-01-01

414

Oxygen rocking aqueous batteries utilizing reversible topotactic oxygen insertion/extraction in iron-based perovskite oxides Ca1-xLaxFeO3-?  

NASA Astrophysics Data System (ADS)

Developments of large-scale energy storages with not only low cost and high safety but also abundant metals are significantly demanded. While lithium ion batteries are the most successful method, they cannot satisfy all conditions. Here we show the principle of novel lithium-free secondary oxygen rocking aqueous batteries, in which oxygen shuttles between the cathode and anode composed of iron-based perovskite-related oxides Ca0.5La0.5FeOz (2.5 <= z <= 2.75 and 2.75 <= z <= 3.0). Compound Ca0.5La0.5FeOz can undergo two kinds of reduction and reoxidation of Fe4+/Fe3+ and Fe3+/Fe2+, that are accompanied by reversible and repeatable topotactic oxygen extraction and reinsertion during discharge and charge processes.

Hibino, Mitsuhiro; Kimura, Takeshi; Suga, Yosuke; Kudo, Tetsuichi; Mizuno, Noritaka

2012-08-01

415

Oxygen nonstoichiometry and defect structure analysis of B-site mixed perovskite-type oxide (La, Sr)(Cr, M)O{sub 3-{delta}} (M=Ti, Mn and Fe)  

SciTech Connect

The defect chemical relationships in various B-site mixed LaCrO{sub 3}-based ceramics were investigated by means of high-temperature gravimetry. The nonstoichiometric deviation, {delta}, in (La{sub 0.7}Sr{sub 0.3})(Cr{sub 1-y}Ti{sub y})O{sub 3-{delta}} (y=0.1, 0.2 and 0.3) (LSCT){sub ,} (La{sub 0.75}Sr{sub 0.25})(Cr{sub 0.5}Mn{sub 0.5})O{sub 3-{delta}} (LSCM) and (La{sub 0.75}Sr{sub 0.25})(Cr{sub 0.5}Fe{sub 0.5})O{sub 3-{delta}} (LSCF) were measured as a function of oxygen partial pressure, P{sub O{sub 2}}, at temperatures between 973 and 1373 K. The effects of partial replacement of the donor on Cr-sites were examined in LSCT. In LSCM and LSCF, effects of the partial substitution of isovalent transition metals on Cr-sites are discussed. Oxygen nonstoichiometries of various B-site mixed LaCrO{sub 3}-based ceramics were compared with those of A-site substituted perovskite-type oxides, (La{sub 1-x}Sr{sub x})MO{sub 3-{delta}} (where x=0-0.3, M=Cr, Mn and Fe). The partial substitution of the different elements on Cr-sites drastically changed the P{sub O{sub 2}} and temperature dependence of oxygen vacancy formation in LaCrO{sub 3}-based ceramics. The defect equilibrium relationships of the localized electron well explained the oxygen vacancy formation in B-site mixed LaCrO{sub 3}-based ceramics. Oxygen vacancy formation in (La{sub 0.7}Sr{sub 0.3})(Cr{sub 1-y}Ti{sub y})O{sub 3-{delta}} (y=0.1 and 0.2) and (La{sub 0.7}Sr{sub 0.3})(Cr{sub 0.7}Ti{sub 0.3})O{sub 3-{delta}} was explained by redox reaction of Cr and Ti ions, respectively. The defect equilibrium relationships of LSCM and LSCF were interpreted by redox reaction of Mn ions and Fe ions, respectively. No significant change in valence state of Cr{sup 3+} ions in LSCM and LSCF was confirmed under the experimental conditions. - Graphical abstract: Oxygen nonstoichiometry of (La{sub 0.75}Sr{sub 0.25})(Cr{sub 0.5}Fe{sub 0.5})O{sub 3-{delta}} was plotted as the functions of partial oxygen pressure and temperature. The results were well explained by the localized electron on the Fe-sites and the equilibrium constants of the defect chemical equation were determined. A hysteresis was observed under the reducing atmospheres above 1173 K due to decomposition of Fe ions.

Oishi, Masatsugu [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan)], E-mail: oishi@mail.tagen.tohoku.ac.jp; Yashiro, Keiji; Sato, Kazuhisa; Mizusaki, Junichiro [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Kawada, Tatsuya [Graduate School of Environmental Studies, Tohoku University, 6-6-01 Aoba, Aramaki, Aoba-ku, Sendai 980-8579 (Japan)

2008-11-15

416

Double perovskite oxides Sr{sub 2}MMoO{sub 6} (M = Fe and Co) as cathode materials for oxygen reduction in alkaline medium  

SciTech Connect

Graphical abstract: The oxygen reduction over the surface of the electrocatalysts exhibiting high currents shows that SCMO/C electrocatalyst is slightly more active than the SFMO/C one. The relatively high electrochemical activity of the first may be ascribed to its high specific surface area providing a higher electrode current. Highlights: Black-Right-Pointing-Pointer SCMO/C and SFMO/C as catalysts for oxygen reduction were studied. Black-Right-Pointing-Pointer SCMO/C catalyst showed a relatively high activity. Black-Right-Pointing-Pointer A change in the reaction mechanism from a direct 'four-electron pathway' to a 'peroxide pathway' was observed. -- Abstract: The oxygen reduction reaction (ORR) was studied on Sr{sub 2}MMoO{sub 6} (M = Fe and Co) double perovskites, prepared by a solid-state reaction, in 0.5 M NaOH at 25 Degree-Sign C with a rotating disk electrode (RDE). The two oxide powders were characterized by X-ray diffraction, scanning electron microscopy and BET analysis. The electrochemical techniques considered are linear voltammetry, steady state polarization and ac impedance spectroscopy. The electrocatalysts (SFMO/C, SCMO/C) consisting of the double perovskite oxides and carbon (Vulcan XC-72) were mixed and spread out into a thin layer on a glassy carbon substrate. At room temperature, a significantly electrocatalytic activity is observed for both electrocatalysts. Compared to SFMO/C, the SCMO/C electrocatalyst was found to show a relatively high electrocatalytic activity for O{sub 2} reduction, which agrees well with the results obtained using the ac impedance spectroscopy.

Cheriti, Mabrouk [Laboratoire d'Energetique et d'Electrochimie des Solides, Universite F. Abbas de Setif, 19000 Setif (Algeria)] [Laboratoire d'Energetique et d'Electrochimie des Solides, Universite F. Abbas de Setif, 19000 Setif (Algeria); Kahoul, Abdelkrim, E-mail: Kahoulabdelkrim@yahoo.fr [Laboratoire d'Energetique et d'Electrochimie des Solides, Universite F. Abbas de Setif, 19000 Setif (Algeria)] [Laboratoire d'Energetique et d'Electrochimie des Solides, Universite F. Abbas de Setif, 19000 Setif (Algeria)

2012-01-15

417

Electronic structure of double perovskite A2FeReO6 (A = Ba and Ca): interplay between spin-orbit interaction, electron correlation, and lattice distortion.  

PubMed

We have investigated the electronic structure of double perovskites, Ba(2)FeReO(6) (metallic) and Ca(2)FeReO(6) (insulating) using optical and x-ray absorption spectroscopy. By comparing the experimental results with the density functional theory calculations, we found that the electronic structure of Ba(2)FeReO(6) could be determined from the interaction of the electron correlation and spin-orbit coupling. On the other hand, for Ca(2)FeReO(6), the lattice distortion and electron correlation are important in determining the electronic structure. Additionally, the insulating gap in Ca(2)FeReO(6) is realized by the spin-orbit coupling. Our work shows that the subtle interplay of the spin-orbit interaction, electron correlation, and lattice distortion should be taken into account to understand the electronic structure of the 5d transition metal oxides. PMID:21403258

Jeon, B C; Kim, Choong H; Moon, S J; Choi, Woo Seok; Jeong, Hogyun; Lee, Y S; Yu, J; Won, C J; Jung, J H; Hur, N; Noh, T W

2010-09-01

418

Development of double-perovskite compounds as cathode materials for low-temperature solid oxide fuel cells.  

PubMed

A class of double-perovskite compounds display fast oxygen ion diffusion and high catalytic activity toward oxygen reduction while maintaining excellent compatibility with the electrolyte. The astoundingly extended stability of NdBa1-x Cax Co2 O5+? (NBCaCO) under both air and CO2 -containing atmosphere is reported along with excellent electrochemical performance by only Ca doping into the A?site of NdBaCo2 O5+? (NBCO). The enhanced stability can be ascribed to both the increased electron affinity of mobile oxygen species with Ca, determined through density functional theory calculations and the increased redox stability from the coulometric titration. PMID:25200006

Yoo, Seonyoung; Jun, Areum; Ju, Young-Wan; Odkhuu, Dorj; Hyodo, Junji; Jeong, Hu Young; Park, Noejung; Shin, Jeeyoung; Ishihara, Tatsumi; Kim, Guntae

2014-11-24

419

Journal of Magnetism and Magnetic Materials 272276 (2004) 122123 LSD-SIC studies of localization in the 4d-transition metal  

E-print Network

Journal of Magnetism and Magnetic Materials 272­276 (2004) 122­123 LSD-SIC studies of localization Published by Elsevier B.V. PACS: 75.50.Gg; 75.47.Pq Keywords: LSD-SIC; Localization Although many density (LSD) [3] calculations to study how close these 4d-transition metal oxides are to a localization

Svane, Axel Torstein

420

Enhanced visible-light absorption of mesoporous TiO2 by co-doping with transition-metal/nitrogen ions  

SciTech Connect

Titanium (IV) oxide, TiO2, has been the object of intense scrutiny for energy applications. TiO2 is inexpensive, non-toxic, and has excellent corrosion resistance when exposed to electrolytes. A major drawback preventing the widespread use TiO2 for photolysis is its relatively large band gap of ~3eV. Only light with wavelengths shorter than 400 nm, which is in the ultraviolet portion of the spectrum, has sufficient energy to be absorbed. Less than 14 percent of the solar irradiation reaching the earth s surface has energy exceeding this band gap. Adding dopants such as transition metals has long been used to reduce the gap and increase photocatalytic activity by accessing the visible part of the solar spectrum. The degree to which the band gap is reduced using transition metals depends in part on the overlap of the d-orbitals of the transition metals with the oxygen p-orbitals. Therefore, doping with anions such as nitrogen to modify the cation-anion orbital overlap is another approach to reduce the gap. Recent studies suggest that using a combination of transition metals and nitrogen as dopants is more effective at introducing intermediate states within the band gap, effectively narrowing it. Here we report the synthesis of mesoporous TiO2 spheres, co-doped with transition metals and nitrogen that exhibit a nearly flat absorbance response across the visible spectrum extending into the near infrared.

Mathis, John [Embry-Riddle Aeronautical University; Bi, Zhonghe [ORNL; Bridges, Craig A [ORNL; Kidder, Michelle [ORNL; Paranthaman, Mariappan Parans [ORNL

2013-01-01

421

The development of a biological interface for transition metal implants  

NASA Astrophysics Data System (ADS)

The specific goal of this research was to develop an in vitro model for a root-form endosseous dental implant that contains a periodontal ligament and that is biologically integratable into alveolar bone. This objective was based on the following two hypotheses. (1) The chemical attachment of extracellular matrix proteins to the surface of transition metals increases the number of fibroblast cells attached to the surface of the metal. (2) The chemical attachment of extracellular matrix proteins to the surface of transition metals increases the strength of the fibroblast cell attachment to the surface of the metal. The model needed to have a well-controlled surface that was reproducible. Thus, a layer of Au was deposited over a Ti base, and dithiobis(succinimidylpropionate) (DSP) a chemical containing disulfide groups was adsorbed to the Au. Next, extracellular matrix proteins which are periodontal ligament components were attached to the free end group of the chemical that was adsorbed to the Au. This surface served as an attachment substrate on which additional periodontal ligament components such as fibroblast cells could grow. From this model a new implant interface may be developed. This model was tested using the following polypeptides; collagen type I, collagen type IV, fibronectin, and poly-D-lysine. L929 cells were grown on Ti, Ti + Au, Ti + Au + polypeptide, and Ti + Au + DSP + polypeptide. After 72 hours, the live cells were stained with neutral red. The substrates were then subjected to increasing centrifugal forces. The viable stained cells were fixed onto the substrates and cells were counted. The hypotheses were proven for three polypeptides: fibronectin, collagen type I, and poly-D-lysine. The strongest attachment was found with collagen type I. Collagen type IV did not provide any advantage for attachment over uncoated transition metals.

Melton, Kim R.

422

Cross-plane thermal properties of transition metal dichalcogenides  

SciTech Connect

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

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

2013-02-25

423

Valley photothermoelectric effects in transition-metal dichalcogenides  

NASA Astrophysics Data System (ADS)

We theoretically investigate photothermoelectric effects, i.e., the photoenabled versions of the Seebeck and Nernst effects in monolayer transition metal dichalcogenides (TMDCs) using semiclassical transport theory. We find that monolayer TMDCs subjected to circular polarized light show anomalous thermoelectric properties as a result of strong spin-orbit interaction and broken inversion symmetry. The Seebeck coefficient for photogenerated carriers is relatively large and changes its sign at a critical carrier density. In addition, a nontrivial photo-Nernst effect emerges in the absence of an external magnetic field or magnetic moments.

Konabe, Satoru; Yamamoto, Takahiro

2014-08-01

424

Exploring Transition Metal Catalyzed Reactions via AB Initio Reaction Pathways  

NASA Astrophysics Data System (ADS)

The study and prediction of chemical reactivity is one of the most influential contributions of quantum chemistry. A central concept in the theoretical treatment of chemical reactions is the reaction pathway, which can be quite difficult to integrate accurately and efficiently. This talk will outline our developments in the integration of these pathways on ab initio potential energy surfaces. We will also describe results from recent studies on the kinetics of transition metal catalyzed reactions, including the importance of vibrational coupling to the reaction coordinate and the role of this coupling in catalytic rate enhancement.

Hratchian, Hrant P.

2011-06-01

425

Rare earth-transition metal scrap treatment method  

DOEpatents

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

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

1992-02-11