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1

Electronic structure of double-perovskite transition-metal oxides  

Microsoft Academic Search

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

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

2000-01-01

2

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

Microsoft Academic Search

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

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

2006-01-01

3

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

NASA Astrophysics Data System (ADS)

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

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

2006-08-01

4

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

NASA Astrophysics Data System (ADS)

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

Nian, Yibo

5

Investigations of the electronic structure of d0 transition metal oxides belonging to the perovskite family  

NASA Astrophysics Data System (ADS)

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 (Ti 4+, Nb 5+, Ta 5+, Mo 6+, and W 6+) were examined primarily in perovskite and perovskite-related structures. In these compounds the top of the valence band is primarily oxygen 2 p non-bonding in character, while the conduction band arises from the ? ? interaction between the transition metal t2 g orbitals and oxygen. For isostructural compounds the band gap increases as the effective electronegativity of the transition metal ion decreases. The effective electronegativity decreases in the following order: Mo 6+>W 6+>Nb 5+˜Ti 4+>Ta 5+. The band gap is also sensitive to changes in the conduction band width, which is maximized for structures possessing linear M-O- M bonds, such as the cubic perovskite structure. As this bond angle decreases (e.g., via octahedral tilting distortions) the conduction band narrows and the band gap increases. Decreasing the dimensionality from 3-D (e.g., the cubic perovskite structure) to 2-D (e.g., the K 2NiF 4 structure) does not significantly alter the band gap, whereas completely isolating the MO 6 octahedra (e.g., the ordered double perovskite structure) narrows the conduction band width dramatically and leads to a significant increase in the band gap. Inductive effects due to the presence of electropositive "spectator" cations (alkali, alkaline earth, and rare-earth cations) tend to be small and can generally be neglected.

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

2003-10-01

6

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

Microsoft Academic Search

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

Louis Whaley

2007-01-01

7

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

SciTech Connect

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

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

2014-01-01

8

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

9

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

NASA Astrophysics Data System (ADS)

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 t2g systems. Slave-boson mean-field analyses indicate the possibility of novel superconducting states induced by carrier doping into the Mott-insulating parent systems, suggesting the present model systems as unique playgrounds for studying correlation-induced novel phenomena. Possible experimental realizations are also discussed.

Okamoto, Satoshi

2013-02-01

10

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

Microsoft Academic Search

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,

Farshid Ramezanipour

2011-01-01

11

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

NASA Astrophysics Data System (ADS)

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

Misra, Sunasira

2012-07-01

12

A comparison in activity between transition-metal oxides and transition metals  

NASA Astrophysics Data System (ADS)

Transition-metal oxides are widely used materials in catalysis as substrates and promoters, but also as the active catalyst materials themselves. We compare the reactivity of transition-metal oxides with the one of transition metals. The comparison is exemplified for the ammonia synthesis reaction. First we show that there exist characteristic Brřnsted-Evans Polanyi (BEP) relations (linear relations between transition state and dissociation energies) for dissociation of molecules on transition-metal oxides in the rutile and perovskite structure. It is well-known that the (211) metal surface is several orders of magnitude more reactive than the (111) metal surface due to the lower BEP line for the 211 facet. We find that both rutiles and perovskites follow BEP relations that are lower than the one of the 211 facet. Second we utilize the established BEP relations together with calculated adsorption energetics in a micro-kinetic model to obtain a volcano plot for the catalytic activity. We find that oxides have a higher turn over frequency as compared with metals. Hence, oxides intrinsically have a great advantage in terms of catalytic activity which opens up for catalyst design.

Vojvodic, Aleksandra; Studt, Felix; Abild-Pedersen, Frank; Bligaard, Thomas; Nřrskov, Jens

2012-02-01

13

Mechanism for bipolar resistive switching in transition metal oxides  

Microsoft Academic Search

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

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

2010-01-01

14

Nanostructured transition metal oxides useful for water oxidation catalysis  

DOEpatents

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

Frei, Heinz M; Jiao, Feng

2013-12-24

15

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

DOEpatents

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

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

2013-12-24

16

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

Microsoft Academic Search

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

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

2006-01-01

17

Catalytic oxidations using transition-metal carbonyls  

SciTech Connect

During the past year we have been working primarily on four separate projects, all of which are related to our goal of discovering new science which will allow development of new homogeneous catalysts for selective oxidations of hydrocarbons. These four projects are: the Re/sub 2/(CO)/sub 10/ photocatalyzed decomposition of hydrogen peroxide, the oxidative decarbonylation of an iridium carbonyl complex having a phosphine amine chelate ligand, the elucidation of mechanistic pathways and the detection of carbonylrhodium intermediates in the Rh/sub 6/(CO)/sub 16/ catalyzed-co-oxidation of CO and triphenylphosphine, and synthesis and chemistry of new d/sup 6/ and d/sup 8/ transition metal complexes having hydroxo or oxo ligands.

Roundhill, D.M.

1981-01-01

18

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

SciTech Connect

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

Vojvodic, Aleksandra

2011-08-22

19

Dielectric response of sputtered transition metal oxides  

NASA Astrophysics Data System (ADS)

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

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

2004-06-01

20

PEROVSKITE-TYPE THERMOELECTRIC OXIDES AND OXYNITRIDES  

Microsoft Academic Search

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

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

21

Surface symmetry-breaking and strain effects on orbital occupancy in transition metal perovskite epitaxial films  

NASA Astrophysics Data System (ADS)

The electron occupancy of 3d-orbitals determines the properties of transition metal oxides. This can be achieved, for example, through thin-film heterostructure engineering of ABO3 oxides, enabling emerging properties at interfaces. Interestingly, epitaxial strain may break the degeneracy of 3d-eg and t2g orbitals, thus favoring a particular orbital filling with consequences for functional properties. Here we disclose the effects of symmetry breaking at free surfaces of ABO3 perovskite epitaxial films and show that it can be combined with substrate-induced epitaxial strain to tailor at will the electron occupancy of in-plane and out-of-plane surface electronic orbitals. We use X-ray linear dichroism to monitor the relative contributions of surface, strain and atomic terminations to the occupancy of 3z2-r2 and x2-y2 orbitals in La2/3Sr1/3MnO3 films. These findings open the possibility of an active tuning of surface electronic and magnetic properties as well as chemical properties (catalytic reactivity, wettability and so on).

Pesquera, D.; Herranz, G.; Barla, A.; Pellegrin, E.; Bondino, F.; Magnano, E.; Sánchez, F.; Fontcuberta, J.

2012-11-01

22

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

Microsoft Academic Search

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

Ming Yin

2005-01-01

23

Topochemical reactions of layered transition-metal oxides  

NASA Astrophysics Data System (ADS)

Low-temperature topochemical reactions performed on complex transition metal oxides allow the synthesis of novel, metastable phases often with unusual transition metal oxidation states and/or coordination geometries. Layered materials offer many opportunities to control the structural and chemical selectivity of these types of reactions to allow the preparation of desired phases in a rational manner. Using complex oxides adopting Ruddlesden–Popper type structures as examples, recent progress in the low-temperature topochemical reduction by anion de-intercalation, and oxidation by anion insertion, is reviewed.

Hayward, M. A.

2014-06-01

24

Half-metallic transition metal oxides  

Microsoft Academic Search

We present an application of the self-interaction corrected local spin density approximation to study the electronic structure of half-metallic double perovskites Ba2FeMoO6, Ca2FeMoO6, Sr2FeMoO6, Ca2FeReO6, and charge order in Fe3O4.

Z. Szotek; W. M. Temmerman; A. Svane; L. Petit; G. M. Stocks; H. Winter

2004-01-01

25

[Transition metals and nitric oxide production in human endothelial cells].  

PubMed

The bioavailability of endothelial nitric oxide (NO) is regulated by transition metals but their mechanisms of action on NO synthesis and degradation are not clearly understood. Using differential pulse amperometry and NO microelectrodes, local NO concentration was measured at the surface of cultured human umbilical vein endothelial cells (HUVECs) stimulated by histamine or thrombin in the presence of transition metal chelators. The agonist-activated NO release required both extracellular Ca2+ and transition metals. In the presence of 1 mM external Ca2+, a low concentration of EGTA (5 microM) inhibited by 40% the NO release from stimulated HUVECs. In the presence of extracellular L-arginine, the inhibitory effect of EGTA was even more marked and, in its absence, it was suppressed by adding exogenous superoxide dismutase. The decrease in NO release induced by the copper chelators, cuprizone and DETC, suggests that extracellular traces of Cu2+ could regulate NO availability. PMID:11212498

David-Dufilho, M; Privat, C; Brunet, A; Richard, M J; Devynck, J; Devynck, M A

2001-01-01

26

Single crystal growth of transition metal oxides at high pressures of several GPa  

Microsoft Academic Search

Single crystals of various transition metal oxides exhibiting fascinating physical properties were grown by flux method at high pressures of several GPa. The growth conditions were determined based on synchrotron powder X-ray diffraction studies at high-pressure and high-temperature conditions. Results on a S=1\\/2 one dimensional alternating exchange antiferromagnet (VO)2P2O7, perovskites PrNiO3, CaFeO3, BiMnO3 and an oxychloride high-TC superconductor Ca2?xNaxCuO2Cl2 are

M. Azuma; T. Saito; S. Ishiwata; I. Yamada; Y. Kohsaka; H. Takagi; M. Takano

2003-01-01

27

High-temperature and electrochemical oxidation of transition metal silicides  

Microsoft Academic Search

High-temperature and electrochemical oxidation of transition metal silicides, which are widely used in microelectronics as\\u000a ohmic contacts and protective coatings for high-temperature alloys, are discussed in this review. The process of oxide film\\u000a formation during annealing or anodizing is extremely important for both applications of silicides. It is discussed for three\\u000a disilicides: MoSi2, WSi2, and TiSi2. It has been shown

A. D. Chirkin; V. O. Lavrenko; V. M. Talash

2009-01-01

28

Vapor growth of electrochromic thin films of transition metal oxides  

NASA Astrophysics Data System (ADS)

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.

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

2008-04-01

29

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

Microsoft Academic Search

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

Clarence Zener

1951-01-01

30

Monolayered nanodots of transition metal oxides.  

PubMed

Monolayered nanodots of titanium, tungsten, and manganese oxides were obtained by exfoliation of the nanocrystals through aqueous solution processes at room temperature. The precursor nanocrystals of the layered compounds, such as sodium titanate (Na(0.80)Ti(1.80)?(0.2)O4ˇxH2O, ?: vacancy (x < 1.17)), cesium tungstate (Cs4W11O35ˇyH2O (y < 10.5)), and sodium manganate (Na0.44MnO2ˇzH2O (z < 0.85)), were synthesized in an aqueous solution. These nanocrystals of the layered compounds were delaminated into the monolayered nanodots through introduction of a bulky organic cation in the interlayer space. The resultant monolayered nanodots of the titanate and tungstate 2-5 nm in lateral size showed a remarkable blueshift of the bandgap energies. The calculation studies supported the blueshifts of the bandgap energies. The results suggest that syntheses of monolayered nanodots can expand the tuning range of the properties based on size effect. The present approaches for generation of ultrathin tiny objects can be applied to a variety of nanomaterials. PMID:23441590

Nakamura, Keisuke; Oaki, Yuya; Imai, Hiroaki

2013-03-20

31

Three-coordinate metal centers in extended transition metal oxides.  

PubMed

The n = 3 Ruddlesden-Popper phase Sr3LaFe1.5Co1.5O10+/-delta is capable of sustaining O contents as low as O7.5 with a mean metal oxidation state of +2 and three coordination at the central site in the trilayer of originally octahedral transition metal sites. The shortening of the axial bonds to the flanking octahedral layers stabilizes the low oxidation state and consequent unusual low coordination number of the Fe2+ and Co2+ cations within the extended structure. PMID:17002328

Bowman, Amy; Allix, Mathieu; Pelloquin, Denis; Rosseinsky, Matthew J

2006-10-01

32

Ionically-mediated electromechanical hysteresis in transition metal oxides  

SciTech Connect

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

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

2012-01-01

33

Resonant Ultrasound Studies of Complex Transition Metal Oxides  

Microsoft Academic Search

Department of Energy EPSCoR ;\\u000aThe University of Mississippi;\\u000aAward: DE-FG02-04ER46121;\\u000aResonant Ultrasound Spectroscopy Studies of Complex Transition Metal Oxides;\\u000a;\\u000aThe central thrust of this DOE funded research program has been to apply resonant ultrasound spectroscopy (RUS), an elegant and efficient method for determining the elastic stiffness constants of a crystal, to the complex and poorly understood class of

Henry Bass; J. R. Gladden

2008-01-01

34

Electronic transitions and multiferroicity in transition metal oxides  

Microsoft Academic Search

Four systems have been studied for the localized-itinerant electronic transition in transition-metal oxides: (i) In CaV1- xTixO3, substitution of Ti(IV) introduces Anderson-localized states below a mobility edge mu c that increases with x, crossing epsilon F in the range 0.2 < x= 0.1. (ii) The properties of LaTiO3+delta reveal that a hole-poor, strongly correlated electronic phase coexists with a hole-rich,

Haidong Zhou

2006-01-01

35

Transition metal dioxygen complexes as intermediates in homogeneous catalytic oxidations  

NASA Astrophysics Data System (ADS)

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

Simándi, Lászlň I.

36

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

SciTech Connect

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

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

2011-01-01

37

Double-hole-induced oxygen dimerization in transition metal oxides  

NASA Astrophysics Data System (ADS)

Rather than being free carriers or separated single-hole polarons, double holes in anatase TiO2 prefer binding with each other, to form an O-O dimer after large structural distortion. This pushes the hole states upward into the conduction band and traps the holes. Similar double-hole-induced O-O dimerization (a bipolaron) exists also in other transition metal oxides (TMOs) such as V2O5 and MoO3, which have the highest valence bands composed mainly of O 2p states, loose lattices, and short O-O distances. Since the dimerization can happen in impurity-free TMO lattices, independent of any extrinsic dopant, it acts as an intrinsic and general limit to the p-type conductivity in these TMOs.

Chen, Shiyou; Wang, Lin-Wang

2014-01-01

38

GW calculations on post-transition-metal oxides  

NASA Astrophysics Data System (ADS)

In order to establish the reliable GW scheme that can be consistently applied to post-transition-metal oxides (post-TMOs), we carry out comprehensive GW calculations on electronic structures of ZnO, Ga2O3,In2O3, and SnO2, the four representative post-TMOs. Various levels of self-consistency (G0W0, GW0, and QPGW0) and different starting functionals (GGA, GGA + U, and hybrid functional) are tested and their influence on the resulting electronic structure is closely analyzed. It is found that the GW0 scheme with GGA + U as the initial functional turns out to give the best agreement with experiment, implying that describing the position of metal-d level precisely in the ground state plays a critical role for the accurate dielectric property and quasiparticle band gap. Nevertheless, the computation on ZnO still suffers from the shallow Zn-d level and we propose a modified approach (GW0+Ud) that additionally considers an effective Hubbard U term during GW0 iterations and thereby significantly improves the band gap. It is also shown that a GGA + U-based GW0(+Ud) scheme produces an accurate energy gap of crystalline InGaZnO4, implying that this can serve as a standard scheme that can be applied to general structures of post-TMOs.

Kang, Youngho; Kang, Gijae; Nahm, Ho-Hyun; Cho, Seong-Ho; Park, Young Soo; Han, Seungwu

2014-04-01

39

Theoretical study of first-row transition metal oxide cations  

NASA Astrophysics Data System (ADS)

The equilibrium geometries, dissociation energies, and electronic structures of the ground and low-lying excited states for the first-row transition metal oxide cations, MO+ (M=Sc to Zn), have been studied using the multireference singles and doubles configuration interaction (MR-SDCI) and the multireference second-order Mřller-Plesset methods. To investigate the applicability of the density functional theory (DFT) to an electronic structure system with a multiconfigurational character, the Becke exchange functional with the Lee-Yang-Parr correlation functional, the Becke exchange functional with the one-parameter progressive correlation functional (BOP), and the Becke three-parameter hybrid exchange functional with the Lee-Yang-Parr correlation functional (B3LYP) methods have also been applied. The DFT predicts the ground state M-O bond lengths in good agreement with the multireference-based methods except for MnO+ and CuO+, which have a multiconfigurational electronic structure. With respect to the dissociation energies, the B3LYP results are in good agreement with the multireference-based methods, while the DFT with pure functionals overestimates the energetics by about 20 kcal/mol compared to the MR-SDCI method.

Nakao, Yoshihide; Hirao, Kimihiko; Taketsugu, Tetsuya

2001-05-01

40

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

PubMed

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

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

2013-12-16

41

Transition-metal acceptor complexes in zinc oxide  

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

42

First-Principles Study on the Surfaces of Transition-Metal Perovskites: Sr_2RuO4 and Sr_1-xCa_xVO_3  

Microsoft Academic Search

Trying to bridge the gap between the rich experiment data, which are surface sensitive, and the little understanding about the surface phases of transition metal perovskites, we study the surfaces of Sr_2RuO4 and Sr_1-xCa_xVO3 as examples of 214 and 113 compounds respectively by first-principles calculations based on the density function theory. For layered perovskite Sr_2RuO_4, we found the surface is

Zhong Fang; Priya Mahadevan; Kiyoyuki Terakura

2000-01-01

43

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

PubMed

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

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

2001-10-21

44

Methane Production from Carbon Oxides Over Borohydride-Reduced Transition Metals.  

National Technical Information Service (NTIS)

This study was undertaken to continue the examination of the utility of borohydride-reduced transition metals as catalysts for the hydrogenation of carbon oxides to produce synthetic fuels. While most related efforts deal only with carbon monoxide (the pr...

T. W. Russell

1978-01-01

45

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

Microsoft Academic Search

Zinc oxide nanowires were grown by vapor transport using the vapor-liquid-solid growth mechanism. The zinc oxide nanowires were implanted with transition metals (Co, Fe or Ni) and subsequently annealed in air at 700 °C for 30 min. Energy-dispersive x-ray spectroscopy and electron energy loss spectroscopy measurements reveal a successful incorporation of the desired transition metals. Transmission electron microscopy analysis of

Sven Müller; Minjie Zhou; Quan Li; Carsten Ronning

2009-01-01

46

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

Microsoft Academic Search

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

Boffa

1994-01-01

47

Hubbard U and Hund exchange J in transition metal oxides: Screening versus localization trends from constrained random phase approximation  

NASA Astrophysics Data System (ADS)

In this work, we address the question of calculating the local effective Coulomb interaction matrix in materials with strong electronic Coulomb interactions from first-principles. To this purpose, we implement the constrained random phase approximation into a density functional code within the linearized augmented plane-wave framework. We apply our approach to the 3d and 4d early transition metal oxides SrMO3 (M= V, Cr, Mn) and (M= Nb, Mo, Tc) in their paramagnetic phases. For these systems, we explicitly assess the differences between two physically motivated low-energy Hamiltonians: The first is the three-orbital model comprising the t2g states only, which is often used for early transition metal oxides. The second choice is a model where both metal d and oxygen p states are retained in the construction of Wannier functions, but the Hubbard interactions are applied to the d states only (“d-dp Hamiltonian”). Interestingly, since (for a given compound) both U and J depend on the choice of the model, so do their trends within a family of these compounds. In the 3d perovskite series SrMO3, the effective Coulomb interactions in the t2g Hamiltonian decrease along the series due to the more efficient screening. The inverse, generally expected, trend, increasing interactions with increasing atomic number, is however recovered within the more localized “d-dp Hamiltonian.” Similar conclusions are established in the layered 4d perovskites series Sr2MO4 (M= Mo, Tc, Ru, Rh). Compared to their isoelectronic and isostructural 3d analogs, the 4d perovskite oxides SrMO3 (M= Nb, Mo, Tc) exhibit weaker screening effects. Interestingly, this leads to an effectively larger U on 4d than on 3d shells when a t2g model is constructed.

Vaugier, Loďg; Jiang, Hong; Biermann, Silke

2012-10-01

48

Numerical studies of strongly correlated electrons in transition metal oxides  

NASA Astrophysics Data System (ADS)

The purpose of this dissertation is to study different properties of the transition metal oxides, especially the high-Tc superconductors. Applying Monte Carlo methods to a Spin-Fermion model, the behavior of the band structure, Fermi surface, pairing correlations, and optical conductivity are studied. The numerical simulations are done at different temperatures, and densities relevant for the cuprates. Previous Monte Carlo simulations of this model have shown the existence of charge stripes separated by antiferromagnetic domains upon doping. These results are consistent with neutron scattering experiments. At half filling, the ground state of the Spin-Fermion model is an insulator. The doped holes contribute to the formation of midgap bands by modifying the valence and the conduction band. The ground state appears to change from an insulator to a conductor. In the metallic regime the lower midgap and conduction bands overlap each other giving rise to a pseudogap in the density of states at the chemical potential. This agrees with the results from ARPES experiments. Both midgap and valence bands determine the Fermi surface. The D-wave pairing correlations, for all values of parameters, are stronger than S-wave. The D-wave pairing correlations are the strongest in the direction perpendicular to the dynamic stripes which appear in the ground state at some dopings. An optimal doping, where correlations are maximized, is observed close to 25% with an estimated critical temperature Tc = 100--200 K in qualitative agreement with high-Tc cuprates phenomenology. The optical conductivity and Drude weight are studied as a function of electronic density and temperature. As temperature is reduced, spectral weight is transferred from high to low frequencies in agreement with the behavior observed experimentally. Varying the hole density, the Drude weight has a maximum at the optimal doping for the model are stronger. The inverse of the Drude weight, which is roughly proportional to resistivity, decreases linearly with temperature at the optimal doping, and it is abruptly reduced when robust pairing correlations develop upon further reducing the temperature. The general form of the optical conductivity is in good agreement with the experimental results for the cuprates.

Moraghebi, Mohammad

2003-10-01

49

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

PubMed

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

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

2008-10-01

50

High sensitivity of 17O NMR to p-d hybridization in transition metal perovskites: First principles calculations of large anisotropic chemical shielding  

NASA Astrophysics Data System (ADS)

A first principles embedded cluster approach is used to calculate O chemical shielding tensors, ??, in prototypical transition metal oxide ABO3 perovskite crystals. Our principal findings are (1) a large anisotropy of ?? between deshielded ?x~=?y and shielded ?z components (z along the Ti-O bond); (2) a nearly linear variation, across all the systems studied, of the isotropic ?iso and uniaxial ?ax components, as a function of the B-O-B bond asymmetry. We show that the anisotropy and linear variation arise from large paramagnetic contributions to ?x and ?y due to virtual transitions between O(2p) and unoccupied B(nd) states. The calculated isotropic ?iso and uniaxial ?ax chemical shifts are in good agreement with recent BaTiO3 and SrTiO3 single crystal 17O NMR measurements. In PbTiO3 and PbZrO3, calculated ?iso are also in good agreement with NMR powder spectrum measurements. In PbZrO3, ?iso calculations of the five chemically distinct sites indicate a correction of the experimental assignments. The strong dependence of ?? on covalent O(2p)-B(nd) interactions seen in our calculations indicates that 17O NMR spectroscopy, coupled with first principles calculations, can be an especially useful tool to study the local structure in complex perovskite alloys.

Pechkis, Daniel L.; Walter, Eric J.; Krakauer, Henry

2009-11-01

51

Magnetism in transition-metal-substituted semiconducting oxides  

NASA Astrophysics Data System (ADS)

The nascent field of spintronics requires materials that exhibit room-temperature ferromagnetism while retaining their semiconducting properties. A clever strategy for creating these materials is by substituting magnetic transition metals onto the cation sites of commonly used binary semiconductors in order to incorporate magnetic property (e.g. Mn-substituted GaAs). A materials system of great interest is transition-metal substituted ZnO, which was predicted by Dietl and co-workers [1] to be a room temperature ferromagnet with manganese substitution and hole doping. Despite a great deal of effort in preparing thin films of transition-metal substituted ZnO, there has not been reproducible evidence of ferromagnetism in this system; Curie temperatures and magnetic moments vary significantly between studies. In our work, bulk transition metal substituted ZnO samples were prepared and characterized in order to accurately determine their properties. We find no evidence for ferromagnetic behavior in either the Zn1-xCo xO nor the Zn1-xMn xO systems; rather the dominant nearest-neighbor interactions are antiferromagnetic. A similar behavior is observed in nanoparticulate analogs of the bulk materials. Along with substituted ZnO, the 'end-member' of the Zn1-xCox O system, novel wurzite CoO was also prepared and studied. Finally, solid solutions of a dilute ferrimagnetic semiconductor system, iron-substituted ZnGa2O4, were prepared and found to possess long-range magnetic ordering ferromagnetic hysteresis at low temperatures. Optical spectroscopy indicates that the iron substitution does not greatly alter the position of the band edge, hence maintaining the semiconducting properties. Such promising results suggest that dilute ferrimagnetic semiconductors, which do not require conduction electrons to induce magnetism, are worthy of further investigation.

Risbud, Aditi S.

52

Perovskite oxides: Oxygen electrocatalysis and bulk structure  

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

53

Perovskite oxides: Oxygen electrocatalysis and bulk structure  

NASA Astrophysics Data System (ADS)

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

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

1987-09-01

54

Bonding Constraints,Elasticity and Electronic Heterogeneity in Transition Metal Oxides*  

NASA Astrophysics Data System (ADS)

We describe a multiscale "systems" scenario for doped transition metal oxides and related "strongly correlated" electronic materials, in which local polarizable "hotspots" (pairing centers, polarons, charge-transfer centers, etc.) induce elastic strains, which self-consistently drive self-assembly and coherent responses - macroscopically but heterogeneously. The elastic fields are a result of the highly-directional, local bonding "compatibility" constraints, and provide structural templates which couple strongly to electronic wave-functions because of (oxygen) polarizabilities and (metal-oxygen) charge-transfers. This leads to intrinsic "landscapes" of heterogeneous ground and metastable states (and associated multiscale dynamics), which are globally sensitive to local perturbations. Heterogeneity at atomic scales (e.g. filamentary/clump charge/spin localization and perovskite unit cell distortions) are intimately coupled, in multiscale systems, to mesoscale structural textures (twinning, tweed, etc). We describe selected signatures of heterogeneous textures in spin, charge and lattice degrees-of-freedom. We emphasize the importance of soft filamentary phases as the typical consequences of coexisiting anistropic short- and long-range fields and suggest generalizations to other hard, soft and biological matter. We speculate on the role of strain fields in controlling pseudogroups, correlated percolation, soft mesoscopic dynamics, filamentary dielectric breakdown and proximity effects, and effective pairing symmetry. 1)Intrinsic multiscale structure and dynamics in complex electronic oxides, eds. A. Bishop, S. Shenoy, S. Sridhar (World Scientific 2003); 2) A. Bishop et al, Euro. Phys. Lett. 63, 289 (2003); 3) J-X Zhu et al, Phys. Rev. Lett. 91, 057004; 4) J. C. Phillips et al, Rep. Prog. Phys. 66, 2111 (2003). *This work was performed in collaboration with K. Ahn, T. Lookman, A. Saxena, S. Shenoy, J-X Zhu, and work at Los Alamos was supported by the USDOE Office of Basic Energy Sciences-Division of Materials

Bishop, Alan

2004-03-01

55

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

PubMed

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. PMID:24925579

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

2014-07-01

56

Perovskite catalysts for oxidative coupling  

DOEpatents

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

Campbell, Kenneth D. (Charleston, WV)

1991-01-01

57

Perovskite catalysts for oxidative coupling  

DOEpatents

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

Campbell, K.D.

1991-06-25

58

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

PubMed

Two-dimensional (2D) transition metal oxide systems present exotic electronic properties and high specific surface areas, and also demonstrate promising applications ranging from electronics to energy storage. Yet, in contrast to other types of nanostructures, the question as to whether we could assemble 2D nanomaterials with an atomic thickness from molecules in a general way, which may give them some interesting properties such as those of graphene, still remains unresolved. Herein, we report a generalized and fundamental approach to molecular self-assembly synthesis of ultrathin 2D nanosheets of transition metal oxides by rationally employing lamellar reverse micelles. It is worth emphasizing that the synthesized crystallized ultrathin transition metal oxide nanosheets possess confined thickness, high specific surface area and chemically reactive facets, so that they could have promising applications in nanostructured electronics, photonics, sensors, and energy conversion and storage devices. PMID:24814859

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

2014-01-01

59

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

60

Factors that affect Li mobility in layered lithium transition metal oxides  

Microsoft Academic Search

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

Kisuk Kang; Gerbrand Ceder

2006-01-01

61

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

Microsoft Academic Search

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

Mayfair C. Kung; Harold H. Kung

1985-01-01

62

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

EPA Science Inventory

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

63

Methane production from carbon oxides over borohydride reduced transition metals. II. Final report  

Microsoft Academic Search

This study was undertaken to continue the examination of the utility of borohydride-reduced transition metals as catalysts for the hydrogenation of carbon oxides to produce synthetic fuels. While most related efforts deal only with carbon monoxide (the predominant oxide in coal gasification processes), we have included carbon dioxide in our work. Work with copper, cobalt, nickel and palladium has resulted

1980-01-01

64

Compositional dependence of elastic moduli for transition-metal oxide spinels  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

65

Transition metal oxides as the buffer layer for polymer photovoltaic cells  

NASA Astrophysics Data System (ADS)

Polymer-based photovoltaic cells have been fabricated by inserting a thin, transparent, transition metal oxide layer between the transparent anode (indium tin oxide) and the polymer layer. Two different transition metal oxides, namely vanadium oxide and molybdenum oxide, were used and the device performance was compared. The surface of the oxide films and the interface between the polymer and the oxide was studied with the help of atomic force microscopy. The effect of the thickness of the oxide layer on electrical characteristics of the device was also studied and optimized thickness was achieved to give high power conversion efficiency of 3.3% under simulated AM1.5G illumination of 100 mW/cm2.

Shrotriya, Vishal; Li, Gang; Yao, Yan; Chu, Chih-Wei; Yang, Yang

2006-02-01

66

Charge Self-Regulation Upon Changing the Oxidation State of Transition Metals in Insulators  

SciTech Connect

Transition-metal atoms embedded in an ionic or semiconducting crystal can exist in various oxidation states that have distinct signatures in X-ray photoemission spectroscopy and 'ionic radii' which vary with the oxidation state of the atom. These oxidation states are often tacitly associated with a physical ionization of the transition-metal atoms--that is, a literal transfer of charge to or from the atoms. Physical models have been founded on this charge-transfer paradigm, but first-principles quantum mechanical calculations show only negligible changes in the local transition-metal charge as the oxidation state is altered. Here we explain this peculiar tendency of transition-metal atoms to maintain a constant local charge under external perturbations in terms of an inherent, homeostasis-like negative feedback. We show that signatures of oxidation states and multivalence--such as X-ray photoemission core-level shifts, ionic radii and variations in local magnetization--that have often been interpreted as literal charge transfer are instead a consequence of the negative-feedback charge regulation.

Raebiger, H.; Lany, S.; Zunger, A.

2008-06-01

67

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

Microsoft Academic Search

This thesis reports 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, ((1x1)O\\/W(110)) x12. We have analyzed the

Scot Arthur Kellar

1997-01-01

68

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

SciTech Connect

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

S.E. Ziemniak

2000-05-18

69

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

PubMed

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

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

2014-04-01

70

Transition metal oxides as charge injecting layer for admittance spectroscopy  

NASA Astrophysics Data System (ADS)

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

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

2008-05-01

71

Secondary ion emission of selected transition metals under nitrogen oxides  

Microsoft Academic Search

The emission of various positive secondary ions has been investigated for polycrystalline targets of Ti, V, Cr, Nb, Ta, Co, Ni, Cu, Pd and Pt, which were bombarded by Ar+ ions under “dynamic” SIMS (DSIMS) conditions in the presence of the gaseous nitrogen oxides N2O, NO and NO2 at fixed pressure and under residual gas. Besides ions of the Me+

Margarete M. Brudny; Wolfgang Rybczynski; Wolfhart Seidel; Dieter Thiel

1990-01-01

72

Properties of Lanthanide Oxides as Supports for Transition Metal Catalysts. Progress Report, May 1, 1985-April 30, 1986.  

National Technical Information Service (NTIS)

Objective of this project is to determine the role played by oxidic support materials, particularly lanthanide oxides, in influencing the catalytic behaviors of dispersed transition metals. The investigation is currently focused primarily on studies of su...

M. P. Rosynek

1986-01-01

73

Effect of transition metal oxide anode interlayer in bulk heterojunction solar cells  

NASA Astrophysics Data System (ADS)

We performed a comprehensive study of the effect of transition metal oxide anode interlayer in bulk heterojunction solar cells based on P3HT:PCBM. We have investigated the influence of different metal oxides including tungsten oxide (WO3), vanadium oxide (V2O5) and molybdenum oxide (MoO3) on the solar cell performance. In addition, the influence of different deposition techniques (solution process and e-beam deposition/ thermal evaporation) has also been investigated. We found that deposition techniques play a significant role on the film quality and morphology and hence affect the photovoltaic performance. Obtained results are discussed in detail.

Ng, A.; Liu, X.; Djuriši?, A. B.; Ng, A. M. C.; Chan, W. K.

2013-03-01

74

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

PubMed

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

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

2011-02-01

75

Synthesis of Binary Magnesium--Transition Metal Oxides via Inverse Coprecipitation  

NASA Astrophysics Data System (ADS)

Synthesis of binary magnesium--transition metal oxides, MgM2O4 (M: Cr, Mn, Fe, Co) and MgNiO2, was performed by calcination at relatively low temperatures of 500 and 750 °C for 24 h through inverse coprecipitation of carbonate hydroxide precursors. The important roles of the precipitation agent, sodium carbonate, were clarified by considering equilibria in an aqueous solution. The structure parameters of the obtained binary magnesium--transition metal oxide powders, specifically the occupancy of atomic sites, were evaluated from synchrotron X-ray diffraction (XRD) profiles by Rietveld refinement in addition to the magnetic properties at room temperature. The present work provides general guidelines for low-cost and high-volume synthesis of complex oxides, which are easily decomposed at high temperatures.

Yagi, Shunsuke; Ichikawa, Yuya; Yamada, Ikuya; Doi, Takayuki; Ichitsubo, Tetsu; Matsubara, Eiichiro

2013-02-01

76

Development of transition-metal doped copper oxide and zinc oxide dilute magnetic semiconductors  

NASA Astrophysics Data System (ADS)

The field of spintronics has recently attracted much attention because of its potential to provide new functionalities and enhanced performance in conventional electronic devices. Oxide materials provide a convenient platform to study the spin-based functionality in host semiconducting material. Recent theoretical treatments predict that wide band-gap semiconductors, including ZnO, can exhibit high temperature ferromagnetic ordering when doped with transition metals. This work focused on the possibility of using wide band-gap oxide semiconductors as potential spintronic materials. The structure, magnetic, and electronic transport properties of transition-metal doped ZnO and Cu 2O were investigated. Mn and Co were used as transition metal dopants. Thin films of these materials were fabricated using pulsed laser deposition (PLD). The Mn solubility in Cu2O was found to be small and the precipitation of Mn-oxides was favored at high growth temperatures. Phase pure Mn-doped Cu2O samples were found to be non-magnetic. Samples were p-type with carrier concentrations on the order of 1014-10 16 cm-3. The effects of carrier concentration on the magnetic properties of Mn-doped ZnO were studied using Sn and P as electronic codopants. Sn acts as an n-type dopant providing extra electrons to the ZnO. P acts as a p-type dopant that supplies excess holes to compensate the native electron concentration in ZnO. The electron concentration was decreased using P, but the films remained n-type. An inverse correlation was found between the ferromagnetism and the electron concentration; the ferromagnetic coupling between Mn spins increased with decreasing electron concentration. The nature of ferromagnetism in Co-doped ZnO was also investigated. Ferromagnetism was found in films deposited at 400°C in vacuum, while films deposited in oxygen or at higher temperatures were non-magnetic. Films deposited under vacuum had rather high electron concentrations and were presumably doped with oxygen vacancies. The Co-doped films also exhibited peculiar magnetoresistance (MR) that had a strong dependence on the carrier concentration. At low temperatures, a progression from positive to negative MR was observed with increased electron concentration as the films crossed over the metal-to-insulator transition (MIT).

Ivill, Mathew P.

77

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

PubMed

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

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

2009-04-01

78

Nanostructure sensitization of transition metal oxides for visible-light photocatalysis  

PubMed Central

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

Chen, Hongjun

2014-01-01

79

Hydrazine reduction of transition metal oxides: In situ characterization using x-ray photoelectron spectroscopy  

Microsoft Academic Search

Among the first row transition metal oxides from VâOâ to ZnO, CuO was found to be the most easily reduced by hydrazine. CuO surfaces exposed to hydrazine at approx.10⁝⁜ Torr could be reduced to the metallic state at room temperature. Reduction kinetics, continuously measured at the surface using in situ x-ray photoelectron spectroscopy (XPS) at hydrazine pressures of 6 x

D. M. Littrell; B. J. Tatarchuk

1986-01-01

80

Surface Electronic Structure and Chemisorption on Corundum Transition-Metal Oxides  

Microsoft Academic Search

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

Richard Leigh Kurtz

1983-01-01

81

Electrocoloration in SrTiO3: Vacancy Drift and Oxidation-Reduction of Transition Metals  

Microsoft Academic Search

Application of dc electric fields, at temperatures of ~100 to ~325°C, to samples of SrTiO3 doped with transition metals leads to the appearance of colored regions, characteristic of reduced material at the cathode and oxidized material at the anode. This process is reversible upon reversal of the polarity of the applied field. We have measured the space and time dependencies

Joseph Blanc; David L. Staebler

1971-01-01

82

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

Microsoft Academic Search

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

M. E. Lines

1991-01-01

83

Charge Ordering and Long-Range Interactions in Layered Transition Metal Oxides  

Microsoft Academic Search

We study the competition between long-range and short-range interactions among holes within a continuum formulation of the spin density wave picture of layered transition metal oxides. We focus on the problem of charge ordering and the charge phase diagram. The main interactions are the long-range Coulomb interaction and a magnetic dipolar short-range interaction generated by short-range antiferromagnetic fluctuations. Four different

Branko P. Stojkovic; Z. G. Yu; A. R. Bishop; Gro; A. H. Neto

1999-01-01

84

Charge ordering and long-range interactions in layered transition metal oxides: A quasiclassical continuum study  

Microsoft Academic Search

The competition between long-range and short-range interactions among holes moving in an antiferromagnet (AF) is studied within a model derived from the spin-density-wave picture of layered transition metal oxides.A novel numerical approach is developed that allows one to solve the problem at finite hole densities in very large systems (of the order of hundreds of lattice spacings), albeit in a

Branko P. Stojkovic; Z. G. Yu; A. L. Chernyshev; A. R. Bishop; A. H. Castro Neto; Niels Groenbech-Jensen

2000-01-01

85

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

NASA Astrophysics Data System (ADS)

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

Skone, Jonathan H.; Galli, Giulia

2013-03-01

86

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

87

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

SciTech Connect

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

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

2012-01-01

88

Screening study of mixed transition-metal oxides for use as cathodes in thermal batteries  

SciTech Connect

Over 100 candidates were examined, including commercial materials and many that were synthesized in house. The mixed oxides were based on Ti, V, Nb, Cr, Mo, W, Mn, Fe, Co, Ni, and Cu doped with other transition metals. A number of individual (single-metal) oxides were included for comparison. The candidates were tested in single cells with Li(Si) anodes and separators based on LiCl-KCl eutectic. Screening was done under constant-current conditions at current densities of 125 me/cm{sup 2} and, to a lesser extent, 50 me/cm{sup 2} at 500 C. Relative performance and limitations of the oxide cathodes are discussed.

Guidotti, R.A.; Reinhardt, F.W.

1996-05-01

89

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

NASA Astrophysics Data System (ADS)

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.

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

2007-12-01

90

CO Sensing Property of Transition Metal Oxide-Loaded SnO2 in a Reducing Atmosphere  

Microsoft Academic Search

CO sensing properties of various transition metal oxide-loaded SnO2 sensors were investigated in a reducing atmosphere such as wet H2 gas. Among transition metal oxide-loaded SnO2 sensors used in the present study, CuO-loaded SnO2 sensor exhibited the highest sensor response to 1% CO in wet 50% H2 at around 150°C, while it showed no sensor response in dry 50% H2.

Hiroyuki Yamaura; Mari Nakaoka; Shinsuke Hirao; Akihiro Fujiwara; Hidenori Yahiro

2010-01-01

91

Separate and independent control of interfacial band alignments and dielectric constants in transition metal rare earth complex oxides  

Microsoft Academic Search

Spectroscopic studies of transition metal (Tm) and rare earth (Re) oxides, combined with ab initio theory, identify the band edge electronic structure of alternative high-k dielectrics. The lowest conduction band states are derived from anti-bonding transition metal d*-states with a ? symmetry and show strong final state effects. Applied to the complex Tm\\/Re mixed oxides of the general form ReTmO3,

G. Lucovsky; Y. Zhang; J. L. Whitten; D. G. Schlom; J. L. Freeouf

2004-01-01

92

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

SciTech Connect

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

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

1994-07-01

93

Transition-Metal-Catalyzed Oxidation of Metallic Sn in NiO/SnO2 Nanocomposite.  

PubMed

It is well accepted that metallic tin as a discharge (reduction) product of SnOx cannot be electrochemically oxidized below 3.00?V versus Li(+) /Li(0) due to the high stability of Li2 O, though a similar oxidation can usually occur for a transition metal formed from the corresponding oxide. In this work, nanosized Ni2 SnO4 and NiO/SnO2 nanocomposite were synthesized by coprecipitation reactions and subsequent heat treatment. Owing to the catalytic effect of nanosized metallic nickel, metallic tin can be electrochemically oxidized to SnO2 below 3.00?V. As a result, the reversible lithium-storage capacities of the nanocomposite reach 970?mAh?g(-1) or above, much higher than the theoretical capacity (ca. 750?mAh?g(-1) ) of SnO2 , NiO, or their composites. These findings extend the well-known electrochemical conversion reaction to non-transition-metal compounds and may have important applications, for example, in constructing high-capacity electrode materials and efficient catalysts. PMID:24648283

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

2014-04-25

94

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

NASA Astrophysics Data System (ADS)

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

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

95

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

USGS Publications Warehouse

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

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

1996-01-01

96

Dehydrogenation of ethylbenzene with nitrous oxide in the presence of mesoporous silica materials modified with transition metal oxides.  

PubMed

The novel mesoporous templated silicas (MCM-48, SBA-15, MCF, and MSU) were used as supports for transition metal (Cu, Cr, or Fe) oxides. The catalysts were synthesized using the incipient wetness impregnation, and characterized by low-temperature N2 sorption, DRIFT, photoacoustic IR spectroscopy, UV-vis diffuse reflectance spectroscopy, and temperature-programmed desorption of ammonia. It was shown that the preparation method used results in different distributions and dimensions of the transition metal oxide clusters on the inert support surface. The prepared catalysts were tested in the reaction of oxidative dehydrogenation of ethylbenzene in the presence of nitrous oxide. The iron-containing catalysts showed the highest catalytic activity. The presence of isolated Fe3+ was found to be the most important factor influencing the ethylbenzene conversion. The undesirable effect of the increase in selectivity toward CO2 was observed for the samples with the highest concentrations of acidic surface sites. PMID:16833351

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

2005-01-20

97

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

SciTech Connect

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

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

2010-07-08

98

Band gaps and electronic structure of alkaline-earth and post-transition-metal oxides  

Microsoft Academic Search

The electronic structure in alkaline-earth AeO (Ae=Be,Mg,Ca,Sr,Ba) and post-transition-metal oxides MeO (Me=Zn,Cd,Hg) is probed with oxygen K -edge x-ray absorption and emission spectroscopy. The experimental data are compared with density-functional theory electronic-structure calculations. We use our experimental spectra of the oxygen K edge to estimate the band gaps of these materials and compare our results to the range of values

J. A. McLeod; R. G. Wilks; N. A. Skorikov; L. D. Finkelstein; M. Abu-Samak; E. Z. Kurmaev; A. Moewes

2010-01-01

99

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

PubMed

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

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

2011-09-14

100

Synthesis of transition metal nitride by nitridation of metastable oxide precursor  

SciTech Connect

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

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

2012-10-15

101

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

102

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

PubMed

Fabricating complex transition metal oxides with a tunable bandgap without compromising their intriguing physical properties is a longstanding challenge. Here we examine the layered ferroelectric bismuth titanate and demonstrate that, by site-specific substitution with the Mott insulator lanthanum cobaltite, its bandgap can be narrowed by as much as 1 eV, while remaining strongly ferroelectric. We find that when a specific site in the host material is preferentially substituted, a split-off state responsible for the bandgap reduction is created just below the conduction band of bismuth titanate. This provides a route for controlling the bandgap in complex oxides for use in emerging oxide optoelectronic and energy applications. PMID:22353719

Choi, Woo Seok; Chisholm, Matthew F; Singh, David J; Choi, Taekjib; Jellison, Gerald E; Lee, Ho Nyung

2012-01-01

103

Methods to protect and recover work function of air exposed transition metal oxide thin films  

NASA Astrophysics Data System (ADS)

Insertion of high work function (WF) transition metal oxide (TMO) layers between the anode and the hole transport layer is established to substantially enhance the performance of organic light emitting diodes (OLED). The high WF of transition metal oxide layer has been demonstrated to be the most crucial for the enhancement. The WF of a TMO layer decreases substantially with air exposure, and noticeably by the ambient even inside a low vacuum system. In the present work we discuss various methods to protect and recover the high WF after a TMO thin film has been exposed to air. We report covering a thin organic layer on top of MoOx to protect the high work function. We found that a thin layer of 1-2 nm organic layer was sufficient to protect the work function of MoOx thin film underneath. We further report methods to recover already decreased TMO WF due to air exposure. We performed oxygen plasma cleaning of air exposed MoOx film and found out that oxygen plasma could substantially recover the WF of as deposited MoOx film. We also performed annealing of air exposed MoOx film inside an ultra high vacuum system and observed a thin layer of oxygenrich adsorbate layer, which desorbed upon annealing that in turn substantially recovered the MoOx WF. We discuss the vacuum annealing and the effect of resulting surface on the interface energy level alignment.

Irfan, Irfan; Wang, Chenggong; Turinske, Alexander J.; Gao, Yongli

2012-09-01

104

Theoretical investigation of hyperfine fields in fluoromethanes and transition metal oxides  

NASA Astrophysics Data System (ADS)

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.

Gopalakrishnan, Gowri

105

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

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

106

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

NASA Astrophysics Data System (ADS)

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.

Lu, Weier

1995-01-01

107

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

NASA Astrophysics Data System (ADS)

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

Lany, Stephan

2013-02-01

108

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

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

109

Synthesis of indazoles and azaindazoles by intramolecular aerobic oxidative C-N coupling under transition-metal-free conditions.  

PubMed

A transition-metal-free oxidative C-N coupling method has been developed for the synthesis of 1H-azaindazoles and 1H-indazoles from easily accessible hydrazones. The procedure uses TEMPO, a basic additive, and dioxygen gas as the terminal oxidant. This reaction demonstrates better reactivity, functional group tolerance, and broader scope than comparable metal catalyzed reactions. PMID:24590598

Hu, Jiantao; Xu, Huacheng; Nie, Pengju; Xie, Xiaobo; Nie, Zongxiu; Rao, Yu

2014-04-01

110

High sensitivity of ^17O NMR to p-d hybridization in transition metal perovskites: first principles calculations of large anisotropic chemical shielding  

NASA Astrophysics Data System (ADS)

First principles calculations are used to show that O chemical shielding tensors, ?, are a sensitive indicator of local structure in transition metal ABO3 perovskites, due to their strong dependence on covalent O(2p)-B(nd) interactions.footnotetextPechkis et al., JCP 131, 184511 (2009); references therein. This indicates that ^17O NMR spectroscopy, coupled with first principles calculations, can be an especially useful tool to study the local structure in complex perovskite alloys. Our principal findings are 1) a large anisotropy between deshielded ?x˜?y and shielded ?z components; 2) a nearly linear variation of isotropic ?iso and uniaxial ?ax components, as a function of the B-O-B bond asymmetry, across all the systems studied; 3) the demonstration that the anisotropy and linear variation arise from large paramagnetic contributions to ?x and ?y, due to virtual transitions between O(2p) and unoccupied B(nd) states. 4) Very good agreement with recent BaTiO3 and SrTiO3 single crystal ^17O NMR measurements of isotropic ?iso and uniaxial ?ax chemical shifts, and good agreement with PbTiO3 and PbZrO3 powder spectrum ?iso measurements.footnotetextmark[2

Pechkis, Daniel L.; Walter, Eric J.; Krakauer, Henry

2010-03-01

111

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

SciTech Connect

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

Scalettar, Richard T.; Pickett, Warren E.

2004-07-01

112

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

SciTech Connect

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

Richard T. Scalettar; Warren E. Pickett

2005-08-02

113

Perovskite-type oxides - Oxygen electrocatalysis and bulk structure  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

114

Electrochemical characterization of transition metal oxide aerogels for secondary lithium batteries  

NASA Astrophysics Data System (ADS)

The ability of transition metals to exist in multiple valence states, along with the fact that many transition metal oxides have a layered structure, has made transition metal oxides prime candidates as electrodes for the emerging technology of secondary lithium batteries. Traditionally, the electrochemical behavior of these materials is considered to be intrinsic to the material. In order to obtain different electrochemical performance needs, different materials need to be selected. The principal objective of this dissertation is to correlate electrochemical behavior with the microstructure of a material, allowing a material to meet different application requirements through the control of its microstructure. In this research, three different studies are used to explore the interrelationship between microstructure and electrochemical behavior. Sol-gel chemistry is used exclusively to prepare the electrochemically active materials as this process enables one to control the resulting microstructure and morphology. The first study looks at the influence of the degree of crystallinity in MoO3 aerogels on lithium capacity. The degree of crystallinity is controlled through heat treatment and observed to affect the lithium capacity. The nanocrystalline MoO3 aerogel exhibited higher lithium capacity (1.5 Li/Mo) compared to both the amorphous (1.1 Li/Mo) and crystalline (1.1 Li/Mo) samples. The second study involves the synthesis of organic/inorganic hybrids, achieved by simultaneously polymerizing the polypyrrole network within the Mo-O-Mo network. The addition of the conducting polymer phase increases both the electrical conductivity (4 x 10-3 S/cm) and the lithium capacity (1.7 Li/Mo) compared to that of MoO3 aerogels. The third study emphasizes the use of the "sticky carbon" electrode to study the effects of high surface area and pore size on the lithium intercalation properties of V2O5 aerogels. A series of V2O 5 aerogels with varying surface areas (10 to 280 m2/g) is prepared through the ambient drying process for this study. The sticky carbon method, combined with the open structure of the aerogel, allow better lithium ion accessibility to the V2O5 aerogel cathode, leading to a much higher lithium capacity (˜6 Li/V2O5 ) compared to using the traditional composite cathode (3--4 LiV 2O5). A pseudocapacitive behavior (˜2000 F/g) is also observed in addition to the lithium intercalation.

Dong, Winny

115

Limitations of the hybrid functional approach to electronic structure of transition metal oxides  

NASA Astrophysics Data System (ADS)

During the past decade, ab initio methods to calculate the electronic structure of materials based on hybrid functionals have increasingly become widely popular. Here we show that, in the case of small gap transition metal oxides, such as VO2, with rather subtle physics in the vicinity of the Fermi surface, such hybrid functional schemes without the inclusion of “expensive” fully self-consistent GW corrections fail to yield this physics and incorrectly describe the features of the wave function of states near the Fermi surface. While a fully self-consistent GW on top of a hybrid functional approach does correct these wave functions as expected, and is found to be in general agreement with the results of a fully self-consistent GW approach based on semilocal functionals, it is much more computationally demanding as compared to the latter approach for the benefit of essentially the same results.

Coulter, John E.; Manousakis, Efstratios; Gali, Adam

2013-07-01

116

Charge Ordering and Long-Range Interactions in Layered Transition Metal Oxides  

SciTech Connect

We study the competition between long-range and short-range interactions among holes within a continuum formulation of the spin density wave picture of layered transition metal oxides. We focus on the problem of charge ordering and the charge phase diagram. The main interactions are the long-range Coulomb interaction and a magnetic dipolar short-range interaction generated by short-range antiferromagnetic fluctuations. Four different phases depending on the strength of the dipolar interaction and the density of holes exist: Wigner crystal, diagonal stripes, horizontal-vertical stripes (loops). and a glassy-clumped phase. The effect of temperature, disorder, and lattice effects on these phases are discussed. {copyright} {ital 1999} {ital The American Physical Society}

Stojkovic, B.P.; Yu, Z.G.; Bishop, A.R.; Gro/nbech-Jensen, N. [Theoretical Division and Center for Nonlinear Studies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Neto, A.H. [Department of Physics, University of California, Riverside, California 92521 (United States)] [Department of Physics, University of California, Riverside, California 92521 (United States)

1999-06-01

117

Designing ferromagnetism in early transition metal oxides in bulk and superlattice forms  

NASA Astrophysics Data System (ADS)

The circumstances under which early transition metal oxides could exhibit ferromagnetism are determined using density functional plus single-site dynamical mean field methods. Particular attention is paid to the consequences of the GdFeO3 distortion and other octahedral rotations. Ferromagnetism is favored by the combination of intermediate carrier concentration (formal valence ˜d^1.5) and large tilt angle. The decrease of GdFeO3 distortion amplitude with hole doping away from d^2 is shown to keep the bulk solid solution La1-xSrxVO3 outside of the ferromagnetic regime. In superlattices such as (LaVO3)m(SrVO3)1, carrier concentration and tilt angle may be decoupled, potentially enabling ferromagnetism as suggested by experiment[1].[4pt] [1] U. L"uders, W. C. Sheets, A. David, W. Prellier, and R. Frésard, Phys. Rev. B 80, 241102(R) (2009).

Dang, Hung; Millis, Andrew

2013-03-01

118

Site-specific mapping of transition metal oxygen coordination in complex oxides  

NASA Astrophysics Data System (ADS)

We demonstrate site-specific mapping of the oxygen coordination number for transition metals in complex oxides using atomically resolved electron energy-loss spectroscopy in an aberration-corrected scanning transmission electron microscope. Pb2Sr2Bi2Fe6O16 contains iron with a constant Fe3+ valency in both octahedral and tetragonal pyramidal coordination and is selected to demonstrate the principle of site-specific coordination mapping. Analysis of the site-specific Fe-L2,3 data reveals distinct variations in the fine structure that are attributed to Fe in a six-fold (octahedron) or five-fold (distorted tetragonal pyramid) oxygen coordination. Using these variations, atomic resolution coordination maps are generated that are in excellent agreement with simulations.

Turner, S.; Egoavil, R.; Batuk, M.; Abakumov, A. A.; Hadermann, J.; Verbeeck, J.; Van Tendeloo, G.

2012-12-01

119

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

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

120

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

NASA Astrophysics Data System (ADS)

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

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

2011-09-01

121

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

PubMed

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

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

2012-10-23

122

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

PubMed

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

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

2014-06-19

123

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

SciTech Connect

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

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

2011-10-25

124

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

NASA Astrophysics Data System (ADS)

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

Getman, Rachel B.

125

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

NASA Astrophysics Data System (ADS)

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 generation and energy conversion, however, high crystallinity and controlled mesoporosity are a prerequisite. To this end, here we report on an approach established for group-IV (titanium) and group-V (niobium) oxides, with potential applications to photovoltaic cells and fuel cells, respectively, which overcomes previous limitations. It gives direct access to the desired materials in a `one-pot' synthesis using block copolymers with an sp2-hybridized carbon-containing hydrophobic block as structure-directing agents which converts to a sturdy, amorphous carbon material under appropriate heating conditions. This in situ carbon is sufficient to act as a rigid support keeping the pores of the oxides intact while crystallizing at temperatures as high as 1,000?C.

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

2008-03-01

126

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

NASA Astrophysics Data System (ADS)

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

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

1998-03-01

127

Resistive switching memory devices composed of binary transition metal oxides using sol-gel chemistry.  

PubMed

We describe a novel and versatile approach for preparing resistive switching memory devices based on binary transition metal oxides (TMOs). Titanium isopropoxide (TIPP) was spin-coated onto platinum (Pt)-coated silicon substrates using a sol-gel process. The sol-gel-derived layer was converted into a TiO2 film by thermal annealing. A top electrode (Ag electrode) was then coated onto the TiO2 films to complete device fabrication. When an external bias was applied to the devices, a switching phenomenon independent of the voltage polarity (i.e., unipolar switching) was observed at low operating voltages (about 0.6 VRESET and 1.4 VSET). In addition, it was confirmed that the electrical properties (i.e., retention time, cycling test and switching speed) of the sol-gel-derived devices were comparable to those of vacuum deposited devices. This approach can be extended to a variety of binary TMOs such as niobium oxides. The reported approach offers new opportunities for preparing the binary TMO-based resistive switching memory devices allowing a facile solution processing. PMID:19317425

Lee, Chanwoo; Kim, Inpyo; Choi, Wonsup; Shin, Hyunjung; Cho, Jinhan

2009-04-21

128

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

NASA Technical Reports Server (NTRS)

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.

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

1986-01-01

129

Photocatalysis on Fine Powders of Perovskite Oxides  

Microsoft Academic Search

Fine powders of semiconductor oxides have been widely used as photocatalysts for many reactions. Among the various photocatalytic reactions, water splitting has been given much importance, since it is a promising chemical route for solar energy conversion. Perovskite oxides, in particular SrTiO, have been commonly used as photocatalysts because some of them can decompose H,O into H, and 0, without

T. R. N. Kutty; M. Avudaithai

1992-01-01

130

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

SciTech Connect

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

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

2010-01-01

131

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

Microsoft Academic Search

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

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

2008-01-01

132

Surface structure determination of nanoscale transition metal oxide films using x-ray photoelectron diffraction and low energy electron diffraction  

Microsoft Academic Search

In this study, attempts were made to grow well-ordered chromium- and iron-oxide films on Ag(111) and Ag(001) surfaces, respectively. Two sample preparation techniques, multilayer growth and sequential growth, were used to grow these transition metal oxide films. Both sample preparation techniques result in a (&surd;3x&surd;3)R30° LEED pattern for high coverage CrOx on Ag(111). The high coverage phase is identified as

Weerasinghe Priyantha

2005-01-01

133

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

SciTech Connect

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

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

1997-05-01

134

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

NASA Astrophysics Data System (ADS)

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

Ehsan, Soheyli; Hekmat Shoar, Mohammad Hossein

2014-07-01

135

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

NASA Astrophysics Data System (ADS)

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.

Lam, Ching Yee

136

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

NASA Astrophysics Data System (ADS)

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

Zhang, Bo; Duan, Yuhua; Johnson, Karl

2012-02-01

137

Charge ordering and long-range interactions in layered transition metal oxides: A quasiclassical continuum study  

SciTech Connect

The competition between long-range and short-range interactions among holes moving in an antiferromagnet (AF) is studied within a model derived from the spin-density-wave picture of layered transition metal oxides.A novel numerical approach is developed that allows one to solve the problem at finite hole densities in very large systems (of the order of hundreds of lattice spacings), albeit in a quasiclassical limit, and to correctly incorporate the long-range part of the Coulomb interaction. The focus is on the problem of charge ordering and the charge phase diagram: at low temperatures four different phases are found, depending on the strength of the magnetic (dipolar) interaction generated by the spin-wave exchange and the density of holes. The four phases are the Wigner crystal, diagonal stripes, a grid phase (horizontal-vertical stripe loops), and a glassy-clumped phase. In the presence of both in-plane and out-of-plane charged impurities the stripe ordering is suppressed, although finite stripe segments persist. At finite temperatures multiscale (intermittency) dynamics is found, reminiscent of that in glasses. The dynamics of stripe melting and its implications for experiments is discussed. (c) 2000 The American Physical Society.

Stojkovic, Branko P. [Theoretical Division and Center for Nonlinear Studies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Yu, Z. G. [Department of Chemistry, Iowa State University, Ames, Iowa 50011 (United States); Chernyshev, A. L. [Department of Physics, University of California, Riverside, California 92521 (United States); Bishop, A. R. [Theoretical Division and Center for Nonlinear Studies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Castro Neto, A. H. [Department of Physics, University of California, Riverside, California 92521 (United States); Groenbech-Jensen, Niels [Department of Applied Science, University of California, Davis, California 95616 and NERSC, Lawrence Berkeley Laboratory, Berkeley, California 94720 (United States)

2000-08-15

138

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

NASA Astrophysics Data System (ADS)

The impact of illumination on the connection part of the tandem organic light-emitting diodes was studied by using a special organic multilayer sample consisted of two organic active layers coupled with different transition metal oxide (TMO)-based intermediate connectors (ICs). Through measuring the current density-voltage characteristic, interfacial electronic structures, and capacitance-voltage characteristic, we observe an unsymmetrical phenomenon in current density-voltage and capacitance-voltage curves of Mg:Alq3/MoO3 and MoO3 composed devices, which was induced by the charge spouting zone near the ICs region and the recombination state in the MoO3 layer. Moreover, Mg:Alq3/MoO3 composed device displays a photovoltaic effect and the Voc shifts to forward bias under illumination. Our results demonstrate that the TMO-based IC structure coupled with photovoltaic effect can be a good approach for the study of photodetector, light sensor, and so on.

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

2014-06-01

139

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

SciTech Connect

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

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

2007-05-20

140

Water adsorption and hydrolysis on molecular transition metal oxides and oxyhydroxides.  

PubMed

Addition of water to molecular transition metal oxides (TiO2(g) and CrO3(g)) and oxyhydroxides (ScO(OH)(g), VO2(OH)(g), and MnO3(OH)(g)) was studied by means of quantum chemistry. In the investigated reactions, each reaction step comprised the breaking of one M=O bond and the formation of two OH groups. Exothermicity was observed when the product had tetrahedral or lower oxygen coordination. The reactions were found to involve stable water complexes as intermediates. The stabilities of such complexes were accentuated in the addition reaction Sc(OH)3(g) + H2O(g), in which the formation of a tetrahedral complex was found exothermic. For VO(OH)3(g), CrO2(OH)2(g), and MnO3(OH)(g), water addition to the remaining M=O bonds was found endothermic, whereas the formation of water complexes, using hydrogen bonds and preserving the oxyhydroxide kernel, was preferred. Thus, the sequence of such kernels for water clustering in the investigated reactions was found to be Sc(OH)3.H2O(g), Ti(OH)4(g), VO(OH)3(g), CrO2(OH)2(g), and MnO3(OH)(g). These stability considerations are important, as CrO2(OH)2(g) is believed to be the product of water-induced degradation of the protective chromium oxide scale on stainless steel at elevated temperatures. PMID:11196853

Johnson, J R; Panas, I

2000-07-24

141

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

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

142

Electrochemical and thermal stability of a siloxane-based electrolyte on a lithium transition metal oxide cathode  

Microsoft Academic Search

The compounds deposited on a lithium transition metal oxide charged in a siloxane-based electrolyte were analyzed by Fourier transformation infrared (FT-IR) spectroscopy and thermal analysis. The decomposition of the siloxane-based electrolyte occurred at voltages above 4.2V, and the compounds that deposited on the cathode surface consisted of species from both the decomposed siloxane molecule and the electrolyte salt. Differential scanning

Hiroshi Nakahara; Manabu Tanaka; Sang-Young Yoon; Steven Nutt

2006-01-01

143

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

Microsoft Academic Search

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

Hong Pi; Ying Xiong; Shaoyun Guo

2005-01-01

144

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

NASA Astrophysics Data System (ADS)

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

Ramond, Tanya Michelle

145

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

SciTech Connect

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.

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

2008-09-04

146

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

NASA Astrophysics Data System (ADS)

The spatial hole-state properties of partly oxidized one-dimensional (1 D) organometallic solids with weak metal-metal interactions (either due to large separations between the corresponding building blocks or due to bridging organic ligand functions) have been studied in the crystal orbital (CO) formalism based on the tight-binding technique. The numerical analysis is restricted to insulating band states. The employed computational model is a semiempirical self-consistent-field (SCF) Hartree-Fock (HF) CO variant derived within the INDO (intermediate neglect of differential overlap) approximation. We have adopted a simple averaging procedure for the “open shell” systems which is based on a density operator that has its origin in the grand canonical (GC) ensemble in order to avoid the numerical difficulties of restricted or unrestricted tight-binding calculations on the oxidized 1 D chains. The present method, however, is not related to temperature-dependent equilibria in statistical mechanics but is only a formal, highly efficient approach for the formation of average-states in the mean-field approximation. As one-dimensional models we have adopted the infinite tetracyanatonickelate(II), Ni(CN){4/2-} 1, and the cyclopentadienylmanganese(I), MnCp 2, systems. The electron removal processes in both 1 D materials are more ( 1) or less ( 2) metal-centered (3d_{z^2 } states). The mean-field ground states of both oxidized modifications correspond to broken symmetry CDW (charge density wave) solutions that lead to mixed valence states with inequivalent numbers of electrons at adjacent transition metal centers. This symmetry breaking guarantees that important left-right correlations between the 3 d atoms are taken into account even in the SCF HF approximation. The valence trapping in 1 is strong, i.e. the mutual charge separation between the Ni centers amounts to 0.87 e. The bridging organic ? ligands in 2 prevent such pronounced differences of the net charges at the Mn centers and cause a reduction of the charge separation to 0.09 e 0.14 e.

Böhm, Michael C.

1984-06-01

147

Nanoparticle Delivery of Transition-Metal Chelators to the Brain: Oxidative Stress will Never See it Coming!  

PubMed Central

The pathological lesions typical of Alzheimer disease (AD) are sites of significant and abnormal metal accumulation. Metal chelation therapy, therefore, provides a very attractive therapeutic measure for the neuronal deterioration of AD, though its institution suffers fundamental deficiencies. Namely, chelating agents, which bind to and remove excess transition metals from the body, must penetrate the blood-brain barrier (BBB) to instill any real effect on the oxidative damages caused by the presence of the metals in the brain. Despite many advances in chelation administration, however, this vital requirement remains therapeutically out of reach: the most effective chelators—i.e., those that have high affinity and specificity for transition metals like iron and copper—are bulky and hydrophilic, making it difficult to reach their physiological place of action. Moreover, small, lipophilic chelators, which can pass through the brain’s defensive wall, essentially suffer from their over-effectiveness. That is, they induce toxicity on proliferating cells by removing transition metals from vital RNA enzymes. Fortunately, research has provided a loophole. Nanoparticles, tiny, artificial or natural organic polymers, are capable of transporting metal chelating agents across the BBB regardless of their size and hydrophilicity. The compounds can thereby sufficiently ameliorate the oxidative toxicity of excess metals in an AD brain without inducing any such toxicity themselves. We here discuss the current status of nanoparticle delivery systems as they relate to AD chelation therapy and elaborate on their mechanism of action. An exciting future for AD treatment lies ahead.

Bonda, David J.; Liu, Gang; Men, Ping; Perry, George; Smith, Mark A.; Zhu, Xiongwei

2014-01-01

148

Electron-lattice interactions in nickel-oxide perovskites  

SciTech Connect

The AMO{sub 3} perovskites containing a first-row transition-metal atom M allow study of the cross-over from localized to itinerant electronic behavior in a single-valent MO{sub 3} array dominated by (180 deg. -{phi}) M-O-M interactions. The LnNiO{sub 3} perovskites with Ln a lanthanide have one electron per low-spin Ni(III) in a narrow {sigma} band that approaches cross-over from the itinerant-electron side. Transport measurements are reported that add to the mounting evidence for a heterogeneous electronic transition in the perovskites rather than the homogeneous transition assumed in conventional treatments of the Mott-Hubbard transition.

Goodenough, J. B.; Zhou, J.-S. [Texas Materials Institute, ETC 9.102, University of Texas at Austin, Austin, Texas 78712-1063 (United States); Dabrowski, B. [Department of Physics, Northern Illinois University, DeKalb, Illinois 60116 (United States)

1999-09-01

149

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

NASA Astrophysics Data System (ADS)

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

Ozawa, Tadashi C.

150

Non-DMS related ferromagnetism in transition metal doped zinc oxide  

Microsoft Academic Search

We review pitfalls in recent efforts to make a conventional semiconductor, namely ZnO, ferromagnetic by means of doping with transition metal ions. Since the solubility of those elements is rather low, formation of secondary phases and the creation of defects upon low temperature processing can lead to unwanted magnetic effects. Among others, ion implantation is a method of doping, which

Kay Potzger; Shengqiang Zhou

2009-01-01

151

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

PubMed Central

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

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

2011-01-01

152

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

NASA Astrophysics Data System (ADS)

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

Zhai, Hua-Jin; Wang, Lai-Sheng

2010-11-01

153

Catalytic activity of first row transition metal oxides in the conversion of p-nitrophenol to p-aminophenol  

Microsoft Academic Search

The catalytic activities of first row transition metal oxides in the conversion of p-nitrophenol to p-aminophenol were investigated. The conversion was carried out at room temperature (30°C) using aqueous sodium borohydride. The reduction process was accelerated by CuO, Co3O4, Fe2O3 and NiO. The oxides such as TiO2, V2O5, Cr2O3, MnO2 and ZnO were found to be inactive towards the conversion

Triveni Rajashekhar Mandlimath; Buvaneswari Gopal

154

Incoherent Charge Dynamics in Perovskite Manganese Oxides  

NASA Astrophysics Data System (ADS)

A minimal model is proposed for the perovskite manganese oxides showing strongly incoherent charge dynamics with a suppressed Drude weight in the ferromagnetic and metallic phase near the insulator. We investigate a generalized double-exchange model whichincludes three elements; the orbital degeneracy of eg conduction bands, the Coulomb interaction and fluctuating Jahn-Teller distortions. We demonstrate that Lanczös diagonalization calculations combined with Monte Carlo sampling of the largely fluctuating lattice distortions result in the optical conductivity which quantitatively accounts for the experimental indications. It is found that all three elements are indispensable for understanding the charge dynamics in these compounds.

Nakano, Hiroki; Motome, Yukitoshi; Imada, Masatoshi

2000-05-01

155

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

Microsoft Academic Search

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

Ching Yee Lam

2009-01-01

156

On the transition-metal doping efficiency of zinc oxide nanocrystals  

Microsoft Academic Search

Using first-principles density functional theory calculations, we investigate the mechanism of doping colloidal ZnO nanocrystals with the transition-metal elements Mn, Co, and Ni. We find that the dopant atoms have high binding energies for adsorption onto the Zn-vacancy site of the (0001) surface and the O-vacancy site of the (0001) surface of the wurtzite-structure ZnO crystal; therefore, these surface vacancies

Tejinder Singh; T. J. Mountziaris; Dimitrios Maroudas

2010-01-01

157

First-principles calculations on magnetism of transition metal doped zinc oxide  

Microsoft Academic Search

We calculated the electronic structure and magnetism of 3d or 4d transition metal-doped ZnO (TM0.25Zn0.75O: TM=Ti, Cr, Mn, Fe, Co, Ni, Ru, Pd, and Ag), using the full potential linearized augmented plane method based on general gradient approximation for exchange–correlation potential. The magnetic moments of Ti, Cr, Mn, Fe, Co, Ni, Ru, Pd, and Ag in the systems were calculated

Sun Young Yun; Gi-Beom Cha; Youngsoo Kwon; Sunglae Cho; Soon C. Hong

2004-01-01

158

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)

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.

Charrier, J. G.; Anastasio, C.

2012-10-01

159

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

Microsoft Academic Search

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

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

2002-01-01

160

Manganese: a transition metal protects nigrostriatal neurons from oxidative stress in the iron-induced animal model of parkinsonism.  

PubMed

It has been suggested that transition metals such as iron and manganese produce oxidative injury to the dopaminergic nigrostriatal system. which may play a critical role in the pathogenesis of Parkinson's disease. Intranigral infusion of ferrous citrate (0 to 8.4 nmol, i.n.) acutely increased lipid peroxidation in the substantia nigra and dopamine turnover in the caudate nucleus. Subsequently, it caused a severe depletion of dopamine levels in the rat caudate nucleus. In contrast to iron's pro-oxidant effect, manganese (up to 30 nmol, i.n.) causes neither lipid peroxidation nor nigral injury/dopamine depletion. Manganese (1.05 to 4.2 nmol, i.n.) dose-dependently protected nigral neurons from iron-induced oxidative injury and dopamine depletion. Manganese also suppressed acute increase in dopamine turnover and contralateral turning behaviour induced by iron. In brain homogenates manganese (0 to 10 microM) concentration-dependently inhibited propagation of lipid peroxidation caused by iron (0 to 5 microM). Without the contribution of manganese-superoxide dismutase manganese was still effective in sodium azide and/or heat-pretreated brain homogenates. Surprisingly, iron but not manganese, catalysed the Fenton reaction or the conversion of hydrogen peroxide to hydroxyl radicals. The results indicate that iron and manganese are two transition metals mediating opposite effects in the nigrostriatal system, as pro-oxidant and antioxidant, respectively. In conclusion, intranigral infusion of iron, but not manganese, provides an animal model for studying the pathophysiological role of oxidant and oxidative stress in nigrostriatal degeneration and Parkinsonism. The present results further suggest that the atypical antioxidative properties of manganese may protect substantia nigra compacta neurons from iron-induced oxidative stress. PMID:9681949

Sziráki, I; Mohanakumar, K P; Rauhala, P; Kim, H G; Yeh, K J; Chiueh, C C

1998-08-01

161

Review of magnetocaloric effect in perovskite-type oxides  

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

162

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

PubMed

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

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

2013-11-01

163

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

SciTech Connect

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

Peng, H.; Lany, S.

2012-05-15

164

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

SciTech Connect

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

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

2009-01-01

165

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

NASA Astrophysics Data System (ADS)

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

Yan, Jun; Nřrskov, Jens K.

2013-12-01

166

Cooperative and frustration effects in novel perovskite-related phases  

Microsoft Academic Search

.  \\u000a We report on magnetic and electronic properties of various perovskite-type oxides containing 4d- and 5d-transition metals.\\u000a The compounds under investigation crystallize in (distorted) cubic, layered, and hexagonal perovskite-related structures.\\u000a These changes in structural dimensionality are reflected by different ordering phenomena. (Pseudo-) cubic perovskites ACu3B4O12 (with A = alkali, alkaline earth or rare earth; B = Ru, Ti) possess an

S. G. Ebbinghaus; S. Riegg; T. Götzfried; A. Reller

2009-01-01

167

Topological Oxide Insulator in Cubic Perovskite Structure  

PubMed Central

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

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

2013-01-01

168

Control of Copper and Iron Oxidation States in Some Triple- and Double-Perovskite Oxides.  

National Technical Information Service (NTIS)

This thesis consists of eight publications and a summary of the obtained experimental results, reviewed together with the most essential literature related to the topic. The work deals with ways of tuning and analyzing the transition metal oxidation state...

K. Lehmus

2003-01-01

169

Self-consistent linear density response within the LDA+U method: Application to transition-metal oxides(*)  

NASA Astrophysics Data System (ADS)

We formulate a scheme to calculate self-consistently the dynamical linear density-response function based on correlated LDA+U theory. The orbital dependent VU term in the Kohn- Sham potential, leads to an additional self-consistent condition in the density fluctuations. The end result is a density response function which includes electron-hole interactions (that is, it goes beyond the random-phase approximation). We assess the performance of our scheme by calculating the electron-hole excitation spectrum of prototype transition metal oxides for arbitrary momentum transfers. (*) DOE-CMSN PCSCS collaboration. (1) Supported by NSF ITR-DMR 0219332. (2) Managed by UT-Battelle for the U.S. DOE under contract DE- AC05-00OR22725. (3) Supported by DOE Grant DE-FG03-01ER45876

Eguiluz, A. G.; Restrepo, O. D.; Kunes, J.; Pickett, W. E.

2006-03-01

170

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

Microsoft Academic Search

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

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

171

New concepts and modeling strategies to design and evaluate photo-electro-catalysts based on transition metal oxides.  

PubMed

Photocatalytic production of transportation fuels should be among our long term strategies to achieve energy and environmental sustainability for the planet, but the technology is hampered by a lack of sufficiently efficient catalysts. Although efficiency is ultimately determined by laboratory measurements, theory and computation have become powerful tools for examining underlying mechanisms and guiding avenues of inquiry. In this review, we focus on first principles calculations of transition metal oxide semiconductor photocatalysts. We discuss how theory can be applied to investigate various aspects of a photocatalytic cycle: light absorption, electron/hole transport, band edge alignments of semiconductors, and surface chemistry. Emphasis is placed on identifying accurate models for specific properties and theoretical insights into improving photocatalytic performance. PMID:23111395

Liao, Peilin; Carter, Emily A

2013-03-21

172

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

PubMed

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

Tatsumi, Kazuyoshi; Muto, Shunsuke; Rusz, Ján

2013-12-01

173

Atomic force microscopy and photoemission electron microscopy study of the low-pressure oxidation of transition metal nitrides  

NASA Astrophysics Data System (ADS)

The oxidation of transition metal nitrides is examined by atomic force microscopy (AFM) and photoemission electron microscopy (PEEM) in the temperature range of 25-800 °C in an ultrahigh vacuum study. The roughness of the surfaces of thin film coatings of vanadium (V), vanadium nitride (VN), titanium nitride (TiN), and TiAlVN, monitored as a function of (a) constant dose of 50 000 L (1 L=10-6 Torr s) O2 at various temperatures and (b) oxygen dose at a constant temperature of 800 °C, is found to increase for all samples except TiAlVN. The morphological parameters (roughness and oxide grain volume) obtained from AFM are used to determine the extent of oxidation. The activation energy for the growth of oxide on the surface is calculated to be in the range of 0.4-0.5 eV for all samples containing V atoms and 1.6 eV for TiN. PEEM images of the pristine surfaces of TiN and TiAlVN show surface precipitates of the order of 5-50 ?m size. The workfunction of all surfaces and precipitates, obtained from photoemission spectra using PEEM, in combination with the effective activation energies measured by AFM, suggests that the main surface precipitate of TiAlVN is VN or VOxNy.

Fleming, A. J.; Surnev, S.; Netzer, F. P.

2007-10-01

174

Chemical Characterization of Transition Metal Spinel-Type Oxides. Part 2. Manganese-Chromium-Iron Spinels.  

National Technical Information Service (NTIS)

Spinel oxides of the type formed on Advanced Gas Cooled Reactor cladding contain manganese, chromium, and iron. A range of standard spinels containing these metals have been prepared by solid state reaction of the appropriate single oxides at temperatures...

G. C. Allen J. A. Jutson P. A. Tempest

1987-01-01

175

Honeycomb supported perovskite catalysts for ammonia oxidation processes  

Microsoft Academic Search

Pechini route (M.P. Pechini. U.S. Patent no. 3,330,697 (1967)) was used for supporting perovskite – like systems LaBO3 (B=Mn, Fe, Co, Ni, Cu) on thin-wall (0. 35mm) cordierite honeycomb support with low thermal expansion coefficient to prepare stable to thermal shocks supported catalysts for high-temperature processes of ammonia oxidation into NO in nitric acid production. In this preparation route, perovskites

L. A. Isupova; E. F. Sutormina; N. A. Kulikovskaya; L. M. Plyasova; N. A. Rudina; I. A. Ovsyannikova; I. A. Zolotarskii; V. A. Sadykov

2005-01-01

176

Functionalization of the semiconductor surfaces of diamond (100), Si (100), and Ge (100) by cycloaddition of transition metal oxides: a theoretical prediction.  

PubMed

The viability of functionalization of the semiconductor surfaces of diamond (100), Si (100), and Ge (100) by traditional [3 + 2] cycloaddition of transition metal oxides has been predicted using effective cluster models in the framework of density functional theory. The cycloaddition of transition metal oxides (OsO(4), RuO(4), and MnO(4)(-)) onto the X (100) (X = C, Si, and Ge) surface is much more facile than that of other molecular analogues including ethylene, fullerene, and single-walled carbon nanotubes because of the high reactivity of surface dimers of X (100). Our computational results demonstrate the plausibility that the well-known [3 + 2] cycloaddition of transition metal oxides to alkenes in organic chemistry can be employed as a new type of surface reaction to functionalize the semiconductor X (100) surface, which offers the new possibility for self-assembly or chemical functionalization of X (100) at low temperature. More importantly, the chemical functionalization of X (100) by cycloaddition of transition metal oxides provides the molecular basis for preparation of semiconductor-supported catalysts but also strongly advances the concept of using organic reactions to modify the solid surface, particularly to modify the semiconductor C (100), Si (100), and Ge (100) surfaces for target applications in numerous fields such as microelectronics and heterogeneous photocatalysis. PMID:19499936

Xu, Yi-Jun; Fu, Xianzhi

2009-09-01

177

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

PubMed

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

Berger, Matthias; Neumeyer, Felix; Auner, Norbert

2013-10-21

178

Quantum Spin Hall Effect in a Transition Metal Oxide Na(sub 2)I(sub r)O(sub 3).  

National Technical Information Service (NTIS)

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-principle...

H. Katsura H. Shitade J. Kunes N. Nagaosa S. Zhang X. Qi

2010-01-01

179

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

NASA Astrophysics Data System (ADS)

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

Ding, Yunshuang

180

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

SciTech Connect

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.

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

1983-05-18

181

Elastic properties of the transition metal oxides Ca2-xSrxRuO4  

NASA Astrophysics Data System (ADS)

Layered perovskite ruthenates have attracted considerable interest since the discovery of superconductivity in Sr2RuO4, the only copper-free superconductor isostructural to the cuprates. Among the doped varieties of Sr2RuO4, the Ca2-xSrxRuO4 series is heavily studied, as it connects the Mott insulator Ca2RuO4 with the superconductor Sr2RuO4 and exhibits a variety of physical properties. The current work focuses on the elastic properties of Ca2-xSrxRuO4. Resonant Ultrasound Spectroscopy (RUS) has been used to study the elastic response of the samples, and results are presented for single crystals with x = 0.2, 0.3, 0.4, 0.5, 1, 1.5, 1.9 and 2.0. The temperature-dependence of the elastic behavior is found to be quite unusual and reflects the rich phase diagram of these materials. Almost all measured Ca2-xSrxRuO4 samples show a soft phonon mode at low temperatures, which is believed to be associated with the dynamics of the RuO6 octahedra.

Luan, Yanbing; Keppens, Veerle; Jin, Rongying; Mandrus, David

2008-03-01

182

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

PubMed

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

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

2013-11-25

183

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

PubMed

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

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

2011-08-10

184

Raman spectroscopic observation of laser-induced oxidation of transition-metal borides, carbides, and nitrides  

SciTech Connect

Laser Raman microprobe examination in air of small-particle-sized(powders and whiskers) TiN, TiB/sub 2/, TiC, WC, ZrN, and NbN revealedthe formation of surface oxides, which were induced by laser heating. Therate of oxide formation varied with the particle size of the samples andthe laser power density applied. The oxides produced were characterizedby their Raman spectra. Thus, the Raman spectra obtained with a microprobeshould always be carefully analyzed to ascertain whether oxidation ordecomposition of so-called inert materials, especially in powder form, hasoccurred.

Begun, G. M.; Bamberger, C. E.

1989-01-01

185

Catalytic Oxidation of Phosphines by Transition Metal-Activated Carbon Dioxide.  

National Technical Information Service (NTIS)

The complexes (Ph3P) 3RhCl and (cyclooctene) 2RhCl 2 have been found to catalyze the oxidation of phosphines by carbon dioxide in refluxing decalin. The rate of oxidation increases in the order PPh3 less than PBuPh2 less than PEt3. (Author)

K. M. Nicholas

1979-01-01

186

Superconductors and Complex Transition Metal Oxides for Tunable THz Plasmonic Metamaterials  

SciTech Connect

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

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

2012-07-13

187

Facile Cycloaddition of Transition Metal Oxides onto the Sidewall of Boron-Doped Fullerene  

Microsoft Academic Search

The viability of facile oxidation and cycloaddition of fullerene C60 with ruthenium tetraoxide (RuO4) has been confirmed by means of density functional theory calculations. Owing to the powerful capability of RuO4 as an oxidant, the addition process has been found to occur readily in the absence of organic base as a catalyst, which is in remarkable contrast to the base-catalyzed

Zi-Rong Tang

2009-01-01

188

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

PubMed

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

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

2014-07-01

189

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

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

190

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

SciTech Connect

The detailed science and technology of crystalline oxide film growth using vacuum methods is reviewed and discussed with an eye toward gaining fundamental insights into the relationships between growth process and parameters, film and interface structure and composition, and electronic, magnetic and photochemical properties. The topic is approached first from a comparative point of view based on the most widely used growth methods, and then on the basis of specific material systems that have generated very high levels of interest. Emphasis is placed on the wide diversity of structural, electronic, optical and magnetic properties exhibited by oxides, and the fascinating results that this diversity of properties can produce when combined with the degrees of freedom afforded by heteroepitaxy.

Chambers, Scott A.

2010-01-12

191

Hot electron transport in a strongly correlated transition-metal oxide  

PubMed Central

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

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

2013-01-01

192

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

PubMed

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

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

2013-01-01

193

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

Microsoft Academic Search

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

Gerbrand Ceder; Anton Van der Ven

1999-01-01

194

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

Microsoft Academic Search

\\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

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

195

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

Microsoft Academic Search

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

Michael C. Böhm

1984-01-01

196

The structural stability of transition metal oxides for lithium rechargeable cells  

Microsoft Academic Search

This research considered the crystal structural or phase stability of lithium-cobalt and lithium-manganese oxides used as positive electrodes in lithium rechargeable cells. Using previous experimental observations, first principle calculations reported in the literature and a novel method of internal energy calculation developed here, a hypothesis of the relative crystal structural stability of the layered and spinel-type structures was proposed. This

Yang Shao-Horn

1998-01-01

197

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

PubMed

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

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

2006-05-01

198

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

PubMed

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

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

2012-02-01

199

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

PubMed

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

Neamtu, Jenica; Volmer, Marius

2014-01-01

200

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

NASA Astrophysics Data System (ADS)

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

Feiping, Lu; Yingquan, Peng; Yongzhong, Xing

2014-04-01

201

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

202

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

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

203

Sulphur poisoning of transition metal oxides used as catalysts for methane combustion  

Microsoft Academic Search

Different bulk metal oxides (NiO, CuO, Mn2O3, Cr2O3 and Co3O4) were prepared and tested for the combustion of methane–air lean mixtures (5000ppmV of CH4) in presence of SO2 (40ppmV). Methane combustion experiments were carried out at ambient pressure, 425 and 625°C and a space time of 93.3ghmolCH4?1. Catalysts aged (60h on stream) both in absence and in presence of SO2,

Salvador Ordóńez; José R. Paredes; Fernando V. Díez

2008-01-01

204

Oxide-Ion Conduction in Anion-Deficient Perovskites  

Microsoft Academic Search

Strategies for the design of an improved oxide -ion electrolyte for medium-temperature fuel cells, sensors, and oxygen pumps are outlined. Anion-deficient oxides with the perovskite structure were chosen for study. Stoichiometric oxides contain a high fraction of vacancies, but vacancy ordering suppresses ionic conductivity. Nevertheless, the brownmillerite rm Ba_2In_2O _5 undergoes an order-disorder transition at 930^circC that allows an estimate

Man Feng

1995-01-01

205

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

NASA Astrophysics Data System (ADS)

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

Xu, Linping

206

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

PubMed

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

Johnson, J R; Panas, I

2000-07-24

207

Transition metal sulfide loaded catalyst  

DOEpatents

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

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

1994-01-01

208

Transition metal sulfide loaded catalyst  

DOEpatents

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

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

1994-04-26

209

Separate and independent control of interfacial band alignments and dielectric constants in complex rare-earth\\/transition metal (Re\\/Tm) oxides  

Microsoft Academic Search

This paper introduced a new class of complex rare earth\\/transition metal oxides in which the energies of the lowest conduction band states can be controlled through bonding of the constituent Re and Tm atoms to a common oxygen atom. The electronic structure of GdScO3, the electronic band edge structure of Sc2O3, and an ab initio theory were studied.

G. Lucovsky; Yu Zhang; J. L. Whitten; D. G. Scholm; J. L. Freeouf

2003-01-01

210

Theory of many-body effects in valence, core-level and isochromat spectroscopies along the 3d transition metal series of oxides  

Microsoft Academic Search

Core level X-ray photoemission and absorption spectra (XPS and XAS) are calculated for some transition metal (TM) insulating compounds, especially oxides, using a configuration-interaction impurity-Anderson model combined with the influences of the core effect. Our model calculation is able to explain well the core-XPS of a series of early TM compounds, characterized by a nominally 3d0 configuration in the ground

J. C. Parlebas; M. A. Khan; T. Uozumi; K. Okada; A. Kotani

1995-01-01

211

Crystal structure of double oxides of the perovskite type  

Microsoft Academic Search

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

Helen D Megaw

1946-01-01

212

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

NASA Astrophysics Data System (ADS)

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

Samanta, Kousik

213

Transport studies of perovskite oxide BaPb1-xZrxO3  

NASA Astrophysics Data System (ADS)

We have synthesized perovskite oxide BaPb1-x Zrx O3 by solid-state reaction in different atmospheres and performed x-ray diffraction (XRD) analyses, electrical resistivity and thermoelectric power measurements on them. Nearly single-phase samples with cubic symmetry were obtained in the range 0.0 0.25. As x increased, a metal-insulator (MI) transition occurred at a critical doping level xc , which depended on the sintering atmosphere of the samples. Meanwhile, a jump in resistivity was found. At low temperatures (13 Kicons/Journals/Common/le" ALT="le" ALIGN="TOP"/> Ticons/Journals/Common/le" ALT="le" ALIGN="TOP"/> 100 K), the temperature dependence of resistivity followed the power law when 0 xc . When prepared in oxygen and in air, the resistivity decreased linearly with the rising temperature in the range between 100 and 300 K. However, the unusual linear behaviour was absent when the doped oxides were sintered in N2 . An anomalous broad peak was also observed in the thermoelectric power of the air-sintered samples. The results are discussed in terms of the effects of disorder and electron-electron interactions, oxygen vacancies and the crystal-field splitting of the 4d levels of transition metal Zr.

Zhao, Y. D.; Qian, Y. T.; Zhang, H.; Yang, P. F.; Tang, K. B.; Ruan, Y. Z.; Zhang, Y. H.

2000-02-01

214

Evaluation of first-row transition metal oxides supported on clay minerals for catalytic growth of carbon nanostructures  

Microsoft Academic Search

In the present work we employed various transition metals (Cr, Mn, Fe, Co, Ni, Cu and Zn) loaded on different smectite clays (laponite and montmorillonite) as catalysts in synthesis of carbon nanostructures (mainly nanotubes) and we report the effect of the nature of the catalytic centers and type of aluminosilicate layers in the morphology, quality and structure on the final

Theodoros Tsoufis; Lubos Jankovic; Dimitrios Gournis; Pantelis N. Trikalitis; Thomas Bakas

2008-01-01

215

Temperature-independent sensors based on perovskite-type oxides  

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

216

Perovskite-type oxides: Oxygen electrocatalysis and bulk structure  

NASA Astrophysics Data System (ADS)

Perovskite-type oxides have been considered for use as oxygen reduction and generation electrocatalysts in alkaline electrolytes. This paper is concern Perovskite oxides have not been found, in general, to be very active for oxygen reduction, although substantial catalytic activity for hydrogen peroxid A series of compounds of the type LaFe xNi 1- xO 3 has been used as a model system to gain information on the possible relationships be MES also shows that the introduction of Ni into the FE(III) matrix of LaFeO 3 forces some of the FE(III) into the unusual FE(IV) state, while part o The hydrogen peroxide decomposition rates have been found to undergo a substantial change in the range 0.25 < x < 0.5. A correlation has been f

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

217

The effects of transition metal oxides on the methane oxidative coupling activity of doped MgO catalysts  

SciTech Connect

Magnesium oxide samples doped with different loadings of zinc and manganese oxides with and without lithium carbonate being present in the preparation were evaluated for their catalytic activity towards the oxidative coupling of methane to higher hydrocarbons. When Li{sub 2}CO{sub 3} is excluded, the exhaustive reactions of methane to form carbon oxides are favored. With a doped Li{sub 2}CO{sub 3} is excluded, the exhaustive reactions of methane to form carbon oxides are favored. With a doped Li{sub 2}CO{sub 3}/MgO catalyst, a methane conversion of > 25% and a selectivity to C{sub 2} hydrocarbons of near 60% was retained but not enhanced in the presence of different loadings of Zn oxide at 805 C. Low loading of Mn oxide on Li{sub 2}CO{sub 3}/MgO resulted in a methane conversion of > 35% and a selectivity to C{sub 2} hydrocarbons of near 50%. At high Mn oxide loadings the methane conversion decreases and the C{sub 2} selectivity is less than 30% due to more exhaustive oxidation. The activity of the doped catalyst is related to the physico-chemical properties, especially surface morphology, and metal oxide reducibility on the basis of SEM, XRD and electron microprobe analysis.

Larkins, F.P.; Nordin, M.R. (Univ. of Tasmania, Hobart (Australia))

1991-07-01

218

Oxide perovskite crystals for HTSC film substrates microwave applications  

NASA Technical Reports Server (NTRS)

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

Bhalla, A. S.; Guo, Ruyan

1995-01-01

219

Magnetic phase diagram of perovskite Mn oxides at  

Microsoft Academic Search

:   Minimizing total free energy by numerical calculations, we obtain the magnetic phase diagram of perovskite Mn oxides, such\\u000a as with , Ca, Sr, etc. in the whole doping region from x\\u000a =0 to x\\u000a =1 at temperature T\\u000a =0. It is discovered that a spiral state is stable in a low concentration of X ions while a canted state

Y. Liu; J. Dong; D. Y. Xing

1998-01-01

220

Giant magnetoresistance of manganese oxides with a layered perovskite structure  

Microsoft Academic Search

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

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

1996-01-01

221

Dry reforming of methane over Ni perovskite type oxides  

Microsoft Academic Search

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),

Gustavo Valderrama; Mireya R. Goldwasser; Caribay Urbina de Navarro; Jean M. Tatibouët; Joël Barrault; C. Batiot-Dupeyrat; Fernando Martínez

2005-01-01

222

Method for dry etching of transition metals  

DOEpatents

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

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

1998-09-29

223

Method for dry etching of transition metals  

DOEpatents

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

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

1998-01-01

224

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

NASA Astrophysics Data System (ADS)

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

Liu, Hongxue

225

New insights on photocatalytic H2 liberation from water using transition-metal oxides: lessons from cluster models of molybdenum and tungsten oxides.  

PubMed

Molecular hydrogen (H2) is an excellent alternative fuel. It can be produced from the abundantly present water on earth. Transition-metal oxides are widely used in the environmentally benign photocatalytic generation of H2 from water, thus actively driving scientific research on the mechanisms for this process. In this study, we investigate the chemical reactions of W3O5(-) and Mo3O5(-) clusters with water that shed light on a variety of key factors central to H2 generation. Our computational results explain why experimentally Mo3O5(-) forms a unique kinetic trap in its reaction while W3O5(-) undergoes a facile oxidation to form the lowest-energy isomer of W3O6(-) and liberates H2. Mechanistic insights on the reaction pathways that occur, as well as the reaction pathways that do not occur, are found to be of immense assistance to comprehend the hitherto poorly understood pivotal roles of (a) differing metal-oxygen and metal-hydrogen bond strengths, (b) the initial electrostatic complex formed, (c) the loss of entropy when these TMO clusters react with water, and (d) the geometric factors involved in the liberation of H2. PMID:24171388

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

2013-11-13

226

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

SciTech Connect

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

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

2009-09-14

227

Autothermal reforming catalyst having perovskite structure  

DOEpatents

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

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

2009-03-24

228

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

SciTech Connect

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

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

2013-04-15

229

Perovskite-type oxides as catalysts for selective reduction of nitric oxide by ethylene  

NASA Astrophysics Data System (ADS)

The selective catalytic reduction of NO with C 2H 4 (C 2H 4-SCR) was investigated over perovskites containing Co, Mn, Fe, Cr, Al, Sn and Ti as host B-site cations. The C 2H 4-SCR activity was observed over Al-, Sn- and Ti-based oxides which were free from redox-active metal cations such as Co and Cu and innately poor in oxidation activity. Over perovskites containing redox-active metal cations, the undesirable consumption of C 2H 4 by O 2 proceeded preferentially.

Harada, T.; Teraoka, Y.; Kagawa, S.

1997-11-01

230

Oxide Perovskite Crystals for Htsc Film Substrates Microwave Applications.  

National Technical Information Service (NTIS)

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 candid...

1995-01-01

231

Cermets based on transition metal borides, their production and use  

US Patent & Trademark Office Database

A cermet useful in the fabrication of metal cutting, rockdrilling and mineral tools, as well as wear parts. The cermet comprises (i) a hard phase of a simple boride of a transition metal, a mixture of simple borides of transition metals, or a mixed boride of transition metals; (ii) a binder phase of Fe, Ni, Co, Cr, or alloys thereof; (iii) a dispersion of particles of oxides of transition metals in which the oxygen can be replaced by nitrogen and/or carbon; and (iv) a dispersion of oxides of metals chosen from aluminum and Group IIA and IIIA metals.

1995-08-08

232

Interface transport properties and resistance switching in perovskite-oxide heterojunctions  

Microsoft Academic Search

Electric field induced resistance switching has been investigated for perovskite-oxide heterojunctions consisting of various metal electrodes and p-type or n-type semiconducting perovskite oxides such as Pr0.7Ca0.3MnO3 or Nb-doped SrTiO3, respectively. The metal\\/perovskite-oxide heterojunction devices show either ohmic or rectifying I-V characteristics similar to those of a Schottky junction, depending on the work function of the metals. In addition, the rectifying

A. Sawa; T. Fujii; M. Kawasaki; Y. Tokura

2005-01-01

233

Structural transformations in cubic structure of Mn/Co perovskites in reducing and oxidizing atmospheres  

NASA Astrophysics Data System (ADS)

ABO ( A=La, Pr; B=Mn, Co), ABBx'O ( A=La, Pr; B=Mn, Co; B=Co, Pd), and ABCoPdO ( A=La, Pr; B=Fe, Mn) ( x=0.05, 0.37; y=0.38) perovskites were synthesized via malic acid complexation. O 2-TPD, O 2-TPO, and H 2-TPR treatments were carried out to study the oxidation and reduction behavior of the synthesized perovskites. LaCo 0.95Pd 0.05O 3, PrCo 0.95Pd 0.05O 3, and PrCoO 3 perovskites had the highest desorption, oxidation, and reduction activity within the studied perovskite series. Powder XRD studies revealed structural transformation of the cubic structure of all synthesized perovskites except LaFe 0.57Co 0.38Pd 0.05O 3 in H 2/Ar atmosphere when the temperature was over 400 °C. The decomposed structure reverted to the original perovskite structure under oxidizing atmosphere. This reversion was accompanied by increased oxygen desorption activity. It was noticed that the Co and Mn combinations in the B-site of the perovskites structure decreased the thermal stability of the synthesized perovskites.

Koponen, Markus J.; Suvanto, Mika; Kallinen, Kauko; Kinnunen, Toni-J. J.; Härkönen, Matti; Pakkanen, Tapani A.

2006-05-01

234

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

235

Interfacial transport properties between a strongly correlated transition metal oxide and a metal: Contact resistance in Fe3O4/M ( M=Cu , Au, Pt) nanostructures  

NASA Astrophysics Data System (ADS)

Multiterminal measurements have typically been employed to examine electronic properties of strongly correlated electronic materials such as transition metal oxides without the influence of contact effects. In contrast, in this work we investigate the interface properties of Fe3O4 with different metals, with the contact effects providing a window on the physics at work in the correlated oxide. Contact resistances are determined by means of four-terminal electrical measurements as a function of source voltage and temperature. Contact resistances vary systematically with the work function of the electrode metal, ?(M) , M=Cu , Au, and Pt, with higher work function yielding lower contact resistance. This trend and the observation that contact resistances are directly proportional to the Fe3O4 resistivity are consistent with modeling the oxide as an effective p -type semiconductor with hopping transport. The jumps in contact resistance values at the bias-driven insulator-metal transition have a similar trend with ?(M) , consistent with the transition mechanism of charge gap closure by electric field.

Fursina, A. A.; Sofin, R. G. S.; Shvets, I. V.; Natelson, D.

2010-12-01

236

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

NASA Astrophysics Data System (ADS)

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

Martin, Boris E.

237

Formation of perovskite type phases during the high temperature oxidation of stainless steels coated with reactive element oxides  

Microsoft Academic Search

The beneficial effects of reactive elements (RE) on the high temperature (HT) oxidation behavior of stainless steels have previously been attributed to the formation of perovskite compounds on oxide grain boundaries. In order to verify the ability of Cr2O3 to form perovskite compounds with reactive element oxides RE2O3 (RE=La, Nd, Sm, Gd, Yb, Y), mixtures of Cr2O3 and RE2O3 powders

S Chevalier; J. P Larpin

2002-01-01

238

Oxide cathode with perovskite structure for rechargeable lithium batteries  

NASA Astrophysics Data System (ADS)

Lithium ions were electrochemically inserted into perovskite-type oxides SrVO 3-? and La 0.50Li 0.37TiO 2.94 using galvanic cell: Li|1 M LiClO 4 in PC|SrVO 3-? or La 0.50Li 0.37TiO 2.94. It is found that the lattice parameters of SrVO 3-? will be increased and the discharge capacity of SrVO 3-? will be decreased as ? increased. At the composition where all of A-site vacancies in La 0.50Li 0.37TiO 2.94 are just occupied by the lithium ions, the lattice parameter shows a sudden increase. The chemical diffusion coefficients of lithium ions in SrVO 3-? and La 0.50Li 0.37TiO 2.94 were determined to be the values in the range from 10 -8 to 10 -12 cm 2 s -1. Both oxides can be considered as a useful cathode of rechargeable lithium batteries. The charge/discharge characteristic can be improved by mixing of a small amount of carbon powder with the oxide.

Shan, Yue Jin; Chen, Liquan; Inaguma, Yoshiyuki; Itoh, Mitsuru; Nakamura, Tetsuro

239

Copper catalysts for soot oxidation: alumina versus perovskite supports.  

PubMed

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

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

2008-10-15

240

Hybrid functionals applied to perovskites  

NASA Astrophysics Data System (ADS)

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.

Franchini, Cesare

2014-06-01

241

Hybrid functionals applied to perovskites.  

PubMed

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

Franchini, Cesare

2014-06-25

242

Supported transition metal oxides as acid cracking catalysts: periodic trends and their relationship to activity and selectivity  

SciTech Connect

Surface phase oxides bonded to a support such as alumina have not been recognized previously to have acid cracking activities in the league of amorphous silica-alumina to the best of their knowledge. In this paper the relative gas-oil cracking activities of all Group IV, V, and VIB oxides supported on alumina (including alumina and rhenia on alumina) are reported. All of the supported oxides are at a surface coverage about one-third that of a monolayer. Tungsten oxide and niobium oxide on alumina have been identified as solids acids with high activity; while molybdenum oxide and rhenium oxide on alumina lead to high coke and gas make even with steam present as a cofeed in the cracking test. The periodic trends of cracking activity are those expected from the charge-to-radius ratio of the metal cation. This class of surface phase oxide solid acids has a wide range of activities (two orders of magnitude) and may prove useful for matching acid strength to specific reactions. In addition, this class of solid acids maintains surface area and cracking activity following high temperature steam treatment, in contrast to many conventional solid acid catalysts.

Murrell, L.L.; Grenoble, D.C.; Kim, C.J.; Dispenziere, N.C. Jr.

1987-10-01

243

Microstructure of perovskite oxide thin films grown on miscut\\/small lattice-mismatched substrates  

Microsoft Academic Search

Perovskite oxides exhibit a wide range of physical properties, such as high dielectric, piezoelectric, pyroelectric, ferroelectric\\/multiferroic, non-linear optical and high temperature superconducting properties. The unique combination of these properties makes possible the use of perovskite oxide thin films as core elements in the next generation devices for sensors and electric\\/electronic\\/optical circuits. Recent studies demonstrate that it is possible to tailor

Yanbin Chen

2008-01-01

244

Transition Metal Compounds as Cathodic Materials in Rechargeable Lithium Cells.  

National Technical Information Service (NTIS)

A comparison was made between rechargeable lithium batteries, based on lithium intercalation or lithium interstitial compounds of transition metal chalcogenides or oxides, and nickel-cadmium batteries. Several chalcogenides and oxides show promise as cath...

H. F. Hunger J. E. Ellison

1977-01-01

245

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

PubMed

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

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

2013-01-01

246

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

DOEpatents

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

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

2001-01-01

247

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

PubMed

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

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

2014-01-01

248

A soft chemical route to multicomponent lithium transition metal oxide nanowires as promising cathode materials for lithium secondary batteries  

Microsoft Academic Search

We have synthesized 1D nanowires of lithium nickel manganese oxides with two different crystal structures through the chemical oxidation reaction of solid-state precursor LiMn0.5Ni0.5O2 under hydrothermal condition. According to X-ray diffraction and elemental analyses, the nanowires obtained by persulfate treatments at 65 and 120°C crystallize with a hexagonal layered and an ?-MnO2-type structure, respectively, in which nickel and manganese ions

Dae-Hoon Park; Seung-Tae Lim; Seong-Ju Hwang

2006-01-01

249

Transition Metal Switchable Mirror  

ScienceCinema

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

None

2010-01-08

250

Transition Metal Switchable Mirror  

SciTech Connect

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

None

2009-01-01

251

Transition Metal Switchable Mirror  

SciTech Connect

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

2009-08-21

252

Transition Metal Switchable Mirror  

ScienceCinema

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

253

Transition Metal Switchable Mirror  

ScienceCinema

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

254

Transition Metal Switchable Mirror  

ScienceCinema

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

None

2013-05-29

255

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

256

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

PubMed Central

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

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

257

From alkaline earth ion aggregates via transition metal coordination polymer networks towards heterometallic single source precursors for oxidic materials.  

PubMed

Heterometallic oxides are used as materials in many applications, e.g. from ferroelectrics to superconductors. Making these compounds usually requires high temperatures and long reaction times. Molecular precursors may contribute to render their processing shorter and accessible at lower temperatures, thus cheaper in energy and time. In this review article, different approaches toward oxide materials will be shown, starting with homometallic clusters and coordination polymers and highlighting recent results with heterometallic single source precursors. On the way to the latter, we came across many exciting results which themselves allowed applications in different fields. This work will give an overview on how these fields were brought together for the current mixed metallic compounds as precursors for heterometallic oxides. PMID:21138074

Gschwind, Fabienne; Crochet, Aurélien; Maudez, William; Fromm, Katharina M

2010-01-01

258

Peculiarities of transition metals dispersed on oxide support in catalysis phenomena. Example of model Co foil catalyst  

NASA Astrophysics Data System (ADS)

Industrial catalysts are complex metal and metal oxide systems of poor-defined structure. The paper presents an approach to study and design these materials using well-characterised model materials—cobalt foil catalyst as an example. An active Co-foil catalyst shows reproducible properties and has a sandwich-like structure consisting of CoO layer attached to Co bulk, on which highly dispersed Co phase is located. This phase contains active centres for hydrogenation reactions in form of cobalt clusters. To obtain such a catalyst a special procedure of activation has been developed based on high-temperature reduction/oxidation and reduction at mild temperatures. Various complementary surface techniques have been engaged to study evolution of surface phases of the catalyst at various stages of its activation and work during catalytic reactions.

?ojewska, Joanna; Dziembaj, Roman

2005-02-01

259

Sr(3)Co(2)O(4.33)h(0.84): an extended transition metal oxide-hydride.  

PubMed

Reaction of the n = 2 Ruddlesden-Popper oxide Sr(3)Co(2)O(5.80) with CaH(2) yields an extended oxide-hydride phase: Sr(3)Co(2)O(4.33)H(0.84). Neutron powder diffraction data reveal the material adopts a body-centered orthorhombic structure (Immm: a = 3.7551(5) Ĺ, b = 3.7048(4) Ĺ, c = 21.480(3) Ĺ) in which the hydride ions are accommodated within disordered CoO(1.16)H(0.46) layers. Low temperature neutron powder diffraction data show no evidence for long-range magnetic order, suggesting the chemical disorder in the anion lattice of the material leads to magnetic frustration. PMID:21033678

Helps, Rebecca M; Rees, Nicholas H; Hayward, Michael A

2010-12-01

260

Ab initio calculation of the intercalation voltage of lithium-transition-metal oxide electrodes for rechargeable batteries  

Microsoft Academic Search

A first-principle's method to predict the intercalation voltage for lithium in metal oxides is presented. Although the intercalation voltage for lithium is often related to aspects of the electronic structure, this voltage can only be accurately calculated from the lithium chemical potential in the anode and cathode. Using the pseudopotential technique the average intercalation voltage of LiMO2 cathodes is computed

M. K. Aydinol; A. F. Kohan; G. Ceder

1997-01-01

261

Recent advances in the study of layered lithium transition metal oxides and their application as intercalation electrodes  

Microsoft Academic Search

A review is presented on the extensive work carried out during the last 30 years on layered oxides structurally related to\\u000a LiCoO2 and LiNiO2. The studies considered here range from the structural and chemical characterization of the layered solids to the detailed\\u000a evaluation of their aptitude towards lithium deintercalation-intercalation reactions, which form the basis of their successful\\u000a application in rechargeable

R. Alcántara; P. Lavela; J. L. Tirado; E. Zhecheva; R. Stoyanova

1999-01-01

262

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

NASA Astrophysics Data System (ADS)

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

Tang, Yu Ming

263

Ab initio Low-Energy Model of Transition-Metal-Oxide Heterostructure LaAlO3/SrTiO3  

NASA Astrophysics Data System (ADS)

We develop a multiscale ab initio scheme for correlated electrons (MACE) for transition-metal-oxide heterostructures, and determine the parameters of the low-energy effective model. By separating Ti t2g bands near the Fermi level from the global Kohn--Sham (KS) bands of LaAlO3 (LAO)/SrTiO3 (STO), which are highly entangled with each other, we are able to calculate the parameters of the low-energy effective model of the interface with the help of constrained random phase approximation (cRPA). The on-site energies of the Ti t2g orbitals in the 1st layer is about 650 meV lower than those in the second layer. In the 1st layer, the transfer integral of the Ti t2g orbital is nearly the same as that of bulk STO, while the effective screened Coulomb interaction becomes about 10% larger than that of bulk STO. The differences in the parameters from bulk STO decrease rapidly with increasing distance from the interface. Our present versatile method enables us to derive effective ab initio low-energy models and to study interfaces of strongly correlated electron systems from first principles.

Hirayama, Motoaki; Miyake, Takashi; Imada, Masatoshi

2012-08-01

264

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

PubMed

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

Eichel, Rüdiger-A

2011-01-14

265

FT-IR study on the adsorption of benzoic acid and its derivatives on transition-metal oxides  

NASA Astrophysics Data System (ADS)

The present study gives the results of our attempts to gain more knowledge on the interaction between an aromatic carboxylic acid and an oxide catalyst. There is quite a difference in the coordination of benzoic (and salicylic) acid with an acid-base catalyst (?-Al 2O 3) or a redox one (?-Mn 3O 4). When a substituent is incorporated into the ring, the difference becomes even larger. These differences can perhaps explain the difficulties in the catalytic reduction from (substituted) benzoic acids to the corresponding aldehydes.

Koutstaal, C. A.; Ponec, V.

1993-06-01

266

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

267

Dense perovskite membrane reactors for partial oxidation of methane to syngas  

Microsoft Academic Search

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

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

1997-01-01

268

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

PubMed

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

Oyedepo, Gbenga A; Wilson, Angela K

2011-12-01

269

Magnetism in 3d Transition Metals at High Pressures.  

National Technical Information Service (NTIS)

This research project examined the changes in electronic and magnetic properties of transition metals and oxides under applied pressures, focusing on complex relationship between magnetism and phase stability in these correlated electron systems. As part ...

V. Iota

2006-01-01

270

Structure-property relationships of nanoscale engineered perovskite oxides  

NASA Astrophysics Data System (ADS)

Recent advances in the synthesis of nanoscale customized structure have demonstrated that reactive molecular beam epitaxy (MBE) can be used to construct nanostructure of oxides with atomic control. The ability to engineer the structure and chemistry of oxides at the nanometer scale makes possible for the creation of new functional materials that can be designed to have exceptional properties. This thesis focused on understanding structure-property relationships of such nanoscale customized oxides utilizing state-of-the-art transmission electron microscopy (TEM). Epitaxial thin films of n = 1--5 members of Ruddlesden-Popper homologous series Srn+1Ti nO3n+1 were synthesized by reactive MBE. We investigated the structure and microstructure of these thin films by x-ray diffraction along with high-resolution transmission electron microscopy (HRTEM) in combination with computer image simulations. We found that the thin films of n = 1--3 members are nearly free of intergrowths, e.g. phase-pure, while n = 4 and 5 thin films contain noticeably more intergrowth defects and anti-phase boundaries in their perovskite sheets. We show that these results are consistent with what is known about the thermodynamics of Sr n+1TinO3 n+1 phases. We also investigated the atomic structure and interfacial structure of artificial PbTiO3/SrTiO3 and BaTiO3/SrTiO 3 superlattices grown by MBE both with and without digital compositional grading. Both of these systems form a solid solution over their entire composition range. Thus, these layered heterostructures are metastable. We demonstrated, however, that the thermodynamically metastable superlattices can be kinetically stabilized via layer-by-layer growth. In addition, we found that the interfaces between two constituents in the heterostructures are atomically-abrupt. The superlattice thin films were made fully coherent with the substrates, resulting in a homogeneous large strain in the BaTiO3 layers due to the lattice mismatch between BaTiO3 and SrTiO3 (˜2.3%). Atomic positions of cations and anions in the strained BaTiO3 unit cell were determined by quantitative HRTEM. A strain-induced enhancement of spontaneous polarization of BaTiO3 was found. The experimental results agree quantitatively with the theoretical calculations. Finally, the structural stability of the layered heterostructures at high temperatures was investigated.

Tian, Wei

271

Thermal expansion match between molybdenum (TZM alloy) and oxides of the perovskite and spinel type  

Microsoft Academic Search

Thermal expansion measurements to 1200°C have been made by the Bureau of Mines of a wide selection of complex oxides of both the perovskite and spinel structures. These are compared with the thermal expansion of molybdenum and the molybdenum alloy TZM to find suitable expansion matches for oxide coating development. A dilatometric technique was employed which makes use of a

J. L. Henry; G. G. Thompson

1976-01-01

272

Partial oxidation of methane over Ni catalysts based on hexaaliminate- or perovskite-type oxides  

Microsoft Academic Search

Ni\\/Al2O3, hexaaluminate-type BaNixAl12?xO19?? and perovskite-type LaAl5\\/6Ni1\\/6O3 were investigated for partial oxidation of methane (POM). The hexaaluminate-type BaNiAl11O19?? calcined at 1400°C demonstrated more stable and higher activity than Ni\\/Al2O3 calcined at 1000°C. The BaNiAl11O19?? catalyst reduced at 1000°C was more active than the catalyst reduced at 800°C. The results from XPS analysis revealed that the hexaaluminate-type catalysts calcined and reduced at

Toshimasa Utaka; Saud Abdulaziz Al-Drees; Jun Ueda; Yasuyuki Iwasa; Tatsuya Takeguchi; Ruji Kikuchi; Koichi Eguchi

2003-01-01

273

Preparation and characterization of A-site doped Perovskite-type manganese oxides  

NASA Astrophysics Data System (ADS)

Perovskite type manganese oxide is a kind of in solid state chemistry and the field of condensed matter physics are used extensively in the study of materials. Application of sol-gel method on perovskite type manganese oxide doping, preparation out series of samples La0.6BaxSr(0.4-x)MnO3, including powder and flake. After annealing treatment, the X ray diffraction tests of different annealing temperature on the influence of the structure of the samples was studied.

Huang, Yingqun; Li, Xiong; Che, Xinglai; Ju, Hailang

2013-08-01

274

Selenophene transition metal complexes  

SciTech Connect

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

White, C.J.

1994-07-27

275

Preparation of Mixed Perovskite Oxides for Blue-Green Lasers.  

National Technical Information Service (NTIS)

Mixed crystals of the perovskite type structure of the system La A1 1-x Sc x, O3 were examined over the compositions of x= 0.15-0.30. Single crystals were grown from melts in iridium crucibles using the Czochralski method. Seed crystals of (111) pure La A...

R. F. Belt R. Uhrin

1984-01-01

276

Interface Effects in Perovskite Thin Films  

NASA Astrophysics Data System (ADS)

The control of matter properties (transport, magnetic, dielectric,…) using synthesis as thin films is strongly hindered by the lack of reliable theories, able to guide the design of new systems, through the understanding of the interface effects and of the way the substrate constraints are imposed on the material. The present Letter analyzes the energetic contributions at the interfaces, and proposes a model describing the microscopic mechanisms governing the interactions at an epitaxial interface between a manganite and another transition metal oxide in perovskite structure (as for instance SrTiO3). The model is checked against experimental results and literature analysis.

Lepetit, Marie-Bernadette; Mercey, Bernard; Simon, Charles

2012-02-01

277

Oxidation Reactions of Ethane over Ba-Ce-O Based Perovskites  

Microsoft Academic Search

Ethane oxidation reactions were studied over pure and Ca-, Mg-, Sr-, La-, Nd-, and Y-substituted BaCeOâ 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 COâ at temperatures below 650 C. At higher temperatures, the oxidative dehydrogenation (ODH) to ethylene becomes significant. Conversions and ethylene

James E. Miller; Allen G. Sault; Daniel E. Trudell; Tina M. Nenoff; Steven G. Thoma; Nancy B. Jackson

1999-01-01

278

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

NASA Astrophysics Data System (ADS)

The major part of this thesis deals with the synthesis and magnetic characterization of low dimensional spin systems in the 3d transition metal oxides. Such systems are of interest due to the simplicity of their structures, allowing theoretical modeling of their electronic and magnetic behavior. Exotic properties are also often encountered. Studies involving layered magnetic materials based on triangle lattices, in particular, have resulted in many observations of unusual low temperature spin dynamics, and have presented new challenges for the theoretical understanding of magnetic systems. The magnetic properties of some compounds exhibiting these triangle-based lattices are described here in detail. BaNi2V2O8 is a spin-1 antiferromagnet on a honeycomb net. Susceptibility chi(T), specific heat C(T), and neutron diffraction measurements on this compound reveal the onset of antiferromagnetic (AFM) long-range ordering (LRO) close to 50 K. Diffuse diffraction peaks that are characteristic of two-dimensional (2D) short-range order are also observed up to 100 K. chi(T) of Ba(Ni1-xMgx)2V 2O8 shows the gradual disappearance of LRO with doping. Ni3V2O8, Co3V2O 8, and beta-Cu3V2O8 have spin-1, spin-3/2, and spin-1/2 magnetic lattices that are a new anisotropic variant of the Kagome net, wherein edge-sharing MO6 octahedra form the rises and rungs of a "Kagome staircase". The anisotropy largely relieves the geometric frustration, but results in rich magnetic behavior. Characterization of the magnetization of polycrystalline samples of Ni 3V2O8 and Co3V2O8 reveals that the compounds are ferrimagnetic in character. C(T) show four distinct magnetic phase transitions below 9 K for Ni3V2O 8 and two below 11 K for Co3V2O8. In the case of beta-Cu3V2O8, chi(T) and C(T) show the onset of short-range ordering at approximately 75 K, and a magnetic phase transition with the characteristics of antiferromagnetism at around 29 K. The second part of this thesis describes the bulk synthesis of M9132 at temperatures as low as 500 to 550°C with good superconducting properties. Most reported bulk synthesis of MgB2 has been done at high temperatures (e.g. 900°C), which is not favorable for thin film synthesis. The results of this work confirm the potential of developing an "in-situ" thin film technology based on MgB2.

Rogado, Nyrissa S.

279

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

Microsoft Academic Search

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

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

1998-01-01

280

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

NASA Astrophysics Data System (ADS)

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

Tauer, Tania Allison

281

Achieving Novel Magnetic States in Perovskite Oxides through Heteroepitaxy  

NASA Astrophysics Data System (ADS)

This dissertation is focused on controlling the spin state and long-range magnetic order in cobaltites by heteroepitaxial thin-film growth. I explore the growth of two different cobaltite materials, LaCoO3 and PrCoO 3, on lattice-mismatched substrates to determine the role of epitaxial strain in giving rise to long-range magnetic order. This magnetic order is not found in the bulk cobaltite material and warrants the detailed investigations carried out in this work. I investigate changes in structure and stoichiometry that influence the electronic structure and the long-range magnetic order in these materials. In the LaCoO3 system, I explore the changes in structure in the films under tensile strain and compressive strain by growth on SrTiO 3, LaSrAlTaO3, and LaAlO3 substrates and film growth between 8 nm -133 nm thick. Substrate-dependent oxygen vacancy ordering in the films is found using microstructural characterization, presumably related to the amount of stress in each of the films. By carrying out a study of the effects on the film structure from the oxygen growth pressure, I find an overall increase in the out-of-plane lattice parameter with lower oxygen growth pressures. These structural and stoichiometry changes in the LaCoO3 films to trends appear to be related to the stabilization of long-range magnetic order. Highest moment is found in the films in tension (which also have the most defects) on SrTiO3 and LaSrAlTaO3 substrates and the lowest moment is found in films in compression on LaAlO3. Element-specific X-ray absorption techniques reveal contributions from Co in different spin and valence states. I show how strain affects the electronic structure and distribution of these different states and relate these observations to trends observed in the magnetism. Strained films in tension have the highest amount of high spin Co3+ and high spin Co2+, while relaxed films appear to have mostly low spin Co3+ at 25 K. I present some scenarios to explain how these different Co ions combine to give rise to long-range ferromagnetic order in LaCoO3 films. In the PrCoO3 system, I explore whether long-range magnetic order can be observed using heteroepitaxial synthesis similar to the efforts in the LaCoO3 thin film system despite PrCoO3 having a more stable low spin state configuration in the bulk. The PrCoO3 films in tension are ferromagnetic, similar to the LaCoO3 system. Thus, epitaxial strain dominates the effects of chemical pressure which stabilize a low spin state. The strained films have more high spin Co3+. The implication of Co sublattice ordering on the ordering of the Pr sublattice is explored using X-ray magnetic circular dichroism. A rare ordering of the Pr ions anti-parallel to the orientation of the moments on the Co sublattice appears to occur in this system. These studies demonstrate the power of heteroepitaxial synthesis to give rise to new magnetic functionality in perovskite oxide systems.

Mehta, Virat Vasav

282

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

PubMed

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

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

2008-05-16

283

Oxidation of toluene on lanthanum cobaltite perovskite (LaCoO 3 ) catalyst  

Microsoft Academic Search

Vapor phase oxidation of toluene to benzaldehyde has been studied on lanthanum cobaltite, LaCoO3, with a perovskite structure. Experimental data were obtained in the temperature range 350 to 600°C and contact time 0.2 to 2 h. The overall kinetic analysis indicated the oxidation of toluene to benzaldehyde to be first order, with a frequency factor of 0.62 h?1 and an

K. L. Madhok

1986-01-01

284

A Facile and General Approach for the Direct Fabrication of 3D, Vertically Aligned Carbon Nanotube Array/Transition Metal Oxide Composites as Non-Pt Catalysts for Oxygen Reduction Reactions.  

PubMed

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

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

2014-05-01

285

Lattice distortion and magnetism of 3d-t2g perovskite oxides  

NASA Astrophysics Data System (ADS)

Several puzzling aspects of interplay of the experimental lattice distortion and the magnetic behavior of four narrow t2g -band perovskite oxides ( YTiO3 , LaTiO3 , YVO3 , and LaVO3 ) are clarified using results of first-principles electronic structure calculations. First, we derive parameters of the effective Hubbard-type Hamiltonian for the isolated t2g bands using newly developed downfolding method for the kinetic-energy part and a hybrid approach, based on the combination of the random-phase approximation and the constraint local-density approximation, for the screened Coulomb interaction part. Apart from the above-mentioned approximation, the procedure of constructing the model Hamiltonian is totally parameter free. The results are discussed in terms of the Wannier functions localized around transition-metal sites. The obtained Hamiltonian was solved using a number of techniques, including the mean-field Hartree-Fock (HF) approximation, the second-order perturbation theory for the correlation energy, and a variational superexchange theory, which takes into account the multiplet structure of the atomic states. We argue that the crystal distortion has a profound effect not only on the values of the crystal-field (CF) splitting, but also on the behavior of transfer integrals and even the screened Coulomb interactions. Even though the CF splitting is not particularly large to fully quench the orbital degrees of freedom (ODF), the crystal distortion imposes a severe constraint on the form of the possible orbital states, which favor the formation of the experimentally observed magnetic structures in YTiO3 , YVO3 , and LaVO3 even at the level of mean-field HF approximation. Particularly, LaVO3 presents an interesting example of the system where the ODF are well quenched only in one of the monoclinic planes and remain relatively flexible in the second plane, leaving some room for the orbital fluctuations. It is also remarkable that for all three compounds, the main results of all-electron calculations can be successfully reproduced in our minimal model derived for the isolated t2g bands. We confirm that such an agreement is possible only when the nonsphericity of the Madelung potential is explicitly included into the model. Beyond the HF approximation, the correlation effects systematically improve the agreement with the experimental data and additionally stabilize the experimentally observed G - and C -type antiferromagnetic states in YVO3 and LaVO3 . Using the same type of approximations we could not obtain the correct magnetic ground state for LaTiO3 . However, we expect that the situation may change by systematically improving the level of approximations for treating the correlation effects.

Solovyev, I. V.

2006-08-01

286

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

Microsoft Academic Search

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

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

2000-01-01

287

Intergranular Giant Magnetoresistance in a Spontaneously Phase Separated Perovskite Oxide  

NASA Astrophysics Data System (ADS)

We present small-angle neutron scattering data proving that, on the insulating side of the metal-insulator transition, the doped perovskite cobaltite La1-xSrxCoO3 phase separates into ferromagnetic metallic clusters embedded in a nonferromagnetic matrix. This induces a hysteretic magnetoresistance, with temperature and field dependence characteristic of intergranular giant magnetoresistance (GMR). We argue that this system is a natural analog to the artificial structures fabricated by depositing nanoscale ferromagnetic particles in a metallic or insulating matrix; i.e., this material displays a GMR effect without the deliberate introduction of chemical interfaces.

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

2005-01-01

288

Resonant x-ray reflectivity study of perovskite oxide superlattices  

NASA Astrophysics Data System (ADS)

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. These results are consistent with scanning transmission electron microscopy and electron energy loss spectroscopy.

Kemik, N.; Gu, M.; Yang, F.; Chang, C.-Y.; Song, Y.; Bibee, M.; Mehta, A.; Biegalski, M. D.; Christen, H. M.; Browning, N. D.; Takamura, Y.

2011-11-01

289

Reducibility of Co 3+ in perovskite-type LaCoO 3 and promotion of copper on the reduction of Co 3+ in perovskite-type oxides  

NASA Astrophysics Data System (ADS)

The reducibility of Co 3+ in LaCoO 3 and the promotion of copper on the reduction of Co 3+ in perovskite-type oxides have been studied by temperature programmed reduction (TPR), temperature programmed oxidation (TPO), X-ray diffraction (XRD) and infrared spectroscopy (IR). Quantitative TPR and TPO analyses propose that the reduction of Co 3+ in LaCoO 3 to Co 0 belongs to a one-step process and that every TPR peak represents the reduction of every Co 3+ species to Co 0 in the crystallite structure. Accordingly, the produced Co 0 is assumed to be atomically located in the perovskite lattice provided the perovskite structure is retained after reduction. Quantitative TPR analyses also indicates that copper located in LaCo 0.85Cu 0.15O 3 promotes regularly the reduction of various Co 3+ species whereas copper doped on LaCoO 3 does irregularly. The action of the latter leads to more efficient reduction of Co 3+ to atomically dispersed Co 0 over a useful temperature range for catalytic purposes. TPR, XRD and IR studies show that the perovskite structure of LaCo 0.85Cu 0.15O 3 is somewhat less stable than that of LaCoO 3 and that the perovskite structural stability of LaCoO 3 is not weakened by the doping of copper.

Huang, Lin; Bassir, Mahbod; Kaliaguine, Serge

2005-04-01

290

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

PubMed

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

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

2014-07-21

291

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

Microsoft Academic Search

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

Igor Djerdj; Denis Arcon; Zvonko Jaglicic; Markus Niederberger

2008-01-01

292

Electrical Conductivity in Transition Metals  

ERIC Educational Resources Information Center

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

Talbot, Christopher; Vickneson, Kishanda

2013-01-01

293

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

SciTech Connect

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

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

2008-07-15

294

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

PubMed

Strong correlation between spins and conduction electrons is key in spintronic materials and devices. A few ferro- or ferrimagnetic transition metal oxides such as La1-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. PMID:24849185

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

2014-01-01

295

Lanthanum cobaltite perovskite supported onto mesoporous zirconium dioxide: Nature of active sites of VOC oxidation  

Microsoft Academic Search

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

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

2011-01-01

296

Acetone gas sensing properties of SmFe 1? x Mg x O 3 perovskite oxides  

Microsoft Academic Search

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

Xing Liu; Jifan Hu; Bin Cheng; Hongwei Qin; Minhua Jiang

2008-01-01

297

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

Microsoft Academic Search

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

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

2001-01-01

298

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

NASA Astrophysics Data System (ADS)

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

Zhou, Xiaolan

299

Atomic level observation of octahedral distortions at the perovskite oxide heterointerface  

NASA Astrophysics Data System (ADS)

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.

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

2013-07-01

300

Atomic level observation of octahedral distortions at the perovskite oxide heterointerface  

PubMed Central

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

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

2013-01-01

301

Optical and energy-loss spectra of the antiferromagnetic transition metal oxides MnO, FeO, CoO, and NiO including quasiparticle and excitonic effects  

NASA Astrophysics Data System (ADS)

We calculate the frequency-dependent dielectric function for the series of antiferromagnetic transition metal oxides (TMOs) from MnO to NiO using many-body perturbation theory. Quasiparticle, excitonic, and local-field effects are taken into account by solving the Bethe-Salpeter equation in the framework of collinear spin polarization. The optical spectra are based on electronic structures which have been obtained using density-functional theory with a hybrid functional containing screened exchange (HSE03) and a subsequent quasiparticle calculation in the GW approximation to describe exchange and correlation effects adequately. These sophisticated quasiparticle band structures are mapped to electronic structures resulting from the computationally less expensive GGA+U+? scheme that includes an on-site interaction U and a scissors shift ? and allows us to calculate the large number of electronic states that is necessary to construct the Bethe-Salpeter Hamiltonian. For an accurate description of the optical spectra, an appropriate treatment of the strong electron-hole attraction is mandatory to obtain agreement with the experimentally observed absorption-peak positions. The itinerant s and p states as well as the localized transition metal 3d states have to be considered on an equal footing. We find that a purely atomic picture is not suitable to understand the optical absorption spectra of the TMOs. Reflectivity spectra, absorption coefficients, and loss functions at vanishing momentum transfer are computed in a wide spectral range and discussed in light of the available experimental data.

Rödl, Claudia; Bechstedt, Friedhelm

2012-12-01

302

Electrospun Zn(1-x)Mn(x)Fe2O4 nanofibers as anodes for lithium-ion batteries and the impact of mixed transition metallic oxides on battery performance.  

PubMed

The structural and electrochemical properties of the mixed transition metallic oxides Zn1-xMnxFe2O4 nanofibers, which crystallize in a cubic spinel AFe2O4 structure, are investigated systematically with a gradual substitution of Zn by Mn. The crystal structural information studied by X-ray diffraction (XRD) depicts the formation of single phase spinel structure, while electron-dispersive X-ray spectroscopy (EDS) reveals the stoichiometric ratio between Zn and Mn. ZnFe2O4 exhibits a good capacity of ~532 mAh g(-1) at 50th cycle through the interbeneficial conversion reaction and alloy-dealloy mechanism, with a first discharge working voltage of ~0.83 V. Subsequently, the characteristic redox potential of each spinel is gradually reduced with the replacement of Mn. Furthermore, Zn0.3Mn0.7Fe2O4 demonstrates the highest capacity of ~612 mA h g(-1) at 50th cycle among the solid solution series. Ex situ characterization by high-resolution transmission electron microscope (TEM) and electron energy loss spectroscopy (EELS) is conducted to study the participation of Mn in the battery performance. This report represents an example of how the electrochemical performance could be flexibly adjusted by tuning the ratio of transition metals within the spinel. PMID:23688028

Teh, Pei Fen; Pramana, Stevin Snellius; Sharma, Yogesh; Ko, Yah Wen; Madhavi, Srinivasan

2013-06-26

303

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

NASA Astrophysics Data System (ADS)

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

Vajifdar, Kayzad Jimmy

304

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

NASA Astrophysics Data System (ADS)

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

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

2008-06-01

305

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

PubMed

Bismuth is doped to lanthanum strontium ferrite to produce ferrite-based perovskites with a composition of La0.8-xBixSr0.2FeO3-? (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 (Kchem), and chemical diffusion coefficient (Dchem) are explored as a function of bismuth content. While ? decreases with x due to the reduced Fe(4+) content, Dchem and Kchem increase since the oxygen vacancy concentration is increased by Bi doping. Consequently, the electrochemical performance is substantially improved and the interfacial polarization resistance is reduced from 1.0 to 0.10 ? cm(2) at 700 °C with Bi doping. The perovskite with x = 0.4 is suggested as the most promising composition as solid oxide fuel cell cathode material since it has demonstrated high electrical conductivity and low interfacial polarization resistance. PMID:24971668

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

2014-07-23

306

Protons and lattice defects in perovskite-related oxides  

SciTech Connect

The recent work on this project has focused on two perovskite- structured materials: single crystalline KTaO{sub 3} doped with iron-group ions, and ceramic BaCeO{sub 3} doped with Nd, Gd, Sc and Ca. In the case of KTaO{sub 3}, we have shown that protons are introduced into the crystal from H{sub 2}O vapor so that it becomes primarily a protonic conductor. The defect reactions involved have been considered in detail with the aid of EPR and IR measurements. In the study of BaCeO{sub 3}, it was found that the Nd-doped material is an excellent protonic conductor with activation energy for proton hopping of only 0.54 eV. In addition, weight-change measurements were used to determine the amount of water uptake, while Nernst-cell measurements gave values for the transport numbers of oxygen and of protons. In contrast to the case of Nd doping, Gd or Yb-doped material are not protonic conductors. Other studies include those of high-{Tc} superconductors, the first showing a large elastic constant and internal friction anomaly in La{sub 2x}Sr{sub x}CuO{sub 4}, and the second showing under what conditions degradation occurs due to H{sub 2}O and CO{sub 2} annealing treatments. Finally, a study of dielectric loss in Li-borate glasses shows that the dielectric loss peak in glasses widely believed to be due to a bulk phenomenon, is actually an electrode blocking effect.

Nowick, A.S.

1990-01-01

307

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

Microsoft Academic Search

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

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

2000-01-01

308

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

PubMed

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

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

2011-08-01

309

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

SciTech Connect

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

Not Available

1993-05-01

310

[Non-empirical interatomic potentials for transition metals  

SciTech Connect

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

Not Available

1993-01-01

311

Stable singlet carbenes as mimics for transition metal centers  

PubMed Central

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

Martin, David; Soleilhavoup, Michele

2011-01-01

312

Transition metal-substituted cobalt ferrite nanoparticles for biomedical applications.  

PubMed

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

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

2013-03-01

313

Layered PrBaCo 2O 5+ ? perovskite as a cathode for proton-conducting solid oxide fuel cells  

Microsoft Academic Search

The layered PrBaCo2O5+? (PBCO) perovskite oxides were synthesized by modified Pechini method and investigated as a cathode material for solid oxide fuel cells (SOFCs) based on a stable and easily sintered perovskite oxide BaCe0.5Zr0.3Y0.16Zn0.04O3?? (BCZYZ) as electrolyte. The fabricated single cell of NiO-BCZYZ\\/BCZYZ (?20?m)\\/PBCO was operated from 550 to 700°C with humidified hydrogen (?5% H2O) as fuel and the static

Meifang Jin; Xiuling Zhang; Yu’e Qiu; Jianmin Sheng

2010-01-01

314

Interactional effects between coadsorbed species on single crystal transition metal surfaces  

Microsoft Academic Search

Transition metal catalysts have long been of technological importance in the hydrogenation and oxidation of CO. The performance of these catalysts can be altered by the presence of impurity species which either promote or poison the catalyst. In an attempt to better understand the effect of modifier adatoms on transition metal catalysts a series of studies have been performed on

Uram

1986-01-01

315

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

NASA Astrophysics Data System (ADS)

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

Balachandran, Prasanna V.; Rondinelli, James M.

2013-08-01

316

Basic properties of the F-type centers in halides, oxides and perovskites  

NASA Astrophysics Data System (ADS)

We present a short survey of the optical properties of primary radiation-induced point defects in alkali halides, simple oxides and some ABO 3 perovskites. We discuss in details the optical properties of single electron F and F+ centers in rock-salt (f.c.c.) alkali halides and oxides and show that the Mollwo-Ivey law well-known for the F-type centers in alkali halides may be extended for other rock-salt structure insulators. We also discuss the major differences in point defect production mechanisms in halides and oxides. We show that the Rabin-Klick diagram may be generalized for a whole family of alkali halides. The F-type center migration and aggregation into metal colloids in alkali halides and oxides is also discussed.

Popov, A. I.; Kotomin, E. A.; Maier, J.

2010-10-01

317

Brazing perovskite ceramics with silver\\/copper oxide braze alloys  

Microsoft Academic Search

In this study the feasibility of eutectic braze alloys based on the silver\\/copper oxide (Ag\\/CuO) system were investigated for use in joining lead magnesium niobate (PMN) ceramics. PMN was successfully brazed in air at 1050 and 1100°C using Ag\\/CuO alloys. The brazed samples had an average four-point-bend fracture strength of approximately 40 percent of the average monolithic PMN strength (with

K. M. Erskine; A. M. Meier; S. M. Pilgrim

2002-01-01

318

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

SciTech Connect

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

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

2011-12-31

319

Transition-metal-mediated thiosulfinate ester synthesis  

SciTech Connect

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

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

1989-10-11

320

Nanostructured magnetoelectric thin films of ferroelectric perovskite and magnetic oxides  

Microsoft Academic Search

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

Ce-Wen Nan

2008-01-01

321

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

Microsoft Academic Search

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

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

2007-01-01

322

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

Microsoft Academic Search

New results on the oxygen permeability of perovskite-type oxides SrCo0.8B'0.2O3żż (with B'=Cr, Fe, Co and Cu) and La0.6Sr0.4CoO3żż are presented. The occurrence of order-disorder transitions at elevated temperatures (790ż940°C) in these phases has been confirmed by DSC measurements and, in some cases, by X-ray powder diffraction of samples either slowly cooled or quenched from high temperature after annealing in different

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

1993-01-01

323

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

Microsoft Academic Search

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

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

1995-01-01

324

A facile route for producing single-crystalline epitaxial perovskite oxide thin films.  

PubMed

We report how a low vacuum pressure process followed by a few-minute annealing enables epitaxial stabilization, producing high-quality, phase-pure, single-crystalline epitaxial, and misfit dislocation-free BiFeO3(001) thin films on SrTiO3(001) at ?450 °C less than current routes. These results unambiguously challenge the widely held notion that atomic layer deposition (ALD) is not appropriate for attaining high-quality chemically complex oxide films on perovskite substrates in single-crystalline epitaxial form, demonstrating applicability as an inexpensive, facile, and highly scalable route. PMID:24063419

Akbashev, Andrew R; Chen, Guannan; Spanier, Jonathan E

2014-01-01

325

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

SciTech Connect

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

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

2006-12-31

326

Examples of high-resolution electron microscopy (HREM) investigation of complex oxides related to perovskite.  

PubMed

The properties of oxides may be drastically influenced by their microstructures. Thus the knowledge of nonstoichiometric mechanisms is an essential tool for the conception of new inorganic compounds by solid-state chemist. Through three chosen examples of complex oxides with perovskite-related structure, these points are illustrated. The new families of phosphate tungsten bronzes, the antiferromagnetic AMn1-xFexO3-y, and the copper oxides LCuO3-x (L = Ba, Y, La) were studied by high-resolution electron microscopy (HREM) in order to analyze the mechanisms of nonstoichiometry, the defects of which can modify their physical properties (magnetism or electronic conductivity) and the factors that govern their stabilization. PMID:2723802

Hervieu, M

1989-03-01

327

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

PubMed Central

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

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

2013-01-01

328

Synthesis of transition metal carbonitrides  

SciTech Connect

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

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

1994-01-01

329

High-pressure Mössbauer spectroscopy of perovskite high valence iron oxides under external magnetic field  

NASA Astrophysics Data System (ADS)

The magnetic properties of SrFeO3 (SFO), CaFeO3 (CFO) and Sr2/3La1/3FeO3 (SLFO), which are perovskite iron oxides with a high valence state of Fe, have been investigated by high-pressure Mössbauer spectroscopy under external magnetic field. These perovskite oxides have been found to switch electronic ground state drastically from the antiferromagnetic (AF) state to the ferromagnetic (FM) state under high pressure. CFO and SLFO, which show a charge-disproportionation (CD: {\\mathrm {2Fe^{4+}\\to Fe^{3+}+ Fe^{5+}}} and {\\mathrm {3Fe^{11/3+}\\to 2Fe^{3+}+Fe^{5+}}} , respectively) at low temperature, switch magnetic ordering from the AF state to the FM state simultaneously with the suppression of the CD in a critical pressure of about 19 and 23 GPa, respectively. SFO, which does not show any CD, switches its magnetic ordering from the AF state to the FM state at about 7 GPa. These pressure-induced transitions from the AF state to the FM state are accompanied by the discontinuous reduction of the magnetic hyperfine fields.

Kawakami, Takateru; Nasu, Saburo

2005-03-01

330

Competing magnetic phases in mixed-valent manganese oxide perovskites  

NASA Astrophysics Data System (ADS)

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

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

2004-12-01

331

Photodissociation Spectroscopy of Anionic Transition Metal Complexes  

NASA Astrophysics Data System (ADS)

Transition metal complexes play an important role in many aspects of chemistry; whether in supporting biological functions, as catalysts for organic reactions, in the environment, or in industry. This thesis is comprised of gas-phase spectroscopic studies of four transition metal species with implications for many different chemical applications. Most knowledge of the target molecules in this thesis are derived from studies in the condensed phase, where the chemical environment can change molecular properties. As a result, it is difficult to gain an understanding of the intrinsic properties in solution as well as a molecular-level picture of chemical reactions that take place where many oxidation states, molecular species, and solvent interactions occur. By isolating one particular species in the gas phase, we are able to observe how each species interacts with light independent of perturbing effects of solvent and counter ions. In this thesis, we perform spectroscopic experiments on mass-selected ions in the gas phase, where we are able to gain information on intrinsic molecular properties without the influence of a condensed phase chemical environment. We employ photodissociation spectroscopy, where we mass-select a particular ionic species from solution and irradiate that molecular ion with the output of a tunable laser in the ultraviolet and visible regions. By monitoring the fragments produced, we can obtain an electronic absorption spectrum of the isolated species as well as gain insight into the photochemistry of the ions under study from the fragmentation pathways observed. We combine this method with solution absorption spectra as well as electronic structure calculations.

Kaufman, Sydney Hamilton

332

Preparation of nanosized LaCoO3 perovskite oxide using amorphous heteronuclear complex as a precursor at low temperature  

Microsoft Academic Search

Nanosized LaCoO3 cobaltite oxide powder with perovskite structure was successfully synthesized at a relatively low calcination temperature using an amorphous heteronuclear complex, LaCo(DTPA)ˇ6H2O, as a precursor. The precursor decomposed completely into cobaltite oxide above 400 °C according to the DTA and TGA results. XPS revealed that the decomposed species was composed of LaCoO3 cobaltite oxide after the precursor was calcined

Yongfa Zhu; Ruiqin Tan; Tao Yi; Shishan Ji; Xiaoyan Ye; Lili Cao

2000-01-01

333

Research on the electrochemistry of oxygen ion conductors in the former Soviet Union. II. Perovskite-related oxides  

Microsoft Academic Search

The review is devoted to the analysis of experimental results on electrochemical and physicochemical properties of the perovskite-related\\u000a oxide phases obtained at scientific centers of the former Soviet Union. The main attention is focused on oxides with high\\u000a electronic conductivity, which are potentially useful as electrodes for high-temperature electrochemical cells with oxygen-ion\\u000a conducting solid electrolytes and interconnectors of solid oxide

Vladislav V. Kharton; Aleksey A. Yaremchenko; Evgeny N. Naumovich

1999-01-01

334

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

DOEpatents

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

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

2010-07-20

335

Electrically conductive spinel and perovskite phases for solid oxide fuel cell interconnect applications  

NASA Astrophysics Data System (ADS)

As the operating temperature of solid oxide fuel cell (SOFC) reduces to below 800°C, metallic alloys can be used as the interconnect material. Mn1+xCr2-xO4 spinel was found to form on the surface of the interconnect alloy Crofer, as well as near the interface of LaMnO3-based cathode and Cr2O3-forming interconnect alloys such as Ebrite during long-term operation. However, the effect of the spinel formation on the performance of the fuel cell stack is yet unclear. The fundamental properties of the Mn1+xCr2-xO 4 spinel were studied in this dissertation. Spinel phase based on Mn 1+xCr2-xO4 (0 ? x ? 1) was synthesized and characterized. The lattice parameter of the spinel was found to increase with increasing Mn content up to x = 0.7. At x > 0.7, the cubic spinel changed to tetragonal because of Jahn-Teller distortion. The electrical conductivity of the spinel also increased with increasing Mn content. Electrical conduction in this phase was likely through a small polaron hopping mechanism. The spinel phase showed similar electrical conductivity in both oxidizing and reducing environments expected in solid oxide fuel cell operation. In addition, the chemical compatibility between the spinel phase Mn 1.5Cr1.5O4 and the SOFC cathode materials La 0.8Sr0.2MO3 (M = Mn, Co, Fe) was studied and its impact on SOFC stack performance was discussed. While no new phases were formed after annealing, interdiffusion of the cations in the perovskite and spinel phases was detected. After high temperature annealing, the bulk and interfacial resistivities changed due to interdiffusion of the cations in the two phases, which was revealed from AC impedance spectra. Finally, electrically conductive perovskite coating on Cr2O 3-forming alloy interconnect was proposed to slow down the Cr2 O3 scale growth on metallic alloy and to mitigate the evaporation problem. An economical dip coating process was used to synthesize LaCrO 3 coating on the ferritic alloy Ebrite substrate. XRD results indicated that the LaCrO3 perovskite phase was formed after annealing for both the LaCrO3 and La2O3 precursors. The LaCrO3 coatings were found to cause a pronounced reduction in oxidation rate of the alloy, especially with low La content precursors. The area specific resistance of the oxide scales formed on the bare and coated alloy substrates was also evaluated and discussed.

Lu, Zigui

336

Methodology for robust superhydrophobic fabrics and sponges from in situ growth of transition metal/metal oxide nanocrystals with thiol modification and their applications in oil/water separation.  

PubMed

Solid surfaces possessing both superhydrophobic and superoleophilic properties have attracted significant interest in fundamental investigations and potential applications in the fields of self-cleaning surfaces, oil/water separation, and microfluidic channels. In this paper, a general methodology for robust superhydrophobic fabrics and sponges was proposed via the in situ growth of both transition-metal oxides and metallic nanocrystals, including the simple neutralization reaction and oxidation-reduction reaction. The porous surfaces coated with Group VIII and IB nanocrystals (such as Fe, Co, Ni, Cu, and Ag) can not only present multiscale surface roughness, but also readily coordinate with thiols, leading to special wettability. In our previous work, it has been confirmed that the interaction between the nanocrystals and thiols plays a significant role in the introduction of hydrophobic ingredients. In this work, it has been demonstrated that the efficient control of the nucleation and growth of Group VIII and IB nanocrystals on the porous surfaces becomes the key factor in the formation of multiscale surface roughness, resulting in the achievement of controllable special wettability. In addition, these as-prepared superhydrophobic and superoleophilic fabrics and sponges were successfully used for application in oil/water separation. PMID:23388070

Wang, Ben; Li, Jing; Wang, Guiyuan; Liang, Weixin; Zhang, Yabin; Shi, Lei; Guo, Zhiguang; Liu, Weimin

2013-03-13

337

New cathode materials for solid oxide fuel cells: Ruthenium pyrochlores and perovskites  

SciTech Connect

The ruthenium pyrochlores, A{sub 2}Ru{sub 2}O{sub 7{minus}{delta}} (A = Pb, Bi), and ruthenium perovskites, ARuO{sub 3} (A = Ca, Sr) were characterized as new electrode materials for solid oxide fuel cells. The electrical conductivity, cathodic polarization, thermal expansion, and reactivity with yttria-stabilized zirconia were examined. The pyrochlores showed low cathodic overpotential even at 800 C, metallic behavior with high electrical conductivity, and no reaction with yttria-stabilized zirconia at 900 C. The thermal expansion coefficient of the bismuth pyrochlore was comparable to yttria-stabilized (8 mol % Y{sub 2}O{sub 3} content) zirconia. The pyrochlores are very attractive for application as cathode materials in a solid oxide fuel cell with low operating temperature.

Takeda, Takashi; Kanno, Ryoji; Kawamoto, Yoji; Takeda, Yasuo; Yamamoto, Osamu

2000-05-01

338

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

PubMed

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

Valavanidis, Athanasios; Vlahoyianni, Thomais; Fiotakis, Konstantinos

2005-10-01

339

Electronic State Calculation of Manganese Dioxide Electrode with Additive Transition Metals  

Microsoft Academic Search

The electronic states of manganese dioxide substituted with transition metals were theoretically calculated by DV-Xalpha method, cluster model was Mn15O56 and Mn14XO56 (X = transition metal). The energy band gap of manganese-X oxides is lower than that of manganese dioxide from theoretical calculation. Also it is identified that the electrical conductivity of manganese-tungsten oxide is better than that of manganese

Bong-Seo Kim; Su-Dong Park; Hee-Woong Lee; Dong-Yoon Lee; Won-Sub Chung

2006-01-01

340

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

NASA Astrophysics Data System (ADS)

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

Young, Joshua; Rondinelli, James M.

2014-05-01

341

Hetero-epitaxy of perovskite oxides on GaAs(001) by molecular beam epitaxy  

SciTech Connect

Hetero-epitaxy of single-crystal perovskite SrTiO{sub 3} on GaAs(001) was achieved using molecular beam epitaxy. The growth was accomplished by deposition of a submonolayer of titanium on GaAs(001), followed by the co-deposition of strontium and titanium initiated at a low-temperature, low-oxygen-pressure condition. X-ray photoelectron spectroscopy showed that the Ti prelayer reacted with As and formed TiAs-like species on the As terminated GaAs(001) surface. Reflection-high-energy-electron diffraction showed that SrTiO{sub 3} grew coherently on the GaAs(001) at early stage of growth. This coherent behavior began to degrade when SrTiO{sub 3} thickness exceeded 20 A ring . Cross-sectional transmission electron microscopy revealed an abrupt interface between SrTiO{sub 3} and GaAs and good crystallinity of the SrTiO{sub 3} film. An epitaxial relationship between SrTiO{sub 3} and GaAs was further confirmed by x-ray diffraction. The success of growth of SrTiO{sub 3} on GaAs paves the way for integration of various functional perovskite oxides with GaAs.

Liang, Y.; Kulik, J.; Eschrich, T.C.; Droopad, R.; Yu, Z.; Maniar, P. [Microelectronics and Physical Sciences Laboratory, Process and Materials Characterization Laboratory, and Microelectronics and Physical Sciences Laboratory, Motorola Inc., 2100 East Elliot Road, Tempe, Arizona 85284 (United States)

2004-08-16

342

Site and oxidation-state specificity yielding dimensional control in perovskite ruthenates.  

PubMed

Sr(3)CaRu(2)O(9), a new 2:1 B-site ordered perovskite ruthenate, was synthesized and its structure determined based on powder X-ray, neutron and electron diffraction data. It is composed of one layer of CaO(6) alternating with two layers of RuO(6) perpendicular to the [111] axis of the cubic perovskite structure. The ordering leads to a [-Ru-Ru-Ca-] repeat unit along each of the pseudocubic directions. Sr(3)CaRu(2)O(9) is the first example of this structure-type to include a majority metal with d electrons (Ru(V), d(3)). Three-dimensional Sr(3)CaRu(2)O(9) can be transformed to the layered Ruddlesden-Popper phase Sr(1.5)Ca(0.5)RuO(4) (i.e., Sr(3)CaRu(2)O(8)) by reduction at 1200 degrees C in flowing argon. The original structure can be restored by oxidation of Sr(1.5)Ca(0.5)RuO(4) at 1000 degrees C in flowing oxygen. This remarkable transformation highlights the structural versatility afforded by the combination of ruthenium and calcium. PMID:11878943

Rijssenbeek, Job T; Malo, Sylvie; Caignaert, Vincent; Poeppelmeier, Kenneth R

2002-03-13

343

Transition metals and mitochondrial metabolism in the heart  

PubMed Central

Transition metals are essential to many biological processes in almost all organisms from bacteria to humans. Their versatility, which arises from an ability to undergo reduction–oxidation chemistry, enables them to act as critical cofactors of enzymes throughout the cell. Accumulation of metals, however, can also lead to oxidative stress and cellular damage. The importance of metals to both enzymatic reactions and oxidative stress makes them key players in mitochondria. Mitochondria are the primary energy-generating organelles of the cell that produce ATP through a chain of enzymatic complexes that require transition metals, and are highly sensitive to oxidative damage. Moreover, the heart is one of the most mitochondrially-rich tissues in the body, making metals of particular importance to cardiac function. In this review, we focus on the current knowledge about the role of transition metals (specifically iron, copper, and manganese) in mitochondrial metabolism in the heart. This article is part of a Special Issue entitled ‘Focus on Cardiac Metabolism’.

Rines, Amy K.; Ardehali, Hossein

2013-01-01

344

The Activation of Hydrocarbon CH Bonds over Transition Metal Oxide Catalysts: A FTIR Study of Hydrocarbon Catalytic Combustion over MgCr 2O 4  

Microsoft Academic Search

The interaction of light hydrocarbons (methane, ethane, propane, propene, n-butane, isobutane, 1-butene, benzene, and toluene) with the oxidized surface of the spinel MgCr2O4 (an active hydrocarbon combustion catalyst) has been investigated by FTIR spectroscopy in the temperature range 300-773 K. This interaction results in the reduction of the catalyst and the production of oxygen-containing adsorbed species. These species have been

E. Finnocchio; G. Busca; V. Lorenzelli; R. J. Willey

1995-01-01

345

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

Microsoft Academic Search

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

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

2007-01-01

346

Syntheses of perovskite oxides nanoparticles La 1? x Sr x MO 3? ? (M = Co and Cu) as anode electrocatalyst for direct methanol fuel cell  

Microsoft Academic Search

Conventionally, noble metals such as Pt and Pt–Ru bimetallic system were utilized as electrocatalyst for methanol oxidation in acid and alkaline media. However, during the oxidation reaction, these noble metals are poisoned by the methanol oxidation intermediates, such as CO or COH species. Therefore, the utilization of electrochemically active conducting metal oxide (substituted perovskite oxide) may be a solution for

Ho-Chieh Yu; Kuan-Zong Fung; Tz-Chiang Guo; Wen-Li Chang

2004-01-01

347

Oxygen transport kinetics of the oxygen interstitial system lanthanum praseodymium nickel oxide and cation ordered double perovskite-Ln barium cobalt oxide (Ln = praseodymium and neodymium) oxides  

Microsoft Academic Search

The main purpose of this dissertation is the development of the new cathode materials for intermediate temperature solid oxide fuel cells (SOFC). The oxygen transport kinetics of the oxygen interstitial system La xPr2-xNiO4+delta and cation ordered double perovskite---LnBaCo2O5+delta (Ln = Pr and Nd) by electrical conductivity relaxation (ECR), DC conductivity, and AC impedance spectroscopy were studied. The measured values were

Guntae Kim

2005-01-01

348

Comparative study of the synthesis of layered transition metal molybdates  

Microsoft Academic Search

Mixed metal oxides (MMOs) prepared by the mild thermal decomposition of layered double hydroxides (LDHs) differ in their reactivity on exposure to aqueous molybdate containing solutions. In this study, we investigate the reactivity of some T–Al containing MMOs (T=Co, Ni, Cu or Zn) towards the formation of layered transition metal molybdates (LTMs) possessing the general formula AT2(OH)(MoO4)2ˇH2O, where A=NH4+, Na+

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

2010-01-01

349

Autothermal reforming of propane on Ni-supported perovskite, hydrotalcite, and metal oxide catalysts.  

PubMed

This study evaluated the autotherrmal reforming of propane over Ni-supported perovskite (LaAlO3), hydrotalcite as a layered structure (MgAl), and metal oxide (alpha-Al2O3, ZrO2) catalysts. The catalysts were also characterized via physicochemical property analysis, XRD, SEM, TEM, and TPR. The order of catalytic activity was ZrO2 > or = LaAlO3 > Al2O3 > MgAl, and coincided with the reducibility of these catalysts to reduce the Ni2+ metallic ion of the NiO, as measured via TPR. Finally the reducility of Ni in the form of NiO was important to the reaction in the ATR process. The diffraction peak of Ni was observed after a 600 degrees C reduction in ZrO2, LaAlO3, and alpha-Al2O3. PMID:21456265

Park, Namcook; Kim, WooRi; Moon, DongJu; Seo, Gon; Kim, YoungChul

2011-02-01

350

First-principles modeling of resistance switching in perovskite oxide material  

NASA Astrophysics Data System (ADS)

We report a first-principles study on SrRuO3/SrTiO3 interface in the presence of the oxygen vacancy. While the oxygen vacancy on the side of SrTiO3 significantly lowers the Schottky barrier height, the oxygen vacancy close to the interface or inside the metallic electrode results in a Schottky barrier comparable to that of the clean interface. Based on these results, we propose a model for resistance-switching phenomena in perovskite oxide/metal interfaces where electromigration of the oxygen vacancy plays a key role. Our model provides a consistent explanation of a recent experiment on resistance switching in SrRuO3/Nb:SrTiO3 interface.

Jeon, Sang Ho; Park, Bae Ho; Lee, Jaichan; Lee, Bora; Han, Seungwu

2006-07-01

351

Ab Initio Calculations on Spin Transitions in Perovskite  

NASA Astrophysics Data System (ADS)

Spin transitions in perovskite and magnesiowustite have become the subject of considerable interest since they have been experimentally observed to occur under mantle conditions. Experimental results, however, are not always mutually consitent and a variety of transition pressures have been observed. We have, therefore, performed GGA, LDA, and hybrid-functional calculations on MgSiO3 perovskite containing 6%, 12% and 100% ferric and/or ferrous iron. Although the GGA and LDA calculations suffer from the well-know problem of predicting transition metal oxide insulators to be metallic, the hybrid-functionals do not do this. By using both methods we hope to increase confidence in the results. In agreement with previous work on Al3+ and Fe3+ bearing perovskites (Li et al, 2004) we find a wide range of transition pressures, which are related to the mechanism of iron incorporation. Compositions with just Fe2+ generally have the highest transition pressures, while compositions with just Fe3+ have the lowest. Using these results we are able to explain the spin transitions observed by different experimental groups. The spin state of iron has a small effect on the density, bulk and shear modulus of perovskite, but at the low concentrations expected in the mantle this is unlikely to be seismically visible.

Brodholt, J. P.; Stackhouse, S.; Alfredsson, M.; Price, G. D.

2006-05-01

352

Transition metals: a double edge sward in ROS generation and signaling.  

PubMed

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

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

2013-03-01

353

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

SciTech Connect

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

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

2011-09-15

354

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

NASA Astrophysics Data System (ADS)

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

Wellons, Matthew S.

355

Band offsets in heterojunctions formed by oxides with cubic perovskite structure  

NASA Astrophysics Data System (ADS)

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

Lebedev, A. I.

2014-05-01

356

Reaction of group V and VI transition metal oxide and oxyhydroxide anions with O[sub 2], H[sub 2]O, and HCl  

SciTech Connect

Negatively charged oxides and oxyhydroxides of tantalum, niobium, vanadium, and tungsten were produced, and their properties and reactivity with O[sub 2], HCl, and H[sub 2]O were investigated in a fast-flow reactor. Importantly, the oxyhydroxide anions of niobium and tantalum are found to undergo acid-base type reactions with HCl which bear analogy to those known to occur in the condensed phase; e.g., the Cl of HCl replaces an OH unit on the metal center and H[sub 2]O is given off as the neutral product. By contrast, in cases where there are no OH units bonded to the metal atom, HCl reacts to transform a bound oxygen atom into an OH unit, with the Cl unit becoming bonded to the metal center. Quantitative rate coefficients, ranging from about 10[sup [minus]9] to 10[sup [minus]11] cm[sup 3] s[sup [minus]1], were measured for each of four sequential additions of HCl to the individual niobium and tantalum systems. Interestingly, only the trioxide and pentoxide of niobium and tantalum undergo observable reactions with H[sub 2]O (to form the dioxydihydroxide ion), while reaction with O[sub 2] (k [approx] 10[sup [minus]11]-10[sup [minus]13] cm[sup 3] s[sup [minus]1]), in general, occurs 2-3 orders of magnitude more slowly than the observable H[sub 2]O reactions. A reversible reaction is found between the pentoxide anion reacting with H[sub 2]O and the (product) dioxydihydroxide reacting with O[sub 2], yielding equilibrium constant values of K = 370 and 48 for niobium and tantalum, respectively. Comparing the reaction rates demonstrates the influence of the electronic shell of the metal atom on reactivity, where the relative ease of the period six metals to accommodate additional ligands beyond those of the initial reactant contrasts with the decreased facility for period five metals. 31 refs., 3 figs., 3 tabs.

Sigsworth, S.W.; Castleman, A.W. Jr. (Pennsylvania State Univ., University Park (United States))

1992-12-16

357

Multiferroic materials based on organic transition-metal molecular nanowires.  

PubMed

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

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

2012-09-01

358

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

359

Slicing the perovskite structure into layers. Synthesis of novel three-dimensional and layered perovskite oxides, ALaSrNb[sub 2]M[sup II]O[sub 9] (A = Na, Cs)  

SciTech Connect

As a part of our continuing efforts to synthesize novel layered oxides exhibiting interlayer chemistry, we investigated the formation of perovskite-related phases for the compositions ALaSrNb[sub 2]M[sup II]O[sub 9] (A = alkali metal and M = Co, Ni, Cu, or Zn). To our surprise, the compositions adopted a cubic (3-D) perovskite structure when A = Na and a layered (2-D) perovskite structure, related to CsCa[sub 2]Nb[sub 3]O[sub 10], when A = Cs. This result, which is reported in this communication, reveals the interesting possibility of tailoring perovskite (ABO[sub 3]) oxides into 2-D or 3-D structures by the appropriate choice of A-site cations. Furthermore, the strategy can be extended to synthesize layered perovskite oxides of variable thickness by choosing appropriate chemical compositions. We believe that the present discovery assumes greater significance in light of the current interest in artificially tailoring oxide materials into thin layers of nanometer scale. 18 refs., 3 figs., 1 tab.

Gopalakrishnan, J.; Uma, S.; Vasanthacharya, N.Y.; Subbanna, G.N. (Indian Inst. of Science, Bangalore (India))

1995-03-01

360

Solid Electrolyte NOx Gas Sensor Using Perovskite-Type Oxide Electrodes  

NASA Astrophysics Data System (ADS)

Electrochemical devices based on coupling an oxygen ionic conductor (Y2O3-stabilized ZrO2 : YSZ) with a perovskite-type oxide (LaFeO3) were found to exhibit promising performance for the sensing of NO2 at 400 and 450°C. EMF values of the (Pt)LaFeO3/YSZ/Pt sensor increased in NO2 atmosphere with a quick response time. The increase in EMF value has been attributed to an increase in LaFeO3 conductivity in the presence of oxidizing gas. The polarization curves showed a nonlinear behavior in NO2 gas. The nonlinear behaviour could be explained to be due to the potential drop at the electrode interfaces. The electrochemical impedance spectroscopy (EIS) analysis of the devices showed that the resistance and reactance at the electrolyte/electrode interfaces decreased with introduction of NO2 gas. This would induce the lowering of electrode overvoltage and a current increase through the solid electrolyte.

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

2000-12-01

361

Oxygen doping in SrFe 1 ? x Co xO 3 perovskite oxides by the electrochemical method  

Microsoft Academic Search

SrFe1 ? xCoxO3 ? z (0 ? x ? 1, z?0.1) of the cubic perovskite type was prepared by treating mixtures of grossly oxygen-deficient samples obtained at room temperature, using an electrochemical oxidation technique. The ferromagnetic Curie temperature has been found to be raised above 300 K for 0.4 $?-x ? 1.0 (340 K at x = 0.4) by the

Chikara Okazoe; Yasuo Takeda; Nobuyuki Imanishi; Osamu Yamamoto; Mikio Takano; Ryoji Kanno

1996-01-01

362

Chemical Pressure Effects On Tc In Double Perovskite Oxides A2FeMoO6 (A = Ba, Sr)  

Microsoft Academic Search

The effect of chemical pressure on the ferromagnetic transition temperature has been investigated in the double perovskite oxides Sr2FeMoO6 and Ba2FeMoO6 using first principle electronic structure calculations. While the Curie temperature is found to be larger by 50-100 K for Sr2FeMoO6 over that for Ba2FeMoO6 in experiments, the difference we find in our calculations is smaller.

Ashis K. Nandy; Priya Mahadevan; D. D. Sarma

2008-01-01

363

Chemical Pressure Effects On Tc In Double Perovskite Oxides A2FeMoO6 (A = Ba, Sr)  

NASA Astrophysics Data System (ADS)

The effect of chemical pressure on the ferromagnetic transition temperature has been investigated in the double perovskite oxides Sr2FeMoO6 and Ba2FeMoO6 using first principle electronic structure calculations. While the Curie temperature is found to be larger by 50-100 K for Sr2FeMoO6 over that for Ba2FeMoO6 in experiments, the difference we find in our calculations is smaller.

Nandy, Ashis K.; Mahadevan, Priya; Sarma, D. D.

2008-04-01

364

Investigation of spontaneous nanometer-scale pattern formation in lithium-containing A-site deficient perovskite oxides  

Microsoft Academic Search

This dissertation describes the synthesis and structural characterization of a group of perovskite oxides which form spontaneous patterns on the nanometer length scale. The subject of the first area of study is the solid solution (Nd2\\/3-xLi3x)TiO3 which is found to spontaneously and periodically phase-separate, to form nanometer-scale superlattices in two-dimensions. The phases comprising both of the two end members are

Beth Sara Guiton

2008-01-01

365

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

NASA Astrophysics Data System (ADS)

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

Fitting Kourkoutis, L.

2010-03-01

366

Activation of methane by transition metal-substituted aluminophosphate molecular sieves  

DOEpatents

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

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

1991-01-01

367

Bimacrocyclic NHC transition metal complexes  

Microsoft Academic Search

The preparation of seven concave NHC metal complexes derived from bimacrocyclic imidazolinium salt 1 is reported. The silver complex 2, obtained in 86% yield by reacting 1 with silver(I) oxide, was used to give copper complex 3, rhodium complex 5 and iridium complex 6 by transmetalation in good yields. Palladium complex 4 was obtained by reaction of the azolium salt

Ole Winkelmann; Christian Näther; Ulrich Lüning

2008-01-01

368

Method of boronizing transition-metal surfaces  

SciTech Connect

A method is presented for preparing a boride layer on a transition metal substrate for use in corrosive environments or as a harden surface in machine applications. This method is particularly useful in treating current collectors for use within a high temperature and corrosive electrochemical cell environment. A melt of a alkali metal boride tetrafluoride salt including such as KF to lower its melting point is prepared including a dissolved boron containing material, for instance NiB, MnB/sub 2/, or CrB/sub 2/. A transition metal to be coated is immersed in the melt at a temperature of no more than 700/sup 0/C and a surface boride layer of that transition metal is formed within a period of about 24 hours on the substrate surface.

Koyama, K.; Shimotake, H.

1981-08-28

369

Method of boronizing transition metal surfaces  

DOEpatents

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

Koyama, Koichiro; Shimotake, Hiroshi.

1983-08-16

370

Method of boronizing transition metal surfaces  

SciTech Connect

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

Koyama, Koichiro (Hyogo, JP); Shimotake, Hiroshi (Hinsdale, IL)

1983-01-01

371

Alloy perovskite oxide thin film as resistance switching non-volatile memory  

NASA Astrophysics Data System (ADS)

Nonvolatile memory that permanently stores data is indispensable for computers and hand-held devices. In the last few years, resistance memory (RRAM) has emerged as an intriguing possibility that might replace flash memory one day, which is widely used in hand-held and portable-storage devices. The newest, rapidly growing interest in resistance switching is focused on semiconducting oxides and other related materials. In this dissertation, a novel material system for oxide RRAM that offers unique advantages over all the other existing oxide RRAM materials was designed and systematically investigated. The primary aim of these studies is to obtain a material system with the intrinsic property that allows electrically-induced metal-insulator transition, which is regulated by electron trapping and release at some interval sites. A series of alloy perovskite oxides thin film systems were designed by combining a wide band gap insulator (CaZrO3 or LaAlO3) and a conductor with a narrow bandwidth (SrRuO3 or LaNiO3 ), with the conductor concentration near the percolation threshold. These alloy perovskite oxides thin films are almost atomically flat without any defects, such as cracks or crosshatches, which is achieved using well controlled deposition conditions that favor domain-boundary relaxation of the large misfit strain. The bottom electrode is a single crystalline SrRuO 3 thin film, deposited on a single crystal substrate of SrTiO3 which exhibits high conductivity and ferromagnetic transition at ˜150K. The alloy thin films manifest an anisotropic percolation phenomenon: below a critical thickness a metallic conducting path always exists across the film thickness direction but not along the in-plane direction, which ensures electrical isolation between neighboring memory cells. These initially conducting films present excellent resistance switching properties: low switching voltages (1-3 V), high switching ratio (˜100), fast switching speed (50 ns), good switching reliability and long retention time. A variety of experiments have been conducted to explore the resistance switching mechanism. These include variation of film orientation, film strain and top electrode material, as well as UV irradiation and temperature dependent transport measurements. All the experimental results consistently suggest that the resistance switching is of an electronic nature. During the low resistance (LR) to high resistance (HR) switching, electrons are injected into the alloy film through the electrode with a lower work function, and the electrons are released through the same electrode during the HR to LR switching. Accompanying the electron trapping/release, disorder is introduced to or removed from the initially conducting paths due to electrostatic interaction. As the disorder raises or lowers the mobility edge above or below the Fermi level, the insulator-metal transition is electrically triggered enabling a robust non-volatile memory.

Wang, Yudi

372

Gas sensing with semiconducting perovskite oxide LaFeO 3  

NASA Astrophysics Data System (ADS)

This paper reports results of gas-sensing studies with antiferromagnetic perovskite oxide LaFeO 3 thick films, for a possible use of the films in semiconductor gas sensors for monitoring pollutant, toxic and flammable gases in atmospheric air. Conductance responses of the nanocrystalline LaFeO 3 thick films with both Au and Pt electrodes were measured at exposure of the films to CO, CH 4 and NO 2 at different concentrations in air and also at different temperatures. Different temperatures can be used to make the films sensitive to different gases. This gives a possibility to use an array of films for a selective detection in the case of a gas mixture. The sensitivity of the films was found to be high and it was possible to detect, e.g., CO and CH 4 concentrations down to a few tens of ppm, and NO and NO 2 concentrations already in the sub-ppm region. An array of two sensing films, operating at 270°C and 420°C, respectively, was used to monitor different mixtures of CO and CH 4. The results point to a possibility to use semiconductor gas sensors based on LaFeO 3 thick films for monitoring, e.g., flammable gases in coal mines.

Toan, N. N.; Saukko, S.; Lantto, V.

2003-04-01

373

Investigation of hyperfine interactions in GdCrO3 perovskite oxide using PAC spectroscopy  

NASA Astrophysics Data System (ADS)

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

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

2010-04-01

374

Magnetic, transport, and magnetocaloric properties of double perovskite oxide LaCaMnCoO6  

NASA Astrophysics Data System (ADS)

Magnetic, magnetoresistive, and magnetocaloric properties of a novel double perovskite oxide, namely, LaCaMnCoO6 have been studied. Polycrystalline sample of LaCaMnCoO6 has been synthesized by sol-gel technique. It has cubic crystal structure (space group Fm3m) at room temperature. The temperature variation in magnetization reveals a steep increase in magnetization around 168 K (TC). The magnetization does not even saturate at 5 K and a magnetic moment of 0.7?B/f.u. is obtained at 5 K in an applied field of 50 kOe. The electrical resistivity measurement indicates that the material is semiconducting-like in the temperature range of ~300-50 K and below ~50 K the sample becomes insulating. A maximum magnetoresistance (MR) of about 8% is found at 200 K in an applied field of 7 T and MR has a negative sign. The magnetocaloric effect is calculated from the magnetization versus temperature data and a maximum magnetic entropy change of 3.1 J/kg K for a field change of 11 kOe is obtained near TC. Thus a moderate magnetocaloric effect is achieved in rather low magnetic fields.

Mahato, Rabindra Nath; Bharathi, K. Kamala; Sethupathi, K.; Sankaranarayanan, V.; Nirmala, R.; Nigam, A. K.; Lamsal, Jagat

2009-04-01

375

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

NASA Astrophysics Data System (ADS)

High-detectivity metal-semiconductor-metal ultraviolet photodetectors have been fabricated based on SrTiO3 with different types of metal electrodes (Ag, Ni, and Pt), and the effects of the different types of the electrodes on the photoelectric properties were investigated. Comparing with three types of the metal electrodes, the largest responsivity of 0.517 A/W and the smallest dark current of 2.215 × 10-11 A were obtained by using Ag electrode due to the largest Schottky barrier between Ag electrode and SrTiO3. The detectivities of all the photodetectors are achieved about 1012 cmˇHZ1/2/W, which can be comparable to Si-based photodetectors. Furthermore, a transient photovoltaic signal with a rise time of ˜360 ps and a full width at half-maximum of ˜576 ps are obtained in the Ag/SrTiO3/Ag photodetectors under the illumination of a 355 nm laser with 15 ps duration. These results provide a useful guide for designing high-performance photodetectors based on perovskite oxides and the appropriate metal electrode selected.

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

2013-12-01

376

Determination of the surface spin-polarization of perovskite oxides using point-contact Andreev reflection spectroscopy  

NASA Astrophysics Data System (ADS)

Materials with surface spin-polarization are invaluable for incorporation into devices that utilize spin-polarized currents. Point-contact Andreev reflection spectroscopy is currently one of the few techniques capable of direct measurement of surface spin-polarization. Niobium wire was electrochemically etched in a potassium hydroxide solution to form sharp tips which were used to form point-contacts with perovskite oxides in single crystal and thin film forms. Surface spin-polarization values were determined at 4.2 K for several materials including La0.7Sr0.3MnO3, which is a material with purported 100% spin polarization. The results show that surface spin polarization of perovskites is smaller than theoretically predicted.

Grimley, Everett; Biswas, Amlan

2013-03-01

377

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

SciTech Connect

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

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

1997-09-01

378

Transparent and conductive oxide films with the perovskite structure: La- and Sb-doped BaSnO3  

NASA Astrophysics Data System (ADS)

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 and mobility at room temperature of about 2×1021 cm-3 and 0.69 cm2/V s, respectively, and a direct allowed band gap of 4.02 eV. The effect of deposition temperature on structural, optical, and electric properties of the Sb-doped Ba(Sn0.93Sb0.07)O3 films was also demonstrated.

Wang, H. F.; Liu, Q. Z.; Chen, F.; Gao, G. Y.; Wu, Wenbin; Chen, X. H.

2007-05-01

379

Single-crystalline transparent and conductive oxide films with the perovskite structure: Sb-doped SrSnO3  

NASA Astrophysics Data System (ADS)

Perovskite-type transparent and conductive oxide films, Sb-doped SrSnO3 (SSSO), were grown on SrTiO3(001) substrates by the pulsed laser deposition method. It is revealed that the films can be grown at relatively lower temperatures and show high single crystallinity with a cubic perovskite structure with lattice constant of 4.036 A?. These films show good optical transmittance in the visible range, with the direct allowed band gap of 4.53 eV, and behave as an n-type semiconductor with resistivity of 23 m? cm at room temperature. The effect of growth temperature on structural, electrical, and optical properties of the SSSO films was probed, and a diode based on n-SSSO/p-La0.67Ca0.33MnO3 structure was also demonstrated.

Liu, Q. Z.; Wang, H. F.; Chen, F.; Wu, Wenbin

2008-05-01

380

Epitaxial heterojunctions of oxide semiconductors and metals on high temperature superconductors  

NASA Astrophysics Data System (ADS)

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

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

1994-04-01

381

Epitaxial heterojunctions of oxide semiconductors and metals on high temperature superconductors  

NASA Astrophysics Data System (ADS)

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

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

1992-03-01

382

Epitaxial heterojunctions of oxide semiconductors and metals on high temperature superconductors  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

383

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

NASA Astrophysics Data System (ADS)

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

Mohammadi, Alidad

384

CH functionalization of heteroaromatic compounds by transition metal catalysis  

NASA Astrophysics Data System (ADS)

Transition metal-catalyzed CH functioanlization of thiazoles and thiophenes are carried out. The reaction of thiophene with aryl halide in the presence of a palladium catalyst underwent the CC bond forming reaction at the CH bond of thiophene. By employing the reaction head-to-tail-type oligothiophene is synthesized in a stepwise manner. When several azoles are treated with secondary amines and amides in the presence of a copper catalyst, oxidative CH-NH coupling took place to form the carbon-nitrogen bond.

Tanba, Shunsuke; Fujiwara, Taiki; Monguchi, Daiki; Mori, Atsunori

2010-06-01

385

Deuteron stopping cross sections in transition metal hydrides  

NASA Astrophysics Data System (ADS)

The stopping cross sections of deuterons incident on deutende and tritide films of eight transition metals (Sc, Ti, Y, Zr, Gd, Er, Hf and Ta) have been determined at deuteron energies between 40 and 200 keV. The stopping cross sections were extracted from measurements of the yields of the D(d, p)T and T(d, ?)n reactions as functions of the incident deuteron energy for thick deutende and tritide films of each metal. Corrections due to elastic scattering effects and surface oxides are incorporated in the analysis. Deviations from Bragg's rule are found in these materials and these deviations are discussed.

Malbrough, D. J.; Brice, D. K.; Cowgill, D. F.; Borders, J. A.; Shope, L. A.; Harris, J. M.

1987-11-01

386

High Pressure Synthesis of Transition Metal Carbonyls.  

ERIC Educational Resources Information Center

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

Hagen, A. P.; And Others

1979-01-01

387

Method of Boronizing Transition-Metal Surfaces.  

National Technical Information Service (NTIS)

A method is presented for preparing a boride layer on a transition metal substrate for use in corrosive environments or as a harden surface in machine applications. This method is particularly useful in treating current collectors for use within a high te...

K. Koyama H. Shimotake

1981-01-01

388

New Lasers Based on Transition Metal Complexes.  

National Technical Information Service (NTIS)

The purpose of this program has been to investigate the possibility that luminescent transition metal complexes (TM complexes) might serve as the basis for a new class of lasers tunable in the visible spectral region. At the beginning of the program, suff...

L. Andrews E. Johnson A. Lempicki

1979-01-01

389

Transition metal and nitrogen doped carbon nanostructures  

Microsoft Academic Search

We review our theoretical first-principle studies of carbon nanostructures based on graphene sheets, carbon nanotubes, nanocones and fullerenes that are substitutionally doped with transition metal and nitrogen atoms. The results obtained show that metal doping leads to more stable systems in buckled rather than planar structures. The hybrid structures have low-lying excited states, allowing for catalytic activity, in analogy to

Stanislav R. Stoyanov; Alexey V. Titov; Petr Král

2009-01-01

390

Control of Copper and Iron Oxidation States in Some Triple- and Double-Perovskite Oxides.  

National Technical Information Service (NTIS)

This thesis consists of eight publications and a summary of the obtained experimental results, reviewed together with the most essential literature related to the topic. The work deals with ways of tuning and analyzing the translation metal oxidation meta...

K. Lehmus

2003-01-01

391

Photoinduced structural conversions of transition metal chalcogenide materials.  

PubMed

The conversions of NiAs-type structures of transition metal chalcogenides (FeS and CoSe) to pyrite-type structures of dichalcogenides (FeS(2) and CoSe(2), respectively) under irradiation by HeNe laser (wavelength, 632.8 nm; intensity, 6 x 10(4) W/cm(2)) have been investigated using Raman spectroscopy. The laser-induced conversions give rise to Raman peaks corresponding to vibrations of S-S or Se-Se bonds of respective pyrite structures. The results are of interest for the characterization and fabrication of pyrite-like structures necessary for applications as oxygen reduction reaction catalysts. Material modifications at the micrometer and submicrometer levels are attainable. The structural conversions are accompanied by self-polymerization of excess chalcogen. Extended laser irradiation (>500 s) in air induces the substitution of chalcogen (S or Se) by oxygen in the chalcogenide materials and the subsequent formation of transition metal (Fe or Co) oxides. Excess chalcogen appears to prevent further oxidation. The article also presents conditions necessary to avoid laser-induced structural changes and oxidation of metal chalcogenide materials during Raman measurements. PMID:20218701

Teo, M Y C; Kulinich, S A; Plaksin, O A; Zhu, A L

2010-04-01

392

Perovskite-type halo-oxide La{sub 1-x}SrâFeO{sub 3-δ}X{sub Ď} (X=F, Cl) catalysts selective for the oxidation of ethane to ethene  

Microsoft Academic Search

The catalytic performance and characterization of perovskite-type halo-oxide La{sub 1-x}SrâFeO{sub 3-δ}X{sub Ď} (X = F, Cl) as well as La{sub 1-x}SrâFeO{sub 3-δ} (x = 0--0.8) for the oxidative dehydrogenation of ethane (ODE) to ethene have been investigated. XRD results indicate that the catalysts had oxygen-deficient perovskite structures and TGA results demonstrated that the F- and Cl-doped perovskites were thermally stable.

H. X. Dai; C. F. Ng; C. T. Au

2000-01-01

393

Perovskite-Type Halo-oxide La 1? x Sr x FeO 3?? X ? ( X=F, Cl) Catalysts Selective for the Oxidation of Ethane to Ethene  

Microsoft Academic Search

The catalytic performance and characterization of perovskite-type halo-oxide La1?xSrxFeO3??X? (X=F, Cl) as well as La1?x SrxFeO3?? (x=0–0.8) for the oxidative dehydrogenation of ethane (ODE) to ethene have been investigated. XRD results indicate that the catalysts had oxygen-deficient perovskite structures and TGA results demonstrated that the F- and Cl-doped perovskites were thermally stable. Under the reaction conditions of C2H6\\/O2\\/N2=2\\/1\\/3.7, temperature=660°C, and

H. X. Dai; C. F. Ng; C. T. Au

2000-01-01

394

Temperature-Induced Intersite Charge Transfer Involving Cr ions in A-Site-Ordered Perovskites ACu3 Cr4 O12 (A=La and Y).  

PubMed

Changes in the valence state of transition-metal ions in oxides drastically modify the chemical and physical properties of the compounds. Intersite charge transfer (ISCT), which involves simultaneous changes in the valence states of two valence-variable transition-metal cations at different crystallographic sites, further expands opportunities to show multifunctional properties. To explore new ISCT materials, we focus on A-site-ordered perovskite-structure oxides with the chemical formula AA'3 B4 O12 , which contain different transition-metal cations at the square-planar A' and octahedral B sites. We have obtained new A-site-ordered perovskites LaCu3 Cr4 O12 and YCu3 Cr4 O12 by synthesis under high-pressure and high-temperature conditions and found that they showed temperature-induced ISCT between A'-site Cu and B-site Cr ions. The compounds are the first examples of those, in which Cr ions are involved in temperature-induced ISCT. In contrast to the previously reported ISCT compounds, LaCu3 Cr4 O12 and YCu3 Cr4 O12 showed positive-thermal-expansion-like volume changes at the ISCT transition. PMID:24975031

Zhang, Shoubao; Saito, Takashi; Mizumaki, Masaichiro; Shimakawa, Yuichi

2014-07-28

395

Structural analysis and characterization of layer perovskite oxynitrides made from Dion-Jacobson oxide precursors  

SciTech Connect

A three-layer oxynitride Ruddlesden-Popper phase Rb{sub 1+x}Ca{sub 2}Nb{sub 3}O{sub 10-x}N{sub x}.yH{sub 2}O (x=0.7-0.8, y=0.4-0.6) was synthesized by ammonialysis at 800{sup o}C from the Dion-Jacobson phase RbCa{sub 2}Nb{sub 3}O{sub 10} in the presence of Rb{sub 2}CO{sub 3}. Incorporation of nitrogen into the layer perovskite structure was confirmed by XPS, combustion analysis, and MAS NMR. The water content was determined by thermal gravimetric analysis and the rubidium content by ICP-MS. A similar layered perovskite interconversion occurred in the two-layer Dion-Jacobson oxide RbLaNb{sub 2}O{sub 7} to yield Rb{sub 1+x}LaNb{sub 2}O{sub 7-x}N{sub x}.yH{sub 2}O (x=0.7-0.8, y=0.5-1.0). Both compounds were air- and moisture-sensitive, with rapid loss of nitrogen by oxidation and hydrolysis reactions. The structure of the three-layer oxynitride Rb{sub 1.7}Ca{sub 2}Nb{sub 3}O{sub 9.3}N{sub 0.7}.0.5H{sub 2}O was solved in space group P4/mmm with a=3.887(3) and c=18.65(1)A, by Rietveld refinement of X-ray powder diffraction data. The two-layer oxynitride structure Rb{sub 1.8}LaNb{sub 2}O{sub 6.3}N{sub 0.7}.1.0H{sub 2}O was also determined in space group P4/mmm with a=3.934(2) and c=14.697(2)A. GSAS refinement of synchrotron X-ray powder diffraction data showed that the water molecules were intercalated between a double layer of Rb+ ions in both the two- and three-layer Ruddlesden-Popper structures. Optical band gaps were measured by diffuse reflectance UV-vis for both materials. An indirect band gap of 2.51eV and a direct band gap of 2.99eV were found for the three-layer compound, while an indirect band gap of 2.29eV and a direct band gap of 2.84eV were measured for the two-layer compound. Photocatalytic activity tests of the three-layer compound under 380nm pass filtered light with AgNO{sub 3} as a sacrificial electron acceptor gave a quantum yield of 0.025% for oxygen evolution.

Schottenfeld, Joshua A. [Department of Chemistry, Pennsylvania State University, University Park, PA 16802 (United States); Benesi, Alan J. [Department of Chemistry, Pennsylvania State University, University Park, PA 16802 (United States); Stephens, Peter W. [Department of Physics and Astronomy, State University of New York, Stony Brook, New York 11794 (United States); Chen, Gugang [Departments of Physics, Pennsylvania State University, University Park, PA 16802 (United States); Eklund, Peter C. [Departments of Physics, Pennsylvania State University, University Park, PA 16802 (United States); Mallouk, Thomas E. [Department of Chemistry, Pennsylvania State University, University Park, PA 16802 (United States)]. E-mail: tom@chem.psu.edu

2005-07-15

396

(Electronic structure and reactivities of transition metal clusters)  

SciTech Connect

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

Not Available

1992-01-01

397

[Electronic structure and reactivities of transition metal clusters  

SciTech Connect

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

Not Available

1992-08-01

398

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

Microsoft Academic Search

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

Anthony Petric; Peng Huang; Frank Tietz

2000-01-01

399

Phonon self energy in transition metals  

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

400

Phonon-phonon interactions in transition metals  

NASA Astrophysics Data System (ADS)

In this paper the phonon self-energy produced by anharmonicity is calculated using second-order many-body perturbation theory for all bcc, fcc, and hcp transition metals. The symmetry properties of the phonon interactions are used to obtain an expression for the self-energy as a sum over irreducible triplets, very similar to integration in the irreducible part of the Brillouin zone for one-particle properties. The results obtained for transition metals shows that the lifetime is on the order of 10-10 s. Moreover, the Peierls approximation for the imaginary part of the self-energy is shown to be reasonable for bcc and fcc metals. For hcp metals we show that the Raman-active mode decays into a pair of acoustic phonons, their wave vector being located on a surface defined by conservation laws.

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

2011-09-01

401

Transition metal catalyzed synthesis of aryl sulfides.  

PubMed

The presence of aryl sulfides in biologically active compounds has resulted in the development of new methods to form carbon-sulfur bonds. The synthesis of aryl sulfides via metal catalysis has significantly increased in recent years. Historically, thiolates and sulfides have been thought to plague catalyst activity in the presence of transition metals. Indeed, strong coordination of thiolates and thioethers to transition metals can often hinder catalytic activity; however, various catalysts are able to withstand catalyst deactivation and form aryl carbon-sulfur bonds in high-yielding transformations. This review discusses the metal-catalyzed arylation of thiols and the use of disulfides as metal-thiolate precursors for the formation of C-S bonds. PMID:21242940

Eichman, Chad C; Stambuli, James P

2011-01-01

402

Single-layer transition metal sulfide catalysts  

DOEpatents

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

Thoma, Steven G. (Albuquerque, NM)

2011-05-31

403

Chemical interaction of fluoropolymers with transition metals  

Microsoft Academic Search

Chemical interaction of transition metals (Mo, W, Ta, Nb, and Ti) with a tetrafluoroethylene-vinylidene fluoride (TFE-VDF)\\u000a copolymer (21 mol % TFE + 79 mol % VDF) has been studied by differential scanning calorimetry (DSC) and mass spectrometry.\\u000a The DSC curves of mixtures of the fluoropolymer with Ta, Nb, and Ti showed exothermic peaks, and those of composites with\\u000a W and

A. V. Tarasov; A. S. Alikhanian; I. V. Arkhangel’skii

2009-01-01

404

Transition metal-silicate analogs of zeolites  

Microsoft Academic Search

The synthesis and characterization of three transition metal (Fe3+, Ti4+ and V4+)-silicate molecular sieves are discussed. The key factors for a successful incorporation of these metal ions in the growing silicate network during gel preparation\\/hydrothermal synthesis (e.g. avoidance of insoluble\\/sparingly soluble metal hydroxides\\/oxyhydroxides (Fe3+ and Ti4+) and alkali metal ions (Ti4+and V4+\\/5+)) as well as the effects of post synthesis

Paul Ratnasamy; Rajiv Kumar

1993-01-01

405

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

NASA Astrophysics Data System (ADS)

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

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

2010-03-01

406

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

NASA Astrophysics Data System (ADS)

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

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

1992-04-01

407

Investigation of spontaneous nanometer-scale pattern formation in lithium-containing A-site deficient perovskite oxides  

NASA Astrophysics Data System (ADS)

This dissertation describes the synthesis and structural characterization of a group of perovskite oxides which form spontaneous patterns on the nanometer length scale. The subject of the first area of study is the solid solution (Nd2/3-xLi3x)TiO3 which is found to spontaneously and periodically phase-separate, to form nanometer-scale superlattices in two-dimensions. The phases comprising both of the two end members are found to extend to the nanoscale, and as such this compound represents what is to our knowledge the first example of truly periodic phase separation in any inorganic solid. The compositions of the two phases are estimated to be (Nd 1/2Li1/2)TiO3 and Nd2/3TiO3; the ratio of these two end members and the periodicity of the superlattice is correspondingly tuned by choice of overall composition. The second area of study involves the synthesis of a range of new Li-containing perovskite oxides related to (Nd2/3-xLi3x)TiO 3 by substitution of Ti4+ on the B-site. These chemical substitutions lead to a change in the kinetics of formation---allowing the mechanism for phase separation to be probed---and to compounds which display a wide variety of different nanometer-scale patterns.

Guiton, Beth Sara

408

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

NASA Astrophysics Data System (ADS)

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

Kavich, Jerald J., Jr.

409

Transition metal bimetallic oxycarbides: Synthesis, characterization, and activity studies  

SciTech Connect

A new family of bimetallic oxycarbide compounds M{sup I}-M{sup II}-O-C (M{sup I} = Mo, W; M{sup II} = V, Nb, Cr, Fe, Co, Ni) has been synthesized by carburizing bimetallic oxide precursors using a temperature-programmed method. The oxide precursors are prepared by conventional solid-state reaction between two appropriate monometallic oxides. The synthesis involves passing a 20 mol% CH{sub 4} in H{sub 2} mixture over the oxide precursors while raising the temperature at a linear rate of 8.3 {times} 10{sup {minus}2} K/s (5 K/min) to a final temperature (T{sub max}) which is held for a period of time (t{sub hold}). The synthesis, chemisorption properties, and reactivation of the materials indicate that the compounds can be divided into two groups of different reducibility (high and low). Their surface activity and surface area are evaluated based on CO chemisorption and N{sub 2} physisorption measurements. It is found that the CO number density correlates with the reducibility of the compounds. The catalysts were evaluated for hydroprocessing in a three-phase trickle-bed reactor operated at 3.1 MPa and 643 K. The feed was a model liquid mixture containing 3000 ppm sulfur (dibenzothiophene), 2000 ppm nitrogen (quinoline), 500 ppm oxygen (benzofuran), 20 wt% aromatics (tetralin), and balance aliphatics (tetradecane). The bimetallic oxycarbides had moderate activity for HDN of quinoline, with Nb-Mo-O-C showing higher HDN than a commercial sulfided Ni-Mo/Al{sub 2}O{sub 3} catalyst tested at the same conditions. X-ray diffraction of the spent catalysts indicated that the oxycarbides of the early transition metals were tolerant of sulfur, while those involving the late transition metals showed bulk sulfide phases.

Oyama, S.T.; Yu, C.C.; Ramanathan, S. [Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (United States). Environmental Catalysis and Materials Lab.] [Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (United States). Environmental Catalysis and Materials Lab.

1999-06-10

410

Ethanol adsorption on transition-metal surfaces: A DFT investigation  

NASA Astrophysics Data System (ADS)

The development of low-cost and long-term stability catalyst compounds for the production of hydrogen from ethanol is one of the main problems to be solved for large scale use of direct- ethanol fuel cells. Steam reforming, which is one of the main routes to obtain hydrogen from ethanol, as well as ethanol oxidation, are critically dependent on the choice of the catalyst devices. Therefore, an atom-level understanding of the interaction of ethanol with catalysts systems is on the first problems to be addressed. In this talk, we will report first- principles calculations based on density functional theory for the adsorption of ethanol on close-packed transition-metal surfaces at the limit of low-coverage. In particular, we will report the following properties, namely, adsorption energy, work function changes, and structural parameters for a large number of substrates, which will be used to build up a simple picture to describe the interaction of ethanol with transition-metal surfaces. This work is supported by FAPESP.

da Silva, Juarez L. F.

2010-03-01

411

XRD and FTIR studies the effect of heat treatment and doping the transition metal oxide on LiNbO3 and LiNb3O8 nano-crystallite phases in lithium borate glass system.  

PubMed

Glasses of various compositions in the system 90 Li2B4O7-10 Nb2O5 mixed with T.M ions (where T.M is the transition metal) were prepared by quenching technique. Heat-treatment of the parent glasses was performed at 540, 570 and 620 °C, for 5 and 16 h. The glass structure evolution during the controlled crystallization was examined by XRD and FT-IR spectroscopy analysis. The crystalline phases present in the glass ceramics were identified via X-ray diffraction as a function of heat treatment. The FT-IR data propose for these glasses and heat-treated glass network structures mainly built by: di-, tri-, tetra-, penta-and ortho-borate groups. It was found that the quantitative evolution of these various borate species in the glass structures is influenced by the transition metal. A detailed discussion relating to the N4 evolution with the T.M content was made. PMID:23708372

Kashif, Ismail; Soliman, Ashia A; Sakr, Elham M; Ratep, Asmaa

2013-09-01

412

XRD and FTIR studies the effect of heat treatment and doping the transition metal oxide on LiNbO3 and LiNb3O8 nano-crystallite phases in lithium borate glass system  

NASA Astrophysics Data System (ADS)

Glasses of various compositions in the system 90 Li2B4O7sbnd 10 Nb2O5 mixed with T.M ions (where T.M is the transition metal) were prepared by quenching technique. Heat-treatment of the parent glasses was performed at 540, 570 and 620 °C, for 5 and 16 h. The glass structure evolution during the controlled crystallization was examined by XRD and FT-IR spectroscopy analysis. The crystalline phases present in the glass ceramics were identified via X-ray diffraction as a function of heat treatment. The FT-IR data propose for these glasses and heat-treated glass network structures mainly built by: di-, tri-, tetra-, penta-and ortho-borate groups. It was found that the quantitative evolution of these various borate species in the glass structures is influenced by the transition metal. A detailed discussion relating to the N4 evolution with the T.M content was made.

Kashif, Ismail; Soliman, Ashia A.; Sakr, Elham M.; Ratep, Asmaa

2013-09-01

413

Effects of transition-metal additions on the properties of AlN  

SciTech Connect

Transition-metal oxide additions to AlN ceramics produced no significant deterioration in thermal conductivity. In the present study, TiN, ZrN, TaC, NbC, W, and unidentified Hf phases, found as fine particles located inter- and intragranularly, were distributed randomly in the AlN. Phases containing Fe, Co, and Cr, on the contrary, always were located at the three grain points. Most of the added transition-metal compounds turned the ceramics black or gray. The shading mechanism was attributed to optical absorption by the surfaces of the electrically conductive fine particles and to multiple reflections among these particles.

Kasori, Mitsuo; Ueno, Fumio; Tsuge, Akihiko (Toshiba Corp., Kanagawa (Japan). R D Center)

1994-08-01

414

CN coupling on transition metal surfaces: A density functional theory study  

Microsoft Academic Search

We have investigated the formation of C-N bonds from individual atoms and single hydrogenated moieties on a series of transition metals. These reactions play a role in HCN formation at high oxygen coverage, also known as Andrussow oxidation, and they are fundamental to understand the ability of other materials to form part of alloys where Pt is the major component.

Jaime Gómez-Díaz; Crisa Vargas-Fuentes; Núria López

2011-01-01

415

Room-Temperature Ferromagnetism in Transparent Transition Metal-Doped Titanium Dioxide  

Microsoft Academic Search

Dilute magnetic semiconductors and wide gap oxide semiconductors are appealing materials for magnetooptical devices. From a combinatorial screening approach looking at the solid solubility of transition metals in titanium dioxides and of their magnetic properties, we report on the observation of transparent ferromagnetism in cobalt-doped anatase thin films with the concentration of cobalt between 0 and 8%. Magnetic microscopy images

Yuji Matsumoto; Makoto Murakami; Tomoji Shono; Tetsuya Hasegawa; Tomoteru Fukumura; Masashi Kawasaki; Parhat Ahmet; Toyohiro Chikyow; Shin-ya Koshihara; Hideomi Koinuma

2001-01-01

416

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

SciTech Connect

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

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

2009-04-15

417

Comparative study of the synthesis of layered transition metal molybdates  

SciTech Connect

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

Mitchell, S.; Gomez-Aviles, A.; Gardner, C. [Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW (United Kingdom); Jones, W., E-mail: wj10@cam.ac.u [Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW (United Kingdom)

2010-01-15

418

Oxygen transport kinetics of the oxygen interstitial system lanthanum praseodymium nickel oxide and cation ordered double perovskite-Ln barium cobalt oxide (Ln = praseodymium and neodymium) oxides  

NASA Astrophysics Data System (ADS)

The main purpose of this dissertation is the development of the new cathode materials for intermediate temperature solid oxide fuel cells (SOFC). The oxygen transport kinetics of the oxygen interstitial system La xPr2-xNiO4+delta and cation ordered double perovskite---LnBaCo2O5+delta (Ln = Pr and Nd) by electrical conductivity relaxation (ECR), DC conductivity, and AC impedance spectroscopy were studied. The measured values were compared with those obtained from isotope exchange and depth profiling (IEDP). The ECR experiment gave the oxygen transport kinetics parameters---oxygen diffusion coefficients ( DO2- ) and surface exchange coefficients (kex) for bulk dense samples. Assuming the ALS model which contains DO2- and kex, the cathode performance of La xPr2-xNiO4+delta was estimated by AC impedance spectroscopy for porous samples. The oxygen transport kinetics from different techniques had a good agreement. It was found that both values of DO2- and kex for PrBaCo2O5+delta (PBCO) and NdBaCo2O5+delta (NBCO) measured by ECR were remarkably high at low temperatures (300 ˜ 500 °C). The dense thin films with well-defined microstructures and geometry were studied for La2NiO4+delta (LNO) and PBCO by ECR and IEDP. The ECR and isotope measurements agree well, though the ECR data indicate the presence of two distinct kinetics pathways. The oxygen surface exchange kinetics of PBCO thin film is much faster than those of disordered perovskite LaSrCo2O6-delta. The oxygen transport studies by AC impedance for LNO and PBCO polycrystalline thin film on YSZ single crystal substrates suggested the rate determining step of the oxygen reduction reaction. Two different oxygen reduction models were proposed for PBCO.

Kim, Guntae

419

Stable lithium-ion conducting perovskite lithium–strontium–tantalum–zirconium–oxide system  

Microsoft Academic Search

High lithium-ion conductivity, especially at room temperature, and chemical stability against reducing lithiated negative electrodes are two main requirements for a solid electrolyte in an all solid-state lithium battery. Perovskite-type materials ABO3 in which A=La, Li and B=Ti exhibit high lithium ion conductivities, with a bulk conductivity of 1.2 mS\\/cm at 30 °C and an apparent grain-boundary conductivity of 0.03

C. H. Chen; S. Xie; E. Sperling; A. S. Yang; G. Henriksen; K. Amine

2004-01-01

420

Magnetic Properties and Spin State Transition of Gallium Doped Perovskite Cobaltite Oxide  

Microsoft Academic Search

A series of Ga doping perovskite cobaltite La2\\/3Sr1\\/3(Co1-yGay)O3 (y = 0, 0.1, 0.2, 0.3 and 0.4) are prepared by the standard solid-state reaction method. Their magnetic properties and Co ions spin state transitions are studied. Upon doping, no appreciable structure changes can be found. However, the corresponding Curie temperature sharply decreases and the magnetization is greatly reduced, indicating that Ga

Zhi-Min Wu; Xin-Qiang Wang; Fang-Wei Wang

2007-01-01