Sample records for perovskite transition-metal oxides

  1. Electronic structure of double-perovskite transition-metal oxides

    Microsoft Academic Search

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

    2000-01-01

    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

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

    Microsoft Academic Search

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

    2006-01-01

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

  3. Investigations of the electronic structure of d 0 transition metal oxides belonging to the perovskite family

    Microsoft Academic Search

    Hank W. Eng; Paris W. Barnes; Benjamin M. Auer; Patrick M. Woodward

    2003-01-01

    Computational and experimental studies using linear muffin tin orbital methods and UV-visible diffuse reflectance spectroscopy, respectively, were performed to quantitatively probe the relationships between composition, crystal structure and the electronic structure of oxides containing octahedrally coordinated d0 transition metal ions. The ions investigated in this study (Ti4+, Nb5+, Ta5+, Mo6+, and W6+) were examined primarily in perovskite and perovskite-related structures.

  4. Simple and perovskite oxides of transition-metals: Why some are metallic, while most are insulating

    NASA Astrophysics Data System (ADS)

    Torrance, Jerry B.; Lacorro, Philippe; Asavaroengchai, Chinnarong; Metzger, Robert M.

    1991-01-01

    Some 76 simple and perovskite transition-metal oxides are classified as "metals," "insulators," and those exhibiting metal-insulator transitions. Using the framework of Zaanen, Sawatzky, and Allen and a simple ionic model to estimate the two relevant energies ( ?0 and U' 0), we can find boundaries which separate the insulating oxides from two types of metals: low ?0 metals and low U' 0 metals. In addition, compounds with metal-insulator transitions are found to be on (or near) these boundaries. It is concluded that the large differences in conductivity behavior of oxides are largely due to differences in the ionization potentials of the transition metal cations.

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

    PubMed

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

    2015-04-01

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

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

    Microsoft Academic Search

    Louis Whaley

    2007-01-01

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

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

    SciTech Connect

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

    2014-01-01

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

  8. Electronic structure of perovskite-type transition metal oxides LaMO3 (M=TiCu) by U+GW approximation

    Microsoft Academic Search

    Yoshiro Nohara; Susumu Yamamoto; Takeo Fujiwara

    2009-01-01

    We investigate electronic structures of LaMO3 (M=TiCu) systematically by means of U+GW approximation. In these strongly correlated systems, it is important to treat large on-site Coulomb interactions and their dynamical screening effects. Transition-metal ions in perovskite-type lanthanum oxides are trivalent and their physics is qualitatively different from that of divalent transition-metal ions in transition-metal mono-oxides. The localization of wave functions

  9. Phase control of a perovskite transition-metal oxide through oxygen displacement at the heterointerface.

    PubMed

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

    2015-06-21

    Controlling structural distortions that are closely related to functional properties in transition-metal oxides is a key not only to exploring novel phenomena but also to developing novel oxide-based electronic devices. In this review article, we overview investigations revealing that oxygen displacement at the heterointerface is a key parameter characterizing structure-property relationships of heterostructures. We further demonstrate that the interface engineering of the oxygen displacement is useful to control structural and electronic properties of strained oxides. PMID:25848647

  10. Magnetism, orbital ordering and lattice distortion in perovskite transition-metal oxides

    Microsoft Academic Search

    K. Terakura

    2007-01-01

    Magnetism of matters has two basic ingredients. While exchange and correlation are responsible to the stability of magnetic moment, magnetic ordering is controlled by orbital hybridization, which depends on the atomic arrangement and the mode of orbital occupation. Transition-metal oxides serve as an important playground where unique properties and phenomena can be observed as results of close correlation among magnetism,

  11. Variation of optical gaps in perovskite-type 3d transition-metal oxides

    Microsoft Academic Search

    T. Arima; Y. Tokura; J. B. Torrance

    1993-01-01

    The optical study of trivalent 3d transition-metal-oxide compounds (RMO3) with the perovskitelike structure has revealed the variation of their electronic structure with the 3d element (M) as well as the A-site rare-earth element (R). The crossover of the gap nature from the Mott type to charge-transfer (CT) type with increasing atomic number of M is observed to occur around M=Cr.

  12. Variation of optical gaps in perovskite-type 3d transition-metal oxides

    NASA Astrophysics Data System (ADS)

    Arima, T.; Tokura, Y.; Torrance, J. B.

    1993-12-01

    The optical study of trivalent 3d transition-metal-oxide compounds (RMO3) with the perovskitelike structure has revealed the variation of their electronic structure with the 3d element (M) as well as the A-site rare-earth element (R). The crossover of the gap nature from the Mott type to charge-transfer (CT) type with increasing atomic number of M is observed to occur around M=Cr. The variation of Mott and CT gaps with M species is quantitatively consistent with the tendency expected from an ionic model. However, for the low-energy electronic structures for the narrow-gap (or metallic) compounds (M=Ti,Co,Ni), the effects of the M-3d-O-2p hybridization must be included.

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

    SciTech Connect

    Okamoto, Satoshi [ORNL

    2013-01-01

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

  14. SYNTHESIS, CRYSTAL STRUCTURE AND MAGNETISM OF PEROVSKITE-BASED TRANSITION METAL OXIDES

    Microsoft Academic Search

    Farshid Ramezanipour

    2011-01-01

    A series of layered perovskite-based compounds were synthesized and studied as follows.\\u000aLa5Mo2.76(4)V1.25(4)O16 is a new pillared-perovskite synthesized by solid state chemistry method. It has layers of corner-sharing octahedra separated by dimers of edge-sharing octahedra, and is the first Mo-based pillared-perovskite whose magnetic structure was determined by neutron diffraction.\\u000aCa2FeMnO5 is an oxygen-deficient-perovskite with a brownmillerite-type ordering of oxygen vacancies,

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

    NASA Astrophysics Data System (ADS)

    Misra, Sunasira

    2012-07-01

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

  16. Magnetic Interactions in Transition-Metal Oxides

    Microsoft Academic Search

    I. V. Solovyev

    2003-01-01

    This a review article, which presents a general framework for the analysis of interatomic magnetic interactions in the spin-density-functional theory, which is based on the magnetic force theorem, make a link with the models for transition-metal oxides, and gives several examples of how this strategy can be used for the analysis of magnetic properties of colossal-magnetoresistive perovskite manganites, double perovskite

  17. Semiconducting transition metal oxides

    NASA Astrophysics Data System (ADS)

    Lany, Stephan

    2015-07-01

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

  18. Semiconducting transition metal oxides.

    PubMed

    Lany, Stephan

    2015-07-22

    Open shell transition metal oxides are usually described as Mott or charge transfer insulators, which are often viewed as being disparate from semiconductors. Based on the premise that the presence of a correlated gap and semiconductivity are not mutually exclusive, this work reviews electronic structure calculations on the binary 3d oxides, so to distill trends and design principles for semiconducting transition metal oxides. This class of materials possesses the potential for discovery, design, and development of novel functional semiconducting compounds, e.g. for energy applications. In order to place the 3d orbitals and the sp bands into an integrated picture, band structure calculations should treat both contributions on the same footing and, at the same time, account fully for electron correlation in the 3d shell. Fundamentally, this is a rather daunting task for electronic structure calculations, but quasi-particle energy calculations in GW approximation offer a viable approach for band structure predictions in these materials. Compared to conventional semiconductors, the inherent multivalent nature of transition metal cations is more likely to cause undesirable localization of electron or hole carriers. Therefore, a quantitative prediction of the carrier self-trapping energy is essential for the assessing the semiconducting properties and to determine whether the transport mechanism is a band-like large-polaron conduction or a small-polaron hopping conduction. An overview is given for the binary 3d oxides on how the hybridization between the 3d crystal field symmetries with the O-p orbitals of the ligands affects the effective masses and the likelihood of electron and hole self-trapping, identifying those situations where small masses and band-like conduction are more likely to be expected. The review concludes with an illustration of the implications of the increased electronic complexity of transition metal cations on the defect physics and doping, using as an example the diversity of possible atomic and magnetic configurations of the O vacancy in TiO2, and the high levels of hole doping in Co2ZnO4 due to a self-doping mechanism that originates from the multivalence of Co. PMID:26126022

  19. High-pressure synthesis of the 4d and 5d transition-metal oxides with the perovskite and the perovskite-related structure and their physical properties

    NASA Astrophysics Data System (ADS)

    Cheng, Jinguang

    A Walker-type multianvil high-pressure facility is capable of high-pressure syntheses and measurements beyond 10 GPa and has been utilized in my research to synthesize the 4d Ruthenium and Rhodium and the 5d Iridium oxides with the perovskite-related structures. Under high-pressure and high-temperature conditions, these families of oxides can be enlarged to a great extent so that enables us not only to address the long-standing problem about ferromagnetism in the perovskite ruthenates but also explore new phenomena associated with the structural and electronic properties in the iridates and rhodates. In the perovskite ruthenates ARuO3 (A= Ca, Sr, and Ba), a systematic study of the variations of the ferromagnetic transition temperature Tc and the critical isothermal magnetization as a function of the average A-site cation size and the size variance as well as external high pressures reveals explicitly the crucial role of the local lattice strain and disorder on Tc and the nature of the localized-electron ferromagnetism. However, such a steric effect is dominated by the electronic effect in another perovskite ruthenate PbRuO3, which is a paramagnetic metal down to 1.8 K and undergoes a first-order structural transition to a low-temperature Imma phase at Tt ? 90 K. Bandwidth broadening due to orbital hybridization between Pb-6s and Ru-4d plays an important role in suppressing the ferromagnetism in the Sr1-zPbzRuO3 system. The high-pressure sequence of the 9R-BaIrO3 was explored and three more polytypes, i.e. 5H, 6H and 3C, were identified under 10 GPa. With increasing fraction of the corner- to face-sharing IrO6/2 octahedra, the ground states of BaIrO3 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 near a quantum critical point in the 6H phase. In addition to the perovskite SrRhO3, a new 6H polytype was synthesized for the first time under high pressure and a pressure-temperature phase diagram was given for the 6H-perovskite transformation. Restoration of the Curie-Weiss behavior in the high-temperature magnetic susceptibility chi(T) of the perovskite SrRhO3 resolves the puzzle about unusual dependence of chi -1 ? T2 reported earlier and highlights the importance of spin-orbit coupling in the 4d and 5d transition-metal oxides.

  20. Electronic structures of perovskite oxides of transition metals of the type LaMO[sub 3] (M = Ti-Ni) as revealed by MSX[alpha] investigations

    SciTech Connect

    Sarma, D.D.; Santra, A.K.; Rao, C.N.R. (Indian Institute of Science, Bangalore (India))

    1994-06-01

    Systematic investigations of the electronic structures of MO[sup 9-][sub 6] (M = Ti-Ni) clusters, as in the LaMO[sub 3] type perovskite oxides, have been carried out by employing the multiple-scattering X[alpha] (MSX[alpha]) method. The crystal-field splitting of the metal d level is found to increase, while the oxygen-to-metal charge-transfer energy decreases across the transition metal series. Systematic trends are also seen in the mixing (covalency) between the metal d and the oxygen 2p orbitals in the series.

  1. Quantum Transport in Transition Metal Oxides

    E-print Network

    Takada, Yasutami

    Quantum Transport in Transition Metal Oxides Anomalous transport properties in transition metal to strong correlation. Another aspect of the transition-metal oxides, in particular in manganese the anomalous current in transition-metal compounds from a viewpoint of the band theory, we have recently

  2. Synthesis and crystal growth of novel perovskite-based transition metal oxides: Characterization of the magnetic and transport properties

    Microsoft Academic Search

    Guerman Popov

    2003-01-01

    The synthesis and characterization of novel perovskite-related materials is reported in this dissertation with the goal to develop new correlated electronic materials with enhanced magnetic, transport and magnetoresistance properties using rational solid state chemistry design approach and specific synthetic techniques. A simple method of LnMn2O5 single-crystal growth by fused salt electrolysis is presented. Conventionally high pressure is required for the

  3. Mechanism for bipolar resistive switching in transition metal oxides

    Microsoft Academic Search

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

    2010-01-01

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

  4. SHG on Transition Metal Oxides

    Microsoft Academic Search

    O. Ney

    2005-01-01

    Optical second harmonic generation (SHG), within the electric-dipole approximation, is known to be sensitive to the surface electronic structure of inversion symmetric media. Besides, it allows to distinguish magneto-optically ferromagnetic from antiferromagnetic order of cubic (001) surfaces. Here, we compute the SHG from NiO(001) and CoO(001) surfaces from first principles. To address the notoriously difficult electronic correlations of transition metal

  5. Orbital polarization transition metal oxides (invited) (abstract)

    Microsoft Academic Search

    M. R. Norman

    1991-01-01

    One of the most controversial topics in condensed matter physics concerns the nature of the electronic structure of transition metal oxides. Unpolarized band structure calculations predict metallic ground states for these oxides, whereas experimentally they are insulating. This led to the development of the Mott insulator picture for these materials fifty years ago. Later, though, Slater’s group showed that by

  6. Muon Sites in Transition Metal Oxides

    Microsoft Academic Search

    Kwaichow Benjamin Chan

    1988-01-01

    Muon behavior in a selected series of transition -metal oxides has been investigated by the Muon Spin Rotation (muSR) technique. The materials studied are the corundum structured oxides (M_2 O_3: M = Fe, Cr, V, Ti) and the high-Tc superconducting oxides in Y-Ba-Cu-O system. The muon is first implanted into the oxide crystalline and its subsequent behavior in the presence

  7. Wettability of transition metal oxide surfaces

    Microsoft Academic Search

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

    1998-01-01

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

  8. The gel route to transition metal oxides

    Microsoft Academic Search

    J. Livage

    1986-01-01

    The so-called ``sol-gel'' process offers new approaches to the synthesis of transition metal oxides. Based on inorganic polymerization from molecular precursors, it leads to highly condensed species or colloids. These colloids are actually two-phase systems in which small oxide particles are dispersed in a liquid medium. A very large interface separates both phases and interfacial phenomena, at the oxide-water interface,

  9. Nanostructured transition metal oxides useful for water oxidation catalysis

    DOEpatents

    Frei, Heinz M; Jiao, Feng

    2013-12-24

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

  10. THEORY OF MOTTTRANSITION : APPLICATION S TO TRANSITION METAL OXIDES

    E-print Network

    Paris-Sud XI, Université de

    125 THEORY OF MOTTTRANSITION : APPLICATION S TO TRANSITION METAL OXIDES M. CYROT Institut Laue discuss the relevance of the theory to transition metal oxides. The main qualitative features in transition metal oxides. These oxides form a very interesting class of materials [1]. Their electrical

  11. Amorphous transition metal oxide films

    Microsoft Academic Search

    Neil Heiman; N. S. Kazama

    1979-01-01

    We have been able to prepare amorphous oxides of Fe and Cr by sputter deposition. Magnetization measurements were made between 4.2 K and 300 K. Mössbauer spectra were obtained for the iron oxide samples in the same temperature range. Amorphous CrO2 films showed no evidence of magnetic order. For the amorphous Fe oxide films, the 4.2 K Mössbauer spectrum showed

  12. MATERIALS THEORY From transition metal oxides to cosmic strings

    E-print Network

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

  13. Transition metal oxides on organic semiconductors Yongbiao Zhao a

    E-print Network

    Demir, Hilmi Volkan

    Transition metal oxides on organic semiconductors Yongbiao Zhao a , Jun Zhang b , Shuwei Liu Accepted 14 January 2014 Available online 1 February 2014 Keywords: p-doping Transition metal oxide Organic semiconductor Diffusion Organic light-emitting diode a b s t r a c t Transition metal oxides (TMOs) on organic

  14. Topological crystalline insulators in transition metal oxides.

    PubMed

    Kargarian, Mehdi; Fiete, Gregory A

    2013-04-12

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

  15. Quantum Criticality in Transition-Metal Oxides

    Microsoft Academic Search

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

    2010-01-01

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

  16. Orbital Physics in Transition-Metal Oxides

    Microsoft Academic Search

    Y. Tokura; N. Nagaosa

    2000-01-01

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

  17. Electronic structure and orbital ordering in perovskite-type 3d transition-metal oxides studied by Hartree-Fock band-structure calculations

    Microsoft Academic Search

    T. Mizokawa; A. Fujimori

    1996-01-01

    We have studied transition-metal 3d-oxygen 2p lattice models, where full degeneracy of transition-metal 3d and oxygen 2p orbitals and on-site Coulomb and exchange interactions between 3d electrons are taken into account, by means of a spin- and orbital-unrestricted Hartree-Fock (HF) approximation. The electronic-structure parameters deduced from the cluster-model analyses of the photoemission spectra are used as input. We have applied

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

    E-print Network

    Spinu, Leonard

    of New Transition-Metal Oxyhalide Perovskites Gabriel Caruntu, Liliana Viciu, Leonard Spinu, Weilie Zhou-layered perovskites with divalent transition-metal halides leads to the templated assembly of metal-anion layers4+ , Mn4+ , Nb4+ , Mo4+ ), have been prepared by a direct route. INTRODUCTION Layered perovskites

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

    Microsoft Academic Search

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

    2006-01-01

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

  20. Magnetic correlations in doped transition metal oxides

    SciTech Connect

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

    1995-02-15

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

  1. Compensation Mechanisms and Functionality of Transition Metal Oxide Surfaces and

    E-print Network

    Compensation Mechanisms and Functionality of Transition Metal Oxide Surfaces and Interfaces metal oxide surfaces and interfaces can lead to properties and functionality that are not observed-code on HLRBI and HLRBII. 1 Introduction The surfaces and interfaces of transition metal oxides represent

  2. Copyright A. J. Millis 2013 Columbia University Transition Metal Oxides

    E-print Network

    Millis, Andrew

    Copyright A. J. Millis 2013 Columbia University Transition Metal Oxides A. J. Millis Department and Prospects #12;Copyright A. J. Millis 2013 Columbia University Transition metal ``oxides and Electronic Structure 4. Theory--General 5. Dynamical Mean Field Theory and Oxides 6. Applications

  3. MEDICINAL CHEMISTRY: OXIDATION OF DISACCHARIDES TO SYNTHESIZE TRANSITION METAL COMPLEXANTS

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The carbohydrate trehalose was a preliminary test model to be used as a replacement conjugate in an alternate transition-metal complex. Using an oxidant, we hypothesized that if the primary alcohols formed aldehyde functional groups upon oxidation then the transition metal could complex with the tr...

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

    SciTech Connect

    Vojvodic, Aleksandra

    2011-08-22

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

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

    NASA Astrophysics Data System (ADS)

    Chi, Miaofang

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

  6. Methanol oxidation over nonprecious transition metal oxide catalysts

    Microsoft Academic Search

    Umit S. Ozkan; Richard F. Kueller; Edgar Moctezuma

    1990-01-01

    This paper reports methanol oxidation over nonprecious transition metal oxide catalysts studied in a gradient less external recycle reactor. The catalysts (oxides of Cr, Mn, Fe, Co, Ni, Cu), which were prepared by using the incipient wetness technique, were supported on 1\\/8 in.γ-AlâOâ tablets. The catalysts were characterized by using BET surface area measurement, X-ray diffraction, laser Raman spectroscopy, scanning

  7. Photoelectron spectroscopy of transition metal oxide interfaces

    NASA Astrophysics Data System (ADS)

    Zegenhagen, Jörg

    2015-05-01

    In the present paper we review applications of the photoelectron spectroscopy (PES) technique to the investigation of transition metal oxide (TMO) interfaces. We summarize very briefly some of the principle, specific characteristics of TMOs. Because of the buried nature of the interfaces, the photoelectrons must penetrate certain thicknesses of material, which is easier with higher kinetic energies in the keV range. Thus, we also briefly summarize some of the hallmarks of hard X-ray photoelectron spectroscopy (HAXPES), before presenting four explicit samples of the analysis of TMO interfaces: The LaAlO3/SrTiO3 (0 0 1) interface, which had attracted attention because of the discovery of a sheet of high mobility electrons below the thin layer of LaAlO3; superlattices of the two insulators CaCuO2 and SrTiO3, which can be prepared to become superconducting at about 40 K; epitaxial films of the 90 K superconductor GdBa2Cu3O7-? on NdGaO3; and finally the analysis of the nucleation of the 90 K superconductor YBa2Cu3O7-? on SrTiO3 (0 0 1). The latter two cases of the investigation of the superconducting films are examples of photoelectron spectroscopy by X-ray standing wave (XSW) excitation. Because of this, the bare essential features of the XSW technique are also briefly reviewed.

  8. First-principles study on the electronic structure of bismuth transition-metal oxides

    Microsoft Academic Search

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

    2004-01-01

    The electronic structure, magnetic and electric properties, and lattice stability of multiferroic BiMnO3 as a typical system in perovskite Bi transition-metal oxides (BiMO3) are studied from first principles. It is demonstrated theoretically for the first time that the orbital ordering within the Mn eg orbitals is actually realized in BiMnO3, being consistent with crystallographic data, and plays a crucial role

  9. Electrolytic separation of crystals of transition-metal oxides

    NASA Technical Reports Server (NTRS)

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

    1969-01-01

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

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

    E-print Network

    Senn, Mark Stephen

    2013-06-29

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    E-print Network

    Andrzej M. Ole?

    2012-07-12

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

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

    PubMed

    Ole?, Andrzej M

    2012-08-01

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

  14. Transition Metal Oxides: Extra Thermodynamic Stability as Thin Films

    Microsoft Academic Search

    Charles T. Campbell

    2006-01-01

    Introduction.—Transition metals are used as industrial catalysts for a wide range of oxidation reactions of great importance in fuel processing, chemical production, and pollution cleanup. A key fundamental question is whether the surface under catalytic reaction conditions is metallic or is, instead, the metal's oxide. We show here that since these oxides often wet their metals, an? 1n mthick film

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

    E-print Network

    Lin, Xi

    Chemistry of Sulfur Oxides on Transition Metals. II. Thermodynamics of Sulfur Oxides on Platinum-containing molecules on transition metal catalysts has been of interest to scientists for more than 2 decades.1. How- ever, sulfur chemistry on transition metal surfaces is so complicated that it remains far from

  16. Magnetism and transport properties of transition metal oxides and nanoparticles

    Microsoft Academic Search

    Dane Thomas Gillaspie

    2006-01-01

    This dissertation is devoted to the study of the properties of transition metal oxides in both thin film and nanocrystalline forms. The first section is devoted to the transport properties of manganese oxide thin film samples. The colossal magnetoresistance in these materials is usually explained using double-exchange, but this explanation is only partially correct. Recent theoretical and experimental work has

  17. Vapor growth of electrochromic thin films of transition metal oxides

    Microsoft Academic Search

    K. A. Gesheva; T. Ivanova; B. Marsen; G. Zollo; M. Kalitzova

    2008-01-01

    Mixed oxide films of transition metals gain considerable much attention due to their interesting optoelectronic properties. The low temperature chemical vapor growth processing of thin films of mixed W and Mo oxides is presented. The investigation is related to optimization of films structure and the related optoelectronic properties in dependence on the chemical vapor deposition (CVD) process parameters. Their electrochromic

  18. Electronic entanglement in late transition metal oxides

    E-print Network

    Thunström, Patrik; Eriksson, Olle

    2012-01-01

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

  19. Nanostructured transition metal oxides for aqueous hybrid electrochemical supercapacitors

    Microsoft Academic Search

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

    2006-01-01

    In this paper, we wish to present an overview of the research carried out in our laboratories with low-cost transition metal\\u000a oxides (manganese dioxide, iron oxide and vanadium oxide) as active electrode materials for aqueous electrochemical supercapacitors.\\u000a More specifically, the paper focuses on the approaches that have been used to increase the capacitance of the metal oxides\\u000a and the cell

  20. Kinetics of Catalytic Combustion of Propane on Transition Metal Oxides

    Microsoft Academic Search

    RAVI PRASAD; LAWRENCE A. KENNEDY; ELI RUCKENSTEIN

    1982-01-01

    Experiments have been conducted to determine the global kinetics for lean-fuel propane oxidation on a transition metal oxide catalyst. The catalyst used was composed of chromium and cobalt oxides (Cr2O3, CO3O4) deposited on alumina washcoated honeycomb ceramic substrates.The heterogeneous propane oxidation was modelled by a global mechanism consisting of the following three first order reactions;To determine the rate parameters it

  1. Electronic entanglement in late transition metal oxides

    E-print Network

    Patrik Thunström; Igor Di Marco; Olle Eriksson

    2013-01-28

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

  2. Disorder driven quantum phase transitions in transition metal oxides

    Microsoft Academic Search

    Kohjiro Kobayashi; Nandini Trivedi

    2007-01-01

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

  3. Quadrupole terms in defect energies in transition metal oxides

    Microsoft Academic Search

    A. M. Stoneham; M. J. L. Sangster; J. H. Harding

    1990-01-01

    In a previous paper it was shown that, for defects in transition metal oxides, there was evidence for an additional term in the potential energy beyond the usual monopole and dipole terms of the shell model. This appeared to be a quadrupole term in which the open 3d shells of the host ions, as well as any impurities, responded to

  4. Hydrothermal synthesis of transition metal oxides under mild conditions

    Microsoft Academic Search

    M Stanley Whittingham

    1996-01-01

    A notable development in mild (? 200°C) hydrothermal synthesis in the past few years has been the extension of the synthesis technique from zeolites and metal phosphates to binary and ternary transition metal oxides. This low-temperature technique is critical to the formation of metastable phases not obtainable using traditional high-temperature methods. New phases, as well as known materials, of the

  5. Novel Extended Solids Composed of Transition Metal Oxide Clusters

    Microsoft Academic Search

    M. Ishaque Khan

    2000-01-01

    Transition metal oxide clusters and their derivatives offer an unmatched variety of structural motifs that are potential building blocks for the design and development of extended solids. In view of the proven applications of these clusters in catalysis, molecular recognition, environmental decontamination, clinical and analytical processes, materials science, nanotechnology, and medicine, their usage as building blocks promises the development of

  6. Efficient photocarrier injection in a transition metal oxide heterostructure

    Microsoft Academic Search

    Y Muraoka; T Yamauchi; Y Ueda; Z Hiroi

    2002-01-01

    An efficient method for doping a transition metal oxide (TMO) with hole carriers is presented: photocarrier injection (PCI) in an oxide heterostructure. It is shown that an insulating vanadium dioxide (VO2) film is rendered metallic under light irradiation by PCI from an n-type titanium dioxide (TiO2) substrate doped with Nb. Consequently, a large photoconductivity, which is exceptional for TMOs, is

  7. Electronic structure systematics of 3d transition metal oxides

    Microsoft Academic Search

    R. Zimmermann; P. Steiner; R. Claessen; F. Reinert; S. Hüfner

    1998-01-01

    The electronic structure of a series of 3d transition metal oxides is investigated by core-level and valence band photoemission spectroscopy. The results are analyzed in terms of metal–ligand interactions and on-site correlation energies, using a simple cluster model approach. For some oxides we also present a comparison with band structure calculations. It is shown that the electronic structure of the

  8. Electronic Hamiltonian for transition-metal oxide compounds

    Microsoft Academic Search

    Erwin Müller-Hartmann; Elbio Dagotto

    1996-01-01

    An effective electronic Hamiltonian for transition-metal oxide compounds is presented. For Mn oxides, the Hamiltonian contains spin-2 ``spins'' and spin-3\\/2 ``holes'' as degrees of freedom. The model is constructed from the Kondo-lattice Hamiltonian for mobile eg electrons and localized t2g spins, in the limit of a large Hund's coupling. The effective electron-bond-hopping amplitude fluctuates in sign as the total spin

  9. Vapor growth of electrochromic thin films of transition metal oxides

    NASA Astrophysics Data System (ADS)

    Gesheva, K. A.; Ivanova, T.; Marsen, B.; Zollo, G.; Kalitzova, M.

    2008-04-01

    Mixed oxide films of transition metals gain considerable much attention due to their interesting optoelectronic properties. The low temperature chemical vapor growth processing of thin films of mixed W and Mo oxides is presented. The investigation is related to optimization of films structure and the related optoelectronic properties in dependence on the chemical vapor deposition (CVD) process parameters. Their electrochromic behavior and photoelectrode properties were studied.

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

    E-print Network

    Ceder, Gerbrand

    Role of Electronic Structure in the Susceptibility of Metastable Transition-Metal Oxide Structures transition-metal ions in an oxide and how these factors in turn affect the resistance of metastable 3d transition-metal oxides against transformation. This is a relevant topic to the Li rechargeable battery field

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

    E-print Network

    Electronic structure of high-k transition metal oxides and their silicate and aluminate alloys G alloys of: i group IIIB, IVB, and VB transition metal TM oxides and ii first row RE oxides with SiO2 addresses differences between the electronic structure of: i alternative high-k transition metal TM rare

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

    E-print Network

    Alexander, Becky

    Transition metal-catalyzed oxidation of atmospheric sulfur: Global implications for the sulfur(IV)) oxidation by O2 catalyzed by transition metals. Due to the lack of photochemically produced OH and H2O2), Transition metal-catalyzed oxidation of atmospheric sulfur: Global implications for the sulfur budget, J

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

    E-print Network

    Metz, Ricardo B.

    Methane-to-Methanol Conversion by Gas-Phase Transition Metal Oxide Cations: Experiment and Theory-phase transition metal oxide cations can convert methane to methanol. Methane activation by MO+ is discussed-phase transition metal oxides with methane are thus a simple model system for the direct conversion of methane

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

    E-print Network

    2008-01-01

    Physica B 403 (2008) 1401­1403 Probing nanoscale inhomogeneities in transition metal oxides the universality of phase coexistence in complex transition metal oxides. r 2007 Elsevier B.V. All rights reserved-temperature superconductivity and colossal magnetoresistance in transition metal oxides is an intense area of contemporary

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

    Microsoft Academic Search

    Christian. Brandt; Rudi. van Eldik

    1995-01-01

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

  16. Novel Extended Solids Composed of Transition Metal Oxide Clusters

    NASA Astrophysics Data System (ADS)

    Ishaque Khan, M.

    2000-06-01

    Transition metal oxide clusters and their derivatives offer an unmatched variety of structural motifs that are potential building blocks for the design and development of extended solids. In view of the proven applications of these clusters in catalysis, molecular recognition, environmental decontamination, clinical and analytical processes, materials science, nanotechnology, and medicine, their usage as building blocks promises the development of new materials whose properties could be rationalized in terms of their constituents. Although the technique of assembling appropriate transition metal oxide clusters to generate new solids is still underdeveloped, recent progress made in this direction is promising. During our ongoing research program focused on this aspect, we have been able to prepare and characterize a series of novel framework materials, composed of well defined vanadium oxide clusters {V18O42(XO4)} (X=V, S, Cl). We have also prepared three-dimensional composite solids by incorporating organic ligands into the transition metal oxide framework. Some of the results of this work are reviewed with reference to the synthesis, structure, and physicochemical properties of the newly prepared extended solids.

  17. Colossal dielectric constants in transition-metal oxides

    Microsoft Academic Search

    P. Lunkenheimer; S. Krohns; S. Riegg; S. G. Ebbinghaus; A. Reller; A. Loidl

    2009-01-01

    .  \\u000a Many transition-metal oxides show very large (“colossal”) magnitudes of the dielectric constant and thus have immense potential\\u000a for applications in modern microelectronics and for the development of new capacitance-based energy-storage devices. In the\\u000a present work, we thoroughly discuss the mechanisms that can lead to colossal values of the dielectric constant, especially\\u000a emphasising effects generated by external and internal interfaces,

  18. Intermediate-valence behavior of the transition-metal oxide CaCu3Ru4O12

    Microsoft Academic Search

    A. Krimmel; A. Günther; W. Kraetschmer; H. Dekinger; N. Büttgen; V. Eyert; A. Loidl; D. V. Sheptyakov; E.-W. Scheidt; W. Scherer

    2009-01-01

    The transition-metal oxide CaCu3Ru4O12 with perovskite-type structure shows characteristic properties of an intermediate-valence system. The temperature-dependent susceptibility exhibits a broad maximum around 150-160 K. At this temperature, neutron powder diffraction reveals a small but significant volume change whereby the crystal structure is preserved. Moreover, the temperature-dependent resistivity changes its slope. NMR Knight shift measurements of Ru reveal a cross-over from

  19. Electrochromic displays with transition-metal oxide as counterelectrode

    Microsoft Academic Search

    Katsumi Kuwabara; Shoichi Ichikawa; Kohzo Sugiyama

    1987-01-01

    Amorphous WO3 electrochromic displays (ECD) with transition-metal oxides were investigated to determine fundamental factors for developing all-solid-state ECDs. The oxides examined were coO, NiO, SnO, Fe3O4, Co3O4, Ir2O3, VO2 and MnO2. Layers of solid electrolyte (tin phosphate) and each oxide were prepared by a spray method. The ECDs with VO2, Ir2O3 and MnO2 were found to give excellent characteristics such

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

    E-print Network

    Ceder, Gerbrand

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

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

    E-print Network

    Downs, Robert T.

    MAGNETIC COLLAPSE AND THE BEHAVIOR OF TRANSITION METAL OXIDES: FeO AT HIGH PRESSURES ** *** ****R- putations using the GGA (PW91) [8] and the LMTO-ASA method [9] were performed on the transition metal oxides insulator. Implications for geophysics are discussed. At low pressures transition metal ions such as ferrous

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

    E-print Network

    Ceder, Gerbrand

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

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

    E-print Network

    Ceder, Gerbrand

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  5. NEXAFS investigations of transition metal oxides, nitrides, carbides, sulfides and other interstitial compounds

    Microsoft Academic Search

    J. G. Chen

    1997-01-01

    Owing to their unique physical and chemical properties, transition metal compounds, especially transition metal oxides, nitrides, carbides and sulfides, have been the subject of many surface science investigations. In this article we will review applications of the near-edge X-ray absorption fine structure (NEXAFS) technique in the investigations of electronic and structural properties of transition metal compounds. This review covers NEXAFS

  6. Low temperature synthesis of transition metal oxides containing surfactant ions

    NASA Astrophysics Data System (ADS)

    Janauer, Gerald Gilbert

    1998-11-01

    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 transition metallates with long chain amine surfactants, such as dodecyltrimethylammonium bromide yielded interesting new products many of which are layered phases. DTAsb4\\ Hsb2Vsb{10}Osb{28}. 8Hsb2O, 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 P1-, cell parameters a=9.8945(3)A, b=11.5962(1)A, c=21.9238(2)A, alpha=95.153(2)sp°,\\ beta=93.778(1)sp°, and gamma=101.360(1)sp°. Additionally, a novel tungsten, a molybdenum and a dichromate phase will be discussed. Both the tungsten and the dichromate materials were indexed from their powder diffraction patterns yielding monoclinic unit cells. The tungsten material was found to have a=50.56(4)A, b=54.41(4)A, c=13.12(1)A, and beta=99.21sp°. The dichromate compound was determined to have a=26.757(5)A, b=10.458(2)A, c=14.829(3)A and beta=98.01(1)sp°. Interlayer spacings for the lamellar dichromate and molybdenum phases were d001 = 28.7 A, and d001 = 22.9 A. The synthesis, characterization, composition, and structure of these transition metal oxide-surfactant materials will be discussed.

  7. Resonant electron-exchange excitations in transition-metal oxides

    Microsoft Academic Search

    B. Fromme; M. Möller; C. Bethke; U. Brunokowski; E. Kisker

    1998-01-01

    Electron-exchange processes in dipole-forbidden d-d excitations of the 3d transition-metal oxides NiO, CoO, and MnO have been investigated by spin-polarized electron-energy-loss spectroscopy over a wide primary energy range and for different scattering geometries. At primary energies corresponding to certain excitation thresholds, the d-d excitations in CoO and MnO show resonant enhancement, similar to the resonances previously found for NiO. The

  8. Ionically-mediated electromechanical hysteresis in transition metal oxides

    SciTech Connect

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

    2012-01-01

    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.

  9. Thiosulfate oxidation: Catalysis of synthetic sphalerite doped with transition metals

    NASA Astrophysics Data System (ADS)

    Xu, Yong; Schoonen, Martin A. A.; Strongin, Daniel R.

    1996-12-01

    The rate of thiosulfate oxidation to tetrathionate by dissolved molecular oxygen was measured in aqueous suspensions of synthetic sphalerites doped with first row transition metals (Mn, Fe, Co, Ni, Cu). Pure sphalerite and Mn-doped sphalerite show no catalytic activity for this reaction. Catalytic activity increases from Fe to Ni, which has maximum activity, with a slight decrease moving to Cu. The catalytic activity of the doped sphalerites is proportional to the concentration of dopant. This trend in catalytic activity from pure sphalerite to Cu-doped sphalerite can be explained using the band structures of these solids.

  10. Scanning tunneling spectroscopy study of charge ordering, stripes and phase separation in manganese perovskite oxides

    Microsoft Academic Search

    Christoph Renner

    2007-01-01

    Colossal magnetoresistance (CMR) in perovskite-based transition metal oxides keeps challenging our understanding. Constant progress in scanning tunneling microscopy investigations is enabling increasingly detailed experimental insight into the different electronic and structural phases nucleating in these complex materials. I shall review the latest findings emerging from experiments on perovskite- and bilayer-manganites [1], which in particular, reveal the importance of lattice degrees

  11. New solid state routes to lithium transition metal oxides via reactions with lithium oxide

    Microsoft Academic Search

    Marco D. Aguas; Graham C. Coombe; Ivan P. Parkin

    1998-01-01

    Thermolysis of a mixture of lithium oxide and transition metal halides MXn (M = Ti, Zr, Hf, V, Nb, Ta, Mo, W, Fe, Mn) at 800°C for 2–12 h produces crystalline lithium transition metal oxides Li2MO3 (M = Ti, Zr, Hf, Mn), Li3MO4 (M = V, Nb, Ta), Li2MnO3 Li2Fe3O4 and Li2MO4 (M = Mo, W). For M = Cr,

  12. Oxidation energies of transition metal oxides within the GGA+U framework

    Microsoft Academic Search

    Lei Wang; Thomas Maxisch; Gerbrand Ceder

    2006-01-01

    The energy of a large number of oxidation reactions of 3d transition metal oxides is computed using the generalized gradient approach (GGA) and GGA+U methods. Two substantial contributions to the error in GGA oxidation energies are identified. The first contribution originates from the overbinding of GGA in the O2 molecule and only occurs when the oxidant is O2 . The

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

    E-print Network

    Wu, Junqiao

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

  14. Catalytic decomposition of N 2O over monolithic supported noble metal-transition metal oxides

    Microsoft Academic Search

    Viviane Boissel; Saad Tahir; Carolyn Ann Koh

    2006-01-01

    The decomposition of nitrous oxide to nitrogen and oxygen using a series of monolithic (ceria-alumina washcoated cordierite) supported transition metal (Cu, Fe, Co, Ni, Mn) and noble metal (Ir, Rh) oxide catalysts has been studied using gas chromatography. The effect of combining a transition metal with a noble metal has also been investigated. A synergetic effect was observed between transition

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

    E-print Network

    Islam, M. Saif

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

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

    PubMed Central

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

    2015-01-01

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

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

    PubMed

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

    2015-01-01

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

  18. Surface oxygen bond energy of Period IV transition metal oxides in the oxidation of carbon monoxide

    Microsoft Academic Search

    V. I. Marshneva; G. K. Boreskov

    1974-01-01

    The bond energies of oxygen have been determined by thermodesorption from Period IV transition metal oxides, both after treatment with oxygen and under steady state conditions of the catalytic oxidation of CO. With the exception of V2O5, there are several (2–3) forms of adsorbed oxygen with different bond energies on the surface of the oxide treated with oxygen.

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

    NASA Astrophysics Data System (ADS)

    Quan, Yundi; Pickett, Warren

    2015-03-01

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

  20. Catalytic Oxidation of 1,2Dichlorobenzene over Supported Transition Metal Oxides

    Microsoft Academic Search

    Sundaram Krishnamoorthy; Juan A. Rivas; Michael D. Amiridis

    2000-01-01

    The catalytic oxidation of 1,2-dichlorobenzene has been systematically investigated over a series of transition metal oxides (i.e., Cr2O3, V2O5, MoO3, Fe2O3, and Co3O4) supported on TiO2 and Al2O3. The activity of the different catalysts for this reaction depends on the nature of the transition metal oxide used, with Cr2O3-and V2O5-based catalysts being the most active ones. With the exception of

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

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

    Microsoft Academic Search

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

    2008-01-01

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

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

    E-print Network

    Savrasov, Sergej Y.

    Calculated Momentum Dependence of Zhang-Rice States in Transition Metal Oxides Quan Yin,1 Alexey in insulating transition metal oxides (TMOs) such as classical Mott­Hubbard systems or undoped high temperature to obtain accurate spectra of transition metal oxides and, in particular, describe full momentum dependent

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

    E-print Network

    Tebbens, Jurjen Duintjer

    Electronic structure of mixed valence transition metal oxides P. Nov´ak1 1 Institute of Physics: 1 #12;I. INTRODUCTION The character of the charge carriers in oxides of transition metals belongs repeatedly tried to understand the physics of the mixed valence transition metal oxides. Number of results

  5. Inter-network magnetic interactions in GdMe x Mn 1? x O 3 perovskites (Me=transition metal)

    Microsoft Academic Search

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

    2007-01-01

    The gadolinium-based manganite GdMnO3 of perovskite structure has been partially substituted at the manganese site by transition metal elements Me like Cu, Ni and Co, leading to a general formula GdMexMn1?xO3, in which different magnetic entities (e.g., Gd3+, Cu2+, Ni2+, Co2+, Co3+, Mn3+, Mn4+) can coexist, depending on charge equilibrium conditions. For divalent cations such as Cu2+ and Ni2+, the

  6. Spectroscopic studies of metal high-k dielectrics: transition metal oxides and silicates, and complex rare earth\\/transition metal oxides

    Microsoft Academic Search

    G. Lucovsky; J. G. Hong; C. C. Fulton; Y. Zou; R. J. Nemanich; H. Ade; D. G. Scholm; J. L. Freeouf

    2004-01-01

    This paper uses X-ray absorption spectroscopy to the study of electronic structure of the transition metal oxides TiO2, ZrO2 and HfO2, Zr and Hf silicate alloys, and the complex oxides, GdScO3, DyScO3 and HfTiO4. Qualitative and quantitative differences are identified between dipole allowed intra-atomic transitions from core p-states to empty d*- and s*-states, and inter-atomic transitions from transition metal and

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

    E-print Network

    Lin, Xi, 1973-

    2003-01-01

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

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

    E-print Network

    Sivakumar, Vikram

    2008-01-01

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

  9. Transition-Metal Oxides in Warm Circumstellar Environments

    NASA Astrophysics Data System (ADS)

    Schmidt, Miros?aw R.; Kaminski, Tomasz; Tylenda, Romuald

    2013-06-01

    We report on detections and simulations of electronic bands of transition-metal oxides, i.e. ScO, TiO, VO, CrO, YO, and of AlO, in spectra of two red novae V838 Mon and V4332 Sgr. These objects experienced a stellar merger event in 2002 and 1994, respectively, and have very rich circumstellar environments abundant in dust and molecules. We analyzed optical spectra of V838 Mon which show a presence of outflowing material. In this object, electronic systems of oxides are observed in absorption against a photospheric spectrum which resembles that of a late-type supergiant. We present simulations of the absorption bands which allowed us to derive the excitation temperatures of 300-500 K and constrain column densities, which turned out to be very high. Among many interesting features discovered, we identified forbidden transitions of TiO in the b^1?-X^3? and c^{1}?-X^{3}? systems, which are seen owing to the high column densities and the relatively low temperatures. In the case of the older red nova V4332 Sgr, the main object is surrounded by a circumstellar disc which is seen almost edge-on and obscures the central star. The molecular spectra are seen in emission in this object, what is very unusual in astrophysical sources observed at optical wavelengths. We show that these emission bands arise owing to the special geometry of the star-disk system and that radiative pumping is responsible for excitation of the molecules. From the shapes of the rotational contours, we derive temperatures of about 120 K in this object. Remarkably, the spectra of V4332 Sgr contain features of CrO, which is the first identified signature of this molecule in an astrophysical object. In addition to the excitation and radiative-transfer analysis of the molecular spectra, we discuss chemical pathways that could lead to the observed variety of metal oxides seen in these enigmatic sources. T. Kaminski, M. Schmidt, R. Tylenda, M. Konacki, and M. Gromadzki ApJSuppl., {182} (33), 2009. T. Kaminski, M. Schmidt and R. Tylenda Astronomy and Astrophysics, {522} (A75), 2010.

  10. Hybrid uranium-transition-metal oxide cage clusters.

    PubMed

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

    2014-12-15

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

  11. Transition-metal acceptor complexes in zinc oxide

    NASA Astrophysics Data System (ADS)

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

    2013-02-01

    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.

  12. Synthesis and characterization of transition metal and metal oxide nanoparticles inside mesoporous carbon CMK-3

    Microsoft Academic Search

    Holger Huwe; Michael Fröba

    2007-01-01

    Transition metal oxides were synthesized inside the pore system of mesoporous carbon CMK-3. By a wet impregnation, drying and calcination procedure iron, copper, nickel, cobalt, manganese and zinc oxides were formed almost exclusively within the mesopores. A reduction into the metal forms with regard to structural array in the case of zinc oxide and a reduction to manganese(II) oxide for

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

    PubMed

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

    2008-10-01

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

  14. The electronic structure of lithium transition metal oxides

    NASA Astrophysics Data System (ADS)

    Kocher, Michael P.

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

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

    SciTech Connect

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

    2009-06-15

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

  16. The 1s x-ray absorption pre-edge structures in transition metal oxides

    Microsoft Academic Search

    We develop a general procedure to analyse the pre-edges in 1s x-ray absorption near edge structure (XANES) of transition metal oxides and coordination complexes. Transition metal coordination complexes can be described from a local model with one metal ion. The 1s 3d quadrupole transitions are calculated with the charge-transfer multiplet program. Tetrahedral coordination complexes have more intense pre-edge structures due

  17. The 1s x-ray absorption pre-edge structures in transition metal oxides

    Microsoft Academic Search

    Frank de Groot; György Vankó; Pieter Glatzel

    2009-01-01

    We develop a general procedure to analyse the pre-edges in 1s x-ray absorption near edge structure (XANES) of transition metal oxides and coordination complexes. Transition metal coordination complexes can be described from a local model with one metal ion. The 1s 3d quadrupole transitions are calculated with the charge-transfer multiplet program. Tetrahedral coordination complexes have more intense pre-edge structures due

  18. Magnetic Collapse in Transition Metals Oxides at High Pressures

    Microsoft Academic Search

    R. E. Cohen; I. I. Mazin; D. G. Isaak

    1997-01-01

    We predict magnetic collapse (i.e. high-spin low-spin transitions) in transition metal ions using LMTO-ASA and LAPW methods and the GGA. Magnetic collapse under pressure results from band widening, rather than from changes in crystal field splitting. We find that the extended Stoner model is accurate in predicting the magnetic moments and transition pressures compared with our self-consistent calculations. The GGA

  19. Perovskite oxides: Oxygen electrocatalysis and bulk structure

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

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

  20. Factors that affect Li mobility in layered lithium transition metal oxides

    Microsoft Academic Search

    Kisuk Kang; Gerbrand Ceder

    2006-01-01

    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

  1. IR Studies of NH3, Pyridine, CO, and NO Adsorbed on Transition Metal Oxides

    Microsoft Academic Search

    Mayfair C. Kung; Harold H. Kung

    1985-01-01

    Chemisorption of small molecules is often used as a probe for By probing the surface properties of transition metal oxides. the interaction of molecules with the surface, information is often obtained on the oxidation state, the coordination symmetry, the degree of coordination unsaturation of the surface cations, the acid-base properties of the surface hydroxyl groups, and the presence and the

  2. Optical and ESR investigation of borate glasses containing single and mixed transition metal oxides

    Microsoft Academic Search

    A. K. Bandyopadhyay

    1981-01-01

    The optical and electron spin resonance (ESR) spectra of barium borate glasses, containing the oxides of V, Fe and Cu separately and in mixed proportions, have been studied. The optical spectra of the single transition metal (TM) oxide glasses showed the usual features, while those for the mixed glasses showed single bands without showing individual features of the single TM

  3. Ablation of transition metal oxides by different laser pulse duration and thin films deposition

    Microsoft Academic Search

    A. Giardini Guidoni; C Flamini; F Varsano; M Ricci; R Teghil; V Marotta; T. M Di Palma

    2000-01-01

    Thin films of transition metal oxides are of interest in many applications such as anticorrosion coatings and optical and electrochromic devices. In this work, the effect of different wavelength and pulse duration on ablation of oxides target has been investigated. The plume has been characterized by mass spectrometry and optical spectroscopy. Ablation thresholds have been measured by detecting ion emission

  4. Perovskite catalysts for oxidative coupling

    DOEpatents

    Campbell, K.D.

    1991-06-25

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

  5. Strong magnetic fluctuations in transition metal oxides (invited) Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, Maryland 21218

    E-print Network

    Broholm, Collin Leslie

    Strong magnetic fluctuations in transition metal oxides (invited) C. Broholm Department of Physics transition metal oxides. We discuss V1 xCrx 2O3, in which orbital fluctuations appear to limit spin effect. Emphasis is placed on the common features of exchange interactions in these oxides

  6. Transition Metal Oxide Catalyzed Carbon Black Oxidation: A Study with 18O 2

    Microsoft Academic Search

    Guido Mul; Freek Kapteijn; Ciska Doornkamp; Jacob A. Moulijn

    1998-01-01

    Physical mixtures of carbon black and several transition metal oxides (Cr2O3, Co3O4, Fe2O3, MoO3, V2O5, and K2MoO4) were treated batchwise in18O2at 625–675 K in a high-vacuum batch reactor. Three reaction mechanisms are proposed to be operative in the catalyzed oxidation of carbon black. The isotopic reaction product composition (C16O, C18O, C16O2, C16O18O, and C18O2) in experiments, in which18O2and16O2were fed alternately,

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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

    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.

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

    Microsoft Academic Search

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

    2004-01-01

    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

  9. TOPICAL REVIEW: Transition metal oxides using quantum Monte Carlo

    NASA Astrophysics Data System (ADS)

    Wagner, Lucas K.

    2007-08-01

    The transition metal-oxygen (TM-O) bond appears prominently throughout chemistry and solid-state physics. Many materials, from biomolecules to ferroelectrics to the components of supernova remnants contain this bond in some form. Many of these materials' properties strongly depend on fine details of the TM-O bond and intricate correlation effects, which make accurate calculations of their properties very challenging. We present quantum Monte Carlo, an explicitly correlated class of methods, to improve the accuracy of electronic structure calculations over that of more traditional methods like density functional theory. We find that unlike s-p type bonding, the amount of hybridization of the d-p bond in TM-O materials is strongly dependent on electronic correlation.

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

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

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

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

    SciTech Connect

    S.E. Ziemniak

    2000-05-18

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

  12. Structure and stability of rare-earth and transition-metal oxides

    Microsoft Academic Search

    Luca Marsella; Vincenzo Fiorentini

    2004-01-01

    The structural parameters of rare-earth oxides lanthania (La2O3) and ytterbia (YbO), and of transition-metal oxides yttria (Y2O3) and lutetia (Lu2O3), candidate replacements of silica as gate insulators in nanometric Si electronics, are determined via ab initio calculations. The stability against formation of silica, silicides, and silicates for these oxides in contact with silicon is also investigated: we find stability against

  13. OPTICAL COATINGS OF CVD-TRANSITION METAL OXIDES AS FUNCTIONAL LAYERS IN \\

    Microsoft Academic Search

    K. A. Gesheva; T. Ivanov; F. Hamelmann

    The paper presents the recent study on the technology and investigation of thin metal oxide films based on transition metals, such as W and Mo. Defined is the application aspect of the research, by describing the optical systems based on these films, namely the electrochromic device and the X-ray mirror. Results on the optical absorption in the films are presented,

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

    Microsoft Academic Search

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

    1999-01-01

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

  15. Microwave insertion loss measurements in phosphate glasses containing transition metal oxides

    Microsoft Academic Search

    P Bergo; W M Pontuschka; J M Prison; C C Motta

    2006-01-01

    The scope of this work is to report the results of microwave insertion loss measurements as a function of frequency and composition of some selected phosphate glasses containing transition metal oxide. Borosilicate glasses are commonly used in microwave travelling wave tubes, microwave windows, etc. They present very high microwave transmittance (low microwave insertion loss) in a certain frequency domain, which

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

    Microsoft Academic Search

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

    2008-01-01

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

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

    Microsoft Academic Search

    Tao He; Jiannian Yao

    2006-01-01

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

  18. Carbonyl clusters of transition metals on oxide supports as heterogeneous catalysts for hydrocarbon synthesis

    SciTech Connect

    Kuznetsov, B.N.; Koval`chuk, V.I. [Institute of Chemistry of Natural Organic Sources, Krasnoyarsk (Russian Federation)

    1995-05-01

    The methods of preparation of heterogeneous catalysts by immobilization of carbonyl clusters of transition metals on oxide supports, as well as the study of the state of supported compounds and their catalytic properties in CO hydrogenation and olefin hydroformulation are briefly reviewed.

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

    Microsoft Academic Search

    L. Bonneviot; M. Curie

    1988-01-01

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

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

    E-print Network

    Lin, Xi

    Chemistry of Sulfur Oxides on Transition Metals. III. Oxidation of SO2 and Self-Diffusion of O, SO2 to be an efficient ap- proach to determining the thermodynamics of sulfur oxides on transition metals such as Cu10 to be an effective SO2 oxidation and reduction catalyst. Interest in the chemistry of sulfur oxides on transition

  1. Orbital moment determination of simple transition metal oxides using magnetic X-ray diffraction

    Microsoft Academic Search

    W. Neubeck; C. Vettier; F. de Bergevin; F. Yakhou; D. Mannix; L. Ranno; T. Chatterji

    2001-01-01

    Non-resonant magnetic X-ray scattering (NRXMS) is a unique tool allowing the separation of the spin and orbital moment density contributions to the total magnetization density. This method has been successfully applied to the simple transition metal oxides: MnO, CoO and CuO. It is common habit to consider the orbital moment of these oxides to be quenched by the cubic crystal

  2. Reminiscences on the discovery of electrochromic phenomena in transition metal oxides

    Microsoft Academic Search

    Satyen K Deb

    1995-01-01

    It has long been known that transition metal oxides of the types WO3, MoO3, TiO2, V2O5, etc., show considerable variation in stoichiometry, and that very often the non-stoichiometric compounds are characterized by strong coloration. This observation led to the fabrication of highly disordered thin films of some of these oxides—ones that showed strong coloration upon optical excitation. Back in the

  3. Structure formation upon reactive direct current magnetron sputtering of transition metal oxide films

    SciTech Connect

    Ngaruiya, J.M.; Kappertz, O.; Mohamed, S.H.; Wuttig, M. [I. Physikalisches Institut der RWTH Aachen, D-52056 Aachen, Germany and Jomo Kenyatta University of Agriculture and Technology, Box 62000 Nairobi (Kenya); I. Physikalisches Institut der RWTH Aachen, D-52056 Aachen (Germany)

    2004-08-02

    A comparative study of reactive direct current magnetron sputtering for different transition metal oxides reveals crystalline films at room temperature for group 4 and amorphous films for groups 5 and 6. This observation cannot be explained by the known growth laws and is attributed to the impact of energetic particles, originating from the oxidized target, on the growing film. This scenario is supported by measured target characteristics, the evolution of deposition stress of the films, and the observed backsputtering.

  4. Spin and orbital ordering in ternary transition metal oxides 

    E-print Network

    Kimber, Simon A. J.

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

  5. IVb Transition Metal Oxides and Silicates: An Ab Initio Study

    Microsoft Academic Search

    Gian-Marco Rignanese

    Using density-functional theory, we investigate the structural, vibrational and dielectric properties of group IVb transition\\u000a metals (M=Hf, Zr, Ti) oxides and silicates which have drawn considerable attention as alternative high-k materials. For the\\u000a oxides, three crystalline phases of dioxide are considered. The first two are the cubic and tetragonal structures which exist\\u000a for hafnia HfO2 or zirconia ZrO2, while it

  6. Magnetopolaron-induced optical response in transition metal oxides

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

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

  7. Anti-microbial activities of aerosolized transition metal oxide nanoparticles.

    PubMed

    Wang, Zhipeng; Lee, Yi-Hsuan; Wu, Bing; Horst, Angela; Kang, Yisheng; Tang, Yinjie J; Chen, Da-Ren

    2010-07-01

    This study used the electrospray method to create airborne droplets of metal oxide nanoparticles (NPs) and examined their anti-microbial activities, employing Escherichia coli as a model microbial species. We tested the anti-microbial activities of six metal oxide NPs (NiO, ZnO, Fe(2)O(3), Co(3)O(4), CuO, and TiO(2)) in both an aqueous culture medium and an aerosol exposure mode (spraying the particles directly onto the cell surface). In the aqueous medium, the both NPs and stressed E. coli cells severely aggregated. Only NiO NPs (>20 mgL(-1)) showed significant growth inhibition of E. coli ( approximately 30%). In contrast to aqueous exposure, where the direct interactions between NPs and bacteria were limited, aerosol exposure of three metal oxide NPs to E. coli enhanced NP toxicity to cells and dramatically reduced cellular viability. Electrospraying NiO, CuO, or ZnO NPs (20 nm, 20 microg, in 10 min) reduced the total number of living E. coli by more than 88%, 77% and 71%, respectively (compared to the control experiments). However, TiO(2), Co(3)O(4), and Fe(2)O(3) NPs showed no significant antibacterial activities in either the aqueous exposure mode or the aerosol exposure mode. The above observations suggest the potential application of electrosprayed metal oxide NPs to disinfect airborne pathogens. PMID:20478610

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

    PubMed

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

    2015-01-28

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

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

    Microsoft Academic Search

    Harrell Sellers; Evgeny Shustorovich

    1997-01-01

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

  10. Theoretical investigation of hyperfine fields in fluoromethanes and transition metal oxides

    Microsoft Academic Search

    Gowri Gopalakrishnan

    1998-01-01

    Ab-initio Hartree-Fock Cluster procedure has been used to study Nuclear Quadrupole Interaction effects in molecular solid systems and Magnetic Hyperfine properties in antiferromagnetic transition metal oxides. Using the molecular orbital wave functions obtained from the Hartree-Fock calculations, the nuclear quadrupole interaction parameters, namely, the asymmetry parameter and quadrupole coupling constants are calculated at the fluorine site in CHsb{4-n}Fsb{n} (n =

  11. Self-interaction correction in multiple scattering theory -- Application to transition metal oxide

    Microsoft Academic Search

    Markus W Daene; Wolfram Hergert; Arthur Ernst; D. Ködderitzsch; Zdzislawa Szotek; Walter Temmerman; Hergert Wolfam

    2009-01-01

    In this work we study the electronic structure of 3d-transition metal oxides as obtained with the self-interaction corrected-local spin density approximation method, implemented within multiple scattering theory. We briefly describe the formalism and discuss important technical issues of its implementation within the KKR band structure method.We present results of such important properties as lattice constants, local magnetic moments, band gaps

  12. Thermal Expansion of the Heavy Fermion Transition Metal Oxide LiV_2O_4

    Microsoft Academic Search

    S. Kondo; C. A. Swenson; D. C. Johnston; O. Chmaissem; J. D. Jorgensen

    1998-01-01

    A crossover at ~30 K from high temperature (T) local moment to low-T heavy fermion (HF) behaviors in the metallic transition metal oxide LiV_2O4 was recently discovered.(S. Kondo et al.), Phys. Rev. Lett. 78, 3729 (1997). From neutron diffraction measurements(O. Chmaissem et al.), Phys. Rev. Lett. 79, 4866 (1997)., the linear thermal expansion coefficient alpha(T) decreases upon cooling from 295

  13. Electric quadrupole transitions in x-ray spectra: 3d transition-metal oxides

    Microsoft Academic Search

    N. V. Dobrodey; Yu. V. Luniakov

    1995-01-01

    The intensities of the electric quadrupole transitions in the x-ray spectra of the 3d-transition-metal monoxide diatomic molecules were calculated using the discrete variational method of the local-density approximation. The quadrupole transition intensities have been found to be negligible for the left-hand-side 3d metal oxides. It was shown that the electric quadrupole transitions can appreciably contribute to the MKbeta5 emission spectra

  14. LETTER TO THE EDITOR: High-resolution electron energy loss studies of some transition metal oxides

    Microsoft Academic Search

    J. P. Kemp; S. T. P. Davies; P. A. Cox

    1989-01-01

    High resolution electron energy loss spectra have been measured for a variety of first-row transition metal oxides for loss energies of up to 5 eV. The features observed are qualitatively consistent with the electronic properties of these materials (i.e., a highly damped plasmon for metals, and local d-d excitations for insulators), with the notable exception of CuO. Quantitatively, however, the

  15. Al 2O 3-supported transition-metal oxide catalysts for catalytic incineration of toluene

    Microsoft Academic Search

    Ching-Huei Wang

    2004-01-01

    The catalytic incineration of toluene over ?-Al2O3-supported transition-metal oxide catalysts in the temperature range of 200–380 °C was investigated employing a fixed bed flow reactor. CuO\\/?-Al2O3 was found to be the most active of seven catalysts tested. Using this catalyst with different wt% Cu in the incineration of toluene, we found that the optimal Cu content was 5 wt%. X-ray

  16. Mechanisms for Metal-Nonmental Transitions in Transition-Metal Oxides and Sulfides

    Microsoft Academic Search

    David Adler

    1968-01-01

    Transition-metal oxides and sulfides can be insulators, semiconductors, or metals, or undergo metal-nonmetal transitions. The experimental situation in these materials is briefly reviewed. Pure Bloch-Wilson theory predicts that many of the insulators should be metallic, so this class cannot be explained in terms of pure band theory. However, it now appears likely that band theory can be adapted to describe

  17. Thermoelectric properties of transition-metal oxide NaCo2O4 system

    Microsoft Academic Search

    H. Yakabe; K. Kikuchi; I. Terasaki; Y. Sasago; K. Uchinokura

    1997-01-01

    A transition-metal oxide NaCo2O4 system has been synthesized by a standard solid-state reaction method, and the thermoelectric properties have been measured. The resistivity ? and the thermoelectric power ? of the as-sintered NaCo2O 4 is 2 m?cm and 100 ?V\\/K at room temperature, respectively. By hot-pressing, the electrical resistivity is reduced to about 60%, and by Ba- or Bi-substitution for

  18. Synthesis and characterization of reduced transition metal oxides and nanophase metals with hydrazine in aqueous solution

    Microsoft Academic Search

    Zhou Gui; Rong Fan; Weiqin Mo; Xianhui Chen; Ling Yang; Yuan Hu

    2003-01-01

    Reduction of the first row (3d) transition metal complexes in aqueous solution using hydrazine as the reducing agent has been investigated systematically. Nanoscale reduced metal oxides such as VO2(B), Cr2O3 were obtained through hydrazine reduction followed by proper thermal treatments. Nanocrystalline ?-Mn2O3 was synthesized directly through aqueous phase reduction at room temperature. Nanoclusters of cobalt, copper and the one-dimensional single

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

    Microsoft Academic Search

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

    1989-01-01

    The oxygen 1s x-ray-absorption edges of a series of 3d-transition-metal oxides have been measured. The structures at the edge arise from covalent mixing of the metal and oxygen states, which introduces oxygen p character in unoccupied states of mainly metal character. The spectra can be divided into two regions: The first is a double-peaked sharp structure near threshold, which can

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

    Microsoft Academic Search

    George P. Anipsitakis; Dionysios D. Dionysiou

    2004-01-01

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

  1. Electronic structure and magnetic interactions in strongly correlated transition-metal oxides

    Microsoft Academic Search

    D. Ködderitzsch; W. Hergert

    2004-01-01

    Strongly correlated 3d-transition-metal oxides show a variety of interesting magnetic and electronic properties which make them potential candidates in the new field of spintronics. Due to strong on-site Coulomb-repulsions of 3d-electrons, density functional theory in local spin-density approximation (DFT–LSD) fails in giving an adequate electronic structure of these materials. Self-interacton corrected (SIC)–DFT–LSD strongly improves the description of such systems. Here

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

    Microsoft Academic Search

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

    2007-01-01

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

  3. Muon Localization in Transition Metal Oxides: NiO, CoO and CuO

    Microsoft Academic Search

    Steven Maples; Wayne Dawson; Carel Boekema; Kusuo Nishiyama

    1998-01-01

    Transition metal oxides form the basis for many unique phenomena in magnetism, superconductivity and ferroelectricity. CuO forms the framework structure of the majority of the high-temperature superconductors. The experimental results of recent muon spin rotation measurements in antiferromagnetic CuO, CoO, and NiO have been modeled using a combination of potential energy calculations and magnetic dipole calculation. Based upon this model,

  4. Late transition metal-oxo compounds and open-framework materials that catalyze aerobic oxidations

    Microsoft Academic Search

    Rui Cao; Jong Woo Han; Travis M. Anderson; Daniel A. Hillesheim; Kenneth I. Hardcastle; Elena Slonkina; Britt Hedman; Keith O. Hodgson; Martin L. Kirk; Djamaladdin G. Musaev; Keiji Morokuma; Yurii V. Geletii; Craig L. Hill

    2008-01-01

    After decades of speculation and attempted synthesis, terminal metal-oxo compounds of the late transition metal elements have been prepared. Terminal Pt-, Pd-, and Au-oxo complexes have been made using polytungstate ligands that share geometrical and electronic structural features and chemical properties (acid-base and others) in common with the metal oxides used as supports for these metals in myriad industrial catalytic

  5. Quantum confinement in transition metal oxide quantum wells

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    We report on the quantum confinement in SrTiO3 (STO) quantum wells (QWs) grown by molecular beam epitaxy. The QW structure consists of LaAlO3 (LAO) and STO layers grown on LAO substrate. Structures with different QW thicknesses ranging from two to ten unit cells were grown and characterized. Optical properties (complex dielectric function) were measured by spectroscopic ellipsometry in the range of 1.0 eV-6.0 eV at room temperature. We observed that the absorption edge was blue-shifted by approximately 0.39 eV as the STO quantum well thickness was reduced to two unit cells. This demonstrates that the energy level of the first sub-band can be controlled by the QW thickness in a complex oxide material.

  6. Tuning Magnetic Order in Transition Metal Oxide Thin Films

    NASA Astrophysics Data System (ADS)

    Grutter, Alexander John

    In recent decades, one of the most active and promising areas of condensed matter research has been that of complex oxides. With the advent of new growth techniques such as pulsed laser deposition and molecular beam epitaxy, a wealth of new magnetic and electronic ground states have emerged in complex oxide heterostructures. The wide variety of ground states in complex oxides is well known and generally attributed to the unprecedented variety of valence, structure, and bonding available in these systems. The tunability of this already diverse playground of states and interactions is greatly multiplied in thin films and heterostructures by the addition of parameters such as substrate induced strain and interfacial electronic reconstruction. Thus, recent studies have shown emergent properties such as the stabilization of ferromagnetism in a paramagnetic system, conductivity at the interface of two insulators, and even exchange bias at the interface between a paramagnet and a ferromagnet. Despite these steps forward, there remains remarkable disagreement on the mechanisms by which these emergent phenomena are stabilized. The contributions of strain, stoichiometry, defects, intermixing, and electronic reconstruction are often very difficult to isolate in thin films and superlattices. This thesis will present model systems for isolating the effects of strain and interfacial electronic interactions on the magnetic state of complex oxides from alternative contributions. We will focus first on SrRuO3, an ideal system in which to isolate substrate induced strain effects. We explore the effects of structural distortions in the simplest case of growth on (100) oriented substrates. We find that parameters including saturated magnetic moment and Curie temperature are all highly tunable through substrate induced lattice distortions. We also report the stabilization of a nonmagnetic spin-zero configuration of Ru4+ in tetragonally distorted films under tensile strain. Through growth on (110) and (111) oriented substrates we explore the effects of different distortion symmetries on SrRuO3 and demonstrate the first reported strain induced transition to a high-spin state of Ru 4+. Finally, we examine the effects of strain on SrRuO3 thin films and demonstrate a completely reversible universal out-of-plane magnetic easy axis on films grown on different substrate orientations. Having demonstrated the ability to tune nearly every magnetic parameter of SrRuO 3 through strain, we turn to magnetic properties at interfaces. We study the emergent interfacial ferromagnetism in superlattices of the paramagnetic metal CaRuO3 and the antiferromagnetic insulator CaMnO3 and demonstrate that the interfacial ferromagnetic layer in this system is confined to a single unit cell of CaMnO3 at the interface. We discuss the remarkable oscillatory dependence of the saturated magnetic moment on the thickness of the CaMnO3 layers and explore mechanisms by which this oscillation may be stabilized. We find long range coherence of the antiferromagnetism of the CaMnO3 layers across intervening layers of paramagnetic CaRuO3. Finally, we utilize the system of LaNiO3/CaMnO3 to separate the effects of intermixing and interfacial electronic reconstruction and conclusively demonstrate intrinsic interfacial ferromagnetism at the interface between a paramagnetic metal and an antiferromagnetic insulator. We find that the emergent ferromagnetism is stabilized through interfacial double exchange and that the leakage of conduction electrons from the paramagnetic metal to the antiferromagnetic insulator is critical to establishing the ferromagnetic ground state.

  7. Low potential Li insertion in transition metal oxides

    SciTech Connect

    Leroux, F.; Nazar, L.F.

    1998-07-01

    Low-potential Li insertion materials comprised of molybdenum oxides (A{sub x}MoO{sub 3}) have been prepared by a chimie douce route. Li insertion below 200 mV is associated with dramatic transformation of the structure, leading to a material which displays good cycloability with a high reversible specific capacity of 940 mA/g in the voltage window 3.0--0.005V (volumetric capacity of 4,000 mAh/cc), albeit with notable polarization on charge. The structural and compositional changes on discharge to 200 mV have been studied by a combination of XRD, and XAS. The interlayer ions have also been exchanged for Sn, and the electrochemical characteristics of these materials are compared with the alkali derivatives.

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

    Microsoft Academic Search

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

    2003-01-01

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

  9. High temperature Faraday balance for in situ measurement of magnetization in transition metal oxides

    NASA Astrophysics Data System (ADS)

    Baskar, D.; Adler, S. B.

    2007-02-01

    We report the design of a Faraday balance that can be used to measure the magnetization of transition metal oxides at high temperatures and under controlled atmosphere. The instrument is sufficiently sensitive and stable to quantify the magnetic force on diamagnetic and paramagnetic samples at temperatures up to 1000°C and in oxygen partial pressures as low as 100ppm. We demonstrate the performance of the instrument by presenting preliminary magnetic measurements of lanthanum strontium cobalt oxide (La1-xSrxCoO3-?) and aluminum oxide (Al2O3).

  10. Bonding Model for Transition Metal and Rare Earth Monoxides and Laser Spectroscopy of Nickel-Oxide

    NASA Astrophysics Data System (ADS)

    Srdanov, Vojislav I.

    We discovered that, for the transition metal and the rare earth monoxide series, the sum of the ionization potential of the metal, the energy of the lowest ( ...np) configuration of the metal ion and the thermochemical dissociation energy of the molecule adds up to a constant number. The correlation is particularly striking for the rare earth monoxides where the standard deviation is less than 1%. Based on this correlation we developed a new bonding scheme common for both the transition metal and rare earth monoxides. We propose that the bonding is invariant within the series and consists of an ionic and a covalent contribution. In our model a covalent contribution to the bonding of the inner-core d and f orbitals is negligible. This is in contrast to the current paradigm regarding the significant role of the d orbitals in the bonding in the first and second row transition metal oxides. Our model also appears to be in conflict with the M^{2+} O^{2-} ligand-field bonding model currently accepted for the rare earth monoxides. Based on the empirical correlation and the proposed bonding mechanism, however, we give a number of predictions regarding yet unmeasured fundamental quantities of some of the oxides such as permanent dipole moments, dissociation energies and equilibrium bond distances. We also present the results of the first high resolution laser spectroscopic study of the NiO molecule. Several bands in the green spectral region were found to originate from the ground state of NiO; their analysis allowed us to determine the following fundamental parameters: Ground state symmetry: ^3Sigma^-; Vibrational frequency: omega_{ rm e} = 8.39.1 cm^{ -1}; Equilibrium distance: r_ {rm e} = 1.627 A. With this work the determination of the ground state parameters for the first row transition metal oxides is now complete.

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

    DOEpatents

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

    1985-08-16

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

  12. High-Pressure Synthesis of 5d Cubic Perovskite BaOsO3 at 17 GPa: Ferromagnetic Evolution over 3d to 5d Series

    E-print Network

    Wang, Wei Hua

    . INTRODUCTION Transition metal oxides, which are electronically and magneti- cally active, are emerging a series of transition metal oxides that can aid in the mapping of the properties of these materials would of transition metal oxides have focused on perovskite-based 5d oxides since the properties of the correlated 5d

  13. Are matrix isolated species really “isolated”? Infrared spectroscopic and theoretical studies of noble gas-transition metal oxide complexes

    Microsoft Academic Search

    YanYing Zhao; MingFei Zhou

    2010-01-01

    In this review, we summarize our recent results on matrix isolation infrared spectroscopic studies and theoretical investigations\\u000a of noble gas-transition metal oxide complexes. The results show that some transition metal oxide species trapped in solid\\u000a noble gas matrices are chemically coordinated by one or multiple noble gas atoms forming noble gas complexes and, hence, cannot\\u000a be regarded as isolated species.

  14. Anisotropic grain growth of mullite in high-energy ball milled powders doped with transition metal oxides

    Microsoft Academic Search

    L. B. Kong; T. S. Zhang; J. Ma; F. Boey

    2003-01-01

    Dense mullite ceramics with anisotropic grains were derived from the high-energy ball milled mixtures of Al2O3 and amorphous silica with the presence of transition metal oxides (FeO1.5, CoO and NiO). The mullitization and grain growth behavior of the unmilled mixture without the addition of the transition metal oxides and the undoped system of Al2O3 and amorphous silica with and without

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

    NASA Astrophysics Data System (ADS)

    Wang, Huamin; Wu, Zijie; Kong, Jing; Wang, Zhiqiang; Zhang, Minghui

    2012-10-01

    Metastable transition metal oxides were used as precursors to synthesize transition metal nitrides at low temperature. Amorphous MoO2 was prepared by reduction of (NH4)6Mo7O24 solution with hydrazine. As-synthesized amorphous MoO2 was transformed into fcc ?-Mo2N at 400 °C and then into hexagonal ?-MoN by further increasing the temperature to 600 °C under a NH3 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 Ni2Mo3N 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.

  16. Ultrasonic study on some borosilicate glasses doped with different transition metal oxides

    NASA Astrophysics Data System (ADS)

    Marzouk, S. Y.; Gaafar, M. S.

    2007-12-01

    Longitudinal and shear ultrasonic wave velocities were measured in borosilicate glasses doped with different transition metal oxides (TMOs) (where TMO=NiO, V 2O 5, Fe 2O 3, MnO 2, TiO 2, Cr 2O 3, CoO, CuO) using the pulse echo technique. Measurements were carried out at 4 MHz frequency and at room temperature. Elastic moduli and some other physical parameters such as acoustic impedance, softening temperature, Debye temperature, thermal expansion coefficient, and latent heat of melting have been calculated. Results indicated that these parameters depend upon the TMO modifier, i.e., the ionic radius of the transition metal cation. A quantitative analysis has been carried out, in order to obtain more information about the structure of these glasses, based on bond compression model, and the Makishima and Mackenzie model, i.e., the cation-anion bond of each TMO.

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

    SciTech Connect

    Boffa, A B [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry

    1994-07-01

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

  18. Electric quadrupole transitions in x-ray spectra: 3d transition-metal oxides

    NASA Astrophysics Data System (ADS)

    Dobrodey, N. V.; Luniakov, Yu. V.

    1995-02-01

    The intensities of the electric quadrupole transitions in the x-ray spectra of the 3d-transition-metal monoxide diatomic molecules were calculated using the discrete variational method of the local-density approximation. The quadrupole transition intensities have been found to be negligible for the left-hand-side 3d metal oxides. It was shown that the electric quadrupole transitions can appreciably contribute to the MK?5 emission spectra of the right-hand-side 3d metal oxides, along with the dipole transitions.

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

    Microsoft Academic Search

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

    2003-01-01

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

  20. Styrene epoxidation over gold supported on different transition metal oxides prepared by homogeneous deposition–precipitation

    Microsoft Academic Search

    N. S. Patil; B. S. Uphade; D. G. McCulloh; S. K. Bhargava; V. R. Choudhary

    2004-01-01

    Epoxidation of styrene by anhydrous tert-butyl hydroperoxide over a number of transition metal oxide (viz. TiO2, Cr2O3, MnO2, Fe2O3, Co3O4, NiO, CuO, ZnO, Y2O3, ZrO2, La2O3 and U3O8) supported nano-size gold catalysts, prepared by the homogeneous deposition–precipitation method, has been investigated. The supported gold catalysts (except Au\\/MnO2 and Au\\/U3O8) showed good styrene conversion activity and selectivity for styrene oxide in

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

    Microsoft Academic Search

    S. Tsivilis; G. Kakali

    1997-01-01

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

  2. Ablation of transition metal oxides by different laser pulse duration and thin films deposition

    NASA Astrophysics Data System (ADS)

    Giardini Guidoni, A.; Flamini, C.; Varsano, F.; Ricci, M.; Teghil, R.; Marotta, V.; Di Palma, T. M.

    2000-02-01

    Thin films of transition metal oxides are of interest in many applications such as anticorrosion coatings and optical and electrochromic devices. In this work, the effect of different wavelength and pulse duration on ablation of oxides target has been investigated. The plume has been characterized by mass spectrometry and optical spectroscopy. Ablation thresholds have been measured by detecting ion emission from the target and from the onset of the plume luminescence. Morphology and optical properties of thin films deposited in different conditions are presented.

  3. A facile approach toward transition metal oxide hierarchical structures and their lithium storage properties.

    PubMed

    Zhang, Cuimiao; Chen, Jing; Zeng, Yi; Rui, Xianhong; Zhu, Jixin; Zhang, Wenyu; Xu, Chen; Lim, Tuti Mariana; Hng, Huey Hoon; Yan, Qingyu

    2012-06-21

    A simple, non-template, non-surfactant and environmentally friendly hydrothermal method is presented based on the controlled release of the reactants into the reaction solvents to induce slow nucleation and growth of three-dimensional hierarchical nanostructures of transition metal oxides. This method is a general approach, which can be used to prepare Co(3)O(4), CuO, and Ni(OH)(2)/NiO. These metal oxides with hierarchical nanostructures can be used as anode materials for lithium-ion batteries with good Li storage performance, e.g. high specific capacities and stable cyclability. PMID:22618758

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

    PubMed

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

    2013-11-18

    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

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

    E-print Network

    Goddard III, William A.

    Methane Activation by Transition-Metal Oxides, MOx (M ) Cr, Mo, W; x ) 1, 2, 3) Xin Xu,# Francesco a MoO3/HZSM-5 catalyst stimulated us to examine methane activation by the transition-metal oxide oxidation state form (MO3) of the heavier metals, as well as all chromium oxides (CrOx). Instead, oxidative

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

    USGS Publications Warehouse

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

    1996-01-01

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

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

    PubMed

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

    2014-04-25

    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

  8. A facile approach toward transition metal oxide hierarchical structures and their lithium storage properties

    NASA Astrophysics Data System (ADS)

    Zhang, Cuimiao; Chen, Jing; Zeng, Yi; Rui, Xianhong; Zhu, Jixin; Zhang, Wenyu; Xu, Chen; Lim, Tuti Mariana; Hng, Huey Hoon; Yan, Qingyu

    2012-05-01

    A simple, non-template, non-surfactant and environmentally friendly hydrothermal method is presented based on the controlled release of the reactants into the reaction solvents to induce slow nucleation and growth of three-dimensional hierarchical nanostructures of transition metal oxides. This method is a general approach, which can be used to prepare Co3O4, CuO, and Ni(OH)2/NiO. These metal oxides with hierarchical nanostructures can be used as anode materials for lithium-ion batteries with good Li storage performance, e.g. high specific capacities and stable cyclability.A simple, non-template, non-surfactant and environmentally friendly hydrothermal method is presented based on the controlled release of the reactants into the reaction solvents to induce slow nucleation and growth of three-dimensional hierarchical nanostructures of transition metal oxides. This method is a general approach, which can be used to prepare Co3O4, CuO, and Ni(OH)2/NiO. These metal oxides with hierarchical nanostructures can be used as anode materials for lithium-ion batteries with good Li storage performance, e.g. high specific capacities and stable cyclability. Electronic supplementary information (ESI) available: XRD, SEM, BET, Coulombic efficiency, and cycling performance of the as-obtained products. See DOI: 10.1039/c2nr30525a

  9. The Study of Transition Metal Oxides using Dynamical Mean Field Theory

    NASA Astrophysics Data System (ADS)

    Dang, Hung The

    In this thesis, we study strong electron correlation in transition metal oxides. In the systems with large Coulomb interaction, especially the on-site interaction, electrons are much more correlated and cannot be described using traditional one-electron picture, thus the name "strongly correlated systems". With strong correlation, there exists a variety of interesting phenomena in these systems that attract long-standing interests from both theorists and experimentalists. Transition metal oxides (TMOs) play a central role in strongly correlated systems, exhibiting many exotic phenomena. The fabrication of heterostructures of transition metal oxides opens many possible directions to control bulk properties of TMOs as well as revealing physical phases not observed in bulk systems. Dynamical mean-field theory (DMFT) emerges as a successful numerical method to treat the strong correlation. The combination of density functional and dynamical mean-field theory (DFT+DMFT) is a prospective ab initio approach for studying realistic strongly correlated materials. We use DMFT as well as DFT+DMFT methods as main approaches to study the strong correlation in these materials. We focus on some aspects and properties of TMOs in this work. We study the magnetic properties in bulk TMOs and the possibility of enhancing the magnetic order in TMO heterostructures. We work on the metallic/insulating behaviors of these systems to understand how the metal-insulator transition depends on the intrinsic parameters of materials. We also investigate the effect of a charged impurity to the neighborhood of a correlated material, which can be applied, for example, to the study of muon spin relaxation measurements in high-Tc superconductors.

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

    NASA Astrophysics Data System (ADS)

    Ralko, Arnaud; Merino, Jaime; Fratini, Simone

    2015-04-01

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

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

    SciTech Connect

    Lucovsky, G.; Luning, J.

    2009-06-04

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

  12. Reactive Ion Etching Process of Transition-Metal Oxide for Resistance Random Access Memory Device

    NASA Astrophysics Data System (ADS)

    Takano, Fumiyoshi; Shima, Hisashi; Muramatsu, Hidenobu; Kokaze, Yutaka; Nishioka, Yutaka; Suu, Koukou; Kishi, Hirofumi; Buntimil Arboleda, Nelson, Jr.; David, Melanie; Roman, Tanglaw; Kasai, Hideaki; Akinaga, Hiro

    2008-08-01

    The reactive ion etching (RIE) of the binary transition-metal oxides (TMOs) NiO, CuO and CoO, which are expected to be key materials of resistance random access memory (RRAMTM), was investigated. We found that inductively coupled plasma using CHF3-based discharge, which is highly compatible with conventional semiconductor RIE, is effective for the TMOs studied here. Furthermore, device fabrication using Pt/CoO/Pt trilayers is carried out, and a large change in resistance, which is an essential functionality of RRAM, was successfully observed. This should be definite evidence of a successful RIE realized in the present device fabrication.

  13. X-ray emission spectra and valence band structure of the 3d transition metal oxides

    Microsoft Academic Search

    V. R. Galakhov; S. M. Butorin; E. Z. Kurmaev; M. A. Korotin

    1991-01-01

    X-ray emission oxygen Kalpha and 3d transition metal Lalpha spectra for MnO, FeO, CoO, NiO, and CuO have been compared in the same energy scale by using Me 2p and O 1s binding energies. In the valence band of CuO the so-called d-p resonance between Cu 3d and O 2p states was observed. The 3d metal Lalpha-spectra for these oxides

  14. Oxygen 17 NMR on the 5d transition metal oxide Sr2IrO4

    NASA Astrophysics Data System (ADS)

    Crocker, John; Shapiro, Maxwell; Fisher, Ian; Riggs, Scott; Curro, Nicholas

    2014-03-01

    5d transition metal oxides (TMO) have attracted attention in recent years due to their high spin orbit coupling which can cause the crystal field wavefunctions to become complex. One TMO, Sr2IrO4, has been shown to exhibit ferromagnetic and non-ohmic behavior. Here we present O-17 nuclear magnetic resonance (NMR) measurements on a single crystal Sr2IrO4. After substituting O-16 for O-17 we are able to observe the temperature dependence of the oxygen resonances and are able to extract: knight shift (K), electronic field gradient (EFG), and spin lattice relaxation rate (1/T1) parameters.

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

    SciTech Connect

    Shitade, Atsuo

    2010-05-26

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

  16. Catalytic behavior of transition metal oxide in graphite gasification by oxygen, water, and carbon dioxide

    SciTech Connect

    Pan, Z.J.; Yang, R.T. (State Univ. of New York, Buffalo (USA))

    1991-07-01

    Vanadium oxide is used as a model transition metal-oxide catalyst for the gasification of graphite by O{sub 2}, H{sub 2}O, and CO{sub 2}. The following catalyst actions on the graphite basal plane are common in all three reactions: deep layer channeling, monolayer channeling, edge recession, and widening monolayer channeling. The steady-state oxidation states of vanadium in the reactions with CO{sub 2} and H{sub 2}O are, respectively, V{sub 3}O{sub 5} and V{sub 2}O{sub 3} under the reaction conditions. The rate-limiting step in all channeling actions (for all three gasification reactions) is oxidation on the surface of the metal-oxide to increase the oxygen activity. Oxygen then diffuses through the nonstoichiometric metal-oxide particle to reach the carbon active sites where gasification takes place. (However, based on the channeling and TGA rate data, the catalyst surface oxidation is the rate-limiting step; the subsequent steps of diffusion of oxygen anion and C-C bond breakage steps are not rate-limiting.) This mechanism can explain the fact that transition metal-oxides are the most active catalysts for the C + O{sub 2} reaction but are only weakly active for the C + H{sub 2}O and C + CO{sub 2} reactions. The origin of the phenomenon of the widening monolayer channels is attributed to the anisotropy of the catalyzed reactivities of two adjacent zigzag edges of graphite.

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

    E-print Network

    Napp, Nils

    Reports The interactions between transition metal nanoparticles and their metal- oxide supports at the metal-support interface is widely regarded as the key step in room-temperature CO oxidation (13 water, surface hydroxyls, and the metal-support inter- face interact during CO oxidation over Au/TiO2

  18. Low temperature synthesis of lamellar transition metal oxides containing surfactant ions

    SciTech Connect

    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

    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.

  19. Dielectric properties of crystalline and amorphous transition metal oxides and silicates

    NASA Astrophysics Data System (ADS)

    Rignanese, Gian-Marco

    2004-03-01

    Until recently, silicon dioxide has been the dielectric of choice in integrated MOS devices. By 2004, the thickness of this insulating layer is expected to decrease to 1.0 nm to 1.5 nm (about five silicon atoms deep) precluding its effective use due to severe leakage problems. An alternative high-permittivity (high-k) gate dielectric is required. In this framework, transition metal oxides and silicates have attracted considerable attention as possible substitutes. Their dielectric properties constitute an issue of great practical relevance. In particular, it is highly desirable to develop a better understanding of how the permittivity is related to the underlying microstructure. This is the aim of the present work. Using first-principles calculations, we investigate the dielectric properties of group IVB transition metal (Ti, Zr, and Hf) oxides and silicates. We first study various crystalline phases for the oxides (cubic, tetragonal, and rutile) and the silicates (zircon). Then, the amorphous silicates are considered. We introduce a scheme which relates the dielectric constants to the local bonding of silicon and metal atoms. This scheme is based on the definition of parameters characteristic of the basic structural units formed by silicon and metal atoms and their nearest neighbors, and allows us to avoid heavy large-scale calculations, which are beyond current computational capabilities. Applied to amorphous Zr silicates, our scheme provides a good description of the measured dielectric constants, and highlights the role of sixfold coordinated metal atoms.

  20. Lithium Diffusion in Lithium-Transition-Metal Oxides Detected by ?+SR

    NASA Astrophysics Data System (ADS)

    Sugiyama, Jun; Mukai, Kazuhiko; Nozaki, Hiroshi; Harada, Masashi; Kamazawa, Kazuya; YutakaIkedo; Månsson, Martin; Ofer, Oren; Ansaldo, Eduardo J.; Brewer, Jess H.; Chow, Kim H.; IsaoWatanabe; Miyake, Yasuhiro; Ohzuku, Tsutomu

    Diffusion of Li+ ionsin solidsisa basic principle behindthe operationof Li-ion batteries. Suchdiffusive behavior is represented by the diffusion equation (Fick's law), J = -D × ??/?x, where J is the diffusion flux, D is the self diffusion coeffcient, ? is the concentration, and x is the position. Although D of Li+ ions(DLi)in solids is usually evaluatedby 7Li-NMR, diffculties arise for materials that contain magnetic ions. This is because the magnetic ions contribute additional spin-lattice relaxation processes thatis considerably larger than the1/T1 expected from only Li diffusion[1-3]. This implies that 7Li-NMRprovidesa rough estimateof DLi for the positive electrode materials of Li-ion batteries, which include transition metal ions in order to compensate charge neutrality during a Li+ intercala-tion/deintercalation reaction. This is an unsatisfactory situation since DLi is one of the primary parameters that govern the charge/discharge rate of a Li-ion battery. We have, therefore, attempted to measure DLi for lithium-transition-metal-oxides with muon-spin relaxation (?+SR) since 2005 [4-6]. Muons do not feel fluctuating magnetic moments at high T, but instead sense the change in nuclear dipole field due to Li diffusion. Even if magnetic moments still affect the muon-spin depolarization rate, such aneffectis, in principle, distinguishablefromthatof nucleardipole fields.In particular,aweak longitudinal field can be applied that decouples the magnetic and nuclear dipole interactions [7,8]. Here, we wish to summarize our ?+SR study on the lithium-transition-metal-oxides, LixCoO2, LiNiO2, and LiCrO2.

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

    SciTech Connect

    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

    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.

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

    SciTech Connect

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

    2014-07-28

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

  3. Theoretical investigation of hyperfine fields in fluoromethanes and transition metal oxides

    NASA Astrophysics Data System (ADS)

    Gopalakrishnan, Gowri

    Ab-initio Hartree-Fock Cluster procedure has been used to study Nuclear Quadrupole Interaction effects in molecular solid systems and Magnetic Hyperfine properties in antiferromagnetic transition metal oxides. Using the molecular orbital wave functions obtained from the Hartree-Fock calculations, the nuclear quadrupole interaction parameters, namely, the asymmetry parameter and quadrupole coupling constants are calculated at the fluorine site in CHsb{4-n}Fsb{n} (n = 1,2,3) and CHClFsb2 molecules. In addition to these molecules, the possibility of complexing of HF* molecule to these host molecules is also investigated. This complex formation is found to give rise to a second frequency at the fluorine site arising from the fluorine atom of the HF* hydrogen bonded to the host molecule. All of these results agree well with those from Time Dependent Perturbed Angular Distribution measurements of quadrupole interactions at the fluorine site in these systems. Theoretical investigations have also been carried out for the transition metal oxides NiO and MnO in antiferromagnetic state. The location of the muon in the two oxides and the associated electronic structure and muon hyperfine properties have been investigated. Eight equilibrium positions for the muon are found around each oxygen ion in the crystal, of which two are found to have substantially stronger stability than the other six. Direct and exchange contributions to the contact and dipolar hyperfine fields from within the cluster and dipolar fields from outside, are evaluated for each of the equilibrium locations of the muon and are shown to lead to three sets of hyperfine fields. The nature of the potential experienced by the muon as it travels between the equilibrium sites is studied to understand its dynamics inside the solid. The rates of hopping between each of the two equivalent most stable sites, where the muon most strongly trapped, and the other six sites are studied. In each case, the combination of tunneling and rotational diffusion effects was most pronounced for movement of the muon to three other neighboring sites, the frequency of muon hopping to these being four orders of magnitude stronger than the muon precession frequencies at the four sites. This justifies taking an average of the hyperfine fields at the four sites leading one to expect only a single hyperfine field in both NiO and MnO, in agreement with the from muon spin rotation (mu SR) measurements. Additionally, after inclusion of spin fluctuation effects in the antiferromagnetic state, the calculated hyperfine fields agree with experiment to within fifteen percent in both cases. The temperature dependence of the mu SR frequencies are quite well explained by those of the magnetic moments on the transition metal ions. These good agreements between experiment and theory demonstrate that the Hartree-Fock Cluster procedure can provide simultaneously satisfactory descriptions of the locations of muons, associated electronic structure and the dynamics of muon in transition metal oxides. Suggestions are made for further improvements in theory, involving the role of many-body effects in solid fluoromethanes and muons in transition metal oxides and detailed investigations of lattice distortion in the latter systems. Possible reasons emerging from the present work to explain the multiple mu SR frequencies in CoO and CuO are discussed.

  4. Electrochemical characterization of lithiated transition metal oxide cathode particles in the absence of carbon, binders and other additives

    Microsoft Academic Search

    Dana A Totir; Boris D Cahan; Daniel A Scherson

    1999-01-01

    A novel method is herein described for the electrochemical characterization of lithiated transition metal oxides in powder form as cathode materials for lithium ion batteries. The procedure involves application of sufficiently high pressures to a layer of oxide powder evenly dispersed on the surface of a Au foil so as to embed the particles into the soft metal substrate, thereby

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

    PubMed

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

    2015-01-01

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

  6. STM Image Contrast Interpretation and its Role in Determining the Structure of Transition Metal Oxide Surfaces

    NASA Astrophysics Data System (ADS)

    Lu, Weier

    1995-01-01

    The surfaces of transition metal oxides play a critical role in many applications such as heterogeneous catalysis, gas detection, thermionic emission, electrolysis, and photolysis. Understanding the mechanisms of such surface processes requires a detailed knowledge of the surface microscopic structure. Since its invention in the early 1980's, scanning tunneling microscopy (STM) has come to be a popular tool for oxide surface studies. However, despite some experimental successes, interpretation of the contrast in STM images of metal oxides has remained challenging due to the numerous contributing factors such as nonstoichiometry, structural complexity, surface disorder, and uncertainties regarding the bonding and termination layers in such multicomponent systems. In this thesis work, a computer simulation scheme that explores these effects separately has been developed to assist the interpretation of atomic-scale contrast in STM images. A semiquantitative technique, based on the one -dimensional square well tunneling model, is used to simulate constant current STM images. This model provides an efficient mechanism to test and explore effects of various ill-defined experimental parameters. The method was applied to the atomic-scale resolution STM study of three transition metal oxides: {rm M_{x}WO _3} (M=Rb, Na), {rm Mo_{18}O_{52}}, and V_2{rm O}_5. Our observations include surface termination layer variations, surface ordering, surface relaxations, surface steps caused by crystallographic shear (CS) planes, surface oxygen vacancies and other defects. In each case, the competition between geometric and electronic contributions to the image contrast is evident. Tunneling spectroscopy experiments and calculations were also performed on the sodium tungsten bronzes and the implication to their electronic structures is discussed.

  7. ACCEPTED MANUSCRIPT Oxidation kinetics of Ni metallic films: formation of NiO-based resistive switching structures

    E-print Network

    Paris-Sud XI, Université de

    ) structures in which the resistive oxide was simple transition metal oxide thin films such as NiO or TiO2) to inorganic materials (e.g. chalcogenide alloys, perovskite-type oxides or transition metal oxides (i.e. ON state). Among transition metal oxides, NiO is a promising material due to its compatibility

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

    NASA Astrophysics Data System (ADS)

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

    2013-01-01

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

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

    SciTech Connect

    Richard T. Scalettar; Warren E. Pickett

    2005-08-02

    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: (i) Mott transitions in transition metal oxides, (ii) magnetism in half-metallic compounds, and (iii) large volume-collapse transitions in f-band metals.

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

    SciTech Connect

    Scalettar, Richard T.; Pickett, Warren E.

    2004-07-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

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

  12. Preparation and characterisation of transition metal oxide micro-thermistors and their application to immersed thermistor bolometer infrared detectors

    Microsoft Academic Search

    P. Umadevi; C. L. Nagendra

    2002-01-01

    Transition metal oxide thermistors consisting of manganese oxide (Mn3O4), nickel oxide (NiO) and cobalt oxide (CoO) in the ratio of 52:16:32 parts by weight are prepared by tape casting technique followed by high temperature calcination and sintering. The resultant thermistors whose linear dimensions, length (l), width (w) and thickness (t) are 650, 150 and 15?m, respectively show evidence of phase

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

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

    SciTech Connect

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

    2013-09-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

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

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

    E-print Network

    Continetti, Robert E.

    Laser Desorption/Ionization of Transition Metal Atoms and Oxides from Solid Argon Lester Andrews spectrometry. Adding the C6H5Br chromophore to the Ar/O2 gas mixture also enhanced the metal and oxide ion, laser ablation has been used to provide transition metal atoms for reactions with small molecules

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

    PubMed

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

    2014-09-15

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

  18. Cluster chemistry in the solid state: Structured diffuse scattering, oxide\\/fluoride ordering and polar behaviour in transition metal oxyfluorides

    Microsoft Academic Search

    Ray L. Withers; F. J. Brink; Yun Liu; Lasse Norén

    2007-01-01

    Oxide\\/fluoride ordering in three families of ‘disordered’ transition metal oxyfluoride compounds is carefully investigated and used to obtain insight into why the constituent inherently acentric octahedral units do not usually order in a long range ordered polar sense. Observed highly structured diffuse intensity distributions are used in each case to analyze the local crystal chemistry and orientational ordering rules governing

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

    DOEpatents

    Tracy, C. Edwin (Golden, CO); Benson, David K. (Golden, CO); Ruth, Marta R. (Golden, CO)

    1987-01-01

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

  20. The basic atomic processes of corrosion II. Defect structures and cation transport in transition-metal oxides

    Microsoft Academic Search

    C. R. A. Catlow; W. C. Mackrodt; M. J. Norgett; A. M. Stoneham

    1979-01-01

    An earlier discussion of the fundamental processes controlling corrosion is extended with an account of cation transport in cubic divalent transition-metal oxides. The results of calculations of the energies of defect interaction and activation are given. Our results show that the common interpretations of the experimental data on these materials are inadequate. In particular, we suggest that vacancy clustering in

  1. Hydroxide oxidation and peroxide formation at embedded binuclear transition metal sites; TM = Cr, Mn, Fe, Co.

    PubMed

    Busch, M; Ahlberg, E; Panas, I

    2011-09-01

    Key steps in electro-catalytic water oxidation on binuclear Transition Metal (TM) sites are addressed. These comprise (a) two one-electron oxidation steps of TM-OH moieties to form the corresponding two TM=O oxy-groups, and (b) a chemical step whereby the two oxy-species form a TM-O-O-TM peroxy-bridge. A test rig representing a generic low crystal field oxide support is described and employed. The energetics for homo-nuclear Cr(III-V), Mn(III-V), Fe(II-IV) and Co(II-IV) sites are compared. The uniqueness of the tyrosine/tyrosyl-radical (TyrOH/TyrO?) reference potential for driving the oxidation steps is demonstrated. The oxidation of adsorbed TM-OH moieties on binuclear Mn and Co candidates requires an overpotential of approximately 0.5 V relative to the chosen reference potential. Correspondingly, the subsequent O-O bond formation becomes strongly exothermic, of the order of 1 eV. The hydroxide oxidation steps on binuclear CrCr and FeFe systems are, in total, exothermic by 1.21 and 0.61 eV, respectively, relative to the TyrOH/TyrO? reference potential. Consequently, the chemical step for transforming the TM=O moieties to the peroxo species is found to be endothermic by the order of 0.7 eV. Based on these findings, a catalyst containing one TM from each class is suggested. The validity of this concept is demonstrated for the FeCo binuclear site. The results are discussed in the context of experimental observations, which display a preference for mixed oxide systems. PMID:21773631

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

    SciTech Connect

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

    2011-10-25

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

  3. Ferroelectric fatigue in perovskite oxides

    SciTech Connect

    Warren, W.L.; Tuttle, B.A.; Dimos, D. [Sandia National Laboratories, Albuquerque, New Mexico 87185-1349 (United States)] [Sandia National Laboratories, Albuquerque, New Mexico 87185-1349 (United States)

    1995-09-04

    We find that the reduction of the switchable polarization in BaTiO{sub 3} crystals via repeated polarization reversals (fatigue) is accompanied by the trapping of electronic charge and atomic scale distortions in the perovskite oxygen octahedron. The distortions are proposed to involve oxygen vacancies. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

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

    SciTech Connect

    Das, Supriyo

    2010-05-16

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

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

    PubMed

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

    2006-11-01

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

  6. Nanoparticles of 3d transition metal oxides in mesoporous MCM-48 silica host structures: Synthesis and characterization

    Microsoft Academic Search

    Ralf Köhn; Michael Fröba

    2001-01-01

    Transition metal oxide nanoparticles were synthesized within mesoporous MCM-48 silica phases. By wet impregnation, drying, and calcination procedures, it was possible to form iron, iron\\/cobalt, cobalt, nickel, and copper oxide nanoparticles almost exclusively within the pore system. Nitrogen sorption measurements still revealed mesoporosity for the host\\/guest compounds accompanied by a reduction of the surface area and pore radius, both indications

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

    Microsoft Academic Search

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

    2008-01-01

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

  8. Transition-metal cluster ions in the gas phase. Oxide chemistry of dimeric and trimeric clusters containing iron and cobalt

    Microsoft Academic Search

    D. B. Jacobson; B. S. Freiser

    1986-01-01

    The oxide chemistry of both dimeric and trimetric transition-metal cluster ions containing iron and cobalt was studied in the gas phase by using Fourier transform mass spectrometry (FTMS). The dimers Feâ\\/sup +\\/, CoFe\\/sup +\\/, and Coâ\\/sup +\\/ react rapidly with ethylene oxide by sequentially abstracting two oxygen atoms, while the trimers FeCoâ and Coâ\\/sup +\\/ abstract up to three oxygen

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

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Mráz, Stanislav; Schneider, Jochen M.

    2006-07-01

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

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

    NASA Astrophysics Data System (ADS)

    Lam, Ching Yee

    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 oxide thin films and electrical rectifying property of an all-oxide p-n diode have been studied. The resistive switching of anatase phase TM-doped TiO 2 has been determined using two top-down configurations of Ag/TM-doped TiO2/Pt and In/TM-doped TiO2/TiN. Despite the fact that same transition-metal oxide was used, the switching characteristics of these two configurations were significantly different. For example, both the unipolar and bipolar switching were observed in pure TiO2 films. Heterostructures of Ag/TiO2/Pt have also been deposited on flexible PET substrates at room temperature by PLD. These oxide films on flexible substrate not only show resistive switching, but produce an average switching ratio as high as over 6 orders of magnitude. The resistive switching in In/CuxO/Pt and In/Mn-doped CuxO/Pt films have also been demonstrated in the present study. Our results indicate clearly that the switching stability of the In/CuxO/Pt systems is improved by the Mn-doping. Our ultimate goal is to produce a ferromagnetic all-oxide p-n junction diode. We obtained room-temperature ferromagnetism in the epitaxially grown anatase n-type Co-doped TiO2 and possible p-type Fe-doped TiO 2 thin films. At the same time, the 3.7 at.% Mn-doped Cu2O epitaxial films have been prepared. They are p-type conducting and have been properly utilized to form good rectifying all-oxide heterojunction with the n-type Nb-SrTiO3 substrates. The p-type Mn-doped Cu2O films that we have made so far, although exhibit ferromagnetism at low temperatures <50K, do not reveal any room temperature ferromagnetic characteristics. It is believed that room temperature ferromagnetism in Mn-doped Cu2O is still possible if the Mn-doping level is kept well below the solubility limit of Mn in Cu2O. The experimental investigations carried out so far in the present research do provide strong indication and support for realization of spintronic heterojunctions based on n-type Co-TiO2/p-type Mn-doped Cu2O.

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

    E-print Network

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

    2014-01-01

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

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

    SciTech Connect

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

    1997-05-01

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

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

    SciTech Connect

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

    2010-03-05

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

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

    PubMed

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

    2015-03-11

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

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

    SciTech Connect

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

    2014-06-02

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

  17. Growth of epitaxial poly-crystalline transition metal oxide thin films

    NASA Astrophysics Data System (ADS)

    Woo, Sungmin; Jeong, Hoidong; Lee, Sang A.; Seo, Hosung; Lacotte, Morgane; David, Adrian; Kim, Hyun You; Prellier, Wilfrid; Kim, Yunseok; Choi, Woo Seok

    2015-03-01

    By comparing single- and poly-crystalline transition metal oxides (TMOs), one can study intriguing physical phenomena such as electronic and ionic conduction at the grain boundaries, phonon propagation, and various domain properties. In this work, we propose an approach to simultaneously fabricate single- and poly-crystalline epitaxial TMO thin films using substrate epitaxy of poly-crystalline SrTiO3 (STO). In order to grow TMO thin films epitaxially with atomic precision, an atomically flat surface of the substrate is required. We first examined (100), (110), and (111) oriented single-crystalline STO surfaces, which required different annealing conditions to achieve an atomically flat surface. A poly-crystalline STO surface was then prepared at the optimum condition for which all the domains with different crystallographic orientations could be successfully flattened. Studying the surface properties (surface potential, topography, and orientation) of poly-crystalline STO helped us to understand the formation of the atomically flat surface. Based on our research, we envision expansion of the studies regarding the epitaxial poly-crystalline TMO thin films and heterostructures..

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  19. Pressure dependence of exchange interactions and Neel temperature in transition metal oxides

    NASA Astrophysics Data System (ADS)

    Ojwang, Julius; Cohen, Ronald; Shulenburger, Luke; Wan, Xiangang; Savrasov, Serjey

    2010-03-01

    We perform first-principles linear response computations within LDA+U and GGA+U to systematically investigate the pressure dependence of magnetic exchange interactions for archetypal transition metal oxides (TMOs): MnO, FeO, CoO, and NiO. We obtain the Neel temperatures (TN) using Monte Carlo simulations. We find that the magnitude of the next nearest neighbor coupling constant, J2, which dominates TN, increases with increasing pressure, while the nearest neighbor, J1, behaves differently for the four TMOs. The variation of TN with pressure is influenced by interplay between the nearest and next nearest neighbor exchange coupling constants. Our results are found to be in agreement in general with most experiments [1-3]. [4pt] [1] Massey et al. Phys. Rev. B 42:8776, 1990[0pt] [2] Sidorov Appl. Phys. Lett. 72:2174, 1998[0pt] [3] Badro et al. Phys. Rev. Lett. 83:4101, 1999[0pt] [4] Pasternak et al. Phys. Rev. Lett. 79:5046, 1997

  20. Metastable defect ferromagnetic phases by low temperature interface reactions between transition metal oxides

    NASA Astrophysics Data System (ADS)

    Kundaliya, Darshan C.; Lofland, S. E.

    2005-03-01

    Recently we showed [Nature Materials 3, 709 (2004)] that the room temperature ferromagnetism observed in low temperature (500 ^oC) processed mixtures of 2 at% MnO2 with ZnO [Nature Materials 2, 673 (2003)] is caused by an interface phase suggested to be of the form Mn2-xZnxO3-?, wherein Zn is incorporated into Mn2O3. In order to establish the anticipated generic nature of the process, experiments were performed on low temperature sintering of 2 at% MnO2 with other transition metal oxides such as NiO, TiO2 or CuO. Room temperature ferromagnetism was observed in all the three cases. Our results suggest that ferromagnetism in these new cases also resides at the interface. The same mixtures when sintered at 800 ^oC resulted in compound phases (e.g. NiMn2O4 in the Ni-Mn-O case) that are nonmagnetic at room temperature. We suggest a new mechanism of ferromagnetism based on the valence and spin controlled defect state in the interface phases.

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

    NASA Astrophysics Data System (ADS)

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

    2010-04-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

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

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

    E-print Network

    Paris-Sud XI, Université de

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

  4. Colossal magnetoresistance in manganese oxide perovskites

    Microsoft Academic Search

    M. R. Ibarra; J. M. De Teresa

    1998-01-01

    The large magnetoresistance observed in the manganese-oxide-based perovskites is explained on the basis of a strong electron-phonon and ferromagnetic interactions which provide the mechanism for the existence of dynamic electronic phase segregation in the form of magnetic polarons. These entities are responsible for the magnetic and lattice effects observed in these compounds. In this experimental work we give evidence of

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

    Microsoft Academic Search

    Richard T. Scalettar; Warren E. Pickett

    2004-01-01

    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

  6. X-Ray Resonant Scattering as a Direct Probe of Orbital Ordering in Transition-Metal Oxides

    Microsoft Academic Search

    Michele Fabrizio; Massimo Altarelli; Maurizio Benfatto

    1998-01-01

    X-ray resonant scattering at the K-edge of transition-metal oxides is shown to measure the orbital order parameter, supposed to accompany magnetic ordering in some cases. Virtual transitions to the 3d orbitals are quadrupolar in general. In cases with no inversion symmetry, such as V2O3, treated in detail here, a dipole component enhances the resonance. Hence, we argue that the detailed

  7. Partial oxidation of light alkanes in transition-metal ion containing zeolite: Quarterly report, March 15June 14, 1987

    Microsoft Academic Search

    K. Klier; J. Lin

    1987-01-01

    First SWX..cap alpha.. calculations have been carried out using (ZnâOââ)⁻¹⁴ and (ZnâCuOââ)⁻¹⁴ clusters as model for transition-metal ions in oxide matrices. Bandgap, valence band edge and valence band width can be predicted with accuracy when the Watson sphere radius is reduced to cancel the dipole moment at the cluster boundaries. 15 refs., 4 figs., 1 tab.

  8. Electron energy-loss near-edge structures of 3d transition metal oxides recorded at high-energy resolution

    Microsoft Academic Search

    C. Mitterbauer; G. Kothleitner; W. Grogger; H. Zandbergen; B. Freitag; P. Tiemeijer; F. Hofer

    2003-01-01

    Near-edge fine structures of the metal L2,3 and O K-edges in transition metal-oxides have been studied with a transmission electron microscope equipped with a monochromator and a high-resolution imaging filter. This system enables the recording of EELS spectra with an energy resolution of 0.1eV thus providing new near-edge fine structure details which could not be observed previously by EELS in

  9. Lowering the Switching Current of Resistance Random Access Memory Using a Hetero Junction Structure Consisting of Transition Metal Oxides

    Microsoft Academic Search

    Kentaro Kinoshita; Tetsuro Tamura; Masaki Aoki; Yoshihiro Sugiyama; Hitoshi Tanaka

    2006-01-01

    Both lowering the ``reset'' current of resistance random access memory (ReRAM) and raising the resistance in the low resistance state are crucial for practical use of ReRAM. These requirements have been satisfied by using a hetero junction structure consisting of transition metal oxides, NiOy\\/TiOx\\/Pt, combining direct contact with the NiOy using a W-probe. It is considered that this configuration brought

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

    Microsoft Academic Search

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

    1995-01-01

    Stimulated by the discovery of high-temperature superconductivity, the electronic structure of late 3d transition-metal oxides is presently one of the most extensively studied subjects in condensed matter physics. In this review, we hope to summarize the progress we have made and the problems we are facing. The emphasis of the review is on the latest angle-resolved photoemission studies that have

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

    Microsoft Academic Search

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

    2011-01-01

    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). 10at.% Co, 4at.% Ni, and 1at.% Cu substitution on B-site of 20at.% Ca-doped yttrium chromite led to a close match of thermal expansion coefficient (TEC) with that

  12. Electrochromism in some thin-film transition-metal oxides characterized by x-ray electron spectroscopy

    Microsoft Academic Search

    Richard J. Colton; Alberto M. Guzman; J. Wayne Rabalais

    1978-01-01

    Qualitative results of an x-ray photoelectron and optical investigation of three thin-film transition-metal oxides, namely, WO3, MoO3, and V2O5 are reported. Data were obtained on films that were notcolored and colored by an electrochromic process. The particular electrochromic coloration process used is electrolytic in nature and employs a sandwich-structure electrochromic cell and electrolyte pool. The optical spectra show increased absorption

  13. Electrochromism in some thin-film transition-metal oxides characterized by x-ray electron spectroscopy

    Microsoft Academic Search

    Richard J. Colton; Alberto M. Guzman; J. Wayne Rabalais

    1978-01-01

    Qualitative results of an x-ray photoelectron and optical investigation of three thin-film transition-metal oxides, namely, WO3, MoO3, and V2O5 are reported. Data were obtained on films that were not colored and colored by an electrochromic process. The particular electrochromic coloration process used is electrolytic in nature and employs a sandwich-structure electrochromic cell and electrolyte pool. The optical spectra show increased

  14. Low-Temperature Synthesis of Tunable Mesoporous Crystalline Transition Metal Oxides and Applications as Au Catalyst Supports

    SciTech Connect

    Wang, Donghai; Ma, Zhen; Dai, Sheng; Liu, Jun; Nie, Zimin; Engelhard, Mark H.; Huo, Qisheng; Wang, Chong M.; Kou, Rong

    2008-09-04

    Mesoporous transition metal oxides are of great potential as catalyst supports, shape-selective catalysts, photocatalysts, and sensor materials. Previously stable crystalline mesoporous oxides were mostly obtained by thermally induced crystallization or by segregating the nanocrystals with an amorphous phase. Here we report a novel direct approach to crystalline mesoporous frameworks via the spontaneous growth and assembly of transition metal oxide nanocrystals (i.e., rutile TiO2, fluorite CeO2, cassiterite SnO2, and anatase SnxTi1-xO2) by oxidative hydrolysis and condensation in the presence of anionic surfactants. The influences of synthesis time, surfactants with different chain lengths, concentrations of the oxidant (i.e., hydrogen peroxide), and synthesis temperatures on the composition and morphologies of the resulting materials were investigated by X-ray diffraction (XRD), N2-sorption, transmission electron microscopy (TEM), selected area electron diffraction (SAED), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). A mechanism for the templated synthesis of crystalline mesoporous metal oxides was tentatively proposed. To demonstrate the catalytic applications of these materials, gold nanoparticles were loaded on mesoporous rutile TiO2 and fluorite CeO2 supports, and their catalytic performance in CO oxidation and water-gas shift was surveyed. Au nanoparticles supported on the mesoporous crystalline metal oxides exhibit higher reactivity and excellent on-stream stability towards CO oxidation and water-gas shift reaction compared with commercial TiO2 and CeO2.

  15. Energetics of lithium transition metal oxides applied as cathode materials in lithium ion batteries

    NASA Astrophysics Data System (ADS)

    Wang, Miaojun

    In this work, high temperature oxide melt solution calorimetry was employed to investigate the thermodynamic properties of several representative lithium transition metal oxide systems applied as cathode materials in lithium ion batteries: layered alpha-NaFeO2 structure LiNi1-x COxO2 solid solution, Li1+xMn 2-xO4 spinel, LiMO2 (M = Mn, Fe and Co), and chemically delithiated LixCoO2. The enthalpies of formation and enthalpies of mixing for LiNi1-x COxO2 solid solution series (0 ? x ? 1) were determined using high temperature oxide melt solution calorimetry. The enthalpies of formation at 298 K from binary oxides (Li2O, NiO and CoO) and O2, and the lattice parameters decrease approximately linearly with the Co content x in LiNi1-xCOxO 2. The solid solution deviates slightly positively from ideality. Lithium substituted spinel Li1+xMn2-xO 4 (0 ? x ? 1/3) samples synthesized are stoichiometric at x < 0.25, and oxygen deficient at x ? 0.25. The enthalpy of formation from binary oxides (Li2O, Mn2O3 and MnO2 ) becomes more exothermic with x in Li1+xMn2-x O4 for stoichiometric compounds, and deviates endothermically from this trend for oxygen deficient compounds. This energetic trend is related to two competing substitution mechanisms of lithium for manganese (oxidation of Mn3+ to Mn4+ versus formation of oxygen vacancies). LiMO2 samples (M = Mn, Fe, and Co) with different structures were synthesized and their enthalpies of formation from oxides (Li2O and M2O3) or oxides (Li2O and MO) plus oxygen at 298 K were determined. The relative stability of the polymorphs of LiMO 2 was established based on their enthalpies of formation. Phase transformations in LiFeO2 were investigated by differential scanning calorimetry and high temperature oxide melt solution calorimetry. The gamma phase is the stable form of LiFeO2 at room temperature and the a phase is stable at high temperature. Energetics of chemically delithiated LixCoO2 samples (0.5 ? x ? 1.0) with the alpha-NaFeO2 structure (O 3 type) was studied. The enthalpies of formation from binary oxides (Li2O and CoO) and oxygen vary linearly with x and LixCoO 2 becomes less stable with decreasing x. The enthalpies of formation from oxides and oxygen for monoclinic Li0.5CoO2 and O3-CoO2 were estimated by extrapolation from the linear trend.

  16. Insights on Hydrogen Liberation from Water Using Anionic Transition Metal Oxide Clusters: a Combined Computational and Spectroscopic Study

    NASA Astrophysics Data System (ADS)

    Ramabhadran, Raghunath O.; Mann, Jenniffer E.; Waller, Sarah. E.; Rothgeb, David W.; Jarrold, Caroline C.; Raghavachari, Krishnan

    2013-06-01

    Transition Metal Oxides (TMOs) offer widespread applications in catalysis and the generation of alternate sources of energy. Cluster models are useful to model the defect sites in these TMO surfaces which are responsible for their catalytic activities. In this combined computational (DFT) and spectroscopic (PES/MS) study, we present the interesting features in the chemical reactions of molybdenum oxide and tungsten oxide clusters with water. The results obtained provide valuable insights on the roles played by differing metal-oxygen bond strengths, the initial electrostatic complex formed and the geometric factors involved in the liberation of hydrogen gas from water.

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

    E-print Network

    Broholm, Collin Leslie

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

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

    NASA Astrophysics Data System (ADS)

    Ramond, Tanya Michelle

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

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

    PubMed Central

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

    2014-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

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

  1. High content screening in zebrafish speeds up hazard ranking of transition metal oxide nanoparticles.

    PubMed

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

    2011-09-27

    Zebrafish is an aquatic organism that can be used for high content safety screening of engineered nanomaterials (ENMs). We demonstrate, for the first time, the use of high content bright-field and fluorescence-based imaging to compare the toxicological effect of transition metal oxide (CuO, ZnO, NiO, and Co(3)O(4)) nanoparticles in zebrafish embryos and larvae. High content bright-field imaging demonstrated potent and dose-dependent hatching interference in the embryos, with the exception of Co(3)O(4) which was relatively inert. We propose that the hatching interference was due to the shedding of Cu and Ni ions, compromising the activity of the hatching enzyme, ZHE1, similar to what we previously proposed for Zn(2+). This hypothesis is based on the presence of metal-sensitive histidines in the catalytic center of this enzyme. Co-introduction of a metal ion chelator, diethylene triamine pentaacetic acid (DTPA), reversed the hatching interference of Cu, Zn, and Ni. While neither the embryos nor larvae demonstrated morphological abnormalities, high content fluorescence-based imaging demonstrated that CuO, ZnO, and NiO could induce increased expression of the heat shock protein 70:enhanced green fluorescence protein (hsp70:eGFP) in transgenic zebrafish larvae. Induction of this response by CuO required a higher nanoparticle dose than the amount leading to hatching interference. This response was also DTPA-sensitive. We demonstrate that high content imaging of embryo development, morphological abnormalities, and HSP70 expression can be used for hazard ranking and determining the dose-response relationships leading to ENM effects on the development of the zebrafish embryo. PMID:21851096

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

    NASA Astrophysics Data System (ADS)

    Trotochaud, Lena

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

  3. Molecular adsorption on the surface of strongly correlated transition-metal oxides: A case study for CO\\/NiO(100)

    Microsoft Academic Search

    A. Rohrbach; J. Hafner; G. Kresse

    2004-01-01

    It is well known that the physical properties of some transition-metal compounds (mostly oxides) are strongly affected by intra-atomic correlations. Very recently, investigations of the adsorption of small molecules such as CO on the surfaces of transition-metal oxides have led to rather surprising results: the weak adsorbate-substrate bonding and the asymmetric (tilted) adsorption geometries contrast sharply the strong bonding and

  4. Redox and crystal chemistry of complex alkaline earth transition-metal oxides: Stabilization of unusual oxidation states

    Microsoft Academic Search

    Maarit Karppinen; Hisao Yamauchi

    All known high-Tc superconductive copper oxides, expressed as MmA2Qn-1CunOm+2+2n±? or M- m (A) 2 (Q) (n-1)n:P\\/RS (P\\/RS stands for perovskite\\/rock-salt type charge reservoir) (1), involve at least one alkaline earth element. The larger Ba II and Sr II ions tend to sit at the A-cation site with a coordination number (CN) ranging from 8 up to 10, while the smaller

  5. Magnetic Collapse in Transition Metal Oxides at High Pressure: Implications for the Earth

    Microsoft Academic Search

    Ronald E. Cohen; I. I. Mazin; Donald G. Isaak

    1997-01-01

    Magnetic collapse in transition metal ions is predicted from first-principles computations at pressures reached in the Earth's lower mantle and core. Magnetic collapse would lead to marked changes in geophysically important properties, such as elasticity and con- ductivity, and also to different geochemical behavior, such as element partitioning, than estimated by extrapolating low-pressure data, and thus change the understanding of

  6. The effect of NO x and CO on the rate of transition metal oxide catalyzed carbon black oxidation: An exploratory study

    Microsoft Academic Search

    Guido Mul; Weidong Zhu; Freek Kapteijn; Jacob A Moulijn

    1998-01-01

    The catalytic activity of Cr2O3, Co3O4, and CuO for the oxidation of carbon black in various gas compositions is reported. In 10% O2 in Ar, the carbon black oxidation activity is improved considerably by intensifying the contact between the transition metal oxide (TMO) and carbon black by ball-milling (creation of `tight contact') or impregnation, and also by increasing the surface

  7. Selective oxidation of ammonia to nitrogen on transition metal containing mixed metal oxides

    Microsoft Academic Search

    Lucjan Chmielarz; Piotr Ku?trowski; Alicja Rafalska-?asocha; Roman Dziembaj

    2005-01-01

    The selective catalytic oxidation of ammonia to nitrogen (NH3-SCO) has been studied over hydrotalcite derived mixed metal oxides containing Cu, Co, Fe or Ni. XRD, BET, NH3-TPD and TPR techniques were used for catalysts characterization. Results of NH3-SCO were compared with those of selective catalytic reduction of NO with NH3 (NO-SCR). Reaction mechanism was studied by temperature-programmed surface reaction (TPSR)

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

    NASA Astrophysics Data System (ADS)

    Erten, Onur

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

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

    Microsoft Academic Search

    Gerald Lucovsky; James C. Phillips

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

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

    NASA Astrophysics Data System (ADS)

    Charrier, J. G.; Anastasio, C.

    2012-10-01

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

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

    NASA Astrophysics Data System (ADS)

    Charrier, J. G.; Anastasio, C.

    2012-05-01

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

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

    PubMed Central

    Charrier, J. G.; Anastasio, C.

    2013-01-01

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

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

    Microsoft Academic Search

    W M Temmerman; W Hergert; Physikalische Chemie

    2009-01-01

    We apply to transition metal monoxides the self-interaction corrected (SIC) local spin density approximation, implemented locally in the multiple scattering theory within the Korringa-Kohn-Rostoker (KKR) band structure method. The calculated electronic structure and in particular magnetic moments and energy gaps are discussed in reference to the earlier SIC results obtained within the linear muffin-tin orbital atomic sphere approximation band structure

  14. LiV2O4: A Heavy Fermion Transition Metal Oxide

    Microsoft Academic Search

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

    1997-01-01

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

  15. Rare earth or yttrium, transition metal oxide thermistors. [for temperature compensation of oxygen meters

    SciTech Connect

    Laud, K.R.; Logothetis, E.M.; Park, J.K.

    1980-11-04

    Thermistors comprising transition metal such as iron, rare earth of the lanthanide series or yttrium, and oxygen exhibit sufficient independence to variation in oxygen partial pressure over a range of exhaust gas conditions of internal combustion engines as to make them particularly suitable for temperature compensation of oxygen sensors such as those derived from titania as well as temperature sensing in other oxygen varying environments.

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

    Microsoft Academic Search

    K. A. GESHEVA; D. S. GOGOVA

    1993-01-01

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

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

    Microsoft Academic Search

    Richard T. Scalettar; Warren E. Pickett

    2005-01-01

    This project involves research into the thermodynamic properties;\\u000aof f-electron metals, transition metal oxides, and half-metallic;\\u000amagnets at high pressure. These materials are ones in which the;\\u000achanging importance of electron-electron interactions as;\\u000athe distance between atoms is varied;\\u000acan tune the system through phase transitions;\\u000afrom localized to delocalized electrons,;\\u000afrom screened to unscreened magnetic moments,;\\u000aand from normal

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

    Microsoft Academic Search

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

    1999-01-01

    The preparative method, characterization, and magnetic susceptibility chi measurements versus temperature T of the heavy-fermion transition-metal oxide LiV2O4 are reported in detail. The intrinsic chi(T) shows a nearly T-independent behavior below ~30 K with a shallow broad maximum at ~16 K, whereas Curie-Weiss-like behavior is observed above ~50-100 K. Field-cooled and zero-field-cooled magnetization Mobs measurements in applied magnetic fields H=10-100

  19. Electron-energy-loss near-edge structures in the oxygen Kedge spectra of transition-metal oxides

    Microsoft Academic Search

    H. Kurata; E. Lefèvre; C. Colliex; R. Brydson

    1993-01-01

    Oxygen K-edge electron-energy-loss spectra have been recorded for several transition-metal oxides (NiO, MnO, MnO2, TiO2, Cr2O3, Mn2O3) of different crystal structures. The origin of the distinct features which can be identified over 40 eV above threshold is discussed in terms of resonance scattering within shells of neighboring anionic backscatterers. Full multiple-scattering calculations corroborate and correct the simple approach. The first

  20. Electrochemical Characteristics of Lithium Transition-Metal Oxide as an Anode Material in a Lithium Secondary Battery

    Microsoft Academic Search

    Chil-Hoon Doh; Bong-Soo Jin; Jung-Hwan Lim; Seong-In Moon

    2002-01-01

    Lithium transition-metal oxides (LiTMOs) such as LiCoO2 and LiMn2O4 were investigated for their use as anode material for the lithium secondary battery. Ni?Li0?LiPF6(lM, EC + DEC (1 : l))?LiTMO?Cu cell was fabricated and its electrochemical properties were examined. LiCoO2 and LiMn2O4 showed fairly good characteristics as anode material as well as cathode material. At the 1st cathodic process, LiCoO2 had

  1. Calculation and interpretation of K-shell x-ray absorption near-edge structure of transition metal oxides

    Microsoft Academic Search

    H. Modrow; S. Bucher; J. J. Rehr; A. L. Ankudinov

    2003-01-01

    Simultaneous calculations of both K-edge x-ray-absorption near-edge structure (XANES) and ground-state electronic structure of 3d transition-metal oxides are presented. The calculations are based on a self-consistent one-electron real-space Green's-function approach, with many-body effects incorporated in terms of final-state potentials and a complex energy-dependent self-energy. The results are found to be in semiquantitative agreement with experiment at the metal K edges,

  2. Synthesis of fluorine-graphite intercalation compounds by elemental fluorine and high oxidation-state transition-metal fluorides

    Microsoft Academic Search

    T. Nakajima; Y. Matsuo; B. žemva; A. Jesih

    1996-01-01

    Fluorine-graphite intercalation compounds have been synthesized using high purity fluorine gas and high oxidation-state transition-metal fluorides, AgF3 and NiF3, at room temperature and at ?78 °C. At room temperature, a mixture of stage 1 + 2 ? 4 compounds with compositions, C4.2F to C14.6F were obtained. On the other hand, stage 2–4 compounds with compositions C5.6F to C14.2F were synthesized

  3. Effects of strain, d-band filling, and oxidation state on the bulk electronic structure of cubic 3d perovskites.

    PubMed

    Akhade, Sneha A; Kitchin, John R

    2011-09-14

    The properties of the d-band structure of the transition metal atom in cubic LaBO(3) and SrBO(3) perovskites (where B = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) and their dependence on strain, d-band filling, and oxidation state were investigated using density functional theory calculations and atom-projected density of states. The strain dependence of the d-band width is shown to depend systematically on the size of the B atom. We show that the transition metal d-band width and center are linearly correlated with each other in agreement with a rectangular band model. A simple matrix element formalism based on the solid state table can readily predict the strain dependence of the d-band width. PMID:21932913

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

    E-print Network

    Eom, Chang Beom

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

  5. Electric field effects in oxide perovskite systems.

    NASA Astrophysics Data System (ADS)

    Ogale, Satishchandra

    2000-03-01

    Recently, the suggested and partly demonstrated existence of stripe phases in oxide perovskite systems, and the suggestion of percolative phase separation as a primary transport mechanism in manganites, have raised interesting questions about the nature of response of such electronically inhomogeneous systems to external perturbations such as strain, defects and applied fields. We have explored the status of such perovskites as a channel in an electric field effect configuration. Our recent data on a modified and improved manganite/PZT based heterostructure show colossal electric field effects, which along with their systematics under applied magnetic field strongly favor an electronically inhomogeneous picture for the manganite channel over the traditional uniform channel picture. In fact the magneto-resistance and electro-resistance are found to exhibit complimentary behavior. It will be argued based on the various length-scale related physical considerations that nanometer scale channels could lead to even more novel features in field induced perturbations. 1. D. M. Newns et al. Appl. Phys. Lett. 73, 780 (1998). 2. S. B. Ogale et al. Phys. Rev. Letts. 77, 1159 (1996). 3. Emery, V. J. et al. Phys. Rev. B. 56, 6120 (1997). 4. M. Uehara et al. Nature 399, 560 (1999).

  6. Evidence for an Oxygen Diffusion Model for the Electric Pulse Induced Resistance Change Effect in Transition-Metal Oxides

    Microsoft Academic Search

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

    2007-01-01

    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

  7. Influence of perovskite termination on oxide heteroepitaxy

    NASA Astrophysics Data System (ADS)

    Schmidt, D. A.; Ohta, Taisuke; Yu, Q.; Olmstead, Marjorie A.

    2006-06-01

    We report a combined high-temperature scanning tunneling microscopy, ion scattering spectroscopy, and photoelectron spectroscopy study of bare lanthanum aluminate [LaAlO3(LAO)] and of the initial stages of anatase TiO2 growth on LAO(001). LAO(001) exhibits mixed La-O and Al-O2 surface terminations at 400 °C. Heteroepitaxial TiO2, grown by evaporating Ti metal in O2, nucleates near step edges, growing out to cover both upper and lower terraces uniformly, regardless of termination, indicating that the substrate cations and perovskite surface polarity play little direct role in controlling the morphology of this single-metal oxide heteroepitaxy. TiO2 films of 1.5 nm in thickness exhibit a surface reconstruction similar to the bulk anatase (1×4).

  8. hal-00153592,version2-2Oct2007 The crucial importance of the t2geg hybridization in transition metal oxides

    E-print Network

    Paris-Sud XI, Université de

    metal oxides Sylvain Landron1 and Marie-Bernadette Lepetit1 1 CRISMAT, ENSICAEN-CNRS UMR6508, 6 bd. Mar properties of transi- tion metal oxides, such as the CoO2-based compounds, is the analysis of the crystalline field splitting of the d orbitals of the transition metal atom. Indeed, depending on this splitting

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

    SciTech Connect

    Peng, H.; Lany, S.

    2012-05-15

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

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

    PubMed

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

    2015-07-01

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

  11. Topological Oxide Insulator in Cubic Perovskite Structure

    PubMed Central

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

    2013-01-01

    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

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

    NASA Astrophysics Data System (ADS)

    Das, Supriyo

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

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

    SciTech Connect

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

    2009-01-01

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

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

    PubMed

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

    2015-04-01

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

  15. Oxidative dehydrogenation (ODH) of ethane with O2 as oxidant on selected transition metal-loaded zeolites

    E-print Network

    Poeppelmeier, Kenneth R.

    suggest that the catalyst support can affect ODHE performance. Zeolites, which have molecular scale pore-loaded zeolites Xufeng Lin, Cathleen A. Hoel, Wolfgang M.H. Sachtler, Kenneth R. Poeppelmeier *, Eric Weitz productivity and selectivity Transition metal Y Zeolite a b s t r a c t Ni-, Cu-, and Fe-loaded acidic

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

    E-print Network

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

    2004-01-01

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

  17. LOMI (low oxidation-state transition metal ion) decontamination reagents and related preoxidation processes: Final report

    Microsoft Academic Search

    T. Swan; M. G. Segal; W. J. Williams; M. E. Pick

    1987-01-01

    The development of the LOMI decontamination system is described covering aspects from the initial laboratory oxide dissolution studies through to the application on a full reactor primary circuit. Limited work on advanced LOMI reagents for the dissolution of chromium containing oxide is also described. The optimization of potassium-permanganate based pre-oxidation reagents for high chromium oxides is discussed, leading to the

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

    PubMed

    Tatsumi, Kazuyoshi; Muto, Shunsuke; Rusz, Ján

    2013-12-01

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

  19. Interlayer exchange interactions in perovskite oxide heterostructures

    NASA Astrophysics Data System (ADS)

    Nikolaev, Konstantin Rudolfovich

    2000-10-01

    Magnetism in systems of reduced dimension has been an extremely dynamic research area in condensed matter physics. Among the major advances are the discovery of giant magnetoresistance and oscillatory exchange coupling in magnetic metallic multilayers. Over a bit more than a decade, this activity has progressed from being a fundamental scientific issue to a matter of important technological applications. Doped lanthanum manganese oxides, the materials that exhibit colossal magnetoresistance in large magnetic fields, have been yet another topic of intensive research lately. Their high degree of carrier spin polarization makes these compounds very attractive for applications in spintronics. Touching upon both issues, this thesis focuses on the investigation of magnetism and transport in a new class of magnetic multilayers---artificially layered films combining colossal magnetoresistive ferromagnetic manganites with structurally compatible paramagnetic or antiferromagnetic perovskite oxides. Single-crystal atomically-defined heterostructures, with nanometer scale periodicity have been fabricated by ozone-assisted molecular beam epitaxy and characterized by a number of techniques. In this work, in particular, the phenomena of oscillatory interlayer exchange coupling and magnetoresistance have been studied in heterostructures of two metallic oxides: ferromagnetic La2/3Ba1/3MnO 3 and paramagnetic LaNiO3. The experimental data have been interpreted within a conventional Ruderman-Kittel-Kasuya-Yosida model employing an ab initio calculated band structure of LaNiO3, taking into account strong electron scattering in the nickelate spacer. In another development, unidirectional magnetotransport anisotropy has been studied in ultrathin films of exchange-biased manganites. The effect is attributed to the influence of the exchange-induced anisotropy on transport in magnetoresistance ferromagnets. The results obtained are evaluated in the context of current research in this field, and the possibilities and challenges that lie ahead are outlined.

  20. Oxyanions in perovskites: from superconductors to solid oxide fuel cells.

    PubMed

    Hancock, C A; Porras-Vazquez, J M; Keenan, P J; Slater, P R

    2015-06-21

    In this article we review work on oxyanion (carbonate, borate, nitrate, phosphate, sulphate, silicate) doping in perovskite materials beginning with early work on doping studies in superconducting cuprates, and extending to more recent work on doping into perovskite-type solid oxide fuel cell materials. In this doping strategy, the central atom of the oxyanion group occupies the perovskite B cation site, with the associated oxide ions filling 3 (carbonate, nitrate, borate) or 4 (phosphate, sulphate, silicate) of the available 6 anion sites around this site, albeit displaced so as to achieve the required geometry for the oxyanion. We highlight the potential of this doping strategy to prepare new systems, stabilize phases that cannot be prepared under ambient pressure conditions, and lead to modifications to the electronic and ionic conductivity. We also highlight the need for further work in this area, in particular to evaluate the carbonate content of perovskite phases in general. PMID:25407324

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

    Microsoft Academic Search

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

    2002-01-01

    This article describes the kinetics of reactions that result in substrate consumption during formation of ultrathin transition metal oxides on silicon. Yttrium silicate films (~40 Å) with an equivalent silicon dioxide thickness of ~11 Å are demonstrated by physical vapor deposition (PVD) routes. Interface reactions that occur during deposition and during postdeposition treatment are observed and compared for PVD and

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

    PubMed

    Berger, Matthias; Neumeyer, Felix; Auner, Norbert

    2013-10-21

    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

  3. The design of new ligands and transition metal compounds for the oxidation of organic compounds 

    E-print Network

    Grill, Joseph Michael

    2009-06-02

    ........................................................................................... 108 APPENDIX B............................................................................................ 215 APPENDIX C............................................................................................ 225 VITA... ............................................................... 59 3.5 TEM images of nickel oxide particles derived from the decomposition of nickel oxide hydroxide ....................................... 60 3.6 TEM images of nickel oxide hydroxide prepared from ozone and nickel hydroxide...

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

    PubMed

    Khaleel, Abbas; Nawaz, Muhammad

    2015-03-01

    High-surface-area mesoprous powders of ?-Al2O3 doped with Cu(2+), Cr(3+), and V(3+) ions were prepared via a modified sol-gel method and were investigated as catalysts for the oxidation of chlorinated organic compounds. The composites retained high surface areas and pore volumes comparable with those of undoped ?-Al2O3 and the presence of the transition metal ions enhanced their surface acidic properties. The catalytic activity of the prepared catalysts in the oxidation of 1,2-dichloroethane (DCE) was studied in the temperature range of 250-400°C. The catalytic activity and product selectivity were strongly dependent on the presence and the type of dopant ion. While Cu(2+)- and Cr(3+)-containing catalysts showed 100% conversion at 300°C and 350°C, V(3+)-containing catalyst showed considerably lower conversion. Furthermore, while the major products of the reactions over ?-alumina were vinyl chloride (C2H3Cl) and hydrogen chloride (HCl) at all temperatures, Cu- and Cr-doped catalysts showed significantly stronger capability for deep oxidation to CO2. PMID:25766029

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

    PubMed

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

    2013-11-25

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

  6. Reversible oxidation and rereduction of entire thin films of transition-metal phthalocyanines

    SciTech Connect

    Green, J.M.; Faulkner, L.R.

    1983-05-18

    Thin films (1000 to 2000A thick) of iron(II) (Fe), cobalt(II) (Co), nickel(II) (Ni), copper(II) (Cu), and zinc(II) (Zr) phthalocyanines (Pc) on gold or indium oxide electrodes undergo stoichiometric oxidation and rereduction. Except for FePc and CoPc, the process is essentially reversible. Chronocoulometry showed that ZnPc films oxidized to the extent of 1.21 electrons per ZnPc molecule; CoPc required 1.92 electrons per molecule. Charge compensation is attained upon oxidation by uptake of anions from the electrolyte and by expulsion of anions upon reduction. Auger electron spectrometry allowed detection of the ions and characterization of their distributions. In partially oxidized films, the anions appear to be homogeneously distributed. Oxidation seems to proceed at all grains with equal probability, with anions entering and departing along grain boundaries. Smaller anions allow full oxidation at rapid rates; larger ones inhibit the oxidation with respect to rate. Optical spectroscopy showed evidence for reorganizaton of the crystalline lattices. The rereduced form is not the same as the original material, but it can be restored to the original form by annealing at 125/sup 0/C. In cyclic oxidations and rereductions, there is a gradual loss of charge-consuming ability, apparently related to electrical isolation of small domains, perhaps grains. The oxidations and rereductions are electrochromic, and the various color changes are described. 10 figures, 1 table.

  7. Optically passive counter electrodes for electrochromic devices: transition metal–cerium oxide thin films

    Microsoft Academic Search

    A Azens; L Kullman; D. D Ragan; C. G Granqvist

    1998-01-01

    Films of W–Ce oxide and Ti–Ce oxide were made by reactive DC magnetron sputtering. Li+ intercalation\\/deintercalation showed that the electrochromic coloration efficiency depended on the Ce\\/W and Ce\\/Ti ratio, and at proper values of these ratios the films remained transparent irrespective of their ion content. Ti–Ce oxide combines this property with good electrochemical cycling durability, and this material can serve

  8. Magnetoelectric and multiferroic properties in layered 3D transition metal oxides

    NASA Astrophysics Data System (ADS)

    Hwang, Jungmin

    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.

  9. Catalytic reduction of SO 2 over supported transition-metal oxide catalysts with C 2H 4 as a reducing agent

    Microsoft Academic Search

    Ching-Huei Wang; Shiow-Shyung Lin; Pei-Chang Sung; Hung-Shan Weng

    2003-01-01

    This work investigates performances of supported transition-metal oxide catalysts for the catalytic reduction of SO2 with C2H4 as a reducing agent. Experimental results indicate that the active species, the support, the feed ratio of C2H4\\/SO2, and pretreatment are all important factors affecting catalyst activity. Fe2O3\\/?-Al2O3 was found to be the most active catalyst among six ?-Al2O3-supported metal oxide catalysts tested.

  10. Ascorbate does not act as a pro-oxidant towards lipids and proteins in human plasma exposed to redox-active transition metal ions and hydrogen peroxide

    Microsoft Academic Search

    Jung Suh; Ben-Zhan Zhu; Balz Frei

    2003-01-01

    The combination of ascorbate, transition metal ions, and hydrogen peroxide (H2O2) is an efficient hydroxyl radical generating system called “the Udenfriend system.” Although the pro-oxidant role of ascorbate in this system has been well characterized in vitro, it is uncertain whether ascorbate also acts as a pro-oxidant under physiological conditions. To address this question, human plasma, used as a representative

  11. Oxidative Genome Damage and Its Repair in Neurodegenerative Diseases: Function of Transition Metals as a Double-Edged Sword

    PubMed Central

    Hegde, Muralidhar L.; Hegde, Pavana M.; Rao, K.S.J.; Mitra, Sankar

    2013-01-01

    The neurons in the central nervous system (CNS) with high O2 consumption and prolonged life span are chronically exposed to high levels of reactive oxygen species (ROS). Accumulation of ROS-induced genome damage in the form of oxidized bases and single-strand breaks (SSBs) as well as their defective or reduced repair in the brain has been implicated in the etiology of various neurological disorders including Alzheimer’s/Parkinson’s diseases (AD/PD). Although inactivating mutations in some DNA repair genes have been linked to hereditary neurodegenerative diseases, the underlying mechanisms of repair deficiencies for the sporadic diseases is not understood. The ROS-induced DNA damages are predominantly repaired via highly conserved and regulated base excision/SSB repair (BER/SSBR) pathway. We recently made an interesting discovery that transition metals iron (Fe) and copper (Cu) which accumulate excessively in the brains of AD, PD and other neurodegenerative diseases, act as a ‘double-edged sword’ by inducing genotoxic ROS and inhibiting DNA damage repair at the same time. These metals inhibit the base excision activity of NEIL family DNA glycosylases by oxidizing them, changing their structure, and inhibiting their binding to downstream repair proteins. Metal chelators and reducing agents partially reverse the inhibition, while curcumin with both chelating and reducing activities reverses the inhibition nearly completely. In this review, we have discussed the possible etiological linkage of BER/SSBR defects to neurodegenerative diseases and therapeutic potential of metal chelators in restoring DNA repair capacity. PMID:21441656

  12. LOMI (low oxidation-state transition metal ion) decontamination reagents and related preoxidation processes: Final report

    SciTech Connect

    Swan, T.; Segal, M.G.; Williams, W.J.; Pick, M.E.

    1987-12-01

    The development of the LOMI decontamination system is described covering aspects from the initial laboratory oxide dissolution studies through to the application on a full reactor primary circuit. Limited work on advanced LOMI reagents for the dissolution of chromium containing oxide is also described. The optimization of potassium-permanganate based pre-oxidation reagents for high chromium oxides is discussed, leading to the establishment of the dilute NP (nitric permanganate) and AP (alkaline permanganate) reagents for use in combination with LOMI and also the POD (PWR oxidative decontamination) system using NP and citrox reagents. An outline of the extensive materials compatibility studies required to clear the reagents for reactor use is given. Much of this work has been conducted by organizations independent of the CEGB, e.g., United Kingdom Atomic Energy Authority, General Electric, Agesta Project. For such work overall conclusions only are presented. A wide range of materials corrosion work has been undertaken in the joint CEGB/EPRI studies and some more sensitive issues such as the corrosion of Stellite have been addressed in detail. Waste management techniques have been developed to minimize the volume of arisings. These involve both the optimization of reagent composition to avoid use of excess chemicals and also the development of ion exchange techniques for the direct treatment of pre-oxidation reagents and for the control of reagent pH. The kinetics of chromium leaching using ozone as a pre-oxidation reagent have been investigated in detail since this gives low waste arisings.

  13. Study of transition metal oxide doped LaGaO 3 as electrode materials for LSGM-based solid oxide fuel cells

    Microsoft Academic Search

    Fanglin Chen; Meilin Liu

    1998-01-01

    Transition metal oxide doped lanthanum gallates, La0.9Sr0.1Ga0.8M0.2O3 (where M=Co, Mn, Cr, Fe, or V), are studied as mixed ionic-electronic conductors (MIECs) for electrode applications. The\\u000a electrochemical properties of these materials in air and in H2 are characterized using impedance spectroscopy, open cell voltage measurement, and gas permeation measurement. Three single\\u000a cells based on La0.9Sr0.1Ga0.8 Mg0.2O3 (LSGM) electrolyte (1.13 to 1.65?mm

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

    SciTech Connect

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

    2012-07-13

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

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

    E-print Network

    Tennyson, Andrew Gregory

    2008-01-01

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

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

    E-print Network

    La O', Gerardo Jose Cordova

    2008-01-01

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

  17. A model of phase transition induced antiphase boundaries in perovskite and layered perovskite oxides

    NASA Astrophysics Data System (ADS)

    Ding, Y.; Liang, D. D.

    2002-11-01

    A structural model of the antiphase boundaries (APBs) induced by phase transition in perovskite and layered perovskite oxides is put forward. Besides the distortion of oxygen octahedra, the existence of two types of ion with different sizes on A sites in perovskite blocks and their ordering in local areas might be the reasons for the occurrence of APBs. It could explain why APBs exist in SrBi2Ta2O9, Bi3.25La0.75Ti3O12, La2-xBaxCuO4, and La2/3Ca1/3MnO3, but not in Bi4Ti3O12 and Nd2NiO4 through their specific structure phase transitions. The formation of APBs might reflect the chemical inhomogeneity in local areas. Empirical results support this model.

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

    NASA Astrophysics Data System (ADS)

    Rangaraju, Raghu Raj

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

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

    PubMed

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

    2015-05-13

    Solution-processed p-n heterojunction photodiodes have been fabricated based on transition-metal oxides in which NiO and ternary Zn1-xMgxO (x = 0-0.1) have been employed as p-type and n-type semiconductors, respectively. Composition-related structural, electrical, and optical properties are also investigated for all the films. It has been observed that the bandgap of Zn1-xMgxO films can be tuned between 3.24 and 3.49 eV by increasing Mg content. The fabricated highly visible-blind p-n junction photodiodes show an excellent rectification ratio along with good photoresponse and quantum efficiency under ultraviolet (UV) illumination. With an applied reverse bias of 1 V and depending on the value of x, the maximum responsivity of the devices varies between 0.22 and 0.4 A/W and the detectivity varies between 0.17 × 10(12) and 2.2 × 10(12) cm?(Hz)(1/2)/W. The photodetectors show an excellent UV-to-visible rejection ratio. Compositional nonuniformity has been observed locally in the alloyed films with x = 0.1, which is manifested in photoresponse and X-ray analysis data. This paper demonstrates simple solution-processed, low cost, band tunable photodiodes with excellent figures of merit operated under low bias. PMID:25898025

  20. X-ray absorption spectroscopy studies of spin-orbit coupling in 5d transition metal oxides.

    PubMed

    Cho, Deok-Yong; Park, Junghwan; Yu, Jaejun; Park, Je-Geun

    2012-02-01

    In order to examine the effects of strong valence band spin-orbit coupling (SOC) in 5d transition metal oxides (TMOs), we have investigated the L(2) and L(3) edge white-line intensities of the x-ray absorption spectra of several 5d TMOs. The white-line intensities at both edges are found to decrease monotonously with increasing 5d electron occupancy, while their ratio showed anomalous behavior for late 5d TMOs (IrO(2), PtO(2), and Au(2)O(3)), deviating significantly from the theoretical value of 2 expected for the case of weak SOC. This observation serves as a clear experimental indication of strong SOC effects in 5d TMOs. We also discussed how the 5d TMOs can have charge transfer effects different from their counterpart 5d elemental metals by making comparative studies. Our works demonstrate the importance of j quantum states due to strong SOC in the 5d system. PMID:22227572

  1. Short-range order in disordered transition metal oxides, carbides, and nitrides with the B1 structure

    NASA Astrophysics Data System (ADS)

    Kostenko, M. G.; Rempel, A. A.; Sharf, S. V.; Lukoyanov, A. V.

    2015-04-01

    A method has been proposed for the simulation of the atomic structure of disordered phases of nonstoichiometric transition metal oxides, carbides, and nitrides with the B1 structure taking into account the short-range order in the arrangement of structural vacancies. The simplest structural models constructed with allowance for pair correlations between vacancies within the first four coordination spheres have been considered. A computer simulation of the atomic structure of disordered phases with the inclusion of the short-range order has been performed. For each structural model, the maximum possible concentration of vacancies and the short-range order parameters at different concentrations have been calculated. For a further experimental verification, the influence of the short-range order on the shape of the X-ray scattering spectrum has been investigated by calculating the theoretical X-ray diffraction patterns according to the Debye formula. The influence of the short-range order on the total energy of the disordered phases has been analyzed by ab initio methods. It has been shown that, in some cases, the proposed structural models of the short-range order are energetically favorable as compared to the model of statistical arrangement of vacancies.

  2. Structures, energetics and reaction mechanisms of nitrous oxide on transition-metal-doped and -undoped single-wall carbon nanotubes.

    PubMed

    Pannopard, Panvika; Khongpracha, Pipat; Warakulwit, Chompunuch; Namuangruk, Supawadee; Probst, Michael; Limtrakul, Jumras

    2012-02-01

    The catalytic activity of carbon nanotubes (CNTs) for the removal of greenhouse gases, like nitrous oxide (N(2)O), can be fine-tuned by metal doping. We modify the inert surfaces of CNTs with Sc, Ti and V transition metals in order to investigate their capability of converting N(2)O to N(2). The stable composite catalysts of Sc-, Ti- and V-doped (5,5)single-walled carbon nanotubes (SWCNTs), along with the unmodified one were investigated by periodic DFT calculations. Without metal doping, the N(2) O decomposition on the bare tube proceeds over a high energy barrier (54.3 kcal mol(-1)) which in the presence of active metals is reduced to 3.6, 8.0 and 10.2 kcal mol(-1) for V-, Ti- and Sc-doped (5,5)SWCNTs, respectively. The superior reactivity is a result of the facilitated electron transfer between the tube and N(2)O caused by the overlap between the d orbitals of the metal and the p orbitals of N(2)O. PMID:22241847

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

    NASA Astrophysics Data System (ADS)

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

    2006-05-01

    Systems of iron tellurite glasses were prepared by melt quenching with compositions of [85%TeO 2 + 5%Fe 2O 3 + 10%TMO], where transition metal oxides (TMO) are TiO 2, V 2O 5, MnO, CoO, NiO and CuO. Furthermore, the main structural units of these samples have been characterized by means of Raman spectra (150-1200 cm -1) as well as wavenumber predictions by means of Gaussian 98 ab initio calculations for the proposed site symmetries of TeO 44- triagonal bipyramid ( C2v) and Te 2O 76- bridged tetrahedra ( Cs and C1). Aided by normal coordinate analysis, calculated vibrational frequencies, Raman scattering activities, force constants in internal coordinates and potential energy distributions (PEDs), revised vibrational assignments for the fundamental modes have been proposed. The main structural features are correlated to the dominant units of triagonal bipyramid (tbp) or bridged tetrahedral (TeO 3+1 binds to TeO 3 through TeOTe bridge; corner sharing). Moreover, the Raman spectra of the investigated tellurites reflect a structural change from tbp (coordination number is four) to triagonal pyramidal (coordination number is three).

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

    PubMed

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

    2006-05-01

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

  5. TOPICAL REVIEW: Dielectric properties of crystalline and amorphous transition metal oxides and silicates as potential high-? candidates: the contribution of density-functional theory

    NASA Astrophysics Data System (ADS)

    Rignanese, G.-M.

    2005-02-01

    A review is given of various first-principles studies of the dielectric properties of crystalline and amorphous transition metal oxides and silicates, which have drawn considerable attention as potential high-? materials. After a brief summary of the principal equations of density-functional theory related to the dielectric properties of solids, the results obtained for group IVb M = (Hf,Zr,Ti) and IIIb M = (Y,La,Lu) transition metals crystalline oxides and/or silicates are discussed. For the group IVb transition metals, four crystalline phases (cubic, tetragonal, monoclinic and rutile) of dioxide MO2 with M = (Hf,Zr,Ti) have been considered in the literature. The results of density-functional theory calculations of the dielectric properties of three crystalline transition metal silicates (hafnon HfSiO4, zircon ZrSiO4 and a hypothetical TiSiO4 structure) are also presented. For the group IIIb transition metals, two crystalline phases (cubic and hexagonal) of sesquioxides M2O3 with M = Lu have been investigated within density-functional theory. Finally, the first-principles results that have been obtained for the amorphous silicates are discussed. A presentation is given of a scheme recently introduced which relates the dielectric constants to the local bonding of Si and metal atoms. It is based on the definition of parameters characteristic of the basic structural units centred on Si and metals atoms and including their nearest O neighbours. Applied to amorphous Zr silicates, it provides a good description of the measured dielectric constants, both of the optical and the static ones.

  6. Local structure and oxidation state of Mn and Ni atoms in LaNi1-xMnxO3+delta perovskites.

    PubMed

    Sánchez, M C; Subías, G; Pérez-Cacho, J; García, J; Blasco, J

    2001-03-01

    X-ray absorption spectroscopy has been used to study LaNi1-x Mn(x)O3+delta perovskites (x = 0.1, 0.25, 0.5, 0.75, 0.9). We have analysed both, the oxidation state and the local structure around the transition metal atoms. XANES spectra of these samples suggest a mixed valence state for both transition metal atoms. The Mn K-edge is shifted to high energies as the Ni content is increased up to x=0.5. The opposite behavior is found instead, for the Ni K-edge. Samples with x=0.5 and x=0.25 present the Mn K-edge at the same energy but the absorption features are different for both samples. The local structure has also been studied by means of the EXAFS technique. The first coordination shell nicely reflects the structural change observed in this series from rhombohedral perovskites (x>0.5) to orthorhombic perovskites x<0.5). The changes in the local structure for Ni and Mn atoms agree with the variation of the oxidation state observed in the XANES spectra. PMID:11512972

  7. Selective CO oxidation in the presence of hydrogen over supported Pt catalysts promoted with transition metals

    Microsoft Academic Search

    Eun-Yong Ko; Eun Duck Park; Kyung Won Seo; Hyun Chul Lee; Doohwan Lee; Soonho Kim

    2006-01-01

    Selective CO oxidation in the presence of excess hydrogen was studied over supported Pt catalysts promoted with various transition\\u000a metal compounds such as Cr, Mn, Fe, Co, Ni, Cu, Zn, and Zr. CO chemisorption, XRD, TPR, and TPO were conducted to characterize\\u000a active catalysts. Among them, Pt-Ni\\/?-Al2O3 showed high CO conversions over wide reaction temperatures. For supported Pt-Ni catalysts, Alumina

  8. Phase diagrams of lithium transition metal oxides: investigations from first principles

    Microsoft Academic Search

    Gerbrand Ceder; Anton Van der Ven

    1999-01-01

    The thermodynamics and phase transitions in lithium intercalation oxides are discussed. Changes in the host structure can be driven by configurational Li-vacancy interactions, variations in electron count or by changes in the stability of the oxygen packing. The formalism to predict the lithium-vacancy ordered configurations and their free energy is presented and calculations of the phase diagram of LixCoO2 in

  9. Transition Metals and Other Forms of Oxidative Protein Damage in Renal Disease

    Microsoft Academic Search

    Vincent M. Monnier; Ina Nemet; David R. Sell; Miriam F. Weiss

    \\u000a Oxidative and carbonyl stresses are dramatically increased in chronic renal disease, whereby an inverse relationship usually\\u000a exists between renal clearance and the accumulation of low molecular weight compounds ultimately responsible for the damage\\u000a to plasma constituents. Damage to proteins results from primary attack to protein residues by reactive oxygen species with\\u000a or without metal catalyst, or via myeloperoxidase and hypochlorous

  10. Comparison of modified transition metal-exchanged zeolite catalysts for oxidation of chlorinated hydrocarbons

    Microsoft Academic Search

    S. Chatterjee; H. L. Greene; Y. J. Park

    1992-01-01

    Complete catalytic oxidation of low-molecular-weight chlorinated hydrocarbons, such as methylene chloride, trichloroethylene, and carbon tetrachloride, was studied in air over several cation-exchanged Y zeolite catalysts. The reactions were carried out under atmospheric pressure with temperatures varying from 150 to 400[degrees]C and in presence of [approximately]13000 ppm of water. Primarily, three different cordierite-supported (washcoated) zeolite catalysts (Co-Y, Cr-Y, and Mn-Y) were

  11. Electrochromic phenomena in transition metal oxide thin films prepared by thermal evaporation

    Microsoft Academic Search

    S. Papaefthimiou; G. Leftheriotis; P. Yianoulis

    1998-01-01

    We present an experimental study on the electrochromic properties of MoO3, WO3 and mixed WO3-MoO3 thin films prepared by thermal evaporation. We have constructed symmetric and quasi-symmetric electrochromic cells incorporating\\u000a the evaporated oxide films as electrochromic layers. Li+ doped V2O5 films served as ion storage layers. The symmetric cells were found to exhibit significantly improved optical properties compared\\u000a to the

  12. InMnO[sub 3]: A new transition metal oxide with an unusual ABO[sub 3] structure

    SciTech Connect

    Giaquinta, D.M.; Loye, H.C. zur (Massachusetts Inst. of Technology, Cambridge (United States))

    1992-12-30

    The authors report the synthesis and structure of a new, unusual indium manganese oxide, InMnO[sub 3], with a hexagonal layered structure containing manganese in trigonal bipyramidal coordination. Several common ABO[sub 3] structural types are known, such as perovskite, corundum, ilmenite, and bixbyite, and radius ratio rules, such as Goldschmidt's tolerance factor, will generally predict which structural type will form for any given pair of cations. Two common ABO[sub 3] structural families are characterized by (1) A and B cations of approximately equal size and of a size suitable for octahedral coordination by oxygen and (2) an A cation comparable in size to O[sup 2[minus

  13. Electric field effects in transition metal oxides, their surfaces and heterostructures

    NASA Astrophysics Data System (ADS)

    Held, Karsten

    2015-03-01

    Modern computational tools such as density functional theory and its merger with dynamical mean field theory are nowadays inevitable for the modeling and understanding of oxides, their heterostructures and surfaces. In this talk, I will concentrate on the impact of electric fields, how they affect the physical properties and how to make use of them. Substantial internal electric fields are created at polar surfaces, and even for an isopolar-interface the electronic reconstruction can lead to a charge transfer and hence a dipole field. Such internal fields can be employed to efficiently separate electrons and holes in a oxide solar cell. Even if the polar dipole field is compensated by a surface reconstruction, a local surface potential remains, and makes SrTiO3 (110) the arguably simplest 2 dimensional electron gas (2DEG). External electric fields, on the other hand, can trigger ``gigantic'' responses, since correlated oxides are prone to small perturbations. For example, a field effect Mott transistor can be realized in a few layers of SrVO3 with ideal on-off (metal-insulator) switching properties; and interfacing a ferroelectric, BaTiO3, plus a 2DEG with large spin-orbit coupling, BaOsO3, allows for a giant switchable Rashba effect. Support by the ERC through Grant Agreement No. 306447 is gratefully acknowledged.

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

    Microsoft Academic Search

    Arata Tanaka; Takeo Jo

    1994-01-01

    We present calculated 3d, 3p and 3s resonant photoemission (RPE) spectra in the transition metal (TM) compounds CuO, NiO, CoO, FeO, MnO and TiO2 at TM 2p core threshold on the basis of a cluster model. Our model includes the intraatomic multipole electron-electron interactions and the hybridization between transition metal ions and ligand. The imaginary part of the self-energy matrix

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

    E-print Network

    Paris-Sud XI, Université de

    551 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) research of substitutional defects in ABO3 double oxides crystallizing in the perovskite structure

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

    E-print Network

    Zhong, Zhaohui

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

  17. Heterogeneous selective oxidation catalysts based on coordination polymer MIL101 and transition metal-substituted polyoxometalates

    Microsoft Academic Search

    N. V. Maksimchuk; M. N. Timofeeva; M. S. Melgunov; A. N. Shmakov; Yu. A. Chesalov; D. N. Dybtsev; V. P. Fedin; O. A. Kholdeeva

    2008-01-01

    Titanium- and cobalt-monosubstituted Keggin heteropolyanions, [PW11CoO39]5? and [PW11TiO40]5?, were electrostatically bound to the chromium terephthalate polymer matrix MIL-101. The MIL-supported polyoxometalate (POM) catalysts were characterized by elemental analysis, XRD, N2 adsorption, and FT-IR-spectroscopy. The catalytic performance of both MIL-101 and the novel composite materials M-POM\\/MIL-101 was assessed in the oxidation of three representative alkenes—?-pinene, caryophyllene, and cyclohexene—using molecular oxygen and

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

    NASA Astrophysics Data System (ADS)

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

    2011-10-01

    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.

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

    PubMed

    Qiu, Jun; Zhang, Ronghua

    2014-07-01

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

  20. Magnetic ordering in a ternary rare earth-transition metal oxide, R_2RuO_5, R=Pr, Gd and Tb

    Microsoft Academic Search

    R. P. Guertin; S. McCall; C. S. Alexander; Z. X. Zhou; G. Cao; J. E. Crow; C. Mielke

    2001-01-01

    In the insulating rare earth-transition metal oxide series R_2RuO_5, magnetic coupling is associated with both cation species. For R=Gd and Tb, (T_M=10 K and 18 K, respectively), the ordering is likely canted antiferromagnetic. For R=Pr (T_M= 8 K) ordering is spin glass-like, related to the partly structural frustration of the lattice. Field induced magnetic anomalies are observed for T.lt.TM for

  1. Effect of atomic magnetic moments on the relative intensity of the L ? and L ? components in x-ray emission spectra of 3 d transition metal oxides

    Microsoft Academic Search

    V. I. Grebennikov; V. R. Galakhov; L. D. Finkel’shtein; N. A. Ovechkina; É. Z. Kurmaev

    2003-01-01

    The integrated-intensity ratio R of the L\\u000a ? and L\\u000a ? lines in x-ray emission spectra of 3d transition metal oxides was measured. The magnitude of the ratio was found to depend nonmonotonically on the atomic number\\u000a of the 3d elements, with a sharp rise in the middle of the series. In terms of the theory of one-electron resonant x-ray

  2. Effect of transition metal oxides on densification and electrical properties of Si-containing Ce 0.8Gd 0.2O 2? ? ceramics

    Microsoft Academic Search

    T. S. Zhang; J. Ma; Y. J. Leng; S. H. Chan; P. Hing; J. A. Kilner

    2004-01-01

    Ce0.8Gd0.2O2?? (CGO20) ceramic has been considered as one of the most promising electrolytes for intermediate temperature (IT) fuel cells. It has been reported that some transition metal oxides (TMO), such as MnO2, Fe2O3 and Co3O4, are effective sintering aids for the densification of ceria-based electrolytes. However, very little information is available regarding the effect of TMO addition on the electrical

  3. Dielectric properties of crystalline and amorphous transition metal oxides and silicates as potential high-? candidates: the contribution of density-functional theory

    Microsoft Academic Search

    G-M Rignanese

    2005-01-01

    A review is given of various first-principles studies of the dielectric properties of crystalline and amorphous transition metal oxides and silicates, which have drawn considerable attention as potential high-? materials. After a brief summary of the principal equations of density-functional theory related to the dielectric properties of solids, the results obtained for group IVb M = (Hf,Zr,Ti) and IIIb M

  4. Electronic Origins of Structural Distortions in Post-Transition Metal Oxides: Experimental and Theoretical Evidence for a Revision of the Lone Pair Model

    Microsoft Academic Search

    D. J. Payne; R. G. Egdell; A. Walsh; G. W. Watson; J. Guo; P.-A. Glans; T. Learmonth; K. E. Smith

    2006-01-01

    Structural distortions in post-transition metal oxides are often explained in terms of the influence of sp hybrid ``lone pairs.'' Evidence is presented here showing that this model must be revised. The electronic structures of prototypically distorted alpha-PbO and alpha-Bi2O3 have been measured by high-resolution x-ray photoemission and soft x-ray emission spectroscopies. In contrast with the expectations of the lone pair

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

    PubMed

    Murahashi, Shun-Ichi

    2011-01-01

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

  6. Evidence against strong correlation in 4d transition-metal oxides CaRuO3 and SrRuO3

    Microsoft Academic Search

    Kalobaran Maiti; Ravi Shankar Singh

    2005-01-01

    We investigate the electronic structure of 4d transition-metal oxides CaRuO3 and SrRuO3 . The analysis of the photoemission spectra reveals significantly weak electron correlation strength (U\\/ Wtilde 0.2) as expected in 4d systems and resolves the long-standing issue that arose due to the prediction of large U\\/W similar to 3d systems. It is shown that the bulk spectra, thermodynamic parameters,

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

    Microsoft Academic Search

    Dirk Reinen; Michail Atanasov; Show-Ling Lee

    1998-01-01

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

  8. Linker rectifiers for covalent attachment of transition-metal catalysts to metal-oxide surfaces.

    PubMed

    Ding, Wendu; Negre, Christian F A; Palma, Julio L; Durrell, Alec C; Allen, Laura J; Young, Karin J; Milot, Rebecca L; Schmuttenmaer, Charles A; Brudvig, Gary W; Crabtree, Robert H; Batista, Victor S

    2014-04-14

    Linkers that favor rectification of interfacial electron transfer are likely to be required for efficient photo-driven catalysis of multi-electron reactions at electrode surfaces. Design principles are discussed, together with the synthesis and characterization of a specific pair of molecular linkers, related by inversion of the direction of an amide bond in the heart of the molecule. The linkers have a terpyridyl group that can covalently bind Mn as in a well-known water oxidation catalyst and an acetylacetonate group that allows attachment to TiO2 surfaces. The appropriate choice of the sense of the amide linkage yields directionality of interfacial electron transfer, essential to enhance electron injection and slow back-electron transfer. Support comes from electron paramagnetic resonance and terahertz spectroscopic measurements, as well as computational modeling characterizing the asymmetry of electron transfer properties. PMID:24668518

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

    NASA Astrophysics Data System (ADS)

    Jin, Lei

    2011-12-01

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

  10. Crystal structure of double oxides of the perovskite type

    Microsoft Academic Search

    Helen D Megaw

    1946-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

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

  12. Transition metal oxides and silicates as high-? dielectrics: a first-principles investigation

    NASA Astrophysics Data System (ADS)

    Rignanese, Gian-Marco; Gonze, Xavier; Pasquarello, Alfredo

    2003-03-01

    Using first-principles calculations, we investigate the structural, vibrational and dielectric properties of the Hf-Si-O and Zr-Si-O systems which have drawn considerable attention as alternative high-? materials. For the oxides, both the cubic and tetragonal phases of hafnia (HfO_2) and zirconia (ZrO_2) are studied. For the silicates, we analyze first the crystalline phases: hafnon (HfSiO_4) and zircon (ZrSiO_4). Then, the amorphous silicates are considered. We introduce a scheme which relates the dielectric constants to the local bonding of Si and M=(Hf, Zr) atoms. This scheme is based on the definition of parameters characteristic of the basic structural units (SUs) formed by Si and M=(Hf, Zr) atoms and their nearest neighbours, and allows us to avoid heavy large-scale calculations, which are beyond current computational capabilities. Applied to amorphous Zr silicates, our scheme provides a good description of the measured dielectric constants, and highlights the role of sixfold coordinated M=(Hf, Zr) atoms.

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

    PubMed Central

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

    2013-01-01

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

  14. Transition metal sulfide loaded catalyst

    DOEpatents

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

    1994-01-01

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

  15. Transition metal sulfide loaded catalyst

    DOEpatents

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

    1994-04-26

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

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

    NASA Astrophysics Data System (ADS)

    Samanta, Kousik

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

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

    E-print Network

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

    2014-01-01

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

  18. 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

    Halpin, Carolyn F.

    1986-01-01

    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... to the Graduate College of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE December 1986 Major Subject: Chemistry ELECTRONIC STRUCTURES OF TRANSITION METAL TO HYDROGEN BONDS: OXIDATIVE ADDITION...

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

    NASA Astrophysics Data System (ADS)

    Goodenough, John B.; Zhou, Jianshi

    2015-06-01

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

  20. Oxygen vacancy motion in perovskite oxides

    SciTech Connect

    Warren, W.L.; Vanheusden, K.; Dimos, D.; Pike, G.E.; Tuttle, B.A. [Sandia National Labs., Albuquerque, NM (United States). Advanced Materials Lab.

    1996-02-01

    Using electron paramagnetic resonance, the motion of oxygen vacancies within the oxygen octahedron in perovskite BaTiO{sub 3} 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 concurrent with oxygen vacancy motion. This result spectroscopically demonstrates that oxygen vacancy migration in the lattice is likely responsible for the observed degradation.

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

    PubMed

    Ma, Jing-jing; Yi, Wen-bin; Lu, Guo-ping; Cai, Chun

    2015-03-14

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

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

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

    SciTech Connect

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

    2014-06-19

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

  4. Dry reforming of methane over Ni perovskite type oxides

    Microsoft Academic Search

    Gustavo Valderrama; Mireya R. Goldwasser; Caribay Urbina de Navarro; Jean M. Tatibouët; Joël Barrault; C. Batiot-Dupeyrat; Fernando Martínez

    2005-01-01

    La1?xSrxNiO3 perovskite type oxides were synthesized by the auto combustion method and tested as catalysts precursors in the dry reforming of methane with CO2 to syngas at 700°C and 1atm. In order to understand the catalyst behavior, the reaction was studied by a pulse technique using a CH4\\/CO2 ratio close to one. The solids were characterized by X-ray diffraction (XRD),

  5. Oxide perovskite crystals for HTSC film substrates microwave applications

    NASA Technical Reports Server (NTRS)

    Bhalla, A. S.; Guo, Ruyan

    1995-01-01

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

  6. Oxide perovskite crystals for HTSC film substrates microwave applications

    SciTech Connect

    Bhalla, A.S.; Guo, R.

    1995-04-01

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

  7. Accurate electronic and chemical properties of 3d transition metal oxides using a calculated linear response U and a DFT + U(V) method.

    PubMed

    Xu, Zhongnan; Joshi, Yogesh V; Raman, Sumathy; Kitchin, John R

    2015-04-14

    We validate the usage of the calculated, linear response Hubbard U for evaluating accurate electronic and chemical properties of bulk 3d transition metal oxides. We find calculated values of U lead to improved band gaps. For the evaluation of accurate reaction energies, we first identify and eliminate contributions to the reaction energies of bulk systems due only to changes in U and construct a thermodynamic cycle that references the total energies of unique U systems to a common point using a DFT + U(V) method, which we recast from a recently introduced DFT + U(R) method for molecular systems. We then introduce a semi-empirical method based on weighted DFT/DFT + U cohesive energies to calculate bulk oxidation energies of transition metal oxides using density functional theory and linear response calculated U values. We validate this method by calculating 14 reactions energies involving V, Cr, Mn, Fe, and Co oxides. We find up to an 85% reduction of the mean average error (MAE) compared to energies calculated with the Perdew-Burke-Ernzerhof functional. When our method is compared with DFT + U with empirically derived U values and the HSE06 hybrid functional, we find up to 65% and 39% reductions in the MAE, respectively. PMID:25877590

  8. Accurate electronic and chemical properties of 3d transition metal oxides using a calculated linear response U and a DFT + U(V) method

    NASA Astrophysics Data System (ADS)

    Xu, Zhongnan; Joshi, Yogesh V.; Raman, Sumathy; Kitchin, John R.

    2015-04-01

    We validate the usage of the calculated, linear response Hubbard U for evaluating accurate electronic and chemical properties of bulk 3d transition metal oxides. We find calculated values of U lead to improved band gaps. For the evaluation of accurate reaction energies, we first identify and eliminate contributions to the reaction energies of bulk systems due only to changes in U and construct a thermodynamic cycle that references the total energies of unique U systems to a common point using a DFT + U(V ) method, which we recast from a recently introduced DFT + U(R) method for molecular systems. We then introduce a semi-empirical method based on weighted DFT/DFT + U cohesive energies to calculate bulk oxidation energies of transition metal oxides using density functional theory and linear response calculated U values. We validate this method by calculating 14 reactions energies involving V, Cr, Mn, Fe, and Co oxides. We find up to an 85% reduction of the mean average error (MAE) compared to energies calculated with the Perdew-Burke-Ernzerhof functional. When our method is compared with DFT + U with empirically derived U values and the HSE06 hybrid functional, we find up to 65% and 39% reductions in the MAE, respectively.

  9. Electronic transport and mixed conductivity in perovskite type oxides

    SciTech Connect

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

    1992-03-03

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

  10. Transition-metal cluster ions in the gas phase. Oxide chemistry of dimeric and trimeric clusters containing iron and cobalt

    SciTech Connect

    Jacobson, D.B.; Freiser, B.S.

    1986-01-08

    The oxide chemistry of both dimeric and trimetric transition-metal cluster ions containing iron and cobalt was studied in the gas phase by using Fourier transform mass spectrometry (FTMS). The dimers Fe/sub 2//sup +/, CoFe/sup +/, and Co/sub 2//sup +/ react rapidly with ethylene oxide by sequentially abstracting two oxygen atoms, while the trimers FeCo/sub 2/ and Co/sub 3//sup +/ abstract up to three oxygen atoms from ethylene oxide. The dimers and trimers also react with dioxygen. In addition, the bimetallic carbonyl cations Fe/sub 2/(CO)/sub 4//sup +/, CoFe(CO)/sub 3//sup +/, and Co(CO)/sub 3//sup +/ react rapidly with dioxygen by displacing all the carbonyls forming M'MO/sub 2//sup +/ exclusively. The trimetallic carbonyl cations FeCo/sub 2/(CO)/sub 5//sup +/ and Co/sub 3/(CO)/sub 6//sup +/ react rapidly with dioxygen by displacing up to four carbonyls to generate M'M/sub 2/(O)/sub 2/(CO)/sub n//sup +/ (n = 1-3). These species undergo a subsequent reaction with dioxygen which displaces the remaining carbonyls to generate both M'M/sub 2/O/sub 4//sup +/ and M'M/sub 2/O/sub 3//sup +/. The M'M/sub 2/O/sub 4//sup +/ species subsequently transfers an oxygen atom to dioxygen to generate M'M/sub 2/O/sub 3//sup +/ and presumably O/sub 3/. No fragmentations were observed for collisional activation of the M'MO/sup +/, while the M'MO/sub 2//sup +/ species yielded M/sup +/ and M'MO/sup +/ in low efficiency, the M'M/sub 2/O/sub 3//sup +/ species yielded M/sup +/ and M'MO/sup +/ in very low efficiency, and the M'MO/sub 2/O/sub 4//sup +/ species yielded M'M/sub 2/O/sub 3//sup +/. Finally, the observed ion-molecule reactions yield D/sup 0/(M'M/sup +/-O) > 119 kcal/mol, 204 kcal/mol < D/sup 0/(M'M/sup +/-20) < 238 kcal/mol, D/sup 0/(M'M/sub 2//sup +/-O) > 85 kcal/mol D/sup 0/(M'M/sub 2/O/sup +/-O) >85 kcal/mol, D/sup 0/(M'M/sub 2/O/sub 2//sup +/-O) > 85 kcal/mol, and D/sup 0/(M'M/sub 2/O/sub 3//sup +/-O) < 25.5 kcal/mol. 49 references, 1 table.

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

    PubMed

    Modeshia, Deena R; Walton, Richard I

    2010-11-01

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

  12. Oxidative cross-coupling of pyridine N-oxides and ethers between C(sp(2))-H/C(sp(3))-H bonds under transition-metal-free conditions.

    PubMed

    Sun, Wei; Xie, Zuguang; Liu, Jie; Wang, Lei

    2015-04-21

    A novel and efficient method based on the cross-coupling reactions of pyridine N-oxides with ethers between C(sp(2))-H/C(sp(3))-H bonds in the presence of TBHP was developed. The strategy provides an alternative approach to the pyridine moiety under transition-metal-free conditions. PMID:25785666

  13. Preparation and structural investigations of the mixed bismuth niobates, containing transition metals

    Microsoft Academic Search

    I. V. Piir; D. A. Prikhodko; S. V. Ignatchenko; A. V. Schukariov

    1997-01-01

    Mixed bismuth niobium oxides, containing transition metals were synthesized by using solid-state reactions in the systems Bi2O3-Nb2O5-MO(M2O3), M-Cr, Mn, Fe, Co, Cu. Powder X-ray diffraction studies of these compounds show, that crystal phases with structures as the orthorhombic BiNbO4, the layer perovskite-like and the pyrochlore-type ones can be formed depending on the metal oxides molar ratio and the conditions of

  14. A theory of the pressure-induced high-spin-low-spin transition of transition-metal oxides

    Microsoft Academic Search

    Shuhei Ohnishi

    1978-01-01

    The pressure-induced high-spin-low-spin transition of the transition-metal ions in octahedral coordination is studied theoretically. The relation between the crossover point and the transition point is discussed and the formula to determine the transition point is given in terms of the crystal-field splitting Delta and the spin-pairing energy Pi asDelta = alphaPi. The numerical coefficient alpha is determined by the ratio

  15. Transition Metal Oxide Chemistry:  Electronic Structure Study of WO 3 , ReO 3 , and NaWO 3

    Microsoft Academic Search

    M. G. Stachiotti; C. R. A. Catlow; C. O. Rodriguez

    1997-01-01

    In this paper, we present the results of electronic structure, ab initio calculations performed on ReO3 ,W O 3 , and the stoichiometric tungsten bronze NaWO3. We examine the relation between the structural and the electronic properties of the three materials and comment on the solid state chemistry governing the interaction between the transition metal and its oxygen ligands. We

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

    Microsoft Academic Search

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

    2002-01-01

    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,

  17. Evidence against strong correlation in 4d transition-metal oxides CaRuO3 and SrRuO3

    NASA Astrophysics Data System (ADS)

    Maiti, Kalobaran; Singh, Ravi Shankar

    2005-04-01

    We investigate the electronic structure of 4d transition-metal oxides CaRuO3 and SrRuO3 . The analysis of the photoemission spectra reveals significantly weak electron correlation strength (U/ Wtilde 0.2) as expected in 4d systems and resolves the long-standing issue that arose due to the prediction of large U/W similar to 3d systems. It is shown that the bulk spectra, thermodynamic parameters, and optical properties in these systems can consistently be described using first-principles calculations. The observation of different surface and bulk electronic structures in these weakly correlated 4d systems is unusual.

  18. 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)

    Liu, Hongxue

    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.

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

    E-print Network

    Poeppelmeier, Kenneth R.

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

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

    SciTech Connect

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

    2009-09-14

    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.

  1. Transition Metal Compounds

    NASA Astrophysics Data System (ADS)

    Khomskii, Daniel I.

    2014-10-01

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

  2. Autothermal reforming catalyst having perovskite structure

    DOEpatents

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

    2009-03-24

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

  3. Smoothing of ultrathin silver films by transition metal seeding

    E-print Network

    Anders, Andre; Byon, Eungsun; Kim, Dong-Ho; Fukuda, Kentaro; Lim, Sunnie H.N.

    2006-01-01

    the presence of the transition metal (oxide) islands. Thistransition metals as well as noble metals have a thermodynamic tendency to cluster into 3D islands on oxides.transition metals have the highest affinity to oxygen. To consider whether or not they can reduce the oxide

  4. Oligocyclopentadienyl transition metal complexes

    SciTech Connect

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

    2002-01-18

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

  5. Ligand-Assisted Co-Assembly Approach toward Mesoporous Hybrid Catalysts of Transition-Metal Oxides and Noble Metals: Photochemical Water Splitting.

    PubMed

    Liu, Ben; Kuo, Chung-Hao; Chen, Jiejie; Luo, Zhu; Thanneeru, Srinivas; Li, Weikun; Song, Wenqiao; Biswas, Sourav; Suib, Steven L; He, Jie

    2015-07-27

    A bottom-up synthetic approach was developed for the preparation of mesoporous transition-metal-oxide/noble-metal hybrid catalysts through ligand-assisted co-assembly of amphiphilic block-copolymer micelles and polymer-tethered noble-metal nanoparticles (NPs). The synthetic approach offers a general and straightforward method to precisely tune the sizes and loadings of noble-metal NPs in metal oxides. This system thus provides a solid platform to clearly understand the role of noble-metal NPs in photochemical water splitting. The presence of trace amounts of metal NPs (?0.1?wt?%) can enhance the photocatalytic activity for water splitting up to a factor of four. The findings can conceivably be applied to other semiconductors/noble-metal catalysts, which may stand out as a new methodology to build highly efficient solar energy conversion systems. PMID:26073465

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

    PubMed

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

    2014-11-18

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

  7. Intermediate-Valence Behavior in the Transition-Metal Oxide CaCu3Ru4O12

    Microsoft Academic Search

    Wolfgang Kraetschmer; Norbert Buettgen; Alois Loidl; Ernst-Wilhelm Scheidt

    2010-01-01

    A detailed study of the electronic properties of strongly correlated CCRO will be presented. Along with transport, \\\\chi(T) and specific heat, we focus on NMR\\/NQR. CCRO is a metallic system with perovskite structure showing non-Fermi-liquid behavior below 2&,slash;K which is inferred from Cp\\/&,slash;T? -ln(T) and a deviation of 1\\/&,slash;T1 (T) from the Korringa law at the copper site [PRB {78},

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

    PubMed

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

    2014-09-21

    Graphene oxide (GO) is employed as a hole conductor in inverted planar heterojunction perovskite solar cells, and the devices with CH?NH?PbI?-xClx as absorber achieve an efficiency of over 12%. The perovskite film grown on GO exhibits enhanced crystallization, high surface coverage ratio as well as preferred in-plane orientation of the (110) plane. Efficient hole extraction from the perovskite to GO is demonstrated. PMID:25081348

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

    SciTech Connect

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

    2013-04-15

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

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

    E-print Network

    Zhu, Xiangdong

    2008-01-01

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

  11. Tuning ferromagnetism at interfaces between insulating perovskite oxides.

    PubMed

    Ganguli, Nirmal; Kelly, Paul J

    2014-09-19

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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

  14. Oxide Spintronics

    Microsoft Academic Search

    Manuel Bibes; Agns Barthelemy

    2007-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

  17. Transition-metal-free tandem oxidative removal of benzylic methylene group by C-C and C-N bond cleavage followed by intramolecular new aryl C-N bond formation under radical conditions.

    PubMed

    Laha, Joydev K; Tummalapalli, K S Satyanarayana; Gupta, Ankur

    2014-09-01

    A novel tandem oxidative conversion of 10,11-dihydro-5H-dibenzo[b,e][1,4]diazepines to phenazines has been achieved under transition-metal-free, mild conditions using K2S2O8 or DDQ as the oxidizing agent. The transformation proceeds through oxidative removal of a benzylic methylene group by C-C and C-N bond cleavage followed by a new aryl C-N bond formation under radical conditions. PMID:25119523

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

    E-print Network

    Poeppelmeier, Kenneth R.

    in strong, short metal-oxide bonds causing the metal ion to distort toward the oxide ligand. This primary protonated, exhibits distortions in the anion reflecting both factors. Crystal data for [HNC6H6OH]2[Cu(NC5H5 and filled oxide p orbitals, which has been quantified by single point density functional theory (DFT

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

    E-print Network

    Ottino, Julio M.

    includes investigation of direct oxidation of olefins to epoxides catalyzed by methyltrioxorhenium (MTO examination. Approach: Mechanistic aspects of olefins epoxidation by MTO and CO oxidation by a supported gold,3-dimethyl-2-butene with styrene oxide is possible using MTO as a catalyst. Although not all side products

  20. Electronic and silver ionic conductions in perovskite and related oxides

    SciTech Connect

    Matsumoto, Yasumichi; Funaki, Kenji; Hombo, Jukichi; Ogawa, Yoriyuki (Kumamoto Univ. (Japan))

    1992-08-01

    Electronic and silver ionic conductivities in some silver-containing oxides with perovskite and related structures, such as AgNbO{sub 3} (perovskite), AgSbO{sub 3} (pyrochlore-related structure), and Ag-doped Bi-(Pb)-Sr-Ca-Cu-O-system superconductor, were measured by four-probe techniques using Pt electrodes and Ag-{beta}{double prime}-Al{sub 2}O{sub 3} electrodes with silver ionic conduction, respectively. Both AgNbO{sub 3} and AgSbO{sub 3} were n-type semiconductors and their electronic conductivities increased with an increase in the silver content. The electronic conductivity of AgSbO{sub 3} was higher than that of AgNbO{sub 3}, due to the presence of a large amount of oxygen vacancies. Sb{sup 4+} and/or Sb{sup 3+} in AgSbO{sub 3}, and Nb{sup 4+} in AgNbO{sub 3} will act as a donor. Silver ionic conductivities were always lower than the electronic conductivities brought about by the above donors for both AgNbO{sub 3} and AgSbO{sub 3} ceramics. The activation energies of silver ionic conductivity were in the ranges of 1.01-1.58, 0.78-0.90, and 0.94-1.12 eV for AgNbO{sub 3}, AgSbO{sub 3}, and Ag-doped Bi-system superconductors, respectively. The silver ion was assumed to move via the Ag sites in the bulk for AgNbO{sub 3}, but to move in the grain boundaries for AgSbO{sub 3} and the Bi-system superconductor. The mechanisms of the electronic and silver ionic conductions are discussed for the present oxide ceramics.

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

    NASA Astrophysics Data System (ADS)

    Martin, Boris E.

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  3. Transition metals in superheat melts

    NASA Technical Reports Server (NTRS)

    Jakes, Petr; Wolfbauer, Michael-Patrick

    1993-01-01

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

  4. Oxidation Reactions of Ethane over Ba-Ce-O Based Perovskites

    SciTech Connect

    Miller, James E.; Sault, Allen G.; Trudell, Daniel E.; Nenoff, Tina M.; Thoma, Steven G.; Jackson, Nancy B.

    1999-08-18

    Ethane oxidation reactions were studied over pure and Ca-, Mg-, Sr-, La-, Nd-, and Y-substituted BaCeO{sub 3} perovskites under oxygen limited conditions. Several of the materials, notably the Ca- and Y-substituted materials, show activity for complete oxidation of the hydrocarbon to CO{sub 2} at temperatures below 650 C. At higher temperatures, the oxidative dehydrogenation (ODH) to ethylene becomes significant. Conversions and ethylene yields are enhanced by the perovskites above the thermal reaction in our system in some cases. The perovskite structure is not retained in the high temperature reaction environment. Rather, a mixture of carbonates and oxides is formed. Loss of the perovskite structure correlates with a loss of activity and selectivity to ethylene.

  5. Recent advances in methane dehydro-aromatization over transition metal ion-modified zeolite catalysts under non-oxidative conditions

    Microsoft Academic Search

    Yide Xu; Liwu Lin

    1999-01-01

    The effective activation and direct conversion of methane to higher hydrocarbons is a topic of great challenge in catalysis science. Besides oxidative activation such as oxidative coupling of methane to C2+, non-oxidative activation of methane to produce aromatics over Mo\\/HZSM-5 catalysts in a continuous flow mode has attracted significant interest since 1993. This paper reviews the recent advances in catalytic

  6. Calixarene supported transition metal clusters 

    E-print Network

    Taylor, Stephanie Merac

    2013-06-29

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

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

    E-print Network

    Paris-Sud XI, Université de

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

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

    Microsoft Academic Search

    Harrell Sellers; Evgeny Shustorovich

    1996-01-01

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

  9. Photofragment spectroscopy of covalently bound transition metal complexes: a window into CH and CC bond

    E-print Network

    Metz, Ricardo B.

    of Massachusetts, Amherst, MA 01003, USA Transition metal cations Mþ and metal oxide cations MOþ can activate C­4]. In many cases, the transition metal oxides MOþ are even more reactive, able to perform difficultPhotofragment spectroscopy of covalently bound transition metal complexes: a window into C­H and C

  10. Hybrid functionals applied to perovskites.

    PubMed

    Franchini, Cesare

    2014-06-25

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

  11. The Hydride Anion in an Extended Transition Metal Oxide Array: LaSrCoO3H0.7

    Microsoft Academic Search

    M. A. Hayward; E. J. Cussen; J. B. Claridge; M. Bieringer; M. J. Rosseinsky; C. J. Kiely; S. J. Blundell; I. M. Marshall; F. L. Pratt

    2002-01-01

    We present the synthesis and structural characterisation of a transition\\u000ametal oxide hydride, LaSrCoO_3H_{0.7}, which adopts an unprecedented structure\\u000ain which oxide chains are bridged by hydride anions to form a two- dimensional\\u000aextended network. The metal centers are strongly coupled by their bonding with\\u000aboth oxide and hydride ligands to produce magnetic ordering up to at least 350\\u000aK.

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

    SciTech Connect

    Michael John Vasbinder

    2006-12-12

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

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

    DOEpatents

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

    2001-01-01

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

  14. Transition metal complexes coupled to vacancies in oxides: origin of different properties of Cr3+ in MgO bounded to a <100> or <110> Mg2+ vacancy.

    PubMed

    Aramburu, J A; García-Fernández, P; Barriuso, M T; Moreno, M

    2013-11-27

    Despite the importance of vacancies over the properties of insulating oxides its influence on neighboring transition metal ions is far from being understood. This work is devoted to find the origin of various up to now unexplained properties of chromium bounded either to a <100> or a <110> Mg(2+) vacancy in MgO. In these model systems particular attention is paid to understand, by means of ab initio calculations, why the cubic field splitting parameter, 10Dq, is surprisingly 1600 cm(-1) higher for a <100> than for a <110> vacancy, a fact behind the suppression of the sharp (2)E ? (4)A2 luminescence in the latter case. Our calculations, which reproduce the main experimental facts, prove that the average Cr(3+)-O(2-) distance is the same within 0.8% for both systems, and thus, the low 10Dq value for a <110> vacancy is shown to be due mainly to the electrostatic potential from the missing Mg(2+) ion, which increases the energy of antibonding t(2g) (?xy, xz, yz) levels. By contrast, for a <100> Mg(2+) vacancy that potential provides a supplementary increase of the e(g) (?x(2) - y(2), 3z(2 )- r(2)) level energy and thus of 10Dq. The existence of the (2)E ? (4)A2 luminescence for Cr(3+)-doped MgO under perfect cubic symmetry or with a <100> vacancy is shown to be greatly helped by the internal electric field created by the rest of the lattice ions on the CrO6(9-) unit, whose importance is usually ignored. The present results underline the role of ab initio calculations for unveiling the subtle effects induced by a close vacancy on the properties of transition metal ions in oxides. At the same time they stress the failure of the empirical superposition model for deriving the equilibrium geometry of C4v and C2v centers in MgO:Cr(3+). PMID:24164414

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  16. Electronic conduction in La-based perovskite-type oxides

    NASA Astrophysics Data System (ADS)

    Kozuka, Hisashi; Ohbayashi, Kazushige; Koumoto, Kunihito

    2015-04-01

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

  17. Covalent bonding and hybridization effects in the corundum-type transition-metal oxides V2O3 and Ti2O3

    NASA Astrophysics Data System (ADS)

    Eyert, V.; Schwingenschlögl, U.; Eckern, U.

    2005-06-01

    The electronic structure of the corundum-type transition-metal oxides V2O3 and Ti2O3 is studied by means of the augmented spherical wave method, based on density-functional theory and the local density approximation. Comparing the results for the vanadate and the titanate allows us to understand the peculiar shape of the metal 3d a1g density of states, which is present in both compounds. The a1g states are subject to pronounced bonding-antibonding splitting due to metal-metal overlap along the c-axis of the corundum structure. However, the corresponding partial density of states is strongly asymmetric with considerably more weight on the high-energy branch. We argue that this asymmetry is due to an unexpected broadening of the bonding a1g states, which is caused by hybridization with the eg? bands. In contrast, the antibonding a1g states display no such hybridization and form a sharp peak. Our results shed new light on the role of the a1g orbitals for the metal-insulator transitions of V2O3. In particular, due to a1g-eg? hybridization, an interpretation in terms of molecular orbital singlet states on the metal-metal pairs along the c-axis is not an adequate description.

  18. Cation order\\/disorder in lithium transition-metal oxides as insertion electrodes for lithium-ion batteries

    Microsoft Academic Search

    E. Zhecheva; R. Stoyanova; R. Alcántara; P. Lavela; J.-L. Tirado

    2002-01-01

    Results on the local cation ordering in layered lithium-nickel\\/cobalt oxides and metal-substituted lithium-manganese spinels are presented. It is shown that electron spin res- onance of Ni3+ and Mn4+ and magnetic susceptibility measurements are powerful tools to monitor the short-range cation ordering in these compounds, which is not accessible by dif- fraction techniques. Thus, owing to the different strength of the

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

    Microsoft Academic Search

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

    1998-01-01

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

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

    Microsoft Academic Search

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

    2000-01-01

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

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

    Microsoft Academic Search

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

    1997-01-01

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

  2. a Study of Core Excitation Spectra in 3d Transition Metals and Oxides by Electron Energy Loss Spectroscopy and X-Ray Absorption Spectroscopy.

    NASA Astrophysics Data System (ADS)

    Grunes, Lee Alan

    The core excitation spectra of 3d transition metals and oxides are measured by electron energy loss spectroscopy (EELS) and X-ray absorption spectroscopy (XAS). EELS experiments are performed on thin polycrystalline films using a conventional transmission electron microscope equipped with a Wien filter spectrometer. XAS experiments are performed on metal foils or fine powders dusted onto scotch tape, at the Cornell High Energy Synchrotron Source (CHESS). Comparisons are made to theory for both the metal and oxide data. We concentrate on the spectral near edge structure (NES) and attempt to interpret its origins. The dipole forbidden M(,1) 3s (--->) d transitions measured by EELS appear at large but not small momentum transfers, as predicted by the single scattering cross section. The L(,23) edges measured by EELS are dominated at threshold by intense "white lines" due to 2p (--->) d transitions. Comparisons are made to one electron theory for the core edges in the metal. In doing so, we discover anomalous L(,3)/L(,2) white line intensity ratios present in the data but not in the calculations. Oxygen K (O K) edges measured by EELS display multipeaked fine structure near threshold which varies markedly between oxides despite the similar local atomic structures. Metal K edges in both the metals and oxides are obtained using XAS. For the metals, we find excellent agreement between the data and one electron calculations. Finally we compare the oxide NES of the metal L(,23), K, and O K edges altogether. These are found to agree with each other and to molecular orbital (MO) theory only for TiO(,2). The mismatch of the three NES's in the other oxides indicates the failure of one electron theory for insulators. New theory for TiO(,2) and NiO by collaborating theorists is compared to our data. While the TiO(,2) calculation corroborates the one electron MO picture, the NiO calculation shows the O K edge to be dominated by core excitons. The existence of excitons explains the lack of agreement between the NES for core excitations of different atoms in the same solid.

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

    NASA Astrophysics Data System (ADS)

    Sellers, Harrell; Shustorovich, Evgeny

    1996-06-01

    We have employed the bond order conservation-Morse potential (BOC-MP) method to analyze the chemistry of sulfur oxides on the copper and nickel group metals. Specifically, we have calculated the reaction energetics (heats of adsorption, reaction enthalpies and intrinsic activation barriers) of the decomposition and oxidation of sulfur dioxide at low coverages on fcc (111) surfaces of Cu, Ag, Au, Ni, Pd and Pt. The accuracy of the BOC-MP heats of adsorption has been corroborated by high quality ab initio calculations of the heats of SO2 adsorption on Ag and Pd surfaces. We have addressed the following issues: (1) the dissociation of SO2; (2) the stability of adsorbed SO and its likelihood of being a product of SO2 decomposition; (3) the oxidation of SO2; and, (4) the nature of adsorbed SO3 and SO4. The major model projections (obtained for low coverages and without considering diffusional effects) are: (1) the dissociation of SO2?SO + O is unfavorable on all the metals considered, but, the dissociation of SO2?S + O + O, showing distinct periodic trends, is feasible on Cu and particularly on Ni; in the presence of carbon monoxide the dissociation, SO2 + CO?S + O + CO2, may occur on all the metals examined; (2) on the Pt, Pd, Ni and Cu surfaces, SO is unstable; (3) the oxidation of SO2 to SO3 may be achieved with O, O2, H2O2 and NO as oxygen sources on Ag, Au, Pd and Pt surfaces. Although adsorbed SO3 may be readily obtained, it may be impossible to desorb SO3 intact at low coverages because SO3 will decompose to SO2 + O before desorption. (4) The most stable oxygen sulfur specie that withstands elevated temperatures should be dianion sulfate. The relevant experimental data have been discussed. Most of the model projections are in agreement with experiment, but, some suggest reconsideration of the reported experimental data or represent predictions to be verified.

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

    PubMed Central

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

    2015-01-01

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

  5. Transition Metal Switchable Mirror

    SciTech Connect

    2009-08-21

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

  6. Transition Metal Switchable Mirror

    SciTech Connect

    None

    2009-01-01

    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

  7. Oxidation of alkylaromatics to benzylic ketones using TBHP as an oxidant over LaMO 3 (M = Cr, Co, Fe, Mn, Ni) perovskites

    Microsoft Academic Search

    Savita J. Singh; Radha V. Jayaram

    2009-01-01

    A series of LaMO3 (M=Cr, Co, Fe, Mn, Ni) perovskites were synthesized by citrate precursor decomposition method and characterized by XRD technique. The catalytic activity of the synthesized perovskites was investigated for the oxidative functionalization of alkylaromatics to benzylic ketones using TBHP as an oxidant. Of various perovskites screened, LaCrO3 exhibited remarkable catalytic activity providing the oxidation of alkylarenes selectively

  8. Dependence of non-linearity coefficients on transition metal oxide concentration in simplified compositions of ZnO+Bi 2 O 3 +MO varistor ceramics (M=Co or Mn)

    Microsoft Academic Search

    S. Ezhilvalavan; T. R. N. Kutty

    1996-01-01

    Ceramics with simplified compositions of ZnO + Bi2O3 + CoO or MnO show non-linearity coefficients (a) of 40–65 provided the concentration of transition metal ions is > 1.5mol.... Samples doped with Co have higher non-linearity coefficients than those with Mn. This is attributed to the stability of multiple oxidation states of Co(III) + Co(II) in contrast to Mn(II) as the

  9. First-principles study of multiferroic oxides Tamio OGUCHI

    E-print Network

    Katsumoto, Shingo

    on double-perovskite bis- muth transition-metal oxides. 1 Introduction Any condensed matter system reveals) order of the microscopic de- grees of freedom, magnetic moments, electric dipoles and atomicFirst-principles study of multiferroic oxides Tamio OGUCHI Department of Quantum Matter, ADSM

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

    PubMed

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

    2013-05-20

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

  11. Mapping the Valence States of Transition-Metal Elements Using Energy-Filtered Transmission Electron Microscopy

    E-print Network

    Wang, Zhong L.

    The properties of transition-metal oxides are related to the presence of elements with mixed valences, such as MnMapping the Valence States of Transition-Metal Elements Using Energy-Filtered Transmission Electron and Co. Spatial mapping of the valence-state distribution of transition-metal elements is a challenge

  12. Three oxidation states and atomic-scale p–n junctions in manganese perovskite oxide from hydrothermal systems

    Microsoft Academic Search

    Shouhua Feng; Hongming Yuan; Zhan Shi; Yan Chen; Yongwei Wang; Keke Huang; Changmin Hou; Jixue Li; Guangsheng Pang; Ying Hou

    2008-01-01

    Perovskite oxides have provided magical structural models for superconducting and colossal magnetoresistance, and the search\\u000a for nano-scale and\\/or atomic-scale devices with particular property by specific preparations in the same systems has been\\u000a extensively conducted. We present here the three oxidation states of manganese (Mn3+, Mn4+, Mn5+) in the perovskite oxide, La0.66Ca0.29K0.05MnO3, which most interestingly shows the rectifying effect as atomic-scale

  13. Soft chemical control of the crystal and magnetic structure of a layered mixed valent manganite oxide sulfide

    NASA Astrophysics Data System (ADS)

    Blandy, Jack N.; Abakumov, Artem M.; Christensen, Kirsten E.; Hadermann, Joke; Adamson, Paul; Cassidy, Simon J.; Ramos, Silvia; Free, David G.; Cohen, Harry; Woodruff, Daniel N.; Thompson, Amber L.; Clarke, Simon J.

    2015-04-01

    Oxidative deintercalation of copper ions from the sulfide layers of the layered mixed-valent manganite oxide sulfide Sr2MnO2Cu1.5S2 results in control of the copper-vacancy modulated superstructure and the ordered arrangement of magnetic moments carried by the manganese ions. This soft chemistry enables control of the structures and properties of these complex materials which complement mixed-valent perovskite and perovskite-related transition metal oxides.

  14. K-edge x-ray absorption spectra in transition-metal oxides beyond the single-particle approximation: Shake-up many-body effects

    NASA Astrophysics Data System (ADS)

    Calandra, M.; Rueff, J. P.; Gougoussis, C.; Céolin, D.; Gorgoi, M.; Benedetti, S.; Torelli, P.; Shukla, A.; Chandesris, D.; Brouder, Ch.

    2012-10-01

    Near-edge structures in K-edge x-ray absorption spectra (XAS) are widely investigated to understand the electronic and local structure in materials. The precise interpretation of these spectra with the help of calculations is hence of prime importance, especially for the study of correlated materials which have a complicated electronic structure per se. The single-particle approach, for example, has generally limited itself to the dominant dipolar cross section. It has long been known, however, that effects beyond this approach should be taken into account, due to both the inadequacy of such calculations when compared to experiment and the presence of shakeup many-body satellites in core-level photoemission spectra of correlated materials. This effect should manifest itself in XANES spectra, and the question is first how to account for it theoretically and second how to verify it experimentally. By using state-of-the-art first-principles electronic structure calculations and 1s photoemission measurements, we demonstrate that shakeup many-body effects are present in K-edge XAS dipolar spectra of NiO, CoO, and CuO at all energy scales. We show that shakeup effects can be included in K-edge XAS spectra in a simple way by convoluting the single-particle first-principles calculations including core-hole effects with the 1s photoemission spectra. We thus describe all features appearing in the XAS dipolar cross section of NiO and CoO and obtain a dramatic improvement with respect to the single-particle calculation in CuO. These materials being prototype correlated magnetic oxides, our work points to the presence of shakeup effects in K-edge XANES of most correlated transition-metal compounds and shows how to account for them, paving the way to a precise understanding of their electronic structure.

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

    NASA Astrophysics Data System (ADS)

    Carraher, Jack McCaslin

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

  16. Perovskite oxides MRuO3 (M = Sr, Ca and Ba): Structural distortion, electronic and magnetic properties with GGA and GGA-modified Becke-Johnson approaches

    NASA Astrophysics Data System (ADS)

    Abbes, Labdelli; Noura, Hamdad

    Electronic and magnetic properties of transition-metal oxides are a continuing research theme due to the variety of ground states and their technological applications. In the present paper, we present first-principles calculations using the full-potential linear augmented plane-wave methods (FP-LAPW) on the structural, electronic and magnetic properties of tree cubic (Pm-3m space group) perovskite oxides SrRuO3, BaRuO3, and CaRuO3 in comparison with other phases ((4H) four-layered hexagonal (P63/mmc space group), (2H) two-layered hexagonal (P63/mmc space group) and orthorhombic (Pnma space group). The current study is given within the density-functional theory basis DFT. The exchange-correlation potential is introduced by different approaches. We computed the equilibrium lattices, bulk modulus and its pressure derivatives and equilibrium volume. Our obtained results agree successfully with the theoretical and experimental data. The spin magnetic moments of these oxides have been obtained to investigate the magnetic properties. We report a detailed analysis of the different ground states properties for considerable oxides using GGA and GGA-modified Becke-Johnson computational approaches.

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

    Microsoft Academic Search

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

    2000-01-01

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

  18. Transition metal transporters in plants

    Microsoft Academic Search

    J. L. Hall; Lorraine E. Williams

    2003-01-01

    Transition metals such as Fe, Cu, Mn, and Zn are essential minerals for normal plant growth and devel- opment, although they can be toxic when present in excess. Thus, for healthy plant growth, a range of transition metals must be acquired from the soil, dis- tributed around the plant, and their concentrations carefully regulated within different cells and orga- nelles.

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

    NASA Astrophysics Data System (ADS)

    Lee, Yueh-Lin

    2011-12-01

    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.

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

    E-print Network

    zur Loye, Hans-Conrad

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-07-01

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

  2. Thermal decomposition of transition metal dithiocarbamates

    Microsoft Academic Search

    S. Singhal; A. N. Garg; K. Chandra

    2004-01-01

    Transition metal dithiocarbamate complexes, [M(S2CN(C2H5)(CH2CH2OH)] (M=Co, Ni, Cu, Zn and Cd) have been prepared and characterized by elemental analysis and infrared spectra. Thermal decomposition of all the complexes occurs in two or three stages. The first stage in all the complexes is always fast with 65–70% mass loss. In all cases the end product is metal oxide except in the

  3. Studies of magnetism in rhenium and manganese based perovskite oxides

    Microsoft Academic Search

    Christopher Ryan Wiebe

    2003-01-01

    The bulk of this thesis consists of studies of geometric frustration in S = ½ FCC perovskites based upon the chemical formula A2BReO 6. The magnetism of these materials is expected to exhibit geometric frustration, a situation in which the ideal spin arrangements cannot be achieved for antiferromagnetic interactions between adjacent spins. It is proposed that subtle quantum effects are

  4. Studies of Magnetism in Rhenium and Manganese Based Perovskite Oxides

    Microsoft Academic Search

    Christopher Ryan Wiebe

    2002-01-01

    The bulk of this thesis consists of studies of geometric frustration in S = 1\\/2 FCC perovskites based upon the chemical formula A?BReO?. The magnetism of these materials is expected to exhibit geometric frustration, a situation in which the ideal spin arrangements cannot be achieved for antiferromagnetic interactions between adjacent spins. It is proposed that subtle quantum effects are driving

  5. 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

    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

    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

  6. Wet oxidation of phenol over transition metal oxide catalysts supported on Ce0.65 Zr0.35 O2 prepared by continuous hydrothermal synthesis in supercritical water.

    PubMed

    Kim, Kyoung-Hun; Kim, Jeong-Rang; Ihm, Son-Ki

    2009-08-15

    The mixed oxide (Ce(0.65)Zr(0.35)O(2)) prepared by supercritical synthesis was applied as a support of transition metal (Mn, Fe, Co, Ni, and Cu) oxide catalysts for catalytic wet oxidation (CWO) of phenol in view of their higher thermal stability, better oxygen storage capacity, and higher surface area. The prepared catalysts showed an enhanced catalytic activity for CWO of phenol due to the excellent redox properties of ceria-zirconia mixed oxide. Among the prepared catalysts, the CuO(x)/Ce(0.65)Zr(0.35)O(2) was the most effective catalyst in view of catalytic activity and CO(2) selectivity. The leached copper ions seem to contribute to the higher conversion of phenol over the CuO(x)/Ce(0.65)Zr(0.35)O(2) via homogeneous catalysis. The characterization with XPS, XANES, and TPR experiments confirmed that the active copper species in the CuO(x)/Ce(0.65)Zr(0.35)O(2) is highly dispersed Cu(2+) clusters. Although the MnO(x)/Ce(0.65)Zr(0.35)O(2) showed a high conversion of phenol and TOC, the converted phenol was mainly changed to carbon deposits on the surface of catalyst resulting in catalyst deactivation. PMID:19264401

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

    NASA Astrophysics Data System (ADS)

    Tauer, Tania Allison

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

  8. Selenophene transition metal complexes

    SciTech Connect

    White, C.J.

    1994-07-27

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

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

    PubMed

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

    2014-01-01

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

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

    PubMed Central

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

    2014-01-01

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

  11. 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

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

    2014-05-21

    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

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

    PubMed

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

    2008-05-16

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

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

    PubMed

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

    2014-07-21

    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

  14. 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

    Igor Djerdj; Denis Arcon; Zvonko Jaglicic; Markus Niederberger

    2008-01-01

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

  15. Perovskite-type catalytic materials for environmental applications

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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

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

    PubMed

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

    2014-01-01

    Strong correlation between spins and conduction electrons is key in spintronic materials and devices. A few ferro- or ferrimagnetic transition metal oxides such as La1-(x)Sr(x)MnO3, Fe3O4, CrO2 and Sr2FeMoO6 have spin-polarized conduction electrons at room temperature, but it is difficult to find other spin-polarized oxides with high Curie temperatures (well above room temperature) and large magnetizations for spintronics applications. Here we show that an A- and B-site-ordered quadruple perovskite oxide, CaCu3Fe2Re2O12, has spin-polarized conduction electrons and is ferrimagnetic up to 560 K. The couplings between the three magnetic cations lead to the high Curie temperature, a large saturation magnetization of 8.7 ?B and a half-metallic electronic structure, in which only minority-spin bands cross the Fermi level, producing highly spin-polarized conduction electrons. Spin polarization is confirmed by an observed low-field magnetoresistance effect in a polycrystalline sample. Optimization of CaCu3Fe2Re2O12 and related quadruple perovskite phases is expected to produce a new family of useful spintronic materials. PMID:24849185

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  18. Characterization of carbon paste electrodes modified with manganese based perovskites-type oxides from the amperometric determination of hydrogen peroxide

    Microsoft Academic Search

    Guillermina L. Luque; Nancy F. Ferreyra; A. Gabriela Leyva; Gustavo A. Rivas

    2009-01-01

    This work proposes the amperometric determination of hydrogen peroxide reduction and oxidation as a tool for the characterization of La1?xAxMnO3 perovskites dispersed in a graphite composite electrode (carbon paste electrode, CPE). The catalytic activity of perovskites towards the oxidation and reduction of hydrogen peroxide is highly dependent on the nature of the A cation and on the temperature and time

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

    Microsoft Academic Search

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

    2007-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Jin, Fangjun; Li, Lei; He, Tianmin

    2015-01-01

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

  1. Resonant x-ray reflectivity study of perovskite oxide superlattices

    Microsoft Academic Search

    N. Kemik; M. Gu; F. Yang; C.-Y. Chang; Y. Song; M. Bibee; A. Mehta; M. D. Biegalski; H. M. Christen; N. D. Browning; Y. Takamura

    2011-01-01

    Resonant x-ray reflectivity (XRR) is utilized to characterize the structural properties of La0.7Sr0.3MnO3\\/La0.7Sr0.3FeO3 superlattices. XRR spectra at the Mn and Fe absorption edges provide additional structural information compared to spectra obtained with a conventional Cu x-ray source. We demonstrate that this technique provides individual layer thicknesses and intermixing behavior of perovskite superlattices with small density contrast in a non-destructive manner.

  2. Spin-Orbital Superstructure in Strained Ferrimagnetic Perovskite Cobalt Oxide

    NASA Astrophysics Data System (ADS)

    Fujioka, J.; Yamasaki, Y.; Nakao, H.; Kumai, R.; Murakami, Y.; Nakamura, M.; Kawasaki, M.; Tokura, Y.

    2013-07-01

    We have investigated the Co-3d spin-orbital state in a thin film of perovskite LaCoO3 to clarify the origin of strain induced spontaneous magnetization (TC=94K) by means of x-ray diffraction, optical spectroscopy, and magnetization measurements. A lattice distortion with the propagation vector (1/4 -??1/4 1/4) and an anomalous activation of optical phonons coupled to Co-3d orbital are observed below 126 K. Combined with the azimuthal angle analysis of superlattice reflection, we propose that the ordering of Co-3d orbital promoted by an epitaxial strain produces a unique ferrimagnetic structure.

  3. Studies of magnetism in rhenium and manganese based perovskite oxides

    NASA Astrophysics Data System (ADS)

    Wiebe, Christopher Ryan

    The bulk of this thesis consists of studies of geometric frustration in S = ½ FCC perovskites based upon the chemical formula A2BReO 6. The magnetism of these materials is expected to exhibit geometric frustration, a situation in which the ideal spin arrangements cannot be achieved for antiferromagnetic interactions between adjacent spins. It is proposed that subtle quantum effects are driving these systems to unique ground states in the absence of chemical disorder. Both compounds Sr2CaReO 6 and Sr2MgReO6 exhibit spin glass behaviour at low temperatures (TG ˜ 14 K and TG ˜ 50 K respectively), in which the magnetic moments freeze out in random orientations instead of an ordered array. This work shows that these materials possess several unconventional properties, which suggest that interesting spin dynamics may be present. Other perovskite and perovskite-related materials studied in this thesis include the magnetoresistive CaMnO3-delta and the "pillared" material La5Re3MnO16. Neutron diffraction studies have shown that both CaMnO2.94 and CaMnO2.89 order at TN ˜ 125 K, but possess unique yet related magnetic structures. CaMnO2.94 orders into a simple G-type magnetic structure, as observed in the compound CaMnO3. The slightly more doped sample CaMnO2.89, on the other hand, orders into a magnetic structure related to the G-type, and involves a Mn3+/Mn 4+ charge ordering over every four lattice spacings. The new material La5Re3MnO16 consists of layers of corner shared ReO6 and MnO6 octahedra that are separated by layers of Re2O10 dimer units. Metal-metal bonding involving Re atoms have been postulated for these dimers which separate the Re/Mn layers by approximately 10 A. The magnetic behaviour exhibited by this new class of materials is rich and complex. Despite the large distances separating the perovskite layers, the Re and Mn magnetic moments order into a ferrimagnetic Q = (0, 0, ½) structure below a relatively high T N of 161 K. There may be an additional spin rearrangement at lower temperatures as evidenced by weak magnetic Bragg peaks below ˜50 K.

  4. Compositional engineering of perovskite oxides for highly efficient oxygen reduction reactions.

    PubMed

    Chen, Dengjie; Chen, Chi; Zhang, Zhenbao; Baiyee, Zarah Medina; Ciucci, Francesco; Shao, Zongping

    2015-04-29

    Mixed conducting perovskite oxides are promising catalysts for high-temperature oxygen reduction reaction. Pristine SrCoO3-? is a widely used parent oxide for the development of highly active mixed conductors. Doping a small amount of redox-inactive cation into the B site (Co site) of SrCoO3-? has been applied as an effective way to improve physicochemical properties and electrochemical performance. Most findings however are obtained only from experimental observations, and no universal guidelines have been proposed. In this article, combined experimental and theoretical studies are conducted to obtain fundamental understanding of the effect of B-site doping concentration with redox-inactive cation (Sc) on the properties and performance of the perovskite oxides. The phase structure, electronic conductivity, defect chemistry, oxygen reduction kinetics, oxygen ion transport, and electrochemical reactivity are experimentally characterized. In-depth analysis of doping level effect is also undertaken by first-principles calculations. Among the compositions, SrCo0.95Sc0.05O3-? shows the best oxygen kinetics and corresponds to the minimum fraction of Sc for stabilization of the oxygen-vacancy-disordered structure. The results strongly support that B-site doping of SrCoO3-? with a small amount of redox-inactive cation is an effective strategy toward the development of highly active mixed conducting perovskites for efficient solid oxide fuel cells and oxygen transport membranes. PMID:25849591

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

    SciTech Connect

    Djerdj, Igor [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

    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.

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

    NASA Astrophysics Data System (ADS)

    2014-11-01

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

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

    E-print Network

    Goddard III, William A.

    oxides. I. Introduction While the electronic structureof neutral transition-metal oxides has been of empirical properties of transition-metal oxides reveals that early metal-oxo compounds exhibit highJ. Phys. Chem. 1988, 92, 2109-2115 2109 Early- versus Late-Transition-Metal-Oxo Bonds

  8. Thermal decomposition of transition metal dithiocarbamates

    Microsoft Academic Search

    S. Singhal; A. N. Garg; K. Chandra

    2004-01-01

    Transition metal dithiocarbamate complexes, [M(S2CN(C2H5)(CH2CH2OH)] (M=Co, Ni, Cu, Zn and Cd) have been prepared and characterized by elemental analysis and infrared spectra. Thermal decomposition\\u000a of all the complexes occurs in two or three stages. The first stage in all the complexes is always fast with 65-70% mass loss.\\u000a In all cases the end product is metal oxide except in the

  9. Acetone gas sensing properties of SmFe 1? x Mg x O 3 perovskite oxides

    Microsoft Academic Search

    Xing Liu; Jifan Hu; Bin Cheng; Hongwei Qin; Minhua Jiang

    2008-01-01

    Novel sensing materials, SmFe1?xMgxO3, were applied for an acetone vapor sensor. Fine powders of the oxides were prepared by a sol–gel method using citric acid. The compounds had a perovskite phase. The Mg-doping restrained the growth of the grain size. The Mg-doping strongly influenced the resistance, activation energy for conduction and gas response of the SmFeO3. The highest response to

  10. Ab initio determination of heavy oxide perovskite related structures from precession electron diffraction data.

    PubMed

    Boulahya, Khalid; Ruiz-González, Luisa; Parras, Marina; González-Calbet, José M; Nickolsky, M S; Nicolopoulos, Stavros

    2007-01-01

    Two complex perovskite-related structures were solved by ab initio from precession electron diffraction intensities. Structure models were firstly derived from HREM images and than have been confirmed independently using two and three-dimensional sets of precession intensities. Patterson techniques prove to be effective for ab initio structure resolution, specially in case of projections with no overlapping atoms. Quality of precession intensity data may be suitable enough to resolve unknown heavy oxide structures. PMID:17254714

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

    Microsoft Academic Search

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

    2001-01-01

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

  12. Lanthanum cobaltite perovskite supported onto mesoporous zirconium dioxide: Nature of active sites of VOC oxidation

    Microsoft Academic Search

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

    2011-01-01

    Novel catalytic nano-sized materials based on LaCoOx perovskite nanoparticles incapsulated in the mesoporous matrix of zirconia were prepared, characterized by physicochemical methods and tested in complete methanol oxidation. LaCoOx nanoparticles were prepared inside the mesopores of ZrO2 by decomposition of bimetallic La–Co glycine precursor complexes. The catalysts have been studied by diffuse-reflectance FTIR-spectroscopy using such probe molecules as CO, CD3CN

  13. Engineered interfaces of artificial perovskite oxide superlattices via nanosheet deposition process.

    PubMed

    Li, Bao-Wen; Osada, Minoru; Ozawa, Tadashi C; Ebina, Yasuo; Akatsuka, Kosho; Ma, Renzhi; Funakubo, Hiroshi; Sasaki, Takayoshi

    2010-11-23

    Combining different materials into desired superlattice structures can produce new electronic states at the interface and the opportunity to create artificial materials with novel properties. Here we introduce a new, rather unexpected, and yet simple way to such a superlattice assembly of perovskite oxides: in the Dion-Jacobson phase, a model system of layered perovskites, high-quality bicolor perovskite superlattices (LaNb(2)O(7))(nL)(Ca(2)Nb(3)O(10))(nC) are successfully fabricated by a layer-by-layer assembly using two different perovskite nanosheets (LaNb(2)O(7) and Ca(2)Nb(3)O(10)) as a building block. The artificially fabricated (LaNb(2)O(7)/Ca(2)Nb(3)O(10)) superlattices are structurally unique, which is not feasible to create in the bulk form. By such an artificial structuring, we found that (LaNb(2)O(7)/Ca(2)Nb(3)O(10)) superlattices possess a new form of interface coupling, which gives rise to ferroelectricity. PMID:21049905

  14. The effect of different types of additives on the catalytic activity of Au\\/Al 2O 3 in propene total oxidation: transition metal oxides and ceria

    Microsoft Academic Search

    Andreea Catalina Gluhoi; Nina Bogdanchikova; Bernard E. Nieuwenhuys

    2005-01-01

    The total oxidation of C3H6 was investigated over Au\\/Al2O3, and multicomponent Au\\/MOx\\/Al2O3 (M: Ce, Mn, Co, Fe) catalysts prepared by deposition-precipitation with urea. The catalysts have been characterized by means of X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), total surface area (BET), and diffuse reflectance ultra-violet–visible spectroscopy DR\\/UV–Vis. Based on this characterization, it was concluded

  15. High Mobility in a Stable Transparent Perovskite Oxide

    NASA Astrophysics Data System (ADS)

    Kim, Hyung Joon; Kim, Useong; Kim, Hoon Min; Kim, Tai Hoon; Mun, Hyo Sik; Jeon, Byung-Gu; Hong, Kwang Taek; Lee, Woong-Jhae; Ju, Chanjong; Kim, Kee Hoon; Char, Kookrin

    2012-06-01

    We discovered that La-doped BaSnO3 with the perovskite structure has an unprecedentedly high mobility at room temperature while retaining its optical transparency. In single crystals, the mobility reached 320 cm2 V-1 s-1 at a doping level of 8×1019 cm-3, constituting the highest value among wide-band-gap semiconductors. In epitaxial films, the maximum mobility was 70 cm2 V-1 s-1 at a doping level of 4.4×1020 cm-3. We also show that resistance of (Ba,La)SnO3 changes little even after a thermal cycle to 530 °C in air, pointing to an unusual stability of oxygen atoms and great potential for realizing transparent high-frequency, high-power functional devices.

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

    PubMed

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

    2013-01-01

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

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

    PubMed Central

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

    2013-01-01

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

  18. Volume Collapse Transitions in Transition Metals and Compounds at High Pressures

    Microsoft Academic Search

    Choong-Shik Yoo; B. Maddox; M. Hu; P. Chow; V. Iota; B. Baer; W. Evans; H. Cynn; D. Hausermann

    2004-01-01

    Unusual phase transitions driven by electron correlation effects occur in many transition metals and transition metal compounds at high pressures, some accompanied with large volume collapses (5-17% in rare-earth metals and 10-15% in magnetic 3d transition metal oxides, for example). However, the exact nature of these transitions has not been well understood, including the relationships between the crystal and electronic

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

    PubMed

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

    2013-02-14

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

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

    Microsoft Academic Search

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

    2000-01-01

    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-

  1. A New Bipolar Type Transistor Created Based on Interface Effects of Integrated All Perovskite Oxides

    NASA Astrophysics Data System (ADS)

    Xia, Feng-Jin; Wu, Hao; Fu, Yue-Ju; Xu, Bo; Yuan, Jie; Zhu, Bei-Yi; Qiu, Xiang-Gang; Cao, Li-Xin; Li, Jun-Jie; Jin, Ai-Zi; Wang, Yu-Mei; Li, Fang-Hua; Liu, Bao-Ting; Xie, Zhong; Zhao, Bai-Ru

    2012-10-01

    Oxide transistor is the basic device to construct the oxide electronic circuit that is the backing to develop integrated oxide electronics with high efficiency and low power consumption. By growing the perovskite oxide integrated layers and tailoring them to lead semiconducting functions at their interfaces, the development of oxide transistors may be able to perform. We realize a kind of p-i-n type integrated layers consisting of an n-type cuprate superconductor, p-type colossal magnetoresistance manganite, and a ferroelectric barrier (i). From this, bipolar transistors were fabricated at the back-to-back p-i-n junctions, for which the Schottky emission and p-n junction barriers, as well as the ferroelectric polarization, were integrated into the interfaces to control the transport properties; a preliminary but distinct current gain greater than 1.6 at input current of microampers order was observed. These results present a real possibility to date for developing bipolar all perovskite oxide transistors.

  2. Application of Two Dimensional Flourescence Spectroscopy to Transition Metal Clusters.

    NASA Astrophysics Data System (ADS)

    Kokkin, Damian L.; Steimle, Timothy

    2014-06-01

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

  3. Catalytic and electrocatalytic oxidation of ethylene on a perovskite electrode in a solid electrolyte cell

    Microsoft Academic Search

    G. Marnellos; C. Athanasiou; T. Angelidis; M. Stoukides

    1997-01-01

    The catalytic and electrocatalytic behavior of the La0.6Sr0.4Co0.8Fe0.2O3?a perovskite-type oxide deposited on Yttria Stabilized Zirconia, was studied during the reaction of ethylene oxidation. Experiments\\u000a were carried out in a continuous-flow well-mixed reactor (CSTR) at atmospheric total pressure and at temperatures between\\u000a 350 and 550 C. Under open circuit, the technique of solid-electrolyte potentiometry (SEP) was used in order to monitor

  4. Transparent and conductive oxide films with the perovskite structure: La and Sb-doped BaSnO3

    Microsoft Academic Search

    H. F. Wang; Q. Z. Liu; F. Chen; G. Y. Gao; Wenbin Wu; X. H. Chen

    2007-01-01

    We report that (La0.07Ba0.93)SnO3 films grown epitaxially on SrTiO3(001) substrates by laser ablation at 760 °C show a cubic perovskite structure of lattice constant 4.121 A?, excellent optical transmittance in the visible range, and a weak metallic behavior with low resistivity of about 4 m? cm within 10–300 K. The transparent perovskite oxide films are n-type conductors, with carrier concentration

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

    NASA Astrophysics Data System (ADS)

    Yang, Kesong; Nazir, Safdar; Behtash, Maziar

    2015-03-01

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

  6. Perovskite-type oxide thin film integrated fiber optic sensor for high-temperature hydrogen measurement.

    PubMed

    Tang, Xiling; Remmel, Kurtis; Lan, Xinwei; Deng, Jiangdong; Xiao, Hai; Dong, Junhang

    2009-09-15

    Small size fiber optic devices integrated with chemically sensitive photonic materials are emerging as a new class of high-performance optical chemical sensor that have the potential to meet many analytical challenges in future clean energy systems and environmental management. Here, we report the integration of a proton conducting perovskite oxide thin film with a long-period fiber grating (LPFG) device for high-temperature in situ measurement of bulk hydrogen in fossil- and biomass-derived syngas. The perovskite-type Sr(Ce(0.8)Zr(0.1))Y(0.1)O(2.95) (SCZY) nanocrystalline thin film is coated on the 125 microm diameter LPFG by a facile polymeric precursor route. This fiber optic sensor (FOS) operates by monitoring the LPFG resonant wavelength (lambda(R)), which is a function of the refractive index of the perovskite oxide overcoat. At high temperature, the types and population of the ionic and electronic defects in the SCZY structure depend on the surrounding hydrogen partial pressure. Thus, varying the H(2) concentration changes the SCZY film refractive index and light absorbing characteristics that in turn shifts the lambda(R) of the LPFG. The SCZY-coated LPFG sensor has been demonstrated for bulk hydrogen measurement at 500 degrees C for its sensitivity, stability/reversibility, and H(2)-selectivity over other relevant small gases including CO, CH(4), CO(2), H(2)O, and H(2)S, etc. PMID:19681577

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

    PubMed

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

    2014-07-23

    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

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

    PubMed

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

    2011-08-01

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

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

    PubMed Central

    2015-01-01

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

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

    Microsoft Academic Search

    Igor Solovyev

    2011-01-01

    “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

  11. Iron Partitioning And Oxidation State In Mg-Perovskite And Ferropericlase At Lower Mantle Conditions

    NASA Astrophysics Data System (ADS)

    Auzende, A.; Badro, J.; Gloter, A.

    2005-12-01

    Many processes that occur within the Earth are determined by the physical properties of the lower mantle. Albeit their thermodynamic stability in the lower mantle, the physical and chemical properties of its two main phases, namely (Mg,Fe)SiO3 magnesium silicate perovskite and (Mg,Fe)O ferropericlase, are affected by variations in the chemistry of iron. We report results concerning the behaviour of iron under lower mantle conditions. Iron partitioning experiments between Mg-perovskite and ferropericlase were conducted on samples synthesized from a San Carlos olivine compressed in a laser-heated diamond anvil cell. Recovered run products were thinned to electron transparency by focused ion beam and studied by analytical transmission electron microscopy (ATEM). Energy-dispersive x-ray measurements were used to calculate the partitioning coefficients of the iron between the phases at relevant lower mantle conditions. As the oxidation state of iron is known to influence the distribution of iron in the mantle phases, there is a strong motivation to achieve a quantitative determination of Fe3+ content in the lower mantle assemblage Mg-perovskite and ferropericlase. The Fe3+ /Fe concentrations were determined by electron energy loss spectroscopy. We also heated a (Mg0.83 Fe0.17)O at 92 GPa and investigated the recovered samples by ATEM. We see no evidence of decomposition into magnesium oxide and ferrous rich oxide components, which is at odds with a recent report. Our work provides important data on Fe/Mg partitioning and the oxidation state in the two main phases of lower mantle.

  12. Hybrid density functional calculations of redox potentials and formation energies of transition metal compounds

    E-print Network

    Ceder, Gerbrand

    , and formation energies of transition metal compounds. Conventional DFT functionals significantly underesti- mate-Fock ex- change. For formation energies, HSE06 performs well for transition metal compounds, which the results of nontransi- tion metal oxides. Hence, we find that hybrid functionals provide a good alternative

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    Interface engineering of structural distortions is a key for exploring the functional properties of oxide heterostructures and superlattices. In this paper, we report on our comprehensive investigations of oxygen octahedral distortions at the heterointerface between perovskite oxides SrRuO3 and BaTiO3 on GdScO3 substrates and of the influences of the interfacially engineered distortions on the magneto-transport properties of the SrRuO3 layer. Our state-of-the-art annular bright-field imaging in aberration-corrected scanning transmission electron microscopy revealed that the RuO6 octahedral distortions in the SrRuO3 layer have strong dependence on the stacking order of the SrRuO3 and BaTiO3 layers on the substrate. This can be attributed to the difference in the interfacial octahedral connections. We also found that the stacking order of the oxide layers has a strong impact on the magneto-transport properties, allowing for control of the magnetic anisotropy of the SrRuO3 layer through interface engineering. Our results demonstrate the significance of the interface engineering of the octahedral distortions on the structural and physical properties of perovskite oxides.

  14. [Non-empirical interatomic potentials for transition metals

    SciTech Connect

    Not Available

    1993-01-01

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

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

    SciTech Connect

    Not Available

    1993-05-01

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

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

    SciTech Connect

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

    2011-12-31

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

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

    NASA Astrophysics Data System (ADS)

    Balachandran, Prasanna V.; Rondinelli, James M.

    2013-08-01

    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.

  18. Transition metal-substituted cobalt ferrite nanoparticles for biomedical applications.

    PubMed

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

    2013-03-01

    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

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

    NASA Astrophysics Data System (ADS)

    Yao, Takeshi; Ito, Toyoji; Kokubo, Tadashi

    1995-05-01

    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.

  20. Highly Conductive SrVO3 as a bottom electrode for functional perovskite oxides.

    PubMed

    Moyer, Jarrett A; Eaton, Craig; Engel-Herbert, Roman

    2013-07-12

    Stoichiometric SrVO3 thin films grown by hybrid molecular beam epitaxy are demonstrated, meeting the stringent requirements of an ideal bottom electrode material. They display an order of magnitude lower room temperature resistivity and superior chemical stability, compared to the commonly employed SrRuO3 , as well as atomically smooth surfaces. Excellent structural compatibility with perovskite and related structures renders SrVO3 a high performance electrode material with the potential to promote the creation of new functional oxide electronic devices. PMID:23703901